WO2012110081A1 - Processing data in an optical network - Google Patents

Processing data in an optical network Download PDF

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Publication number
WO2012110081A1
WO2012110081A1 PCT/EP2011/052212 EP2011052212W WO2012110081A1 WO 2012110081 A1 WO2012110081 A1 WO 2012110081A1 EP 2011052212 W EP2011052212 W EP 2011052212W WO 2012110081 A1 WO2012110081 A1 WO 2012110081A1
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WO
WIPO (PCT)
Prior art keywords
optical
decentralized
component
data
centralized
Prior art date
Application number
PCT/EP2011/052212
Other languages
French (fr)
Inventor
Erich Gottwald
Original Assignee
Nokia Siemens Networks Oy
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 Nokia Siemens Networks Oy filed Critical Nokia Siemens Networks Oy
Priority to CN201180067618.4A priority Critical patent/CN103348614B/en
Priority to PCT/EP2011/052212 priority patent/WO2012110081A1/en
Priority to EP11703679.8A priority patent/EP2676391B1/en
Priority to US13/985,767 priority patent/US9178643B2/en
Publication of WO2012110081A1 publication Critical patent/WO2012110081A1/en

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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
    • H04B10/27—Arrangements for networking
    • H04B10/272—Star-type networks or tree-type networks
    • 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
    • H04B10/40—Transceivers
    • 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
    • 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
    • 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
    • H04J14/0238—Wavelength allocation for communications one-to-many, e.g. multicasting 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
    • H04J14/0241—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
    • 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
    • H04J14/0257—Wavelength assignment algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/06—Polarisation multiplex systems

Definitions

  • the invention relates to a method for processing data in an optical network and to components of such optical network.
  • a passive optical network is a promising approach regarding fiber-to-the-home (FTTH) , fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) scenarios, in particu ⁇ lar as it overcomes the economic limitations of traditional point-to-point solutions.
  • Con ⁇ ventional PONs distribute downstream traffic from the opti ⁇ cal line terminal (OLT) to optical network units (ONUs) in a broadcast manner while the ONUs send upstream data pack ⁇ ets multiplexed in time to the OLT.
  • OLT opti ⁇ cal line terminal
  • ONUs optical network units
  • communication among the ONUs needs to be conveyed through the OLT involv ⁇ ing electronic processing such as buffering and/or scheduling, which results in latency and degrades the throughput of the network.
  • wavelength-division multi ⁇ plexing is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry dif ⁇ ferent signals. This allows for a multiplication in capac- ity, in addition to enabling bidirectional communications over one strand of fiber.
  • WDM systems are divided into different wavelength patterns, conventional or coarse and dense WDM.
  • WDM systems provide, e.g., up to 16 channels in the 3rd transmission window (C- band) of silica fibers of around 1550 nm.
  • Dense WDM uses the same transmission window but with denser channel spac- ing.
  • Channel plans vary, but a typical system may use 40 channels at 100 GHz spacing or 80 channels at 50 GHz spac ⁇ ing. Some technologies are capable of 25 GHz spacing.
  • Am ⁇ plification options enable the extension of the usable wavelengths to the L-band, more or less doubling these num ⁇ bers .
  • Optical access networks e.g., coherent Ultra-Dense Wave ⁇ length Division Multiplex (UDWDM) networks, are deemed to be a promising approach for future data access.
  • UDWDM coherent Ultra-Dense Wave ⁇ length Division Multiplex
  • NGOA Next Generation Optical Ac ⁇ cess
  • optical wavelengths may have a spectral distance of a few gigahertz and can be used either for a ultra dense wavelength grid optical access system like NGOA where each user may be assigned a wavelength of his own or for a transmission of high data rates such as 100 Gbit/s where a multitude of wavelengths are bundled and are transmitted over a small spectral range.
  • Single sideband modulators are known to generate a single sideband, modulated with user data, onto either the low- or high frequency side of a spectrum. Such SSBMs lead to a rather complex transmitter design.
  • first data is conveyed from the centralized component to at least two decentralized components, wherein the at least two decentralized components share an optical resource;
  • second data is conveyed from the decentral ⁇ ized component to the decentralized component via at least one separate optical resource.
  • the several decentralized components may each use its own optical resource for conveying upstream data to the centralized component.
  • the down- stream and upstream data use different optical resources, e.g., wavelength or frequency ranges.
  • this approach does not require single side ⁇ band modulators, which is in particular beneficial as it simplifies the design of the components involved.
  • a single side band modulator or IQ modulator
  • IQ modulator typically comprises two nested Mach Zehnder modula ⁇ tors
  • a simple Mach Zehnder modulator is sufficient. This reduces the complexity at the transmitter of the central- ized component, e.g., of an optical line terminal (OLT) , because instead of two DACs and two modulator amplifiers only a single DAC and only one amplifier are required.
  • the optical resource and the at least one separate optical resource are not identical and in particu ⁇ lar occupy different bandwidths .
  • the optical resource and the at least one separate optical resource corresponds to a wave ⁇ length range around at least one carrier frequency.
  • the optical resource shared by the at least two decentralized components comprises a dual side-band spectrum.
  • the first data received at the at least two decentralized components is decoded and only the portion of the first data that is addressed to the particu ⁇ lar decentralized component is further processed by this particular decentralized component.
  • the shared optical resource is used to convey equal or different amounts of first data to each of the at least two decentralized components.
