Improvement of a glass integrated optical displacement sensor interferometer using acousto-optic effect

Abstract

Optical interferometer displacement sensors are well known for their high resolution, up to 10−7 m in a stabilized environment, over a wide measuring range which can reach several metres. Moreover, the measurements are carried out without any mechanical contact with the target object. Two optical outputs are however needed to determine the displacement sign. A glass integrated sensor with only one optical output that still measures the displacement sign is proposed here. It is derived from a Michelson interferometer but is realized by ion exchange on a glass substrate. A piezoelectric element placed over the reference arm produces a longitudinal acoustic wave that creates a small phase modulation in the reference light beam at a high frequency (1.28 MHz). A small modulation of the output signal is thus produced. The direction determination is based on the comparison between the phases of the excitation acoustic signal and of the high frequency part of the sensor's output signal after proper signal processing. A theoretical and an experimental demonstration of that principle are presented. A precision of 158 nm was obtained with simple numerical signal processing.

Integrated acousto-optic polarization analyzer sensor

“…This model allows to calculate the strains and stresses at each mechanical interface. [7] The stress F 0 at the interface between the coupling layer and the glass is evaluated and is used next to calculate the strain applied to the optical waveguide. Mechanical and dielectric losses are taken into account in this circuit.…”

Determination of refractive index variation of a glass-integrated optical waveguide by the acousto-optic effect

“…In this context, in a previous work, we used the acousto-optic effect to modulate guided light on a glass substrate for an interferometric displacement sensor application. The acoustooptic effect allowed us to propose an original simplified design with only one optical output [6].…”

Development of an optical accelerometer with a DVD pick-up head

“…Optical sensing techniques have been broadly applied in the development of measurement systems in recent years. For example, Poffo et al [4] proposed a glass-integrated sensor capable of indicating the sign of the displacement using a single optical output. The optical interferometer displacement sensor designed in their study used a piezoelectric element positioned over a reference arm to produce a longitudinal acoustic wave, which then created a small phase modulation of the reference light beam at a high frequency (1.28 MHz).…”