Tunable and channel spacing precisely controlled comb filters based on the fused taper technology.

We propose and demonstrate an adjustable all-fiber comb filter with precisely controlled channel spacing by employing a tapered fiber in one arm of a Mach-Zehnder interferometer (MZI) for the first time. Using fused taper technology to draw the fiber, we can precisely control the optical path difference between the two arms of the MZI, thus realizing a precisely controllable channel spacing. By rotating the polarization controller state in the other arm of the MZI, the transmission spectrum wavelength can be continuously tuned. Comb filters with controllable channel spacings from 0.2 to 3.0 nm have been numerically studied and achieved in experiment. Applications of a filter based on a multi-wavelength tunable all-fiber laser source are also demonstrated.