  • the first data conveyed to each of the at least two decentralized components via the shared optical resource is logically separated into data portions for each of the at least two decentralized compo ⁇ nents or for all or a group of the at least two decentral ⁇ ized components.
  • the first data conveyed in downstream di ⁇ rection towards the several decentralized components can be logically separated at the de- centralized components.
  • each decentralized component can use a particular code or key in order to properly decode the portion of the first data that was in ⁇ tended to be received and processed by this particular de ⁇ centralized component.
  • the decentralized com- ponents using the same optical resource can each use a con ⁇ stant or varying amount of bandwidth of this resource, e.g., 25%, 50%, 80%, etc.
  • the amount of resource shared can be dynamically assigned by the centralized component and/or dynamically requested by the decentralized component. It is also an option that a certain portion of this resource is used for broadcast or multicast purposes, i.e. a portion of the first data can be received and processed by all (broad ⁇ cast) or by several (multicast) decentralized components.
  • the centralized optical compo ⁇ nent comprises a Mach-Zehnder modulator, a two-beam inter- ferometer or a Michelson interferometer structure.
  • the centralized optical component may in particular be a centralized electrical-optical component.
  • the problem stated above is also solved by a device com ⁇ prising a processing unit that is arranged such that the method as described herein is executable thereon.
  • processing unit can comprise at least one, in particular several means that are arranged to execute the steps of the method described herein.
  • the means may be logically or physically separated; in particu ⁇ lar several logically separate means could be combined in at least one physical unit.
  • Said processing unit may comprise at least one of the fol- lowing: a processor, a microcontroller, a hard-wired circuit, an ASIC, an FPGA, a logic device.
  • - comprising a processing unit that is arranged - for conveying first data from the centralized component to at least two decentralized compo ⁇ nents via a common optical resource;
  • the centralized component is an optical line terminal connected to several optical network units.
  • the decentralized component is an op- tical network unit connected to an optical line terminal.
  • a commu ⁇ nication system comprising at least one of the devices as described herein.
  • Fig.l shows a schematic diagram of a signal generation arrangement as it can be provided by an OLT
  • Fig.2A shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising downstream channels (from an OLT to several ONUs) around car ⁇ rier frequencies located at a given (frequency) distance from a base frequency fO;
  • Fig.2B shows a schematic diagram (frequency plan) of a
  • Fig.3 shows an exemplary frequency diagram in the optical domain
  • Fig.4A to Fig.4D each shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes a particular signal utilizing an electrical bandpass filter;
  • Fig.5 shows a frequency diagram in an electrical domain
  • Fig.6 shows an exemplary diagram of an N-carrier transceiver that could be located in an OLT.
  • the solution presented herein describes a method of gener ⁇ ating and/or detecting a multitude of individually modu- lated optical wavelengths with a spectral distance of, e.g., (only) a few GHz, wherein the optical wavelengths may be generated based on a single laser source.
  • ultra dense wavelength grid optical access systems like NGOA, which may provide a wavelength (or wavelength range) for every user or subscriber .
  • NGOA ultra dense wavelength grid optical access systems
  • NGOA which could pro ⁇ vide for each subscriber, user or service (or group
  • a separate wavelength i.e. at least one wave ⁇ length range
  • a particular wavelength i.e. wavelength range
  • the solution further allows for an arbitrary split between broadcast data and individual (user) data. Also, a pair- wise split between two channels transmitted at the same wavelength amount in down-stream direction can efficiently be realized.
  • optical modulated carriers can be created twice in downstream direction as dual side-band spectrum thereby doubling a data rate (e.g., 1 Gb/s to 2 Gb/s) ; hence, each signal comprises information for two optical network units (ONUs) .
  • a separation of the two different downstream sig ⁇ nals conveyed via the same optical frequency (wavelength) can be done, e.g., logically: For example,
  • a percentage amounting to X of the data can be as ⁇ signed to the first ONU and a percentage of 100-X can be assigned to the second ONU;
  • - ONU-individual decoding mechanism can be used in order to ensure that only the correct ONU is able to decode the user data.
  • the bandwidth- capability of the modulator does not have to be twice as high, because it depends primarily on the highest carrier frequency .
  • the ONUs can be assigned pair-wise to the upper and to the lower sideband channels, the separation of traffic con ⁇ veyed from the ONUs to the OLT in upstream direction can be achieved via a heterodyne receiver as each ONU may use a different optical carrier frequency.
  • Fig.l shows a schematic diagram of a signal generation arrangement as it can be provided by an OLT.
  • a light source 101 (e.g., a laser source, in particular a laser diode) is connected to a modulator 102, which can be realized as a Mach-Zehnder-Modulator .
  • the signal of the light source 101 is fed to a coupler 103 and further via a phase adjustment 104 and a phase modulator 105 to a coupler 107.
  • the phase adjustment 104 can be controlled via a bias signal 110.
  • the output of the coupler 103 is also conveyed via a phase modulator 106 to said coupler 107.
  • the modulator 102 is controlled by an electrical signal 108 which comprises several data signals (e.g., several chan- nels 1...N utilizing N/2 carriers in the electrical domain) .
  • Fig.2A shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising downstream channels (from an OLT to several ONUs) around carrier frequencies located at a given (frequency) distance from a base frequency f0.
  • a channel Ch3 is located at a carrier frequency +8GHz and -8GHz from the base frequency f0.
