GB2169398A - Optical sensors - Google Patents

Optical sensors Download PDF

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Publication number
GB2169398A
GB2169398A GB08500517A GB8500517A GB2169398A GB 2169398 A GB2169398 A GB 2169398A GB 08500517 A GB08500517 A GB 08500517A GB 8500517 A GB8500517 A GB 8500517A GB 2169398 A GB2169398 A GB 2169398A
Authority
GB
United Kingdom
Prior art keywords
fibre
optical
leaky
alarm
detectors
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.)
Granted
Application number
GB08500517A
Other versions
GB2169398B (en
Inventor
Kevin Christopher Byron
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
STC PLC
Original Assignee
STC PLC
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by STC PLC filed Critical STC PLC
Priority to GB08500517A priority Critical patent/GB2169398B/en
Priority to FR8600156A priority patent/FR2576423A1/en
Priority to JP147286A priority patent/JPS61210916A/en
Publication of GB2169398A publication Critical patent/GB2169398A/en
Application granted granted Critical
Publication of GB2169398B publication Critical patent/GB2169398B/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/181—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems
    • G08B13/183—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier
    • G08B13/186—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier using light guides, e.g. optical fibres
    • 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
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/255—Details, e.g. use of specially adapted sources, lighting or optical systems
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/08—Optical fibres; light guides

Abstract

A leaky optical fibre is used to radiate light into the environment and the radiated light is detected at one or more places along the fibre. Smoke or an intruder, for example, blocking the transmission path between the fibre and a photodetector will produce a loss of photocurrent which can be used to trigger an alarm. The same principles can also be employed in a spectrometer, since for example, different gases absorb at different wavelengths.

