Contents
2021
Volume: 19 Issue 8
22 Article(s)

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Research Articles
Imaging Systems and Image Processing
High-speed multimode fiber imaging system based on conditional generative adversarial network
Zhenming Yu, Zhenyu Ju, Xinlei Zhang, Ziyi Meng, Feifei Yin, and Kun Xu
Chinese Optics Letters
  • Publication Date: May. 25, 2021
  • Vol.19 Issue, 8 081101 (2021)
Integrated Optics
Near-infrared lasing and tunable upconversion from femtosecond laser inscribed Nd,Gd:CaF2 waveguides | Editors' Pick
Ruonan Li, Lifei Sun, Yangjian Cai, Yingying Ren, Hongliang Liu, Mark D. Mackenzie, and Ajoy K. Kar
Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd:CaF2 laser crystals by using ultrafast laser inscription. Waveguide properties are investigated in terms of guiding behaviors and localized laser-induced lattice damages. Under an optical pump of 808 nm light, continuous-wave waveguide lasing at 1.06 μm is achieved, with a single-mode operation and a minimum lasing threshold of 98.8 mW. Furthermore, the visible emissions of Nd3+ with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process. The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.
Chinese Optics Letters
  • Publication Date: Apr. 27, 2021
  • Vol.19 Issue, 8 081301 (2021)
Lasers, Optical Amplifiers, and Laser Optics
Design of a single-mode directly modulated orbital angular momentum laser
Xiang Ma, Shuang Zheng, Jia Liu, Quanan Chen, Qiaoyin Lu, and Weihua Guo
We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It is a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulations and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number, while the complex top grating can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band, and L band.
Chinese Optics Letters
  • Publication Date: Apr. 27, 2021
  • Vol.19 Issue, 8 081401 (2021)
External focusing dependence of spatial distribution of air lasers during femtosecond laser filamentation in air
Jiayun Xue, Hui Gao, Nan Zhang, Lu Sun, Lie Lin, and Weiwei Liu
The spatial distribution of the forward-propagating amplified spontaneous emission (ASE) of nitrogen molecular ions during femtosecond laser filamentation in air is studied via numerical simulations. The results suggest that the divergence angle and signal intensity are extremely sensitive to the external focal length. Concurrently, we show that the optical Kerr effect plays a significant role in concentrating the directivity of ASE signals, particularly in cases of loose focusing. Furthermore, the simulations demonstrate that ASE signals are enhanced for a tight focus, although the corresponding filament length is shorter. The main physical mechanism underlying this process is the competition between the plasma defocusing and optical Kerr effects. The result is important for filamentation-based light detection and ranging applied to remote sensing.
Chinese Optics Letters
  • Publication Date: May. 08, 2021
  • Vol.19 Issue, 8 081402 (2021)
Damage characteristics of dual-band high reflectors affected by nodule defects in the femtosecond regime
Bin Ma, Jiaqi Han, Jing Li, Ke Wang, Shuang Guan, Xinshang Niu, Haoran Li, Jinlong Zhang, Hongfei Jiao, Xinbin Cheng, and Zhanshan Wang
The influence of nodule defects on the characteristics of femtosecond laser-induced damage has not been fully investigated. In this study, two types of 800 nm/1064 nm dual-band HfO2/SiO2 high-reflection films with different configurations were analyzed. Combined with finite-difference time-domain electric field simulation and focused ion beam analysis, the initial state and growth process of femtosecond laser damage of nodules were explored. In particular, the sequence of blister damage determined by the film design and the inner damage caused by nodules were clarified. The rule of the laser-induced damage threshold of different size nodules was obtained. The difference in the damage behavior of nodules in the two types of films was elucidated.
