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Lasers, Optical Amplifiers, and Laser Optics|202 Article(s)
Time transfer over a 2061 km telecommunication fiber-optic network with single-fiber and two-wavelength approach
Xinxing Guo, Bo Liu, Shaoshao Yu, Qian Jing, Jiang Chen, Lin Wu, Tao Liu, Ruifang Dong, and Shougang Zhang
In this paper, we demonstrate the single-fiber and two-wavelength time transfer (SFTWTT) over a 2061 km field fiber loop-back link network with a synchronous wavelength-division and time-division multiplexing access (WD-TDMA). This system utilizes wavelength-division multiplexing to avoid the impact of backscatter. In order to achieve high-precision time transfer, time-division multiplexing access is employed. This approach facilitates multiple bidirectional comparisons between local and remote devices. A digital phase-locked loop (PLL), which matches the bandwidth of the transfer system, and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system. The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated. Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved. The precision of time transfer over a 2061 km fiber-optic network, employing a single-fiber and two-wavelength approach, has been significantly enhanced. This study presents an average time difference of 52 ps across the distance, with a system uncertainty budgeted at 41.8 ps. This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer, facilitating the development of a high-precision ground-based time service system. In this paper, we demonstrate the single-fiber and two-wavelength time transfer (SFTWTT) over a 2061 km field fiber loop-back link network with a synchronous wavelength-division and time-division multiplexing access (WD-TDMA). This system utilizes wavelength-division multiplexing to avoid the impact of backscatter. In order to achieve high-precision time transfer, time-division multiplexing access is employed. This approach facilitates multiple bidirectional comparisons between local and remote devices. A digital phase-locked loop (PLL), which matches the bandwidth of the transfer system, and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system. The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated. Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved. The precision of time transfer over a 2061 km fiber-optic network, employing a single-fiber and two-wavelength approach, has been significantly enhanced. This study presents an average time difference of 52 ps across the distance, with a system uncertainty budgeted at 41.8 ps. This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer, facilitating the development of a high-precision ground-based time service system.
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041404 (2025)
280 W near-diffraction-limited picosecond amplifier system with two-segmented doped Nd:YVO4 crystals
Yiwen Jin, Zhibin Ye, Xiang Zhang, Yang Liu, Xiaoyan Qiu, Yuhong Shen, Yichao Peng, Miao Hu, Chong Liu, and Dong Liu
A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32. A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32.
Chinese Optics Letters
- Publication Date: Apr. 17, 2025
- Vol. 23, Issue 4, 041403 (2025)
Flip-chip bonded 8-channel DFB laser array with highly uniform 400 GHz spacing and high output power for optical I/O technology
Jie Zhao, Zhenxing Sun, Pan Dai, Jin Zhang, Yanqiu Xu, Yue Zhang, Zhuoying Wang, Jiaqiang Nie, Wenxuan Wang, Rulei Xiao, and Xiangfei Chen
In this paper, we proposed and experimentally demonstrated an 8-channel O-band distributed feedback (DFB) laser array with highly uniform 400 GHz spacing and high output power for optical input/output (I/O) technology. The grating phase is precisely controlled, and an equivalent π phase shift is implemented in the laser cavity via the reconstruction equivalent chirp (REC) technology. Anti-reflection (AR) and high-reflection (HR) films are coated on the front and rear facets, respectively, to enhance output power. The equivalent π phase shift is strategically placed near the HR film facet to improve the yield of the single longitudinal mode. Operating with a 400 GHz wavelength spacing, the proposed DFB laser array meets the continuous wave-wavelength division multiplexing multi-source agreement (CW-WDM MSA) specifications. The proposed DFB laser array is flip-chip bonded to a thin-film circuit with an aluminum nitride (AlN) submount to reduce the thermal resistance and enhance the output power. Compared to the p-side-up structure, the flip-chip bonding design significantly reduces junction temperature by 28% and increases maximum output power by approximately 20%. This design effectively lowers the thermal resistance of the chip and enhances its heat dissipation properties. At a bias current of 110 mA, the laser demonstrates wavelength deviations below 1.579 GHz and side-mode suppression ratios above 50 dB. The far-field divergence is measured at 25.8° × 30.1°, and the Lorentzian linewidth is 3.28 MHz. Increasing the bias