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Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Pore-size dependent THz absorption of nano-confined water

Chi-Kuang Sun, Borwen You, Yu-Ru Huang, Kao-Hsiang Liu, Shusaku Sato, Akiyoshi Irisawa, Motoki Imamura, and Chung-Yuan Mou

Doc ID: 234712 Received 13 Feb 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We performed THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21 of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk–water–like THz absorption behavior in the core water region and a solid–like THz absorption behavior in the interfacial water region.

Effects of multiphoton absorption on parametric comb generation in silicon microresonators

Ryan Lau, Alexander Gaeta, Yoshitomo Okawachi, and Michael Lamont

Doc ID: 235489 Received 03 Mar 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We investigate theoretically parametric frequency comb generation in silicon microresonators at telecom and mid-infrared (MIR) wavelengths in the presence of multiphoton absorption and free-carrier effects using a modiffied Lugiato-Lefever model. We show that parametric oscillation may occur at MIR wavelengths, provided that the free-carrier lifetime is sufficiently short or the optical pump power is sufficiently low, but is inhibited at telecom wavelengths. In addition, we propose an etchless, air-clad silicon microresonator that enables an octave-spanning frequency comb in a completely passive device.

Secure optical GFBMC system based on cubic constellation masked method

Bo Liu, Lijia Zhang, and Xiangjun Xin

Doc ID: 236985 Received 27 Mar 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: A secure optical generalized filter bank multi-carrier (GFBMC) system with carrier-less amplitude-phase (CAP) modulation is proposed in the letter. The security is realized through cubic constellation masked method. Large key space and more flexibility masking can be obtained by cubic constellation masking aligning with the filter bank. An experiment with 18Gb/s encrypted GFBMC/CAP system is performed to demonstrate the feasibility of the proposed method.

Characterizing coherence vortices through the geometry

Alcenisio Silva, Eduardo Fonseca, and Cleberson Alves

Doc ID: 237634 Received 08 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We produce experimentally and numerically coherence vortices and study the dependence of their bright ring area and dark region with their different orders. This is a linear dependence with slope proportional to the bright ring or dark area. We show that it is possible to obtain any order of coherence vortices, including the fractional ones, just by calculating the bright ring or dark area of vortices for the specific parameters of the incident beam.

Extraordinary transmission in optical Helmholtz resonators

Patrick Bouchon, Paul Chevalier, Emilie SAKAT, Jean-Luc Pelouard, Fabrice Pardo, and Riad Haidar

Doc ID: 238337 Received 17 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: Optical Helmholtz resonators have been adapted from acoustics designs for light absorbing structures, exhibiting extreme light confinement. Here, extraordinary transmission of light is theoretically demonstrated through symmetric optical Helmholtz resonators, comprising a cavity with two λ/500 narrow slits on either side. This device has appealing features to act as a spectral bandpass filter in the context of multispectral imaging, in particular its high angular tolerance due to the localized nature of the resonance. Besides, the cavity can be modeled as an inductor and the two slits as capacitors, the whole design acting as a LC circuit thus preventing any harmonic features.

Two-dimensional single-pixel imaging by cascaded orthogonal line spatial modulation

Randy Bartels and David Winters

Doc ID: 238426 Received 20 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: Two dimensional images are taken using a single-pixel detector by temporally multiplexing spatial frequency projections from orthogonal, time varying spatial line modulation gratings. Unique temporal frequencies are applied to each point in two dimensional space, applying a continuous spread of frequencies to one dimension, and an offset frequency applied to each line in the orthogonal dimension. The object contrast information can then be recovered from the electronic spectrum of the single pixel, and through simple processing be reformed into a spatial image.

Hermetic Optical Fiber Iodine Frequency Standard

Philip Light, James Anstie, Fetah Benabid, and Andre Luiten

Doc ID: 240157 Received 04 May 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We have built an optical frequency standard based on interrogating iodine vapour that has been trapped within the hollow core of a hermetically-sealed kagome-lattice photonic crystal fiber. A frequency-doubled Nd:YAG locked to a hyperfine component of the P(142)37-0 ¹²⁷I₂ transition using modulation transfer spectroscopy shows a frequency stability of 3×10^-11 at 100 seconds. We discuss the impediments in integrating this all-fiber standard into a fully optical-fiber based system, and suggest approaches that could improve performance of the frequency standard substantially.

High-power mid-infrared high repetition-rate supercontinuum source based on a chalcogenide step-index fiber

Stefan Kedenburg, Tobias Steinle, Florian Mörz, Andy Steinmann, and Harald Giessen

Doc ID: 236877 Received 30 Mar 2015; Accepted 18 May 2015; Posted 19 May 2015  View: PDF

Abstract: We demonstrate a tunable and robust femtosecond supercontinuum source that covers a total spectral width of 2600 nm, reaching the mid-infrared region and extending from 2300 nm up to 4900 nm with a maximum output power of 550 mW. As₂S₃ chalcogenide step-index fibers with core diameters of 7 μm and 9 μm are pumped at different wavelengths from 2.5 μm up to 4.1 μm with femtosecond pulses by means of a post-amplified optical parametric oscillator pumped by an Yb:KGW laser. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy as demonstrated for the CS₂-absorption bands around 3.5 μm.

