Bent waveguide couplers for (de) multiplexing of arbitrary broadly-separated wavelengths using two-mode interference

A novel technique is presented for the optimization of waveguide couplers configured as broad-band wavelength (de) multiplexers. We show that bending the coupler to an appropriate radius modifies the beat lengths at each wavelength, so that two-mode interference can be used to achieve efficient multiplexing performance with a compact device. Calculated and experimental results for such a device implemented in a silicon oxynitride deeply-etched rib waveguide system are presented. Almost 20-dB and 14-dB contrast are achieved in the demultiplexer configuration at 1550-nm and 850-nm wavelengths, respectively, with a coupler only 145 μm long.