a highly sensitive refractive-index sensor based on the long-period grating pair with a fiber-taper in-between
We report an improved structure of long-period gratings (LPGs), i.e. long-period grating pair with a fiber-taper in-between (LPGP-FTI), as a highly sensitive refractive-index sensor. Since a taper is introduced in-between the LPG pair, the guided core mode will be transmitted to a cladding mode as the fiber tapers down, and thus the evanescent field of the selected cladding mode in the external medium is increased. In this way the effective index difference is enlarged, so that the sensitivity can be greatly improved. The experimental results have shown that the sensitivity of the LPG pair to the change in the RI of the measurand can be efficiently improved by a fiber taper, and can be flexibly tailored by the tapering degree. Enhanced sensitivity, which is about five times higher than that of a normal LPG pair, is achieved in the experiment. Such a highly sensitive fiber-optic RI sensor is good for use as a chemical or biological sensor.
fiber-taper refractive index (ri) measurement optical fiber sensor long-period fiber gratings (lpgs)