There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

There is described a distributed optical fibre sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fibre, as a function of position along the sensor fibre. The sensor uses probe light pulses of different wavelengths. At least some of the probe light pulses may also be of different pulse lengths. The relative phase bias between interferometric signals in backscattered probe light of different wavelength pulses may also be controlled.

Distributed Optical Fibre Sensor

We report experimental measurements of the strain and temperature sensitivity of the optical phase in a singlemode polymer optical fibre. These values were obtained by measuring optical path length change using a Mach-Zender interferometer.

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Strain and temperature sensitivity of a single-mode polymer optical fiber

In one embodiment, a force sensor apparatus is provided including a tube portion having a plurality of radial ribs and a strain gauge positioned over each of the plurality of radial ribs, a proximal end of the tube portion that operably couples to a shaft of a surgical instrument that operably couples to a manipulator arm of a robotic surgical system, and a distal end of the tube portion that proximally couples to a wrist joint coupled to an end effector.

Ribbed force sensor

A wide variety of Fiber Bragg writing devices comprising solid state lasers are provided. The solid state lasers emit moderate peak-power output beams which are suitable for efficient production of fiber Bragg gratings without causing embrittlement of the optical waveguide. These solid state lasers generate output beams with wavelengths of approximately 240 nm, in order to match the primary absorption peak in the ultraviolet range for a typical optical waveguide. In some embodiments, the solid state lasers comprise Ti:sapphire lasers which are tuned to produce fundamental wavelengths which are frequency-multiplied. In other embodiments, the output beam of a Ti:sapphire laser is mixed with a harmonic beam from a pump laser. Some embodiments output the third harmonic of a fundamental beam.

Method and apparatus for fiber bragg grating production

Fiber optic sensor with transmission/reflection analyzer for detection and localization of a perturbation that generates additional losses in the test fiber. The sensor includes a test fiber having a first port and a second port; a light source for producing a beam of light propagating along the test fiber; a fiber optic beamsplitter having a first port connected to the light source, a second port connected to the first port of the test fiber, and a third and a fourth port; a plurality of reflectors positioned along the test fiber and a plurality of loss-inducing members positioned along the test fiber, wherein said each of the reflectors is matched to each loss-inducing members, wherein at least one reflector is placed between each consecutive loss-inducing member; an optical reflection detector to receive a light flux, the optical reflection detector connected to the third port of optic beamsplitter, wherein the reflection detector is adapted to sense changes in the power of the light reflected from the reflectors; an optical transmission detector adapted to receive the light flux, connected to the second port of test fiber, said transmission detector being operable to sense changes in the power of the light transmitted through the test fiber; and a transmission/reflection analyzer connected to reflection and transmission detectors, said analyzer adapted to measure the value and identify the location of the disturbance along the test fiber by using a unique relation between transmitted and reflected powers for different locations of the disturbance along the test fiber.

Fiber optic sensor with transmission/reflection analyzer

A fiber optic sensor, which includes an interference energy analyzer, is used to measure strain and temperature distribution along a test fiber. The sensor includes the following: a plurality of double-Bragg grating elements positioned along a test fiber, a broadband light source which produces a broadband spectral profile that propagates along the test fiber, an optical filter that is able to change the parameters of the broadband spectral profile, an optical reflection detector, a fiber optic beamsplitter, and an interference energy analyzer. Each double-Bragg grating element consists of two weak Bragg gratings, separated by a distance unique to each element. The interference energy analyzer calculates the energies of the interference patterns, which are created by beams reflected from double-Bragg grating elements. The energy of the interference signal changes when the gratings in one element non-uniformly change its parameters due to non-equal temperature or strain influence on two gratings.

Differential fiber optical sensor with interference energy analyzer

This invention pertains to alarm condition fiber optic sensor with storage transmission-reflection analyzer for detection and localization of any number of consecutive loss-inducing disturbances along the test fiber. The sensor includes a test fiber having a first port and a second port; a light source for producing a beam of light propagating along the test fiber; a fiber optic beamsplitter having a first port connected to the light source, a second port connected to the first port of the test fiber, and a third and a fourth port; a plurality of reflectors positioned along the test fiber and a plurality of loss-inducing members positioned along the test fiber, wherein said each of the reflectors is matched to each loss-inducing members, wherein at least one reflector is placed between each consecutive loss-inducing members; an optical reflection detector to receive a light flux, the optical reflection detector connected to the third port of optic beamsplitter, wherein the reflection detector is adapted to sense changes in the average power of the light reflected from the reflectors; an optical transmission detector adapted to receive the light flux, connected to the second port of test fiber, said transmission detector being operable to sense changes in the average power of the light transmitted through the test fiber; and a storage transmission-reflection analyzer connected to reflection and transmission detectors, and adapted to measure time-behavior of the transmission-reflection dependencies of test fiber, said analyzer being operable to identify the locations and values of any number of consecutive loss-inducing disturbances along the test fiber by using stored locations and values of previous perturbations and the slope of dependence of normalized reflected average power versus the square of normalized transmitted average power for current loss-inducing perturbation.

Alarm condition distributed fiber optic sensor with storage transmission-reflection analyzer

We report on the detection of a loss-inducing perturbation with variable localization accuracy along a test fiber based on the analysis of transmitted and reflected powers of an unmodulated continuous-wave light source. The required accuracy of localization is provided by suitable distribution of the differential reflectivity along the fiber. The localization accuracy for a strong disturbance has been estimated as /spl plusmn/ 1.0 m along the 3.939-km single-mode test fiber and as /spl plusmn/ 5.0 mm along a designated 10-cm fiber part for both strong and weak perturbations.

Localization of a loss-inducing perturbation with variable accuracy along a test fiber using transmission-reflection analysis

We present experimental results on testing a twin-grating fiber optic sensor for the measurement of static strain and temperature. The sensor is built with two identical Bragg gratings closely spaced in a single-mode fiber. It produces a reflection spectrum modulated by interference. As in traditional fiber Bragg grating sensors, strain of the fiber leads to the wavelength shift of the reflection spectrum. This shift can be determined precisely by measuring phase changes for corresponding components of Fourier transform of the reflection spectrum. Such an approach allows an absolute strain measurement with an interferometric sensitivity. Resolution of 0.2 ?m/m and range to resolution ~ 104: 1 were demonstrated experimentally for static strain measurements using a pair of 0.7-mm-long Bragg gratings with reflectivity of 1% each.

Vasilii V. Spirin

Papers

Fiber optic sensor with transmission/reflection analyzer

Differential fiber optical sensor with interference energy analyzer

Alarm condition distributed fiber optic sensor with storage transmission-reflection analyzer

Localization of a loss-inducing perturbation with variable accuracy along a test fiber using transmission-reflection analysis

Static strain measurement with sub-micro-strain resolution and large dynamic range using a twin-Bragg-grating Fabry-Perot sensor