Information transmission method and system

Abstract

The invention discloses a method and a system for transmitting information. A method for transmitting information from a plurality of nodes to at least one destination comprises: 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, where for each intermediate position the binary set consists of: a modulation value 1, and a predetermined amplitude scaling factor S greater than 0 and less than 1; detecting a signal at the destination after the signal transmission passes through all the intermediate positions; and mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicating a number at which intermediate positions of the signal are modulated by a predetermined amplitude scaling factor.

Description

[0001] This application is a divisional application of the patent application for invention with the application date of May 21, 2021, application number 202110555227.2, and invention title "Optoelectronic Computing Platform".

[0002] Cross - reference to related applications

[0003] This application claims the priority of U.S. Provisional Patent Application 63 / 048,439, filed on Jul. 6, 2020, the entire content of which is incorporated herein by reference. Technical field

[0004] This disclosure relates to optoelectronic computing platforms. Background art

[0005] Computations performed on electronic data encoded in electrical signals (e.g., voltage or current), either in analog or digital form, are typically implemented using electronic computing hardware such as analog or digital electronic devices (e.g., processors, application - specific integrated circuits (ASICs), or systems - on - a - chip (SoCs)) implemented in integrated circuits, electronic circuit boards, or other electronic circuits. Optical signals have been used for long - distance and short - distance (e.g., within a data center) data transmission. Operations performed on such optical signals often occur in the context of optical data transmission, such as within devices for switching or filtering optical signals in a network. The use of optical signals in computing platforms is more restricted. Summary of the invention

[0006] Generally, in a first aspect, an integrated circuit interposer includes: a semiconductor substrate layer; a 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 for electrically coupling to a first semiconductor die by controlled collapse chip connection, and the second metal contact segment including a plurality of metal contacts arranged for electrically coupling to a second semiconductor die by controlled collapse chip connection. The interposer includes: a 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 at a second distance different from the first distance from the semiconductor substrate layer, including a plurality of individually photomask-patterned waveguide segments. The second patterned layer includes: a first waveguide spanning at least one boundary between the individually photomask-patterned waveguide segments; a first modulator coupled to the first waveguide at a first position along the first waveguide for modulating light waves in the first waveguide based on an electrical signal received at a first metal contact of the first metal contact segment; and a second modulator coupled to the first waveguide at a second position along the first waveguide for modulating light waves in the first waveguide based on an electrical signal received at a second metal contact of the first metal contact segment or the second metal contact segment.

[0007] Aspects may include one or more of the following features. The waveguide segments may include a first waveguide segment and a second waveguide segment, the first waveguide segment including a first portion of the first waveguide that couples a guided mode to an edge of the first waveguide segment, and the second waveguide segment including a second portion of the first waveguide that couples a guided mode to an edge of the second waveguide segment.

[0008] The metal path segments 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.

[0009] The metal path segments 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.

[0010] The integrated circuit interposer may further include a second metal contact layer at a second surface of the integrated circuit interposer, including a plurality of metal contact segments.

[0011] The integrated circuit interposer may further include at least one capacitor or inductor electrically coupled to at least one of the first semiconductor die or the second semiconductor die.

[0012] The first modulator and the second modulator may be amplitude modulators configured to modulate the optical wave in the first waveguide with the same predetermined amplitude scaling factor.

[0013] Generally, in another aspect, a method of fabricating an integrated circuit interposer includes: forming a first metal contact layer on a semiconductor wafer at a first surface of the integrated circuit interposer, the first metal contact layer 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 for electrically coupling to the first semiconductor die by controlled collapse chip connection, and the second metal contact segment including a plurality of metal contacts arranged for electrically coupling to the second semiconductor die by controlled collapse chip connection. The method includes: forming a first patterned layer on the semiconductor wafer at a first distance from the 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 different from the first distance from the semiconductor substrate layer, including patterning a plurality of waveguide segments respectively. The second patterned layer includes: a first waveguide that spans at least one boundary between the waveguide segments patterned by separate photomask patterns; a first modulator coupled to the first waveguide at a first position along the first waveguide for modulating the optical wave in the first waveguide based on an electrical signal received at the first metal contacts in the first metal contact segment; and a second modulator coupled to the first waveguide at a second position along the first waveguide for modulating the optical wave in the first waveguide based on an electrical signal received at the second metal contacts in the first metal contact segment or the second metal contact segment.

[0014] In general, on the other hand, a device 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 circuitry; 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 location 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 location 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 circuitry. The first waveguide enables the optical signal to travel from a source location to a target location across at least one boundary between the individually photomask-patterned waveguide segments, and the optical signal is modulated by the first and second modulators as the optical signal travels from the source location to the target location.

[0015] Aspects may include one or more of the following features. The first metal contact layer may include a second metal contact configured to be electrically coupled to a second die including circuitry.

[0016] The first metal contact may be electrically coupled to the first die by controlled collapse chip connection, and the second metal contact may be electrically coupled to the second die by controlled collapse chip connection.

