Patent Description:
This section introduces aspects that may help facilitate a better understanding of the disclosure.

The rapid growth of data-center traffic is well documented. For example, a data center configured to serve cloud-type applications may soon be required to support and/or handle traffic loads on the order of <NUM> to <NUM> Pbit/second. It is believed that the use of optical transport technologies in such data centers may be needed to provide this kind of technical capabilities.

<CIT> discloses a communication method executed at a master optical transceiver coupled to one side of the optical interconnect that enables the transceiver to establish an optical communication link with any one of a plurality of slave optical transceivers coupled to the other side of the optical interconnect. A communication method executed at a slave optical transceiver that enables the transceiver to communicate with the master optical transceivers without having its own light source and, instead, modulating data onto previously un-modulated signaling dimensions of the incoming optical waveforms, which are then turned around and broadcast back to the master optical transceivers. Some embodiments enable the slave optical transceivers to establish a temporary fully switchable network for the corresponding network nodes, wherein the switching is performed by electrically switching the electrical switch engine.

<CIT> discloses implementations of an apparatus including a plurality of racks, wherein each rack houses a plurality of networking devices and each networking device includes a communication port. An optical circuit switch can be coupled to each of the plurality of communication ports in one or more of the plurality of racks, and a plurality of top-of-rack (TOR) switches can be coupled to the optical circuit switch.

Disclosed herein are various embodiments of a communication system that can be used, e.g., to provide high-speed access to the servers of a data center. In an example embodiment, the communication system transports data using wavelength-division-multiplexed (WDM) optical signals. The downlink WDM signals have some WDM components that are modulated with data and some WDM components that are not modulated with data. The uplink WDM signals are generated at the server end of the system by modulating with data the unmodulated WDM components received through the downlink. Appropriately connected wavelength multiplexers, wavelength demultiplexers, and/or optical filters can be used to properly apply the various modulated WDM components to the corresponding optical receivers and the unmodulated WDM components to the corresponding optical transmitters. The resulting system architecture advantageously enables, e.g., the use of a single, conveniently located multi-wavelength light source to provide carrier wavelengths for both uplink and downlink optical traffic.

According to an example embodiment, provided is an apparatus according to claim <NUM>.

Other aspects, features, and benefits of various disclosed embodiments will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which:.

<FIG> shows a block diagram of a communication system <NUM> according to an embodiment. Some embodiments of system <NUM> can be used, e.g., in a Layer <NUM> (L2) network of a data center. As used herein, the term "data center" refers to a pool of resources (e.g., computational, storage, communication) interconnected using a communication network. Some of communication-network architectures and the corresponding layered topologies <NUM> suitable for implementing a data center are reviewed, e.g., in <NPL>.

In some embodiments, system <NUM> can be configured to transport data based on Ethernet technologies. In such embodiments, the data forwarding decisions are made, e.g., based on the Ethernet header of a data packet and its corresponding entry in the forwarding table.

In an example embodiment, system <NUM> comprises a router <NUM> and a plurality of network hosts (e.g., servers) <NUM>-II0N operatively connected as described in more detail below. Router <NUM> is configured to (i) serve as a gateway to system <NUM> by connecting the latter to a Level <NUM> (L3) network, a wide area network (WAN), and/or the Internet and (ii) route data packets to, from, and between network hosts <NUM>. Although <FIG> illustrates an embodiment in which, N≥<NUM>, in various alternative embodiments of system <NUM>, N can be any (e.g., technically feasible) positive integer greater than one.

Herein, a signal traveling toward network hosts <NUM> may sometimes be referred to as a "downlink" signal. A signal traveling toward router <NUM> may sometimes be referred to as an "uplink" signal. For clarity, the following description also refers to the relative locations of some elements of system <NUM> using the terms "north" and "south," and to the relative signal-propagation directions using the terms "northward" and "southward. " The use of these terms in the description of system <NUM> is strictly for pedagogical purposes and should not be construed to limit the topology and/or layout of this system to any or the corresponding north-south geographic orientation.

Each network host <NUM> may have a respective network interface card (NIC) <NUM>. Each of NICs <NUM><NUM>-<NUM>N may have an associated unique MAC (Medium Access Control) or IP (Internet Protocol) address that enables router <NUM> to appropriately route data packets originating from and/or directed to any of network hosts <NUM><NUM>-<NUM>N.

Router <NUM> and NICs <NUM><NUM>-<NUM>N are interconnected using optical transceivers <NUM><NUM>-<NUM>N, an optical interface <NUM>, a fiber-optic cable <NUM>, an optional <NUM>×<NUM> optical switch <NUM>, a fiber-optic cable <NUM>, and an electro-optical interface <NUM>. If present, switch <NUM> can be used to provide optical-path redundancy that enables the data traffic to bypass fiber-optic cable <NUM>, electro-optical interface <NUM>, and router <NUM> by way of a fiber-optic cable <NUM> connected to the switch, e.g., as explained in more detail below in reference to <FIG>. In an example embodiment, each of fiber-optic cables <NUM>, <NUM>, and <NUM> may include a respective pair of optical fibers, with the two fibers of the pair being configured to carry optical signals propagating in respective opposite directions. In an embodiment in which switch <NUM> is absent, fiber-optic cables <NUM> and <NUM> are directly end-connected to one another at the putative location of the switch.