Chinese Optics Letters
  • Publication Date: May. 08, 2021
  • Vol.19 Issue, 8 081403 (2021)
Spectroscopic and laser properties of Er3+, Pr3+ co-doped LiYF4 crystal | Editors' Pick
Zhengda Sun, Feifei Wang, Haiping Xia, Hongkun Nie, Kejian Yang, Ruihua Wang, Jingliang He, and Baitao Zhang
In this paper, the absorption and fluorescence spectra of Er3+, Pr3+ co-doped LiYF4 (Er,Pr:YLF) crystal were measured and analyzed. The Pr3+ co-doping was proved to effectively enhance the Er3+:I411/2→I413/2 mid-infrared transition at the 2.7 μm with 74.1% energy transfer efficiency from Er3+:I413/2 to Pr3+:F34. By using the Judd–Ofelt theory, the stimulated emission cross section was calculated to be 1.834×10-20 cm2 at 2685 nm and 1.359×10-20 cm2 at 2804.6 nm. Moreover, a diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time, to the best of our knowledge. The maximum output power was determined to be 258 mW with a slope efficiency of 7.4%, and the corresponding beam quality factors Mx2=1.29 and My2=1.25. Our results suggest that Er,Pr:YLF should be a promising material for 2.7 μm laser generation.
Chinese Optics Letters
  • Publication Date: May. 08, 2021
  • Vol.19 Issue, 8 081404 (2021)
Fiber-based optical frequency comb at 3.3 µm for broadband spectroscopy of hydrocarbons [Invited]
Karol Krzempek, Dorota Tomaszewska, Aleksandra Foltynowicz, and Grzegorz Sobon
A 125 MHz fiber-based frequency comb source in the mid-infrared wavelength region is presented. The source is based on difference frequency generation from a polarization-maintaining Er-doped fiber pump laser and covers a spectrum between 2900 cm-1 and 3400 cm-1 with a simultaneous bandwidth of 170 cm-1 and an average output power up to 70 mW. The source is equipped with actuators and active feedback loops, ensuring long-term stability of the repetition rate, output power, and spectral envelope. An absorption spectrum of ethane and methane was measured using a Fourier transform spectrometer to verify the applicability of the mid-infrared comb to multispecies detection. The robustness and good long- and short-term stability of the source make it suitable for optical frequency comb spectroscopy of hydrocarbons.
Chinese Optics Letters
  • Publication Date: Aug. 05, 2021
  • Vol.19 Issue, 8 081406 (2021)
Microwave Photonics
Optimization of optical signal-to-distortion ratio in a channel-interleaved photonic ADC via a coherent multi-frequency RF driver
Junyan Li, Na Qian, Shiyu Hua, and Weiwen Zou
A microwave-chip-based coherent multi-frequency RF driver is developed for a channel-interleaved photonic analog-to-digital converter (PADC) system, which comprises a multi-class optical demultiplexer and supports a sampling speed of 40 GSa/s. The generated signals from the RF driver are adjustable in both amplitude and phase. We analyze the relationship between the characteristics of the generated RF driver signals and the demultiplexing performance in theory based on the optical signal-to-distortion ratio (OSDR). It is the most effective parameter to evaluate the performance of the demultiplexer in a PADC system without an electronic analog-to-digital converter. By precisely adjusting the amplitude and phase of signals, the OSDR is optimized. The results verify the compatibility between the RF driver and the PADC system.
Chinese Optics Letters
  • Publication Date: Apr. 20, 2021
  • Vol.19 Issue, 8 083901 (2021)
Nanophotonics, Metamaterials, and Plasmonics
Surface-plasmonic sensor using a columnar thin film in the grating-coupled configuration [Invited]
Kiran Mujeeb, Muhammad Faryad, Akhlesh Lakhtakia, and Julio V. Urbina
The excitation of a surface-plasmon-polariton (SPP) wave guided by a columnar thin film (CTF) deposited on a one-dimensional metallic surface-relief grating was investigated for sensing the refractive index of a fluid infiltrating that CTF. The Bruggemann homogenization formalism was used to determine the relative permittivity scalars of the CTF infiltrated by the fluid. The change in the refractive index of the fluid was sensed by determining the change in the incidence angle for which an SPP wave was excited on illumination by a p-polarized plane wave, when the plane of incidence was taken to coincide with the grating plane but not with the morphologically significant plane of the CTF. Multiple excitations of the same SPP wave were found to be possible, depending on the refractive index of the fluid, which can help increase the reliability of results by sensing the same fluid with more than one excitation of the SPP wave.
