Patent Publication Number: US-11031666-B2

Title: Waveguide comprising a dielectric waveguide core surrounded by a conductive layer, where the core includes multiple spaces void of dielectric

Description:
CLAIM OF PRIORITY 
     This patent application is a U.S. National Stage Application under 35 U.S.C. 371 from International Application No. PCT/US2016/054832, filed Sep. 30, 2016, published as WO2018/063341, which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments pertain to high speed interconnections in electronic systems, and more specifically to waveguides for implementing communication interfaces between electronic devices. 
     BACKGROUND 
     As more electronic devices become interconnected and users consume more data, the demand on server system performance continues to increase. More and more data is being stored in internet “clouds” remote from devices that use the data. Clouds are implemented using servers arranged in server clusters (sometimes referred to as server farms). The increased demand for performance and capacity has led server system designers to look for ways to increase data rates and increase the server interconnect distance in switching architectures while keeping power consumption and system cost manageable. 
     Within server systems and within high performance computing architectures there can be multiple levels of interconnect between electronic devices. These levels can include within blade interconnect, within rack interconnect, rack-to-rack interconnect and rack-to-switch interconnect. Shorter interconnect (e.g., within rack interconnect and some rack-to-rack_interconnect) is traditionally implemented with electrical cables (e.g., Ethernet cables, co-axial cables, twin-axial cables, etc.) depending on the required data rate. For longer distances, optical cables are sometimes used because fiber optic solutions offer high bandwidth for longer interconnect distances. 
     However, as high performance architectures emerge (e.g., 100 Gigabit Ethernet), traditional electrical approaches to device interconnections that support the required data rates are becoming increasingly expensive and power hungry. For example, to extend the reach of an electrical cable or extend the bandwidth of an electrical cable, higher quality cables may need to be developed, or advanced techniques of one or more of equalization, modulation, and data correction may be employed which increases power of the system and adds latency to the communication link. For some desired data rates and interconnect distances, there is presently not a viable solution. Optical transmission over optical fiber offers a solution, but at a severe penalty in power and cost. The present inventors have recognized a need for improvements in the interconnection between electronic devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a waveguide in accordance with some embodiments; 
         FIG. 2  illustrates cross sections of waveguides in accordance with some embodiments; 
         FIG. 3  is an illustration of a method of forming a conductive layer of a waveguide in accordance with some embodiments; 
         FIG. 4  is an illustration of another embodiment of a waveguide in accordance with some embodiments; 
         FIG. 5  is a block diagram of an electronic system in accordance with some embodiments; 
         FIG. 6  is an illustration of another embodiment of a waveguide in accordance with some embodiments; 
         FIG. 7  is a flow diagram of an embodiment of making a waveguide in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
     Traditional electrical cabling may not meet the emerging requirements for electronic systems such as server clusters. Fiber optics may meet the performance requirements, but may result in a solution that is too costly and power hungry. 
       FIG. 1  is an illustration of an embodiment of a waveguide. The waveguide includes an outer layer of conductive material  102  such as metal. The inside of the waveguide can be hollow and air filled or can include a dielectric material  103 . A waveguide can be used to propagate electromagnetic waves having a wavelength in millimeters (mm) or micrometers (μm). Electromagnetic waves travel along the length of the waveguide. A transceiver and an antenna (sometimes referred to as a “waveguide launcher”) can be used to send electromagnetic waves along the waveguide from the transmitting end. A transceiver at the receiving end can receive the propagated signals using a receiving antenna. Waveguides offer the bandwidth needed to meet the emerging requirements. 
     However, a waveguide that only includes a conductive layer and an empty center can be difficult to work with as such waveguides can be prone to buckling or kinking when bending the waveguide or trying to apply the waveguide to a physical connector. A waveguide that includes a conductive layer around a solid waveguide core of a standard dielectric material (as in the example of  FIG. 1 ) can exhibit significant losses if the operating frequency of the waveguide is 100 gigahertz (GHz) or higher. To reduce the losses, very low loss dielectric materials can be used, but these materials can be relatively expensive and can also present challenges in manufacturing that lead to higher cost. Additionally, some very low loss dielectric materials are ceramic-based or ceramic-compound based and may not have the desired flexibility for the waveguide application. 
