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WO2024183874A1 - Communication optique cohérente - Google Patents

Communication optique cohérente Download PDF

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Publication number
WO2024183874A1
WO2024183874A1 PCT/EP2023/055486 EP2023055486W WO2024183874A1 WO 2024183874 A1 WO2024183874 A1 WO 2024183874A1 EP 2023055486 W EP2023055486 W EP 2023055486W WO 2024183874 A1 WO2024183874 A1 WO 2024183874A1
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WO
WIPO (PCT)
Prior art keywords
optical
communication system
coherent
signal
supply
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PCT/EP2023/055486
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English (en)
Inventor
Fabio Cavaliere
Luca Giorgi
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Telefonaktiebolaget LM Ericsson AB
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Telefonaktiebolaget LM Ericsson AB
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Priority to PCT/EP2023/055486 priority Critical patent/WO2024183874A1/fr
Publication of WO2024183874A1 publication Critical patent/WO2024183874A1/fr
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

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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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2587—Arrangements specific to fibre transmission using a single light source for multiple stations

Definitions

  • the present disclosure relates to coherent optical communication and in particular, but not exclusively, to coherent optical communication systems, a computing system and methods in a coherent optical communication system.
  • optical transceiver such as in the form of a chiplet
  • electronic processing circuitry e.g., an integrated circuit (IC)
  • IC integrated circuit
  • the electronic processing circuitry may be interfaced with the optical transceiver via an electrical connection that may allow for handling high speed communications.
  • the electronic processing circuitry may control generation of optical signals by the optical transceiver, where the optical signals may encode information in accordance with a communications protocol.
  • the electronic processing circuitry may receive electronic signals generated by the optical transceiver based on optical signals received by the optical transceiver.
  • the electronic processing circuitry may process the received electronic signals to extract information from the received optical signals.
  • the copackaged design may provide a compact and efficient package for integration into a computing system that uses optical communications to exchange data between nodes of the computing system.
  • the term co-packaged optics (CPO) may be used to refer to such a copackaged optical transceiver.
  • CPO may have applications in computing systems such as large packet switches and high-performance computers.
  • the use of CPO at nodes of packet switches may decrease the power consumption and increase the optical connections density at the front panel of the nodes compared to an implementation with optical pluggable transceivers.
  • the use of CPO in high-performance computers may facilitate a high bandwidth density per surface area required by the interconnection of memories and processing units.
  • RAN radio access networks
  • external connectivity links between baseband, units radio units, or switches
  • internal connectivity short links connecting boards or modules in the same antenna or baseband site
  • on-board connectivity links between ICs in the same board
  • the Optical Internetworking Forum defined a Co-packaged Framework Project, including an implementation agreement (I A) of a 3.2T Co-Packaged Optical Module that targets Ethernet switching applications utilizing 100G electrical lanes.
  • I A implementation agreement
  • Another IA in the same framework concerns an External Laser Small Form-Factor Pluggable (ELSFP) module for that CPO transceiver.
  • ELSFP External Laser Small Form-Factor Pluggable
  • the optical front-end of a CPO transceiver does not include the laser source but only an optical modulator and photodetector, realized in silicon photonics. The light to be modulated is generated by an external laser source.
  • CMOS Complementary Metal Oxide Semiconductor
  • ELS external laser source
  • CPO Complementary Metal Oxide Semiconductor
  • Coherent optical communication is pervasive in optical networks, due to advantages in transmission capacity, link distance and cost.
  • DWDM dense wavelength division multiplexing
  • DP-QPSK dual polarization quadrature phase shift keying
  • DP-16QAM dual-polarization order-16 quadrature amplitude modulation
  • RO ADM reconfigurable optical add-drop multiplexers
  • a coherent receiver may detect the amplitude, phase and polarization state of the input signal. Coherent detection may make it possible to compensate, through electronic equalization, any signal distortion caused by linear propagation effects in the fiber link. Coherent optical transmission systems can achieve link distances of a few thousands of kilometers, with the help of optical amplification but without regeneration of an intermediate signal.
  • the current cost of a 100 or 400 Gbit/s coherent transceiver is one or two order of magnitudes higher than the cost of a DWDM or gray direct detection transceiver, respectively.
  • the transmission frequency is not stabilized and can vary over a wide frequency range.
  • Coherent transmission systems may provide a significant cost saving in metro and long-haul network due to the capability to compensate for linear fiber impairments by means of digital signal processing (DSP).
  • DSP digital signal processing
  • the OIF IA specifies a power budget for the CPO module (or channel insertion loss, according to the IEEE 802.3 terminology) of 3 dB, according to the 100GBASE-DR4 standard. Although this is a small power budget, it implies that a high-power external light source (ELS) is needed such as >20 dBm due to the insertion loss of connectors and modulator, and the need to split the ELS light into different optical lanes. It may be desirable to reduce the ELS power for reliability reason and to stay in the laser Safety Class 1. The ELS power may be reduced by increasing the receiver sensitivity.
  • ELS external light source
  • the OIF specification refers to a socketed module with a digital electrical retimed interface, for example the CEI-112G-XSR interface defined by the OIF.
  • a linear (i.e., analog and non-retimed) interface may be desirable to reduce the power consumption with respect to optical pluggable modules.
  • An example is the CEI-112G Linear interface under development at the OIF.
  • the use of a linear interface reduces the performance because the impairments of the electrical and the optical link sum up, making it difficult even to meet 3dB of channel attenuation. Improving the receiver sensitivity would be beneficial.
  • a coherent optical transceiver may allow receiver sensitivity to be improved.
  • the current implementation is too costly, complex to fit in a co-packaged format and excessively power consuming for short reach applications (e.g., of the order of up to tens of meters).
  • optical amplifiers are not used, and the chromatic dispersion may not be an issue so that all common advantages of coherent transmission systems may be lost.
  • Certain embodiments described herein may be used to facilitate the use of coherent optical communication in a wider range of applications while reducing or obviating problems with existing solutions.
  • a coherent optical communication system comprising a first optical source configured to generate a first optical supply signal.
  • the coherent optical communication system further comprises a first side communication system comprising a first side transmitter.
  • the coherent optical communication system further comprises a first side optical supply connection configured to supply the first optical supply signal to the first side transmitter.
  • the coherent optical communication system further comprises a second side communication system comprising a second side receiver.
  • the coherent optical communication system further comprises a second side optical supply connection configured to supply the first optical supply signal to the second side receiver.
  • the coherent optical communication system further comprises an optical communication connection between the first side transmitter and the second side receiver.
  • the first side transmitter is configured to modulate the first optical supply signal with first information to generate a first modulated signal.
  • the first side transmitter is further configured to transmit the first modulated signal to the second side receiver via the optical communication connection.
  • the second side receiver is configured to use the first optical supply signal to perform coherent detection on the first modulated signal.
  • a computing system comprising the coherent optical communication system the first aspect.
  • the first side communication system is configured to: receive an input of first information; generate the first modulated signal based on the first information; and transmit the first modulated signal to the second side communication system.
  • the second side communication system is configured to: receive the first modulated signal; perform coherent detection on the first modulated signal to extract the first information; and output the first information.
  • the coherent optical communication system comprises a first side communication system and a second side communication system.
  • the method comprises generating, with a first optical source of the optical communication system, a first optical supply signal.
  • the method further comprises supplying the first optical supply signal to a first side transmitter of the first side communication system.
  • the method further comprises supplying the first optical supply signal to a second side receiver of the second side communication system.
  • the method further comprises using the first side transmitter to: modulate the first optical supply signal with first information to generate a first modulated signal; and transmit the first modulated signal to the second side receiver.
