外差干涉技術是一重要的精密量測方法，據此所發展的感測系統可以在量測變化時有極佳的線性、穩定性與精密度。由此所設計的感測系統必須有調變訊號，將訊號作調變的方法有很多，其中以電光調變器是最典型的一種。

雙折射材料的雙折射特性是許多研究領域中熱門的一個話題，近來更對其相關晶體或生化物質的主軸軸向與外界的關係產生興趣。目前已有其他發表利用E-O modulator的外差調變技術來量測birefringence變化，也有利用Faraday Rotator的外差調變技術來測量雙折射晶體的主軸軸向。

本文將欲利用新式Synthetic Heterodyne解調變電路將共路干涉中試件的birefringence變化造成的相位延遲解析出來，並同時發展一套由共路干涉為基礎，配合電光調變器的量測系統，以達同時量測雙折射材料的birefringence及主軸軸向因外界影響所產生的變化。此方法論，在目前的文獻中是屬於創新的設計，若能設計出高敏感同時量測birefringence及主軸軸向變化的量測儀器，必對相關晶體與生化量測有其重要貢獻。

Heterodyne interferometry is an important technique for precise measurement. According to these developed sensing system, we can get the optimum linear stability and precision. This sensing system we developed must have modulated signal. There are many different methods to modulate signal. The most typical case of those modulation methods is by using electro-optic modulator.

The birefringent characteristic of birefringent material is a hot topic in many research fields. Recently years, we are interested in finding the relations between the principal axis direction changes in the environment. The heterodyne modulator techniques with an E-O modulator to measure the birefringence change and with a Faraday Rotator to measure the principal axis rotation have been presented.

In this study we want to use new Synthetic Heterodyne demodulation circuit to measure the phase retardation caused by the birefringence change. We also develop a measuring system based on the common-path interferometry and using the EO modulator in order to simultaneously measure the birefringence change and the principal axis rotation caused by the environment change. According to knowledge, this novel setup is first proposed in this study. Successfully, it would make a great contribution in the related crystal or biomaterial.

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