Modulation instability in highly-nonlinear fiber for pulsed random bit generation

Xie Wang, Sze-Chun Chan, Kenneth Kin-Yip Wong, and Xiao-Zhou Li

Doc ID: 236769 Received 24 Mar 2015; Accepted 18 May 2015; Posted 18 May 2015  View: PDF

Abstract: A simple yet high-speed scheme by utilizing modulation instability (MI) on pulsed generation of random bits is proposed and demonstrated experimentally. MI pulses are developed when a highly-nonlinear fiber is pumped by a mode-locked laser. They contain fluctuating pulse-to-pulse variations of peak intensities for extraction into random bits. At a repetition rate of 10 GHz, 5 bits are extracted from each anti-Stokes pulse in generating random bits at 50 Gbps, as verified by the National Institute of Standards and Technology test suite.

Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies

Sean Knight, Stefan Schoeche, Vanya Darakchieva, Philipp Kuehne, Jean-Francois Carlin, Nicolas Grandjean, Craig Herzinger, Mathias Schubert, and Tino Hofmann

Doc ID: 237567 Received 08 Apr 2015; Accepted 18 May 2015; Posted 18 May 2015  View: PDF

Abstract: The effect of a tunable, externally coupled Fabry-P\'{e}rot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this communication. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-P\'{e}rot cavity, are presented and discussed. Tuning the externally coupled Fabry-P\'{e}rot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence and magnetic field direction and strength.

Tilt-tuned etalon locking for tunable laser stabilization

Bradley Gibson and Benjamin McCall

Doc ID: 237963 Received 14 Apr 2015; Accepted 18 May 2015; Posted 18 May 2015  View: PDF

Abstract: Locking to a fringe of a tilt-tuned etalon provides a simple, inexpensive method for stabilizing tunable lasers. Here, we describe the use of such a system to stabilize an external-cavity quantum cascade laser; the locked laser has an Allan deviation of approximately 1 MHz over a one-second integration period, and has a single-scan tuning range of approximately 0.4 wavenumbers. The system is robust, with minimal alignment requirements and automated lock acquisition, and can be easily adapted to different wavelength regions or more stringent stability requirements with minor alterations.

Optimized emission in nanorod arrays through quasi-aperiodic inverse design

Patrick Anderson and Michelle Povinelli

Doc ID: 235534 Received 06 Mar 2015; Accepted 17 May 2015; Posted 18 May 2015  View: PDF

Abstract: We investigate a new class of quasi-aperiodic nanorod structures for enhancement of incoherent emission. We identify one optimized structure using an inverse design algorithm and the finite-difference time-domain method. We carry out emission calculations on both the optimized structure as well as a simple periodic array. The optimized structure achieves maximum theoretical light extraction while maintaining a high spontaneous emission rate. Overall, the optimized structure can achieve a 20-48% increase in external quantum efficiency relative to a simple periodic design, depending on material quality.

A generalized Kerker condition for highly directive nanoantennas

Rasoul Alaee, Robert Filter, Dennis Lehr, Falk Lederer, and Carsten Rockstuhl

Doc ID: 236651 Received 27 Mar 2015; Accepted 17 May 2015; Posted 18 May 2015  View: PDF

Abstract: A nanoantenna with balanced electric and magnetic dipole moments, known as the first Kerker condition, exhibits a directive radiation pattern with zero backscattering. Whereas an enhanced directionality has been already observed for nanoantennas characterized by multipole moments beyond the dipole moments, a theory that extrapolates the traditional Kerker condition to higher order multipole moments has not yet been concisely formulated. Here, we provide a blueprint for such extension and formulate a generalized Kerker condition at the example of nanoantennas supporting electric and magnetic dipole and electric quadrupole moments. We study the consequences of meeting the Kerker condition at the example of a plasmonic nanoring antenna that is dominated by electric dipole and quadrupole moments. Nanoring antennas are extremely suitable since both multipole moments can be independently tuned to meet the generalized Kerker condition.

Multiwavelength phase-shifting digital holography selectively extracting wavelength information from wavelength-multiplexed holograms

Tatsuki Tahara, Ryota Mori, Shuhei Kikunaga, Yasuhiko Arai, and Yasuhiro Takaki

Doc ID: 235146 Received 23 Feb 2015; Accepted 16 May 2015; Posted 18 May 2015  View: PDF

Abstract: Multiwavelength phase-shifting digital holography that selectively extracts wavelength information from wave-length-multiplexed holograms is presented. Specific phase shifts are introduced for respective wavelengths to remove the crosstalk components and to extract only the object wave at the desired wavelength from the holograms. Object waves in multiple wavelengths are selectively extracted by utilizing 2π ambiguity and the subtraction procedures based on phase-shifting interferometry. Numerical results show the validity of the proposed technique in case of du-al-wavelengths. The proposed technique is also experimentally demonstrated.

