Abstract: A shaping encoder configured to generate a stream of output bit-words, wherein different bit-word values have different respective rates of occurrence to cause the optical transmitter connected to the shaping encoder to transmit constellation symbols of relatively high energy less frequently than constellation symbols of relatively low energy. The stream of output bit-words is self-referencing in that it encodes one of the input bitstreams applied to the shaping encoder in one or more designated bits of the output bit-words and is generated using a dither stream that can be recovered by the shaping decoder solely based on those one or more designated bits. As a result, some of the circuitry used in the shaping encoder at the transmitter and in the shaping decoder at the receiver can be identical, which can advantageously be used, e.g., to reduce the production costs.

Abstract: A shaping encoder configured to generate a stream of output bit-words, wherein different bit-word values have different respective rates of occurrence to cause the optical transmitter connected to the shaping encoder to transmit constellation symbols of relatively high energy less frequently than constellation symbols of relatively low energy. The stream of output bit-words is self-referencing in that it encodes one of the input bitstreams applied to the shaping encoder in one or more designated bits of the output bit-words and is generated using a dither stream that can be recovered by the shaping decoder solely based on those one or more designated bits. As a result, some of the circuitry used in the shaping encoder at the transmitter and in the shaping decoder at the receiver can be identical, which can advantageously be used, e.g., to reduce the production costs.

Abstract: We disclose a multichannel optical transceiver having a first optical channel used for client-data transmission over an optical fiber and a second optical channel that enables secure transport of encryption keys over the same optical fiber. In an example embodiment, the first channel uses a first carrier wavelength at which the optical fiber supports a single guided mode. The second channel uses a second carrier wavelength at which the optical fiber supports multiple guided modes. The secure transport of encryption keys can be achieved, e.g., by scrambling the encryption-key data over multiple space-division-multiplexed optical signals transmitted by way of the multiple guided modes. The securely transported encryption keys can then be used to enable the client data transmitted using the first optical channel to be encrypted to frustrate or prevent eavesdropping along the fiber length.

Abstract: A shaping encoder configured to generate a stream of output bit-words, wherein different bit-word values have different respective rates of occurrence to cause the optical transmitter connected to the shaping encoder to transmit constellation symbols of relatively high energy less frequently than constellation symbols of relatively low energy. The stream of output bit-words is self-referencing in that it encodes one of the input bitstreams applied to the shaping encoder in one or more designated bits of the output bit-words and is generated using a dither stream that can be recovered by the shaping decoder solely based on those one or more designated bits. As a result, some of the circuitry used in the shaping encoder at the transmitter and in the shaping decoder at the receiver can be identical, which can advantageously be used, e.g., to reduce the production costs.

Abstract: We disclose a multichannel optical transceiver having a first optical channel used for client-data transmission over an optical fiber and a second optical channel that enables secure transport of encryption keys over the same optical fiber. In an example embodiment, the first channel uses a first carrier wavelength at which the optical fiber supports a single guided mode. The second channel uses a second carrier wavelength at which the optical fiber supports multiple guided modes. The secure transport of encryption keys can be achieved, e.g., by scrambling the encryption-key data over multiple space-division-multiplexed optical signals transmitted by way of the multiple guided modes. The securely transported encryption keys can then be used to enable the client data transmitted using the first optical channel to be encrypted to frustrate or prevent eavesdropping along the fiber length.

Abstract: A network switch having one or more multi-endpoint (MEP) optical transceivers configured to provide an interface for optical data transport through the corresponding network. The use of MEP optical transceivers advantageously enables the network switch to be compatible with multiple network topologies. As a result, various embodiments of the disclosed network switch may be used to provide a builder and/or an operator of the corresponding network with a great deal of flexibility in choosing a network topology and/or degree of redundancy better suitable for the network's intended purpose and/or application without having to change some of the underlying hardware.

