Research On The Gain Flatness Of Quasi-phase-matching Fiber-optic Parametric Amplifier

To meet the rapid development of network and the increasing growth of information, communication network is upgrading towards all-optical network with high-speed, large-capacity and long-distance. But the effect of fiber loss, dispersion and nonlinearity are the main obstacles. The appearance and industrialization of optical amplification technology became one of the most important achievements in optical communication system. This technology not only overcomes the effect of fiber loss that the optical transmission can be as long as several thousand kilometers, but also propels the development of optical solution communication, optical multiplexing techniques and all-optical network forward. With the rapid development of dense wavelength division multiplexing (DWDM) communication technique, however, a large number of optical amplifiers such as erdium-doped fiber amplifier (EDFA), fiber Raman amplifier (FRA) and semiconductor optical amplifier (SOA) have been in pritical stage. In recent years, Fiber-optic parametric amplifiers (FOPA) became the focal point of the research in optical amplification, as its unique properties. FOPA relying on four-wave mixing (FWM) can not only amplify at any arbitrary wavelength in theory, but also provide broader gain bandwidth and exhibit noise figure. From the basic theory of signal transmission, the gain flatness of quasi-phase-matching FOPA is studied in the dissertation. The main research work and results are as follow:1 At first, we have introduced the significance, process and application prospect of FOPA research and discussed the advantages and disadvantages of several kinds of amplifier.2 Fiber loss, dispersion and nonlinear effect are introduced in chapter 2, then the influence of dispersion effect, self-phase modulation (SPM) and cross-phase modulation (XPM) on light signal transmitting system is analyzed. Finally some actual and applied dispersion compensation technologies are introduced.3 In chapter 3, we have presented the origins theory and application of optical parametric processes in wavelength division multiplexing (WDM) system in detail, which include second and third nonlinear effect of optical fiber.4 In chapter 4, we have theoretically investigated a new FOPA scheme which using four–section HNLF arrangement and a dual-pump configuration that allows one to generate a nearly flat gain over ultrabroad bands without any qain-equalization filter.5 In chapter 5, the research on the gian flatness FOPA using a composite fiber is presented. We hypothetically divide high nonlinear fiber (HNLF) into small segments equally, and then insert segments of dispersion compensated fiber (DCF) at regular intervals which can compensate the dispersion of the next HNLF and obtain a flat gain over a wide spectral rang. The results show that he gain fluctuation of FOPA has a relationship with parameters such as the inserting number of DCFs, the power and wavelength of pumps, the length and nonlinear parameter of HNLF.With the increase of the inserting number of DCFs, the fluctuation of FOPA gain has been improved obviously, which can realize a flat gain over. In addition, the shape of gain spectrum is influenced by the difference of pump wavelengths, thus we should choose an appropriate difference of pump wavelengths.