Classifications

• • 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
  • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
  • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
  • H04B10/077—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using a supervisory or additional signal
  • H04B10/0773—Network aspects, e.g. central monitoring of transmission parameters
• • 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
  • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
  • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
  • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
  • H04B10/0795—Performance monitoring; Measurement of transmission parameters
  • H04B10/07957—Monitoring or measuring wavelength
• • 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
  • H04B10/27—Arrangements for networking
  • H04B10/272—Star-type networks or tree-type networks
• • 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
  • H04J14/0228—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths
  • H04J14/023—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON]
  • H04J14/0232—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for downstream transmission
  • H04J14/0234—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for downstream transmission using multiple wavelengths
• • 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
  • H04J14/0228—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths
  • H04J14/023—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON]
  • H04J14/0235—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for upstream transmission
  • H04J14/0236—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for upstream transmission using multiple wavelengths
• • 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
  • H04J14/0254—Optical medium access
  • H04J14/0256—Optical medium access at the optical channel layer
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0278—WDM optical network architectures
  • H04J14/0282—WDM tree architectures
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0278—WDM optical network architectures
  • H04J14/0283—WDM ring architectures
• • 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
  • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
  • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
  • H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
  • H04J14/0246—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU using one wavelength per ONU
• • 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
  • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
  • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
  • H04J14/0249—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU
  • H04J14/025—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU using one wavelength per ONU, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU

Definitions

• the present invention relates to a communication system comprising a tunable laser, and in particular to a communication unit, where one part is intended to be located at an end-user location (a domicile, an office, a block of flats) and where one part is common for a number of the said parts located at the end users.
• end-user locations such as domiciles and offices, etc.
• a communication laser be located at each end-user location that is connected, where it is required that the cable is connected at its second end to a communication laser, which is provided with information from a source of information. It must be possible to tune such lasers in order for it to be possible to select the channel, i.e. the frequency or wavelength, for the communication.
• ECL-laser Extra Cavity Laser
• This comprises an amplifier chip, connective optical components and one or several external optical filters.
• the mutual alignment of the components must be of very high precision in such lasers, and this means that the manufacturing costs and the material costs are both high.
• An ECL laser gives a very high spectral purity.
• a second type of laser is that known as a DFB-laser (Distributed Feedback) , where an array of DFB lasers is used.
• DFB-laser Distributed Feedback
• Each DFB laser can be tuned by means of the temperature of the laser.
• the light emitted from each one of the DFB lasers is directed into the same optical fibre by means of an MEMS mirror (Micro-Electromechanical Mirror) , or through the use of a passive N:l combiner, where N is the number of lasers in the array.
• MEMS mirror Micro-Electromechanical Mirror
• N passive N:l combiner
• N:l combiner leads to damping by at least a factor of 1/N, which leads to the requirement that the signal, the light, be amplified. Furthermore, the thermal tuning is slow.
• a further type of laser is a DBR laser (Distributed Bragg Reflector) .
• An SGDBR laser (Sampled Grating Distributed Bragg Reflector), and a digital super-mode (DS) DBR laser, and an MG-Y laser are all monolithic arrangements, i.e. the complete tunable laser consists of a single chip of InP with waveguides of InGaAsP. Such lasers are manufactured on a single wafer, and this means that the manufacture is cost- effective.
• An MG-Y laser is described in the Swedish patent number 529492. Since these lasers are tuned by means of current injection into one or several sections, the tuning is very rapid. These lasers are also the smallest tunable lasers .
• the present invention solves this problem by using an approach that differs from that which is prevalent in laser communication systems.
• the present invention thus relates to a communication system that comprises a communication unit with a first part and a number of a second part, where the second part is arranged to be located at an end-user location, such as a domicile, of- fice room or equivalent, and where the first part is common for a number of the said second parts, where the first part and each second part comprise a laser, where each second part is connected to the first part by means of a fibre optic cable and a frequency filter, and where the first part and the relevant second part are arranged to exchange information by means of laser light, and is characterised in that each one of the second parts comprises a tunable laser, in that the first part is arranged to analyse light received from a second part, and in that the first part is arranged to trans- mit information to the second part while the first part is receiving light from the second part, and in that the said information contains information for the second part that it should adjust, where required, its frequency or wavelength, and in that the second part is thereby arranged to change its frequency or wavelength.
• Figure 2 illustrates an embodiment of the invention
• Figure 3a illustrates data traffic from one end user to a base station in the example shown in Figure 2
• FIG. 3b illustrates data traffic from a base station to an end user in the example shown in Figure 2
• Figure 1 shows a communication system that comprises a communication unit with a first part 1 (Central Office) and a number of a second part 2 (End User) , where the second part 2 is arranged to be located at the location of an end user, such as a domicile, office or equivalent.
• the present invention can be used in all situations in which a central unit is connected to a number of end users. Only a single second part 2 is shown in Figure 1.
• the first part 1 is common for a number of the said second parts 2, where the first part 1 and the second part 2 both comprise a laser.
• Each second part 2 is connected to a first part 1 by means of a fibre optic cable 3 and a frequency filter 4 (Optical FiI- ter) , and where the first part and the relevant second part are arranged to exchange information by means of laser light. Also the first part in Figure Ia can transmit light to the second part 2 through the fibre optic cable 5.
• a frequency filter 4 Optical FiI- ter
• the frequency filter 4 it is only necessary for the frequency filter 4 to be located in the connection from the second part 2 to the first part 1. There may be a filter also in the connection from the first part 1 to the second part 2, but this is not an absolute requirement. If a filter is present in the connection from the first part 1 to the second part 2, it need not be the same filter as that in the connection from the second part 2 to the first part 1.
• the communication from the second part 2 to the first part 1 will take place in another frequency band than the communication from the first part 1 to the second part 2.
• Each one of the second parts 2 comprises, according to the invention, a tunable laser 6 (Tunable Transmitter) .
• the first part 1 is arranged to analyse light received from the second part 2 by means of a receiver 7 (Rx) , as shown in Figures 2 and 3a.
• the first part 1 is arranged to transmit information to the second part 2 by means of a transmitter 8 (Tx) in the form of a laser, while the first part 1 is receiving light from the second part 2.
• Tx transmitter 8
• the arrow 5 illustrates that information is transmitted from the first part 1 to the second part 2.
• the said information to the second part 2 contains, according to the invention, instructions to adjust the frequency or wavelength when this is necessary, and that the second part 2 is thereby arranged to change its frequency or wavelength.
• a transmitter (Tx) in the form of a laser is located in a base station (Central Office) , and this transmitter transmits a light signal downstream in a fibre 3.
• the signal is distributed into different fibres 9, 10, 11, at a point that lies close to a group of end users 2 (End User) , as shown in Figure 3b.
• Each one of the said fibres runs to a single end user.
• the said fibres 3 may be long, 10-20 km for example, while the final fibres 9, 10, 11 to the end users are only, for example, 100 m long.
• the lengths are determined, naturally, by geographical conditions.
• the transmitter in the base station comprises an array of lasers that transmit signals of different frequencies or wavelengths.
• the different signals are inserted into the fibre 3 with the aid of a wavelength multiplexer 12 (MUX) .
• MUX wavelength multiplexer 12
