Research On The Gain Saturation And Wavelength Bistability Characteristics Of Vertical-Cavity Semiconductor Optical Amplifiers

Optical amplifier is the key opto-electric device in modern optical communications. With the development of vertical cavity devices, a kind of semiconductor optical amplifier based on vertical micro Fabry-Perot resonant cavity, vertical cavity semiconductor optical amplifier (VCSOA), are proposed and widely developed in recent years. Compared with conventional edge-emitting semiconductor amplifiers, VCSOA has the inherent advantage of high fiber coupling efficiency, polarization insensitivity, and easy for fabricating two-dimensional arrays on wafer. It has a wide range of potential applications in optical communication networks, optical signal processing, optical computations.Considering the fact that coupling efficiency into VCSOA and mirror loss is variable about amplifier gain in existing rate equation, which is discommodious to be used, and spontaneous emission factor is ignored during deducting. So from the boundary condition of Fabry-Perot, deducing the relationship between photon density inside cavity and input signal optical power, and utilizing carrier rate equation, the characteristics is researched.The method has been used by Adams to analyze characteristics of edge-emitting semiconductor optical amplifiers. Considering distinction between edge-emitting semiconductor optical amplifiers, two facets have to be taken into account. The multi-quantum-well stacks are placed at the three central peaks of the standing optical wave in order to enhance single pass gain. Gain enhancement factor has to be introduced to show the standing wave effect. The reflectivity of DBR diminishes as a result of diffraction effect when the active cavity area is small. So the boundary condition of Fabry-Perot has to be modified. Based on all the factors, the influence of active cavity area, DBR mirror periods, pump current density and spontaneous emission factor on gain saturation characteristic is investigated.At present, researches aiming at bistable characteristic focus on output power bistable characteristic for VCSOA. From the relationship between average photon density in cavity and input signal optical power, considering connection between carrier density in cavity and effective refractive index, in the paper, wavelength bistable characteristic under reflection mode for VCSOA is first to be investigated numerically. The conditions of wavelength bistability appearance are analyzed and the relationship between the parameter of VCSOA and wavelength bistable loop width is probed into, pump current density, top mirror reflectivity and input optical power.