Journals >Chinese Optics Letters
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2024
Volume: 22 Issue 4
21 Article(s)
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Reviews
Fiber optics and optical communications
Low-cost, large-coverage, and high-flexibility coherent PON for next-generation access networks: advances, challenges, and prospects [Invited] | On the Cover
Sizhe Xing, Junwen Zhang, Wangwei Shen, An Yan... and Nan Chi|Show fewer author(s)
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 Articles
Atmospheric, Oceanic, Space, and Environmental Optics
Coherent Doppler lidar wind retrieval for a typhoon based on the genetic simulated annealing algorithm
Zhen Liu, Lucheng Yuan, Jie Tang, Yunpeng Zhang... and Weibiao Chen|Show fewer author(s)
A method of spectrum estimation based on the genetic simulated annealing (GSA) algorithm is proposed, which is applied to retrieve the three-dimensional wind field of typhoon Nangka observed by our research group. Compared to the genetic algorithm (GA), the GSA algorithm not only extends the detection range and guarantees the accuracy of retrieval results but also demonstrates a faster retrieval speed. Experimental results indicate that both the GA and GSA algorithms can enhance the detection range by 35% more than the least squares method. However, the convergence speed of the GSA algorithm is 17 times faster than that of the GA, which is more beneficial for real-time data processing.A method of spectrum estimation based on the genetic simulated annealing (GSA) algorithm is proposed, which is applied to retrieve the three-dimensional wind field of typhoon Nangka observed by our research group. Compared to the genetic algorithm (GA), the GSA algorithm not only extends the detection range and guarantees the accuracy of retrieval results but also demonstrates a faster retrieval speed. Experimental results indicate that both the GA and GSA algorithms can enhance the detection range by 35% more than the least squares method. However, the convergence speed of the GSA algorithm is 17 times faster than that of the GA, which is more beneficial for real-time data processing..
Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 040101 (2024)
Biophotonics
Iterative multi-photon adaptive compensation technique for deep tissue two-photon fluorescence lifetime imaging
Kexin Wang, Wenhui Yu, Junle Qu, Changrui Liao... and Liwei Liu|Show fewer author(s)
Fluorescence lifetime imaging can reveal the high-resolution structure of various biophysical and chemical parameters in a microenvironment quantitatively. However, the depth of imaging is generally limited to hundreds of micrometers due to aberration and light scattering in biological tissues. This paper introduces an iterative multi-photon adaptive compensation technique (IMPACT) into a two-photon fluorescence lifetime microscopy system to successfully overcome aberrations and multiple scattering problems in deep tissues. It shows that 400 correction modes can be achieved within 5 min, which was mainly limited by the frame rate of a spatial light modulator. This system was used for high-resolution imaging of mice brain tissue and live zebrafish, further verifying its superior performance in imaging quality and photon accumulation speed.Fluorescence lifetime imaging can reveal the high-resolution structure of various biophysical and chemical parameters in a microenvironment quantitatively. However, the depth of imaging is generally limited to hundreds of micrometers due to aberration and light scattering in biological tissues. This paper introduces an iterative multi-photon adaptive compensation technique (IMPACT) into a two-photon fluorescence lifetime microscopy system to successfully overcome aberrations and multiple scattering problems in deep tissues. It shows that 400 correction modes can be achieved within 5 min, which was mainly limited by the frame rate of a spatial light modulator. This system was used for high-resolution imaging of mice brain tissue and live zebrafish, further verifying its superior performance in imaging quality and photon accumulation speed..
Chinese Optics Letters
- Publication Date: Apr. 26, 2024
- Vol. 22, Issue 4, 041702 (2024)
Fiber Optics and Optical Communications
Neural network equalization based on delta-sigma modulation
Bo Liu, Jianxin Ren, Xiangyu Wu, Shuaidong Chen... and Li Zhao|Show fewer author(s)
We propose a neural network equalization delta-sigma modulation (DSM) technique. After performing DSM on the multi-order quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signal at the transmitting end, neural network equalizer technology is used in the digital signal processing at receiving end. Applying this technology to a 4.6 km W-band millimeter wave system, it is possible to achieve a 1 Gbaud 8192-QAM OFDM signal transmission. The data rate reached 23.4 Gbit/s with the bit error rate at 3.8 × 10-2, lower than soft-decision forward-error correction threshold (4 × 10-2).We propose a neural network equalization delta-sigma modulation (DSM) technique. After performing DSM on the multi-order quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signal at the transmitting end, neural network equalizer technology is used in the digital signal processing at receiving end. Applying this technology to a 4.6 km W-band millimeter wave system, it is possible to achieve a 1 Gbaud 8192-QAM OFDM signal transmission. The data rate reached 23.4 Gbit/s with the bit error rate at 3.8 × 10-2, lower than soft-decision forward-error correction threshold (4 × 10-2)..