Nonlinear compression of ultrashort-pulse thulium-based fiber laser to sub-70 fs in Kagome photonic crystal fiber

Martin Gebhardt, Christian Gaida, Steffen Hädrich, Fabian Stutzki, Cesar Jauregui, Jens Limpert, and Andreas Tünnermann

Doc ID: 236358 Received 18 Mar 2015; Accepted 16 May 2015; Posted 18 May 2015  View: PDF

Abstract: Nonlinear pulse compression of ultrashort pulses is an established method for reducing the pulse duration and increasing the pulse peak power beyond the intrinsic limits of a given laser architecture. In this proof-of-principle experiment we demonstrate nonlinear compression of the pulses emitted by a high repetition rate thulium-based fiber CPA system. The initial pulse duration of about 400 fs has been shortened to <70 fs with 19.7 μJ of pulse energy, which corresponds to about 200 MW of pulse peak power.

Discrete-mode ZnO microparticle random laser

Toshihiro Nakamura, Shohei Sonoda, Taisei Yamamoto, and Sadao Adachi

Doc ID: 238189 Received 15 Apr 2015; Accepted 16 May 2015; Posted 18 May 2015  View: PDF

Abstract: A random laser incorporating irregular-shaped ZnO microparticles exhibits a small number of lasing lines with stable lasing intensities and negligibly low background emission. This unique feature is in direct contrast to that observed for a conventional ZnO nanoparticle film random laser. Gain competition between the discrete laser modes also occurs in this microparticle random laser. This lasing characteristics are due to the intra-particle confinement of the laser cavity modes in each ZnO microparticle.

The fluctuation-dissipation relation in a resonantly driven quantum medium

Maria Erukhimova and Mikhail Tokman

Doc ID: 233481 Received 02 Feb 2015; Accepted 15 May 2015; Posted 19 May 2015  View: PDF

Abstract: We calculate the radiation noise level associated with the spontaneous emission of a coherently driven medium. The significant field-induced modification of relation between the noise power and damping constant in a thermal reservoir is obtained. The nonlinear noise exchange between different atomic frequencies leads to violation of standard relations dictated by the fluctuation-dissipation theorem. This result can cardinally modify the conditions of successful manipulations with nonclassical field states in EIT-based schemes which are attractive for realization of different quantum-information processing devices.

Quantitative polarized light microscopy using spectral multiplexing interferometry

Yizheng Zhu and Chengshuai Li

Doc ID: 237228 Received 08 Apr 2015; Accepted 15 May 2015; Posted 15 May 2015  View: PDF

Abstract: We propose an interferometric spectral multiplexing method for measuring birefringent specimens with simple configuration and high sensitivity. The retardation and orientation of sample birefringence are simultaneously encoded onto two spectral carrier waves, generated interferometrically by a birefringent crystal through polarization mixing. A single interference spectrum hence contains sufficient information for birefringence determination, eliminating the need for mechanical rotation or electrical modulation. The technique is analyzed theoretically and validated experimentally on cellulose film. System simplicity permits the possibility of mitigating system birefringence background. Further analysis demonstrates the technique’s exquisite sensitivity as high as ~20pm for retardation measurement.

High power efficient SESAM-mode-locked Yb:KGW bulk laser

Alexander Rudenkov, Viktor Kisel, Anatoliy Pavlyuk, Alexander Kovalyov, Valeri Preobrazhenskii, Michail Putyato, Nataliya Rubtsova, Boris Semyagin, and Nikolai Kuleshov

Doc ID: 238140 Received 17 Apr 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: High-power diode-pumped SESAM mode-lockedYb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at pulse repetition frequency of 62MHz. For Np-polarization 143-fs pulses with pulse energy 139 nJ and average output power up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Optical Detection of Harmonic Oscillations in Fluorescent Dye-Loaded Microbubbles Ensonified by Ultrasound

Carolyn Schutt, Stuart Ibsen, Michael Benchimol, Mark Hsu, and Sadik Esener

Doc ID: 232767 Received 21 Jan 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: A new optical contrast agent has been developed by exposing dye-loaded microbubbles to a rapid-cooling thermal treatment to homogenize the dye distribution across the surface. Ultrasound causes these microbubbles to oscillate in size which changes the self-quenching efficiency of the dye molecules creating a “blinking” signal. We demonstrate for the first time that these microbubbles can reproducibly generate 2nd, 3rd, and even 4th harmonic fluorescence intensity modulations in addition to the fundamental frequency of the driving ultrasound. Detecting these harmonic signals could produce a higher signal-to-noise ratio for fluorescence imaging in medical applications by allowing fundamental frequency interference and artifacts to be filtered out.

