Kishore Bhowmik

Experimental Study and Analysis of Hydrostatic Pressure Sensitivity of Polymer Fibre Bragg Gratings

The intrinsic hydrostatic pressure sensitivity of polymer optical fiber Bragg grating (POFBG) with different diameters are investigated. POFBGs are inscribed in single-mode polymer fiber and etched down to different diameters. We have experimentally demonstrated that the material properties of the polymer optical fiber can change after etching and thus the etching procedure can have an impact on the pressure sensitivity of the POFBG. It is observed from the experimental results that hydrostatic pressure induces a positive wavelength shift to the POFBG and the pressure sensitivity of the POFBG shows significant increase as the fiber diameter reduces through etching. A pressure sensitivity of 0.20 pm/kPa is obtained for an unetched POFBG while for an etched POFBG with 55-μm diameter a sensitivity of 0.75 pm/kPa is observed. Temperature compensation techniques are also successfully implemented to extract the true intrinsic pressure sensitivity of the POFBG. Through this study, the intrinsic pressure sensitivity of POFBG with different diameters are obtained and also the significance of etching and its impact on pressure sensitivity is demonstrated. This information can lead to further research and development on high sensitivity pressure transducers based on etched POFBGs.

Intrinsic High-Sensitivity Sensors Based on Etched Single-Mode Polymer Optical Fibers

The significance of etched single-mode polymer optical fibers and their potential for the development of high-sensitivity sensors are presented. A polymethyl methacrylate-based single-mode polymer optical fiber is etched to various diameters and it is observed that etching can lead to change in the material properties of the fiber, such as Youngs modulus and thermal expansion coefficient. This can play a vital role in improving the intrinsic sensing capabilities of sensors based on etched polymer optical fiber. To demonstrate that the modified material properties of the etched polymer fiber can enhance its intrinsic sensing capabilities, sensing characteristics of etched polymer fiber Bragg gratings for strain, temperature, and pressure are obtained. From the results, it is confirmed that the sensors based on etched polymer fibers exhibit high intrinsic sensitivity compared with un-etched ones. The potential of developing a sensing system for simultaneous measurement of strain and temperature is also demonstrated.

High Intrinsic Sensitivity Etched Polymer Fiber Bragg Grating Pair for Simultaneous Strain and Temperature Measurements

A sensing configuration for simultaneous measurement of strain and temperature with enhanced intrinsic sensitivity based on a fiber Bragg grating (FBG) pair with one grating inscribed in the etched and the other in unetched polymer fiber region is demonstrated. A poly (methyl methacrylate) based single-mode polymer fiber is etched to different diameters, and it is observed that etching can lead to change in the material properties of the fiber, such as Youngs modulus and thermal expansion coefficient, which can play a vital role in improving its intrinsic sensing capabilities. Thus, exploiting the different strain and temperature sensitivities exhibited by etched and unetched polymer FBGs, strain and temperature can be simultaneously measured with very high sensitivity. Experimental results show that rms deviations of ±8.42 με and ±0.39 °C for strain and temperature, respectively, in a real simultaneous measurement. The effect of individual thermal and strain sensitivity coefficients on measurement accuracy is also analyzed.

Etching Process Related Changes and Effects on Solid-Core Single-Mode Polymer Optical Fiber Grating

Etching process related material and mechanical changes on solid-core singlemode polymer optical fiber (POF) and their influence on the characteristic properties of polymer fiber Bragg gratings (PFBGs) are studied. A poly(methyl methacrylate)-based POF is etched to different diameters, and it is experimentally demonstrated that etching can lead to a change in the Youngs modulus of the fiber. It is found that etching process induced material changes of the polymer fiber can enhance the reflectivity and inherent sensitivity of PFBGs. It is demonstrated that gratings based on etched POF exhibit higher reflectivity with a shorter exposure time compared with unetched ones. Highest reflectivity of 98.54% is observed within 7 seconds of exposure for a diameter of 85 μm. The stability of fabricated Bragg gratings is also studied. By tailoring the etching diameter of POF, Bragg gratings with high sensitivity and high reflectivity can be fabricated.

