M-PPM Fast Delay Unit Based on Silicon-on-Insulator Coupled Resonator Optical Waveguides

A discrete delay system, that consists of N cascaded stages of coupled resonator optical waveguides (CROWs), is proposed to be implemented in M-ary pulse-position modulation (M-PPM) techniques. The cascaded stages allocate delay times of an emerging optical pulse to be one of 2 ^N possibilities. The number of ring resonators in a CROW intermediate stage is a multiple of that in the preceding stage and provides two different time delays, which are multiples of that in previous stage. The system design is developed analytically and time delay simulation is performed to validate our theoretical analysis. Both 4- and 8-PPM schemes with one pulse transmitted in each frame are used in our simulation to ensure allocating the propagating optical pulse in the convenient position. Both theoretical and simulation results are in good agreement in characterizing the device parameters and performance.