Cavity Ring-Down Sensing Apparatus and Methods
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Abstract
We describe an evanescent wave cavity-based optical sensor. The sensor comprises an optical cavity including a reflection from one or more totally internally reflecting (TIR) surfaces generating an evanescent wave to provide a sensing function; a light source to optically excite said cavity at least two different wavelengths; and a detector to monitor a ring-down characteristic of said cavity at each of said two wavelengths; and wherein said one or more TIR surfaces are provided with at least two functionalising materials one responsive at each of said wavelengths such that an interaction between a said functionalising material and one or more targets to be sensed is detectable as a change in absorption of a said evanescent wave at a said wavelength.
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Citations
117 Claims
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1-58. -58. (canceled)
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59. An evanescent wave cavity-based optical sensor, the sensor comprising:
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an optical cavity formed by a pair of highly reflective surfaces such that light within said cavity makes a plurality of passes between said surfaces, an optical path between said surfaces including a reflection from a totally internally reflecting (TIR) surface, said reflection from said TIR surface generating an evanescent wave to provide a sensing function;
a light source to inject a pulse of light into said cavity;
a detector to detect decaying oscillations of said light pulse within said cavity; and
a signal processor coupled to said detector and configured to provide a time-resolved output responsive to a light level within said cavity and having a time-resolution corresponding to a set of said light pulse oscillations, whereby said sensing function operates at substantially said time-resolution. - View Dependent Claims (60, 61, 62, 63, 64)
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65. A method of performing time-resolved sensing using an optical cavity including a sensing surface, a sensing interaction at said sensing surface modifying an optical ring-down characteristic of said cavity, the method comprising:
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injecting a pulse of light into said cavity; and
monitoring an optical ring-down of said pulse within said cavity to monitor said sensing interaction; and
wherein said monitoring is performed substantially on a pulse-by-pulse basis such that said sensing is time-resolved at a resolution of at least an integral number of round trip times of said cavity. - View Dependent Claims (66, 67)
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68. An evanescent-wave cavity-based optical sensor system, the system comprising:
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an optical cavity formed by a pair of highly reflective surfaces such that light within said cavity makes a plurality of passes between said surfaces, an optical path between said surfaces including a reflection from one or more totally internally reflecting (TIR) surfaces, a said reflection from a TIR surface generating an evanescent wave to provide an attenuated TIR sensing function;
a light source to optically excite said cavity at least two different wavelengths; and
a detector to monitor a ring-down characteristic of said cavity at each of said two wavelengths; and
wherein said one or more TIR surfaces are provided with at least two functionalising materials one responsive at each of said wavelengths such that an interaction between a said functionalising material and one or more targets to be sensed is detectable as a change in absorption of a said evanescent wave at a said wavelength. - View Dependent Claims (69, 70, 71, 72, 73, 74)
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75. A method of wavelength division multiplexing sensors of an evanescent wave cavity ring-down sensor system, the method comprising:
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applying a plurality of different functionalising materials to one or more evanescent wave sensing regions of a cavity of said sensor system, said different functionalising materials having sensing responses at different wavelengths;
exciting said cavity at a plurality of different wavelengths corresponding to wavelengths of said sensing responses of said functionalising materials; and
monitoring a ring-down characteristic of said cavity at each of said exciting wavelengths.
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76. A waveguide-based cavity ring-down sensor for sensing an environmental variable, the sensor comprising:
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an optical cavity including a waveguide;
a light source for exciting the optical cavity; and
a detector for monitoring a ring-down characteristic of the cavity; and
a signal processor coupled to said detector and configured to provide a signal output responsive to a change in optical propagation loss within said cavity as determined from said ring-down characteristic; and
wherein a change in said environmental variable causes a change in optical propagation loss in said waveguide to provide said signal output. - View Dependent Claims (77, 78, 79, 80, 81, 82)
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83. A waveguide-based sensing method for sensing an environmental variable using an optical cavity including a waveguide, the method comprising:
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determining an optical ring-up or ring-down time for the cavity to determine a cavity loss; and
determining a change in said cavity loss from a change in said ring-up or ring-down time, said change in loss being caused by an effect of a change in said environmental variable on said waveguide, to sense said change in said environmental variable. - View Dependent Claims (84, 85, 86)
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87. Fibre optic system characterising apparatus for characterising a fibre optic system using optical ring-down, the apparatus comprising:
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an optical cavity configurable to include said fibre optic system;
a light source for exciting said cavity;
a detector for monitoring an optical ring-down of said cavity; and
a signal processor coupled to said detector and configured to determine a characteristic of said fibre optic system from said cavity optical ring-down. - View Dependent Claims (88, 89, 90, 91, 92, 93, 94)
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95. A method of characterising a fibre optic system using optical ring-down, the method comprising:
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forming an optical cavity including said fibre optic system;
exciting said optical cavity using a light source;
monitoring a ring-down of said cavity following said excitation; and
determining a characteristic of said fibre optic system from said monitoring. - View Dependent Claims (96, 97, 98, 99, 100, 101)
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102. A fibre optic sensor, the sensor comprising:
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an optical cavity including a fibre optic;
a light source for exciting the optical cavity; and
a detector for monitoring a ring-down characteristic of the cavity; and
wherein said fibre optic is configured such that a change in a sensed variable causes a physical change in said fibre optic configuration modifying said ring-down characteristic. - View Dependent Claims (103, 104, 105, 106, 107, 108, 109)
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110. A method of sensing using distortion of a fibre optic, the fibre optic comprising at least part of an optical cavity, the method comprising:
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determining an optical ring-up or ring-down time of said cavity;
distorting said fibre optic with a sensed variable; and
determining a change in said ring-up or ring-down time to sense said distortion. - View Dependent Claims (111, 112, 113)
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114. An evanescent-wave cavity-ring down sensing system, the system comprising:
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an evanescent-wave optical cavity;
an optical pump to provide a pump pulse to said optical cavity at a first wavelength; and
an optical probe to provide a probe pulse to said optical cavity at a second wavelength. - View Dependent Claims (115, 116, 117)
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Specification