| Summary: | 碩士 === 國立聯合大學 === 光電工程學系碩士班 === 102 === In various of technology of interferomerty , two kinds of interferometer are the most accurate such as phase-shifting interferometry and heterodyne interferometry. The heterodyne interferometry gets the signal from the certain beating with fixed frequency and removes extended-band noise. So, the heterodyne interferomtry possess superior ratio of signal to noise. In phase-shifting interferomtry, we have to obtain many frames of interferogram by phase-shifting scheme for retrieve phase signal. The algorithm for phase retrieve adopts the method of subtraction of interferograms. In process of interferogram-subtraction, the fixed noise in interferograms can be cancelled and gets superior phase signal. So, phase-shifting interferometry is superior tool for phase measurement until now.
Nevertheless, two types for getting many interferograms by phase-shifting scheme：one is so called simultaneous phase-shifting, and another is called time-domain phase shifting. Simultaneous phase-shifting technology possesses merits of avoiding random noise but the whole system is complex and expensive.
We adopt the traditional time-domain phase-shifting interferometry, but we use the modified Sagnac parallel interferometers. One interferometer is for measuring the object and the other is used for monitoring the random noise. We can obtain two sets of phase diagram simultaneously. In similar process of subtraction, we can get accurate phase signal with cancelled random-noise. We proof that our scheme of the parallel interferometer is good result similar to simultaneous phase-shifting interferometry but the whole optical system is more simple and low-cost.
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