Long period fiber grating based temperature-compensated high performance sensor for bio-chemical sensing applications

We report a stable, robust, and extremely sensitive refractive index sensor based on long period gratings written in optical fibers (LPFGs). By splitting the LPFG transmission spectrum at its phase-matching turnaround point, we show that it is possible to achieve an ultra-high sensitivity (similar to 2500 nm per refractive index unit) for biological/chemical samples. The splitting has been achieved by introducing an optical path difference of similar to 0.39 mu m between the core and cladding modes within the grating region of the optical fiber. In contrast to the widely used surface plasmon resonance (SPR) based sensors, no bulky prism, circulator or metal deposition is required in our sensor, making the present sensor extremely accurate, very compact and cost effective. We also demonstrate that a simultaneous measurement of refractive index and temperature/strain can be carried out using this sensor. (C) 2012 Elsevier B.V. All rights reserved.