Out-of-band communication channel of subcarrier-based optical communication system

Abstract

In a network or system, a hub or master node can communicate with multiple leaf nodes or secondary nodes. The hub node can operate or have a capacity greater than the capacity of the leaf node. Therefore, relatively inexpensive leaf nodes can be deployed to receive data carrying optical signals from the hub node and provide data carrying optical signals to the hub node. For example, one or more connections can couple each leaf node to the hub node, whereby each connection can include, for example, one or more spans or segments of an optical fiber, an optical amplifier, an optical splitter / combiner, and an optical add / drop multiplexer. Optical subcarriers can be sent through such connections, each of which carries a data stream. As the bandwidth or capacity requirements of the leaf node change, the number of subcarriers, and therefore the amount of data provided to each node, may change accordingly.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application Nos. 16 / 578,390, 16 / 578,391, 16 / 578,393, 16 / 578,396, 16 / 578,397, filed on September 22, 2019, and 16 / 578,398, filed on September 23, 2019, each of which claims the benefit of U.S. Provisional Patent Application No. 62 / 813,151, filed on March 4, 2019, the contents of all of the above applications are hereby incorporated by reference in their entirety. Technical Field

[0003] The present disclosure relates to optical communication systems. Background Art

[0004] In some optical communication systems, multiple optical signals are multiplexed onto an optical fiber, each optical signal having a corresponding wavelength, and each optical signal is modulated to carry a different data stream. In such systems, a laser and a modulator may be provided to generate each optical signal. Thus, in order to increase the capacity of such systems, additional lasers, modulators, and associated circuits are employed. Therefore, as capacity increases, the costs associated with such systems may increase. Thus, a more cost-effective network that requires fewer components, such as those described above, is desired.

[0005] In addition, conventional optical communication systems may include high-speed circuits and components for generating high-speed optical signals at the transmitting end of the system. At the receiving end, corresponding high-speed circuits may be provided to detect incoming data and forward or distribute such data to lower capacity nodes. Therefore, there is also a need to reduce costs by providing high-capacity signals to cheaper, low-capacity nodes without using intermediate high-speed circuits and components at the receiving end of the system.

[0006] Furthermore, in some conventional optical communication systems, data may be sent as a series of frames, each frame including a payload portion, which includes client or user data, and a header or overhead portion, which includes operations, administration, and maintenance ("OAM") information associated with the system. As network complexity increases, the amount of such control or OAM information also increases, which may limit the amount of client data sent. Therefore, there is also a need to send OAM information more efficiently so that more client data can be sent. Summary of the invention

[0007] According to the present disclosure, a network or system is provided in which a hub or master node can communicate with multiple remote nodes, such as leaf nodes or secondary nodes. The hub node can operate or have a capacity that can be greater than the leaf node. Therefore, relatively inexpensive leaf nodes can be deployed, which receive data carrying optical signals from the hub node and provide the data carrying optical signals to the hub node. One or more connections can couple each leaf node to the hub node, whereby each connection can include, for example, one or more spans or segments of an optical fiber, an optical amplifier, an optical splitter / combiner, and an optical add / drop multiplexer. Consistent with aspects of the present disclosure, optical subcarriers can be sent through such connections, each of which carries a data stream. Subcarriers can be generated by a combination of lasers and modulators, thereby eliminating the need for multiple lasers and modulators and reducing costs. In addition, subcarriers can be utilized using multiple access techniques (e.g., frequency division multiplexing multiple access (FDMA)), whereby a given subcarrier group is detected at a corresponding leaf node. In addition, as the bandwidth or capacity requirements of the leaf node change, the number of subcarriers and therefore the amount of data provided to each node may change accordingly. In another example, each subcarrier within the dedicated subcarrier group may carry OAM or control channel information to the corresponding leaf node, and such information may be used by the leaf node to configure the leaf node to have a desired bandwidth or capacity.

[0008] Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

[0009] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments and, together with the description, serve to explain the principles of the invention.

[0010] Other aspects, features, and advantages will be apparent from the detailed description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 and Figure 2 is a block diagram illustrating an example of a network consistent with aspects of the present disclosure;

[0012] Figure 3 is a block diagram illustrating examples of a primary node and a secondary node, respectively, according to another aspect of the present disclosure;

[0013] Figure 4 is an example of a spectrum diagram showing an optical subcarrier consistent with aspects of the present disclosure;

[0014] Figure 5 is a block diagram illustrating an example of a network consistent with another aspect of the present disclosure;

[0015] Figure 6 is an example of a spectrum diagram showing an optical subcarrier consistent with another aspect of the present disclosure;

[0016] Figure 7 is a block diagram illustrating an example of a network consistent with another aspect of the present disclosure;

[0017] Figure 8 is an example of a spectrum diagram showing an optical subcarrier consistent with another aspect of the present disclosure;

[0018] Fig. 9 An example of a master node transmitter consistent with the present disclosure is shown;

[0019] Fig.10a is a block diagram illustrating an example of a master node transmitter digital signal processor (DSP) consistent with another aspect of the present disclosure;

[0020] Fig.10b A portion of a master node transmitter DSP consistent with aspects of the present disclosure is shown in greater detail;

[0021] Fig.10c A portion of a master node transmitter DSP consistent with another aspect of the present disclosure is shown in greater detail;

[0022] Fig.11a An example of a secondary node receiver consistent with the present disclosure is shown; and

[0023] Fig.11b An example of a loan associated with a secondary node is shown;

[0024] Fig.12 An example of a secondary node receiver DSP consistent with the present disclosure is shown;

[0025] Fig.13a An example of a secondary node transmitter consistent with aspects of the present disclosure is shown;

[0026] Figures 13b to 13j is an example of a spectrum diagram of subcarriers output from a secondary node consistent with additional aspects of the present disclosure;

[0027] Figure 13k is an example of a spectrum diagram showing a combined subcarrier provided to a master node receiver;

[0028] Fig.14 An example of a master node receiver consistent with aspects of the present disclosure is shown;

[0029] Fig.15 An example of a guard band consistent with aspects of the present disclosure is shown;

[0030] Fig.16 An example of a mesh network configuration consistent with another aspect of the present disclosure is shown;

[0031] Fig.17 , Figure 18a-Figure 18c as well as Fig.19 A diagram illustrating that subcarrier data allocation may vary over time consistent with another aspect of the present disclosure;

[0032] Fig. 20 is a flow chart of a method for determining time of flight and data transmission timing according to aspects of the present disclosure;

[0033] Fig.21 is a flow chart of a method for scheduling time slots to avoid conflicts;

[0034] Fig. 22 is a graph showing an example of hub request and leaf response times and corresponding TOF times.

[0035] Fig.23 is a table showing an example of TOF data associated with the second node.

[0036] Fig.24 An example timing diagram is shown.

[0037] Fig.25 An example of a transceiver consistent with the present disclosure is shown that includes a common laser shared between a transmitter and a receiver. DETAILED DESCRIPTION

[0038] Reference will now be made in detail to the current embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Generally, in the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. The terms "hub," "hub node," and "master node" are used interchangeably herein. Additionally, the terms "leaf," "leaf node," and "secondary node" are used interchangeably herein.

[0039] Figure 1An example of an aggregation network 100 consistent with the present disclosure is shown in which a master node 110 can communicate with a plurality of secondary nodes 112-j through 112-m, which can sometimes be individually or collectively referred to as secondary nodes 112. In one example, secondary node 112 is remote from master node 110. Master node 110 can send optical subcarriers in a downstream direction onto an optical communication path 111, which, as described in more detail below, like each of optical communication paths 113-j through 113-m, can include one or more fiber segments, and one or more optical amplifiers, reconfigurable add / drop multiplexers (ROADMs), or other fiber optic communication devices. Splitter 114 can be coupled to one end of optical communication path 111 to receive the optical subcarriers and provide a power split portion of each subcarrier to a corresponding one of secondary nodes 112-j through 112-m via a corresponding one of optical communication paths 113-j through 113-m.

[0040] like Figure 1 As further shown, the master node 110 has a data capacity for receiving n Gbits / second of data (e.g., data streams) for transmission to the secondary nodes 112. Each secondary node 112 can receive and output a portion of the data input to the master node 110 to a user or client. In this example, the secondary nodes 112-j, 112-k, 112-1, and 112-m output j Gbits / second, k Gbits / second, l Gbits / second, and m Gbits / second of data (data streams), respectively, whereby the sum of j, k, l, and m can be equal to n (where j, k, l, m, and n are positive numbers).

[0041] Figure 2 The transmission of additional subcarriers in the upstream direction from the secondary nodes 112-j to 112-m to the primary node 110 is shown. Figure 2 As further shown, each of the secondary nodes 112-j to 112-m may send a corresponding set of subcarriers or one subcarrier via a corresponding one of the optical communication paths 115-1 to 115-m to the optical combiner 116. The optical combiner 116 may in turn combine the optical subcarriers received from the secondary nodes 112-j to 112-m onto the optical communication path 117. The optical communication paths 115-1 to 115-m and 117 may have a similar structure to the optical communication paths 111 and 112-1 to 112-m.

[0042] like Figure 2As further shown, each of the secondary nodes 112-j through 112-m receives a respective data stream having a respective data rate of j Gbits / sec, k Gbits / sec, l Gbits / sec, and m Gbits / sec. At the master node 110, the data contained in these streams may be output such that the aggregate data provided by the master node 110 is n Gbits / sec, such that n may be equal to the sum of j, k, l, and m, as described above.

[0043] In another example, the subcarriers may be sent in the upstream and downstream directions on the same optical communication path. Specifically, selected subcarriers may be sent in the downstream direction from the primary node 110 to the secondary node 112, and other subcarriers may be sent in the upstream direction from the secondary node 112 to the primary node 110.

[0044] In some embodiments, the network 100 may include additional master nodes and / or secondary nodes and optical communication paths, fewer master nodes and / or secondary nodes and optical communication paths, or may have a configuration different from that described above. For example, the network 100 may have a mesh configuration or a point-to-point configuration.

[0045] Figure 3 Master node 110 is shown in greater detail. Master node 110 may include a transmitter 202 that provides downstream modulated optical signals including subcarriers, and a receiver 204 that may receive upstream subcarriers carrying data originating from secondary nodes (eg, nodes 112-j through 112-m).

[0046] Figure 3 Also shown is a block diagram of one of the secondary nodes 112, which may include receiver circuitry 302 for receiving one or more subcarriers transmitted downstream and transmitter circuitry 304 for transmitting one or more subcarriers in an upstream direction.

