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Lasers and Laser Optics|29 Article(s)
Power Stability of a Semiconductor Laser Used in Atomic Clocks
Shuhong ZHANG, Peter YUN, Tao YANG, Qiang HAO, and Xin WANG
Based on using the Acousto-optic Modulator （AOM） as a feedback device， we design the power locked setup of the 780 nm laser in the common band of atomic clocks. Through low-noise design and parameter optimization， the suppression of key sources of the noise and the laser power locking are achieved. In the frequency deviation range of 20~10 000 Hz， the relative intensity noise of laser beam is effectively suppressed. Especially at the frequency of 1 300 Hz， 20 dB suppression of RIN has been reached. At the same time， the relative power stability in the mid-term （9 000 s） has been increased 78 times from ±0.754% to ±0.009 68%. According to the typical parameters of CPT atomic clock， the influence of relative intensity noise of the laser on the frequency stability of an atomic clock is only 2.1×10–14@1 s. In addition， the mid-term stability improved from 4.67×10-2 in unlocked state to 8.67×10-5 in locked state，and it will be helpful to improve the intermediate period frequency stability of the atomic clock. Based on using the Acousto-optic Modulator （AOM） as a feedback device， we design the power locked setup of the 780 nm laser in the common band of atomic clocks. Through low-noise design and parameter optimization， the suppression of key sources of the noise and the laser power locking are achieved. In the frequency deviation range of 20~10 000 Hz， the relative intensity noise of laser beam is effectively suppressed. Especially at the frequency of 1 300 Hz， 20 dB suppression of RIN has been reached. At the same time， the relative power stability in the mid-term （9 000 s） has been increased 78 times from ±0.754% to ±0.009 68%. According to the typical parameters of CPT atomic clock， the influence of relative intensity noise of the laser on the frequency stability of an atomic clock is only 2.1×10–14@1 s. In addition， the mid-term stability improved from 4.67×10-2 in unlocked state to 8.67×10-5 in locked state，and it will be helpful to improve the intermediate period frequency stability of the atomic clock.
Acta Photonica Sinica
- Publication Date: Sep. 25, 2021
- Vol. 50, Issue 9, 0914002 (2021)
Design and Experiment of Raman Laser System for Atom Interferometric Measurement
Xianhua WANG, Sen JIA, and Junqiang LI
Based on optical phase-locked loop technology， a Raman laser system including three lasers，reference， master and slave lasers， is studied. Among which， the reference laser was firstly frequency-locked by modulated transfer spectrum technology and then as a standard frequency； the master laser， which has a frequency difference of 1 GHz relative to the reference laser， was red detuned from excited stated to prevent direct interaction between lasers and atoms； the salve laser， having a frequency difference of 6.8 GHz relative to the master laser， was used to excite the transmission between the hyperfine energy levels of ground state 87Rb atoms. Respectively， the master and slave lasers were locked by two sets of optical phase-locked loop. The measurement results reveal that the phase noises of the two sets of optical phase-locked loop are within the range of 100 Hz to 1 MHz and lower than -70 dBc/Hz and -65 dBc/Hz respectively， and accordingly， the influence of phase noise on atom interferometric gravity measurement is as low as 5.3×10-7 per shot. The master and slave lasers are amplified by two separate taped-amplifiers to ensure that the master laser’s power is half to that of the slave laser； the composition， polarization unification， and frequency modulation of both the master and slave lasers are realized by the combination laser transmission in fiber and free space. As a result， the Raman laser with a total power of 180 mW is realized， and the maximum fluctuation of total power less than 5% is achieved in long-term power measurement depended not on any additional power stabilizer， satisfying the experimental requirement of atom interferometry measurement. Based on optical phase-locked loop technology， a Raman laser system including three lasers，reference， master and slave lasers， is studied. Among which， the reference laser was firstly frequency-locked by modulated transfer spectrum technology and then as a standard frequency； the master laser， which has a frequency difference of 1 GHz relative to the reference laser， was red detuned from excited stated to prevent direct interaction between lasers and atoms； the salve laser， having a frequency difference of 6.8 GHz relative to the master laser， was used to excite the transmission between the hyperfine energy levels of ground state 87Rb atoms. Respectively， the master and slave lasers were locked by two sets of optical phase-locked loop. The measurement results reveal that the phase noises of the two sets of optical phase-locked loop are within the range of 100 Hz to 1 MHz and lower than -70 dBc/Hz and -65 dBc/Hz respectively， and accordingly， the influence of phase noise on atom interferometric gravity measurement is as low as 5.3×10-7 per shot. The master and slave lasers are amplified by two separate taped-amplifiers to ensure that the master laser’s power is half to that of the slave laser； the composition， polarization unification， and frequency modulation of both the master and slave lasers are realized by the combination laser transmission in fiber and free space. As a result， the Raman laser with a total power of 180 mW is realized， and the maximum fluctuation of total power less than 5% is achieved in long-term power measurement depended not on any additional power stabilizer， satisfying the experimental requirement of atom interferometry measurement.
