Narrow-band fibre reflector based on a fibre Bragg grating reflection interferometer

Narrow-band filtering in reflected light using a reflection interferometer with a fibre Bragg grating (FBG) as its back mirror is demonstrated for the first time. The reflection interferometer is made in SMF-28e single-mode fibre, and the faces of its front mirror, which includes a thin metallic film, differ in reflectance. The reflection bandwidth of a test sample is 0.5 pm (62 MHz) at a wavelength of 1556 nm (Q-factor of 3 × 10⁶), its maximum reflectance is 0.21, and its contrast is 10². The use of a narrow-band FBG instead of thin-film broadband mirrors allows spectral selection to be significantly improved owing to an increase in the length of the interferometer base.