Optical transceivers <NUM><NUM>-<NUM>N are connected to NICs <NUM><NUM>-<NUM>N using ports <NUM><NUM>-<NUM>N, respectively. Example embodiments of an optical transceiver <NUM>n (where n=<NUM>, <NUM>,. , N) are described in more detail below in reference to <FIG>.

In an example embodiment, optical interface <NUM> is a passive optical device that connects optical transceivers <NUM><NUM>-<NUM>N to fiber-optic cable <NUM> by way of optical fibers <NUM><NUM>-<NUM>N and <NUM><NUM>-<NUM>N connected to the corresponding south ports of the optical interface. Optical fibers <NUM><NUM>-<NUM>N are configured to direct downlink optical signals from optical interface <NUM> to optical transceivers <NUM><NUM>-<NUM>N, respectively. Optical fibers <NUM><NUM>-<NUM>N are configured to direct uplink optical signals from optical transceivers <NUM><NUM>-<NUM>N, respectively, to optical interface <NUM>. Optical interface <NUM> also has a north port <NUM> optically connected to fiber-optic cable <NUM>. An embodiment of optical interface <NUM> is described in more detail below in reference to <FIG>.

Electro-optical interface <NUM> has (i) a south port <NUM> optically connected to fiber-optic cable <NUM> and (ii) N north ports <NUM><NUM>-<NUM>N electrically connected to the corresponding ports of router <NUM>, e.g., as indicated in <FIG>. South port <NUM> is configured to (i) receive, through fiber-optic cable <NUM>, the optical signals carrying data transmitted southward and (ii) apply to fiber-optic cable <NUM> the optical signals carrying data transmitted northward. North ports <NUM><NUM>-<NUM>N are configured to (i) receive from router <NUM> the electrical signals carrying data transmitted southward and (ii) apply to router <NUM> the electrical signals carrying data transmitted northward. Electro-optical interface <NUM> includes circuits and/or devices (not explicitly shown in <FIG>) configured to perform (i) electrical-to-optical (E/O) conversion of the southward-propagating signals and (ii) optical-to-electrical (O/E) conversion of the northward-propagating signals. An example embodiment of electro-optical interface <NUM> is described in more detail below in reference to <FIG>.

Router <NUM> is capable of routing data packets between ports <NUM><NUM>-<NUM>N and between any of the ports <NUM><NUM>-<NUM>N and an "L3" port <NUM>. For example, router <NUM> can be designed to electrically route data packets (i) between any port <NUM>i and any port <NUM>j, where i≠j, and (ii) between any port <NUM>i and port <NUM>, where i=<NUM>, <NUM>,. , N and j=<NUM>, <NUM>,.

In some embodiments, router <NUM> can be a conventional router. In some other embodiments, router <NUM> can be replaced by a device comprising a suitable switch fabric capable of performing the functions of a router that are pertinent to the intended purpose and/or functionality of system <NUM>. As such, the term "router" used in the claims should be construed to also cover the switch-fabric-based embodiments thereof.

In some embodiments, any number (e.g., some or all) of the device pairs connected to ports <NUM>, each of such device pairs consisting of a respective network host <NUM> and a respective NIC <NUM>, can each be replaced by any other (e.g., L2) data source, such as an Ethernet switch port. The latter configuration can be realized, e.g., when the corresponding network hosts are configured to communicate, via their respective NICs, to a top-of-rack Ethernet switch. The Ethernet switch can then be connected to a corresponding port <NUM> to connect the corresponding network hosts to system <NUM>.

<FIG> shows a block diagram of electro-optical interface <NUM> (<FIG>) according to an embodiment. As shown in <FIG>, electro-optical interface <NUM> comprises a plurality of optical transceivers <NUM>/<NUM> electrically connected to ports <NUM>-146N and optically connected to fiber-optic cable <NUM>. Each of optical transceivers <NUM>/<NUM> comprises a respective one of optical transmitters <NUM>-210N and a respective one of optical receivers <NUM>-250N. In the shown embodiment, fiber-optic cable <NUM> comprises optical fibers <NUM> and <NUM>, with optical fiber <NUM> being configured to transmit southward-propagating optical signals, and optical fiber <NUM> being configured to transmit northward-propagating optical signals (also see <FIG>).

Each of optical transmitters <NUM>-21ON is configured to: (i) receive a respective one of carrier wavelengths A1-AN; (ii) modulate the received carrier wavelength with data received by way of a respective one of ports <NUM>-146N; and (iii) apply the resulting modulated optical signal <NUM> to an optical wavelength multiplexer (MUX) <NUM>. For example, optical transmitter 210n (where n=I, <NUM>,. , N) is configured to generate a modulated optical signal 220n using an optical modulator 218n and a driver circuit 214n connected as indicated in <FIG>. In various alternative embodiments, other suitable transmitter structures and/or architectures known in the pertinent art may also be used to implement optical transmitters. Optical wavelength multiplexer <NUM> is configured to receive optical signals <NUM>-220N and <NUM>-228N. As indicated above, optical signals <NUM>-22ON have carrier wavelengths A1-AN, respectively, and are modulated with data. In contrast, optical signals <NUM>-228N have carrier wavelengths AN+<NUM>-A2N, respectively, and are not modulated with data.

