Sang-Mae Lee

Simultaneous Measurement of Refractive Index, Temperature, and Strain Using Etched-Core Fiber Bragg Grating Sensors

This study demonstrates simultaneous measurement of three parameters viz. refractive index of surrounding medium, temperature, and strain using etched-core fiber Bragg grating sensors. Simultaneous measurement is achieved by exciting higher order modes in the sensor using an asymmetric nonadiabatic taper and measuring difference in their Bragg wavelength shifts due to different parameters. In order to simultaneously measure three parameters, three different order modes were excited in the sensor. The ability to measure multiple parameters is useful in bio-chemical measurements as it allows us to compensate for the change in Bragg wavelength with respect to change in temperature or strain. Thus, the sensors do not need to be stabilized.

High-Performance Optical Gating in Junction Device based on Vanadium Dioxide Thin Film Grown by Sol-Gel Method

In this paper, a high-performance optical gating in a junction device based on a vanadium dioxide dioxide (VO 2 ) thin film grown by a sol-gel method was experimentally demonstrated by directly illuminating the VO 2 film of the device with an infrared light at ~1554.6 ㎚. The threshold voltage of the fabricated device could be tuned by ~76.8 % at an illumination power of ~39.8 ㎽ resulting in a tuning efficiency of ~1.930 %/㎽, which was ~4.9 times as large as that obtained in the previous device fabricated using the VO 2 thin film deposited by a pulsed laser deposition method. The rising and falling times of the optical gating operation were measured as ~50 ㎳ and ~200 ㎳, respectively, which were ~20 times as rapid as those obtained in the previous device.

Etched-Core Fiber Bragg Grating Sensors Integrated With Microfluidic Channels

In this paper, we demonstrate a fiber Bragg grating sensor for bio-chemical detection. In the sensor area, the fiber has been chemically etched to the core with a diameter of 7 μm. Due to increased index contrast, the etched-core fiber Bragg grating supports multiple guided modes which respond differently to the refractive index of the surrounding medium, temperature and the strain. An asymmetric adiabatic taper is created between the etched and the unetched parts of the fiber resulting in excitation of both the symmetrical and the asymmetrical modes which can be interrogated with an erbium doped fiber amplifier amplified spontaneous emission source. The sensor is integrated with a Polydimethylsiloxane (PDMS) microfluidic channel for introduction of chemicals to be tested. A refractive index sensitivity of 92 nm/riu was achieved using the 3rd order mode. Further the sensor can simultaneously measure the refractive index, temperature and strain to an accuracy of 1 × 10-4, 0.32°C and 10 με assuming a wavelength resolution of 0.01 nm. By using signal processing, these resolutions can be improved by a factor of 10.

Optical characterization of refractive index sensors based on planar waveguide Fabry-Perot Bragg grating cavity

Abstract. The evanescent field–based polymeric planar waveguide refractive index sensors having a high Q Fabry–Pérot (FP) cavity between identical dual Bragg gratings corrugated on the surface of the planar waveguide were developed. The FP Bragg gratings cavity was fabricated with a cavity size of 5 and 7 mm, respectively. The spectra of light reflected from fabricated Bragg gratings, which were butt joined, were measured and compared with different indices of surrounding media. It was obtained that the FP Bragg gratings cavity is more sensitive than the single Bragg grating. The sensor developed shows much promise in the application of biomedical diagnostics such as a biosensor and/or environmental monitoring systems.

Parametric discrimination between refractive index, temperature and strain using etched-core FBG

Using asymmetrical non-adiabatic tapers we excite 3 modes in an etched-core-fiber-Bragg-grating sensor and show that the refractive index, temperature and strain can be measured simultaneously in bio-chemical sensing experiments.

High Sensitivity Bio-Sensor Based on an Etched Fiber Bragg Grating

Sensitivity of fiber-Bragg-grating sensors to index of surrounding medium is increased by etching core of fiber. The sensor is used to detect hybridization of DNA by measuring change of index on surface of the fiber.

Photonic-crystal-fiber-based temperature-insensitive polarimetric fiber strain sensor with reduced length of sensing fiber

Based on a Sagnac birefringence loop composed of polarization-maintaining photonic crystal fibers, we have demonstrated a temperature-insensitive polarimetric fiber strain sensor with the reduced length of the sensing fiber, which had a sensitivity of 1.91 pm/με and a measurement range of 0~6 mε.

Etched core fiber Bragg grating sensor integrated with microfluidic channel

We demonstrate an etched-core fiber Bragg grating sensor for detection of bio-chemical agents. The fiber Bragg grating of the sensor is etched to a diameter of 7 μm. The transition between the etched and the unetched core consists of an asymmetric taper resulting in excitation of multiple modes. The different excited modes respond differently to change in refractive index, temperature and strain. This allows for measurements for changes in these three parameters in a single measurement by simultaneous measurement of reflections in Bragg wavelengths for different modes. This parametric discrimination is confirmed experimentally by measuring the refractive index of water as temperature is increased. The sensor is then integrated in a micro-fluidic channel fabricated using Polydimethylsiloxane (PDMS) substrate and tested by introducing different chemicals. The sensitivity of the sensor to refractive index change is 92 nm/riu close to the refractive index of water. Assuming a wavelength resolution of 1 pm, index resolution of 1x10-5, a strain resolution of 1 microstrain, and a temperature resolution of 0.032 ºC is achieved by the sensor.