Optical transmitters and receivers coupled to a same laser source forward path, including examples of coherent communication

Abstract

An optical transmitter and receiver system splits laser inputs into multiple channels for transmission and reception. The optical transmitter receives a laser input from a forward laser path of a laser source, splits the input into a plurality of transmit channels, and transmits the channels to a destination. The optical receiver receives another laser input from the same forward laser path, splits the input into a plurality of receive channels, and processes the channels to receive data. The optical transmitter and receiver can be used in a variety of applications, including telecommunications, data centers, and industrial control systems.

Description

OPTICAL TRANSMITTERS AND RECEIVERS COUPLED TO A SAMELASER SOURCE FORWARD PATH, INCLUDING EXAMPLES OF COHERENTCOMMUNICATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119 of the earlier filing date of U.S. Provisional Application Serial No. 63 / 657,033 filed June 6. 2024, the entire contents of which is hereby incorporated by reference in its entirety for any purpose.STATEMENT REGARDING RESEARCH & DEVELOPMENT

[0002] This invention was made with government support under Grant No. #2142996, awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] Examples described herein relate generally to optical transmitters and optical receivers. Examples of optical transmitters and optical receivers coupled to a same laser source forward path are described, including examples of coherent communication.BACKGROUND

[0004] In pluggable computing systems utilizing optical communication, compute nodes may generally be arranged in trays of racks. Each compute node may include, for example, one or more processors which may be packaged in one or more packages on one or more trays, such as boards. Outputs of the compute nodes may be electrical outputs from the compute nodes. In order to provide optical communication, optical converters may be provided, for example at the edges of each of the trays, boards, and / or rack units. The number of cables used to provide for this optical communication conversion at the edges may be undesirable and / or prohibitive.

[0005] Accordingly, co-packaged compute nodes may be used. In a co-packaged compute node, a package may include processing elements (e.g., one or more processors) and / or other electrical components such as memory. The package may further include an optical input and / or output. In this manner, a conversion between electrical and optical signals may occur within a package in examples of compute nodes using co-packagedoptics. However, the amount of data which may be communicated by or to a co-packaged compute node may be limited.

[0006] The advent of computationally intensive applications such as artificial intelligence (Al) and machine learning (ML) have increased a need for dense and ultralow power multi-TB / s inter / intra-rack optical communications as well as low-latency chip- to-chip interconnects. Edge-to-cloud connectivity and distributed radar, phased-array, and even multiple input multiple output (MIMO) systems have similar need for high-density, low power communication. Silicon photonic transceivers (TRx) have been used to copackage optical transceivers with high performance processors (e.g., GPU / FPGA / SoCs) in a same package (also referred to herein as ‘Ao-packaged optics7’ or CPO). These copackaged systems may have limitations in the available data rates they may achieve.

[0007] Wavelength division multiplexing (WDM) has been used to provide optical communication in co-packaged systems. However, scaling the modulation to allow for even higher data rates seems infeasible due to the significant signal to noise ratio (SNR) overheads.SUMMARY

[0008] Examples of sy stems are described herein. An example system includes an optical transmitter and an optical receiver. The optical transmitter may be configured to receive a laser input from a forward laser path of a laser source. The optical transmitter may be configured to split the laser input into a plurality of transmit channels. The optical receiver may be configured to receive another laser input from the forward laser path of the laser source, the optical receiver may be configured to split the another laser input into a plurality of receive channels.

[0009] In some examples, the laser input and the another laser input are multi-wavelength inputs.

[0010] In some examples, the transmit channels include circuitry for amplitude and phase modulation of transmit signals using the laser input. In some examples, the modulation is QAM modulation.

[0011] In some examples, the receive channels include circuitry for demodulation of modulated signals received from the transmit channels, the demodulation including amplitude and phase recovery. In some examples, the demodulation comprises QAM demodulation.

[0012] In some examples, the optical transmitter is packaged in a first integrated circuit package, and wherein the optical receiver is packaged in a second integrated circuit package.

[0013] In some examples, the optical transmitter is positioned within a first rack of computing components, and wherein the optical receiver is positioned within a second rack of computing components.

[0014] In some examples, the optical transmitter comprises a phase-constant amplitude modulator. In some examples, the phase-constant amplitude modulator is a micro-ring resonator.

[0015] In some examples, the optical receiver includes a dual polarization receiver. The dual polarization receiver may include a polarization controller configured to separate, in accordance with a control signal, optical signals encoded with a first polarization from optical signals encoded with a second polarization. The dual polarization receiver may include a first polarization receiver configured to decode in-phase and quadrature transmit data encoded with the first polarization. The dual polarization receiver may include a first combiner configured to generate a first metric based on one or more combinations of the in-phase and quadrature transmit data decoded by the first polarization receiver. The dual polarization receiver may include a second polarization receiver configured to decode in- phase and quadrature transmit data encoded with the second polarization. The dual polarization receiver may include a second combiner configured to generate a second metric based on one or more combinations of the in-phase and quadrature transmit data decoded by the second polarization receiver. The dual polarization receiver may include a polarization estimation controller configured to provide the control signal to the polarization controller, the control signal generated based on the first metric and the second metric.

[0016] Examples of methods are described herein. An example method includes generating transmit data using electronic circuitry, transmitting the transmit data over an optical link, the optical link including a transmitter configured to receive the transmit data and optical energy from a laser, the transmitter configured to utilize QAM modulation to modulate the optical energy' with the transmit data to provide optical signals having modulated data. The method may further include forwarding optical energy from the laser to a receiver configured to receive the modulated data.

[0017] In some examples, the electronic circuitry' comprises a processor.

[0018] In some examples, the electronic circuitry comprises a switch.

[0019] In some examples, the optical link includes a plurality of optical fibers, including one for each channel of the transmitter.

[0020] In some examples, forwarding optical energy includes forwarding the optical energy over an optical fiber.

[0021] An example system may include a first transceiver, a second transceiver, a first laser configured to provide optical energy to a transmitter of the first transceiver and a receiver of the second transceiver, the first laser having a first polarization, a second laser configured to provide optical energy to a transmitter of the second transceiver and a receiver of the first transceiver, the second laser having a second polarization, different from the first polarization, and a fiber configured to forward optical energy from the first laser to the second transceiver and to forward optical energy from the second laser to the first transceiver.

[0022] In some examples, the transmitter of the first transceiver is coupled to the receiver of the second transceiver using multiple optical fibers.

[0023] In some examples, the receiver of the first transceiver is coupled to the transmitter of the second transceiver using multiple optical fibers.

[0024] In some examples, the system may further include a multiplexer configured to multiplex energy from the first laser with additional optical energy from another laser prior to forwarding on the fiber.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic illustration of a system arranged in accordance with examples described herein.

[0026] FIG. 2 is a schematic illustration of a multi-wavelength system arranged in accordance with examples described herein.

[0027] FIG. 3 is a schematic illustration of a system for use in chip-to-chip communication arranged in accordance with examples described herein.

[0028] FIG. 4 is a schematic illustration of a system for use in box-to-box communication arranged in accordance with examples described herein.

[0029] FIG. 5 is a schematic illustration of a system for use with near-package optics arranged in accordance with examples described herein.

[0030] FIG. 6 is a schematic illustration of a transmitter arranged in accordance with examples described herein.

[0031] FIG. 7 is a schematic illustration of a receiver arranged in accordance with examples described herein.

[0032] FIG. 8 is a schematic illustration of a transmitter supporting dual polarization arranged in accordance with examples described herein.

[0033] FIG. 9 is a schematic illustration of a receiver supporting dual polarization arranged in accordance with examples described herein.

[0034] FIG. 10 is a schematic illustration of a bidirectional dual-polarization system arranged in accordance with examples described herein.

[0035] FIG. 11 is a schematic illustration of a system sharing a laser forwarding path in a single fiber using dual polarization with multiple lasers using separate laser forwarding fibers, arranged in accordance with examples described herein.

[0036] FIG. 12 is a schematic illustration of a system sharing laser forwarding in a single fiber using dual polarization and wavelength division multiplexing arranged in accordance with examples described herein.

[0037] FIG. 13 is a sheet of equations referred to herein.

[0038] FIG. 14 is a plot of simulations of required laser power for an example 8 links each at 400 Gb / s (3.2 Tb / s bidirectional bandwidth) for various modulation techniques in accordance with examples described herein.DETAILED DESCRIPTION

[0039] Certain details are set forth herein to provide an understanding of described embodiments of technology. However, other examples may be practiced without various of these particular details. In some instances, w?ell-known circuits, control signals, timing protocols, packaging components, optical components, and / or software operations have not been shown in detail in order to avoid unnecessarily obscuring the described embodiments. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter and / or claims presented here.

[0040] An optical transmitter and receiver system splits laser inputs into multiple channels for transmission and reception. The optical transmitter receives a laser input from a forward laser path of a laser source, splits the input into a plurality of transmit channels,and transmits the channels to a destination. The optical receiver receives another laser input from the same forward laser path, splits the input into a plurality of receive channels, and processes the channels to receive data. The optical transmitter and receiver can be used in a variety of applications, including telecommunications, data centers, and industrial control systems.

