CA1058293A - Wired tv broadcasting system using an optical fibre, transducer and detector - Google Patents
Wired tv broadcasting system using an optical fibre, transducer and detectorInfo
- Publication number
- CA1058293A CA1058293A CA214,880A CA214880A CA1058293A CA 1058293 A CA1058293 A CA 1058293A CA 214880 A CA214880 A CA 214880A CA 1058293 A CA1058293 A CA 1058293A
- Authority
- CA
- Canada
- Prior art keywords
- central station
- optical fibre
- subscribers
- signals
- fibre
- 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
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17345—Control of the passage of the selected programme
- H04N7/17354—Control of the passage of the selected programme in an intermediate station common to a plurality of user terminals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2589—Bidirectional transmission
- H04B10/25891—Transmission components
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/22—Adaptations for optical transmission
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Multimedia (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Computer Networks & Wireless Communication (AREA)
- Optical Communication System (AREA)
- Optical Couplings Of Light Guides (AREA)
- Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
Abstract
A B S T R A C T
A wired broadcasting system is provided in which a signal path between a central station and at least some of a plurality of subscribers includes an optical fibre extending between an electro-optical transducer and a photo-sensitive detector. The optical fibre may extend over the whole length of the transmission path between the central station and each of the plurality of subscribers, or the optical fibre may extend between the central station and a distribution point from which signals may be conveyed to a group of subscribers over conductive paths, or an optical fibre may be arranged to extend between each of the plurality of subscribers and a programme selector located at a programme exchange.
A wired broadcasting system is provided in which a signal path between a central station and at least some of a plurality of subscribers includes an optical fibre extending between an electro-optical transducer and a photo-sensitive detector. The optical fibre may extend over the whole length of the transmission path between the central station and each of the plurality of subscribers, or the optical fibre may extend between the central station and a distribution point from which signals may be conveyed to a group of subscribers over conductive paths, or an optical fibre may be arranged to extend between each of the plurality of subscribers and a programme selector located at a programme exchange.
Description
' 1~5~293 This invention relates to wired broadcasting systems and seeks to provide an improved form thereof.
Wired broadcasting systems comprise two general types.
In the first type a plurality of television signals are distri-buted between a central station and each of a plurality of sub-scribers over a single signal path, usually in the form of a coaxial cable, the plurality of signals being frequency distinc-tive. Commonly the range of frequencies employed extends through-out the VHF spectrum, for example, from about 40-300 ~Hz. In the second type, a plurality of television signals are distributed between a central station and each of a plurality of subscribers over separate signal paths usually in the form of twisted pairs of conductors contained within a common cable. The desired sig-nal is selected for reception by establishing a connection between the subscribers equipment and that pair of conductors carrying the signal required. Commonly the signals all have the same nominal carrier frequency somewhere in the range 2-20 MEIz.
Both types of known sys-tem referred to above suffer from various disadvantages. With the first type the transmission losses are relatively high due to the frequencies involved and intermodulation in the repeater amplifiers is a problem due to the large number of signals which have to be amplified simultan-eously. With the second type crosstalk between the separate signal paths within the common cable is a limitation and in systems where a large number of programmes are distributed the immense number of physical connections between the various con-ductors introduce maintenance problems.
~115~ 3 It is an object of the pxesent invention to provide a wired broadcasting system in which the disadvantages of the presently known systems are minimised.
Accordingly the invention provides a broadcasting system conveying signals by a signal path between a central station and a plurality of subscribers, comprising in combination, a common optical fibre in said signal path carrying signals to said plura-lity of subscribers from said central station, said fibre extend-ing between an electro-optical transducer at said central station producing a light beam and photosensitive detector means at a reception position near the subscribers station, transmission means at the central station modulating the light beam for trans-mission through said optical fibre, said transmission means including modulation means producing a light beam incorporating a high frequency carrier modulated with video broadcast signals, conventional television receivers at the subscriber stations responsive to receive said high frequency carrier modulated with video broadcast signals, detection means at said reception position responsive to said photo-sensitive detector to convert said light beam into demodulated high frequency carrier radio wave signals modulated with video broadcast signals, and means coupling said demodulated signals from said reception position to said subscriber stations in a form suitable for direct applic-ation to said conventional television receivers without further si~nal processing.
