Ginu Rajan

Low-cost wavelength measurement based on a macrobending single-mode fiber

A low-cost all-fiber wavelength measurement technique is proposed and demonstrated. A macrobending standard single-mode fiber is developed as an edge filter with an optimal design and simple surface processing. A ratiometric wavelength measurement system employing the developed macrobending fiber filter demonstrates a resolution of approximately 10 pm in a wavelength range from 1,500 to 1,560 nm with ease of assembly and calibration.

Overview of Fiber Optic Sensor Technologies for Strain/Temperature Sensing Applications in Composite Materials.

This paper provides an overview of the different types of fiber optic sensors (FOS) that can be used with composite materials and also their compatibility with and suitability for embedding inside a composite material. An overview of the different types of FOS used for strain/temperature sensing in composite materials is presented. Recent trends, and future challenges for FOS technology for condition monitoring in smart composite materials are also discussed. This comprehensive review provides essential information for the smart materials industry in selecting of appropriate types of FOS in accordance with end-user requirements.

Polarization dependence of bend loss for a standard singlemode fiber

Polarization dependence of bend loss caused by the polymer coating layer for a standard singlemode fiber (SMF28) is investigated theoretically and experimentally. Bend loss for SMF28 for both the TE and TM mode is calculated separately. Normalized polarization dependent loss is proposed for the characterization of the polarization sensitivity of bend loss for different bend radii. Corresponding experimental tests are presented, which agree with the theoretical results. Both the theoretical and experimental results show that the polymer coating layer has a significant influence on the polarization dependence of bend loss.

An Optimized Macrobending-Fiber-Based Edge Filter

An optimized all-fiber edge filter is developed, based on a one-turn macrobending bare fiber structure. The discrimination range is 16.32 dB over a wavelength range from 1500 to 1600 nm, which can be employed for wavelength measurement applications. It offers a simpler structure compared to the previously developed macrobending fiber loss edge filters, without an increase in the polarization-dependent loss.

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.

Resolution Investigation of a Ratiometric Wavelength Measurement System

Theoretical analysis and experimental investigations are presented on the resolution of a ratiometric wavelength measurement system. Theoretical modeling indicates that the resolution of a ratiometric wavelength measurement system is determined by the signal-to-noise ratio of the input signal and the noise of the photodetectors associated with optical-to-electronic conversion. For experimental verification, a ratiometric system employing a macrobending standard single-mode fiber is developed and corresponding results are in good agreement with the theoretical prediction.

Experimental Study and Analysis of a Polymer Fiber Bragg Grating Embedded in a Composite Material

The characteristics of polymer fiber Bragg gratings (FBGs) embedded in composite materials are studied in this paper and are compared with characteristics of their silica counterparts. A polymer FBG of 10 mm length which exhibits a peak reflected wavelength circa 1530 nm is fabricated and characterized for this purpose. A silica FBG with a peak reflected wavelength circa 1553 nm is also embedded in the composite material for a comparison study. The fabricated composite material sample with embedded sensors is subjected to temperature and strain changes and the corresponding effects on the embedded polymer and silica FBGs are studied. The measured temperature sensitivity of the embedded polymer FBG was close to that of the same polymer FBG in free space, while the silica FBG shows elevated temperature sensitivity after embedding. With an increase in temperature, spectral broadening was observed for the embedded polymer FBG due to the stress induced by the thermal expansion of the composite material. From the observed wavelength shift and spectral bandwidth change of the polymer FBG, temperature and thermal expansion effects in the composite material can be measured simultaneously.

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.

Temperature dependence of a macrobending edge filter based on a high-bend loss fiber

The temperature dependence of a macrobending bare-fiber-based edge filter is investigated both theoretically and experimentally. The fiber used is a high-bend loss fiber, type 1060XP. The experimental results show a good agreement with the proposed theoretical model over a temperature range from 0 degrees C to 80 degrees C. It is shown that the strong temperature dependence of a high-bend loss fiber has a significant influence on the performance of a fiber edge filter used in a wavelength measurement application. However, it is also concluded that such a temperature-dependent performance can be beneficially utilized in a fiber temperature sensing application.

Hybrid Fiber Optic Sensor System for Measuring the Strain, Temperature, and Thermal Strain of Composite Materials

This paper proposes a hybrid optical fiber sensor system for simultaneously sensing the strain, temperature, and thermal strain of composite materials. The hybrid fiber optic sensor system involves a combination of three sensors: 1) a polarimetric sensor based on an acrylate coated polarization maintaining photonic crystal fiber (PM-PCF); 2) a coating stripped PM-PCF sensor; and 3) a fiber Bragg grating sensor (FBG). Temperature is sensed using the FBG sensor, axial strain is sensed using the acrylate coated PM-PCF sensor, and thermal strain is sensed using the coating stripped PM-PCF. The hybrid sensor system presented operates in the intensity domain by converting the polarization and wavelength information from the polarimetric sensors and the FBG, respectively, into detectable linear intensity variations. Subsequently, by deriving a characteristic matrix for the hybrid sensors, information about temperature, axial strain, and thermal strain can be simultaneously determined. An experimental demonstration of the hybrid sensor system is described based on a glass fiber reinforced composite material sample within which the three different sensors are embedded. The proposed sensor configuration can be employed in composite material structural health monitoring applications.