Method and apparatus for measuring the phase shift induced in a light signal by a sample
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Abstract
A first light source emits a light signal along a measurement optical path that includes a sample and a second light source emits a light signal along a dummy measurement optical path. A measurement circuit receives the light signals and provides outputs separated in time which are indicative of the phase of the respective light signals. A phase shift is induced in light in the measurement optical path by the sample. A reference circuit receives a signal indicative of the phase of the light signals emitted by the first and second light sources. Circuitry compares the phases of light output from the two circuits to provide output indicative of a first measured phase difference during operation of the first light source. Correction is applied to this measurement by taking a similar phase difference measurement during operation of the second light source and comparing the two phase differences.
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Citations
80 Claims
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1-60. -60. (canceled)
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61. Apparatus for measuring a phase shift induced in a light signal by a sample, the apparatus comprising:
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a first light source for emitting a light signal along a measurement optical path, wherein the measurement optical path includes a sample location; a second light source for emitting a light signal along a dummy measurement optical path, the first and second light sources being arranged for alternate operation; a measurement electronic circuit for receiving the light signals from the measurement and dummy measurement optical paths, the measurement electronic circuit being arranged to provide outputs separated in time which are respectively indicative of the phase of the light signals received from each of the measurement and dummy measurement optical paths, wherein in use a phase shift is induced in light in the measurement optical path by a sample in said sample location such that the phase of light of the first light source received from the measurement optical path is different to the phase of light emitted from the first light source; a reference electronic circuit for receiving a signal indicative of the phase of the light signals emitted by the first and second light sources; circuitry to compare the phase of light indicated by the output of the measurement electronic circuit responsive to the first light source with the phase of light indicated by the reference electronic circuit to provide an output indicative of a first measured phase difference and to compare the phase of light indicated by the output of the measurement electronic circuit responsive to the second light source with the phase of light indicated by the reference electronic circuit to provide an output indicative of a second measured phase difference, and circuitry to apply a correction to the first measured phase difference on the basis of the second measured phase difference to correct for errors in said first measured phase difference due to phase changes induced by said measurement and reference electronic circuits so as to obtain an improved measurement of the shift in phase induced in the light of the first light source by the sample. - View Dependent Claims (62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73)
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74. A method of measuring a phase shift induced in a light signal by a sample, comprising the steps of:
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emitting a first light signal along a measurement optical path, wherein the measurement optical path includes a sample location; emitting a second light signal along a dummy-measurement optical path, the first and second light signals being emitted alternately; receiving light signals from the measurement and dummy-measurement optical paths in a measurement electronic circuit; providing outputs separated in time from the measurement electronic circuit, wherein the outputs are respectively indicative of the phase of the light signals received from each measurement and dummy-measurement optical path; receiving a signal indicative of the phase of the first and second light signals in a reference electronic circuit; comparing the phase of light indicated by the output of the measurement electronic circuit and responsive to the first light signal with the phase of light indicated by the reference electronic circuit; providing an output indicative of the first measured phase difference; comparing the phase of light indicated by the output of the measurement electronic circuit in response to the second light signal with the phase of light indicated by the reference electronic circuit; providing an output indicative of a second measured phase difference; applying a correction to the first measured phase difference on the basis of the second measured phase difference to correct errors in said first measured phase difference due to phase changes induced by said measurement and reference electronic circuit so as to obtain an improved measurement of the shifting phase induced in the light of the first light source by the sample. - View Dependent Claims (75, 76, 77, 78, 79, 80)
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Specification