GB2213588A - Improvements relating to optically driven vibrating sensors - Google Patents
Improvements relating to optically driven vibrating sensors Download PDFInfo
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- GB2213588A GB2213588A GB8728664A GB8728664A GB2213588A GB 2213588 A GB2213588 A GB 2213588A GB 8728664 A GB8728664 A GB 8728664A GB 8728664 A GB8728664 A GB 8728664A GB 2213588 A GB2213588 A GB 2213588A
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour in optical waveguides, not otherwise provided for in this subclass
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/35377—Means for amplifying or modifying the measured quantity
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/3538—Optical fibre sensor using a particular arrangement of the optical fibre itself using a particular type of fiber, e.g. fibre with several cores, PANDA fiber, fiber with an elliptic core or the like
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour in optical waveguides, not otherwise provided for in this subclass
- G02F1/0115—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour in optical waveguides, not otherwise provided for in this subclass in optical fibres
- G02F1/0118—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour in optical waveguides, not otherwise provided for in this subclass in optical fibres by controlling the evanescent coupling of light from a fibre into an active, e.g. electro-optic, overlay
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0128—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on electro-mechanical, magneto-mechanical, elasto-optic effects
- G02F1/0131—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on electro-mechanical, magneto-mechanical, elasto-optic effects based on photo-elastic effects, e.g. mechanically induced birefringence
- G02F1/0134—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on electro-mechanical, magneto-mechanical, elasto-optic effects based on photo-elastic effects, e.g. mechanically induced birefringence in optical waveguides
Abstract
A sensor comprises an optical fibre having light-to-mechanical strain transducer means formed integrally therewith for responding to the propagation of modulated light along said optical fibre to drive the optical fibre or part thereof into mechanical resonance. The value of an external parameter influencing the sensor (e.g. temperature, tension, pressure) is determined by monitoring characteristics (e.g. phase or intensity) of the light output from the sensor which are indicative of the effects of the vibration of the sensor on the light propagating therethrough. In one form, as shown, the optical fibre 1 has a light-propagative core 4 and a light-absorbtive region 2 within cladding 3. Optical fibres of quite different cross-sectional configurations are also contemplated and various mounting arrangements are disclosed. <IMAGE>
Description
IMPROVEMENTS RELATING TO OPTICAL SENSORS
This invention relates to optical sensors of the kind including miniature mechanical resonators for producing changes (eg phase modulation) in light propagating therethrough in response to the vibration of said resonators.
It is already known to use such mechanical resonators comprising resonant structures of silicon or quartz crystals, for example, which are driven into resonance by an optical excitation signal. The optical excitation signal may comprise an intensitymodulated light beam which is used to produce vibration of the resonator by means of an optically-induced thermal expansion or by means of the mechanical output of a piezo-electric or electromagnetic transducer which receives an alternating electrical input from a photo-voltaic detector to which the intensity-modulated light beam is applied.
Micro-machined mechanical resonant structures of the general form described form the subject of our co-pending Patent
Application No. 8721113.
One problem with such mechanical resonators resides in the interfacing of these resonators with the ends of optical fibres in fibre-coupled sensing systems.
According to the present invention as broadly conceived there is provided an optical sensor comprising an optical fibre in which light-to-mechanical strain transducer means is formed integrally
therewith to provide an integral mechanical resonator which
responds to intensity-modulated light propagating along said optical fibre in order to effect mechanical distortion of the fibre to drive the fibre or a part thereof into oscillation (ie resonance) the frequency of which can be detected by monitoring the light output from the sensor for the purpose of measuring an external physical parameter influencing the fibre (eg temperature, tension, external pressure, or contaminant coverage of the fibre etc.).
As will be appreciated, the provision of the mechanical resonator as an integral part of the optical fibre sensor greatly facilitates the coupling of the sensor into fibre-coupled sensing systems.
In carrying out the invention intensity-modulated light may be applied to the optical fibre sensor to produce mechanical resonance of the resonator the vibration of the sensor or part thereof producing changes (ie. attenuation coefficient, reflection or phase change coefficient changes) in the modulated light applied to the sensor, these changes being detected in order to monitor physical parameters affecting the optical sensor. Alternatively, light from two different sources may be applied to the sensor, light from one of which is intended to set the mechanical resonator into vibration and the other of which is used for monitoring purposes in determining the parameter to be measured.