Acta Photonica Sinica
- Publication Date: Sep. 25, 2021
- Vol. 50, Issue 9, 0914001 (2021)
Wavelength Tunable Dissipative Soliton Mode-locked Fiber Laser Based on Nonlinear Amplifier Loop Mirror
Jianyi DING, Baole LU, Kaile WANG, Haowei CHEN, and Jintao BAI
A figure-8 cavity wavelength-tunable mode-locked Ytterbium-doped fiber laser based on nonlinear amplification loop mirror is reported. When pump power is 240 mW， the dissipative soliton is output with a central wavelength of 1 064.1 nm， 3 dB bandwidth of 7.7 nm， repetition rate of 18.8 MHz， optical signal noise ratio of 71.2 dB and pulse duration of 867 fs， respectively. In addition， wavelength tunable of the mode-locked fiber laser at 1 032.8~1 065.1 nm and 1 037.4~1 041.9 nm can be achieved by adjusting the polarization controller and pump power respectively. The characteristics of the spectra and pulses in different mode-locked states are explored， and a Gaussian pulse whose time bandwidth product is close to the Fourier transform limit is obtained. The fiber laser is simple in structure and easy to tune， and has a stable performance， which provides technical reference for achieving wavelength tunable and dissipative soliton mode-locked. A figure-8 cavity wavelength-tunable mode-locked Ytterbium-doped fiber laser based on nonlinear amplification loop mirror is reported. When pump power is 240 mW， the dissipative soliton is output with a central wavelength of 1 064.1 nm， 3 dB bandwidth of 7.7 nm， repetition rate of 18.8 MHz， optical signal noise ratio of 71.2 dB and pulse duration of 867 fs， respectively. In addition， wavelength tunable of the mode-locked fiber laser at 1 032.8~1 065.1 nm and 1 037.4~1 041.9 nm can be achieved by adjusting the polarization controller and pump power respectively. The characteristics of the spectra and pulses in different mode-locked states are explored， and a Gaussian pulse whose time bandwidth product is close to the Fourier transform limit is obtained. The fiber laser is simple in structure and easy to tune， and has a stable performance， which provides technical reference for achieving wavelength tunable and dissipative soliton mode-locked.
Acta Photonica Sinica
- Publication Date: Jul. 25, 2021
- Vol. 50, Issue 7, 260 (2021)
Laser Cleaning Process Monitoring of Metal Surface Based on Image Processing and LIPS Analysis
Rongwei ZHA, Lidong YU, Ben LI, and Yang BAI
Laser cleaning processing monitoring is essential to accurately remove the rust layer and effectively avoid the damages of the metal substrate. The variations between the number of cleaning and the rust cleaning rate at different spot overlap ratios on 30 mm×30 mm Q235B steel plate were studied by image processing to obtain the optimum spot overlap ratio of 50%. The changing trends of the Pearson correlation coefficient following the number of cleaning on 0.47 mm×0.47 mmQ235B steel plate were studied by Laser-induced Plasma Spectroscopy （LIPS） and the optimum number of cleaning was obtained under different thick dust layer. On this basis， the cooperation of image processing and LIPS is not only to dynamically correct the optimum number of cleaning but also to cover the shortage that image processing can not control the process of laser cleaning accurately. The results show that the cooperation of two methods can monitor the process of laser cleaning on a large area of Q235B steel plate and achieve high-quality laser cleaning with a 99.1% cleaning rate. Laser cleaning processing monitoring is essential to accurately remove the rust layer and effectively avoid the damages of the metal substrate. The variations between the number of cleaning and the rust cleaning rate at different spot overlap ratios on 30 mm×30 mm Q235B steel plate were studied by image processing to obtain the optimum spot overlap ratio of 50%. The changing trends of the Pearson correlation coefficient following the number of cleaning on 0.47 mm×0.47 mmQ235B steel plate were studied by Laser-induced Plasma Spectroscopy （LIPS） and the optimum number of cleaning was obtained under different thick dust layer. On this basis， the cooperation of image processing and LIPS is not only to dynamically correct the optimum number of cleaning but also to cover the shortage that image processing can not control the process of laser cleaning accurately. The results show that the cooperation of two methods can monitor the process of laser cleaning on a large area of Q235B steel plate and achieve high-quality laser cleaning with a 99.1% cleaning rate.
