An aluminum coated all-fiber mirror and a Mach-Zehnder interferometer for developing a switchable and tunable multi-wavelength laser

In this paper, a tunable and switchable multi-wavelength erbium doped linear fiber laser, based on an optical fiber loop mirror containing a Mach-Zehnder interferometer (MZI) and an aluminum coated optical fiber cleaved end is presented. The MZI, obtained by core-offset splicing a piece of photonic crystal fiber (PCF) between two segments of a single mode fiber (SMF), acts as a wavelength selective filter (WSF). The full reflecting mirror implemented is obtained by thermal evaporation of aluminum on a cleaved fiber end, technique which has not been deeply explored for compact fiber laser configurations. In this way, both optical loop mirror and the aluminum coated fiber work together to make a resonant cavity. By rotating the wave plates of a polarization controller, the polarization state of the cavity modes diversifies, and the laser setup can emit one, two, three or four laser wavelengths, which can be switched from 1526 to 1562 nm. In addition, this laser arrangement can be tuned within a 5 nm interval and has a side-mode suppression ratio of 42 dB for single-wavelength operation. Finally, the proposed laser configuration achieved a high stability for more than an hour at room temperature.