Abstract

The potential of a Yb3+/Ho3+ co-doped lead-germanate glass as a laser gain medium around 2 µm is investigated by spectroscopic measurements and rate equation modelling. The glass, based on the molar composition of 56GeO2-31PbO-4Ga2O3-9Na2O and co-doped with 1.5 mol% Yb2O3 and 0.4 mol% Ho2O3, possesses a broad Ho3+ emission spectrum covering ∼1.8 µm to 2.2 µm for the Ho3+:5I75I8 transition, and a long 5I7 fluorescence lifetime of (7.74 ± 0.03) ms. We estimate a competitive 2 µm quantum efficiency (76%) compared to other germanate glasses. The intensity parameters are calculated to be Ω2 = 3.0×10−20 cm2, Ω4 = 1.2×10−20 cm2 and Ω6 = 2.0×10−20 cm2. The energy transfer analysis from Ho3+ to OH group represents a low Ho3+-OH clustering factor (γ = 0.15) compared to phosphate and other germanate glasses. Applying these parameters to the laser model predicts > 15% laser slope efficiency for cavity losses ≤ 0.5 dB using 976 nm pumping. The results show that this Yb3+/Ho3+ co-doped lead-germanate glass is a promising candidate for efficient lasing around 2 µm.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Enhanced 2 µm mid-IR eye-safe lasers can open up new applications including high resolution spectroscopy, remote sensing, atmospheric monitoring, biomedical imaging, medical surgery, quality control, and has applications in the defense sector [1]. To obtain efficient lasers around 2 µm, glasses are doped with Tm3+ or Ho3+ rare earth ions [2]. The emission cross-section of Ho3+ at ∼ 2 µm is at least 4 times higher than that of the Tm3+ emission [3], combined with a long upper-state lifetime that is favorable for Q-switched laser applications.

2 µm laser emission in Ho3+ requires out of band pumping at either 900 nm or 1150 nm, or resonant in-band pumping at 1945nm (e.g. via a thulium fiber laser). The pump lasers operating at these wavelengths are expensive and commercially scarce hence the addition of a sensitizer ion along with the active ion helps utilize more readily available laser diodes (LDs) [2]. Relevant sensitizers include Tm3+ or Yb3+. In this study, Yb3+ is used as the sensitizer for two reasons. Firstly, Yb3+ has a strong absorption at 976 nm, which is a wavelength where high-power single-mode laser diodes are readily available. Secondly, the energy transfer coefficient from Yb3+ to Ho3+ was previously found to be high in silicate [4] and oxyfluoride [5] glasses.

Small-cavity mid-IR lasers (e.g. waveguide lasers) are targeted in this study as high optical gain and high efficiencies can be achieved. Besides this, monolithic devices can be manufactured by integrating waveguide lasers with other photonic devices on a single chip. Previous studies on small-cavity lasers have focused on silicate [6] and fluoride [7] glass hosts. Silicate glasses have high damage threshold and superior thermal stability compared to any other host glasses reported as waveguide lasers, however their transmission does not extend to the mid-IR. By contrast, fluorides have a wide transmission spectrum extending into the mid-IR region, however low thermal conductivity and mechanical strength limit the power scaling potential. Alternative glasses are heavy metal oxides including tellurite and germanate [8].

Lead-germanate glasses are promising host materials for 2 µm laser application due to their high chemical and thermal stability compared to other mid-IR transmitting glasses. One of the most widely investigated lead-germanate glasses has the molar composition of 56GeO2-31PbO-4Ga2O3-9Na2O (GPGN). The broad transmission spectrum of GPGN glass allows a wide range of laser wavelengths to be considered. GPGN glass is melted at a lower temperature of 1200°C-1250°C [9] compared to the extensively studied BaO-Ga2O3-GeO2 germanate glass system, which melts at ∼1500°C [10]. This lower melting temperature allows convenient melting of GPGN in dry atmosphere using a glove-box based melting facility.

Lead-germanate glasses also possess a high refractive index compared to other glasses in the germanate family [11] which make them a suitable candidate for the fabrication of optical elements (eg. lenses). High refractive index is also useful for dispersion compensation and high-power non-linear applications (e.g. broadband supercontinuum generation and four-wave mixing). Another compelling feature of lead-germanate glass is its capacity to accommodate large concentrations of dopants unlike other glass hosts [12], making it a suitable candidate for single frequency laser operations, where short cavity lengths with sufficient net gain are required.

The Ho3+ based 2 µm laser properties have been investigated in singly doped and co-doped germanate glasses. Based on a Ho3+ singly doped lead-germanate glass with molar composition of 50GeO2-5SiO2-20PbO-20CaO-5K2O, Ho3+ laser generation with 47% quantum efficiency was achieved using in-band pumping with a Tm3+ fiber laser at 1.94 µm [13]. A higher quantum efficiency of 79% was obtained in GeO2- BaF2-Ga2O3-LiF glass when co-doped with Yb3+ and pumped with 976 nm LD due to high energy transfer from Yb3+ to Ho3+ [14]. Several studies also revealed laser operation in Ho3+ doped and co-doped germanate glass fibers. These include a Ho3+ singly doped germanate fiber laser with similar composition as in [13]. resulting in a 35% laser slope efficiency when pumped at 1.94 µm [15]. A single frequency tunable laser operation in a 2 cm long Ho3+ doped germanate fiber was reported in [16] which also used a 1.94 µm in-band Tm3+ fiber laser pumping scheme. A low laser slope efficiency of 4.7% was observed in a BGG glass co-doped with Tm3+ using 796 nm LD pumping, with an energy transfer efficiency of 63% from Tm3+ to Ho3+ [17]. To the best of our knowledge, planar and channel waveguide lasers have yet to be demonstrated for Ho3+ singly doped or Yb3+/Ho3+ co-doped germanate glasses.

In this paper, we investigate the potential of a new, in-house fabricated Yb3+/Ho3+ co-doped lead-germanate glass for 2 µm waveguide laser application. The main aim of the study was to develop a small cavity laser system that can be pumped with readily available high-power 976 nm LD source and efficiently emit at 2 µm. This study was also undertaken to validate the 2 µm laser performance in Yb3+/Ho3+: GPGN based on the experimentally measured/calculated spectroscopic parameters. The rare-earth (RE) concentrations were chosen to address our longer-term aim to develop a high efficiency waveguide cavity laser. For short cavity laser operation, we selected 3 mol% of sensitizer ion (Yb3+) to achieve efficient pump absorption (97% in 5 mm). A relatively low concentration (0.8 mol%) of active ion (Ho3+) was selected due to: (i) Ho3+ is efficient even at low concentrations and (ii) to avoid the very common ion clustering in Ho3+ doped materials. Based on absorption and emission measurements combined with Judd-Ofelt analysis, we determined a range of spectroscopic parameters (absorption and emission cross sections, fluorescence lifetime and energy transfer microparameter) for 2 µm waveguide laser simulations using rate equation modelling. Energy transfer efficiency of ∼ 94% for Yb3+:2F5/2→Ho3+:5I6 was estimated using the rate equations. A high Ho3+:5I75I8 quantum efficiency of 76% and a measured Ho3+:5I7 lifetime of (7.74 ± 0.03) ms were determined for the glass.

2. Experimental procedures

The fabricated Yb3+/Ho3+ co-doped GPGN glass has a mol% composition of (56-x)GeO2 - (31−y)PbO - 4Ga2O3 - 9Na2O with x=1.5Yb2O3 and y=0.4Ho2O3, and was synthesized by a conventional melt-quench technique described in [18]. This glass sample is henceforth referred to as Yb3+/Ho3+:GPGN. This specific composition of lead-germanate glass was selected as GPGN possesses higher thermal stability against crystallization (previously demonstrated in [9]) compared to other lead-germanate glasses [11]. The 20 g batch was physically mixed and placed in a platinum crucible for melting at a temperature of ∼ 1250°C for 70 min under dry melting environment (80% N2 and 20% O2) in a glove-box. The molten glass was poured into a pre-heated brass mold and placed in the annealing furnace for ∼15 hours (∼ 390$^{\circ}{\textrm C})$ below the glass transition temperature (${T_g}$∼ 390°C) resulting in a glass block with dimensions of 20×15×5 mm3.

