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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optics Express  

Spectral peaking, which converts sharp intensity or phase modulation into an intense spectral peak, is a useful phenomenon for comb mode selection, which is important for highly sensitive spectroscopy. However, the optical power of the selected peak is small, and power scaling is an important technical issue. In this work, we investigated the power scaling of a spectral peaked optical frequency comb at 1.65 µm using a fiber Raman amplifier. A 1 km length of Raman fiber was used as the gain fiber, and the fundamental characteristics of amplification were examined for a CW beam, a spectral peaked comb, and a conventional pulsed comb. Coherence-preserved, low-noise amplification with 22 dB gain was achieved for the spectral peaked comb. Low-noise similariton-like amplification was demonstrated for the comb pulse input both experimentally and numerically. As far as we know, this is the first power scaling of an optical frequency comb using a fiber Raman amplifier. This technique can be applied to a wide wavelength band, and is very useful for spectroscopic applications.

DOI： 10.1364/OE.547619

Open Access

Web of Science

Scopus

Language：English   Publisher：Optical Fiber Technology  

Periodical spectral peaking is an attractive phenomenon for selecting optical frequency comb modes for highly sensitive comb spectroscopy. Here we proposed and demonstrated a spectral peak filtering technique using a nonlinear polarization interferometer (NPI). When we introduce an ultrashort pulse suffering from sharp absorption or phase modulation into the NPI, the ultrashort pulse and spectral peaks emerge from different output ports as a result of interference and the difference in nonlinear phase shift. The characteristics were examined both experimentally and numerically. Spectral peaks with a high signal-to-background ratio of 20 dB were obtained experimentally. The experimental results were almost in agreement with the numerical ones. The system consists of polarization-maintaining fiber devices and shows long-term stable operation. In principle, the proposed technique is applicable to any wavelength range and is useful for spectroscopic applications.

DOI： 10.1016/j.yofte.2024.104079

Open Access

Web of Science

Scopus

Language：English   Publisher：Applied Sciences (Switzerland)  

Featured Application: This study presents a novel method for simulating fiber pulse propagation using the DeepONet architecture, significantly reducing computation time compared to traditional methods. The approach is highly applicable in fields requiring real-time fiber optic system control and optimization, such as telecommunications, medical imaging, and high-precision laser systems. The ability to accurately simulate complex fiber dynamics with minimal computational resources opens new possibilities for real-time applications and system design. Traditional femtosecond laser modeling relies on the iterative solution of the Nonlinear Schrödinger Equation (NLSE) using the Split-Step Fourier Method (SSFM). However, SSFM’s high computational complexity leads to significant time consumption, particularly in automatic control and system optimization, thus limiting control model responsiveness. Recent studies have suggested using neural networks to simulate fiber dynamics, offering faster computation and lower costs. In this study, we introduce a novel fiber propagation method utilizing the DeepONet architecture for the first time. By separately managing fiber parameters and input–output pulses in the branch and trunk networks, this method can simulate various fiber configurations with high accuracy and without altering the architecture. Additionally, while SSFM generation time increases linearly with fiber length, the GPU-accelerated AI generation time remains consistent at around 0.0014 s, regardless of length. Notably, in high-order soliton (HOS) compression over a 12 m distance, the AI method is approximately 56,865 times faster than SSFM.

DOI： 10.3390/app14188154

Open Access

Web of Science

Scopus

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

The Yb-doped thin-disk laser is an ultrashort pulsed laser source with the highest average output power and pulse energy at present, due to its small thermo-optical distortion and nonlinear optical effects suppression. Although Yb:YAG has been widely used as a gain medium in thin-disk lasers, its narrow fluorescence bandwidth has limited availability of shorter pulses. Therefore, we are developing a thin-disk laser using a potassium double tungstate gain medium, Yb:KREW (Yb:KRE(WO4)2, RE = Y, Gd, Lu) for future applications to broadband ultrashort pulse laser oscillators and amplifiers. Yb:KREW is a promising group of gain media that combines a wide gain bandwidth and high gain coefficient, while they have drawbacks such as strong anisotropy in thermal and mechanical properties. In this study, we demonstrated the first Kerr lens mode-locked thin-disk laser operation with one of the tungstate gain media, Yb:KLuW by reducing anisotropic thermal distortion through low thermal resistance bonding techniques. Under OC transmittance of 0.6% and GDD-1400 fs2 conditions, the pulse duration of 48.9 fs and spectral bandwidth of 32.0 nm were demonstrated. This is the first KLM thin-disk laser demonstration of this material and its family (Yb-doped tungstate-based gain medium), and the pulse duration obtained was the smallest value using the same material reported so far. The average power, however, was limited to 425 mW by the low OC transmittance. In the future, through optimization of the cavity, further increases in power output are expected while maintaining the short pulse duration.

DOI： 10.1117/12.3037436

Scopus

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Advanced Solid State Lasers, ASSL 2024 in Proceedings Laser Congress 2024 (ASSL, LAC, LS and C) - Part of Optica Laser Congress and Exhibition  

We demonstrated the first Kerr-lens mode-locked Yb:KLuW thin-disk laser operating with 48.9-fs pulses and 32-nm bandwidth at 425 mW of average power.This is the shortest pulse duration achieved by any oscillator based on Yb:KREW.

