| Narrow-linewidth frequency-stabilized laser has attracted considerable attention inoptical coherent communication, Doppler wind LIDAR, cold atoms physics,gravitational-wave detection and quantum optics, etc. Passive frequency stabilization couldpromote the frequency stability well, yet an active frequency stabilization system is still badlyneeded to achieve frequency stability better than10-8. Due to its great tolerance to thewavelength to be stabilized, good short-term frequency stability, optical resonator frequencystabilization techniques such as the PDH technique are generally considered to be thepreferable techniques in active frequency stabilization. However, the high finesse Fabry-Perotinterferometer, as the discriminator of the techniques, is always found to be expensive, largein size, fragile and very sensitive to the environment. Meanwhile, the existence of free-spacecomponent means rigid optical alignment, complex polarization controlling and geometricmode-matching, which complicates the debug of frequency-discriminating system. Becauseof the weaknesses mentioned above, based on the passive frequency stabilization, thisdissertation would focus on the all-fiber configuration exploration of frequency stabilizationtechniques in narrow-linewidth single longitudinal mode fiber laser.In addition, analog circuits are always adopted to deal with the error signal in traditionalfrequency stabilization circuits. However, digial signal processing is more flexible, remotelyaccessible and automatic. As a result, this dissertation would handle the error signal digitally,which would also lay a good foundation for the all-digital configuration of the frequencystabilization part. Foucusing on the frequency stabilization techniques of narrow-linewidthsingle longitudinal mode fiber laser, the main contents of this dissertation are as follows.(1). The first part presents the configuration and frequency stabilization rationale ofnarrow-linewidth single longitudinal mode linearly tunable DBR fiber laser. Theoretically andexperimentally, it analyses PZT-based tunable property of the fiber laser. The spectralcharacteristics of Fabry-Parot interferometer, fiber ring resonator and unbalanced Michesloninterferometer are also analysed theoretically and experimentally; based on this, it investigatesthe Fiber Bragg Grating fringe-locking and unbalanced Michelson interferometer side-lockingtechniques. For the Fiber Bragg Grating discriminating system, reflection of the Fiber BraggGrating is60%; temperature of the fiber laser resonator is tuned to achieve an error signal andthe sensitivity of this system is calculated to be5.6MHz/mV. For the100m unbalancedMichelson interferometer discriminating system, the optical path difference of theinterfermoter is tuned to achieve an error signal and the bandwidth of this system is found to be300Hz. Moreover, the frequency of the error signal is in good agreement with the PZTtuning frequency, which validates it to be reasonable.(2). The second part presents the design of related circuits in passive and activefrequency stabilization techniques. For the passive frequency stabilization circuits, the LDpump driver operating in the automatic power control mode is proved to be in stable andreliable operation and the power fluctuation of the fiber laser is tested to be less than0.5%（80min）. Theoretically and experimentally, it analyses the DAC output module based on PWMwave shape, which has great potential in integrated and intelligent control system such as highpower fiber laser system. A combination method of PWM and linearly continue driving,operating in high efficiency and low ripple wave, is used to control the current across TEC.The final temperature stability is verified to be better than0.1℃. With these two circuits inoperating (passive stabilization), frequency fluctuation of the single-frequency fiber laser in40minutes is less than80MHz. By the way, these two circuits have been prototyped andoperated stablely and reliably in our laboratory. For the active frequency stabilization circuits,the filering and mixing circuits have been utilized together with the unbalanced Michelsoninterferometer frequency-discriminating system to obtain an error signal whose frequencyagrees well with the PZT tuning frequency (300Hz). ADC and DAC modules of thedigitalized servo part have been tested to track the input signal well. PZT high voltage drvingcircuits can provide a voltage range of0-100V with the bandwidth more than10kHz.Utilizing this circuit, a maxium linear tunable range of more than700MHz has beenachieved. |
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