A spectrophotometer (Agilent Cary 5000) was used to collect the absorption spectrum of the optically polished glass block to measure its ground state absorption bands. The fluorescence emission spectrum of the sample was collected with a near infrared spectrometer (Ocean Optics NIRQUEST) using a CW 976 nm LD for excitation. All measurements were taken at room temperature. The fluorescence lifetime for the fabricated glass was measured using a spectrofluorimeter (Edinburgh Instruments FLS980). The density of the glass was measured using Archimedes’ Principle.

3. Results and discussion

3.1 Yb3+/Ho3+: GPGN spectroscopic analysis

3.1.1 Density and Refractive index

The density of the Yb3+/Ho3+:GPGN glass was measured to be 5.60 ± 0.02 g/cm3. Based on this value and the doping concentration, the ion density of Yb3+ and Ho3+ was determined as ${N_{Yb}}$= 6.94×1020 ion/cm3 and ${N_{Ho}}$ = 1.85×1020 ions/cm3, respectively.

The refractive index n for undoped GPGN glass [9] was used for Fresnel reflection based absorbance subtraction and Judd-Ofelt calculations. The index at 1.5 µm is n = 1.8222 ± 0.0004. The refractive index as a function of wavelength is defined by the Sellmeier equation of the form given in Eq. (1)

$${n^2}(\lambda ) = A + \frac{B}{{1 - C/{\lambda ^2}}} + \frac{D}{{1 - E/{\lambda ^2}}}$$

By fitting Eq. (1) to the measured index values of GPGN given in [9], the Sellmeier coefficients of GPGN glass were calculated to be A=2.029, B=1.267, C=5.4×10−2, D=4.4×10−4 and E=0.2993.

3.1.2 Rare-earth and OH- absorption spectrum

The absorbance spectrum was collected to determine the ground state absorption bands of the doped rare earth ions and the absorption band of the fundamental vibration of OH groups in the Yb3+/Ho3+:GPGN glass fabricated. The baseline of the measured absorbance spectrum (i.e. the absorbance of the glass excluding rare earth ion and OH absorption bands) consists of the absorbance due to Fresnel reflections (E0) at the glass sample surfaces, absorbance due to scattering at surface imperfections and absorbance due to impurities and defects in the glass volume. For high-purity glass samples with an optically flat surface finish, the absorbance from surface imperfections, impurities and defects is negligible. The E0 component of absorbance E(λ) as a function of wavelength was determined using log10((n2(λ) + 1)/2n(λ)). The absorption coefficient, α(λ), was then obtained by subtracting the Fresnel based absorbance E0(λ) from the measured absorbance E(λ) and diving it by the sample’s thickness L= (1.61 ± 0.05) mm using the expression α (λ) = ln10 (E(λ)-E0(λ))/L (Fig. 1(a)).

 

Fig. 1. (a) Absorption coefficient spectrum for Yb3+/Ho3+:GPGN glass from 400 nm – 2500nm representing different absorption bands of Ho3+ and Yb3+. Inset to the Fig. is the OH absorption coefficient spectrum peaking at ∼3100 nm in Yb3+/Ho3+:GPGN. (b) Comparison of Yb3+ absorption in GPGN with silica [19] and ZBLAN [20].

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The Ho3+ absorption peaks are shown in Fig. 1(a) and centered at 418 nm (5G5), 450 nm (5F1+5G6), 540 nm (5F4+5S2), 642 nm (5F5), 1150 nm (5I6) and 1945nm (5I7). The absorption cross section, ${\sigma _{abs\; }}(\lambda )$ of Ho3+ in Yb3+/Ho3+:GPGN was calculated using the absorption coefficient, α(λ), divided by the ion density of Ho3+ $({{N_{Ho}}} )$. ${\sigma _{abs\; }}$ for the Ho3+:5I7 absorption band was estimated as 4.5×10−21 cm2.

The Yb3+ absorption band (2F5/2) shown in Fig. 1(a) ranges from ∼ 870 nm to 1100 nm, with distinct peaks at 905 nm and 976 nm. The 905 nm peak is narrower, and blue shifted compared to other hosts such as silica and fluoride, where the peak is located at ∼ 920 nm (Fig. 1(b)). The Yb3+ absorption band in Yb3+/Ho3+:GPGN can be fitted with 5 peaks at locations 905 nm, 932 nm, 950 nm, 976 nm and 1020 nm, unlike silica with 3 peaks (920 nm, 974 nm and 1020 nm) and ZBLAN with 4 peaks (925 nm, 942 nm, 976 nm and 1010 nm).

The broad absorption band covering 2800 nm – 3300 nm with a peak at 3100 nm (Fig. 1(a)) is due to the fundamental vibration of OH groups, which are usually observed in heavy metal oxide glasses. These OH groups are known to quench mid-IR fluorescence transitions [15], including Ho3+:5I65I7 (2.8 µm) and Ho3+:5I75I8 (2 µm) and, therefore, the estimation of the OH content is required to predict the OH quenching rate. The OH concentration (${N_{OH}}$) in terms of number of OH groups per cm3 is usually determined from the OH absorption coefficient at the peak wavelength of the OH absorption band at 3 µm using Eq. (2) [21].

$${N_{OH}} = {\alpha _{OH}}\frac{{{N_A}}}{{{\varepsilon _{OH}}}}$$
where NA is the Avogadro’s number and ${\varepsilon _{OH}}$ is the molar absorptivity of OH in the glass. Yb3+/Ho3+:GPGN exhibits ${\alpha _{OH}}$= 0.8 cm-1 (Fig. 1 inset). Due to the unavailability of ${\varepsilon _{OH}}$ for germanate, the molar absorptivity of OH in silicate (${\varepsilon _{OH}}$ = 49.1×103 cm2/mol [22]) is used in Eq. (2) as it has also previously been utilized for other germanate and non-silica glasses [13]. This results in ${N_{OH}}$ ∼ 4.3×1018 OH/cm3 in Yb3+/Ho3+:GPGN.

3.1.3 Judd-Ofelt analysis for intensity parameter calculations

Judd-Ofelt (JO) intensity parameters Ω2, Ω4 and Ω6 play an important part in the prediction of the spectroscopic properties of rare earth ions in a host material. According to the JO theory, the absorption line strength of an electric-dipole transition from initial manifold J to the excited manifold $J^{\prime}$ is given by Eq. (3)

$${S_{ed}}(J \to {J^{\prime}}) = \sum\limits_{t = 2,4,6} {{\Omega _t}} |< J||{U^{(t)}}||{J^{\prime}} > {|^2}$$
The squared term in the above equation represents the matrix elements of the unit tensor U(t) (t=2,4,6) for the doped Ho3+ ions. As the matrix elements are almost independent of the host material, the U(t) values for Ho3+ in this study were taken from Weber et al. [23].

The electric $({{S_{ed}}} )$ and the magnetic dipole $({{S_{md}}} )$ line strengths are associated with the integral of the absorption coefficient, $\alpha (\lambda )$, for a specific absorption band and are represented by Eq. (4)

$$\int\limits_{band} {\alpha (\lambda )d(\lambda )} = \frac{{8{\pi ^3}{e^2}{\lambda ^{\prime}}{N_{Ho}}}}{{3ch(2J + 1)}}\left[ {\frac{{{{({n^2} + 2)}^2}}}{{9n}}{S_{ed}}(J \to {J^{\prime}}) + {n^3}{S_{md}}} \right]$$
where $\lambda ^{\prime}$ is the peak absorption wavelength for the relevant band, ${N_{Ho}}$ is the ion concentration of Ho3+ and n is the refractive index for the respective transition. ${S_{md}}$ was determined from the magnetic dipole contribution of oscillator strength, ${P_{md}}$, using Eq. (5)
$${S_{md}}(J \to {J^{\prime}}) = \frac{{3h{\lambda ^{\prime}}{e^2}(2J + 1)}}{{8{\pi ^2}mn{c^2}}} \times {P_{md}}(J \to {J^{\prime}})$$
where m and e are the mass and charge of electron. ${P_{md}}$ was evaluated from the product of magnetic dipole contribution of the oscillator strength in vacuum and the refractive index of Yb3+/Ho3+:GPGN using the expression ${P_{md}} = n \times 29.5 \times {10^{ - 8}}$ [24].

