Passive aligned assembly of an integrated optical displacement sensor based on a reflective Mach-Zehnder interferometer with a 3 x 3 directional coupler

An integrated optical displacement sensor based on a reflective Mach-Zehnder interferometer (MZI) was developed. The sensor features a low-loss autocollimation measurement head fabricated using a 62.5-mu m gradient index fiber as lens, which separates the incoming and reflected light. The mounting of the lenses and the fiber coupling were performed using a passive alignment assembly technology. Using a 3 x 3 directional coupler (DC), the direction of the phase shift can be resolved. The measurement head exhibits low losses compared to a conventional DC to separate the reflected light. A measurement range of 225 mu m could be achieved in good agreement with the expected 230 mu m. The results show a good agreement between simulation and measurements. Using basic measurement electronics, movements of 2 nm can be resolved, while a resolution of <1 nm is expected using optimized measurement equipment. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)