Showing papers by "David A. Jackson published in 1989"
TL;DR: In this paper, it was demonstrated that stimulated Brillouin scattering (SBS) occurring in the core of an optical fiber can be used in the construction of a distributed temperature sensor.
Abstract: It is demonstrated that stimulated Brillouin scattering (SBS) occurring in the core of an optical fibre may be used in the construction of a distributed temperature sensor. Initial experiments with a length of fibre have shown that the sensitivity of the Stokes frequency to temperature is approximately 5.5 MHz/ degrees C and that different Stokes frequencies may be observed according to the temperature distribution along the fibre.<
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218 citations
TL;DR: A novel accelerometer in which the sensing element is a weighted diaphragm that is measured using a miniature hemispherical air-spaced Fabry-Perot interferometer, of which one mirror is mounted on the diphragm.
Abstract: We describe a novel accelerometer in which the sensing element is a weighted diaphragm. The displacement of the diaphragm produced by acceleration is measured using a miniature hemispherical air-spaced Fabry-Perot interferometer, of which one mirror is mounted on the diaphragm. The interferometer is illuminated by a diode laser and addressed through a monomode optical fiber.
95 citations
TL;DR: In this paper, the first-order chromatic dispersion coefficient (D( lambda )) resolution of 0.07 ps was achieved for a 1-m length of fiber, equivalent to 0.06% resolution in the measurement technique.
Abstract: Chromatic dispersion measurements on short lengths of monomode optical fiber by the technique of 'white light' interferometry are presented. Improved optoelectronic signal processing and rigorous data reduction techniques have resulted in a temporal resolution of >or=7*10/sup -5/ ps.nm/sup -1/ in a 1-m length of fiber, equivalent to 0.06% resolution in the measurement technique. This is equivalent to a first-order chromatic dispersion coefficient (D( lambda )) resolution of 0.07 ps.nm/sup -1/./sup -1/. The second-order chromatic dispersion coefficient (S( lambda )) resolution was 0.02 ps.nm/sup -2/.nm/sup -1/. Experimental results of D( lambda ) and S( lambda ) for three different fibers are compared to theoretical calculation of material and waveguide dispersion. >
91 citations
73 citations
TL;DR: In this paper, the back-scattered signals independently generated by stimulated Brillouin scattering in two separate optical fibres may be mixed to produce narrowband radio-frequency signals.
Abstract: Experimental data are presented which show for the first time that the back-scattered signals independently generated by stimulated Brillouin scattering in two separate optical fibres may be mixed to produce narrowband radio-frequency signals. This mechanism can be exploited for microwave generation and distributed temperature sensing.
26 citations
TL;DR: In this paper, the authors describe a number of multiplexing techniques which may be used for fiber-optic sensors in which the sensing element is a ring resonator, which can be used to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer.
Abstract: We describe a number of multiplexing techniques which may be used for fibre-optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. A number of such units may be combined to form an array, using coherence multiplexing techniques. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. When a high-coherence source is used, then multiplexing may be accomplished using frequency-division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realizing a large sen...
24 citations
TL;DR: A novel accelerometer in which the sensing element is a weighted diaphragm designed to have minimal cross coupling, and the output of the two interferometers is processed such that the detrimental effects caused by wavelength drift of the source and variation in temperature of the sensor are reduced.
Abstract: We describe a novel accelerometer in which the sensing element is a weighted diaphragm designed to have minimal cross coupling. The displacement of the diaphragm, produced by acceleration, is measured by using two miniature hemispherical air-spaced Fabry–Perot interferometers, one constructed on either side of the diaphragm. The output of the two interferometers is processed such that the detrimental effects caused by wavelength drift of the source and variation in temperature of the sensor are reduced by 45.8 and 27.3 dB, respectively, compared with those of a single interferometer.
18 citations
18 citations
TL;DR: DNA sequences which act as a transcription terminator when placed in heterologous RNA polymerase II genes are defined and defined by two independent approaches that elicit authentic transcriptional termination.