Chinese Optics Letters
  • Publication Date: May. 20, 2021
  • Vol.19 Issue, 8 083601 (2021)
Nanoplasmonic magneto-optical isolator [Invited] | On the Cover
Vahid Foroughi Nezhad, Chenglong You, and Georgios Veronis
We introduce a nanoplasmonic isolator that consists of a cylindrical resonator placed close to a metal-dielectric-metal (MDM) waveguide. The material filling the waveguide and resonator is a magneto-optical (MO) material, and the structure is under an externally applied static magnetic field. We theoretically investigate the properties of the structure and show that the cavity mode without MO activity splits into two modes when the MO activity is present. In addition, we find that the presence of the MDM waveguide leads to a second resonance due to the geometrical asymmetry caused by the existence of the waveguide. We also show that, when MO activity is present, the cavity becomes a traveling wave resonator. Thus, the transmission of the structure depends on the direction of the incident light, and the proposed structure operates as an optical isolator.
Chinese Optics Letters
  • Publication Date: Aug. 02, 2021
  • Vol.19 Issue, 8 083602 (2021)
Nonlinear Optics
Real-time and ultrafast optical pulse quantization based on slicing the supercontinuum
Ya Guo, Qiang Cai, Zhiwei Jia, Bingjie Xu, Zhensen Gao, Qianwu Zhang, Ruonan Zhang, Adonis Bogris, K. Alan Shore, Yuncai Wang, and Pu Li
All-optical analog-to-digital conversion is a paramount issue in modern science. How to implement real-time and ultrafast quantization to optical pulses with different intensities in an all-optical domain is a central problem. Here, we report a real-time demonstration of an all-optical quantization scheme based on slicing the supercontinuum in a nonlinear fiber. In comparison with previous schemes through off-line analysis of the power of different optical spectral components in the supercontinuum, this, to the best of our knowledge, is the first demonstration of such functionality online in the time domain. Moreover, the extinction ratio among the quantized outputs can exceed 10 dB, which further confirms the feasibility of the proposed quantization scheme. The current 3 bit resolution in the proof-of-principle experiment is limited by the current experimental condition, but it can be expected to be greatly enhanced through improving both the spectral width of the generated supercontinuum and the number of filtering channels used.
Chinese Optics Letters
  • Publication Date: Apr. 27, 2021
  • Vol.19 Issue, 8 081901 (2021)
Mode-locked all-fiber laser with high stability based on cobalt oxyfluoride
Ximei Liu, Mengli Liu, Yaorong Wang, Kai Huang, Ming Lei, Wenjun Liu, and Zhiyi Wei
Recent years have witnessed the exploration of fiber laser technology focused on numerous pivotal optoelectronic applications from laser processing and remote sensing to optical communication. Here, using cobalt oxyfluoride (CoOF) as the nonlinear material, a 156 fs mode-locked fiber laser with strong stability is obtained. The rapid thermal annealing technique is used to fabricate the CoOF, which is subsequently transferred to the tapered region of the microfiber to form the effective pulse modulation device. CoOF interacts with the pulsed laser through the evanescent field to realize the intracavity pulse shaping, and then the stable mode-locked pulse is obtained. The mode-locked operation is maintained with the pulse duration of 156 fs and repetition rate of 49 MHz. In addition, the signal-to-noise ratio is about 90 dB. Those experimental results confirm the attractive nonlinear optical properties of CoOF and lay a foundation for the ultrafast application of low-dimensional transition metal oxides.
Chinese Optics Letters
  • Publication Date: May. 25, 2021
  • Vol.19 Issue, 8 081902 (2021)
Optical Design and Fabrication
Fabrication of microholes array on titanium foil by a femtosecond laser and a surface’s wettability switching
Cong Wang, Bo Liu, Zhi Luo, Kaiwen Ding, and Ji’an Duan
In this study, an effective method is proposed for controlling a titanium foil surface’s wettability. A microholes array series is fabricated on the surface of titanium foil by a femtosecond laser under different laser energy and pulse number. The changes of the titanium surface’s morphology are characterized. When placed in a darkroom with high-temperature treatment and immersed in alcohol under UV irradiation, respectively, the femtosecond laser treated surfaces display switchable wettability. It is demonstrated that the changing between Ti-OH and Ti-O prompts the transformation between superhydrophilic and superhydrophobic. Compared with existing reports, the switchable wetting cycle is shortened to 1.5 h. The functional surfaces with switchable wettability have potential applications in oil–water separation and water mist collection.