[0017] The first metal contact may be located in a first region corresponding to a first individually photomask-patterned waveguide segment; and the second metal contact may be located in a second region corresponding to a second individually photomask-patterned waveguide segment different from the first individually photomask-patterned waveguide segment.

[0018] The device may include: a detector configured to detect the optical signal after the optical signal has traveled through the first and second modulators to generate a detected signal; and circuitry configured to map the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of modulators through which the signal was modulated.

[0019] The device may include: a detector configured to detect the optical signal after the optical signal has traveled through the first and second modulators to generate a detected signal; and circuitry configured to map the detected phase of the detected signal using a predetermined phase scale indicative of the number of modulators through which the signal was modulated.

[0020] The apparatus may include: a detector configured to detect an optical signal after the optical signal has been transmitted through first and second modulators to generate a detected signal; and circuitry configured to map a detected polarization of the detected signal using a predetermined polarization scale indicative of a number of modulators through which a modulation signal has passed.

[0021] Each individually photomask-patterned waveguide section may be fabricated by exposing a corresponding photomask using a lithography system, and different individually photomask-patterned waveguide sections may be fabricated by different exposures of the same photomask or different photomasks.

[0022] The first metal contact may be electrically coupled to the first die by controlled collapse chip connection.

[0023] The apparatus may include a first die.

[0024] The apparatus may include first and second dies.

[0025] In some examples, the first modulator may be configured to modulate an amplitude of the optical signal.

[0026] In some examples, the first modulator may be configured to modulate a phase or polarization of the optical signal.

[0027] The patterned waveguide layer may include: a first individually photomask-patterned waveguide section including a first portion of a first waveguide that couples a guided mode to an edge of the first waveguide section; and a second individually photomask-patterned waveguide section including a second portion of the first waveguide that couples the guided mode to an edge of the second waveguide section.

[0028] 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.

[0029] 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.

[0030] The first substrate may include a semiconductor substrate.

[0031] 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.

[0032] In general, on the other hand, a method includes: at a first position along a first waveguide formed on a first substrate, modulating an optical signal in the first waveguide based on a first electrical signal received at a first metal contact electrically coupled to a first die including circuitry; at a second position along the first waveguide, modulating the optical signal in 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 circuitry; and transmitting the modulated optical signal from a waveguide section patterned by a first separate photomask disposed on the first substrate to a waveguide section patterned by a second separate photomask disposed on the first substrate, wherein the first separate photomask patterned waveguide section is fabricated by a first exposure of the first photomask using a lithography system, the second separate photomask patterned waveguide section is fabricated by a second exposure of the second photomask using a lithography system, the first exposure is different from the second exposure, and the first photomask is the same as or different from the second photomask.

[0033] Aspects may include one or more of the following features. The first metal contact may be located in a first region corresponding to the first separate photomask patterned waveguide section, and the second metal contact may be located in a second region corresponding to the second separate photomask patterned waveguide section.

[0034] The method may include detecting the modulated optical signal at a destination position downstream of an intermediate position at which the optical signal is modulated to generate the detected signal; and mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of intermediate positions at which the signal is modulated.

[0035] The first separate photomask patterned waveguide section may be fabricated by a first exposure of the first photomask using a lithography system, the second separate photomask patterned waveguide section may be fabricated by a second exposure of the second photomask using a lithography system, the first exposure may be different from the second exposure, and the first photomask may be the same as or different from the second photomask.

[0036] The first metal contact may be electrically coupled to the first die by controlled collapse chip connection.

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

[0038] The first substrate may include a semiconductor substrate.

[0039] 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 the separate photomask patterned waveguide sections.

[0040] The first position and the second position along the first waveguide may be located on the same separate photomask patterned waveguide section.

[0041] The first and second positions along the first waveguide can be located on different separately optically masked patterned waveguide sections.

[0042] The method can include filtering a signal on the first die or the second die using a filtering capacitor deployed on a first substrate, where the first die or the second die includes a second substrate different from the first substrate.

[0043] The method can include decoupling a first circuit portion from a second circuit portion using a decoupling capacitor deployed on a first substrate, where the first circuit portion is on the first or second die and the second circuit portion is on the first or second die.

[0044] Generally, in another aspect, an apparatus includes an interposer. The interposer includes: an interposer substrate; and a first metal contact layer formed on the interposer substrate, where the first metal contact layer includes a first metal contact, a second metal contact, and a third metal contact, the first metal contact being configured to be electrically coupled to a first die including a circuit, the second metal contact being configured to be electrically coupled to the first die or a second die including a circuit, the first die including a first substrate different from the interposer substrate, and the second die including a second substrate different from the interposer substrate. The interposer includes a patterned waveguide layer formed on the interposer substrate, where 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 the 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 the 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 scale indicating the number of modulators that modulate the signal in a predetermined manner, where the output signal is electrically coupled to the third contact, and the third contact is electrically coupled to at least one of the first die, the second die, or a third die.

[0045] Aspects can include one or more of the following features. The first metal contact can be electrically coupled to the first die by controlled collapse chip connection.

