Theoretical And Experimental Study Of Photonic Crystal Fibers And Related Optoelectronics Technology In Communications

The research works of this dissertation are supported by the National Basic Research Program of China (973 Project, Grant 2003CB314906), the Foundation for the Key Program of Ministry of Education of China (Grant 104046), the National 863 High Technology Project of China (2003AA311010) and the Foundation from the Education Commission of Beijing (Grant XK100130437).Optical fibers have many important applications, particularly in communication systems, sensors, medical instrumentation, and many kinds of optical components. During the past few years, a great deal of effort has been devoted to the development of new types of optical fibers with the aim of improving the performance of fibers in these applications. Photonic crystal fiber (PCF) is one of the most recent advances in fiber-optic technology that has attracted considerable interest from many researchers around the world. PCFs consist of a central defect region surrounded by multiple air holes that run along the fiber length. By varing the size and pattern of the air holes, the mode propagation properties of the PCFs can be easily controlled. The use of microstructures in optical fibers have opened new developments in various areas of fiber applications, and it is interesting that each of these areas actually takes advantage of different aspects of the enhanced physical performance enabled by the location of microstructures in the fibers. PCFs provide a novel waveguide platform for photonic devices and a number of functionalities have been demonstrated. Those fibers show great potential for various applications in the fields of telecommunications, nonlinear fiber optics, sensor technology and many other novel fiber devices. Because of their novel structure and unique properties that cannot be achieved from conventional step-index fibers, PCFs continue to be an active area of research in the foreseeable future. In this dissertation, PCFs and related optical communication technologies were studied both theoretically and experimentally. The main contents and achievements are as follows. 1. Combinning anisotropic perfectly matched layer (APML) for the boundary treatment, finite-difference time-domain method (FDTD) is introduced to model PCF. The formulations of FDTD and PML techniques are discussed in detail, and this method is successfully used to analyze the properties of PCFs.2. An improved effective index method (IEIM) is proposed for accurate analysis of PCF. IEIM is developed form a conventional fully vectorial EIM and is shown to give more accure results than the conventional one. The results obtaioned by IEIM agree well with accurate numerical results obtained by other methods as well as the previously reported experimental data. IEIM is a powerful tool for analyzing PCFs.3. Dispersion-flattened PCF with small normal dispersion is proposed for generating a flat and broad supercontinuum in the telecommunication band. The chromatic dispersion of the PCF is a convex function of wavelengths and has no zero-dispersion wavelengths over the whole part of the fiber. Numerical simulation is used to study the effect of fiber parameters and pumping conditions on supercontinuum generation in the PCFs.4. Dispersion-flattened PCFs with small normal dispersion are designed for flat broadband supercontinuum generation. Also, multi-wavelength pulse sources based on spectral slicing is presented,5. A tapered-photonic crystal fiber is designed by combining the advantageous properties of photonic crystal fiber and tapering for generating flat broadband supercontinuum. The fiber is characterized by flattened chromatic dispersion which also decreases from a positive value to a negative one with fiber length. Supercontinuum generation in this photonic crystal fiber was theoretical study. It is shown through theoretical results that the proposed fiber offers the possibility of efficient and flat supercontinuum generation in the telecommunication window using a few picosecond pulses.6. The generation of a flat supercontinuum spectrum of over 90nm in the 1.55μm region by injecting high repetition rate picosecond pulses into a nonlinear dispersion-flattened PCF is demonstrated originally. This flat broadband supercontinuum can simultaneously supply more than 1100 multi-wavelength channels with 10-GHz spacing. The multi-wavelength pulse trains at 10Gbit/s based on spectral slicing are demonstrated experimentally. This supercontinuum source has important applications in dense wavelength division multiplexing (DWDM) optical transmission systems and optical wavelength conversion. Furthermore, numerical simulation is also used to study the generation of supercontinuum in the PCF. An excellent agreement between the simulations and the results of experiment is obtained.7. All-optical regeneration based on self-phase modulation in PCF is proposed and the feasibility of this scheme is investigated both theoretically and experimentally. By combining the PCF with a bandpass filter, a near step-like power transfer function with no pulse distortion is achieved. The device is shown to operate with pecosecond pulses, thus demonstrating the feasibility of this device operating with high bit-rate data signals. The research results confirm the suitability of nonlinear PCF with normal dispersion for all-optical 2R regeneration.8. A highly nonlinear PCF with large anomalous dispersion is proposed to construct nonlinear optical loop mirrors (NOLMs) for pulse compression and shaping. It is shown from numerical results that the proposed NOLMs compress the pulses efficiently and significantly suppresses the pedestals of the pulses.9. Dispersion and dispersion slope compensation of 10 Gbit/s pulses using PCF is demonstrated experimentally. A 26 m PCF was used to compensate the dispersion of 2 km standard singe mode fiber in a 20-nm range in C band. The further research results show that the PCF can compensate the anomalous dispersion of a single mode fiber within±0.3 ps.nm^-1.km^-1 over a 50-nm range from a wavelength of 1520nm to 1570nm.10. All-optical wavelength conversion using four-wave mixing (FWM) in PCF is investigated. The conversion of 10 Gbit/s signal based on FWM in a 30m dispersion-flattened PCF is experimentally demonstrated. The conversion efficiency is around -19.5dB with the fluctuation of less than±1.4dB, which covers a conversion bandwidth of 20nm.