Abstract: A communication network that employs a plurality of multi-endpoint (MEP) optical transceivers in a leaf (or functionally similar) layer thereof. The use of MEP optical transceivers enables the communication network to support a pair of parallel paths for any source/destination pair of network nodes. In an example configuration, data packets that flow through one of the parallel paths go from the source node to the destination node via an electronic packet switch in the network's spine layer. Data packets that flow through another one of the parallel paths go from the source node to the destination node via an optical cross-connect switch. In operation, a network controller may dynamically select which one of the parallel paths to enable for each particular source/destination pair of network nodes, with the selection being made, e.g., based on the data volume to be transmitted between the two nodes.

Abstract: We disclose an optical transport system configured to transport the same data using two different channels of an optical transport link in a manner that enables an optical receiver to use direct detection of the optical power received through each of the two channels to measure the in-phase and quadrature components of the modulating electromagnetic field. In an example embodiment, an optical carrier of the modulated optical signal transported using the first of the two channels and an optical carrier of the modulated optical signal transported using the second of the two channels have a fixed relative phase offset of approximately 90 degrees. The resulting ability of the optical receiver to measure each of the in-phase and quadrature components of the modulating electromagnetic field advantageously enables the optical receiver to perform electronic signal equalization, including but not limited to electronic dispersion compensation.

Abstract: We disclose a network switch having one or more multi-endpoint (MEP) optical transceivers configured to provide an interface for optical data transport through the corresponding network. The use of MEP optical transceivers advantageously enables the network switch to be compatible with multiple network topologies. As a result, various embodiments of the disclosed network switch may be used to provide a builder and/or an operator of the corresponding network with a great deal of flexibility in choosing a network topology and/or degree of redundancy better suitable for the network's intended purpose and/or application without having to change some of the underlying hardware.

Abstract: We disclose a communication network that employs a plurality of multi-endpoint (MEP) optical transceivers in a leaf (or functionally similar) layer thereof. The use of MEP optical transceivers enables the communication network to support a pair of parallel paths for any source/destination pair of network nodes. In an example configuration, data packets that flow through one of the parallel paths go from the source node to the destination node via an electronic packet switch in the network's spine layer. Data packets that flow through another one of the parallel paths go from the source node to the destination node via an optical cross-connect switch. In operation, a network controller may dynamically select which one of the parallel paths to enable for each particular source/destination pair of network nodes, with the selection being made, e.g., based on the data volume to be transmitted between the two nodes.

Abstract: A disclosed optical transport system is configured to use hierarchical modulation for better utilization of the available BER margin, e.g., to increase data-transport capacity per carrier wavelength in the system. For example, hierarchical modulation may be used to reduce the number of carrier wavelengths assigned to support a given volume of bidirectional data transport between a set of nodes in an optical backbone network. An embodiment of the disclosed optical transport system can advantageously be constructed by modifying a conventional WDM system, e.g., by adding configurable hierarchical-layer mappers at some of the nodes and modifying some of the ROADMs used therein to enable a drop-and-continue mode of operation.

Abstract: We disclose communication methods using which a cluster of network nodes is interconnected via an optical interconnect and an electrical switch engine. A communication method executed at a master optical transceiver coupled to one side of the optical interconnect enables that transceiver to establish an optical communication link with any one of a plurality of slave optical transceivers coupled to the other side of the optical interconnect. A communication method executed at a slave optical transceiver enables that transceiver to communicate with the master optical transceivers without having its own light source and, instead, modulating data onto previously un-modulated signaling dimensions of the incoming optical waveforms, which are then turned around and broadcast back to the master optical transceivers.

Abstract: We disclose an optical transport system configured to transport an additional data stream using hierarchical modulation. In an example embodiment, copies of the additional data stream are encoded onto enhancement layers of multiple hierarchically modulated optical waves transported through the system in a multiplexed manner. An optical receiver coupled to a remote end of the optical transport link is configured to use this redundant transmission of the additional data stream to improve the bit-error rate thereof, e.g., by first extracting the signal components corresponding to the enhancement layers of the different hierarchically modulated optical waves and then combining the extracted signal components in a manner that tends to reduce, through averaging, the relative magnitude of noise in the combined signal compared to that in the individual extracted signal components. The disclosed signal-transmission format is suitable for various types of multiplexing, e.g.