For the measurement of such parameters transmissive or reflective monitoring arrangements may be employed.
By way of example various embodiments of the present invention will now be described with reference to the accompanying drawings in which:
Figures 1, 2 and 3 show cross-sectional views of three different forms of optical fibre sensor with integral transducer means requiring external support means;
Figure 4 shows an optical fibre sensor according to Figure 1, 2 or 3 arranged as a bridging structure on support means:
Figures 5 to 8 show cross-sectional views of different selfsupporting optical fibre sensors with integral transducer means according to the invention;
Figures 9, 10 and 11 show various optical sensing systems incorporating optical fibre sensors of the supported and selfsupported kind; and,
Figures 12 and 13 depict optical sensing systems incoporating optical fibre sensors of the form depicted in Figure 5, 7 or 8.
Referring to Figure 1 of the drawings, this shows longitudinal and transverse cross-sectional views of an optical fibre 1 having embodied therein a light-responsive mechanical resonator. This resonator comprises a relatively high light-absorptive region 2 provided in the cladding 3 contiguous to but asymmetrically positioned relative to the axis of the optical fibre core 4. The relatively high absorptive region may, alternatively, actually extend into the core 4.
As intensity-modulated light propagates along the optical fibre core 4 in use of the optical fibre sensor some of the intensitymodulated light will be absorbed in the region 2 and this will produce modulated asymmetrical heating of the optical fibre which in turn produces modulated bending or oscillation of the fibre due to modulated differential thermal expansion. The oscillation of the fibre causes modulation (eg attenuation or phase) of the intensitymodulated light signals propagating along the core 4. The frequency of the intensity-modulated light can be varied so as to drive the optical fibre into resonance the frequency of which may be varied in dependence upon an external parameter (eg temperature pressure) to which the sensor in subjected and which the sensor is required to sense.The parameter concerned may be determined simply by monitoring the changes in phase or attenuation coefficients of the fibre sensor and thus the resonant frequency of the optical fibre.
Referring to Figure 2 of the drawings, this shows longitudinal and transverse cross-sectional views of an alternative form of optical fibre with integral mechanical resonator. In this embodiment the optical fibre 5 has parallel twin cores 6 and 7 embodied within cladding 8. The core 6 includes relatively high light-responsive absorptive material whereas the core 7 is composed of the usual low light absorptive material. As will readily be appreciated, intensitymodulated light caused to propagate along both cores 6 and 7 simultaneously, as by launching an intensity-modulated light beam into both cores 6 and 7 from a relatively large light-guiding core region 9 of an input fibre 10 will produce oscillatory bending of the optical fibre 5 due to the asymmetrical heating of the fibre by the relatively high absorption of light and consequential heating of the core 6.The fibre sensor may be used in the same way as the Figure 1 sensor for determining external parameters.
In another form of optical fibre sensor comprising an optical fibre with integral mechanical resonator as depicted in Figure 3, a segment of the cladding 11 of the optical fibre 12 is omitted or removed, as shown, and a layer of relatively high light-absorptive material 13 is provided in close proximity to the core 14 of the optical fibre so that it will receive the evanescent field from the lattcr. Once again a proportion of an intensity-modulated light beam propagating along the light guiding core 14 will be absorbed by the high-absorptive layer 13 and consequently produce oscillatory bending of the optical fibre and changes in the phase and/or attenuation coefficients of the light output from the fibre sensor.
It may here be mentioned that the light-absorptive region of the fibre sensor of Figures 1 to 3 may be produced by introducing suitable dopants (eg transition and rare earth elements) into the regions of the fibre concerned (eg glass core or fibre cladding). These dopants may themselves also be doped with materials which cause the glass or cladding material, as the case may be, to have an increased thermal expansion coefficient in order to increase the degree of distortion or bending of the fibre for a given intensitymodulated light beam.
Instead of using doped glass for the material of the absorptive regions of the optical fibre a metal or other solid non-vitreous material could be used. In this case the material could either be introduced into the optical fibre during the fibre drawing process or subsequently injected in molten or gaseous form into a cavity formed in the fibre during the drawing process.
