Optoelectronic computing platform

Abstract

An integrated circuit interposer includes: a semiconductor substrate layer; a first metal contact layer, which includes a first metal contact segment and a second metal contact segment, the first metal contact segment includes a metal contact arranged to be electrically coupled to a first semiconductor die with a controlled collapse chip connection, and the second metal contact segment includes a metal contact arranged to be electrically coupled to a second semiconductor die with a controlled collapse chip connection. The first patterned layer includes a metal path segment patterned by a separate photomask. The second patterned layer includes a waveguide segment patterned by a separate photomask, including a first waveguide that spans at least one boundary between the waveguide segments patterned by the separate photomasks. A first modulator is coupled to the first waveguide for modulating an optical wave in the first waveguide based on an electrical signal received at a first metal contact in the first metal contact segment, and a second modulator is coupled to the first waveguide for modulating an optical wave based on an electrical signal received at a second metal contact in the first metal contact segment or the second metal contact segment.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 048,439, filed on July 6, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to optoelectronic computing platforms. Background Art

[0004] Computations performed on electronic data encoded in analog or digital form on electrical signals (e.g., voltage or current) are typically implemented using electronic computing hardware, such as analog or digital electronics implemented in integrated circuits (e.g., processors, application specific integrated circuits (ASICs), or systems on a chip (SoCs)), electronic circuit boards, or other electronic circuits. Optical signals have been used to transmit data over long distances and short distances (e.g., within data centers). Operations performed on such optical signals often occur in the context of optical data transmission, such as within devices used to switch or filter optical signals in a network. The use of optical signals in computing platforms is more limited. Summary of the invention

[0005] In general, in a first aspect, an integrated circuit interposer includes: a semiconductor substrate layer; a first metal contact layer, the first metal contact layer at a first surface of the integrated circuit interposer, including a plurality of metal contact segments, the metal contact segments including a first metal contact segment and a second metal contact segment, the first metal contact segment including a plurality of metal contacts arranged to be electrically coupled to a first semiconductor die with a controlled collapse chip connection, the second metal contact segment including a plurality of metal contacts arranged to be electrically coupled to a second semiconductor die with a controlled collapse chip connection. The interposer includes: a first patterned layer, the first patterned layer at a first distance from the semiconductor substrate layer, including a plurality of individually photomask patterned metal path segments; and a second patterned layer, the second patterned layer at a second distance from the semiconductor substrate layer different from the first distance, including a plurality of individually photomask patterned waveguide segments. The second patterned layer includes: a first waveguide that spans at least one boundary between waveguide segments patterned by separate photomasks; a first modulator coupled to the first waveguide at a first position along the first waveguide for modulating an optical wave in the first waveguide based on an electrical signal received at a first metal contact in a first metal contact segment; and a second modulator coupled to the first waveguide at a second position along the first waveguide for modulating an optical wave in the first waveguide based on an electrical signal received at a second metal contact in the first metal contact segment or a second metal contact segment.

[0006] Aspects may include one or more of the following features. A waveguide segment may include a first waveguide segment including a first portion of a first waveguide that couples a guided mode to an edge of the first waveguide segment and a second waveguide segment including a second portion of the first waveguide that couples a guided mode to an edge of the second waveguide segment.

[0007] The metal path segment may include a first metal path segment that overlaps at least a portion of the first metal contact segment and at least a portion of the second metal contact segment and provides at least one metal path between at least one metal contact of the first metal contact segment and at least one metal contact of the second metal contact segment.

[0008] The metal path segment may include a second metal path segment that overlaps at least a portion of the first metal contact segment and does not overlap any portion of the second metal contact segment and provides at least one metal path connected to at least one metal contact of the first metal contact segment.

[0009] The integrated circuit interposer may further include a second metal contact layer including a plurality of metal contact segments at a second surface of the integrated circuit interposer.

[0010] The integrated circuit interposer may also include at least one capacitor or inductor electrically coupled to at least one of the first semiconductor die or the second semiconductor die.

[0011] The first modulator and the second modulator may be amplitude modulators configured to modulate the light wave in the first waveguide with the same predetermined amplitude scaling factor.

[0012] In general, in another aspect, a method of manufacturing an integrated circuit interposer includes: forming a first metal contact layer on a semiconductor wafer, the first metal contact layer at a first surface of the integrated circuit interposer, including a plurality of metal contact segments. The metal contact segments include a first metal contact segment and a second metal contact segment, the first metal contact segment including a plurality of metal contacts arranged to be electrically coupled to a first semiconductor die with a controlled collapse chip connection, and the second metal contact segment including a plurality of metal contacts arranged to be electrically coupled to a second semiconductor die with a controlled collapse chip connection. The method includes: forming a first patterned layer on the semiconductor wafer at a first distance from a semiconductor substrate layer, including patterning a plurality of metal path segments respectively; and forming a second patterned layer on the semiconductor wafer at a second distance from the semiconductor substrate layer different from the first distance, including patterning a plurality of waveguide segments respectively. The second patterned layer includes: a first waveguide that spans at least one boundary between waveguide segments patterned by separate photomasks; a first modulator coupled to the first waveguide at a first position along the first waveguide for modulating an optical wave in the first waveguide based on an electrical signal received at a first metal contact in a first metal contact segment; and a second modulator coupled to the first waveguide at a second position along the first waveguide for modulating an optical wave in the first waveguide based on an electrical signal received at a second metal contact in the first metal contact segment or a second metal contact segment.

[0013] In general, in another aspect, an apparatus includes an interconnect module. The interconnect module includes: a first substrate; a first metal contact layer formed on the first substrate, wherein the first metal contact layer includes a first metal contact configured to be electrically coupled to a first die including a circuit; and a patterned waveguide layer including a plurality of individually photomask patterned waveguide segments disposed on the substrate, wherein the patterned waveguide layer includes a first waveguide that spans at least one boundary between the individually photomask patterned waveguide segments. The interconnect module includes: a first modulator coupled to the first waveguide at a first position along the first waveguide and configured to modulate an optical signal traveling in the first waveguide based on a first electrical signal received from the first die at the first metal contact; and a second modulator coupled to the first waveguide at a second position along the first waveguide and configured to modulate the optical signal in the first waveguide based on a second electrical signal received at a second metal contact, the second metal contact being electrically coupled to the first die or a second die including the circuit. The first waveguide enables an optical signal to travel from a source location to a target location across at least one boundary between individually photomask patterned waveguide segments and causes the optical signal to be modulated by the first and second modulators as the optical signal travels from the source location to the target location.

