摘要
面向空间引力波探测对激光光源相对强度噪声的严苛需求,开展了极低相对强度噪声在低频段的测试表征技术研究。构建了基于低噪声光电探测器、高精度数字万用表以及快速傅里叶(FFT)频谱分析仪在低频段0.1 mHz~100 kHz的相对强度噪声测试系统。利用高精度数字万用表及FFT分段Smooth窗函数平滑算法实现对0.1 mHz~0.5 Hz的极低频段内相对强度噪声测试,本底噪声低于-99 dBc/Hz,同时利用低噪声放大器及FFT频谱分析仪测试在1 mHz~100 kHz的相对强度噪声,本底噪声低于-105 dBc/Hz。两种测试手段在1 mHz~0.5 Hz重叠频段内噪声测试结果的一致性验证了所构建测试系统在低频段测试结果的准确性。利用所构建的相对强度噪声测试系统对自研空间引力波探测用平面波导环形腔(NPRO)激光器、商用光纤激光器、商用外腔半导体激光器等多种激光器进行测试评估,并对其噪声成分及来源进行分析。所构建的低频段相对强度噪声测试系统可满足空间引力波探测对激光强度噪声评估的需求,同时也适用于其他低频段精密测量应用的激光光源噪声评估。
Objective Combined with current testing technology and spacebased gravitational wave detection requirements,relative intensity noise(RIN)testing must cover the frequency range of 0.1 mHz‒5 GHz.Currently,lownoise spectrum analyzer is used for RIN testing in the higher frequency band of 50 kHz‒5 GHz,and relevant theories and testing methods are relatively mature.OEWaves of the USA SYCATUS of Japan and Shanghai Institute of Optical Machinery have launched corresponding standard test instruments.However,the current test methods in the lowfrequency band are limited in the test band or have high background noise,which cannot fully meet the requirements of RIN low frequency band test and evaluation of laser light source for spacebased gravitational wave detection.It is necessary to develop the low background noise measurement technology and complete and accurate evaluation standard of all low frequency band.Methods In this study,the lowfrequency RIN within 0.1 mHz‒100 kHz is completely tested and characterized,and the background noise of the test system is reduced to form a standardized test system and test algorithm.First,based on lownoise photodetector,highprecision digital multimeter,Labview control data acquisition,and data processing algorithm programming,the test characterization of laser RIN in the frequency band of 0.1 mHz‒0.5 Hz was realized.In the time domain,the highprecision acquisition was conducted using the Labview software to control DMM.The fast Fourier transform(FFT)algorithm was used to analyze the noise characteristics of the collected data in the frequency domain.The smoothing function of different resolutions was used in the calculation of RIN to ensure that the test results in the lowfrequency band are not true,while the serious trailing phenomenon in the highfrequency band was reduced.Besides,frequency domain analysis can be performed immediately upon the completion of the time domain collection,and the data can be stored in real time.Combined with the data of different sampling time,the accuracy of the verylowfrequency test results was verified.Second,FFT spectrum analyzer(SR770,Stanford Research Systems)was used to test the RIN of laser in the frequency band of 1 mHz‒100 kHz.By adding low noise amplifier(LNA)into the test system,the background noise in the frequency band of 1 mHz‒1 Hz was effectively reduced.The testing capacity was reduced by 18 dB.Finally,the consistency of the test results of the two test methods in the overlapping frequency band was compared to verify the uniformity and accuracy of the two test results.Finally,the lowbackgroundnoise RIN test band was expanded to 0.1 mHz‒100 kHz.The RIN noise measurement system has the advantages of wide coverage of lowfrequency band,high precision,and high accuracy.It can provide a standardized measurement means for the relative intensity noise of laser in space gravitational wave detection and can also be applied to other lowfrequency precision measurement applications of laser light source noise assessment.Results and Discussions According to the sampling time listed in Table 3,data segments ranging from 10000 s to 8000 s are captured to calculate the laser verylowfrequency RIN,respectively,and the results are shown in Fig.7.It can be seen that the highfrequency tail after Smooth piecewise smoothing algorithm is only 2 dB;in the range of 0.04 Hz to 0.5 Hz,different data lengths have little influence on RIN results.However,in the frequency range of 0.1 mHz‒0.04 Hz,the sampling time of 8000 s is significantly different from that of 10000 s,and more noise information can be detected at 80000 s.Moreover,Fig.7 shows that the curves with the sampling time of 10000 s and 2000 s have poor coincidence compared with other long periods.This is because the short test time leads to fewer data points in the frequency band of 0.1 mHz‒0.04 Hz,resulting in decreased accuracy.In combination with the abovementioned and theoretical analysis,it can be seen that the longer the sampling time,the more accurate the test results.Figure 8(a)shows the RIN test results of two kinds of highprecision DMM and FFT spectrum analyzer simultaneously.Their test frequency bands cover 0.1 mHz‒0.5 Hz and 1 mHz‒100 kHz,respectively.As can be seen from Fig.8(a),the two maintain a good consistency within 1 mHz‒0.5 Hz in the overlapping frequency band,which on the one hand verifies the correctness of the test results.On the other hand,a complete test of RIN characteristics in the frequency band of 0.1 mHz‒100 kHz can be completed by splicing the noise spectrum of the two test results.Figure 8(b)shows the complete relative intensity noise spectrum of the lowfrequency band of 0.1 mHz‒100 kHz obtained after splicing.The test technique in this paper is applied to test the RIN of different types of lasers,and the characteristics of laser RIN in the lowfrequency band are obtained to guide the development and optimization design of the laser and the parameter performance of the application system.Conclusions Based on the strict demand for laser noise in spacebased gravitational wave detection,we complete the establishment of lowbackground relative intensity noise test characterization system in the lowfrequency band,background noise up to-99 dBc/Hz@0.1 mHz,-165 dBc/Hz@100 kHz.This technology converts the optical signal of the laser into an electrical signal based on lownoise photodetector and performs the complete and accurate characterization of intensity noise in the range of 0.1 mHz‒100 kHz through the combination of highprecision DMM,FFT spectrum analyzer,and other test means.The RIN of four typical lasers is tested and analyzed.The main noise characteristics of each laser and the subsequent available intensity noise suppression technology are obtained,and according to the noise performance of the selfdeveloped NPRO laser,the direction of improving the relative intensity noise in the verylowfrequency band is proposed in the next stage.The relative laser intensity noise characterization test can provide accurate and unified evaluation method for laser source noise level in space gravitational wave detection and provide reference for laser source noise suppression.
作者
胡海林
虞逸航
陈迪俊
孙广伟
杨康文
魏芳
杨飞
Hu Hailin;Yu Yihang;Chen Dijun;Sun Guangwei;Yang Kangwen;Wei Fang;Yang Fei(School of Optical and Computer Engineering,University of Shanghai for Science and Technology,Shanghai,200093,China;Key Laboratory of Space Laser Communication and Detection Technology,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2023年第23期80-88,共9页
Chinese Journal of Lasers
基金
科技部重点研发计划(2020YFC2200302,2022YFB3902503)
国家自然科学基金(12293033,62275253)
中国科学院先导项目(XDB43030401)
中国科学院青年创新促进会(YIPA2019251)
上海市自然科学基金(21ZR1472100)
中科院科研仪器设备研制项目(YJKYYQ20210017)。
关键词
单频激光器
噪声测试
相对强度噪声
快速傅里叶变换
空间引力波探测
single frequency laser
noise test
relative intensity noise
fast Fourier transform
space gravitational wave detection
