Method and apparatus for generation and transmission of high energy optical pulses for long range measurements
First Claim
1. A sensing system for sending electromagnetic signals along a waveguide and sensing conditions at one or more sensing locations along the waveguide, the system comprising a transmitting means and a receiving means, wherein the transmitting means is arranged to generate two or more streams of pulses having spatially separate paths, the pulses of one of the streams having a suitable shape to cause a controlled conversion of the pulses to a different wavelength, before combining the streams to form a combined stream and sending the combined stream along the waveguide, and the receiving means is arranged to receive signals returned from the one or more sensing locations, by detecting an up shifted component returned from one of the pulses at a first wavelength, and a down shifted component returned from one of the pulses transmitted at a higher wavelength, down shifted to the first wavelength and the receiving means is adapted to compensate for different losses along the waveguide at different wavelengths and determine the conditions based on the received signals.
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Abstract
A method and apparatus for generating and transmitting high energy optical pulses are described. Distributed temperature sensors usually use Raman scattering in optical fibers as the means to determine the temperature. Here, light from a laser source is sent down a fiber and the small amount of light that is scattered back towards the source is analysed. As the fiber length increases, the resolutions of the temperature and loss measurements become poorer. This is because losses in an optical fiber attenuate the signal. An obvious solution to this problem is to launch more light into the fiber to compensate for the losses but stimulated Raman scattering limits how much light may be launched. The present invention solves this problem by using a pulse conversion method to maximize the resultant pulse energy while the power is kept below SRS threshold.
13 Citations
24 Claims
- 1. A sensing system for sending electromagnetic signals along a waveguide and sensing conditions at one or more sensing locations along the waveguide, the system comprising a transmitting means and a receiving means, wherein the transmitting means is arranged to generate two or more streams of pulses having spatially separate paths, the pulses of one of the streams having a suitable shape to cause a controlled conversion of the pulses to a different wavelength, before combining the streams to form a combined stream and sending the combined stream along the waveguide, and the receiving means is arranged to receive signals returned from the one or more sensing locations, by detecting an up shifted component returned from one of the pulses at a first wavelength, and a down shifted component returned from one of the pulses transmitted at a higher wavelength, down shifted to the first wavelength and the receiving means is adapted to compensate for different losses along the waveguide at different wavelengths and determine the conditions based on the received signals.
- 6. A sensing system for sending electromagnetic signals along a sensing waveguide and sensing conditions at one or more sensing locations along the sensing waveguide, the system comprising a transmitting means arranged to transmit pulses of suitable shape to cause a controlled conversion of the pulses to a different wavelength by a stimulated inelastic scattering process in the sensing waveguide before reaching a first sensing location, the system comprising a receiving means arranged to receive signals returned from the first sensing location, and to determine the conditions based on the received signals, the power of the pulses being such that the different wavelength undergoes one or more further conversions to further different wavelengths by a stimulated inelastic scattering process beyond the first sensing location such that different parts of the sensing waveguide are illuminated by different wavelengths, and the receiving means is arranged to distinguish the returning optical signals at each of the different wavelengths.
- 12. A sensing system for sending electromagnetic signals along a waveguide and sensing conditions at one or more sensing locations along the waveguide, the system having a receiving means and a transmitting means having a source for generating a stream of pulses, a splitter arranged to split the pulses into two or more streams, and a convertor for converting the wavelength of one of the streams to a different wavelength, before sending the streams along the waveguide, the receiving means being arranged to receive signals returned from the sensing location, and to determine the conditions based on the received signals, the receiving means being arranged to compensate for different losses along the waveguide at different wavelengths by detecting an up shifted component returned from one of the pulses at a first of the wavelengths, and a down shifted component returned from one of the pulses transmitted at a higher of the wavelengths, down shifted to the first wavelength.
- 15. Apparatus for generating and transmitting high energy optical pulses along a waveguide which provides a scattering medium which apparatus comprises an optical pulse generator for generating the high energy optical pulses, an optical arrangement for lengthening a duration of each pulse located before the waveguide to reduce a peak power such that stimulated Raman light is suppressed while maintaining pulse energy for transmission along the waveguide, and a receiver for measuring different components of backscattered light from the waveguide for remote sensing.
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21. A method of sensing conditions at one or more sensing locations along a waveguide, comprising:
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generating two or more streams of pulses having spatially separate paths, the pulses of one of the streams having a suitable shape to cause a controlled conversion of the pulses to a different wavelength; combining the streams to form a combined stream; sending the combined stream along the waveguide; receiving signals returned from the one or more sensing locations, by detecting an up shifted component returned from one of the pulses at a first wavelength, and a down shifted component returned from one of the pulses transmitted at a higher wavelength, down shifted to the first wavelength; compensating for different losses along the waveguide at different wavelengths; and determining the conditions based on the received signals.
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22. A method of sensing conditions at one or more sensing locations along a waveguide, comprising:
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transmitting pulses of suitable shape to cause a controlled conversion of the pulses to a different wavelength by a stimulated inelastic scattering process in the waveguide before reaching a first sensing location, the power of the pulses being such that the different wavelength undergoes one or more further conversions to further different wavelengths by a stimulated inelastic scattering process beyond the first sensing location such that different parts of the waveguide are illuminated by different wavelengths; receiving signals returned from the first sensing location; distinguishing the returning optical signals at each of the different wavelengths; and determining the conditions based on the received signals.
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23. A method of sensing conditions at one or more sensing locations along a waveguide, comprising:
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generating a stream of pulses; splitting the pulses into two or more streams; converting the wavelength of one of the streams to a different wavelength, before sending the streams along the waveguide; receiving signals returned from the sensing location; compensating for different losses along the waveguide at different wavelengths by detecting an up shifted component returned from one of the pulses at a first of the wavelengths, and a down shifted component returned from one of the pulses transmitted at a higher of the wavelengths, down shifted to the first wavelength; and determining the conditions based on the detected components.
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24. A method for generating and transmitting high energy optical pulses along a waveguide which provides a scattering medium comprising:
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generating high energy optical pulses; lengthening a duration of each pulse before each pulse enters the waveguide to reduce a peak power such that stimulated Raman light is suppressed in the waveguide while maintaining pulse energy for transmission along the waveguide; and measuring different components of backscattered light from the waveguide for remote sensing.
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Specification