Alternatively, instead of using light-absorptive material which responds to the light propagating along the optical fibre piezoelectric material or non-linear material could be used which responds to the intensity-modulated electric field produced by the intensity-modulated light beam propagating along the optical fibre sensor. The electric field acting on the piezo-electric material or nonlinear material, as the case may be, will cause mechanical distortion or bending of the optical fibre to produce the results previously described for parameter sensing purposes.
Figure 4 depicts one method of mounting any of the optical fibre sensors described with reference to Figures 1 to 3. As will be seen from the drawings, the optical fibre sensor 15 is supported at its ends by means of a rigid support structure 16 so that the fibre sensor defines a bridge element which can oscillate as shown in dotted form.
As can readily be appreciated from Figure 4, the optical fibre sensors of Figures 1 to 3 oscillate in the axial plane of the optical fibres. Figures 5 to 7, however, depict different optical fibre sensors which oscillate in directions transverse to the axis of the optical fibre.
This mode of oscillation has the advantage that a potentially higher resonant frequency can be achieved and greater miniaturisation is possible since the fibre itself provides support for the vibrating mechanical resonant element resonator element within it.
Referring now to Figure 5 of the drawings, this shows a transverse cross-sectional view of an optical fibre sensor 17 which includes a light-guiding core 18 and a cladding 19 which forms part of a bridging member 20 of a tubular glass structure 21. The bridging member 20 is provided on one side with a relatively high light-absorptive region 22 which may be doped vitreous material or it may be of metal or non-vitreous material as previously described.
Piezo-electric material could also be used.
In response to the propagation of intensity-modulated light propagating along the light-guiding core 18 an evanescent field impinging on the relatively high light-absorptive material layer 22 will be absorbed to cause asymmetrical heating and thus bending of the bridging element 20 of the fibre in the transverse direction as shown in dotted form. This transverse oscillation of the bridging member and core 18 will produce modulation of the light output from the fibre. This sensor may be used to measure temperature and for this purpose the resonating bridging member 20 may be provided with other layers (not shown) of different thermal expansion coefficients to produce differences in lateral tension.The sensor may also be used for measuring pressure and for this purpose this particular construction of optical fibre sensor has the advantage that the ends of the tubular sensor structure may be sealed with the interior of the tube containing air or being evacuated. In this way the resonant frequency of the mechanical resonator of the sensor would be dependent upon the internal or external pressure, as the case may be.
Referring now to Figure 6 of the drawings the sensor shown is similar to Figure 5 but does not have a tubular support structure for the resonant bridging element 23 including core 24 and cladding 25.
Instead, separate support structures 26 and 27 having relatively heavy inertial mass are provided between which the bridging element can oscillate as indicated by the dotted lines.
Referring to Figure 7, this optical fibre sensor shown in transverse cross-section utilises a tubular light guiding section 28.
Such tubular light guides can guide light relatively efficiently over short sections as a result of Fresnel reflections from the internal surface of the tubular guide. The tubular light guide 28 is provided with diametrically-opposed relatively high light-absorptive layers 29 and 30 on the inner surface of the guide 28, as shown, but such layers could alternatively be provided on the outer surface of the tubular guide 28 but in any event the tubular guide 28 will be set in vibration in response to the propagation of intensity-modulated light along the optical fibre sensor, as indicated by the dotted lines.
Alternatively, a single absorptive layer may be provided on one side only of the light guide 28 in order to produce asymmetric bending of the tube.
As in the case of the Figure 5 sensor, the ends of the tubular guide may be closed so that the resonant frequency of the sensor will be dependent upon the internal or external pressure when the sensor is used as a pressure sensor. When the sensor is used as a temperature sensor, however, layers of material of different thermal expansion coefficients may be applied to the tubular light guide.
Referring now to Figure 8 of the drawings, this shows a transverse cross-sectional view of an optical fibre sensor similar to that of Figure 3 which includes means for increasing the phase change in the light propagating along the sensor as the bridging element is set in vibration by the intensity-modulated light propagating along the sensor. The fibre sensor comprises a core 30 with cladding 31 forming part of a diametric bridging element 32 integral with tubular support structure 33. The bridging element 32 has an absorptive layer 34 on one side thereof.
