GB2184910A

GB2184910A - Optical multiplex system

Info

Publication number: GB2184910A
Application number: GB08628567A
Authority: GB
Inventors: Roger Alan Edwards; Peter Thomas Gardiner
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1985-12-18
Filing date: 1986-11-28
Publication date: 1987-07-01
Also published as: JPH0779330B2; FR2591764B1; IT1199692B; JPS62155631A; GB8628567D0; GB2184910B; IT8622558A0; DE3640920A1; GB8531150D0; FR2591764A1; US4761777A

Description

GB2184910A 1 SPECIFICATION movable member with different radiation char

acteristics in different regions of the member Optical multiplex systems and methods such that movement of said member alters the characteristics of radiation output by the This invention relates to optical multiplex sys- 70 transducer device. The movable member may tems and methods. have one region with a neutral characteristic Optical transducers are becoming more com- and another region which attenuates radiation mon, such as for detecting various functions in a said respective narrow band of wave in aircraft. Because of the large number of length, or may have a radiation characteristic transducers that may be necessary in a sys- 75 that varies progressively over the member.

tem, it is desirable to multiplex them in order The movable member is preferably optically to reduce the number of cables and connectransparent and has different radiation tions in the system. transmission characteristics in different regions Commonly, multiplexing is achieved in one over its surface.

of two different ways. in time-division multi- 80 The receiver means preferably includes de plex systems, each transducer provides an tector means responsive to each of said nar output at a different time and a de-multiplexer row bands of wavelength and filter means in is used to provide outputs in respect of each termediate said detector means and said opti transducer by interrogating each transducer in cal radiation guide means, said filter means turn when that transducer is providing its out85 being adjustable selectively to pass to said put. Time-division multiplex systems are, how- detector means only radiation within any indi ever, difficult to use in optical systems be- vidual one of said narrow bands of wave cause of the difficulty of triggering the trans- lengths.

ducers to provide an output only at specified The filter means may be an electro-optical times. 90 device having a narrow transmission band In optical frequency-or wavelength-division which can be changed to different wave multiplex systems, the transducers are respon- lengths by electrical control, or the said filter sive only to radiation within a specific band of means may have different transmission charac wavelengths and each transducer is respon- teristics in different regions of its surface, the sive to different bands. Such systems include 95 receiver means including means for displacing several radiation sources, that each supply the the filter means to select the narrow band of radiation to respective ones of the trans- wavelengths passed to the detector means.

ducers, and several receivers responsive to ra- The optical radiation guide means peferably diation in the respective narrow bands so that includes a fibre-optic cable. The receiver the output of each transducer can be continu- 100 means may be arranged to provide outputs on ously monitored. Whilst wavelength-division separate lines in respect of each said trans multiplex systems can function satisfactorily, ducer device. The said source may include a they can be complex because of the need to light-emitting diode.

provide individual radiation sources associated According to an-other aspect of the present with each transducer. Furthermore, failure of 105 invention there is provided a method of multi one source may go undetected since it is in- plexing an optical system including the steps distinguishable from a low output of its asso- of: emitting radiation within a broad band of ciated transducer. wavelengths; supplying said radiation to each It is an object of the present invention to of a plurality of transducer devices via a single provide an optical multiplex system and 110 optical radiation guide, said transducer devices method by which these disadvantages can be being arranged to respond to radiation within alleviated. respective narrow bands of wavelength that According to one aspect of the present in- differ from one another within said broad vention there is provided an optical multiplex band; supplying radiation from said transducer system including a source of optical radiation 115 devices to a single optical radiation guide; and adapted to emit radiation within a broad band detecting radiation from said optical radiation of wavelengths, a plurality of transducer de- guide output from said transducers in each of vices arranged to receive radiation from said said narrow bands of wavelengths.

source, the transducer devices being respon- An optical multiplex system and its method sive to radiation within respective narrow 120 of operation, in accordance with the present bands of wavelength that differ from one invention, will now be described, by way of another within said broad band, optical radia- example, with reference to the accompanying tion receiver means arranged to respond to drawings, in which:

radiation within each of said narrow bands of Figure 1 shows the system schematically; wavelength and produce respective outputs in 125 Figures 1A to 1D show radiation spectra at accordance therewith, and optical radiation different points in the system; guide means arranged to transmit radiation Figure 1E shows a transmission character from the transducer devices to the receiver istic of a filter in a receiver unit of the sys means. tem; The transducer devices preferably include a 130 Figure 2 shows a transducer of the system 2 GB2184910A 2 schematically in perspective; shaft 14.