Carrier wavelengths A1-A:m used in electro-optical interface <NUM> can be generated using any suitable external or internal light source, e.g., comprising a corresponding plurality of lasers or a wavelength-comb generator. In some embodiments, each of carrier wavelengths A1-A2N can be generated using a respective CW laser. In some other embodiments, carrier wavelengths A1 -A2N can be generated using a suitable pulsed light source. An example external light source <NUM> that can be used to supply carrier wavelengths A1-A2N to electro-optical interface <NUM> is described in more detail below in reference to <FIG>.

In some embodiments, wavelengths A1-A2"~ can be spectrally arranged in accordance with a frequency grid, e.g., compliant with the ITU-T G. <NUM> Recommendation.

Optical wavelength multiplexer <NUM> is further configured to (i) generate a WDM signal <NUM> by optically multiplexing optical signals <NUM><NUM>-<NUM>N and <NUM><NUM>-<NUM>N and (ii) apply WDM signal <NUM> to optical fiber <NUM><NUM> as indicated in <FIG>. As a result, WDM signal <NUM> has some WDM components that are modulated with data and some WDM components that are not modulated with data. In an example embodiment, optical wavelength multiplexer <NUM> can be implemented as known in the pertinent art, e.g., using an arrayed waveguide grating (AWG) or a wavelength-selective switch (WSS).

Depending on the embodiment, the sequence of wavelengths λ<NUM>, λ<NUM>,. , λ2N may or may not be monotonic. In general, the wavelength set {λ<NUM>, λ<NUM>,. , λ2N} may consist of 2N different wavelengths arranged in any order such that the subscript value used to label the wavelength in the set may or may not be indicative of the relative spectral position of that wavelength. For example, in some embodiments, the wavelength value λ<NUM> may be smaller than the wavelength value λ<NUM> and greater than the wavelength value λ2N. The wavelength value λN+<NUM> may be smaller than the wavelength value λN and greater than the wavelength value λN+<NUM>, etc..

In some embodiments, the sequence of wavelengths λ<NUM>, λ<NUM>,. , λ2N may be monotonic. For example, in one embodiment, the wavelengths λ<NUM>-λ2N may be selected such that λ<NUM>>λ<NUM>>. > λN>λN+<NUM>>. >λ2N-<NUM>> λ2N. In another embodiment, the wavelengths λ<NUM>-λ2N may be selected such that λ<NUM><λ<NUM><. < λN<λN+<NUM><. <λ2N-<NUM>< λ2N.

Optical receivers <NUM><NUM>-<NUM>N are connected to an optical wavelength demultiplexer (DMUX) <NUM> as indicated in <FIG>. Optical wavelength demultiplexer <NUM> is connected to optical fiber <NUM><NUM> to receive therefrom a WDM signal <NUM> having carrier wavelengths λN+<NUM>-λ2N. In an example embodiment, optical interface <NUM> operates to apply WDM signal <NUM> to optical wavelength demultiplexer <NUM> by way of fiber-optic cables <NUM> and <NUM> (also see <FIG> and <FIG>). Optical wavelength demultiplexer <NUM> operates to (i) separate WDM signal <NUM> into modulated optical signals (WDM components) <NUM><NUM>-<NUM>N having carrier wavelengths λN+<NUM>-λ2N, respectively, and (ii) apply each of the modulated optical signals <NUM><NUM>-<NUM>N to a respective one of optical receivers <NUM><NUM>-<NUM>N. Each of optical receivers <NUM><NUM>-<NUM>N then operates to (i) recover the data encoded in the respective one of the modulated optical signals <NUM><NUM>-<NUM>N and (ii) direct the recovered data to the respective one of ports <NUM><NUM>-<NUM>N.

In some embodiments, optical receiver <NUM>n may be configured, as known in the pertinent art, for direct detection of modulated optical signal <NUM>n, e.g., using a photodetector configured to convert that optical signal into a corresponding electrical signal proportional to the optical power (e.g., squared electric field) thereof. In some other embodiments, optical receiver <NUM>n may be configured, as known in the pertinent art, for coherent detection of modulated optical signal <NUM>n, e.g., using a respective optical local oscillator signal <NUM>n. In some of the latter embodiments, a plurality of optical taps <NUM><NUM>-<NUM>N may be used to provide optical local oscillator signals <NUM><NUM>-<NUM>N to optical receivers <NUM><NUM>-<NUM>N, respectively, by diverting some of the optical power of optical signals <NUM><NUM>-<NUM>N, e.g., as indicated in <FIG>.

In an example embodiment, optical wavelength demultiplexer <NUM> can be implemented similar to optical wavelength multiplexer <NUM>, e.g., using an AWG or a WSS. However, optical wavelength demultiplexer <NUM> can generally be smaller in size than optical wavelength multiplexer <NUM>. For example, as indicated in <FIG>, optical wavelength demultiplexer <NUM> has (N+<NUM>) optical ports, whereas optical wavelength multiplexer <NUM> has (2N+<NUM>) optical ports.

