Single-polarization single-frequency DFB fiber laser with transverse mode switchable output

A single-polarization single-frequency (SPSF) 1030 nm distributed feedback (DFB) fiber laser with mode switchable output is achieved. The DFB fiber laser is realized based on a 5 cm long pi-phase shifted fiber Bragg grating (PS-FBG). A maximum output power of 84 mW with single-polarization operation is achieved. The polarization extinction ratio (PER) is around 17 dB and the linewidth is 18 kHz. The slope efficiency is 13% and the spectrum at the highest power shows an excellent optical signal to noise ratio of about 75 dB. Moreover, LP11 mode single-frequency lasing is achieved by adopting an acoustically-induced fiber grating (AIFG). The mode purity is estimated to be higher than 96%. These results, to the best of our knowledge, show the highest output power among the reports that achieve single-frequency 1030 nm DFB laser output with single-polarization operation. Furthermore, it is the first time to realize transverse mode switchable single-frequency fiber laser based on an AIFG. The high order mode single-frequency 1030 nm fiber laser has much potential to find applications in multiplexing system.