Figure 2A shows the transmission character- The wavelength spectra of radiation istic of a neutral region of a filter plate in the transmitted along the cable 2 after each trans transducer; and ducer 11 to 13 is modified in the manner Figures 213 to 2D show the transmission 70 shown in Figures 113 to 1D respectively, as characteristics of the filtering region of each suming that the shaft 14 of each transducer is transducer. pushed in, so that the radiation passes With reference first to Figure 1, the system through the filtering region 17 of each respec includes an optical radiation source 1 which tive filter plate 15. In this example, the radiasupplies radiation via a fibre-optic cable 2 to a 75 tion supplied to the sensor unit 3 has the receiver unit 3. Three transducers 11, 12 and spectrum shown in Figure 1D in which the 13 are connected in series along the cable 2 wavelengths over the bands AA, AA, and AA, and modify the radiation transmitted to the have been substantially attenuated.

receiver unit in accordance with the functions The receiver unit 3 includes a detector 30, sensed by the transducers. 80 such as a photodiode, which is responsive to The source 1 emits radiation over a rela- at least the wavelengths covering the narrow tively broad band of wavelengths, as shown bands AA, AA, and AA3. The receiver unit 3 in the graph of Figure 1 A, which may be in also includes a variable filter 31 located inter the infra red, visible or ultra violet parts of the mediate the detector 30 and the end of the spectrum. The source 1 is preferably provided 85 fibre-optic cable 2 so that all radiation emitted by a wavelength stable device such as a light- by the end of the cable passes through the emitting diode. It should be noted that only filter before reaching the detector.

one source of radiation is needed. The filter 31 is an electro-optical devie with The fibre-optic cable 2 is of conventional a narrow transmission band which can be dis form and provides a single optical radiation 90 placed to different wavelengths by electrical guide between the source 1 and the receiver control from a unit 32, as shown in the unit 3 via the three transducers 11 to 13. transmission characteristic of Figure 1 E. Alter Other forms of optical radiation guides can be natively, the filter 31 could have different used instead of a fibre-optic cable. transmission characteristics in different regions The transducers 11 to 13 may be of many 95 of its surface, the filter itself being displaced different forms. In the present example, the so that radiation is passed through regions transducers 11 to 13 are displacement trans- with different transmission characteristics. The ducers arranged to respond to the position of control unit 32 also supplies signals to an out a valve member and are illustrated in Figure 2. put unit 33 which receives electrical output Each transducer 11 to 13 has an input shaft 100 signals from the detector 30 and provides 14 that is coupled at one end to the valve output signals on three output lines 34 to 36 member (not shown) and that is displaceable in respect of the response of each transducer along its length in accordance with displace- 11 to 13 respectively.

ment of the valve member. At the other end In operation, it will be seen that the level of of the shaft 14 is mounted a filter plate or 105 radiation supplied to the receiver unit 3 within similar member 15 having two distinct regions the bands A.,, A;., and A;., will be dependent 16 to 17. One region 16 of the plate 15 is on the position of the shaft 14 of each trans neutrally transparent to radiation within the ducer 11 to 13. The control unit 32 varies the band-width emitted by the source 1, as characteristics of the filter 31 so that its band shown in the transmission characteristic in 110 pass is displaced periodically and successively Figure 2A. The other region 17 of the filter between wavelengths covering the bands A;., plate 15 in each transducer 11 to 13 differs A;., and A;., The detector 30 thereby receives one from the other, being highly transparent radiation successively from each of these to radiation except that within different narrow three bands and provides outputs to the out- bands of wavelength A;.,, A;2 and A;3 respec- 115 put unit 33 accordingly. The signal supplied to tively, where the filter of each transducer has the output unit 33 from the control unit 32 a low transmission. The transmission charac- indicates which wavelength band is being teristics of the filtering regions 17 of the three passed by the filter 31 and hence identifies transducers 11 to 13 are shown in Figures the transducer from which the signals are be 2B, 2C and 2D respectively. These three nar- 120 ing received. The output unit 33, after any row bands of wavelength fall within the broad appropriate amplification or scaling, supplies a band of wavelengths emitted by the source 1. signal to the appropriate output line 34, 35 or The fibre-optic cable 2 extends through 36 according to the position of the associated each transducer 11 to 13, the cable being transducer shaft. The signals on lines 34 to interrupted an opposite sides of the filter plate 125 36 may be simple ON/OFF signals where it is so that all radiation transmitted on the only desired to know whether the valve asso cable 2 downstream of the transducer 11 to ciated with each transducer 11 to 13 is on or 13 has been passed through either the neutral off. In other applications the transducer may region 16 or the filtering region 17 of the respond to change in a variable value in which filter plate 15, according to the position of the130 case analogue or digital signal representations 3 GB2184910A 3 of this value are provided on the output lines and another region which attenuates radiation 34 to 36. In this example, the filtering region in a said respective narrow band of wave of the filter plate in each transducer may vary length.

