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Gopinath Mudhana

Bio: Gopinath Mudhana is an academic researcher from Gwangju Institute of Science and Technology. The author has contributed to research in topics: Fiber optic sensor & Graded-index fiber. The author has an hindex of 5, co-authored 16 publications receiving 319 citations. Previous affiliations of Gopinath Mudhana include Shanmugha Arts, Science, Technology & Research Academy & VIT University.

Papers
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Journal ArticleDOI
TL;DR: A cross-talk free simultaneous measurement system for temperature and external refractive index (ERI) implemented by dual-cavity Fabry-Perot (FP) fiber interferometer demonstrated, which showed that temperature could be determined independently from the spatial frequency shift without being affected by the ERI.
Abstract: We propose and demonstrate a cross-talk free simultaneous measurement system for temperature and external refractive index (ERI) implemented by dual-cavity Fabry-Perot (FP) fiber interferometer. The sensing probe consists of two cascaded FP cavities formed with a short piece of multimode fiber (MMF) and a micro-air-gap made of hollow core fiber (HOF). The fabricated sensor head was ultra-compact; the total length of the sensing part was less than 600 mum. Since the reflection spectrum of the composite FP structures is given by the superposition of each cavity spectrum, the spectrum measured in the wavelength domain was analyzed in the Fourier or spatial frequency domain. The experimental results showed that temperature could be determined independently from the spatial frequency shift without being affected by the ERI, while the ERI could be also measured solely by monitoring the intensity variation in the spatial frequency spectrum. The ERI and the temperature sensitivities were approximately 16 dB/RIU for the 1.33-1.45 index range, and 8.9 nm/ degrees C at low temperature and 14.6 nm/ degrees C at high temperature, respectively. In addition, it is also demonstrated that the proposed dual-cavity FP sensor has potential for compensating any power fluctuation that might happen in the input light source.

167 citations

Journal ArticleDOI
TL;DR: The non-invasive cross-sectional images of biomedical samples as well as a transparent glass plate obtained with implemented all-fiber delay line having the axial resolution of 100 mum and the dynamic range of 50dB are presented to validates the imaging performance and demonstrate the feasibility of the delay line for optical coherence tomography.
Abstract: We have implemented an all-fiber optical delay line using two linearly chirped fiber Bragg gratings cascaded in reverse order and all-fiber optics components. The features of the proposed all-fiber based technique for variable delay line are discussed theoretically and demonstrated experimentally. The non-invasive cross-sectional images of biomedical samples as well as a transparent glass plate obtained with implemented all-fiber delay line having the axial resolution of 100 mum and the dynamic range of 50dB are presented to validates the imaging performance and demonstrate the feasibility of the delay line for optical coherence tomography.

76 citations

Journal ArticleDOI
TL;DR: In this article, a double cladding fiber interferometer consisting of a long-period fiber grating pair for simultaneous measurement of temperature and strain was presented, and it was shown that the relative phase of interference fringes is solely dependent on the strain, whereas the ambient temperature causes a shift in the envelope of the fringes.
Abstract: We present a double cladding fiber interferometer consisting of a long-period fiber grating pair for simultaneous measurement of temperature and strain. The insensitivity of the inner cladding mode to the external contact enabled easy handling of the interferometer without affecting the interference; thereby, strain could be applied only to the grating-free region between the two gratings. We show that the relative phase of the interference fringes is solely dependent on the strain, whereas the ambient temperature causes a shift in the envelope of the fringes. The temperature and strain were measured with sensitivities of approximately 0.038 nm/degC and -1.05 rad/mepsiv, respectively, without appreciable cross-sensitivity.

39 citations

Journal ArticleDOI
TL;DR: In this paper, a fiber-optic sensor for measuring the refractive index (RI) of a liquid sample is constructed from an extrinsic cavity formed by a micromirror and a lensed photonic crystal fiber (PCF) tip.
Abstract: We report a fiber-optic sensor for measuring the refractive index (RI) of a liquid sample. The sensing probe is constructed from an extrinsic cavity formed by a micromirror and a lensed photonic crystal fiber (PCF) tip. We show that PCF lens with an unconventionally large radius of curvature is bifunctional; an effective reflector as well as a collimator and thus suitable for realizing long single-arm interferometers, with a cavity length of the order of few mm. A sensing head suitable for measuring the refractive index (RI) of liquids is constructed by encapsulating the bifunctional lens tip and a micromirror in a glass tube. A hole is made in the glass-tube to allow free-flow of the liquid sample in-and-out of the cavity. The cavity length was about 1 mm. The group index of the liquid samples is obtained from the Fourier peak position of the interference signal measured in wavelength with optical spectrometer. The RIs of distilled water, acetone and ethanol (at 829 nm, 20°C) were measured to be 1.32822, 1.35416, and 1.35715, respectively. The resolution of the sensor was analytically found to be 2.6 × 10-5 and the response was experimentally shown to be linear.