[0041] Examples described herein relate generally to co-packaged optics. Examples of systems, apparatuses, and methods are disclosed which facilitate use of a single laser source by both multiple transmit channels and multiple receive channels. The multiple transmit channels and multiple receive channels may be used for optical coherent communication. Any of a variety of data may be transmitted and / or received in accordance with examples described herein, including models, databases, computational results, and / or control signals.

[0042] Examples described herein utilize compute nodes having co-packaged optics. However, use cases for optical communication between co-packaged compute nodes may advantageously utilize large amounts of data. Accordingly, examples described herein may utilize coherent communication between optical transmitters and receivers. In coherent communication techniques, generally both amplitude and phase modulation are used to encode data. Coherent communication may accordingly generally increase an amount of data that can be communicated between two compute nodes using co-packaged optics. In coherent communication, the optical receiver may detect both phase and amplitude of received optical signals. Accordingly, a laser is utilized at the optical receiver as well as the optical transmitter. In examples described herein, a same forward laser path may be shared between multiple channels of an optical transmitter and multiple channels of an optical receiver.

[0043] Accordingly, note that modulations like quadrature amplitude modulation (QAM) can be advantageously utilized to increase spectral-efficiency and overall aggregated bandwidths per fiber for CPO. Examples of optical TRx (e.g., those which may be used for long-haul applications with up to 1000 km-ranges) are described which may be advantageously used in CPO applications. In some examples, devices and systems described herein may avoid drawbacks such as (1 ) a bulky area of Mach-Zender modulators may not be desirable to avoid limiting the area / shoreline bandwidth densities per package, and (2) use of local lasers and DSP-based laser carrier recovery' which may limit energy-efficiencies.

[0044] Examples described herein may provide Coherent CPO (C2PO) for QAM modulation by sharing a laser forwarded link among multiple channels and multiple ports. In some examples, links up to 100m may be used, although other lengths may be used in other examples.

[0045] Moreover, to avoid complexity of having an optical local oscillator (LO) (e.g., a local laser) at the receiver (Rx) without the need for a power-hungry DSP, example examples described herein may utilize a laser forwarded approach where the laser line is forwarded from the Tx module to Rx side. To amortize the overhead of this forwarded laser path, examples may split that over multiple channels (e.g., N channels as described herein).

[0046] Interconnect systems described herein accordingly may be utilized to achieve massively parallelized multi-channel energy / area efficient coherent optical links. Such optical links may be utilized in electronic devices including but not limited to. servers, blades, processors, desktops, laptops, tablets, smartphones, wearable devices, vehicles, and / or appliances. Technologies such as generative Al, autonomous vehicles, AR / VR and 6G all may utilize such interconnects to communicate data between various components. Examples described herein can be extended to higher QAM modulations such as QAM16 / 64 to support data-rates of +400G per wavelength per channel.

[0047] Examples of systems described herein may advantageously achieve metrics for applications in AI / ML supercomputing (e.g.. GPU clusters), as well as high bandwidth data aggregation in distributed phased array systems. Examples of pre-forward error coding (FEC) bit error rate (BER) of le-6 may be achieved in examples described herein which may help ensure error-free and / or reduced error communication (e g., BER<le-15) after a lite-FEC with low coding latency of 5ns. Accordingly, systems described herein may be utilized with emerging interconnect standards such as PCIe gen 6. Using advanced 3D integration of sub-1 Onm CMOS with silicon photonics examples described herein can achieve energy efficiencies of sub-lpJ / b by exploiting both wavelength division multiplexing (WDM) and / or QAM modulations.[004S] FIG. 1 is a schematic illustration of a system arranged in accordance with examples described herein. The system 100 of FIG. 1 includes laser 102, splitter 104, transmitter 126. receiver 128, and optical fibers 120. The splitter 104 provides first forward path laser signal 108 and second forward path laser signal 110 along a forward laser path 112. The transmitter 126 includes splitter 106 which may split first forwardpath laser signal 108 into transmit channels 116. The receiver 128 includes receive channels 118 which may be coupled to splitter 122. The splitter 122 may split the second forward path laser signal 110 into the receive channels 118. The optical fibers 120 may couple the transmit channels 116 and receive channels 118.

[0049] The components of FIG. 1 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0050] Examples described herein include transmitters and receivers, such as transmitter 126 and receiver 128 of FIG. 1. Transmitters and receivers described herein generally refer to optical transmitters and optical receivers, which will input and output optical energy (e.g., laser light and / or modulated laser lights). Optical fibers are generally utilized to carry' optical signals between components described herein.

[0051] Examples described herein include one or more lasers, such as laser 102. A laser may be implemented using a laser source, such as a laser diode. A single wavelength laser diode may be used in some examples. Other laser sources may be used in other examples.

[0052] Examples described herein may include a splitter such as splitter 104 of FIG. 1. A splitter may have an optical input and multiple optical outputs. The energy input to the optical input may be split to the multiple outputs. Any fraction or proportion of splitting may be used in various examples. In some examples, energy at the optical input is evenly split to multiple optical outputs, such as to two optical outputs as depicted with splitter 104 of FIG. 1. For example, the laser 102 may provide an input laser beam to splitter 104. The splitter 104 may split 50% of the optical energy' to a first optical output, and 50% of the optical energy to a second optical output. Other proportions may be used in other examples. The first optical output may provide first forward path laser signal 108. The second optical output may provide second forward path laser signal 110. Both the first forward path laser signal 108 and second forward path laser signal 110 may be referred to as a forward laser path 112. The forward laser path 112 of the laser 102 includes first forward path laser signal 108and second forward path laser signal 110. The first forward path laser signal 108 may be carried using one or more optical fibers. The second forward path laser signal 110 may be carried using one or more optical fibers.

[0053] In this manner, a single laser may provide optical energy which is provided to, and utilized by, both a receiver and a transmitter in systems described herein. For example, the laser 102 may provide optical energy to both transmitter 126 and receiver 128. The first forward path laser signal 108 may be provided to the transmitter 126. The secondforward path laser signal 110 may be provided to the receiver 128. In this manner, a second laser (e.g.. a local laser) may not be utilized at the receiver 128. This may avoid a need for a local oscillator and / or digital signal processor (DSP) at the receiver 128.

[0054] Examples of systems described herein include transmitters, such as the transmitter 126 of FIG. 1. The transmitter 126 may be implemented using circuitry and / or other electronic components. The transmitter 126 may be provided, for example, on a chip, rack, board, or other electronic substrate.

[0055] Examples of transmitters described herein may include a splitter, such as splitter 106 of FIG. 1. A splitter may have an optical input and multiple optical outputs. The energy input to the optical input may be split to the multiple outputs. Any fraction or proportion of splitting may be used in various examples. In some examples, energy at the optical input is evenly split to multiple optical outputs, such as to N optical outputs as depicted with splitter 106 of FIG. 1.

[0056] Examples of transmitters described herein may include a plurality of transmit channels, such as transmit channels 116 in FIG. 1. The transmit channels may be implemented using circuitry, including optical circuitry, as described herein. Any number of transmit channels may generally be used, with the number N depicted in FIG. 1. In some examples, 2, 4, 8, 16, 32, 64, or another number of channels may be used. In some examples, the channels may carry data independent of other ones of the channels. For example, each channel may communicate an independent data stream. In some examples, each channel may carry a portion of a data stream.

[0057] Examples of systems described herein include receivers, such as the receiver 128 of FIG. 1. The receiver 128 may be implemented using circuitry and / or other electronic components. The receiver 128 may be provided, for example, on a chip, rack, board, or other electronic substrate. Accordingly, for example, the transmitter 126 may be positioned on one rack of a computing system, and the receiver 128 positioned on another rack. Communication links described herein may be used for rack-to-rack communication between transmitter 126 a receiver 128. In other examples, communication links may be used for package-to-package and / or box-to-box communication. Systems described herein may be used for communication between other locations in other examples.

[0058] Examples of receivers described herein may include a splitter, such as splitter 122 of FIG. 1. A splitter may have an optical input and multiple optical outputs. The energy input to the optical input may be split to the multiple outputs. Any fraction or proportionof splitting may be used in various examples. In some examples, energy at the optical input is evenly split to multiple optical outputs, such as to N optical outputs as depicted with second forward path laser signal 110 of FIG. 1.

[0059] Examples of receivers described herein may include a plurality of receive channels, such as receive channels 118 in FIG. 1. The receive channels may be implemented using circuitry, including optical circuitry, as described herein. In some examples, each of the receive channels may correspond with a particular frequency range. Any number of receive channels may generally be used, with the number N depicted in FIG. 1. In some examples, 2. 4, 8, 16, 32, 64, or another number of channels may be used. Generally, a same number of receive channels may be used as transmit channels. In this manner, each transmit channel may provide transmit signals to a corresponding receive channel. However, other configurations may be used (e.g., where a single transmit channel provides transmit signals to multiple receive channels and / or where multiple transmit channels provide transmit signals to a single receive channel).

