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Soliton regulation in microcavities induced by fundamental-second-harmonic mode coupling

Xiaoxiao Xue, Xiaoping Zheng, and Bingkun Zhou

Doc ID: 327943 Received 09 Apr 2018; Accepted 12 Aug 2018; Posted 17 Aug 2018  View: PDF

Abstract: Microcomb generation with simultaneous χ(2) and χ(3) nonlinearities brings new possibilities for ultra-broadband and potentially self-referenced integrated comb sources. However, the evolution of the intracavity field involving multiple nonlinear processes shows complex dynamics that is still poorly understood. Here we report on strong soliton regulation induced by fundamental-second-harmonic (FD-SH) mode coupling. The formation of solitons from chaos is extensively investigated based on coupled Lugiato–Lefever equations. The soliton generation shows more deterministic behaviors in the presence of FD-SH mode interaction, in sharp contrast to the usual cases where the soliton number and relative locations are stochastic. Deterministic single soliton transition, soliton binding and prohibition are observed, depending on the phase matching condition and coupling coefficient between the fundamental and second-harmonic waves. Our finding provides important new insights into the soliton dynamics in microcavities with simultaneous χ(2) and χ(3) nonlinearities, and can be immediate guidance for broadband soliton comb generation with such platforms.

Irreversible denaturation of DNA: a method to precisely control optical and thermo-optic properties of DNA thin solid films

Hayoung Jeong, Bjorn Paulson, Seongjin Hong, Seunguk Cheon, and Kyunghwan Oh

Doc ID: 331560 Received 14 May 2018; Accepted 26 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: Denaturation of double-stranded deoxyribonucleic acid (ds-DNA) has been well-known to break nucleobase bonds resulting in single-stranded deoxyribonucleic acid (ss-DNA) in solutions, which can recombine themselves to form ds-DNA in a reversible manner. We developed an efficient process to irreversibly maintain various DNA denaturation levels in thin solid films, in order to investigate impacts of the denaturation on the optical properties of DNA films. By adding NaOH in an aqueous solution of salmon testis DNA we flexibly controlled the level of denaturation in the solution, which was then spin-coated on Si and silica substrates to irreversibly bind ss-DNAs in a thin solid film. Denaturation of DNA in thin solid films was experimentally confirmed by UV-visible and FT-IR spectroscopic investigations, whose level could be controlled by the NaOH content in the aqueous solution precursor. By this irreversible denaturation process, we developed a new method to flexibly vary the refractive index of DNA thin solid films in a wide range of Δn > 0.02 in the visible to near IR range. Thermo-optic coefficients, dn/dT, of the films were also experimentally measured in the temperature range from 40 to 90 oC to confirm the significant impacts of denaturation. Detailed thin film processes and optical characterizations are discussed.

PtSe2 as a new Saturable Absorber for Q-switching and Mode-locking in Er-doped Fiber Laser

KANG ZHANG, Ming Feng, Yangyang Ren, XINGSHUO CHEN, Fang Liu, JIE YANG, Xiao-Qing Yan, Feng Song, and Jian-Guo Tian

Doc ID: 335211 Received 14 Jun 2018; Accepted 25 Jul 2018; Posted 25 Jul 2018  View: PDF

Abstract: we report a passively Q-switched and Mode-locked erbium-doped fiber laser (EDFL) based on PtSe2, a new two-dimentional material, as saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW the maximum single Q-switched pulse energy is 143.2 nJ. Due to the polarization dependent characteristics of PtSe2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state, and a mode-locked pulse train with a repetition rate of .3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained till pump power up to maximum 450 mW. The maximum single mode-locked pulse energy is 0.53 nJ. This is the first time to obtain successful generation of stable Q-switched and Mode-locked pulses in fiber laser by using the PtSe2 as a saturable absorber.

212 kHz-linewidth, transform-limited pulses from a single-frequency Q-switched fiber laser based on few-layer Bi₂Se₃ saturable absorber

Weiwei Li, Jinhai Zou, Yizhong Huang, Kaijie Wang, Tuanjie Du, Zhengqian Luo, and Shuisen Jiang

Doc ID: 338121 Received 18 Jul 2018; Accepted 24 Jul 2018; Posted 25 Jul 2018  View: PDF

Abstract: Conventional Q-switched fiber lasers operating at multi-longitudinal-mode (MLM) oscillation usually suffer from self-mode-locking induced temporal instability, relatively strong noise and low coherence. Here, we address the challenge through demonstrating, for the first time, a single-longitudinal-mode (SLM) Er-doped fiber (EDF) laser Q-switched by a few-layer Bi₂Se₃ saturable absorber (SA). The Bi₂Se₃ SA prepared by the liquid-phase exfoliation method shows a modulation depth of ~5% and saturation optical intensity of 1.8 MW/cm². A section of 1 m unpumped EDF together with a 0.06 nm-bandwidth fiber Bragg gratings is used as ultra-narrow autotracking filter to realize SLM oscillation. Stable SLM Q-switching operation at 1.55 μm is successfully achieved with the spectral linewidth as narrow as 212 kHz and the pulse duration of 2.54 μs, manifesting near-transform-limited pulses with a time-bandwidth product of 0.53. In particular, we found that the SLM Q-switching possesses the higher signal-to-noise ratios of 62 dB (optical) and 48 dB (radio-frequency), exhibiting its advantages of low noise and high stability. Such SLM Q-switched fiber laser could gain great interest to some applications in coherent detection, coherent optical communications and high-sensitivity optical sensing.

