# Photonic crystal waveguide polarization filter

Polarization control is one of the central themes in integrated silicon photonics. Different polarization modes not only allow for more information-carrying channels but also enable a wide range of applications given their different characteristics. For example, waveguide TE modes usually have better confinement and thus they are less prone to sidewall roughness. TM modes, on the other hand, have a larger penetration depth into the top and bottom claddings, which makes them suitable for sensing applications. As a result, integrated silicon photonic filters that selectively transmit or block certain polarization are very useful.

This example demonstrates the modeling of a compact TM-pass polarization filter based on photonic crystal waveguide. The photonic crystal is an air-bridged silicon slab with periodic air holes arranged in a triangular lattice. It is possible to achieve a TM-pass but TE-block device within a frequency range by utilizing bandgap engineering and index guiding mechanism. The design parameters adopted from Chandra Prakash and Mrinal Sen , “Optimization of silicon-photonic crystal (PhC) waveguide for a compact and high extinction ratio TM-pass polarization filter”, Journal of Applied Physics 127, 023101 (2020) (opens new window) are optimized for the telecom frequency to have a ~-0.5 dB TM transmission and ~-40 dB TE transmission.

To view the full example in Python, please click here (opens new window).

To view the example in our web GUI, please click here (opens new window).