<FIG> shows a block diagram of optical interface <NUM> (<FIG>) according to an embodiment. As shown, optical interface <NUM> comprises an optical wavelength demultiplexer (DMUX) <NUM> and an optical wavelength multiplexer (MUX) <NUM>. In the shown embodiment, fiber-optic cable <NUM> comprises optical fibers <NUM><NUM> and <NUM><NUM>, with optical fiber <NUM><NUM> being configured to apply WDM signal <NUM> to optical wavelength demultiplexer <NUM>, and optical fiber <NUM><NUM> being configured to transmit out the WDM signal <NUM> applied thereto by optical wavelength multiplexer <NUM> (also see <FIG> and <FIG>).

Optical wavelength demultiplexer <NUM> operates to (i) separate WDM signal <NUM> into optical signals <NUM><NUM>-<NUM>N and (ii) apply optical signals <NUM><NUM>-<NUM>N to optical fibers <NUM><NUM>-<NUM>N, respectively (also see <FIG>). Each of optical signals <NUM><NUM>-<NUM>N is a WDM signal having two respective WDM components. More specifically, optical signal <NUM>n has (i) a first WDM component <NUM>n,<NUM> having carrier wavelength λn and (ii) a second WDM component <NUM>n,<NUM> having carrier wavelength λN+n (also see <FIG>).

WDM component <NUM>n,<NUM> of optical signal <NUM>n can substantially be a copy of modulated optical signal <NUM>n (see <FIG>). As used herein, the term "substantially" indicates that (i) WDM component <NUM>n,<NUM> and modulated optical signal <NUM>n carry the same data and (ii) any differences between the optical waveforms of WDM component <NUM>n,<NUM> and modulated optical signal <NUM>n are caused by the optical losses and/or signal distortions imposed by the various optical elements of system <NUM> located in the optical path between optical transmitter <NUM>n (see <FIG>) and optical transceiver <NUM>n (<FIG>). As indicated above, those optical elements include at least optical wavelength multiplexer <NUM> (<FIG>), fiber-optic cable <NUM> (<FIG>), fiber-optic cable <NUM> (<FIG>), and optical wavelength demultiplexer <NUM>.

WDM component <NUM>n,<NUM> of optical signal <NUM>n is typically an attenuated copy of optical signal <NUM>n (see <FIG>). As such, WDM component <NUM>n,<NUM> is not modulated with data.

In an example embodiment, optical wavelength demultiplexer <NUM> can be implemented as known in the pertinent art, e.g., using an AWG or a WSS.

Optical wavelength multiplexer <NUM> is configured to: (i) receive modulated optical signals <NUM><NUM>-<NUM>N from optical transceivers <NUM><NUM>-<NUM>N, respectively; (ii) generate WDM signal <NUM> by optically multiplexing modulated optical signals <NUM><NUM>-<NUM>N; and (ii) apply WDM signal <NUM> to optical fiber <NUM><NUM> as indicated in <FIG>. In an example embodiment, optical wavelength multiplexer <NUM> can be implemented as known in the pertinent art, e.g., using an AWG or a WSS.

<FIG> show block diagrams of optical transceiver <NUM>n according to an embodiment. More specifically, <FIG> shows an overall block diagram of optical transceiver <NUM>n. <FIG> show several possible embodiments of an optical drop filter <NUM>n that can be used in the embodiment of optical transceiver <NUM>n shown in <FIG>.

For illustration purposes and without any implied limitations, embodiments of optical transceiver <NUM>n are described in reference to a waveguide circuit. Based on the provided description, a person of ordinary skill in the art will understand how to make and use alternative embodiments of optical transceiver <NUM>n using suitable hybrid circuits and/or free-space optics.

Referring to <FIG>, optical transceiver <NUM>n comprises an optical drop filter <NUM>n, an optical receiver <NUM>n, and an optical transmitter <NUM>n connected by optical waveguides <NUM>-<NUM> as indicated in <FIG>.

Optical drop filter <NUM>n operates to: (i) couple WDM component <NUM>n,<NUM> of optical signal <NUM>n received through waveguide <NUM> into waveguide <NUM>; and (ii) couple WDM component <NUM>n,<NUM> of optical signal <NUM>n into waveguide <NUM>. Waveguides <NUM> and <NUM> then operate to apply WDM components <NUM>n,<NUM> and <NUM>n,<NUM> to optical receiver <NUM>n and optical transmitter <NUM>n, respectively.

Optical receiver <NUM>n operates to: (i) receive WDM component <NUM>n,<NUM> from optical waveguide <NUM>; (ii) recover the data encoded in WDM component <NUM>n,<NUM>; and (iii) direct the recovered data to port <NUM>n (also see <FIG>).

Optical transmitter <NUM>n operates to: (i) receive WDM component <NUM>n,<NUM> from optical waveguide <NUM>; (ii) modulate carrier wavelength λN+n of the received WDM component <NUM>n,<NUM> with data received by way of port <NUM>n; and (iii) apply a resulting modulated optical signal <NUM>n to optical waveguide <NUM>. In the embodiment shown in <FIG>, optical transmitter <NUM>n comprises an optical modulator <NUM>n and a driver circuit <NUM>n connected as indicated in <FIG>. In various alternative embodiments, other suitable transmitter structures and/or architectures known in the pertinent art may also be used to implement optical transmitter <NUM>n.

