Study On The Mechanism And Characteristics Of Tunable Multi-wavelength Narrow Linewidth Fiber Laser

Tunable multi-wavelength narrow linewidth fiber laser are widely used in high-speed optical communication systems?sensors?precision measurement. which has the advantages of tunable wavelength, small bulk and easy to be coupled with optical fiber, narrow linewidth, etc. At present, it is one of the hot issues in this field that how to realize multi-wavelength, narrow linewidth and tunable performance.Therefore, in this paper, we make full use of the stimulated Brillouin scattering and stimulated Rayleigh scattering effect of fiber and propose possible technical solutions.In this paper, the main work of this paper are as follows:The theories on stimulated Brillouin scattering and stimulated Rayleigh scattering are described briefly in this thesis. Based on theoretical analysis, we developed methods to increase the threshold of stimulated Brillouin scattering, such as by increasing temperature, stress, and changing optical fiber structure, which can provide theoretical guidance for production of high-threshold stimulated Brillouin optical fiber. We have focused on changing the structure of the fiber to increase the threshold of stimulated Brillouin scattering. We have studied the method of measuring the linewidth of fiber laser and compared the three methods of measurement.Meanwhile, we focused on studying the principle of delayed self-heterodyne method.We have proposed and demonstrated a novel tunable multi-wavelength narrow linewidth fiber laser assisted by Rayleigh backscattering in a high-threshold stimulated Brillouin optical fiber in a ring laser configuration. The stimulated Rayleigh scattering feedback in a high-threshold stimulated Brillouin optical fiber is a key mechanism as linewidth narrowing for laser output. A compound laser cavity ensured that the EDFL operated in the single longitudinal mode state and a saturable absorber is employed to form a gain grating for both filtering and improving wavelength stability. The fiber laser can output dual wavelengths simultaneously or operate at single wavelength in a switchable manner. Under the assistance of stimulated Rayleigh scattering feedback, the laser linewidths are compressed by around three times.At last, a stable tunable multi-wavelength narrow linewidth fiber laser has been proposed and demonstrated experimentally by employing a high-threshold stimulated Brillouin optical fiber and a sub-cavity structure. Here in, a short high-thresholdstimulated Brillouin optical fiber was utilized to enhance interaction between photons(light) and phonons(acoustic waves) to achieve more wavelength lasing than single mode fiber. Meanwhile, a subring-cavity structure is employed to ensure that each order of Stokes components works in single longitudinal mode based on Vernier effect.