Six absorption bands with peaks at 1945nm (5I7), 1150 nm (5I6), 642 nm (5F5), 540 nm (5F4+5S2), 448 nm (5F1+5G6) and 418 nm (5G5) were considered in this study. Multiple regression of all these bands resulted in the intensity parameters to be Ω2 = 3.0×10−20 cm2, Ω4 = 1.2×10−20 cm2 and Ω6 = 2.0×10−20 cm2. Small RMS value indicates that the ${S_{ed}}$ values predicted through the multiple regression are in close approximation to the measured values. The calculated and measured electric dipole line strengths for the ground state absorption bands of Ho3+ in Yb3+/Ho3+:GPGN are presented in Table 1.

Tables Icon

Table 1. Measured and calculated electric dipole line strengths (Sed) and refractive index values for respective transition bands of Ho3+ and the JO intensity parameters Ω2, Ω4 and Ω6 in Yb3+/Ho3+:GPGN. * represents the electric (Aed) and magnetic (Amd) contributions for Ho3+:5I75I8 radiative transition probability.

The radiative transition probability for a specific energy level is related to the electric (${S_{ed}})$ and magnetic (${S_{md}}$) line strengths for the respective absorption bands and is represented by Eq. (6). For the given Ho3+:5I75I8 transition, ${A_r}$ was evaluated as 99 s-1.

$${A_r}(J \to {J^{\prime}}) = \frac{{64{\pi ^4}}}{{3h{\lambda ^{\prime3}}(2J + 1)}}\left[ {\frac{{n{{({n^2} + 2)}^2}}}{9}{S_{ed}}(J \to {J^{\prime}}) + {n^3}{S_{md}}} \right]$$

3.1.4 Emission spectrum and lifetime measurements

The emission cross-section $({{\sigma_{ems}}(\lambda )} )$ plays an important role in the estimation of laser transition probability and the laser performance. For 2 µm laser emission in Yb3+/Ho3+:GPGN, the peak emission cross-section $({{\sigma_{ems}}} )$ was calculated using the Füchtbauer-Ladenburg Eq. (7)

$${\sigma _{ems}}(\lambda ) = \frac{\lambda {^{\prime4}}}{{8\pi c{n^2}{\tau _r}}} \times \frac{{I(\lambda )}}{{\smallint I(\lambda )d(\lambda )}}$$
where ${\tau _r}\; $is the measured radiative lifetime of Ho3+:5I7, n is the refractive index of the GPGN glass (1.82), c is the speed of light, $\lambda ^{\prime}$ is the peak transition wavelength (2 µm) and I(λ) is the collected fluorescence spectrum for the glass.

The emission spectrum I(λ) in Eq. (7) was collected using the configuration shown in Fig. 2(a), where the collimated beam from a 976 nm LD strikes the edge of the sample and the fluorescence is collected orthogonally to avoid fluorescence being reabsorbed by the ground state. I(λ) was collected from 950 nm to 2400 nm (Fig. 2(b)). The broad fluorescence up to 1150 nm in Fig. 2(b) is due to the Yb3+ in Yb3+/Ho3+:GPGN [25]. This broadening is attributed to the large stark splitting of Yb3+ in germanate glass [26].

 

Fig. 2. (a) Experimental setup to collect fluorescence data from the edge of the Yb3+/Ho3+:GPGN using 976 nm pumping source (b) Fluorescence spectrum I(λ).

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The fluorescence decay curves were measured for Ho3+ and Yb3+ in Yb3+/Ho3+:GPGN as well as for Yb3+ in GPGN glass of the same composition but singly doped with Yb3+ (Yb3+:GPGN), which was fabricated in our previous work [25]. The fluorescence decay curves were fitted to a single coefficient exponential equation, thus allowing the lifetimes of the respective ions to be determined (decay to 1/e), and then to be used to estimate the energy transfer efficiency from Yb3+:2F5/2 to Ho3+:5I6, which is discussed in 3.1.5.

The measured fluorescence lifetime of Ho3+:5I7 in the Yb3+/Ho3+:GPGN glass is (7.74 ± 0.03) ms (Fig. 3(a)), similar to the Ho3+:5I7 lifetime (7.68 ms) reported in GeO2-BaF2-Ga2O3-LiF germanate glass [14].

 

Fig. 3. Measured fluorescence decay curves in blue (dotted lines). Single coefficient best fit exponential decay curves are given in brown (solid lines) for (a) Ho3+:5I7 in Yb3+/Ho3+: GPGN with τm = 7.74 ms. (b) Yb3+:2F5/2 in Yb3+:GPGN with τYb = 1.76 ms.

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The lifetime of the upper state of Yb3+:2F5/2 in the singly doped Yb3+:GPGN glass is (1.76 ± 0.01) ms (Fig. 3(b)), whereas in co-doped Yb3+/Ho3+:GPGN glass, this lifetime is reduced to 0.1 ms.

Using the integrated emission spectrum 1800nm – 2200 nm and the measured lifetime of Ho3+:5I7 in Eq. (7), the peak emission cross section, σems, at ∼ 2 µm is calculated to be 4.2×10−21 cm2 (Fig. 4). In comparison, the σems of Ho3+ is 4.9×10−21 cm2 in GeO2-BaF2-Ga2O3-LiF glass [14] and 3.1×10−21 cm2 in La2O3-Al2O3-GeO2 glass [27].

 

Fig. 4. Absorption (blue) and emission (brown) cross sections for the Ho3+:5I75I8 transition at ∼2 µm. The fluorescence emission spectrum was obtained by exciting the sample with a 976 nm LD.

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Quantum efficiency plays an important role to estimate the laser performance in a gain medium. It is defined as the product of measured lifetime and the radiative transition probability (τm${\times} $ Ar). The quantum efficiency for the Ho3+:5I75I8 transition in Yb3+/Ho3+:GPGN was predicted to be 76%, which is larger compared to phosphate glass (51%), LiF3 crystal (64%) or in another lead-germanate glass type (47%) [13]. This high predicted quantum efficiency in Yb3+/Ho3+:GPGN indicates that the glass is a promising candidate for efficient 2 µm laser application.

3.1.5 2 µm energy transfer pathway

This section investigates the energy transfer pathway from Yb3+ (donor ion, D) to Ho3+ (acceptor ion, A). The Yb3+ ions in the ground state (2F7/2) are excited to the upper state (2F5/2) when pumped with a 976 nm LD. Based on this excitation wavelength, three energy transfers (ET) were observed from Yb3+:2F5/2 to three different states of Ho3+ (Fig. 5). (i) ET1 is the phonon assisted energy transfer to Ho3+:5I6 that populates the upper laser level 5I7 via multi-phonon decay process from where it depopulates to the ground state. (ii) ET2 is the up-conversion energy transfer to Ho3+:5F5 transition that leads to unwanted red fluorescence and (iii) ET3 is the up-conversion energy transfer to Ho3+:5F4 that leads to unwanted green fluorescence.

 

Fig. 5. Energy transfers (ET) pathways in Yb3+/Ho3+:GPGN. Solid transfer lines represent dominating processes.

