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.