[0060] Transmit and receive channels described herein may generally be optical channels. Accordingly, the transmit channels may each have an optical output. The receive channels may each have an optical input. The transmit and receive channels may be coupled using optical media, such as one or more optical fibers 120 of FIG. 1. For example, a transmit channel (e.g., transmit channel #1 of FIG. 1) may be coupled to a receive channel (e.g., receive channel #1 of FIG. 1) using an optical fiber. In this manner, an optical signal may be provided by the transmit channel and received by the receive channel.

[0061] FIG. 2 is a schematic illustration of a multi-wavelength system arranged in accordance with examples described herein. The system 202 of FIG. 2 includes laser 204, splitter 206, transmitter 224, receiver 226, and optical fibers 220. The splitter 206 provides first forward path laser signal 210 and second forward path laser signal 212 along a forward laser path 214. The transmitter 224 includes splitter 208 which may split first forward path laser signal 210 into transmit channels 216. The receiver 226 includes receive channels 218 which may be coupled to splitter 222. The splitter 222 may split the second forward path laser signal 212 into the receive channels 218. The optical fibers 220 may couple the transmit channels 216 and receive channels 218. These components may be implemented and operate the same and / or analogously to the components shown and described with respect to FIG. 1. How ever, the example of FIG. 2 is specifically a multi-wavelength system. Accordingly, laser 204 may be implemented using a multiwavelength laser.

[0062] The system 202 of FIG. 2 includes schematic illustration of components used in transmit and receive channels of a multi- wavelength system. For example, each of the transmit channels 216 may include a demultiplexer, such as demultiplexer 234 depicted for channel #N in FIG. 2. The demultiplexer 234 may demultiplex an input optical signal into wavelength channels 236. The wavelength channels 236 may be coupled to multiplexer 240. The multiplexer 240 may combine signals from the wavelength channels 236 to a multi -wav elength transmit signal. Each of the receive channels 218 may include a multiplexer, such as demultiplexer 242 of FIG. 2. The demultiplexer 242 may demultiplex a received optical signal into wavelength channels 244.

[0063] In this manner, wavelength division multiplexing (WDM) may be used in systems described herein. Coarse or dense WDM may be used in various examples. In some examples, phase division multiplexing may additionally or instead be used to further increase data rates per fiber. The components of FIG. 2 are exemplary7. Additional, fewer, and / or different components may be used in other examples. While wavelength division multiplexing components are shown for transmit and receive channel #N in FIG. 2. it is to be understood that analogous components may be present for each transmit and receive channel of the transmit channels 216 and receive channels 218.

[0064] Examples described herein may accordingly include a multi-wavelength laser, such as laser 204 of FIG. 2. The laser 204 may generate optical energy at a plurality of wavelengths, such as in a range of wavelengths.

[0065] Transmit channels described herein may include a plurality of wavelength channels in some examples. For example, one or more transmit channels may include a demultiplexer, such as demultiplexer 234 of FIG. 2 in transmit channel #N. The demultiplexer may receive an input signal (e.g., first forward path laser signal 210 split to transmit channel #N) and may split the signal into a plurality of output signals, each having a particular wavelength or range of wavelengths. In the example of FIG. 2, the demultiplexer 234 splits the input for transmit channel #N into wavelength channels 236. Each of the wavelength channels 236 may represent a single wavelength and / or a range of wavelengths.

[0066] Examples of systems described herein may accordingly have a plurality of wavelength channels, such as wavelength channels 236 of FIG. 2. The wavelengthchannels 236 are transmit wavelength channels. The wavelength channels may include circuitry, photonics, and / or other components used to operate on the wavelength and / or range of wavelengths for that channel.

[0067] Transmit channels described herein may include a multiplexer, such as multiplexer 240 of FIG. 2. The multiplexer 240 may be coupled to outputs of the wavelength channels 236 and may combine the signals from the wavelength channels 236 to a multi-wavelength signal. The multi -wav elength signal may be provided to a receiver described herein, such as to receiver 226 over one of the optical fibers 220.

[0068] Receive channels described herein may include a plurality of wavelength channels in some examples. For example, one or more receive channels may include a demultiplexer, such as demultiplexer 242 of FIG. 2 in receive channel #N. The demultiplexer may receive an input signal (e.g., output from channel #N of transmitter 224) and may split the signal into a plurality of output signals, each having a particular wavelength or range of wavelengths. In the example of FIG. 2, the wavelength channels 244 splits the input at receive channel #N into wavelength channels 244. Each of the wavelength channels 244 may represent a single wavelength and / or a range of wavelengths.

[0069] Examples of systems described herein may accordingly have a plurality of wavelength channels for receive signals, such as wavelength channels 244 of FIG. 2. The wavelength channels 244 are receive wavelength channels. The wavelength channels may include circuitry, photonics, and / or other components used to operate on the wavelength and / or range of wavelengths for that channel.

[0070] In this manner, systems described herein may be combined with wavelength division multiplexing techniques. While the example of FIG. 2 illustrates the use of wavelength division multiplexing demultiplexers and multiplexers, in some examples transmit and receive channels described herein may additionally or instead be wavelength selective. For example, transmit channels 116 of FIG. 1 and / or transmit channels 216 of FIG. 2 may be wavelength selective. For example, one or more of the transmit channels 116 and / or one or more of the transmit channels 216 may include a resonator, such as a micro-ring resonator (MRM) to provide wavelength selectivity to the channel. Similarly, one or more of the receive channels 118 of FIG. 1 and / or receive channels 218 of FIG. 2 may include a resonator, such as an MRM, to provide wavelength selectivity to the channel.

[0071] Examples of systems having architectures described herein, such as system 100 of FIG. 1 and / or system 202 of FIG. 2 may be compatible with external laser source schemes utilized in co-packaged optics (CPO). In some examples, analog based phase recovery is used (e.g., in transmitters and / or receivers described herein) to reduce and / or eliminate the need for power hungry DSP based carrier recovery. Since in some examples the link distance may be a few 100 meters, chromatic dispersion compensation can be neglected in some examples, and clock and data recovery (CDR) and equalization may also be performed in an analog domain (e g., by transmitters and / or receivers described herein).

[0072] Systems described herein may be utilized in a variety of architectures in various applications to provide multi-channel coherent CPO using laser forwarding. Data may be encoded in the transmitted signals utilizing phase of the laser signals as described herein (e.g., utilizing QAM). While in some examples only amplitude modulation may be used (e.g.. pulse amplitude modulation (PAM)), it may be advantageous to provide coherent communication (e.g., communication where information is encoded in phase or in both phase and amplitude).

[0073] FIG. 3 is a schematic illustration of a system for use in chip-to-chip communication arranged in accordance with examples described herein. The example of FIG. 3 includes package 302, package 304, and laser 316. The package 302 includes XPU 308 and multiple CPOs, including CPO 312. The laser 316 is coupled to CPO 312 and CPO 314. The package 304 includes XPU 310 and multiple CPOs, including CPO 314. The CPO 312 is coupled to the CPO 314 by optical fibers (e.g., 2N fibers depicted in FIG. 3). The CPO 312 includes splitter 326, transmitter 318, and receiver 322. The CPO 314 includes splitter 328, receiver 324, and transmitter 320.

[0074] The components of FIG. 3 are exemplary. Additional, fewer, and / or different components may be used in other examples. The transmitter 318 and transmitter 320 may be implemented using transmitters described herein, such as transmitter 126 of FIG. 1 and / or transmitter 224 of FIG. 2. The receiver 322 and receiver 324 may be implemented using receivers described herein, such as receiver 128 of FIG. 1 and / or receiver 226 of FIG 2.

[0075] Accordingly, the example of FIG. 3 depicts a communication architecture for communication between two chips (also referred to as integrated circuits). One integrated circuit may be packaged in package 302 while another integrated circuit is packaged inpackage 304. Any of a variety' of integrated circuit packaging techniques may be used. The integrated circuits may include processing circuitry. For example, the package 302 may include XPU 308 and the package 304 may include XPU 310. The XPUs may be implemented using processing circuitry including, but not limited to, one or more central processing units (CPUs), graphics processing units (GPUs), tensor processing units (TPUs), processor cores, field programmable gate arrays (FPGAs). and / or application specific integrated circuits (ASICs). The CPOs are provided to facilitate optical communication from package 302 to package 304 - e.g., from XPU 308 to XPU 310 and / or from XPU 310 to XPU 308.

[0076] Both packages - the package 302 and the package 304 - may be present in a larger enclosure 306. The enclosure 306 may be implemented, for example, using a box, a blade, and / or a machine. Communication between package 302 and package 304 may advantageously aid in operation of the electronic device represented by enclosure 306. Accordingly, an enclosure described herein may refer to a unit of compute in a datacenter's rack which may contain one or more processing units (e.g., XPUs).

