Wavelength demultiplexing by chirped waveguide gratings

The performance of a chirped waveguide grating as a wavelength demultiplexer has been investigated. Considerations include TE-TE, TE-TM and TM-TM mode coupling for different incident angles and waveguide parameters. The spectral response of the chirped sinusoidal surface relief grating in the optical waveguide has been studied by means of Local Normal Mode Expansion (LNME) theory to account for the varying thickness of a corrugated waveguide. A matrix technique has been applied to account for the varying grating period, the grating being divided into segments with constant periods and coupling coefficients. A nonslanted first-order diffraction grating is considered and contradirectional coupling between guided modes in phase synchronism at arbitrary incident angles. We show the effect of geometry and waveguide parameters on the performance of the chirped grating as a wavelength demultiplexer. Also, we demonstrate how the bandwidth of the filtering and demultiplexing characteristics and the spectral shift between different polarization modes can be controlled.