For the purpose of increasing the effect of the phase change coefficient of the core 30 when the bridging element 32 is vibrated in response to intensity-modulated light propagating along the core the tubular support is formed with a radially extending projection 35. In this construction the resonant bridging element 32 as it vibrates is caused to approach the projection 35 which has a higher refractive index than that of a gas, such as air or vacuum surrounding the bridging element 32. Thus, if the evanescent electric field of the sensor fibre extends outside of the central lightguiding resonant member 32 (to achieve this the cladding 31 must be thin eg about 1 micrometre) the proximity of the projection 35 will influence the propagation constant by virtue of evanescent field leakage into the projection 35.
Referring now to Figures 9 to 13, these show various arrangements for incorporating the optical fibre sensors hereinbefore described in optical fibre-coupled sensing systems.
In Figure 9 an optical fibre sensor 36 of the form shown in
Figure 1, 2 or 3 is coupled at one end to an input optical fibre 37 which launches light from a modulated light source 38 into the sensor and is coupled at its other end to an output optical fibre 39 which conveys the phase-modulated output signal from the sensor 36 to a phase modulation detector 40. The output fibres 37 and 39 are preferably butt-jointed to the optical sensor fibre 36 which spans a support structure 41 to allow the sensor to vibrate freely as indicated.
In the Figure 10 arrangement input and output optical fibres 42 and 43 are preferably butt-jointed to the respective ends of an output fibre sensor 44 which is of the self-supporting form shown in
Figure 5, 6 or 8. Modulated light from light source 45 propagates through the sensor 44 and the modulated light output is detected by detector 46.
In the Figure 11 arrangement reflection monitoring of a vibrating optical fibre sensor 47 is utilised. The sensor 47 may be externally supported as shown in Figure 9 or it may be selfsupporting as depicted in Figure 10. Light from a modulated light source 48 is fed through an input branch of an optical fibre coupler 49 into the optical fibre sensor 47 to which the coupler 49 is preferably butt-jointed. The modulated light propagating through the fibre sensor 47 to set it in vibration is reflected back along the sensor 47 to the coupler 49 which provides a modulated output from an output branch of the coupler which is fed to a detector 50.
Referring to Figures 12 and 13 these show alternative arrangements for coupling the tubular self-supporting optical fibre sensor depicted in Figure 7. In Figure 12 input optical fibre 51 which is connected to a modulated light source 52 is arranged to project into one end of tubular sensor 53 which bridges a support structure 54 as shown. An output optical fibre 55 connected to detector 56 may be arranged to project into the other end of sensor 53, as shown, or a mirror may be positioned over the output end to reflect light back along the sensor to the input fibre which will comprise part of an optical fibre coupler to a detector. The light in the Figure 12 arrangement is reflected from the surfaces of the tubular wall of the sensor 53.
Figure 13 shows an arrangement, however, in which modulated light received from a modulated light source 58 is launched by an input optical fibre 59 into the wall of sensor 60 which is supported by support structure 61 as shown. The modulated light emerging from the output end of the sensor wall may be received by an output fibre 62 or it may be reflected back along the sensor wall by a suitably positioned mirror. The output light from the sensor with or without reflection from the sensor is detected by a detector, such as detector 63.
In yet another arrangement not shown in the drawings the optical fibre sensor may be coupled between input and output fibres.
The input fibre carries light from two light sources one of which produces intensity-modulated light for producing mechanical oscillation of the sensor and the other of which produces light which is intended to be used for monitoring the optical path length changes which occur as a result of the mechanical oscillation of the fibre sensor and which is guided via the output fibre to a detector. Light from the monitoring light source is also guided by a separate optical route or guided path to the detector in order to provide an optical interferometer for the conversion of optical path length changes in the path containing the vibrating sensor to intensity changes in the detector due to the coherent interference of mutually delayed light beams in the interferometer in order to facilitate monitoring of the oscillation of the fibre sensor.
The optical fibre sensors hereinbefore described may be manufactured by known continuous drawing techniques with the relatively high absorptive layers being introduced during or after the drawing process. The continuous length of drawn fibre sensor may then be cut into short lengths suitable for use as individual sensors.
