Study On Multi-wavelength, Single Longitudinal Mode Fiber Lasers

Fiber lasers have attracted much interest because of their potential applications in wavelength division multiplexed fiber communication systems, optical time division multiplexed fiber communication systems, radio over fiber communication systems, long distance optical fiber sensing systems with ultra-high resolution, coherent optical communication and so on. Under the supports of national 863 high technology program and national nature science foundation, this thesis is devoted to design and optimize the structure of the multi-wavelength fiber lasers and narrow linewidth single longitudinal mode fiber lasers, mainly including proposing and optimizing the structures of fiber lasers and deeply investigating the characteristics of fiber lasers. And the main achievements of this thesis are listed as follows:1. A stable and single-polarization, switchable dual-wavelength erbium doped fiber laser at room temperature with two polarization maintaining fiber Bragg gratings directly written in a polarization maintaining and photosensitive erbium doped fiber is presented and experimentally demonstrated. The working principle of the fiber laser which is based on the polarization hole burning is also analysed. Furthermore, a multi-wavelength erbium doped fiber laser using two polarization maintaining fiber Bragg gratings in the symmetrical linear cavities at room temperature is also experimentally realized. The laser cavity is composed by the Sagnac loop mirror connected with two polarization maintaining fiber Bragg gratings, and stable four-wavelength lasing emission can be generated at room temperature. Moreover, two kinds of multi-wavelength erbium doped fiber ring laser at room temperature are proposed and experimentally demonstrated. With the removal of the optical circulator, switchable dual-wavelength lasing outputs are achieved based on the use of one polarization maintaining fiber Bragg grating within a Sagnac loop interferometer as the wavelength-selective filter. Switchable four-wavelength lasing outputs are also obtained with cascaded polarization maintaining fiber Bragg grating within a Sagnac loop interferometer.2. A switchable multi-wavelength erbium doped fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer comb filter at room temperature is presented. The comb filter is formed by splicing a section of twin-core fiber between two single mode fibers. The temperature and strain characteristics of the comb filter are experimentally investigated. The laser can be made to operate in stable single-, dual-and three-wavelength lasing states. Some interesting phenomena are observed and discussed.3. Switchable dual-wavelength fiber lasers based on a polarization maintaining fiber Bragg grating and a semiconductor optical amplifier in three different laser configurations at room temperature are proposed and experimentally demonstrated. The difference between the EDFA-based fiber laser and the SOA-based fiber laser are discussed and analysed. Moreover, multi-wavelength fiber ring lasers based on the semiconductor optical amplifier with sampled fiber Bragg grating and chirped moire fiber Bragg grating as the wavelength-selective filter are proposed. Stable four-wavelength lasing and triple-wavelength lasing have been stably generated, respectively.4. A single longitudinal mode erbium doped fiber laser with asymmetric two cavities is proposed and experimentally realized. It consists of three FBGs directly written in a photosensitive erbium doped fiber to form asymmetric two cavities, which can effectively increase the longitudinal mode spacing. The fiber laser has no intra-cavity fusion splices, and the single longitudinal mode operation with linewidth of less than 5-kHz is confirmed, which provide a highly-efficient narrow-linewidth fiber laser source for long distance optical fiber sensing systems.5. Switchable single longitudinal mode dual-wavelength erbium doped fiber lasers with linear and ring cavities using the polarization maintaining fiber Bragg grating as the wavelength-selective filter are demonstrated, respectively, which are mainly based on the polarization hole burning effect. The stable single longitudinal mode operation is guaranteed by the feedback fiber loop and unpumped erbium doped fiber as the saturable absorber.