A highly efficient thermally controlled loss-tunable long-period fiber grating on corrugated metal substrate

We demonstrate a new approach for fabricating a compact loss-tunable long-period fiber grating (LPFG) by gluing a fiber onto a corrugated metal substrate filled with ultraviolet-cured epoxy. The strain caused by the difference in thermal expansion among the adhesive, the substrate, and the silica fiber induces a periodic microbending along the fiber when the device temperature is changed. The LPFG has an initial flat spectrum at room temperature. With 35 grating periods, a tuning range of -21 dB is achieved through core-cladding coupling for a temperature change from room temperature to 4°C. A theoretical model is presented to explain the high tuning efficiency and the operating mechanisms of the device.