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Chinese Optics Letters 第19卷 第7期

Author Affiliations
Abstract
1 Department of Instrument and Science in Engineering, School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2 Ngee Ann Polytechnic, Singapore 599489, Singapore
Aperture synthesis is an important approach to improve the lateral resolution of digital holography (DH) techniques. The limitation of the accuracy of registration positions between sub-holograms affects the quality of the synthesized image and even causes the failure of aperture synthesis. It is a major issue in aperture synthesis of DH. Currently intensity images are utilized to find the registration positions of sub-holograms in aperture synthesis. To improve the accuracy of registration positions, we proposed a method based on similarity calculations of the phase images between sub-holograms instead of intensity images. Furthermore, a quantitative indicator, degree of image distortion, was applied to evaluate the synthetic results. Experiments are performed and the results verify that the proposed phase-image-based method is better than the state-of-the-art intensity-image-based techniques in the estimation of registration positions and provides a better synthesized final three-dimensional shape image.
digital holography synthetic aperture registration position phase image 
Chinese Optics Letters
2021, 19(7): 070501
Author Affiliations
Abstract
1 Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communication, Institute of Photonics Technology, Jinan University, Guangzhou 511443, China
2 Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education/Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
The pure-silica hollow-core fiber (HCF) has excellent thermostabilities that can benefit a lot of high-temperature sensing applications. The air-core microstructure of the HCF provides an inherent gas container, which can be a good candidate for gas or gas pressure sensing. This paper reviews our continuous efforts to design, fabricate, and characterize the high-temperature and high-pressure sensors with HCFs, aiming at improving the sensing performances such as dynamic range, sensitivity, and linearity. With the breakthrough advances in novel anti-resonant HCFs, sensing of high temperature and high pressure with HCFs will continuously progress and find increasing applications.
hollow-core fiber high-temperature sensing high-pressure sensing 
Chinese Optics Letters
2021, 19(7): 070601
Author Affiliations
Abstract
1 State Key Laboratory of Modern Optical Instrumentation, College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310007, China
2 Institute of Microelectronics, Chinese Academic Society, Beijing 100029, China
3 Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang Province, School of Engineering, Westlake University, Hangzhou 310007, China
4 Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou 310023, China
As a promising spectral window for optical communication and sensing, it is of great significance to realize on-chip devices at the 2 µm waveband. The development of the 2 µm silicon photonic platform mainly depends on the performance of passive devices. In this work, the passive devices were fabricated in the silicon photonic multi-project wafer process. The designed micro-ring resonator with a 0.6 µm wide silicon ridge waveguide based on a 220 nm silicon-on-insulator platform achieves a high intrinsic quality factor of 3.0×105. The propagation loss is calculated as 1.62 dB/cm. In addition, the waveguide crossing, multimode interferometer, and Mach–Zehnder interferometer were demonstrated at 2 µm with good performances.
silicon photonics integrated photonics grating coupler multimode interferometer waveguide crossing 
Chinese Optics Letters
2021, 19(7): 071301
Author Affiliations
Abstract
1 State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
2 Chongqing Institute of East China Normal University, Chongqing 401147, China
3 Jinan Institute of Quantum Technology, Jinan 250101, China
In this paper, we demonstrated a series of short-living mode-locking (ML) states (each lasting a few to a hundred microseconds) that happened before a fiber laser reached a steady ML state. With time-stretched dispersion Fourier transform spectroscopy, a rich diversity of transient multi-pulse dynamics were revealed spectrally and temporally. As a result, we found that the formation of the short-living ML states was related to abundant pump power, and their decaying evolution dynamics were possibly governed by gain depletion and recovery. Our results revealed unexpected transient lasing behaviors of a soliton laser and thus might be useful to understand the complex dynamics of mode-locked lasers.
mode-locking soliton fiber laser 
Chinese Optics Letters
2021, 19(7): 071401
Songqing Zha 1,2Yujin Chen 1,*Bingxuan Li 1,3Yanfu Lin 1[ ... ]Ge Zhang 1,3,5,**
Author Affiliations
Abstract
1 Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
2 Fuzhou University, Fuzhou 350002, China
3 Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China, Fuzhou 350108, China
4 Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
5 Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Device, Fuzhou 350108, China
End-pumped by a 976 nm diode laser, a high-repetition-rate Er:Yb:YAl3(BO3)4 microchip laser passively Q-switched by a Co2+:MgAl2O4 crystal is reported. At a quasi-continuous-wave pump power of 20 W, a 1553 nm passively Q-switched laser with the repetition rate of 544 kHz, pulse duration of 8.3 ns, and pulse energy of 3.9 μJ was obtained. To the best of our knowledge, the 544 kHz is the highest reported value for the 1.5 μm passively Q-switched pulse laser. In the continuous-wave pumping experiment, the maximum repetition rate of 144 kHz with the pulse duration of 8.0 ns and pulse energy of 1.7 μJ was obtained at the incident pump power of 6.3 W.
