Planar-integrated interferometric sensor with holographic gratings

Planar integration of various optical systems appears for some years as a way to reduce alignment problem and to build small size, robust and monolithic devices. An original planar integrated interferometric sensor is presented in this paper. It is based on the separation and control of polarization states in a substrate mode holographic system in order to obtain the optical path difference between two scanning spots. A unique planar system is used for projection of the spot and for recombination of probe beam reflected on the tested surface. The monolithicity and the differential nature of the element lead to a very good insensitivity to external vibrations. The sensor is a multilayered structure composed of a reflective polarizing holographic element sandwiched between two planar substrates. Probe beams are coupled in and out of the system by diffraction on a reflective Substrate Mode Hologram that constitutes a fourth layer. These two types of holographic elements are recorded in high index modulation photopolymer: Omnidex(TM) HFR-600 from DuPont. Design, realization and application are demonstrated and discussed.