Femtosecond mode-locking of the fiber laser using a CoSb₃-skutterudite-based saturable absorber

Ju Han Lee, Jinho Lee, Yoontaek Kim, and Kuyngtaek Lee

Doc ID: 334216 Received 01 Jun 2018; Accepted 24 Jul 2018; Posted 25 Jul 2018  View: PDF

Abstract: We experimentally demonstrate an ultrafast mode-locker based on CoSb₃ skutterudite topological insulator for femtosecond mode-locking of a fiber laser. The mode-locker was implemented on a side-polished fiber platform by depositing a CoSb₃/PVA composite. The measured modulation depth and the saturation power for the TE mode input were ~5% and ~8.7 W, respectively, while they were ~2.8% and ~10.6 W for the TM mode input. By incorporating this mode-locker into an erbium-doped fiber-based ring cavity, we were able to readily generate mode-locked, soliton pulses having a pulse width of ~833 fs at 1557.9 nm. The 3-dB bandwidth of the output pulses and time-bandwidth product were ~3.44 nm and 0.353, each. To the best of the author’s knowledge, this is first time demonstration of the use of a skutterudite-based saturable absorber for femtosecond mode-locked pulse generation.

Antimonene: a long-term stable two-dimension (2D) saturable absorption material under ambient condition for the mid-infrared spectral region

Hongyu Luo, XiangLing Tian, Ying Gao, Rongfei Wei, Jianfeng Li, Jianrong Qiu, and Yong Liu

Doc ID: 334079 Received 05 Jun 2018; Accepted 20 Jul 2018; Posted 23 Jul 2018  View: PDF

Abstract: We experimentally demonstrate a long-term stable 2D saturable absorption material under ambient condition — antimonene feasible for the mid-infrared spectral region, for the first time. The multi-layer antimonene material prepared using liquid-phase exfoliation method was coated on a Quartz/CaF2 for characterizations and an Au mirror as a reflection-type SA device. It has a modulation depth of 10.5%, a saturation peak intensity of 0.26 GW/cm2, and a non-saturation loss of 19.1% measured at 2868.0 nm using typical power dependent method. By introducing the SA device into a linear-cavity Ho3+/Pr3+ codoped fluoride fiber laser at 2865.0 nm, stable Q-switched pulses were obtained. It generated the maximum output power of 112.3 mW and pulse energy of 0.72 μJ, while the shortest pulse duration and largest repetition rate were 1.74 μs and 156.2 kHz, respectively. The long-term stability of the SA device was also checked using the same laser setup within 28 days. The results indicate that antimonene material is a type of promising long-term stable SA under ambient condition which can be applied in the mid-infrared spectral region.

Modulation properties of solitary and optically injected phased-array semiconductor lasers

Nianqiang Li, Hadi Susanto, Ben Cemlyn, Ian Henning, and Michael Adams

Doc ID: 328119 Received 12 Apr 2018; Accepted 17 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: We study modulation properties of two-element phased-array semiconductor lasers that can be described by coupled mode theory. We consider four different waveguide structures and modulate the array either in phase or out of phase within the phase-locked regions, guided by stability diagrams obtained from direct numerical simulations. Specifically, we find that out-of-phase modulation allows for bandwidth enhancement if the waveguide structure is properly chosen; for example for a combination of index antiguiding and gain-guiding, the achievable modulation bandwidth in the case of out-of-phase modulation could be much higher than the one when they are modulated in phase. Proper array design of the coupling, controllable in terms of the laser separation and the frequency offset between the two lasers is shown to be beneficial to slightly improve the bandwidth but not the resonance frequency, while the inclusion of the frequency offset leads to the appearance of double peak response curves. For comparison, we explore the case of only modulating one element of the phased array, and find that double peak response curves are found. To improve the resonance frequency and the modulation bandwidth, we introduce simultaneous external injection into the phased array and modulate the phased array or its master light within the injection locking region. We observe a significant improvement of the modulation properties, and in some cases, by modulating the amplitude of the master light before injection, the resulting 3-dB bandwidths could be enhanced up to 160 GHz. Such a record bandwidth for phased-array modulation could pave the way for various applications, notably optical communications that require high-speed integrated photonic devices.

