GB2415847A - Bi-directional optical transmission control - Google Patents
Bi-directional optical transmission control Download PDFInfo
- Publication number
- GB2415847A GB2415847A GB0414838A GB0414838A GB2415847A GB 2415847 A GB2415847 A GB 2415847A GB 0414838 A GB0414838 A GB 0414838A GB 0414838 A GB0414838 A GB 0414838A GB 2415847 A GB2415847 A GB 2415847A
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- United Kingdom
- Prior art keywords
- receiver
- signal
- transmitter
- control means
- optical fibre
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- 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
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
Abstract
A multi-mode optical fibre communications network comprises control means that cause control signals to be transmitted simultaneously with the data signals. The effect of transmission on the control signals can be measured and the transmission of the data can be varied to reduce these effects. The dispersion of the control signals may be measured. Additionally, the magnitude of the zero level may be varied in accordance with the number of consecutive zeroes.
Description
COMMUNICATIONS NETWORK
The present invention relates to communications networks and in particular to communications networks comprising multi- mode fibre communication links.
Optical fibres are now used extensively in communications networks, with single-mode optical fibres being used commonly in long distance routes, for example between cities and when connecting telephone exchanges and multi-mode optical fibres being used commonly for LANs and shorter routes. The core of a single-mode optical fibre is designed so that only a single optical mode propagates along the fibre, whereas the core of a multi-mode optical fibre is substantially larger (typically 50pm or 62.5ym for a multi-mode optical fibre and around 7 10pm for a single-mode optical fibre) such that a number of optical modes will propagate within the fibre. As the different modes will propagate along different optical paths, each of the modes will travel along a different path length and thus will take a different time to propagate along a given route. The result of this is that the different optical modes will be launched into one end of a multi-mode optical fibre at the same time but will be received at the other end at different times, leading to the received pulse being dispersed. As the pulse dispersion increases the receiver will not be able to discriminate between '1' and '0' signals, which will cause transmission errors. The effect of dispersion increases with both the transmission data rate and the length of the communications link. Various techniques have been proposed to compensate, or partially compensate, for this dispersion but they generally do not address the situation where the degree of dispersion is varying.
According to a first aspect of the present invention there is provided an optical communications network comprising a first transmitter, a first receiver and a first multi mode optical fibre communications link, the first transmitter being communicatively connected to the first receiver via the first multi mode optical fibre communications link; a second transmitter, a second receiver and a second multi mode optical fibre communications link the second transmitter being communicatively connected to the second receiver via the second multi mode optical fibre communications link; the network being characterized in that the network further comprises first and second control means, the first control means being configured to i) generate a first control signal; ii) send the first control signal to the first transmitter for transmission to the first receiver; and iii) vary the transmission of a first data signal in response to a first feedback signal, the first feedback signal being generated by the second control means in response to the state of the first control signal at the first receiver. The second control means may send the first feedback signal to the first control means via the second multi mode optical fibre communications link.
The optical communications network may be further characterized in that the second control means is configured to iv) generate a second control signal; v) send the second control signal to the second transmitter for transmission to the second receiver; and vi) vary the transmission of a second data signal in response to a second feedback signal, the second feedback signal being generated by the first control means in response to the state of the second control - 3 signal at the second receiver. The first control means may send the second feedback signal to the second control means via the first multi mode optical fibre communications link.
The variation of the transmission of the first or second data signals may comprise a variation in the in the magnitude of the data signals. The first or second data signals may comprise a digital signal and the magnitude of the zero signal may be varied in accordance with the number of consecutive zeros.
The invention will now be described, by way of example only, with reference to the following Figures in which: Figure 1 shows a schematic depiction of a communications network according to the present invention; and Figure 2 shows a schematic depiction of a communications network 110 according to a second embodiment of the present invention.
Figure 1 shows a schematic depiction of a communications network 10 according to the present invention. The communications network 10 comprises a first transmitter 20 that is communication with a first receiver 40 via a first optical fibre communications link 30. Furthermore, second transmitter 22 is in communication with second receiver 42 via second optical fibre communications link 32. The first transmitter 20 and second receiver 42 are substantially co located at first location 50 and second transmitter 22 and first receiver 40 are substantially co-located at second - 4 location 52. Typically first and second locations comprise a telephone exchange or a similar building.
Data is provided to the first transmitter 20 at input 20a, with the transmitter modulated the optical signal launched into the first optical fibre communications link in accordance with the data received from input 20a. The data is transmitted over the first optical fibre communications link to the first receiver, which converts the optical signal to an electrical signal and then extracts the data. The data can then be sent from the first receiver 40 via output 40a.
