Research On Dual-wavelength Fiber Laser With Narrow Line Width Based On Phase Shifted Fiber Bragg Grating

In this thesis, the Dual-wavelength fiber laser with narrow linewidth based on thephase-shifted grating was designed. The focuses were how to obtain a dual-wavelength andnarrow line width filter and how to design the structure of the fiber laser. Standing wavecondition of the equivalent resonator, as a new method, was used to discuss the structure andreflection spectrum characteristics of phase-shifted grating, including the single anddual-phase-shift grating and the phase-shifted sampled grating. Laser with narrow linewidthbased on different laser structures can be obtained experimentally. The details were describedas follows:(1) Phase-shifted grating was regard as a resonator formed by two FBGs. According to thecouple mode and transfer matrix theory, combined with phase changes caused byreflection coefficient of the FBG, using standing wave condition of the equivalentresonator, transmission peak wavelength dependence of factors were analyzed. Thefollows can be demonstrated: there were one transmission peak in the bandwidth of thereflection; the wavelength space was influenced by value and position of the phase shift.when the phase shift was π, the transmission wavelength was not related to the positionof the phase shift, when the value of phase shift was deviated from π, the wavelength ofthe transmission peak was not only related to the value of phase shift, but also theposition of phase shift.(2) Using standing wave condition of the equivalent resonator, structural of the dual-phase-shifted grating and factors affecting transmission wavelength were analyzed, Thefollows can be demonstrated: there were two transmission peaks in the bandwidth of thereflection, the wavelength space was influenced by value and position of the phase shift.When the value of the phase shift was unchangeable, the wavelength spacing becamesmaller with the increasing distance of the two phase shifts. With invariable distance ofthe two phase shifts, the wavelength spacing became bigger with the increasing of phasedifference. With the increasing of distance between phase shifts, the value of the phaseshift impact on the wavelength space was more obvious.(3) With appropriately parameters, dual-wavelength reflection peaks in the reflection of thesampled grating can be obtained. When Phase shift was inserted, two new transmissionpeaks can be gained separately in the bandwidth of the two reflection peaks. Accordingto standing wave condition, transmission wavelength dependence of factors weredemonstrated: the transmission wavelength was related to the value and position of thephase shift. When value of the phase shift changed, both the transmission wavelengthsbecame bigger or smaller；With phase shift position deviated from the center, phaseshifted sampled grating has a more obvious wavelength change versus the value of phase shift, but there will be a high loss.(4) Two different kinds of fiber laser were studied experimentally:1. Grating pair wascarved on the EDF, due to the EDF between the pair can be regarded as phase shift, asingle phase shifted DFB fiber laser can be obtained. Single-wavelength narrowlinewidth laser was carried out.2. Dual-phase-shifted grating and FBG were used as thefilter, a dual-wavelength ring fiber laser was made up, dual-wavelength laser was carriedout.