GB1588012A - Optical fibre sensing device - Google Patents
Optical fibre sensing device Download PDFInfo
- Publication number
- GB1588012A GB1588012A GB1545676A GB1545676A GB1588012A GB 1588012 A GB1588012 A GB 1588012A GB 1545676 A GB1545676 A GB 1545676A GB 1545676 A GB1545676 A GB 1545676A GB 1588012 A GB1588012 A GB 1588012A
- Authority
- GB
- United Kingdom
- Prior art keywords
- light
- plane
- fibre
- ribbon
- sensing device
- 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.)
- Expired
Links
- 239000013307 optical fiber Substances 0.000 title claims description 23
- 239000000835 fiber Substances 0.000 claims description 27
- 230000005540 biological transmission Effects 0.000 claims description 12
- 239000004020 conductor Substances 0.000 claims description 10
- 230000000694 effects Effects 0.000 claims description 9
- 239000002184 metal Substances 0.000 claims description 9
- 238000005253 cladding Methods 0.000 claims description 7
- 239000000463 material Substances 0.000 claims description 6
- 238000005452 bending Methods 0.000 claims description 5
- 230000008878 coupling Effects 0.000 claims description 5
- 238000010168 coupling process Methods 0.000 claims description 5
- 238000005859 coupling reaction Methods 0.000 claims description 5
- 230000002745 absorbent Effects 0.000 claims description 2
- 239000002250 absorbent Substances 0.000 claims description 2
- 230000003247 decreasing effect Effects 0.000 claims description 2
- 230000007425 progressive decline Effects 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 claims description 2
- 230000002459 sustained effect Effects 0.000 claims description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000005670 electromagnetic radiation Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
- G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect
-
- 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
- G01D5/344—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 using polarisation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Nonlinear Science (AREA)
- Optics & Photonics (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
Description
(54) OPTICAL FIBRE SENSING DEVICE
(71) We, THE PLESSEY COMPANY LIMI
TED, a British Company of Vicarage Lane, Ilford, Essex do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
This invention relates to sensing devices employing optical fibres.
According to the invention there is provided a sensing device for receiving an external stimulus including an optical fibre for transmitting light from a source at one end of the fibre, which light is polarised in two mutually orthogonal states; in which the optical fibre is so constructed or arranged to provide differential loss control means effective to impose a greater transmission loss on light transmitted in a first one of said states of polarisation than is imposed on light transmitted in the second one of said states; a detector associated with the other end of the optical fibre to detect the light output from the optical fibre; in which in operation the optical fibre is placed within the field 'of the external stimulus to be measured in such a manner that the first and second states of polarisation are coupled relative to each other by the external stimulus whereby the greater transmission loss applicable to light transmitted in the first state is also applicable at least in part to light transmitted in the second state thereby decreasing the overall light output from the fibre in dependence on the intensity of the stimulus, the detector thereby registering an output proportional to the stimulus without the use of any polarising filters.
If the extent of coupling is quantitatively related to the strength of the stimulus, the sensing device may be calibrated and used for measurement.
In accordance with custom, the term "light" is used in this specification to include not only visible light but related froms of electromagnetic radiation such as infra-red radiation.
The invention will now be described with reference to linear polarisation and with reference to the drawings accompanying the provisional specification in which:
Figure 1 is a cross section of a conventional optical fibre,
Figure 2 is a graph showing known power distribution characteristics applicable to light transmitted by an optical fibre.
Figure 3 shows a first differential loss control means according to the invention,
Figures 4, 5 are cross sections of second and third differential loss control means respectively,
Figure 6 shows a sensing device according to the invention which employs the differential loss control means of Figure 5.
As shown in Figure 1, a known optical fibre comprises a core 1 of elliptical (with circular as a special case) cross section enclosed within a cladding 2. The fibres shown are not drawn to scale and in practice the core diameter will be much smaller in relation to the diameter of the cladding 2. It is known to transmit, along the fibre, light which is polarised in two mutually perpendicular planes AA', BB'. It is known that different modes have different patterns of power distribution in relation to the core axis.
These range from a mode in which the power is concentrated at a relatively small radius r from the axis as shown at 3 in Figure 2, to a mode in which the power is less concentrated and is dispersed over a larger radius R as shown at 4.