  • the channel Ch3 is used to convey downstream traffic to an ONU5 and to an ONU6.
  • a channel Ch2 is located at a car ⁇ rier frequency +5GHz and -5GHz from the base frequency f0.
  • the channel Ch2 is used to convey downstream traffic to an ONU3 and to an ONU4.
  • a channel Chi is located at a carrier frequency +2GHz and -2GHz from the base frequency f0.
  • the channel Chi is used to convey downstream traffic to an ONU1 and to an ONU2.
  • Fig.2B shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising upstream channels (from the several ONUs to the OLT) in view of the base fre ⁇ quency f0.
  • the ONU1 uses a carrier fre- quency f0+3GHz
  • the ONU3 uses a carrier frequency fO-6GHz
  • the ONU5 uses a carrier frequency fO+9GHz.
  • the ONU2 uses the carrier frequency fO-lGHz
  • the ONU4 uses the carrier frequency fO-4GHz
  • the ONU6 uses the carrier frequency fO-7GHz.
  • the frequency plans indicated in Fig.2A and Fig.2B can be determined based on the Nyquist-Shannon-Theorem. However, a sampling rate amounting to 1.2 times larger the maximum frequency can be used.
  • a signal bandwidth fs can be determined as follows: fs > 1/Ts, wherein Ts is the duration of a symbol.
  • bandpass filters can be used based on the assumption that a signal requires a bandwidth amounting to 1.5/Ts.
  • the following shows a table comprising exemplary values for data rate, modulation format, symbol rate and occupied bandwidth. This allows considering guard bands and filter imperfections .
  • the parameter A indicates an arbitrary data rate.
  • Fig.3 shows an exemplary frequency diagram in the optical domain.
  • a local oscillator frequency 301 at the OLT (also referenced as f L0 OLT) is a reference frequency for the other frequencies.
  • the diagram shows signals in upstream direc ⁇ tion from the ONUs to the OLT such as 303 and signals in downstream direction from the OLT to the ONUs such as 305. Each signal has a certain bandwidth.
  • the large signals 303, 305 comprise user data, while the small signals 304, 306 are back reflections.
  • the arrows 302 pointing in downward direction indicate carrier frequencies of the local oscillators at the ONUs.
  • the upstream signals according to Fig.3 are denoted as “l up “ to “10 up “, wherein the signals “l up “ and “2 up “ are separated by a frequency "4 ⁇ ", wherein ⁇ may depend on an occupied bandwidth for upstream and downstream signals.
  • the remaining adjacent up- stream signals are separated by a frequency amounting to "3 ⁇ " .
  • the signals "l down “ to "10 do allocate” are arranged symmetrically around the frequency 301 (see also Fig.2A) . It is noted that dual sideband modulation can be used to convey traffic in downstream direction.
  • Fig.4A shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "l down " 402 utilizing an electrical bandpass filter 401.
  • the diagram further shows the signals 2 down 403, 3 d0 administratn 404, 4 down 405, 5 d0 gownn 406, 6 d0 memon 407 and 7 down 408. Also, back- reflected signals are depicted, in particular a reflection 409 of the signal l up , a reflection 410 of the signal 3 up , a reflection 411 of the signal 2 up , a reflection 412 of the signal 5 up , a reflection 413 of the signal 4 up , a reflection 414 of the signal 7 up and a reflection 415 of the signal
  • a reflection could comprise a mere reflection and/or a back-scattering, e.g., Rayleigh scattering.
  • Fig.4B shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "2 down " 403 utilizing an electrical bandpass filter 416.
  • the diagram further shows the signals 4 down 405, l d0W n 401 and 6 d0 memon 407, 8 d0 memon 404 and 3 d0 memon 419 as well as back- reflected signals, in particular the reflection 411 of the signal 2 up , the reflection 413 of the signal 4 up , the re- flection 409 of the signal l up , the reflection 415 of the signal 6 up , the reflection 410 of the signal 3 up , a reflec- tion 418 of the signal 8 up and the reflection 412 of the signal 5 up .
  • Fig.4C shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "3 d0 wn" 404 utilizing an electrical bandpass filter 420.
  • Fig.4D shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "4down" 405 utilizing an electrical bandpass filter 422.
  • Fig.5 shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the OL .
  • the data signals lup to lOup are each filtered by bandpass filters 501 (indicated by the dashed lines) .
  • the back-reflections of the down ⁇ stream signals are also shown within band gaps between the data signals.
  • the reflection of the signal l d0 wn is referred to as Rl ciown / etc.
  • an allocation of signals also referred to (logical) channels) could be determined as follows:
  • the channel spacing between the signals amounts to 3 ⁇
  • an intermediate frequency can be set to 1.4
  • the ADC sampling rate may thus be in the range between 4.1 Gsamples/s and less than 5 Gsamples/s.
  • the following table shows an exemplary frequency plan for a data rate amounting to 1.244 Gb/s per ONU utilizing a DQPSK modulation format at the OLT (2.488 Gb/s) and an OOK modu ⁇ lation format at the ONU (1.244 Gb/s).
  • the channel spacing between the signals amounts to 3 ⁇
  • 8 channels occupy about 43 GHz in the optical domain and 21.5 GHz in the electrical domain resulting in sample rates of 43 to 52 Gsamples/s to be processed via the DACs and the ADCs .
  • the intermediate frequency can be set to
  • the ADC sampling rate may thus be in the range of 5 Gsamples/s.
