EP1224761A1 - Optical data signals - Google Patents

Optical data signals

Info

Publication number
EP1224761A1
EP1224761A1 EP00960879A EP00960879A EP1224761A1 EP 1224761 A1 EP1224761 A1 EP 1224761A1 EP 00960879 A EP00960879 A EP 00960879A EP 00960879 A EP00960879 A EP 00960879A EP 1224761 A1 EP1224761 A1 EP 1224761A1
Authority
EP
European Patent Office
Prior art keywords
optical
control information
data signal
optical data
modulation technique
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.)
Withdrawn
Application number
EP00960879A
Other languages
German (de)
French (fr)
Inventor
Kenneth Guild
Dimitra Simeonidou
Anna Tzanakaki
Michael O'mahony
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.)
BTG International Ltd
Original Assignee
BTG International Ltd
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 BTG International Ltd filed Critical BTG International Ltd
Publication of EP1224761A1 publication Critical patent/EP1224761A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • 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
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • 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
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5051—Laser transmitters using external modulation using a series, i.e. cascade, combination of modulators
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/5161—Combination of different modulation schemes
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/532—Polarisation modulation
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/54—Intensity modulation
    • H04B10/541—Digital intensity or amplitude modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0298—Wavelength-division multiplex systems with sub-carrier multiplexing [SCM]