Abstract: We disclose demultiplexing processing for an adaptive MIMO equalizer of a receiver of multiplexed communication signals implemented in a manner that significantly reduces the occurrence of singularities at the equalizer output without a significant concomitant increase in the required computational power. The receiver includes an equalizer controller that operates to dynamically track the degree of correlation of one or more pairs of equalized signals outputted by the MIMO equalizer and to use the tracking results to configure the MIMO equalizer in a manner that substantially prevents any two outputs of the MIMO equalizer from converging to the same state. In an example embodiment, the degree of correlation can be determined in a computationally efficient manner by identifying and comparing quadrants in which complex values produced at the different outputs of the MIMO equalizer are located over a plurality of time slots.

Abstract: We disclose communication methods using which a cluster of network nodes is interconnected via an optical interconnect and an electrical switch engine. A communication method executed at a master optical transceiver coupled to one side of the optical interconnect enables that transceiver to establish an optical communication link with any one of a plurality of slave optical transceivers coupled to the other side of the optical interconnect. A communication method executed at a slave optical transceiver enables that transceiver to communicate with the master optical transceivers without having its own light source and, instead, modulating data onto previously un-modulated signaling dimensions of the incoming optical waveforms, which are then turned around and broadcast back to the master optical transceivers.

Abstract: We disclose an optical transport system configured to transport the same data using two different channels of an optical transport link in a manner that enables an optical receiver to use direct detection of the optical power received through each of the two channels to measure the in-phase and quadrature components of the modulating electromagnetic field. In an example embodiment, an optical carrier of the modulated optical signal transported using the first of the two channels and an optical carrier of the modulated optical signal transported using the second of the two channels have a fixed relative phase offset of approximately 90 degrees. The resulting ability of the optical receiver to measure each of the in-phase and quadrature components of the modulating electromagnetic field advantageously enables the optical receiver to perform electronic signal equalization, including but not limited to electronic dispersion compensation.

Abstract: We disclose a communication system in which a cluster of network nodes is interconnected using an optical interconnect and an electrical switch engine. A bidirectional communication channel between any two of the network nodes can be set up using two bidirectional optical links established through the optical interconnect and one bidirectional electrical link configured to connect the ends of the two bidirectional optical links through the switch engine. The optical interconnect has a structure that enables the communication system to be (re)configurable for a desired level of oversubscription. Some embodiments of the communication system can advantageously be used in a data-center network.

Abstract: We disclose an optical transport system configured to transport an additional data stream using hierarchical modulation. In an example embodiment, copies of the additional data stream are encoded onto enhancement layers of multiple hierarchically modulated optical waves transported through the system in a multiplexed manner. An optical receiver coupled to a remote end of the optical transport link is configured to use this redundant transmission of the additional data stream to improve the bit-error rate thereof, e.g., by first extracting the signal components corresponding to the enhancement layers of the different hierarchically modulated optical waves and then combining the extracted signal components in a manner that tends to reduce, through averaging, the relative magnitude of noise in the combined signal compared to that in the individual extracted signal components. The disclosed signal-transmission format is suitable for various types of multiplexing, e.g.

Abstract: A disclosed optical transport system is configured to use hierarchical modulation for better utilization of the available BER margin, e.g., to increase data-transport capacity per carrier wavelength in the system. For example, hierarchical modulation may be used to reduce the number of carrier wavelengths assigned to support a given volume of bidirectional data transport between a set of nodes in an optical backbone network. An embodiment of the disclosed optical transport system can advantageously be constructed by modifying a conventional WDM system, e.g., by adding configurable hierarchical-layer mappers at some of the nodes and modifying some of the ROADMs used therein to enable a drop-and-continue mode of operation.

Abstract: A digitally locking coherent receiver and a method of coherently receiving a data signal. One embodiment of the receiver includes: (1) a detector configured to recover a composite signal with respect to a local oscillator signal, the composite signal being a combination of a data signal and a reference signal, and (2) a digital signal processor (DSP) communicably coupled to the detector and configured to recognize and compensate for drift in the local oscillator signal with respect to the reference signal.