Passively Q-switched fs-laser-written thulium waveguide laser based on evanescent field interaction with carbon nanotubes

Esrom Kifle, Pavel Loiko, Javier Vazquez de Aldana, Carolina Romero, Airan Rodenas, Sun Young Choi, Ji Eun Bae, Fabian Rotermund, Viktor Zakharov, Andrei Veniaminov, Magdalena Aguilo, Francesc Diaz, Uwe Griebner, Valentin Petrov, and Xavier Mateos

Doc ID: 336536 Received 29 Jun 2018; Accepted 17 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: Surface channel waveguides (WGs) were fabricated in a monoclinic Tm3+:KLu(WO4)2 crystal by femtosecond direct laser writing (fs-DLW). The WGs consisted of a half-ring cladding with a diameter of 50 and 60 µm located just beneath the crystal surface. They were characterized by confocal laser microscopy and µ-Raman spectroscopy, indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In the continuous-wave mode, under Ti:Sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm corresponding to a slope efficiency η of 37.8% for the 60 µm diameter WG. The WG propagation loss was 0.7±0.3 dB/cm. The top surface of the WGs was spin-coated by a PMMA film containing randomly-oriented (spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched (PQS) operation was achieved. The PQS 60 µm diameter WG laser generated a record output power of 150 mW at 1846.8 nm with η = 34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics (energy / duration) were 105.6 nJ / 98 ns at a repetition rate of 1.42 MHz.

Integration of nanoscale light emitters: an efficient ultraviolet and blue random lasing from NaYF4:Yb/Tm hexagonal nanocrystals

Ya-Pei Peng, Wei Lu, Pengpeng Ren, Yiqun Ni, Yunfeng Wang, Long Zhang, Yujia Zeng, Wenfei Zhang, and Shuangchen Ruan

Doc ID: 331812 Received 17 May 2018; Accepted 17 Jul 2018; Posted 13 Aug 2018  View: PDF

Abstract: NIR light-controlled release of payloads from UV-sensitive polymer hydrogels or nanocarriers is one the most promising strategies for biotherapy. Here, we propose a unique concept of light activation of NaYF4:20%Yb,2%Tm nanocrystals(NCs). NaYF4:20%Yb,2%Tm NCs are synthesized by a solvothermal method. Effective upconversion luminescence from NaYF4:20%Yb,2%Tm NCs excited by continuous wave(CW) 980nm laser is obtained. On this basis, the NaYF4:20%Yb,2%Tm nanocrystals are ultilized as laser gain medium and sandwiched between Al and quartz reflectors to form laser microcavities. Ultraviolet (UV) and blue up-converted random lasing is obtained from the laser microcavities. Hence, we verify explicitly that the NaYF4:Yb,Tm nanocrystals support UV and blue upconversion random lasing via 980nm nanosecond laser excitation. Our work provides a new concept for precision and localized cancer therapy by external light excitation.

Mid-infrared high-Q germanium nanocavity

Tinghui Xiao, Ziqiang Zhao, Wen Zhou, Mitsuru Takenaka, Hon Tsang, Zhenzhou Cheng, and Keisuke Goda

Doc ID: 328993 Received 23 Apr 2018; Accepted 16 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: Mid-infrared (MIR) integrated photonics has attracted broad interest due to its promising applications in biochemical sensing, environmental monitoring, disease diagnosis, and optical communication. Among MIR integration platforms, germanium-based platforms hold many excellent properties, such as wide transparency windows, high refractive indices, and high nonlinear coefficients, but the development of MIR germanium photonic devices is still in its infancy. Specifically, MIR high-Q germanium resonators with comparable or even superior performance to their silicon counterparts remain unprecedented. Here we experimentally demonstrate an MIR germanium nanocavity with a Q factor of ~18,000, the highest-to-date of reported nanocavities across all MIR integration platforms. This is achieved through a combination of feasible theoretical design, Smart-Cut methods for wafer development, and optimized device fabrication processes. Our nanocavity, with its high Q factor and ultrasmall mode volume, opens new avenues for on-chip applications in the whole fingerprint spectral region (2 - 15 µm).

Anomalous transport of light at the phase transition to localization: Strong dependence with incident angle

Ernesto Jimenez Villar, Mario Cesar Xavier, Niklaus Wetter, Valdeci junior, Weliton Martins, Gilberto de Sa, Gabriel Basso, Francisco Marques, and Viktor Ermakov

Doc ID: 326761 Received 26 Mar 2018; Accepted 05 Jun 2018; Posted 09 Jul 2018  View: PDF

Abstract: Disordered optical media have seen a growing interest in recent year due their potentials applications in solar collectors, random lasers, light confinement and other advance photonic functions. This paper studies the transport of light for different incidence angles in a strongly disordered optical medium composed by core-shell TiO2@Silica nanoparticles suspended in ethanol solution. A decrease of optical conductance and an increase of absorption near the input border are reported when the incidence angle increases. The specular reflection, measured for the photons that enter the sample, is lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a non-reciprocal propagation of light. This study represents a novel approach in order to understand the complex physics involved at the phase transition to localization.

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