Investigation On Stimulated Brillouin Scattering And Four-wave Mixing In Photonic Crystal Fiber

In recent years, the photonic crystal fiber (PCF) technology has made great progress. Due to design flexibility of PCF, it has endlessly single-mode characteristic, peculiar dispersion characteristic and high nonlinearity characteristic. Through the rational design of PCF, its nonlinear is typically 1 or 2 orders of magnitude larger than that of a conventional single-mode fiber. Therefore, a lot of research has been carried out about the nonlinear in PCF. Stimulated Brillouin Scattering (SBS) is an important nonlinear effect in fiber, and it has a low threshold, which makes SBS have both positive role and negative role in optical communication system. SBS effect can be used in Brillouin fiber lasers and amplifiers, which is the positive side. On the contrary, for other nonlinear effects in fiber, such as four-wave mixing (FWM), the occurrence of SBS will diminish the efficiency of FWM, therefor SBS needs to be supressed. The SBS and FWM in PCF have been studied in this paper in terms of the use of SBS and suppression of SBS.The steady-state model of SBS in fiber Bragg grating Fabry-Perot (F-P) cavity using PCF for the gain medium is analyzed. Under the condition of considering the PCF loss, the relationship between transmission (reflection) power of fiber Bragg grating F-P cavity and input pump power is studied. Pump power and Stokes power distribution along F-P cavity are simulated. The relationship between the length of the PCF and SBS threshold of fiber Bragg grating F-P cavity is discussed. On the basis of above theory, we provide what we believe to be the first experiment demonstration of dual-frequency Brillouin laser based on fiber Bragg grating F-P cavity using PCF for the gain medium. Resonant cavity of laser consists of 25-m-long highly nonlinear PCF and two fiber Bragg gratings. Such a cavity is beneficial to increasing conversion efficiency and decreasing laser threshold. The laser reaches threshold for input power of 35 mW, and the experimental laser conversion efficiency achieves 18% for input power of 130 mW. Compared to previous PCF Brillouin laser, the PCF dual-frequency Brillouin laser proposed in the paper achieves a minimum threshold using the shortest fiber.In optical communication systems, useful signal is modulated to optical signal with microwave for transmission, therefore, the generation of microwave signal is very important. A novel microwave signal generator based on PCF dual-frequency Brillouin laser is forwarded in the paper. By choosing the fiber Bragg grating with a certain reflection spectrum, PCF Brillouin laser can only produce 1st-order Stokes wave, and suppresses the high-order Stokes waves. Frequency difference between pump and 1st-Stokes wave falls in microwave frequency range, so we may obtain microwave signal through mixing the pump with the lst-order Stokes wave. When pump power is 57 mW and pump wavelength is near 1550 nm, a 9.78 GHz microwave signal whose bandwidth is 3 MHz is obtained. Compared to previous microwave sinal generator based on PCF Brillouin laser, the microwave signal is generated under the condition of lower pump power in the paper.In the microwave transmission systems with fiber link, microwave signals need modulating to optical carrier for transmission, which requires solving the issue of optical carrier suppression. A novel carrier filter based on the SBS in the PCF is provided after a research of SBS model in fiber ring. The fiber ring consists of a section of fiber and two circulators, which serves as carrier filter. SBS threshold in PCF is effectively reduced in this fiber ring structure, and the highly nonlinear PCF can greatly reduce the fiber length in fiber ring. A 25-m-long PCF is used as Brillouin gain medium, when the carrier of 70 mW input the filter, microwave photon signal received 3.38 dB of RF gain. The filter effectively reduces carrier power and realizes automatic match of the center wavelength of the filter and optical carrier.The development of phase modulation signal research in optical communication system calls for a suitable wavelength conversion technology as a support, FWM meets the request of all-optical system due to its instantaneous response of Kerr nonlinearity of fiber. Phase matching condition is met more easily in dispersion flat PCF, which is beneficial to increasing the wavelength conversion range. A wavelength converter based on FWM in a highly nonlinear dispersion flat PCF is provided. SBS will decrease the efficiency of FWM in PCF, so a suitable pump source is selected to suppress SBS on the basis of the research on SBS. We obtain 100-nm wavelength conversion range, which is almost equal to the widest bandwidth of wavelength conversion realized in FWM of PCF. Experiment proved that the wavelength converter can complete the wavelength conversion of multi-channel signal at the same time.