模式清洁器的噪声转化与输出场噪声分析

Noise Conversion of a Mode-cleaner Cavity and Noise Analysis of Output Fields

根据三镜腔模式清洁器的反射光场及透射光场的传输特性,推导了反射光场和透射光场中振幅和相位两个正交分量的噪声转化函数,理论证明模式清洁器可以实现半导体激光器振幅噪声和相位噪声的相互转化。搭建三镜腔模式清洁器和自平衡零拍探测实验系统,测量了模式清洁器反射光场和透射光场的振幅噪声谱,实验结果与理论结果一致。根据模式清洁器的噪声转化模型,利用实验中模式清洁器共振与非共振锁定情况下测量的反射光振幅噪声谱,计算了半导体激光器的相位噪声。研究结果可为深入理解模式清洁器噪声转化过程提供参考,同时说明利用模式清洁器的噪声转化机制可以实现半导体激光器相位噪声的测量和评估。

Semiconductor laser is one of the very important sources in a variety of modern physics experiments,the measured quantities in quantum precision measurement will be demonstrated to the laser parameters such as amplitude,frequency,and phase,so researching semiconductor laser’s phase noise and amplitude noise is significant in the domain of phase-sensitive amplification and interferometric phase measurement. As an optical cavity to improve beam quality and beam mode,mode-cleaner cavity has important applications in quantum precision measurement,quantum communication,quantum computing,quantum key distribution and gravitational wave detection. The noise conversion functions of phase and amplitude fluctuation of a light beam can be deduced,according to the properties of reflection field and transmission field for the mode-cleaner cavity. The mode-cleaner cavity and the balanced homodyne detection are constructed after locking the laser’s frequency. The balanced homodyne detection measures amplitude noise of reflection field and transmission field,the experimental results show that the amplitude noise of transmission field decreases gradually with the detection frequency,and the noise at the frequency far larger than the linewidth reaches the shot noise limit. Nevertheless,the amplitude noise of the reflection field is far larger than that of the transmission field. As a whole,the amplitude noise also decreases gradually with the detection frequency. Linewidth of mode-cleaner cavity is calculated as 2.5 MHz by transmission spectrum,mode cleaner can be regarded as a low-pass filter under the condition of meeting the resonance in the transmission field,the high-frequency noise is greatly suppressed. In this case,when the detection frequencies range from 0 to 2.5 MHz,the amplitude noise of the transmission field is far larger than the shot noise limit. In the range of detection frequencies from 2.5~20 MHz,the amplitude noise decreases gradually with the increase of the analysis frequency in the transmission field. When the detection frequency is 15 MHz,the amplitude noise of the transmission field reaches the shot noise limit.However,when the detection frequencies range from 0 to 20 MHz,the amplitude noise of the reflection field is far larger than the shot noise limit. On the one hand,the mode-cleaner cavity can be regarded as a high-pass filter in the reflection field,which makes a significant contribution to the results. On the other hand, mode-cleaner cavity can interconvert the phase noise and amplitude noise after reflection or transmission. The amplitude noise of transmission field and reflection field can be calculated theoretically based on the noise conversion functions. By comparing the theoretical results with experimental results,the experimental results are consistent with the theoretical results. The phase noise of semiconductor laser is analyzed by measuring the amplitude noise of the reflection field with on-resonance locking and nearresonance locking. The results indicate that the experimental results are consistent with the theoretical results under the condition of on-resonance locking and near-resonance locking. Thus the research demonstrates that phase noise of semiconductor laser can be measured and evaluated by the noise conversion function. Moreover, this study provides a theoretical basis and provides an important complement for the noise conversion of mode-cleaner cavity. The mode-cleaner cavity is studied from the point of noise conversion in this paper,and the research demonstrates that the experimental results are consistent with the theoretical results in the transmission and reflection field. At the same time,the phase noise of semiconductor laser is measured and evaluated,which promotes the development of quantum precision measurement.