Definitions

  • This invention relates to a method of encoding control information on an optical data signal, to a transmitter configured to encode such information, and to a method of modifying or removing control information carried by an optical data signal.
  • wavelength converters will be an enabling technology for dynamic routing of optical packets through the network and for resolving contention within the switching nodes.
  • the routing control is a critical function; the packets of data have a routing tag or header and the ability dynamically to update or modify the routing tag/header is essential in certain types of network architectures. This functionality must be performed with minimal impact on the optical payload and several techniques for achieving this have been previously proposed.
  • the present invention aims at providing a particularly effective technique permitting the modification of control tags or headers associated with packets transmitted through an optical network, which technique has a minimal effect on the data itself.
  • a method of encoding control information on an optical data signal to be transmitted through an optical network comprising operating an optical source to generate a substantially coherent continuous-wave light beam, amplitude-modulating the light beam with a data stream to produce an optical data signal, and also modulating the data signal with control information, using a substantially constant amplitude modulation technique.
  • an optical data signal transmitter adapted to encode control information on an optical data signal to be transmitted through an optical network, which transmitter comprises an optical source arranged to generate a substantially coherent continuous-wave light beam, an amplitude-modulator which modulates said light beam with a data stream to produce an optical data signal, and a substantially constant amplitude modulator arranged also to modulate the data signal with control information, using a non-amplitude modulation technique.
  • a third aspect of this invention provides a method of modifying control information carried by an optical data signal transmitted through an optical network, comprising the steps of encoding the control information on the optical signal in a non-amplitude varying format so as to be associated with a stream of data, transmitting the optical signal to a traffic processor, reading and decoding the control information and then deciding upon the routing of the stream of data depending upon the decoded information, and passing the optical data signal through a wavelength converter based on a semiconductor optical amplifier thereby simultaneously removing the control information.
  • IM intensity-modulated
  • XGM cross-gain modulation
  • SOA semi-conductor optical amplifier
  • An SOA is therefore opaque to modulation formats that convey information in a non amplitude-varying fashion.
  • a preferred form of the method of this invention employs a subcarrier signaling format and encodes this information on the polarisation of the continuous-wave light preceding the payload of an optical packet.
  • the header information is extracted using direct -detection and the original header is removed without any additional guard bands or timing control .
  • Figure 1 illustrates an example of an optical packet transmitter
  • Figure 2 illustrates a technique for control information decoding and removal
  • Figure 3a shows the header information at the input to the polarisation modulator and Figures 3b and 3c the output of decoder in a switching node;
  • Figure 4 shows the optical spectral output after the A G;
  • Figure 5 shows the AWG output after wavelength conversion.
  • a data packet is l. ⁇ s in duration and consists of a payload containing a pseudo-random bit sequence (PRBS) at 2.5Gbit/s, an 8-bit header and a conservative guard band of 20ns.
  • PRBS pseudo-random bit sequence
  • the header consists of a byte of 78Mbit/s nonreturn-to- zero (NRZ) data: start and stop bits for synchronisation and six data bits that denote the packet destination.
  • the baseband header amplitude modulates a 2.7GHz subcarrier in the microwave mixer.
  • a 5Gbit/s iNb0 3 phase modulator was used for modulating polarisation states.
  • the linearly polarised signal from the Mach-Zehnder interferometer was rotated to be 45° to the principal axis of the phase modulator, and the drive voltage adjusted such that orthogonal polarisation states were assigned for a peak and trough of the subcarrier cosine.
  • An erbium-doped fibre amplifier (EDFA) amplifies the resulting signal.
  • the polarisers are arranged to pass horizontally polarised light through one arm, polarisation states at +45° to the vertical through a second arm, and right hand circular through the third arm. In this way, the incoming polarisation-modulated subcarrier will always result in an amplitude-varying component at 2.7GHz at the output when a "one" is received for all evolutionary states of the signal .
  • the sum of the components is the recovered header.
  • the control electronics process the baseband header information to determine the wavelength to which the payload is to be converted. After passing through an optical delay equal to the electronic processing time
  • the signal is coupled into the wavelength converter using an optical circulator.
  • Cross-gain modulation in a SOA is used to translate the wavelength of the packet to 1552nm.
  • a counter-propagating arrangement is employed, and the input/output wavelengths are chosen to lie in the stop-and pass-bands of the arrayed-waveguide grating (AWG) . In this way, very high rejection of the residual input signal, due to the SOA residual facet reflectivity, is achieved.
  • alternate packets may be encoded with a "10101001" header.
  • a lookup table is updated at the start of the process to direct such packets to output port 1 of the AWG by activating the 1552nm laser at the appropriate time.
  • Figure 3a shows the header signal at the input to the polarisation modulator after up-conversion in the microwave mixer.
  • the output of the optical packet generator is fed directly into the optical switching node arrangement.
  • the polarisation controller at the input of the header receiver allows the state of polarisation of the signal to be adjusted in order to present a variety of polarisation states to the receiver.
  • Figure 4 shows the routed packets at output port 1 of the AWG after wavelength conversion.
  • the residual input signal at 1554.4nm is suppressed to more than 45dB less than the converted signal, and the time-domain plots are illustrated in Figure 5.
  • Owing to the inverting nature of the SOA the header is extinguished and no polarisation to amplitude conversion is visible (lower trace) .
  • Confirmation of suppression of the header can be obtained by feeding the output of the wavelength converter to a header decoder; tests have shown that no residual header could be observed.
  • the header can be transmitted at a higher bit-rate.
  • the header data aggregate can be increased by employing frequency division multiplexing of additional subcarrier signals.
  • the depolarising tone, driving the scrambler may be modulated with the inverse of the header information to impose the header information on to the optical packet.
  • the invention provides a technique for polarisation-encoding subcarrier multiplexed headers on to an optical packet .
  • the XGM functionality of an SOA is used effectively to remove the header without the addition of any timing control, and without the need for a guard band between the header and payload.
  • a simple direct-detection receiver can be used to decode the header information and all -optical wavelength conversion and routing of 2.5Gbit/s payloads is thereby possible .

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)

Abstract

A method of encoding control information on an optical data signal to be transmitted through an optical network, comprising operating an optical source to generate a substantially coherent continuous-wave light beam, amplitude-modulating the light beam with a data stream to produce an optical data signal, and also modulating the data signal with control information, using a substantially constant amplitude modulation technique.

