Wavelength Tunable Er: YAG Mid-infrared Pulse Laser Based on Pump Control
SANG Youbao, WANG Pengyuan, CHEN Ying, SU Xinjun, LIU Jinbo, GUO Jingwei, and SANG Fengting
This work achieves a variety of wavelength output modes in the same laser by analyzing the energy level lifetime and thestimulated emission cross section. The laser realizes the result by the regulation of the pump pulse mode without any tuning components in the cavity and does not change the output coupling transmittance.The laser modes include: 1.06 mJ single-wavelength 2 699 nm laser mode, 1.25 mJ single-wavelength 2 803 nm laser mode, alternate sequence pulse mode with dual-wavelength of 1.06 mJ 2 699 nm and 0.86 mJ 2 803 nm, alternate sequence pulse mode withdual wavelength of 1.06 mJ 2 699 nm laser and 1.35 mJ 2 830 nm.The research in this paper is expected to be the laser source of the differential absorption radar for measuring the concentration of organic matter, enabling a single detector to achieve differential measurement, while greatly simplifying the detection system of differential absorption radar and reducing costs.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 68 (2021)
  • DOI:10.3788/gzxb20215005.0514001
Wavelength Tuning Characteristics of Nd:YAG/Cr4+:YAG Laser Based on Volume Bragg Grating
MENG Peibei, QI Ming, RONG Wei, LI Menglong, WANG Chunhui, and TAO Yuliang
In theory, the tuning characteristics including tunable range, spectrum, energy and pulse width were simulated under different pump power, volume Bragg grating central diffraction efficiencies and spectral widths by setting up a rating equation model including volume Bragg grating wavelength property. A laser diode pumped Nd:YAG/Cr4+:YAG laser with a volume Bragg grating as output coupler was set up. The laser wavelength, linewidth, energy and pulse width were measured at different volume Bragg grating temperatures and pump power. The experimental results and theoretical results are in agreement. At the repetition rate of 10 kHz, pump pulse width of 40 μs, pump peak power of 10.7 W, tunable range from 1 063.77 to 1 064.48 nm is obtained. When the volume Bragg grating temperature is 50 ℃, output energy of 109.5 μJ, pulse width of 1.71 ns, wavelength of 1 064.432 nm, linewidth of 38.3 pm, M2 factor of less than 1.2 is achieved. The investigating results can be a reference of volume Bragg grating application, spectral analysis and design of laser.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 102 (2021)
  • DOI:10.3788/gzxb20215005.0514005
Critical Coupling Condition and Preparation Technology of Aluminum Nitride Microring Resonator
HAN Yishuai, SUN Tianyu, JIA Huimin, TANG Jilong, FANG Dan, WANG Dengkui, WANG Xiaohua, ZHANG Baoshun, and WEI Zhipeng
Aiming at the difficulty of achieving critical coupling conditions for aluminum nitride microring resonators, an aluminum nitride bending-coupled microring resonator is designed and prepared. Through the analysis of the coupling coefficient formula of the microring resonator, the advantages and disadvantages of various solutions to improve the coupling strength are respectively explained. Finally, a curved coupling zone structure is selected to enhance the coupling strength, and a solution to achieve critical coupling conditions under a wide coupling gap is obtained. A high-quality aluminum nitride single crystal film is grown on a sapphire substrate. Conductive glue is used to overcome the non-conductivity of the material. The electron beam exposure system is used to make the bending angle of 40°, the coupling gap of 0.190 μm, and the waveguide width of 0.41 μm. The microring resonant cavity is patterned, a number of aluminum nitride etching parameters are analyzed and optimized, and the pattern is finally transferred to the aluminum nitride layer to obtain a curved coupled aluminum nitride microring resonant cavity with uniform coupling gap and flat sidewalls. This research provides a reference for the selection of critical coupling conditions for aluminum nitride microring resonators.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 86 (2021)
  • DOI:10.3788/gzxb20215005.0514003