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For the 2 µm laser model, we are only considering the phonon assisted ET1 and ignoring ET2 and ET3 because the measured decay rates of Ho3+:5F4 (${\tau _1}$ = 52 µs) and Ho3+:5F5 (${\tau _2}\; \,$=115 µs) are fast compared to the decay rate of Ho3+:5I7 (${\tau _m}$=7.7 ms). This makes ET2 and ET3 negligible compared to the dominating ET1 process. For the phonon assisted ET1, the energy gap between Yb3+:2F5/2 and Ho3+:5I6 is ∼ 1200 cm-1. Thus, 1 or 2 phonons are required to take part in the transfer as the phonon energy of the lead-germanate glass is ∼ 800 cm-1 [28]. The rate of this energy transfer (WET) is given in Eq. (8)

$${W_{ET}} = \frac{1}{{{\tau _D}}} - \frac{1}{{{\tau _{Yb}}}}$$
where τD = 102 µm is the quenched fluorescence lifetime of Yb3+ in Yb3+/Ho3+:GPGN (i.e. with energy transfer) while τYb = (1.76 ± 0.03) ms is the lifetime of Yb3+ in GPGN without Ho3+ (i.e. without energy transfer). The energy transfer rate is calculated to be 9236 s-1. The efficiency of this transfer is given by ${\eta _{ET}} = 1 - {\raise0.7ex\hbox{${{\tau _D}}$} \!\mathord{\left/ {\vphantom {{{\tau_D}} {{\tau_{Yb}}}}} \right.}\!\lower0.7ex\hbox{${{\tau _{Yb}}}$}}$ and is 94%. This high energy transfer efficiency in GPGN is attributed to the high concentration of both the Yb3+ and Ho3+ in the glass.

The energy transfer microparameter, CDA, from Yb3+:2F5/2 to Ho3+:5I6 is defined by WET = CDA×NYb×NHo. In [14], an energy transfer coefficient, CD, is defined as WET = CD×NHo, with CD = CDA×NYb. To be able to compare CDA of Yb3+/Ho3+:GPGN with that of Yb3+/Ho3+ co-doped GeO2-BaF2-Ga2O3-LiF (GBGL) glass in [14], we calculated CDA from the CD values given in [14]. As the Yb3+ concentration in [14] is only given in mol%, we calculated CDA in unit cm3.mol%/s (Table 2). The plot of the energy transfer microparameter as a function of the Ho3+ concentration (Fig. 6) shows a linear dependence, which indicates that the energy transfer rate scales with NHo2 for ≥ 0.1 mol% Ho2O3, i.e. WET = kDA×NYb×NHo2, where kDA = CDA/NHo is the slope of the line in Fig. 6. Further work is needed to understand the mechanism of the nonlinear dependence of the energy transfer rate on the Ho3+ concentration for ≥ 0.1 mol% Ho2O3.

 

Fig. 6. Linear dependence of energy transfer microparameter on the Ho3+ concentration (plotted using data in blue from [14] and this work (brown)). Data points > 0.1mol% Ho2O3 were used for linear fitting (green).

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Tables Icon

Table 2. Comparison of current study with published Yb3+/Ho3+ GBGL where the Yb3+ lifetime is measured for a range of Ho3+ concentrations.

3.1.6 Effect of OH on Ho3+:5I7 lifetime:

The depopulation of the metastable state of Ho3+ (5I7) is accompanied by the radiative decay rate, ${A_r}$, determined by the radiative lifetime, ${\tau _r}$, and the non-radiative decay rate having two contributions of (i) multi-phonon decay for Ho3+:5I75I8 (${W_{MP}}$) and (ii) energy transfer to the OH groups (${W_{OH}}$). ${\tau _m}$ is, therefore, given by Eq. (9)

$${\tau _m}^{ - 1} = {\tau _r}^{ - 1} + {W_{MP}} + {W_{OH}}$$

WMP in Eq. (9) is estimated using the well-known energy gap law defined in [29] where the non-radiative energy transfer within a host material follows an exponential decay path, ${W_{MP}} = a \times \exp[{ - b({\Delta E - 2\hbar \omega } )} ]$, where a and b are the non-radiative decay parameters that depend on the glass type. The values for germanate glass were taken from [29], $\Delta E$ is the energy gap between 5I6 and 5I7 (∼5000 cm-1) and $\hbar \omega $ is the phonon energy of GPGN (∼ 820 cm-1). Using these values, ${W_{MP}}$ is ∼ 12 s-1.

With the calculated WMP, as well as the known measured and radiative lifetime of the Ho3+:5I7 level, Eq. (9) is used to calculate ${W_{OH}}$ to be 18 s-1. To compare this value with other germanate glass, we consider the Ho3+-OH energy migration assisted energy transfer model in [13], which was adopted from the Er3+-OH migration assisted energy transfer model in [30]. This model is based on three main assumptions, (i) only a fraction of OH ions is coupled to Ho3+, (ii) the number of Ho3+ ions coupled to OH groups is proportional to the number of OH groups with the proportionality constant given by $\gamma $, (iii) the excited energy migrates between Ho3+ ions that are not coupled to OH to Ho3+ ions that are coupled to OH, and from these coupled Ho3+ ions fast energy transfer to their proximate OH groups occurs. According to this model, the rate of the overall Ho3+-OH energy transfer process, WOH, is determined by the energy migration between Ho3+ ions, which depends on the total concentration of Ho3+ ions, and the energy transfer between coupled Ho3+ and OH, which depends on the OH concentration according to assumption (ii). This is given by Eq. (10), which is adapted from [30],

$${W_{OH}} = 8\pi \times {C_{Ho}} \times {N_{Ho}} \times \gamma \times {N_{OH}}$$
where γ is a measure of the portion of Ho3+ and OH ions involved in the energy migration assisted energy transfer process, and CHo is the microparameter of the transfer process. According to the Förster-Dexter theory, the microparameter of a donor-acceptor energy transfer is given by the overlap between the emission band of the donor and the absorption band of the acceptor [31], represented by Eq. (11)
$${C_{Ho}} = \frac{{3c{A_r}}}{{8{\pi ^4}{n^2}}}\frac{{(2J + 1)}}{{(2{J^{\prime}} + 1)}}\int {\sigma _{ems}^D} (\lambda )\sigma _{abs}^A(\lambda )$$

As the rate of the energy transfer between coupled Ho3+ and OH is much faster than that of the energy migration between Ho3+ ions, CHo is the microparameter of the energy migration, where Ho3+ is donor and acceptor. Hence, CHo is calculated using the experimentally determined emission and absorption cross sections of the Ho3+:5I75I8 transition at 2 µm, yielding 63 × 10−40 cm6/s. Using this CHo value, WOH = 18 s-1 as calculated from Eq. (9), NHo and NOH, Eq. (10) yields γ ∼ 0.15 in GPGN.

In GeO2-SiO2-PbO-CaO-K2O (GSPCK) germanate glass, linear regression of the non-radiative decay rate 1/τm-1/τr as a function of ${N_{Ho}} \times {N_{OH}}$ (Fig. 7(b)) according to Eq.(9) yielded WMP=33 s-1 from the intercept and γ = 0.24 from the slope [32]. The lower value of WMP=12 s-1 for GPGN is consistent with the absence of high phonon energy component SiO2 in GPGN compared to GSPCK. It is important to note that the linear dependence of the non-radiative decay rate on ${N_{Ho}} \times {N_{OH}}$ (Figure 7(b)) indicates that γ is a characteristic parameter for a specific glass composition (Table 3 and Fig. 7(b)) and cannot be linked only to Ho3+ coupled to OH as assumed in the quenching model in [13]. The lower γ value in GPGN (0.15) compared to GSPCK (0.24) suggests reduced tendency of OH ions to cluster with Ho3+ ions. In comparison, for phosphate glasses, cluster formation between rare earth ions and OH groups was derived from energy transfer analysis [33] which is consistent with the high γ = 0.6 value for Er3+-OH energy migration assisted energy transfer in phosphate glass [30].

 

Fig. 7. (a) Simplified ET diagram for depopulation of 5I7 energy state of Ho3+. (b) Non-radiative decay rate as a function of Ho3+ and OH concentrations for GSPCK and GPGN glass, with similar slope in both glasses.

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Tables Icon

Table 3. Measured and calculated parameters for GPGN and GSPCK for different concentrations of Ho3+ and OH for the calculation of γ and the respective quantum efficiency (QE).

