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1 Issue (s), 11 Article (s)
Vol. 22, Iss.4—Apr.1, 2024 • pp: 040603- Spec. pp:
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ReviewsVol. 22, Iss.4-Apr..1,2024
Fiber Optics and Optical Communications
Low-cost, large-coverage, and high-flexibility coherent PON for next-generation access networks: advances, challenges, and prospects [Invited]Sizhe Xing, Junwen Zhang, Wangwei Shen, An Yan, Guoqiang Li, Aolong Sun, Ji Zhou, Dong Guo, Jianyang Shi, Ziwei Li, Chao Shen, and Nan Chi
Increasing bandwidth requirements have posed significant challenges for traditional access networks. It is difficult for intensity modulation/direct detection to meet the power budget and flexibility requirements of the next-generation passive optical network (PON) at 100G and beyond considering the new requirements. This is driving researchers to develop novel optical access technologies. Low-cost, wide-coverage, and high-flexibility coherent PON is emerging as a strong contender in the competition. In this article, we will review technologies that reduce the complexity of coherent PON (CPON), enabling it to meet the commercial requirements. Also, advanced algorithms and architectures that can enhance system coverage and flexibility are also discussed.Increasing bandwidth requirements have posed significant challenges for traditional access networks. It is difficult for intensity modulation/direct detection to meet the power budget and flexibility requirements of the next-generation passive optical network (PON) at 100G and beyond considering the new requirements. This is driving researchers to develop novel optical access technologies. Low-cost, wide-coverage, and high-flexibility coherent PON is emerging as a strong contender in the competition. In this article, we will review technologies that reduce the complexity of coherent PON (CPON), enabling it to meet the commercial requirements. Also, advanced algorithms and architectures that can enhance system coverage and flexibility are also discussed.
Chinese Optics Letters
- Publication Date: Apr. 18, 2024
- Vol. 22, Issue 4, 040604 (2024)
Research ArticlesVol. 22, Iss.4-Apr..1,2024
Fiber Optics and Optical Communications
Picosecond gain-switched polymer fiber random lasersWenyu Du, Sen Gao, Xiaojuan Zhang, Siqi Li, Yan Kuai, Zhiqiang Wang, Zhigang Cao, Feng Xu, Yu Liu, Lin Xu, Junxi Zhang, Kang Xie, Benli Yu, and Zhijia Hu
Random lasers are a type of lasers that lack typical resonator structures, offering benefits such as easy integration, low cost, and low spatial coherence. These features make them popular for speckle-free imaging and random number generation. However, due to their high threshold and phase instability, the production of picosecond random lasers has still been a challenge. In this work, we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers. Notably, stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 µJ, indicating the gain-switching mechanism. Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value, the number of inversion populations in the “scattering cavity” surpasses the threshold rapidly. Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon. This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.Random lasers are a type of lasers that lack typical resonator structures, offering benefits such as easy integration, low cost, and low spatial coherence. These features make them popular for speckle-free imaging and random number generation. However, due to their high threshold and phase instability, the production of picosecond random lasers has still been a challenge. In this work, we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers. Notably, stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 µJ, indicating the gain-switching mechanism. Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value, the number of inversion populations in the “scattering cavity” surpasses the threshold rapidly. Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon. This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 040603 (2024)
Imaging Systems and Image Processing
Non-blind super-resolution reconstruction for laser-induced damage dark-field imaging of optical elementsQian Wang, Fengdong Chen, Yueyue Han, Fa Zeng, Cheng Lu, and Guodong Liu