[0047] Figure 4 An example of a transmission spectrum that can accommodate twenty subcarriers (SC0 to SC19) that can be output from the master node transmitter 202 is shown. Each of the subcarriers SC0 to SC19 has a corresponding frequency in frequencies f0 to f19. In one example, the subcarriers SC0 to SC19 are Nyquist subcarriers, which are a group of optical signals, each of which carries data, where (i) the spectrum of each such optical signal within the group is sufficiently non-overlapping so that the optical signals remain distinguishable from each other in the frequency domain, and (ii) the group of optical signals is generated by modulation of light from a single laser. In general, each subcarrier can have a spectral bandwidth at least equal to the Nyquist frequency, which is determined by the baud rate of such subcarrier.

[0048] As described above, each of the secondary nodes 112 may include components that are less expensive than components included in the primary node 110. Therefore, the bandwidth or data capacity of the secondary nodes 112 may be less than the capacity associated with the primary node 110, such that the capacity associated with each secondary node 112 is less than the capacity of the primary node 110.

[0049] For example, Figure 4 As further shown in FIG. 1 , the primary node 110 may have a bandwidth BW-P such that data carried by each of the subcarriers SC1 to SC20 may be processed, recovered, and output from the transmitter 202 or received from the receiver 204. On the other hand, in this example, each of the secondary nodes 112-j to 112-m may have a respective one of bandwidths BWj to BWm such that each secondary node has data processing capabilities or is capable of processing and outputting data carried by up to nine subcarriers.

[0050] As described above, to reduce network costs, in some examples, less expensive components (e.g., optical components and certain electrical components) may be able to process signals over a limited frequency range or bandwidth that is smaller than the signal frequency range that can be accommodated by the optical and electrical components in the primary node 110. For example, electrical components such as digital-to-analog (DACs), analog-to-digital converters (ADCs), and digital signal processors (DSPs), as well as optical components such as modulators in the secondary node 112 may have an associated bandwidth that is less than the corresponding but more expensive components in the primary node 110.

[0051] Figure 4 1. Example bandwidths for each of the secondary nodes 112 are further shown in FIG. That is, bandwidth BWj associated with secondary node 112-j extends over or includes a range of frequencies f0 to f8 including subcarriers SC0 to SC8, respectively; bandwidth BWk associated with secondary node 112-k extends over or includes a range of frequencies f5 to f13 including subcarriers SC5 to SC13, respectively; bandwidth BWI associated with secondary node 112-1 extends over or includes a range of frequencies f10 to f18 including subcarriers SC10 to SC18, respectively; and bandwidth BWm associated with secondary node 112-m extends over or includes a range of frequencies f11 to f19 including subcarriers SC11 to SC19, respectively. On the other hand, bandwidth BW-P of primary node 110 includes the entire range of frequencies f0-f19 of subcarriers SC0 to SC19.

[0052] like Figure 4As further shown, certain subcarriers have frequencies that fall within multiple bandwidths. For example, subcarriers SC5 and SC6 have frequencies that fall within bandwidth BWj and bandwidth BWk. Therefore, data carried by such subcarriers can be detected and selectively output from secondary node 112-j or 112-k. For example, if a customer requires more data to be received and output from secondary node 112-k and less data to be output from secondary node 112-j, nodes 112-j and 112-k can be controlled or dynamically configured so that data carried by subcarriers SC5 and SC6 can be allocated to and output from secondary node 112-k, but not secondary node 112-j. Therefore, as described in more detail below, the data output from each node can adapt to customer needs that change over time.

[0053] like Figure 4 As further shown, certain subcarriers, such as subcarriers SC2, SC7, SC12, and SC17, may be designated or dedicated to carry information related to parameters or characteristics associated with one or more of the secondary nodes 112. For example, such parameters may correspond to an amount of data, a data rate, or a capacity to be output by one or more of the secondary nodes. Specifically, such subcarriers may carry information, for example, to configure or adjust the amount of data, the capacity, or the data rate of data output from the secondary nodes 112-j to 112-m, respectively, as described above. In another example, each of these subcarriers may carry user or customer data (also referred to as client data) in addition to control information. Figure 4 In the example shown, only subcarriers SC2, SC7, SC12 and S17 are transmitted.

[0054] In another example, subcarriers SC2, SC7, SC12, and SC17 are modulated to carry control or OAM information and related data corresponding to parameters associated therewith, such as the capacity and status of node 112. In another example, subcarrier SC2 is modulated to carry such control and parameter information associated with node 112-j, subcarrier SC7 is modulated to carry such control and parameter information associated with node 112-k, subcarrier SC12 is modulated to carry such control and parameter information associated with node 112-l, and subcarrier SC17 is modulated to carry such control and parameter information associated with node 112-m. In another example, as described below with respect to Figure 19-Figure 24 As described in detail, such a SC is modulated to carry information related to parameters associated with the timing and scheduling of data transmission from the node 112 to the master node 110.

[0055] Figure 5 An example is shown in which each of the secondary nodes 112-j through 112-m outputs an equal amount of user data originating from the primary node 110, and Figure 6 shows how subcarriers SC0 to SC19 may be allocated or associated to each secondary node 112 to satisfy Figure 5 In addition, Figure 5 and Figure 6 In the example shown, the aggregate data input to the master node 110 may be 20 Gbit / s (n=20), and each of the secondary nodes 112 outputs an equal portion of such data, i.e., 5 Gbit / s, such that j=k=l=m=5. In other words, based on the control information received by the node 112-j, e.g., the data

[0056] Here, subcarriers SC0, SC1, SC3, and SC4 may be allocated to secondary node 112-j (subcarrier SC2 is also allocated to secondary node 112-j and carries control channel information for secondary node 112-j); subcarriers SC5, SC6, SC8, and SC9 may be allocated to secondary node 112-k (subcarrier SC7 is also allocated to secondary node 112-k and carries control channel information for secondary node 112-k); subcarriers SC10, SC11, SC113, and SC14 may be allocated to secondary node 112-1 (subcarrier SC12 is also allocated to secondary node 112-1 and carries control channel information for secondary node 112-1); and subcarriers SC15, SC16, SC18, and SC19 may be allocated to secondary node 112-m (subcarrier SC17 is also allocated to secondary node 112-m and carries control channel information for secondary node 112-m). In this example, each subcarrier may have an associated data rate of 1 Gbit / sec.

[0057] In other words, based on the control information carried by subcarrier SC2 received by node 112-j, for example, a first portion of the data associated with subcarriers SC0, SC1, SC3, and SC4, which is input to DSP 902 described below, and any user data carried by subcarrier SC2 is output from node 112-j. Additionally, based on the control information carried by subcarrier SC7 received by node 112-k, for example, a second portion of the data associated with subcarriers SC5, SC6, SC8, and SC9, which is input to DSP 902, and any user data carried by subcarrier SC7 is output from node 112-k.

[0058] Figure 7 Another example is shown in which the data allocation to the secondary nodes 112-j through 112-m may be changed based on, for example, changing capacity requirements. Figure 6The illustrated subcarrier allocations are associated with a later point in time at which node 112-j, for example, may require more data than node 112-k. Here, control information is carried by subcarriers SC2, SC7, SC12, and SC17. Figure 8 shows how subcarriers SC0 to SC19 may be allocated to or associated with each secondary node 112 to satisfy Figure 7 . In this example, secondary node 112-j is allocated the maximum data capacity, i.e., data carried by seven subcarriers (SC0, SC1 to SC3-SC6, and SC8) and any client data that may be carried by subcarrier SC2; secondary node 112-k is allocated 1 / 3 (i.e., 3 / 9) of the maximum data capacity, i.e., data carried by three subcarriers (SC9-SC11) and any client data that may be carried by subcarrier SC7; secondary node 112-l is allocated 5 / 9 of the maximum data capacity, i.e., data carried by four subcarriers (SC13-SC16) and any client data that may be carried by subcarrier SC12; and secondary node 112-m is allocated 1 / 3 (i.e., 3 / 9) of the maximum data capacity, i.e., data carried by two subcarriers (SC18 and SC19) and any client data that may be carried by subcarrier SC17.

[0059] That is to say, in the above Figure 8 In the depicted example, based on the additional (third) control information carried by subcarrier SC2 received by node 112-j, for example, a third portion of data associated with subcarriers SC0, SC1, SC3-SC6, and SC8 input to DSP 902 and any user data carried by subcarrier SC2 is output from node 112-j. Additionally, based on the (fourth) control information carried by subcarrier SC7 received by node 112-k, for example, a fourth portion of data associated with subcarriers SC9-SC11 input to DSP 902 and any user data carried by subcarrier SC7 is output from node 112-k.

[0060] Thus, by transmitting control information to the secondary nodes, the amount of data, e.g., the data rate, allocated for the output of each secondary node 112 may be controlled or varied over time based on such control information. In the examples discussed above, the control information may identify the subcarriers associated with each node, and thus the amount of data or data rate allocated to each node based on the number of subcarriers carrying data to be output from that node. As described above, such allocation may change dynamically, e.g., based on changing data traffic demands in the network 100, and such allocation information may, for example, be carried by selected or dedicated subcarriers, such as subcarriers SC2, SC7, SC12, and SC17, as described above.

[0061] Next reference Fig. 9 and Figure 10a-Figure 10c To describe data allocation and subcarrier transmission.

[0062] Fig. 9 The transmitter 202 of the master node 110 is shown in more detail. The transmitter 202 includes a plurality of circuits or switches SW, as well as a transmitter DSP (TX DSP) 902 and a D / A and optical block 901. In this example, twenty switches (SW-0 to SW-19) are shown, but more than Fig. 9 , or more or fewer switches than those shown in . In some instances, each switch may have two inputs: a first input may receive user data, and a second input may receive control information or a signal (CNT). Each switch SW-0 to SW-19 may receive a corresponding one of the control signals SWC-0 to SWC-19 output from a control circuit 971, which may include a microprocessor, a field programmable gate array (FPGA), or other processor circuits. Based on the received control signal, each switch SW-0 to SW19 selectively outputs any one of the data streams D-0 to D-19, or a control signal CNT-0 to CNT-19. The control signal CNT may be any combination of configuration bits for control and / or monitoring purposes. For example, the control signal CNT may include instructions to one or more secondary nodes 112 to change the data output from such secondary nodes 112, such as by identifying the subcarrier associated with such data. In another example, the control signal may include a series of known bits used in the secondary node 112 to "train" the receiver to detect and process such bits so that the receiver can further process subsequent bits. In another example, the control channel CNT includes information that can be used by the polarization mode dispersion (PMD) equalizer circuit 1125 discussed below to correct errors caused by polarization rotation of the X and Y components of one or more subcarriers (SC). In another example, the control information CNT is used to recover or correct the phase difference between the laser emitting side laser 908 and the local oscillator laser 1110 in each secondary node 112. This detected phase difference can be referred to as a cycle slip. In another example, the control information CNT can be used to recover, synchronize or correct the timing difference between the clocks provided in the master node (110) and the secondary node 112.