[0014] Aspects may include one or more of the following features.The first metal contact layer may include a second metal contact configured to electrically couple to a second die including circuitry.

[0015] The first metal contact may be electrically coupled to the first die in a controlled collapse chip connection, and the second metal contact may be electrically coupled to the second die in a controlled collapse chip connection.

[0016] The first metal contact may be located at a first region corresponding to a first individually photomask patterned waveguide segment; and the second metal contact may be located at a second region corresponding to a second individually photomask patterned waveguide segment that is different from the first individually photomask patterned waveguide segment.

[0017] The apparatus may include: a detector configured to detect an optical signal after the optical signal is transmitted through first and second modulators to generate a detected signal; and a circuit configured to map a detected amplitude of the detected signal using a predetermined amplitude scale indicating the number of modulators through which the signal was modulated.

[0018] The apparatus may include: a detector configured to detect an optical signal after the optical signal is transmitted through first and second modulators to generate a detected signal; and a circuit configured to map a detected phase of the detected signal using a predetermined phase scale indicating the number of modulators by which the signal was modulated.

[0019] The apparatus may include: a detector configured to detect an optical signal after the optical signal is transmitted through first and second modulators to generate a detected signal; and a circuit configured to map a detected polarization of the detected signal using a predetermined polarization scale indicating the number of modulators by which the signal was modulated.

[0020] Each individually photomask-patterned waveguide segment can be fabricated by exposing a corresponding photomask using a photolithography system, and different individually photomask-patterned waveguide segments can be fabricated by different exposures of the same photomask or different photomasks.

[0021] The first metal contact may be electrically coupled to the first die in a controlled collapse chip connection.

[0022] The device may include a first die.

[0023] The device may include first and second dies.

[0024] In some examples, the first modulator can be configured to modulate the amplitude of the optical signal.

[0025] In some examples, the first modulator can be configured to modulate the phase or polarization of the optical signal.

[0026] The patterned waveguide layer may include: a first individually photomask patterned waveguide segment including a first portion of a first waveguide coupling a guided mode to an edge of the first waveguide segment; and a second individually photomask patterned waveguide segment including a second portion of the first waveguide coupling a guided mode to an edge of the second waveguide segment.

[0027] The apparatus may include a second metal contact layer including a second metal contact, wherein the first metal contact is disposed on a first side of the substrate and the second metal contact is disposed on a second side of the substrate.

[0028] The interconnect module may include an optoelectronic interposer, wherein the substrate, the first metal contact layer, the patterned waveguide layer, the first modulator, and the second modulator are part of the optoelectronic interposer.

[0029] The first substrate may include a semiconductor substrate.

[0030] The interconnect module may include a filter capacitor or a decoupling capacitor electrically coupled to at least one of the first die or the second die.

[0031] In general, on the other hand, a method includes: modulating an optical signal in a first waveguide at a first location along a first waveguide formed on a first substrate based on a first electrical signal received at a first metal contact electrically coupled to a first die including a circuit; modulating the optical signal in the first waveguide at a second location along the first waveguide based on a second electrical signal received at a second metal contact electrically coupled to the first die or a second die including the circuit; and transmitting the modulated optical signal from a first separate photomask patterned waveguide segment disposed on the first substrate to a second separate photomask patterned waveguide segment disposed on the first substrate, wherein the first separate photomask patterned waveguide segment is manufactured by performing a first exposure to a first photomask using a photolithography system, and the second separate photomask patterned waveguide segment is manufactured by performing a second exposure to a second photomask using a photolithography system, the first exposure is different from the second exposure, and the first photomask is the same as or different from the second photomask.

[0032] Aspects may include one or more of the following features. A first metal contact may be located at a first region corresponding to a first separate photomask patterned waveguide segment, and a second metal contact may be located at a second region corresponding to a second separate photomask patterned waveguide segment.

[0033] The method may include detecting a modulated optical signal at a destination location downstream of an intermediate location where the optical signal was modulated to generate a detected signal; and mapping a detected amplitude of the detected signal using a predetermined amplitude scale indicating the number of intermediate locations at which the signal was modulated.

[0034] A first separately photomask-patterned waveguide segment can be manufactured by performing a first exposure of a first photomask using a lithography system, and a second separately photomask-patterned waveguide segment can be manufactured by performing a second exposure of a second photomask using a lithography system, the first exposure can be different from the second exposure, and the first photomask can be the same as or different from the second photomask.

[0035] The first metal contact may be electrically coupled to the first die in a controlled collapse chip connection.

[0036] The first die may include a semiconductor die.

[0037] The first substrate may include a semiconductor substrate.

[0038] The second metal contact may be electrically coupled to the second die, and the method may include transmitting the modulated optical signal along the first waveguide across at least one boundary between waveguide segments patterned by the individual photomasks.

[0039] The first location and the second location along the first waveguide may be located on the same single photomask patterned waveguide segment.

[0040] The first location and the second location along the first waveguide may be located on different, separately photomask patterned waveguide segments.

[0041] The method may include filtering a signal on the first die or the second die using a filter capacitor disposed on the first substrate, wherein the first die or the second die includes a second substrate different from the first substrate.

[0042] The method may include decoupling a first circuit portion from a second circuit portion using a decoupling capacitor disposed on a first substrate, wherein the first circuit portion is on a first or second die and the second circuit portion is on the first or second die.

[0043] In general, in another aspect, a device includes an interposer. The interposer includes: an interposer substrate; and a first metal contact layer formed on the interposer substrate, wherein the first metal contact layer includes a first metal contact, a second metal contact, and a third metal contact, the first metal contact is configured to be electrically coupled to a first die including a circuit, the second metal contact is configured to be electrically coupled to the first die or the second die including the circuit, the first die includes a first substrate different from the interposer substrate, and the second die includes a second substrate different from the interposer substrate. The interposer includes a patterned waveguide layer formed on the interposer substrate, wherein the patterned waveguide layer includes a first waveguide. The interposer includes: a first modulator coupled to the first waveguide at a first position along the first waveguide and configured to modulate an optical signal traveling in the first waveguide based on a first electrical signal received at a first metal contact to generate a first modulated optical signal; and a second modulator coupled to the first waveguide at a second position along the first waveguide and configured to modulate the first modulated optical wave in the first waveguide based on a second electrical signal received at a second metal contact to generate a second modulated optical signal. The interposer includes: a detector configured to detect the second modulated optical signal to generate a detected signal; and a detection circuit configured to map a detected characteristic of the detected signal to an output signal using a predetermined metric indicating a number of modulators by which the signal was modulated in a predetermined manner, wherein the output signal is electrically coupled to a third contact, and the third contact is electrically coupled to at least one of the first die, the second die, or the third die.