  • Fig.6 shows an exemplary diagram of an N-carrier transceiver that could be located in an OL .
  • the transceiver comprises a transceiver module 601 and a digital processing unit 602.
  • An optical input signal "Optical In” is conveyed to a receiver 605.
  • a laser serves as a local oscillator LO 603 and conveys a signal via a splitter 604 to the modula ⁇ tor structure 102 (see also, e.g., Fig.l) and to the re- DCver 605.
  • the receiver 605 conveys two analog signals to A/D convert ⁇ ers 606 (processing a horizontal polarization), 607 (processing a vertical polarization) .
  • the digital signal pro- vided by the A/D converters 606, 607 is processed via a software defined radio (SDR) 608 and further via a process ⁇ ing unit 609, which produces N digital streams (or chan ⁇ nels) 610 at a data rate amounting to, e.g., lGbit/s each.
  • a software defined radio is a synonym for a signal process- ing unit that's functionality is configurable by software.
  • the processing unit 609 provides in particular framing, a general frame procedure, a forward error correction, OAM services, and a broadcast capability.
  • N digital data streams (or chan ⁇ nels) 620 are each fed to a processing unit 617 to 619 and further via a QPSK modulation unit 614 to 616 to a carrier generation and modulation unit 613 providing N/2 channels.
  • the output thereof is converted to an analog signal by a D/A converter 612 and forwarded to the modulation structure 102.
  • the modulation structure 102 provides the optical out ⁇ put signal "Optical Out”.
  • the bias signal 110 is provided by the processing unit 602 in order to control the phase adjustment 104 of the modulation structure 102 (see Fig.l) .
  • the optical receivers can be (balanced) polarization-diversity receivers.
  • DQPSK can be used.
  • N/2 carriers can be generated, but with a data-rate of 2 channels (in this example: 2 Gb/s) .
  • the solution presented allows a simplified transmitter de ⁇ sign, in particular of the OLT . It is also an advantage that no single sideband modulators are required. Further ⁇ more, no costly electrical 90-degree hybrid or orthogonal sine-wave generation means is required. Advantageously, only a single high-frequency modulation signal (instead of 2 or 4 HF signals) is processed. The approach further al- lows processing of only N/2 carriers in the electrical do ⁇ main, but with the doubled data rate.
  • the down-stream capacity can advantageously be split pair-wise (e.g., flexibly in a range from 0 to

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Abstract

201002029 22 Abstract Processing data in an optical network A method devices for processing data in an optical network 5 are provided, wherein a centralized component is connected to several decentralized components; wherein first data is conveyed from the centralized component to at least two de- centralized components, wherein the at least two decentral- ized components share an optical resource; and wherein sec-10 ond data is conveyed from the decentralized component to the decentralized component via at least one separate opti- cal resource. Furthermore, a communication system is sug- gested comprising said device. 15 Fig.3

Description

Description
Processing data in an optical network The invention relates to a method for processing data in an optical network and to components of such optical network.
A passive optical network (PON) is a promising approach regarding fiber-to-the-home (FTTH) , fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) scenarios, in particu¬ lar as it overcomes the economic limitations of traditional point-to-point solutions.
Several PON types have been standardized and are currently being deployed by network service providers worldwide. Con¬ ventional PONs distribute downstream traffic from the opti¬ cal line terminal (OLT) to optical network units (ONUs) in a broadcast manner while the ONUs send upstream data pack¬ ets multiplexed in time to the OLT. Hence, communication among the ONUs needs to be conveyed through the OLT involv¬ ing electronic processing such as buffering and/or scheduling, which results in latency and degrades the throughput of the network. In fiber-optic communications, wavelength-division multi¬ plexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry dif¬ ferent signals. This allows for a multiplication in capac- ity, in addition to enabling bidirectional communications over one strand of fiber.
WDM systems are divided into different wavelength patterns, conventional or coarse and dense WDM. WDM systems provide, e.g., up to 16 channels in the 3rd transmission window (C- band) of silica fibers of around 1550 nm. Dense WDM uses the same transmission window but with denser channel spac- ing. Channel plans vary, but a typical system may use 40 channels at 100 GHz spacing or 80 channels at 50 GHz spac¬ ing. Some technologies are capable of 25 GHz spacing. Am¬ plification options enable the extension of the usable wavelengths to the L-band, more or less doubling these num¬ bers .
Optical access networks, e.g., coherent Ultra-Dense Wave¬ length Division Multiplex (UDWDM) networks, are deemed to be a promising approach for future data access.
Data transmission of spectrally densely spaced wavelengths is utilized by applications as Next Generation Optical Ac¬ cess (NGOA) systems allowing high data rates of, e.g., 100 Gbit/s.
In these optical scenarios, a multitude of optical wave¬ lengths are required in order to be individually modulated. Such optical wavelengths may have a spectral distance of a few gigahertz and can be used either for a ultra dense wavelength grid optical access system like NGOA where each user may be assigned a wavelength of his own or for a transmission of high data rates such as 100 Gbit/s where a multitude of wavelengths are bundled and are transmitted over a small spectral range.
Single sideband modulators (SSBMs) are known to generate a single sideband, modulated with user data, onto either the low- or high frequency side of a spectrum. Such SSBMs lead to a rather complex transmitter design.
