2D photonic crystal cavity-based WDM multiplexer

We designed a multiport two-dimensional (2D) photonic crystal (PhC) multiplexer based on contra-directional coupling and standing-wave resonators. The device is composed of PhC filters with up to 12 cavities in the same micro-patterned structure: adjacent strips with different periods contain a single cavity, and by selecting the proper lattice constants we tune the dropped frequency of each cavity. Each filter has 1.16 nm bandwidth, at a central wavelength 1550 nm, and the channels are 10 nm spaced. The variations in the local lattice period are very small, and the mismatch between two adjacent structures does not affect the propagation of the beam in the bus channel. The PhC structure has been analyzed by using the plane wave expansion method and the device performance has been investigated with the finite-difference time-domain technique. The transmittance of each drop filter is about 74%, with a non-uniformity between channels less than 5%. The overall longitudinal dimension of the multiplexer is less than 20 μm.