CA2128315A1 - Apparatus and method of sensing using distributed excitation of an optical guidedwave structure by ambient radiation - Google Patents
Apparatus and method of sensing using distributed excitation of an optical guidedwave structure by ambient radiationInfo
- Publication number
- CA2128315A1 CA2128315A1 CA002128315A CA2128315A CA2128315A1 CA 2128315 A1 CA2128315 A1 CA 2128315A1 CA 002128315 A CA002128315 A CA 002128315A CA 2128315 A CA2128315 A CA 2128315A CA 2128315 A1 CA2128315 A1 CA 2128315A1
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- Prior art keywords
- optical
- guidedwave
- section
- sensor
- ambient radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N2021/7769—Measurement method of reaction-produced change in sensor
- G01N2021/7786—Fluorescence
Abstract
Distributed transverse excitation of an optical guidedwave structure by means of ambient radiation from a natural or man made source avoids the need to connect a source through one end of the device. This permits a wide range of sensing with significant improvement in the ease of installation and lower costs than conventional guidedwave sensors. In this type of sensor the local environment, the state of the sensor, or some measurand of interest can modulate its output optical power by modifying the transmission of radiant energy through the device. A unique aspect of transverse excitation is that distributed sensing of the local environment is also possible through direct control of the level of excitation. The optical guidedwave structure can thus be made to sense its state, or its local environment. When transverse distributed excitation with low level ambient radiation is combined with visual inspection the sensor becomes "self-contained", extremely simple and very low cost.
Description
INTELLECTUAL PROPERTY
DISTR!CT OFFICE
DISTR!CT OFFICE
2 2 8 ~ 5 ~ TORONTO
BUREAU G~ ~ISTRICT
Title of Invention: PRoPR!E-rE INTELLEc-ruEL~F
An Apparatus and Method of Sensing Using Distributed Excitation of an Optical Guidedwave Structure by Ambient Rr~inti~n Field of Invention The invention relates to an apparatus and a method for undertaking a broad range of sensing by means of an optical guidedwave structure that is excited by distributed ambient {natural or artificial} radiation. The excitation mechanisms include: induced fluorescence; an optical device {such as a Bragg grating}; or scattering. This type of sensor could be used to detect: the exceedance of a threshold temperature, the presence of certain chemicals, the process of eorrosion or erosion and the deposition of materials. The sensor can also be used to monitor ehanges in its state, such as caused by crack formation or bending of a host structure.
Background of the Invention The present invention relates to optical guidedwave sensors, the most popular form being fiber optic sensors. Currently, these sensors are excited through one end by a man made source, such as: a laser {often a semiconductor laser diode}; a light emitting diode; or a superluminescent diode. This mode of excitation represents a significant fraction of the cost of the sensor, restricts distributed sensing, complicates installation and limits the use of the sensor as some form of guidedwave lead-in section is required. Although fiber optic distributed temperature sensing is possible using Raman scattering, and distributed strain and temperature sensing is possible with Brillouin scattering, the spatial resolution of the former is limited to greater than a meter, while the latter is limited to greater than five meters. Furthermore, the cost of these systems are appreciable.
There iS a significant number of sensing applications that are rendered impractical by the need for a physical connection between the guidedwave sensing element and a source of excitation.
Other applications are impeded by the cost of the source of excitation. The situation is further complicated if some form of detector has to be employed as this device then has to be connected either directly, or indirectly through some intervening section of optical guidedwave structure to the sensing element. In a transmission based sensor the source of excitation is connected to one end of the optical guidedwave structure, while the detector is connected to the other end. In many situations, such as structural sensing, the source and the detector cannot be positioned close to the sensing section so two guidedwave leads are required. This complicates installation and makes embedding within composite materials impractical in many situations. In the case of a reflective based sensor only one lead is required, but some form of optical splitter or coupler is then necessary. This represents a serious impediment for many structural sensing applications as only a low profile guidedwave structure can be adhered to, or embedded within, the host structure.
