Reflection mode 2-dimensional photonic crystal slab waveguide based micro-pressure sensor

Photonic crystals (PhCs) have recently been the focus for the developing micro-and nano-optical sensors, due to its capability to control and manipulate light on planar devices. This paper presents a novel design of micro-optical pressure sensor based on 2-dimensional PhC slab suspended on Si substrate. A line defect was introduced to the PhC slab to guide and reflect light with frequency in the photonic bandgap in the plane of the slab. The structure, with certain surface treatment, can be used in miro-scale pressure catheters in heart ablation surgeries and other biomedical applications. The working principle of the device is to modify light reflection in the PhC line defect waveguide by moving a substrate vertically in the evanescent field of the PhC waveguide. Evanescent field coupling is the critical step that affects light transmission and reflection. High resolution electron-beam lithography and isotropic wet etching have been used to realize the device on the top layer of a Si-On-Insulator (SOI) wafer. The PhC slab is released by isotropic wet etch of the berried oxide layer. The output reflection spectrum of the device under different pressure conditions is simulated using 3-dimensional finite difference time domain (FDTD) method. The result showed that when the PhC slab is close enough to the substrate (less than 400 nm), the reflected light intensity decreases sharply when the substrate moves towards the PhC slab. Mechanical response of the sensor is also studied.