progressively over its surface so that a vari- 4. An optical multiplex system according to

Claims

able transmission is produced in accordance 70 Claim 2, wherein the said

movable member with the position of the filter plate, that is, the has a radiation characteristic that varies pro degree of attenuation within the narrow band gressively over the member.

of wavelengths varies over the surface of the 5. An optical multiplex system according to filter plate. any one of Claims 2 to 4, wherein the said The transducers may be responsive to many 75 movable member is optically transparent and different variables such as, for example, temhas different radiation transmission character perature, pressure, attitude and so on. istics in different regions over its surface.

The transducers need not have a movable 6. An optical multiplex system according to member but could have some other device any one of the preceding claims, wherein the that varies the characteristic of radiation 80 receiver means includes detector means re passed through the transducer in accordance sponsive to each of said narrow bands of with the variable being sensed by the trans- wavelength and filter means intermediate said ducer. For example, the transducer could in- detector means and said optical radiation clude a substance which changes chemically guide means, said filter means being adjust with temperature change such as to vary its 85 able selectively to pass to said detector radiation transmission characteristics. Where a means only radiation within any individual one movable member is used this could be reflec- of said narrow bands of wavelengths.

tive rather than transmissive. 7. An optical multiplex system according to It will be seen that, because the outputs of claim 6, wherein the said filter means is an the transducers are monitored in turn one 90 electro-optical device having a narrow after the other, this provides a discontinous transmission band which can be changed to output. However, the sampling rate can be different wavelengths by electrical control.

high and this is satisfactory for all cases ex- 8. An optical multiplex system according to cept where very rapidly changing variables Claim 6, wherein the said filter means has need to be monitored. The arrangement of the 95 different transmission characteristics in differ present invention has the advantage of only ent regions of its surface, and wherein the requiring a single source and a single detector receiver means includes means for displacing thereby avoiding complexity. Furthermore, fail- the filter means to select the narrow band of ure of the source is rapidly apparent by a wavelengths passed to the detector means.

total loss of signals to the sensor. This en- 100 9. An optical multiplex system according to ables remedial action to be taken such as by any one of the preceding claims, wherein the automatically bringing a back-up system into optical radiation guide means includes a fibre operation. optic cable.

10. An optical multiplex system according CLAIMS 105 to any one of the preceding claims, wherein 1. An optical multiplex system including a the receiver means is arranged to provide out- source of optical radiation adapted to emit ra- puts on separate lines in respect of each said diation within a broad band of wavelengths, a transducer device.

plurality of transducer devices arranged to re- 11. An optical multiplex system according ceive radiation from said source, the trans- 110 to any one of the preceding claims, wherein ducer devices being responsive to radiation the said source includes a light-emitting diode.

within respective narrow bands of wavelength 12. An optical multiplex system substantially that differ from one another within said broad as hereinbefore described with reference to band, optical radiation receiver means ar- the accompanying drawings.

ranged to respond to radiation within each of 115 13. A method of multiplexing an optical said narrow bands of wavelength and produce system including the steps of: emitting radia respective outputs in accordance therewith, tion within a broad band of wavelengths; sup and optical radiation guide means arranged to plying said radiation to each of a plurality of transmit radiation from the transducer devices transducer devices via a single optical radia- to the receiver means. 120 tion guide, said transducer devices being ar 2. An optical multiplex system according to ranged to respond to radiation within respec Claim 1, wherein the transducer devices in- tive narrow bands of wavelength that differ clude a movable member with different radia- from one another within said broad band; sup tion characteristics in different regions of the plying radiation from said transducer devices member such that movement of said member 125 to a single optical radiation guide; and detect alters the characteristics of radiation output by ing radiation from said optical radiation guide the transducer device. output from said transducers in each of said 3. An optical multiplex system according to narrow bands of wavelengths.

Claim 2, wherein the said movable member 14. A method substantially as hereinbefore has one region with a neutral characteristic 130 described with reference to the accompanying 4 GB2184910A 4 drawings.

15. Any novel feature or combination of features as hereinbefore described.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.