If desired, the optical fibre may be arranged to extend over the whole length of the transmission path between said central station and each of the plurality of subscribers. In such an arrangement, a plurality of optical fibres may be provided extending over the whole length of the transmission path between the central station and each of the plurality of subscribers, each subscriber being able to select a desired programme signal on any ~ - 3 -z~
one o~ the optical fibres by deriving the si~nals from a photo-sensitive detector associated with the said one optical fibre.
Alternatively, the optical fibre may extend between the central station and a distribution point from which signals may be conveyed to a~ relatively small group of subscribers over convent-ional conductive paths.
In a alternative arrangemen-t an optical fibre may be arranged to extend between each of the plurality of subscribers and a programme exchange at which input signals for each subscribers optical fibre may be selected from one of a~plurality of available programme sources. Control of each subscribers programme selection means at the programme exchange may be 3a - 3a -`` ~05~Z93 effected either over a conductive signalling path associated with his optical fibre or over an auxiliary optical fibre. The signals transmitted over the optical fibres may comprise a light beam modulated in respect of video frequency signals, one or more high frequency modulated carrier waves of differing carrier fre-quency or a combination of video frequency signals and one or more high frequency modulated carrier waves~ Each optical fibre may carry two or more light beams of different frequency (color) each modulated as described above.
Further features and advantages of the present invention will become apparent from the following description of some embod-iments thereof given by way of example only with reference to the accompanying drawings in which:
Figure 1 is a block schematic diagram of one form of wired broadcasting system in accordance with the present inven-tion;
Figure 2 is a block schematic diagram of a second form of wired broadcasting system in accordance with the present inven-tion;
Figure 3 is a block schematic diagram of a third form of wire broadcasting system in accordance with the present inven-tion, and Figure 4 is a block schematic diagram of a fourth form of wired broadcasting system in accordance with the present inven-tion.
In the wired broadcasting system shown in Figure 1 a central station 1 is connected to each of a plurality of sub-scribers 2, 3, by means of an optical fibre 4 extending between an electro-optical transducer 5 and a photo-sensitive detector 6,7. The electro-optical transducer 5 may comprise a light emitting diode or an injection laser the light output of which is controlled in 5~
response to the output signals of a modulation amplifier 8 to which the video and/or high frequency carrier wave signals are applied on the output line 9. In a case of the electro-optical transducer 5 being a light emitting diode the diode may be formed as a Burras diode and have as its active constituent zinc or aluminium doped gallium arsenide. In some applications the mod-ulation characteristic of the electro-optical transducer may be unacceptably non-linear. In this event the modulation signal applied thereto may be such as to cause it to operate in a pulsed mode. The photo-sensitive detectors 6,7 may comprise PN photo-diodes associated with low noise pre-amplifier devices.
The signals applied to the input line 9 may comprise video frequency signals, one or more high frequency modulated carrier waves of different carrier frequency or a combination of video frequency signals and one or more high frequency modulated carrier waves. In the event that said signals are high frequency modulated carrier waves the output signals provided by the photo-sensitive detectors 6,7 may be of a form suitable for direct application to the television receivers 10,11 if these are of a type designed for use in high frequency wired broadcasting systems.
There may be a modest advantage in utilising video frequency sig-nals and in this event the output signals from the photo-sensitive detectors may be applied directly to the post detector stages of the receivers lO,ll.
