Design of a Grating-Assisted Lateral Directional Coupler by Impurity-Induced Quantum-Well Intermixing of InGaAs/GaAs

An asymmetric waveguide grating-assisted coupler, which is suitable for a coarse wavelength division multiplexing system, based on a quantum-well intermixing process in InGaAs/GaAs, has been designed. The proposed device processing is similar to that used in nominal microelectronics processing. The device has been modeled from the first principle of refractive- index change due to F-implantation and anneal. The coupler has been analyzed by quasi-static effective index as well as finite difference methods in conjunction with an orthonormal-mode beam propagation method. A power-coupling ratio of ~90% at a wavelength of 1.51 mum with a coupled wavelength bandwidth of ~22 nm has been obtained. The coupler lengths are within a few millimeters, and the device is suitable for multiwavelength integration.