Description

SPECIFICATION Optical sensors This invention relates to optical sensors and in particular to optical sensors employing optical fibres.
According to one aspect of the present invention there is provided an optical sensor comprising a leaky optical fibre and one or more photodetectors disposed to detect light radiated from the fibre along its length in use of the sensor, the photodetector output being affected by the interposition of a thing to be sensed between the fibre and the respective photodetector.
According to another aspect of the present invention there is provided a method of sensing the presence of a thing comprising radiating light from a leaky optical fibre along its length and detecting the radiated light, the magnitude of the detected light being reduced by the presence of the thing between the fibre and means performing the detection.
Optical fibres are generally configured to prevent or minimise the radiation of power from their cores. Conventional optical sensors employing such optical fibres operate in various different ways and employ the following properties of the fibre, namely: transparency; radiation from its end; finite propagation velocity; sensitivity to external stimuli (eg pressure, temperature, magnetic field) with respect to phase changes, amplitude changes, polarisation changes; frangibility and flexibility.
An optical fibre which radiates power, rather than transmits it along its length can also be employed in an optical sensor. For this purpose a leaky optical fibre is used to radiate light into the environment and detectors spaced apart from the fibre at intervals along its length are employed to detect the radiated signal. In the case of such an optical sensor employed as a smoke alarm, any smoke blocking out the transmission path between the fibre and a detector will produce a loss of detector photocurrent which loss is employed to trigger an alarm. For this purpose the detectors are electricaliy connected in a suitable alarm circuit.
In the case of such an optical sensor employed as an intruder alarm, the intruder will similarly block the transmission path between the fibre and detectors and trigger an alarm.
For such alarms the fibre and detectors are disposed at the appropriate places relative to one another for the particular surroundings to ensure that the alarm will be triggered by the appropriate possible blocking agent and in the case of an intruder alarm to ensure that it is not possible to calculate a "safe" path through the array of detectors. The detectors may consist of photodiodes or photodiode arrays and their small size facilitates concealment. It should be noted that the alarms will not be susceptible to being triggered by spurious electrical signals and that any break in the fibre will activate rather than de-activate the alarm.
Since different gases absorb optical radiation at different wavelengths the basic principle of a leaky fibre smoke sensor can be extended to detect specific atmospheric pollutants by using selected wavelengths for the source whose optical power is launched into one end of the leaky optical fibre and appropriately responsive detectors. A further extension of this is the use as a spectrometer. A leaky optical fibre is disposed to extend through a chamber into which unknown gases, for example, can be introduced. Photodetectors are disposed to detect the radiated signal from the fibre and their output coupled to circuit means which provides an indication of loss of photocurrent when gases are introduced into the chamber and thus sensing thereof.In order to be able to detect a number of different gases with the same equipment detectors responsive to different wavelengths are required and the fibre must either be capable of transmitting and radiating the different wavelengths or comprise a number of fibres each radiating at a specific wavelength.
The leaky optical fibre may have various forms. It may be a single mode fibre operating at a V value below 1.5, in which case 50% of the power is in the cladding. Alternatively, it may be of a design having controlled leaky mode properties, for example a deeply depressed fibre. A further possibility is to make use of the Raman effect in fibres, in which case the leaky radiation is at the first Stokes shift away from the transmitted wavelength. In this case the fibre is designed to be above the cut-off wavelength for the transmitted signal into the fibre core but below the cut-off for the Raman shifted wavelength of the core material.Considering a step-index single mode fibre with a core diameter of 5.1Hm (An = 5 X 10 3 operating at 1.3,am, with a V value of 1.5 and with a pump and signal wavelength separation of 60nm, the change in transmitted power (excluding scattering, absorption etc) for the first Stokes shift will be 5%, which power will be radiated into free-space.
1. An optical sensor comprising a leaky optical fibre and one or more photodetectors disposed to detect light radiated from the fibre along its length in use of the sensor, the photodetector output being affected by the interposition of a thing to be sensed between the fibre and the respective photodetector.
2. An optical sensor as claimed in claim 1 and for detecting smoke.
3. An optical sensor as claimed in claim 1 and for detecting intruders.
4. An optical sensor as claimed in any one of the preceding claims and including alarm
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical sensors This invention relates to optical sensors and in particular to optical sensors employing optical fibres. According to one aspect of the present invention there is provided an optical sensor comprising a leaky optical fibre and one or more photodetectors disposed to detect light radiated from the fibre along its length in use of the sensor, the photodetector output being affected by the interposition of a thing to be sensed between the fibre and the respective photodetector. According to another aspect of the present invention there is provided a method of sensing the presence of a thing comprising radiating light from a leaky optical fibre along its length and detecting the radiated light, the magnitude of the detected light being reduced by the presence of the thing between the fibre and means performing the detection. Optical fibres are generally configured to prevent or minimise the radiation of power from their cores. Conventional optical sensors employing such optical fibres operate in various different ways and employ the following properties of the fibre, namely: transparency; radiation from its end; finite propagation velocity; sensitivity to external stimuli (eg pressure, temperature, magnetic field) with respect to phase changes, amplitude changes, polarisation changes; frangibility and flexibility. An optical fibre which radiates power, rather than transmits it along its length can also be employed in an optical sensor. For this purpose a leaky optical fibre is used to radiate light into the environment and detectors spaced apart from the fibre at intervals along its length are employed to detect the radiated signal. In the case of such an optical sensor employed as a smoke alarm, any smoke blocking out the transmission path between the fibre and a detector will produce a loss of detector photocurrent which loss is employed to trigger an alarm. For this purpose the detectors are electricaliy connected in a suitable alarm circuit. In the case of such an optical sensor employed as an intruder alarm, the intruder will similarly block the transmission path between the fibre and detectors and trigger an alarm. For such alarms the fibre and detectors are disposed at the appropriate places relative to one another for the particular surroundings to ensure that the alarm will be triggered by the appropriate possible blocking agent and in the case of an intruder alarm to ensure that it is not possible to calculate a "safe" path through the array of detectors. The detectors may consist of photodiodes or photodiode arrays and their small size facilitates concealment. It should be noted that the alarms will not be susceptible to being triggered by spurious electrical signals and that any break in the fibre will activate rather than de-activate the alarm. Since different gases absorb optical radiation at different wavelengths the basic principle of a leaky fibre smoke sensor can be extended to detect specific atmospheric pollutants by using selected wavelengths for the source whose optical power is launched into one end of the leaky optical fibre and appropriately responsive detectors. A further extension of this is the use as a spectrometer. A leaky optical fibre is disposed to extend through a chamber into which unknown gases, for example, can be introduced. Photodetectors are disposed to detect the radiated signal from the fibre and their output coupled to circuit means which provides an indication of loss of photocurrent when gases are introduced into the chamber and thus sensing thereof.In order to be able to detect a number of different gases with the same equipment detectors responsive to different wavelengths are required and the fibre must either be capable of transmitting and radiating the different wavelengths or comprise a number of fibres each radiating at a specific wavelength. The leaky optical fibre may have various forms. It may be a single mode fibre operating at a V value below 1.5, in which case 50% of the power is in the cladding. Alternatively, it may be of a design having controlled leaky mode properties, for example a deeply depressed fibre. A further possibility is to make use of the Raman effect in fibres, in which case the leaky radiation is at the first Stokes shift away from the transmitted wavelength. In this case the fibre is designed to be above the cut-off wavelength for the transmitted signal into the fibre core but below the cut-off for the Raman shifted wavelength of the core material.Considering a step-index single mode fibre with a core diameter of 5.1Hm (An = 5 X 10 3 operating at 1.3,am, with a V value of 1.5 and with a pump and signal wavelength separation of 60nm, the change in transmitted power (excluding scattering, absorption etc) for the first Stokes shift will be 5%, which power will be radiated into free-space. CLAIMS
1. An optical sensor comprising a leaky optical fibre and one or more photodetectors disposed to detect light radiated from the fibre along its length in use of the sensor, the photodetector output being affected by the interposition of a thing to be sensed between the fibre and the respective photodetector.
2. An optical sensor as claimed in claim 1 and for detecting smoke.
3. An optical sensor as claimed in claim 1 and for detecting intruders.
4. An optical sensor as claimed in any one of the preceding claims and including alarm means which is triggered by a fall in photodetector output current.
5. An optical sensor as claimed in claim 1 and configured such that light of different wavelengths is radiated whereby to allow detection of different gases which absorb optical radiation at different wavelengths.
6. An optical sensor including a leaky optical fibre and substantially as herein described.
7. A method of sensing the presence of a thing comprising radiating light from a leaky optical fibre along its length and detecting the radiated light, the magnitude of the detected light being reduced by the presence of the thing between the fibre and means performing the detection.
GB08500517A 1985-01-09 1985-01-09 Optical sensors Expired GB2169398B (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB08500517A GB2169398B (en) 1985-01-09 1985-01-09 Optical sensors
FR8600156A FR2576423A1 (en) 1985-01-09 1986-01-08 OPTICAL DETECTOR AND OPTICAL DETECTION METHOD
JP147286A JPS61210916A (en) 1985-01-09 1986-01-09 Photosensor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08500517A GB2169398B (en) 1985-01-09 1985-01-09 Optical sensors