[0077] Multiple CPOs may be included in each package. Note that XPUs may be formed in a system-in-package (SiP). where multiple co-packaged optics (CPO) engines / dies (e.g., either a single chip monolithic silicon photonics, or 3D electronic integrated circuit (EIC) and photonic IC (PIC), or a pure PIC) are converting the electrical signals of the XPU into optical signals. In the example of FIG. 3, the package 302 includes four CPOs, including the CPO 312. The package 304 includes four CPOs, including the CPO 314. Accordingly, CPOs may be present in a same package as processing circuitry'. In some examples, the CPOs may be formed in a same substrate as the processing circuitry. In some examples, the CPOs may be electrically connected to the processing circuitry', such as on a same board (e g., printed circuit board), or other substrate. The CPOs may receive electrical signals indicative of data from the XPUs and may transmit data optically to another package or component. For example, the CPO 314 may receive data from XPU 310 and transmit data optically to CPO 312. The CPO 312 may receive optical signals encoding data from the CPO 314 and may decode (e.g., demodulate) the data and provide the data as electrical signals to the XPU 308. Similarly, the CPO 312 may obtain electrical signals encoding data form the XPU 308. The CPO 312 may transmit data optically to the CPO 314. The CPO 314 may decode (e.g., demodulate) the data and provide data as electrical signals to the XPU 310.

[0078] Accordingly, the CPO 312 may include splitter 326, transmitter 318, and receiver 322. The splitter 326 may split optical energy from the laser 316 to the transmitter 318 and the receiver 322. The transmitter 318 may include a splitter which may split the optical energy into multiple channels (e.g., N channels shown in FIG.3). The receiver 322 may include a splitter which may split the optical energy into multiple receive channels (e.g., N channels shown in FIG. 3). The CPO 314 may include a splitter 328 may split optical energy from the laser 316 to the receiver 324 and transmitter 320. The receiver 324 may include a splitter which may split the optical energy into multiple channels (e g., N channels shown in FIG. 3). The transmitter 320 may include a splitter which may split the optical energy into multiple transmit channels (e.g., N channels shown in FIG. 3).

[0079] The transmit channels of the transmitter 318 are coupled to the receive channels of the receiver 324 using respective optical fibers (e.g., N optical fibers in FIG. 3). The transmit channels of the transmitter 320 are coupled to the receive channels of the receiver 322 using respective optical fibers (e.g.. N optical fibers in FIG. 3).

[0080] In this manner the laser 316 may include a forward path which provides both a laser signal to a transmitter of the CPO 312 and a corresponding receiver of the CPO 314. The laser 316 may additionally provide a laser signal to a receiver of the CPO 312 and a transmitter of the CPO 314.

[0081] In examples of chip-to-chip optical input-output (I / O) systems such as shown in FIG. 3. example optical link distances may be up to tens of centimeters in some examples. The laser within the enclosure can be shared between packages to establish the links. The laser generally can provide multiple output ports (e.g., 2xM) and each port may be shared among N channels. So the total number of the links may be M X N Tx and Rx channels over M x (21V + 1) fibers.

[0082] FIG. 4 is a schematic illustration of a system for use in box-to-box communication arranged in accordance with examples described herein. The example of FIG. 4 includes enclosure 406 and enclosure 432. The enclosure 406 includes package 402 and laser 436. The enclosure 432 includes package 404 and laser 416. The package 402 includes XPU 408 and multiple CPOs, including CPO 412 and CPO 434. The package 404 includes XPU 410 and multiple CPOs, including CPO 414 and CPO 430. The CPO 412 is coupled to the CPO 414 by optical fibers. The CPO 434 is coupled to the CPO 430 by optical fibers. The laser 416 is coupled to CPO 430 and CPO 434. The laser 436 is coupled to CPO 412 and CPO 414.

[0083] The CPO 434 includes splitter 426. transmitter 418. and receiver 422. The CPO 430 includes splitter 428, receiver 424, and transmitter 420. The laser 416 provides input laser signals to both the splitter 428 and the splitter 426.

[0084] The components of FIG. 4 are exemplary. Additional, fewer, and / or different components may be used in other examples. The transmitter 418 and transmitter 420 may be implemented using transmitters described herein, such as transmitter 126 of FIG. 1 and / or transmitter 224 of FIG. 2. The receiver 422 and receiver 424 may be implemented using receivers described herein, such as receiver 128 of FIG. 1 and / or receiver 226 of FIG. 2.

[0085] Accordingly, the example of FIG. 4 depicts a communication architecture for communication between two enclosures (e.g., boxes). Communication may be between enclosure 406 and enclosure 432. The enclosures may be implemented, for example, using a box, a blade, and / or a machine. Communication between enclosure 406 and enclosure 432 may advantageously aid in operation of a system including those components. An enclosure described herein may refer to a unit of compute in a datacenter’s rack which may contain one or more processing units (e.g., XPUs).

[0086] The enclosures may include one or more packages. For example, the package 404 may be in enclosure 432 and the package 402 may be included in enclosure 406. One chip may be packaged in package 402 while another chip is packaged in package 404. Any of a variety of semiconductor chip packaging techniques may be used. The chips may include processing circuitry. For example, the package 402 may include XPU 408 and the package 404 may include XPU 410. The XPUs may be implemented using processing circuitry including, but not limited to, one or more central processing units (CPUs), graphics processing units (GPUs), tensor processing units (TPUs). processor cores, field programmable gate arrays (FPGAs), and / or application specific integrated circuits (ASICs). The CPOs are provided to facilitate optical communication from enclosure 406 to enclosure 432 - e.g., from package 402 and / or XPU 308 to package 404 and / or XPU 310.

[0087] Multiple CPOs may be included in each package. Note that XPUs may be formed in a system-in-package (SiP), where multiple co-packaged optics (CPO) engines / dies (e.g., either a single chip monolithic silicon photonics, or 3D integrated electronic IC (EIC) and photonic IC (PIC), or a pure PIC) are converting the electrical signals of the XPU into optical signals. In the example of FIG. 4, the package 402 includes four CPOs, includingCPO 412 and CPO 434. The package 404 includes four CPOs, including CPO 414 and CPO 430. Accordingly, CPOs may be present in a same package as processing circuitry. In some examples, the CPOs may be formed in a same substrate as the processing circuitry. In some examples, the CPOs may be electrically connected to the processing circuitry, such as on a same board (e.g., printed circuit board), or other substrate. The CPOs may receive electrical signals indicative of data from the XPUs and may transmit data optically to another package or component. For example, the CPO 414 may receive data from XPU 410 and transmit data optically to CPO 412. The CPO 412 may receive optical signals encoding data from the CPO 414 and may decode (e.g., demodulate) the data and provide the data as electrical signals to the XPU 408. Similarly, the CPO 412 may obtain electrical signals encoding data form the XPU 408. The CPO 412 may transmit data optically to the CPO 414. The CPO 414 may decode (e.g., demodulate) the data and provide data as electrical signals to the XPU 410.

[0088] Accordingly, the CPO 434 may include splitter 426. transmitter 418, and receiver 422. The splitter 426 may split optical energy from the laser 416 to the transmitter 418 and the receiver 422. The transmitter 418 may include a splitter which may split the optical energy into multiple channels (e g., N channels shown in FIG. 4). The receiver 422 may include a splitter which may split the optical energy into multiple receive channels (e.g., N channels shown in FIG. 4). The CPO 430 may include a splitter 428 may split optical energy from the laser 416 to the receiver 424 and transmitter 420. The receiver 424 may include a splitter which may split the optical energy into multiple channels (e.g., N channels shown in FIG. 4). The transmitter 420 may include a splitter which may split the optical energy into multiple transmit channels (e.g., N channels shown in FIG. 4).

[0089] The transmit channels of the transmitter 418 are coupled to the receive channels of the receiver 424 using respective optical fibers (e g., N optical fibers in FIG. 4). The transmit channels of the transmitter 420 are coupled to the receive channels of the receiver 422 using respective optical fibers (e.g., N optical fibers in FIG. 4).

[0090] In this manner the laser 416 may include a forward path which provides both a laser signal to a transmitter of the CPO 430 and a corresponding receiver of the CPO 434, and vice versa.

[0091] Examples of box-to-box optical input / output (I / O) systems such as shown in FIG. 4, may be used for communication between two racks and / or two boxes within a singlerack. In some examples, each CPO engine (or a group of them) may be supported by either a laser source from enclosure 406 or enclosure 432.

[0092] For both cases (e.g., chip-to-chip and box-to-box) examples can be used to interconnect more than two packages within a box, or multiple boxes together. In some scenarios such as (e.g.. top-of-the rack switch), the packages can contain a switch chip additionally to or instead of an XPU. In some examples, an optimal ratio of splitting power between the signal path and laser forwarded may be 50 / 50 in some examples to maximize the received coherent signal at the Rx.

[0093] Proposed methods are also compatible with pluggable solutions as well as other emerging alternatives such as on-board optics (or known as near package-optics (NPO)) as shown in FIG. 5.

