High-efficiency, double-clad fiber coupler, cladding mode sensor using a tilted fiber Bragg grating

A high-efficiency sensor for reflected cladding modes generated by a tilted fiber Bragg grating (TFBG) is demonstrated using a double-clad fiber (DCF) coupler (DCFC). The specially designed DCFC is spliced to a reflective TFBG written into photosensitive single mode fiber, tapered to match the inner cladding diameter of the DCFC. The DCFC is made by tapering and fusing two double-clad fibers (DCF) together. The device is capable of capturing low and high order backward propagating cladding modes to allow each mode to be clearly discriminated. A new mode of operation for refractive index sensing of a surrounding medium is possible with this sensor.