Optimization and applications of planar silicon-based photonic crystal devices

Very low propagation losses in straight planar photonic crystal waveguides have previously been reported. A next natural step is to add functionality to the photonic crystal waveguides and create ultra compact optical components. We have designed and fabricated such structures in a silicon-on-insulator material. The photonic crystal is defined by holes with diameter 250 nm arranged in a triangular lattice having lattice constant 400 nm. Leaving out single rows of holes creates the planar photonic crystal waveguides. Different types of couplers and splitters, as well as 60, 90 and 120 degree bends have been realized. We have designed and fabricated components displaying more than 200 nm of useful bandwidth around 1550 nm. Design strategies to enhance the performance include systematic variation of design parameters using finite-difference time-domain simulations and inverse design methods such as topology optimization. We have also investigated a new device concept for coarse wavelength division de-multiplexing based on planar photonic crystal waveguides. The filtering of the wavelength channels has been realized by shifting the cut-off frequency of the fundamental photonic band gap mode in consecutive sections of the waveguide. Preliminary investigations show that this concept allows coarse de-multiplexing to take place, but that optimization is required in order to reduce cross talk between adjacent channels and to increase the overall transmission. In this work the design, fabrication and performance of these planar photonic crystal waveguide components are reviewed and discussed.