Two-wavelength planar add/drop WDM filter employing a three-mode coupling Bragg grating

A novel six-port planar waveguide device for adding and dropping two wavelengths from a wavelength division multiplexing singlemode fibre using a single blazed grating is presented. By writing a Bragg grating into a multi-moded core at a particular angle to the waveguide propagation direction, power can be coupled from the fundamental mode into only the backward-propagating higher-order modes, which are then separated using an adiabatic mode splitter. Modelling results indicate that > 99.9% of the power in the fundamental can be transferred to the higher-order modes at their respective Bragg wavelengths, with crosstalk between channels of < -30dB.