2D Photonic Crystal Cavity-Based WDM Multiplexer

We designed an innovative frequency multiplexer based on contra-directional coupling and standing-wave resonators within a photonic crystal (PhC) structure. Three add-drop filters were cascaded, and the lattice periods of the PhC strips containing the cavities were changed to tune the dropped frequencies, with a very high degree of freedom. Each filter has a 1 nm bandwidth around 1550 nm and the three channels are 10 nm spaced. The variation of the local lattice period is very small, and the mismatch between the two adjacent structures does not affect the beam travelling the bus channel. The PhC structure was analyzed by using the plane wave expansion method and the device performance was investigated with the finite-difference time-domain technique. The transmittance of each drop channel is about 74%, with a non-uniformity between channels smaller than 5%. The overall longitudinal dimension of the multiplexer is less than 20 mum, so that the device is ultra-compact