All-fiber all-optical phase controller based on F-P interferometer and Er/Yb co-doped fiber

•In this letter, we propose an all-fiber all-optical phase modulator based on an active Fabry-Perot interferometer (FPI) with Er/Yb co-doped fiber (EYDF). The rare earth dopants in active fiber act as heaters, effectively changing the refractive index and phase of the F-P cavity via the thermo-optic effect.•A maximum phase shift of 2.53 π with a slope of 0.0167 π/mW is obtained in the experiments.•Note that the dopants and the optical signal transmission are both in fiber core, while the cladding of the fiber acts as a natural protective barrier for insulating the outside environment pollution. Therefore, the design of all optical fiber without material coating not only makes the device simple to manufacture and has a small footprint, but also offers good long-term environmental stability.