[0094] FIG. 5 is a schematic illustration of a system for use with near-package optics arranged in accordance with examples described herein. The example of FIG. 5 includes enclosure 506 and enclosure 532. The enclosure 506 includes XPU 508 and near-package optics 502. The near-package optics 502 includes optical transmitter 534. optical receiver 512, and laser 536. The enclosure 532 includes XPU 510 and near-package optics 504. The near-package optics 504 includes optical receiver 530, optical transmitter 514, and laser 516.

[0095] The components of FIG. 5 are exemplary. Additional, fewer, and / or different components may be used in other examples. The optical transmitter 534 and optical receiver 530 may be implemented using transmitters described herein, such as transmitter 126 of FIG. 1 and / or transmitter 224 of FIG. 2. The optical receiver 512 and optical transmitter 514 may be implemented using receivers described herein, such as receiver 128 of FIG. 1 and / or receiver 226 of FIG. 2.

[0096] Accordingly, the example of FIG. 5 depicts a communication architecture for communication between two enclosures (e.g., boxes) utilizing near-package optics. Communication may be between enclosure 506 and enclosure 532. The enclosures may be implemented, for example, using a box, a blade, and / or a machine. Communication between enclosure 506 and enclosure 532 may advantageously aid in operation of a system including those components. An enclosure described herein may refer to a unit of compute in a datacenter’s rack which may contain one or more processing units (e.g., XPUs) and / or switches.

[0097] The enclosures may include one or more near-package optics. For example, the near-package optics 504 may be in enclosure 532 and the near-package optics 502 may be included in enclosure 506. Any of a variety of optical or photonic techniques may be used to provide the near-package optics. The near-package optics may be provided as a pluggable or otherwise connectable substrate to electrically couple to circuitry, such as one or more processors or switches. The near-package optics may accordingly connect (e.g.. plug) into a substrate such as a board to electrically connect with other components on the board. For example, the enclosure 506 may include XPU 508 and the enclosure 532 may include XPU 510. The XPUs may be implemented using processing circuitry including, but not limited to, one or more central processing units (CPUs), graphics processing units (GPUs), tensor processing units (TPUs). processor cores, field programmable gate arrays (FPGAs), and / or application specific integrated circuits (ASICs). Other electronic components may be used, such as one or more switches. The near-package optics are provided to facilitate optical communication from enclosure 506 to enclosure 532.

[0098] The near-package optics may receive electrical signals indicative of data from the XPUs or switches and may transmit data optically to another package or component. For example, the near-package optics 504 may receive data from XPU 510 and transmit data optically to near-package optics 502. The near-package optics 502 may receive optical signals encoding data from the XPU 510 and may decode (e.g., demodulate) the data and provide the data as electrical signals to the XPU 508. Similarly, the near-package optics 502 may obtain electrical signals encoding data form the XPU 508. The near-package optics 502 may transmit data optically to the near-package optics 504. The near-package optics 504 may decode (e.g., demodulate) the data and provide data as electrical signals to the XPU 510.

[0099] Accordingly, the near-package optics 504 may include optical receiver 530, optical transmitter 514, and laser 516. The near-package optics 502 may include optical transmitter 534, optical receiver 512, and laser 536. A splitter may split optical energy from the laser 516 to the optical transmitter 514 and the optical receiver 512. The optical transmitter 514 may include a splitter which may split the optical energy into multiple channels as described herein. The optical receiver 512 may include a splitter which may split the optical energy into multiple receive channels as described herein. A splitter may split optical energy from the laser 536 to the optical transmitter 534 and the optical receiver530. The optical transmitter 534 may include a splitter which may split the optical energy into multiple channels as described herein. The optical receiver 530 may include a splitter which may split the optical energy into multiple receive channels as described herein.

[0100] The transmit channels of the optical transmitter 534 are coupled to the receive channels of the optical receiver 530 using respective optical fibers. The transmit channels of the optical transmitter 514 are coupled to the receive channels of the optical receiver 512 using respective optical fibers.

[0101] In this manner the laser 516 may include a forward path which provides both a laser signal to a transmitter of the near-package optics 504 and a corresponding receiver of the near-package optics 502. The laser 536 may provide a laser signal to a receiver of the near-package optics 504 and a transmitter of the near-package optics 502.

[0102] Regardless of the implementation approach (e.g., chip-to-chip, box-to-box, and / or near-package optics), optical transceivers described herein may include optical transmitter (Tx) components and systems, optical receiver (Rx) components and systems, and laser components. Each laser can be shared among multiple links (e.g., multi-channel) depending on optical link budget, and availability of laser diodes to provide enough optical power. In some examples, there may be multiple laser diodes in each optical transceiver block.

[0103] In examples of transceivers described herein, area and energy may advantageously be within the usage of CPO in artificial intelligence and / or machine learning applications. One component of examples of optical transmitters described herein may be a phase-constant amplitude modulator (PCAM). Micro-ring resonator (MRM)- based systems may be used that can provide offset-QAM modulations (OQAM) using silicon photonics.

[0104] FIG. 6 is a schematic illustration of a transmitter arranged in accordance with examples described herein. The example of FIG. 6 includes modulator 602 which may receive input laser energy.and provide a modulated optical outputAn implementation of such a modulator 602 may include splitter 604 to splitinto two paths. On a first path, modulator 606 may be provided. The modulator 606 may be a phase-constant amplitude modulator that may receive the first path of laser energy and transmit data. On a second path, modulator 608 may be provided followed by phase shifter 610. The modulator 608 may be a phase-constant amplitude modulator which may receive the second path of laser energy' and transmit data. An output of the modulator 608may be coupled to phase shifter 610 which may provide a pi / 2 phase shift. The transmit data provided to modulator 606 may be in-phase (I) components of a transmit signal. The transmit data provided to modulator 608 may be quadrature components (Q) of a transmit signal. The output of the two paths is coupled to splitter 612 to combine the output of the two paths to ETX,OUI.

[0105] The transmitter of FIG. 6 may be used to implement transmitters described herein, such as transmitter 126 of FIG. 1 and / or transmitter 224 of FIG. 2. For example, the components shown in FIG. 6 may be included in each of transmit channels described herein, such as transmit channels 116 of FIG. 1 and / or transmit channels 216 of FIG. 2.

[0106] The components shown in FIG. 6 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0107] Transmitters described herein, such as one or more transmit channels, may transmit data. The transmitted data may be data generated by electronic circuitry. For example, the XPUs and / or switches shown and described with respect to FIG. 3 - FIG. 5 may generate data. The data may be provided to transmitters. The data may be modulated symbols. For example, the data may be QAM-16 symbols as shown in FIG. 6.

[0108] Energy from a laser may be received at a splitter, such as the splitter 604 of FIG.6. The laser may be implemented, for example, using the laser 102 of FIG. 1 and / or the laser 204 of FIG. 2. The splitter may split the laser energy into two paths. In a first path, the modulator 606 may utilize the first path of laser energy to modulate in accordance with the transmit data provided to modulator 606. The transmit data provided to the first path modulator 606 may be the in-phase (I) symbol of the QAM-16 symbols. The modulator 606 may provide phase-constant amplitude modulation, such as by using one or more MCAMs. Phase-constant amplitude modulation generally refer to modulation which may modulate an amplitude of the laser energy in accordance with the data, but may apply a constant phase and / or constant phase change across various amplitudes. The modulator 606 may accordingly output laser energy in the first path modulated in accordance with the transmit data (e.g., the in-phase potion of the transmit data).

[0109] In a second path, the modulator 608 may utilize the second path of laser energy to modulate in accordance with the transmit data provided to modulator 608. The transmit data provided to the 608 may be the quadrature (Q) symbols of the QAM-16 symbols. The modulator 608 may provide phase-constant amplitude modulation, such as by using one or more MCAMs. In some examples, a phase shift provided by the modulator 608 may beequal to a phase shift provided by the modulator 606, however other relationships of phase may be used. An output of the modulator 608 may be provided to phase shifter 610. The phase shifter 610 may shift a phase of the signal output of the modulator 608 to provide a phase shifted signal. In some examples the phase shift provided by the phase shifter 610 may be pi / 2, although other phase shifts may be used.

[0110] The output of the first and second paths (e.g., an output of the modulator 606 and an output of the phase shifter 610) may be provided to splitter 612. The splitter 612 may combine the outputs to provide the optical transmit signals.

[0111] FIG. 7 is a schematic illustration of a receiver arranged in accordance with examples described herein. The receiver is a coherent optical receiver. The example of FIG. 7 includes coherent receiver 702 which may receive input laser energy, Elaser and modulated energy’ encoding transmit data, Erx,out and decode (e.g.. demodulate) the transmit data. An implementation of such a coherent receiver 702 may include phase shift tuning block 704 which may receive the laser energy and output the laser energy with tuned phase. In this manner, a LO laser signal may be generated by phase-shifting the forwarded laser (E_Laser). The modulated energy encoding transmit data Erx,out and the laser energy with tuned phase may be provided to optical hybrid block 706. An incoming optical signal (e.g., E_Tx_out) may be mixed with a local oscillator (LO) laser in a 90° optical hybrid (e.g., n / 2 hybrid 706).