It is therefore possible to transmit light over a fibre in two modes, each mode experiencing its own particular degree of loss. The apparatus to be described exploits this facility by controlling the differential loss and detecting its effects. Differential loss may be induced in a number of ways, as will now be discussed.
These effects may be enhanced by imparting anisotropic qualities to the fibre by giving the fibre an anisotropic cross-sectional shape, for example an elliptical shape.
A first form of differential loss control means according to the invention is obtained b) bending a known fibre in one plane, as shown in Figure 3 in respect of the plane AA'. One mode, not necessarily the same mode, is used in each plane of polarisation.
The transmission of light which is polarised in the plane BB' is largely unaffected by the bending. But the transmission of light which is polarised in the plane AA' is adversely affected by the bending, the effects of which are at a maximum at the outer arc of the bend. Now if the plane of polarisation BB' is rotated about the core axis so as to become inclined to the plane AA', the greater transmission loss applicable to light polarised in the plane AA be comes increasingly applicable to light polarised in the plane BB'. This is particularly true if the fibre is surrounded by a lossy jacket 5 as in
Figure 4. Consequently, as the rotation of the plane BB' progresses, there is a progressive decrease in the light transmitted in the plane
BB', and therefore also in the total quantity of light transmitted by the fibre.
In a second form of differential loss control means, bending of the fibre is not required.
Instead in Figure 4 a fibre of anisotropic cross section is provided with sleeve 5 of a material which has the property of absorbing energy of the kind transmitted by the fibre. One mode, not necessarily the same mode, is used in each plane of polarisation. In each mode some of the energy is capable of entering the absorbent material of the sleeve. For each plane of polarisation a mode is used in which the energy is dispersed over a radius greater than the external radius of the cladding 2, so that some energy enters the sleeve 5 and is absorbed. If the plane
BB' is rotated about the core axis, the energy polarised in this plane is increasingly coupled to the energy polarised in the plane AA' so reducing the quantity of light energy that is transmitted.
In a third differential loss control means, the core 11, and cladding 12 of a conventional fibre are flattened into the form of a ribbon, as shown in Figure 5. A number of modes may be used in each plane of polarisation. Differential loss control may be obtained in different ways.
Most conveniently, differential loss control is obtained by covering the flat surfaces of the ribbon with metal strips 7, 8 respectively. Light polarised in the pane BB' - that is in the plane of the ribbon - is less affected by the metal strips 7, 8 than light polarised in the plane AA'.
Light polarised in the plane AA' induces surface plasmons on the metal strips 7, 8, and thereby suffers greater loss. If now the plane BB' is rotated, the light polarised in this plane becomes increasingly affected by the metal strips 7, 8, and increasingly suffers loss.
A sensing device according to the invention will now be described. The device described employs the third type of differential loss control means. The stimulus which the device senses is an electric current. In this device, the ribbon of Figure 5 is wound into a helix 9 as shown in Figure 6. If the helix is regarded as being wound on an imaginary cylinder, the ribbon 9 would lie on the surface of the cylinder. Light passed from a source (not shown) at one end of the ribbon to a detector (not shown) at the other end of the ribbon. The helix 9 is threaded by an electrical conductor 10. If an electric current is passed through the conductor 10, a magnetic field is produced. The effect of this field is to provide a coupling between the polarisations in the planes AA', BB' of the ribbon 9. This is known as the Faraday effect.
This coupling may be regarded as causing the plane BB' to become inclined to the plane AA', with consequent light loss as already described.
The loss of light is quantitatively related to the strength of the current in the conductor 10.
The sensitivity of the device may be increased by increasing the number of turns in the helix 9.
On account of the quantitative relationship between the light loss and the strength of the current, the detector may be calibrated in terms of the current, or of a quantity represented by the current. Thus the sensing device may be used as a measuring instrument. Further, if the current in the conductor 10 is continuous, the output of the detector (not shown) is continuous; and if the current is also variable, the detector output is correspondinly variable.
Fibres with circular cores may be used in the sensing device, but this arrangement is not very convenient. With these means, a polariser is required as well as the helix 9, and even one polariser for each turn of the helix may be necessary. A more serious disadvantage is that, in certain circumstances, it may not be possible to distinguish between the effects of a low current in the conductor 10 and those of a high current.