Description

OPTICAL DATA SIGNALS
Field of the Invention
This invention relates to a method of encoding control information on an optical data signal, to a transmitter configured to encode such information, and to a method of modifying or removing control information carried by an optical data signal.
Background to the Invention
In an all-optical packet-switched network, the signal remains in the optical domain from source to destination. In these networks, wavelength converters will be an enabling technology for dynamic routing of optical packets through the network and for resolving contention within the switching nodes. The routing control is a critical function; the packets of data have a routing tag or header and the ability dynamically to update or modify the routing tag/header is essential in certain types of network architectures. This functionality must be performed with minimal impact on the optical payload and several techniques for achieving this have been previously proposed.
Summary of the Invention
The present invention aims at providing a particularly effective technique permitting the modification of control tags or headers associated with packets transmitted through an optical network, which technique has a minimal effect on the data itself.
According to one aspect of this invention, there is provided a method of encoding control information on an optical data signal to be transmitted through an optical network, comprising operating an optical source to generate a substantially coherent continuous-wave light beam, amplitude-modulating the light beam with a data stream to produce an optical data signal, and also modulating the data signal with control information, using a substantially constant amplitude modulation technique.
According to a second aspect of this invention, there is provided an optical data signal transmitter adapted to encode control information on an optical data signal to be transmitted through an optical network, which transmitter comprises an optical source arranged to generate a substantially coherent continuous-wave light beam, an amplitude-modulator which modulates said light beam with a data stream to produce an optical data signal, and a substantially constant amplitude modulator arranged also to modulate the data signal with control information, using a non-amplitude modulation technique.
A third aspect of this invention provides a method of modifying control information carried by an optical data signal transmitted through an optical network, comprising the steps of encoding the control information on the optical signal in a non-amplitude varying format so as to be associated with a stream of data, transmitting the optical signal to a traffic processor, reading and decoding the control information and then deciding upon the routing of the stream of data depending upon the decoded information, and passing the optical data signal through a wavelength converter based on a semiconductor optical amplifier thereby simultaneously removing the control information. It will be appreciated that the present invention relies on the fact that only intensity-modulated (IM) signals are wavelength- converted when employing cross-gain modulation (XGM) in a semi-conductor optical amplifier (SOA) . An SOA is therefore opaque to modulation formats that convey information in a non amplitude-varying fashion. A preferred form of the method of this invention employs a subcarrier signaling format and encodes this information on the polarisation of the continuous-wave light preceding the payload of an optical packet. The header information is extracted using direct -detection and the original header is removed without any additional guard bands or timing control .
Brief Description of the Drawings
By way of example only, further details of methods of and apparatus for performing this invention will now be described, referring to the accompanying drawings, in which: -
Figure 1 illustrates an example of an optical packet transmitter; Figure 2 illustrates a technique for control information decoding and removal;
Figure 3a shows the header information at the input to the polarisation modulator and Figures 3b and 3c the output of decoder in a switching node; Figure 4 shows the optical spectral output after the A G; and
Figure 5 shows the AWG output after wavelength conversion.
Detailed Description