There are a number of sensing application for which there are no suitable sensing systems currently available. A good example of this is the detection of corrosion within the aging fleet of aluminium based aircraft. Although a number of retrofit sensors have been proposed including fiber optic based systems their high cost, complexity of installing and operating have precluded their implementation to date.
Although it would be desirable to be able to excite an optical guidedwave structure with ambient radiation and avoid the need for a physical connection to a man made source of radiation, the very nature of a guidedwave structure, such as an optical fiber or a thin film, precludes coupling sufficient ambient radiation into the end of such a structure. In general a source has to be relatively intense and focussed to fill the acceptance solid angle of an optical guidedwave structure.
Summary of the Invention:
The present invention overcomes the limitation of end pumping an optical guidedwave structure with ambient radiation by using transverse excitation distributed over a length that is very large compared to the lateral dimensions of the guidedwave structure. In this way even low level ambient radiation is harvested over a relatively large area and builds along the length of the guidedwave structure to become adequate for sensing.
According to the invention ambient radiation {taken to mean throughout from a natural or artificial source} distributed over an area of optical guidedwave structure that is very large compared to the end face area is used to sense the state, some measurand of interest, or the local environment, of some section of the optical guidedwave structure. Illumination of the sensing section of the device is achieved either through some redirection mechanism, or indirectly through the generation of fluorescence. When this transverse excitation by ambient radiation is combined with visual inspection the sensor is self-contained, very low cost, and simple to use with a broad range of applications.
The invention is an optically guided sensing, or measuring device, that comprises the following elements:
1. A suitable length of optical guidedwave structure {which can take the form of an optical fiber or a thin film} that is transversely excited by distributed ambient radiation. Mechanisms that permit distributed transverse excitation, include: generation of fluorescence; an optical device ~such as a Bragg grating}; or scattering.
2. An optical guidedwave section that serves as the sensing element. This section can coincide with the transverse excitation section if the degree of transverse excitation is modulated in accordance with the state of the sensor, its local environment, or some measurand of interest.
Otherwise, modification of the transmission characteristics of a separate section is used as a means of monitoring the state of the sensor, its local environment, or some measurand of interest.
BUREAU G~ ~ISTRICT
Title of Invention: PRoPR!E-rE INTELLEc-ruEL~F
An Apparatus and Method of Sensing Using Distributed Excitation of an Optical Guidedwave Structure by Ambient Rr~inti~n Field of Invention The invention relates to an apparatus and a method for undertaking a broad range of sensing by means of an optical guidedwave structure that is excited by distributed ambient {natural or artificial} radiation. The excitation mechanisms include: induced fluorescence; an optical device {such as a Bragg grating}; or scattering. This type of sensor could be used to detect: the exceedance of a threshold temperature, the presence of certain chemicals, the process of eorrosion or erosion and the deposition of materials. The sensor can also be used to monitor ehanges in its state, such as caused by crack formation or bending of a host structure.
Background of the Invention The present invention relates to optical guidedwave sensors, the most popular form being fiber optic sensors. Currently, these sensors are excited through one end by a man made source, such as: a laser {often a semiconductor laser diode}; a light emitting diode; or a superluminescent diode. This mode of excitation represents a significant fraction of the cost of the sensor, restricts distributed sensing, complicates installation and limits the use of the sensor as some form of guidedwave lead-in section is required. Although fiber optic distributed temperature sensing is possible using Raman scattering, and distributed strain and temperature sensing is possible with Brillouin scattering, the spatial resolution of the former is limited to greater than a meter, while the latter is limited to greater than five meters. Furthermore, the cost of these systems are appreciable.
There iS a significant number of sensing applications that are rendered impractical by the need for a physical connection between the guidedwave sensing element and a source of excitation.
