Research On Slow And Fast Light In Nested Fiber Ring Resonator And Enhancing The Sensitivity Of Interferometer

Subluminal and superluminal group velocities can be observed by large normal or anomalous dispersion. Slow light is expected to become instrumental in enabling applications on the cutting edge of twenty-first century technology—high-capacity communication networks, quantum computing, ultrafast all-optical information processing, agile microwave systems, and so on. This transformation of slow light from a scientific curiosity to a rapidly growing field with many potential applications has been made possible by rapid developments in the technologies required for practical implementation of slow light. Under this background, we study theoretically and experimentally on the physical mechanism of the slow and fast light transmission in the fiber ring resonator, the influencing elements on the group velocity of light. The sensitive enhancement of the fiber interferometer is also demonstrated through using fiber ring resonators.There are two ways to control the velocity of light: one is using the dispersion of the medium, for example, the Electromagnetically Induced Transparency, Stimulated Brillouin Scattering, Coherent Population Oscillation, Stimulated Raman Scattering technology, etc; the other is using the dispersion of the structure, for example, Coupling Resonance Induced Transparency, Coupling Resonance Induced Absorption, Perot Fabry - Resonator, Photonic crystal, etc. This paper firstly reviewed the progress of various research methods, and analyzes their respective advantages and disadvantages. Usually "slow light" (v_g < c, v_g is the group velocity in a medium or structure for light transmission, c is the velocity of light in vacuum.) and "fast light" (v_g >c or v_g < 0) mean the physics of the phenomenon of light propagation in media and structures with reduced group velocity. We defined several types of the velocities of light, in order to drive it home. And then we introduced the Kramers - Kronig (K-K) relations as well as the basic theory of this thesis—the direction coupled theory and basic theoretical knowledge of the slow light optical interferometers.Secondly, we researched the physical mechanism of the slow light in a single fiber ring nested resonator, and its absorptive response, internal intensity magnification and dispersive response (the effective phase shift, dispersive response and group delay, etc.). In addition, measured transmission spectrum and the group delay of the fiber ring resonator are illustrated for varing coupling coefficients.Then, we demonstrated a novel nested fiber ring resonator which could produce both superluminal and subluminal propagation simultaneously. There are two output ports of the nested fiber ring resonator, and the two outputs of the resonator exhibit different absorption characteristics that produce opposite dispersion performance. These properties make it produce slow and fast light simultaneously. Moreover, we demonstrated the influence of the structure parameters (such as, reflection coefficients, attenuation coefficients, the length of the fiber ring, and so on) on the transmission, dispersive response and group delay. The results show that: (1) The nested fiber ring resonator vary from under coupling to critically coupling and over coupling with the changes of the coupling coefficients, which lead to the change of the transmission, the dispersive response and the group delay of the two output ports; (2) Increasing attenuation coefficient leads to the enhancement of the dispersive response of the nested fiber ring resonator, and the group delay will be increased. (3) The free spectral range and the full width at half maximum will be changed with the length of the ring. In addition, the center wavelength at resonance also changes with the length of the ring. (4) The analyses in this paper suggests that elaborate design of structure parameters make the group delay varies from hundreds of nanoseconds to tens of microseconds.Finally, we studied theoretically and experimentally enhancing the sensitivity of Mach Zehnder (M-Z) fiber interferometer by coupled fiber ring resonator in the arm of the interferometer. In addition, we suggested a novel method to enhance the sensitivity of the M-Z interferometer by combining the anomalous dispersion and normal dispersion at the resonance region. The theoretical and experimental results show: (1) The sensitivity of the fiber ring resonator coupled Mach-Zehnder interferometer will be strongly enhanced in resonance region, and get its maximum value at resonance. (2) The enhancement factor of the fiber ring resonator coupled Mach-Zehnder interferometer varies with the coupling coefficient, and reaches its maximum at critical coupling conditions. (3) The sensitivity of the fiber ring resonator coupled Mach-Zehnder interferometer will further enhanced by combining the the anomalous dispersion with normal dispersion.