In the system shown in Figure 2 a central station 12 is 1(~5~3~93 provided with an electro-optical transducer 13 modulated by the output signals of a modulation amplifier 14 which receives its input signals over the line 15. The resulting modulated light signals are passed over an optical fibre 16 to distribution sta-tions one of which is ~hown at 17. Each distribution station is provided with a photo-sensitive detector 18, output signals from which are passed to a launching amplifier 19 from which a conduc-tive network 20 extends to the receivers 21,22. In this system it is convenient to arrange that the modulation signals applied to the line 15 comprise high frequency modulated carrier waves.
In this event, the launching amplifier 19 and receivers 21,22 may be of the kind presently employed in high frequency wired broad-casting systems.
Turning now to Figure 3, the system shown therein is arranged to provid~ two television programmes each distributed over separate optical fibre lines 23,24. The signals applied to each of these lines are provided by electro optical transducers 25,26 having associated therewith corresponding modulation ampli-fiers 27,28 arranged to receive input signals over the lines 29, 30 and arranged within a central station. The separate optical fibres extend to each subscriber 31,32. Each subscriber is pro-vided with programme selecting means 33,34 to which each of the optical fibres are connected and by means of which signals may be derived from a photo-sensitive detector associated with that optical fibre which carries the desired programme signal. The desired signal from the programm~selection device 33,34 is then applied to the associated television receiver 35,36.
~5~3Z~33 The arrangement of Figure 4 is an alternative sys-tem to that shown in Figure 3. In this arrangement an optical fibre 37, 38, 39, 40 is arranged to extend between a programme exchange 41 and each of a plurality of subscriber installations 42, 43, 44, 45. The signals applled to each optical fibre are derived from a corresponding programme selection device 46, 47, 48, 49 each of which comprises means whereby an electro optical transducer may be made responsive to one of the programmes available at the pro-gramme exchange 41 and generate a light beam for transmission to the subscriber. Each programme selection device is arranged to be capable of selecting programmes from any one of the programme ampli~iers 50, 51, 52, 53 which receive their input signals over corresponding lines 54, 55, 56, 57. Each subscriber installation comprises a photo-sensitive detector 58, 59, 60, 61 from which signals may be applied to the associated television receiver 62, 63, 64, 65. Each subscriber installation is provided with a pro-gramme selector control means 66, 67, 68, 69 which are connected to the corresponding programme selection device 46, 47, 48, 49 over a control signal path 70, 71,'72, 73 associated with that subscribers optical fibre. The control signal path may comprise one or more conductors or an auxiliary optical fibre.
The programme capacity of any of the systems described above may be increased by arranging that each optical ibre carries two or more light beams of a different frequency (colour).
Each light beam may be modulated in respect of one or more than one television or other signal. The light beams may be coupled into and out o the optical fibre by means of systems of di-chroic mirrors. If ~imu]taneous reception of the separate li~ht beams is not requ:ired the photo-sensitive detector ma~ be rendered responsive to the appropriate li~ht beam by means of a ~uitable colour filter.
i
Wired broadcasting systems comprise two general types.
In the first type a plurality of television signals are distri-buted between a central station and each of a plurality of sub-scribers over a single signal path, usually in the form of a coaxial cable, the plurality of signals being frequency distinc-tive. Commonly the range of frequencies employed extends through-out the VHF spectrum, for example, from about 40-300 ~Hz. In the second type, a plurality of television signals are distributed between a central station and each of a plurality of subscribers over separate signal paths usually in the form of twisted pairs of conductors contained within a common cable. The desired sig-nal is selected for reception by establishing a connection between the subscribers equipment and that pair of conductors carrying the signal required. Commonly the signals all have the same nominal carrier frequency somewhere in the range 2-20 MEIz.
Both types of known sys-tem referred to above suffer from various disadvantages. With the first type the transmission losses are relatively high due to the frequencies involved and intermodulation in the repeater amplifiers is a problem due to the large number of signals which have to be amplified simultan-eously. With the second type crosstalk between the separate signal paths within the common cable is a limitation and in systems where a large number of programmes are distributed the immense number of physical connections between the various con-ductors introduce maintenance problems.