Publications (2)

Publication Number Publication Date
GB2169398A true GB2169398A (en) 1986-07-09
GB2169398B GB2169398B (en) 1988-04-13

Family

ID=10572599

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08500517A Expired GB2169398B (en) 1985-01-09 1985-01-09 Optical sensors

Country Status (3)

Country Link
JP (1) JPS61210916A (en)
FR (1) FR2576423A1 (en)
GB (1) GB2169398B (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2666163A1 (en) * 1990-08-22 1992-02-28 Bertin & Cie Opto-electronic device for detecting smoke or gas in suspension in air
US10957176B2 (en) 2016-11-11 2021-03-23 Carrier Corporation High sensitivity fiber optic based detection
US11127270B2 (en) 2016-11-11 2021-09-21 Carrier Corporation High sensitivity fiber optic based detection
US11132883B2 (en) 2016-11-11 2021-09-28 Carrier Corporation High sensitivity fiber optic based detection
US11145177B2 (en) 2016-11-11 2021-10-12 Carrier Corporation High sensitivity fiber optic based detection
US11151853B2 (en) 2016-11-11 2021-10-19 Carrier Corporation High sensitivity fiber optic based detection

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1398977A (en) * 1971-10-07 1975-06-25 Emi Ltd Gas detector
DE2508366C3 (en) * 1975-02-26 1979-05-17 Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch Optical device with a light curtain
US4379289A (en) * 1979-03-08 1983-04-05 Gte Laboratories Incorporated Fiber optics security system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2666163A1 (en) * 1990-08-22 1992-02-28 Bertin & Cie Opto-electronic device for detecting smoke or gas in suspension in air
US10957176B2 (en) 2016-11-11 2021-03-23 Carrier Corporation High sensitivity fiber optic based detection
US11127270B2 (en) 2016-11-11 2021-09-21 Carrier Corporation High sensitivity fiber optic based detection
US11132883B2 (en) 2016-11-11 2021-09-28 Carrier Corporation High sensitivity fiber optic based detection
US11145177B2 (en) 2016-11-11 2021-10-12 Carrier Corporation High sensitivity fiber optic based detection
US11151853B2 (en) 2016-11-11 2021-10-19 Carrier Corporation High sensitivity fiber optic based detection

Also Published As

Publication number Publication date
JPS61210916A (en) 1986-09-19
GB2169398B (en) 1988-04-13
FR2576423A1 (en) 1986-07-25

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