Optically tunable fiber Bragg grating based on a photo-mechanical tuning mechanism

We present an optically tunable fiber Bragg grating (FBG) based on a photo-mechanical tuning mechanism. Azobenzene containing polymer was utilized as a photo-mechanical tuning agent coated over a bare section of FBG. Controlled by ultraviolet (UV) irradiation, the polymer coating acts as a micro-actuator that deforms the fiber structure. Reversible tunability was obtained by the coating locally stretching the embedded FBG fiber by the intensity and the spatial distribution of the UV light. We found that our tunable FBG could linearly tune its center wavelength as large as 2.2 nm in a symmetric UV irradiation. We also found that a chirp of grating periods could be produced by an asymmetric irradiation, where the center of the UV irradiation profile is offset to that of the FBG device. The spectral width measured at 10 dB could be broadened from 0.4 to 1.2 nm by simply adjusting the relative position of the UV light source. The direction of the chirp, in either normal or anomalous dispersion, could be easily switched as well. Our observations demonstrated that our device provides a versatile means of tunable filters or dispersion generators, which is useful in various applications.