Dual-Core Terahertz Fiber Directional Coupler
Huang Xu, Luo Xingfang, Zuo Xiangyu, Wang Shaohua, and Zhu Yuanfeng
In this paper, a two-core terahertz fiber directional coupler is proposed. Two dielectric cylinders are suspended in the interior of two annular dielectric layers to form two fiber cores. By adjusting the structural parameters, the coupling length of the two polarization modes can be equal, thus realizing polarization independence of the coupling length. The length of the coupler can be one half of the coupling length of the fiber mode, and the transmission loss can be reduced with the short length of the device. The coupler is numerically analyzed by finite element method. The results show that the length of the coupler is 0.535 cm, and the transmission loss of x and y polarization modes is 0.23 dB and 0.19 dB, respectively. Under the premise that the coupling length difference between the two polarization modes is less than 1%, the bandwidth reaches 220 GHz.
  • Jan. 19, 2022
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0206006 (2022)
  • DOI:10.3788/AOS202242.0206006
Analysis and Experimental Study on Transmission Characteristics of Double Sagnac Loop Filter
Cui Wenxiang, Zhou Xuefang, Hu Miao, Bi Meihua, Yang Guowei, Li Qiliang, and Wang Tianshu
ConclusionsIn this study, the transmission characteristics of a double Sagnac loop filter, composed of two segments of PMF in parallel, are analyzed, simulated and measured in detail, which proves that the proposed double Sagnac loop filter has the polarization-independent characteristic and the tunable channel spacing. According to the results of simulation and measurement, a channel spacing tunable multi-wavelength erbium-doped fiber laser utilizing a double Sagnac loop filter with the assistance of the FWM effect is designed. The laser can output multi-wavelength lasing lines with channel spacings of 0.35 nm and 0.9 nm. Owing to the polarization-independent characteristic of the double Sagnac loop filter, the polarization-dependent devices are not interfere with the transmission spectra of the filter. Thus, the double Sagnac loop filter exhibits the simple structure, polarization-independence, the tunability of channel spacing, and a great potential application in the field of multi-wavelength fiber lasers.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 4 0406006 (2022)
  • DOI:10.3788/CJL202249.0406006
Respiration and Heartbeat Signal Acquisition Method Based on Fiber Optic Sensing
Li Yuhuan, Chen Yong, Liu Huanlin, and Jiang Tao
ConclusionsWe propose a method to acquire respiration and heartbeat signals based on FBG sensors. A combined variational mode decomposition with improved wavelet threshold function (VMD-IWT) noise reduction algorithm is used to remove noise interference existing in signals. The simulation results show that our proposed algorithm realizes the best SNR, RMSE, and other indicators, and makes actual signals smoother after noise reduction. We use a band-pass filter to separate signals and calculate their frequencies. The maximum error rate of heart rate is 8.75% with respect to the reference value, and the maximum deviation of respiration rate from the reference value is 1 bpm, which proves the better accuracy of the proposed method. This provides a more convenient and economical way to monitor health at home.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 4 0406004 (2022)
  • DOI:10.3788/CJL202249.0406004
Atmospheric Turbulence Suppression Methods for Near the Earth Wireless Laser Communication Channels Based on Avalanche Photodiode Adaptive Gain Control
Zhou Chang, Yu Xiaonan, Jiang Huilin, Wang Tong, and An Ning
ConclusionsThis study investigated the effect of atmospheric turbulence on laser communication systems and proposed a communication detection and reception method based on closed-loop regulation of the APD gain factor. Building a wireless laser communication experiment verifies that the APD gain closed-loop regulation method significantly improves the system performance under the turbulence fading channel. The above experiments show that the APD gain control can effectively suppress the optical power fluctuations generated by atmospheric turbulence jitter; thus, significantly improving the communication performance. Under weak turbulence conditions, the power spectrum curve with AGC is more consistent with the 5/3 power-law spectrum. The variance of light intensity flicker is reduced from 0.057 to 0.023; the system RBE is reduced from 1.75×10-8 to 3.99×10-10, a reduction of two orders of magnitude. Finally, the turbulence intensity and corresponding system average RBE variation curves under different periods are calculated. This shows that the adaptive gain control algorithm effectively suppresses turbulence-induced signal power fluctuations and achieves high interference immunity for wireless laser communication.