The laser-induced damage detection images used in high-power laser facilities have a dark background, few textures with sparse and small-sized damage sites, and slight degradation caused by slight defocus and optical diffraction, which make the image superresolution (SR) reconstruction challenging. We propose a non-blind SR reconstruction method by using an exquisite mixing of high-, intermediate-, and low-frequency information at each stage of pixel reconstruction based on UNet. We simplify the channel attention mechanism and activation function to focus on the useful channels and keep the global information in the features. We pay more attention on the damage area in the loss function of our end-to-end deep neural network. For constructing a high-low resolution image pairs data set, we precisely measure the point spread function (PSF) of a low-resolution imaging system by using a Bernoulli calibration pattern; the influence of different distance and lateral position on PSFs is also considered. A high-resolution camera is used to acquire the ground-truth images, which is used to create a low-resolution image pairs data set by convolving with the measured PSFs. Trained on the data set, our network has achieved better results, which proves the effectiveness of our method.The laser-induced damage detection images used in high-power laser facilities have a dark background, few textures with sparse and small-sized damage sites, and slight degradation caused by slight defocus and optical diffraction, which make the image superresolution (SR) reconstruction challenging. We propose a non-blind SR reconstruction method by using an exquisite mixing of high-, intermediate-, and low-frequency information at each stage of pixel reconstruction based on UNet. We simplify the channel attention mechanism and activation function to focus on the useful channels and keep the global information in the features. We pay more attention on the damage area in the loss function of our end-to-end deep neural network. For constructing a high-low resolution image pairs data set, we precisely measure the point spread function (PSF) of a low-resolution imaging system by using a Bernoulli calibration pattern; the influence of different distance and lateral position on PSFs is also considered. A high-resolution camera is used to acquire the ground-truth images, which is used to create a low-resolution image pairs data set by convolving with the measured PSFs. Trained on the data set, our network has achieved better results, which proves the effectiveness of our method.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 041701 (2024)
Integrated Optics
Erbium-ytterbium co-doped lithium niobate single-mode microdisk laser with an ultralow threshold of 1 µWMinghui Li, Renhong Gao, Chuntao Li, Jianglin Guan, Haisu Zhang, Jintian Lin, Guanghui Zhao, Qian Qiao, Min Wang, Lingling Qiao, Li Deng, and Ya Cheng
We demonstrate single-mode microdisk lasers in the telecom band with ultralow thresholds on erbium-ytterbium co-doped thin-film lithium niobate (TFLN). The active microdisk was fabricated with high-Q factors by photolithography-assisted chemomechanical etching. Thanks to the erbium-ytterbium co-doping providing high optical gain, the ultralow loss nanostructuring, and the excitation of high-Q coherent polygon modes, which suppresses multimode lasing and allows high spatial mode overlap between pump and lasing modes, single-mode laser emission operating at 1530 nm wavelength was observed with an ultralow threshold, under a 980-nm-band optical pump. The threshold was measured as low as 1 µW, which is one order of magnitude smaller than the best results previously reported in single-mode active TFLN microlasers. The conversion efficiency reaches 4.06 × 10-3, which is also the highest value reported in single-mode active TFLN microlasers.We demonstrate single-mode microdisk lasers in the telecom band with ultralow thresholds on erbium-ytterbium co-doped thin-film lithium niobate (TFLN). The active microdisk was fabricated with high-Q factors by photolithography-assisted chemomechanical etching. Thanks to the erbium-ytterbium co-doping providing high optical gain, the ultralow loss nanostructuring, and the excitation of high-Q coherent polygon modes, which suppresses multimode lasing and allows high spatial mode overlap between pump and lasing modes, single-mode laser emission operating at 1530 nm wavelength was observed with an ultralow threshold, under a 980-nm-band optical pump. The threshold was measured as low as 1 µW, which is one order of magnitude smaller than the best results previously reported in single-mode active TFLN microlasers. The conversion efficiency reaches 4.06 × 10-3, which is also the highest value reported in single-mode active TFLN microlasers.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 041301 (2024)
Lasers, Optical Amplifiers, and Laser Optics
Experiments and simulation on the overall DMG of long-haul cascade FM-EDFA systemsXinrui Jiang, Baojian Wu, Wei Yan, Feng Wen, and Kun Qiu
All-fiber few-mode erbium-doped fiber amplifiers (FM-EDFAs) with isolation and wavelength division multiplexers (IWDMs) have been developed to enable flexible pumping in different directions. The FM-EDFA can achieve >30 dB modal gain with <0.3 dB differential modal gain (DMG). We experimentally simulate the DMG performance of a cascade FM-EDFA system using the equivalent spectrum method. The overall DMG reaches 1.84 dB after 10-stage amplification. We also build a recirculating loop to simulate the system, and the developed FM-EDFA can support transmission up to 3270 km within a 2 dB overall DMG by optimizing the few-mode fiber length in the loop.
