Study On Mode Instabilities And Synergetic Properties Of Self-organized Feedback Fiber Ring Lasers

Aiming at meeting the rigorous demands in applications of the major projects, thisthesis studies the instabilities of a new type of self-organized feedback fiber ring lasers,and searches the effective methods to stabilize the lasers through a full understanding onits instability properties. This research involves some complex physical process such asthe nonlinear dynamics and chaos, and provides an ideal physical model and anempirical route for the synergetic study on the complex systems that contain theself-organized feedback mechanism.Self-organized feedback fiber ring lasers possess excellent coherence and tunability.However, its mode hopping phenomena, especially the occurrent and sustained modeshopping, have great impacts on the engineering applications. It is hard to handle theinstability and state jump problems in a complex system by traditional electromagnetictheory of lasers. In this thesis, the Haken’s synergetic method is used to study thegeneration and the breakdown of the system cooperation, which is aimed to reveal thedeep physical insight of the laser mode hopping, by treating the lasers as a complexsystem with the mode intensities as the order parameters. However, the Haken’s lasermodel can not be utilized to directly solve the instability problems of the objective lasersystem, for lacking of the self-organized feedback mechanism. In this thesis, bystarting from the Maxwell-Bloch equation which describes the processes of theinteraction of light with two-level system, we derive the laser equation which containsthe feedback mechanism provided by the erbium-doped saturable absorberself-organized fiber grating based on the real laser structure. The newly derived modelpossesses the interaction mechanism between the self-organized modes and their livingenvironment, which we call the self-organized feedback mechanism and it is a generalproperty in many important complex systems. Furthermore, this self-organized feedbackmechanism can behave two opposite effects such as maintaining the cooperation anddestroying the cooperation. Further analyse on the backscattering light at the unmatchedfusing point show that a parasitic gain grating is formed in the gain media and it playsan important role in weakening the major oscillating mode which possess the superiority,and in undermining the current cooperation. Based on these analyses, we establish a fullset of the theoretical model and laser equations, which contain both of the positive andnegative self-organized feedback mechanism. This equation not only describes thephysical mechanism of the breakdown of the laser cooperation, but also is a perfectphysical interpretation on the failure of the “Matthew Effect”. According to thesimulation results of the new laser model, an optimized design is provided and theperformance improvement is achieved. We also develop a novel method to measure thesaturable absorber self-organized fiber grating, and a set of tools to monitor the change of the laser modes, which is helpful to confirm the correctness of the laser model andthe effectivity of the improvement of the laser stability.The state changes of the practice self-organized feedback fiber ring lasers are theresults of associated influences of multiple factors. We employ the state space methodof the complex systems to map the stability state versus both the pump parameter andthe relative cavity length drift, and the results show that the system stability variesgreatly with laser structures. This method provides a powerful tool for the analysis ofthe laser stability in engineer applications and the results possess abundance materialsfor the synergetic study on the complex systems.The self-organized feedback fiber ring lasers in this thesis belong to the class Blasers, and will not generate chaos without additional degrees of freedom according tothe traditional chaos theory. The status of the order parameter of this laser system underspontaneous sustained mode hopping state is measured, and the phase spacereconstruction of the measured data show chaotic characteristics.The main works are provided as follows:：1. A novel experimental method to precisely measure the transient reflectancespectra of the saturable absorber self-organized gratings is proposed, and it alsoprovides a solid physical foundation for the synergetic model which contains theself-organized feedback mechanism.2. The synergetic system model, which takes the mode intensities as its orderparameters, is established. A set of experimental measurement methods for the orderparameter through the coherent detection are given. These methods not only provideeffective tools for researches on the laser instabilities, but also provide empirical routesto study the complex systems contain self-organized feedback mechanism.3. According to the practical physical structure of the self-organized feedbackfiber ring lasers, the theoretical model and the laser equations that contain both thepositive and negative self-organized feedback mechanisms are established. This modelprovides a theoretical foundation for quantization analyses on the maintaining and thebreaking cooperation of the self-organized feedback lasers and corresponding complexsystems with isomorphic mechanisms.4. Some experimental evidences that the class B laser system without additionaldegrees of freedom can generate signals with multiple chaotic properties byself-organized feedback mechanism are obtained.