[0044] Aspects can include one or more of the following features.The first metal contact can be electrically coupled to the first die in a controlled collapse chip connection.

[0045] The second metal contact may be electrically coupled to the second die in a controlled collapse chip connection.

[0046] The third metal contact may be electrically coupled to the third die in a controlled collapse chip connection.

[0047] The first metal contact layer may include a first metal contact section that may include a plurality of metal contacts arranged for electrical coupling to the first die and a second metal contact section that may include a plurality of metal contacts arranged for electrical coupling to the second die.

[0048] A plurality of metal contacts in the first metal contact section may be electrically coupled to the first die in a controlled collapse chip connection.

[0049] The plurality of metal contacts in the second metal contact section may be electrically coupled to the second die in a controlled collapse chip connection.

[0050] The apparatus may include a first patterned metal layer formed on an interposer substrate, the first patterned metal layer may include a plurality of individually photomask patterned metal path segments.

[0051] The patterned waveguide layer may include a plurality of individually photomask patterned waveguide segments, and the first waveguide may span at least one boundary between the individually photomask patterned waveguide segments.

[0052] The first metal contact may be located at a first region corresponding to a first individually photomask patterned waveguide segment; and the second metal contact may be located at a second region corresponding to a second individually photomask patterned waveguide segment that is different from the first individually photomask patterned waveguide segment.

[0053] In general, in another aspect, an apparatus includes an interposer configured to perform distributed pulse-amplitude modulation on an optical signal in a first optical waveguide based on a first electrical signal and a second electrical signal, wherein the first electrical signal is received from a first die electrically coupled to the interposer, and the second electrical signal is received from either the first die or a second die electrically coupled to the interposer.

[0054] Aspects may include one or more of the following features: The interposer may include an interposer substrate, and the first die may include a first substrate different from the interposer substrate.

[0055] The second die may include a second substrate different from the interposer substrate.

[0056] The first die may be electrically coupled to the interposer using a controlled collapse chip connection.

[0057] The second die may be electrically coupled to the interposer using a controlled collapse chip connection.

[0058] The interposer may include: an interposer substrate; and a first metal contact layer formed on the interposer substrate, wherein the first metal contact layer includes a first metal contact, a second metal contact, and a third metal contact, the first metal contact is configured to be electrically coupled to the first crystal grain, and the second metal contact is configured to be electrically coupled to the first crystal grain or the second crystal grain.

[0059] The interposer may include a first optical waveguide, a first modulator, and a second modulator. The first modulator may be configured to modulate an optical signal in the first optical waveguide based on a first electrical signal received at a first metal contact. The second modulator may be configured to modulate an optical signal in the first optical waveguide based on a second electrical signal received at a second metal contact.

[0060] The apparatus may include: a detector configured to detect an optical signal after the optical signal is transmitted through first and second modulators to generate a detected signal; and a detection circuit configured to map a detected amplitude of the detected signal to an output signal using a predetermined amplitude scale indicating the number of modulators through which the signal was modulated.

[0061] The output signal may be electrically coupled to a third contact electrically coupled to at least one of the first die, the second die, or the third die.

[0062] In general, in another aspect, a method for transmitting information from a plurality of nodes to at least one destination is provided. The method includes: transmitting a signal having a predetermined preliminary amplitude from a source onto a transmission medium; modulating the amplitude of the signal at each of a plurality of intermediate positions between the source and the destination by a selected modulation value from a binary set of two possible modulation values, wherein for each intermediate position, the binary set consists of a modulation value of 1 and a predetermined amplitude scaling factor S greater than 0 and less than 1. The method includes: detecting the signal at the destination after the signal has been transmitted through all the intermediate positions; and mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicating the number of intermediate positions at which the signal was modulated by the predetermined amplitude scaling factor.

[0063] Aspects may include one or more of the following features. The predetermined amplitude scale may include a maximum detected amplitude substantially equal to the predetermined preliminary amplitude, and a maximum detected amplitude substantially equal to S N The minimum detected amplitude is , where N is the number of intermediate positions.

[0064] For each intermediate position, the predetermined amplitude scaling factor S may be different.

[0065] For each intermediate position, the predetermined amplitude scaling factor S may be equal.

[0066] The predetermined amplitude scaling factor S may be substantially equal to (k-1) / k, where k is the number of intermediate positions.

[0067] The signal transmitted from the source may have a predetermined preliminary amplitude in each of a plurality of time slots including the first time slot.

[0068] Modulation of the signal amplitude at each of the plurality of intermediate locations may occur in a first time slot after a propagation delay based on a propagation distance between each intermediate location and the source.

[0069] The method may also include maintaining time synchronization between the plurality of nodes, the source, and the destination.

[0070] The transmission medium may include an optical waveguide.

[0071] The optical waveguide may be formed in an integrated circuit interposer including metal contacts arranged for electrical coupling to at least one semiconductor die in a controlled collapse chip connection.

[0072] Selected modulation values ​​at one or more of the intermediate locations may be provided based on electrical signals from the semiconductor die.

[0073] In general, in another aspect, a system for transmitting information from a plurality of nodes to at least one destination is provided. The system includes: a transmission medium; a source configured to transmit a signal having a predetermined preliminary amplitude onto the transmission medium; and a plurality of amplitude modulators coupled to the transmission medium at respective intermediate locations between the source and the destination, each amplitude modulator configured to modulate the amplitude of the signal by a selected modulation value from a binary set of two possible modulation values. For each amplitude modulator, the binary set consists of a modulation value 1 and a predetermined amplitude scaling factor S greater than 0 and less than 1. The system includes: a detector at the destination configured to detect the signal after the signal has been transmitted through all intermediate locations; and a circuit configured to map a detected amplitude of the detected signal using a predetermined amplitude scale indicating the number of intermediate locations at which the signal was modulated by a common amplitude scaling factor.

[0074] In general, on the other hand, a method includes: transmitting a signal having predetermined preliminary optical characteristics from a source onto a transmission medium; modulating the optical characteristics of the signal at each of a plurality of intermediate positions between the source and a destination by a selected modulation value; detecting the signal at the destination after the signal has been transmitted through the intermediate positions; and mapping the detected optical characteristics of the detected signal using a predetermined scale indicating the number of intermediate positions at which the signal was modulated.

