All-fiber Mach–Zehnder interferometric comb filter based on macrobend single-mode optical fiber for selecting lasing performance in 1-micron region

Abstract We report on a new method to select between tunable single- and multi-wavelength switchable lasing performances in continuous-wave (CW) ytterbium-doped fiber laser (YDFL). The wavelength selection and switching techniques are based on the whispering gallery mode (WGM) effect in a Mach–Zehnder interferometric comb-filter formed by bending a standard single-mode fiber (SMF) into a balloon like shape. By incorporating the proposed comb-filter into the laser ring cavity and adjusting the SMF’s bending diameter to control the spectral cavity losses, the single-wavelength lasing was tuned from 1065.26 to 1048.6 nm. Furthermore, by appropriately rotating the polarization controller (PC) cascaded with the filter, the laser can be switched between the dual-and triple-wavelength lasing operations. Two sets of switchable triple-wavelength lasing operations around 1045 nm were obtained with a side-mode suppression ratio (SMSR) of 26.9 dB and 22.4 dB, respectively. To the best of our knowledge, this is the first demonstration of a balloon-like interferometer based comb-filter using a bare bending SMF. The experimental results indicate that the proposed filter provides a promising method to achieve tunable single- or switchable multi-wavelength YDFL.