Micro-Displacement Sensor With Large Dynamic Range Based on Photonic Crystal Co-Directional Coupler

A novel micro-displacement sensor based on a photonic crystal (PhC) co-directional coupler and its sensing technique are presented. The coupler consists of a fixed and a movable PhC segments. Due to the translational symmetry of the PhC structure, this sensing technique is valid for a large displacement on the order of na (n is an integer, and a is the lattice constant of the PhC). After optimization, the outputs of the sensor are approximately sine functions of the displacement, thus it has the potential to achieve high resolution using a subdivision approach. These two characteristics ensure the large dynamic range of the micro-sensor. The properties of the micro-displacement sensor are analyzed using the coupled-mode theory and simulated using the finite-difference time-domain method