Fundamental Investigations Of Slow And Fast Light In Fiber Optical Parametric Amplifier

Recently, controlling the group velocity of light becomes a key issue in photonics. Its importance not only lies on the theory, but also attributes to its potential values in the area of optical communication, optical sensor technology and microwave photonics. Up to now, the method generating the slow and fast light mainly contains: the large dispersion in atom system, the design of waveguide structure and the nonlinear amplification of signal wave. The slow and fast light in FPOA is realized by the nonlinear amplification of signal wave. We theoretically investigate the phenomenon of slow and fast light in both the wideband FOPA and the narrowband FOPA because this new mechanism contains following advantages:relatively large delay bandwidth, the delay time fitted for high speed telecommunication and the tunable ability for delay time. The major contributions of this paper can be summarized as follows:1) The comprehensive characters of delay time in fiber optical parametric amplifier are investigated theoretically. The analytical relation between the maximum delay time and the dispersion parameters, pump power, pump wavelength in this type of FOPA is deduced. Then the delay character of single pulse, data stream with certain bit pattern and pseudo random data stream are analyzed comprehensively. The results show that the delay time will reduce to the half of the value under narrow band condition when the signal with the bandwidth 50GHz is located at the wavelength with maximum delay time. Finally, the selection of pump power and fiber length is present, and long fiber benefits to the large delay time when the signal gain is fixed.2) The delay time in the band-edge of gain spectrum of wide band FOPA is deduced for the first time, and a novel method is proposed theoretically to generate the slow and fast light with large bandwidth and low gains. In our scheme, the formula of the signal wavelength is demonstrated, and then signal waves will be delayed or advanced with low signal gains because of the peculiar feature of signal gain and phase shift in certain signal wavelength region. At last, the simulation results of delayed signal waves are shown. The tunable range of delay(advanced) time is from Ops to 22.4ps for the signal bandwidth of lOGHz, and their signal gains are from 1.29dB to 3dB. This proposal can provide the new mechanism to make tunable delay time independent of the signal gain in both optical buffer and synchronization.3) By considering both the real and imaginary part of the Raman susceptibility, a delay time formula in the stimulated Raman scattering assisted fiber optical parametric amplifier is presented to calculate the delay time spectrum. The wavelengths with maximum delay and advanced time are calculated numerically. Then we find some frequency regions with the enhanced slow and fast light in both stokes and anti-stokes regions, which is the result of the interaction between the stimulated Raman scattering and four-wave-fixing effect at the strong absorption region. Simulation shows that the delay time by using signal waves with 1.5GHz and 1 GHz can reach over 200ps and 300ps, respectively. The group index can reach the order of 10-4, which is ten times larger than the former delay time in conventional frequency regions.4) The changes of delay time are investigated in two nonideal cases:the changing of polarization states and signal saturation. By analyzing the delay time with different polarization states of pump wave, signal wave and idler wave, we propose a formula containing the changing of polarization states in FOPA. Then the influence of the signal saturation on the delay time is analyzed. The results show that the delay time calculated numerically is only one half of the result from the analytical formula when the signal wave is located in the band-edge of the gain spectrum in FOPA.5) We propose an approach to measure the microwave frequency in optical domain with adjustable measurement range and resolution by using four wave mixing process in the single mode fiber. Results show that the measurement range of this scheme can be adjusted easily by changing the pump power. After the elaborate selection of the fiber parameters and initial signal power, the measurement range 20-45 GHz is obtained by choosing 500 mW pump power and 3km fiber.