[0075] Aspects may include one or more of the following features.The optical property may include an amplitude.

[0076] Modulating the optical property may include modulating the amplitude of the signal at each of the plurality of intermediate positions by a modulation value selected from a binary set of two possible modulation values. For each intermediate position, the binary set consists of a modulation value of 1 and a predetermined amplitude scaling factor S greater than 0 and less than 1.

[0077] Mapping the detected optical characteristic of the detected signal may include mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicating a number of intermediate positions at which the signal is modulated by a predetermined amplitude scaling factor.

[0078] The predetermined amplitude scale may include a maximum detected amplitude substantially equal to the predetermined preliminary amplitude and a maximum detected amplitude substantially equal to S NThe minimum detected amplitude is , where N is the number of intermediate positions.

[0079] For each intermediate position, the predetermined amplitude scaling factor S may be different.

[0080] For each intermediate position, the predetermined amplitude scaling factor S may be equal.

[0081] The predetermined amplitude scaling factor S may be substantially equal to (k-1) / k, with k being the number of intermediate positions.

[0082] The signal transmitted from the source may have a predetermined preliminary amplitude in each of a plurality of time slots including the first time slot.

[0083] Modulation of the signal amplitude at each of the plurality of intermediate locations may occur in a first time slot after a propagation delay based on a propagation distance between each intermediate location and the source.

[0084] The method may also include maintaining time synchronization between the plurality of nodes, the source, and the destination.

[0085] The transmission medium may include an optical waveguide.

[0086] The optical waveguide may be formed in an integrated circuit interposer including metal contacts arranged for electrical coupling to at least one semiconductor die in a controlled collapse chip connection.

[0087] Selected modulation values ​​at one or more of the intermediate locations may be provided based on electrical signals from the semiconductor die.

[0088] Modulating the optical property may include modulating the amplitude of the signal at each of the plurality of intermediate positions by a modulation value selected from a binary set of two possible modulation values. For each intermediate position, the binary set consists of a modulation value of 1 and a predetermined amplitude scaling factor S greater than 1.

[0089] Optical properties may include phase or polarization.

[0090] In general, on the other hand, a method includes: transmitting a signal having a predetermined preliminary first optical characteristic and a predetermined preliminary second optical characteristic from a source onto a transmission medium; modulating the first or second optical characteristic of the signal at each of a plurality of intermediate positions between the source and a destination by a selected modulation value; detecting the signal at the destination after the signal is transmitted through the intermediate positions; and mapping the detected first and second optical characteristics of the detected signal using a predetermined scale indicating the number of intermediate positions at which the signal was modulated.

[0091] Aspects may include one or more of the following features.The first optical property may include amplitude and the second optical property may include phase.

[0092] The first optical property may include amplitude and the second optical property may include polarization.

[0093] The first optical property may include phase and the second optical property may include polarization.

[0094] The signal may have a predetermined preliminary third optical characteristic, and the method may include modulating the first, second or third optical characteristic of the signal at each of a plurality of intermediate positions between a source and a destination by a selected modulation value; and mapping the detected first, second and third optical characteristics of the detected signal using a predetermined scale indicating the number of intermediate positions at which the signal was modulated.

[0095] The first optical property may include amplitude, the second optical property may include phase, and the third optical property may include polarization.

[0096] In general, on the other hand, a system includes: a transmission medium; a source configured to transmit a signal having a predetermined preliminary optical characteristic onto the transmission medium; a plurality of optical characteristic modulators coupled to the transmission medium at corresponding intermediate locations between the source and a destination; a detector at the destination configured to detect the signal after the signal has been transmitted through the intermediate locations; and a circuit configured to map the detected optical characteristic of the detected signal using a predetermined scale indicating the number of intermediate locations at which the signal was modulated.

[0097] Aspects may include one or more of the following features. Each optical property modulator may include an amplitude modulator configured to modulate the amplitude of the signal by a selected modulation value from a binary set of two possible modulation values.

[0098] For each amplitude modulator, the binary set may consist of a modulation value of 1 and a predetermined amplitude scaling factor S greater than 0 and less than 1.

[0099] For each amplitude modulator, the binary set may consist of a modulation value of 1 and a predetermined amplitude scaling factor S greater than 1.

[0100] Each optical property modulator may comprise a phase or polarization modulator configured to modulate the phase or polarization of the signal by a selected modulation value from a binary set of two possible modulation values.

[0101] Aspects may have one or more of the following advantages.

[0102] Data can be modulated onto any of a variety of types of signals. The transmission or processing of certain types of signals has certain advantages over other types of signals. Examples of different types of signals include: optical signals corresponding to light waves that have been modulated by the signal data, and electrical signals (e.g., voltage or current) corresponding to electrical waveforms that have been modulated by the signal data. Various modulations, such as amplitude modulation, phase modulation, or a combination of amplitude and phase modulation, can be used according to a predetermined constellation diagram. Light waves used as the underlying signal carrier of optical signals have certain advantages over electrical waveforms used as the underlying signal carrier of electrical signals. For example, light waves typically have a higher bandwidth capacity than electrical waveforms. There is also typically a lower power requirement and shorter time delay (or "latency") associated with transmitting data for optical signals over a given distance.

[0103] Optical signals can be used to transmit data between different electronic nodes in a system or device (e.g., computing nodes in a data center or integrated circuits in a device package). However, there is often an overhead in the complexity associated with using such optical communication links, including conversion between optical signals and electrical signals used as inputs and / or outputs of electronic modules. There is also added latency associated with timing synchronization for signal conversion.

[0104] Some of the embodiments of the optoelectronic computing platform described herein can reduce the complexity required to incorporate communication via optical signals into the platform. As described in more detail below, by using large (e.g., wafer-level) optoelectronic interposers, collections of integrated circuits can be combined in an efficient manner. As described in more detail below, techniques for distributed pulse-amplitude modulation (PAM) aggregation can also be used in such optoelectronic computing platforms or other platforms or computing systems to combine communication and computing in an efficient manner.

[0105] The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, drawings, and claims.

[0106] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. In the event of a conflict with a patent application or patent application publication incorporated herein by reference, the present specification, including definitions, will control. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] The present disclosure can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not drawn to scale. Instead, the sizes of the various features are arbitrarily enlarged or reduced for clarity.