The continuous length of fibre may be produced with a progressively reduced cross-section in order to provide a gradation of properties (eg resonant frequency, optical coupling to lossy regions) and thereby enable a variety of sensors having varying characteristics to be cut from a single continuous length of fibre.
In the foregoing description reference has been made to an intensity-modulated light signal applied to fibre sensor for setting the fibre or part thereof in vibration but it should be understood that the signal may comprise two components derived, for example, from two sources of different optical wavelengths. One of these components may be modulated to produce mechanical oscillation of the fibre or part thereof whilst the other component provides for the measurement of the transmission modulation (eg intensity or phase) resulting from the mechanical oscillation.
Claims (19)
1. An optical sensor comprising an optical fibre having light-tomechanical strain transducer means formed integrally therewith for responding to the propagation of modulated light along said optical fibre to drive the optical fibre or part thereof into mechanical resonance, in which the value of an external parameter influencing the sensor (eg. temperature, pressure) is determined by monitoring characteristics (eg phase or intensity) of the light output from the sensor which are indicative of the effects of the vibration of the sensor on the light propagating therethrough.
2. An optical sensor as claimed in claim 1, in which the optical fibre comprises a light-guiding core surrounded by cladding which includes a region of electric field-responsive or light-responsive relatively high absorption material defining said transducer means and located in close proximity to or extending into the fibre core and positioned eccentrically in the transverse direction relative to the core axis.
3. An optical sensor as claimed in claim 1, in which the optical fibre comprises two parallel light-guiding cores surrounded by cladding and in which one of the cores which defines the transducer means comprises electric field-responsive or relatively high lightresponsive absorptive material.
4. An optical sensor as claimed in claim 1, in which the optical fibre comprises a light-guiding core embodied in cladding material a segmental part of which is omitted or cut away and the exposed surface provided with a layer of electric field-responsive or relatively high light-absorptive material which defines the light-tomechanical strain transducer means located in close proximity to or contiguous with the light-guiding core.
5. An optical sensor as claimed in claim 1, in which the optical fibre comprises a light-guiding core surrounded by cladding integral with a diametrical bridging member of a tubular supporting structure and in which the bridging member includes as transducer means a region of electric field-responsive or relatively high lightresponsive absorptive material positioned in close proximity to the light-guiding core and asymmetrically located relative to the axis thereof.
6. An optical sensor as claimed in claim 5, in which the tubular supporting structure has a radially-extending projection which terminates in close proximity to the cladding surrounding the lightguiding core for enhancing the phase change coefficient of the core when the bridging member is driven into mechanical resonance.
7. An optical sensor as claimed in claim 1, in which the optical fibre comprises a light-guiding core surrounded by cladding integral with a bridging member extending between two high inertial support members and in which the bridging member includes as the transducer means a region of electric field-responsive or relatively high light-responsive absorptive material positioned in close proximity to the light-guiding core and asymmetrically located relatively to the axis thereof.
8. An optical sensor as claimed in claim 1, in which the optical fibre comprises a tubular light-guiding structure having on the inner or outer surface thereof one or more regions of relatively high lightresponsive absorptive material or electric field-responsive material which defines the transducer means.
9. An optical sensor as claimed in claim 8, in which two diametrically opposed regions of field-responsive or relatively high light-absorptive material are provided on the inner or outer surface of the tubular light-guiding structure.
10. An optical sensor as claimed in any preceding claim, in which the light-absorptive material comprises doped glass, metal or other solid non-vitreous material introduced into the optical fibre during or after the normal drawing process.
11. An optical fibre as claimed in claim 10, in which the dopant composition of the doped glass is chosen or is itself doped with further material in order to increase the thermal expansion coefficient of the material.
12. An optical sensing system comprising an optical sensor as claimed in any of the preceding claims, in which intensity-modulated light propagating in the sensor to drive the transducer means into mechanical resonance is further intensity-modulated by the vibrations and in which the further intensity-modulation of the light is monitored by detection means for determining the external parameter influencing the optical fibre sensor.
