Amardeep Kaur

High-temperature fiber-optic Fabry–Perot interferometric pressure sensor fabricated by femtosecond laser

In this Letter, we report on a fiber-optic Fabry-Perot interferometric pressure sensor with its external diaphragm surface thinned and roughened by a femtosecond laser. The laser-roughened surface helps to eliminate outer reflections from the external diaphragm surface and makes the sensor immune to variations in the ambient refractive index. The sensor is demonstrated to measure pressure in a high-temperature environment with low-temperature dependence.

Long-Period Grating Inscribed on Concatenated Double-Clad and Single-Clad Fiber for Simultaneous Measurement of Temperature and Refractive Index

In this letter, a kind of long-period fiber grating (LPFG) that is capable of simultaneous measurement of temperature and surrounding refractive index (RI) is fabricated and demonstrated. The compact LPFG is written on a piece of spliced standard single-mode fiber (SMF) and double-clad fiber (DCF) with the CO2 laser point-by-point irradiation technique. The LPFG section in the DCF is solely sensitive to temperature, while the section of the LPFG in the SMF is sensitive to both temperature and surrounding RI. After temperature and RI calibration, the LPFG has been used to measure the RI change of ethylene glycol with the change of temperature to demonstrate its capability for dual parameter simultaneous measurement.

Reflection-based phase-shifted long period fiber grating for simultaneous measurement of temperature and refractive index

Abstract. We report a reflection-based phase-shifted long period fiber grating (PS-LPFG) and demonstrate its capability for simultaneous measurement of temperature and external reflective index (RI). The sensor device comprises a grating directly written by CO2 laser and silver-coated end face. A π-shifted LPFG is presented with two attenuation bands through its reflection spectrum. These two bands have different sensitivity towards temperature and external RI that can be used for simultaneous measurement of the two variables. The experimental results show that this probe-type PS-LPFG performs well in terms of linearity and sensitivity.

Microcavity strain sensor for high temperature applications

Abstract. A microcavity extrinsic Fabry–Perot interferometric (EFPI) fiber-optic sensor is presented for measurement of strain. The EFPI sensor is fabricated by micromachining a cavity on the tip of a standard single-mode fiber with a femtosecond (fs) laser and is then self-enclosed by fusion splicing another piece of single-mode fiber. The fs-laser-based fabrication makes the sensor thermally stable to sustain temperatures as high as 800°C. The sensor exhibits linear performance for a range up to 3700  με and a low temperature sensitivity of only 0.59  pm/°C through 800°C.

Embeddable fiber optic strain sensor for structural monitoring

An extrinsic Fabry-Perot interferometric (EFPI) fiber optic sensor is presented for measurement of strain at high ambient temperatures. The sensor is fabricated using a femto-second (fs) laser. The EFPI sensor is fabricated by micromachining a cavity on the tip of a standard single-mode fiber and is then self-enclosed by fusion splicing another piece of singlemode fiber. The fs-laser based fabrication makes the sensor thermally stable to sustain temperatures as high as 800 °C. The sensor is relatively insensitive towards the temperature as compared to its response towards the applied strain. The sensor can be embedded in Carbon fiber/Bismaleimide (BMI) composite laminates for strain monitoring at high ambient temperatures.

Strain monitoring using distributed fiber optic sensors embedded in carbon fiber composites

A distributed fiber optic strain sensor based on Rayleigh backscattering, embedded in a fiber-reinforced polymer composite, has been demonstrated. The optical frequency domain reflectometry (OFDR) technique was used to analyze the backscattered signal. The shift in the Rayleigh backscattered spectrum (RBS) was observed to be linear to the change in strain of the composite material. The sensor (standard single-mode fiber) was embedded between the layers of the composite laminate. A series of tensile loads were applied to the laminate using an Instron testing machine, and the corresponding strain distribution of the laminate was measured. The results show a linear response indicating a seamless integration of the optic fiber in the composite material and a good correlation with the electrical-resistance strain gauge results. In this study, distributed strain measurements in a composite laminate were successfully obtained using an embedded fiber optic sensor.

Strain monitoring of a composite wing

An instrumented composite wing is described. The wing is designed to meet the load and ruggedness requirements for a fixed-wing unmanned aerial vehicle (UAV) in search-and-rescue applications. The UAV supports educational systems development and has a 2.1-m wingspan. The wing structure consists of a foam core covered by a carbon-fiber, laminate composite shell. To quantify the wing characteristics, a fiber-optic strain sensor was surface mounted to measure distributed strain. This sensor is based on Rayleigh scattering from local index variations and it is capable of high spatial resolution. The use of the Rayleigh-scattering fiber-optic sensors for distributed measurements is discussed.

Monitoring cure properties of out-of-autoclave BMI composites using IFPI sensor

A non-destructive technique for inspection of a Bismaleimide (BMI) composite is presented using an optical fiber sensor. High performance BMI composites are used for Aerospace application for their mechanical strength. They are also used as an alternative to toughened epoxy resins. A femtosecond-laser-inscribed Intrinsic Fabry-Perot Interferometer (IFPI) sensor is used to perform real time cure monitoring of a BMI composite. The composite is cured using the out-of-autoclave (OOA) process. The IFPI sensor was used for in-situ monitoring; different curing stages are analyzed throughout the curing process. Temperature-induced-strain was measured to analyze the cure properties. The IFPI structure comprises of two reflecting mirrors inscribed on the core of the fiber using a femtosecond-laser manufacturing process. The manufacturing process makes the sensor thermally stable and robust for embedded applications. The sensor can withstand very high temperatures of up to 850 °C. The temperature and strain sensitivities of embedded IFPI sensor were measured to be 1.4 pm/μepsilon and 0.6 pm/μepsilon respectively.

Strain monitoring of bismaleimide composites using embedded microcavity sensor

Abstract. A type of extrinsic Fabry–Perot interferometer (EFPI) fiber optic sensor, i.e., the microcavity strain sensor, is demonstrated for embedded, high-temperature applications. The sensor is fabricated using a femtosecond (fs) laser. The fs-laser-based fabrication makes the sensor thermally stable to sustain operating temperatures as high as 800°C. The sensor has low sensitivity toward the temperature as compared to its response toward the applied strain. The performance of the EFPI sensor is tested in an embedded application. The host material is carbon fiber/bismaleimide (BMI) composite laminate that offer thermally stable characteristics at high ambient temperatures. The sensor exhibits highly linear response toward the temperature and strain. Analytical work done with embedded optical-fiber sensors using the out-of-autoclave BMI laminate was limited until now. The work presented in this paper offers an insight into the strain and temperature interactions of the embedded sensors with the BMI composites.

Monitoring of out-of-autoclave BMI composites using fiber optic sensors

Bismaleimide (BMI) composites are used in applications that require good mechanical properties at high temperatures. In this paper, a Non-destructive inspection technique for BMI composites which can be used at high temperatures is presented. Cavity based External Fabry-Perot Interferometer (EFPI) optical sensors have been developed and embedded in the laminates. These sensors are capable of operating in temperatures up to 800°C. The embedded sensors are used to perform real time cure monitoring of a BMI composite. The composite is cured using an out-of-autoclave (OOA) process. Once the composite is cured, the same sensors are used to measure mechanical performance of the laminate. The performance of the embedded sensor is investigated under tensile loading at room temperature as well as elevated temperatures.