All-fiber few-mode erbium-doped fiber amplifiers (FM-EDFAs) with isolation and wavelength division multiplexers (IWDMs) have been developed to enable flexible pumping in different directions. The FM-EDFA can achieve >30 dB modal gain with <0.3 dB differential modal gain (DMG). We experimentally simulate the DMG performance of a cascade FM-EDFA system using the equivalent spectrum method. The overall DMG reaches 1.84 dB after 10-stage amplification. We also build a recirculating loop to simulate the system, and the developed FM-EDFA can support transmission up to 3270 km within a 2 dB overall DMG by optimizing the few-mode fiber length in the loop.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 041401 (2024)
Lasers, Optical Amplifiers, and Laser Optics
Eye-safe intra-cavity diamond cascaded Raman laser with high peak-power and narrow linewidthXiaobo Mi, Chaonan Lin, Yongsheng Hu, Houjie Ma, Jiuru He, Fengying Ma, Li Fan, and Chongxin Shan
The 1.4–1.8 µm eye-safe lasers have been widely used in the fields of laser medicine and laser detection and ranging. The diamond Raman lasers are capable of delivering excellent characteristics, such as good beam quality concomitantly with high output power. The intra-cavity diamond Raman lasers have the advantages of compactness and low Raman thresholds compared to the external-cavity Raman lasers. However, to date, the intra-cavity diamond cascaded Raman lasers in the spectral region of the eye-safe laser have an output power of only a few hundred milliwatts. A 1485 nm Nd:YVO4/diamond intra-cavity cascaded Raman laser is reported in this paper. The mode matching and stability of the cavity were optimally designed by a V-shaped folded cavity, which yielded an average output power of up to 2.2 W at a pulse repetition frequency of 50 kHz with a diode to second-Stokes conversion efficiency of 8.1%. Meanwhile, the pulse width of the second-Stokes laser was drastically reduced from 60 ns of the fundamental laser to 1.1 ns, which resulted in a high peak power of 40 kW. The device also exhibited single longitudinal mode with a narrow spectral width of < 0.02 nm.The 1.4–1.8 µm eye-safe lasers have been widely used in the fields of laser medicine and laser detection and ranging. The diamond Raman lasers are capable of delivering excellent characteristics, such as good beam quality concomitantly with high output power. The intra-cavity diamond Raman lasers have the advantages of compactness and low Raman thresholds compared to the external-cavity Raman lasers. However, to date, the intra-cavity diamond cascaded Raman lasers in the spectral region of the eye-safe laser have an output power of only a few hundred milliwatts. A 1485 nm Nd:YVO4/diamond intra-cavity cascaded Raman laser is reported in this paper. The mode matching and stability of the cavity were optimally designed by a V-shaped folded cavity, which yielded an average output power of up to 2.2 W at a pulse repetition frequency of 50 kHz with a diode to second-Stokes conversion efficiency of 8.1%. Meanwhile, the pulse width of the second-Stokes laser was drastically reduced from 60 ns of the fundamental laser to 1.1 ns, which resulted in a high peak power of 40 kW. The device also exhibited single longitudinal mode with a narrow spectral width of < 0.02 nm.
