正弦波位相変調干渉計の帯域制限のない復調法の開発（ノイズフロア・追従速度・分解能の評価）

抄録

In this study, a band-limitless demodulation method for sinusoidal phase modulation (SPM) interferometry is developed. The SPM demodulation (phase-meter) can be achieved by synchronously sampling the interference signal at 12 times the frequency of the modulation signal and calculating simple addition and subtraction between the sampled data. The phase-meter is instrumented in a field-programmable gate array with a 120 MHz/16 bit analogue-digital-converter. 10MHz phase modulation is performed by an electro-optical modulator installed inside the interferometer. The interferometer is made of a monolithic structure of low thermal expansion material to increase stiffness and reduce effects of disturbance. A comb filter as a pre-filter of the phase meter and an inner copper box of a heat-isolation-box containing the interferometer are also introduced to improve resolution (minimum detectable displacement) and stability of it. The interferometer, the digital phase meter, the comb filter and the inner copper box are evaluated by measuring noise floors, maximum measurement speeds, resolutions. This paper describes the experimental principle, instruments and results.