Other applications are impeded by the cost of the source of excitation. The situation is further complicated if some form of detector has to be employed as this device then has to be connected either directly, or indirectly through some intervening section of optical guidedwave structure to the sensing element. In a transmission based sensor the source of excitation is connected to one end of the optical guidedwave structure, while the detector is connected to the other end. In many situations, such as structural sensing, the source and the detector cannot be positioned close to the sensing section so two guidedwave leads are required. This complicates installation and makes embedding within composite materials impractical in many situations. In the case of a reflective based sensor only one lead is required, but some form of optical splitter or coupler is then necessary. This represents a serious impediment for many structural sensing applications as only a low profile guidedwave structure can be adhered to, or embedded within, the host structure.
There are a number of sensing application for which there are no suitable sensing systems currently available. A good example of this is the detection of corrosion within the aging fleet of aluminium based aircraft. Although a number of retrofit sensors have been proposed including fiber optic based systems their high cost, complexity of installing and operating have precluded their implementation to date.
Although it would be desirable to be able to excite an optical guidedwave structure with ambient radiation and avoid the need for a physical connection to a man made source of radiation, the very nature of a guidedwave structure, such as an optical fiber or a thin film, precludes coupling sufficient ambient radiation into the end of such a structure. In general a source has to be relatively intense and focussed to fill the acceptance solid angle of an optical guidedwave structure.
Summary of the Invention:
The present invention overcomes the limitation of end pumping an optical guidedwave structure with ambient radiation by using transverse excitation distributed over a length that is very large compared to the lateral dimensions of the guidedwave structure. In this way even low level ambient radiation is harvested over a relatively large area and builds along the length of the guidedwave structure to become adequate for sensing.
According to the invention ambient radiation {taken to mean throughout from a natural or artificial source} distributed over an area of optical guidedwave structure that is very large compared to the end face area is used to sense the state, some measurand of interest, or the local environment, of some section of the optical guidedwave structure. Illumination of the sensing section of the device is achieved either through some redirection mechanism, or indirectly through the generation of fluorescence. When this transverse excitation by ambient radiation is combined with visual inspection the sensor is self-contained, very low cost, and simple to use with a broad range of applications.
The invention is an optically guided sensing, or measuring device, that comprises the following elements:
1. A suitable length of optical guidedwave structure {which can take the form of an optical fiber or a thin film} that is transversely excited by distributed ambient radiation. Mechanisms that permit distributed transverse excitation, include: generation of fluorescence; an optical device ~such as a Bragg grating}; or scattering.
2. An optical guidedwave section that serves as the sensing element. This section can coincide with the transverse excitation section if the degree of transverse excitation is modulated in accordance with the state of the sensor, its local environment, or some measurand of interest.
Otherwise, modification of the transmission characteristics of a separate section is used as a means of monitoring the state of the sensor, its local environment, or some measurand of interest.
3. An output end of the optical guidedwave structure that is positioned for visual inspection, or monitored by means of a photodetector, possibly through another guidedwave section.
These forgoing aspects of the invention, together with other aspects and advantages thereof will be more apparent from the following description of the preferred embodiment thereof, taken in conjunction with the following drawings.
Brief Description of the Drawings FIG. 1 is a schematic diagram of the invention illustrating the fluorescence based method of distributed transverse excitation of the optical guidedwave structure by ambient radiation.
FIG. 2 is a schematic diagram of the invention illustrating distributed transverse excitation of a guidedwave structure by ambient radiation by means of an intra-guide Bragg grating.
FIG. 3 is a schematic diagram of the invention illustrating distributed transverse excitation of a guidedwave structure by ambient radiation by means of a scattering section.
FIG. 4 is a schematic diagram of a plt;fel.~d embodiment of the invention illustrating transverse excitation through the generation of fluorescence within an optical fiber by ambient radiation and crack detection through loss of the transmitted radiation.
FIG. 5 is a schematic diagram of an alternative preferred embodiment of the invention illustrating detection of corrosion at some location along the optical fiber by the disappearance of its shielding metal coating allowing the generation of fluorescence through transverse excitation at this location by ambient radiation.
21~831S
Detailed Description of the Preferred Embodiments The invention involves the following novel features:
1. Distributed transverse excitation allows use of low level ambient radiation and avoids connection of a man made radiation source to one end of the sensor.