Dual-state dissipative solitons from an all-normal-dispersion Erbium-doped fiber laser: continous wavelength-tuning and multi-wavelength emission

Fu Songnian, Wu Zhichao, Chen Changxiu, Ming Tang, Shum Ping, and Dengming Liu

Doc ID: 237171 Received 02 Apr 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: We propose and experimentally demonstrate switchable operation of dissipative solitons (DSs) in erbium-doped fiber laser (EDFL). By managing normal dispersion of laser cavity, the 3dB spectral bandwidth up to 8.1nm can be obtained with the help of semiconductor saturable absorber mirror (SESAM). Using an inline polarizer, the fiber laser can be separately operated at either wavelength-tunable or multi-wavelength emission. The central wavelength of DS can be continuously tuned from 1554nm to 1561nm with its spectra maintaining standard rectangular shape. Alternatively, triple-wavelength DSs at 1535nm, 1544nm, and 1553nm can be simultaneously obtained.

Cryogenic Yb:YAG composite-thin-disk for high energy and average power amplifiers

Luis Zapata, Hua Lin, Anne-Laure Calendron, Huseyin Cankaya, Michaël Hemmer, Fabian Reichert, Wenqian Huang, Eduardo Granados, Kyung-Han Hong, and FRANZ KAERTNER

Doc ID: 236593 Received 25 Mar 2015; Accepted 12 May 2015; Posted 12 May 2015  View: PDF

Abstract: A cryogenic composite-thin-disk amplifier with amplified spontaneous emission (ASE) rejection is implemented that overcomes traditional laser system problems in high-energy pulsed laser drivers of high average power. A small signal gain of 8 dB was demonstrated compared to 1.5 dB for an uncapped thin-disk without ASE mitigation under identical pumping conditions. A strict image-relayed 12-pass architecture using an off-axis vacuum telescope and polarization switching extracted 110 mJ at 250 Hz in high beam quality stretched 700 ps pulses of 0.6-nm bandwidth.

Frequency-doubling characteristics of high-power, ultrafast phase singular optical beams

Goutam K. Samanta, Apurv Chaitanya N, Aadhi A, and Jabir M. V.

Doc ID: 238055 Received 15 Apr 2015; Accepted 12 May 2015; Posted 12 May 2015  View: PDF

Abstract: We report on collinear interaction of high-power, ultrafast phase singular optical beams in nonlinear medium. More precisely, optical vortex beams of different topological charges (orders) interact with second order nonlinear medium in collinear geometry generating a new vortex beam with double the frequency and topological charge of the input beam. Based on single-pass second harmonic generation (SHG) in 1.2-mm long bismuth triborate (BIBO) crystal, we generate ultrafast optical vortices with power as high as 900 mW and topological charge as high as 12. We observe decreasing SHG efficiency with input vortex order, which can be attributed to the increasing area of the vortices with order. Like Gaussian beam, optical vortices have focusing dependent conversion efficiency. However, under similar experimental conditions, the optimum focusing condition for optical vortices is reached at tighter focusing with orders. We observe higher angular acceptance bandwidth in case of optical vortices than that of Gaussian beam, however, there is no substantial change in angular acceptance bandwidth with vortex order. Additionally, we also observe that in frequency-doubling, the topological charge has negligible or no effect in temporal and spectral properties of the beams.

Longwave infrared, single-frequency, tunable, pulsed optical parametric oscillator based on orientation-patterned GaAs for gas sensing

Antoine Godard, Quentin Clement, Jean-Michel Melkonian, Jean-Baptiste Dherbecourt, Myriam Raybaut, Arnaud Grisard, Eric Lallier, Bruno Gérard, Basile Faure, and Grégoire Souhaité

Doc ID: 236862 Received 25 Mar 2015; Accepted 12 May 2015; Posted 13 May 2015  View: PDF

Abstract: We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 µJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning enables to cover the 10.3–10.9 μm range with a quasi-phase-matching period of 72.6 µm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 µnm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

On a propagation-invariant, orthogonal modal expansion on the unit disk: going beyond Nijboer-Zernike theory of aberrations.

Omar El Gawhary

Doc ID: 237594 Received 08 Apr 2015; Accepted 12 May 2015; Posted 13 May 2015  View: PDF

Abstract: Nijboer-Zernike's circle polynomials are broadly used for the evaluation of aberrations of optical systems or, more generally, wavefront analysis. This because they are orthogonal over a unit circle and are directly related to the balanced classical aberrations for imaging systems with circular pupils. However, such expansion, and successive extensions of the original theory, suffers from a key limitation: it does not preserve its form under propagation. This means that even if a Nijboer-Zernike expansion for a field is known on a given reference plane, as soon as another plane is considered, a new, different, set of polynomials, for the same field, appears. The origin of this problem is to be ascribed to the fact that Nijboer-Zernike polynomials are a useful mathematical tool which, however, are not bound to the physics of the electromagnetic problem they are employed in. In this work, we show that a more appropriate modal expansion does exist which is not only orthogonal on the unit disk but it is also invariant on propagation. Beside impacting on the field of aberrations analysis and retrieval, the modal expansion introduced here holds an enormous potential for digital classical and quantum optical communications, optical metrology, adaptive optics, too. The practical implementation, physical interpretation and visualization of this new modal expansion are all very straightforward.

