Semiconductor Dispersion Compensator Based on Two Vertically Coupled Asymmetric Ridge Waveguides

Abstract

A semiconductor dispersion compensator based on two vertically coupled asymmetric InGaAsP/InP ridge waveguides was designed and fabricated. This device consists of a dispersion-compensation region sandwiched between two mode converters. Two types of coupled modes, symmetric and antisymmetric, simultaneously exist in the dispersion-compensation region and have significant group-velocity dispersion (GVD) with opposite signs, making shrinkage of the device possible. The mode converters serve as mode selectors, exciting only the coupled mode needed for dispersion compensation with a high degree of efficiency. The compression of a 5.4-ps down-chirped pulse was demonstrated by the device; the pulse compression ratio was 55%. A theoretical study showed that the observed pulse compression was explained well by the dispersion compensation caused by the GVD of the coupled modes, and that the selectivity of the mode converter was approximately 80% for the symmetric coupled mode.