The problem to be solved is to overcome the disadvantage stated above and in particular to provide an efficient so¬ lution for conveying data across an optical network. This problem is solved according to the features of the in¬ dependent claims. Further embodiments result from the de¬ pending claims. In order to overcome this problem, a method for processing data in an optical network is provided
- wherein a centralized component is connected to
several decentralized components;
- wherein first data is conveyed from the centralized component to at least two decentralized components, wherein the at least two decentralized components share an optical resource;
- wherein second data is conveyed from the decentral¬ ized component to the decentralized component via at least one separate optical resource.
In particular, the several decentralized components may each use its own optical resource for conveying upstream data to the centralized component. Preferably, the down- stream and upstream data use different optical resources, e.g., wavelength or frequency ranges.
Advantageously, this approach does not require single side¬ band modulators, which is in particular beneficial as it simplifies the design of the components involved. Instead of using a single side band modulator (or IQ modulator) , which typically comprises two nested Mach Zehnder modula¬ tors, a simple Mach Zehnder modulator is sufficient. This reduces the complexity at the transmitter of the central- ized component, e.g., of an optical line terminal (OLT) , because instead of two DACs and two modulator amplifiers only a single DAC and only one amplifier are required.
In an embodiment, the optical resource and the at least one separate optical resource are not identical and in particu¬ lar occupy different bandwidths . In another embodiment, the optical resource and the at least one separate optical resource corresponds to a wave¬ length range around at least one carrier frequency. In a further embodiment, the optical resource shared by the at least two decentralized components comprises a dual side-band spectrum.
In a next embodiment, the first data received at the at least two decentralized components is decoded and only the portion of the first data that is addressed to the particu¬ lar decentralized component is further processed by this particular decentralized component. It is also an embodiment that the shared optical resource is used to convey equal or different amounts of first data to each of the at least two decentralized components.
Pursuant to another embodiment, the first data conveyed to each of the at least two decentralized components via the shared optical resource is logically separated into data portions for each of the at least two decentralized compo¬ nents or for all or a group of the at least two decentral¬ ized components.
It is noted that the first data conveyed in downstream di¬ rection towards the several decentralized components, in particular to two of the decentralized components via dual side-band modulation, can be logically separated at the de- centralized components. For example, each decentralized component can use a particular code or key in order to properly decode the portion of the first data that was in¬ tended to be received and processed by this particular de¬ centralized component. Furthermore, the decentralized com- ponents using the same optical resource can each use a con¬ stant or varying amount of bandwidth of this resource, e.g., 25%, 50%, 80%, etc. The amount of resource shared can be dynamically assigned by the centralized component and/or dynamically requested by the decentralized component. It is also an option that a certain portion of this resource is used for broadcast or multicast purposes, i.e. a portion of the first data can be received and processed by all (broad¬ cast) or by several (multicast) decentralized components.
According to an embodiment, the centralized optical compo¬ nent comprises a Mach-Zehnder modulator, a two-beam inter- ferometer or a Michelson interferometer structure.
The centralized optical component may in particular be a centralized electrical-optical component. The problem stated above is also solved by a device com¬ prising a processing unit that is arranged such that the method as described herein is executable thereon.
It is noted that the steps of the method stated herein may be executable on this processing unit as well.
It is further noted that said processing unit can comprise at least one, in particular several means that are arranged to execute the steps of the method described herein. The means may be logically or physically separated; in particu¬ lar several logically separate means could be combined in at least one physical unit.
Said processing unit may comprise at least one of the fol- lowing: a processor, a microcontroller, a hard-wired circuit, an ASIC, an FPGA, a logic device.
The problem above is also solved by a centralized component in an optical network
- that is connected to several decentralized compo¬ nents,
- comprising a processing unit that is arranged - for conveying first data from the centralized component to at least two decentralized compo¬ nents via a common optical resource;
- for receiving second data from at least one of the decentralized components via at least one separate optical resource.
According to an embodiment, the centralized component is an optical line terminal connected to several optical network units.
The problem indicated above is further solved by a decen¬ tralized component in an optical network
- that is connected to a centralized component,
- comprising a processing unit that is arranged
- for receiving first data from the centralized
component, which is also conveyed to at least one other decentralized component via a common opti¬ cal resource;
- for conveying second data to the centralized com¬ ponent via at least one separate optical re¬ source .
In yet an embodiment, the decentralized component is an op- tical network unit connected to an optical line terminal.
Furthermore, the problem stated above is solved by a commu¬ nication system comprising at least one of the devices as described herein.
Embodiments of the invention are shown and illustrated in the following figures:
Fig.l shows a schematic diagram of a signal generation arrangement as it can be provided by an OLT; Fig.2A shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising downstream channels (from an OLT to several ONUs) around car¬ rier frequencies located at a given (frequency) distance from a base frequency fO;
Fig.2B shows a schematic diagram (frequency plan) of a
spectrum in an optical domain comprising upstream channels (from the several ONUs to the OLT) in view of the base frequency fO;
Fig.3 shows an exemplary frequency diagram in the optical domain; Fig.4A to Fig.4D each shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes a particular signal utilizing an electrical bandpass filter;
Fig.5 shows a frequency diagram in an electrical domain
(depicting an electrical frequency in view of a spectral density) at a receiver of the OLT; Fig.6 shows an exemplary diagram of an N-carrier transceiver that could be located in an OLT.
