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.