Referring initially to Figure 1, a data packet is l.βμs in duration and consists of a payload containing a pseudo-random bit sequence (PRBS) at 2.5Gbit/s, an 8-bit header and a conservative guard band of 20ns. The latter allows for the laser turn-on/turn-off times associated with the wavelength converter within the node. The header consists of a byte of 78Mbit/s nonreturn-to- zero (NRZ) data: start and stop bits for synchronisation and six data bits that denote the packet destination. The baseband header amplitude modulates a 2.7GHz subcarrier in the microwave mixer. A 5Gbit/s iNb03 phase modulator was used for modulating polarisation states. The linearly polarised signal from the Mach-Zehnder interferometer (amplitude modulator) was rotated to be 45° to the principal axis of the phase modulator, and the drive voltage adjusted such that orthogonal polarisation states were assigned for a peak and trough of the subcarrier cosine. An erbium-doped fibre amplifier (EDFA) amplifies the resulting signal.
At the switching node (Figure 2) , the optical signal is filtered by the demultiplexer (λ3dB = 1.8nm) and the tap coupler directs 10% of the signal to three polarisers via an optical splitter. (This may be implemented using a Stokes Analyser) . The polarisers are arranged to pass horizontally polarised light through one arm, polarisation states at +45° to the vertical through a second arm, and right hand circular through the third arm. In this way, the incoming polarisation-modulated subcarrier will always result in an amplitude-varying component at 2.7GHz at the output when a "one" is received for all evolutionary states of the signal . After optical to electrical conversion (O/E) , each of the signals are band-pass filtered (fc = 2.7GHz, f3dB = 120MHz), rectified using a microwave mixer and filtered using a low-pass filter (f3dB = 50MHz) . The sum of the components is the recovered header.
The control electronics process the baseband header information to determine the wavelength to which the payload is to be converted. After passing through an optical delay equal to the electronic processing time
(50ns) , the signal is coupled into the wavelength converter using an optical circulator. Cross-gain modulation in a SOA is used to translate the wavelength of the packet to 1552nm. To obviate the need for an output filter, a counter-propagating arrangement is employed, and the input/output wavelengths are chosen to lie in the stop-and pass-bands of the arrayed-waveguide grating (AWG) . In this way, very high rejection of the residual input signal, due to the SOA residual facet reflectivity, is achieved. To demonstrate the principle of operation, alternate packets may be encoded with a "10101001" header. Within the switching node, a lookup table is updated at the start of the process to direct such packets to output port 1 of the AWG by activating the 1552nm laser at the appropriate time. Figure 3a shows the header signal at the input to the polarisation modulator after up-conversion in the microwave mixer. The output of the optical packet generator is fed directly into the optical switching node arrangement. The polarisation controller at the input of the header receiver allows the state of polarisation of the signal to be adjusted in order to present a variety of polarisation states to the receiver.
The decoded signal at the output of the electrical combiner in the switching node is shown in Figure 3b. To observe the effects of pattern dependence, a 223 -1 PRBS sequence was transmitted and the resulting data eye is shown in Figure 3c.
Figure 4 shows the routed packets at output port 1 of the AWG after wavelength conversion. The residual input signal at 1554.4nm is suppressed to more than 45dB less than the converted signal, and the time-domain plots are illustrated in Figure 5. Owing to the inverting nature of the SOA, the header is extinguished and no polarisation to amplitude conversion is visible (lower trace) .
Confirmation of suppression of the header can be obtained by feeding the output of the wavelength converter to a header decoder; tests have shown that no residual header could be observed. By increasing the bandwidth of the band-pass filter, the header can be transmitted at a higher bit-rate. Alternatively, the header data aggregate can be increased by employing frequency division multiplexing of additional subcarrier signals. For optical packet-switched networks where polarisation scrambling is required for the high bit-rate payloads, and the described technique of this invention may easily be implemented. In this scenario the depolarising tone, driving the scrambler, may be modulated with the inverse of the header information to impose the header information on to the optical packet. From the above, it can be seen that the invention provides a technique for polarisation-encoding subcarrier multiplexed headers on to an optical packet . The XGM functionality of an SOA is used effectively to remove the header without the addition of any timing control, and without the need for a guard band between the header and payload. A simple direct-detection receiver can be used to decode the header information and all -optical wavelength conversion and routing of 2.5Gbit/s payloads is thereby possible .