Chinese Optics Letters
  • Publication Date: Apr. 20, 2021
  • Vol.19 Issue, 8 082201 (2021)
Optical Materials
Optoelectronics
Optical tensor core architecture for neural network training based on dual-layer waveguide topology and homodyne detection
Shaofu Xu, and Weiwen Zou
Chinese Optics Letters
  • Publication Date: Apr. 20, 2021
  • Vol.19 Issue, 8 082501 (2021)
Ultra-low detection delay drift caused by the temperature variation in a Si-avalanche-photodiode-based single-photon detector
Yurong Wang, Linli Wang, Chenyi Wu, Zhaohui Li, Lei Yang, and Guang Wu
Chinese Optics Letters
  • Publication Date: Apr. 20, 2021
  • Vol.19 Issue, 8 082502 (2021)
Cascaded deep ultraviolet light-emitting diode via tunnel junction
Huabin Yu, Zhongjie Ren, Muhammad Hunain Memon, Shi Fang, Danhao Wang, Zhongling Liu, Haochen Zhang, Feng Wu, Jiangnan Dai, Changqing Chen, and Haiding Sun
Chinese Optics Letters
  • Publication Date: Apr. 27, 2021
  • Vol.19 Issue, 8 082503 (2021)
Carrier transport and photoconductive gain mechanisms of AlGaN MSM photodetectors with high Al Content
Zhicheng Dai, Yushen Liu, Guofeng Yang, Feng Xie, Chun Zhu, Yan Gu, Naiyan Lu, Qigao Fan, Yu Ding, Yuhang Li, Yingzhou Yu, and Xiumei Zhang
Chinese Optics Letters
  • Publication Date: Jul. 23, 2021
  • Vol.19 Issue, 8 082504 (2021)
Physical Optics
Temporal Airy–Talbot effect in linear optical potentials
Tianwen Han, Hao Chen, Wenwan Li, Bing Wang, and Peixiang Lu
Chinese Optics Letters
  • Publication Date: Apr. 27, 2021
  • Vol.19 Issue, 8 082601 (2021)
Spectroscopy
VIPA-based two-component detection for a coherent population trapping experiment
Aihua Deng, Zixuan Zeng, and Jianliao Deng
Chinese Optics Letters
  • Publication Date: Jul. 19, 2021
  • Vol.19 Issue, 8 083001 (2021)
Ultrafast Optics and Attosecond/High-field Physics
Reviews
Lasers, Optical Amplifiers, and Laser Optics
Recent development of saturable absorbers for ultrafast lasers [Invited] | Editors' Pick
Mengyu Zhang, Hao Chen, Jinde Yin, Jintao Wang, Jinzhang Wang, and Peiguang Yan
As one of the greatest inventions in the 20th century, ultrafast lasers have offered new opportunities in the areas of basic scientific research and industrial manufacturing. Optical modulators are of great importance in ultrafast lasers, which directly affect the output laser performances. Over the past decades, significant efforts have been made in the development of compact, controllable, repeatable, as well as integratable optical modulators (i.e., saturable absorbers). In this paper, we review the fundamentals of the most widely studied saturable absorbers, including semiconductor saturable absorber mirrors and low-dimensional nanomaterials. Then, different fabrication technologies for saturable absorbers and their ultrafast laser applications in a wide wavelength range are illustrated. Furthermore, challenges and perspectives for the future development of saturable absorbers are discussed and presented. The development of ultrafast lasers together with the continuous exploration of reliable saturable absorbers will open up new directions for the mass production of the next-generation optoelectronic devices.
Chinese Optics Letters
  • Publication Date: Aug. 09, 2021
  • Vol.19 Issue, 8 081405 (2021)

About the Cover

Nanoplasmonic isolator that consists of a plasmonic resonator placed close to a metal-dielectric-metal plasmonic waveguide. A magneto-optical material fills the waveguide and the resonator. The structure is under a static magnetic field.