       FIG. 2  are illustrations of examples of cross sections of waveguides. The cross sections may have a height of 0.5-1.0 mm and a width of 1-2 mm. The waveguides are elongate and may have a length of one to five meters (1-5 m). In certain embodiments, the waveguides are dimensioned to carry signals having frequencies of 30 Gigahertz (GHz) to 300 GHz. In certain embodiments, the waveguides are dimensioned to carry signals having frequencies of 100 GHz to 900 GHz. The example cross sections in the Figure are rectangular, but the cross section may be circular, elliptical, square, or another more complex geometry. Each of the waveguides includes an elongate waveguide core of dielectric material and a conductive layer  202  arranged around the waveguide core. Each of the waveguide cores includes at least one space arranged lengthwise within the waveguide core that is void of the dielectric material. 
     Waveguide  204  includes a waveguide core of the dielectric material in the shape of a hollow tube  206 . The waveguide core includes a single space void of the dielectric material. In certain embodiments the waveguide core is formed using one or more of polyethylene (PE), polytetrafluoroethylene (PTFE), perfluoroalkoxy alkanes (PFA), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), liquid crystal polymer (LCP), or ethylene-tetraflouroethylene (ETFE). The dielectric waveguide core may be formed using a drawing process that draws a continuous tube from a source material. In certain embodiments, the waveguide is formed using an extrusion process. A conductive layer  202  may then be arranged around the waveguide core. The conductive layer  202  may be on the outside of the waveguide or protected by another dielectric layer. The latter case is shown in the example in  FIG. 2 . In certain examples, the conductive layer includes metal, such as one or more of copper, gold, silver, and aluminum. 
     Waveguide  208  includes a waveguide core formed of the dielectric material in the shape of an I-beam  210  arranged lengthwise along the waveguide core. The waveguide core includes two spaces in the dielectric material running parallel through the waveguide. The waveguide core may be formed by injection molding and the conductive layer arranged around the formed dielectric waveguide core. The I-beam shape can provide structural support for the waveguide making it easier to physically install without buckling or kinking. 
     Waveguides  212  and  216  each include a waveguide core formed of the dielectric material in the shape of a cross beam  214  and  218 , respectively, arranged lengthwise along the waveguide core. Each waveguide cores includes four spaces in the dielectric material running parallel through the waveguide. Like the I-beam shaped waveguide core, a cross beam shaped waveguide core may also provide structural support to the waveguide. 
     Waveguides  220  and  224  each include spaces arranged lengthwise through the wave guide in parallel to each other and arranged in a regular pattern to form a lattice cross section of the elongate waveguide core. In waveguide  220  the spaces  222  form circular openings in the cross section of the waveguide, and in waveguide  224  the spaces  226  form rectangular openings in the cross section of the waveguide. Like the I-beam and cross beam versions, the lattice cross sections may provide structural support for the waveguide. The waveguide core examples that have multiple spaces (waveguides  208 ,  212 ,  216 ,  220 , and  224 ) can be formed using injection molding and covered with the conductive layer. The waveguide core may be continuous through the waveguides with the cross section shape continuous through the core, or the wave guide may include sections along the length that are void of the dielectric material 
     In the waveguide examples of  FIG. 2 , the feature dimensions in the cross sections are much smaller than the wavelength of the electromagnetic waves that will travel along the length of the waveguide. The result is that the effective permittivity and the effective loss tangent are between those of a waveguide with an empty or air-filled center, and a waveguide with a waveguide core that is a solid dielectric. In some embodiments, the dielectric material of the waveguide cores in  FIG. 2  comprises twenty percent (20%) or less of a cross section of the elongate waveguide core and the space void of dielectric material comprises eighty percent (80%) or more of the cross section of the elongate waveguide core. 
       FIG. 7  is a flow diagram of a method  700  of making a waveguide. At step  705 , an elongate waveguide core is formed using a dielectric material. The waveguide core can include one or more spaces arranged lengthwise along the waveguide core that is void of the dielectric material. The spaces can be tubes formed in the dielectric material and the tubes may have any of the cross sections shown in the embodiments of  FIG. 2 . 