[0112] The optical hybrid block 706 may provide outputs in two paths. A first path includes balanced photodetector 708 followed by electrical receiver 712. A second path includes balanced photodetector 710 followed by electrical receiver 714. The outputs of electrical receiver 712 and electrical receiver 714 are the demodulated receive data 716. The receive data 716 may be provided to phase recovery loop 718 which may be used to tune phase shift tuning block 704.

[0113] The hybrid 706 may generate four output signals with phase differences of 0°, 90°, 180°. and 270°. The four outputs of the hybrid are directed into two balanced photodetector pairs, balanced photodetector 708 and balanced photodetector 710. The balanced photodetectors perform differential detection to extract the in-phase (I) and quadrature (Q) components of the optical field. This balanced detection may reduce and / or cancel common-mode noise and improves signal-to-noise ratio, allowing for recovery of both the amplitude and phase of the transmitted signal. The resulting electrical I / Q signals are then amplified by the electrical receiver 712 and 714. The amplified signals may bedigitized, and a digital signal processing (DSP) may be used to perform carrier and timing recovery, equalization, and demodulation. This architecture supports advanced modulation formats like QPSK and QAM and may be used to achieve high spectral efficiency and sensitivity in modern high-speed optical links.

[0114] The receiver of FIG. 7 may be used to implement receivers described herein, such as receiver 128 of FIG. 1 and / or receiver 226 of FIG. 2. For example, the components shown in FIG. 6 may be included in each of receive channels described herein, such as receive channels 118 of FIG. 1 and / or receive channels 218 of FIG. 2.

[0115] The components shown in FIG. 7 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0116] Note that, in examples described herein, a same laser may be used to provide the laser energy used by a transmitter and a receiver. Accordingly, a same laser, such as laser 102 of FIG. 1 and / or laser 204 of FIG. 2 may be used to provide the laser energy input into phase shift tuning block 704 of FIG. 7 and splitter 604 of FIG. 6.

[0117] Accordingly, receivers described herein may include electronics which may be used to cancel and / or offset DC photocurrent which may be generated by photodiodes used in the system (e.g., photodiodes associated with one or more lasers described herein). Accordingly, closed-loop feedback may be used to set the output node voltage of transimpedance amplifier (T1A) stage / stages. Since the offset current in OQAM modulation may be used for phase-carrier recovery (and polarization control) loops, examples described herein may cancel average I / Q photo currents from both photodiodes in the first TIA stage, and use these nodes for control loops. The rest of the DC offset can be cancelled in the rest of TIA stages. Alternatively, by optimizing and tuning the bandwidths of DC offset cancellation (DCOC) and phase / polarization recovery loops, one can ensure the order that phase / polarization recovery loops operate at much faster time constants.

[0118] The proposed offset-QAM modulations (OQAM) can also support dualpolarization (DP) in some examples, which may be referred to as DP-OQAM. This effectively makes the bandwidth of the optical link 4x compared with PAM modulation, and 2x compared with single polarization QAM.

[0119] FIG. 8 is a schematic illustration of a transmitter supporting dual polarization arranged in accordance with examples described herein. In the example of FIG. 8, the transmitter includes splitter 802. The splitter 802 may split laser energy Ei aser illtO tWOpaths. A first path is provided to modulator 804, and a second path to modulator 806. The modulator 804 is provided transmit data for one polarization (e.g., X polarization). The modulator 806 is provided transmit data for another polarization (e.g., Y polarization). The outputs of modulator 804 and of modulator 806 are provided to polarization separator and rotator 808. The polarization separator and rotator 808 outputs a dual polarized optical signal Erx.out which encodes the transmit data.

[0120] The transmitter of FIG. 8 may be used to implement transmitters described herein, such as transmitter 126 of FIG. 1 and / or transmitter 224 of FIG. 2. For example, the components shown in FIG. 8 may be included in each of transmit channels described herein, such as transmit channels 116 of FIG. I and / or transmit channels 216 of FIG. 2.

[0121] The components shown in FIG. 8 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0122] Each of the modulator 804 and modulator 806 may be implemented using a coherent QAM modulator in some examples. The output of the two coherent QAM modulators may be combined using the polarization separator and rotator 808. In this manner, both TE / TM polarization on chip can translate to X / Y polarization in the fiber.

[0123] FIG. 9 is a schematic illustration of a receiver supporting dual polarization arranged in accordance with examples described herein. FIG. 9 provides examples of components for a receiver 902. The receiver 902 may receive a dual polarized optical signal encoding transmit data, Erx.out and laser energy which may include both polarizations (e.g., ETX,X + ETX,Y). The receiver 902 of FIG. 9 includes a splitter 906. The splitter 906 may receive laser energy Elaser and split the laser energy to two receivers, the first polarization receiver 908 and the second polarization receiver 910. The receiver of FIG. 9 includes polarization controller 904. Optical signal encoding transmit data, ETX. out may be provided to the polarization controller 904. The polarization controller 904 may split the received optical signal encoding transmit data into multiple polarization components in accordance with a control signal. One of the components. ETX,X may be provided to first polarization receiver 908, while the other, ETX.Y, may be provided to second polarization receiver 910. The first polarization receiver 908 includes combiner 912. The combiner 912 may be used to combine received in-phase and quadrature signals demodulated by the first polarization receiver 908. The second polarization receiver 910 may include combiner 914. The combiner 914 may be used to combine received in-phase and quadrature signals demodulated by the second polarization receiver 910. Thecombined signals from first polarization receiver 908 and second polarization receiver 910 may be provided to polarization estimation and controller 916. The polarization estimation and controller 916 may provide control signals for polarization controller 904 to control the split of the laser energy to the receiver.

[0124] The receiver of FIG. 9 may be used to implement receivers described herein, such as receiver 128 of FIG. 1 and / or receiver 226 of FIG. 2. For example, the components shown in FIG. 9 may be included in each of receive channels described herein, such as receive channels 118 of FIG. 1 and / or receive channels 218 of FIG. 2.

[0125] The components shown in FIG. 9 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0126] The first polarization receiver 908 and second polarization receiver 910 may each be implemented using the receiver architecture of FIG. 7. The first polarization receiver 908 may include combiner 912. The combiner 912 may combine the electrical receive signals from the in-phase and quadrature components as received by the electrical receive blocks of the first polarization receiver 908. In some examples, the combining may include taking an average of a sum of the in-phase and quadrature components and a difference between the in-phase and the quadrature components.

[0127] The second polarization receiver 910 may include combiner 914. The combiner 914 may combine the electrical receive signals from the in-phase and quadrature components as received by the electrical receive blocks of the second polarization receiver 910. In some examples, the combining may include taking an average of a sum of the in- phase and quadrature components and a difference between the in-phase and the quadrature components.

[0128] Output of the combiner 912 and the combiner 914 may be provided to the polarization estimation and controller 916. The polarization estimation and controller 916 may be implemented using circuitry which may calculate an adjustment to a polarization split based on the combiner 912 and the combiner 914. The adjustment may be provided as a control signal to polarization controller 904 to adjust polarization of laser energy provided to first polarization receiver 908 and second polarization receiver 910.

[0129] The polarization controller 904 may be implemented in some examples using phase shift recovery (PSR) and phase-shifters (PS) should be used to sperate the X / Y polarizations. A single polarization receiver may be used in each path (e.g., firstpolarization receiver 908 and second polarization receiver 910) to recover the digital bits / symbols encoded at each respective polarization.

[0130] During operation, an optical signal encoding data at multiple polarizations (Erx,out) may be provided to polarization controller 904. The optical signal may be generated in some examples by transmitters described herein, such as the transmitter shown and described with reference to FIG. 8. The polarization controller 904 may separate the input optical signal into multiple (e.g., two) polarizations - e.g., X and Y of FIG. 9. The energy having one polarization (e.g., polarization X) may be provided to first polarization receiver 908. The energy having the second polarization (e.g., polarization Y) may be provided to second polarization receiver 910.

[0131] A laser source may provide input energy, Elaser, to the splitter 906. The laser source may be implemented using lasers described herein, such as laser 102 of FIG. 1 and / or laser 204 of FIG. 2. The splitter may split the laser energy to first polarization receiver 908 and second polarization receiver 910.

[0132] The first polarization receiver 908 may demodulate the data modulated in the optical signal having a first polarization (e.g.. polarization X of FIG. 9), while the second polarization receiver 910 may demodulate the data modulated in the optical signal having a second polarization (e.g., polarization Y of FIG. 9). Information from the first polarization receiver 908 and second polarization receiver 910 (e.g., combined metrics from combiner 912 and / or combiner 914) may be used to adjust operation of the polarization controller 904. Adjustment of the operation of polarization controller 904 may help ensure that the appropriate polarization separation is occurring for decoding of the separately-encoded data streams.