2. The combination of distributed transverse excitation with visual inspection makes possible a stand alone, self-contained sensor having no connections.
3. Transverse excitation of the sensor allows distributed sensing through the mechanism of modifying the exposure to the ambient pumping radiation by a change in the measurand of interest, the state of the sensor, or the local condition to be detected.
Although the invention will now be specifically described with respect to optical fiber sensors, it is to be understood that the invention is not limited to such devices and can apply to other guidedwave structures, such as thin films.
Ambient radiation at around 400 nm can excite green {490 nm } fluorescence in plastic fibers.
A good example are the polymethylmethacrylate {PMMA}clad-polystrene core fibers manufactured by Bicron Corporation, Ohio, US. Other wavelength ranges are also possible. Distributed transverse excitation over about a 3 cm length of these fibers by ambient radiation, even in the evening of a cloudy day, produces sufficient intensity for them to be used as a sensor with either visual or photodetector monitoring. FIG. 1 presents a schematic illustration of one preferred embodiment of our invention in which a length of optical fiber 1 transmits the optical signal to the output end 2 where visual inspection 3 is employed. For the case illustrated in FIG. 1 the distributed ambient radiation 4 transversely excites the fluorescent section 5 {which may, or may not, be made of the same material as the rest of the optical fiber}and generates a fluorescent signal 6 that is transmitted to the output end 2. In FIG. 2 a Bragg grating 7 is shown to redirect the distributed ambient radiation 8 along the length of the optical fiber 1 towards the output end 2, while in FIG. 3 a scattering section 10 is employed to redirect the distributed ambient radiation 11.
As this optical signal {6, 8 or 11 } is guided through the sensing section of the optical fiber it iS modified in some manner by the state of the optical fiber, or the measurand of interest. For example, in FIG. 4, we show that if the fiber is fractured 14 by a crack to be detected in some host material to which the optical fiber is surface adhered or embedded, there is a sudden loss of fluorescence 14 and a concomitant drop in the emitted fluorescence 12. Visual inspection, or monitoring by a photodetector would then provide information on the state of the fiber and its host material. This could be used as the basis of a structural integrity sensor that could be designed to detect cracks in metal structures, debonding of joints or repair patches, or del~min~tions in advanced composite materials. Lymer et al., 1990 [US patent # 4,936,649] demonstrated a method of tailoring optical fibers to match the damage observed in Kevlar/epoxy. Alternatively, the optical fiber might be bent so as to introduce loss through radiation modes and thereby reduce the radiation transmitted to the detection end. In this way the optical fiber can be used to measure deflection of a structure, or a change in pressure applied to the sensor.
In another preferred embodiment a section of multimode fluorescent optical fiber 5 is shielded by a specially designed coating from exposure to ambient natural, or a man made radiation source.
When this coating is exposed to: a specific chemical, or corrosion, or a threshold temperature, its shielding properties are modified so that the fiber is excited to fluoresce and ilhlminate the remAining length of the optical fiber. The degree of exposure to the environmental change is gauged from the optical power emitted from the output end of the sensor. In FIG. 5 we illustrate the case for the detection of corrosion of a metal structure. In this example the fluorescent section 5 is shielded from the ambient radiation by a metal coating 15 that is designed to be destroyed at the same rate as the host material. Thus initially no fluorescence is observed from the output end of the sensor 16 but as corrosion proceeds to destroy the metal coating 17 fluorescence is seen at the output end. Some degree of quantification of the extent of corrosion may be possible from the extent of the observed fluorescence. It is clear that the same principle can be applied to the detection of specific chemicals that might dissolve a coating, or erosion of a surface, or the exceedance of a threshold temperature that melts, evaporates or sublimes the shielding coating at the applupliate temperature.
The opposite affect, that is the build up of some film or layer, from dirt to a semiconductor material in an MBE machine, could be assessed from the extinction of the output signal of an optical fiber that is suitably positioned. Since absoutely no form of electronics is required in the visual inspection mode this type of sensor might also find application in very high electric and magnetic field environments. It is also possible to use the invention to monitor exposure to a variety of environmental conditions such as the level of X-rays or other forms of radition from the degradation of the output signal. Degradation of the sensor may also be used to monitor the cummulative affects of periods of exposure to an elevated temperature.