The presence of OH in GPGN quenched the lifetime of 5I7 from 10.1 ms down to 7.74 ms. The quantum efficiency (QE) for 5I75I8 in GPGN using Ar/(Ar+WMP+WOH)   =76% is much higher than that in [13] where it was 47% for the sample with high NHo and low NOH (G6). This is because of enhanced energy migration to the Ho3+ ions coupled to the OH (fast WOH) in G6 due to high Ho3+ concentration. In contrast, the QE in G1 with low Ho3+ concentration is 69% despite of high OH content due to low energy migration to the Ho3+ ions coupled to the OH (slow WOH). It is, therefore, important to balance the proportion of both the Ho3+ and OH concentrations to minimize WOH for maximizing the QE of the Ho3+ emission at 2 µm. The QE for GPGN can be further enhanced by reducing the OH content for same Ho3+ concentration via improved dehydration of the glass melt during the fabrication process.

4. 2 µm laser simulations

In this section we present the 2 µm waveguide laser simulation model using the RP fiber power software. This software is designed for laser simulations based on rate-equation modelling to assist in quantitative understanding of the laser performance. Adopting a waveguide mode confinement simplifies the laser model as it conveniently propagates the forward and backward laser signal through the fixed cylindrical gain volume where it remains confined to the waveguide core in the laser cavity. The simulations are based on the spectroscopic parameters obtained for Yb3+/Ho3+:GPGN in the previous sections including ${\sigma _{abs}}(\lambda )$, ${\sigma _{ems}}(\lambda )$, the lifetimes ${\tau _r}$, ${\tau _{Yb}}$, and ${\tau _D}$ for respective states, donor and acceptor ion densities ${N_{Yb}}$ and ${N_{Ho}}$, and the energy transfer microparameter, ${C_{DA}},$ from Yb3+:2F5/2→Ho3+:5I6.

Considering a simple energy model, only three states of Ho3+ were considered. 1 is allotted to ground state (5I8), 2 is the metastable state (5I7), and 3 is the excited state (5I6) with ion populations described as ${N_{1(A )}}$, ${N_{2(A )}}$ and ${N_{3(A )}}$, respectively. The states 4 and 5 were allocated to the Yb3+ ground (2F7/2) and excited (2F5/2) states with ions populations ${N_{1(D )}}$ and ${N_{2(D )}}$, respectively. Equation (12) provided an estimate of the length of the gain medium by our previous measurement of the pump absorption. It can be observed from Fig. 8 that for a 1.5 mol % Yb2O3 concentration, ∼ 90% of the pump is predicted to be absorbed in 3 mm of Yb3+/Ho3+:GPGN.

$$Absorption = 1 - \exp ({ - {N_{Yb}}{\sigma_{abs}}(\lambda )L} )$$
where NYb is the ion concentration of Yb3+, ${\sigma _{abs}}$ is the peak absorption cross section and L is length of the Yb3+/Ho3+:GPGN. By exciting the ground state ions with a 976 nm pump source, ∼ 40% of the excited ions (${N_{2(A )}}$) reach the 5I7 state of Ho3+ assuming the ideal case with no losses within the gain medium. The fractional excitation ${N_{2(A )}}$ of metastable state 5I7 was estimated using the Eq. (13)
$$\frac{\partial }{{\partial t}}{N_{2(A)}} ={-} \frac{{{N_{2(A)}}}}{{{\tau _m}}} - q{N_{Ho}}{N_{2(A)}}^2 + \sum\nolimits_i {\frac{{{P_i}}}{{Ah{\nu _i}}}} [{({1 - {N_{2(A)}}} ){\sigma_{abs}}(\lambda ) - {N_{2(A)}}{\sigma_{ems}}(\lambda )} ]$$
where q is the coefficient reflecting the quenching effect caused by for example OH groups etc., P is the input power, and A is the mode area. ${\sigma _{abs\; }}(\lambda )\; $ and ${\sigma _{ems\; }}(\lambda )\; $ are the absorption and emission cross sections, $h{\upsilon _i}$ is the photon energy and ${\tau _m}$ is the measured lifetime of 5I7 state (quenched by the presence of OH).

 

Fig. 8. (a) Predicted pump absorption in Yb3+/Ho3+:GPGN sample with respect to the position. n2 population in 5I7 is ∼ 40% with no losses (b) Output power as function of wavelength for 2 W of input power.

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For all the above assumptions the ‘ideal’ ∼2 µm gain of the medium was predicted at 0.34 dB using the equation $G = [{\sigma _{ems}}(\lambda ){N_{2(A )}} - {\sigma _{abs}}(\lambda ){N_{1(A )}}$] if no other losses are considered. If more realistic estimate losses are considered, such as 0.7 dB Fresnel reflection loss, 0.7 dB of waveguide loss and assuming the absence of OH quenching losses, the gain drops to1.4 dB loss/ pass for the cavity. Using the waveguide laser model, the presence of OH losses affects the 2 µm laser efficiency by reducing the excited ion population in the 5I7 state from 40% (without losses) to 20% for a total of 1.5 dB loss as can be observed from Fig. 8(a) and Fig. 9(a).

 

Fig. 9. (a) 5I7 population in Yb3+/Ho3+:GPGN reduced to ∼ 20% with 1.8 dB cavity loss (b) Output power as function of wavelength for 2W of input power.

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For the Yb3+/Ho3+:GPGN glass as gain medium, the highest gain was predicted for a 6 mm length of the sample considering no cavity losses (Fig. 8(b)). By setting the loss to 1.8 dB, maximum laser efficiency was estimated for a 2 mm long sample (Fig. 9(b)). To simulate the 2 µm laser, a 30 µm mode diameter of the laser cavity was considered. The input coupler used in the simulation was T=100% @ 976 nm and HR near ∼ 2000 nm, while the output coupler was a R = 95% output-coupler with a broadband reflectively centered at 2000 nm. By assuming no losses in the medium, a laser efficiency of 20% was predicted with a low 200 mW laser threshold. For a 1 dB loss in the glass medium (including the Fresnel and the internal glass absorption loss) the laser efficiency reduces to 15% with an increase in the laser threshold to ∼ 500 mW. Laser efficiency further reduces with an increase in the laser threshold by also considering OH quenching loss. For intra-cavity losses higher than 1.8 dB, no laser action was observed (Fig. 10).

 

Fig. 10. 2 µm laser simulations in Yb3+/Ho3+:GPGN and the effect of losses on the laser efficiency and threshold. No laser action observed for a total cavity loss above 1.8 dB.

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5. Conclusion

The potential of a new co-doped lead-germanate glass (Yb3+/Ho3+:GPGN) for 2 µm waveguide laser application was presented. The intensity parameters were calculated as Ω2 = 3.0×10−20 cm2, Ω4 = 1.2×10−20 cm2 and Ω6 = 2.0×10−20 cm2. The energy transfer efficiency from Yb3+:2F5/2 to Ho3+:5I6 was as high as 94% due to higher concentration of Yb3+ and Ho3+ in GPGN compared to the Yb3+/Ho3+ co-doped germanate glasses reported previously [3,12]. A quantum efficiency of 76% for 2 µm Ho3+ emission with a long measured radiative lifetime of Ho3+: 5I7 = (7.74 ± 0.03) ms was observed compared to other lead-germanate glasses [2,3,12]. The energy transfer analysis from Ho3+ to OH in GPGN resulted in a low value of $\gamma $ (0.15) indicating reduced tendency of OH to cluster with Ho3+ compared to GSPCK (0.24) [2]. Using the spectroscopic data, the simulated waveguide laser results predict that for Yb3+/Ho3+:GPGN, >15% laser efficiency at 2 µm can be achieved for cavity losses ≤ 0.5 dB. The overall spectroscopic analysis and the laser simulations indicate that Yb3+/Ho3+:GPGN is a promising gain medium for 2 µm waveguide laser operation.

Funding

Asian Office of Aerospace Research and Development (AOARD) (FA2386-16-1-4068).

Acknowledgement

The authors would like to acknowledge Alson Kwun Leung Ng for their support in glass fabrication and the OptoFab node of the Australian National Fabrication Facility supported by the Commonwealth and South Australian State Government. Mamoona Khalid would like to acknowledge University of South Australia’s University Presidential Scholarship.

