The analysis of polarization-insensitive characteristics for semiconductor optical amplifiers with tensile strained multiple quantum wells

In this paper, the aims of our study are to analyze the gain of semiconductor optical amplifiers with tensile strained multiple quantum wells and to examine the structure for polarization-insensitive characteristics for the purpose of showing the design guidelines. Since lasers with conventional lattice-matched multiple quantum wells have large optical confinement coefficient and large gain coefficient for TE mode, they are not polarization insensitive. Since the modal gain is the product of the optical confinement coefficient and the gain coefficient, the elimination of polarization sensitivity requires increasing the gain coefficient for the TM mode by applying the tensile strain to the well layer in order to compensate for the difference in the optical confinement factor. Assuming a multiple quantum well structure, the analysis obtains the strain distribution over the structure and an envelope function of the wave function and calculates the gain using a density matrix method by electron relaxation effect. It includes the band mixing effect of valence bands. As a result, a structure with little modal gain difference over a wide range at 1.55-μm wavelength has been designed. Also, as a result of examining the effect of deviation from the designed values, it has been found that the variation in the material composition (amount of strain) has a larger effect on the modal gain difference than the variation in the quantum well thickness.