| Nowadays, People's increasing demand for information exchange to improve the exchange of richer content. The fiber communications technology has emerged because of the invention of lasers. This has brought a revolution for communication in the field, and the large-capacity communications, high-speed have become possible. The so-called fiber communication technology is to use light as a carrier, optical fiber as a transmission medium to achieve information transmission, and to achieve the purpose of a communications technology. Fiber lasers in optical fiber communication systems as a promising light source has been a promising light source, a lot of research has emerged in this field in recent years. It Applies to existing communications systems to support higher transmission speeds, and it is the basis for the DWDM systems and the future of the coherent optical communications.The generation technology of the ultrashort optical pulses is very important for the high-speed OTDM communications systems. The OTDM communication system overall performance dependent on the ultrashort optical pulses source. Mode-locking technique is a main method for generating the ultrashort optical pulses. Because the actively mode-locked fiber laser using mode-locking technique can generate high repetition rate, broadband tunable, ps pulse width, non-chirped optical pulse of transform-limited, and has easy-synchronized, high peak power of output pulse characteristics, so the actively mode-locked fiber laser using mode-locking technique has been used as the ideal optical source in the future long-distance communication systems. But the stability technique problem of the actively mode-locked fiber laser is not solved. So there is a distance of the practical application of actively mode-locked fiber laser. The prerequisite of actively mode-locked fiber laser stable work is that the modulation signal frequency must be the integral multiple to the cavity resonance frequency. Because the cavity of the actively mode-locked fiber laser has the long fiber (usually several dozens to several hundred meters). Fiber lasers are very sensitive to environmental perturbations such as temperature fluctuations and mechanical vibrations due to their relatively long cavity length when the external environment changing . The cavity length drift producing the phase noise and amplitude noise, this can cause the output pulse unstably. When this is serious, the fiber laser will lost the mode-lock. For the modulation frequency and the cavity are very difficult to maintain matching, so it is difficult to guarantee the long time steady work of actively mode-locked fiber laser. It is a problem which must be solved that how to keep the actively mode-locked fiber laser working stably for long time. So it is very valuable to study on it.According to the information can be found in the literature, we think the key to solve the stability of the actively mode-locked fiber laser is controlling and compensating the cavity drifting which generate by environment such as temperature. There are two methods to solve this problem. One is controlling optical delay line to compensate the cavity of laser according to the error signal; the other is controlling PZT to compensate cavity drifting by this error signal. The response rate of optical delay line is slow, so we believe that using PZT is more effective.This paper's main work is based on state National Nature Science Foundation of China fund project (No.60372061)"The study on the real-selfstart and stability of the ultrafast actively mode-locked fiber laser"and Science and Technology Development Planning project of Jilin Province ((2004) technology number (No.1271)) "The study on the mode control and stability of the ultrafast actively mode-locked fiber laser ". In this paper, we study the stability of the actively mode-locked fiber laser theoretically and based on it we study further the compensation technology of the actively mode-locked fiber laser by using PZT. The main contents and achievement of this paper including:(1) Summarizing the purpose and significance of thesis work. Including the development of optical communication techniques and fiber laser's outline, the development and applications of mode-locked fiber laser. The classification, manifestations and reasons of the actively mode-locked fiber laser's stability problem.(2) Studied the elementary theory and structure of the actively mode-locked fiber laser. Mainly includes the typical structure of actively mode-locked fiber laser. We analyze the work principle of the EDFA and the LiNbO3 modulator briefly. This two parts is the main devices of the actively mode-locked fiber laser. We analyze the principle of mode-locked, and the establishment process of actively mode-locked. We explain the work principle of actively mode-locked fiber laser, and proposed a solution of the stability problem of actively mode-locked fiber laser.(3) We analyse the basic principle of Mach-Zehnder fiber interferometer. We finished the constant temperature system applied to the phase measurement in Mach-Zehnder fiber interferometer. By the experimental study, we can know the temperature control precision of this constant temperature that is 0.1℃; the short term stability is±2.6×10-3℃, the long term stability is±0.024℃. It is suit for the phase measurement in Mach-Zehnder fiber interferometer, and it can improve the experimental precision greatly.We calculate the initial phase difference of the Mach-Zehnder fiber interferometer by measuring the interference photocurrent and the photocurrents from the two fiber arms on a temperature control system. This method is very easy to operate without any traditional mechanic phase shifter, and calculate the initial phase difference by measuring the photocurrent directly. We only calculate the phase difference of the fiber interferometer by measuring the stable interference photocurrent and the photocurrents from the two fiber arms at a set temperature. This method is cost lowly, calculating without computer'help, easy to operate, the experiment data are repeatable, and the measurement precision is about 0.04°. Also the fiber is very sensitive to the variation of temperature, so it is necessary to study the temperature characteristics in the phase measurement of Mach-Zehnder fiber interferometer. By the experimental study of this paper, we can know that the phase difference between the two arms of the interferometer varied 1.856°per temperature degree, which means that the variation of the phase difference of the two fiber arms is proportional to the variation of the temperature. This conclusion agrees well with the theory analysis. By studying the temperature characteristics of the phase measurement in Mach-Zehnder fiber interferometer, the coherence of the experiment and the theory shows that this research method is practical and valuable in estimating and compensating the variation of the temperature influence to the phase measurement in Mach-Zehnder fiber interferometer.(4) Completed the PZT driver circuit applied to fiber stress control. By theoretical analysis and experimental argumentation, we can know that this PZT driver circuit has good dynamic response characteristics, the frequency response range of this circuit is wide, the speed of the response is microsecond-level. So it is suit for adjusting fiber stress, and solve the stability of the actively mode-locked fiber laser influenced by the environmental variation especially the variation of temperature, since fiber is very sensitive to those variation. We study the measurement method of piezoelectric ceramic micro-displacement The method used the interferometer to make the PZT displacement transfer into the value of phase change of interference fringes. The phase change value of interference fringes can be retrieved by using Fourier Transform. So we can detected the displacement of PZT. This method can measure the displacement of PZT accurately. It is very important for controlling and compensating the cavity of the actively mode-locked fiber laser by PZT.We discuss the basic theory of controlling the fiber length used by PZT. We can see that PZT can control the fiber length effectively in theory, so we can use PZT to compensate the cavity length of fiber laser, and remain the cavity length of laser stably.In order to study response characteristics of the fiber wounded on PZT to the driving signals added to PZT, We set up a Mach-Zehnder fiber interferometer structure. Because the Mach-Zehnder fiber interferometer has limitations, so we chose an alternative structure—differential Sagnac fiber interferometer structure to measure the response characteristics of the fiber wounded on PZT to the driving signals added to PZT. In differential Sagnac interferometer structure, the system need not work in orthogonal state, there is no need to use polarization controller. As the two coherent light beams propagate in the same path, the system can work stably with the temperature, stress and other environmental factors'disturbance. From the theory analysis and experiment results we can know that the variation of the fiber length wounded on PZT can response successfully to the driving signals added to PZT when the frequency of the driving signals is no more than 2000Hz. For the cavity variation of the actively mode-locked fiber laser is usually induced by the slow environment fluctuation such as temperature's turbulence, stress etc, so it is efficient to use PZT to compensate the cavity variation of the actively mode-locked fiber laser. The fundamental research and the experiment analyses of this paper have great meaning for controlling and compensating the cavity length drift of the actively mode-locked fiber laser. Also these analyses have great significance for the stability of the actively mode-locked fiber laser.
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