In a phase extraction based phase-sensitive optical time domain reflectometry (Φ-OTDR), external perturbation induced phase variation of Rayleigh backscattered light-wave (RBL) is obtained from time varying interference signal that is comprised of two RBLs with a spatial shift along the sensing fiber. In this paper, the phase of the interference signal in the phase extraction based Φ-OTDR is studied. Derivation is performed on the interference signal considering the interference of multiple RBL within probe pulse covered fiber section. Theoretical analysis and experimental results reveal that the phase of interference signal are wavelength independent while the intensity of interference signal are wavelength dependent.
In this papers, the influence of the line-width of probe light on the phase noise of phase extracted based phase-sensitive optical time domain reflectometry (Φ-OTDR) is theoretical analyzed and experimentally investigated. Analysis indicates that broad line-width probe light suffers time varying wavelength drift and high level of laser phase noise, and thus guarantees high level phase noise of the Φ-OTDR. In distributed acoustic sensing along 500 m sensing fiber, the phase noise is evaluated for probe lights of different line-widths, and experimental results display that the phase noise increases as the line-width of probe light broadens.
The temperature-dependent refractive index of zinc telluride film can be used to develop a tiny, low cost and film-coated optical fiber temperature sensor. Pulse reference-based compensation technique is used to largely reduce the background noise which makes it possible to detect the minor reflectivity change of the film in different temperatures. The temperature sensitivity is 0.0034dB/℃ and the background noise is measured to be 0.0005dB, so the resolution can achieve 0.2℃.
We proposed a refractive index sensor based on optical fiber end face using pulse reference-based compensation technique. With good compensation effect of this compensation technique, the power fluctuation of light source, the change of optic components transmission loss and coupler splitting ratio can be compensated, which largely reduces the background noise. The refractive index resolutions can achieve 3.8 × 10-6 RIU and1.6 × 10-6 RIU in different refractive index regions.
The rudimental microparticle contaminants and airborne molecular contaminants (AMCs) will obviously reduce the lifetime of the lens widely used in the high peak power laser system. An inline contaminants sensor based on the optical microfiber (OM) is here proposed. Due to Van Der Waals force and electrostatic attraction, contaminants are easily adhered to the surface of OM, which will cause an obvious perturbation to the evanescent field transmitted in the OM. The additional loss, caused by the adhered contaminants, has been theoretically analyzed and simulated. The corresponding experiments have also been carried out, and the experimental results agree well with the simulation. The inline containments sensor based on OM has potentially wide sensing range for many kinds of determinate absorptive materials.
An in-line fluidic absorption coefficient sensor based on the optical microfiber (OM) is proposed. We calculate the
insertion loss of the OM per millimeter after immerged into liquid with various absorption coefficients. Then a 1.8μm
diameter OM with 10 millimeters uniform waist region is used to analyze the absorption of pure water, and the
absorption spectrum from 1525nm-1565nm is achieved from the experiment, agreeing well with the reported absorption
coefficient. The in-line fluidic absorption coefficient sensor has potentially wide sensing range by controlling the
construction of OM for many kinds of absorptive liquids with lower refractive index than silica.
Optical microfibers have attracted much attention in recent years due to its physical flexibility and low bending loss,
which enables the possibility to make compact active optical components when combined with small-size piezoelectric
ceramic transducers. Here, we present the demonstration of OM embedded in low refractive index polymer wound
around a piezoceramic rod of 1 mm diameter and 6 mm length as a compact optical phase modulator, which showed a
frequency response up to 1 MHz. We also report the fabrication of a compact tunable optical resonator from a 3 mm
diameter, 1 mm thick piezoceramic disc with a 50 pm shift when 600 V is applied across its electrodes.
The minimum bend radius of optical microfiber allows very compact flexural disc accelerometers to be manufactured
without significant degradation of the optical signal in terms of attenuation and depolarization. Such compact sensors
have potentially very high responsivity in small packages. We demonstrate a responsivity of 4 rad/g between 100-1000
Hz for a disc wound with microfiber of 60-millimeter length and 10-micron diameter microfiber. We report the
successful fabrication of a 0.4-meter length and 10-micron diameter microfiber using a new tapering setup and an
automated technique is proposed for efficiently winding long lengths of microfiber onto the flexural disc.
A review of passive devices and sensors manufactured from optical fiber microwires at the Optoelectronics Research
Centre (University of Southampton) is presented.
For the irregular shape of a fiber coupler, the coupling characteristics of it are usually studied in its different sections
separately. It's necessary to build a united model to simulate the coupling characteristics of each section all together.
Some appropriate geometrical configurations were employed, and modal field in a coupler was obtained by the weighted
superposition of triangular distribution and Gaussian distribution, in the condition of lossless propagation. With that a
united model was obtained by the variation technique, combined with the concept of local modes. It's a more refined
model, which is available on condition that the core radius in the neck waist is around 1 μm and can provide theoretical
guidance for the practical design and fabrication of a fused-tapered single-mode fiber coupler. In its effective area, there
is a good agreement between the theoretical result and experimental result.
This paper presents comprehensive research on fused-tapered Bragg reflection integrative FGC where high-quality and
easy-fabricating are two main considerations. The technical procedure of FGC fabrication is fixed after a series of
experiments. The possible factors that may determine the device performance were carefully analyzed. The
fused-tapered FGC was successfully fabricated and a novel testing system was established. The adding and dropping
functions of FGC were investigated experimentally.
We propose and experimentally demonstrate a novel fiber optic acoustic/rotation sensor array based on the Sangac
interferometer. The feasibility of sensing acoustic signal and rotation with a simpler signal processing in an array is
illustrated.
A polarization maintaining fiber (PMF) magnetic field sensor based on a digital phase generated carrier (PGC)
technology is presented. A magnetic sensor constructed with two magnetostrictive strips attached on the sensing fiber is
joined in the sensing arm of a fiber Michelson interferometer. The fiber optic interferometric system is made of all PMF,
which inhibits the polarization-induced signal fading. The light source is a fiber laser which can be modulated directly.
The PGC metnod is used to demodulate magnetic field signal avoiding phase induced interferometric signal fading, and
ensure the sensing partto be all fiber structure. A fiber optic magnetic field sensor with appreciate size for the fiber optic
hydrophone towed array is obtained, which can be used to sense the enviromental magnetic field along the sensing
direction.This sensor is a good choice for the directional angle measurement through sensing the Earth magnetic field in
the array shape measurement of a fiber optic hydrophone towed array.
The finite element method was used to analyze the interior stress distributions and the birefringence of the side hole fiber. The paper has analyzed the dependence of the birefringence of the side hole fiber on the side holes' physical dimensions. The calculation result shows that the fast axis of the fiber is along the line which links the two holes' centers, the geometrical birefringence can be neglected, and the birefringence can be improved through increasing the radius of the side holes or reducing the distance between the core and the side hole centers.
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