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 4 0406002 (2022)
  • DOI:10.3788/CJL202249.0406002
High-Speed Secure Key Distribution Based on Symmetric Phase-Shift-Keying Chaos Synchronization
Wu Chaoren, Gao Hua, Wang Longsheng, Guo Yuanyuan, Wang Anbang, and Wang Yuncai
ConclusionsIn this study, we propose a high-speed secure key distribution scheme based on symmetric-phase-shift-keying chaotic synchronization. Using the delayed self-interference of an unbalanced M-Z interferometer, the correlation between the drive and response signals is reduced to 0.25. The eavesdropper cannot directly obtain part of the relevant key from the chaotic drive signal to improve the key distribution security. An open-loop chaotic synchronization structure is constructed by a commonly driven semiconductor laser without external cavity feedback, which avoid multiple oscillations of chaotic signals in the feedback external cavity in the closed-loop structure, shorten the recovery time of chaotic synchronization to 1.8 ns, and improve the key distribution rate. Finally, when the BER is 3.8×10-3, a high-speed secure key distribution at a rate of 1.28 Gbit/s is realized.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 4 0406001 (2022)
  • DOI:10.3788/CJL202249.0406001
All-Fiber Mode Selective Coupler Based on Vector Modes
Guo Yinghao, Liu Mei, Tang Min, Ren Wenhua, and Ren Guobin
ConclusionsIn this paper, an all-fiber mode selective coupler based on vector modes is proposed, which consists of a single mode fiber and an air-core ring few mode fiber. Based on the mode-coupling theory, the coupling characteristics of this vector mode selective coupler are investigated. In addition, we explore the influences of core distance on the crosstalk between high order vector modes and the working bandwidth. The results show that this vector mode selective coupler can realize the coupling from the fundamental mode to the special high order mode with a high coupling efficiency in the wavelength range of 15431556 nm. The crosstalk and the working bandwidth can be regulated by changing the core distance. Moreover, the low crosstalk and the wide bandwidth mode coupling are achieved at a core distance of 11 μm. The results in this paper can find applications in fiber lasers, optical tweezers, and mode division multiplexing systems.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 3 0306004 (2022)
  • DOI:10.3788/CJL202249.0306004
Simulation Analysis of SRS Crosstalk in Super-PON System
Yu Peihua, Li Zhengxuan, Xu Yan, and Song Yingxiong
ConclusionsIn this paper, the influence of SRS crosstalk on the Super-PON system is investigated by simulation in which two cases are considered. The one case is using C-band for US and L-band for DS, and the other case is using C-band for DS and L-band for US. The simulation results show that when using C-band for DS and L-band for US, the power impairment of signals is the smallest, which is 0.43 dB (the single wavelength input optical powers of US and DS are 10 dBm and 13 dBm, respectively). Therefore, this combination mode is the best band-allocation scheme for the Super-PON system. Besides, we simulate the power impairment of signals caused by SRS when the Super-PON US and DS coexist with EPON US and 10G-EPON DS systems, and the results show that the SRS effect has little influence on them which can be basically ignored.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 3 0306003 (2022)
  • DOI:10.3788/CJL202249.0306003
Design of Low Crosstalk Double Coupling Ring Assisted 6-LP Fiber
Zang Hongfei, Tian Feng, and Wang Yongjun
