Relative humidity (RH) sensor employing etched fiber Bragg grating (FBG) is reported where RH variations are captured using effective-index-modulation, rather than traditional strain-modulation. Additionly, linear sensor response over wide dynamic range with optimum characteristics is focused. Comprehensive experimental investigation is carried out for the sensor that comprises uniformly etched cladding in the FBG region. Obtained results are observed to be in agreement with the theoretical analysis. Sensor response is observed to be linear over dynamic range 3–94%RH with ~ 0.082 pm/%RH sensitivity, ~0.6%RH resolution, ~ ±2.5%RH accuracy, ~ ±0.2 pm average discrepancy and ~ 0.2s response time during humidification/desiccation.
An optical fiber relative humidity (RH) sensor exploiting Localized Surface Plasmon Resonance (LSPR) is designed in order to achieve a linear response over a large dynamic range with an optimized sensitivity. To further enhance the sensitivity, in-house developed gold nanoparticle film was also synthesized onto a U-shaped and an etched-core region of the optical fiber. A throughout linear response over a dynamic range of ~20-90% RH with a very high sensitivity is observed. Importantly, reducing the core diameter resulted in four time sensitivity enhancement. In addition, the sensor response was observed to be highly reversible and repeatable.
A novel fiber optic prototype sensor based on Raman spectroscopy for qualitative and quantitative monitoring of various chemicals in the sample was developed. The sensor employs a high power 670nm laser diode as an excitation light source and a specially designed fiber optic Raman probe with launching and collecting fibers. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. The uniqueness of the sensor lies in its compact and stable design configuration, that includes carefully aligned optical components, viz. laser diode, filter holder, and miniature spectrometer. Developed sensor is immune to ambient light fluctuation and offers a cost effective solution for probing several species in harsh environment. Various issues like system fabrication, optimization, functional stability, signal/noise ratio, repeatibility etc are well addressed and presented in this paper.
A comprehensive experimental study of a fiber optic relative humidity (RH) sensor is carried out in terms of characterization and performance optimization against various parameters that affect the sensor response and sensitivity e.g., film composition, film thickness, fiber core diameter, and the sensor geometry. The sensor is based on evanescent wave absorption spectroscopy and utilizes a specific reagent immobilized permeable polymer membrane cladding on a declad U-bend optical fiber. An optimum film thickness and an optimum film composition exist. In addition, a fiber with a smaller core diameter was observed to be more sensitive, unlike the previously reported results. The sensitivity further increases with a decrease in the bending radius. The sensor is found to be sensitive to RH ranging from ~1.6 to ~92%, exhibiting a very fast response time, an extremely good degree of reversibility, repeatability, and a large dynamic range.
Laser-induced fluorescence (LIF) is an accurate, sensitive and rapid method for the diagnosis of a normal and malignant tissue. In this paper, an optical fiber sensor was developed to enhance spectral difference between the normal and malignant tissue with sensor optimization to improve the accuracy of cancer diagnosis. This instrument incorporated a pulsed laser operating at 355 nm (frequency triple Nd:YAG and Q-switched Nd:YAG pump dye laser) with bifurcated optical fiber to allow illumination of tissue and collection of fluorescence with a single fiber. Using the laser excitation, the detection of the fluorescence signal from the tissue was performed almost instantaneously. A sufficient fluorescence contrast (of the order of more than 22.22 times) for malignant versus normal tissue was obtained. The results of our approach were compared with histopathology results and indicated excellent agreement in the classification of normal and malignant tissue.
Auto fluorescence of tissue depends not only on the concentration of fluoro-phores present in tissues but also on the configuration of optical fiber sensor. In this paper, feasibility of using laser induced fluorescence spectroscopy as a diagnostic tool for distinguishing malignant animal tissue from its normal counterpart under various design configurations is explored. Three different design configurations are tested for the performance optimization. The optimized Y-shaped optical reflection fiber probe gives the best laser induced fluorescence signal comparing to other probes. This instrument incorporated a continuous wave (CW) Nd:YAG laser operating at 532 nm.
Ethanol and methanol form the essential components in the hydrocarbon-based fuels, serving as transportation fuels also; and will likely play an increasingly important role in the future as crucial fuel components. The motivation of the present work is to differentiate such hydrocarbons from their mixture sample on the basis of their spectrum analysis for various ratios of their composition. A fiber optic Spontaneous Raman sensor is developed as a probe indicator for component detection of such hydrocarbon mixtures. The sensor employs a frequency doubled 532 nm continuous ND:YAG laser and a specially designed fiber optic Raman probe. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. Attractiveness of our scheme lies in the online determination of sample constituents without employing specially designed IR fiber with much-complicated and expensive IR spectroscopy and, with no alteration in sample physico-chemical structure. Spectral analysis techniques based on spectral shape band intensities and areas and some multi-component analysis are being tested to find the most effective tool for measuring ethanol and methanol from the mixture. The analysis results from these tests will be presented in the paper.
We report a novel fiber optic relative humidity sensor based on the evanescent wave absorption spectroscopy. A comprehensive study of the sensor was made in terms of performance optimization against various parameters, which affects the sensor response and sensitivity e.g. film composition, film thickness, fiber core diameter and the sensor geometry. The sensor was compared against a commercially available relative humidity sensor and was found to be sensitive to relative humidity ranging from ~1.6 % to ~92%. We found that the sensor was having a very fast response to the relative humidity, and was fully reversible, repeatable with an extremely large dynamical range.
The motivation of this work is to monitor the real time concentration of nitrates in the radioactive wastes, as they are the key molecules in the solution. The effect of different optical configurations of the probes on the Raman signal was studied using acetone as the test sample. We found that InPhotonicsTM Raman probe give best signal-to-noise data comparing to the other two probes evaluated. The Raman spectra of 10% NaNO3 solution were then successfully recorded with this probe. The Raman signal of Nitrate at 1054 cm-1 is very strong with 500 ms sampling time. The initial study shows that the Raman sensor is capable to monitor the nitrate in the nuclear waste tank.
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