One of the advantages of this invention is the elimination of the need to connect a light source to one end of the optical fiber. This greatly simplifies the design, installation and cost of the sensor. When used with visual inspection the sensor is completely self-contained and requires no connection making it extremely low cost, simple to install and very easy to use. Another advantage of this invention is that there is very little to go wrong, particularly, when using natural ambient radiation combined with visual inspection. The light source is obvious and so the observer provides the detector. These attributes open broad areas of application where conventional fiber optic sensors would not be practical or desirable. Degradation of the optical fiber might be one source of error but this could be checked with the manufacturer.
In many applications it may be desirable to use a reference system. This is particularly the case where the intensity of the output power is intended to convey some sensing information rather than just the presence or absence of an optical output, and variations in the ambient radiation is possible.
A reference system would comprise a similar length of optical fiber as the sensing optical fiber, especially the excitation section, and be exposed to the same ambient radiation. However, it would be designed to not respond to the condition, or measurand, of interest.
It will be apparent that many other changes may be made to the illustrated embodiment, while falling within the scope of the invention and it is intended that all such changes be covered by the claims appended hereto.
These forgoing aspects of the invention, together with other aspects and advantages thereof will be more apparent from the following description of the preferred embodiment thereof, taken in conjunction with the following drawings.
Brief Description of the Drawings FIG. 1 is a schematic diagram of the invention illustrating the fluorescence based method of distributed transverse excitation of the optical guidedwave structure by ambient radiation.
FIG. 2 is a schematic diagram of the invention illustrating distributed transverse excitation of a guidedwave structure by ambient radiation by means of an intra-guide Bragg grating.
FIG. 3 is a schematic diagram of the invention illustrating distributed transverse excitation of a guidedwave structure by ambient radiation by means of a scattering section.
FIG. 4 is a schematic diagram of a plt;fel.~d embodiment of the invention illustrating transverse excitation through the generation of fluorescence within an optical fiber by ambient radiation and crack detection through loss of the transmitted radiation.
FIG. 5 is a schematic diagram of an alternative preferred embodiment of the invention illustrating detection of corrosion at some location along the optical fiber by the disappearance of its shielding metal coating allowing the generation of fluorescence through transverse excitation at this location by ambient radiation.
21~831S
Detailed Description of the Preferred Embodiments The invention involves the following novel features:
1. Distributed transverse excitation allows use of low level ambient radiation and avoids connection of a man made radiation source to one end of the sensor.
2. The combination of distributed transverse excitation with visual inspection makes possible a stand alone, self-contained sensor having no connections.
3. Transverse excitation of the sensor allows distributed sensing through the mechanism of modifying the exposure to the ambient pumping radiation by a change in the measurand of interest, the state of the sensor, or the local condition to be detected.
Although the invention will now be specifically described with respect to optical fiber sensors, it is to be understood that the invention is not limited to such devices and can apply to other guidedwave structures, such as thin films.
Ambient radiation at around 400 nm can excite green {490 nm } fluorescence in plastic fibers.
A good example are the polymethylmethacrylate {PMMA}clad-polystrene core fibers manufactured by Bicron Corporation, Ohio, US. Other wavelength ranges are also possible. Distributed transverse excitation over about a 3 cm length of these fibers by ambient radiation, even in the evening of a cloudy day, produces sufficient intensity for them to be used as a sensor with either visual or photodetector monitoring. FIG. 1 presents a schematic illustration of one preferred embodiment of our invention in which a length of optical fiber 1 transmits the optical signal to the output end 2 where visual inspection 3 is employed. For the case illustrated in FIG. 1 the distributed ambient radiation 4 transversely excites the fluorescent section 5 {which may, or may not, be made of the same material as the rest of the optical fiber}and generates a fluorescent signal 6 that is transmitted to the output end 2. In FIG. 2 a Bragg grating 7 is shown to redirect the distributed ambient radiation 8 along the length of the optical fiber 1 towards the output end 2, while in FIG. 3 a scattering section 10 is employed to redirect the distributed ambient radiation 11.