[0046] The second metal contact can be electrically coupled to the second die by controlled collapse chip connection.

[0047] The third metal contact can be electrically coupled to the third die by controlled collapse chip connection.

[0048] The first metal contact layer may include a first metal contact section and a second metal contact section. The first metal contact section may include a plurality of metal contacts arranged for electrical coupling to a first die, and the second metal contact section may include a plurality of metal contacts arranged for electrical coupling to a second die.

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

[0050] The plurality of metal contacts in the second metal contact section may be electrically coupled to the second die by controlled collapse chip connection.

[0051] The device may include a first patterned metal layer formed on an interposer substrate, and the first patterned metal layer may include a plurality of individually photomask-patterned metal path sections.

[0052] The patterned waveguide layer may include a plurality of individually photomask-patterned waveguide sections, and a first waveguide may span at least one boundary between the individually photomask-patterned waveguide sections.

[0053] The first metal contact may be located in a first region corresponding to a first individually photomask-patterned waveguide section; and the second metal contact may be located in a second region corresponding to a second individually photomask-patterned waveguide section different from the first individually photomask-patterned waveguide section.

[0054] Generally, in another aspect, a device 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 the first die or a second die electrically coupled to the interposer.

[0055] 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.

[0056] The second die may include a second substrate different from the interposer substrate.

[0057] The first die may be electrically coupled to the interposer by controlled collapse chip connection.

[0058] The second die may be electrically coupled to the interposer by controlled collapse chip connection.

[0059] The interposer layer 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 being configured to be electrically coupled to a first die, and the second metal contact being configured to be electrically coupled to the first die or a second die.

[0060] The interposer layer 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 the first metal contact. The second modulator may be configured to modulate the optical signal in the first optical waveguide based on a second electrical signal received at the second metal contact.

[0061] The apparatus may include: a detector configured to detect the optical signal after the optical signal has passed through the first and second modulators to generate a detected signal; and a detection circuit configured to map the detected amplitude of the detected signal to an output signal using a predetermined amplitude scale indicative of the number of modulators through which the signal was modulated.

[0062] The output signal may be electrically coupled to a third contact, which is electrically coupled to at least one of the first die, the second die, or a third die.

[0063] Generally, 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 onto a transmission medium from a source; modulating the amplitude of the signal at each of a plurality of intermediate positions between the source and the destination by a modulation value selected 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 passed through all the intermediate positions; and mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of intermediate positions at which the signal was modulated by the predetermined amplitude scaling factor.

[0064] 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 minimum detected amplitude substantially equal to S N where N is the number of intermediate positions.

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

[0066] For each intermediate position, the predetermined amplitude scaling factor S may be equal.

[0067] The predetermined amplitude scaling factor S may be substantially equal to , where k is the number of intermediate positions.

[0068] The signal transmitted from the source can have a predetermined initial amplitude within each of a plurality of time slots including a first time slot.

[0069] Modulation of the signal amplitude at each of the plurality of intermediate positions can occur within the first time slot after a propagation delay based on the propagation distance between each intermediate position and the source.

[0070] The method can further include maintaining time synchronization among a plurality of nodes, the source, and the destination.

[0071] The transmission medium can include an optical waveguide.

[0072] The optical waveguide can be formed in an integrated circuit interposer that includes metal contacts arranged for controlled collapse chip connection to electrically couple to at least one semiconductor die.

[0073] Selected modulation values at one or more of the intermediate positions can be provided based on electrical signals from the semiconductor die.

[0074] Generally, 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 initial amplitude onto the transmission medium; and a plurality of amplitude modulators coupled to the transmission medium at respective intermediate positions 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 positions; and circuitry configured to map 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 a common amplitude scaling factor.

[0075] Generally, in another aspect, a method includes: transmitting a signal having a predetermined initial optical characteristic from a source onto a transmission medium; modulating the optical characteristic of the signal at each of a plurality of intermediate positions between the source and the 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 characteristic of the detected signal using a predetermined scale indicating the number of intermediate positions at which the signal was modulated.

[0076] Aspects can include one or more of the following features. The optical characteristic can include amplitude.

[0077] The modulating optical characteristic can include modulating the amplitude of a signal at each of a 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.

[0078] The detected optical characteristic of the detected signal can include mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of intermediate positions at which the signal is modulated by the predetermined amplitude scaling factor.

[0079] The predetermined amplitude scale can include a maximum detected amplitude substantially equal to a predetermined preliminary amplitude and a minimum detected amplitude substantially equal to S N where N is the number of intermediate positions.

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

[0081] For each intermediate position, the predetermined amplitude scaling factor S can be equal.

[0082] The predetermined amplitude scaling factor S can be substantially equal to where k is the number of intermediate positions.

[0083] The signal transmitted from the source can have a predetermined preliminary amplitude within each of a plurality of time slots including a first time slot.

[0084] The modulation of the signal amplitude at each of the plurality of intermediate positions can occur within the first time slot after a propagation delay based on the propagation distance between each intermediate position and the source.