Claims

1. A method of encoding control information on an optical data signal to be transmitted through an optical network, comprising operating an optical source to generate a substantially coherent continuous-wave light beam, amplitude-modulating the light beam with a data stream to produce an optical data signal, and also modulating the data signal with control information, using a substantially constant amplitude modulation technique.
2. A method as claimed in claim 1, wherein the control information is added to the optical data signal by means of a polarisation modulation technique.
3. A method as claimed in claim 1, wherein the control information is added to the optical data signal by means of a phase-shift-keying modulation technique.
4. A method as claimed in claim 1, wherein the control information is added to the optical data signal by means of a frequency-shift -keying modulation technique.
5. A method as claimed in claim 4, wherein the substantially constant amplitude modulation technique is applied to the optical beam before the modulation thereof with the data stream.
6. A method as claimed in claim 5, wherein the substantially constant amplitude modulation technique is applied directly to the optical source.
7. A method as claimed in any of claims 1 to 4 , wherein following the modulation of the light beam with the data stream, the optical data signal is passed a constant amplitude modulator to which is supplied the control information to be applied to the optical data signal.
8. A method as claimed in any of the preceding claims, wherein the data stream is applied to the light by means of a Mach-Zehnder interferometer to which is supplied the data stream, so as to produce an amplitude-modulated optical data signal.
9. A method of encoding control information on an optical data signal to be transmitted through an optical network as claimed in claim 1 and substantially as hereinbefore described, with reference to the accompanying drawings.
10. An optical data signal transmitter adapted to encode control information on an optical data signal to be transmitted through an optical network, which transmitter comprises an optical source arranged to generate a substantially coherent continuous-wave light beam, an amplitude-modulator which modulates said light beam with a data stream to produce an optical data signal, and a substantially constant amplitude modulator arranged also to modulate the data signal with control information, using a non-amplitude modulation technique.
11. An optical data signal transmitter as claimed in claim 10, wherein the optical source comprises a laser source.
12. A method of modifying control information carried by an optical data signal transmitted through an optical network, comprising the steps of encoding the control information on the optical signal in a non-amplitude varying format so as to be associated with a stream of data, transmitting the optical signal to a traffic processor, reading and decoding the control information and then deciding upon the routing of the stream of data depending upon the decoded information, and passing the optical data signal through a wavelength converter based on a semiconductor optical amplifier thereby simultaneously removing the control information.
13. A method as claimed in claim 12, wherein further control information is encoded on the optical signal following wavelength conversion thereof, so as to be associated with the wavelength-converted data signal.
14. A method as claimed in claim 13, wherein the further control information is encoded on the optical signal by a substantially constant amplitude modulation technique.
15. A method as claimed in claim 14, wherein the further control information is added to the wavelength-converted optical data signal by means of a polarisation modulation technique .
16. A method as claimed in claim 12, wherein the further control information is added to the wavelength- converted optical data signal by means of a phase-shift-keying modulation technique.
17. A method as claimed in claim 12, wherein the further control information is added to the wavelength-converted optical data signal by means of a frequency-shift-keying modulation technique.
18. A method as claimed in any of claims 12 to 17, wherein the optical data signal comprises time-division multiplexed data packets each of which has associated therewith individual control information.
19. A method as claimed in any of claims 12 to 18, wherein the optical data signal are carried by wavelength division multiplexed optical channels each of which has associated therewith individual control information.
20. A method as claimed in claim 18, wherein the control information comprises a data header or tag for the data stream contained in each packet .
21. A method of modifying control information carried by an optical data signal transmitted through an optical wavelength-multiplexed network as claimed in claim 12 and substantially as hereinbefore described, with reference to the accompanying drawings .
EP00960879A 1999-09-25 2000-09-22 Optical data signals Withdrawn EP1224761A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB9922678.9A GB9922678D0 (en) 1999-09-25 1999-09-25 Optical data signals
GB9922678 1999-09-25
PCT/GB2000/003646 WO2001024431A1 (en) 1999-09-25 2000-09-22 Optical data signals

Publications (1)

Publication Number Publication Date
EP1224761A1 true EP1224761A1 (en) 2002-07-24

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP00960879A Withdrawn EP1224761A1 (en) 1999-09-25 2000-09-22 Optical data signals

Country Status (6)

Country Link
EP (1) EP1224761A1 (en)
JP (1) JP2003510960A (en)
AU (1) AU7303900A (en)
CA (1) CA2386660A1 (en)
GB (1) GB9922678D0 (en)
WO (1) WO2001024431A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6626589B1 (en) * 1999-12-29 2003-09-30 Nortel Networks Limited Optical packet switching
DE102004036493A1 (en) * 2004-07-28 2006-03-23 Siemens Ag Method for transmitting data signals and additional signals in an optical network
JP4915605B2 (en) * 2005-03-09 2012-04-11 独立行政法人情報通信研究機構 Optical device
JP2006319709A (en) 2005-05-13 2006-11-24 Fujitsu Ltd Sub-signal modulation device, sub-signal demodulation device, and sub-signal modulation-demodulation system
JP4996587B2 (en) * 2008-12-02 2012-08-08 日本電信電話株式会社 Optical transceiver and optical transmission system using the same

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0410722A (en) * 1990-04-27 1992-01-14 Hitachi Ltd Coherent communication method, crossconnecting device and exchange
GB2257861A (en) * 1991-07-18 1993-01-20 Northern Telecom Ltd Polarisation state insensitive optical discriminator

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0124431A1 *

Also Published As

Publication number Publication date
AU7303900A (en) 2001-04-30
GB9922678D0 (en) 1999-11-24
CA2386660A1 (en) 2001-04-05
JP2003510960A (en) 2003-03-18
WO2001024431A1 (en) 2001-04-05

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