Similarly, data is be sent to the second transmitter 22 at input 22a, which is used to modulate the optical single launched into the second optical fibre communications link 32. The second receiver 42 receives this optical signal, converts it into an electrical format and de-modulates the signal to recover the data, which can be sent from the second receiver 40 via output 42a.
Conventionally, when a communications network is installed, the transmission parameters used are adjusted to compensate for the dispersion that will occur when light propagates through the network. A disadvantage of this technique is that the amount of dispersion can vary with time and thus the performance of a network can degrade in a relatively short period of time.
According to the present invention, the first receiver additionally transmits a first control signal along with the modulated data signal. The first control signal will be received by the first receiver, converted into the electrical domain and then separated from the data signal. Analysis of - 5 the received first control signal indicates the extent of dispersion present in the first optical fibre communications link. A first feedback signal, which indicates the dispersion in the first optical fibre communications link, may then be sent from the second transmitter to the first transmitter via the second and first receivers. The first feedback signal can be used to alter the operation of the first transmitter so that the effect of the dispersion in the first optical fibre communications link can be partially or substantially compensated for.
In a similar fashion, the second transmitter may send a second control signal, which is received by the second receiver and is analysed to provide a second feedback signal.
The second feedback signal is returned to the second transmitter such that the operation of the second transmitter can be varied to reduce the effect of dispersion in the second communications link.
Figure 2 shows a schematic depiction of a communications network 110 according to a second embodiment of the present invention. The network 110 comprises first transmitter 120, second transmitter 220, first receiver 140, second receiver 240, first optical fibre communications link 130 and second optical fibre communications link 230. The first transmitter is connected to the first receiver by the first optical fibre communications link and similarly the second transmitter is connected to the second receiver via the second optical fibre communications link. Conventionally the first transmitter and the second receiver are substantially co-located at a first location and the second transmitter and the first receiver are substantially co- located at a second location. 6 -
The first transmitter 120 comprises transmission driver 121, first data input 123 and first optical source 122. A data stream to be transmitted to the first receiver is received at the first data input 123 by the first transmission driver and is used to determine the signals sent by the first transmission driver to the first optical source. The first transmission driver is in communication with the first control means 300a and in use receives control signals that are used to vary the signals sent by the first transmission driver to the first optical source.
The optical signals generated by first optical source are carried over the first optical fibre communications link and are received by the first receiver 140. The first receiver comprises first optical detector 141, first post-receiver amplifier 142, first data amplifier 143, first filter unit 144, first control signal amplifier 145 and second control signal amplifier 146. The first control signal amplifier and second control signal amplifier are in communication with the second control means 300b. The second transmitter 220 and second receiver 240 are connected by second optical fibre communications link 230 and are similar to the first transmitter and first receiver described above.
In use, the first control means 300a sends a control signal to the first transmitter driver, which comprises a low frequency tone (for example less than lOOkHz). The control signal is then transmitted simultaneously with the data received at the first data input over the first optical fibre communications link. The first optical detector converts both the received control and data signals from optical 7 - signals into electrical signals and these electrical signals are amplified by the first post-receiver amplifier 142. The first post- receiver amplifier presents two outputs: the signals from one of these outputs is amplified by first data amplifier and the data signals extracted for further processing (for example by appropriate selection of the gain band of the first data amplifier). The signals from the second output are filtered to recover the first control signal that is then amplified by first control signal amplifier 145 and sent to second control means 300b.
The second control means 300b analyses the received first control signal to determine the effect of dispersion on the first control signal as it was transmitted across in the first optical fibre communications link 130. The second control means then generates a first feedback signal, which is determined by the analysis of the received first control signal that is sent to the second transmitter driver to be transmitted over the second optical fibre communications link, along with a second data signal. The first feedback signal may comprise a low frequency tone or a low frequency data stream.
The second feedback is filtered out from the electrical signal that is created by the second optical detector 241 and amplified by the second post-receiver amplifier 242, by the fourth control signal amplifier 246 and is sent to the first control means 300a. The first control means 300a analyses the first feedback signal to determine the magnitude of dispersion in the first optical fibre communications link.
The signalling scheme used by the first transmitter driver can then be modified accordingly to compensate, or partially - 8 compensate, for the dispersion in the first optical fibre communications link. This can be done, for example, by varying the transmitter waveform so that the signal at the receiver has a more uniform output. This may be achieved by increasing the contrast between a '1' and a '0' signal, for example by increasing the magnitude of the '1' signal and/or decreasing the magnitude of the 'O' signal. The degree by which the magnitude of a 'O' or a '1' signal is altered may be dependent upon the length of a sequence of 'O' or '1' signals.
It will be understood that the dispersion in the second optical fibre communications link can be determined and compensated, or partially compensated, for in a similar manner. That is, the second control means causes a second control signal to be transmitted over the second optical fibre communications link; the first control means analyses the second control signal to determine the effect of dispersion within the second optical fibre communications link and sends a second feedback signal to the second control means. The second control means controls the second transmission driver accordingly in order to compensate for the effects of dispersion in the second optical fibre communications link.