Disclosures

The authors declare no conflicts of interest.

References

1. A. B. Seddon, Z. Tang, D. Furniss, S. Sujecki, and T. M. Benson, “Progress in rare-earth-doped mid-infrared fiber lasers,” Opt. Express 18(25), 26704–26719 (2010). [CrossRef]  

2. M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019). [CrossRef]  

3. J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019). [CrossRef]  

4. R. Cao, M. Cai, Y. Lu, Y. Tian, F. Huang, S. Xu, and J. Zhang, “Ho3+/Yb3+ codoped silicate glasses for 2 µm emission performances,” Appl. Opt. 55(8), 2065–2070 (2016). [CrossRef]  

5. J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010). [CrossRef]  

6. X. Wang, P. Zhou, Y. He, and Z. Zhou, “Erbium silicate compound optical waveguide amplifier and laser [Invited],” Opt. Mater. Express 8(10), 2970–2990 (2018). [CrossRef]  

7. D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

8. J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018). [CrossRef]  

9. X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009). [CrossRef]  

10. M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

11. H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013). [CrossRef]  

12. L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009). [CrossRef]  

13. X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+ doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015). [CrossRef]  

14. M. Cai, B. Zhou, F. Wang, Y. Tian, J. Zhou, S. Xu, and J. Zhang, “Highly efficient mid-infrared 2 µm emission in Ho3+/Yb3+-codoped germanate glass,” Opt. Mater. Express 5(6), 1431–1439 (2015). [CrossRef]  

15. P.-W. Kuan, X. Fan, X. Li, D. Li, K. Li, L. Zhang, C. Yu, and L. Hu, “High-power 2.04 µm laser in an ultra-compact Ho-doped lead germanate fiber,” Opt. Lett. 41(13), 2899–2902 (2016). [CrossRef]  

16. J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

17. M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019). [CrossRef]  

18. J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

19. P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008). [CrossRef]  

20. F. Piantedosi, G. Y. Chen, T. M. Monro, and D. G. Lancaster, “Widely tunable, high slope efficiency waveguide lasers in a Yb-doped glass chip operating at 1  µm,” Opt. Lett. 43(8), 1902–1905 (2018). [CrossRef]  

21. F. Huang, X. Liu, W. Li, L. Hu, and D. Chen, “Energy transfer mechanism in Er3+ doped fluoride glass sensitized by Tm3+ or Ho3+ for 2.7-\mu m emission,” Chin. Opt. Lett. 12(5), 051601 (2014). [CrossRef]  

22. L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970). [CrossRef]  

23. M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972). [CrossRef]  

24. C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012). [CrossRef]  

25. M. Khalid, G. Y. Chen, J. Bei, H. Ebendorff-Heidepriem, and D. G. Lancaster, “Microchip and ultra-fast laser inscribed waveguide lasers in Yb3+ ermanate glass,” Opt. Mater. Express 9(8), 3557–3564 (2019). [CrossRef]  

26. B. Yang, X. Liu, X. Wang, J. Zhang, L. Hu, and L. Zhang, “Compositional dependence of room-temperature Stark splitting of Yb3+ in several popular glass systems,” Opt. Lett. 39(7), 1772–1774 (2014). [CrossRef]  

27. Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009). [CrossRef]  

28. H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

29. J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983). [CrossRef]  

30. Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995). [CrossRef]  

31. B. Di Bartolo and V. Goldberg, Radiationless Processes (Springer Science & Business Media, 2012).

32. X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015). [CrossRef]  

33. H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

References

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  • |
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  • |

  1. A. B. Seddon, Z. Tang, D. Furniss, S. Sujecki, and T. M. Benson, “Progress in rare-earth-doped mid-infrared fiber lasers,” Opt. Express 18(25), 26704–26719 (2010).
    [Crossref]
  2. M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
    [Crossref]
  3. J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
    [Crossref]
  4. R. Cao, M. Cai, Y. Lu, Y. Tian, F. Huang, S. Xu, and J. Zhang, “Ho3+/Yb3+ codoped silicate glasses for 2 µm emission performances,” Appl. Opt. 55(8), 2065–2070 (2016).
    [Crossref]
  5. J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010).
    [Crossref]
  6. X. Wang, P. Zhou, Y. He, and Z. Zhou, “Erbium silicate compound optical waveguide amplifier and laser [Invited],” Opt. Mater. Express 8(10), 2970–2990 (2018).
    [Crossref]
  7. D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.
  8. J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
    [Crossref]
  9. X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
    [Crossref]
  10. M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.
  11. H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
    [Crossref]
  12. L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
    [Crossref]
  13. X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+ doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015).
    [Crossref]
  14. M. Cai, B. Zhou, F. Wang, Y. Tian, J. Zhou, S. Xu, and J. Zhang, “Highly efficient mid-infrared 2 µm emission in Ho3+/Yb3+-codoped germanate glass,” Opt. Mater. Express 5(6), 1431–1439 (2015).
    [Crossref]
  15. P.-W. Kuan, X. Fan, X. Li, D. Li, K. Li, L. Zhang, C. Yu, and L. Hu, “High-power 2.04 µm laser in an ultra-compact Ho-doped lead germanate fiber,” Opt. Lett. 41(13), 2899–2902 (2016).
    [Crossref]
  16. J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.
  17. M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
    [Crossref]
  18. J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).
  19. P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
    [Crossref]
  20. F. Piantedosi, G. Y. Chen, T. M. Monro, and D. G. Lancaster, “Widely tunable, high slope efficiency waveguide lasers in a Yb-doped glass chip operating at 1  µm,” Opt. Lett. 43(8), 1902–1905 (2018).
    [Crossref]
  21. F. Huang, X. Liu, W. Li, L. Hu, and D. Chen, “Energy transfer mechanism in Er3+ doped fluoride glass sensitized by Tm3+ or Ho3+ for 2.7-\mu m emission,” Chin. Opt. Lett. 12(5), 051601 (2014).
    [Crossref]
  22. L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970).
    [Crossref]
  23. M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
    [Crossref]
  24. C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012).
    [Crossref]
  25. M. Khalid, G. Y. Chen, J. Bei, H. Ebendorff-Heidepriem, and D. G. Lancaster, “Microchip and ultra-fast laser inscribed waveguide lasers in Yb3+ ermanate glass,” Opt. Mater. Express 9(8), 3557–3564 (2019).
    [Crossref]
  26. B. Yang, X. Liu, X. Wang, J. Zhang, L. Hu, and L. Zhang, “Compositional dependence of room-temperature Stark splitting of Yb3+ in several popular glass systems,” Opt. Lett. 39(7), 1772–1774 (2014).
    [Crossref]
  27. Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
    [Crossref]
  28. H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.
  29. J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983).
    [Crossref]
  30. Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
    [Crossref]
  31. B. Di Bartolo and V. Goldberg, Radiationless Processes (Springer Science & Business Media, 2012).
  32. X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015).
    [Crossref]
  33. H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

2019 (4)

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

M. Khalid, G. Y. Chen, J. Bei, H. Ebendorff-Heidepriem, and D. G. Lancaster, “Microchip and ultra-fast laser inscribed waveguide lasers in Yb3+ ermanate glass,” Opt. Mater. Express 9(8), 3557–3564 (2019).
[Crossref]

2018 (3)

F. Piantedosi, G. Y. Chen, T. M. Monro, and D. G. Lancaster, “Widely tunable, high slope efficiency waveguide lasers in a Yb-doped glass chip operating at 1  µm,” Opt. Lett. 43(8), 1902–1905 (2018).
[Crossref]

X. Wang, P. Zhou, Y. He, and Z. Zhou, “Erbium silicate compound optical waveguide amplifier and laser [Invited],” Opt. Mater. Express 8(10), 2970–2990 (2018).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

2016 (2)

2015 (3)

2014 (2)

2013 (1)

2012 (1)

C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012).
[Crossref]

2010 (2)

J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010).
[Crossref]

A. B. Seddon, Z. Tang, D. Furniss, S. Sujecki, and T. M. Benson, “Progress in rare-earth-doped mid-infrared fiber lasers,” Opt. Express 18(25), 26704–26719 (2010).
[Crossref]

2009 (3)

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

2008 (1)

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

1998 (1)

H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

1995 (1)

Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
[Crossref]

1983 (1)

J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983).
[Crossref]

1972 (1)

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

1970 (1)

L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970).
[Crossref]

Afshar, S.

