Tunable fiber laser based on the refractive index characteristic of MMI effects

•A tunable Erbium-doped all-fiber laser based on the refractive index characteristic of MMI effects has been demonstrated in this paper.•A thinner no-core fiber with a diameter of 104 μm has been used to fabricate the tunable fiber filter.•The tunable fiber filter shows a very sensitive response to the change of its surrounding refractive index.•The tunable laser we fabricated has a tunability of 32 nm.•The 3 dB bandwidth is less than 0.02 nm with the signal-to-noise ratio of about 40 dB.

A tunable erbium-doped all-fiber laser has been demonstrated. This tunable laser is based on a tunable fiber filter using the refractive index characteristics of multimode interference effects. A thinner no-core fiber with a diameter of 104 μm is used to fabricate the tunable fiber filter. The joint point of the thinner no-core fiber with SMF is a taper, which improves its sensitivity for refractive index changes. The filter exhibits a very sensitive response to the change of the environmental refractive index, which is about 1000 nm/RIU in the RI range from 1.418 to 1.427. The tunable fiber laser based on the filter achieved a tunability of 32 nm, with the wavelength tuned from 1532 nm to 1564 nm covering the full C-band. The 3 dB bandwidth of the tunable laser is less than 0.02 nm with the signal-to-noise ratio of about 40 dB.