32 citations


Cited by
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Journal ArticleDOI
23 Feb 2012-Sensors
TL;DR: Each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields and some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications.
Abstract: Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

524 citations

Journal ArticleDOI
30 Jul 2015-Sensors
TL;DR: Recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi-point and distributed sensing techniques.
Abstract: In-service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real-time in-situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability, and high bandwidth, which allows a great number of sensors to operate in the same system, and the possibility to be integrated within the material. However, more effort is still needed to bring the technology to a fully mature readiness level. In this paper, recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi-point and distributed sensing techniques.

461 citations

Journal Article
TL;DR: Two applications are presented: the noninvasive measurement of anterior eye structure in a rabbit inυiυo and the characterization of reflections and interelement spacing in a multielement lens.
Abstract: We describe a high-speed optical coherence domain reflectometer. Scan speeds of 40 mm/s are achieved with a dynamic range of >90 dB and a spatial resolution of 17 μm. Two applications are presented: the noninvasive measurement of anterior eye structure in a rabbit in vivo and the characterization of reflections and interelement spacing in a multielement lens.

393 citations

Journal ArticleDOI
TL;DR: In this paper, an analytical expression of the average power-coupling coefficient (PCC) based on an exponential autocorrelation function is derived, resulting in no need for heavy numerical computations.
Abstract: In order to realize fast and accurate estimation of intercore crosstalk in bent multicore fibers (MCFs), an analytical expression of the average power-coupling coefficient (PCC) based on an exponential autocorrelation function is, for the first time, derived, resulting in no need for heavy numerical computations. It is revealed that, when the bending radius is large and the correlation length is large, the average PCC is inversely proportional to the correlation length and to the square of the propagation constant difference Δβmn between core m and core n, and when the bending radius is small and the correlation length is large, the average PCC is proportional to the bending radius and is independent of the correlation length. When the correlation length is small, on the other hand, the average PCC is proportional to the correlation length and is independent of the bending radius. For homogeneous MCFs (Δβmn = 0) with small bending radius, the average PCC coincides with the mean crosstalk increase per unit length derived from the coupled-mode theory of Hayashi et al. that is proportional to the bending radius. Average crosstalk values calculated by using the analytical expression derived here are in excellent agreement with those of numerical solutions of coupled-power equations, irrespective of the values of bending radius and correlation length.

343 citations

Journal ArticleDOI
TL;DR: Experimental results showed that the liquid refractive index information can be simultaneously provided from measuring the sensitivity of the liquid level and from employing a multimode fiber as a mode coupler in the thinned fiber based Mach-Zehnder interferometer.
Abstract: We propose and demonstrate a thinned fiber based Mach-Zehnder interferometer for multi-purpose sensing applications. The sensor head is formed by all-fiber in-line singlemode-multimode-thinned-singlemode (SMTS) fiber structure, only using the splicing method. The principle of operation relies on the effect that the thinned fiber cladding modes interference with the core mode by employing a multimode fiber as a mode coupler. Experimental results showed that the liquid refractive index information can be simultaneously provided from measuring the sensitivity of the liquid level. A 9.00 mm long thinned fiber sensor at a wavelength of 1538.7228 nm exhibits a water level sensitivity of -175.8 pm/mm, and refractive index sensitivity as high as -1868.42 (pm/mm)/RIU, respectively. The measuring method is novel, for the first time to our knowledge. In addition, it also demonstrates that by monitoring the wavelength shift, the sensor at a wavelength of 1566.4785 nm exhibits a refractive index sensitivity of -25.2935 nm/RIU, temperature sensitivity of 0.0615 nm/°C, and axial strain sensitivity of -2.99 pm/μe, respectively. Moreover, the sensor fabrication process is very simple and cost effective.

312 citations