Afshar, V. S.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Ahmed, Naveed

J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

Baranowska, A.

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

Barua, P.

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

Bei, J.

Benson, T. M.

Cai, M.

Cao, R.

Chavez-Pirson, A.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Chen, D.

F. Huang, X. Liu, W. Li, L. Hu, and D. Chen, “Energy transfer mechanism in Er3+ doped fluoride glass sensitized by Tm3+ or Ho3+ for 2.7-\mu m emission,” Chin. Opt. Lett. 12(5), 051601 (2014).
[Crossref]

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

Chen, G.

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

Chen, G. Y.

De Waal, H.

Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
[Crossref]

Di Bartolo, B.

B. Di Bartolo and V. Goldberg, Radiationless Processes (Springer Science & Business Media, 2012).

Dodson, C. M.

C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012).
[Crossref]

Donlan, V.

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

Dorosz, D.

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Dorosz, J.

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Ebendorff-Heidepriem, H.

M. Khalid, G. Y. Chen, J. Bei, H. Ebendorff-Heidepriem, and D. G. Lancaster, “Microchip and ultra-fast laser inscribed waveguide lasers in Yb3+ ermanate glass,” Opt. Mater. Express 9(8), 3557–3564 (2019).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Ebendorff-Heidepriem, Heike

J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

Ehrt, D.

H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

Faber, A. J.

Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
[Crossref]

Fan, X.

Fuerbach, A.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Furniss, D.

Goldberg, V.

B. Di Bartolo and V. Goldberg, Radiationless Processes (Springer Science & Business Media, 2012).

Górny, A.

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Götz, J.

L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970).
[Crossref]

Gross, S.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Haiping, X.

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

He, Y.

Hu, L.

Huang, F.

Ikushima, A.

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

Jäger, M.

Jelen, P.

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Jha, A.

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

Jiang, X.

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

Jinhao, W.

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

Khalid, M.

Kochanowicz, M.

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Kuan, P.

Kuan, P.-W.

Kuwik, M.

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

Lancaster, D.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Lancaster, D. G.

Leich, M.

Lesniak, M.

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

Leung Ng, Alson Kwun

J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

Li, D.

Li, K.

Li, W.

Li, X.

Liu, X.

Lousteau, J.

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

Lu, Y.

Manzani, D.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Matsinger, B.

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

Miluski, P.

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Monro, T.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Monro, T. M.

Munasinghe, H. T.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Nemec, L.

L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970).
[Crossref]

Ng, S.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Pan, J.

J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010).
[Crossref]

Pengfei Wang, J. B.

J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

Peyghambarian, N.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Piantedosi, F.

Pisarska, J.

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Pisarski, W. A.

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Qiongfei, L.

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

Qiu, J.

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

Ragin, T.

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Richards, B.

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

Sailong, H.

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

Saito, K.

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

Schiele, C.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Schuurmans, M.

J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983).
[Crossref]

Schwuchow, A.

Seddon, A. B.

Sekiya, E.

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

Sitarz, M.

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Soltys, M.

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Sujecki, S.

Surratt, G.

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

Tang, Z.

Tian, Y.

Van Dijk, J.

J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983).
[Crossref]

Wang, F.

Wang, X.

Weber, M.

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

Winterstein-Beckmann, A.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Withford, M.

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

Wondraczek, L.

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

Wu, J.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Xu, R.

J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010).
[Crossref]

Xu, S.

Yan, Y.

Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
[Crossref]

Yang, B.

Yao, Z.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Yu, C.

Yu, J.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Zhang, G.

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

Zhang, J.

Zhang, L.

Zhang, Q.

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

Zhang, Y.

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

Zhou, B.

Zhou, J.

Zhou, P.

Zhou, Z.

Zia, R.

C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012).
[Crossref]

Zmojda, J.

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

Zong, J.

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

Appl. Opt. (1)

Chin. Opt. Lett. (1)

Glass Science and Technology-Glastechnische Berichte (1)

H. Ebendorff-Heidepriem and D. Ehrt, “Optical spectroscopy of rare earth ions in glasses,” Glass Science and Technology-Glastechnische Berichte 71, 289–299 (1998).

J. Am. Ceram. Soc. (1)

L. Němec and J. Götz, “Infrared absorption of OH− in E glass,” J. Am. Ceram. Soc. 53(9), 526 (1970).
[Crossref]

J. Appl. Phys. (1)

Q. Zhang, G. Chen, G. Zhang, J. Qiu, and D. Chen, “Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer,” J. Appl. Phys. 106(11), 113102 (2009).
[Crossref]

J. Chem. Phys. (2)

J. Van Dijk and M. Schuurmans, “On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4 f–4 f transitions in rare-earth ions,” J. Chem. Phys. 78(9), 5317–5323 (1983).
[Crossref]

M. Weber, B. Matsinger, V. Donlan, and G. Surratt, “Optical transition probabilities for trivalent holmium in LaF3 and YAlO3,” J. Chem. Phys. 57(1), 562–567 (1972).
[Crossref]

J. Lumin. (2)

M. Kochanowicz, J. Żmojda, P. Miluski, A. Baranowska, T. Ragin, J. Dorosz, M. Kuwik, W. A. Pisarski, J. Pisarska, and M. Leśniak, “2 µm emission in gallo-germanate glasses and glass fibers co-doped with Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+,” J. Lumin. 211, 341–346 (2019).
[Crossref]

J. Pisarska, M. Kuwik, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Holmium doped barium gallo-germanate glasses for near-infrared luminescence at 2000nm,” J. Lumin. 215, 116625 (2019).
[Crossref]

J. Non-Cryst. Solids (2)

P. Barua, E. Sekiya, K. Saito, and A. Ikushima, “Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass,” J. Non-Cryst. Solids 354(42-44), 4760–4764 (2008).
[Crossref]

Y. Yan, A. J. Faber, and H. De Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995).
[Crossref]

J. Rare Earths (1)

L. Qiongfei, X. Haiping, Y. Zhang, W. Jinhao, J. Zhang, and H. Sailong, “Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions,” J. Rare Earths 27(1), 76–82 (2009).
[Crossref]

Opt. Express (1)

Opt. Lett. (3)

Opt. Mater. (2)

X. Jiang, J. Lousteau, B. Richards, and A. Jha, “Investigation on germanium oxide-based glasses for infrared optical fibre development,” Opt. Mater. 31(11), 1701–1706 (2009).
[Crossref]

J. Pan, R. Xu, Y. Tian, K. Li, L. Hu, and J. Zhang, “2.0 µm Emission properties of transparent oxyfluoride glass ceramics doped with Yb3+–Ho3+ ions,” Opt. Mater. 32(11), 1451–1455 (2010).
[Crossref]

Opt. Mater. Express (7)

X. Wang, P. Zhou, Y. He, and Z. Zhou, “Erbium silicate compound optical waveguide amplifier and laser [Invited],” Opt. Mater. Express 8(10), 2970–2990 (2018).
[Crossref]

X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+ doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015).
[Crossref]

M. Cai, B. Zhou, F. Wang, Y. Tian, J. Zhou, S. Xu, and J. Zhang, “Highly efficient mid-infrared 2 µm emission in Ho3+/Yb3+-codoped germanate glass,” Opt. Mater. Express 5(6), 1431–1439 (2015).
[Crossref]

M. Kochanowicz, J. Zmojda, P. Miluski, A. Baranowska, M. Leich, A. Schwuchow, M. Jäger, M. Kuwik, J. Pisarska, W. A. Pisarski, and D. Dorosz, “Tm3+/Ho3+co-doped germanate glass and double-clad optical fiber for broadband emission and lasing above 2 µm,” Opt. Mater. Express 9(3), 1450–1458 (2019).
[Crossref]