<FIG> shows a block diagram of a first example embodiment of optical drop filter <NUM>n. In this embodiment, optical drop filter <NUM>n comprises a <NUM>-dB power splitter <NUM> and optical filters <NUM> and <NUM>. Optical filter <NUM> has spectral characteristics that cause this filter to pass through WDM component <NUM>n,<NUM> while stopping WDM component <NUM>n,<NUM>. Optical filter <NUM> has spectral characteristics that cause this filter to pass through WDM component <NUM>n,<NUM> while stopping WDM component <NUM>n,<NUM>. In some embodiments, one or both of optical filters <NUM> and <NUM> may be tunable.

<FIG> shows a block diagram of a second example embodiment of optical drop filter <NUM>n. In this embodiment, optical drop filter <NUM>n comprises an AWG <NUM>. The pass bands of AWG <NUM> are such that WDM components <NUM>n,<NUM> and <NUM>n,<NUM> are directed from optical waveguide <NUM> to optical waveguides <NUM> and <NUM>, respectively.

<FIG> shows a block diagram of a third example embodiment of optical drop filter <NUM>n. In this embodiment, optical drop filter <NUM>n comprises a ring resonator <NUM> coupled to optical waveguides <NUM>-<NUM> using optical couplers <NUM> and <NUM>. The resonant frequency of ring resonator <NUM> is such that the ring resonator causes (i) WDM component <NUM>n,<NUM> to be dropped from waveguide <NUM> into waveguide <NUM> and (ii) WDM component <NUM>n,<NUM> to be transferred from waveguide <NUM> into waveguide <NUM> without significant attenuation. In some embodiments, the resonant frequency of ring resonator <NUM> may be tunable.

<FIG> shows a block diagram of a communication system <NUM> according to another embodiment. System <NUM> comprises M nominal copies of system <NUM> (<FIG>), which are labeled <NUM><NUM>-<NUM>M, respectively. System <NUM> further comprises an M×<NUM> optical switch <NUM>, an electro-optical interface <NUM>M+<NUM>, and a router <NUM>M+<NUM>. Electro-optical interface <NUM>M+<NUM> is a nominal copy of electro-optical interface <NUM> (see <FIG>). Router <NUM>M+<NUM> is a nominal copy of router <NUM> (<FIG>).

Optical switch <NUM> has M south ports <NUM>, <NUM>,. , M and a north port <NUM>. In operation, optical switch <NUM> can connect a selected one of its south ports <NUM>, <NUM>,. , M to the north port <NUM> in response to a control signal <NUM> applied to the switch by a network controller. South ports <NUM>, <NUM>,. , M of optical switch <NUM> are connected to systems <NUM><NUM>-<NUM>M using fiber-optic cables <NUM><NUM>-<NUM>M, respectively (also see <FIG>). North port <NUM> of optical switch <NUM> is connected to south port <NUM>M+<NUM> of electro-optical interface <NUM>M+<NUM> using a fiber-optic cable <NUM>.

During normal operation of system <NUM>m (where m=<NUM>, <NUM>,. , M), the network controller is used to configure the corresponding optical switch <NUM> to end-connect fiber-optic cables <NUM> and <NUM> of that system (see <FIG>). As a result, in this configuration, the network hosts <NUM> of system <NUM>m can communicate with external entities by way of the L3 port <NUM>m, e.g., as described above in reference to <FIG>. In addition, system <NUM> provides the network hosts <NUM> of any system <NUM>m with a redundant communication path to the external entities by way of the L3 port <NUM>M+<NUM> of router <NUM>M+<NUM>. This redundant communication path provides fault protection against certain system faults and can be engaged by appropriately configuring optical switch <NUM> (<FIG>) and the optical switch <NUM> (see <FIG>) of system <NUM>m. More specifically, to direct data traffic through the L3 port <NUM>M+<NUM> of router <NUM>M+<NUM> instead of the L3 port <NUM>m of system <NUM>m, the optical switch <NUM> of system <NUM>m is configured by the network controller to end-connect fiber-optic cables <NUM> and <NUM>m. The network controller can then apply an appropriate control signal <NUM> to configure optical switch <NUM> to connect the south port m and north port <NUM> thereof, thereby end-connecting fiber-optic cables <NUM>m and <NUM>.

<FIG> shows a block diagram of a light source <NUM> that can be used to supply carrier wavelengths to interfaces <NUM> (<FIG>) and/or <NUM> (<FIG>) according to an embodiment. Light source <NUM> comprises (i) CW lasers <NUM><NUM>-<NUM>2N configured to generate CW optical signals <NUM><NUM>-<NUM>2N having carrier wavelengths λ<NUM>-λ2N, respectively, and (ii) an optional optical amplifier <NUM>. Optical amplifier <NUM> can be used, e.g., to boost the optical power of optical signals <NUM><NUM>-<NUM>2N if appropriate or necessary for proper operation of system <NUM>.

The above-described architecture of system <NUM> advantageously enables the use of a single, conveniently located light source <NUM> to provide carrier wavelengths for both uplink and downlink optical traffic through that system.