Abstract: Previous studies [1,2] suggested but did not prove that the sea urchin H2A histone gene possesses strong transcriptional termination signals close to, but separate from, the 3' processing signals. In this study we have demonstrated by two independent approaches that these sequences elicit authentic transcriptional termination. First we show by nuclear run off analysis that nascent transcription terminates in the immediate 3' flanking region of the H2A gene, in an A-rich region. Second we show that these termination signals prevent transcriptional read through when placed in the intron of a globin gene. The intronic position of the termination signal rules out any effect on steady state mRNA levels. We have therefore defined DNA sequences which act as a transcription terminator when placed in heterologous RNA polymerase II genes.
12 citations
TL;DR: An optical configuration employing two conventional Michelson interferometers and a fiber Fabry-Perot interferometer connected in parallel is used to demonstrate the principle of common mode rejection of both the amplitude and frequency noise of a semiconductor laser.
Abstract: An optical configuration employing two conventional Michelson interferometers and a fiber Fabry–Perot interferometer connected in parallel is used to demonstrate the principle of common mode rejection of both the amplitude and frequency noise of a semiconductor laser. Common mode noise rejection is maximized when the outputs of the two interferometers with matched path imbalance, fringe visibility and amplitude are differentially combined. One interferometer is used as a reference, and the other as a sensing interferometer. The fiber Fabry–Perot interferometer is used as the sensing interferometer and is demonstrated as a miniature acoustic sensing element.
9 citations
TL;DR: In this paper, an optical configuration for remote measurement of magnetic field and hence electric current is described and problems associated with polarisation state changes in the optical fiber link between the instrument head and the sensing element are overcome and techniques for signal processing for high and low bandwidth applications are presented.
TL;DR: In this article, a form of liquid refractometer is described in which the optical length of a cavity containing the liquid is monitored interferometrically, and the refractive index of the cavity is measured by an interferometric sensor.
Abstract: We describe a novel form of liquid refractometer in which the optical length of a cavity containing the liquid is monitored interferometrically.
TL;DR: It is shown that other factors, such as changes in cytoskeletal function, must be considered together with any contribution from DNA damage, in order to account for the lethal effects of MTX.
Abstract: The survival of cells cultured in medium containing the chemotherapeutic drug methotrexate (MTX) is related directly to drug concentration. Changes in DNA resulting from a severe imbalance in the cells9 nucleotide pools are thought to account for this cytotoxicity. We have attempted to clarify the gross biochemical changes that might lead to cell death. DNA strand breaks occur in cells treated with high concentrations of MTX but it is not clear that these are sufficient to account for cytotoxicity at lower doses. We observed dramatic changes in cytoskeletal morphology. Gross reorganization of the cytoskeleton is shown by immunolabelling but is high-lighted dramatically when cells are lysed to leave ‘nucleoids’. The nature of the changes seen in MTX-treated cells is characteristic of the cells’ general stress response, seen originally following heat shock. This study shows that other factors, such as changes in cytoskeletal function, must be considered together with any contribution from DNA damage, in order to account for the lethal effects of MTX.
29 Oct 1989
TL;DR: In this article, a non-contacting optical vibration sensor was developed using a fibre-optic system that is suitable for use as a reference grade device, based around a fibre Michelson interferometer configuration in which an optical carrier is produced by imposing a sinusoidal phase modulation of specific amplitude in the interferometers and electronically gating and bandpass filtering the resulting output signal.
Abstract: A non-contacting optical vibration sensor has been developed using a fibre-optic system that is suitable for use as a reference grade device. It is based around a fibre Michelson interferometer configuration in which an optical carrier is produced by imposing a sinusoidal phase modulation of specific amplitude in the interferometer and electronically gating and bandpass filtering the resulting output signal. In order to achieve a primary reference grade sensor, the carrier modulation induced by the vibrating surface is demodulated in the phase domain using a digital phase-tracker, and the time dependence of the surface displacement is recovered relative only to the wavelength of radiation used.