[0108] Figure 1 is a schematic diagram of an example of an optoelectronic computing platform.

[0109] Figure 2A is a schematic diagram of an example of a data channel provided by an optoelectronic interposer IC.

[0110] Figure 2B is a schematic diagram of an example optoelectronic interposer IC including passive electronic components.

[0111] Figure 3 is a schematic diagram of an example of an optoelectronic interposer IC.

[0112] Figure 4A and 4B is a schematic diagram of an example of movement of partial results in a distributed sum calculation.

[0113] Figure 5A , 5B 5C are schematic diagrams of examples of data flows in a distributed computing architecture.

[0114] Figure 6 is a schematic diagram of an example of a distributed PAM aggregation technique.

[0115] Figure 7 is a circuit diagram of example digital logic used to map analog sum results to digital sum results.

[0116] Figure 8 is a table of examples of bits that are summed to produce the analog amplitude.

[0117] Fig. 9 is a collection of graphs showing how the minimum step size varies with modulation depth.

[0118] Fig.10 is a schematic diagram of an example system configuration.

[0119] Fig.11A and 11B is a schematic diagram of an example system layout.

[0120] Like reference numbers and numerals in the various drawings indicate like elements. DETAILED DESCRIPTION

[0121] Figure 1An example of an optoelectronic computing platform 100 is shown. The platform 100 includes an array of computing nodes, each of which is coupled to an optoelectronic interposer integrated circuit (OIIC). In addition to metal paths that provide electrical signal connections between nodes within one or more metal layers, as in a typical electronic interposer IC, the OIIC in this example also includes optical waveguides that provide optical signal connections between nodes. Manufacturing challenges have been overcome to enable the OIIC to be manufactured on a large substrate (e.g., an entire semiconductor wafer, such as a silicon-on-insulator (SOI) wafer) to support a relatively large number of computing nodes and relatively long waveguides in at least one photonic layer of the OIIC. Each computing node is implemented on a semiconductor die that is connected to the OIIC using a conductive bump (e.g., a solder bump) on an arrangement of metal contacts on the surface of the OIIC with a controlled collapse chip connection (or "flip chip" connection). Near the left and right edges of the array of computing nodes, there are input / output (I / O) modules that are also connected to the OIIC, which enable signals to be coupled into and out of the computing platform 100. The I / O modules can couple the computing platform 100 to various devices, including dynamic random access memory (DRAM) chips or other types of memory devices. To support interfaces to such devices, the I / O modules can include circuits configured according to any of a variety of device protocols (including DDR SDRAM, PCI (e), USB, Ethernet, etc.). In this example, each computing node of the 3×4 array of twelve computing nodes includes a main computing unit (e.g., a CPU or GPU) and a multiplexer (MUX), and each I / O module includes an I / O circuit and a MUX. When the MUXes are coupled to or coupled out of the OIIC, they enable the selection and routing of electrical signals. On the other side of the OIIC is a packaging substrate, for example, which can provide electrical connections for signals and / or power. Also shown in this example, near the top edge of the array is a row of interface ports that provide another method of coupling signals directly to or from the OIIC. The various features of the OIIC described herein enable power efficient integration of a variety of different functional chips on the wafer-level optoelectronic computing platform 100.

[0122] Figure 2AAn example of a data channel provided by an OIIC is shown. For computing nodes that are relatively close to each other, the metal paths within the OIIC enable electrical signals to propagate directly between nodes. For example, an advanced interface bus (AIB) technology for connecting different chips (or "chiplets") in a multi-chip platform can be used to support electrical data channels on metal paths. In some embodiments, the pattern of the metal path is defined by the pattern of the corresponding photomask, where the pattern on the photomask is transferred to the substrate of the optoelectronic interposer integrated circuit using a photolithography system. The short distance between nearby nodes is defined by a distance less than the length of the longest straight metal path, which can be generated using a single photomask (or "reticle") for patterning a single segment of the metal path. For computing nodes that are relatively far from each other, or for computing nodes that are relatively far from an I / O module, the optical waveguide within the OIIC enables optical signals that are converted / converted from the electrical signal of the node to the electrical signal of the node to propagate between nodes. In some embodiments, a long distance is defined by a distance greater than the longest dimension of a segment patterned with a single photomask. This long optical path provides a low latency and power efficient optical data channel, which avoids the need for long wires in large (e.g., wafer-level) platforms, which would present difficult to overcome manufacturing and performance challenges. The platform 100 selects the appropriate type of data channel (i.e., electrical or optical) based on the propagation distance between the source and the destination. Adjacent compute nodes can take advantage of the short electrical signal paths provided by the OIIC. At the same time, as shown in this example, a compute node (on a compute die) anywhere in the array can have a direct optical connection to an I / O module (on an I / O die) and its connected devices (e.g., DRAM or PCI(e) devices) with high bandwidth and low latency similar to the short electrical connections between adjacent compute nodes. This breaks the access limitations that the central die in a large multi-chip platform might otherwise encounter.

[0123] In some embodiments, the conversion between an electrical signal and an optical signal for an optical channel occurs at a bidirectional transceiver within the photonic layer of the OIIC. For example, for electrical-optical conversion, the bidirectional transceiver may include an optical modulator (e.g., a Mach-Zehnder interferometer) that receives an electrical signal (e.g., a voltage signal) for controlling the amplitude modulation of a light wave provided by a light source to generate a modulated light wave. The light source may be, for example, a laser integrated into the platform 100, or a port of an edge coupler or a surface grating coupler that receives a light wave, for example, from an optical fiber coupled to an external laser. For optical-electrical conversion, the bidirectional transceiver may include a photodetector that converts the optical power of the light wave into a generated current signal. The current signal may then be converted into a voltage signal within a computing node (e.g., using a transimpedance amplifier). For example, the electrical signal may be transmitted to or from a metal contact on the surface of the OIIC via a through-silicon via (TSV).

[0124] Figure 2B Examples of other kinds of components that can be included in the OIIC are shown. In this example, along with metal interconnects (e.g., some for carrying signals and some for carrying power) and optical waveguide interconnects, there are also areas including metal capacitors and planar inductors. For example, passive electronic components (such as capacitors and inductors) can be useful for better utilizing the limited area within each computing grain coupled to the OIIC. For example, capacitors can be used for power decoupling in electronic circuits, where it is useful for power decoupling capacitors to be relatively close to the electronic circuits. Metal TSVs (not shown) can be used as needed to charge and discharge these capacitors from one of the metal contacts connected to the computing grain. These passive components can take up a relatively large amount of space, and the available space in the OIIC can be more than the available space in the computing grain. Since (one or more) passive components can be placed directly below the computing grain including the circuit using (one or more) passive components, the distance of the metal conductive path for making electrical connections is relatively short.