  • the method further comprises receiving, by the second side receiver, the first modulated signal.
  • the method further comprises performing, by the second side receiver, coherent detection on the first modulated signal using the first optical supply signal.
  • Certain embodiments of the present disclosure may provide one or more of the following technical benefits. For example, certain embodiments may facilitate the use of coherent optical communication in a wider range of applications. Certain embodiments may exploit, e.g., in short reach interconnects, the higher performance of coherent optical communications compared to (incoherent) direct detection-based optical communications. Certain embodiments may allow a coherent optical communication system to be deployed while minimizing the cost of deployment. Certain embodiments may use polarization maintaining optics to simplify the receiver front end, for example, by reducing or obviating the need to perform power consuming equalization for polarization recovery. Certain embodiments may make efficient use of one or more remote/extemal optical sources by sharing such optical source(s) between the different sides of the communication system.
  • the remote/extemal optical source may be deployed flexibly in such a way to reduce complexity/bulkiness and better manage heat dissipated by the remote/extemal optical source.
  • a separate local oscillator may not be needed to be incorporated onto the same platform as the receiver in order to implement coherent detection since the remote/extemal optical source provides the signal corresponding to the local oscillator used in coherent detection. Certain embodiments described herein may save cost, enable homodyne detection where no frequency recovery is needed (leading to further energy savings) and/or enable efficient use of space in the computing infrastructure hosting the coherent communication system.
  • Figure 1 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 2 is a schematic diagram illustrating a computing system according to an embodiment
  • Figure 3 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 4 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 5 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 6 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 7 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 8 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 9 is a schematic diagram illustrating a coherent optical communication system according to an embodiment
  • Figure 10 is a flowchart of a method in a coherent optical communication system according to an embodiment
  • Figure 11 is a flowchart of a method in a coherent optical communication system according to an embodiment.
  • Figure 12 is a schematic diagram illustrating a processor and a machine-readable medium for implementing certain embodiments.
  • references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
  • coherent optical communications may provide various advantages over direct direction-based optical communications in terms of data capacity, efficiency and sensitivity in certain scenarios such as in long-haul networks.
  • some advantages of coherent optical communications may not be realized e.g., due to the cost, complexity, power consumption, etc., involved in installation and operating a coherent optical communication system.
  • Certain embodiments described herein may offer a solution to one or more of the problems highlighted herein.
  • Figure 1 is a schematic diagram illustrating a coherent optical communication system 100 according to an embodiment.
  • a coherent optical communication system 100 could be implemented in a short reach application (e.g., of the order of up to tens of meters) where a coherent communication link may be provided for communicating data between entities in the coherent optical communication system 100.
  • the coherent optical communication system 100 may include co-packaged optics.
  • the coherent optical communication system 100 may facilitate communications between an entity such as a co-packaged optical transceiver (comprising electronic processing circuitry and an optical transceiver) and one or more other entities such as another copackaged optical transceiver.
  • Embodiments described herein may be used to provide high data capacity communications between nodes of computing systems such as large packet switches and high-performance computers (e.g., where there may be a short reach between nodes, as described above). Although embodiments described herein generally refer to being implemented in short reach applications, embodiments described herein could also be used in certain longer reach applications such as more than the tens of meters described in relation to short reach applications, even in metro and long-haul networks.
  • the coherent optical communication system 100 has a first side and a second side.
  • the first side may include an optical transceiver and any associated equipment such as optics and electronic processing circuitry at one side of the coherent optical communication system 100.
  • the second side may include an optical transceiver and any associated equipment such as optics and electronic processing circuitry at another side of the coherent optical communication system 100.
  • the right-hand side of the figure refers to the first side.
  • the left-hand side of the figure refers to the second side.
  • Entities such as transmitters and receivers described herein may be at the first side or second side and are named according to whether such transmitters or receivers are associated with the first side or second side of the coherent optical communication system 100.
  • the coherent optical communication system 100 comprises a first optical source 102.
  • the first optical source 102 is configured to generate a first optical supply signal.
  • the first optical supply signal is for use in coherent communication. That is, the first optical supply signal may be modulated according to a modulation scheme suitable for implementing coherent communication (i.e., where coherent communication is implemented).
  • an optical source may comprise a laser such as a laser diode configured to produce an optical signal (i.e., an optical supply signal).
  • the optical source may have properties such as an appropriate wavelength stability and linewidth to facilitate a coherent optical communication scheme.
  • the coherent optical communication system 100 comprises a first side communication system 104.
  • the components of the first side communication system 104 may be included in the same hardware platform (such as a co-packaged transceiver) or housed within the same enclosure.
  • one or more components of the first side communication system 104 may be separate to one or more of the other components (i.e., the components may not be included in the same hardware platform or housed within the same enclosure).
  • the first side communication system 104 comprises a first side transmitter 106.
  • a transmitter may modulate an optical supply signal input to the transmitter (e.g., in the above case, the optical supply signal is the first optical supply signal) to represent digital data input to the transmitter in the generated (optical) output of the transmitter.
  • a modulator such as an optical modulator (e.g., an electro-optic modulator) configured to modulate the amplitude and/or phase of the optical supply signal to generate the output, which represents the digital data via modulation symbols according to the modulation scheme used.
  • modulation schemes for implementation by embodiments described herein include, and are not limited to, quadrature phase-shift keying (QPSK), quadrature amplitude modulation (QAM), 8B10B encoding, 64B66B encoding, and Manchester coding.
  • QPSK quadrature phase-shift keying
  • QAM quadrature amplitude modulation
  • 8B10B encoding 64B66B encoding
  • Manchester coding 8B10B encoding
  • the first optical source 102 may be remote (or external) to the first side communication system 104. That is, the first optical source 102 is not included in (or may be external to) a hardware platform of the first side communication system 104.
  • some coherent optical transceivers may use an optical source such as a laser built into the transceiver to generate the modulated optical output
  • certain embodiments described herein refer to transmitters configured to implement (e.g., electro-optic) modulation of the optical supply signal supplied to the transmitter from the (remote) first optical source 102 (e.g., via an optical fiber).
  • Digital signal processing is a technique capable of implementing modulation or demodulation schemes as described herein (i.e., at the transmitter and a corresponding receiver).
  • DSP techniques at the transmitter may be used to cause an optical modulator (e.g., of the transmitter) to modulate an optical supply signal to generate the optical output.
  • an optical modulator e.g., of the transmitter
  • a digital to analog converter associated with the DSP may generate one or more (electrical) analog signals representative of a digital data stream (e.g., demultiplexed into two analog signals).
  • Such analog signal(s) may cause the optical modulator to modulate the amplitude and/or phase of one or more optical supply signals to generate one or more modulated optical signals (i.e., the optical output of the transmitter).
  • Some transmitters may use an optical phase shift component to impart a phase delay between two or more of the modulated optical signals to prevent interference between such modulated optical signals, when combined onto the same optical path.
  • the optical output of the optical modulator is representative of the digital data stream and can be demodulated at a receiver that implements appropriate DSP techniques, as explained below.
  • the coherent optical communication system 100 further comprises a first side optical supply connection 108.
  • the first side optical supply connection 108 is configured to supply the first optical supply signal to the first side transmitter 106.
  • the first side optical supply connection 108 may comprise one or more optical fibers (e.g., to carry one or more optical supply signals) to one or more components of the first side communication system 104.
  • such optical fibers and other optics used in the coherent optical communication system 100 as described below) may be polarization maintaining. Using polarization maintaining optics may reduce compute resources dedicated to implementing DSP techniques such as recovering polarization information.