current to 250 mA results in a laser output power exceeding 80 mW. Furthermore, the relative intensity noise (RIN) for all 8 channels is below -135.3 dB/Hz. The proposed flip-chip bonded 8-channel high-power DFB laser array demonstrates uniform wavelength spacing, high output power, and stable single longitudinal mode performance, making it a promising candidate for multiple wavelength laser sources in optical I/O technology. In this paper, we proposed and experimentally demonstrated an 8-channel O-band distributed feedback (DFB) laser array with highly uniform 400 GHz spacing and high output power for optical input/output (I/O) technology. The grating phase is precisely controlled, and an equivalent π phase shift is implemented in the laser cavity via the reconstruction equivalent chirp (REC) technology. Anti-reflection (AR) and high-reflection (HR) films are coated on the front and rear facets, respectively, to enhance output power. The equivalent π phase shift is strategically placed near the HR film facet to improve the yield of the single longitudinal mode. Operating with a 400 GHz wavelength spacing, the proposed DFB laser array meets the continuous wave-wavelength division multiplexing multi-source agreement (CW-WDM MSA) specifications. The proposed DFB laser array is flip-chip bonded to a thin-film circuit with an aluminum nitride (AlN) submount to reduce the thermal resistance and enhance the output power. Compared to the p-side-up structure, the flip-chip bonding design significantly reduces junction temperature by 28% and increases maximum output power by approximately 20%. This design effectively lowers the thermal resistance of the chip and enhances its heat dissipation properties. At a bias current of 110 mA, the laser demonstrates wavelength deviations below 1.579 GHz and side-mode suppression ratios above 50 dB. The far-field divergence is measured at 25.8° × 30.1°, and the Lorentzian linewidth is 3.28 MHz. Increasing the bias current to 250 mA results in a laser output power exceeding 80 mW. Furthermore, the relative intensity noise (RIN) for all 8 channels is below -135.3 dB/Hz. The proposed flip-chip bonded 8-channel high-power DFB laser array demonstrates uniform wavelength spacing, high output power, and stable single longitudinal mode performance, making it a promising candidate for multiple wavelength laser sources in optical I/O technology.
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041402 (2025)
Compact monolithic dual-wavelength distributed feedback laser with tunable wavelength spacing based on REC technique
Zhuoying Wang, Jie Zhao, Zizhuo Li, Zhenxing Sun, Wentao Sun, Jiaqiang Nie, Yue Zhang, Zhiqian Yin, Wenxuan Wang, Rulei Xiao, and Xiangfei Chen
We propose and experimentally demonstrate the monolithic dual-waveguide (DW) distributed feedback (DFB) laser with tunable wavelength spacing. The differences in the chirp sampled grating with various index modulation amplitudes are theoretically elaborated. The wavelength spacing properties of the DW laser at different Bragg spacings are compared and analyzed. To validate the numerical investigation, the DW laser consisting of three sections is fabricated and implemented, where the chirp sampled grating with two equivalent π phase shifts is located. The simulated relationship between the Bragg wavelength spacing and the mode spacing is consistent with the experimental results. Owing to the prominent contribution of the three-section structure and chirp sampled grating, the tuning range of the wavelength spacing is extended significantly, and the cavity of the DW laser becomes compact. The experimental results indicate that the proposed scheme achieves a tuning range from 59.50 to 116.25 GHz. The proposed scheme paves an extraordinary avenue for the integration of laser devices in the applications of optical sensing and THz communication. We propose and experimentally demonstrate the monolithic dual-waveguide (DW) distributed feedback (DFB) laser with tunable wavelength spacing. The differences in the chirp sampled grating with various index modulation amplitudes are theoretically elaborated. The wavelength spacing properties of the DW laser at different Bragg spacings are compared and analyzed. To validate the numerical investigation, the DW laser consisting of three sections is fabricated and implemented, where the chirp sampled grating with two equivalent π phase shifts is located. The simulated relationship between the Bragg wavelength spacing and the mode spacing is consistent with the experimental results. Owing to the prominent contribution of the three-section structure and chirp sampled grating, the tuning range of the wavelength spacing is extended significantly, and the cavity of the DW laser becomes compact. The experimental results indicate that the proposed scheme achieves a tuning range from 59.50 to 116.25 GHz. The proposed scheme paves an extraordinary avenue for the integration of laser devices in the applications of optical sensing and THz communication.
