Displacement sensing using evanescent tunneling between guided resonances in photonic crystal slabs

Using both analytic theory and first-principles finite-difference time-domain simulations, we introduce a displacement sensing mechanism using photonic crystal slabs coupled in the near-field regime. In this regime, the operating characteristics are completely different from conventional resonant optical sensors, and high sensitivity can be obtained without the use of highly reflecting mirrors. This enables high displacement sensitivity combined with low sensitivity to wavelength and to structural disorders, thereby simplifying operation and fabrication of high-sensitivity displacement sensors.