  • the coherent optical communication system 100 further comprises a second side communication system 110.
  • the components of the second side communication system 110 may be included in the same hardware platform (such as a co-packaged transceiver) or housed within the same enclosure. In some cases, one or more components of the second side communication system 110 may be separate to one or more of the other components (i.e., the components may not be included in the same hardware platform or housed within the same enclosure).
  • the second side communication system 110 comprises a second side receiver 112.
  • a (coherent) receiver may demodulate the optical output received from the transmitter to extract the digital data that was originally input to the transmitter.
  • the receiver implements the corresponding demodulation scheme as the modulation scheme used by the transmitter in order to extract the digital data.
  • the receiver may comprise one or more photodetectors with a responsivity suitable for the modulation rate of the optical output.
  • a further optical signal produced by a local oscillator (discussed below) is used by the receiver (where implemented as a coherent detector) to extract the digital data from the optical output.
  • a beat signal generated as a result of interference between the local oscillator’s optical signal and the transmitter’s optical output can be processed in order to extract the original digital data (e.g., via a DSP of the receiver).
  • Example receiver implementations for coherent detection include polarization-maintaining coherent homodyne detection, optical-based phase recovery coherent homodyne detection and phase diversity homodyne detection.
  • Each of these example receiver implementations may include DSP according to the type of homodyne detection being implemented. The complexity of the DSP depends on the type of homodyne detection. Some embodiments described herein do not use coherent detection, in which case a direct detectionbased demodulation scheme may be implemented by the receiver.
  • the coherent optical communication system 100 further comprises a second side optical supply connection 114.
  • the second side optical supply connection 114 is configured to supply the first optical supply signal (i.e., the same optical supply signal as supplied to the first side transmitter 106) to the second side receiver 112.
  • the second side optical supply connection 114 may comprise one or more optical fibers (e.g., to carry one or more optical supply signals) to one or more components of the second side communication system 110.
  • the second side optical supply connection 114 may be polarization maintaining.
  • the coherent optical communication system 100 further comprises an optical communication connection 116 between the first side transmitter 106 and the second side receiver 112.
  • the optical communication connection 116 may comprise one or more optical fibers to carry the optical output of the first side transmitter 106 to the second side receiver 112.
  • the optical communication connection 116 carries data for communications between the first side communication system 104 and the second side communication system 110.
  • the optical communication connection 116 may be polarization maintaining.
  • the first side transmitter 106 is configured to modulate the first optical supply signal with first information to generate a first modulated signal.
  • the first side transmitter 106 further is configured to transmit the first modulated signal to the second side receiver 112 via the optical communication connection.
  • the first side transmitter 106 may receive digital data corresponding to the first information.
  • the first side transmitter 106 may use DSP techniques to cause the first optical supply signal to be modulated to generate the first modulated signal (corresponding to the optical output of the first side transmitter 106), which is then transmitted to the second side receiver 112.
  • the second side receiver 112 is configured to use the first optical supply signal to perform coherent detection on the first modulated signal. That is, the first optical supply signal may represent the local oscillator of a coherent detector, and the first modulated signal may represent the received modulation symbols to be demodulated by the coherent detector.
  • Certain embodiments of the present disclosure may provide one or more of the following technical benefits. For example, certain embodiments may facilitate the use of coherent optical communication in a wider range of applications. Certain embodiments may exploit, e.g., in short reach interconnects, the higher performance of coherent optical communications compared to (incoherent) direct detection-based optical communications. Certain embodiments may allow a coherent optical communication system to be deployed while minimizing the cost of deployment. Certain embodiments may use polarization maintaining optics to simplify the receiver front end, for example, by reducing or obviating the need to perform power consuming equalization for polarization recovery.
  • Certain embodiments may make efficient use of one or more remote/extemal optical sources (i.e., the first optical source 102 and any other optical sources) by sharing such optical source(s) between the different sides of the communication system.
  • the remote/extemal optical source may be deployed flexibly in such a way to reduce complexity/bulkiness and better manage heat dissipated by the remote/extemal optical source.
  • a separate local oscillator may not be needed to be incorporated onto the same platform as the receiver in order to implement coherent detection since the remote/ external optical source provides the signal corresponding to the local oscillator used in coherent detection. Certain embodiments described herein may save cost, enable homodyne detection where no frequency recovery is needed (leading to further energy savings) and/or enable efficient use of space in the computing infrastructure hosting the coherent communication system.
  • Embodiments described herein provide an interconnection system between the sides of the coherent optical communication system 100.
  • the coherent optical communication system 100 refers to a coherent transmitter (first side transmitter 106) at one side and a coherent receiver (second side receiver 112) at the other side.
  • each side of the coherent optical communication system includes an optical transceiver.
  • coherent homodyne detection is implemented in one or both directions between the sides of the coherent optical communication system 100.
  • the optical communication connection 116 may comprise one or more optical fibers to facilitate communication of data between the sides of the coherent optical communication system.
  • the remote/extemal optical source may supply the first optical supply signal into ports of both sides of the coherent optical communication system such that the same optical source is shared by both sides of the coherent optical communication system.
  • One port corresponds to a local oscillator input for a coherent receiver.
  • the other port corresponds to the optical input to the transmitter (which may or may not be a coherent transmitter, depending on the set-up).
  • a coherent receiver may have a single-polarization optical front-end.
  • the DSP at the coherent receiver may not need to perform polarization recovery (e.g., due to use of polarization maintaining optics) or frequency offset recovery (e.g., due to using the same optical source the local oscillator and modulated signal).
  • the optical supply signal is in the O band (1260 nm to 1360 nm), where chromatic dispersion is low, so that DSP implemented by the receiver does not involve chromatic dispersion compensation.
  • other communication bands may still be used, and the relevant DSP implemented, if needed.
  • the first side communication system 104 is housed by a first package (e.g., a hardware platform).
  • the second side optical communication system may be housed by a second package (e.g., a hardware platform).
  • the first optical source 102 may be housed externally (i.e., remotely) to one or more of: the first package and the second package.
  • the first package may comprise electronic processing circuitry (e.g., a processor) communicatively coupled to the first side transmitter 106, which may be considered to provide an electrical-to-optical interface to allow electrical communication signals to be converted to optical communication signals (e.g., the first modulated signal).
  • the electronic processing circuitry is configured to cause the first side transmitter 106 to generate the first modulated signal and transmit the first modulated signal to the second side receiver 112.
  • the second package may comprise electronic processing circuitry communicatively coupled to the second side receiver 112, which may be considered to provide an electrical-to-optical interface to allow optical communications to be converted to electrical communications.
  • the electronic circuitry is configured to cause the second side receiver 112 to use the first optical supply signal to perform coherent detection on the first modulated signal.
  • the first package further comprises a first side receiver. In some embodiments, the second package further comprises a second side transmitter.
  • the second side receiver comprises a homodyne coherent receiver.
  • one or more of: the first side optical supply connection 108; second side optical supply connection 114 and the optical communication connection 116 comprise polarization maintaining optics (e.g., polarization maintaining fiber).
  • Embodiments described below include features of the coherent optical communication system 100.
  • FIG. 2 is a schematic diagram illustrating a computing system 200 according to an embodiment.
  • the computing system 200 comprises a coherent optical communication system corresponding to any of the embodiments described herein.
  • the computing system 200 is representative of an example implementation of a coherent optical communication system such as a large-scale packet switch or a high-performance computer. Reference numerals for features of the computing system 200 that correspond to or have similar functionality to features of the coherent optical communication system 100 are incremented by 100.
