Study On Balancing Gain Spectrum And Refractive Index Change Spectrum Of Mixed Strain Multiple Quantum Well With Low Polarization Dependence

All-optical communication technology can solve the bottleneck problem of optical-electrical-optical exchange in the current optical communication system.It is a research hotspot in the current optical communication field.The key devices of all-optical networks include optical switches and wavelength converters,etc.The carrier-induced refractive index change is the basis of the above-mentioned devices.At the same time,these devices also need gains during operation.In addition,such devices also need to be insensitive to the polarization state of incident signal light.Therefore,this paper studies balancing gain spectrum and refractive index change spectrum of mixed strain multiple quantum well with low polarization dependence.In this paper,the theoretical analysis model of quantum well material gain and refractive index changes is established.First,based on Bloch’s theorem and k.p method,the energy band theory is given.Then consider the heavy hole zone,light hole zone and spin-orbit split zone,using k.p method and effective mass theory to analyze the effect of strain on the energy band.Then the finite difference method is used to solve the energy eigen equation.Then,the non-uniform distribution of the injected carriers in the multiple quantum well is given,and the calculation model of the optical confinement factor is analyzed.Then the optical gain is obtained according to the Fermi distribution function and the momentum matrix element.Finally,considering the effects such as band filling,Kramers-Kronig transformation is used to obtain the refractive index change of the quantum well material.Based on the above theoretical model,this paper calculates the quantum well gain and refractive index changes.The effects of strain and well width on the gain and refractive index change spectra of the TE and TM modes of a single quantum well are studied,and the physical mechanism is analyzed.Then considering the optical confinement factor of the waveguide and the non-uniformity of the carrier concentration distribution in the multiple quantum well,a multi-parameter matching method is proposed:using two types of quantum wells with different well widths to make the gain and refractive index change of the TE and TM mode larger,setting appropriate strains for the two types of wells to move the gain spectrum and refractive index change spectrum to the working band（C-band）,adjusting the number of two types of wells to reduce the polarization dependence,setting the barrier thickness and the waveguide layer thickness appropriately to increase the optical confinement factor and reduce the polarization dependence.Based on the method above,a low-polarization quantum well structure that can balance the gain spectrum and the refractive index change spectrum in the C-band（1530～1565 nm）is designed.Finally,the effect of carrier concentration is analyzed and the appropriate carrier concentration is selected.When the carrier concentration is 3.22×10²⁴m^-3,the overlap region area of3d B spectrum width of the two spectra of the TE and TM mode are 84.81 nm/cm and74.50 nm/cm,respectively,and the gain polarization dependence and refractive index polarization dependence are maintained at within 4%and 6%.The results of this paper will help the optimal design of related devices in the all-optical network in the future.