Therotical And Experimental Study Of Multi-Wavelength And Mode-Locked Fiber Lasers

Generation of multi-wavelength signals and ultra-short pulses are of great importance for a wide range of applications such as in wavelength-division-multiplexed(WDM) and optical time-division-multiplexed(OTDM) fiber communication systems, fiber sensing, nonlinear optics, optical instrument testing, and time-resolved spectroscopy. Actively mode-locked erbium-doped fiber lasers(EDFLs) with a high repetition rate and multi-wavelength fiber lasers are attractive optical sources in future ultra-high speed and all-optical communication systems. In this dissertation, we carried out theoretical and experimental study in the fields of multi-wavelength fiber lasers and actively mode-locked fiber lasers. The main contents are as follows:1. The spectral characteristics of a multimode fiber Bragg grating are theoretically and experimentally studied. On this basis, we successfully propose and demonstrate a simple switchable dual-wavelength ytterbium-doped fiber laser and an EDFL operating in L-band based on a multimode fiber grating, respectively. Both can be operated in stable dual-wavelength mode due to the polarization hole burning or switch between two wavelengths at room temperature, only by simple adjustment of a polarization controller.2. The spectral characteristics of a fiber Bragg grating(FBG) under both axial and transverse strain are theoretically and experimentally studied. A switchable and spacing-tunable dual-wavelength linear cavity EDFL is demonstrated experimentally using this kind of Bragg grating for wavelength selection. It exploits the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled while axial strain shifts both wavelengths together.3. We theoretically analyze spectral characteristics of a fiber grating in polarization- maintaining(PM) fiber under axial and transverse strain. A switchable and spacing-tunable dual-wavelength linear cavity EDFL is demonstrated experimentally using this kind of Bragg grating for wavelength selection. A polarization controlled switchable multi-wavelength EDFL with overlapping cavities is proposed. The wavelengths are specified by two Bragg gratings in PM fibers. The proposed laser can be designed to operate in stable four-wavelength or wavelength switching modes only by simple adjustment of two polarization controllers. Two Moire Bragg gratings in PM fibers are respectively fabricated successfully through stretching and double, triplicate...