As this optical signal {6, 8 or 11 } is guided through the sensing section of the optical fiber it iS modified in some manner by the state of the optical fiber, or the measurand of interest. For example, in FIG. 4, we show that if the fiber is fractured 14 by a crack to be detected in some host material to which the optical fiber is surface adhered or embedded, there is a sudden loss of fluorescence 14 and a concomitant drop in the emitted fluorescence 12. Visual inspection, or monitoring by a photodetector would then provide information on the state of the fiber and its host material. This could be used as the basis of a structural integrity sensor that could be designed to detect cracks in metal structures, debonding of joints or repair patches, or del~min~tions in advanced composite materials. Lymer et al., 1990 [US patent # 4,936,649] demonstrated a method of tailoring optical fibers to match the damage observed in Kevlar/epoxy. Alternatively, the optical fiber might be bent so as to introduce loss through radiation modes and thereby reduce the radiation transmitted to the detection end. In this way the optical fiber can be used to measure deflection of a structure, or a change in pressure applied to the sensor.
In another preferred embodiment a section of multimode fluorescent optical fiber 5 is shielded by a specially designed coating from exposure to ambient natural, or a man made radiation source.
When this coating is exposed to: a specific chemical, or corrosion, or a threshold temperature, its shielding properties are modified so that the fiber is excited to fluoresce and ilhlminate the remAining length of the optical fiber. The degree of exposure to the environmental change is gauged from the optical power emitted from the output end of the sensor. In FIG. 5 we illustrate the case for the detection of corrosion of a metal structure. In this example the fluorescent section 5 is shielded from the ambient radiation by a metal coating 15 that is designed to be destroyed at the same rate as the host material. Thus initially no fluorescence is observed from the output end of the sensor 16 but as corrosion proceeds to destroy the metal coating 17 fluorescence is seen at the output end. Some degree of quantification of the extent of corrosion may be possible from the extent of the observed fluorescence. It is clear that the same principle can be applied to the detection of specific chemicals that might dissolve a coating, or erosion of a surface, or the exceedance of a threshold temperature that melts, evaporates or sublimes the shielding coating at the applupliate temperature.
The opposite affect, that is the build up of some film or layer, from dirt to a semiconductor material in an MBE machine, could be assessed from the extinction of the output signal of an optical fiber that is suitably positioned. Since absoutely no form of electronics is required in the visual inspection mode this type of sensor might also find application in very high electric and magnetic field environments. It is also possible to use the invention to monitor exposure to a variety of environmental conditions such as the level of X-rays or other forms of radition from the degradation of the output signal. Degradation of the sensor may also be used to monitor the cummulative affects of periods of exposure to an elevated temperature.
One of the advantages of this invention is the elimination of the need to connect a light source to one end of the optical fiber. This greatly simplifies the design, installation and cost of the sensor. When used with visual inspection the sensor is completely self-contained and requires no connection making it extremely low cost, simple to install and very easy to use. Another advantage of this invention is that there is very little to go wrong, particularly, when using natural ambient radiation combined with visual inspection. The light source is obvious and so the observer provides the detector. These attributes open broad areas of application where conventional fiber optic sensors would not be practical or desirable. Degradation of the optical fiber might be one source of error but this could be checked with the manufacturer.
In many applications it may be desirable to use a reference system. This is particularly the case where the intensity of the output power is intended to convey some sensing information rather than just the presence or absence of an optical output, and variations in the ambient radiation is possible.
A reference system would comprise a similar length of optical fiber as the sensing optical fiber, especially the excitation section, and be exposed to the same ambient radiation. However, it would be designed to not respond to the condition, or measurand, of interest.
It will be apparent that many other changes may be made to the illustrated embodiment, while falling within the scope of the invention and it is intended that all such changes be covered by the claims appended hereto.
