Polarization Switching And Bistability In A 1550 Nm VCSEL Subject To Orthogonal Optical Injection With Time-varying Injection Power

Due to weak anisotropy of the cavity and gain medium in vertical cavity surface emitting laser(VCSEL),there may be two orthogonal linearly polarized lights along the lattice direction in VCSEL.Under external disturbances,two special dynamics:polarization switching(PS)and polarization bistability(PB)may emerge.PS and PB in VCSEL have shown some promising applications,including optical storage,all-optical switching,and all-optical information conversion,and so on.Optical injection is a kind of external disturbance with good controllability,which can be introuded to induce PS and PB effects.In recent years,the PS and PB phenomena induced by optical injection have been extensively studied,but the influence of the sweep rate of the injection parameter have not been considered in experimental investigations.There are only a few investigations theoretically researching the PS and PB characteristics in VCSEL subject to optical injection with time-varying injection parameters.The PS and PB characteristics induced by time-varying injection power can be applied to the field of high-speed optical information processing.To our knowledge,no relevant experimental results about the PS and PB characteristics of VCSEL under orthogonal optical injection with time-varying injection power have been reported.In this work,we experimentally demonstrate PS and PB characteristics in a 1550nm VCSEL under orthogonal optical injection with time-varying injection power,and the influences of the power sent to a Mach-Zehnder modulator(MZM)P₀?frequency detuning???the modulation frequency f_m on the performances of PS and PB are analyzed.In order to obtain the injection light with time-varying power,the triangular electric wave from the arbitrary waveform generator is used to modulate the MZM in the experiment.Within the period 1/f_m of the triangular wave,the output power of MZM changes with time and undergoes a gradually increasing and then gradually decreasing procedure.The experimental results demonstrate that under suitable parameters,PS and PB can be observed within a region of P₀,and the minimum and maximum within this region are labeled as P_0,min and P_0,max,respectively.As P₀ increases from P_0,min to P_0,max,the width of the hysteresis loop gradually decreases.Under different??(=v_inj-v₀,v_injis the frequency of the injection light,v₀ is the frequency of the suppressed polarization mode of the solitary 1550 nm VCSEL),the range of P₀ required to cause the PB characteristic is different.With the increase of??from a negative value to a positive value,both P_0,min and P_0,max decrease firstly and then increase.For??=1 GHz,P_0,minand P_0,max reach their minimums.In addition,with the increase of f_m,the width of the hysteresis loop increases rapidly at the beginning,then increase slowly,and finally tend to saturation.