Optical Fiber Based Supercontinuum Generation, Parametric Amplifier And Its Applications

The response of fiber to light becomes nonlinear for intense electric fields. Nonlinearity in fibers has the advantages of being ultrafast, easy to control, and creating new frequency componets. Thus, it has found numerous applications in diverse fields. Aim to optimize and explore applications of nonlinear fiber optics, this thesis analyses supercontinuum (SC) generation, broadband fiber optic parametric amplifier (FOPA), and phase sensitive amplifiers (PSA) based wireless-to-optics conversion technology, respectively. The main research efforts are summarized as follow.1. SC generation and related dynamics of soliton and dispersive waveProviding a method to choose arbitrarily frequency components in a wide region, SC generation has found numerous applications in such diverse fields as spectroscopy, pulse compression, and the design of tunable ultrafast femtosecond laser sources. To interpret the physics underlying the spectral broadening and reveal the subtle features in this processe, people did lots of numerical studies. Most previous investigations considered the self-steepening (SS) effect as a perturbation and neglected it. Based on frequency domain generalized nonlinear Shrodinger equation, the influence of SS effect on supercontinuum generation has been analysed. It is found that SS would evidently decrease both the spectral bandwidth and the energy of supercontinuum, although it would increase the energy in normal dispersion region. The influence is more obviously for widely broadened supercontinuum. To explain this phenomenon, the thesis discusses the DW generation and trapping process independently, which are the main reason for supercontinuum generation. It is found that SS would increase the energy of generated DW, this is because that SS would decrease the frequency shift of soliton and thus decrease the energy extended in the normal dispersion region. It is demonstrated for the first time that the energy of the DW increases with propagation due to the SS-induced photon number conservation, and its frequency shift is greatly reduced as well. Analytically the frequency shift and energy evolution in the traping process are studied, and good agreements were demonstrated between the analytical predictions and the numerical simulations. These equations allow accurate predictions for the pulse-trapping-based wavelength conversion applications.2. Broaden gain bandwidth of FOPABased on four waves mixing, FOPA transfers energy from the strong pump to signal and idler. It has the advantage of large gain, phase conjugation, controllable gain bandwidth, and so no. These characteristics of FOPA, taken alone or in combination, indicate that they could match or exceed the performance of other existing devices in various applications.In the thesis, we propose a new and promising freedom to optimize the flatness and broaden the bandwidth of a fiber-optic parametric amplifier by introducing a wavelength-dependent loss in the idler band. This is because the distributed idler loss would increase the signal gain in the non-phase-matched region, while decrease the gain in the phase-matched region. The former is explained physically:the idler loss breaks the balance between the signal and idler, which leads to a continuous pump-to-sideband power transfer. A design example is numerically studied, and the conversion efficiency is found kept high in spite of the loss. The proposed method could be combined with other gain-spectrum-extending ones, such as the dispersion engineering, etc.3. Effective wireless-to-optics conversion based on PSARadio over fiber is proposed and considered as an ideal platform for future wireless signal processing. It can eliminate the so-called electronic bottleneck and meanwhile lead to lots of unique advantages, such as small size, light weight, and low energy consumption etc. Wirelss-to-optics conversion is the foundation of this platform, however, there is a tradeoff between the bandwidth and efficiency. In this thesis, we explore a new approach to realize bandwidth, effective wirelss-to-optics conversion, and propose to realize modulation enhancement based on PSA.The PSA is an especial kind of FOPA, it can realize selective amplification according to the relative phase, and is known to be capable of realizing noiseless amplification. As a result, PSA is extensively studied in the digital communications. We apply, for the first time to our knowledge, PSA to analog optical communications, and propose a PSA based wirelss-to-optics conversion scheme. Different from the previous realization of PSA, this scheme modulates relative phase via polarization control, which avoids creating additional phase noise in different optical paths. As a result, the system is more stable. To achive the lower noise figure in a fixed link gain, the attenuation region was chosen to be the system action region. Compared with traditional phase-to-intensity method based on interference, we verify that this scheme evidently decreases the modulator halfwave voltage, and the modulation efficiency is increases with the pump power.