1.5?μm microchip laser passive Q-switching Er:Yb:YAl34 crystal high-repetition-rate laser pulse 
Chinese Optics Letters
2021, 19(7): 071402
Author Affiliations
Abstract
1 College of Internet of Things Engineering, Hohai University, Changzhou 213022, China
2 College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
3 Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
In modern optics, particular interest is devoted to the phase singularities that yield complicated and twisted phase structures by photons carrying optical angular momentum. In this paper, the traditional M-line method is applied to a vortex beam (VB) by a symmetric metal cladding waveguide chip, which can host numerous oscillating guided modes via free space coupling. These ultrahigh-order modes (UOMs) result in high angular resolution due to the high finesse of the resonant chip. Experiments show that the reflected pattern of a VB can be divided into a series of inner and outer rings, whilst both of them are highly distorted by the M-lines due to the UOMs’ leakage. Taking the distribution of the energy flux into account, a simple ray-optics-based model is proposed to simulate the reflected pattern by calculating the local incident angle over the cross section of the beam. The theoretical simulations fit well with the experimental results, and the proposed scheme may enable new applications in imaging and sensing of complicated phase structures.
vortex beam M-line method planar waveguide 
Chinese Optics Letters
2021, 19(7): 071403
Author Affiliations
Abstract
Jilin Key Laboratory of Solid Laser Technology and Application, School of Science, Changchun University of Science and Technology, Changchun 130022, China
We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd:Y3Al5O12 (Nd:YAG) laser. In the time interval of 100–1000 ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24 ns, 28 ns, and 36.6 ns, respectively. The energy is 32.5 mJ, and the optical efficiency is 10.8%. The multi-step Q-switched method does not require the insertion of other optical elements into the traditional Q-switched laser, and it is very suitable to obtain pulse group output with several nanosecond pulse intervals.
nanosecond interval pulse multi-step Q-switching Nd:YAG laser 
Chinese Optics Letters
2021, 19(7): 071404
Author Affiliations
Abstract
Key Laboratory of In-fiber Integrated Optics, Ministry of Education, Harbin Engineering University, Harbin 150001, China
We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period gratings (ULPGs) for the first time, to the best of our knowledge. Study found that the ULPG can be used as both a mode-locker for pulse shaping and a comb filter for multi-wavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six-, and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength soliton pulses, their pulse width is about 7.8 ps. The maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of a four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multi-wavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application.
ultra-long-period grating fiber laser ultrafast laser multi-wavelength 
Chinese Optics Letters
2021, 19(7): 071405
Author Affiliations
Abstract
1 State Key Laboratory of Precision Electronics Manufacturing Technology and Equipment, Guangdong University of Technology, Guangzhou 510006, China
2 Key Laboratory of Optic-Electronics and Communication, Jiangxi Science and Technology Normal University, Nanchang 330038, China
Photoacoustic microscopy (PAM) has quickly developed into a noninvasive biomedical imaging technique to achieve detection, diagnosis, and monitoring. Compared with Q-switched neodymium-doped yttrium aluminum garnet or optical parametric oscillator lasers, a low-cost and small-size laser diode (LD) used as an alternative light source is conducive to achieving the miniaturization and integration for preclinical transformation. However, the LD’s low peak output power needs the high numerical aperture objective to attain tight focus, which limits the working distance (WD) of the system in only 2–3 mm, resulting in not achieving the backward coaxial confocal mode. Here, we present a compact visible LD-based PAM system with a reflective objective to achieve a 22 mm long WD and a 10 µm lateral resolution. Different depth subcutaneous microvascular networks in label-free mouse ears have successfully reappeared in vivo with a signal-to-noise ratio up to 14 dB by a confocal alignment. It will be a promising tool to develop into a handy tool for subcutaneous blood vessel imaging.
photoacoustic microscopy long working distance laser diode reflective objective 
Chinese Optics Letters
2021, 19(7): 071701
Author Affiliations
Abstract
1 MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, China
2 Guangdong Provincial Key Laboratory of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, China
We proposed a nonlinear photoacoustic (PA) technique as a new imaging contrast mechanism for tissue thermal-nonlinearity characterization. When a sine-modulated Gaussian temperature field is introduced by a laser beam, in view of the temperature dependence of the thermal diffusivity, the nonlinear PA effect occurs, which leads to the production of second-harmonic PA (SHPA) signals. By extracting the fundamental frequency PA and SHPA signal amplitudes of samples through the lock-in technique, a parameter that only reflects nonlinear thermal-diffusivity characteristics of the sample then can be obtained. The feasibility of the technique for thermal-nonlinearity characterization has been studied on phantom samples. In vitro biological tissues have been studied by this method to demonstrate its medical imaging capability, prefiguring great potential of this new method in medical imaging applications.
