TUNABLE PRESSURE AND TEMPERATURE SENSOR BASED ON 2D GaAs PHOTONIC CRYSTAL

Abstract

Photonic crystals (PhCs) offer unprecedented control over the propagation of light through the existence of a photonic band gap (PBG)—a range of frequencies that is forbidden inside the periodic dielectric lattice. When the optical properties of the constituent material are made to depend on an external stimulus, the band gap, and consequently the optical response of the crystal, becomes tunable, which is the operating principle of a photonic-crystal sensor. This dissertation presents the design and computational analysis of a tunable pressure and temperature sensor based on a two-dimensional (2D) Gallium Arsenide (GaAs) photonic crystal. Two complementary device geometries are investigated. For pressure sensing, a 2D square lattice of GaAs rods (ε = 12.96, r = 0.2a) in an air background is modelled using the Plane Wave Expansion (PWE) method implemented in MIT Photonic Bands (MPB). A wide Transverse-Magnetic (TM) band gap is obtained between the normalized frequencies 0.286 and 0.421. The elasto-optic effect is modelled as a linear increase of the rod refractive index with hydrostatic pres sure, and the resulting systematic red-shift of the mid-gap wavelength yields a pressure sensitivity of 2.171 nm/GPa. For temperature sensing, a finite hexag onal two-dimensional photonic-crystal ring resonator (2DPCRR) is analysed using the Finite-Difference Time-Domain (FDTD) method implemented in Meep. The thermo-optic effect (dn/dT = 2.3×10−4◦C−1) shifts the resonant transmission peak linearly over the range 0–360◦C, giving a temperature sensitivity of 27.9 pm/◦C. A complementary complete-PBG analysis of a triangular lattice confirms the linear thermal tuning trend with a mid-gap sensitivity of 0.0704 nm/K. All simulations were carried out in Python on an Ubuntu (WSL) environment using the open-source MPB and Meep libraries. The results establish GaAs as a high-contrast, highly linear platform for near-infrared photonic-crystal sensing and provide a foundation for future defect-engineered, high-Q resonant sensor designs.