[0063] In another example, one or more switches SW may be omitted and the control signal CNT may be provided directly to the DSP 902. In addition, each input to the DSP 902, such as the FEC encoder 1002 described below (see Fig.10a ) input, in another example, receiving a combination of the control information described above and user data.

[0064] In yet another example, the control signal CNT includes information related to the number of subcarriers that can be output from each of the secondary nodes 112. Figure 10a-Figure 10c Although such description is related to the primary node DSP 902, similar circuitry may be included in the secondary node TX DSP 1302 (FIG. 13) to adjust or control the number of subcarriers output therefrom.

[0065] Based on the outputs of switches SW-0 to SW-19, the DSP 902 can provide multiple outputs to the D / A and optical block 901, which includes digital-to-analog conversion (DAC) circuits 904-1 to 904-4 that convert digital signals received from the DSP 902 into corresponding analog signals. The D / A and optical block 901 also includes driver circuits 906-1 to 906-2 that receive the analog signals from the DACs 904-1 to 904-4 and adjust the voltage or other characteristics of these analog signals to provide drive signals to corresponding modulators in the modulators 910-1 to 910-4.

[0066] The D / A and optical block 901 also includes modulators 910-1 to 910-4, each of which may be, for example, a Mach-Zehnder modulator (MZM) that modulates the phase and / or amplitude of the optical output from the laser 908. Fig. 9 As further shown, light output from laser 908 (also included in block 901) is split such that a first portion of the light is provided to a first MZM pair including MZMs 910-1 and 910-2, and a second portion of the light is provided to a second MZM pair including MZMs 910-3 and 910-4. The first portion of the light is further split into third and fourth portions such that the third portion is modulated by MZM 910-1 to provide an in-phase (I) component of an X (or TE) polarization component of a modulated optical signal, and the fourth portion is modulated by MZM 910-2 and fed to phase shifter 912-1 to shift the phase of such light by 90 degrees to provide a quadrature (Q) component of the X polarization component of the modulated optical signal. Similarly, the second portion of the light is further split into fifth and sixth portions such that the fifth portion is modulated by MZM 910-3 to provide an I component of the Y (or TM) polarization component of the modulated optical signal, and the sixth portion is modulated by MZM 910-4 and fed to phase shifter 912-2 to shift the phase of such light by 90 degrees so as to provide a Q component of the Y polarization component of the modulated optical signal.

[0067] The optical outputs of MZMs 910-1 and 910-2 are combined to provide an X-polarized optical signal including I and Q components and are fed to a polarization beam combiner (PBC) 914 provided in block 901. In addition, the outputs of MZMs 910-3 and 910-4 are combined to provide an optical signal that is fed to a polarization rotator 913 (which is further provided in block 901), which rotates the polarization of such optical signal to provide a modulated optical signal having a Y (or TM) polarization. The Y-polarized modulated optical signal is also provided to PBC 914, which combines the X and Y polarized modulated optical signals to provide a polarization multiplexed ("dual polarized") modulated optical signal onto, for example, an optical fiber 916, which can be included as a section of optical fiber in the optical communication path 111, for example.

[0068] The polarization multiplexed optical signal output from the D / A and optical block 401 includes the above-mentioned subcarriers SC0-SC19, such that each subcarrier has X and Y polarization components and I and Q components. In addition, each subcarrier SC0 to SC19 can be associated with or correspond to a corresponding output of the outputs of switches SW-0 to SW-19. In an example, switches SW2, SW7, SW12, and SW17 can provide control information carried by a corresponding one of control signals CNT-2, CNT-7, CNT-12, and CNT-17 to DSP 902. Based on such control signals, DSP 902 provides outputs that cause optical subcarriers SC2, SC7, SC12, and SC17 to carry data indicating the control information carried by CNT-2, CNT-7, CNT-12, and CNT-17, respectively, such as Figure 4 , Figure 6 and Figure 8 In addition, the remaining subcarriers SC0, SC1, SC3 to SC6, SC8 to SC11, SC13 to SC16, and SC18 to SC20 carry information indicating a corresponding one of the data streams D-0, D-1, D-3 to D-6, D-8 to D-11, D-13 to D-16, and D-18 to D-20 output from a corresponding one of the switches SW0, SW1, SW3 to SW-6, SW-8 to SW11, SW13 to SW16, and SW18 to SW20, as shown. Figure 4 , Figure 6 and Figure 8 As shown further.

[0069] Fig.10aAn example of the TX DSP 902 is shown in more detail. The TX DSP 902 may include FEC encoders 1002-0 to 1002-19, each of which may receive a corresponding output from a plurality of outputs of switches SW0 to SW19. The FEC encoders 1002-0 to 1002-19 perform forward error correction encoding on a corresponding one of these switch outputs, for example, by adding parity bits to the received data. The FEC encoders 1002-0 to 1002-19 may also provide timing skew between subcarriers to correct for skew caused by the link between the above-mentioned nodes 110 and 112-j to 112-m. In addition, the FEC encoders 1002-0 to 1002-19 may interleave the received data.

[0070] Each of the FEC encoders 1002-0 to 1002-19 provides an output to a corresponding circuit in a plurality of bit-to-symbol circuits 1004-0 to 1004-19 (collectively referred to herein as "1004"). Each bit-to-symbol circuit 1004 can map a coded bit to a symbol on a complex plane. For example, the bit-to-symbol circuit 1004 can map four bits to a symbol in a dual-polarization QPSK constellation. Each circuit in the bit-to-symbol circuit 1004 provides a first symbol having a complex representation XI+j*XQ associated with a corresponding one of the switch outputs (e.g., D-0) to the DSP portion 1003. Data indicating such a first symbol is carried by the X-polarization component of each subcarrier SC0-SC19.

[0071] Each bit-to-symbol circuit 1004 may also provide a second symbol having a complex representation YI+j*YQ, which is also associated with a corresponding output of switches SW0-SW19. However, data indicative of such a second symbol is carried by the Y polarization component of each of subcarriers SC-0 to SC-19.

[0072] In one example, such a mapping carried by approximately circuits 1004-0 to 1004-19 defines a specific modulation format for each subcarrier. That is, such a circuit may define a mapping for all optical subcarriers indicating a binary phase shift keying (BPSK) modulation format, a quadrature phase shift keying (QPSK) modulation format, or an m quadrature amplitude modulation (QAM, where m is a positive integer, such as 4, 8, 16, or 64) format. In another example, one or more of these optical subcarriers may have a modulation format different from that of other optical subcarriers. That is, one of these optical subcarriers has a QPSK modulation format, while another optical subcarrier has a different modulation format, such as 8-QAM or 16-QAM. In another example, one of these optical subcarriers has an 8-QAM modulation format, while another optical subcarrier has a 16QAM modulation format. Thus, while all optical subcarriers may carry data at the same data and / or baud rate, consistent with aspects of the present disclosure, one or more optical subcarriers may carry data at a different data or baud rate than one or more other optical subcarriers. Additionally, modulation formats, baud rates, and data rates may change over time, depending on, for example, capacity requirements. Adjustment of these parameters may be accomplished, for example, by applying appropriate signals to the mapper 1004 based on control information or data described herein and communication of such data between the hub and leaf nodes as further disclosed herein.

[0073] like Fig.10a As further shown, each first symbol from each circuit in the bit-to-symbol circuit 1004 is provided to a corresponding buffer in the first overlap and save buffers 1005-0 to 1005-19, which can buffer, for example, 256 symbols (collectively referred to herein as overlap and save buffers 1005). Each of the overlap and save buffers 1005 can receive 128 first symbols or another number of such symbols at a time from the corresponding circuit in the bit-to-symbol circuit 1004. Therefore, the overlap and save buffer 1005 can combine the 128 new symbols from the bit-to-symbol circuit 1005 with the previous 128 symbols received from the bit-to-symbol circuit 1005.

[0074] Each overlap and save buffer 1005 provides an output in the time domain to a corresponding one of the fast Fourier transform (FFT) circuits 1006-0 to 1006-19 (collectively referred to as "FFT 1006"). In one example, the output includes 256 symbols or other number of symbols. Each FFT in FFT 1006 converts the received symbols to the frequency domain using or based on, for example, a fast Fourier transform. Each FFT in FFT 1006 can provide frequency domain data to a bin and switch blocks 1021-0 to 1021-19. As discussed in more detail below, the bin and switch block 1021 includes, for example, a memory or register, also referred to as a frequency bin (FB) or point, which stores the frequency components associated with each subcarrier SC.

[0075] The selected frequency bin FB is as follows Fig.10b As shown. Such a group of frequency bins FB is associated with a given subcarrier. Thus, for example, a first group of frequency bins FB0-0 to FB0-n is associated with SC0, while a second group of frequency bins FB19-0 to FB19-n is associated with SC19 (where n is a positive integer). Fig.10b As further shown, each of the frequency bins FB is also coupled to a corresponding one of the switches SW. For example, each of the frequency bins FB0-0 to FB0-n is coupled to a corresponding one of the switches SW0-0 to SW0-n, and each of FB19-0 to FB19-n is coupled to a corresponding one of the switches or switch circuits SW19-0 to SW19-n.

[0076] Each switch SW selectively provides frequency domain data output from one of the FFT circuits 1006-0 to 1006-19 or a predetermined value, such as 0. In order to block or eliminate the transmission of a particular subcarrier, the switches SW associated with a set of frequency bins FB associated with the subcarrier are configured to provide a zero value to the corresponding frequency bin. Thus, for example, to block subcarrier SC0, switches SW0-0' to SW0-n' provide a zero (0) value to the corresponding frequency bins in the frequency bins FB0-0 to FB0-n. As described below, further processing of the zero (0) value by the replicator component 1007 and other components and circuits in the DSP 902 results in a drive signal provided to the modulator 910 such that the subcarrier SC0 is omitted from the optical output of the modulator.