Switchable Multi-wavelength Erbium-doped Fiber Laser Based on a Microfiber Sagnac Loop
JI Yancheng, CHEN Yupei, LIU Wen, SUN dan, LI Shuai, ZHANG Guoan, and ZHU Xiaojun
A switchable multi-wavelength erbium-doped fiber laser based on a microfiber Sagnac loop is proposed and experimentally demonstrated. The microfiber Sagnac loop comb filter is fabricated by inserting a 5.5 cm polarization maintaining fiber between two outputs of an optical microfiber coupler with a waist diameter of 5.68 μm. The filter is fused into the fiber ring cavity and the four-wavelength output laser is realized by adjusting the polarization controller. In addition, the output of single-, dual-, triple- wavelength laser can be switched, and the outputs interval of dual-, triple-wavelength are tunable. The experimental results show that the 3 dB linewidths of laser output spectra are less than 0.027 nm and the side-mode suppression ratio are more than 40 dB, up to 58 dB. When the fiber laser operates at triple-wavelength, the wavelength shift and peak power fluctuation are within 0.028 nm and 0.9 dB in one hour. The laser has stable output and good monochromaticity, which can be applied in fields of wavelength division multiplexing and all-optical communication systems.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 76 (2021)
  • DOI:10.3788/gzxb20215005.0514002
Single Longitudinal Mode 589 nm Laser in Composite-cavity
YANG Fei, LI Mengmeng, and GAO Lanlan
A laser-diode pumped Nd:YVO4 and Nd:YAG single-longitudinal-mode 589 nm laser is presented. The fundamental waves of 1 064 nm and 1 319 nm simultaneously oscillate through an L type composite resonator. Through intracavity sum-frequency-generation in a KTP crystal (cut at type II phase matching),the single longitudinal mode 589 nm continuous wave is obtained by a birefringent filter which is consisted of a Brewster plate and the KTP crystal. The losses of S- and P- elements of the two fundamental waves are calculated by Jones matrix method. The losses of the first sub-longitudinal modes for 1 064 nm and 1 319 nm are 0.5% more and 2% more than their peak transmission modes respectively. Based on the above mentioned, a single-longitudinal-mode 589 nm laser is realized in experiment. The maximum output power is 58 mW, the amplitude fluctuation is less than 0.36%, and the line width is about 30 MHz. The results show that the birefringent filter technology is effective for single-longitudinal-mode double-wavelength oscillation and sum-frequency-generation lasers.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 95 (2021)
  • DOI:10.3788/gzxb20215005.0514004
Modeling of a SiGeSn quantum well laser
Bahareh Marzban, Daniela Stange, Denis Rainko, Zoran Ikonic, Dan Buca, and Jeremy Witzens
We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with k·p theory to adapt transport, optical gain, and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption, and intervalence band absorption). Good consistency is obtained with experimental data, and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover, they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers, taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.
  • Jun. 16, 2021
  • Photonics Research
  • Vol.9 Issue, 7 07001234 (2021)
  • DOI:10.1364/PRJ.416505
Superior performance of a 2 kHz pulse Nd:YAG laser based on a gradient-doped crystal
Meng’en Wei, Tingqing Cheng, Renqin Dou, Qingli Zhang, and Haihe Jiang
Herein, we report a homemade new Nd:YAG crystal rod that contains a gradient dopant of 0.39–0.80 at.% Nd3+ from end to end, achieving superior performance of a 2 kHz Nd:YAG pulse laser at 1064 nm. The optical-to-optical conversion efficiency reached 53.8%, and the maximum output power of the laser was 24.2 W, enhanced by 35.9% compared with a uniform crystal rod with the same total concentration of Nd3+. Significantly, our experiments revealed that the gradient concentration crystal produced a relatively even pumping distribution along the rod axis, greatly reducing the temperature gradient as well as having a smaller thermal effect. The pump and thermal distribution smoothing obviously improved the features of laser oscillation and output.