Chinese Optics Letters
2021, 19(7): 071702
Chenguang Xin 1,2,3,*Jie Qi 1,2Rui Zhang 1,2Li Jin 1,2Yanru Zhou 4,**
Author Affiliations
Abstract
1 Academy for Advanced Interdisciplinary Research, North University of China, Taiyuan 030051, China
2 School of Instrument and Electronics, North University of China, Taiyuan 030051, China
3 State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
4 School of Information and Communication Engineering, North University of China, Taiyuan 030051, China
Based on the transverse second-harmonic generation (TSHG) effect, we demonstrate a method for in-situ modal inspection of nonlinear micro/nanowaveguides. Pumping lights are equally split and coupled into two ends of a single CdS nanobelt (NB). As pumping light counter-propagates along the NB, transverse second-harmonic (TSH) interference patterns are observed. The influence of multimode interaction on the TSHG effect is discussed in detail. Using fast Fourier transform, TSH interference patterns are analyzed, indicating the existence of at least four modes inside the NB. Experimental beat lengths are found to be in agreement with calculated results.
micro/nanowaveguides transverse second-harmonic generation multimode interference modal inspection 
Chinese Optics Letters
2021, 19(7): 071901
Author Affiliations
Abstract
1 School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China
2 Guangdong Full-Spectra Laser Technology Co., Ltd., Dongguan 523808, China
3 Dongguan Sanhang Innovation Research Institute, Dongguan 523808, China
We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation (SHG) in subwavelength x-cut and z-cut lithium niobate (LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly. Under the scheme of optimal modal phase matching (MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them. Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.
lithium niobate thin film modal phase matching nonlinear coupled-mode theory second-harmonic generation 
Chinese Optics Letters
2021, 19(7): 071902
Author Affiliations
Abstract
Key Laboratory of Optical Fiber Sensing and Communication Networks, School of Information and Communication Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
We demonstrate a novel method to control the free spectral range (FSR) of silica micro-rod resonators precisely. This method is accomplished by iteratively applying laser annealing on the already-fabricated micro-rod resonators. Fine and repeatable increasing of resonator FSR is demonstrated, and the best resolution is smaller than 5 MHz, while the resonator quality-factor is only slightly affected by the iterative annealing procedure. Using the fabricated micro-rod resonators, single dissipative Kerr soliton microcombs are generated, and soliton repetition frequencies are tuned precisely by the iterative annealing process. The demonstrated method can be used for dual-comb spectroscopy and coherent optical communications.
microcavities nonlinear optics pulse propagation temporal solitons 
Chinese Optics Letters
2021, 19(7): 071903
Author Affiliations
Abstract
School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 201800, China
A fiber-based source that can be exploited in a stimulated emission depletion (STED) inspired nanolithography setup is presented. Such a source maintains the excitation beam pulse, generates a ring-shaped depletion beam, and automatically realizes dual-beam coaxial alignment that is critical for two beam nanolithography. The mode conversion of the depletion beam is realized by using a customized vortex fiber, which converts the Gaussian beam into a donut-shaped azimuthally polarized beam. The pulse width and repetition frequency of the excitation beam remain unchanged, and its polarization states can be controlled. According to the simulated point spread function of each beam in the focal region, the full width at half-maximum of the effective spot size in STED nanofabrication could decrease to less than 28.6 nm.
nanolithography vortex fiber direct laser writing STED controlled fabrication 
Chinese Optics Letters
2021, 19(7): 072201
Author Affiliations
Abstract
Hubei Key Laboratory of Modern Manufacturing Quality Engineering, School of Mechanical Engineering, Hubei University of Technology, Wuhan 430068, China
Heterodyne detectors as phase-insensitive (PI) devices have found important applications in precision measurements such as space-based gravitational-wave (GW) observation. However, the output signal of a PI heterodyne detector is supposed to suffer from signal-to-noise ratio (SNR) degradation due to image band vacuum and imperfect quantum efficiency. Here, we show that the SNR degradation can be overcome when the image band vacuum is quantum correlated with the input signal. We calculate the noise figure of the detector and prove the feasibility of heterodyne detection with enhanced noise performance through quantum correlation. This work should be of great interest to ongoing space-borne GW signal searching experiments.