Inherent photoluminescence Stokes shift in GaAs

Puspendu Barik, Bruno Ullrich, Akhilesh Singh, Mithun Bhowmick, and Haowen Xi

Doc ID: 235243 Received 26 Feb 2015; Accepted 12 May 2015; Posted 12 May 2015  View: PDF

Abstract: The intrinsic photoluminescence Stokes shift, i.e., the energy difference between optical band gap and emission peak, of 350 μm thick semi-insulating GaAs wafers is found to be 4 meV at room temperature. The result is based on the determination of the optical bulk band gap from the transmission trend via modified Urbach rule whose result is confirmed with the transmission derivative method. The findings reveal the detailed balance of the optically evoked transitions and disclose the intrinsic link between Stokes shift and the Urbach tail slope parameter.

Plasmon enhanced near-infrared quantum cutting of KYF4:Tb3+, Yb3+doped with Ag nanoparticles

Biao Zheng, Zhiqiang Zheng, Lin Lin, Senyuan Xu, zhezhe wang, and Zhuohong Feng

Doc ID: 235704 Received 18 Mar 2015; Accepted 11 May 2015; Posted 12 May 2015  View: PDF

Abstract: A novel quantum cutting (QC) phosphor KYF4:Tb3+, Yb3+ doped Ag nanoparticles (NPs) was prepared by using the sol-gel method. Plasmon enhanced near-infrared (NIR) QC involving Yb3+ ion at 975nm (2F5/2→2F7/2) emission was achieved under the excitation of 374nm (7F6→5D3) and 485nm (7F6→5D4) of Tb3+ ions, respectively. The effect of Ag NPs on NIR QC luminescence is investigated, and the results show that QC luminescence intensity first increases, then decreases with the increasing concentration of Ag NPs. The maximum enhancement factor is about 1.9 when the concentration of Ag NPs increases to 0.5%. Our study may have potential application in the field of silicon-based solar cells.

Tunable slow light via stimulated Brillouin scattering at 2 μm based on Tm-doped fiber amplifiers

Xiong Wang, Pu Zhou, Xiaolin Wang, Hu Xiao, and Zejin Liu

Doc ID: 235427 Received 04 Mar 2015; Accepted 11 May 2015; Posted 11 May 2015  View: PDF

Abstract: We present a slow light system based on stimulated Brillouin scattering (SBS) at 2 μm. A single frequency fiber laser with Tm-doped fiber amplifiers was used to generate the SBS signal laser and the Brillouin pump light at 1.971 μm. The maximum delay time reaches 16 ns for pulses with 43 ns width, and the pulse width is broadened to 56.4 ns. The maximum delay time for 57 ns pulses reaches 33.4 ns, and the pulse width is broadened to 77.6 ns. The relative delays are 0.37 and 0.58 for 43 ns and 57 ns pulses, respectively. This is first demonstration, as far as we know, on slow light system at 2 μm, which may be substantial for future optical communications and LIDAR systems employing laser sources near 2 μm band.

Near-field evanescent wave scattering from spatially deterministic and anisotropic medium

Jia Li, Liping Chang, and Zhefu Wu

Doc ID: 236982 Received 27 Mar 2015; Accepted 11 May 2015; Posted 14 May 2015  View: PDF

Abstract: The scattering of light waves by either spatially random or deterministic anisotropic medium has attracted substantial interest where the measurement of the internal structures of scatterers is concerned. However, to date, no literature has discussed the statistics of near-zone evanescent waves scattered by a spatially-deterministic anisotropic medium. Integral expressions are given to describe the behaviors of evanescent waves in the near-zone scattered field. The degree to which the intensity distributions of scattered light depends on the diffraction length of the scattering medium and the effective size of the scattering potential (ESSP) is also shown using numerical simulations. Potential applications of these finding include optical microscopy of nano-structure images on a sub-wavelength scale.

High efficient Er/Yb-codoped fiber amplifier with an Yb-band fiber Bragg grating

Qun Han, Yunzhi Yao, Yaofei Chen, Fangchao Liu, T. Liu, and Hai Xiao

Doc ID: 237592 Received 06 Apr 2015; Accepted 11 May 2015; Posted 12 May 2015  View: PDF

Abstract: In this Letter, a high-power Er/Yb-codped fiber amplifier (EYDFA) with a high-reflection Yb-band fiber Bragg grating (FBG) at the pump-end is experimentally investigated. The FBG was inscribed on a piece of double-clad fiber with a center wavelength of 1032 nm. Due to the selective reflection of the backward Yb-band amplified spontaneous emission (Yb ASE) by the FBG, a co-pump-propagating Yb-band auxiliary signal was generated. Because the stimulated amplification and reabsorption of the auxiliary signal, the Yb ASE was dramatically suppressed and the pump-conversion-efficiency (PCE) of the EYDFA was notably improved. An output power of 6.48W was achieved at a pump power of 16.5W, which equivalent to a PCE of ~39.27%. The slope-efficiency relative to applied pump power was 40.04%. The maximum output power was improved ~19.78% because the introduction of the FBG.