Chinese Optics Letters
- Publication Date: Apr. 18, 2024
- Vol. 22, Issue 4, 041402 (2024)
Lasers, Optical Amplifiers, and Laser Optics
High-power all-fiber linearly polarized Yb-doped chirped pulse amplifier based on active polarization controlTao Wang, Shuai Ren, Hongxiang Chang, Bo Ren, Kun Guo, Can Li, Pengfei Ma, Jinyong Leng, and Pu Zhou
High-power ultrafast laser amplification based on a non-polarization maintaining fiber chirped pulse amplifier is demonstrated. The active polarization control technology based on the root-mean-square propagation (RMS-prop) algorithm is employed to guarantee a linearly polarized output from the system. A maximum output power of 402.3 W at a repetition rate of 80 MHz is realized with a polarization extinction ratio (PER) of > 11.4 dB. In addition, the reliable operation of the system is verified by examining the stability and noise properties of the amplified laser. The M2 factor of the laser beam at the highest output power is measured to be less than 1.15, indicating a diffraction-limited beam quality. Finally, the amplified laser pulse is temporally compressed to 755 fs with a highest average power of 273.8 W. This is the first time, to the best of our knowledge, that the active polarization control technology was introduced into the high-power ultrafast fiber amplifier.High-power ultrafast laser amplification based on a non-polarization maintaining fiber chirped pulse amplifier is demonstrated. The active polarization control technology based on the root-mean-square propagation (RMS-prop) algorithm is employed to guarantee a linearly polarized output from the system. A maximum output power of 402.3 W at a repetition rate of 80 MHz is realized with a polarization extinction ratio (PER) of > 11.4 dB. In addition, the reliable operation of the system is verified by examining the stability and noise properties of the amplified laser. The M2 factor of the laser beam at the highest output power is measured to be less than 1.15, indicating a diffraction-limited beam quality. Finally, the amplified laser pulse is temporally compressed to 755 fs with a highest average power of 273.8 W. This is the first time, to the best of our knowledge, that the active polarization control technology was introduced into the high-power ultrafast fiber amplifier.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 041403 (2024)
Lasers, Optical Amplifiers, and Laser Optics
5 kW-level single-mode fiber amplifier based on low-numerical-aperture fiberYisha Chen, Yun Ye, Liangjin Huang, Huan Yang, Hanshuo Wu, Zhiping Yan, Zhiyong Pan, Xiaolin Wang, Zefeng Wang, and Pu Zhou
A low-numerical-aperture (NA) concept enables large-mode-area fiber with better single-mode operation ability, which is beneficial for transverse mode instability and nonlinear effects suppression. In this contribution, we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400 µm. The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated. As a result, an output of 4.80 kW and a beam quality factor of ∼1.33 were finally obtained, which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber. The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.A low-numerical-aperture (NA) concept enables large-mode-area fiber with better single-mode operation ability, which is beneficial for transverse mode instability and nonlinear effects suppression. In this contribution, we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400 µm. The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated. As a result, an output of 4.80 kW and a beam quality factor of ∼1.33 were finally obtained, which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber. The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.
Chinese Optics Letters
- Publication Date: Apr. 18, 2024
- Vol. 22, Issue 4, 041404 (2024)
Microwave Photonics
Demonstration of radar-aided flexible communication in a photonics-based W-band distributed integrated sensing and communication system for 6GJunlian Jia, Boyu Dong, Li Tao, Jianyang Shi, Nan Chi, and Junwen Zhang
This paper experimentally demonstrates a distributed photonics-based W-band integrated sensing and communication (ISAC) system, in which radar sensing can aid the communication links in alignment and data rate estimation. As a proof-of-concept, the ISAC system locates the users, guides the alignment, and sets a communication link with the estimated highest data rate. A peak net data rate of 68.6 Gbit/s and a target sensing with a less-than-1-cm error and a sub-2-cm resolution have been tested over a 10-km fiber and a 1.15-m free space transmission in the photonics-based W-band ISAC system. The achievable net data rates of the users at different locations estimated by sensing are experimentally verified.This paper experimentally demonstrates a distributed photonics-based W-band integrated sensing and communication (ISAC) system, in which radar sensing can aid the communication links in alignment and data rate estimation. As a proof-of-concept, the ISAC system locates the users, guides the alignment, and sets a communication link with the estimated highest data rate. A peak net data rate of 68.6 Gbit/s and a target sensing with a less-than-1-cm error and a sub-2-cm resolution have been tested over a 10-km fiber and a 1.15-m free space transmission in the photonics-based W-band ISAC system. The achievable net data rates of the users at different locations estimated by sensing are experimentally verified.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 043901 (2024)
