Conventional Fiber Optic Sensors Research Articles

Application of cavity Maxwell Garnett theory in SPR based fiber optic sensor with porous alumina structure

The present manuscript describes the theoretical understanding of nanoporous alumina based fiber optic sensing structures. The Cavity Maxwell Garnett theory is used to calculate the dielectric functions of the proposed layer. The performance of the proposed sensing structure is evaluated in terms of its sensitivity towards change in the refractive index of the nearby medium. The sharpness of the resonance has also been calculated as an estimation of the performance parameters. It has been observed that the proposed structure is approximately 13 times more sensitive than the conventional fiber optic sensors. The study has further been extended by replacing the nanolayer of aluminum with the nanolayer of the gold. A comparative study has been provided in terms of the efficiency of the fiber optic probe. The effects of change in pore radius, thickness of the adsorbed medium and shell radius have also been studied.

Photonic crystal fiber long-period grating absorption gas sensor based on a tunable erbium-doped fiber ring laser

It has been a persistent challenge to quantify gas emissions from industrial byproducts and warfare agents for environmental protection purposes, especially to detect multiple gas species using one device with high sensitivity and selectivity. To overcome this issue, a photonic crystal fiber (PCF)-based spectroscopic absorption sensing platform is proposed. We combine the PCF and long-period grating (LPG), two fundamental elements of fiber optics, into one functional unit to investigate the coupling properties of various PCF cladding modes. Further, we synchronize the PCF–LPG with a tunable Er-doped fiber ring laser into a thermo-stable and compact absorption spectroscopic sensor as a proof-of-concept for gas sensing. Because the Er-doped fiber ring laser can be tuned within the C-band wavelength, multiple gases can be recorded with the absorption spectra in one sensing operation. As a demonstration, the sensor was tested in NH3 with multiple gases combined, a sensitivity up to 17.3nW/ppm was achieved. The PCF–LPG-based gas sensors are easy-to-fabricate, cost-effective, and can be used in various applications where conventional fiber-optic sensors are not applicable.

Acidity measurements based on a hetero-core structured fiber optic sensor

A noble sensing technique using a hetero-core structured fiber optic sensor is described based on evanescent wave interaction for the purpose of acidity measurements. The hetero-core sensing element reported in this work have been fabricated only by cleaving and fusion splicing. Since the sensor has no need to eliminate the cladding of the fiber to expose the core, this technique offers the advantages in terms of the fabrication complexity which the conventional fiber optic sensors have been confronted with. Acidity measurements have been demonstrated through the experiments using Chromoxane Cyanine R (CCR) indicator solved in solutions. Two acid solutions of HNO 3 and H 2SO 4 are examined for the acidities ranged between 0.066–0.66 and 0.0895–0.716 M, respectively. The sensor response exhibited remarkable increases of absorption with increasing acidity at the wavelength of around 520 nm. The sensitivities of 11.5 and 14.2 dB/M have been obtained for HNO 3 and H 2SO 4 solutions, respectively.

Sensitivity Enhancement in Capillary/Fiber-Optic Fluorometric Sensors

Fluorometric measurements acquired with capillary/fiber-optic sensors offer greater sensitivity and detectability as compared to those obtained with conventional fiber-optic sensors. The sensitivity enhancement has been theoretically derived, and it depends on the relative diameter of the fiber and the capillary and on the length of the capillary relative to the effective depth of the fiber. Fluorescence measurements obtained experimentally with conventional and capillary/double-fiber-optical sensors indicate sensitivity enhancement factors of almost 2 orders of magnitude and improvements in the detection limits of 1 order of magnitude