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, D. Manzani, L. Wondraczek, S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Lead-germanate glasses and fibers: a practical alternative to tellurite for nonlinear fiber applications,” Opt. Mater. Express 3(9), 1488–1503 (2013).
[Crossref]

M. Khalid, G. Y. Chen, J. Bei, H. Ebendorff-Heidepriem, and D. G. Lancaster, “Microchip and ultra-fast laser inscribed waveguide lasers in Yb3+ ermanate glass,” Opt. Mater. Express 9(8), 3557–3564 (2019).
[Crossref]

X. Fan, P. Kuan, K. Li, L. Zhang, D. Li, and L. Hu, “Spectroscopic properties and quenching mechanism of 2 µm emission in Ho3+doped germanate glasses and fibers,” Opt. Mater. Express 5(6), 1356–1365 (2015).
[Crossref]

Phys. Rev. B (1)

C. M. Dodson and R. Zia, “Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths,” Phys. Rev. B 86(12), 125102 (2012).
[Crossref]

Spectrochim. Acta, Part A (1)

J. Pisarska, M. Sołtys, A. Górny, M. Kochanowicz, J. Zmojda, J. Dorosz, D. Dorosz, M. Sitarz, and W. A. Pisarski, “Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties,” Spectrochim. Acta, Part A 201, 362–366 (2018).
[Crossref]

Other (6)

D. Lancaster, S. Gross, S. Ng, H. Ebendorff-Heidepriem, T. Monro, A. Fuerbach, and M. Withford, “A new class of 2µm waveguide lasers produced by fs direct-writing of Tm3+ and Ho3+ doped ZBLAN glass,” in Conference on Lasers and Electro-Optics/Pacific Rim (Optical Society of America, 2011), p. C888.

J. B. Pengfei Wang, Naveed Ahmed, Alson Kwun Leung Ng, and Heike Ebendorff-Heidepriem, “Development of low-loss lead-germanate glass for mid-infrared fiber optics, Part I: Optimization of the glass preparation,” Journal of The American Ceramics Society, accepted for publication (September 2020).

J. Wu, Z. Yao, J. Zong, A. Chavez-Pirson, N. Peyghambarian, and J. Yu, “Single-frequency fiber laser at 2.05 um based on ho-doped germanate glass fiber,” in Fiber Lasers VI: Technology, Systems, and Applications (International Society for Optics and Photonics, 2009), p. 71951K.

M. Kochanowicz, J. Żmojda, P. Miluski, T. Ragin, P. Jeleń, M. Sitarz, and D. Dorosz, “Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass,” in Optical Fibers and Their Applications 2015 (International Society for Optics and Photonics, 2015), p. 981605.

B. Di Bartolo and V. Goldberg, Radiationless Processes (Springer Science & Business Media, 2012).

H. T. Munasinghe, A. Winterstein-Beckmann, C. Schiele, L. Wondraczek, D. Manzani, V. S. Afshar, T. M. Monro, and H. Ebendorff-Heidepriem, “Fabrication and properties of lead-germanate glasses for high nonlinearity fibre applications,” in 39th European Conference and Exhibition on Optical Communication (ECOC 2013) (IET, 2013), pp. 1–3.

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Figures (10)

Fig. 1.
Fig. 1. (a) Absorption coefficient spectrum for Yb3+/Ho3+:GPGN glass from 400 nm – 2500nm representing different absorption bands of Ho3+ and Yb3+. Inset to the Fig. is the OH absorption coefficient spectrum peaking at ∼3100 nm in Yb3+/Ho3+:GPGN. (b) Comparison of Yb3+ absorption in GPGN with silica [19] and ZBLAN [20].
Fig. 2.
Fig. 2. (a) Experimental setup to collect fluorescence data from the edge of the Yb3+/Ho3+:GPGN using 976 nm pumping source (b) Fluorescence spectrum I(λ).
Fig. 3.
Fig. 3. Measured fluorescence decay curves in blue (dotted lines). Single coefficient best fit exponential decay curves are given in brown (solid lines) for (a) Ho3+:5I7 in Yb3+/Ho3+: GPGN with τm = 7.74 ms. (b) Yb3+:2F5/2 in Yb3+:GPGN with τYb = 1.76 ms.
Fig. 4.
Fig. 4. Absorption (blue) and emission (brown) cross sections for the Ho3+:5I75I8 transition at ∼2 µm. The fluorescence emission spectrum was obtained by exciting the sample with a 976 nm LD.
Fig. 5.
Fig. 5. Energy transfers (ET) pathways in Yb3+/Ho3+:GPGN. Solid transfer lines represent dominating processes.
Fig. 6.
Fig. 6. Linear dependence of energy transfer microparameter on the Ho3+ concentration (plotted using data in blue from [14] and this work (brown)). Data points > 0.1mol% Ho2O3 were used for linear fitting (green).
Fig. 7.
Fig. 7. (a) Simplified ET diagram for depopulation of 5I7 energy state of Ho3+. (b) Non-radiative decay rate as a function of Ho3+ and OH concentrations for GSPCK and GPGN glass, with similar slope in both glasses.
Fig. 8.
Fig. 8. (a) Predicted pump absorption in Yb3+/Ho3+:GPGN sample with respect to the position. n2 population in 5I7 is ∼ 40% with no losses (b) Output power as function of wavelength for 2 W of input power.
Fig. 9.
Fig. 9. (a) 5I7 population in Yb3+/Ho3+:GPGN reduced to ∼ 20% with 1.8 dB cavity loss (b) Output power as function of wavelength for 2W of input power.
Fig. 10.
Fig. 10. 2 µm laser simulations in Yb3+/Ho3+:GPGN and the effect of losses on the laser efficiency and threshold. No laser action observed for a total cavity loss above 1.8 dB.

Tables (3)

Tables Icon

Table 1. Measured and calculated electric dipole line strengths (Sed) and refractive index values for respective transition bands of Ho3+ and the JO intensity parameters Ω2, Ω4 and Ω6 in Yb3+/Ho3+:GPGN. * represents the electric (Aed) and magnetic (Amd) contributions for Ho3+:5I75I8 radiative transition probability.

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Table 2. Comparison of current study with published Yb3+/Ho3+ GBGL where the Yb3+ lifetime is measured for a range of Ho3+ concentrations.

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Table 3. Measured and calculated parameters for GPGN and GSPCK for different concentrations of Ho3+ and OH for the calculation of γ and the respective quantum efficiency (QE).

Equations (13)

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n 2 ( λ ) = A + B 1 C / λ 2 + D 1 E / λ 2
N O H = α O H N A ε O H
S e d ( J J ) = t = 2 , 4 , 6 Ω t | < J | | U ( t ) | | J > | 2
b a n d α ( λ ) d ( λ ) = 8 π 3 e 2 λ N H o 3 c h ( 2 J + 1 ) [ ( n 2 + 2 ) 2 9 n S e d ( J J ) + n 3 S m d ]
S m d ( J J ) = 3 h λ e 2 ( 2 J + 1 ) 8 π 2 m n c 2 × P m d ( J J )
A r ( J J ) = 64 π 4 3 h λ 3 ( 2 J + 1 ) [ n ( n 2 + 2 ) 2 9 S e d ( J J ) + n 3 S m d ]
σ e m s ( λ ) = λ 4 8 π c n 2 τ r × I ( λ ) I ( λ ) d ( λ )
W E T = 1 τ D 1 τ Y b
τ m 1 = τ r 1 + W M P + W O H
W O H = 8 π × C H o × N H o × γ × N O H
C H o = 3 c A r 8 π 4 n 2 ( 2 J + 1 ) ( 2 J + 1 ) σ e m s D ( λ ) σ a b s A ( λ )
A b s o r p t i o n = 1 exp ( N Y b σ a b s ( λ ) L )
t N 2 ( A ) = N 2 ( A ) τ m q N H o N 2 ( A ) 2 + i P i A h ν i [ ( 1 N 2 ( A ) ) σ a b s ( λ ) N 2 ( A ) σ e m s ( λ ) ]

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