In an example embodiment, optical amplifier <NUM> comprises an optical wavelength multiplexer (MUX) <NUM>, an Erbium-doped fiber amplifier (EDFA) <NUM>, and an optical wavelength demultiplexer (DMUX) <NUM>.

Optical wavelength multiplexer <NUM> is configured to: (i) receive CW optical signals <NUM><NUM>-<NUM>2N from lasers <NUM><NUM>-<NUM>2N; (ii) generate a WDM signal <NUM> by optically multiplexing CW optical signals <NUM><NUM>-<NUM>2N; and (iii) apply WDM signal <NUM> to EDFA <NUM>. In an example embodiment, optical wavelength multiplexer <NUM> can be similar to optical wavelength multiplexer <NUM> (<FIG>).

EDFA <NUM> is configured to optically amplify WDM signal <NUM>, thereby generating an amplified WDM signal <NUM>.

Optical wavelength demultiplexer <NUM> is configured to demultiplex WDM signal <NUM> into CW optical signals <NUM><NUM>-<NUM>2N having carrier wavelengths λ<NUM>-λ2N, respectively. In an example embodiment, optical wavelength demultiplexer <NUM> can be a nominal copy of optical wavelength multiplexer <NUM> connected to direct the optical signals transmitted therethrough in the opposite direction.

In an example embodiment, EDFA <NUM> may have a gain spectrum that causes the optical power of each optical signal <NUM>k to be greater than the optical power of the corresponding optical signal <NUM>k, where k=<NUM>, <NUM>,. In some embodiments, EDFA <NUM> may have a gain spectrum that causes greater amplification for optical signals <NUM>N+<NUM>-<NUM>2N than for optical signals <NUM><NUM>-<NUM>N.

According to an example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of <FIG>, provided is an apparatus (e.g., <NUM>, <FIG>, or a part thereof) comprising: a first wavelength demultiplexer (e.g., <NUM>, <FIG>) having an optical input (e.g., at <NUM>, <FIG>) and a plurality of optical outputs (e.g., at <NUM>, <FIG>); a first wavelength multiplexer (e.g., <NUM>, <FIG>) having an optical output (e.g., at <NUM>, <FIG>) and a plurality of optical inputs (e.g., at <NUM>, <FIG>); a plurality of optical drop filters (e.g., <NUM>n, <FIG>), each having a respective optical input (e.g., at <NUM>, <FIG>), a respective first optical output (e.g., at <NUM>, <FIG>), and a respective second optical output (e.g., at <NUM>, <FIG>); and a plurality of first optical modulators (e.g., <NUM>n, <FIG>) optically connected between the plurality of optical drop filters and the first wavelength multiplexer; wherein the respective optical input of each of the plurality of optical drop filters is optically connected to a respective one of the plurality of optical outputs of the first wavelength demultiplexer; and wherein the respective second optical output of each of the plurality of optical drop filters is optically connected to a respective one of the plurality of optical inputs of the first wavelength multiplexer by way of a respective one of the plurality of first optical modulators.

In some embodiments of the above apparatus, the apparatus of further comprises a plurality of optical receivers (e.g., <NUM>n, <FIG>); and wherein the respective first optical output of each of the plurality of optical drop filters is optically connected to a respective one of the plurality of optical receivers.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of network hosts (e.g., <NUM>n, <FIG>); and wherein each of the plurality of optical receivers is electrically connected (e.g., by way of <NUM>n, <FIG>, <FIG>) to a respective one of the network hosts to direct thereto an output data stream generated in response to a respective modulated optical input signal received from the respective first optical output.

In some embodiments of any of the above apparatus, each of the plurality of first optical modulators is electrically connected (e.g., by way of <NUM>n and <NUM>n, <FIG>, <FIG>) to a respective one of the network hosts to generate a respective modulated optical output signal in response to a respective input data stream received from said respective one of the network hosts.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of network hosts (e.g., <NUM>n, <FIG>); and wherein each of the plurality of first optical modulators is electrically connected (e.g., by way of <NUM>n and <NUM>n, <FIG>, <FIG>) to a respective one of the network hosts to generate a respective modulated optical signal in response to a respective input data stream received from said respective one of the network hosts.

In some embodiments of any of the above apparatus, the apparatus further comprises a second wavelength multiplexer (e.g., <NUM>, <FIG>) having an optical output (e.g., at <NUM>, <FIG>) and a plurality of optical inputs (e.g., at <NUM> and <NUM>, <FIG>); and wherein the optical output of the second wavelength multiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical input of the first wavelength demultiplexer.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of second optical modulators (e.g., <NUM>n, <FIG>) optically connected to apply modulated light to a first subset (e.g., <NUM>, <FIG>) of the optical inputs of the second wavelength multiplexer.

In some embodiments of any of the above apparatus, a different second subset (e.g., <NUM>, <FIG>) of the optical inputs of the second wavelength multiplexer is configured to receive continuous-wave light.