Claims (22)
1. An optical guidedwave sensor that comprises:
a section of optical guidedwave structure wherein distributed transverse excitation by ambient radiation takes place along some portion of its length;
a section of optical guidedwave structure that serves as the sensing element and controls the optical power transmitted through this section in accordance with the state of this section;
a section of optical guidedwave structure that transmits the sensor modulated optical power to the output end of the optical guidedwave structure;
a means for monitoring the state of the sensor, or some measurand of interest, or the local environment.
a section of optical guidedwave structure wherein distributed transverse excitation by ambient radiation takes place along some portion of its length;
a section of optical guidedwave structure that serves as the sensing element and controls the optical power transmitted through this section in accordance with the state of this section;
a section of optical guidedwave structure that transmits the sensor modulated optical power to the output end of the optical guidedwave structure;
a means for monitoring the state of the sensor, or some measurand of interest, or the local environment.
2. An optical guidedwave sensor according to claim 1, wherein said means of monitoring is visual inspection making possible a stand alone, self-contained sensor having no optical connections.
3. An optical guidedwave sensor according to claim 1, wherein distributed transverse excitation by ambient radiation generates fluorescence in a suitably doped section of the optical guidedwave structure and;
said fluorescence illuminates the remaining length of the optical guidedwave structure and is modulated by the sensing section;
said fluorescence illuminates the remaining length of the optical guidedwave structure and is modulated by the sensing section;
4. An optical guidedwave sensor according to claim 1, wherein the distributed transverse excitation involves redirecting the ambient radiation along the optical guidedwave structure;
said redirected ambient radiation illuminates the remaining length of the optical guidedwave structure and is modulated by the sensing section;
said redirected ambient radiation illuminates the remaining length of the optical guidedwave structure and is modulated by the sensing section;
5. An optical guidedwave sensor according to claim 4, wherein an intra-guide Bragg grating redirects the ambient radiation into the sensing section of the optical guidedwave structure.
6. An optical guidedwave sensor according to claim 4, wherein a special scattering section redirects the ambient radiation into the sensing section of the optical guidedwave structure.
7. An optical guidedwave sensor according to claims 1-6, wherein said sensor is attached to, or embedded within, a host structure.
8. An optical guidedwave sensor according to claim 1-6, wherein said sensing signal depends on the local environment, condition of host structure, or the value of some measurand of interest.
9. An optical guidedwave sensor according to claim 1-6, wherein optical guidedwave structure is in the form of an optical fiber.
10. An optical guidedwave sensor that comprises:
a section of optical guidedwave structure wherein distributed transverse excitation by ambient radiation takes place along some portion of its length;
said degree of transverse excitation is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
a section of optical guidedwave structure that transmits the sensor modulated optical power to the output end of the optical guidedwave structure;
a means for monitoring the state of the sensor, or some measurand of interest, or the local environment.
a section of optical guidedwave structure wherein distributed transverse excitation by ambient radiation takes place along some portion of its length;
said degree of transverse excitation is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
a section of optical guidedwave structure that transmits the sensor modulated optical power to the output end of the optical guidedwave structure;
a means for monitoring the state of the sensor, or some measurand of interest, or the local environment.
11. An optical guidedwave sensor according to claim 10, wherein said means of monitoring is visual inspection making possible a stand alone, self-contained sensor having no optical connections.
12. An optical guidedwave sensor according to claim 10, wherein distributed transverse excitation by ambient radiation generates fluorescence in a suitably doped section of the optical guidedwave structure and;
said fluorescence is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
said modulated fluorescence is transmitted along the remaining length of the optical guidedwave structure and is monitored at the output end of device.
said fluorescence is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
said modulated fluorescence is transmitted along the remaining length of the optical guidedwave structure and is monitored at the output end of device.
