Optical Fiber Fiber Fabry–Perot Filter With Tunable Cavity for High-Precision Resonance Wavelength Adjustment

In this paper, we propose an optical fiber Fabry-Perot (F-P) filter whose cavity is made of active fiber for high-precision resonance wavelength adjustment. Two high reflective fiber Bragg gratings (FBG) are used as the reflectors and they are connected by a short cobalt-doped single mode fiber to form the F-P structure. The resonant peak of the cavity is the fringe formed on the FBG spectrum. The optical path length of the F-P cavity, i.e, the resonate peak of the filter, is adjustable when the cobalt-doped fiber is heated by a heating laser. Experiment shows wavelength tuning coefficient is 8.1 MHz/mW at 1550 nm (0.065 pm/mW) which indicates the high-precision wavelength adjustment characteristics. The response time is also measured and it is independent to the level of the heating power and the material of the surrounding media. The all-optical controllable feature also makes this filter a promising device in many applications.