Scopus

Publisher：Optics Letters  

Spectral peaking in an optical fiber is a useful phenomenon for comb mode filtering and wavelength standards. However, for highly sensitive spectroscopic applications, it is important to suppress the pedestal components. Here we propose and demonstrate pedestal-suppressed spectral peak generation using a nonlinear fiber loop mirror with a molecular gas cell. The physical mechanism and fundamental properties were investigated numerically, and the output characteristics were examined experimentally. Almost background-free spectral peaks were generated successfully in the 1.65-µm wavelength range using a CH4 gas cell. The maximum signal-to-background ratio was more than 30 dB. Stable operation without any feedback control was achieved. It is expected that the proposed method is useful for highly sensitive spectroscopic applications.

DOI： 10.1364/OL.499798

Web of Science

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

Spectral peak generation is a recently reported phenomenon that narrow spectral dips of the optical spectrum turn into sharp peaks as they propagate through nonlinear optical fibers. We demonstrated the nonlinear polarization rotation-based spectral peak mode filtering to increase the signal-to-background ratio (SBR). The spectral peaks with almost constant frequency separation were generated from the femtosecond pulses absorbed by the CH4 gas through the highly nonlinear fiber. The generated spectral peaks were filtered through the polarizing beam splitter by the nonlinear polarization rotation, and the SBR was improved from 9 dB to ∼20 dB. The spectral peak generation phenomenon and the mode filtering were numerically confirmed by solving the coupled nonlinear Schrödinger equations. The demonstrated method can generate strong comb modes with wide frequency spacing which are useful for highly sensitive environmental gas sensing spectroscopy. The wavelengths of the spectral peaks are fixed by the absorption spectra of the used gas cells. Therefore, this method can generate high quality spectral peaks of any wavelengths with wide spectral ranges through proper combinations of gas cells.

DOI： 10.1364/OE.496731

Open Access

Web of Science

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PubMed

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2659569

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Publisher：2023 Conference on Lasers and Electro-Optics, CLEO 2023  

We demonstrated freely controllable spectral peak generation using 206 MHz figure-9 fiber laser comb, LCOS-SLM, and nonlinear fibers. Selected comb modes were extracted as the spectral peaks with high signal to background ratio >30 dB.

Scopus

Publisher：2023 Conference on Lasers and Electro-Optics, CLEO 2023  

We proposed mode-filtering technique of spectral peaks using nonlinear polarization rotation in optical fiber. Intense, narrow multiple spectral peaks with ~20 dB background ratio were successfully generated with CH4 gas cell and nonlinear fiber.

Scopus

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1364/OL.471957

Open Access

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Applied Sciences (Switzerland)  

Featured Application: Biomedical imaging, Environmental spectroscopy, LIDAR, Medicine, and Laser processing. In this paper, we have demonstrated a dispersion-managed, high-power, Tm-Ho co-doped ultrashort pulse fiber laser using a single walled carbon nanotube (SWNT) dispersed in polyimide film. An in-line type spectral filter was developed to control the output pulse spectra. Two SWNT films with different modulation depths were examined as a mode-locker. Normal dispersion fiber was used in the fiber laser oscillator, and dependence on net cavity dispersion was investigated. Passive mode-locking was achieved in a wide dispersion range, from −0.319 to +0.101 ps2. Stable soliton mode-locking operation and dissipative soliton mode-locking operations were observed. The pumping efficiency was ~3 times higher than that in a Tm-doped fiber laser with a similar configuration. The developed fiber laser showed self-start and stable operations, and this laser is useful for practical applications.

DOI： 10.3390/app122312369

Open Access

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optica Publishing Group  

Here we report the demonstration of a spectral peaking phenomenon in a fiber laser oscillator. An HCN gas cell was inserted in an ultrashort-pulse Er-doped fiber laser with single-wall carbon nanotubes. Sech(2)-shaped ultrashort pulses with intense multiple sharp spectral peaks were stably generated. When the generated pulses were coupled into highly nonlinear fiber, enhanced multiple spectral peaks were generated by periodical spectral peaking in the optical fiber. The characteristics and physical mechanism of spectral peaking in the fiber laser were investigated via numerical simulations. As the magnitude of absorption was increased, the magnitude of the generated spectral peaks increased almost exponentially. It was clarified that the spectral peaks were generated through the accumulation of filtering components generated in each round trip. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

DOI： 10.1364/OL.458643

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Publisher：2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings  

We demonstrated spectral peaking phenomenon in fiber laser cavity for the first time. Ultrashort soliton pulse with multiple sharp spectral peaks were successfully generated in Er-doped SWNT fiber laser with HCN gas cell.

Scopus

Publisher：2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings  

Speckles in OCT hinder visibility of finescale structures. We demonstrated speckle reduced OCT imaging using 1.7 μm tunable Quasisupercontinuum fiber laser source, and the improvement of image contrast in deep tissue imaging was successfully confirmed.