quantum noise quantum correlation heterodyne detection 
Chinese Optics Letters
2021, 19(7): 072701
Author Affiliations
Abstract
College of Precision Instrument and Optoelectronics Engineering, Tianjin University; Key Laboratory of Optoelectronic Information Technology, Ministry of Education, Tianjin 300072, China
The spiderlike structures in the photoelectron momentum distributions of ionized electrons from the hydrogen atom are numerically simulated by using a semiclassical rescattering model (SRM) and solving the time-dependent Schr?dinger equation (TDSE), focusing on the role of the phase of the scattering amplitude. With the SRM, we find that the spiderlike legs shift to positions with smaller transverse momentum values while increasing the phase. The spiderlike patterns obtained by SRM and TDSE are in good agreement upon considering this phase. In addition, the time differences in electron ionization and rescattering calculated by SRM and the saddle-point equations are either in agreement or show very similar laws of variation, which further corroborates the significance of the phase of the scattering amplitude.
photoelectron holography semiclassical rescattering model spiderlike structure 
Chinese Optics Letters
2021, 19(7): 073201
Ke Li 1,2,3Yantao Gao 1Haipeng Zhang 1,2,3Guohao Du 2[ ... ]Tiqiao Xiao 1,2,3,**
Author Affiliations
Abstract
1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
2 Shanghai Synchrotron Radiation Facility/Zhangjiang Lab, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201204, China
3 University of Chinese Academy of Sciences, Beijing 100049, China
Carbon fiber (CF)/pyrolytic graphite (PG) composites are promising structural materials for molten salt reactors because of their superior performance. Due to the minor density difference between CF and PG, existing methods are impractical for efficient three-dimensional characterization of CF/PG composites. Therefore, in this study, a method based on in-line phase-contrast X-ray microtomography was developed to solve the aforementioned problem. Experimental results demonstrate that the method is suitable for comprehensive characterization of CF/PG composites. The relationship between the microporous defects and fiber orientations of such composites was also elucidated. The findings can be useful for improving the manufacturing process of CF/PG composites.
X-ray imaging C/C composite 3D characterization 
Chinese Optics Letters
2021, 19(7): 073401
Author Affiliations
Abstract
1 MOE Key Laboratory of Weak-Light Nonlinear Photonics, School of Physics, Nankai University, Tianjin 300071, China
2 College of Physics and Materials Science, Tianjin Normal University, Tianjin 300387, China
3 Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
We show that inhomogeneous waveguides of slowly varied parity-time (PT) symmetry support localized optical resonances. The resonance is closely related to the formation of exceptional points separating exact and broken PT phases. Salient features of this kind of non-Hermitian resonance, including the formation of half-vortex flux and the discrete nature, are discussed. This investigation highlights the unprecedented uniqueness of field dynamics in non-Hermitian systems with many potential adaptive applications.
resonance exceptional points parity-time symmetry quantum optics 
Chinese Optics Letters
2021, 19(7): 073601
Yi Zhao 1Qiuping Huang 1,2,*Honglei Cai 1Xiaoxia Lin 1[ ... ]Yalin Lu 1,2,3,**
Author Affiliations
Abstract
1 Hefei National Laboratory for Physical Science at the Microscale, University of Science and Technology of China, Hefei 230026, China
2 Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei 230026, China
3 Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
In this paper, we experimentally demonstrate ultrafast optical control of slow light in the terahertz (THz) range by combining the electromagnetically induced transparency (EIT) metasurfaces with the cut wire made of P+-implanted silicon with short carrier lifetime. Employing the optical-pump THz-probe spectroscopy, we observed that the device transited from a state with a slow light effect to a state without a slow light effect in an ultrafast time of 5 ps and recovered within 200 ps. A coupled oscillator model is utilized to explain the origin of controllability. The experimental results agree very well with the simulated and theoretical results. These EIT metasurfaces have the potential to be used as an ultrafast THz optical delay device.
metasurface terahertz active control slow light 
Chinese Optics Letters
2021, 19(7): 073602
Author Affiliations
Abstract
School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian 116024, China
Radio frequency (RF) self-interference is a key issue for the application of in-band full-duplex communication in beyond fifth generation and sixth generation communications. Compared with electronic technology, photonic technology has the advantages of wide bandwidth and high tuning precision, exhibiting great potential to realize high interference cancellation depth over broad band. In this paper, a comprehensive overview of photonic enabled RF self-interference cancellation (SIC) is presented. The operation principle of photonic RF SIC is introduced, and the advances in implementing photonic RF SIC according to the realization mechanism of phase reversal are summarized. For further realistic applications, the multipath RF SIC and the integrated photonic RF SIC are also surveyed. Finally, the challenges and opportunities of photonic RF SIC technology are discussed.
in-band full-duplex radio frequency self-interference cancellation microwave photonics 
Chinese Optics Letters
2021, 19(7): 073901