The optical properties of photonic bandgap (PBG) structures are highly sensitive to environmental variation. PBG structures thus are an attractive platform for biosensing applications. We experimentally demonstrate a label-free biosensor based on a two-dimensional (2-D) photonic crystal microcavity slab. The microcavity is fabricated on a silicon-on-insulator substrate and integrated with tapered ridge waveguides for light coupling. The Finite-Difference Time-Domain (FDTD) method is used to model the sensor. The resonance of the microcavity is designed to be around 1.58 μm. In order to capture the target biological materials, the internal surface of the photonic crystal is first functionalized. Binding of the targets is monitored by observing a red shift of the transmission resonance. The magnitude of the shift depends on the amount of material captured by the internal surface. Compared to 1-D PBG biosensors, 2-D devices require a smaller amount of target material and can accommodate larger targets. Experimental results are compared with the predictions obtained from the FDTD simulations.
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