29 Oct 1989
TL;DR: An optical current sensor has been designed and tested as mentioned in this paper, which employs the Faraday effect in optical fibre to measure electrical current, is intended to be applied in power system protection equipment; it is regarded as a potential replacement for the iron cored current transformer in certain applications.
Abstract: An optical current sensor has been designed and tested. This device, which employs the Faraday effect in optical fibre to measure electrical current, is intended to be applied in power system protection equipment; it is regarded as a potential replacement for the iron cored current transformer in certain applications. A novel polarization analyser arrangement is included in the optical current sensor. The theory of operation of this component is presented and it is shown that a simple graphical representation of the state of polarization may be produced in real time. The operation of the current sensor is described and pre-installation test results are presented.
11 Apr 1989
TL;DR: In this article, the authors describe the design of an optical fiber current sensor, and review the considerations which led to the adoption of this particular design, including outlines of the Faraday effect itself and the major difficulty to be overcome; an effect known as linear birefringence.
Abstract: An optical fibre current sensor has been designed and tested. This device, which uses the Faraday effect in optical fibre to measure electrical current, is intended to be applied to protection systems; it is regarded as a potential replacement for the iron cored current transformer in certain applications. The authors describe the design of an optical fibre current sensor, and review the considerations which led to the adoption of this particular design. Some background optical information is provided in order to make the design process clear, including outlines of the Faraday effect itself and of the major difficulty to be overcome; an effect known as linear birefringence. The results of current measurement tests on the optical fibre current sensor are presented and analysed in comparison with a current transformer. The advantages of the optical fibre current sensor for protection applications are summarized. >
TL;DR: In this paper, two schemes for active cavity length control for close-coupled laser diode to butt-ended fibre are described and it is shown that at specific fibre-to-facet distances a significant reduction in feedback-induced laser frequency noise occurs.
Abstract: Two schemes for active cavity length control for close-coupled laser diode to butt-ended fibre are described and it is shown that at specific fibre-to-facet distances a significant reduction in feedback-induced laser frequency noise occurs.
23 Feb 1989
TL;DR: In this article, the authors describe a number of multiplexing techniques which may be used for fiber optic sensors in which the sensing element is a ring resonator, which can be used to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer.
Abstract: We describe a number of multiplexing techniques which may be used for fibre optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. A number of such units may be combined to form an array, using coherence multiplexing techniques. When a high coherence source is used, then multiplexing may be accomplished using frequency division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realising a large sensor array.
TL;DR: In this article, a novel technique for determining the polarisation mode dispersion in optical fibres is described, which makes use of a sinusoidally frequency modulated source, and is applied to the measurement of the beat length of highly birefringent monomode fibre.
29 Oct 1989
TL;DR: In contrast to gas lasers, semi-conductor laser diodes are small, robust and relatively cheap as discussed by the authors, allowing a number of electronic processing schemes to be used that are not normally possible with a gas laser.
Abstract: In contrast to gas lasers, semi-conductor lasers are small, robust and relatively cheap. The wavelength of the semi-conductor laser is also easily tuned by varying the injection current, allowing a number of electronic processing schemes to be used that are not normally possible with a gas laser. As a consequence of these advantages, the semi-conductor laser is widely used for implementing optical sensors, in particular fibre optic interferometric sensors. However, one major limitation of semi-conductor laser diodes is that they exhibit both amplitude and frequency jitter noise that exceed the noise levels present in for example the HeNe laser.
29 Oct 1989
TL;DR: In this paper, a technique for uniquely recovering the optical path imbalance within an interferometer interferometrically by means of a sinusoidal modulation of the source frequency is described.
Abstract: We describe a technique for uniquely recovering the optical path imbalance within an interferometer interferometrically by means of a sinusoidal modulation of the source frequency. The technique is demonstrated in systems configured to measure displacement, intermodal dispersion in a highly birefringent fibre and the refractive index of a number of liquids.