  • the computing system 200 comprises a first side communication system 204 and a second side communication system 210.
  • the first side communication system 204 is configured to receive an input 218 of first information (representative of digital data to be modulated by the first side transmitter 106). The first side communication system 204 is further configured to generate, by the first side transmitter 106, the first modulated signal based on the first information. The first side communication system 204 is further configured to transmit the first modulated signal to the second side communication system 210 via the optical communication connection 216. The second side communication system 210 is configured to receive, by the second side receiver 112, the first modulated signal. The second side communication system 210 is configured to perform coherent detection on the first modulated signal to extract the first information. The second side communication system 210 is further configured to output 220 the (demodulated) first information.
  • the first optical source 202 is remote to and shared between the first side communication system 204 and the second side communication system 210.
  • the same first optical source 202 could be shared between more than two of the side communication systems 204, 210, 222.
  • first side communication system 204 Although one-way communication from the first side communication system 204 to the second side communication system 210 is depicted, two-way communication between the first side communication system 204 and the second side communication system 210 is possible, as described below.
  • Figure 3 is a schematic diagram illustrating a coherent optical communication system 300 according to an embodiment. Reference numerals for features of the coherent optical communication system 300 that correspond to or have similar functionality to features of the coherent optical communication system 100 of Figure 1 are incremented by 200.
  • Figure 3 shows a scheme where the two sides of the coherent optical communication system 300 are connected by two optical links (e.g., two optical fibers) that are related to the optical communication connection 116 of Figure 1.
  • the coherent optical communication system comprises a first side communication system 304 and a second side communication system 310.
  • the first side communication system 304 comprises a first side transmitter 306.
  • the second side communication system 310 comprises a second side receiver 312.
  • the first side transmitter 306 transmits the first modulated signal to the second side receiver 312 via a first optical communication connection 316a (e.g., a first optical fiber).
  • the first side communication system 304 comprises a first side receiver 332.
  • the second side communication system 310 comprises a second side transmitter 334.
  • the optical communication connection 316 is further between the first side receiver 332 and the second side transmitter 334.
  • the optical communication connection 316 comprises a second optical communication connection 316b (e.g., a second optical fiber).
  • the second side transmitter 334 is configured to modulate the first optical supply signal (which could be considered to be a second optical supply signal in some embodiments) with second information to generate a second modulated signal.
  • the second side transmitter 334 is further configured to transmit the second modulated signal to the first side receiver 332 via the optical communication connection 316 (i.e., the second optical communication connection 316b).
  • the first side receiver 332 is configured to use the first optical supply signal (e.g., as a local oscillator) to demodulate the second modulated signal.
  • the first optical supply signal e.g., as a local oscillator
  • the coherent optical communication system 300 provides two-way communications between the two sides of the coherent optical communication system 300.
  • the first side receiver 332 is configured to perform coherent detection on the second modulated signal.
  • Figure 3 further depicts optical components to enable the first optical supply signal to be supplied to the first and second side communication systems 304, 310.
  • the coherent optical communication system 300 comprises a first coupler 330a, second coupler 330b and third coupler 330c (collectively 330).
  • the couplers 330 are optical components (such as beam splitters or beam combiners) that allow the optical supply signals to be split or combined, where needed, and direct the optical supply signals between components of the coherent optical communication system 300.
  • One or more optical fibers may be installed between the components of the coherent optical communication system 300 to allow the optical supply signals to be directed accordingly.
  • the couplers 330 and other optical components such as one or more optical fibers may be polarization maintaining components.
  • the distribution and positioning of the couplers 330 is an example and other optical set-ups are possible.
  • the first coupler 330a receives the first optical supply signal from the first optical source 302.
  • the first coupler 330a comprises a splitter to direct the first optical supply signal to both the second coupler 330b and the third coupler 330c.
  • the second coupler 330b is associated with the first side communication system 304.
  • the second coupler 330b is depicted as part of the first side communication system 304 (e.g., on the same hardware platform).
  • the second coupler 330b could be external to the first side communication system 304.
  • the second coupler 330b receives the first optical supply signal from the first optical source 302 via the first side optical supply connection 308.
  • the second coupler 330b comprises a splitter to split and direct the first optical supply signal to an input (e.g., a port) of the first side transmitter 306 (so that the first optical supply signal can be modulated) and an input (e.g., a port) of the first side receiver 332 (so that the first optical supply signal can be used as the local oscillator).
  • the third coupler 330c is associated with the second side communication system 310.
  • the third coupler 330c is depicted as part of the second side communication system 310 (e.g., on the same hardware platform).
  • the third coupler 330c could be external to the second side communication system 310.
  • the third coupler 330c receives the first optical supply signal from the first optical source 302 via the second side optical supply connection 314.
  • the third coupler 330c comprises a splitter to split and direct the first optical supply signal to an input (e.g., a port) of the second side transmitter 334 (so that the first optical supply signal can be modulated) and an input (e.g., a port) of the second side receiver 312 (so that the first optical supply signal can be used as the local oscillator).
  • One or more optical fibers and other optical components may be used to communicate the optical supply signals to/from the components described above.
  • Figure 4 is a schematic diagram illustrating a coherent optical communication system 400 according to an embodiment. Reference numerals for features of the coherent optical communication system 400 that correspond to or have similar functionality to features of the coherent optical communication system 300 of Figure 3 are incremented by 100.
  • Figure 4 shows a scheme where the two sides of the coherent optical communication system 400 are connected by a single communication link (rather than the two optical communication connections 316a, 316b of Figure 3).
  • the coherent optical communication system 400 comprises a first side communication system 404 and a second side communication system 410.
  • the first side communication system 404 comprises a first side transmitter 406.
  • the second side communication system 410 comprises a second side receiver 412.
  • the first side transmitter 406 transmits the first modulated signal to the second side receiver 412 via an optical communication connection 416 (e.g., an optical fiber).
  • the first side communication system 404 comprises a first side receiver 432.
  • the second side communication system 410 comprises a second side transmitter 434.
  • the optical communication connection 416 is further between the first side receiver 432 and the second side transmitter 434.
  • the second side transmiter 434 is configured to modulate a second optical supply signal with second information to generate a second modulated signal.
  • the second side transmiter 434 is further configured to transmit the second modulated signal to the first side receiver 432 via the optical communication connection 416 (i.e., the same connection as used to communication the first modulated signal).
  • the coherent optical communication system 400 comprises two optical sources (including a first optical source 402 and a second optical source 440).
  • the second optical source 440 is configured to generate the second optical supply signal.
  • a (first) wavelength of the first optical supply signal is different to a (second) wavelength of the second optical supply signal.
  • the majority of the spectral content of the first optical supply signal (comprising the first wavelength) does not overlap with the majority of the spectral content of the second optical supply signal (comprising the second wavelength) to avoid interference where two modulated signals use the same optical communication connection.
  • the spectrum of the second modulated signal may have a power that is a specified threshold (e.g., 20dB) lower than the power of the first modulated signal.
  • the spectrum of the first modulated signal may have a power that is a specified threshold (e.g., 20dB) lower than the power of the second modulated signal.
  • the first and second optical sources 402, 440 operate at different wavelengths. However, the optical supply signals generated by the first and second optical sources 402, 440 are still shared by the two sides of the coherent optical communication system 400.
  • a first optical supply signal (representing a first wavelength of the first optical source 402) is sent to the first side transmiter 406 (for modulation) and the second side receiver 412 (for the local oscillator), to implement a homodyne coherent communication therebetween.
