A device is disclosed. The device contains a first electro-optical waveguide comprising at least one first grating, a second electro-optical waveguide comprising at least one second grating, a plurality of electrodes disposed adjacent to the first grating and configured to impose an electric field through the first electro-optical waveguide to modify spectra of the first grating, a fiber amplifier configured to propagate a laser radiation between the first electro-optical waveguide and the second electro-optical waveguide, and at least two circulators associated with the fiber amplifier and the first electro-optical waveguide and the second electro-optical waveguide and configured to provide unidirectional propagation of the laser radiation along the fiber amplifier.