[0077] On the other hand, switch SW' can be configured to provide the output of FFT 1006, i.e., frequency domain data FD, to the corresponding frequency bin FB. Further processing of the contents of frequency bin FB by replicator component 1007 and other circuits in DSP 902 results in a drive signal provided to modulator 910, whereby, based on such drive signal, an optical subcarrier is generated corresponding to the frequency bin grouping associated with the subcarrier.

[0078] In the example discussed above, switches SW0-0' to SW0-n' provide frequency domain data FD0-0 to FD-n from FFT 1006-0 to a corresponding one of switches SW0-0 to SW0-n. These switches in turn provide the frequency domain data to a corresponding one of frequency bins FB0-0 to FB0-n for further processing, as described in more detail below.

[0079] Each of the replicator components or circuits or 1007-0 to 1007-19 can replicate the contents of the frequency bin FB and store the contents in a corresponding one of the multiple replicator components (e.g., for T / 2-based filtering of a subcarrier). Such replication may increase the sampling rate. In addition, the replicator components or circuits 1007-0 to 1007-19 can arrange or align the contents of the frequency bins to fall within the bandwidth associated with the pulse shaping filter circuits 1008-0 to 1008-19 described below.

[0080] Each of the pulse shaping filter circuits 1008-0 through 1008-19 may apply a pulse shaping filter to data stored in 512 frequency bins of a respective one of the plurality of replicator components or circuits 1007-0 through 1007-19 to provide a respective one of a plurality of filtered outputs that are multiplexed and subjected to an inverse FFT as described below. The pulse shaping filter circuits 1008-1 through 1008-19 calculate transitions between symbols and a desired subcarrier spectrum so that the subcarriers may be spectrally packed together for transmission, e.g., with close frequency spacing. The pulse shaping filter circuits 1008-0 through 1008-19 may also be used to introduce timing skew between subcarriers to correct for artifacts caused by, for example, Figure 1 The timing skew caused by the links between the nodes shown in . The multiplexer component 1009 (which may include a multiplexer circuit or a memory) may receive the filtered outputs from the pulse shaping filter circuits 1008-0 to 1008-19 and multiplex or combine these outputs together to form an element vector.

[0081] Next, the IFFT circuit or component 1010-1 may receive the element vector and provide a corresponding time domain signal or data based on an inverse fast Fourier transform (IFFT). In one example, the time domain signal may have a rate of 64G samples / second. Take the last buffer or memory circuit 1011-1, for example, can select the last 1024 samples or other number of samples from the output of the IFFT component or circuit 1010-1 and provide the samples to DACs 904-1 and 904-2 at a rate of 64G samples / second (see Fig. 9). As described above, DAC 904-1 is associated with the in-phase (I) component of the Xpol signal, and DAC 904-2 is associated with the quadrature (Q) component of the Ypol signal. Thus, consistent with the complex representation XI+jXQ, DAC 904-1 receives a value associated with XI, and DAC 904-2 receives a value associated with jXQ. Fig. 9 As indicated, based on these inputs, DACs 904-1 and 904-2 provide analog outputs to MZMD 906-1 and MZMD 906-2, respectively.

[0082] like Fig.10a As further shown, each of the bit-to-symbol circuits 1004-0 through 1004-19 outputs a corresponding one of the symbols representing the data carried by the Y polarization component of the polarization multiplexed modulated optical signal output on the optical fiber 916. As described above, these symbols may have a complex representation YI+j*YQ. Each such symbol may be processed by each of the overlap and save buffers 1015-0 to 1015-19, each of the FFT circuits 1016-0 to 1016-19, each of the replicator components or circuits 1017-0 to 517-19, pulse shaping filter circuits 1018-0 to 1018-19, multiplexer or memory 1019, IFFT 1010-2, and taking the last buffer or memory circuit 1011-2 to provide a processed symbol having a representation YI+j*YQ in a manner similar or the same as discussed above for generating a processed symbol XI+j*XQ output from the last circuit 1011-1. In addition, the symbol components YI and YQ are provided to DACs 904-3 and 904-4, respectively ( Fig. 9 ). Based on these inputs, DACs 904-3 and 904-4 provide analog outputs to MZMD 906-3 and MZMD 906-4, respectively, as described above.

[0083] although Fig.10a DSP 902 is shown as including a particular number and arrangement of functional components, but in some implementations, DSP 902 may include additional functional components, fewer functional components, different functional components, or a different arrangement of functional components. Furthermore, the number of overlap and save buffers, FFTs, replicator circuits, and pulse shaping filters associated with the X component may generally be equal to the number of switch outputs, and the number of these circuits associated with the Y component may also be equal to the number of switch outputs. However, in other examples, the number of switch outputs may be different than the number of these circuits.

[0084] As described above, based on the outputs of the MZMDs 906-1 to 906-4, a plurality of optical subcarriers SC0 to SC19 may be output to the optical fiber 916 ( Fig. 9 )superior.

[0085] Consistent with aspects of the present disclosure, the number of subcarriers transmitted from the primary node 110 to the secondary node 112 may vary over time based on, for example, capacity requirements at the primary node and the secondary nodes. For example, if less downstream capacity is initially required at one or more secondary nodes, the transmitter 202 in the primary node 110 may be configured to output fewer optical subcarriers. On the other hand, if more capacity is subsequently required, the transmitter 202 may provide more optical subcarriers.

[0086] Additionally, if adjustments need to be made to a particular secondary node 112 based on changes in capacity requirements, for example, the output capacity of such secondary node may be increased or decreased by increasing or decreasing the number of optical subcarriers output from the secondary node in a corresponding manner.

[0087] As described above, by storing and then processing zeros (0) or other predetermined values ​​in the frequency bin FB group associated with a given subcarrier SC, the subcarrier can be removed or eliminated. To add or restore such a subcarrier, the frequency domain data output from the FFT 1006 can be stored in the frequency bin FB and then processed to provide the corresponding subcarrier. Thus, subcarriers can be selectively added or removed from the optical output ends of the primary node transmitter 202 and the secondary node transmitter 304, so that the number of subcarriers output from these transmitters can be changed as needed.

[0088] In the above example, zero (0) or other predetermined values ​​are stored in the selected frequency bin FB to prevent the transmission of a particular subcarrier SC. Such zero or some values ​​may instead be provided at the output of the corresponding replicator component 1007 or stored in a corresponding location in the memory or multiplexer 1009, for example, in a manner similar to that described above. Alternatively, the above zero or some values ​​may be provided at the corresponding output of the pulse shaping filter 1008, for example, in a manner similar to that described above.

[0089] In another example, a corresponding one of the pulse shaping filters 1008-1 to 1008-19 may selectively generate zero or predetermined values ​​which, when further processed, also result in omitting one or more subcarriers SC from the output of the primary node transmitter 202 or the secondary node transmitter 304. Fig.10cAs shown, pulse shaping filters 1008-0 to 1008-19 are shown as including multiplier circuit groups M0-0 to M0-n...M19-0 to M19-n (also individually or collectively referred to as M). Each multiplier circuit M constitutes a part of a corresponding butterfly filter. In addition, each multiplier circuit group is associated with a corresponding one of the subcarriers SC.

[0090] Each multiplier circuit M receives a corresponding one of the output groups RD0-0 to RD0-n. RD19-0 to Rd19-n come from the replicator component 1007. In order to remove or eliminate one of the subcarriers SC, the multiplier circuit M receiving the outputs within a particular group associated with that subcarrier multiplies those outputs by zero (0) so that each multiplier M within that group generates a product equal to zero (0). The zero product is then further processed similarly to that described above to provide a drive signal to the modulator 910, resulting in the corresponding subcarrier SC being omitted from the output of the transmitter (transmitter 202 or 304).

[0091] On the other hand, to provide a subcarrier SC, each of the multiplier circuits M within a particular group may multiply a corresponding one of the replica outputs RD by a corresponding one of the coefficients C0-0 to C0-n ... C19-0 to C19-n, which results in at least some non-zero products being output. Based on the products output from the corresponding multiplier group, a drive signal is provided to the modulator 910 to output the desired subcarrier SC from the transmitter (transmitter 202 or 304).

[0092] Thus, for example, to block or eliminate subcarrier SC0, each of the multiplier circuits M0-0 to M0-n (associated with subcarrier SC0) multiplies a corresponding one of the replica outputs RD0-0 to RD0-n by zero (0). Thus, each such multiplier circuit provides a product equal to zero, which is further processed, as described above, so that the resulting drive signal causes the modulator 910 to provide an optical output without SC0. To restore SC0, the multiplier circuits M0-0 to M0-n multiply a corresponding one of the appropriate coefficients C0-0 to C0-n by a corresponding one of the replica outputs RD0-0 to RD0-n to provide products, at least some of which are non-zero. Based on these products, a modulator drive signal is generated that causes subcarrier SC0 to be output, as described above.

[0093] The above examples are described in connection with generating or removing the X component of the subcarrier SC. The above processes and circuits are employed or included in the DSP 902 and the optical circuits for generating the Y component of the subcarrier to be blocked. For example, the switch and bin circuit blocks 1022-0 to 1022-19 and the above switch and bin circuit block 1021 have similar structures and operate in a similar manner to provide zero or frequency domain data as appropriate, and may selectively block the Y component of one or more subcarriers SC. Alternatively, a multiplier circuit may be provided, as described above in connection with Fig.10c Those described to provide a zero product output from the selected pulse shaping filter 1018 to block the Y component of a particular subcarrier, or to generate a subcarrier if a non-zero coefficient is provided to the multiplier circuit.

[0094] Thus, the above examples illustrate some mechanisms by which subcarriers SC may be selectively blocked from or added to the output of transmitter 202. As described below, since the DSP and optical circuits provided in the secondary node transmitter 304 are similar to the DSP and optical circuits in the primary node transmitter 202, the above processes and circuits are provided in the secondary node transmitter 304, for example, to selectively add subcarriers SC' to the output of the secondary node transmitter and remove subcarriers SC' from the output of the secondary node transmitter, as combined with Figure 13b-13k In addition, consistent with the present disclosure, the above combined Fig.10b and / or Fig.10c The described circuitry may be configured such that, based on an initial capacity requirement, a first number of optical subcarriers are output from a transmitter (in a primary node 110 or a secondary node 112) during a first time period. Subsequently, during a second time period, a second number of optical subcarriers may be output from the hub and / or leaf transmitters based on a capacity requirement that is different from the first capacity requirement.