     At step  710 , a conductive layer is arranged around the waveguide core. Different methods can be used to form the conductive layer over a waveguide core. If the conductive layer is a metal layer, the conductive layer may be sputtered onto the waveguide core. In some embodiments, a sleeve of conductive material is arranged over the waveguide core. The conductive may be heat-shrinkable and the sleeve may be shrink wrapped over the waveguide core (e.g., using a thermal treatment) to form a conductive layer over waveguide core. According to some embodiments, the conductive layer of the waveguide can be formed by applying a liquid or paste that includes a conductive material (e.g., a conductive polymer or a metal) to the outside surface of the waveguide core. A conductive liquid can be sprayed onto the waveguide core, or the waveguide core can be immersed into a container of the conductive liquid. A conductive paste can be brushed onto the waveguide core. The waveguide core may be dried or heated at different stages. In certain embodiments, sintering steps may be provided at different stages of coatings. In some variations, sintering can involve a laser or photonic sintering process if the dielectric material of the waveguide core is sensitive to thermal sintering temperatures. 
       FIG. 3  is an illustration of another embodiment of forming the conductive layer of a waveguide. Tape  315  or ribbon made of a conductive material is wrapped around the outside surface of a dielectric material waveguide core  304  to form the conductive sheet around the core. In some embodiments, the tape includes metal and the tape can be a foil ribbon. The metallic tape can include one or more of copper, gold, silver, and aluminum. In some embodiments, the tape includes a conductive polymer, such as a polyaniline (PANI), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), or polyethylene terephthalate (PET) for example. The conductive tape wrapped around the waveguide core material may include an adhesive on at least one surface of the conductive tape to provide good adhesion to the waveguide and to the tape itself. The adhesive layer can be very thin (e.g., down to a monolayer of the adhesive material) to minimize impact on the waveguide performance. 
     Which approach (sputtering, sleeve, spraying, brushing, wound tape, etc.) is used to form the waveguide conductive sheet may depend on the geometry of the waveguide core. If the waveguide core has a cross section with smooth corners (e.g., a circle or oval) the tape-winding method may be used. If the waveguide core has a cross section that includes corners (e.g., a rectangle or square) the shrink-wrapped approach may be more desirable due to susceptibility of the tape to tearing. 
       FIG. 4  is an illustration of another embodiment of a waveguide. The waveguide  405  includes a layer of conductive tape wound around a waveguide core. The ends of the waveguide can be operatively connected to transceiver circuits  445  and antennas  450  or waveguide launchers (e.g., patch antennas). The waveguide link can be used in establishing communication among servers in a server cluster or server farm. 
       FIG. 5  is a block diagram of an electronic system  500  incorporating waveguide assemblies in accordance with at least one embodiment of the invention. Electronic system  500  is merely one example in which embodiments of the present invention can be used. The electronic system  500  of  FIG. 5  comprises multiple servers or server boards  555  interconnected as a server cluster that may provide internet cloud services. A server board  555  may include one or more processors  560  and local storage  565 . Only three server boards are shown to simplify the example in the Figure. A server cluster may include hundreds of servers arranged on boards or server blades in a rack of servers, and a server cluster can include dozens of racks of server blades. Racks can be placed side-by-side with a back-plane or back-panel used to interconnect the racks. Server switching devices can be included in the racks of the server cluster to facilitate switching among the hundreds of servers. 
     The server boards in  FIG. 5  are shown interconnected using waveguides  505 A,  505 B, and  505 C, although an actual system would include hundreds of rack-to-rack and within rack interconnections. The waveguides are operatively connected to ports of the servers. There can be multiple levels of interconnect between servers. These levels can include within server blade interconnect, within server rack interconnect, rack-to-rack interconnect and rack-to-switch interconnect. The waveguides  505 A,  505 B, and  505 C are used for at least a portion of the interconnect within the server system, and can be used for any of the within server blade, within server rack, rack-to-rack, and rack-to-switch interconnections. In certain embodiments, the waveguides form at least a portion of back-panel interconnections for a server cluster.  FIG. 6  illustrates a system level diagram, according to one embodiment of the invention. For instance,  FIG. 6  depicts an example of an electronic device (e.g., system) that can include the waveguide interconnections as described in the present disclosure.  FIG. 6  is included to show an example of a higher level device application for the present, invention. In one embodiment, system  600  includes, but is not limited to, a desktop computer, a laptop computer, a netbook, a tablet, a notebook computer, a personal digital assistant (PDA), a server, a workstation, a cellular telephone, a mobile computing device, a smart phone, an Internet appliance or any other type of computing device. In some embodiments, system  600  is a system on a chip (SOC) system. In one example two or more systems, as shown in  FIG. 6  may be coupled together using one or more waveguides as described in the present disclosure. In one specific example, one or more waveguides as described in the present disclosure may implement one or more of busses  650  and  655 . 
