Raman comb lasing in a ring cavity with high-birefringence fiber loop mirror

We demonstrate a 400-wavelength Raman comb lasing based on the nonlinear polarization rotation (NPR) in a ring cavity with high-birefringence fiber loop mirror (HBFLM). The comb-line intensities are equalized by the NPR mechanism. As the length of polarization-maintaining fiber (PMF) in the HBFLM is changed from 5.4 to 120 m, the line spacing varies from 1.17 to 0.0533 nm and the 10 dB spectral bandwidth is kept at the similar level. In case of a 120 m long PMF, more than 400 wavelengths with the signal-noise ratio higher than 10 dB are obtained in the 10 dB bandwidth of 22.4 nm.