[0095] Optical subcarriers SC0 to SC19 can be provided to Figure 1 The secondary node 112 in Fig.11a An example of a receiver circuit 302 in one of the secondary nodes 112 is described below.

[0096] like Fig.11aAs shown, the optical receiver 302 may include Rx optics and A / D block 1100, which in conjunction with DSP 1150 may perform coherent detection. Block 1100 may include a polarization splitter (PBS) 1105 having a first (RX DSP 1105-1) and a second (1105-2) output), a local oscillator (LO) laser 1110, 90 degree optical hybrids or mixers 1120-1 and 1120-2 (collectively referred to as hybrid mixers 1120 and individually as hybrid mixers 1120), detectors 1130-1 and 1130-2 (collectively referred to as detectors 1130 and individually as detectors 1130, each detector 630 including a single photodiode or a balanced photodiode), AC coupling capacitors 1132-1 and 1132-2, transimpedance amplifier / automatic gain control circuits TIA / AGC 1134-1 and 1134-2, and ADCs 1140-1 and 1140-2 (collectively referred to as ADC 1140 and individually as ADC 1140).

[0097] A polarization beam splitter (PBS) 1105 may include a polarization splitter that receives an input polarization multiplexed optical signal including optical subcarriers SC0 to SC19 provided by an optical fiber link 1101, which may be, for example, an optical fiber segment that is part of one of the optical communication paths 113-k to 113-m described above. The PBS 1105 may split the input optical signal into two X and Y orthogonal polarization components. The Y component may be provided to a polarization rotator 1106 that rotates the polarization of the Y component to have an X polarization. A hybrid mixer 1120 may combine the X polarization component and the rotated Y polarization component with light from a local oscillator laser 1110 (which is a tunable laser in one example). For example, hybrid mixer 1120-1 may combine a first polarized signal (e.g., a component of an incoming optical signal having a first or X (TE) polarization output from a first PBS port) with light from a local oscillator 1110, and hybrid mixer 1120-2 may combine a rotated polarized signal (e.g., a component of an incoming optical signal having a second or Y (TM) polarization output from a second PBS port) with light from a local oscillator 1110. In one example, a polarization rotator 1190 may be provided at the PBS output to rotate the Y component polarization to have an X polarization.

[0098] The detector 1130 can detect the mixed products output from the optical mixer to form corresponding voltage signals, which are AC coupled by capacitors 1132-1 and 1132-1, and amplified and gain controlled by TIA / AGC 1134-1 and 1134-2. The outputs of TIA / AGC 1134-1 and 1134-2 and ADC 1140 can convert the voltage signals into digital samples. For example, two detectors (e.g., photodiodes) 1130-1 can detect X-polarized signals to form corresponding voltage signals, and the corresponding two ADCs 1140-1 can convert the voltage signals into digital samples of the first polarized signal after amplification, gain control, and AC coupling. Similarly, two detectors 1130-2 can detect rotated Y-polarized signals to form corresponding voltage signals, and the corresponding two ADCs 1140-2 can convert the voltage signals into digital samples of the second polarized signal after amplification, gain control, and AC coupling. The RX DSP 1150 may process the digital samples associated with the X and Y polarization components to output data associated with one or more subcarriers within a set of subcarriers SC0 to SC19 contained within a bandwidth (one of bandwidths BWj, BWk, BWl, and BWm) associated with the secondary node that accommodates the particular DSP 1150. For example, Figure 6 As shown, subcarriers SC0 through SC8 are within bandwidth BSj, and these subcarriers may be processed by a receiver in secondary node 112-j. However, as described above, subcarriers SC5 through SC13 are within bandwidth BWk, and may be processed by a receiver in secondary node 112-k. That is, bandwidths BWj and BWk overlap, such that subcarriers within the overlapping portions of these bandwidths, i.e., subcarriers SC5 through SC8, will be processed by receivers in both secondary nodes 112-j and 112-k. If data associated with these subcarriers is intended to be output from secondary node 112-k, for example, switching circuitry may be provided to selectively output at node 112-k rather than from node 112-j, as discussed in more detail below.

[0099] although Fig.11a Optical receiver 302 is shown as including a particular number and arrangement of components, but in some embodiments, optical receiver 302 may include additional components, fewer components, different components, or different arrangements of components. The number of detectors 1130 and / or ADCs 1140 may be selected to implement an optical receiver 302 capable of receiving polarization multiplexed signals. In some cases, Fig.11a One of the components shown in the figure may perform the operations described herein by Fig.11a The components shown in FIG. 10 and FIG. 11 are functionally identical to those shown in FIG. 10 , and may be used to identify components that are not identical to those shown in FIG. 10 .

[0100] Consistent with the present disclosure, in order to select a particular subcarrier or group of subcarriers at the secondary node 112, the local oscillator 1110 may be tuned to output light having a wavelength or frequency relatively close to the wavelength of the selected subcarrier, thereby causing a jump between the local oscillator light and the selected subcarrier. For other non-selected subcarriers, such a jump either does not occur or will be significantly attenuated so that the data carried by the selected subcarrier can be detected and processed by the DSP 1150.

[0101] As described above, each secondary node 112 may have a bandwidth that is smaller than the bandwidth associated with the primary node 110. The subcarriers included in each secondary node may be determined by the frequency of the local oscillator laser 1110 in the secondary node receiver 302. For example, Fig.11b As shown, the bandwidth BWj associated with the secondary node 112-j can be centered around the local oscillator frequency fLOj, the bandwidth BWk associated with the secondary node 112-k can be centered around the local oscillator frequency fLOk, the bandwidth BW1 associated with the secondary node 112-1 can be centered around the local oscillator frequency fLO1, and the bandwidth BWm associated with the secondary node 112-m can be centered around the local oscillator frequency fLOm. Thus, each bandwidth BWj to BWm can be shifted according to the frequency of each secondary node local oscillator laser 1110. For example, tuning the local oscillator frequency by changing the temperature of the local oscillator laser 1110 can result in a corresponding shift in the bandwidth to include a different set of subcarriers than the subcarriers detected before such bandwidth shift. The temperature of the local oscillator laser 1110 can be controlled using, for example, a thin film heater disposed near the local oscillator laser or on some portion of the local oscillator laser (e.g., a reflector portion). Alternatively, the local oscillator laser can be frequency tuned by controlling the current supplied to the laser. The local oscillator laser 1110 may be a semiconductor laser, such as a distributed feedback laser or a distributed Bragg reflector laser.

[0102] However, the maximum bandwidth or number of subcarriers that can be received, detected, and processed by the secondary node receiver 302 may be limited based on hardware limitations of various circuit components in the receiver 302, as described above, and therefore, may be fixed in this example. Therefore, as described above, the bandwidth associated with each secondary node 112 may be less than the bandwidth BW-P associated with the primary node 110. In addition, consistent with the present disclosure, the number of secondary nodes may be greater than the number of subcarriers output from the primary node 110. In addition, the number of upstream subcarriers received by the primary node 110 may be equal to the number of subcarriers sent by the primary node 110 in the upstream direction. Alternatively, the number of subcarriers collectively sent in the upstream direction by the secondary nodes 112 may be less than or greater than the number of downstream subcarriers output from the primary node. In addition, in another example, one or more of the secondary nodes 112 may output a single subcarrier.

[0103] like Fig.11b As shown and discussed above, the bandwidths associated with the secondary nodes 112 may overlap such that, as further noted above, certain subcarriers SC may be detected by multiple secondary nodes 112. If data associated with such subcarriers SC is intended for one of those secondary nodes, but not another, then, as described above, switching circuitry may be provided in the secondary nodes to selectively output the data at the intended secondary node, but not at other nodes.

[0104] For example, Fig.11a As further shown, switches or circuits SW-0 to SW-8 may be provided at the output of the DSP 1150 to selectively output data detected from the received subcarriers based on a corresponding one of the control signals CNT-0 to CNT-8 output from the control circuit 1171, which, like the control circuit 971 described above, may include a microprocessor, FPGA, or other processor circuit. The control signal may specify the output of each corresponding switch. Thus, for example, if the data carried by a predetermined subcarrier is intended to be output at a particular secondary node 112, the switch SW at that secondary node may be configured based on the received control signal CNT to provide the desired data but block data not intended for that node.

[0105] Fig.12 1 shows exemplary components of a receiver digital signal processor (DSP) 1150. As described above, analog-to-digital (A / D) circuits 1140-1 and 1140-2 ( Fig.11a ) outputs digital samples corresponding to the analog inputs provided thereto. In one example, each A / D circuit may provide samples at a rate of 64G samples / second. The digital samples correspond to symbols carried by the X polarization of the optical subcarrier and may be represented by the complex number XI+jXQ. The digital samples may be provided to overlap and save buffer 1205-1, such as Fig.12 As shown. FFT component or circuit 1210-1 can receive 2048 vector elements, for example, from overlap and save buffer 1205-1, and convert the vector elements to the frequency domain using, for example, a fast Fourier transform (FFT). As a result of performing the FFT, FFT component 1210-1 can convert the 2048 vector elements into 2048 frequency components, each of which can be stored in a register or "bin" or other memory.

[0106] The frequency components may then be demultiplexed by demultiplexer 1211-1, and the component groups may be provided to a respective one of dispersion equalizer circuits CDEQ 1212-1-0 to 1212-1-8, each of which may include a finite impulse response (FIR) filter for correcting, offsetting, or reducing the effects of transmitted optical subcarrier dispersion or errors associated therewith. Each of CDEQ circuits 1212-1-0 to 1212-1-8 provides an output to a respective polarization mode dispersion (PMD) equalizer circuit 1225-0 to 1225-8 (which may be individually or collectively referred to as 1225).

[0107] The digital samples associated with the Y polarization component of the subcarrier SC1 output from the A / D circuit 640-2 may be processed in a manner similar to the processing of the digital samples associated with the X polarization component of each subcarrier output from the A / D circuit 1240-1. That is, the overlap and save buffer 1205-2, the FFT 1210-2, the demultiplexer 1211-2, and the CDEQ circuits 1212-2-0 to 1212-2-8 may have structures similar to those of the buffer 1205-1, the FFT 1210-1, the demultiplexer 122-1, and the CDEQ circuits 1212-1-0 to 1212-1-8, respectively, and operate in a similar manner. For example, each of the CDEQ circuits 1212-2-0 to 1212-8 may include an FIR filter for correcting, offsetting, or reducing the effects of dispersion of the transmitted optical subcarrier or errors associated therewith. In addition, each of the CDEQ circuits 1212-2-0 through 1212-2-8 provides an output to a corresponding one of the PMDEQs 1225-0 through 1225-8.