     In one embodiment, processor  610  has one or more processing cores including processor core  1   612  and processor core N  612 N, where  612 N represents the Nth processor core inside processor  610  where N is a positive integer. In one embodiment, system  600  includes multiple processors including processor  610  and processor N  605 , where processor N  605  has logic similar or identical to the logic of processor  610 . In some embodiments, processing core  612  includes, but is not limited to, pre-fetch logic to fetch instructions, decode logic to decode the instructions, execution logic to execute instructions and the like. In some embodiments, processor  610  has a cache memory  616  to cache instructions and/or data for system  600 . Cache memory  616  may be organized into a hierarchal structure including one or more levels of cache memory 
     In some embodiments, processor  610  includes a memory controller  614 (MC), which is operable to perform functions that enable the processor  610  to access and communicate with memory  630  that includes a volatile memory  632  and/or a non-volatile memory  634 . In some embodiments, processor  610  is coupled with memory  630  and chipset  620 . Processor  610  may also be coupled to a wireless antenna  678  to communicate with any device configured to transmit and/or receive wireless signals. In one embodiment, the wireless antenna interface  678  operates in accordance with, but is not limited to, the IEEE 802.11 standard and its related family, Home Plug AV (HPAV), Ultra Wide Band (UWB), Bluetooth, WiMax, or any form of wireless communication protocol. 
     In some embodiments, volatile memory  632  includes, but is not limited to, Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM), and/or any other type of random access memory device. Non-volatile memory  634  includes, but is not limited to, flash memory, phase change memory (PCM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), or any other type of non-volatile memory device. 
     Memory  630  stores information and instructions to be executed by processor  610 . In one embodiment, memory  630  may also store temporary variables or other intermediate information while processor  610  is executing instructions. In the illustrated embodiment, chipset  620  connects with processor  610  via Point-to-Point (PtP or P-P) interfaces P-P  617  and P-P  622 . Chipset  620  enables processor  610  to connect to other elements in system  600 . In some embodiments of the invention, interfaces  617  and  622  operate in accordance with a PtP communication protocol such as the Intel® QuickPath Interconnect (QPI) or the like. In other embodiments, a different interconnect may be used. 
     In some embodiments, chipset  620  is operable to communicate with processor  610 , processor N  605 , display device  640 , and other devices  672 ,  676 ,  674 ,  660 ,  662 ,  664 ,  666 ,  677 , etc. Buses  650  and  655  may be interconnected together via a bus bridge  672 . Chipset  620  connects to one or more buses  650  and  655  that interconnect various elements  674 ,  660 ,  662 ,  664 , and  666 . Chipset  620  may also be coupled to a wireless antenna  678  to communicate with any device configured to transmit and/or receive wireless signals. Chipset  620  connects to display device  640  via interface  626  (I/F). Display  640  may be, for example, a liquid crystal display (LCD), a plasma display, cathode ray tube (CRT) display, or any other form of visual display device. In some embodiments of the invention, processor  610  and chipset  620  are merged into a single SOC. In one embodiment, chipset  620  couples with a non-volatile memory  660 , a mass storage medium  662 , a keyboard/mouse  664 , and a network interface  666  via interface  624  (I/F), I/O device(s)  674 , smart TV  676 , and consumer electronics  677  (e.g., PDA, smart phone, tablet, etc.). 
     In one embodiment, mass storage device  662  includes, but is not limited to, a solid state drive, a hard disk drive, a universal serial bus flash memory drive, or any other form of computer data storage medium. In one embodiment, network interface  666  is implemented by any type of well known network interface standard including, but not limited to, an Ethernet interface, a universal serial bus (USB) interface, a Peripheral Component Interconnect (PCI) Express interface, a wireless interface and/or any other suitable type of interface. In one embodiment, the wireless interface operates in accordance with, but is not limited to, the IEEE 802.11 standard and its related family, Home Plug AV (HPAV), Ultra Wide Band (UWB), Bluetooth, WiMax, or any form of wireless communication protocol. 
