Highly Nonlinear Fiber-Assisted Multiwavelength Generation in Linear Cavity Thulium-Doped Fiber Laser

We propose a multiwavelength thulium-doped fiber laser in a linear cavity stabilized by a highly nonlinear fiber (HNLF). Stable multiwavelength operation at 2 μm was obtained by introducing a 500-m HNLF within the cavity to alleviate mode competition caused by homogeneous gain broadening of the thulium gain medium. The presence of HNLF-induced spectral broadening through the FWM effect helped to increase the number of output channels, with 22 lasing lines observed within a 10-dB bandwidth and optical signal-to-noise ratio as high as 30 dB. The laser exhibited power fluctuations of less than 1.325 dB with maximum wavelength dithering of 0.12 nm. This work has demonstrated the use of simple HNLF-integrated linear cavity architecture to generate multiwavelength output without complex nonlinear-based structure.