Waveguide input grating coupler for wavelength-division multiplexing and wavelength encoding

We demonstrate the wavelength-division multiplexing (WDM) and wavelength-encoding capability of input waveguide grating couplers. The couplers are designed to have a predetermined wavelength response in addition to their conventional function of coupling an incident beam from, e.g., an optical fiber into a planar waveguide. The first example shows the WDM function: separating each of four input wavelengths into a different focus position in the waveguide. The second example shows wavelength encoding: translating a certain wavelength into a desired configuration of focus positions that is different for four different input wavelengths. The couplers were fabricated in an InP waveguide for /spl sim/1550-nm wavelength and the separation between the wavelengths was 10 nm. A WDM coupler with a narrower channel separation of 2 nm was also fabricated and successfully demonstrated.