[0125] Figure 3An example of an arrangement 300 of paths within a layer of an OIIC is shown. Because the size of the arrangement is larger than a typical pattern produced by a single mask during semiconductor manufacturing, the arrangement 300 can be manufactured using multiple individual photomask patterned segments formed using one or more photomasks. In some embodiments, a wafer-level OIIC is formed over a large portion of the entire semiconductor wafer. A grid of metal paths 302 provides a power distribution grid within the layer of the OIIC. The power distribution grid can be connected to one or more power supplies, for example, at the edge of the arrangement 300 and / or through TSVs distributed on the arrangement 300. At regular intervals, each group of metal contacts 304 provides a dense array of connections for individual computing dies with controlled collapse chip connections. Short metal paths 306 between arrays of corresponding edge rows of contacts for different computing dies are used for electrical channels (e.g., AIB channels). Although it may be difficult to manufacture metal paths 306 for data that cross the boundaries between segments patterned across multiple individual photomasks due to pattern misalignment, metal paths 302 for power can be manufactured to cross those boundaries due to the much wider thickness of the metal paths. In some embodiments, metal paths 302 and metal paths 306 may be fabricated in different metal layers, or fabricated in a single metal layer.

[0126] In at least one photonic layer separated from the metal layer (one or more), a long waveguide 308 across the boundaries between multiple individual photomask patterned segments is used for optical channels. Techniques can be used to reduce losses that may otherwise be associated with any misalignment between adjacent photomask patterned segments, such as by gradually increasing the waveguide width near the span to reduce losses (maximum of about 10 microns, loss is only about 0.004 dB), as described in the article "Wafer-scale silicon photonic switches beyond die size limit" by Seok et al., which is incorporated herein by reference. Transmitter and receiver devices, or transceiver devices that include both transmitter and receiver devices, are placed at regular intervals to enable optical signals to be sent and received from different computing grains. In some embodiments, there are multiple photonic layers, with waveguides in one direction in one layer and waveguides in a vertical direction in another layer. Alternatively, in some embodiments, a photonic device, such as a directional switch, may be present at the intersection between two waveguides. The switch may be controlled by an electrical signal provided through the compute node, or by an electrical signal provided from a controller external to the compute node.

[0127] As described herein, some embodiments of OIICs may provide a variety of advantages. One potential advantage is that a large number of optical channels can be supported due to the density of optical waveguides that can be manufactured in the (one or more) photonic layers of the OIIC. The density achieved may be limited by the spacing that can be achieved in manufacturing a collection of parallel waveguides, but may be on the order of hundreds or even thousands of waveguides. The number of optical signal paths this produces may be much larger than the number provided by using fiber arrays, which may be limited to a much smaller number (e.g., about 16 or 32). The size of the OIIC also has advantages. Computing nodes that may be more sensitive to manufacturing yields remain small (the size of a single photomask patterned die chiplet). OIICs with better manufacturing yields can be larger (e.g., most of a 30cm×30cm complete wafer). Therefore, the OIIC is large enough to accommodate a large number of chiplet computing nodes, but also small enough to be much more compact than platforms using external photonic couplers, modulators, and switches. Fewer slots within the platform required for photonic devices may also be required, leaving more available space for chiplet computing nodes. Optoelectronic computing platforms using OIIC can also be very flexible by combining any of the various types of computing nodes, as long as the die size and contact / bump arrangement are the same. The application of such a platform can be used for a variety of applications, such as neuromorphic computing or high-performance computing, or customized applications that can benefit from a dense and flexible optical network substrate to reduce power requirements, manage heat dissipation, increase signal bandwidth and / or reduce communication latency.

[0128] In addition to supporting communications between different computing nodes or between computing nodes and I / O modules, the optical channels provided by the OIIC can also be used for efficient forms of distributed computing that can be performed using elements within the OIIC. As an example of such distributed computing is a distributed pulse-amplitude modulation (PAM) aggregation technique that can be used with optical signals transmitted through an optical transmission medium (such as an optical waveguide in the OIIC), or with a variety of other types of signals transmitted through other suitable transmission media. As an example of a distributed PAM aggregation technique, consider a system that includes multiple nodes that generate partial results (e.g., different summands or different partial sums) that need to be added together to produce an aggregated sum at a specific destination in the system.

[0129] Figure 4A An example movement of partial results in a distributed sum computation is shown. Each box represents a different computation node in the system, and the arrows represent the direction of movement of the partial results in the system. The example computation performed is the following dot product of two vectors, which can be part of a larger computation such as the multiplication of a vector and a matrix or the multiplication of two matrices.

[0130] x·w=x1w1+x2w2+x3w3+x4w4

[0131] For example, vector x can be an input vector, and vector w can be a row element of a matrix of weight values. Each computing node in the initial set of computing nodes represented in the top row calculates the different products of each element of the vector in the dot product. The partial results from these calculations are then moved to other computing nodes represented in the middle row, and each node in the other computing nodes calculates the sum of those partial results. Then, the partial results from these calculations are moved to another computing node shown in the bottom, which calculates the final sum to produce a total result, and then the total result may need to be moved to different parts of the system. This is just an example arrangement, in which the accumulation path sinks the result into the center in the physical implementation. In general, a non-contracting architecture may require a bus to have a length that cannot be efficiently scaled.

[0132] Figure 4B An alternative example is shown in which the summation of the final result stage is performed using a transmission medium (e.g., an optical waveguide). As the signal propagates down the waveguide, the amplitudes of the different pulses within the signal are modulated so that the final result is represented by the final amplitude. This example exploits the sinking symmetry of the computation and utilizes the distributed PAM aggregation technique described in more detail below to provide a result quickly (e.g., close to the speed of light) by performing the addition using multiple binary modulation operations to generate a multi-level PAM modulated result.

