Optical Subchannel-Based Cyclical Filter Architecture
The present invention includes novel techniques, apparatus, and systems for optical WDM communications. Tunable lasers are employed to generate respective subcarrier frequencies which represent subchannels of an ITU channel to which client signals can be mapped. In one embodiment, subchannels are polarization interleaved to reduce crosstalk. In another embodiment, polarization multiplexing is used to increase the spectral density. Client circuits can be divided and combined with one another before being mapped, independent of one another, to individual subchannels within and across ITU channels. A crosspoint switch can be used to control the client to subchannel mapping, thereby enabling subchannel protection switching and hitless wavelength switching. Network architectures and subchannel transponders, muxponders and crossponders are disclosed, and techniques are employed (at the subchannel level/layer), to facilitate the desired optical routing, switching, concatenation and protection of the client circuits mapped to these subchannels across the nodes of a WDM network.
1 . An optical subchannel muxponder that can transmit optical signals among a plurality of nodes interconnected by one or more fiber optic cables to form an optical network, the optical subchannel muxponder comprising:
(a) a subchannel mapper that can map each of a plurality of client signals to any available subchannel of any ITU channel, wherein each ITU channel has a predefined ITU frequency and a corresponding plurality of subchannels, and wherein each subchannel has an associated frequency with a predetermined offset from the predefined ITU frequency of the subchannel's corresponding ITU channel;
(b) one or more lasers that can be tuned to generate modulated client signals at frequencies associated with each subchannel; and
(c) a multiplexer that can combine the modulated client signals for transmission onto the fiber optic cables of the optical network.
2 . The optical subchannel muxponder of claim 1 , further comprising:
(a) a receiver that can receive an optical signal via the fiber optic cables of the optical network;
(b) a demultiplexer that can filter the modulated client signals from the received optical signal;
(c) a subchannel demodulator containing one or more optical detectors that can detect and isolate the client signals from the modulated client signals associated with each subchannel; and
(d) a subchannel demapper that can demap the demodulated client signals associated with each subchannel and return the demapped client signals to their respective client transceivers.
3 . The optical subchannel muxponder of claim 2 , further comprising a SERDES-FEC-SERDES block that can perform at least one of the following functions:
(a) insert onto and extract from each client signal performance monitoring information;
(b) add to and remove from each client signal channel overhead information for remote network management;
(c) add to and remove from each client signal channel overhead information including the destination of the client signal; and
(d) encode and decode client signal data for forward error correction; and
4 . The optical subchannel muxponder of claim 1 , further comprising an inverse multiplexer that can divide a client signal into a plurality of signals, each of which can be mapped to a distinct subchannel in a data frame having frame markers that facilitate the reconstruction of the client signal.
5 . The optical subchannel muxponder of claim 1 , further comprising a client signal multiplexer that can combine a plurality of client signals into a single higher-rate signal that can be mapped to a distinct subchannel.
6 . The optical subchannel muxponder of claim 1 , wherein the subchannel mapper contains a crossconnect switch that can map each client signal to any available subchannel of any ITU channel.
7 . The optical subchannel muxponder of claim 6 , wherein the time required to map a client signal to an available subchannel is substantially equivalent to the switching time of the crossconnect switch when the laser associated with the available subchannel has previously been tuned to its associated frequency.
8 . The optical subchannel muxponder of claim 1 , wherein a first modulation format is employed to generate a first modulated client signal and a second modulation format is employed to generate a second modulated client signal, and wherein each of the first and second modulated client signals can be mapped to any available subchannel of any ITU channel.
9 . The optical subchannel muxponder of claim 2 , further comprising independent clock recovery and clock multiplier circuitry with respect to each subchannel to support clock independence among the plurality of client signals.
10 . The optical subchannel muxponder of claim 1 , wherein the subchannel mapper can map each of a first client signal employing a first data protocol and a second client signal employing a second data protocol to any available subchannel of any ITU channel.
11 . The optical subchannel muxponder of claim 1 , wherein each subchannel has a distinct corresponding laser that can be tuned to generate a modulated client signal at the frequency associated with the subchannel.
12 . The optical subchannel muxponder of claim 1 , further comprising a polarization combiner that can transmit adjacent subchannels with orthogonal polarizations.
13 . The optical subchannel muxponder of claim 1 , wherein the relative power levels of transmitters associated with each subchannel are adjusted to optimize overall optical performance of the subchannels.
14 . The optical subchannel muxponder of claim 1 , wherein the frequencies of the subchannel lasers are fine-tuned to optimize overall optical performance of the subchannels.
