Switchable multi-wavelength erbium-doped photonic crystal fiber laser based on nonlinear polarization rotation

• A novel erbium-doped photonic crystal fiber is used as gain medium.
• A multi-wavelength laser based on nonlinear polarization rotation.
• There is no certain specific wavelength selection device in laser cavity any more.
• A polarization-dependent isolator with Ed-PCF is used to form a fiber filter.
• The laser can accomplish multiple-parameter measurement simultaneously in sensor.

A multi-wavelength erbium-doped photonic crystal fiber (ED-PCF) ring laser based on nonlinear polarization rotation was demonstrated experimentally. To the best of our knowledge, this study is the first to use a polarization-dependent isolator with an ED-PCF to form an equivalent fiber filter. The intensity-dependent inhomogeneous loss induced by nonlinear polarization rotation was applied to reduce the mode competition caused by ED-PCF. A detailed theoretical analysis using the Jones matrix method to calculate the transfer function of the laser was presented. The theoretical data, which were confirmed by the experimental results, showed that a multi-wavelength with a spacing of approximately 2.26 nm was achieved by controlling the polarization controller. The proposed fiber laser with a signal-to-noise ratio higher than 40 dB achieved a low threshold power of 30 mW. Therefore, stable multi-wavelength outputs with a power fluctuation of less than 2 dB were generated at room temperature.