[0085] The method can further include maintaining time synchronization among a plurality of nodes, the source, and the destination.

[0086] The transmission medium can include an optical waveguide.

[0087] The optical waveguide can be formed in an integrated circuit interposer including metal contacts arranged for controlled collapse chip connection to electrically couple to at least one semiconductor die.

[0088] The selected modulation value at one or more of the intermediate positions can be provided based on an electrical signal from the semiconductor die.

[0089] The modulating optical characteristic can include modulating the amplitude of a signal at each of a 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.

[0090] The optical properties can include phase or polarization.

[0091] Generally, in another aspect, a method includes: transmitting a signal having a predetermined initial first optical property and a predetermined initial second optical property from a source onto a transmission medium; modulating the first or second optical property of the signal at each of a plurality of intermediate positions between the source and the destination by a selected modulation value; detecting the signal at the destination after the signal has traversed the intermediate positions; and mapping the detected first and second optical properties of the detected signal using a predetermined scale indicative of the number of intermediate positions at which the signal was modulated.

[0092] Aspects can include one or more of the following features. The first optical property can include amplitude and the second optical property can include phase.

[0093] The first optical property can include amplitude and the second optical property can include polarization.

[0094] The first optical property can include phase and the second optical property can include polarization.

[0095] The signal can have a predetermined initial third optical property, and the method can include modulating the first, second, or third optical property of the signal at each of a plurality of intermediate positions between the source and the destination by a selected modulation value; and mapping the detected first, second, and third optical properties of the detected signal using a predetermined scale indicative of the number of intermediate positions at which the signal was modulated.

[0096] The first optical property can include amplitude, the second optical property can include phase, and the third optical property can include polarization.

[0097] Generally, in another aspect, a system includes: a transmission medium; a source configured to transmit a signal having a predetermined initial optical property onto the transmission medium; a plurality of optical property modulators coupled to the transmission medium at respective intermediate positions between the source and the destination; a detector at the destination configured to detect the signal after the signal has traversed the intermediate positions; and circuitry configured to map the detected optical properties of the detected signal using a predetermined scale indicative of the number of intermediate positions at which the signal was modulated.

[0098] Aspects can include one or more of the following features. Each optical property modulator can 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.

[0099] For each amplitude modulator, the binary set can consist of a modulation value 1 and a predetermined amplitude scaling factor S greater than 0 and less than 1.

[0100] For each amplitude modulator, the binary set can consist of a modulation value 1 and a predetermined amplitude scaling factor S greater than 1.

[0101] Each optical property modulator can include a phase or polarization modulator configured to modulate the phase or polarization of a signal by a modulation value selected from a binary set of two possible modulation values.

[0102] Aspects can have one or more of the following advantages.

[0103] Data can be modulated onto any one of a variety of types of signals. Compared to other types of signals, the transmission or processing of certain types of signals has certain advantages. Examples of different types of signals include: optical signals corresponding to light waves that have been modulated by signal data, and electrical signals (e.g., voltage or current) corresponding to electrical waveforms that have been modulated by signal data. According to a predetermined constellation, various modulations can be used, such as amplitude modulation, phase modulation, or a combination of amplitude and phase modulation. Light waves, which serve as the underlying signal carriers for optical signals, have certain advantages compared to electrical waveforms that serve as the underlying signal carriers for electrical signals. For example, light waves generally have a higher bandwidth capacity than electrical waveforms. There are also typically lower power requirements and shorter time delays (or "latencies") associated with transmitting data over a given distance for optical signals.

[0104] Optical signals can be used to transfer data between different electronic nodes in a system or device (e.g., computing nodes within a data center or integrated circuits within a device package). However, there is typically an overhead associated with the complexity of using such optical communication links, including the conversion between optical signals and electrical signals that serve as inputs and / or outputs of electronic modules. A time delay associated with timing synchronization for signal conversion is also added.

[0105] Some embodiments of the optoelectronic computing platforms described herein are capable of reducing the complexity required to incorporate communication via optical signals into the platform. As described in more detail below, by using large (e.g., wafer-scale) optoelectronic interposers, a collection 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 in order to combine communication and computing in an efficient manner.

[0106] 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 specification, the drawings, and the claims.

[0107] 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 this invention belongs. In case of conflict, the present specification, including definitions, will control over any incorporated patent application or patent application publication by reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is to be emphasized that, by convention, the various features of the drawings are not drawn to scale. Instead, the dimensions of the various features are arbitrarily enlarged or reduced for clarity.

[0109] Figure 1 is a schematic diagram of an example of an optoelectronic computing platform.

[0110] Figure 2A is a schematic diagram of an example of a data channel provided by an optoelectronic interposer IC.

[0111] Figure 2B is a schematic diagram of an example optoelectronic interposer IC including passive electronic components.

[0112] Figure 3 is a schematic diagram of an example of an optoelectronic interposer IC.

[0113] Figure 4A and 4B is a schematic diagram of an example of the movement of partial results in distributed summation calculation.

[0114] Figure 5A 、 5B and 5C are schematic diagrams of examples of data flows in a distributed computing architecture.

