基于光折变效应提升啁啾脉冲信噪比的光谱扫描滤波法

基于光谱扫描滤波原理，提出了一种利用光折变效应来提高啁啾脉冲信噪比的扫描滤波方法，并进行了理论分析。针对内置光折变晶体的Fabry-Perot (F-P)标准具光谱扫描滤波装置，定量分析了其透射谱特性，详细讨论了Fabry-Perot(F-P)标准具两平板的反射率、透射谱窗口带宽、外加场的控制参数以及信号光啁啾率变化等对啁啾脉冲信噪比的提升及其滤波透射率的影响。结果表明，F-P两平板的反射率越高，则透射谱越尖锐，透射窗口越窄，滤波效果也就越好。为了得到有效的信噪比提升，一般要求其反射率大于0.99;外加场的控制和信号光啁啾率的变化对扫描滤波的影响较大，在实际工作中，应尽量保证外加场和啁啾率的精确控制，以确保信号光和滤波函数的同步匹配。针对中心波长800 nm的啁啾信号脉冲，采用提出的光谱扫描滤波方法，对放大自发辐射(ASE)的随机噪声与预脉冲进行滤波，可得到近3个量级的信噪比提升效果。

A Spectral Scanning Filtering Method for Improving the SNR of Chirped Pulse Based on the Photorefractive Effect

Based on the principle of spectral scanning filtering method, a new scanning filtering method for improving signal-to-noise ratio (SNR) of the chirped pulse by using the photorefractive effect was proposed and theoretically analyzed. For the scanning filtering implement of Fabry-Perot (F-P) etalon with a built-in photorefractive crystal, the transmittance spectral characteristics of the scanning filter were analyzed quantitatively. Furthermore, the effects of the reflectivity of the parallel-plates of Fabry-Perot etalon, the bandwidth of the transmittance spectral window, the variation of the controlling parameters of the applied field and the variation of the chirped rate to the photorefractive crystal on the SNR improvement and the overall transmittance were discussed in details. The results show that the higher the reflectivity of the F-P parallel-plates is, the transmittance spectral is sharper and the transmittance window is narrower, resulting in the better filtering effect. In order to ensure the efficient SNR improvement, the reflectivity of the F-P parallel-plates should be higher than 0.99. The control of the applied field exhibits significant impact on the scanning filtering. In practical applications, the applied field and chirped rate should be controlled precisely in order to ensure the synchronous matching between the signal pulse and the filtering function. For the chirped signal pulse with the central wavelength 800 nm, the SNR improvement of about 3 orders of magnitude can be obtained via filtering out the amplified spontaneous emission (ASE) random noise and pre-pulse by the use of the spectral scanning filtering method proposed in this paper.