Chinese Optics Letters
- Publication Date: Mar. 25, 2025
- Vol. 23, Issue 3, 031406 (2025)
Watt-level all-solid-state single-frequency Pr:LiYF4 ring laser in the orange spectral region with wavelength tunability
Ye Han, Kun Guo, Yizhen Zhu, Dong Wang, Jianfa Chen, Zhengqian Luo, Bin Xu, Qingli Zhang, and Xudong Cui
In this work, we report on the recent research progress on watt-level all-solid-state single-frequency Pr:LiYF4 (YLF) lasers in the orange spectral region. Combining dual-end pumping and ring-cavity technologies, we have achieved a maximum single-frequency output of 1.19 W at 607 nm with a linewidth of about 20.3 MHz. Based on this study, by inserting a 0.15 mm etalon inside the ring cavity, we find that the 607 nm lasing can be completely suppressed and a single-frequency laser at 604 nm with a 0.69 W output power and a linewidth of about 16.7 MHz can also be obtained. Moreover, the wavelengths of the two single-frequency lasers can be tuned from 607.16 to 607.61 nm and from 603.99 to 605.02 nm, respectively. Furthermore, the single-frequency Pr:YLF laser can also operate in a state of the two orange wavelengths, simultaneously, with a maximum output power of 0.97 W. We believe that this is the highest output power of a direct generation of single-frequency orange lasers and the first demonstration of the wavelength-tuned operation of the achieved single-frequency orange lasers, which could bring opportunities for the application of single-frequency orange lasers. In this work, we report on the recent research progress on watt-level all-solid-state single-frequency Pr:LiYF4 (YLF) lasers in the orange spectral region. Combining dual-end pumping and ring-cavity technologies, we have achieved a maximum single-frequency output of 1.19 W at 607 nm with a linewidth of about 20.3 MHz. Based on this study, by inserting a 0.15 mm etalon inside the ring cavity, we find that the 607 nm lasing can be completely suppressed and a single-frequency laser at 604 nm with a 0.69 W output power and a linewidth of about 16.7 MHz can also be obtained. Moreover, the wavelengths of the two single-frequency lasers can be tuned from 607.16 to 607.61 nm and from 603.99 to 605.02 nm, respectively. Furthermore, the single-frequency Pr:YLF laser can also operate in a state of the two orange wavelengths, simultaneously, with a maximum output power of 0.97 W. We believe that this is the highest output power of a direct generation of single-frequency orange lasers and the first demonstration of the wavelength-tuned operation of the achieved single-frequency orange lasers, which could bring opportunities for the application of single-frequency orange lasers.
Chinese Optics Letters
- Publication Date: Mar. 25, 2025
- Vol. 23, Issue 3, 031405 (2025)
Single-frequency fiber laser at 1440 nm based on a high gain coefficient bismuth-doped fiber
Jinmin Tian, Yafei Wang, Mengting Guo, Fan Wang, Lei Zhang, Meng Wang, Xin Li, Chunlei Yu, and Lili Hu
In this Letter, a homemade bismuth-doped germane silica fiber (BGSF) with a high gain coefficient is fabricated. Based on this fiber, a single-frequency fiber laser (SFFL) operating at 1440 nm is successfully realized. A ring cavity with a short BGSF of 10 m and two cascaded sub-ring cavities ensures the single-longitudinal-mode (SLM) operation. The maximum SLM laser output power of about 6 mW is obtained with the optical signal-to-noise ratio (OSNR) of more than 75 dB. The linewidth of the stable SLM laser is about 745 Hz, measured by the delayed self-heterodyne method. To the best of our knowledge, this is the first SFFL operating at 1440 nm based on the bismuth-doped fiber (BDF), demonstrating the great potential of BDF in expanding the operating band of SFFL. In this Letter, a homemade bismuth-doped germane silica fiber (BGSF) with a high gain coefficient is fabricated. Based on this fiber, a single-frequency fiber laser (SFFL) operating at 1440 nm is successfully realized. A ring cavity with a short BGSF of 10 m and two cascaded sub-ring cavities ensures the single-longitudinal-mode (SLM) operation. The maximum SLM laser output power of about 6 mW is obtained with the optical signal-to-noise ratio (OSNR) of more than 75 dB. The linewidth of the stable SLM laser is about 745 Hz, measured by the delayed self-heterodyne method. To the best of our knowledge, this is the first SFFL operating at 1440 nm based on the bismuth-doped fiber (BDF), demonstrating the great potential of BDF in expanding the operating band of SFFL.
