Small displacement measurements based on an angular-deviation amplifier and interferometric phase detection

Abstract

We propose a method for small displacement measurement based on the angle deviation to phase change transformation. The phase change of common-path heterodyne interferometry due to the angle deviation of incidence of a light at interfaces caused by the displacement is detected by a lock-in amplifier. To obtain more accurate results we used an angular amplifier to increase the angle deviation and utilized a surface plasmon resonance (SPR) sensor to enhance the performance of phase detection. When a translator moves one of two face-to-face plane mirrors at an end and then rotates it a small angle, a light is incident onto the mirrors and reflected N times. The outgoing light is also deflected N times of the angle and incident into a SPR sensor. Thus the phase shift due to the angle deviation is amplified N times. The accumulated phase shift is proportional to the amplified angle deviation and displacement. Therefore, the phase change is obtained and the displacement is measured. The amount of movement required can be as low as 0.13 μm without an SPR sensor or 0.08 μm with an SPR sensor. The maximum measurement range can reach 1000 μm.

Heterodyne Angle Deviation Interferometry in Vibration and Bubble Measurements

“…The heterodyne light can be utilized to measure some parameters in the general environment. The base Heterodyne Angle Deviation Interferometry (HADI) [9] is shown in Figure 1. The frequencies of the s-and p-polarizations are f 1 and f 2 , respectively.…”

“…In order to obtain better sensitivity and larger phase variation, we design a face-to-face parallel metallic plane mirror pair as an angular sensor [9] and let the test light pass through it with twelve reflections for the purpose of magnifying the phase shift. The test light from a heterodyne light source has a beat frequency of 10 kHz ( f " 10 kHz).…”

“…The modulation signals and beat frequency are the same as before. The incident angle of the angular sensor is adjusted at the resonant angle (43.7˝) by using the rotation stage (9). The lock-in amplifier (17) reads and transfers the phase difference between the reference signal I r and the test signal I t into a DC voltage when the phase difference is kept a constant.…”

“…To achieve the best resolution, we proposed Heterodyne Angle Deviation Interferometry (HADI) to measure the deviation angle in order to obtain some physical parameters in general fields. We used two AOM (acousto-optic modulation) devices and a laser to become the heterodyne light source and used the technique of the common-path heterodyne interferometry (CPHI) to measure the phase shift of an angular sensor for displacement measurement [9]. The angular sensor can be a pair of parallel metallic plane mirrors or a surface plasmon resonance (SPR) prism.…”

A review of interferometry for geometric measurement

“…These heterodyne phase detection principle based methods have wide applications [206][207][208][209]. Some adopt acousto-optic modulators [210][211][212] to obtain frequency differences between the measuring and reference beams while others employ oscillating gratings [213].…”