Longitudinal modes tunable fiber laser and spectra analysis

We proposed a narrow linewidth fiber laser that operates tunably between 2 to 17 longitudinal modes. Based on fiber Fabry-Perot Interferometer (FFPI) as main wavelength selective component and high reflectivity uniform FBG as reflector, the fiber laser has simple structure and relatively stable output. Modes number tunability is achieved by changing the overlap of FFPI´s transmission band and uniform FBG´s reflection band. Delayed self-homodyne method is generalized to multi-mode situation and used to study the fine spectrum structure of laser output.