Anton V. Dyshlyuk

Fiber-optic inclinometer for structural health monitoring

A multichannel fiber-optic intensity based sensor for remote inclination measurement has been developed based on light beam displacement by a transparent free hanging parallel sided deflector glass plate. The deflector plate is mounted onto a gimbal suspension to avoid interference between orthogonal tilt directions. In order to enable vibration resistant measurement the deflector is damped by a transparent viscous liquid. Light intensity drift compensation is achieved through the comparison of two output signals obtained from two spaced measuring channels integrated in the sensing element. The specifications of the sensor are as follows: threshold sensitivity - 0,01 deg, dynamic range - 25 dB, measuring angle range ±4 deg. Sensor output signal variation corresponding to 30% input light intensity decrease does not exceed ±4%. Due to the utilization of standard low-loss multimode optical fibers the sensing element can be removed from the light generation and processing units to a distance of up to several kilometers. High sensitivity and stability of the proposed technique allow its wide spread application in structural health monitoring as well as in machine building, seismology and other areas where precision angular positioning or monitoring is required.

Numerical and Experimental Investigation of Surface Plasmon Resonance Excitation Using Whispering Gallery Modes in Bent Metal-Clad Single-Mode Optical Fiber

We present a numerical and experimental study of surface plasmon resonance (SPR) excitation in a bent single-mode optical fiber with metalized cladding. It is shown that with a suitable combination of bend radius and metal film thickness surface plasmon waves can be excited in the film as a result of coupling between fundamental and surface plasmon modes via whispering gallery modes supported by the bent fiber cladding. The coupling brings about a dip in the transmission spectrum at the resonant wavelength which is strongly dependent on the ambient refractive index. This enables one to build a fiber optic SPR-refractometer with a standard single-mode fiber without breaking integrity of the fiber or using any additional elements. Refractometric sensitivity of ∼5 μm per refractive index unit and resolution of ∼4·10−6 are experimentally demonstrated for the measured refractive index around 1.43. The reported results may find wide application in bio- and chemosensing.

Stabilized fiber optic sensor for remote measuring angle of inclination

A fiber optic intensity based sensor for remote inclination measurement has been developed based on light beam displacement caused by a free hanging deflector glass plate as it changes its angular position relative to the body of the sensor. Light intensity drift compensation is achieved through the comparison of two output signals obtained from the two spaced measuring channels integrated in the sensing element. The specifications of the sensor are as follows: threshold sensitivity - O,01°, dynamic range - 25 dB, measuring angle range - ±4°. As a result of sensor performance equalization its output signal variation corresponding to 30% input light intensity decrease does not exceed ±4%.

Experimental verification of surface plasmon resonance excitation in bent single-mode optical fibers using whispering gallery modes

We present an experimental verification of the novel approach to the excitation of surface plasmon resonance (SPR) for biosensing applications. The technique is based on a bent SMF28–type single-mode optical fiber with a thin metal film deposited on its optical cladding. Due to the bending of the fiber, strong coupling can be achieved between the fundamental mode and the surface plasmon mode through the intermediary of whispering gallery modes supported by the fiber cladding, which brings about a resonant dip in the transmission spectrum of the fiber. Since the propagation constant of the surface plasmon mode depends strongly on the refractive index of the surrounding medium so does the coupling wavelength, which enables precision refractometry both in the wavelength and intensity-modulated regimes. As opposed to traditional optical fiber-based SPR refractometers, our approach, while based on a standard single-mode fiber, needs neither additional optical elements (such as long-period or tilted Bragg gratings, etc.) nor mechanical modification of the fiber (such as chemical or mechanical removal of a part of optical cladding). This makes the proposed refractometer structurally simple, reliable, and easy to fabricate.

Differential Reflectometry of Fiber Bragg Gratings

A reflectometric approach is proposed for interrogation of multiple fiber Bragg grating (FBG) sensors recorded in a single fiber optic line, based on the differential registration FBGs’ response to a short probing laser pulse using conventional OTDR. A special optical layout has been developed allowing transformation of FBG’s spectrally modulated signals into intensity modulated signals and at the same time eliminating the susceptibility of the system to light power fluctuations. Threshold sensitivity of the method amounted to ~50 μstrain within the measurement range of ~4000 μstrain. The maximum number of FBGs interrogated by the proposed technique is estimated at several hundred, which by far surpasses the requirements of most practical applications. Due to its simplicity, efficiency and usage of conventional OTDR equipment the proposed FBG interrogation technique can find a wide range of applications, in particular in structural health monitoring.