  • a second optical supply signal (representing a second wavelength of the second optical source 440) is sent to the second side transmiter 434 (for modulation) and the first side receiver 432 (for the local oscillator), to implement a homodyne coherent communication therebetween.
  • the optical communication connection 416 comprises a common connection (e.g., a single optical fiber) between the first side communication system 404 and the second side communication system 410.
  • Figure 4 further depicts optical components to enable the first optical supply signal and the second optical supply signal to be supplied to the first and second side communication systems 404, 410.
  • the coherent optical communication system 400 comprises a first coupler 430a, second coupler 430b, third coupler 430c and fourth coupler 430d (collectively 430).
  • the couplers 430 are optical components (such as beam splitters or beam combiners) that allow the optical supply signals and/or modulated signals to be split or combined, where needed, and direct the optical supply signals and/or modulated signals between components of the coherent optical communication system 400.
  • One or more optical fibers may be installed between the components of the coherent optical communication system 400 to allow the optical supply signals and/or modulated signals to be directed accordingly.
  • the couplers 430 and other optical components such as one or more optical fibers may be polarization maintaining components. The distribution and positioning of the couplers 430 is an example and other optical set-ups are possible.
  • the optical communication connection 416 further comprises the first coupler 430a, which is associated with the first side communication system 404, and may or may not be on the same hardware platform as the first side communication system 404.
  • the optical communication connection 416 further comprises the second coupler 430b, which is associated with the second side communication system 410, and may or may not be on the same hardware platform as the second side communication system 410.
  • the first coupler 430a is configured to direct the first modulated signal from the first side transmitter 406 to the common connection.
  • the first coupler 430a is configured to direct the second modulated signal from the common connection to the first side receiver 432.
  • the second coupler 430b is configured to direct the second modulated signal from the second side transmitter 434 to the common connection.
  • the second coupler 430b is further configured to direct the first modulated signal from the common connection to the second side receiver 412.
  • the third coupler 430c receives the first optical supply signal from the first optical source 402.
  • the third coupler 430c comprises a splitter to direct the first optical supply signal to: (i) a port of the first side transmitter 406 (via a first side optical supply connection 408a) and (ii) to a port of the second side receiver 412 (via a second side optical supply connection 414a).
  • the fourth coupler 430d receives the second optical supply signal from the second optical source 440.
  • the fourth coupler 430d comprises a splitter to direct the second optical supply signal to: (i) a port of the first side receiver 432 (via a first side optical supply connection 408b) and (ii) to a port of the second side transmitter 434 (via a second side optical supply connection 414b).
  • the first side optical supply connection 408a, 408b (collectively 408) therefore supplies both the first and second optical supply signal to the first side communication system 404.
  • the second side optical supply connection 414a, 414b (collectively 414) therefore supplies both the first and second optical supply signal to the second side communication system 410.
  • the first side optical supply connection 408 is further configured to supply the second optical supply signal to the first side receiver 432. Further, the second side optical supply connection is further configured to supply the second optical supply signal to the second side transmitter 434.
  • One or more optical fibers and other optical components may be used to communicate the optical supply signals to/from the components described above.
  • Figure 5 is a schematic diagram illustrating a coherent optical communication system 500 according to an embodiment. Reference numerals for features of the coherent optical communication system 500 that correspond to or have similar functionality to features of the coherent optical communication system 400 of Figure 4 are incremented by 100.
  • Figure 5 is similar to Figure 4 in that the coherent optical communication system 500 comprises two optical sources. However, Figure 5 shows a scheme where a wavelength multiplexer and demultiplexer setup is used to reduce the number of connections (e.g., optical fibers) e.g., compared with the coherent optical communication system 400 of Figure 4.
  • a wavelength multiplexer and demultiplexer setup is used to reduce the number of connections (e.g., optical fibers) e.g., compared with the coherent optical communication system 400 of Figure 4.
  • the coherent optical communication system 500 comprises a first side communication system 504 and a second side communication system 510.
  • the first side communication system 504 comprises a first side transmitter 506.
  • the second side communication system 510 comprises a second side receiver 512.
  • the first side transmitter 506 transmits the first modulated signal to the second side receiver 512 via an optical communication connection 516 (e.g., an optical fiber).
  • the first side communication system 504 comprises a first side receiver 532.
  • the second side communication system 510 comprises a second side transmitter 534.
  • the optical communication connection 516 is further between the first side receiver 532 and the second side transmitter 534.
  • the second side transmiter 534 is configured to modulate a second optical supply signal with second information to generate a second modulated signal.
  • the second side transmiter 534 is further configured to transmit the second modulated signal to the first side receiver 532 via the optical communication connection 516 (e.g., the same connection as used to communication the first modulated signal).
  • the coherent optical communication system 500 comprises two optical sources (including a first optical source 502 and a second optical source 540).
  • the second optical source 540 is configured to generate the second optical supply signal.
  • a (first) wavelength of the first optical supply signal is different to a (second) wavelength of the second optical supply signal.
  • the coherent optical communication system 500 comprises a multiplexing system 542 comprising a multiplexer 544.
  • the coherent optical communication system 500 further comprises a first demultiplexer 546a and a second demultiplexer 546b. Further details of the distribution of the first and second optical supply signals are provided below.
  • the optical communication connection 516 further comprises a first coupler 530a and a second coupler 530b.
  • the first and second couplers 530a, 530b provide the same functionality as the first and second couplers 430a, 430b of the coherent optical communication system 400 of Figure 4.
  • the multiplexing system 542 further comprises a third coupler 530c.
  • the multiplexer 544 is configured to receive and multiplex: (i) the first optical supply signal from the first optical source 502 and (ii) the second optical supply signal from the second optical source 540.
  • the multiplexed signal comprising the first and second optical supply signals is directed to the third coupler 530c (e.g., via the same optical fiber).
  • the third coupler 530 splits the multiplexed signal (by power) so that the multiplexed signal is sent to: (i) the first demultiplexer 546a via a first side optical supply connection 508 and (ii) the second demultiplexer 546b via a second side optical supply connection 514.
  • the first demultiplexer 546 is associated with the first side communication system 504, and may or may not be on the same hardware platform as the first side communication system 504.
  • the second demultiplexer 546 is associated with the second side communication system 510, and may or may not be on the same hardware platform as the second side communication system 510.
  • the first demultiplexer 546a demultiplexes the multiplexed signal into the first optical supply signal (corresponding to the first wavelength, XI) and the second optical supply signal (corresponding to the second wavelength, X2).
  • the first optical supply signal is directed to a port of the first side transmitter 506.
  • the second optical supply signal is directed to a port of the first side receiver 532.
  • the second demultiplexer 546b demultiplexes the multiplexed signal into the first optical supply signal (corresponding to the first wavelength, XI) and the second optical supply signal (corresponding to the second wavelength, X2).
  • the first optical supply signal is directed to a port of the second side receiver 512.
  • the second optical supply signal is directed to a port of the second side transmitter 534.
  • One or more optical fibers and other optical components may be used to communicate the optical supply signals to/from the components described above.
  • the coherent optical communication system 500 of Figure 5 has fewer optical links (e.g., optical fibers) linking the components, which may reduce the complexity of setting up optical links.
  • Figure 6 is a schematic diagram illustrating a coherent optical communication system 600 according to an embodiment. Reference numerals for features of the coherent optical communication system 600 that correspond to or have similar functionality to features of the coherent optical communication system 500 of Figure 5 are incremented by 100.
  • Figure 6 is similar to Figure 5 in that the coherent optical communication system 500 comprises two optical sources. However, Figure 6 shows a scheme where a wavelength multiplexer part of the setup is removed.
