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 turn-around point, we show that it is possible to achieve an ultra-high sensitivity (∼2500 nm per refractive index unit) for biological/chemical samples. The splitting has been achieved by introducing an optical path difference of ∼0.39 μm 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.