[0115] Figure 6 is a schematic diagram of an example of distributed PAM aggregation technology.

[0116] Figure 7 is a circuit diagram of an example digital logic for mapping an analog sum result to a digital sum result.

[0117] Figure 8 is a table of examples of bits that are summed to produce an analog amplitude.

[0118] Figure 9 is a collection of graphs showing the variation of the minimum step size with the modulation depth.

[0119] Figure 10 is a schematic diagram of an example system configuration.

[0120] Figure 11A and 11B are schematic diagrams of an exemplary system layout.

[0121] Like reference numerals and designations in the various figures indicate like elements. Detailed Description

[0122] Figure 1An example of an optoelectronic computing platform 100 is shown. The platform 100 includes an array of computing nodes, each computing node being coupled to an optoelectronic interposer integrated circuit (OIIC). In addition to metal paths that provide electrical signal connections between the 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 the nodes. Manufacturing challenges have been overcome to enable the OIIC to be fabricated 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 conductive bumps (e.g., solder bumps) in a controlled collapse chip connection (or "flip chip" connection) using an arrangement of metal contacts on the surface of the OIIC. Near the left and right edges of the array of computing nodes, there are also input / output (I / O) modules that are also connected to the OIIC, and these modules enable signals to be coupled into and out of the computing platform 100. The I / O modules are capable of coupling 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 may include circuitry configured according to any of a variety of device protocols, including DDR SDRAM, PCI(e), USB, Ethernet, etc. In this example, each computing node in a 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 I / O circuitry and a MUX. When the MUXs are coupled to or from the OIIC, they enable the selection and routing of electrical signals. On the other side of the OIIC is a package substrate, e.g., the package substrate being capable of providing electrical connections for signals and / or power. Also shown in this example is that near the top edge of the array is a row of interface ports that provide another way to directly couple signals to or from the OIIC. The various features of the OIIC described herein enable the power-efficient integration of a variety of different functional chips on the wafer-level optoelectronic computing platform 100.

[0123] Figure 2AShows an example of a data channel provided by the OIIC. For computing nodes that are relatively close to each other, metal paths within the OIIC enable electrical signals to propagate directly between the nodes. For example, advanced interface bus (AIB) technology, which is used to connect different chips (or "chiplets") in a multi-chip platform, can be used to support electrical data channels on the metal paths. In some embodiments, the pattern of the metal paths is defined by the pattern of a corresponding photomask, where the pattern on the photomask is transferred to the substrate of the photoelectric interposer integrated circuit using a lithography system. The short distance between nearby nodes is defined by a distance that is less than the length of the longest straight metal path, which can be generated using a single photomask (or "reticle") for patterning a single section of the metal path. For computing nodes that are relatively far from each other, or for computing nodes that are relatively far from the I / O module, optical waveguides within the OIIC enable optical signals that are converted from / to electrical signals of the nodes to propagate between the nodes. In some embodiments, the long distance is defined by a distance that is greater than the longest dimension of a section patterned by a single photomask. Such long optical paths provide low-latency and power-efficient optical data channels, which avoid the need for long wires in large (e.g., wafer-scale) platforms, which would pose difficult manufacturing and performance challenges. Platform 100 selects an appropriate type of data channel (i.e., electrical or optical) based on the propagation distance between the source and the destination. Adjacent computing nodes can utilize the short electrical signal paths provided by the OIIC. At the same time, as shown in this example, computing nodes (on computing dies) at any location in the array can have a direct optical connection to the I / O module (on an I / O die) and its connected devices (e.g., DRAM or PCI(e) devices), with a large bandwidth and low latency similar to the short electrical connections between adjacent computing nodes. This breaks the access limitations that the central die in a large multi-chip platform might otherwise encounter.

[0124] In some embodiments, the conversion between the electrical signal and the optical signal for the optical channel occurs at the bi-directional transceiver within the photonic layer of the OIIC. For example, for the electro-optical conversion, the bi-directional transceiver may include an optical modulator (e.g., Mach-Zehnder interferometer) that receives an electrical signal (e.g., voltage signal) for controlling the amplitude modulation of the 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 the light wave, for example, from an optical fiber coupled to an external laser. For the opto-electrical conversion, the bi-directional 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 the computing node (e.g., using a transimpedance amplifier). For example, the electrical signal can be transmitted to or from a metal contact on the surface of the OIIC through a through-silicon via (TSV).

[0125] Figure 2B Examples of other types of components that may be included in the OIIC are shown. In this example, along with the metal interconnects (e.g., some for carrying signals and some metal interconnects for carrying power) and the optical waveguide interconnects, there are also regions that include metal capacitors and planar inductors. For example, passive electronic components such as capacitors and inductors can be useful for better utilization of the limited area within each computing die coupled to the OIIC. For example, capacitors can be used for power decoupling in an electronic circuit, where power decoupling capacitors are useful relatively close to the electronic circuit. Metal TSVs (not shown) can be used to charge and discharge these capacitors as needed from one of the metal contacts connected to the computing die. These passive components can occupy a relatively large amount of space, and the available space in the OIIC can be more than the available space in the computing die. Since the (one or more) passive components can be placed directly below the computing die that includes the circuit using the (one or more) passive components, the distance of the metal conduction path for making electrical connections is relatively short.