  • the multiplexer 544 and the 1:2 power splitting provided by the coupler 530c are replaced by a 2x2 coupler/splitter (referred to herein as coupler/splitter 630c).
  • the coupler/splitter 630c may be considered as a multiplexing system 642. However, such a coupler/splitter 630c may reduce the optical loss associated with the multiplexing system 542 of Figure 5.
  • the coherent optical communication system 600 comprises a first side communication system 604 and a second side communication system 610.
  • the first side communication system 604 comprises a first side transmitter 606.
  • the second side communication system 610 comprises a second side receiver 612.
  • the first side transmitter 606 transmits the first modulated signal to the second side receiver 612 via an optical communication connection 616 (e.g., an optical fiber).
  • an optical communication connection 616 e.g., an optical fiber
  • the first side communication system 604 comprises a first side receiver 632.
  • the second side communication system 610 comprises a second side transmitter 634.
  • the optical communication connection 616 is further between the first side receiver 632 and the second side transmitter 634.
  • the second side transmitter 634 is configured to modulate a second optical supply signal with second information to generate a second modulated signal.
  • the second side transmitter 634 is further configured to transmit the second modulated signal to the first side receiver 632 via the optical communication connection 616 (e.g., the same connection as used to communication the first modulated signal).
  • the coherent optical communication system 600 comprises two optical sources (including a first optical source 602 and a second optical source 640).
  • the second optical source 640 is configured to generate the second optical supply signal.
  • a (first) wavelength of the first optical supply signal is different to a (second) wavelength of the second optical supply signal.
  • the coherent optical communication system 600 comprises a multiplexing system 642 comprising the coupler/splitter 630c, a first demultiplexer 646a and a second demultiplexer 646b.
  • the details of the receipt and distribution of the first and second optical supply signals by the first and second demultiplexers 646a, 646b are similar to the corresponding features in the coherent optical communication system 500 of Figure 5.
  • the optical communication connection 616 further comprises a first coupler 630a and a second coupler 630b.
  • the first and second couplers 630a, 630b provide the same functionality as the first and second couplers 530a, 530b of the coherent optical communication system 500 of Figure 5.
  • the coupler/splitter 630c is configured to receive and combine: (i) the first optical supply signal from the first optical source 602 and (ii) the second optical supply signal from the second optical source 640.
  • the coupler/splitter 630c the directs the combined optical supply signals to the first and second demultiplexers 646a, 646b.
  • One or more optical fibers and other optical components may be used to communicate the optical supply signals to/from the components described above.
  • the optical communication system of Figure 6 has more optical links (e.g., optical fibers) linking the components.
  • the optical loss associated with the multiplexing system 642 is reduced.
  • Figure 7 is a schematic diagram illustrating a coherent optical communication system 700 according to an embodiment.
  • the setup of the coherent optical communication system 700 is related to the setup of the coherent optical communication system of Figure 3, but also has similarities to certain other embodiments, as will be described below.
  • reference numerals for features of the coherent optical communication system 700 that correspond to or have similar functionality to features of the coherent optical communication system 300 of Figure 3 are incremented by 400.
  • Figure 7 shows a scheme where the two sides of the coherent optical communication system 700 are connected by a single optical link (e.g., a single optical fiber).
  • a single optical link e.g., a single optical fiber
  • the coherent optical communication system 700 comprises a first side communication system 704 and a second side communication system 710.
  • the first side communication system 704 comprises a first side transmitter 706.
  • the second side communication system 710 comprises a second side receiver 712.
  • the first side transmitter 706 transmits the first modulated signal to the second side receiver 712 via the optical communication connection 716.
  • the first side communication system 704 comprises a first side receiver 732.
  • the second side communication system 710 comprises a second side transmitter 734.
  • the optical communication connection 716 is further between the first side receiver 732 and the second side transmitter 734.
  • the second side transmitter 734 is configured to modulate the first optical supply signal (which could be considered to be a second optical supply signal in some embodiments) with second information to generate a second modulated signal.
  • the second side transmitter 734 is further configured to transmit the second modulated signal to the first side receiver 732 via the optical communication connection 716.
  • Figure 7 further depicts optical components to enable the first optical supply signal to be supplied to the first and second side communication systems 704, 710.
  • the coherent optical communication system 700 comprises a first coupler 730a, second coupler 730b, third coupler 730c, fourth coupler 730d and fifth coupler 730c (collectively 730).
  • the couplers 730 are optical components (such as beam splitters or beam combiners) that allow the various optical signals to be split or combined, where needed, and direct the various optical signals between components of the coherent optical communication system 700.
  • One or more optical fibers may be installed between the components of the coherent optical communication system 700 to allow the optical supply signals to be directed accordingly.
  • the couplers 730 and other optical components such as one or more optical fibers may be polarization maintaining components.
  • the distribution and positioning of the couplers 730 is an example and other optical set-ups are possible.
  • first coupler 730a corresponds to (and has the same functionality as) the first coupler 330a of Figure 3.
  • the second coupler 730b corresponds to (and has the same functionality as) the second coupler 330b of Figure 3.
  • the third coupler 730c corresponds to (and has the same functionality as) the third coupler 330c of Figure 3.
  • the coherent optical communication system 700 has similarities with other embodiments.
  • the fourth coupler 730d corresponds to (and has the same functionality as) the first coupler 430a of Figure 4.
  • the fifth coupler 730e corresponds to (and has the same functionality as) the second coupler 430b of Figure 4.
  • the setup of Figure 7 may be at risk of interference due to the same wavelength being used on the same optical communication connection 716.
  • the setup by properly designing the setup to render lumped and distributed reflections negligible, it is possible to use the same wavelength in the two communication directions.
  • Such a setup may reduce component costs as compared to certain other embodiments.
  • One or more optical fibers and other optical components may be used to communicate the optical supply signals to/from the components described above.
  • Figure 8 is a schematic diagram illustrating a coherent optical communication system 800 according to an embodiment. Reference numerals for features of the coherent optical communication system 800 that correspond to or have similar functionality to features of the coherent optical communication system 400 of Figure 4 are incremented by 400.
  • the setup of the coherent optical communication system 800 is different to previous embodiments in that the optical supply signal(s) are directly supplied to one side, not the two sides, of the coherent optical communication system 800.
  • the optical supply signal(s) are still supplied to both sides, but not directly to one of these sides.
  • a first side communication system 804 of the coherent optical communication system 800 is considered to be a “tail” end that does not directly receive an optical supply signal from a first optical source 802 or second optical source 840 of the coherent optical communication system 800.
  • a second side communication system 810 of the coherent optical communication system 800 is considered to be a “head” end that directly receives an optical supply signal from the first optical source 802 and the second optical source 840.
  • the first side communication system 804 comprises a first side transmitter 806 and a first side receiver 832.
  • the second side communication system comprises a second side receiver 812 and a second side transmitter 834.
  • the operation of the transmitters and receivers is the similar to the embodiments of Figures 3-7 (i.e., the transmitters and receivers implement coherent communication and communicate modulated signals via the optical communication connection 816).
  • the differences in the setup between the coherent optical communication system 800 and e.g., the coherent optical communication system 400 of Figure 4 are now discussed.
  • the first optical source 802 is configured to generate the first optical supply signal (e.g., at the first wavelength).
  • a coupler 830 receives and splits the first optical supply signal, and directs the first optical supply signal towards the second side communication system 810 via a first side optical supply connection 808a (e.g., a first optical fiber) and a second side optical supply connection 814a (e.g., a second optical fiber).
  • the first optical supply signal and corresponding modulated signals generated based on the first optical supply signal are labeled with the letter “G” in Figure 8.