15 . A system for multiplexing, transmitting and demultiplexing polarization-multiplexed signals, the system comprising:
(a) a polarization combiner that combines a first set of signals aligned along a first linear polarization axis with a second set of signals aligned along a second linear polarization axis, wherein the first and second polarization axes are orthogonally polarized;
(b) a transmitting medium which can modify polarization states of the first and second sets of signals, but will maintain orthogonality of the polarization between the sets of signals;
(c) a polarization tracker that receives a plurality of transmitted signals from the first and second sets of signals, and modifies the polarization states of the received signals to transform the polarization state of the first set of signals to a first output linear polarization axis, and correspondingly transform the polarization state of the second set of signals to a second output linear polarization axis that is orthogonal to the first output linear polarization axis;
(d) a polarization beam splitter at the output of the polarization tracker with one of its output linear polarization axes aligned with the first output polarization axis of the polarization tracker, and the other output polarization axis aligned with the second output polarization axis of the polarization tracker;
(e) feedback circuitry that monitors and analyzes one or both outputs of the polarization beam splitter, and provides a control signal back to the polarization tracker to align the signal polarizations of the first set of signals with the first polarization axis of the polarization beam splitter, and to align the signal polarizations of the second set of signals with the second polarization axis of the polarization beam splitter; and
(f) at least one optical filter at the output of each branch of the polarization beam splitter that demultiplexes the signals in each linear polarization.
16 . The system of claim 15 , wherein a third set of client signals is inverse-multiplexed from a higher-bandwidth composite signal.
17 . The system of claim 15 , wherein a first signal from the first set of signals is mapped to a first subchannel of any ITU channel, and a second signal from the second set of signals is mapped to a second subchannel of any ITU channel.
18 . The system of claim 15 , wherein the first and second set of signals can be transmitted to a first node of an optical network, and wherein the polarization axes of a third set of signals added at the first node have the same polarization alignment as the first set of signals, and the polarization axes of a fourth set of signals added at the first node have the same polarization alignment as the second set of signals.
19 . The system of claim 15 wherein low-frequency dither signals are applied to the first and second set of signals to enable narrow-band detection of the signal amplitudes in one or both outputs of the polarization beam splitter.
20 . The system of claim 15 , further comprising circuitry that monitors the total received power of the first and second set of signals, and a variable gain amplifier that adjusts the control signal in response to changes in the total received power.
21 . A method for transmitting optical signals among a plurality of nodes interconnected by one or more fiber optic cables to form an optical network, the method comprising the following steps:
(a) mapping each of a plurality of client signals to any available subchannel of any ITU channel, wherein each ITU channel has a predefined ITU frequency and a corresponding plurality of subchannels, and wherein each subchannel has an associated frequency with a predetermined offset from the predefined ITU frequency of the subchannel's corresponding ITU channel;
(b) tuning one or more lasers to generate modulated client signals at frequencies associated with each subchannel; and
(c) combining the modulated client signals for transmission onto the fiber optic cables of the optical network.
22 . The method of claim 21 , further comprising the following steps:
(a) receiving an optical signal via the fiber optic cables of the optical network;
(b) filtering the modulated client signals from the received optical signal;
(c) demodulating the modulated client signals associated with each subchannel; and
(d) demapping the demodulated client signals associated with each subchannel and returning the demapped client signals to their respective client transceivers.
23 . The method of claim 22 , further comprising at least one of the following steps:
(a) inserting onto and extracting from each client signal performance monitoring information;
(b) adding to and removing from each client signal channel overhead information for remote network management;
(c) adding to and removing from each client signal channel overhead information including the destination of the client signal; and
(d) encoding and decoding client signal data for forward error correction.
24 . The method of claim 21 , further comprising the step of dividing a client signal into a plurality of inverse multiplexed signals, each of which can be mapped to a distinct subchannel in a data frame having frame markers that facilitate the reconstruction of the client signal.
25 . The method of claim 21 , further comprising the step of combining a plurality of client signals into a single higher-rate signal that can be mapped to a distinct subchannel.
26 . The method of claim 21 , further comprising the step of mapping, via a crossconnect switch, each of a plurality of client signals to any available subchannel of any ITU channel.
27 . The method of claim 26 , wherein the time required to map a client signal to an available subchannel is substantially equivalent to the switching time of the crossconnect switch when the laser associated with the available subchannel has previously been tuned to its associated frequency.
