The Research Of Signal Process Circuits Based On The Differentiating Sagnac Interferometer System

Nowadays, the information has become world-wide sharing the resources but the profound influence humanity's progress, the information revolution is causing the people knowledge acquisition and the experience way is having the significant change, along with correspondence flourishing more and more daily, set the more and more high request to the communications system capacity, The soliton correspondence can provide the extremely high transmission speed, it has the conformal transmission the characteristic, can transmit the extremely long distance but not to have the deformation, its transmission capacity outdoes 1 - 2 magnitudes compared to now the best communications system, the relaying distance may amount to hundred kilometers, therefore the soliton correspondence very quickly becomes the research hot spot. The ultra-fast actively mode-locked fiber laser because may produce the ultra-fast soliton pulse,it will be the ideal light source of the future long-distance does not have the relaying optical fiber communications system. But, has not obtained the complete solution throughout about the ultra-fast actively mode-locked fiber laser stable technical difficult problem, causes the ultra-fast actively mode-locked fiber laser to move towards the practical application also to have section of distances. One of actively mode-locked fiber laser steady work prerequisites is the modulation signal frequency characteristic for the cavity in the vertical mold gap integral multiple. When detune not serious, in the output pulse has the phase noise, when the detune is serious, then can cause locks the mold to expire, displays for the output light pulse collapse. Because in the actively mode-locked fiber laser cavity has the long fiber, but the fiber length is extremely easily, it will drift when the external environment influence, thus the modulation frequency and the cavity are very difficult to maintain the match. Therefore it will not guarantee the long time steady work, must take the special measure to stabilize the actively mode-locked fiber laser cavity to be long.An actively mode-locked fiber laser is one of promising candidates as the light source for future high-speed optical communication systems because it is easy to construct and can produce transform-limited pulses with large energy at high repetition rates. However, the stability of the fiber laser still is a problem unsolved completely because its cavity is sensible to the environment perturbations such as temperature fluctuations and mechanical vibrations due to its relatively long cavity length]. PZT usually used to compensate the cavity's variation with a part of fiber wound on it .This paper's main work is based on state National Nature Science Foundation of China fund project (No.60372061)"The study on the real-self start and stability of the ultra-fast 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 ultra-fast actively mode-locked fiber laser ". We studied the response characteristics of the fiber wound on the PZT to the driver signals based on the DSI in order to analyze the instability of actively mode-locked fiber laser. Since the interferometer has the same optical path in two interfering beams and use the differentiating technique, it overcomes several drawbacks of common interferometer 1) temperature sensitivity; 2) requirement for long coherence length source. In the experiments the system worked stably. 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 driver signal added on PZT when the frequency of the driver signals is no more than 2000Hz. So when the frequency of the signal is no more than 2000 Hz, the PZT can compensate the cavity length's variation well, but if the frequency of the signal exceeds the this band, PZT could not response the variation successfully. This explains well why the actively mode-locked fiber laser can work well in mild environment but cannot work stably when the environment changes fiercely.1. Active mode-locking fiber lasers in optical communication system applications. Discusses the optical communications technology, high-speed large-capacity technology, Active mode-locked fiber laser research and fiber interferometer application2. Studied the elementary theory of the actively mode-locked fiber laser. Completed the tournament Sagnac differential interference in the optical system design and the choice of device3. Completed the tournament Sagnac differential interferometer system photoelectric detection preamplifier circuit, the circuit performance enhancing filter circuit, Analysis of the module circuit principles, characteristics and parameters of the device and method for selecting a design principle .Phase compression integral circuit and cosine circuit design. Triangular wave signal added to the PZT to the control signal, the experimental be proportional and input control signals output signal, the system has a very good real-time and linear.4 Analysis of the noise, including : Rayleigh scattering noise, shot noise.Link reflection noise and thermal noise load resistance of the system, Circuit design process against the electromagnetic compatibility and PCB production issues were discussed, and gives a reasonable solution.