Scopus

Publisher：2022 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2022 - Proceedings  

Thermally induced optical pass difference of the thin-disk laser with anisotropic Yb:KRE(WO4)2 crystal, which is promising broadband gain media, was calculated. The results show that the OPD is sufficiently small even at 9.6 kW/cm2 pumping.

DOI： 10.1109/CLEO-PR62338.2022.10432035

Scopus

Publisher：2022 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2022 - Proceedings  

Arbitrary controlled spectral peak generation was demonstrated using ultrashort pulse fiber laser and spectral filter with LCOS-SLM. The intense, sharp spectral peak with record high contrast up to 143 was successfully obtained.

DOI： 10.1109/CLEO-PR62338.2022.10432708

Scopus

Publisher：2022 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2022 - Proceedings  

Characteristics of spectral peaking in fiber laser were investigated both experimentally and numerically. Ultrashort soliton pulse with multiple sharp spectral peaks were generated stably. The peak intensity was increased exponentially for the magnitude of absorption.

DOI： 10.1109/CLEO-PR62338.2022.10432524

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We report, to the best of our knowledge, the highest power conductive-cooled active-mirror amplifier (CcAMA) using Yb:YAG with a pulse energy of 10 J. By using four liquid-nitrogen circulating cooled laser heads, we achieved a repetition rate, pulse energy, and average power of 33.3 Hz, 9.3 J, and 310 W, respectively. The problem of wavefront distortion, which is difficult to solve with a large-aperture active-mirror laser, is suppressed by using reinforcing materials with the same thermal expansion coefficient. We have confirmed that the wavefront distortion is small (0.15 lambda P-V per head) at 100 Hz operation, which paves the way for 100 Hz operation with the CcAMA concept. (C) 2021 Optical Society of America

DOI： 10.1364/OL.414926

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Publisher：Optics InfoBase Conference Papers  

A stable operation of 1.1 J/100 Hz 10 ns laser pulses were achieved from a single cryogenically cooled Yb:YAG rod amplifier with ink-cladding. The efficiency and gain coefficient were 44% and 383, respectively.

Scopus

Language：English   Publisher：Optics InfoBase Conference Papers  

We have developed a conductive-cooled Yb:YAG active-mirror amplifier with an diameter of 50 mm and a liquid-nitrogen circulation system. The high thermal capability that enables 10 J, 50 Hz laser amplification was demonstrated successfully.

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1364/OL.43.005451

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

The first Kerr-lens mode-locked Yb:Lu2O3 ceramic thin-disk laser was demonstrated. The shortest pulse duration was 177 fs with 3.2 W output power. The output power of 17 W with 588 fs pulses was also demonstrated.

DOI： 10.1364/CLEO_SI.2018.SF2N.5

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Highly transparent ceramic is an attractive gain medium for high-power lasers due to its high fracture toughness, homogeneity, and size scalability. Here we report the first Yb3+-doped CaF2-LaF3 ceramics laser. Codoping of La3+ ion can reduce the formation of Yb2+ ions and enhance the laser efficiency. In the laser experiment, the maximum output power of 4.36 W and the maximum slope efficiency of 69.5% were obtained with a 3% La, 2% Yb sample and a 2% La, 1% Yb sample, respectively. Due to the combined properties of Yb: CaF2 and a ceramic laser gain medium, Yb: CaF2-LaF3 ceramic is a promising gain medium for a high-power ultrashort pulse laser and amplifier. (C) 2017 Optical Society of America

DOI： 10.1364/OL.42.001724

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Other Link： http://orcid.org/0000-0002-7082-6145

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

CW Yb: Lu2O3 ceramic thin-disk laser with the maximum output power of 174 W was demonstrated. Slope efficiency was 54%. Disk temperature during lasing was observed and maximum temperature was 84.1 °C under 5.5 kW/cm2 pumping.

DOI： 10.1364/ASSL.2017.JM5A.32

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

We demonstrated SWCNT-assisted Kerr-lens mode-locked Yb:CaF2 laser. The pulse duration of 87 fs with 260-mW output power and the shortest pulse duration of 77 fs with 94-mW output power were obtained.

DOI： 10.1364/CLEO_AT.2017.JTh2A.130

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Yb:LuAG is a promising gain medium for high-power lasers due to its high thermal conductivity and large emission cross section. Although narrowband gain media such as Yb: LuAG are not considered to be suitable for the generation of sub-100 fs pulses, we have achieved generation of 91 fs pulses with Yb: LuAG ceramic by the Kerr-lens mode-locking (KLM) technique. The obtained average power, pulse energy, and peak power were 1.64 W, 20.0 nJ, and 220 kW, respectively. These are, to the best of our knowledge, the first demonstration of KLM and the new records based on both Yb: LuAG ceramic and single crystal. (C) 2016 Optical Society of America

DOI： 10.1364/OL.41.004570

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Other Link： http://orcid.org/0000-0002-7082-6145

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We prepared transparent Yb:CaF2-LaF3 ceramics with different combinations of doping concentrations of Yb3+ and La3+ and obtained CW laser operation with maximum output of 3.97 W. The maximum slope efficiency was as high as 73.1%.

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