  • Jun. 09, 2021
  • Photonics Research
  • Vol.9 Issue, 7 07001191 (2021)
  • DOI:10.1364/PRJ.424989
Simulation of Axial Focal Shift of Optical System Under High-Power Laser
Ding Wei, Wang Fei, Wang Mengjie, and Weng Ningzhi
In a high-power optical cutting system, the laser is focused by the optical system to generate heat, which causes the optical system components to undergo thermal deformation and change in refractive index, which changes the focal length of the lens and affects the processing effect. COMSOL software is used to model the optical system in a multi-physics field, the shape of the mirror and the change of refractive index under the action of continuous laser and quasi-continuous laser are obtained by simulation. The heated data of the lens is imported into ZEMAX for beam tracing, and the axial offset of the focal point of the optical system is calculated by simulation. The higher the power, the greater the focal shift; the larger the pulse width, the smaller the focal shift; the higher the repetition frequency, the smaller the focal shift. Finally, the focus shift is compensated by introducing the convection coefficient, and the position of the focus can be controlled by changing the convection coefficient. This research solves the problem of difficult measurement of the axial focus offset during high-power laser processing and provides a theoretical basis for the focus control of high-power laser cutting equipment.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114011 (2021)
  • DOI:10.3788/LOP202158.1114011
Design of Microstructure Fiber for Direct Down Laser Backlight of Liquid Crystal Displays
Shen Kaifeng, and Wu Zhangqiang
The scheme of an external semiconductor laser with built-in microstructure fiber is designed and studied to achieve fiber-side lighting. This scheme solves the problems associated with traditional direct down liquid crystal modules: these require a large number of light-emitting diode chips, and the volume of the built-in semiconductor laser scheme is too large. The effects of different depths, radii, and the number of microstructures on the optical field are simulated and analyzed. Light field with a peak illumination of 32650 lx, a horizontal viewing angle of 85°, and a vertical viewing angle of 84°33′35″ is obtained. These values meet the requirements of the liquid crystal display (LCD) industry for achieving a peak backlight illumination of 10000 lx, a horizontal viewing angle of 60°, and a vertical viewing angle of 50°. The proposed scheme provides a new method for applying semiconductor lasers in the field of LCD display.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114010 (2021)
  • DOI:10.3788/LOP202158.1114010
Parameters Optimization and Friction and Wear Properties for Laser Cladding Ni60AA Coating on 45 Steel Shaft Surface
Wu Jun, Zhu Dongdong, Yang Richu, Wu Siyu, Huang Yan, and Zhang Yuliang
To improve the service life of 45 steel shaft parts, we aim to study optimum process parameters of laser cladding Ni60AA coating on 45 steel shaft surface. The cladding process test of shaft surface was carried out with multi-pass spiral lap technology, namely, a Ni60AA alloy cladding layer was prepared on a 45 steel substrate. Based on the single variable method, the single factor cladding experiments were carried out on three process parameters, namely laser power, powder feeding rate and shaft speed. The thickness of cladding layer, dilution ratio and micro-hardness were selected as the evaluation indexes of coating quality. Based on the single factor experiment, the orthogonal experiment of three-factor and three-level was completed. The multi-objective comprehensive optimization of the process parameters was finished by the weight matrix method, and the microstructure and micro-hardness of the optimized cladding coating were analyzed. At the same time, friction and wear experiments were carried out at different working temperatures, and the friction coefficient,wear rate and wear scar morphology were analyzed and the feasibility of process optimization is verified. Powder feeding rate has the largest comprehensive influence ability, followed by laser power and shaft speed. The optimal parameters are laser power of 1400 W, powder feeding rate of 16.3 g/min, and shaft speed of 2.3 r/min. The thickness and micro-hardness of the cladding coating were increased by 3.49% and 2.8% respectively compared with those before optimization. When the test temperature is 35, 80 and 125 ℃, the average friction coefficient of the cladding coating is 28.5%, 21.1% and 11.8% lower than that of 45 steel and the wear rate of the cladding coating is 87.6%, 86.6% and 80.9% less than that of the substrate. Ni60AA cladding coating with high forming quality and significantly improved hardness and wear resistance can be obtained by optimizing the laser cladding process parameters.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114008 (2021)
  • DOI:10.3788/LOP202158.1114008