ConclusionsIn order to reduce the problem of inter-mode crosstalk in the low-mode fiber, a new type of dual coupling ring assisted few-mode fiber structure design is proposed, the main influencing factors of crosstalk in the 6-LP mode are analyzed, and five main structural parameters of the new dual coupling ring structure are simulated and analyzed. Based on this designed structure, a 6-LP few-mode fiber is developed, which reduces the inter-mode crosstalk in the few-mode fiber. The results show that in the 6-LP few-mode fiber, the effective mode refractive index difference between the LP21 mode and the LP02 mode is the closest, and the difference is the main factor affecting crosstalk. The double coupling ring structure adjusts the effective mode refractive indices of the LP21 mode and the LP02 mode. In this structure, the minimum refractive index difference between LP21 and LP02 is 1.5×10-3, which is 1.88 times the minimum refractive index difference of the traditional step structure under the same conditions.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 3 0306002 (2022)
  • DOI:10.3788/CJL202249.0306002
Propagation of High-Power Picosecond Pulse at 1064 nm Using Nodeless Anti-Resonant Hollow-Core Fibre
Lu Wenju, Zhang Xin, Zhu Kuan, Du Keming, and Wang Pu
ConclusionsIn this study, we explored the high-power pico-second pulse propagation characteristics using a homemade low-loss NL-HCF. During the high-power propagation of NL-HCF, the fibre was chosen to meet the comprehensive requirements of confinement loss, bending performance, and laser damage threshold. The pulse width of the light source was 15 ps, and its repetition frequency was adjustable. Different lengths of NL-HCF were used for propagation tests. When the input laser was coupled to the NL-HCF with a 403 μJ pulse energy, 40.3 W average power, and 26.8 MW peak power, we obtained a 91.8% propagation efficiency with a maximum output pulse energy of 370 μJ. We analysed the spectral and temporal characteristics of ultra-short pulse passing through different NL-HCF lengths. When the NL-HCF length was 1 m, the laser pulse was propagated without distortion, and the spectrum was slightly deformed. Owing to the non-linear effect, the pulse width of the output laser was increased to 26 ps and the spectrum was expanded to 70 nm when the length of the NL-HCF was increased to 3.3 m. Experiments show that NL-HCF will play an important role in the propagation of ultra-short pulses.
  • Jan. 18, 2022
  • Chinese Journal of Lasers
  • Vol.49 Issue, 3 0306001 (2022)
  • DOI:10.3788/CJL202249.0306001
Biosensor Based on Dual-Resonance Long-Period Fiber Gratings for Detection of H9N2 Subtype Avian Influenza Virus
Shi Shenghui, Nie Qinglin, Jiang Shanghai, Wu Shengxi, Tang bin, and Zhao Mingfu
H9N2 subtype avian influenza virus (AIV) is a low-pathogenicity AIV that seriously threatens the healthy development of the poultry industry and public health systems. By developing rapid, sensitive, and accurate methods suitable for field detection of H9N2 AIV, we could efficiently control the viral infection and its spread over time. This study proposes a novel biosensor with high specificity and a low limit of detection (LOD) for H9N2 AIV detection. The sensor employs a dual-resonance long-period fiber grating (DR-LPFG) modified with TiO2 nanoparticles (nano-TiO2). Anti-H9N2 monoclonal antibody molecules (anti-H9N2 MAbs) are covalently bound to the TiO2 surface carboxyl groups on the surface of the DR-LPFG, thus preparing the biosensor. The biosensor measures the variation of the dual-resonance wavelength spacing (Δλ) caused by the specific interaction between the fixed anti-H9N2 MAbs on the surface of DR-LPFG and H9N2 AIV antigen. In experimental tests, the Δλ sensitivity of the nano-TiO2 coated DR-LPFG sensor is about 1063.44 nm/RIU (where RIU is the refractive index unit) in the refractive index range 1.3320--1.3760. The LOD of the proposed biosensor for H9N2 AIV is ~2.7 ng/mL, 96.1% greater than that of a DR-LPFG-based biosensor modified with Eudragit L100 copolymer. The biosensor saturates at 50 μg/mL, and its affinity coefficient to H9N2 AIV is ~3.57×10 8 mol -1·L. The biosensor also shows a high specificity and a rapid detection for H9N2 AIV, affirming its high application potential in biomedical fields such as clinical diagnosis and drug analysis.
  • Jan. 17, 2022
  • Acta Optica Sinica
  • Vol.42 Issue, 1 0106001 (2022)
  • DOI:10.3788/AOS202242.0106001