  This paper proposes a novel multifunctional sensing platform based on
multimode planar photonic crystals (PPCs). We analytically and numerically
demonstrate that the reflection spectrum of PPCs exhibits multiple high-Q
resonant modes, and the fundamental and higher-order modes respond
distinctively to external mechanical and thermal perturbations, rendering the
PPCs superior capability for detection and discrimination of multiple
parameters. We further demonstrate simultaneous pressure and temperature
sensing with a PPC sensor. Other advantages of PPC sensors include on-chip
integration and wafer-scale fabrications.
