Abstract

The machine tools of the next generation will have to make extensive use of distance- measurement interferometers, which will have to be both inexpensive and compact. Integrated optics is well suited for regrouping all the optical processing functions of a Mach-Zehnder interferometer on a single monolithic platform. In contrast to existing silicon-based integrated optic interferometers, our approach involves interfering fields with full transverse confinement. The technology is K⁺ ion-exchange in BK7 glass. The waveguide circuit is first patterned by photolithography in an aluminum layer deposited on the glass plate, then it is immersed in a KNO₃ bath at 380°C for 3 h. The integrated circuit can have a Michelson or a Mach- Zehnder configuration. The measuring beam is collimated in the air, sent back by the moving comer cube, and coupled back into the chip. The reference arm is reflected at the edge of the chip. Both waveguides reach the phase demodulator, where they interfere. The interference section is a wide waveguide carrying approximately 20 modes¹; its length is chosen so as to provide fourfold subimages of the input branches.² The optical power signals at these points are close to quadrature. They provide the movement direction and the displacement with an accuracy of 0.15µm without interpolation at the 633 nm wavelength.

© 1990 Optical Society of America