[0133] Note that, in examples described herein, the received signal polarization from a single-mode fiber (SMF) at the Rx side may be ambiguous. Accordingly, a closed-loop system may be used to recover the different (e.g., X / Y) polarization signals accurately. To do so, examples of polarization controllers described herein may be controlled by a loop. One advantage of OQAM modulation in some examples is that, simply by using average I±Q signals from each polarization (e.g., from combiner 912 and / or combiner 914), the error in polarization alignment may be identified. To resolve the ambiguity of X / Y polarization (e.g., they might be swapped), by using different offsets in OQAM the system may distinguish the polarizations without a need for pilot sequences, or link pretrainingfor any random data stream (e.g., no coding needed). This loop either can be run simultaneously with the phase recovery loop, or it can be tuned initially.

[0134] In some examples, a bidirectional dual-polarization system may be used. A bidirectional system may advantageously reduce or eliminate a need for additional fibers for each laser forwarding path. A single fiber may be used to forward laser energy for both transmit and receive paths.

[0135] FIG. 10 is a schematic illustration of a bidirectional dual-polarization system arranged in accordance with examples described herein. The system of FIG. 10 includes transmitter 1002, receiver 1008, receiver 1004, and transmitter 1006. The transmitter 1002 has multiple channels coupled to the multiple receive channels of receiver 1008 by fibers 1010. The transmitter 1006 has multiple transmit channels coupled to the multiple receive channels of receiver 1004 by fibers 1012. The system of FIG. 10 includes laser 1014 which is coupled to splitter 1018. The splitter 1018 is coupled to provide output energy to transmitter 1002 and polarization controller 1022. The polarization controller 1022 provides output signals to fiber 1026 and receiver 1004. The system of FIG. 10 further includes laser 1016 which is coupled to splitter 1020. The splitter 1020 is coupled to provide output energy to transmitter 1006 and polarization controller 1024. The polarization controller 1024 provides output signals to fiber 1026 and receiver 1008.

[0136] The transmitters and receivers of FIG. 10 may be implemented by transmitters and receivers described herein, such as transmitter 126 of FIG. 1, transmitter 224 of FIG. 2, receiver 128 of FIG. 1, and / or receiver 226 of FIG. 2. The transmitters and receivers of FIG. 10 may utilize dual polarization QAM, and accordingly the transmitters may include or be implemented using the transmitter of FIG. 8. The receivers of FIG. 10 may be implemented using the receiver of FIG. 9.

[0137] The components of FIG. 10 are exemplary. Additional, fewer, and / or different components may be used in other examples.

[0138] In the example of FIG. 10, the transmitter 1002 and receiver 1004 may be provided, for example, in a same chip, package, and / or enclosure (e.g., box). The receiver 1008 and transmitter 1006 may be provided in another same chip, package, and / or enclosure (e.g., box). Communication between the transmitter 1002 and receiver 1008 may occur over fibers 1010. Communication between the transmitter 1006 and the receiver 1004 may occur over fibers 1012.

[0139] The laser 1014 may provide laser energy to transmitter 1002 (e.g., through splitter 1018). The laser 1014 may additionally provide laser energy to receiver 1008 through a forward path. The forward path may be provided by fiber 1026. In some examples, the laser 1014 may provide energy having a particular polarization (e.g., X polarization in the example of FIG. 10). Accordingly, the fiber 1026 may be used to communicate optical energy having X polarization from the laser 1014 to the receiver 1008 (e.g.. through the splitter 1018, polarization controller 1022, and / or polarization controller 1024).

[0140] The laser 1016 may provide laser energy to transmitter 1006 (e.g., through splitter 1020). The laser 1016 may additionally provide laser energy to receiver 1004 through a forward path. The forward path may be provided by fiber 1026. In some examples, the laser 1016 may provide energy having a particular polarization (e.g., Y polarization in the example of FIG. 10). Accordingly, the fiber 1026 may be used to communicate optical energy having Y polarization from the laser 1016 to the receiver 1004 (e.g.. through the splitter 1020, polarization controller 1024, and / or polarization controller 1022).

[0141] In this manner, a single fiber may carry optical energy of multiple polarizations. For example, the fiber 1026 may communicate optical energy having one polarization from the laser 1014 to the receiver 1008 while communicating optical energy having another polarization from the laser 1016 to the transmitter 1002. This may reduce a number of fibers used to couple chips, boxes, and / or other enclosures to one another.

[0142] In some examples, if a laser supports 2 links (e.g., if there are two transmit and two receive channels), with 5 fibers, 2 Tx and 2 Rx fiber channels may be realized. Two fibers may be used to couple the transmit channels to the receive channels, two fibers may be used to couple the receive channels to the transmit channels, and one fiber for laser forwarding which may be shared among the directions.

[0143] FIG. 11 is a schematic illustration of a system sharing a laser forwarding path in a single fiber using dual polarization with multiple lasers using separate laser forwarding fibers, arranged in accordance with examples described herein.

[0144] The example of FIG. 11 includes transceiver 1102 and transceiver 1104. The transceiver 1102, for example, may be provided on one chip, board, and / or enclosure, while the transceiver 1104 may be provided on another chip, board, and / or enclosure.

[0145] The transceiver 1102 includes a first transmitter which is coupled to a first receiver of the transceiver 1104. The first transmitter may be coupled to the first receiver using N fibers for N channels provided by the transmitter / receiver pair. The firsttransmitter and receiver pair may receive optical energy from laser 1106. The laser 1106 may have a particular polarization, and the output may be forwarded to the transceiver 1104 using fiber 1108. The transceiver 1104 includes a first transmitter which may be coupled to a first receiver of the transceiver 1102 using a number of fibers - e.g., N fibers in FIG. 11. A fiber may be used for each channel of the transmitter / receiver pair. The first transmitter of the transceiver 1104 and the first receiver of the transceiver 1102 may receive optical energy from the laser 1110. The laser 1110 may have a particular polarization, which may be different than a polarization of the laser 1106. Optical energy output of the laser 1110 may be provided to the transceiver 1102 using fiber 1108. Accordingly, a single fiber may be used to forward optical energy of one polarization from transceiver 1104 to transceiver 1102 and of another polarization from transceiver 1102 to transceiver 1104.

[0146] The transceiver 1102 includes a second transmitter which is coupled to a second receiver of the transceiver 1104. The second transmitter may be coupled to the second receiver using N fibers for N channels provided by the transmitter / receiver pair. The second transmitter and receiver pair may receive optical energy from laser 1112. The laser 1112 may have a particular polarization, and the output may be forwarded to the transceiver 1104 using fiber 1116. The transceiver 1104 includes a second transmitter which may be coupled to a second receiver of the transceiver 1102 using a number of fibers - e.g., N fibers in FIG. 11. A fiber may be used for each channel of the transmitter / receiver pair. The second transmitter of the transceiver 1104 and the second receiver of the transceiver 1102 may receive optical energy from the laser 1114. The laser 1114 may have a particular polarization, which may be different than a polarization of the laser 1 112. Optical energy output of the laser 1 114 may be provided to the transceiver 1102 using fiber 1116. Accordingly, a single fiber may be used to forward optical energy of one polarization from transceiver 1104 to transceiver 1102 and of another polarization from transceiver 1102 to transceiver 1104.

[0147] In this manner, a separate forwarding fiber may be used for each laser diode.

[0148] FIG. 12 is a schematic illustration of a system sharing laser forwarding in a single fiber using dual polarization and wavelength division multiplexing arranged in accordance with examples described herein.

[0149] The example of FIG. 12 includes transceiver 1202 and transceiver 1204. In an analogous manner to FIG. 11, the transceiver 1202 includes a first transmitter coupled toa first receiver in the transceiver 1204 using N fibers, one per channel. The transceiver 1202 includes a second transmitter coupled to a second receiver in the transceiver 1204 using N fibers, one per channel. The transceiver 1202 includes a first receiver coupled to a first transmitter in the transceiver 1204 using N fibers, one per channel. The transceiver 1202 includes a second receiver coupled to a second transmitter in the transceiver 1204 using N fibers, one per channel.

[0150] The laser 1206 may provide optical energy to the first transmitter of the transceiver 1202 and the first receiver of the transceiver 1204. The laser 1208, which may have a different polarization than the laser 1206. may provide optical energy to the first transmitter of the transceiver 1204 and the first receiver of the transceiver 1202. Accordingly, a single fiber 1214 may be utilized to carry the differently polarized optical energy from the transceiver 1202 to the transceiver 1204 and vice versa.

[0151] The laser 1210 may provide optical energy to the second transmitter of the transceiver 1202 and the second receiver of the transceiver 1204. The laser 1212, which may have a different polarization than the laser 1210, may provide optical energy to the second transmitter of the transceiver 1204 and the second receiver of the transceiver 1202. Accordingly, the fiber 1214 may be utilized to carry’ the differently polarized optical energy from the transceiver 1202 to the transceiver 1204 and vice versa.

