Contents
2021
Volume: 19 Issue 4
16 Article(s)
Research Articles
Fiber Optics and Optical Communications
Imaging Systems and Image Processing
Enhancement of rapid lifetime determination for time-resolved fluorescence imaging in forensic examination
Xin Zhong, Xinwei Wang, Liang Sun, and Yan Zhou
An enhancement method of rapid lifetime determination is proposed for time-resolved fluorescence imaging to discriminate substances with approximate fluorescence lifetime in forensic examination. In the method, an image-exclusive-OR treatment with filter threshold adaptively chosen is presented to extract the region of interest from dual-gated fluorescence intensity images, and then the fluorescence lifetime image is reconstructed based on the rapid lifetime determination algorithm. Furthermore, a maximum and minimum threshold filtering is developed to automatically realize visualization enhancement of the lifetime image. In proof experiments, compared with traditional fluorescence intensity imaging and rapid lifetime determination method, the proposed method automatically distinguishes altered and obliterated documents written by two brands of highlighters with the same color and close fluorescence lifetime.
Chinese Optics Letters
  • Publication Date: Jan. 08, 2021
  • Vol.19 Issue, 4 041101 (2021)
Anisotropy of the thermal and laser output properties in Yb,Nd:Sc2SiO5 crystal
Yuqing Zhao, Qiangguo Wang, Lihua Meng, Yongping Yao, Shande Liu, Na Cui, Liangbi Su, Lihe Zheng, Huiyun Zhang, and Yuping Zhang
The anisotropy of thermal property in an Yb,Nd:Sc2SiO5 crystal is investigated from the temperature of 293 to 573 K. Based on the systematical study of thermal expansion, thermal diffusivity, and specific heat, the thermal conductivity in Yb,Nd:Sc2SiO5 crystals orientated at (100), (010), (001), and (406) is calculated to be 3.46, 2.60, 3.35, and 3.68 W/(m·K), respectively. The laser output anisotropy of a continuous-wave (CW) and tunable laser is characterized, accordingly. A maximum output power of 6.09 W is achieved in the Yb,Nd:Sc2SiO5 crystal with (010) direction, corresponding to a slope efficiency of 48.56%. The tuning wavelength range in the Yb,Nd:Sc2SiO5 crystal orientated at (100), (010), and (001) is 68, 67, and 65 nm, separately. The effects of thermal properties on CW laser performance are discussed.
Chinese Optics Letters
  • Publication Date: Feb. 22, 2021
  • Vol.19 Issue, 4 041405 (2021)
Instrumentation, Measurement, and Optical Sensing
Simultaneous measurement of strain and temperature using Fabry–Pérot interferometry and antiresonant mechanism in a hollow-core fiber
Chong He, Cheng Zhou, Qian Zhou, Shiyi Xie, Mengzhe Xiao, Jiajun Tian, and Yong Yao
Chinese Optics Letters
  • Publication Date: Jan. 08, 2021
  • Vol.19 Issue, 4 041201 (2021)
Highly sensitive torsion sensor based on triangular-prism-shaped long-period fiber gratings
Senyu Wang, Yiwei Ma, Xiaoyang Li, Yang Yi, Cuiting Sun, Jingyu Lin, Chengguo Tong, Yuxiang Li, Tao Geng, Weimin Sun, and Libo Yuan
Chinese Optics Letters
  • Publication Date: Feb. 04, 2021
  • Vol.19 Issue, 4 041202 (2021)
Integrated Optics
Electro-optic polymer ring resonator modulators [Invited] | Editors' Pick
Feng Qiu, and Yu Han
Electro-optic (EO) ring resonator modulators have a number of communications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, the EO polymer has many promising characteristics, including a high EO coefficient of 100–200 pm/V (3–7 times larger than that of LiNbO3), an ultrafast EO response time (10 fs), a low dielectric constant (3 to 4) with very little dispersion up to at least 250 GHz, and a straightforward spin-coating fabrication process. These inherent characteristics will be able to combine excellent EO properties with simple processing in achieving exceptional performance in a variety of high-speed optical modulation and sensing devices. This review focuses on the research and recent development of ring resonator modulators based on EO polymers. The first part describes the operation principle of EO ring resonator modulators, such as modulation mechanism, EO tunability, and 3 dB bandwidth. Subsequently, the emphasis is placed on the discussion of the ring modulators with EO polymers as the waveguide core and the improvement of EO modulation by using an EO polymer/titanium dioxide hybrid core. At the end, a series of EO polymers on silicon platforms including slot modulators, etching-free modulators, and athermal modulators are reviewed.
