Contents
2019
Volume: 17 Issue 4
20 Article(s)

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Reviews
Fiber optics and optical communications
A tutorial on laser-based lighting and visible light communications: device and technology [Invited]
Yujian Guo, Omar Alkhazragi, Chun Hong Kang, Chao Shen, Yuan Mao, Xiaobin Sun, Tien Khee Ng, and Boon S. Ooi
This tutorial focuses on devices and technologies that are part of laser-based visible light communication (VLC) systems. Laser-based VLC systems have advantages over their light-emitting-diode-based counterparts, including having high transmission speed and long transmission distance. We summarize terminologies related to laser-based solid-state lighting and VLC, and further review the advances in device design and performance. The high-speed modulation characteristics of laser diodes and superluminescent diodes and the on-chip integration of optoelectronic components in the visible color regime, such as the high-speed integrated photodetector, are introduced. The modulation technology for laser-based white light communication systems and the challenges for future development are then discussed.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 040601 (2019)
Impact of optical–electrical conversion responsivity in sub-sampled photonic analog-to-digital converter
Fan Yang, Weiwen Zou, Lei Yu, Shaofu Xu, and Jianping Chen
This Letter investigates the impact of the photodiode (PD) saturation in a sub-sampled photonic analog-to-digital converter (PADC) with two individual pulse lasers. It is essentially proved that when the optical power to the saturated PD increases, the optical–electrical conversion (OEC) responsivity and digitized output power of the PADC decrease. If femtosecond pulses are employed for the PADC sampling clock, the time-stretching process in a dispersive medium is necessary to decrease the impact of the PD saturation. In contrast, when the sampling clock with picosecond pulses is utilized, the PD saturation is more tolerable, and thus, the OEC responsivity can be improved by an increase of the optical power to the PD no matter if the time-stretching process is employed.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 040602 (2019)
FP cavity and FBG cascaded optical fiber temperature and pressure sensor
Hui Li, Qingchao Zhao, Shaodong Jiang, Jiasheng Ni, and Chang Wang
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 040603 (2019)
Research Articles
Atmospheric and oceanic optics
Free-space propagation of autofocusing Airy vortex beams with controllable intensity gradients | On the Cover
Xu Yan, Lixin Guo, Mingjian Cheng, and Shuirong Chai
Vortex splitting is one of the main causes of instability in orbital angular momentum (OAM) modes transmission. Recent advances in OAM modes free-space propagation have demonstrated that abruptly autofocusing Airy vortex beams (AAVBs) can potentially mitigate the vortex splitting effect. However, different modes of vortex embedding will affect the intensity gradients of the background beams, leading to changes in the propagation characteristics of vortex beams. This study presents the unification of two common methods of coupling autofocusing Airy beams with vortices by introducing a parameter (m), which also controls the intensity gradients and focusing properties of the AAVBs. We demonstrate that vortex splitting can be effectively reduced by selecting an appropriate value of the parameter (m) according to different turbulence conditions. In this manner, the performance of OAM-based free-space optical systems can be improved.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 040101 (2019)
Atomic and Molecular Physics
Micro-fabrication process of vapor cells for chip-scale atomic clocks
Yanjun Zhang, Yunchao Li, Xuwen Hu, Lu Zhang, Zhaojun Liu, Kaifang Zhang, Shihao Mou, Shougang Zhang, and Shubin Yan
As the key part of chip-scale atomic clocks (CSACs), the vapor cell directly determines the volume, stability, and power consumption of the CSAC. The reduction of the power consumption and CSAC volumes demands the manufacture of corresponding vapor cells. This overview presents the research development of vapor cells of the past few years and analyzes the shortages of the current preparation technology. By comparing several different vapor cell preparation methods, we successfully realized the micro-fabrication of vapor cells using anodic bonding and deep silicon etching. This cell fabrication method is simple and effective in avoiding weak bonding strengths caused by alkali metal volatilization during anodic bonding under high temperatures. Finally, the vapor cell D2 line was characterized via optical-absorption resonance. According to the results, the proposed method is suitable for CSAC.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 040202 (2019)
Diffraction and Gratings
Imaging Systems
Terahertz imaging using an optical frequency comb source
Dixiang Shao, Chen Yao, Tao Zhou, Rong Zhang, Zhanglong Fu, Songlin Zhuang, and Juncheng Cao
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041101 (2019)
Instrumentation, measurement, and metrology
A miniaturized system for measurement of the refractive index of sub-microliter liquid | Editors' Pick
Minghui Chen, Wenyu Jia, Jintao He, Martial Geiser, and Gang Zheng