~115~ 3 It is an object of the pxesent invention to provide a wired broadcasting system in which the disadvantages of the presently known systems are minimised.
Accordingly the invention provides a broadcasting system conveying signals by a signal path between a central station and a plurality of subscribers, comprising in combination, a common optical fibre in said signal path carrying signals to said plura-lity of subscribers from said central station, said fibre extend-ing between an electro-optical transducer at said central station producing a light beam and photosensitive detector means at a reception position near the subscribers station, transmission means at the central station modulating the light beam for trans-mission through said optical fibre, said transmission means including modulation means producing a light beam incorporating a high frequency carrier modulated with video broadcast signals, conventional television receivers at the subscriber stations responsive to receive said high frequency carrier modulated with video broadcast signals, detection means at said reception position responsive to said photo-sensitive detector to convert said light beam into demodulated high frequency carrier radio wave signals modulated with video broadcast signals, and means coupling said demodulated signals from said reception position to said subscriber stations in a form suitable for direct applic-ation to said conventional television receivers without further si~nal processing.
If desired, the optical fibre may be arranged to extend over the whole length of the transmission path between said central station and each of the plurality of subscribers. In such an arrangement, a plurality of optical fibres may be provided extending over the whole length of the transmission path between the central station and each of the plurality of subscribers, each subscriber being able to select a desired programme signal on any ~ - 3 -z~
one o~ the optical fibres by deriving the si~nals from a photo-sensitive detector associated with the said one optical fibre.
Alternatively, the optical fibre may extend between the central station and a distribution point from which signals may be conveyed to a~ relatively small group of subscribers over convent-ional conductive paths.
In a alternative arrangemen-t an optical fibre may be arranged to extend between each of the plurality of subscribers and a programme exchange at which input signals for each subscribers optical fibre may be selected from one of a~plurality of available programme sources. Control of each subscribers programme selection means at the programme exchange may be 3a - 3a -`` ~05~Z93 effected either over a conductive signalling path associated with his optical fibre or over an auxiliary optical fibre. The signals transmitted over the optical fibres may comprise a light beam modulated in respect of video frequency signals, one or more high frequency modulated carrier waves of differing carrier fre-quency or a combination of video frequency signals and one or more high frequency modulated carrier waves~ Each optical fibre may carry two or more light beams of different frequency (color) each modulated as described above.
Further features and advantages of the present invention will become apparent from the following description of some embod-iments thereof given by way of example only with reference to the accompanying drawings in which:
Figure 1 is a block schematic diagram of one form of wired broadcasting system in accordance with the present inven-tion;
Figure 2 is a block schematic diagram of a second form of wired broadcasting system in accordance with the present inven-tion;
Figure 3 is a block schematic diagram of a third form of wire broadcasting system in accordance with the present inven-tion, and Figure 4 is a block schematic diagram of a fourth form of wired broadcasting system in accordance with the present inven-tion.
In the wired broadcasting system shown in Figure 1 a central station 1 is connected to each of a plurality of sub-scribers 2, 3, by means of an optical fibre 4 extending between an electro-optical transducer 5 and a photo-sensitive detector 6,7. The electro-optical transducer 5 may comprise a light emitting diode or an injection laser the light output of which is controlled in 5~
response to the output signals of a modulation amplifier 8 to which the video and/or high frequency carrier wave signals are applied on the output line 9. In a case of the electro-optical transducer 5 being a light emitting diode the diode may be formed as a Burras diode and have as its active constituent zinc or aluminium doped gallium arsenide. In some applications the mod-ulation characteristic of the electro-optical transducer may be unacceptably non-linear. In this event the modulation signal applied thereto may be such as to cause it to operate in a pulsed mode. The photo-sensitive detectors 6,7 may comprise PN photo-diodes associated with low noise pre-amplifier devices.
