Fiber-taper seeded long-period grating pair as a highly sensitive refractive-index sensor

We report the fabrication and characterization of a highly sensitive refractive-index sensor based on a long-period grating (LPG) pair with a fiber-taper section in between. Two LPGs with /spl sim/3-dB transmissivity form an in-fiber Mach-Zehnder interferometer. A fiber taper is made between the two LPGs to improve and tailor the sensitivity of the sensor. Enhanced sensitivity, which is about five times higher than that of a normal LPG pair, is achieved in the experiment.