[0126] Figure 3An example of the arrangement 300 of the paths within the layer of the OIIC is shown. Since the size of the arrangement is larger than the typical patterns generated by a single photomask in the semiconductor manufacturing process, the arrangement 300 can be fabricated using segments patterned with multiple individual photomask patterns formed using one or more photomasks. In some embodiments, wafer-scale OIIC is formed over most 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 over the arrangement 300. At regular intervals, each group of metal contacts 304 provides a dense connection array for individual compute dies with controlled collapse chip connection. Short metal paths 306 between the corresponding edge rows of contacts for different compute dies are used for electrical channels (e.g., AIB channels). Although it may be difficult to fabricate the metal paths 306 for data crossing the boundaries between segments patterned with multiple individual photomasks due to pattern misalignment, the metal paths 302 for power can be fabricated to span those boundaries since the thickness of the metal paths is much wider. In some embodiments, the metal paths 302 and the metal paths 306 can be fabricated in different metal layers or in a single metal layer.

[0127] In at least one photon layer separate from the (one or more) metal layers, long waveguides 308 spanning the boundaries between segments patterned with multiple individual photomasks are used for optical channels. Techniques can be used to reduce the losses that might otherwise be associated with any misalignment between adjacent segments patterned with photomasks, such as by gradually increasing the waveguide width near the span (up to about 10 microns with a loss of 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 devices and receiver devices, are placed at regular intervals to enable optical signals to be transmitted and received from different compute dies. In some embodiments, there are multiple photon layers with waveguides in one layer along one direction and waveguides in another layer along a perpendicular direction. Alternatively, in some embodiments, photon devices, such as directional switches, can be present at the intersections between two waveguides. The switches can be controlled by electrical signals provided by the compute nodes or by electrical signals provided by a controller external to the compute nodes.

[0128] As described herein, some embodiments of the OIIC can provide a variety of advantages. One potential advantage is the density of optical waveguides that can be fabricated in the (one or more) photonic layers of the OIIC, which can support a large number of optical channels. The density achieved may be limited by the spacing achievable in a collection of parallel waveguides being fabricated, but can be on the order of hundreds or even thousands of waveguides. This results in a much larger number of optical signal paths than can be provided by using an optical fiber array, which may be limited to a much smaller number (e.g., around 16 or 32). The OIIC also has an advantage in size. The compute nodes, which may be more sensitive to manufacturing yield, remain small (the size of a small chip patterned by a single photomask). The OIIC with a better manufacturing yield can be larger (e.g., a large portion of a 30 cm × 30 cm full wafer). Thus, the OIIC is large enough to accommodate a large number of small chip compute nodes, but also small enough to be much more compact than platforms using external photon couplers, modulators, and switches. Fewer in-slot platforms are also required for the photonic devices, leaving more available space for the small chip compute nodes. By incorporating any of a variety of types of compute nodes, as long as the die size and the arrangement of the contacts / bumps are the same, the optoelectronic computing platform using the OIIC can also be very flexible. The applications of such a platform can be used for a variety of applications, such as neuromorphic computing or high-performance computing, or custom 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.

[0129] In addition to supporting communication between different compute nodes or between a compute node and an I / O module, the optical channels provided by the OIIC can also be used for an efficient form of distributed computing that can be performed using the components within the OIIC. An example of such distributed computing is the distributed pulse-amplitude modulation (PAM) aggregation technique, which 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 the distributed PAM aggregation technique, a system will be considered that includes multiple nodes that generate partial results (e.g., different summands or different partial sums), which need to be added together to produce an aggregated sum at a specific destination in the system.

[0130] Figure 4A An example movement of the partial results in a distributed summation calculation is shown. Each box represents a different compute node in the system, and the arrows represent the direction of movement of the partial results in the system. The example calculation performed is the following dot product of two vectors, which can be part of a larger calculation such as the multiplication of a vector and a matrix or the multiplication of two matrices.

[0131]

[0132] For example, vector x can be an input vector, and vector w can be a row of elements of a matrix of weight values. Each computational node in the initial set of computational nodes represented in the top row computes a different product of the respective elements of the vectors in the dot product. Partial results from these computations are then moved to other computational nodes represented in the middle row, and each node in the other computational nodes computes the sum of those partial results. Then, the partial results from these computations are moved to another computational node shown at the bottom, which computes the final sum to produce a total result, and then it may be necessary to move that total result to a different part of the system. This is just one example arrangement where the accumulation path sinks the results to a center in a physical implementation. In general, non-contracting architectures may require buses to have lengths that cannot scale efficiently.