Acta Photonica Sinica
- Publication Date: Jul. 25, 2021
- Vol. 50, Issue 7, 249 (2021)
Study on Optical Force Characteristics of Triangular Metal Nanoparticles
Xiaolei WANG, Guangke JIANG, Yuxin DONG, Siliang LIU, Liping GONG, Jiehui ZHAO, Zhuqing ZHU, and Bing GU
Based on Maxwell's stress tensor theory， the photodynamic properties of polygonal gold nanoparticles in a focused field were studied. Taking triangular gold nanoparticles as an example， the trapping characteristics of triangular gold nanoparticles in focusing field with circular symmetric energy distribution and with triangular energy distribution were studied respectively from the stress conditions of the particles in the focusing field. The results show that the triangular gold nanoparticles with side length of 50~350 nm can be stably captured by using the circular symmetric focusing field. When the triangular focusing field is used， the triangular gold nanoparticles with side length of 100~350 nm can be stably captured under the condition that the particles enter the focusing field at an angle matching the shape of the focusing field. The trapping properties of triangular gold nanoparticles were compared between the circular symmetric focusing field and the triangular focusing field， and we found that the trapping force of the triangular focusing field in the x direction was stronger than that of the circular symmetric focusing field. In the y direction， the capturing range of the triangular focusing field is larger than that of the circular symmetric focusing field. In this work， we studied the optical trapping properties of triangular metal nanoparticles in different focused fields， and laid a theoretical foundation for the application of optical manipulation based on non-spherical metal particles in Raman super-resolution imaging， particle micro-processing and other fields. Based on Maxwell's stress tensor theory， the photodynamic properties of polygonal gold nanoparticles in a focused field were studied. Taking triangular gold nanoparticles as an example， the trapping characteristics of triangular gold nanoparticles in focusing field with circular symmetric energy distribution and with triangular energy distribution were studied respectively from the stress conditions of the particles in the focusing field. The results show that the triangular gold nanoparticles with side length of 50~350 nm can be stably captured by using the circular symmetric focusing field. When the triangular focusing field is used， the triangular gold nanoparticles with side length of 100~350 nm can be stably captured under the condition that the particles enter the focusing field at an angle matching the shape of the focusing field. The trapping properties of triangular gold nanoparticles were compared between the circular symmetric focusing field and the triangular focusing field， and we found that the trapping force of the triangular focusing field in the x direction was stronger than that of the circular symmetric focusing field. In the y direction， the capturing range of the triangular focusing field is larger than that of the circular symmetric focusing field. In this work， we studied the optical trapping properties of triangular metal nanoparticles in different focused fields， and laid a theoretical foundation for the application of optical manipulation based on non-spherical metal particles in Raman super-resolution imaging， particle micro-processing and other fields.
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 144 (2021)
Experimental Research on High Power Cascade Co-pumping Erbium-Ytterbium Co-doped Fiber Laser
Dan WANG, Qun HAN, Panpan NIU, and Tiegen LIU
The amplified spontaneous emission in the Yb band and thermal effect are the main obstacles to the power scaling of high-power Er/Yb-codoped fiber lasers. In order to obtain a high-power and high-efficiency fiber laser， a liquid cooling structure and the cascade co-pumping method are used to carry out experimental research on the erbium-ytterbium co-doped fiber laser. The results show that by using a 2.1 m large core diameter erbium-ytterbium co-doped fiber， a maximum output of 21.6 W at 1 548.9 nm is obtained with a pump power of 47.5 W， and the pump conversion efficiency is 45.7%. The slope efficiency before and after the Yb band oscillation is established are 48.4% and 56.2%， respectively. The amplified spontaneous emission in the Yb band and thermal effect are the main obstacles to the power scaling of high-power Er/Yb-codoped fiber lasers. In order to obtain a high-power and high-efficiency fiber laser， a liquid cooling structure and the cascade co-pumping method are used to carry out experimental research on the erbium-ytterbium co-doped fiber laser. The results show that by using a 2.1 m large core diameter erbium-ytterbium co-doped fiber， a maximum output of 21.6 W at 1 548.9 nm is obtained with a pump power of 47.5 W， and the pump conversion efficiency is 45.7%. The slope efficiency before and after the Yb band oscillation is established are 48.4% and 56.2%， respectively.
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 138 (2021)
Single Longitudinal Mode 589 nm Laser in Composite-cavity
Fei YANG, Mengmeng LI, and Lanlan GAO
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. 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.
Acta Photonica Sinica
- Publication Date: May. 25, 2021
- Vol. 50, Issue 5, 95 (2021)
Critical Coupling Condition and Preparation Technology of Aluminum Nitride Microring Resonator
Yishuai HAN, Tianyu SUN, Huimin JIA, Jilong TANG, Dan FANG, Dengkui WANG, Xiaohua WANG, Baoshun ZHANG, and Zhipeng WEI
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. 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.
Acta Photonica Sinica
- Publication Date: May. 25, 2021
- Vol. 50, Issue 5, 86 (2021)
Switchable Multi-wavelength Erbium-doped Fiber Laser Based on a Microfiber Sagnac Loop
Yancheng JI, Yupei CHEN, Wen LIU, dan SUN, Shuai LI, Guoan ZHANG, and Xiaojun ZHU
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. 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.
Acta Photonica Sinica
- Publication Date: May. 25, 2021
- Vol. 50, Issue 5, 76 (2021)
Wavelength Tunable Er： YAG Mid-infrared Pulse Laser Based on Pump Control
Youbao SANG, Pengyuan WANG, Ying CHEN, Xinjun SU, Jinbo LIU, Jingwei GUO, and Fengting SANG
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. 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.
Acta Photonica Sinica
- Publication Date: May. 25, 2021
- Vol. 50, Issue 5, 68 (2021)
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