High-performance infrared light trapping in nano-needle structured p+ SnOx (x≤1)/thin film n-Ge photodiodes on Si

Jifeng Liu, Xiaoxin Wang, Andrew Wong, Stephanie Malek, and Yan Cai

Doc ID: 237042 Received 27 Mar 2015; Accepted 10 May 2015; Posted 11 May 2015  View: PDF

Abstract: We report nano-needle structured conductive SnOx (x≤1) as a self-assembled electrode for high-efficiency light trapping in thin-film infrared (IR) photonic devices, benefiting from the high scattering efficiency, high density, and low IR loss of the nano-needles. We demonstrate a 2.2× responsivity enhancement for a 1.5 µm-thick Ge absorber in a nano-needled p-SnOx / n-Ge photodiode on Si at λ=1580 nm, in good agreement with theoretical calculation of 2.3× enhancement assuming no IR loss in the nano-needles. Such low-loss light trapping can potentially enable 15-30× absorption enhancement at λ=1600-1650 nm in the Ge layer when integrated with a perfect rear reflector.

Photonic radio frequency dissemination via optical fiber with high phase stability

Xiaocheng Wang, zhangweiyi Liu, Siwei Wang, Dongning Sun, Yi Dong, and Weisheng Hu

Doc ID: 235388 Received 20 Mar 2015; Accepted 09 May 2015; Posted 11 May 2015  View: PDF

Abstract: We demonstrate a photonic radio frequency transmission system via optical fiber. Optical radio frequency signal is generated utilizing a Mach–Zehnder modulator based on double-side-band with carrier suppression modulation scheme. The phase error induced by optical fiber transmission is transferred to an intermediate frequency signal by the dual-heterodyne phase error transfer scheme, and then canceled by a phase locked loop. With precise phase com-pensation, a radio frequency with high phase stability can be obtained at the remote end. We performed 20.07 GHz ra-dio frequency transfer over 100 km optical fiber, and achieved residual phase noise of -65 dBc/Hz at 1 Hz offset fre-quency, the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches 110 fs. The long-term frequency stability also achieves 810-17 at 10000 s averaging time.

Normal incidence narrowband transmission filtering capabilities using symmetry protected modes of a dielectric grating

Justin Foley and James Phillips

Doc ID: 235866 Received 26 Mar 2015; Accepted 09 May 2015; Posted 11 May 2015  View: PDF

Abstract: We computationally study a normal incidence narrowband transmission filter based on a subwavelength dielectric grating that operates through interference between supported guided leaky modes of the system. We characterize the filtering capabilities as the cross section of the grating is manipulated and suggest techniques for experimentally demonstrating normal incidence filtering. Using group theory, we study the plane wave coupling to the supported modes that leads to broadband reflectance and narrowband transmittance responses for rectangular, pentagonal, rhomboidal, and right trapezoidal cross-sectional geometries.

Discrete non-planar reflections from an ultrashort pulse written Volume-Bragg-Grating (VBG)

Daniel Richter, Christian Voigtländer, Ria Krämer, Jens Thomas, Andreas Tünnermann, and Stefan Nolte

Doc ID: 235895 Received 12 Mar 2015; Accepted 07 May 2015; Posted 18 May 2015  View: PDF

Abstract: In this letter we present a direct writing technique for two-dimensional-periodic VBGs in fused silica based on the phase mask technology, ultrashort laser pulses and three-beam-interference. An algorithm to predict the grating pattern and its diffraction behaviour under collimated, spectral broad illumination is developed. The predicted data are in good agreement with the measurements.

Phase-Sensitive Optical Coherence Elastography at 1.5 Million A-lines per Second

Kirill Larin, Manmohan Singh, Chen Wu, Chih hao liu, Jiasong Li, Alexander Schill, and Achuth Nair

Doc ID: 236492 Received 19 Mar 2015; Accepted 06 May 2015; Posted 08 May 2015  View: PDF

Abstract: Shear-wave imaging optical coherence elastography (SWI-OCE) is an emerging method for 3D quantitative assessment of tissue local mechanical properties based on imaging and analysis of elastic wave propagation. Current methods for SWI-OCE involve multiple temporal OCT scans at different spatial locations across tissues surface. This requires an excitation for each measurement position leading to clinically unacceptable long acquisition times up to tens of minutes. In this Letter we demonstrate, for the first time, noncontact true kilohertz frame-rate optical coherence elastography by combining a Fourier Domain Mode Locked swept source laser with an A-scan rate of ~1.5MHz and a focused air-pulse as an elastic wave excitation source. The propagation of the elastic wave in the sample was imaged at a frame rate of ~7.3 kHz. Therefore, to quantify elastic wave propagation velocity, only a single air-pulse is needed. This method was validated by quantifying mechanical properties of tissue-mimicking agar phantoms as well as of a porcine corneas ex-vivo at different intraocular pressures. The results demonstrate that this method can quantify elastic wave propagation in 30 milliseconds or less.

