A. V. Dyshlyuk

Analysis of surface plasmon resonance in bent single-mode waveguides with metal-coated cladding by eigenmode expansion method

A numerical study is presented of surface plasmon waves excitation in a metal film applied to the cladding of a standard bent single-mode optical fiber. It was shown that by adjusting the bend radius and metal film thickness one can achieve effective coupling between the fiber fundamental mode and symmetric surface plasmon mode through the intermediary of whispering gallery modes supported by the cladding of the bent fiber. This effect is demonstrated to allow for refractometric measurement both in the wavelength and intensity-modulated regimes with a resolution of up to 10⁻⁸ RIU. Usage of standard noise reduction techniques for intensity-modulated optical signals promises further increase in accuracy.

Application of Optical Time-Domain Reflectometry for the Interrogation of Fiber Bragg Sensors

A reflectometric approach is proposed for the polling and multiplexing of sensitive elements on fiber Bragg gratings (FBGs). The method is based on the power measurement of the radiation reflected by the FBG using a conventional fiber-optic time-domain reflectometer. The multiplexing of sensors is based on the time separation of signals. Requirements on the Bragg diffraction gratings that provide the linear dependence of the received signal on the FBG mechanical stress and temperature are determined. In the measurements of the FBG relative elongation and temperature, the threshold sensitivities are 0.8 × 10−4 (80 μstrain) and 5°C, respectively. Due to its simplicity and efficiency, the reflectometric method of FBG polling and multiplexing can be used to solve various measurement problems, in particular, the safety monitoring of the stressed-strained elements in building structures.

Surface plasmon resonance excitation in a bent single-mode optical fiber with metal-coated cladding: Numerical simulation

We have numerically simulated the propagation of radiation guided in a bent single-mode optical fiber with metal-coated cladding. The optimum conditions for effective energy transfer from guided radiation to surface plasmon-polariton waves propagating along the metal-external medium interface. It is shown that, using this effect, it is possible to measure the refractive index (RI) of the external medium in both the spectral and amplitude regimes of response signal measurement with a resolution of up to 10−8 RI unit.

Combined time-wavelength interrogation of fiber-Bragg gratings based on an optical time-domain reflectometry

A reflectometric method for the combined time-wavelength multiplexing of the fiber-Bragg-grating (FBG) signals is proposed. The method is based on the spectral filtering of the probe pulses generated by a fiber-optic reflectometer using a bandpass filter consisting of a fiber circulator and FBG. The interrogated Bragg gratings are recorded on a fiber line in groups with identical resonance wavelengths inside groups and different wavelengths from different groups. The separation of the signals of FBGs that have different resonance wavelengths is due to the tuning of the filter passband, and the separation of the signals of FBGs with identical wavelengths involves the time separation of the responses of the Bragg gratings to the probe pulse. The threshold sensitivity of the method in the measurement of the relative elongation of FBG is 0.5 × 10−4. The considerable practical prospects of the method are related to its simplicity, reliability, and the application of the conventional reflectometric equipment.

Differential reflectometry of FBG sensors in the wide spectral range

The paper presents a reflectometric technique for interrogation of multiple fiber Bragg grating (FBG) sensors based on conventional optical time domain reflectometry (OTDR). The method proposed rests on the differential measurement of FBGs’ response to a short probing laser pulse. Implementation of differential measurement principle using several reference FBGs allowed us to eliminate the susceptibility of the system to intensity fluctuations as well as to increase the measurement range as compared to the previous developments. The experimental threshold sensitivity amounted to ∼50 microstrain with the measurement range being defined by the number of reference FBGs and limited only by optical fiber tensile strength. Due to its simplicity, efficiency and usage of conventional OTDR equipment the proposed FBG interrogation technique can find a wide range of applications dealing with strain and temperature measurements.

Surface plasmon resonance in a metal-coated single-mode optical fiber with decreased normalized frequency

We have numerically simulated the excitation of surface plasmon resonance in a bent metal-coated single-mode optical fiber with decreased normalized frequency. It is established that an optimum combination of the normalized frequency, bending radius, and film thickness favors effective energy transfer from guided radiation to a plasmon-polariton wave excited on the surface of a metal film deposited onto the optical cladding. It is shown that, using this effect, it is possible to measure the refractive index (RI) of an external medium with a spectral sensitivity of 70 δm/RI unit and a resolution of up to 3 × 10−7 RI unit.

An interrogation technique for fiber Bragg grating sensors based on optical time-domain reflectometry

A method for fiber Bragg grating (FBG) interrogation is proposed. The method rests on measuring the light intensity reflected from FBG sensors by means of a standard optical time-domain reflectometer. Multiple FBGs along the fiber optic line are interrogated through time division multiplexing. Specifications of FBGs enabling linear response of the sensors to strain and temperature are determined. The threshold sensitivity to strain is 0.8 · 10−4; the threshold sensitivity to temperature is 5°C.

Surface plasmon resonance in a bent single-mode fiber with a metallized cladding experimental research

The processes of surface plasmon resonance excitation in a bent single-mode optical fiber with a metallized cladding have been studied experimentally. It is shown that, for a certain combination of the bending radius of an optical fiber and the thickness of a metal film, a strong coupling between the fundamental and plasmon–polariton mode is achieved through a whispering gallery mode supported by the fiber cladding, which leads to the formation of a resonance dip with a depth of ~30 dB or more in the transmission spectrum of an optical fiber loop. The position of the dip depends strongly on the ambient refractive index, which provides the possibility of refractometric measurements with a spectral sensitivity of ~5 μm/RIU and a resolution of ~4 × 10–6. Limits of measurement of the refractive index are determined by the operating spectral range and the bending radius of the optical fiber and are 1.42–1.44 for the setup used.

Modeling of surface plasmon resonance in metalized optical waveguides with low V number by eigenmode expansion method.

The paper reports on the numerical study of surface plasmon resonance excitation in a bent metal-coated single mode optical fiber with a low V-number. It was shown that by choosing a proper combination of normalized frequency, bend radius, and metal film thickness one can achieve strong coupling between the fundamental mode guided by the fiber core, and symmetric surface plasmon mode supported by the metal layer applied to the fiber cladding. The effect is demonstrated to allow precision refractive index measurement, with spectral sensitivity and resolution estimated at 70 μm/refractive index unit and 3⋅10(-7), respectively.