In another form of sensing device, which is particularly suitable for use as a modulator, the stimulus is a magnetic field. In this device, the ribbon of Figure 5 is placed inside an electrical transmission line. A magnetic field sustained by the line affects the light transmitted by the ribbon in the manner already described. The magnetic field travels along the transmission line at the same speed as the light travels along the ribbon. Under these conditions, a relatively weak magnetic field is sufficient to cause modulation of light incident on the detector.
Other sensing devices may be provided which respond to other stimuli. For example, if the ribbon of Figure 5 is subjected to external pressure, stress birefringence causes inclination of the planes AA', BB'. Again, twisting of the ribbon also brings about inclination of the planes AA', BB'.
Although the sensing devices have been described, for simplicity, in terms of linear polarisation, the devices are also responsive to circular and other forms of polarisation.
WHAT WE CLAIM IS:
1. A sensing device for receiving an external stimulus including an optical fibre for transmitting light from a source at one end of the fibre, which light is polarised in two mutually orthogonal states, in which the optical fibre is so constructed or arranged to provide differential loss control means effective to impose a greater transmission loss on light transmitted in a first one of said states of polarisation than is imposed on light transmitted in the second one of said states; a detector associated with the other end of the optical fibre to detect the light output from the optical fibre; in which in operation the optical fibre is placed within the
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (7)
1. A sensing device for receiving an external stimulus including an optical fibre for transmitting light from a source at one end of the fibre, which light is polarised in two mutually orthogonal states, in which the optical fibre is so constructed or arranged to provide differential loss control means effective to impose a greater transmission loss on light transmitted in a first one of said states of polarisation than is imposed on light transmitted in the second one of said states; a detector associated with the other end of the optical fibre to detect the light output from the optical fibre; in which in operation the optical fibre is placed within the
field of the external stimulus to be measured in such a manner that the first and second states of polarisation are coupled relative to each other by the external stimulus whereby the greater transmission loss applicable to light transmitted in the first state is also applicable at least in part to light transmitted in the second state thereby decreasing the overall light output from the fibre in dependence on the intensity of the stimulus, the detector thereby registering an output proportional to the stimulus without the use of any polarising filters.
2. A sensing device as claimed in Claim 1 in which the optical fibre has a light transmissive core of elliptical cross section and in which the fibre is bent in first plane.
3. A sensing device as claimed in Claim 2 in which the optical fibre has a sleeve of material surrounding the outer cladding layer of the fibre which material has the property to absorb light energy of the kind transmitted by the fibre.
4. A sensing device as claimed in Claim 1 or
Claim 2 in which the optical fibre has a light transmissive core of circular cross section.
5. A sensing device as claimed in any one of
Claims 1 to 3 in which the cross section of the - fibre is flattened into the form of a ribbon and in which metal strips are provided on each of the major surfaces of the ribbon.
6. A sensing device as claimed in Claim 5 in which the ribbon shaped fibre is wound in a helix and in which the metallic strips are each continuous.
7. A sensing device substantially as described with reference to Figure 3 or Figure 4 of
Figure 5 or Figure 6 of the drawings accompanying the provisional specification.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1545676A GB1588012A (en) | 1977-07-13 | 1977-07-13 | Optical fibre sensing device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1545676A GB1588012A (en) | 1977-07-13 | 1977-07-13 | Optical fibre sensing device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1588012A true GB1588012A (en) | 1981-04-15 |
Family
ID=10059467
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1545676A Expired GB1588012A (en) | 1977-07-13 | 1977-07-13 | Optical fibre sensing device |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1588012A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2166257A (en) * | 1983-10-26 | 1986-04-30 | Plessey Co Plc | Optical attenuator |
| GB2168807A (en) * | 1984-12-21 | 1986-06-25 | Robin David Birch | Optical fibres and methods of manufacture thereof |
-
1977
- 1977-07-13 GB GB1545676A patent/GB1588012A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2166257A (en) * | 1983-10-26 | 1986-04-30 | Plessey Co Plc | Optical attenuator |
| GB2168807A (en) * | 1984-12-21 | 1986-06-25 | Robin David Birch | Optical fibres and methods of manufacture thereof |
| US4949038A (en) * | 1984-12-21 | 1990-08-14 | National Research Development Corporation | Optical fiber having a helical core for sensing a magnetic field |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19920713 |