Chinese Optics Letters
- Publication Date: Mar. 17, 2025
- Vol. 23, Issue 3, 031404 (2025)
Flexible anti-radiation thin films for protecting fiber lasers and amplifiers in a radiation environment
Shenzhan Hong, Ning Wang, Lijuan Zhou, Lu Huang, Yikun Bu, and Zhengqian Luo
In this paper, to reduce the damage or absorption caused by radiation to optical fibers, we study lightweight and flexible anti-radiation films based on optical precision deposition technology. At first, anti-radiation composite thin films based on Kapton, ITO, and Cu (or Al) are designed and homemade with different structures. Subsequently, polarization-maintaining (PM) Yb-doped fiber (Yb-fiber) samples protected by these different kinds of anti-radiation films are irradiated with a dose of ∼150 kGy. At last, we comparatively investigate (1) the radiation-induced attenuation (RIA) of these PM Yb-fiber samples and (2) the lasing performance (threshold and slope efficiency) and gain performance of a 1064 nm fiber laser and amplifier using these irradiated PM Yb-fibers as the gain medium, respectively. The results show that such a film can reduce the RIA of the irradiated Yb-fiber by up to 2.84 dB/m and increase the output power by up to 75.3% at most. In addition, we also study the optical recovery of the PM Yb-fibers after radiation. In this paper, to reduce the damage or absorption caused by radiation to optical fibers, we study lightweight and flexible anti-radiation films based on optical precision deposition technology. At first, anti-radiation composite thin films based on Kapton, ITO, and Cu (or Al) are designed and homemade with different structures. Subsequently, polarization-maintaining (PM) Yb-doped fiber (Yb-fiber) samples protected by these different kinds of anti-radiation films are irradiated with a dose of ∼150 kGy. At last, we comparatively investigate (1) the radiation-induced attenuation (RIA) of these PM Yb-fiber samples and (2) the lasing performance (threshold and slope efficiency) and gain performance of a 1064 nm fiber laser and amplifier using these irradiated PM Yb-fibers as the gain medium, respectively. The results show that such a film can reduce the RIA of the irradiated Yb-fiber by up to 2.84 dB/m and increase the output power by up to 75.3% at most. In addition, we also study the optical recovery of the PM Yb-fibers after radiation.
Chinese Optics Letters
- Publication Date: Jan. 27, 2025
- Vol. 23, Issue 3, 031403 (2025)
2-kW all polarization-maintaining fiber ultrafast laser at a GHz repetition rate|Editors' Pick
Hao Xiu, Yiheng Fan, Tianxi Wang, Wenlong Wang, Wei Lin, Xiaoming Wei, and Zhongmin Yang
In this Letter, we report a 2-kW all polarization-maintaining (PM) fiber ultrafast laser from a single fiber link, which has a center wavelength of 1064 nm and a repetition rate of 1.39 GHz. To the best of our knowledge, this is the highest average power from all PM fiber lasers at 1.0 µm. Its beam quality (M2) is measured to be <1.2, and the pulse width after compression is measured to be ∼855 fs. In this Letter, we report a 2-kW all polarization-maintaining (PM) fiber ultrafast laser from a single fiber link, which has a center wavelength of 1064 nm and a repetition rate of 1.39 GHz. To the best of our knowledge, this is the highest average power from all PM fiber lasers at 1.0 µm. Its beam quality (M2) is measured to be <1.2, and the pulse width after compression is measured to be ∼855 fs.
