Study On Optical Bistability And Fiber Lasers

Optical bistability (OB) provides a basis for various optical devices, such as optical logic gates, optical memories, and optical switches. As a signal emitter, multiwavelength laser plays a key role in the modern communication system. High-power single-longitudinal-mode (SLM) fiber laser has great applications for long-range sensors system and optical spectrum analysis system. This dissertation is concerned with the OB in a single erbium-doped fiber (EDF) ring laser, spacing-tunable multiwavelength fiber laser and high-power SLM fiber laser.In our experiments, we observed that OB can exist even in a simple fiber laser employing a long EDF as a gain medium. In order to study the intrinsic mechanism of this OB, gain curves of the EDF at related pump powers are measured. With these gain curves, OB can be explained successfully. By introducing useless pump loss in the classical convective equations, we banished the discrepancy between the experimental and theoretical gain curves of EDF. Various factors which can affect the OB region are analyzed. A fiber ring laser employing two-segment EDF, one EDF acting as an amplifier and the other as an absorber, are designed for tunable OB. OB region can be adjusted from a maximum value to zero by injecting some pump light into the absorber EDF. Further more, signals of different wavelength are used to control the output of an optical bistability fiber laser in out experiment.Lyot-Sagnac filter is composed by several polarization controllers (PC) and several segments of polarization maintaining fiber (PMF). The grid spacing of this comb filter can be switched from one to another by adjusting these PCs. Inhomogeneous broadening of the semiconductor optical amplifier (SOA) makes it an ideal gain medium for multiwavelength fiber lasers. A novel multiwavelength fiber laser employing a SOA is proposed on the basis of the theoretical analysis of the Lyot-Saganc filter with two segments of PMF. This fiber laser can generate 18 multiwavelength laser with signal-to-noise ratio (SNR) 30dB, ranging from 1556nm to 1577nm. The grid spacing of the output laser can be selected between two ITU grid spacings: 0.4nm and 0.8 nm.A high-power SLM fiber ring laser with subtly tunable frequency is also proposed here. By employing a fiber F-P filter, the unpumped EDF serving as a saturable absorber in the laser becomes shorter. Therefore, the cavity loss is reduced, which is a key point for high-power fiber laser. Er/Yb co-doped DC fiber and two LDs with maximal power of 6.5 W provide a high gain. Phase modulator is used for subtle adjustment of frequency. The maximal output power is predicted at 1.6 W.