Investigation On Polarization Switching And Bistability In A 1550 Nm Vertical-cavity Surface-Emitting Laser Under Parallel Optical Injection

Compared with conventional edge-emitting semiconductor lasers?EELs?,vertical-cavity surface-emitting lasers?VCSELs?possess some unique features including reduced manufacturing costs,low threshold current,high coupling efficiency to optical fibers,single-mode operation,and easy fabrication of two-dimensional arrays,etc.,and therefore they are widely used in the fields of optical communication and optical storage.Due to weak material and cavity anisotropies,VCSELs can lase at two polarization modes whose directions are along two orthogonal crystal axes,and the polarization mode with stronger power is named as the dominent mode.Through changing the operation parameters or introducing an external disturbance such as photoelectronic feedback,optical feedback,current modulation,or optical injection,the dominent mode can switch between two orthogonal polarization modes,i.e.,polarization switching?PS?occurs.Moreover,if the value of varied parameter required for generating PS is dependent on its variation route,polarization bistability?PB?can be observed.The phenomena of PS and PB in VCSELs have received considerable attention owe to their potential applications in optical interconnects,optical information processing,and all-optical switching,etc.In recent years,the PS and PB characteristics in VCSELs under orthogonal optical injection and variable optical injection have been investigated extensively,and the PS characteristics in VCSELs under parallel optical injection have also been reported in large numbers,but the research on the PB characteristics is lacking.Under the condition of parallel optical injection,the controllable parameters are the injected optical power and frequency.Therefore,by continuously changing these two parameters,PS may appear in VCSELs,and changing the two parameters along different routes may observe PB phenomenon.At present,the PB characteristics in a 1550 nm-VCSELs induced by the injected optical power had reported.But there are few reports on the PB characteristics in a 1550 nm-VCSELs induced by injected optical frequency.Only our group has carried out preliminary theoretical research work,and the relevant experimental research results have not been reported.Based on this,in this paper,we experimentally investigate the frequency-induced PS and PB characteristics in a 1550 nm-VCSEL under parallel optical injection.Moreover,the influences of injection power and biased current of the laser on the frequency-induced PS and PB have been analyzed.The results show that,for a 1550 nm-VCSEL under parallel optical injection with frequency detuning??(=?_inj–?₀,where?_injnj is the frequency of injection light and?₀ is the frequency of dominant polarization mode of the solitary 1550 nm-VCSEL),type I PS?the dominant polarization mode switches from Y polarization mode with a shorter wavelength to X polarization mode with a longer wavelength?and type II PS?the dominant polarization mode switches from X polarization mode to Y polarization mode?can be observed through continuously scanning the frequency of injection light.Moreover,the values of??required for generating PSs are dependent on the variation route,namely frequency-induced PB phenomenon occurs.In the region with negative??,there exist two hysteresis loops,whose widths are seriously influenced by the injection power and the biased current.