Chinese Optics Letters
  • Publication Date: Feb. 04, 2021
  • Vol.19 Issue, 4 041301 (2021)
Lasers, Optical Amplifiers, and Laser Optics
Dimming control scheme based on hybrid LACO-SCFDM for visible light communications
Siqiao Li, Tiantian Zhang, Yaojun Qiao, and Ji Zhou
This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s-1·Hz-1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.
Chinese Optics Letters
  • Publication Date: Feb. 22, 2021
  • Vol.19 Issue, 4 040601 (2021)
Wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on intracavity loss tuning
Kaile Wang, Zengrun Wen, Haowei Chen, Baole Lu, and Jintao Bai
We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.
Chinese Optics Letters
  • Publication Date: Jan. 11, 2021
  • Vol.19 Issue, 4 041401 (2021)
Combined studies of surface evolution and crack healing for the suppression of negative factors during CO2 laser repairing of fused silica
Chao Tan, Linjie Zhao, Mingjun Chen, Jian Cheng, Zhaoyang Yin, Qi Liu, Hao Yang, and Wei Liao
In order to reveal the evolution mechanism of repaired morphology and the material’s migration mechanism on the crack surface in the process of CO2 laser repairing surface damage of fused silica optics, two multi-physics coupling mathematical models with different scales are developed, respectively. The physical problems, such as heat and mass transfer, material phase transition, melt flow, evaporation removal, and crack healing, are analyzed. Studies show that material ablation and the gasification recoil pressure accompanying the material splash are the leading factors in forming the Gaussian crater with a raised rim feature. The use of low-power lasers for a long time can fully melt the material around the crack before healing, which can greatly reduce the size of the residual air layer. Combined with the experimental research, the methods to suppress the negative factors (e.g., raised rim, deposited debris, air bubbles) in the CO2 laser repairing process are proposed.
Chinese Optics Letters
  • Publication Date: Jan. 08, 2021
  • Vol.19 Issue, 4 041402 (2021)
Speckle characteristics of simulated deep Fresnel region under shadowing effect
Zengshun Jiang, Xingqi An, Yuqin Zhang, Xuan Liu, Xifeng Qin, Yanjie Zhao, Huilin Wang, Guiyuan Liu, and Hongsheng Song
Chinese Optics Letters
  • Publication Date: Feb. 04, 2021
  • Vol.19 Issue, 4 041404 (2021)
Quantum wells micro-ring resonator laser emitting at 1746 nm for gas sensing
Fangyuan Meng, Hongyan Yu, Xuliang Zhou, Yajie Li, Mengqi Wang, Wenyu Yang, Weixi Chen, Yejin Zhang, and Jiaoqing Pan
Chinese Optics Letters
  • Publication Date: Feb. 22, 2021
  • Vol.19 Issue, 4 041406 (2021)
Physical Optics
Floquet spectrum and optical behaviors in dynamic Su–Schrieffer–Heeger modeled waveguide array | Editors' Pick
Ye Yu, Yiwen Song, Tao Chen, Huaiqiang Wang, Songlin Zhuang, and Qingqing Cheng
Floquet topological insulators (FTIs) have been used to study the topological features of a dynamic quantum system within the band structure. However, it is difficult to directly observe the dynamic modulation of band structures in FTIs. Here, we implement the dynamic Su–Schrieffer–Heeger model in periodically curved waveguides to explore new behaviors in FTIs using light field evolutions. Changing the driving frequency produces near-field evolutions of light in the high-frequency curved waveguide array that are equivalent to the behaviors in straight arrays. Furthermore, at modest driving frequencies, the field evolutions in the system show boundary propagation, which are related to topological edge modes. Finally, we believe curved waveguides enable profound possibilities for the further development of Floquet engineering in periodically driven systems, which ranges from condensed matter physics to photonics.
Chinese Optics Letters
  • Publication Date: Jan. 08, 2021
  • Vol.19 Issue, 4 042601 (2021)
Optical beam splitting and asymmetric transmission in bi-layer metagratings | On the Cover
Qiangshi Shi, Xia Jin, Yangyang Fu, Qiannan Wu, Cheng Huang, Baoyin Sun, Lei Gao, and Yadong Xu
Chinese Optics Letters
  • Publication Date: Feb. 22, 2021
  • Vol.19 Issue, 4 042602 (2021)
Ultrafast Optics and Attosecond/High-field Physics