| Vertical-cavity surface-emitting laser(VCSEL)is a new type of semiconductor laser with emitting light from the device surface.Due to the special structure and fabrication processing,the VCSEL possesses a number of unique advantages,such as low threshold current,high coupling efficiency to optical fiber,dynamical single-longitudinal mode operation,low costs,easy-integration into high density two-dimensional arrays,and in the future it will possibly replace the conventional edge emitting laser(EEL)in the key applications of optical communication,optical information processing,parallel optical interconnection,and so on.In recent years,research works have demonstrated that,under suitable external optical or electrical perturbation,VCSEL can exhibit rich nonlinear dynamics including periodic pulsing,frequency locking,double-periodic pulsing,and chaotic pulsing,etc.Besides,the symmetric space structure and weak anisotropy of gain medium in the VCSEL will induce the complex polarization characteristics.Two special polarization dynamics including polarization switching(PS)and polarization bistability(PB)can also be induced as a result of introduction of external optical or electrical perturbation.At present,the studies on the polarized dynamics characteristics open up a new way for the application of VCSELs in the field of all-optical switching,all-optical storage and all-optical information conversion.Meanwhile,it is of great practical significance to understand generation and evolution of nonlinear dynamics in those systems,which contribute to improving the performance of VCSEL-based devices.So,this thesis performs a detailed investigation on nonlinear dynamics and polarization characteristics of the optical injection VCSEL and optoelectronic feedback VCSEL.The purpose is to deeply analyze the static and dynamic characteristics in the VCSEL under different perturbative conditions,to reveal the external manifestation and intrinsic physical mechanism of nonlinear behaviors,and also to seek appropriate ways for controlling the dynamics,PS,and PB.In details,the main results of our studies are summarized as follows:1.Based on the spin flip model of the VCSEL,the nonlinear dynamical characteristics of the VCSEL subject to orthogonal optical injection have been explored numerically.The generation and evolution of nonlinear dynamics for two orthogonal polarization modes in the VCSEL are studied for different injection parameters,and nonlinear dynamics distribution in the injected parameter space is also determined.At the same time,the related analysis shows that the power-induced PS may occur when the appropriate injection conditions are satisfied,and the occurrence of PS is normally accompanied by the competition or coupling between two orthogonal polarization modes.In the injected parameter space,the injected power required for PS and nonlinear dynamic distribution will exhibit the obvious variation with the modification of the bias currents.Hence,the nonlinear dynamical state of the optical injected VCSEL can be effectively controlled by reasonably adjusting the bias current,injected power,and frequency detuning.In addition,a master-slave VCSEL chaotic system is proposed for investigating theoretically the evolution of bandwidth and dynamic complexity of the chaotic signal.In the large positive or negative frequency detuning,it is found that the high injection power is favorable for extending the bandwidths of the chaotic signal.Further analyses show that,the dynamic complexity of chaos can be obtained by selecting the appropriate system parameters which have a relatively large overlap with the case for the wide chaotic bandwidth.In this optimized parameter range,the system can produce the chaotic signal with wide bandwidth and high complexity.2 The physical mechanism and evolution of power-induced PS and PB are investigated theoretically in a 1550 nm-VCSEL subject to the orthogonal optical injection.It shows that the polarization characteristics of the VCSEL presented are closely related with the varied routes of injected power,and two different types of PB can be obtained under certain parameter condition.When the injected power varies along different routes,the study on the nonlinear dynamic distribution of two orthogonal polarization modes reveals the change regulation of the forward PS,reverse PS,and PB.Further research shows that,for the relatively low bias current,the PB can be found only at the large frequency detuning and the corresponding hysteresis widths in positive and negative frequency detuning ranges exhibit different changing trends,respectively.On the other hand,for the large bias current,the changing trend of hysteresis width at large frequency detuning range is similar to the case of the low current,but a special PB with no reverse PS is achieved.According to the physical conditions required for the occurrence of PB,the regions for the two kinds of PB are determined in the parameter space of the bias current and frequency detuning.In addition,considering the rich and flexible perturbation of variable polarization optical injection,an experimental system for a 1550 nm-VCSEL subject to this perturbation is set up to deeply explore the influence of polarization angle on characteristics of power-induced and frequency-induced PB.The studied results show that,under the determinate parameter condition,there exists a polarization angle threshold of injection light for observing power-induced PB,and the value of threshold angle will become greater with the increase of the frequency detuning.Within the suitable parameter range,a smaller polarization angle of injection light and larger bias current will be more lucrative to obtain the power-induced PB with wider hysteresis width.For the frequency-induced PB,the variation of polarization angle also obviously affects the hysteresis width.Additionally,by scanning the polarization angle of injection light along different routes,a polarization angle-induced PB can be observed in the VCSEL and the corresponding hysteresis width has a direct relationship with the injection power,frequency detuning,and bias current.Consequently,by appropriately selecting polarization angle of injection light and other controllable parameters,the system can realize the flexible control to different types of PB.3.An experimental system is constructed to investigate the nonlinear dynamical characteristics of a 1550 nm-VCSEL subject to the negative optoelectronic feedback.The results show that both optoelectronic feedback strength and bias current have significant influences on dynamical behaviours of the VCSEL.The VCSEL subject to negative optoelectronic feedback can exhibit rich nonlinear dynamical states such as regular pulsing,quasiperiodic pulsing,and chaotic pulsing under different parameter conditions.Through measuring a mapping of dynamic states in the parameter space of bias current and feedback strength,it is found that the laser normally operates at stable state for the case of small bias current and weak optoelectronic feedback.For the case of higher bias current,as the feedback strength increases,the dynamical behaviours of the laser follow a repeated route(from regular pulsing to quasiperiodic pulsing and to regular pulsing)to chaotic pulsing state.When the bias current is increased to a certain level,the dynamical behaviours of the laser follow a repeated evolution route(from regular pulsing to quasiperiodic pulsing and then to chaotic pulsing)with the increase of feedback strength.Under several external perturbations,a VCSEL can exhibit more diverse dynamical behaviours and the dynamical distribution in the parameter space is different from the case of single external perturbation.How to realize the effective control of the dynamical behaviours in the VCSEL subject to multi-perturbations is the key in practical applications.So,we perform an experimental investigation on nonlinear dynamical characteristics of a 1550 nm-VCSEL simultaneously subject to negative optoelectronic feedback and orthogonal optical injection.It is shown that the mixed perturbations increase the freedom degree of experimental system,and the nonlinear dynamics in this system is more complex than that of single optical injection.For the certain optical injection,increasing the optoelectronic feedback strength leads to the gradual extension of parameter region corresponding to quasiperiodic pulsing and chaotic pulsing,and the parameter region for periodic pulsing and injection locking will decrease.Meanwhile,the injected strength required for the occurrence of PS also exhibits the obvious variations.By reasonably adjusting the perturbation parameter,the VCSEL can generate the rich and controllable nonlinear dynamics.4.Based on the negative optoelectronic feedback 1550 nm-VCSEL experimental system,the physical mechanism and the evolution of the dynamic bistability induced by the bias current and optoelectronic feedback are studied in detail.The experimental results show that when the bias current or optoelectronic feedback strength vary along different routes,the evolutions of nonlinear dynamics in the VCSEL under different initial conditions are not entirely consistent and can exhibit two types dynamic states which result in the current-and feedback-induced state bistability.The generation of state bistability is determined by the nonlinear effects in the VCSEL and the high sensitivity of the dynamics to the initial conditions.Further studies are to identify the parameter regions for the occurrence of current-induced or feedback-induced state bistability,and the complexity features of dynamic state can characterize the evolution of state bistability. |
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