A fiber Bragg grating (FBG) accelerometer suitable for health monitoring of electrical machines has been proposed. A polymer composite material is used to design the cantilever of the accelerometer. Thus it is ensured that there are no conducting parts in the accelerometer. Detailed finite element analysis of the cantilever is done to optimize the sensitivity and the resonant frequency. The sensitivity is significantly improved compared to the conventional FBG accelerometer having similar bandwidth of operation. Two different configurations, one having sensitivity 14.4 pm/g with resonant frequency 444 Hz, and the other having sensitivity 7.5 pm/g with resonant frequency 940 Hz have been designed and fabricated. The wide band optical accelerometers will enable monitoring of vibration modes of critical components of electrical machines and more importantly using commercially available standard FBG interrogators, instead of using any complex interrogation techniques. A good match between the simulation and experimental results was observed.

A long period fiber grating (LPFG) sensor has been fabricated, after theoretical analysis, obtaining the maximum enhancement of the evanescent field working with the lowest order cladding mode (LP0,2 cladding mode) near turn around point. Both the wavelengths of the dual peak resonance and the coupling conditions of the mode have been analyzed in detail. A flow cell has been fabricated to characterize the sensor in term of surrounding refractive index (SRI) sensitivity. The sensitivity of the sensor resulted to be ~ 8751 nm/SRIU, with a resolution in the order of 10-5, within the SRI range of 1.333 to 1.3335.

We present our theoretical study on the design of LPFG sensor where its Add-Layer sensitivity is enhanced. Add-Layer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes, have been used to enhance the Add-layer sensitivity. Using coupled mode analysis we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.

A new methodology to enhance the sensitivity of a long period fiber grating sensor (LPFG) at the Turn Around Point (TAP) is here presented. The LPFG sensor has been fabricated by etching the fiber up to 20.4 µm, until the sidelobes of dispersed LP_0,2 cladding mode appeared near TAP in aqueous medium. The dual peak sensitivity of the sidelobes was found to be 16,044 nm/SRIU (surrounding refractive index units) in the RI range from 1.333 to 1.3335.

We report our experimental study on the add-layer sensitivity of LP0,11 cladding mode (CM) of Long Period Fiber Grating (LPFG) near turn around point (TAP). The CM response was tuned by controlled modification of the cladding diameter and deposition of overlay layers of polymer material. In this process an add-layer sensitivity of 2.308 nmWL/nmTH has been achieved. It is interesting to observe that add-layer sensitivity obtained in this process is close to the sensitivity of the same CM operated near the mode transition (MT). The advantage is that, the sensor designed as per the proposed methodology will not be plagued by the basic limitations of operating a CM near MT, i.e. loss of contrast of the resonant band and limited dynamic range. In our experiment, the dynamic range has found to be ~ 100 nm where the contrast remains greater than -10 dB throughout the range of measurement which is practically impossible to get for any CM operating at MT. The experimental result was supported by theoretical calculations. Also the SRI sensitivity of the sensor was found out to be 6400 nm/ SRIU.