A stable dual-wavelength single-longitudinal-mode fiber laser with a tunable wavelength spacing based on a chirped phase-shifted grating filter

A stable dual-wavelength with a tunable wavelength spacing fiber laser based on a chirped two phase-shifted grating filter is demonstrated. In the ring cavity, a chirped grating with two pi-phase shifts servers as an ultra-narrow dual-wavelength transmission band filter. The grating is attached in a triangular cantilever for chirp rate tuning. A semiconductor optical amplifier biased in low-gain regime is induced to reduce the gain competition of the two wavelengths caused by erbium-doped fiber. And a feedback fiber loop working as a mode filter guarantees the laser in a single-longitudinal-mode operation. Two lasing lines with different wavelength spacing from approximately 0.15 to 0.37 nm are experimentally demonstrated.