Chinese Optics Letters
- Publication Date: Apr. 26, 2024
- Vol. 22, Issue 4, 040601 (2024)
High-security multi-constellation shaping modulation with asymmetric encryption
Lei Jiang, Bo Liu, Jianxin Ren, Xiangyu Wu... and Feng Tian|Show fewer author(s)
This Letter proposes a high-security modulation scheme for optical transmission systems. By using multi-constellation shaping and asymmetric encryption, the information security can be enhanced and quantum computer cracking can be effectively resisted. Three-dimensional (3D) carrier-less amplitude phase modulation is utilized to superposition and transmit 3D signals. Experimental verification is conducted using a seven-core weakly coupled fiber platform. The results demonstrate that the proposed scheme can effectively protect the system from any illegal attacker.This Letter proposes a high-security modulation scheme for optical transmission systems. By using multi-constellation shaping and asymmetric encryption, the information security can be enhanced and quantum computer cracking can be effectively resisted. Three-dimensional (3D) carrier-less amplitude phase modulation is utilized to superposition and transmit 3D signals. Experimental verification is conducted using a seven-core weakly coupled fiber platform. The results demonstrate that the proposed scheme can effectively protect the system from any illegal attacker..
Chinese Optics Letters
- Publication Date: Apr. 26, 2024
- Vol. 22, Issue 4, 040602 (2024)
Picosecond gain-switched polymer fiber random lasers
Wenyu Du, Sen Gao, Xiaojuan Zhang, Siqi Li... and Zhijia Hu|Show fewer author(s)
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 elements
Qian Wang, Fengdong Chen, Yueyue Han, Fa Zeng... and Guodong Liu|Show fewer author(s)
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, 041101 (2024)
Instrumentation, Measurement, and Optical Sensing
Dynamic range expansion for optical frequency shift detection based on multiple harmonics
Yanru Zhou, Lifan Fan, Kai Xu, Wenyao Liu... and Jun Liu|Show fewer author(s)
Sensors based on optical resonators often have their measurement range limited by their cavity linewidth, particularly in the measurement of time-varying signals. This paper introduces a method for optical frequency shift detection using multiple harmonics to expand the dynamic range of sensors based on optical resonators. The proposed method expands the measurement range of optical frequency shift beyond the cavity linewidth while maintaining measurement accuracy. The theoretical derivation of this method is carried out based on the equation of motion for an optical resonator and the recursive relationship of the Bessel function. Experimental results show that the dynamic range is expanded to 4 times greater than the conventional first harmonic method while still maintaining accuracy. Furthermore, we present an objective analysis of the correlation between the expansion factor of the method and the linewidth and free spectrum of the optical resonator.
Sensors based on optical resonators often have their measurement range limited by their cavity linewidth, particularly in the measurement of time-varying signals. This paper introduces a method for optical frequency shift detection using multiple harmonics to expand the dynamic range of sensors based on optical resonators. The proposed method expands the measurement range of optical frequency shift beyond the cavity linewidth while maintaining measurement accuracy. The theoretical derivation of this method is carried out based on the equation of motion for an optical resonator and the recursive relationship of the Bessel function. Experimental results show that the dynamic range is expanded to 4 times greater than the conventional first harmonic method while still maintaining accuracy. Furthermore, we present an objective analysis of the correlation between the expansion factor of the method and the linewidth and free spectrum of the optical resonator.
.Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 041201 (2024)
Integrated Optics
Erbium-ytterbium co-doped lithium niobate single-mode microdisk laser with an ultralow threshold of 1 µW
Minghui Li, Renhong Gao, Chuntao Li, Jianglin Guan... and Ya Cheng|Show fewer author(s)
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 systems
Xinrui 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)
Eye-safe intra-cavity diamond cascaded Raman laser with high peak-power and narrow linewidth
Xiaobo Mi, Chaonan Lin, Yongsheng Hu, Houjie Ma... and Chongxin Shan|Show fewer author(s)
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)
High-power all-fiber linearly polarized Yb-doped chirped pulse amplifier based on active polarization control
Tao Wang, Shuai Ren, Hongxiang Chang, Bo Ren... and Pu Zhou|Show fewer author(s)
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)
5 kW-level single-mode fiber amplifier based on low-numerical-aperture fiber
Yisha Chen, Yun Ye, Liangjin Huang, Huan Yang... and Pu Zhou|Show fewer author(s)
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)
1.6-µm single-frequency erbium-doped fiber laser based on two cascaded subrings
Yaqi Zhai, Han Wen, Haowei Chen, Baole Lu, and Jintao Bai
We demonstrate a stable narrow linewidth single-frequency erbium-doped fiber laser (EDFL) operating at 1.6 µm. A Fabry–Perot fiber Bragg grating and two cascaded subrings are incorporated in the main ring cavity to achieve single-frequency operation. The experimentally measured optical signal-to-noise ratio is greater than 73 dB. Furthermore, the linewidth of the EDFL is measured to be about 480 Hz by the self-built short-delayed self-heterodyne interferometry device. The laser shows superior stability, with no mode-hopping during the 60-min observation period. The proposed EDFL provides a new experimental idea for realizing a single-frequency fiber laser in the L-band.We demonstrate a stable narrow linewidth single-frequency erbium-doped fiber laser (EDFL) operating at 1.6 µm. A Fabry–Perot fiber Bragg grating and two cascaded subrings are incorporated in the main ring cavity to achieve single-frequency operation. The experimentally measured optical signal-to-noise ratio is greater than 73 dB. Furthermore, the linewidth of the EDFL is measured to be about 480 Hz by the self-built short-delayed self-heterodyne interferometry device. The laser shows superior stability, with no mode-hopping during the 60-min observation period. The proposed EDFL provides a new experimental idea for realizing a single-frequency fiber laser in the L-band..
Chinese Optics Letters
- Publication Date: Apr. 26, 2024
- Vol. 22, Issue 4, 041406 (2024)
Design of a high frequency accuracy heterodyne laser source working in a wide temperature range
Hongxing Yang, Yan Wang, Ziqi Yin, Pengcheng Hu... and Jing Li|Show fewer author(s)
To ensure the frequency accuracy of a heterodyne laser source in the ambient temperature range of -20°C to 40°C, a dual-longitudinal-mode thermally stabilized He–Ne laser based on non-equilibrium power locking was designed. The ambient adaptive preheating temperature setting scheme ensured the laser could operate normally in the range of -20°C to 40°C. The non-equilibrium power-locked frequency stabilization scheme compensated for the frequency drift caused by different stabilization temperatures. The experimental results indicated that the frequency accuracy of the laser designed in this study could reach 5.2 × 10-9 in the range of -20°C to 40°C.To ensure the frequency accuracy of a heterodyne laser source in the ambient temperature range of -20°C to 40°C, a dual-longitudinal-mode thermally stabilized He–Ne laser based on non-equilibrium power locking was designed. The ambient adaptive preheating temperature setting scheme ensured the laser could operate normally in the range of -20°C to 40°C. The non-equilibrium power-locked frequency stabilization scheme compensated for the frequency drift caused by different stabilization temperatures. The experimental results indicated that the frequency accuracy of the laser designed in this study could reach 5.2 × 10-9 in the range of -20°C to 40°C..
Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 041407 (2024)
Microwave Photonics
Demonstration of radar-aided flexible communication in a photonics-based W-band distributed integrated sensing and communication system for 6G
Junlian Jia, Boyu Dong, Li Tao, Jianyang Shi... and Junwen Zhang|Show fewer author(s)
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)
Optical pulse repetition rate division using an optoelectronic oscillator
Ping Li, Kunlin Shao, Yamei Zhang, and Shilong Pan
An approach for frequency division of an optical pulse train (OPT) based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. When the OPT is injected into the OEO, a microwave signal with a frequency equaling fractional multiples of the repetition rate of the OPT is generated. This signal is then fed back to the OEO, maintaining its oscillation, while simultaneously serving as the control signal of a Mach–Zehnder modulator (MZM) in the OEO. The MZM acts as an optical switch, permitting specific pulses to pass through while blocking others. As a result, the repetition rate of the OPT is manipulated. A proof-of-concept experiment is carried out. Frequency division factors of 2 and 3 are successfully achieved. The phase noises of the OPT before and after the frequency division are investigated. Compared to previously reported systems, no external microwave source and sophisticated synchronization structure are needed.An approach for frequency division of an optical pulse train (OPT) based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. When the OPT is injected into the OEO, a microwave signal with a frequency equaling fractional multiples of the repetition rate of the OPT is generated. This signal is then fed back to the OEO, maintaining its oscillation, while simultaneously serving as the control signal of a Mach–Zehnder modulator (MZM) in the OEO. The MZM acts as an optical switch, permitting specific pulses to pass through while blocking others. As a result, the repetition rate of the OPT is manipulated. A proof-of-concept experiment is carried out. Frequency division factors of 2 and 3 are successfully achieved. The phase noises of the OPT before and after the frequency division are investigated. Compared to previously reported systems, no external microwave source and sophisticated synchronization structure are needed..
Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 043902 (2024)
Nanophotonics, Metamaterials, and Plasmonics
Active metasurface via magnetic control for tri-channel polarization multiplexing holography | Editors' Pick
Yu Bi, Lingling Huang, Tuo Li, Changhong Wang... and Guoguo Kang|Show fewer author(s)
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 modulation
Fan 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)
Second-harmonic generation in periodic fork-shaped χ(2) gratings at oblique incidence | Editors' Pick
Yan Sheng, Shan Liu, Xiaokang Hu, Xin Chen... and Wieslaw Krolikowski|Show fewer author(s)
Three-dimensional (3D) nonlinear photonic crystals have received intensive interest as an ideal platform to study nonlinear wave interactions and explore their applications. Periodic fork-shaped gratings are extremely important in this context because they are capable of generating second-harmonic vortex beams from a fundamental Gaussian wave, which has versatile applications in optical trapping and materials engineering. However, previous studies mainly focused on the normal incidence of the fundamental Gaussian beam, resulting in symmetric emissions of the second-harmonic vortices. Here we present an experimental study on second-harmonic vortex generation in periodic fork-shaped gratings at oblique incidence, in comparison with the case of normal incidence. More quasi-phase-matching resonant wavelengths have been observed at oblique incidence, and the second-harmonic emissions become asymmetric against the incident beam. These results agree well with theoretic explanations. The oblique incidence of the fundamental wave is also used for the generation of second-harmonic Bessel beams with uniform azimuthal intensity distributions. Our study is important for a deeper understanding of nonlinear interactions in a 3D periodic medium. It also paves the way toward achieving high-quality structured beams at new frequencies, which is important for manipulation of the orbital angular momentum of light.Three-dimensional (3D) nonlinear photonic crystals have received intensive interest as an ideal platform to study nonlinear wave interactions and explore their applications. Periodic fork-shaped gratings are extremely important in this context because they are capable of generating second-harmonic vortex beams from a fundamental Gaussian wave, which has versatile applications in optical trapping and materials engineering. However, previous studies mainly focused on the normal incidence of the fundamental Gaussian beam, resulting in symmetric emissions of the second-harmonic vortices. Here we present an experimental study on second-harmonic vortex generation in periodic fork-shaped gratings at oblique incidence, in comparison with the case of normal incidence. More quasi-phase-matching resonant wavelengths have been observed at oblique incidence, and the second-harmonic emissions become asymmetric against the incident beam. These results agree well with theoretic explanations. The oblique incidence of the fundamental wave is also used for the generation of second-harmonic Bessel beams with uniform azimuthal intensity distributions. Our study is important for a deeper understanding of nonlinear interactions in a 3D periodic medium. It also paves the way toward achieving high-quality structured beams at new frequencies, which is important for manipulation of the orbital angular momentum of light..
Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 041902 (2024)
X-ray Optics
Angle measurement of pulsars based on spatially modulated X-ray intensity correlation
De Wang, Hong Yu, Zhijie Tan, Ronghua Lu, and Shensheng Han
High-precision angle measurement of pulsars is critical for realizing pulsar navigation. Compared to visible light and radio waves, the wavelength of X-rays is incredibly short, which provides the possibility of achieving better spatial resolution. However, due to the lack of applicable X-ray apparatus, extracting the angle information of pulsars through conventional X-ray methods is challenging. Here, we propose an approach of pulsar angle measurement based on spatially modulated X-ray intensity correlation (SMXIC), in which the angle information is obtained by measuring the spatial intensity correlation between two radiation fields. The theoretical model for this method has been established, and a proof-of-concept experiment was carried out. The SMXIC measurement of observing angles has been demonstrated, and the experimental results are consistent with the theoretical values. The potential of this method in future applications is discussed, and theoretically, the angular measurement at the level of micro-arcsecond can be expected. The sphere of pulsar navigation may benefit from our fresh insights.High-precision angle measurement of pulsars is critical for realizing pulsar navigation. Compared to visible light and radio waves, the wavelength of X-rays is incredibly short, which provides the possibility of achieving better spatial resolution. However, due to the lack of applicable X-ray apparatus, extracting the angle information of pulsars through conventional X-ray methods is challenging. Here, we propose an approach of pulsar angle measurement based on spatially modulated X-ray intensity correlation (SMXIC), in which the angle information is obtained by measuring the spatial intensity correlation between two radiation fields. The theoretical model for this method has been established, and a proof-of-concept experiment was carried out. The SMXIC measurement of observing angles has been demonstrated, and the experimental results are consistent with the theoretical values. The potential of this method in future applications is discussed, and theoretically, the angular measurement at the level of micro-arcsecond can be expected. The sphere of pulsar navigation may benefit from our fresh insights..
Chinese Optics Letters
- Publication Date: Apr. 25, 2024
- Vol. 22, Issue 4, 043401 (2024)
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