  • the coupler 830 may or may not be on the same hardware platform as the second side communication system 810.
  • the first optical supply signal (i.e., a carrier signal), G, is received by a combiner (labeled BC) 850 of the second side communication system 810.
  • the combiner 850 may comprise a spectral beam combiner.
  • the combiner 850 may combine optical signals/beams at different wavelengths from two directions and direct the combined optical signals along the same path, e.g., via an optical fiber, to another component.
  • an optical circulator 852 of the second side communication system 810 receives the first optical supply signal, G, from the combiner 850 and directs the first optical supply signal, G, to the first side communication system 804 via the optical communication connection 816.
  • An optical circulator 854 of the first side communication system 804 receives the first optical supply signal, G, from the optical communication connection 816.
  • the optical circulator 854 directs the received first optical supply signal, G, to a splitter 856 (labeled BS) such as a band splitter.
  • BS splitter 856
  • the splitter 856 directs (in this case, reflects) the first optical supply signal, G, to a port of the first side transmitter 806.
  • the first side transmitter 806 modulates the first side optical supply signal, G, to generate a first modulated signal, G (depicted by the double lobes in Figure 8).
  • the first modulated signal, G is directed to the optical circulator 854.
  • the optical circulator 854 (of the first side communication system 804) further directs the first modulated signal, G, to the second side communication system 810 via the optical communication connection 816.
  • the optical circulator 852 receives the first modulated signal, G, and directs the first modulated signal to a port of the second side receiver 812.
  • the first optical supply signal, G is directed from the coupler 830 to a local oscillator port of the second side receiver 812 via the second side optical supply connection 814.
  • the first optical supply signal, G represents a carrier signal (for use as the local oscillator signal).
  • the first modulated signal, G represents the digital data modulated and transmitted by the first side transmitter 806.
  • the second side receiver 812 implements coherent detection to demodulate the first modulated signal.
  • the second optical source 840 is configured to generate the second optical supply signal and direct the second optical supply signal to the second side transmitter 834 via a connection (e.g., an optical fiber) that could be considered to be both a first side optical supply connection 808b and a second side optical supply connection 814b.
  • a connection e.g., an optical fiber
  • the second optical supply signal and corresponding modulated signals generated based on the second optical supply signal are labeled with the letter “R” in Figure 8.
  • the second side transmitter 834 is configured to modulate the second optical supply signal, R, to generate the second modulated signal.
  • An additional optical coupler (not shown for brevity) reinserts the carrier signal (i.e., the second optical supply signal) into the signal path since the action of the modulation may remove the carrier signal from the resultant second modulated signal.
  • the (second) carrier signal and the second modulated signal are directed to the combiner 850.
  • the second carrier signal and the second modulated signal, R are directed (via the optical circulator 852, the optical communication connection 816 and the optical circulator 854) to the splitter 856.
  • the splitter directs (in this case, transmits) the (different wavelength) second carrier signal and the second modulated signal, R, to an optical filter system 858 (labeled OFS) such as a narrow-band optical filter combined with any other optical components to separate and direct the signals along the different paths.
  • the optical filter system 858 therefore splits the second carrier signal from the second modulated signal.
  • the second carrier signal is directed to a local oscillator port of the first side receiver 832.
  • the second modulated signal (with the second carrier signal removed, and hence has no DC content) is directed to the other port of the first side receiver 832.
  • the first side receiver 832 implements coherent detection to demodulate the second modulated signal.
  • the second optical carrier removed from the second optical supply signal as a result of the second side transmitter 834 generating the second modulated signal is reinserted in the second side communication system for receipt by the first side receiver 832.
  • the first side receiver 832 uses the reinserted optical carrier as a local oscillator for coherent detection.
  • the first side optical supply connection 808a is configured to supply the first optical supply signal, G, to the first side transmitter 806 via the second side communication system 810 and the optical communication connection 816.
  • first side optical supply connection 808b is further configured to supply the second optical supply signal, R, to the first side receiver 832 via the second side communication system 810 and the optical communication connection 816.
  • the first side optical supply connection 808a, 808b comprises the optical communication connection 816.
  • the second side optical supply connection 814a is configured to supply the first optical supply signal, G, to the second side receiver 812 via the second side communication system 810.
  • the second side optical supply connection 814b is configured to supply the second optical supply signal, R, to the second side transmitter 834 via the second side communication system 810.
  • the modulated signals may have no DC component. This is the case in coherent systems that use modulation/demodulation schemes such as, but not limited to, QPSK, QAM, 8B10B, 64B66B and Manchester coding. After the encoding, the spectrum may change from a single lobe centered at the optical carrier frequency to two lobes around the carrier.
  • modulation/demodulation schemes such as, but not limited to, QPSK, QAM, 8B10B, 64B66B and Manchester coding.
  • both sides of the coherent optical communication system 800 implement coherent detection (i.e., two-way coherent detection).
  • the second optical source 840 could be considered to be a remote source (with respect to the first side communication system 804).
  • both the first and second optical sources 802, 840 are considered to be remote from the first side communication system 804. Since both the first and second optical supply signals are directed into the second side communication system 810, the first and second optical sources 802, 840 may be considered to be physically closer to the second side communication system 810 than the first side communication system 804. However, in some embodiments, both the first and second optical sources 802, 840 are still remote/extemal to the second side communication system 810.
  • first and second optical sources 802, 840 could be considered to be on or part of the same platform as the second side communication system 810.
  • the higher sensitivity of coherent detection may facilitate the first optical source 802 being proximal to the second side communication system 810 and distal to the first side communication system 804, in spite of the power loss through the components described previously.
  • Providing the first and second optical sources 802, 840 as remote to the first side communication system 804 (and without a direct optical supply connection to the first side communication system 804) may provide additional deployment flexibility e.g., where it is difficult or more expensive to deploy a remote/extemal optical source proximal to the first side communication system 804. In this manner, coherent homodyne detection can be flexibly deployed in a wider range of scenarios while reducing the complexity and/or cost of the optical setup.
  • Figure 9 is a schematic diagram illustrating a coherent optical communication system 900 according to an embodiment. Reference numerals for features of the coherent optical communication system 900 that correspond to or have similar functionality to features of the coherent optical communication system 800 of Figure 8 are incremented by 100.
  • the setup of the coherent optical communication system 900 is similar to the setup of the coherent optical communication system 800 of Figure 8. Similar to Figure 8, the coherent optical communication system 900 comprises a first optical source 902, a first side communication system 904, a first side transmitter 906, a first side optical supply connection 908a, b, a second side communication system 910, a second side receiver 912, a second side optical supply connection 914a, b, an optical communication connection 916, a coupler 930, a first side receiver 932, a second side transmitter 934, a second optical source 940, a combiner 950, an optical circulator 952, an additional optical circulator 954 and a splitter 956.
  • the first side transmitter 906 and the second side receiver 912 implement coherent communication, as in the previous embodiments.
  • the second side transmitter 934 and the first side receiver 932 do not implement coherent communication.
  • a direct detection scheme is implemented whereby a local oscillator signal is not needed to demodulate the second modulated signal provided by the second side transmitter 934.
  • coherent detection-based communication is enabled.
  • direct detection-based communication is used.
  • the first side receiver 832 is configured to perform direct detection on the second modulated signal.
  • Direct detection may be considered to be a lower cost and lower performance scheme as compared to coherent detection.
  • the second optical source 840 may provide a sufficient high power optical signal to enable the use of direct detection at the first side communication system 904 in view of the lower sensitivity of direct detection.