In some embodiments of any of the above apparatus, each of the plurality of first optical modulators is configured to generate modulated light by modulating continuous-wave light of a respective different carrier wavelength of a first plurality (e.g., λN+<NUM>-λ2N, <FIG>) of carrier wavelengths, the continuous-wave light being received from the respective second optical output; and wherein each of the plurality of second optical modulators is configured to generate modulated light by modulating continuous-wave light of a respective different carrier wavelength of a second plurality (e.g., λ<NUM>-XN, <FIG>) of carrier wavelengths, the first and second pluralities of carrier wavelengths having no carrier wavelength in common.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of lasers (e.g., <NUM>, <FIG>) configured to generate continuous-wave light at a plurality of different carrier wavelengths (e.g., λ<NUM>-λN, <FIG>); and wherein each of the plurality of second optical modulators is configured to generate modulated light by modulating the continuous-wave light of a respective one of the different carrier wavelengths.

In some embodiments of any of the above apparatus, the apparatus further comprises a second wavelength demultiplexer (e.g., <NUM>, <FIG>) having an optical input (e.g., at <NUM>, <FIG>) and a plurality of optical outputs (e.g., at <NUM>, <FIG>); and wherein the optical input of the second wavelength demultiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical output of the first wavelength multiplexer.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of optical receivers (e.g., <NUM>n, <FIG>), each optically connected to receive light from a respective one of the plurality of optical outputs of the second wavelength demultiplexer.

In some embodiments of any of the above apparatus, the first wavelength multiplexer has fewer (e.g., N, <FIG>) optical inputs than the second wavelength multiplexer (e.g., 2N, <FIG>).

In some embodiments of any of the above apparatus, the apparatus further comprises: a second wavelength multiplexer (e.g., <NUM>, <FIG>) having an optical output (e.g., at <NUM>, <FIG>) and a plurality of optical inputs (e.g., at <NUM> and <NUM>, <FIG>); a second wavelength demultiplexer (e.g., <NUM>, <FIG>) having an optical input (e.g., at <NUM>, <FIG>) and a plurality of optical outputs (e.g., at <NUM>, <FIG>); a plurality of second optical modulators (e.g., <NUM>n, <FIG>) optically connected to apply modulated light to some of the optical inputs (e.g., <NUM>, <FIG>) of the second wavelength multiplexer; and a plurality of optical receivers (e.g., <NUM>n, <FIG>), each optically connected to receive light from a respective one of the plurality of optical outputs of the second wavelength demultiplexer; wherein the optical output of the second wavelength multiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical input of the first wavelength demultiplexer; and wherein the optical input of the second wavelength demultiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical output of the first wavelength multiplexer.

In some embodiments of any of the above apparatus, the apparatus further comprises a router (e.g., <NUM>, <FIG>) having a plurality of ports (e.g., <NUM>/<NUM>, <FIG>); wherein each of the plurality of second optical modulators is electrically connected (e.g., by way of <NUM>n and <NUM>n, <FIG>, <FIG>) to a respective one of the ports to generate modulated light in response to a respective input data stream received from said respective one of the ports; and wherein each of the plurality of optical receivers is electrically connected (e.g., by way of <NUM>n, <FIG>) to a respective one of the ports to direct thereto an output data stream generated in response to the light received from the respective one of the plurality of optical outputs of the second wavelength demultiplexer.

In some embodiments of any of the above apparatus, the plurality of ports of the router includes at least one port (e.g., <NUM>, <FIG>) connectable to an external network (e.g., WAN, <FIG>, or the Internet); and wherein the router is configurable to receive the respective input data stream from the external network through said at least one port.

In some embodiments of any of the above apparatus, the plurality of ports of the router includes at least one port (e.g., <NUM>, <FIG>) connectable to an external network (e.g., WAN, <FIG>, or the Internet); and wherein the router is configurable to transmit the output data stream to the external network through said at least one port.

In some embodiments of any of the above apparatus, the router is further configurable to receive the respective input data stream from the external network through said at least one port.

In some embodiments of any of the above apparatus, the apparatus further comprises: a second wavelength multiplexer (e.g., <NUM>, <FIG>) having an optical output (e.g., at <NUM>, <FIG>) and a plurality of optical inputs (e.g., at <NUM> and <NUM>, <FIG>); a second wavelength demultiplexer (e.g., <NUM>, <FIG>) having an optical input (e.g., at <NUM>, <FIG>) and a plurality of optical outputs (e.g., at <NUM>, <FIG>); a plurality of optical receivers (e.g., <NUM>n, <FIG>), each optically connected to receive light from a respective one of the plurality of optical outputs of the second wavelength demultiplexer; and wherein the optical output of the second wavelength multiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical input of the first wavelength demultiplexer; wherein the optical input of the second wavelength demultiplexer is fiber-connected (e.g., using <NUM> and <NUM>, <FIG>, <FIG>, <FIG>) to the optical output of the first wavelength multiplexer; and wherein some of the optical inputs (e.g., <NUM>, <FIG>) of the second wavelength multiplexer have optical taps (e.g., <NUM>, <FIG>) connected thereto, the optical taps being connected to the plurality of optical receivers to direct thereto tapped light (e.g., <NUM>, <FIG>) from said some of the optical inputs.

In some embodiments of any of the above apparatus, at least one of the optical receivers is configured to use the tapped light as an optical local oscillator signal (e.g., <NUM>n, <FIG>) to be optically mixed with the light received from the second wavelength demultiplexer.

