The compulsorily phase locked interferometer using orthogonally polarized light source of a modulated LD with high extinction ratio

摘要

This paper describes the compulsorily phase locked differential interferometer using orthogonally polarized light source of a modulated LD with high extinction ratio for reducing non-linearity of the interferometer due to polarization cross-talk. The current modulated LD are used as a light source for making the interferometer a compact and for scanning phase of the interferometer. A Wollaston prism of high extinction ratio (50 dB) is used as a beams combiner of the polarizing beams for making the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis. In the other light source the polarized output beams have small crossing angle (2.5 mrad ～ 10 mrad) for excluding completely non-linearity of the interferometer due to polarization cross-talk. It is confirmed that the cross-talk components of these developed light sources are very small compared with those of the conventional orthogonally polarized light source using polarizing beam splitters. Using jets of a gas mixture of nitrogen and ethylene, it was demonstrated that the compulsorily phase locked differential interferometer is useful to detect photothermal effect of photothermal velocimeter in turbulent flow.