Fine adjustment of cavity loss by fiber optical loop mirror for dual-wavelength laser

Abstract

We report numerically and experimentally analysis of optic fiber Sagnac interferometer and fine adjustment of cavity loss by the use of the FOLM with a hi-bi fiber in the loop. Changes in transmittance profile amplitude and wavelength shift are caused by the whirl effect in the connectors of a coupler with ports output connected to a birefringent fiber. Also the experimental demonstration of dual wavelength operation of a fiber laser through fine adjustment of cavity loss, using a Fiber Optical Loop Mirror (FOLM) with a high-birefringence fiber in the loop. The reflection and transmission of the FOLM presents a sinusoidal wavelength dependence which can be shifted by controlling the temperature of the hibi fiber. A temperature change of the hi-bi fiber by 0.1°C causes a measurable change in the ratio between the reflectance for the wavelengths R(λ₁)/R(λ₂). Using this adjustment be able to change the generation mode from single wavelength to stable dual wavelength generation with equal powers for λ₁ and λ₂ or to stable dual wavelength generation with unequal powers at λ₁ and λ₂. The change of the ratio between the FOLM reflection R(λ1)/R(λ2) allows the investigation of tolerance of dual wavelength generation on the ratio between cavity loss. Was found that for the switch from a single wavelength emission at λ₁ to single wavelength emission at λ₂ the ratio R(λ₁)/R(λ₂) has to be changed by the order of magnitude of 10^-2. This value shows the tolerance of the dual wavelength laser to the cavity loss adjustment.