Toward athermal silicon-on-insulator (de)multiplexers in the O-band

Badhise Ben Bakir, Karim HASSAN, Corrado Sciancalepore, Julie Harduin, Thomas Ferrotti, and Sylvie MENEZO

Doc ID: 236582 Received 20 Mar 2015; Accepted 06 May 2015; Posted 08 May 2015  View: PDF

Abstract: We report on the design, fabrication, and characterization of a 1 × 4 silicon-on-insulator (SOI) demultiplexer exhibiting a significant reduction of its thermo-optical sensitivity in the O-band. The optical filtering is achieved by cascading several Mach-Zehnder interferometers fabricated on a 300nm-thick SOI platform. Owing to an asymmetric design of the confinement for each MZIs, we found an athermal criterium that satisfies the spectral requirements. The thermal sensitivity of the structure is analyzed by a semi-analytical model in order to create an athermal multiplexer. Fiber-to-fiber thermo-optical testing reveals a thermal sensitivity of around 17pm/°C reduced by 75% compared to the standard devices with promising performances for both the crosstalk (15dB), the insertion losses (4dB) and absolute lambda registration (<0.25nm).

Broadband perfect absorber based on one ultrathin layer of refractory metal

Xiaodong Yang, Jie Gao, David Czaplewski, Daniel Rosenmann, Liliana Stan, Zhigang Li, and Huixu Deng

Doc ID: 238097 Received 16 Apr 2015; Accepted 06 May 2015; Posted 08 May 2015  View: PDF

Abstract: A broadband perfect absorber based on one ultrathin layer of the refractory metal chromium without structure patterning is proposed and demonstrated. The ideal permittivity of the metal layer for achieving broadband perfect absorption is derived based on the impedance transformation method. Since the permittivity of the refractory metal chromium matches this ideal permittivity well in the visible and near-infrared range, a silica-chromium-silica three-layer absorber is fabricated to demonstrate the broadband perfect absorption. The experimental results show that the absorber is incident angle-insensitive and polarization-independent with high absorption above 90% over the wavelength range of 0.4-1.4 μm.

Adaptive linearized microwave downconversion utilizing a single dual-electrode Mach-Zehnder modulator

Yan Pan, Lianshan Yan, Zhiyu Chen, Wei Pan, Bing Luo, Xihua Zou, Jia Ye, and Anlin Yi

Doc ID: 234776 Received 17 Feb 2015; Accepted 04 May 2015; Posted 05 May 2015  View: PDF

Abstract: An Adaptive post-processing approach to improve the linearity of the down-converted analog photonic link has been proposed and experimentally demonstrated. With the inverse transformation for the detected signal, the third-order intermodulation distortion (IMD3) can be significantly suppressed when only the frequency and bandwidth of the signal are known. Experimental results show that the spurious-free dynamic range (SFDR) of the link can reach ~124-dB•Hz4/5 after the proposed compensation scheme.

Integrated ultra-high-Q-cavity diode laser

Zhenda Xie, Wei Liang, Anatoliy Savchenkov, Jinkang Lim, Jan Burkhart, Michael McDonald, Tanya Zelevinsky, Vladimir Ilchenko, Andrey Matsko, Lute Maleki, and Chee Wei Wong

Doc ID: 234504 Received 17 Feb 2015; Accepted 03 May 2015; Posted 05 May 2015  View: PDF

Abstract: We report on a study of a 698 nm extended cavity semiconductor laser with intra-cavity narrowband optical feedback from a microresonator. This laser comprises an ultra-high-Q (>10¹⁰) crystalline whispering gallery mode microresonator supporting stimulated Rayleigh scattering, a diffraction grating wavelength pre-selector, and a reflective semiconductor amplifier. Single longitudinal mode lasing is characterized with sub-kHz linewidth and a 9 nm tuning range is demonstrated. The laser is suitable for interrogation of ¹S₀−³P₀ Strontium clock transition and has potential application in compact precision atomic clocks.

Effects of Phosphor Distribution and Step-Index Remote Configuration on the Performance of White Light-Emitting Diodes

Chung-Hao Chiang, Hung-Yi Tsai, Ting-Shi Zhan, Han-Yu Lin, Ying-Chien Fang, and Sheng-Yuan Chu

Doc ID: 232116 Received 09 Jan 2015; Accepted 01 May 2015; Posted 05 May 2015  View: PDF

Abstract: The phosphor-converted white light-emitting diode (pc-WLED) is fabricated by combining the CaSi2O2N2:Eu2+ and Ca2Si5N8:Eu2+ phosphors with the blue chip. Experimental results demonstrate that placing the red phosphor layer above the yellow one (Y down / R up type) which has the highest luminous efficiency is the preferable phosphor distribution for pc-WLEDs rather than Y up / R down type. This finding suggests that the extent of overlap between the emission spectrum of short emission-wavelength phosphors and the excitation spectrum of long emission-wavelength phosphors and lumen equivalent of them should be simultaneously taken into account as one seeks to study the optical characteristics of pc-WLEDs. Compared with common pc-WLEDs using silicone gel as the remote layer, a step-index remote configuration proposed herein exhibited a superior luminous efficiency because of the reduced Total Internal Reflection (TIR) and Fresnel loss.

