Investigation of cavity loss adjustment between two wavelengths required for dual-wavelength laser generation

Abstract

We show that the cavity quality for generated wavelengths in dual-wavelength laser must be substantially different for stable dual wavelength operation. In experiments the linear cavity included two FBGs and a fiber optical loop mirror (FOLM) with a high-birefringence fiber in the loop. The reflection spectrum of the FOLM shifts through temperature control of the hi-bi fiber loop that allows an adjustment of the ratio between FOLM reflections at generated wavelengths. The dual wavelength operation required an appropriate adjustment of this ratio. We measured the ratio necessary for dual wavelength operation at different wavelength separation. Wavelength separation is tuned by axial tension applied to one of FBG in the range 0.6 - 3 nm. Shorter wavelength always required higher reflection, and ratio between short wavelength reflection and long wavelength reflection increased strongly with wavelength separation. The tolerance of dual wavelength generation to reflection adjustment was measured to be about 1%.