[0133] Figure 5A , 5B 5C show an example of data flow in a distributed vector matrix multiplication (VMM) system with multiple multiplication modules. Figure 5A In , the elements of vector x are distributed to be multiplied with different weight values ​​of the matrix used in the VMM calculation. Figure 5B In , after multiplying the vector element value with the corresponding weight value, the adder tree works inwards towards the center of the multiplication module to generate multiple different partial sum results. Figure 5C In the embodiment of the present invention, for each element of the output vector, the partial sums within each row are added together to accumulate the sum by distributed PAM aggregation performed on the corresponding transmission medium (e.g., the corresponding optical waveguide) for each row. By synchronously driving the optical channels (e.g., within the OIIC), the results can be accumulated and transmitted to the appropriate destination computing nodes within the optoelectronic computing platform at the same time.

[0134] refer to Figure 6Describe a simplified example of distributed PAM aggregation. In this example, there are two nodes, each with a 1-bit value, and those values are added to the sum result being transmitted along the transmission medium to destination D. Node N0 has bit b0, and node N1 has bit b1. Figure 6 The representation in Figure 6 shows the different possible combinations of the values of the 1-bit values and the corresponding values of the result bit and the carry bit, which together represent the sum of two 1-bit values. There is also an amplitude value that corresponds to the amplitude of the modulated signal that has been transmitted from the source onto the transmission line and passed through the respective modulators at each of nodes N0 and N1. The signal starts at a predetermined initial amplitude, which in this example is represented as amplitude 1. When the signal passes through each node, if the 1-bit value is "0", then the node passes the signal through without changing its amplitude (corresponding to modulation value 1), or if the 1-bit value is "1", then the node modulates the signal by a predetermined amplitude scaling factor (or "modulation depth") m, where 0 < m < 1. Thus, a distributed summation operation is performed using distributed multiplication operations.

[0135] In this example, the predetermined modulation depth is 0.5. Ignoring any minor propagation losses that may be associated with the transmission through the modulators at each node, if the 1-bit values of both nodes are 0, then the amplitude of the signal at destination D will still be 1. If the 1-bit value of either node is 1 and the 1-bit value of the other node is 0, then the amplitude of the signal at destination D will be 0.5. If the 1-bit values of both nodes are 1, then the amplitude of the signal at destination D will be 0.25. In other examples, the predetermined modulation depth can be different, but if the predetermined modulation depth is the same at each node, then the amplitude value will represent a count of the number of nodes with value "1". This technique can be scaled to any number of nodes at corresponding intermediate positions along the transmission medium. Any number of 1-bit values can also be transmitted in sequential time slots to add multi-bit values.

[0136] Figure 7 An example of a digital logic circuit is shown, which for the example of Figure 6 Figure 6 can be used to map the detected analog amplitude sum result to a digital sum result. At the input, an analog amplitude sum result can be provided, for example, as the voltage of a transimpedance amplifier that is driven by the photocurrent of a photodetector that detects the light wave in an optical waveguide serving as the transmission medium. Only two comparators are needed to distinguish between the three different possible amplitude values. The circuit then uses XOR gates and AND gates and synchronous digital circuit elements to provide the result and an indication of each new frame. The timing for each bit corresponds to the timing of the respective time slots of the light wave.

[0137] Figure 8A table for aggregating 1-bit values ​​from three nodes at an intermediate position along a transmission medium is shown. As in the previous example, since only the sum is required at the destination, the fact that different possible combinations of 1-bit values ​​can result in the same received signal amplitude is irrelevant. In this example, there are only four different possible amplitude values, so the number of comparisons required in this case is three instead of two. In general, the number of comparisons required will scale with the number of nodes. There will also be carry bits required for additional results and / or additional nodes. The figure shows amplitude values, where the predetermined modulation depth used by each node is 0.5, as in the previous example, but also shows optimized amplitude values, where the predetermined modulation value used by each node is 0.66 (rounded to two decimal places). Using an amplitude based on a 0.5 modulation depth, the step size between the two minimum values ​​0.125 and 0.25 is 0.125. In contrast, under the optimized amplitude based on a 0.66 modulation depth, the larger step size between the two minimum values ​​0.29 and 0.44 is 0.15.

[0138] The following is an example of a calculation for determining an optimal value for a predetermined modulation depth m, where k is the number of summands added together (and the number of modulators at intermediate locations along the transmission medium). The step size between different amplitudes that are closest to each other, and therefore the most difficult to resolve for a given signal-to-noise ratio (also called the minimum step size), is the step size between all k modulators applying the predetermined modulation depth and the k-1 modulators applying the predetermined modulation depth. Therefore, as described below, the optimal modulation depth is determined by maximizing this minimum step size.

[0139] step k-1,k =m k-1 -m k =m k-1 (1-m)

[0140]

[0141]

[0142] Therefore, the optimization technique is characterized in that as more nodes are added, the optimal modulation depth grows, which makes the modulation more power efficient.

[0143] Fig. 9 Examples of different graphs of the value of the minimum step size as a function of the modulation depth for each modulator are shown for a given value of k. For each value of k, the optimal predetermined modulation depth occurs at the maximum value of the minimum step size. By maximizing the minimum step size that needs to be resolved between two amplitude values ​​that are closest to each other, there is less sensitivity to noise, which optimizes performance by reducing the error rate for a given signal-to-noise ratio.

[0144] The following is an example of a calculation, which shows that as k grows, the optimal modulation depth applied by k-1 nodes approaches 1 / e (relatively quickly).

[0145]

[0146]

[0147] Fig.10 An example configuration for using distributed PAM aggregation in a system that performs 4×4 matrix multiplication using 8-bit multiplication is shown. The data elements in the input vector and the coefficients in the weight matrix are multiplied electrically. There are spatially distributed partial sums that are added to produce a 17-bit intermediate result. The bits of each partial sum are aggregated onto an optical transmission medium using a modulator (such as a high-speed underdriven binary segmented carrier injection modulator (SCIM)) to provide a sequence of optical intensities that are deserialized into 18-bit sums. Carrier injection absorption amplitude modulators are useful in some embodiments, for example, due to thermal stability, which helps to reproduce a predetermined modulation depth at multiple modulators. In some embodiments, no single SCIM is driven at full-scale (hence the term "underdriven"), thereby significantly reducing the power / area of ​​the modulator driver. A variety of alternative configurations can be used. For example, different types of modulators can be used, including Mach-Zehnder interferometers or ring modulators. Some configurations may use multiple optical wavelengths, thereby enabling the use of lower serializer-deserializer (SERDES) frequencies.

