| Multi-wavelength laser sources are of great interest in optical communications, spectroscopic measurements, optical sensors, and biomedical images and diagnoses. As the number and complexity of wavelength division multiplexing channels increase, multi-wavelength generation technology becomes more important in the optical communication systems. However, the tunability and application of multi-wavelength output of conventional systems remain quite limited.; In this dissertation, tunable multi-wavelength lasers are proposed to achieve simultaneous multiple wavelength lasing in a single all-optical fiber laser cavity. The single cavity laser system is composed of two main fiber optic sections that include (1) comb filter section to define multiple lasing wavelengths, and (2) cavity section to provide the gain at several wavelengths simultaneously.; As a comb filter, cascaded long period fiber gratings interferometer and fiber Sagnac loop interferometer are theoretically and experimentally demonstrated for fast wavelength tuning and discrete channel space tuning. To fabricate high performance fiber gratings devices, specially designed optical fibers are fabricated with a novel method, and the mechanism of refractive index change is discussed rigorously. In regard to the polarization dependency of polarization-maintaining fiber, the absolute wavelength and relative channel space of transmission spectrum are controlled by adjusting the effective fiber length in Sagnac loop filter.; Multi-wavelength lasings are demonstrated in both erbium-doped fiber ring cavity and Raman fiber ring cavity configurations. In the case of the erbium-doped fiber ring laser, both continuous wave and pulsed mode outputs are considered for various laser operations and applications. Several designs of fiber Raman laser ring laser are developed based on a broad generation of cascaded Raman Stokes wave and nonlinear phenomena. Detailed numerical models are analysed to optimise the laser cavity.; Absolute wavelength tuning and the relative channel space tuning of multi-lasing peaks are demonstrated through the control of optical fiber comb filter, and other characteristics of the lasers are demonstrated. The applications of tunable multi-wavelength laser are also discussed for an optical soliton pulse-train generator, an interleaved wavelength-selective switch, a fast wavelength-swept laser, a biomedical optical coherence tomography source, a temperature and strain sensor, and a differential absorption lidar. |