[0108] like Fig.12 As further shown, the output of one of these CDEQ circuits (e.g., CDEQ 1212-1-0) can be provided to a clock phase detector circuit 1213 to determine the clock phase or clock timing associated with the received subcarriers. Such phase or timing information or data can be provided to ADCs 1140-1 and 1140-2 to adjust or control the timing of the digital samples output from ADCs 1140-1 and 1140-2.

[0109] Each of the PMDEQ circuits 1225 may include another FIR filter that corrects, offsets, or reduces the effects of, or errors associated with, the PMD of the transmitted optical subcarrier. Each of the PMDEQ circuits 1225 may provide a first output to a corresponding one of the IFFT components or circuits 1230-0-1 to 1230-8-1, and a second output to a corresponding one of the IFFT components or circuits 1230-0-2 to 1230-8-2, each of which may convert the vector of 256 elements (in this example) back to the time domain as 256 samples according to, for example, an inverse fast Fourier transform (IFFT).

[0110] The time domain signals or data output from the IFFT 1230-0-1 to 1230-8-1 are provided to a corresponding one of the Xpol carrier phase correction circuits 1240-1-1 to 1240-8-1, which can apply carrier recovery techniques to compensate for the X-polarization transmitter (e.g., laser 908) and receiver (e.g., local oscillator laser 1110) linewidths. In some embodiments, each carrier phase correction circuit 1240-0-1 to 1240-8-1 can compensate or correct the frequency and / or phase difference between the X-polarization of the transmit signal and the X-polarization of the light from the local oscillator 1100 based on the output of the Xpol carrier recovery circuit 1240-0-1, which performs carrier recovery associated with one of the subcarriers based on the output of the IFFT 1230-01. After such X-polarization carrier phase correction, data associated with the X-polarization component can be represented as symbols having a complex representation xi+j*xq in a constellation (e.g., a QPSK constellation or a constellation associated with other modulation forms, such as m-quadrature amplitude modulation (QAM), where m is an integer). In some embodiments, taps of an FIR filter in one or more PMDEQ circuits included in PMDEQ circuit 1225 can be updated based on the output of at least one of carrier phase correction circuits 1240-0-1 to 1240-8-01.

[0111] In a similar manner, the time domain signals or data output from the IFFT 1230-0-2 to 1230-8-2 are provided to a corresponding one of the Ypol carrier phase correction circuits 1240-0-2 to 1240-8-2, which can compensate or correct the line width of the Y polarization transmitter (e.g., laser 908) and receiver (e.g., local oscillator laser 1110). In some embodiments, each carrier phase correction circuit 1240-0-2 to 1240-8-2 can also correct or compensate for the frequency and / or phase difference between the Y polarization of the transmitted signal and the Y polarization of the light from the local oscillator 1110. After such Y polarization carrier phase correction, the data associated with the Y polarization component can be represented as a symbol having a complex representation yi+j*yq in a constellation diagram (e.g., a QPSK constellation diagram or a constellation diagram associated with other modulation forms, such as m quadrature amplitude modulation (QAM), where m is an integer). In some embodiments, the output of one of circuits 1240-0-2 through 1240-8-2 may be used to update taps of an FIR filter in one or more PMDEQ circuits included in PMDEQ circuit 1225, rather than or in addition to the output of at least one of carrier recovery circuits 1240-0-1 through 1240-8-1.

[0112] like Fig.12 As further shown, the output of the carrier recovery circuit (e.g., carrier recovery circuit 1240-0-1) may also be provided to carrier phase correction circuits 1240-1-1 to 1240-8-1 and 1240-0-2 to 1240-8-2, whereby the phase correction circuit may determine or calculate a corrected carrier phase associated with each received subcarrier based on one of the recovered carriers, rather than providing multiple carrier recovery circuits, each associated with a respective subcarrier. The equalizer, carrier recovery, and clock recovery may be further enhanced by utilizing known (training) bits that may be included in the control signal CNT, for example by providing an absolute phase reference between the transmit laser and the local oscillator laser.

[0113] Each of the symbol-to-bit circuits or components 1245-0-1 to 1245-8-1 can receive symbols output from corresponding circuits in circuits 1240-0-1 to 1240-8-1 and map the symbols back to bits. For example, each of the symbol-to-bit components 1245-0-1 to 1245-8-1 can map one X-polarization symbol in a QPSK or m-QAM constellation to Z bits, where Z is an integer. For dual-polarization QPSK modulated subcarriers, Z is 4. The bits output from each of the components 1245-0-1 to 1245-8-1 are provided to a corresponding one of the FEC decoder circuits 1260-0 to 1260-8.

[0114] The Y polarization symbols are output from respective ones of the circuits 1240-0-2 through 1240-8-2, each having a complex representation yi+j*yq associated with the data carried by the Y polarization component. Each Y polarization, like the X polarization symbol mentioned above, may be provided to respective ones of the bits-to-symbol circuits or components 1245-0-2 through 1245-8-2, each having a similar structure and operating in a similar manner as the symbol-to-bit components 1245-0-1 through 1245-8-1. Each of the circuits 1245-0-2 through 1245-8-2 may provide an output to respective ones of the FEC decoder circuits 1260-0 through 1260-8. .

[0115] Each of the FEC decoder circuits 1260 can use, for example, forward error correction to remove errors in the output of the symbol to bit circuit 1245. Such error correction bits may include user data for output from the secondary node 112, which may be provided to one of the corresponding switch circuits SW-0 to SW-8. As described above, the switch circuits SW-0 to SW-8 in each secondary node 112 can selectively provide or block data based on whether the data is intended to be output from the secondary node. In addition, if one of the control information (CNT) of the subcarrier is received, such as information identifying the switch SW that outputs the data and the other switch SW that blocks the data, the control information can be output from one of the switches, and based on such control information, the control circuit 1171 in the secondary node generates a control signal CNT.

[0116] Consistent with another aspect of the present disclosure, data may be blocked from output from DSP 1150 without using switches SW-0 to SW-8. In an example similar to the above example, zeros (0) or other predetermined values ​​may be stored in the frequency bins associated with the blocked data and in the subcarriers corresponding to the blocked data. The above further processing of such zero or predetermined data by circuitry in DSP 1150 will result in, for example, null or zero data output from a corresponding one of FEC decoders 1260. Switching circuitry provided at the output of FFTs 1210-1 and 1210-2 (similar to the above switching circuitry provided at the output of FFTs 1210-1 and 1210-2) may be provided. Fig.10b 11) to selectively insert a zero value or a predetermined value to selectively block the corresponding output data from the DSP 1150. Such a switch may also be provided at the output of or inside the demultiplexers 1211-1 and 1211-2 to selectively provide a zero value or a predetermined value.

[0117] In another example, zeros (0) may be inserted into the dispersion equalizer (CDEQ) circuit 1212 associated with the X and Y polarization components of each subcarrier. In particular, a multiplier circuit (provided in a corresponding butterfly filter circuit), such as the multiplier circuit M described above, may selectively multiply the input of the CDEQ circuit 1212 by zero or a desired coefficient. Fig.10c As discussed, multiplication by zero results in a zero product. When such a zero product is further processed by corresponding circuits in the DSP 1150 (e.g., the corresponding IFFT 1230, carrier phase correction component 1240, symbol to bit component 1245, and FEC decoder), the corresponding output of the DSP 1150 will also be zero. Therefore, data associated with subcarriers SC received by the secondary node receiver 112 but not intended to be output from the receiver can be blocked.

[0118] On the other hand, if capacity requirements change and such previously blocked data is to be output from a given secondary node receiver DSP 1150, appropriate coefficients may be provided to the multiplier circuits so that at least some of the inputs to the multipliers are not multiplied by zero. Upon further processing, as described above, data associated with the inputs to the multiplier circuits and corresponding to particular subcarriers SC are output from the secondary node receiver DSP 1150.

[0119] although Fig.12 DSP 1150 is shown as including a particular number and arrangement of functional components, but in some implementations DSP 650 may include additional functional components, fewer functional components, different functional components, or a different arrangement of functional components.

[0120] The following will refer to Figure 13a-13k as well as Fig.14 An upstream transmission from a secondary node 112 to a primary node 110 is described.

[0121] Fig.13a An example of a secondary node transmitter 304 is shown in more detail. The transmitter 304 includes a plurality of circuits or switches SW. In this example, nine switches (SW-0 to SW-8) are shown, but more than one switch may be provided. Fig.13a 1302. In one example, each switch may have two inputs: a first input may receive user data, and a second input may receive control information or a signal (CNT). Each switch SW-0 to SW-8 also receives a corresponding control signal from the control circuit SWC-0 to SWC-8. Based on the received control signal, each switch SW-0 to SW8 selectively outputs a corresponding one of the data streams D-0 to D-8 and a corresponding one of the control signals CNT-0 to CNT-8 to the DSP 1302.

[0122] Alternatively, in a manner similar to that described above, if the user wishes to omit particular subcarriers so that fewer subcarriers are transmitted, the transmitted subcarriers may be removed by inserting zero amplitudes at the input or output of the FFT, or by programming zero coefficients into selected multiplier inputs of pulse shaping filters 1008 and 1016.

[0123] DSP 1302 may have the same Fig. 9 and Fig.10a 1302. However, in some cases, the capacity of DSP 1302 may be lower than that of DSP 902, and thus, the number of circuits (e.g., FEC encoder, bit-to-symbol mapper, overlap and save buffer, FFT circuit, replicator circuit, and pulse shaping filter) may be reduced, for example, based on the number of inputs to DSP 1302. Therefore, fewer subcarriers may be output from each secondary node 112 than the number of subcarriers output from primary node 110.

[0124] Based on the outputs of switches SW-0 to SW-8, DSP 1302 can provide multiple outputs to D / A and optical block 1301, which can have a similar configuration as D / A and optical block 901 described above to provide X and Y polarized optical signals, each of which includes I and Q components, which are combined by the PBC and output to optical fiber segment 1316, which is included in Figure 2 In one of the optical communication paths 115 shown.

[0125] Alternatively, based on zeros (0) stored or generated in the DSP 1302, subcarriers may be blocked or added in a manner similar to that described above.