Nanophotonics, Metamaterials, and Plasmonics
Active metasurface via magnetic control for tri-channel polarization multiplexing holographyYu Bi, Lingling Huang, Tuo Li, Changhong Wang, Xiaofeng Zou, Lang Zhou, and Guoguo Kang
Active metasurfaces have recently attracted more attention since they can make the light manipulation be versatile and real-time. Metasurfaces-based holography possesses the advantages of high spatial resolution and enormous information capacity for applications in optical displays and encryption. In this work, a tunable polarization multiplexing holographic metasurface controlled by an external magnetic field is proposed. The elaborately designed nanoantennas are arranged on the magneto-optical intermediate layer, which is placed on the metallic reflecting layer. Since the non-diagonal elements of the dielectric tensor of the magneto-optical material become non-zero values once the external magnetic field is applied, the differential absorption for the left and right circularly polarized light can be generated. Meanwhile, the amplitude and phase can be flexibly modulated by changing the sizes of the nanoantennas. Based on this, the dynamic multichannel holographic display of metasurface in the linear and circular polarization channels is realized via magnetic control, and it can provide enhanced security for optical information storage. This work paves the way for the realization of magnetically controllable phase modulation, which is promising in dynamic wavefront control and optical information encryption.Active metasurfaces have recently attracted more attention since they can make the light manipulation be versatile and real-time. Metasurfaces-based holography possesses the advantages of high spatial resolution and enormous information capacity for applications in optical displays and encryption. In this work, a tunable polarization multiplexing holographic metasurface controlled by an external magnetic field is proposed. The elaborately designed nanoantennas are arranged on the magneto-optical intermediate layer, which is placed on the metallic reflecting layer. Since the non-diagonal elements of the dielectric tensor of the magneto-optical material become non-zero values once the external magnetic field is applied, the differential absorption for the left and right circularly polarized light can be generated. Meanwhile, the amplitude and phase can be flexibly modulated by changing the sizes of the nanoantennas. Based on this, the dynamic multichannel holographic display of metasurface in the linear and circular polarization channels is realized via magnetic control, and it can provide enhanced security for optical information storage. This work paves the way for the realization of magnetically controllable phase modulation, which is promising in dynamic wavefront control and optical information encryption.
Chinese Optics Letters
- Publication Date: Apr. 18, 2024
- Vol. 22, Issue 4, 043601 (2024)
Nonlinear Optics
Integrated Fabry–Perot interferometer based on Er/Yb co-doped fiber for all-optical phase modulationFan Wang, Siyu Lin, Yanchen Qu, Xiaopeng Han, and Yundong Zhang
Fast and stable phase control is essential for many applications in optics. Here, we propose an all-fiber all-optical phase modulation scheme based on a Fabry–Perot interferometer (FPI) and an Er/Yb co-doped fiber (EYDF). By using the EYDF as an F-P cavity via rational design, a phase shift with a modulation sensitivity of 0.0312π/mW is introduced to the modulator. The phase shifts in the EYDF consist of a thermal phase shift and a nonlinear phase shift with a ratio of 19:1, and the corresponding temporal responses of the modulation are 204 ms and 2.5 ms, respectively. In addition, the compact FPI is encapsulated to provide excellent stability for the modulator.Fast and stable phase control is essential for many applications in optics. Here, we propose an all-fiber all-optical phase modulation scheme based on a Fabry–Perot interferometer (FPI) and an Er/Yb co-doped fiber (EYDF). By using the EYDF as an F-P cavity via rational design, a phase shift with a modulation sensitivity of 0.0312π/mW is introduced to the modulator. The phase shifts in the EYDF consist of a thermal phase shift and a nonlinear phase shift with a ratio of 19:1, and the corresponding temporal responses of the modulation are 204 ms and 2.5 ms, respectively. In addition, the compact FPI is encapsulated to provide excellent stability for the modulator.
Chinese Optics Letters
- Publication Date: Apr. 17, 2024
- Vol. 22, Issue 4, 041901 (2024)
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20th Anniversary of Wuhan National Laboratory for Optoelectronics (WNLO) (2023)
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