Tunable Fiber Laser by Cascading Twin Core Fiber-Based Directional Couplers

A C-band tunable erbium-doped fiber laser is proposed and experimentally demonstrated by cascading two twin-core fiber (TCF)-based directional couplers. Two TCF-based couplers have different TCF lengths and gave rise to a dense fringe pattern modulated by a sparse one. The lasing wavelength was coarsely tuned by bending one TCF-based coupler with TCF length of 0.14 m, and finely tuned by stretching another TCF-based coupler with TCF length of 1.37 m. Experimental results have shown that the lasing wavelength was linearly and monotonously tuned over 23.2 nm (1541.8-1560 nm) with a uniform tuning step of 0.22 nm, side mode suppression ratio of up to 58 dB, power uniformity of ±0.1 dB. In addition, the output power fluctuation and the wavelength drift have been monitored and found to be <;±0.05 dB and 0.004 nm, respectively.