The signals applied to the input line 9 may comprise video frequency signals, one or more high frequency modulated carrier waves of different carrier frequency or a combination of video frequency signals and one or more high frequency modulated carrier waves. In the event that said signals are high frequency modulated carrier waves the output signals provided by the photo-sensitive detectors 6,7 may be of a form suitable for direct application to the television receivers 10,11 if these are of a type designed for use in high frequency wired broadcasting systems.
There may be a modest advantage in utilising video frequency sig-nals and in this event the output signals from the photo-sensitive detectors may be applied directly to the post detector stages of the receivers lO,ll.
In the system shown in Figure 2 a central station 12 is 1(~5~3~93 provided with an electro-optical transducer 13 modulated by the output signals of a modulation amplifier 14 which receives its input signals over the line 15. The resulting modulated light signals are passed over an optical fibre 16 to distribution sta-tions one of which is ~hown at 17. Each distribution station is provided with a photo-sensitive detector 18, output signals from which are passed to a launching amplifier 19 from which a conduc-tive network 20 extends to the receivers 21,22. In this system it is convenient to arrange that the modulation signals applied to the line 15 comprise high frequency modulated carrier waves.
In this event, the launching amplifier 19 and receivers 21,22 may be of the kind presently employed in high frequency wired broad-casting systems.
Turning now to Figure 3, the system shown therein is arranged to provid~ two television programmes each distributed over separate optical fibre lines 23,24. The signals applied to each of these lines are provided by electro optical transducers 25,26 having associated therewith corresponding modulation ampli-fiers 27,28 arranged to receive input signals over the lines 29, 30 and arranged within a central station. The separate optical fibres extend to each subscriber 31,32. Each subscriber is pro-vided with programme selecting means 33,34 to which each of the optical fibres are connected and by means of which signals may be derived from a photo-sensitive detector associated with that optical fibre which carries the desired programme signal. The desired signal from the programm~selection device 33,34 is then applied to the associated television receiver 35,36.
~5~3Z~33 The arrangement of Figure 4 is an alternative sys-tem to that shown in Figure 3. In this arrangement an optical fibre 37, 38, 39, 40 is arranged to extend between a programme exchange 41 and each of a plurality of subscriber installations 42, 43, 44, 45. The signals applled to each optical fibre are derived from a corresponding programme selection device 46, 47, 48, 49 each of which comprises means whereby an electro optical transducer may be made responsive to one of the programmes available at the pro-gramme exchange 41 and generate a light beam for transmission to the subscriber. Each programme selection device is arranged to be capable of selecting programmes from any one of the programme ampli~iers 50, 51, 52, 53 which receive their input signals over corresponding lines 54, 55, 56, 57. Each subscriber installation comprises a photo-sensitive detector 58, 59, 60, 61 from which signals may be applied to the associated television receiver 62, 63, 64, 65. Each subscriber installation is provided with a pro-gramme selector control means 66, 67, 68, 69 which are connected to the corresponding programme selection device 46, 47, 48, 49 over a control signal path 70, 71,'72, 73 associated with that subscribers optical fibre. The control signal path may comprise one or more conductors or an auxiliary optical fibre.
The programme capacity of any of the systems described above may be increased by arranging that each optical ibre carries two or more light beams of a different frequency (colour).
Each light beam may be modulated in respect of one or more than one television or other signal. The light beams may be coupled into and out o the optical fibre by means of systems of di-chroic mirrors. If ~imu]taneous reception of the separate li~ht beams is not requ:ired the photo-sensitive detector ma~ be rendered responsive to the appropriate li~ht beam by means of a ~uitable colour filter.
i
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A broadcasting system conveying signals by a signal path between a central station and a plurality of subscribers, comprising in combination, a common optical fibre in said signal path carrying signals to said plurality of subscribers from said central station, said fibre extending between an electro-optical transducer at said central station producing a light beam and photo-sensitive detector means at a reception position near the subscribers station, transmission means at the central station modulating the light beam for transmission through said optical fibre, said transmission means including modulation means pro-ducing a light beam modulated by a high frequency carrier which itself is modulated with video broadcast signals, conventional television receivers at the subscriber stations responsive to receive said high frequency carrier modulated with video broad-cast signals, said photo-sensitive detector means being operative to convert said light beam into demodulated high frequency carrier radio wave signals modulated with video broadcast signals, and means coupling said demodulated signals from said reception position to said subscriber stations in a form suitable for direct application to said conventional television receivers without further signal processing.
