Proposal of new narrow-band wavelength filter using grating-assisted vertical contra-directional coupler

We propose a novel wavelength filter using a grating-assisted vertical contra-directional coupler for an add and drop multiplexer (ADM). It is predicted from our calculations that the bandwidths of the filter can be narrow less than 1 nm and easily controllable by means of the optimization of the device parameters. We have successfully fabricated the InP-based semiconductor filter and also demonstrated filtering bandwidth as narrow as 0.7 nm which is consistent with our calculations.