Fabrication and Characterization of 2 × 2 Microfiber Coupler for Generating Two Output Stable Multiwavelength Fiber Lasers

A compact 2 × 2 microfiber coupler (MC) is proposed and experimentally demonstrated for the generation of stable multiwavelength fiber laser in the C-band region. The 2 × 2 MC is fabricated by twisting and fusing together two lateral dual single mode fibers using the flame-brushing technique. The 2 × 2 MC has a waist diameter of 8 μm with a coupling ratio of 38:62 and 45:55 at ports 1 and 2, respectively. The 2 × 2 MC exploits super mode coupling to produce spatial mode beating and suppress mode competition of the homogeneous gain medium in a fiber ring laser. The channel spacing of the output wavelengths is immune to changes in the external environment and can be extracted from the peaks of the 2 × 2 MC's periodic oscillation. The proposed laser is capable of generating stable single, dual, and triple lasing wavelengths from its two output ports over a range of more than 29 nm, which is further enhanced by the polarization rotation mechanism. The generating lasing wavelengths have a 3 dB line-width of less than ~30 pm and peak-to-floor ration of about 58 dB at a pump power of 38 mW.