Continuously tunable fibre attenuator operating in the wavelength range near 1.5 μm

A fibre attenuator is fabricated for the telecommunication wavelength range near 1.5 μm in which a single-mode silica fibre with side polishing is used. The fibre surface is covered by a layer of fluorine-containing polymer with a large thermooptic coefficient. The principle of attenuator operation is based on a change in the conditions of total internal reflection for a guided mode in the polished region due to thermally induced variation in the refractive index of the fluoropolymer layer. The attenuator is insensitive to light polarisation, it has a continuously variable attenuation coefficient in the range 0.2–27 dB, and can be easily incorporated into fibreoptic links.