13. An optical sensing system comprising an optical sensor as claimed in any of claims 1 to 11, in which the intensity-modulated light propagating in the sensor to drive the transducer means into mechanical resonance undergoes a phase change which is monitored by detector means for detecting an external parameter influencing the optical fibre sensor.
14. An optical sensing system comprising an optical sensor as claimed in any of claims 1 to 11, in which light propagating along the optical fibre to set the transducer means into vibration is reflected back along the fibre to signal level detector means.
15. An optical fibre sensor substantially as hereinbefore described and as illustrated in any of Figures 1 to 3 of the accompanying drawings.
16. An optical fibre sensor substantially as hereinbefore described and as illustrated in any of Figures 5, 7 and 8 of the accompanying drawings.
17. An optical fibre sensor substantially as hereinbefore described and as illustrated in Figure 6 of the accompanying drawings.
18. An optical fibre sensor substantially as hereinbefore described and as illustrated in any of Figures 4 and 9 to 13 of the accompanying drawings.
19. An optical fibre sensor as claimed in claim 1 or an optical fibre sensing system incorporating an optical fibre sensor as claimed in claim 1, substantially as hereinbefore described and/or with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8728664A GB2213588B (en) | 1987-12-08 | 1987-12-08 | Improvements relating to optical sensors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8728664A GB2213588B (en) | 1987-12-08 | 1987-12-08 | Improvements relating to optical sensors |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8728664D0 GB8728664D0 (en) | 1988-01-13 |
| GB2213588A true GB2213588A (en) | 1989-08-16 |
| GB2213588B GB2213588B (en) | 1991-07-31 |
Family
ID=10628162
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8728664A Expired - Fee Related GB2213588B (en) | 1987-12-08 | 1987-12-08 | Improvements relating to optical sensors |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2213588B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5265479A (en) * | 1989-10-17 | 1993-11-30 | Lucas Industries Public Limited Company | Micro resonator |
| US5426981A (en) * | 1991-03-19 | 1995-06-27 | Lucas Industries Public Limited Company | Vibrating sensor |
| EP0744595A1 (en) * | 1994-05-23 | 1996-11-27 | Thomas & Betts Corporation | Fiber optic sensors and control systems for automobile occupant protection apparatus |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4294513A (en) * | 1979-09-11 | 1981-10-13 | Hydroacoustics Inc. | Optical sensor system |
| US4297887A (en) * | 1980-02-19 | 1981-11-03 | The United States Of America As Represented By The Secretary Of The Navy | High-sensitivity, low-noise, remote optical fiber |
| GB2125179A (en) * | 1982-08-03 | 1984-02-29 | Standard Telephones Cables Ltd | Distributed sensors |
| GB2125572A (en) * | 1982-08-03 | 1984-03-07 | Standard Telephones Cables Ltd | Optical fibre sensors |
| GB2190187A (en) * | 1986-05-09 | 1987-11-11 | Stc Plc | Optical fibre sensors |
-
1987
- 1987-12-08 GB GB8728664A patent/GB2213588B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4294513A (en) * | 1979-09-11 | 1981-10-13 | Hydroacoustics Inc. | Optical sensor system |
| US4297887A (en) * | 1980-02-19 | 1981-11-03 | The United States Of America As Represented By The Secretary Of The Navy | High-sensitivity, low-noise, remote optical fiber |
| GB2125179A (en) * | 1982-08-03 | 1984-02-29 | Standard Telephones Cables Ltd | Distributed sensors |
| GB2125572A (en) * | 1982-08-03 | 1984-03-07 | Standard Telephones Cables Ltd | Optical fibre sensors |
| GB2190187A (en) * | 1986-05-09 | 1987-11-11 | Stc Plc | Optical fibre sensors |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5265479A (en) * | 1989-10-17 | 1993-11-30 | Lucas Industries Public Limited Company | Micro resonator |
| US5426981A (en) * | 1991-03-19 | 1995-06-27 | Lucas Industries Public Limited Company | Vibrating sensor |
| EP0744595A1 (en) * | 1994-05-23 | 1996-11-27 | Thomas & Betts Corporation | Fiber optic sensors and control systems for automobile occupant protection apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8728664D0 (en) | 1988-01-13 |
| GB2213588B (en) | 1991-07-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19931208 |