In some embodiments of any of the above apparatus, an optical drop filter of the plurality of optical drop filters is tunable.

In some embodiments of any of the above apparatus, an optical drop filter of the plurality of optical drop filters comprises an arrayed waveguide grating (e.g., <NUM>, <FIG>).

In some embodiments of any of the above apparatus, an optical drop filter of the plurality of optical drop filters comprises a ring resonator (e.g., <NUM>, <FIG>).

According to another example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of <FIG>, provided is another apparatus (e.g., <NUM>, <FIG>, or a part thereof) comprising: a plurality of digital data servers (e.g., <NUM>, <FIG>); a first wavelength demultiplexer (e.g., <NUM>, <FIG>) having optical outputs (e.g., at <NUM>, <FIG>) to the digital data servers; a first wavelength multiplexer (e.g., <NUM>, <FIG>) having optical inputs (e.g., at <NUM>, <FIG>) from the digital data servers; an optical switch including a plurality of optical transceivers (e.g., <NUM>, <FIG>), a plurality of optical sources (e.g., <NUM>, <FIG>), a second wavelength multiplexer (e.g., <NUM>, <FIG>), and a second wavelength demultiplexer (e.g., <NUM>, <FIG>); wherein an optical output (e.g., at <NUM>, <FIG>) of the second wavelength multiplexer is fiber-connected to an optical input (e.g., at <NUM>, <FIG>) of the first wavelength demultiplexer; wherein an optical input (e.g., at <NUM>, <FIG>) of the second wavelength demultiplexer is fiber-connected to an optical output (e.g., at <NUM>, <FIG>) of the first wavelength multiplexer; wherein each optical transceiver is configured to transmit to a respective optical input of the first wavelength multiplexer a modulated optical carrier on a corresponding optical transmission wavelength channel and to receive from a respective optical output of the first wavelength demultiplexer a modulated optical carrier on a different optical reception wavelength channel; wherein each optical source is configured to transmit continuous wave light of a respective one of the wavelength reception channels to a respective optical input of the second optical wavelength multiplexer; and wherein each optical transceiver is configured to receive from the first wavelength demultiplexer continuous wave light of a respective one of the optical reception wavelength channels.

In some embodiments of the above another apparatus, each optical transceiver has an optical modulator connected to modulate data onto light of the optical reception wavelength channel received therein in response to the data being received from a respective one of the digital servers.

In some embodiments of any of the above apparatus, each optical transceiver has a respective optical receiver to demodulate data from light of the optical transmission wavelength channel received therein.

In some embodiments of any of the above apparatus, the first wavelength demultiplexer, the first wavelength multiplexer, and the optical transceivers are located in a rack.

While this disclosure includes references to illustrative embodiments, this specification is not intended to be construed in a limiting sense.

For example, in some embodiments, not all of the carrier wavelengths λN+<NUM>-λ2N may need to be transmitted on the downlink as described above. Instead, some of these carrier wavelengths may be generated locally, e.g., at or near the physical location of the corresponding transceivers <NUM>.

Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word "about" or "approximately" preceded the value of the value or range.

It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this disclosure may be made by those skilled in the art without departing from the scope of the disclosure as expressed in the following claims. Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Also for purposes of this description, the terms "couple," "coupling," "coupled," "connect," "connecting," or "connected" refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms "directly coupled," "directly connected," etc., imply the absence of such additional elements.

The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the disclosure is indicated by the appended claims rather than by the description and figures herein.

It will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its scope as defined in the appended claims.

Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claim 1:
An apparatus comprising:
a first wavelength demultiplexer (<NUM>) having an optical input and N optical outputs, each to output a respective optical signal (312n) having a first WDM component (312n,<NUM>) and a second WDM component (312n,<NUM>) ;
a first wavelength multiplexer (<NUM>) having an optical output and N optical inputs,
wherein the first wavelength multiplexer (<NUM>) is configured to receive N data modulated optical signals (<NUM>) on the N optical inputs thereof and generate a WDM signal (<NUM>) therefrom;
characterized by
N optical drop filters (440n), each having a respective optical input, a respective first optical output, and a respective second optical output;
N first optical modulators (468n) optically connected between the N optical drop filters and the first wavelength multiplexer (<NUM>);
a second wavelength multiplexer (<NUM>) having an optical output and 2N optical inputs; and
N second optical modulators (218n) optically connected to apply modulated light to N of the optical inputs of the second wavelength multiplexer (<NUM>);
wherein the optical output of the second wavelength multiplexer (<NUM>) is fiber-connected to the optical input of the first wavelength demultiplexer (<NUM>);
wherein the respective optical input of each of the N optical drop filters is optically connected to a respective one of the N optical outputs of the first wavelength demultiplexer (<NUM>);
wherein the respective first optical output of each of the N optical drop filters is to output the first WDM component (312n,<NUM>) of the respective optical signal (312n); and
wherein the respective second optical output of each of the N optical drop filters is to output the second WDM component (312n,<NUM>) of the respective optical signal (312n) and is optically connected to a respective one of the N optical inputs of the first wavelength multiplexer (<NUM>) by way of a respective one of the N first optical modulators (468n).