The solution presented herein describes a method of gener¬ ating and/or detecting a multitude of individually modu- lated optical wavelengths with a spectral distance of, e.g., (only) a few GHz, wherein the optical wavelengths may be generated based on a single laser source.
An application for such ultra dense wavelength grid could be an optical access system like NGOA, which may provide a wavelength (or wavelength range) for every user or subscriber . It is noted that, e.g., ultra dense wavelength grid optical access systems can be referred to as NGOA which could pro¬ vide for each subscriber, user or service (or group
thereof) a separate wavelength (i.e. at least one wave¬ length range) . Also, a particular wavelength (i.e. wavelength range) can be assigned to at least one subscriber, user or service. The solution further allows for an arbitrary split between broadcast data and individual (user) data. Also, a pair- wise split between two channels transmitted at the same wavelength amount in down-stream direction can efficiently be realized.
Thus, optical modulated carriers can be created twice in downstream direction as dual side-band spectrum thereby doubling a data rate (e.g., 1 Gb/s to 2 Gb/s) ; hence, each signal comprises information for two optical network units (ONUs) . A separation of the two different downstream sig¬ nals conveyed via the same optical frequency (wavelength) can be done, e.g., logically: For example,
- odd bytes can be assigned to a first ONU and even bytes can be assigned to a second ONU;
- a percentage amounting to X of the data can be as¬ signed to the first ONU and a percentage of 100-X can be assigned to the second ONU;
- ONU-individual decoding mechanism can be used in order to ensure that only the correct ONU is able to decode the user data.
It is noted that these examples can be flexibly adjusted according to a particular demand of the system, user and/or operator .
Hence, there is no need for single sideband modulators. This is beneficial as it simplifies the design of the com- ponents involved. Instead of using a single side band modu¬ lator (or IQ modulator) , which typically comprises two nested Mach Zehnder modulators, a simple Mach Zehnder modu¬ lator can be used. This reduces the complexity at the transmitter of the centralized component, e.g., of an opti¬ cal line terminal (OLT) , because instead of two DACs and two modulator amplifiers only a single DAC and only one am¬ plifier are required. Although the channel data rate is doubled, the bandwidth- capability of the modulator does not have to be twice as high, because it depends primarily on the highest carrier frequency . As the ONUs can be assigned pair-wise to the upper and to the lower sideband channels, the separation of traffic con¬ veyed from the ONUs to the OLT in upstream direction can be achieved via a heterodyne receiver as each ONU may use a different optical carrier frequency.
Fig.l shows a schematic diagram of a signal generation arrangement as it can be provided by an OLT.
A light source 101 (e.g., a laser source, in particular a laser diode) is connected to a modulator 102, which can be realized as a Mach-Zehnder-Modulator . The signal of the light source 101 is fed to a coupler 103 and further via a phase adjustment 104 and a phase modulator 105 to a coupler 107. The phase adjustment 104 can be controlled via a bias signal 110. The output of the coupler 103 is also conveyed via a phase modulator 106 to said coupler 107.
The modulator 102 is controlled by an electrical signal 108 which comprises several data signals (e.g., several chan- nels 1...N utilizing N/2 carriers in the electrical domain) . Fig.2A shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising downstream channels (from an OLT to several ONUs) around carrier frequencies located at a given (frequency) distance from a base frequency f0. For example, a channel Ch3 is located at a carrier frequency +8GHz and -8GHz from the base frequency f0. The channel Ch3 is used to convey downstream traffic to an ONU5 and to an ONU6. A channel Ch2 is located at a car¬ rier frequency +5GHz and -5GHz from the base frequency f0. The channel Ch2 is used to convey downstream traffic to an ONU3 and to an ONU4. A channel Chi is located at a carrier frequency +2GHz and -2GHz from the base frequency f0. The channel Chi is used to convey downstream traffic to an ONU1 and to an ONU2.
Fig.2B shows a schematic diagram (frequency plan) of a spectrum in an optical domain comprising upstream channels (from the several ONUs to the OLT) in view of the base fre¬ quency f0. In an upper band, the ONU1 uses a carrier fre- quency f0+3GHz, the ONU3 uses a carrier frequency fO-6GHz and the ONU5 uses a carrier frequency fO+9GHz. In a lower band, the ONU2 uses the carrier frequency fO-lGHz, the ONU4 uses the carrier frequency fO-4GHz and the ONU6 uses the carrier frequency fO-7GHz.
The frequency plans indicated in Fig.2A and Fig.2B can be determined based on the Nyquist-Shannon-Theorem. However, a sampling rate amounting to 1.2 times larger the maximum frequency can be used.
A signal bandwidth fs can be determined as follows: fs > 1/Ts, wherein Ts is the duration of a symbol. Advantageously,
(analog or digital) bandpass filters can be used based on the assumption that a signal requires a bandwidth amounting to 1.5/Ts.
The following shows a table comprising exemplary values for data rate, modulation format, symbol rate and occupied bandwidth. This allows considering guard bands and filter imperfections .
Figure imgf000012_0001
The parameter A indicates an arbitrary data rate.
Fig.3 shows an exemplary frequency diagram in the optical domain. A local oscillator frequency 301 at the OLT (also referenced as fL0 OLT) is a reference frequency for the other frequencies. The diagram shows signals in upstream direc¬ tion from the ONUs to the OLT such as 303 and signals in downstream direction from the OLT to the ONUs such as 305. Each signal has a certain bandwidth. The large signals 303, 305 comprise user data, while the small signals 304, 306 are back reflections.