• the signals are divided up at the end of the fibre 3 into the individual wavelengths by means of a wavelength demultiplexer 13 (DEMUX), as shown in Figure 3b.
• DEMUX wavelength demultiplexer 13
• One advantage of using the WDM-PON technology is that it is relatively simple to upgrade existing PON systems, since it is necessary to exchange only the components at the end points (part 1 and parts 2) and the point of division at which the light is divided up into different wavelengths.
• Signals from the base station to the end users have been described above. It is, however, the case that signal traffic takes place also from the end users to the base station.
• the said DEMUX 13 will take on the properties of a MUX and the said MUX 12 will take on the properties of a DEMUX. It is thus of the highest importance that the light that is transmitted from any specific end user has the correct wavelength, in order for the light be inserted into the said fibre 3 by the MUX.
• transceiver 17 comprises a tunable laser 6.
• the present invention makes it possible to have a universal transceiver (a transmitter and receiver unit) .
• the frequency or wavelength of a laser drifts with time. It is therefore necessary that the control currents, voltages and/or temperature of the laser, and thus also its frequency or wavelength, change with time in order for it to be possible for the communication described above to take place.
• Various arrangements are previously known by which a communication laser can compensate for drift of frequency or wavelength such that the laser maintains its frequency or wavelength, but such arrangements are expensive .
• the present invention is based on the concept of allowing the laser of the end user to drift, but providing it with information that enables it to adjust (usually in an iterative manner) its frequency or wavelength, such that it becomes the frequency or wavelength on which it is to transmit in order to be able to communicate with the base station. The laser of the end user obtains this information from the laser of the base station.
• the laser of the second part is thus not provided with an arrangement comprising a frequency reference, nor with internal arrangements in order to maintain a pre-determined frequency or wavelength.
• the transceiver (a transmitter and receiver unit) 17 of the second part 2 comprises not only a tunable laser 6, but also a receiver 18 (Rx) and a control circuit 19 (Control Logic), as shown in Figure Ic.
• the frequencies that the laser 6 transmits are controlled by the control circuit 19.
• the base station 1 receives the transmitted laser light, provided it has passed the optical filter 4; 12, 13. It has been arranged that the laser 6 will change between different frequencies, and this means that at a certain condition light will be received in the receiver of the base station, and there analysed.
• the first part 1 is arranged to analyse directly or indirectly light that has been received from a second part 2 with respect to its frequency or wavelength.
• the first part 1, the base station is arranged to measure the frequency or wavelength indirectly by measuring the intensity of the light.
• Figure Ib shows a curve of the light power received as a function of the frequency or wavelength.
• the first part is arranged to transmit to the second part 2 the said information requesting that it change the frequency or wavelength.
• the control circuit 19 is arranged to decode this information and then to change the control currents, voltages and/or temperature of the laser 6 such that the frequency or wavelength is changed.
• the first part 1 is arranged to measure the frequency or wavelength directly.
• the first part 1 in the case in which the frequency or wavelength deviates from a pre-determined value, is arranged to transmit information to the second part 2 requesting that it change the frequency or wavelength, whereby the control circuit 19 of the second part 2 is arranged to change the frequency or wavelength, after which the first part 1 once again analyses the frequency or wavelength, and is arranged to transmit, if necessary, further information to the second part 2 requesting that it change the frequency or wavelength further.
• the second part is arranged to frequency modulate the light that is transmitted, and the first part is arranged to measure the derivative and to determine the sign of the derivative of the power received as a function of the frequency or wavelength of the light received. If the wavelength received from the second part lies on a flank of the filter characteristic during its transmission through a MUX/DEMUX, the frequency modulation will be converted into an amplitude modulation. Only if the wavelength lies at the top of the filter characteristic will the amplitude modulation be equal to zero.
• the first part is arranged to measure the amplitude, and to send information to the second part with a request for changes in the frequency or wavelength, based on the result of the measurement.
• a laser in a second part 2 is not capable of being directed to use another frequency or wavelength since it is not possible to increase the control currents, for example, any further.
• the laser of the first part is arranged to transmit information to the control circuit 19 of the second part containing a request to reset or restart the laser of the second part.
• the second part may be arranged to select another working configuration, after receiving information from the first part. This configuration may comprise, for example, another combination of control currents that gives the same frequency or wavelength.
• FIG. 4 A further possible implementation of the invention is shown in Figure 4 in which, m contrast to the embodiments described above, a fibre ring 20 with optical add/drop multiplexers 21, 22, 23 (OADM) is used to connect end users 24, 25, 26.
• An OADM extracts one or several frequencies from an input optical fibre and transmits other frequencies onwards in an output fibre.
• An OADM may also add new signals to an output fibre, where the signals have the same frequencies as those that have been extracted from the input fibre.
• a MUX 27 and a DEMUX 28 are located in the base station.
• the present invention solves the problems described in the introduction and it allows the use of a cheap tunable laser at the locations of end users, by allowing this laser to drift in frequency or wavelength since control is exerted by the base station when it receives light from a certain end user.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Computing Systems (AREA)
• Optical Communication System (AREA)
• Semiconductor Lasers (AREA)

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Cited By (2)

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Citations (10)

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• 2008
  • 2008-10-28 SE SE0850057A patent/SE534444C2/sv not_active IP Right Cessation
• 2009
  • 2009-10-13 US US13/126,087 patent/US8559817B2/en active Active
  • 2009-10-13 WO PCT/SE2009/051166 patent/WO2010050878A1/en not_active Ceased
  • 2009-10-13 EP EP09823898.3A patent/EP2347529A4/en not_active Withdrawn
  • 2009-10-13 JP JP2011534443A patent/JP2012507242A/ja active Pending
• 2014
  • 2014-01-20 JP JP2014007753A patent/JP2014079013A/ja active Pending

Patent Citations (10)

Non-Patent Citations (1)

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