[0126] Figures 13b to 13e It is shown that when Figure 6 1 and 12. An example of subcarriers (SC') outputted in the upstream direction from each of the secondary nodes 112-j to 112-m, respectively, when the subcarriers SC0-SC19 shown in 1 are transmitted in the downstream direction. That is, Fig.13b A first set of subcarriers SC0' to SC4' is shown which may be output from the secondary node 112-j; Fig.13c A second set of subcarriers SC5' to SC9' is shown which may be output from the secondary node 112-k; Fig.13d A third group of subcarriers SC10' to SC14' is shown which may be output from the secondary node 112-1; and Fig.13e A fourth group of subcarriers SC15' to SC19' is shown which may be output from the secondary node 112-m. Figure 2As shown, each group of subcarriers may be combined in combiner 116, for example, and provided to a receiver (eg, Figure 3 Receiver 204 shown in FIG. Fig.13f Such combined optical subcarriers SC0' to SC19' are shown, each subcarrier having a respective one of frequencies f0 to f19.

[0127] Figure 13g to Figure 13j It is shown that when Figure 8 19 is an example of a subcarrier (SC") output in the upstream direction from each of the secondary nodes 112-j to 112-m, respectively, when the subcarriers SC0-SC19 shown in 19 are transmitted in the downstream direction. Specifically, Figure 13g A first set of subcarriers SC0" to SC6" and SC8" is shown which may be output from the secondary node 112-j; Fig.13h A second set of subcarriers SC7″ and SC9″-SC11″ that may be output from the secondary node 112-k is shown; Fig.13i A third group of subcarriers SC12" to SC16" is shown which may be output from the secondary node 112-1; and Fig.13j A fourth group of subcarriers SC17" to SC19" is shown that may be output from the secondary node 112-m. As described above, each group of subcarriers output from a secondary node may be combined in a combiner 116, for example, and provided to a receiver 204 in the primary node 110 via an optical communication path 117. Figure 13k Such combined optical subcarriers SC0' to SC19' are shown, each subcarrier having a respective one of frequencies f0 to f19.

[0128] Fig.14 An example of a master node receiver 204 is shown in more detail. The master node receiver 204 includes an Rx optical device and an A / D block 1400, which has the same Fig.11aThe Rx optical device and receiver block 1100 described above may be similar in structure. For example, block 1400 may include: a polarization beam splitter that receives an upstream polarization multiplexed optical signal that includes optical subcarriers SC0' to SC19' or SC0" to SC19 provided by an optical fiber link 1401, which may be, for example, an optical fiber segment that is part of one of the optical communication paths 115-k to 115-m described above; a local oscillator laser; an optical mixer; a photodiode; a capacitive coupler; a TIA / AGC circuit; and an analog to digital (A / D) converter circuit similar to those discussed above and configured in a manner similar to that described above. Thus, block 1400 provides outputs XI, XQ, YI, and YQ that are similar to the corresponding outputs provided from block 1100. However, the bandwidth associated with each component and circuit in block 1400 may have a greater bandwidth than the corresponding components in the secondary node 112, and therefore, the primary node receiver 204 may detect and process each subcarrier output from the secondary node 112.

[0129] like Fig.14 As further shown, the master node receiver 204 may also include a DSP 1450 that receives signals XI, XQ, YI, and YQ from block 1400. The DSP 1450 may have Fig.11a However, DSP 1450 may have a higher capacity than DSP 1150, and thus, depending on the number of outputs from DSP 1450, the number of circuits (e.g., FEC decoder, symbol to bit mapper, overlap and save buffer, CDEQ circuit, and PMDEQ circuit) may be greater than DSP 1150. Fig.11a The number shown is greater.

[0130] The outputs from the DSP 1450 may then be provided to switches SW-0 to SW-19, which, under control of control signals similar to those described above, selectively output one of: a corresponding one of the data streams D-0 to D-19; and a corresponding one of the control signals CNT-0 to CNT-19. The control information may include, for example, monitoring information or scheduling information associated with the secondary node 112, such as time of flight (TOF) or delta time TOF information, as described below with reference to Figure 20-24 As described.

[0131] Alternatively, based on zeros generated or stored in DSP 1450, data may be selectively provided from each DSP output in a manner similar to that described above.

[0132] In another example consistent with the present disclosure, a guard band or frequency gap may be provided between adjacent subcarriers SC. Fig.15As shown, a guard band GB1 may be provided between subcarriers SC4 and SC5, and a guard band GB2 may be provided between subcarriers SC5 and SC6. Additional guard bands may be provided between the remaining adjacent subcarrier pairs. Such guard bands may be provided so as to more accurately detect and process each subcarrier by reducing crosstalk or other interference between subcarriers.

[0133] As mentioned above, in addition to the above combination Figure 1 and Figure 2 Network configurations other than the aggregate network configuration discussed, such as a mesh network, an example of which (network 1800) is shown in FIG. Fig.16 . Network 1800 may include multiple nodes 1802, 1804, 1806, 1808, 1810, and 1812, which are connected to have multiple paths between each other. For example, node 1802 may communicate with node 1812 via a path including nodes 1806 and 1808 or a path including nodes 1804 and 1810. Nodes 1802, 1804, 1806, 1808, 1810, and 1812 may include at least one primary node similar to node 110 and at least one secondary node 112 similar to those described above. In addition, in a manner similar to that described above, the control information exchanged between each node may be controlled or dynamically adapted to control the secondary node 112. Fig.16 The amount of data or data rate output by each of the nodes shown in .

[0134] Next, we will refer to Fig.17 and Figures 18a to 18c An example of allocation of data carried by subcarriers SC0 to SC19 and output from secondary nodes 112 - j to 112 - m and reallocation of such data output from the secondary nodes is described. Fig.19 is a timing diagram showing the transmission of control information on dedicated subcarriers SC2, SC7, SC12 and SC17, as shown in Figure 4 As further described in Fig.17 As shown in the example depicted in , each of these subcarriers is continuously transmitted from the master node 110, while the remaining subcarriers SC1, SC3-SC6, SC8-SC11, SC13-SC16, SC18 and SC19 are not transmitted. The control information carried by subcarriers SC2, SC7, SC12 and SC17 is associated with nodes 112-j, 112-k, 112-l and 112-m, respectively. In addition, in another example, subcarriers SC2, SC7, SC12 and SC17 may also carry user data associated with each such node.

[0135] Fig.18a Shown with Figure 61 and 12. Here, data associated with node 112-j is transmitted continuously on subcarriers SC0 to SC4, data associated with node 112-k is transmitted continuously on subcarriers SC5 to SC9, data associated with node 112-l is transmitted continuously on subcarriers SC10 to SC14, and data associated with node 112-m is transmitted continuously on subcarriers SC15 to SC19.

[0136] As described above, data associated with secondary node 112 may be reallocated between subcarriers SC0 to SC19. Consistent with the present disclosure, this reallocation may occur on a time slot by time slot basis. Examples of such reallocation include Fig.18b That is, Fig.18b As shown, during time slot TS1, subcarrier S8 carries data associated with node 112-k. However, during time slot TS2, subcarrier S8 carries data associated with node 112-j, and continues to do so until time slot TS6. At this point, subcarrier S8 carries data associated with node 112-k, and also does so through time slot S9. In a similar manner, other time slots may be switched to carry data associated with different nodes, or, as shown, Fig.18b As further shown in FIG. 1 , subcarriers (e.g., subcarriers SC0 to SC4) may continue to carry data associated only with node 112-j. Such reallocation may be based on capacity requirements in the system. Furthermore, as described above, data associated with a particular secondary node 112 is data output from the secondary node based on control information received by the secondary node and the configuration of the second node, as described above with reference to FIG. Fig.10b and Fig.10c as described.

[0137] Fig.18c Another example is shown, where no data is sent without a specific capacity requirement during a given time slot. Fig.18c As shown, during time slot TS5, subcarriers SC11, SC8 and SC4 do not carry any data. These subcarriers are referred to above during time slot TS5. Fig.10b and Fig.10c Describe the circuit blocking.

[0138] The above example describes reallocating data to subcarriers that are transmitted in the downstream direction from the primary node 110 to the secondary nodes 112. In the upstream direction, as described above, one or more subcarriers may be transmitted from one or more secondary nodes 112 to the primary node 110. If the secondary nodes 112 are located at different distances from the primary node 110, the time at which data arrives at the primary node 110 from one secondary node 112 may be different than the time at which data arrives from another secondary node 112. As a result, data input from the secondary nodes 112 to the primary node 110 may be unsynchronized, such that data transmitted on a given subcarrier from a secondary node during one time slot may arrive while the primary node 110 is receiving data from another secondary node, thereby causing data errors or losses at the primary node 110.

[0139] For example, refer to Fig.19 , if node 112-1 is farther from master node 110 than node 112-m, then data output from node 112-1 on subcarrier SC4, for example, will experience a delay td. Such data will not reach master node 110 until time t5+td. Fig.19 As shown, and will continue to be received during the time slot, i.e., until time t6+td. However, at time t6, master node 110 may want to receive data from node 112-m, and due to the delayed data transmission from node 112-1, in this example, master node 110 will receive data from nodes 112-1 and 112-m on subcarrier 4, so that during the time interval t6 to t6+td, the data provided from node 112-1 and the data provided from node 112-m may not be reliably detected.

[0140] According to aspects of the present disclosure, a method is provided by which circuitry in a master node 110 can determine the "time of flight" delay, or the amount of time required for the master node to send a request to a secondary node and receive a response from the secondary node. Based on such time of flight information, the master node 110 can then schedule or coordinate transmissions on various time slots to avoid conflicts, such as Fig.19 As shown in .

[0141] Fig. 20A flow chart of a method for determining the time of flight information of each second node 112 is shown. In step 2002, the circuit in the master node 110 initializes the time of flight (TOF) offset of each leaf 112 to zero. In step 2004, a test message or TOF offset is sent to each leaf node 112, which contains an instruction or request for each such leaf node 12 to respond on a control channel (e.g., an in-band channel sent with data and carried by one of the subcarriers). The circuit in the master node 110 then measures the response time of each leaf node 112 (step 2006). The circuit in the master node 110 then determines the TOF time difference ("delta TOF") of each node, and adjusts each incremental TOF so that the incremental TOF of the leaf node 112 with the longest TOF is zero (step 2008). Next, the circuit in the master node 110 determines when the incremental TOF response time of each leaf node 112 is within a given tolerance or margin (step 2010). If not, steps 2004, 2006, 2008 and 2010 are repeated and will continue to repeat until the incremental response time is within such a margin. If the incremental response time is within the margin, the above method starts again at step 2002 after a predetermined period of X milliseconds to re-evaluate the TOF information.

