Dispersion Process Of Modulation Instability In Erbium-doped Fiber Amplifier

Application of erbium doped fiber amplifier (EDFA) in optical communication system, optical network transmission distance and speed are improved, The light signal is be amplified no longer need to be converted to electrical signal. The cost is saved relative to the traditional optical/electrical/optical switch. It is convenient for operation and maintenance of the system. The EDFA has the advantages such as high output power, high amplification gain, broad-band spectrum and low noise figure. Amplification performance of the EDFA has no relation to system’s bit-rate and data format. EDFA is extensively used in dense wavelength division multiplexing (DWDM) optical communication system and Community Antenna Television (CATV) system.The EDFA have lowers the threshold of modulation instability considerably compared with the case of undoped fibers as a result of the existence of gain so that it very vulnerable to the influence of modulation instability. Modulation instability will affect the performance of the optical communication system that optical amplifier to compensate the periodic fiber loss. If optical amplifier generate noise, modulation instability will led to system performance significantly, this instability appears to be a continuous or quasi-continuous signal radiation split into a list of ultrashort pulses. The gain of distributed optical fiber amplifier are distributed a longer length in low doped on quartz optical fiber, so the nonlinear effect and dispersion effect play an important role for distributed optical fiber amplifier. In order to reduce the bad influence of dispersion to EDFA’s modulation instability, improve signal to noise ratio, this paper study new EDFA which based on the dispersion-decreasing EDF and dispersion-shifted EDF. Details are as follows:1. This paper have elaborated the basic theory, key technologies and study status of EDFA. The transmission equation of erbium-doped optical fiber have analyzed by using the homogeneous broadening two-level model. This transmission equation provide a theoretical framework for the study of pulse propagation in doped fiber amplifiers.2. Modulation instability is studied through a perturbation analysis nonlinear Schrodinger equation in dispersion-decreasing erbium-doped fiber amplifier. The relations of integral gain spectrum of modulation instability to the input signal power, amplifier gain, the length of amplifiers, optical fiber longitudinal dispersion change parameters are analyzed. Modulation instability gain spectrum can be eliminated through making use of amplifier length by analyzing modulation instability gain’s generation length.3. Research does not consider the second order group velocity dispersion (GVD), only consider the third order GVD dispersion-shifted EDFA. Modulation instability of dispersion-shifted EDFA have compared threshold and integral bandwidth and peck, whether to raise signal-to-noise ratio to modulation instability of EDFA by map make use of MATLAB.4. This paper introduces the research progress of two new type of EDFA(dispersion-decreasing EDFA and dispersion-shifted EDFA) respectively, and analyses their advantages and disadvantages, then put forward an effective method to reduce the influence of modulation instability of EDFA by the dispersion management.