Chinese Optics Letters
- Publication Date: Mar. 13, 2025
- Vol. 23, Issue 3, 031402 (2025)
Dual feed-forward neural network for predicting complex nonlinear dynamics of mode-locked fiber laser under variable cavity parameters
Haoyang Yu, Siyu Lai, Qiuying Ma, Zhaohui Jiang, Dong Pan, and Weihua Gui
We propose a dual feed-forward neural network (DFNN) model, consisting of a cavity parameter feature expander (CPFE) and a dynamic process predictor (DPP), for predicting the complex nonlinear dynamics of mode-locked fiber lasers. The output of the CPFE, following layer normalization, is combined with the pulse complex electric field amplitude and then fed into the DPP to predict the dynamics. The pulse evolution process from the detuned steady state to the steady state under different cavity configurations is rapidly calculated. The predicted results of the proposed DFNN are consistent with the numerical split-step Fourier method (SSFM). The simulation speed has been greatly improved with low computational complexity, which is approximately 152 times faster than the SSFM and 4 times faster than the long short-term memory recurrent neural network (LSTM) model. The findings provide a new low computational complexity and efficient machine learning approach to model the complex nonlinear dynamics of mode-locked lasers. We propose a dual feed-forward neural network (DFNN) model, consisting of a cavity parameter feature expander (CPFE) and a dynamic process predictor (DPP), for predicting the complex nonlinear dynamics of mode-locked fiber lasers. The output of the CPFE, following layer normalization, is combined with the pulse complex electric field amplitude and then fed into the DPP to predict the dynamics. The pulse evolution process from the detuned steady state to the steady state under different cavity configurations is rapidly calculated. The predicted results of the proposed DFNN are consistent with the numerical split-step Fourier method (SSFM). The simulation speed has been greatly improved with low computational complexity, which is approximately 152 times faster than the SSFM and 4 times faster than the long short-term memory recurrent neural network (LSTM) model. The findings provide a new low computational complexity and efficient machine learning approach to model the complex nonlinear dynamics of mode-locked lasers.
Chinese Optics Letters
- Publication Date: Mar. 13, 2025
- Vol. 23, Issue 3, 031401 (2025)
162.6 mJ high-energy and high-efficiency KTP optical parametric oscillator at 2 µm
Yuchun Liu, Jiajun Song, Yujie Peng, Enhao Li, Yingbin Long, Jianyu Sun, Liya Shen, Yinfei Liu, Junze Zhu, Yuxin Leng, and Zhizhan Xu
A high-energy and high-efficiency 2 µm nanosecond optical parametric oscillator (OPO) with excellent energy stability is reported. The cavity adopts a plane–plane configuration with two potassium titanyl phosphate (KTP) crystals inserted using a spatial walk-off compensated orientation. The KTP-OPO is pumped by a 1064 nm Nd:YAG Q-switched laser at a repetition rate of 10 Hz and produces a maximum pulse energy of 162.6 mJ at a pump energy of 431 mJ, corresponding to an optical conversion efficiency of 37.7% and a slope efficiency of 45.2%. The energy stability shows a record root mean square (RMS) of 0.4% over 30 min. To our knowledge, this represents the highest 2 µm pulse energy achieved via the 1 µm laser-pumped KTP-OPO scheme, which could be an excellent laser source for driving extreme ultraviolet (EUV) radiations in the subsequent demonstration experiments. A high-energy and high-efficiency 2 µm nanosecond optical parametric oscillator (OPO) with excellent energy stability is reported. The cavity adopts a plane–plane configuration with two potassium titanyl phosphate (KTP) crystals inserted using a spatial walk-off compensated orientation. The KTP-OPO is pumped by a 1064 nm Nd:YAG Q-switched laser at a repetition rate of 10 Hz and produces a maximum pulse energy of 162.6 mJ at a pump energy of 431 mJ, corresponding to an optical conversion efficiency of 37.7% and a slope efficiency of 45.2%. The energy stability shows a record root mean square (RMS) of 0.4% over 30 min. To our knowledge, this represents the highest 2 µm pulse energy achieved via the 1 µm laser-pumped KTP-OPO scheme, which could be an excellent laser source for driving extreme ultraviolet (EUV) radiations in the subsequent demonstration experiments.
Chinese Optics Letters
- Publication Date: Mar. 05, 2025
- Vol. 23, Issue 2, 021401 (2025)
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