The arrows 302 pointing in downward direction indicate carrier frequencies of the local oscillators at the ONUs.
These carrier frequencies are arranged around the frequency 301 as is also indicated in Fig.2B: The upstream signals according to Fig.3 are denoted as "lup" to "10up", wherein the signals "lup" and "2up" are separated by a frequency "4Δ", wherein Δ may depend on an occupied bandwidth for upstream and downstream signals. The remaining adjacent up- stream signals are separated by a frequency amounting to "3Δ" .
In downstream direction, the signals "ldown" to "10do„n" are arranged symmetrically around the frequency 301 (see also Fig.2A) . It is noted that dual sideband modulation can be used to convey traffic in downstream direction.
Fig.4A shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "ldown" 402 utilizing an electrical bandpass filter 401.
The diagram further shows the signals 2down 403, 3d0„n 404, 4down 405, 5d0„n 406, 6d0„n 407 and 7down 408. Also, back- reflected signals are depicted, in particular a reflection 409 of the signal lup, a reflection 410 of the signal 3up, a reflection 411 of the signal 2up, a reflection 412 of the signal 5up, a reflection 413 of the signal 4up, a reflection 414 of the signal 7up and a reflection 415 of the signal
A reflection could comprise a mere reflection and/or a back-scattering, e.g., Rayleigh scattering.
Fig.4B shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "2down" 403 utilizing an electrical bandpass filter 416.
The diagram further shows the signals 4down 405, ld0Wn 401 and 6d0„n 407, 8d0„n 404 and 3d0„n 419 as well as back- reflected signals, in particular the reflection 411 of the signal 2up, the reflection 413 of the signal 4up, the re- flection 409 of the signal lup, the reflection 415 of the signal 6up, the reflection 410 of the signal 3up, a reflec- tion 418 of the signal 8up and the reflection 412 of the signal 5up .
Fig.4C shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "3d0wn" 404 utilizing an electrical bandpass filter 420.
Also, the reflection 410 of the signal 3up is shown. Fig.4D shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the ONU that processes the signal "4down" 405 utilizing an electrical bandpass filter 422.
Also, the reflection 413 of the signal 4up is shown.
Fig.5 shows a frequency diagram in an electrical domain (depicting an electrical frequency in view of a spectral density) at a receiver of the OL . The data signals lup to lOup are each filtered by bandpass filters 501 (indicated by the dashed lines) . The back-reflections of the down¬ stream signals are also shown within band gaps between the data signals. The reflection of the signal ld0wn is referred to as Rl ciown/ etc. Based on the frequency plans shown in these figures and taking into account the fact that bandwidth occupied for upstream and downstream signals shall not be the same, an allocation of signals (also referred to (logical) channels) could be determined as follows:
Data Signal Carrier Frequency [GHz]
(Channel ) (in electrical domain)
1&2 2.8 GHz
3&4 7 GHz
5&6 11.2 GHz
7&8 15.4 GHz This is an exemplary frequency plan for a data rate amount¬ ing to 1.244 Gb/s per ONU utilizing a DQPSK modulation format at the OLT (2.488 Gb/s) and the ONU (1.244 Gb/s). The channel spacing between the signals amounts to 3Δ
(4.2 GHz) except for the signals 1 and 2 (lup and 2up as well as ld0wn and 2down) , for which the channel spacing amounts to 4Δ (5.6 GHz) . Hence, 8 channels occupy about 32 GHz in the optical domain and 16 GHz in the electrical domain resulting in sampling rates of 32 to 38 Gsamples/s to be processed via DACs and ADCs . At the ONU, an intermediate frequency can be set to 1.4
GHz. The ADC sampling rate may thus be in the range between 4.1 Gsamples/s and less than 5 Gsamples/s.
The following table shows an exemplary frequency plan for a data rate amounting to 1.244 Gb/s per ONU utilizing a DQPSK modulation format at the OLT (2.488 Gb/s) and an OOK modu¬ lation format at the ONU (1.244 Gb/s).
Figure imgf000015_0001
Upstream and downstream signals occupy the same bandwidth Therefore the channel spacing basic unit Δ amounts to
Δ = 1.5 x 1/Ts = 1.886 GHz.
The channel spacing between the signals amounts to 3Δ
(5.658 GHz) except for the signals 1 and 2 (lup and 2up as well as ld0wn and 2down) , for which the channel spacing amounts to 4Δ (7.544 GHz).
Hence, 8 channels occupy about 43 GHz in the optical domain and 21.5 GHz in the electrical domain resulting in sample rates of 43 to 52 Gsamples/s to be processed via the DACs and the ADCs .
At the ONU, the intermediate frequency can be set to
1.886 GHz; the ADC sampling rate may thus be in the range of 5 Gsamples/s.
Fig.6 shows an exemplary diagram of an N-carrier transceiver that could be located in an OL . The transceiver comprises a transceiver module 601 and a digital processing unit 602. An optical input signal "Optical In" is conveyed to a receiver 605. A laser serves as a local oscillator LO 603 and conveys a signal via a splitter 604 to the modula¬ tor structure 102 (see also, e.g., Fig.l) and to the re- ceiver 605.
