Narrow spectral linewidth and tunable erbium-doped fiber ring laser using a MZI based on CHCF

Abstract In this paper, a narrow spectral linewidth and wavelength-tunable erbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) as a filter is proposed and experimentally demonstrated. The filter is fabricated by splicing a short length of capillary hollow-core fiber (CHCF) between two small sections of multimode fibers (MMF). The interference pattern generated by the filter has a free spectral range of 10.5 nm and a maximum extinction ratio of 36 dB at 1560 nm. Then, by incorporating the filter inside a ring cavity laser, a single laser emission centered at 1566.46 nm with a spectral width around 0.03 nm and a high SNR of 66 dB (also has a SMSR of 53 dB) is obtained. By changing the temperature of the filter, the wavelength emission of the laser can be tuned from 1566.46 to 1570.09 nm. Considering that the fabrication process of the filter is relatively simple and can be easily implemented in an EDFL, we strongly believe that it can have a great deal of interest in telecom applications.