[0152] However, unlike the example of FIG. 11, in the example of FIG. 12, wavelength division multiplexing is used to allow the fiber 1214 to carry the forwarded optical energy from all four laser sources shown in FIG. 12. The laser 1206 may provide optical energy to a multiplexer 1216 (e.g., a wavelength division multiplexer) prior to being forwarded on fiber 1214. Similarly, the laser 1210 may provide optical energy to the multiplexer 1216. In this manner, the optical energy from laser 1206 and laser 1210 may be multiplexed and forwarded on fiber 1214. On receipt at the transceiver 1204, the optical energy may be provided to demultiplexer 1222 (e.g., wavelength division demultiplexer) before being provided to the first receiver and second receiver, respectively. Note that the laser 1206 and the laser 1210 may accordingly operate at different wavelengths in some examples.

[0153] The laser 1208 may provide optical energy’ to a multiplexer 1218 (e.g., a wavelength division multiplexer) prior to being forwarded on fiber 1214. Similarly, the laser 1212 may provide optical energy to the multiplexer 1218. In this manner, the optical energy from laser 1208 and laser 1212 may be multiplexed and forwarded on fiber 1214.On receipt at the transceiver 1202, the optical energy may be provided to demultiplexer 1220 (e.g.. wavelength division demultiplexer) before being provided to the first receiver and second receiver, respectively. Note that the laser 1208 and the laser 1212 may accordingly operate at different wavelengths in some examples.

[0154] The performance of an example architecture described herein using QAM-16 was compared to a PAM-4 link for a 400G per wavelength case. In order to do this link modeling and simulation, a basic link model may be used as described herein.

[0155] Assume that the required optical power at the laser source is PL(for each wavelength), pcis the fiber to chip coupling loss, r / Lis extra unallocated link budget / loss, and R is the photodiodes (PD) responsivity. The resultant photocurrent at the output of a balanced PD after the hybrid-90 for I / Q branches can be written as Equation 1 in FIG. 13.

[0156] Since each I / Q arm will receive half of the laser power in each channel, the and terms are present in Equation 1. LO forwarded path laser power andRx power can be rewritten at a single channel input as shown in Equation 2 and Equation 3 in FIG. 13.

[0157] In Equations 2 and 3,is the normalized E-field optical modulation amplitude (OMA) of the optical modulator for I / Q branches. Theis in the calculation since the I / Q modulator may inherently lose half of the power due to coherent combination. By combining all three equations, we can have Equation 4 in FIG. 13.

[0158] For comparison assume similar laser power will be used for closing M X 2N links using intensity modulation-direct detect (IM-DD), the received photocurrent will be given as Equations 5 and 6 in FIG. 13.

[0159] In Equation 6, 0MAP TXis the normalized power OMA of optical modulator.

[0160] Note that the calculated PD or balanced PD (BPD) currents are peak-to-peak eye-diagram’s vertical openings. Thus, for the case of PAM-4 and QAM-16, each resulting value may be divided by 3 to find the smallest signal powers to detect the symbols (and bits).

[0161] On the Rx modeling, assume a lite-FEC threshold of BER<l e-6 to estimate the required laser power in some examples. For the Rx specifications, assume the input referred noise is dominated by the electrical Rx thermal noise with a power spectral density (PSD) of Additionally, assume that the electrical Rx requires 5uAinput current OMA to resolve the min / max levels at 25GHz Nyquist bandwidth in some examples. This requirement is linearly going up for higher frequencies.

[0162] For comparing PAM-4, QAM- 16 and offset-QAM-16 for overall data-rates of 400Gb / s per channel per wavelength, the following assumptions are used:

[0163] M=l , N=4 (total of 8 Rx & Tx channels, or 4 full-duplex channels)

[0164]

[0165] For modeling the modulators, assume extinction ratios sufficiently large, modulator electro-optical bandwidth (BW) is 100GHz, and then:

[0166] (for QAM-16, assuming 3dB insertions loss (IL) of modulator)

[0167] (for offset-QAM-16, assuming 3dB IL of modulator)

[0168] (for PAM modulations, assuming 1.5dB of IL)

[0169] Finally, calculate resulting BER / SER using Equation 7 in FIG. 13, where Ixoise is the Nyquist bandwidth times the current noise PSD, and #Levels depends on the modulation scheme which will be 4 for all cases.

[0170] Simulation results are shown in FIG. 14. FIG. 14 is a plot of simulations of required laser power for an example of 8 links each at 400 Gb / s (3.2 Tb / s bidirectional bandwidth) for various modulation techniques in accordance with examples described herein.

[0171] Accordingly, FIG. 14 depicts over 4x lower required optical laser power between examples of laser forwarded multi-channel QAM links and PAM optical links. Actual advantages in many examples may be beyond this basic modeling since PAM-4 / 8 compared with QAM-16 format utilizes higher bandwidth optical elements (e.g., modulators and PDs), as well as higher speed CMOS TRx circuitry.

[0172] Accordingly, examples of techniques and architectures described herein are advantageous for the future of high-data rate optical I / O for both CPO as well as pluggable formfactors to provide low-power and high-density optical links. Examples of these methods utilize a closed-loop phase recovery mechanism at the Rx that can be implemented using analog based solutions.

[0173] From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made while remaining with the scope of the claimed technology.

Claims

CLAIMSWhat is claimed is:

1. A system comprising: an optical transmitter, the optical transmitter configured to receive a laser input from a forward laser path of a laser source, the optical transmitter configured to split the laser input into a plurality of transmit channels; and an optical receiver, the optical receiver configured to receive another laser input from the forward laser path of the laser source, the optical receiver configured to split the another laser input into a plurality of receive channels.

2. The system of claim 1, wherein the laser input and the another laser input are multiwavelength inputs.

3. The system of claim 1, wherein the transmit channels include circuitry for amplitude and phase modulation of transmit signals using the laser input.

4. The system of claim 3. wherein the modulation comprises QAM modulation.

5. The system of claim 1, wherein the receive channels include circuitry for demodulation of modulated signals received from the transmit channels, the demodulation including amplitude and phase recovery.

6. The system of claim 5, wherein the demodulation comprises QAM demodulation.

7. The system of claim 1, wherein the optical transmitter is packaged in a first integrated circuit package, and wherein the optical receiver is packaged in a second integrated circuit package.

8. The system of claim 1. wherein the optical transmitter is positioned within a first rack of computing components, and wherein the optical receiver is positioned within a second rack of computing components.

9. The system of claim 1. wherein the optical transmitter comprises a phase-constant amplitude modulator.

10. The system of claim 9, wherein the phase-constant amplitude modulator comprises a micro-ring resonator.

11. The system of claim 1, wherein the optical receiver comprises a dual polarization receiver, the dual polarization receiver comprising: a polarization controller configured to separate, in accordance with a control signal, optical signals encoded with a first polarization from optical signals encoded with a second polarization; a first polarization receiver configured to decode in-phase and quadrature transmit data encoded with the first polarization; a first combiner configured to generate a first metric based on one or more combinations of the in-phase and quadrature transmit data decoded by the first polarization receiver; a second polarization receiver configured to decode in-phase and quadrature transmit data encoded with the second polarization; a second combiner configured to generate a second metric based on one or more combinations of the in-phase and quadrature transmit data decoded by the second polarization receiver; and a polarization estimation controller configured to provide the control signal to the polarization controller, the control signal generated based on the first metric and the second metric.

12. A method comprising: generating transmit data using electronic circuitry; transmitting the transmit data over an optical link, the optical link including a transmitter configured to receive the transmit data and optical energy from a laser, the transmitter configured to utilize QAM modulation to modulate the optical energy with the transmit data to provide optical signals having modulated data; and forwarding optical energy from the laser to a receiver configured to receive the modulated data.

13. The method of claim 12, wherein the electronic circuitry comprises a processor.

14. The method of claim 12, wherein the electronic circuitry comprises a switch.

15. The method of claim 12, wherein the optical link includes a plurality of optical fibers, including one for each channel of the transmitter.

16. The method of claim 12, wherein said forwarding optical energy includes forwarding the optical energy over an optical fiber.

17. A system comprising: a first transceiver; a second transceiver; a first laser configured to provide optical energy to a transmitter of the first transceiver and a receiver of the second transceiver, the first laser having a first polarization; a second laser configured to provide optical energy7to a transmitter of the second transceiver and a receiver of the first transceiver, the second laser having a second polarization, different from the first polarization; and a fiber configured to forward optical energy from the first laser to the second transceiver and to forward optical energy from the second laser to the first transceiver.

18. The system of claim 17, wherein the transmitter of the first transceiver is coupled to the receiver of the second transceiver using multiple optical fibers.

19. The system of claim 18, wherein the receiver of the first transceiver is coupled to the transmitter of the second transceiver using multiple optical fibers.

20. The system of claim 17, further comprising a multiplexer configured to multiplex energy from the first laser with additional optical energy from another laser prior to forwarding on the fiber.

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