  • the higher sensitivity of coherent detection may facilitate the first optical source 902 being proximal to the second side communication system 910 and distal to the first side communication system 904, in spite of the power loss through the components described previously.
  • the scheme of Figure 9 does not need the carrier reinsertion depicted in the second side communication system 810 and carrier removal at the optical filter system 858 in the first side communication system 804.
  • an optical carrier is removed from the second optical supply signal as a result of the second side transmitter 834 generating the second modulated signal.
  • the second side receiver 912 uses an optical carrier of the first optical supply signal as a local oscillator to perform coherent detection on the first modulated signal generated by the first side transmitter 906.
  • a coupler may be used to inject the optical supply signal (corresponding to local oscillator signal) into a signal path leading to a port of the coherent receiver (e.g., for receipt by a photodetector) so that the local oscillator signal interferes with the modulated signal.
  • the phases of the modulated signal and the local oscillator signal may be different, meaning that non-linear DSP may be needed for phase recovery.
  • the additional DSP adds to the computational complexity.
  • an optical phase shifter (e.g., controlled by the DSP) may be used to impart a phase delay on the optical supply signal to reduce or avoid the need for DSPbased phase recovery.
  • Such a scheme may become practical based on integrated photonics.
  • the DSP is much simpler (for example, it rotates the phase to maximize the received power).
  • a requirement may be to make the control time faster than the optical source phase variation time.
  • the product of laser linewidth and control time is much lower than one.
  • the control time may need to be shorter than 100 ns.
  • the in-phase component of the modulated signal is recovered.
  • a phase diversity scheme may be used.
  • an optical supply signal (local oscillator signal) is split and directed to a first photodetector with associated DSP and a second photodetector with associated DSP.
  • the modulated signal is also split and directed to the first and second photodetector.
  • the optical supply signal is split such that a first component of the optical supply signal is directed towards the first photodetector with a 7i/2 phase delay.
  • the modulated signal is split such that a first component of the modulated signal is also directed towards the first photodetector.
  • the first component of the optical supply signal and the first component of the modulated signal are combined at a coupler to form a quadrature, Q, signal that is directed to the first photodetector.
  • the optical supply signal is split such that a second component of the optical supply signal is directed towards the second photodetector.
  • the modulated signal is split such that a second component of the modulated signal is also directed towards the second photodetector.
  • the second component of the optical supply signal and the second component of the modulated signal are combined at a coupler to form an in-phase, I, signal that is directed to the second photodetector.
  • Figure 10 is a flowchart of a method 1000 in a coherent optical communication system according to an embodiment.
  • the method 1000 may be implemented in any of the coherent optical communication systems described herein. Reference is made to Figure 1 in the description of the method 1000.
  • the method 1000 comprises, at block 1002, generating, with a first optical source 102 of the optical communication system 100, a first optical supply signal.
  • the method 1000 comprises, at block 1004, supplying the first optical supply signal to a first side transmitter 106 of the first side communication system 104.
  • the method 1000 comprises, at block 1006, supplying the first optical supply signal to a second side receiver 112 of the second side communication system 110.
  • the method 1000 comprises, at block 1008, using the first side transmitter 106 to: modulate the first optical supply signal with first information to generate a first modulated signal; and transmit the first modulated signal to the second side receiver 112.
  • the method 1000 comprises, at block 1010, receiving, by the second side receiver 112, the first modulated signal.
  • the method 1000 comprises, at block 1012, performing, by the second side receiver 112, coherent detection on the first modulated signal using the first optical supply signal.
  • Figure 11 is a flowchart of a method 1100 in a coherent optical communication system according to an embodiment.
  • the method 1100 may be implemented in any of the coherent optical communication systems described in relation to Figures 3-9. Reference is made to Figure 3 in the description of the method 1100.
  • the method 1110 may comprise the blocks of the method 1000, and may be implemented before or after the blocks of the method 1000, or at the same time as the method 1000 is implemented.
  • the method 1100 comprises, at block 1102, using a second side transmitter 334 of the second side communication system 310 to: modulate a second optical supply signal with second information to generate a second modulated signal; and transmit the second modulated signal to a first side receiver 332 of the first side communication system 304.
  • the method 1100 further comprises, at block 1104, receiving, by the first side receiver 332, the second modulated signal.
  • the method 1100 further comprises, at block 1106, demodulating, by the first side receiver 332, the second modulated signal.
  • the demodulating at block 1106 may include coherent detection or direct detection.
  • Figure 12 is a schematic diagram illustrating a processor 1200 and a machine- readable medium 1202 (e.g., a memory) for implementing certain embodiments, including any of the methods and related embodiments described herein.
  • the machine-readable medium 1202 stores instructions 1204 which, when executed by the processor 1200, instruct the processor 1200 to implement such methods and related embodiments.
  • a machine-readable medium may include a non-transitory machine-readable medium, where the term “non- transitory” does not encompass transitory propagating signals. Otherwise, any appropriate memory may be used to store the instructions 1204.
  • the processor 1200 and machine-readable medium 1202 may implement functionality of components such as a digital signal processor (e.g., of a transmitter configured to generate a modulated signal or of a receiver configured to demodulate the modulated signal, as described herein).
  • a transmitter or a receiver of any embodiment described herein may comprise the processor 1200 and machine-readable medium 1202 combination.
  • a processor (which includes one or more processors) may include a central processing node (CPU), application specific integrated circuit (ASIC), field programmable gate array (FPGA) or the like.
  • a memory may include one or several types of memory suitable for the processor, such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, solid state disk, hard disk drive, etc.
  • the methods of the present disclosure may be implemented in hardware, or as software modules running on one or more processors. The methods may also be carried out according to the instructions of a computer program, and the present disclosure also provides a computer readable medium having stored thereon a program for carrying out any of the methods described herein.
  • a computer program embodying the disclosure may be stored on a computer readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

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

Abstract

Dans un mode de réalisation, il est prévu un système de communication optique cohérent (100). Le système de communication optique cohérent comprend une première source optique (102) configurée pour générer un premier signal d'alimentation optique ; un système de communication de premier côté (104) comprenant un émetteur de premier côté (106) ; une connexion d'alimentation optique de premier côté (108) configurée pour fournir le premier signal d'alimentation optique à l'émetteur de premier côté ; un système de communication de second côté (110) comprenant un récepteur de second côté (112) ; une connexion d'alimentation optique de second côté (114) configurée pour fournir le premier signal d'alimentation optique au récepteur de second côté ; et une connexion de communication optique (116) entre l'émetteur de premier côté et le récepteur de second côté. L'émetteur de premier côté est configuré pour : moduler le premier signal d'alimentation optique avec de premières informations pour générer un premier signal modulé ; et transmettre le premier signal modulé au récepteur de second côté par l'intermédiaire de la connexion de communication optique. Le récepteur de second côté est configuré pour utiliser le premier signal d'alimentation optique pour réaliser une détection cohérente sur le premier signal modulé.
PCT/EP2023/055486 2023-03-03 2023-03-03 Communication optique cohérente Pending WO2024183874A1 (fr)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190326995A1 (en) * 2016-04-12 2019-10-24 Cable Television Laboratories, Inc Fiber communication systems and methods
WO2022089123A1 (fr) * 2020-10-29 2022-05-05 华为技术有限公司 Appareil et système de transmission optique

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190326995A1 (en) * 2016-04-12 2019-10-24 Cable Television Laboratories, Inc Fiber communication systems and methods
WO2022089123A1 (fr) * 2020-10-29 2022-05-05 华为技术有限公司 Appareil et système de transmission optique

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