Low-threshold wavelength-switchable fiber laser based on few-mode fiber Bragg grating

• The threshold of the laser could be as low as 16 mW.
• The remarkable optical signal to noise ratios more than 72 dB are achieved.
• The operation wavelength for the generation of optical beams is located at C-band.
• The beams operating at cross-coupling can be switchable.
• The beam profile shows a main split beam corresponding to the LP11 mode.

We propose a backward-pump transverse mode fiber laser to generate optical beams based on few-mode fiber Bragg grating. The grating as a transverse mode filter possesses several reflection peaks by adjusting the core-offset. The transverse mode fiber laser operates at extremely low thresholds which are about 20, 16.5 and 16 mW corresponding to different operation wavelengths of 1560.98, 1562.32 and 1563.76 nm, respectively. The optical signal to noise ratios are about 72, 75.5 and 75.8 dB, when the pump power is fixed at 100 mW, respectively. The effectively exciting modes corresponding to each reflection peak interfere with each other. Different optical beams can be achieved by changing the operating wavelength or changing the state of PC. The device maybe find its applications such as sensing, transporting or manipulating microscopic particles.