13. An optical guidedwave sensor according to claim 10, wherein the distributed transverse excitation involves redirecting the ambient radiation along the optical guidedwave structure;
said degree of redirected ambient radiation is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
said modulated redirected ambient radiation is transmitted along the remaining length of the optical guidedwave structure and is monitored at the output end of device.
said degree of redirected ambient radiation is modulated by some measurand of interest; the state of a host structure, or the local environment, making the sensing element coincident with the section that is transversely excited by ambient radiation;
said modulated redirected ambient radiation is transmitted along the remaining length of the optical guidedwave structure and is monitored at the output end of device.
14. An optical guidedwave sensor according to claim 13, wherein an intra-guide Bragg grating redirects the ambient radiation into the sensing section of the optical guidedwave structure.
15. An optical guidedwave sensor according to claim 13, wherein a special scattering section redirects the ambient radiation into the sensing section of the optical guidedwave structure.
16. An optical guidedwave sensor according to claims 10-15, wherein said sensor is attached to, or embedded within, a host structure.
17. An optical guidedwave sensor according to claims 10-15, wherein said state of sensing section depends on the local environment, condition of host structure, or the value of some measurand of interest.
18. An optical guidedwave sensor according to claims 10-15, wherein optical guidedwave structure is in the form of an optical fiber.
19. An optical guidedwave sensor according to claims 10-15, wherein a special coating is used to shield the excitation section from the ambient radiation; and said coating is designed to disappear or allow the transmission of radiation under the action of specific chemicals, the presence of corrosion or erosion, or the exceedance of some critical temperature.
20. An optical guidedwave sensor according to claims 10-15, wherein the deposition of some layer is used to shield the excitation section from the ambient radiation; and said layer thickness build up is monitored through the reduction of sensor optical output.
21. A method for evaluating the state of an optical guidedwave sensor, its local environment, or some measurand of interest;
said method comprises:
transverse excitation by distributed ambient radiation along some length of the optical guidedwave structure;
modulation of this transverse distributed excitation, by some measurand of interest, the state of the optical guidedwave structure, or the local environment;
evaluation of the output optical power from one end of the optical guidedwave structure either by visual inspection or a photodetector, possibly through an intervening length of optical guidedwave structure.
said method comprises:
transverse excitation by distributed ambient radiation along some length of the optical guidedwave structure;
modulation of this transverse distributed excitation, by some measurand of interest, the state of the optical guidedwave structure, or the local environment;
evaluation of the output optical power from one end of the optical guidedwave structure either by visual inspection or a photodetector, possibly through an intervening length of optical guidedwave structure.
22. A method for evaluating the state of an optical guidedwave sensor, its local environment, or some measurand of interest;
said method comprises:
transverse excitation by distributed ambient radiation along some length of the optical guidedwave structure;
modification of the transmission characteristics of the subsequent section of optical guidedwave structure, by some measurand of interest, the state of the optical guidedwave structure, or the local environment;
evaluation of the output optical power from one end of the optical guidedwave structure either by visual inspection or a photodetector, possibly through an intervening length of optical guidedwave structure.
said method comprises:
transverse excitation by distributed ambient radiation along some length of the optical guidedwave structure;
modification of the transmission characteristics of the subsequent section of optical guidedwave structure, by some measurand of interest, the state of the optical guidedwave structure, or the local environment;
evaluation of the output optical power from one end of the optical guidedwave structure either by visual inspection or a photodetector, possibly through an intervening length of optical guidedwave structure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002128315A CA2128315A1 (en) | 1994-07-18 | 1994-07-18 | Apparatus and method of sensing using distributed excitation of an optical guidedwave structure by ambient radiation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002128315A CA2128315A1 (en) | 1994-07-18 | 1994-07-18 | Apparatus and method of sensing using distributed excitation of an optical guidedwave structure by ambient radiation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2128315A1 true CA2128315A1 (en) | 1996-01-19 |
Family
ID=4154031
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002128315A Abandoned CA2128315A1 (en) | 1994-07-18 | 1994-07-18 | Apparatus and method of sensing using distributed excitation of an optical guidedwave structure by ambient radiation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2128315A1 (en) |
-
1994
- 1994-07-18 CA CA002128315A patent/CA2128315A1/en not_active Abandoned
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