Investigation On The Polarization Switching Characteristics In A 1550 Nm VCSEL Under Circularly Polarized Optical Injection

The nonlinear dynamics including optical switching and bistability occurring in edge-emitting semiconductor lasers(EELs) and vertical-cavity surface-emitting lasers(VCSELs) are interesting phenomena and have attracted extensive attention for their potential applications in optical interconnects and all-optical signal processing. Compared to the EELs, VCSELs have some unique advantages such as reduced manufacturing costs, low threshold current, larger modulation bandwidth, single longitudinal-mode operation, circular output beam, etc. More specially, polarization switching(PS) and its associated polarization bistability(PB) in VCSELs can be easily observed due to the instability of output polarization in VCSELs induced by the cylindrical geometry of active region and the weak anisotropy of gain material. PS in VCSELs can be obtained through continuously varying the biased current or device temperature of VCSELs, or introducing an external disturbance such as current modulation, optical feedback, or optical injection. Optical injection, which is commonly introduced to achieve PS, generally includes three types: orthogonal optical injection, variable-polarization optical injection, and circularly polarized optical injection(CPOI). PS characteristics in VCSELs subject to orthogonal optical injection or variable-polarization optical injection have been extensively investigated. However, PS characteristics in VCSELs with CPOI are rarely reported.In this letter, we report an experimental investigation on the PS characteristics in a 1550 nm VCSEL subject to CPOI. The results show that, under different biased current, the solitary 1550 nm VCSEL can operate at y mode, x mode, or two polarization components(PCs) coexisted. For the case that the solitary 1550 nm VCSEL operates at y mode, type I PS(from higher-frequency PC to lower-frequency PC) can be observed after introducing CPOI with a proper injected power Pinj and detuning frequency Δν1(= νinj – νx, νinj and νx are the frequency of the injected light and the x mode in the solitary 1550 nm VCSEL, respectively), and the curve of the minimal injected power Pinj min required for type I PS versus Δν1 exhibits a minimum locating at the negative frequency detuning region. For the solitary 1550 nm VCSEL operating at x mode, type II PS(from lower-frequency PC to higher-frequency PC) can also be observed via CPOI under suitable injected power Pinj and detuning frequency Δν2(= νinj – νy, νinj and νy are the frequency of the injected light and the y mode in the solitary 1550 nm VCSEL, respectively), and the curve of the minimal injected power required for type II PS versus Δν2 exhibits two minima. One locates at negative frequency detuning area, and the other locates at positive frequency detuning area. Lastly, the mappings of nonlinear dynamical states are given in the parameters space of the injected power and frequency detuning.