28 . The method of claim 21 , further comprising the following steps:
(a) generating a first modulated client signal by employing a first modulation format;
(b) generating a second modulated client signal by employing a second modulation format; and
(c) mapping each of the first and second modulated client signals to any available subchannel of any ITU channel.
29 . The method of claim 22 , further comprising the step of independently clocking the first and second client signals by employing independent clock recovery and clock multiplier circuitry with respect to each subchannel.
30 . The method of claim 21 , further comprising the step of mapping each of a first client signal employing a first data protocol and a second client signal employing a second data protocol to any available subchannel of any ITU channel.
31 . The method of claim 21 , wherein each subchannel has a distinct corresponding laser that can be tuned to generate a modulated client signal at the frequency associated with the subchannel.
32 . The method of claim 21 , further comprising the step of employing a polarization combiner to transmit adjacent subchannels with orthogonal polarizations.
33 . The method of claim 21 , further comprising the step of adjusting the relative power levels of transmitters associated with each subchannel to optimize overall optical performance of the subchannels.
34 . The method of claim 21 , further comprising the step of fine-tuning the frequencies of the subchannel lasers to optimize overall optical performance of the subchannels.
35 . A method for multiplexing, transmitting and demultiplexing polarization-multiplexed signals, the method comprising the following steps:
(a) combining a first set of signals aligned along a first liner polarization axis with a second set of signals aligned along a second linear polarization axis, wherein the first and second polarization axes are orthogonally polarized;
(b) launching the combined signals onto a transmitting medium which can modify polarization states of the first and second set of signals, but will maintain orthogonality of the polarization between the sets of signals;
(c) receiving a plurality of transmitted signals from the first and second sets of signals, and modifying the polarization states of the received signals to transform the polarization state of the first set of signals to a first output linear polarization axis, and correspondingly transform the polarization state of the second set of signals to a second output linear polarization axis that is orthogonal to the first output linear polarization axis;
(d) splitting the first set of signals aligned with the first output polarization axis from the second set of signals aligned with the second output polarization axis;
(e) monitoring and analyzing one or both of the split sets of signals, and generating a control signal to align the signal polarizations of the first set of signals with the first output linear polarization axis, and to align the signal polarizations of the second set of signals with the second polarization axis; and
(f) demultiplexing the signals in each linear polarization.
36 . The method of claim 35 , wherein a third set of client signals is inverse-multiplexed from a higher-bandwidth composite signal.
37 . The method of claim 35 , further comprising the step of mapping a first signal from the first set of signals to a first subchannel of any ITU channel, and a second signal from the second set of signals to a second subchannel of any ITU channel.
38 . The method of claim 35 , further comprising the steps of transmitting the first and second set of signals to a first node of an optical network, wherein the polarization axes of a third set of signals added at the first node have the same polarization alignment as the first set of signals, and the polarization axes of a fourth set of signals added at the first node have the same polarization alignment as the second set of signals.
39 . The method of claim 35 , wherein low-frequency dither signals are applied to the first and second set of signals to enable narrow-band detection of the signal amplitudes in one or both of the split sets of signals.
40 . The method of claim 35 , further comprising the steps of monitoring the total received power of the first and second set of signals, and adjusting the control signal in response to changes in the total received power.
41 . An improved method for upgrading optical network equipment that can transmit and receive optical signals among a plurality of nodes interconnected by one or more fiber optic cables to form an optical network, the method comprising the following steps:
(a) deploying a first, second and third legacy transceiver at respective first, second and third network nodes, each legacy transceiver capable of transmitting and receiving a first client signal at a first legacy data rate via a first ITU channel; and
(b) upgrading each of the first and second legacy transceivers by adding the capabilities of:
(i) mapping each of a plurality of second client signals to any available subchannel of any ITU channel, wherein each ITU channel has a predefined ITU frequency and a corresponding plurality of subchannels, and wherein each subchannel has an associated frequency with a predetermined offset from the predefined ITU frequency of the subchannel's corresponding ITU channel, and
(ii) transmitting and receiving each of the plurality of second client signals, each at the first legacy data rate, via the plurality of subchannels to which the plurality of second client signals have been mapped, thereby effectively increasing the bandwidth of each of the first and second legacy transceivers;
(c) whereby the overall effective bandwidth of the system has been increased with minimal or no disruption to the operation of non-upgraded legacy equipment, in that:
(i) the first and second upgraded legacy transceivers can transmit and receive the plurality of second client signals between the first and second nodes at a bandwidth greater than the first legacy data rate, and
(ii) the third legacy transceiver can transmit and receive the first client signal at the first legacy data rate between the third node and either the first or second nodes.