[0142] Once passed Fig. 20 The master node 110 obtains TOF and incremental TOF information by using the method shown in Fig.21 Another method of the associated flow chart shown in is to schedule time slots to avoid conflicts. In the first step 2102 of the scheduling method, the hub 110 evaluates or measures the leaf node utilization of subcarriers and time slots through the control channel mentioned above. Based on the utilization measured in this way, the circuit in the hub 110 determines whether the leaf node is within the TOF tolerance or margin (step 2104). If so, one or more time slots are allocated to the leaf node (step 2106), if not, the hub node provides instructions to allocate one or more subcarriers to such leaf nodes, so that such leaf nodes can continuously send data to the hub node 110 on such allocated subcarriers. Then, the leaf node is configured to continuously send only during the specified time slot or on one or more subcarriers according to the received instructions, for example, through the above-mentioned subcarriers dedicated to sending control channel information (step 2110). In step 2112, the hub monitors the leaf node utilization during a predetermined time period (e.g., a time period of Y milliseconds). The process then returns to step 2102.

[0143] Note that the above-described TOF-related calculations may be performed external to the master node 110 or by circuitry within the master node 110, as described above.

[0144] Fig. 22is a diagram showing an example of hub request and leaf response times and the corresponding TOF times. Fig. 22 As shown, the further away the secondary node is from the primary node, the longer or greater the TOF time. For example, secondary node 112-m is located 100 kilometers from primary node 110 and is therefore the secondary node farthest from primary node 110. In addition, in this example, secondary node 112-1 is 60 kilometers away from primary node 110, while secondary node 112-k is 50 kilometers away from primary node 110. In addition, node 112-j is located 30 kilometers away from primary node 110 and is therefore the secondary node closest to the primary node.

[0145] The TOF value is determined by circuitry in the master node 110 that measures the time it takes for the master node to receive a response from a secondary node following a TOF request response (see steps 2004 and 2006 above). Fig. 22 and 23 As shown, the TOF associated with the second node 112-j is 300μs (or 1.5 time slots (TS), assuming that each time slot is 200μs); the TOF associated with the node 112-k is 500μs (or 2.5TS); the TOF associated with the node 112-l is 600μs (3.0TS); and the TOF associated with the node 112-m is 1000μs (or 5.0TS). As described above, after determining each TOF, for example, the circuit in the master node 110 determines the TOF associated with each node, where the incremental TOF is the difference between the longest TOF (here 1000μs) and the TOF of each remaining secondary node 112 (i.e., the longest TOF-TOF of each remaining secondary node). Therefore, as further shown in Table 2302, the incremental TOF associated with the secondary node 112-j is 700μs (1000μs-300μs=700μs or 3.5TS); the incremental TOF associated with the secondary node 112-k is 500μs (1000μs-500μs=500μs or 2.5TS); the incremental TOF associated with the secondary node 112-l is 400μs (1000μs-600μs=400μs or 2.0TS); and the incremental TOF associated with the secondary node 112-m is 0.0μs (1000μs-1000μs=0.0μs or 0TS).

[0146] When scheduling transmissions from the secondary node 112 to the primary node 110, both the TOF and the delta-TOF are considered in order to obtain the expected arrival time at the primary node 110 for each such transmission. Fig.24 Describe an example of such a schedule.

[0147] Fig.24Example timing diagrams 2402 and 2404 are shown, where, for ease of explanation, only transmissions on subcarriers SC1 to SC4 are shown. Diagram 2402 shows a Fig. 22 and Fig.23 2404 shows the data carried by the various subcarriers originating from these secondary nodes and the corresponding arrival times at the primary node without any conflicts in absolute time. In one example, Fig.24 As shown, the desired node 110 receives data from the secondary nodes 112-j, 112-k, and 112-m on subcarriers SC1, SC2, and SC4, respectively, at the beginning of time slot TS6. As described above, because the secondary node 112-m is farthest from the primary node 110, the secondary node 112-m has an associated incremental TOF of zero (0). Therefore, as shown in the graph 2402, the data is scheduled to be sent during time slot TS1, and as shown in the graph 2404, such data is sent five time slots later during time slot TS6 (see Fig. 22 and 23 ) arrives at node 110 at approximately the same time as the data output from node 112-m. Node 112-k, on the other hand, has a shorter flight time of 2.5 TS. In order to arrive at node 110 at approximately the same time as the data output from node 112-m, the transmission from node 112-k is scheduled to be output or transmitted to node 110 at an amount of time or delay Dk (see graph 2402) approximately equal to the incremental TOF or 2.5 TS associated with node 112-k in graph 2402 after the transmission of the node 112-m data. Therefore, after such a delay, the node 112-k data is further delayed by the TOF (2.5 TS) associated with node 112-k, so that the 112-k data arrives at approximately the same time as the 112-m data (see graph 2404).

[0148] Furthermore, in order for the data sent from node 112-j to arrive at node 110 approximately simultaneously with the data output from node 112-m, the transmission from node 112-j is scheduled to be transmitted to node 110 approximately simultaneously with the transmission of the node 112-m data by an amount of delay Dj (see graph 2402) equal to the incremental TOF associated with node 112-j or 3.5TS. Thus, after Dj, the node 112-k data is further delayed by the TOF associated with node 112-j (1.5TS), so that the 112-j data arrives approximately simultaneously with the 112-m data (see graph 2404).

[0149] Fig.24 Other example emission and arrival times and subcarrier utilization are further shown in .

[0150] In another example, an empty time slot may be provided between a transmission by one node on a given subcarrier and a transmission by another node on the subcarrier to provide sufficient time between time slots to reduce the risk of collisions or data transmissions on a given subcarrier where time slots overlap, e.g. Fig.19 shown.

[0151] Various modifications and other embodiments will be apparent to those skilled in the art in view of this specification, and the above specific embodiments are provided as examples. For example, the digital signal processing disclosed above may be implemented as a programmable gate array circuit (PGA) or a field programmable gate array circuit (FPGA). In addition, although separate lasers 908 and 1110 are provided in the transmitter and receiver, respectively, as described above, a transceiver consistent with the present disclosure may include a common laser that is "shared" between the transmitter and the receiver. For example, Fig.25 2 is a diagram showing an example of a transceiver 110 that uses a shared laser 2502 to provide an optical signal (as a local oscillator signal) for both transmission and reception according to one or more embodiments of the present disclosure. As shown, the laser 2502 generates an optical signal and provides the optical signal to a splitter 2504. The splitter 2504 splits the optical signal into two parts. One part is provided to optical mixers or hybrids 1120-1 and 1120-2, and the other part is provided to modulators 910-1 to 910-4.

[0152] Accordingly, other implementations are within the scope of the following claims.

Claims

1. A transceiver, comprising: A transmitter comprising: a laser operable to output an optical signal; a first digital signal processor operable to receive first data and provide a first plurality of electrical signals based on said first data; a plurality of digital-to-analog conversion circuits operable to provide a second plurality of electrical signals based on the first plurality of electrical signals; a plurality of driver circuits operable to provide a third plurality of electrical signals based on the second plurality of electrical signals; and a modulator operable to modulate the optical signal to provide a first plurality of optical subcarriers based on the third plurality of electrical signals, each of the first plurality of optical subcarriers comprising an in-phase component and a quadrature component, at least one of the first plurality of optical subcarriers carrying control information, the control information identifying which of the first plurality of optical subcarriers is associated with which of a plurality of secondary nodes, wherein the control information is to be transmitted to the plurality of secondary nodes; and A receiver comprising: an optical hybrid circuit that receives a local oscillator optical signal, a first polarization component of a second plurality of optical subcarriers, and a second polarization component of the second plurality of optical subcarriers, and combines the local oscillator optical signal, the first polarization component of the second plurality of optical subcarriers, and the second polarization component of the second plurality of optical subcarriers to provide an optical hybrid product; a photodiode circuit comprising at least one photodiode operable to provide a fourth plurality of electrical signals based on the optical mixing products; a plurality of analog-to-digital conversion circuits that provide a fifth plurality of electrical signals based on the fourth plurality of electrical signals; and A second processor circuit outputs second data based on the fifth plurality of electrical signals.

2. The transceiver according to claim 1, wherein: The number of the second plurality of optical subcarriers is smaller than the number of the first plurality of optical subcarriers.

3. The transceiver according to claim 1, wherein: The number of the second plurality of optical subcarriers is the same as the number of the first plurality of optical subcarriers.

4. The transceiver according to claim 1, wherein: The optical signal is a first optical signal, and the laser also provides the local oscillator optical signal.

5. The transceiver according to claim 1, wherein: A first guard band extends between a first frequency associated with a first photonic subcarrier of the first plurality of photonic subcarriers and a second frequency associated with a second photonic subcarrier of the first plurality of photonic subcarriers.

6. The transceiver according to claim 1, wherein: The receiver includes a local oscillator laser that provides local oscillator light to the optical hybrid circuit.

7. The transceiver according to claim 6, wherein: The local oscillator laser is a tunable laser.

8. An optical communication system, comprising: The transmitter of the master node includes: a laser that outputs an optical signal; a first digital signal processor circuit that receives first data and provides a first plurality of electrical signals based on the first data; a plurality of digital-to-analog conversion circuits that provide a second plurality of electrical signals based on the first plurality of electrical signals; a plurality of driver circuits that provide a third plurality of electrical signals based on the second plurality of electrical signals; and a modulator that modulates the optical signal to provide a first plurality of optical subcarriers based on the third plurality of electrical signals, each of the first plurality of optical subcarriers comprising an in-phase component and a quadrature component, at least one of the first plurality of optical subcarriers carrying control information, the control information identifying which of the first plurality of optical subcarriers is associated with which of a plurality of secondary nodes, wherein the control information is to be transmitted to the plurality of secondary nodes; and A receiver of a secondary node of the plurality of secondary nodes, optically coupled to the optical communication path, the receiver comprising: an optical hybrid circuit that receives a local oscillator light, a first polarization component of the first plurality of optical subcarriers, and a second polarization component of the first plurality of optical subcarriers, and combines the local oscillator light, the first polarization component of the first plurality of optical subcarriers, and the second polarization component of the first plurality of optical subcarriers to provide a plurality of optical hybrid products, wherein each of the first plurality of optical subcarriers is generated by modulating an optical signal output from a laser; a photodiode circuit that provides a first electrical signal based on the plurality of optical mixing products; A second digital signal processor circuit outputs a portion of data associated with a subset of the first plurality of optical subcarriers based on the first electrical signal and the control information.

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