[0133] Figure 4B An alternative example is shown where 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 such that the final result is represented by the final amplitude. This example exploits the sink symmetry of the computation and uses the distributed PAM aggregation technique described in more detail below to quickly provide the result (e.g., at near the speed of light) by performing addition using multiple binary modulation operations to generate a multi-level PAM modulation result.

[0134] Figure 5A 、 5B and 5C show examples of data flows in a distributed vector matrix multiplication (VMM) system with multiple multiplication modules. In Figure 5A , the elements of vector x are distributed to multiply with different weight values of the matrix used in the VMM computation. In Figure 5B , after multiplying the vector element values with the corresponding weight values, the adder tree works inward towards the center of the multiplication modules to generate multiple different partial sum results. In Figure 5C , for each element of the output vector, the partial sums within each row are added together to accumulate the sum through 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 an OIIC), the results can be accumulated and transmitted to the appropriate destination computational nodes within the optoelectronic computing platform simultaneously.

[0135] Refer to Figure 6Describe a simplified example of distributed PAM aggregation technology. In this example, there are two nodes, each with a 1-bit value, and those values are added to the sum result transmitted along the transmission medium to the destination D. Node has bit , and node has bit . 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 in Figure 6 , which together represent the sum of two 1-bit values. There is also an amplitude value, which corresponds to the amplitude of the modulated signal of the corresponding modulator at each node that has been transmitted from the source to the transmission line and passed through nodes and . The signal starts with 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 without changing its amplitude (corresponding to the 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 . Thus, the distributed summation operation is performed using distributed multiplication operations.

[0136] 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 the 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 the destination D will be 0.5. If the 1-bit values of both nodes are 1, then the amplitude of the signal at the 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 the value "1". This technique can be scaled to any number of nodes at the 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.

[0137] Figure 7 shows an example of a digital logic circuit, for Figure 6As an example, the digital logic circuit 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 driven by the photocurrent of a photodetector that detects light waves in an optical waveguide serving as a transmission medium. Only two comparators are needed to distinguish between three different possible amplitude values. The circuit then uses XOR gates, 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.

[0138] Figure 8 A table is shown for aggregating 1-bit values from three nodes at an intermediate position along the transmission medium. As in the previous example, the fact that different possible combinations of 1-bit values can result in the same received signal amplitude is irrelevant since only the sum is needed at the destination. 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 additional results and / or carry bits required for additional nodes. The figure shows the 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 the amplitude based on a modulation depth of 0.5, the step between the two minimum values of 0.125 and 0.25 is 0.125. In contrast, with the optimized amplitude based on a modulation depth of 0.66, the larger step between the two minimum values of 0.29 and 0.44 is 0.15.

[0139] The following is an example of a calculation for determining the optimal value of a predetermined modulation depth m, where k is the number of addends being added together (and the number of modulators at the intermediate position along the transmission medium). The step between different amplitudes that are closest to each other and thus most difficult to resolve for a given signal-to-noise ratio (also known as the minimum step) is the step between all k modulators applying the predetermined modulation depth and k - 1 modulators applying the predetermined modulation depth. Thus, as described below, the optimal modulation depth is determined by maximizing this minimum step.

[0140]

[0141] Thus, the optimization technique is characterized in that as more nodes are added, the optimal modulation depth grows, which makes the modulation more power-efficient.

[0142] Figure 9Shows an example of different curves in which the value of the minimum step size varies with the modulation depth of each modulator for a given value of k. For each value of k, an 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, the sensitivity to noise is lower, which optimizes performance by reducing the error rate for a given signal-to-noise ratio.

[0143] The following is an example of a calculation that shows that as k grows, the optimal modulation depth applied by nodes approaches 1 / e (relatively quickly).

[0144]

[0145]

[0146] Figure 10 Shows an example configuration for using distributed PAM aggregation in a system that performs matrix multiplication using 8-bit multiplication. The data elements in the input vector and the coefficients in the weight matrix are electrically multiplied. There are spatially distributed partial sums that are added together to produce a 17-bit intermediate result. Each partial sum's bits 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 an 18-bit sum. The carrier injection absorption amplitude modulator is useful in some embodiments, for example, due to thermal stability, which helps to reproduce the predetermined modulation depth at multiple modulators. In some embodiments, no single SCIM is driven at full-scale (hence the term "underdriven"), which significantly reduces the power / area of the modulator driver. Multiple alternative configurations can be used. For example, different types of modulators can be used, including Mach-Zehnder interferometers or ring modulators. Some configurations can use multiple optical wavelengths, enabling the use of a lower serializer-deserializer (SERDES) frequency.

[0147] Figure 11A and 11B Shows different example layouts of a system that uses distributed PAM aggregation techniques to distribute and aggregate partial results. In Figure 11A , there are two data modulators along each of the four branches of the waveguide, with a photodiode at the end of the waveguide. A driver (TX) is arranged at a specific location to provide the partial sum result at an intermediate location along the waveguide. In Figure 11BIn [the system], additional photodiodes are provided at the ends of the waveguides, and these photodiodes are separated from the four waveguides, thereby providing multiple destinations for each branch (e.g., to locally store the aggregated results). Thus, the destination where the result is provided is not necessarily at the end of the waveguide.

