Cascade large-optical-path-differece photoelastic modulating interferometer

The present invention relates to a cascade large-optical-path-difference photoelastic modulating interferometer which comprises a light source. A polarizer which modulates emergent light to a certain direction to form an angle with the horizontal direction is arranged in the emergent light direction of the light source. A static birefringent crystal is arranged in the emergent light direction of the polarizer. A plurality of strong light modulators which can make emergent light reflect for a plurality of times are arranged in the emergent light direction of the static birefringent crystal. An analyzer is arranged in the emergent light direction of the strong light modulator. A detector which can acquire interfered light of the analyzer is arranged in the emergent light direction of the analyzer. The cascade large-optical-path photoelastic modulating interferometer generates a periodical driving force through a piezoelectric quartz crystal, and furthermore generates two-dimensional coupling longitudinal oscillation by means of a contour oscillation mode of zinc selenide crystal for obtaining higher modulation optical path difference. Based on a fact that a single photoelastic modulator realizes higher modulation optical path difference, the modulation optical path difference is furthermore increased through a cascade manner, thereby settling a problem of small modulation optical path difference in the existing photoelastic modulating interferometer and ensuring enough light flux.