A closed-loop phase-locked interferometer for wide bandwidth position sensing

Abstract

This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interferogram. In this configuration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics: it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has a bandwidth equal to that of the photodiode. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instrument is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, ultrasonic devices, and sensors such as surface acoustic wave detectors.

Highly compact and easy-to-use optical chip interferometer with picometric performances

“…It is very difficult to compare the PSD between commercial interferometers but, as far as we know, the noise level is very good. A recent example of closed-loop phase-locked prototype 21 shows noise level around 100 pm Hz −1/2 @ 100 Hz and 100 fm Hz −1/2 @ 10 kHz.…”