A scanning filtering method for enhancing the signal-to-noise ratio of chirped laser pulse

Abstract

Based on the principle of scanning filtering, a new optical scanning filtering method for improving signal-to-noise ratio(SNR) of the chirped pulse is proposed. For the scanning filtering scheme of Fabry-Perot (F-P) etalon including an electro-optic crystal, the spectral characteristics of the scanning filter are analyzed quantitatively. Furthermore, the effects of the reflectivity of the parallel-plates of F-P etalon and the types of the electro-optic crystals on the output SNR are discussed in detail, and the influence of the variation of the controlling voltage applied to the electro-optic crystal on the filtering effect is also studied. The results show that the narrower the bandwidth of scanning filter transmission window is, the better the improved SNR will be. In order to ensure the filtering effect, the reflectivity of the parallel-plates of F-P etalon should be more than 0.9. Compared with the scheme of scanning filter built-in ordinary linear electro-optic crystal, the scheme of F-P etalon including an secondary standard electro-optic crystal, i.e., KTa1-xNbxO3 crystal, requires a low voltage, and it is easy to control. The differences of KTa1-xNbxO3 crystal components have little influence on the filtering effect, whereas the variations of controlling voltage and chirp rate of the signal exhibit a greater influence on the filtering effect.