[0148] Various other systems can use distributed PAM aggregation techniques to perform the summation of binary values in different time slots along a transmission medium. For example, in addition to a wafer-level system that uses an intermediate layer to provide optical waveguides as the transmission medium, the system can also use optical fibers as the transmission medium to connect different nodes (e.g., server racks) in a data center. Moreover, some systems can use an electrical modulator to aggregate binary values encoded on electrical signals transmitted along an electrical transmission line.

[0149] The systems and operations described in this specification can 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 can be implemented using one or more modules of computer program instructions encoded on a computer-readable medium and executed by, or controlling the operation of, a data processing apparatus. The computer-readable medium can be a manufactured product, such as a hard disk drive in a computer system or an optical disc sold through a retail channel, or an embedded system. The computer-readable medium can be obtained separately and subsequently encoded with one or more modules of computer program instructions, e.g., by transmitting one or more modules of computer program instructions over a wired or wireless network. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of them.

[0150] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language (including compiled or interpreted languages, declarative or procedural languages), and can 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. The program can be stored in a part of a file that holds other programs or data (e.g., one or more scripts in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, subroutines, or portions of code). The computer program can be deployed to execute on one computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a communication network.

[0151] The processes and logical 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 logical 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).

[0152] Some of the systems described in this specification can provide an optoelectronic platform and / or distributed PAM aggregation functionality for the systems disclosed in U.S. Application No. 16 / 431,167, filed on June 4, 2019, which is incorporated herein by reference.

[0153] Although the present disclosure has been described in connection with certain embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments. 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 accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as are permitted under law.

Claims

1. A method for transmitting information from multiple nodes to at least one destination, the method comprising: Transmitting a signal having a predetermined initial amplitude 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 modulation value selected from a binary set of two possible modulation values, wherein for each of said intermediate positions, the binary set consists of: A modulation value 1, and A predetermined amplitude scaling factor S greater than 0 and less than 1; Detecting the signal at the destination after the signal has traversed all of the intermediate positions; and Mapping the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of intermediate positions at which the signal was modulated by the predetermined amplitude scaling factor.

2. The method according to claim 1, wherein the predetermined amplitude scale includes a maximum detected amplitude substantially equal to a predetermined preliminary amplitude, and a minimum detected amplitude substantially equal to S N , where N is the number of intermediate positions.

3. The method according to claim 1, wherein For each intermediate position, the predetermined amplitude scaling factor S is different.

4. The method according to claim 1, wherein, For each intermediate position, the predetermined amplitude scaling factor S is equal.

5. The method according to claim 4, wherein the predetermined amplitude scaling factor S is substantially equal to , where k is the number of intermediate positions.

6. The method according to any one of claims 1 to 5, wherein the signal transmitted from the source has the predetermined initial amplitude within each of a plurality of time slots including a first time slot.

7. The method according to claim 6, wherein the modulation of the amplitude of the signal at each of the plurality of intermediate positions occurs within the first time slot after a propagation delay based on the propagation distance between each intermediate position and the source.

8. The method according to claim 6, further comprising maintaining time synchronization between the plurality of nodes, the source, and the destination.

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

10. The method according to claim 9, wherein the optical waveguide is formed in an integrated circuit interposer that includes metal contacts arranged for controlled collapse chip connection to electrically couple to at least one semiconductor die.

11. The method according to claim 10, wherein the selected modulation value at one or more of the intermediate positions is provided based on an electrical signal from the semiconductor die.

12. A system for transmitting information from multiple nodes to at least one destination, the system comprising: A transmission medium; A source configured to transmit a signal having a predetermined initial amplitude onto the transmission medium; A plurality of amplitude modulators coupled to the transmission medium at respective intermediate positions between the source and the destination, each amplitude modulator configured to modulate the amplitude of the signal by a modulation value selected from a binary set of two possible modulation values, wherein 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; A detector at the destination configured to detect the signal after the signal has traversed all of the intermediate positions; and A circuit configured to map the detected amplitude of the detected signal using a predetermined amplitude scale indicative of the number of intermediate positions at which the signal was modulated by a common amplitude scaling factor.

13. A method for transmitting information, comprising: Transmit a signal having a predetermined initial first optical characteristic and a predetermined initial second optical characteristic onto a transmission medium; Modulate the first optical characteristic or the second optical characteristic of the signal at each of a plurality of intermediate positions between the source and the destination by a selected modulation value; Detect the signal at the destination after the signal has traversed the intermediate positions; And Map the detected first optical characteristic and second optical characteristic of the detected signal using a predetermined scale indicative of the number of intermediate positions at which the signal was modulated.

14. The method of claim 13, wherein the first optical characteristic comprises amplitude and the second optical characteristic comprises phase.

15. The method of claim 14, wherein the first optical characteristic comprises amplitude and the second optical characteristic comprises polarization.

16. The method of claim 15, wherein the first optical characteristic comprises phase and the second optical characteristic comprises polarization.

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