High-Q mid-infrared 1D photonic crystal waveguide resonator in SOI

1D photonic crystal waveguide resonator has been designed for mid-IR wavelengths. The distinguishing feature of periodic nature of photonic crystals helps to achieve Bragg scattering, which allows waves that meet certain criteria to pass through. Using this principle, we have designed high-Q photonic crystal waveguide cavity for wavelengths centered at 3.8 μm in silicon-on-insulator (SOI), as it is a promising material for mid-IR exhibiting low-loss for wavelengths up to 4 μ m. The design process and optimization has been achieved by performing 3D FDTD simulations using a commercial software. 400 nm thick SOI is used to design well-known L5 cavity. It consists of circularly shaped air-holes placed in Si slab. Circularly shaped cells have been preferred to achieve fabrication tolerance in contrast to other shapes. A line defect is created by removing the five holes from center. A dipole source is place at center to which the cavity is exposed. Two step iterative process has been used to optimize the design and achieve high-Q. First the radius parameter has been optimized which is followed by optimization in period. Finally, an inner air-hole sweep has been performed to maximize the Q factor. High-Q factor of 99,359 has been achieved at 3.9 μm wavelengths. Our design is consistent with the available lithography for achieving integrated mid-IR sensors in SOI. Secondly, monolithic integration can be achieved using single etch process in Multi-Project-Wafer (MPW) run. These sensors can be designed for different gas sensing applications depending upon the wavelengths of gases.