Optical gain analysis of polarization-insensitive semiconductor optical amplifiers with strained quantum wells

Abstract

The importance of semiconductor optical amplifiers (SOAs) as key components in optical communications and integrated optics, covering a wide large of applications for the 1550- and 1300-nm optical windows, has grown in recent years. Polarization sensitivity of the optical of gain in SOAs is an issue that needs to be addressed to improve their performance and enhance their suitability for monolithic integration. We report on optical gain spectra measurements of polarization-insensitive SOAs that have been designed in our laboratory. Polarization insensitivity has been achieved employing a combination of both tensile and compressively strained quantum wells in the active layer of an InGaAsP/InP - based device. The SOA chips were characterized with a continuous wave input signal of a tunable laser at wavelengths between 1430 and 1600 nm. The gain saturation properties were experimentally investigated in order to determine how well the amplifier maintains its polarization insensitivity in the saturation regime. The experimental results were compared with theoretical values. The optical gain dependence on the current density and the length of the amplifier has been studied. The calculated device gain based on amplified spontaneous emission (ASE) spectra measurements was compared with the amplified signal measurements. Broad area lasers with lengths ranging from 500 to 1500 μm were also fabricated and tested to check the material quality and obtain information about the optical gain uniformity. Our amplifiers have an unsaturated gain of 22 dB and in the saturation regime the maximum observed gain difference between the TE and the TM mode gains was 0.5 dB within a spectral width of 60 nm. The measured 3 dB saturation output power was 6 mW.