Figure 2 shows that the control node is separate from the transmitter and receiver with which it is co-located. It will be readily understood that the control mode may alternately be integrated with the respective transmitter or the receiver. Furthermore, each transmitter and receiver can be integrated to form a transceiver and the control means may be integrated with the respective transceiver.
It will be readily apparent to the person skilled in the art that alternative methods of modifying the transmission drivers may be used, or that different techniques may be used to determine the degree of dispersion present in an optical fibre communications link (for example from taps used in an EDC IC) or to feed that value to the respective control means, without departing from the scope of the present invention.
Claims (6)
1. An optical communications network (110) comprising a first transmitter (120), a first receiver (140) and a first multi mode optical fibre communications link (130), the first transmitter being communicatively connected to the first receiver via the first multi mode optical fibre communications link; a second transmitter (220), a second receiver (240) and a second multi mode optical fibre communications link (230) the second transmitter being communicatively connected to the second receiver via the second multi mode optical fibre communications link; the network being characterized in that the network further comprises first and second control means (300a, 300b), the first control means being configured to i) generate a first control signal; ii) send the first control signal to the first transmitter for transmission to the first receiver; and iii) vary the transmission of a first data signal in response to a first feedback signal, the first feedback signal being generated by the second control means in response to the state of the first control signal at the first receiver.
2. An optical communications network according to claim 1, wherein the second control means (300b) sends the first feedback signal to the first control means (300a) via the second multi mode optical fibre communications link (230). - 11
3. An optical communications network according to claim 1 or claim 2, further characterized in that the second control means (300b) is configured to iv) generate a second control signal; v) send the second control signal to the second transmitter for transmission to the second receiver; and vi) vary the transmission of a second data signal in response to a second feedback signal, the second feedback signal being generated by the first control means in response to the state of the second control signal at the second receiver.
4. An optical communications network according to claim 3, wherein the first control means (300a) sends the second feedback signal to the second control means via the first multi mode optical fibre communications link (130).
5. An optical communications network according to any preceding claim, wherein the variation of the transmission of the first or second data signals comprises a variation in the in the magnitude of the data signals.
6. An optical communications network according to claim 5, wherein the first or second data signals comprise a digital signal and the magnitude of the zero signal is varied in accordance with the number of consecutive zeros.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0414838A GB2415847B (en) | 2004-07-02 | 2004-07-02 | Communications network |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0414838A GB2415847B (en) | 2004-07-02 | 2004-07-02 | Communications network |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0414838D0 GB0414838D0 (en) | 2004-08-04 |
| GB2415847A true GB2415847A (en) | 2006-01-04 |
| GB2415847B GB2415847B (en) | 2008-01-09 |
Family
ID=32843448
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0414838A Expired - Fee Related GB2415847B (en) | 2004-07-02 | 2004-07-02 | Communications network |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2415847B (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1573137A (en) * | 1976-08-06 | 1980-08-13 | Aerospatiale | Method and system for transmitting signals by fibre optics |
| EP0331255A2 (en) * | 1988-03-03 | 1989-09-06 | Philips Patentverwaltung GmbH | Optical transmission system |
| US4994675A (en) * | 1989-04-28 | 1991-02-19 | Rebo Research, Inc. | Method and apparatus for checking continuity of optic transmission |
| US6480308B1 (en) * | 1998-06-10 | 2002-11-12 | Sony Corporation | Optical communication apparatus |
| US20040037569A1 (en) * | 2002-08-22 | 2004-02-26 | Kamalov Valey F. | Method and device for evaluating and improving the quality of transmission of a telecommunications signal through an optical fiber |
-
2004
- 2004-07-02 GB GB0414838A patent/GB2415847B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1573137A (en) * | 1976-08-06 | 1980-08-13 | Aerospatiale | Method and system for transmitting signals by fibre optics |
| EP0331255A2 (en) * | 1988-03-03 | 1989-09-06 | Philips Patentverwaltung GmbH | Optical transmission system |
| US4994675A (en) * | 1989-04-28 | 1991-02-19 | Rebo Research, Inc. | Method and apparatus for checking continuity of optic transmission |
| US6480308B1 (en) * | 1998-06-10 | 2002-11-12 | Sony Corporation | Optical communication apparatus |
| US20040037569A1 (en) * | 2002-08-22 | 2004-02-26 | Kamalov Valey F. | Method and device for evaluating and improving the quality of transmission of a telecommunications signal through an optical fiber |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2415847B (en) | 2008-01-09 |
| GB0414838D0 (en) | 2004-08-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20090702 |