[0148] Fig.11A and 11B Different example layouts of systems that use distributed PAM aggregation techniques to distribute and aggregate partial results are shown. Fig.11A In , there are two data modulators along each of the four branches of the waveguide, with photodiodes at the ends of the waveguide. Drivers (TX) are placed at specific locations to provide partial sum results at intermediate locations along the waveguide. Fig. 11B In the embodiment of the invention, there are additional photodiodes at the ends of the waveguides, which are separated from the four waveguides, thereby providing multiple destinations for each branch (e.g., to locally store the results of the aggregation). Therefore, the destination at which the results are provided is not necessarily at the end of the waveguide.

[0149] Various other systems may use distributed PAM aggregation techniques to perform summation of binary values ​​in different time slots along a transmission medium. For example, in addition to wafer-level systems that use an interposer to provide optical waveguides as a transmission medium, systems may use optical fiber as a transmission medium to connect different nodes (e.g., server racks) in a data center. Also, some systems may use electrical modulators to aggregate binary values ​​encoded on electrical signals transmitted along electrical transmission lines.

[0150] The systems and operations described in this specification may be implemented in digital electronic circuits or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in a combination of one or more of them. Embodiments of the subject matter described in this specification may be implemented using one or more modules of computer program instructions encoded on a computer-readable medium that are executed by a data processing device or control the operation of the data processing device. The computer-readable medium may be a manufactured product, such as a hard drive in a computer system or an optical disk sold through a retail channel, or an embedded system. The computer-readable medium may be acquired separately and then encoded with one or more modules of computer program instructions, such as by transmitting one or more modules of computer program instructions over a wired or wireless network. The computer-readable medium may be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of them.

[0151] A computer program (also referred to as a program, software, software application, script, or code) may be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files storing portions of one or more modules, subroutines, or codes). A computer program may be deployed to execute on one computer, or on multiple computers located on one site or distributed on multiple sites and interconnected by a communication network.

[0152] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and the apparatus can also be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0153] Some systems described in this specification may provide optoelectronic platforms and / or distributed PAM aggregation functionality for the systems disclosed in U.S. application Ser. No. 16 / 431,167, filed on Jun. 4, 2019, which is incorporated herein by reference.

[0154] While the present disclosure has been described in conjunction with certain embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments, but on the contrary, it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope should be given the broadest interpretation to encompass all such modifications and equivalent structures permitted by law.

Claims

1. A method for information transmission, comprising: transmitting a signal having predetermined preliminary optical characteristics from a source to a transmission medium; modulating an optical characteristic of the signal at each of a plurality of intermediate locations between the source and the destination by a selected modulation value; detecting the signal at a destination after the signal has been transmitted through the intermediate location; as well as The detected optical characteristic of the detected signal is mapped using a predetermined scale that indicates the number of intermediate locations at which the signal is modulated.

2. The method of claim 1, wherein the optical characteristic comprises amplitude.

3. The method of claim 2, wherein modulating the optical property comprises: The amplitude of the signal at each of the plurality of intermediate positions is modulated by a modulation value selected from a binary set of two possible modulation values, wherein for each of the intermediate positions the binary set consists of: Modulation value 1, and A predetermined magnitude scaling factor S greater than 0 and less than 1.

4. The method of claim 2, wherein mapping the detected optical characteristic of the detected signal comprises mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicating a number of intermediate positions at which the signal is modulated by a predetermined amplitude scaling factor.

5. The method of claim 4, wherein the predetermined amplitude scale comprises a maximum detected amplitude substantially equal to the predetermined preliminary amplitude and a maximum detected amplitude substantially equal to S N The minimum detected amplitude is , where N is the number of intermediate positions.

6. The method according to any one of claims 3 to 5, wherein: For each intermediate position, the predetermined amplitude scaling factor S is different.

7. The method according to any one of claims 3 to 5, wherein: For each intermediate position, the predetermined amplitude scaling factor S is equal.

8. A method as claimed in any one of claims 3 to 5, wherein the predetermined amplitude scaling factor S is substantially equal to (k-1) / k, and k is the number of intermediate positions.

9. The method of any one of claims 3 to 5, wherein the signal transmitted from the source has a predetermined preliminary amplitude in each time slot of a plurality of time slots including the first time slot.

10. The method of claim 9, wherein the modulation of the amplitude of the signal at each of the plurality of intermediate locations occurs in a first time slot after a propagation delay based on a propagation distance between each intermediate location and the source.

11. The method of claim 9, further comprising maintaining time synchronization between the plurality of intermediate locations, the source, and the destination.

12. The method of any one of claims 1 to 5, wherein the transmission medium comprises an optical waveguide.

13. The method of claim 12, wherein the optical waveguide is formed in an integrated circuit interposer, the integrated circuit interposer comprising metal contacts arranged for electrical coupling to at least one semiconductor die in a controlled collapse chip connection.

14. The method of claim 13, wherein the selected modulation values ​​at one or more of the intermediate locations are provided based on electrical signals from the semiconductor die.

15. The method of any one of claims 2 to 5, wherein modulating the optical property comprises: The amplitude of the signal at each of the plurality of intermediate positions is modulated by a modulation value selected from a binary set of two possible modulation values, wherein for each of the intermediate positions the binary set consists of: Modulation value 1, and A predetermined amplitude scaling factor S greater than 1.

16. The method of any one of claims 1 to 5, wherein the optical property comprises phase or polarization.

17. A signal transmission system, comprising: Transmission medium; a source configured to transmit a signal having predetermined preliminary optical characteristics onto said transmission medium; a plurality of optical property modulators coupled to the transmission medium at respective intermediate locations between the source and the destination; a detector at the destination configured to detect the signal after the signal has been transmitted through the intermediate location; as well as Circuitry is configured to map a detected optical characteristic of a detected signal using a predetermined metric indicative of a number of intermediate locations at which the signal is modulated.

18. The system of claim 17, wherein each optical property modulator comprises an amplitude modulator configured to modulate the amplitude of the signal by a selected modulation value from a binary set of two possible modulation values.

19. The system of claim 18, wherein for each of the amplitude modulators, the binary set consists of: Modulation value 1, and A predetermined magnitude scaling factor S greater than 0 and less than 1.

20. The system of claim 18, wherein for each of the amplitude modulators, the binary set consists of: Modulation value 1, and A predetermined amplitude scaling factor S greater than 1.

21. A system as claimed in any one of claims 17 to 20, wherein each optical property modulator comprises a phase or polarization modulator configured to modulate the phase or polarization of the signal by a selected modulation value from a binary set of two possible modulation values.

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