Dual-color three-dimensional STED microscopy with a single high-repetition-rate laser

Kyu Young Han and Taekjip Ha

Doc ID: 236124 Received 12 Mar 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We describe a dual-color three-dimensional stimulated emission depletion (3D-STED) microscopy employing a single laser source with a repetition rate of 80 MHz. Multiple excitation pulses synchronized with a STED pulse were generated by a photonic crystal fiber and the desired wavelengths were selected by an acousto-optic tunable filter with high spectral purity. Selective excitation at different wavelengths permits simultaneous imaging of two fluorescent markers at a nanoscale resolution in three dimensions.

Growth and diode-pumped laser operation of Pr$^{3+}$:β-(Y$_{0.5}$,Gd$_{0.5}$)F$_{3}$ at various transitions

Philip Metz, Daniel-Timo Marzahl, Christian Kraenkel, and Guenter Huber

Doc ID: 237466 Received 03 Apr 2015; Accepted 28 Apr 2015; Posted 08 May 2015  View: PDF

Abstract: We report on the crystal growth of the orthorhombic low temperature β-phase of (Y$_{0.5}$,Gd$_{0.5}$)F$_{3}$ (YGF) single crystals. The crystals were activated with trivalent praseodymium (Pr$^{3+}$) and characterized with respect to their ground state absorption and stimulated emission properties. Under InGaN-laser-diode pumping, laser oscillation was obtained at more than ten wavelengths in the green, orange, red, and dark red spectral region. In these initial experiments, output powers exceeding 100 mW and slope efficiencies between 10 \% and 30 \% were obtained. To the best of our knowledge, these results represent the first application of YGF crystals as laser host material for any active ion.

Evidence of Lasing on the Balmer-alpha Line of OVIII in an Ablative Capillary Discharge

Zeljko Andreic, Hans Kunze, and Inga Tolstikhina

Doc ID: 235324 Received 04 Mar 2015; Accepted 28 Apr 2015; Posted 11 May 2015  View: PDF

Abstract: In a low-inductance ablative discharge through a capillary made of polyacetal (POM) lasing on the Balmer-alpha line of OVIII at 10.24 nm is identified. In line with previous studies of lasing on CVI ions it is argued to be the consequence of charge exchange collisions after a m=0 instability. Lasing in both cases occurred at about the same time after beginning of the discharge, although lasing on the Balmer-alpha line of OVIII was less frequently observed, i.e. in approximately one out of ten discharges. Lasing on the CVI ion was seen in one out of three discharges. This is most probably due to the need of reaching higher electron temperatures to completely strip oxygen ions simultaneously in the hot constrictions (necks) of the plasma instability.

Single-order diffraction with trapezoidal transmission grating

Quanping Fan, wei Liu, Ke Wang, hua yang, lai Wei, Xiaoli Zhu, Changqing Xie, Qiangqiang Zhang, Feng Qian, Yang Yan, Yuqiu Gu, Min Zhou, leifeng cao, and Gang Jiang

Doc ID: 236521 Received 20 Mar 2015; Accepted 24 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: Diffraction grating is a widely used dispersion element in spectral analysis from infrared to X-ray region. Traditionally, it has square wave transmission function, suffering from high-order diffraction contamination. Single-order diffraction can be achieved by sinusoidal amplitude transmission grating, but the fabrication is difficult. Here, we propose a novel idea to design grating based on trapezoidal transmission function, which makes traditional grating as a special case. Grating designed by this idea can not only suppress higher-order diffraction by several orders of magnitude as sinusoidal amplitude grating does, but also greatly reduce the fabrication difficulty to the level of processing for traditional grating. It offers a new opportunity for fabrication of grating with single-order diffraction and measurement of spectrum without contamination of high order harmonic components. This idea can easily extend to varied-line-space grating, concave grating with single order diffraction or zone plates with single foci and will bring great changes in the field of grating applications.

Polarization-modulation setup for ultrafast infrared anisotropy experiments to study liquid dynamics

Sander Woutersen and Martijn Tros

Doc ID: 234751 Received 17 Feb 2015; Accepted 13 Mar 2015; Posted 11 May 2015  View: PDF

Abstract: An infrared pump-probe setup using rapid polarization modulation has been developed to perform time-resolved anisotropy measurements. A photo-elastic modulator is used as a rapidly switchable half-wave plate, enabling the measurement of transient absorptions for parallel and perpendicular polarizations of the pump and probe pulses on a shot-to-shot basis. In this way, infrared intensity-fluctuations are nearly completely cancelled, significantly enhancing the accuracy of the transient-anisotropy measurement. The method is tested on the OD-stretch vibration of HDO in H₂O, for which the signal-to-noise ratio is found to be 4 times better than with conventional methods.

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