The receiver 605 conveys two analog signals to A/D convert¬ ers 606 (processing a horizontal polarization), 607 (processing a vertical polarization) . The digital signal pro- vided by the A/D converters 606, 607 is processed via a software defined radio (SDR) 608 and further via a process¬ ing unit 609, which produces N digital streams (or chan¬ nels) 610 at a data rate amounting to, e.g., lGbit/s each. A software defined radio is a synonym for a signal process- ing unit that's functionality is configurable by software. The processing unit 609 provides in particular framing, a general frame procedure, a forward error correction, OAM services, and a broadcast capability. In the opposite direction for producing an optical output signal "Optical Out" 102, N digital data streams (or chan¬ nels) 620 are each fed to a processing unit 617 to 619 and further via a QPSK modulation unit 614 to 616 to a carrier generation and modulation unit 613 providing N/2 channels. The output thereof is converted to an analog signal by a D/A converter 612 and forwarded to the modulation structure 102. The modulation structure 102 provides the optical out¬ put signal "Optical Out". The bias signal 110 is provided by the processing unit 602 in order to control the phase adjustment 104 of the modulation structure 102 (see Fig.l) . It is noted that the optical receivers can be (balanced) polarization-diversity receivers. As a modulation format, DQPSK can be used. It is further noted that in the electrical domain, only N/2 carriers can be generated, but with a data-rate of 2 channels (in this example: 2 Gb/s) .
Further Advantages:
The solution presented allows a simplified transmitter de¬ sign, in particular of the OLT . It is also an advantage that no single sideband modulators are required. Further¬ more, no costly electrical 90-degree hybrid or orthogonal sine-wave generation means is required. Advantageously, only a single high-frequency modulation signal (instead of 2 or 4 HF signals) is processed. The approach further al- lows processing of only N/2 carriers in the electrical do¬ main, but with the doubled data rate.
It is another benefit of this solution that the modulator bias control is significantly simplified.
Furthermore, the down-stream capacity can advantageously be split pair-wise (e.g., flexibly in a range from 0 to
2Gb/s) . Also, a broadcast of up to 2 Gb/s can be achieved, wherein a flexible split is possible between resources used for broadcast and resources used for individual data trans¬ mission. It is also an advantage that an existing receiver at the OLT does not have to be changed using the approach pre¬ sented herein.
List of Abbreviations:
A/D Analog-to-Digital
ADC Analog-to-Digital Converter
Ch Channel
D/A Digital-to-Analog
DAC Digital-to-Analog Converter
DQPSK Differential Quadrature Phase Modulation
FEC Forward Error Correction
FTTB Fiber-to-the-Business
FTTC Fiber-to-the-Curb
FTTH Fiber-to-the-Home
GFP General Frame Procedure
HF High Frequency
LO Local Oscillator
MZM Mach-Zehnder Modulator
NGOA Next Generation Optical Access
OAM Operation, Administration and Maintenance
OLT Optical Line Terminal
ONU Optical Network Unit
OOK ON-OFF keying
PolMux Polarization Multiplex
PON Passive Optical Network
PSK Phase Shift Keying
QPSK Quadrature PSK
RX Receiver
SDR Software Defined Radio
SSB Single Sideband
SSBM SSB Modulator
SW Software
UDWDM Ultra Dense WDM
WDM Wavelength Division Multiplexing

Claims

A method for processing data in an optical network,
- wherein a centralized component is connected to
several decentralized components;
- wherein first data is conveyed from the centralized component to at least two decentralized components, wherein the at least two decentralized components share an optical resource;
- wherein second data is conveyed from the decentral¬ ized component to the decentralized component via at least one separate optical resource.
The method according to claim 1, wherein the optical resource and the at least one separate optical re¬ source are not identical and in particular occupy dif¬ ferent bandwidths .
The method according to any of the preceding claims, wherein the optical resource and the at least one separate optical resource corresponds to a wavelength range around at least one carrier frequency.
The method according to any of the preceding claims, wherein the optical resource shared by the at least two decentralized components comprises a dual side¬ band spectrum.
The method according to any of the preceding claims, wherein the first data received at the at least two decentralized components is decoded and only the por¬ tion of the first data addressed to the particular de¬ centralized component is further processed by this particular decentralized component.
The method according to claim 5, wherein the shared optical resource is used to convey equal or different amounts of first data to each of the at least two de¬ centralized components.
The method according to any of claims 5 or 6, wherein the first data conveyed to each of the at least two decentralized components via the shared optical re¬ source is logically separated into data portions for each of the at least two decentralized components or for all or a group of the at least two decentralized components .
The method according to any of the preceding claims, wherein the centralized optical component comprises a Mach-Zehnder modulator, a two-beam interferometer or a Michelson interferometer structure.
A centralized component in an optical network
- that is connected to several decentralized compo¬ nents,
- comprising a processing unit that is arranged
- for conveying first data from the centralized
component to at least two decentralized compo¬ nents via a common optical resource;
- for receiving second data from at least one of the decentralized components via at least one separate optical resource.
The centralized component according to claim 9, wherein the centralized component is an optical line terminal connected to several optical network units.
A decentralized component in an optical network
- that is connected to a centralized component,
- comprising a processing unit that is arranged
- for receiving first data from the centralized
component, which is also conveyed to at least one other decentralized component via a common opti¬ cal resource;
- for conveying second data to the centralized com¬ ponent via at least one separate optical re¬ source .
12. The decentralized component according to claim 11, wherein the decentralized component is an optical net¬ work unit connected an optical line terminal.
13. A communication system comprising the at least one of the devices according to any of claims 9 to 12.
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