Backscatter Tolerance of a Travelling-Wave Optical Parametric Oscillator

Abstract

Backscattered light in the squeezing propagation path is a source of low frequency noise. In a gravitational-wave detector with squeezing, this can potentially be a sensitivity-limiting noise source (The influence of backscattered light with squeezed-interferometric readout will be covered in Chap. 10.). A possible back-reflecting source in the squeezing path is the OPO cavity itself. As stated in Chap. 6, the travelling-wave design of the DB-OPO was chosen because of its first-order immunity to backscattered light. This chapter presents analysis and experiment results that quantifies the tolerance of a travelling-wave OPO squeezing cavity to backscattered light. Reported as part of (Chua et al., Opt Lett 36(23):4608, 2011, [1]), this is to the author’s knowledge the first such measurement of its kind. After defining backscattered light, the theoretical framework for calculating the backscatter reflectivity of the OPO is introduced. The experiments performed to determine the intrinsic isolation of a travelling-wave OPO report an isolation factor of $(41 \pm 2)$ dB. This is followed by a calculation of the bi-directional scatter distribution function for the OPO. A discussion on the determined backscatter tolerance value concludes the Chapter.