INTEGRATED-OPTIC HETERODYNE INTERFEROMETER FOR DISPLACEMENT MEASUREMENT

An integrated-optic heterodyne interferometer is proposed and demonstrated for displacement measurement with an accuracy of several nanometers. All guided-wave components required for displacement measurement, including a serrodyne phase modulator, TE-TM mode converters, and a mode splitter, are integrated on a Z-propagating LiNbO3 substrate of 47 x 5 mm2. Using the fabricated optical IC, phase difference between reference and signal beats has been steadily detected without stabilization against substrate temperature change. The phase difference between two beats was successfully measured, showing an accuracy of +/- 3 nm in the displacement measurement.