Design of narrow bandwidth grating-assisted codirectional coupler filter and comparison to the experimental results

A simplified analysis is very important in the design and fabrication of grating-assisted codirectional coupler (GACC) filter because extensive calculations are often required. This is mainly due to a large number of unknown parameters and a very narrow tolerance of the design and fabrication. In this paper, we present a simple method to design an InGaAsP-InP GACC filter having a very narrow bandwidth. The fabricated device has been measured to have a center wavelength of 1530.6 nm and a bandwidth of 1.5 nm. They are in agreement with calculations.