Hydrostatic pressure sensitivity of standard polymer fibre Bragg gratings and etched polymer fibre Bragg gratings

The hydrostatic pressure sensitivity of polymer optical fibre Bragg grating of different diameters is investigated. For this purpose Bragg gratings are inscribed in single-mode polymer fibre and also in etched single-mode polymer fibre. The inherent pressure sensitivity of the grating are experimentally investigated up-to 1MPa by monitoring the change in the reflected peak wavelengths due to pressure. It is observed that polymer FBGs exhibit a positive Bragg wavelength shift and is also more sensitive compared to silica FBGs. The pressure sensitivity of the polymer FBG can be increased by reducing the diameter of the fibre.

Etched Polymer Fibre Bragg Gratings and Their Biomedical Sensing Applications

Bragg gratings in etched polymer fibres and their unique properties and characteristics are discussed in this paper. Due to the change in material and mechanical properties of the polymer fibre through etching, Bragg gratings inscribed in such fibres show high reflectivity and enhanced intrinsic sensitivity towards strain, temperature, and pressure. The short-term and long-term stability of the gratings and the effect of hysteresis on the dynamic characteristics are also discussed. The unique properties and enhanced intrinsic sensitivity of etched polymer fibre Bragg grating are ideal for the development of high-sensitivity sensors for biomedical applications. To demonstrate their biomedical sensing capabilities, a high-sensitivity pressure transducer that operates in the blood pressure range, and a breathing rate monitoring device are developed and presented.

High-sensitivity polymer fibre Bragg grating sensor for biomedical applications

Single-mode polymer optical fibre Bragg gratings (POFBGs) are etched to different diameters and their potential for the development of high-sensitivity sensors are presented. The material properties of the fibre can be changed by etching and thus the etching procedure can have an impact on the performance of POFBGs. To confirm that the material properties of etched polymer fibre can be modified and its sensitivity enhanced, sensing characteristics of different etched POFBGs for pressure, strain and temperature are investigated. From the experimental results, we show that the sensors based on etched polymer fibres exhibit a higher sensitivity and they are more desirable than the un-etched ones for biomedical applications. Two examples of low pressure sensor such as blood pressure sensor and foot pressure sensor are demonstrated. With etching, enhanced sensitivity and bio-compatible polymer fibre sensors could be very useful for biomedical applications.

Etched Polymer Fibre Bragg Gratings

Recently we initiated a new research direction for high-sensitivity and high-reflectivity Bragg grating fabrication based on etched polymer optical fibre, here we report the recent research developments on etched polymer fibre Bragg gratings.

High Sensitivity Polymer Fibre Bragg Grating Sensors and Devices

Research on single-mode polymer optical fibres, Bragg gratings based on polymer optical fibre and their applications has been considerably progressed in the recent years. This chapter provides an overview on recent research developments on solid core polymer fibre Bragg grating sensors, devices and their applications.

Evaluation of the physical properties of dental resin composites using optical fiber sensing technology

OBJECTIVES The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fiber Bragg grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. METHODS A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. Six commercially available dental composites with different filler types and volume are evaluated. The tests are repeated with three sets of samples. The curing characteristics and residual strain gradient exhibited by the cured dental composites were also observed and commented. RESULTS Among the studied samples, SDR shows lowest polymerization shrinkage, while Beautifil FO3 shows the highest. The results also show clear distinction between particle filler type and fiber reinforcement based composites in their polymerization shrinkage properties. The agreement of the results with existing literatures show that FBG based system provides accurate results. Polymerization shrinkage rate of the samples are also obtained. Thermal expansion of the composites are measured using the FBG sensing method for the first time and is correlated with resin type, volume, filler type and glass transition temperature. The water sorption characteristics of the dental composite are also successfully measured using the FBG sensing method. The high level of repeatability and the low standard deviations shown in the results indicate good reliability with the use of FBG sensors. SIGNIFICANCE This study demonstrates how optical fiber technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample. These features are expected to greatly assist material science researchers in dentistry as well as other biomedical fields. Of some interest the phenomenon of stress relaxation of dental composite at higher temperature was observed.