2. A system according to claim 1, wherein the optical fibre extends over the whole length of the transmission path between the central station and each of the plurality of subscribers.
3. A system according to claim 2, wherein said system includes a plurality of said optical fibres, means modulating a light beam carried respectively by each fibre with a different video programme signal, each fibre extends over the whole length of the transmission path between the central station and said detector means, said detector means comprising photo sensing means being positioned at a station location for each of the plurality of subscribers.
4. A system according to claim 1, wherein the central station has means conveying by optical fibre a plurality of programmes, including a programme exchange at said central station providing a programme selector for deriving one of said plurality of programmes, an additional optical fibre is arranged to extend between each of the plurality of subscribers and said programme selector and each subscriber has selection means operable over said additional fibre to select a single one of said plurality programmes.
5. A system as defined in claim 1 including means at said central station conveying over said single optical fibre a plurality of programmes modulated on different carrier frequencies.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB55933/73A GB1486421A (en) | 1973-12-03 | 1973-12-03 | Broadcast relay systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1058293A true CA1058293A (en) | 1979-07-10 |
Family
ID=10475262
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA214,880A Expired CA1058293A (en) | 1973-12-03 | 1974-11-28 | Wired tv broadcasting system using an optical fibre, transducer and detector |
Country Status (7)
| Country | Link |
|---|---|
| AU (1) | AU7590574A (en) |
| CA (1) | CA1058293A (en) |
| ES (1) | ES432542A1 (en) |
| GB (1) | GB1486421A (en) |
| IT (1) | IT1023486B (en) |
| MY (1) | MY7800253A (en) |
| ZA (1) | ZA747630B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1586543A (en) * | 1978-01-23 | 1981-03-18 | Communications Patents Ltd | Wired broadcasting systems |
| DE2934358A1 (en) * | 1979-08-24 | 1981-03-26 | Siemens AG, 1000 Berlin und 8000 München | BROADBAND TELECOMMUNICATION SYSTEM |
| DE3224406A1 (en) * | 1981-07-01 | 1983-01-20 | Canon K.K., Tokyo | IMAGE TRANSFER SYSTEM |
| NL8204722A (en) * | 1982-12-07 | 1984-07-02 | Philips Nv | DISTRIBUTION SYSTEM FOR LOCAL FIBERNET. |
| GB2212021B (en) * | 1987-11-06 | 1991-07-03 | Stc Plc | Radio frequency generator |
-
1973
- 1973-12-03 GB GB55933/73A patent/GB1486421A/en not_active Expired
-
1974
- 1974-11-28 CA CA214,880A patent/CA1058293A/en not_active Expired
- 1974-11-29 ZA ZA00747630A patent/ZA747630B/en unknown
- 1974-11-29 AU AU75905/74A patent/AU7590574A/en not_active Expired
- 1974-12-03 ES ES432542A patent/ES432542A1/en not_active Expired
- 1974-12-03 IT IT54342/74A patent/IT1023486B/en active
-
1978
- 1978-12-31 MY MY1978253A patent/MY7800253A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ES432542A1 (en) | 1977-01-01 |
| ZA747630B (en) | 1975-12-31 |
| GB1486421A (en) | 1977-09-21 |
| IT1023486B (en) | 1978-05-10 |
| AU7590574A (en) | 1976-06-03 |
| MY7800253A (en) | 1978-12-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 19960710 |