This study introduced the research and development of a portable and miniaturized system for the measurement of the refractive index of sub-microliter liquid based on a microfluidic chip. A technical method of double-beam interference, was proposed for use in the measurement. Based on this, by using a laser diode as a light source, changes in the refractive index were calculated by utilizing a complementary metal–oxide–semiconductor to detect the movement of interference fringes of the liquid. Firstly, this study simulated the effects of influencing factors on the interference infringes of two Gaussian beams, such as their spot sizes, distance between two beam spots, and detection range. Secondly, this research introduced the system design and construction of the double-beam interference method and analyzed the results of refractive index tests on sub-microliter aqueous glucose solutions with different concentrations. The measurement accuracy reached 10 4 refractive index units. This system has a compact structure and is rendered portable by using batteries for its power supply. The entire system is designed to be a double Z-shaped structure with a length of about 15 cm, a width of 5 cm, and a height of about 10 cm. It can be used to measure changes in the refractive index of sub-microliter to nanoliter liquids based on the use of a microfluidic chip.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041201 (2019)
Integrated Optics
Integrated optoelectronic chip pair for transmitting and receiving optical signals simultaneously
Kai Liu, Qi Wei, Yongqing Huang, Xiaofeng Duan, Qi Wang, Xiaomin Ren, and Shiwei Cai
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041301 (2019)
Lasers and Laser Optics
Gold nanorods as saturable absorbers for the passively Q-switched Nd:LLF laser at 1.34  μm
Qizhang Qian, Nan Wang, Shengzhi Zhao, Guiqiu Li, Tao Li, Dechun Li, Kejian Yang, Jie Zang, and Houyi Ma
Gold nanorods (GNRs) with two different aspect ratios were successfully utilized as saturable absorbers (SAs) in a passively Q-switched neodymium-doped lutetium lithium fluoride (Nd:LLF) laser emitting at 1.34 μm. Based on the GNRs with an aspect ratio of five, a maximum output power of 1.432 W was achieved, and the narrowest pulse width was 328 ns with a repetition rate of 200 kHz. But, in the case of the GNRs with the aspect ratio of eight, a maximum output power of 1.247 W was achieved, and the narrowest pulse width was 271 ns with a repetition rate of 218 kHz. Our experimental results reveal that the aspect ratios of GNRs have different saturable absorption effects at a specific wavelength. In other words, for passively Q-switched lasers at a given wavelength, we are able to select the most suitable GNRs as an SA by changing their aspect ratio.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041401 (2019)
Generation of few-cycle laser pulses by coherent synthesis based on a femtosecond Yb-doped fiber laser amplification system
Aichen Ge, Bowen Liu, Wei Chen, Haochen Tian, Youjian Song, Lu Chai, and Minglie Hu
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041403 (2019)
Materials
Fractional density of states and the overall spontaneous emission control ability of a three-dimensional photonic crystal
Menglin Chen, Zhijun Luo, Yanan Liu, and Zongsong Gan
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041601 (2019)
Arbitrary linear THz wave polarization converter with cracked cross meta-surface
Han Sun, Lan Wang, Yaxin Zhang, Shixiong Liang, Jiaguang Han, Feng Lan, Xinlan Zhou, and Ziqiang Yang
This Letter presents a double-layer structure combining a cracked cross meta-surface and grating surface to realize arbitrary incident linear terahertz (THz) wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced with the same resonant modes in the unit cell, which results in polarization conversion insensitive to the linear polarization angle. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhances the conversion efficiency. The experimental results show that a more than 70% conversion rate can be achieved under arbitrary linear polarization within a wide frequency band. Moreover, around 0.89 THz nearly perfect polarization conversion is realized.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041602 (2019)
Medical optics and biotechnology
Spectral domain optical coherence tomography with sub-micrometer sensitivity for measurement of central corneal thickness
Lida Zhu, Yi Wang, Yi Yuan, Hongxian Zhou, Yuqian Zhao, and Zhenhe Ma
We demonstrated a method for measurement of central corneal thickness (CCT) with a sub-micrometer sensitivity using a spectral domain optical coherence tomography system without needing a super broad bandwidth light source. By combining the frequency and phase components of Fourier transform, the method is capable of measurement of a large dynamic range with a high sensitivity. Absolute phases are retrieved by comparing the correlations between the detected and simulated interference fringes. The phase unwrapping ability of the present method was quantitatively tested by measuring the displacement of a piezo linear stage. The human CCTs of six volunteers were measured to verify its clinical application. It provides a potential tool for clinical diagnosis and research applications in ophthalmology.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041701 (2019)
Sensing of ultrasonic fields based on polarization parametric indirect microscopic imaging
Yun Cao, Jichuan Xiong, Xuefeng Liu, Zhiying Xia, Weize Wang, N. P. Yadav, and Weiping Liu
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041702 (2019)
Improved recognition of Echinococcus granulosus protoscoleces using visual saliency and scale-invariant features
Zhuang Li, Guodong Lü, and Xiaoyi Lü
Echinococcosis—a parasitic disease caused by Echinococcus granulosus or Echinococcus multilocularis larvae—occurs in many regions in the world. This disease can pose a serious threat to public health and thus requires a convenient and cost-effective method for early detection. So, we developed a novel method based on visual saliency and scale-invariant features that detects the tapeworm parasites. This method improves upon existing bottom-up computational saliency models by introducing a visual attention mechanism. The results indicated that the proposed method offers a higher level of both accuracy and computational efficiency when detecting Echinococcus granulosus protoscoleces, which in turn could improve early detection of echinococcosis.
Chinese Optics Letters
  • Publication Date: Apr. 10, 2019
  • Vol. 17, Issue 4, 041703 (2019)
Remote Sensing and Sensors