     While the modules shown in  FIG. 6  are depicted as separate blocks within the system  600 , the functions performed by some of these blocks may be integrated within a single semiconductor circuit or may be implemented using two or more separate integrated circuits. For example, although cache memory  616  is depicted as a separate block within processor  610 , cache memory  616  (or selected aspects of  616 ) can be incorporated into processor core  612 . 
     ADDITIONAL DESCRIPTION AND EXAMPLES 
     Example 1 can include subject matter (such as an apparatus) comprising a waveguide including: an elongate waveguide core including a dielectric material, wherein the waveguide core includes at least one space arranged lengthwise within the waveguide core that is void of the dielectric material; and a conductive layer arranged around the waveguide core. 
     In Example 2, the subject matter of Example 1 optionally includes an elongate waveguide core that is a hollow tube of dielectric material and includes a single space that is void of the dielectric material. 
     In Example 3, the subject matter of one or both of Examples 1 and 2 optionally includes an elongate waveguide core including multiple spaces arranged lengthwise through the waveguide core that are void of the dielectric material. 
     In Example 4, the subject matter of Example 3 optionally includes the multiple spaces arranged lengthwise through the wave guide core being arranged in a regular pattern to form a lattice cross section of the elongate waveguide core. 
     In Example 5, the subject matter of one or any combination of Examples 1-3 optionally includes an elongate waveguide core includes a cross beam formed of the dielectric material arranged lengthwise along the waveguide core. 
     In Example 6, the subject matter of one or any combination of Examples 1-3 optionally includes an elongate waveguide core includes an I-beam formed of the dielectric material arranged lengthwise along the waveguide core. 
     In Example 7, the subject matter of one or any combination of Examples 1-6 optionally includes the dielectric material comprising twenty percent (20%) or less of a cross section of the elongate waveguide core and space void of dielectric material comprises eighty percent (80%) or more of the cross section of the elongate waveguide core. 
     In Example 8, the subject matter of one or any combination of Examples 1-7 optionally includes a dielectric material including at least one of polyethylene (PE), polytetrafluoroethylene (PTFE), perfluoroalkoxy alkanes (PFA), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), liquid crystal polymer (LCP), or ethylene-tetraflouroethylene (ETFE). 
     In Example 9, the subject matter of one or any combination of Examples 1-8 optionally includes a conductive layer that includes conductive tape wrapped around an outside surface of the elongate waveguide core. 
     In Example 10, the subject matter of one or any combination of Examples 1-9 optionally includes a conductive layer including a metal layer arranged around an outside surface of the elongate waveguide core. 
     In Example 11, the subject matter of one or any combination of Examples 1-10 optionally includes a width of a waveguide of the plurality of waveguides is less than two millimeters (2 mm) and the length of the waveguide is more than one meter (1 m). 
     In Example 12, the subject matter of one or any combination of Examples 1-11 optionally includes a waveguide transceiver circuit operatively coupled to the waveguide. 
     Example 13 can include subject matter (such as a method of making a waveguide), or can optionally be combined with one or any combination of Examples 1-12 to include such subject matter, comprising forming an elongate waveguide core using a dielectric material, wherein the waveguide core is formed to include at least one space arranged lengthwise along the waveguide core that is void of the dielectric material; and arranging a conductive layer around the waveguide core. 
     In Example 14, the subject matter of Example 13 optionally includes extruding a hollow tube of the dielectric material that includes a single space void of the dielectric material. 
     In Example 15, the subject matter or one or both of Examples 13 and 14 optionally includes injection molding multiple spaces in the dielectric material that are arranged lengthwise through the waveguide core and are void of the dielectric material. 
     In Example 16, the subject matter of one or any combination of Examples 13-15 optionally includes arranging a conductive layer around the waveguide core by wrapping the conductive tape around an outside surface of the waveguide core to form the conductive sheet. 
     In Example 17, the subject matter of one or any combination of Examples 13-16 optionally includes applying a liquid including a conductive material to an outside surface of the waveguide core to produce a conductive layer around the waveguide core, wherein the applying of the liquid includes one of: immersing the waveguide core into a container of the liquid including the conductive material, or drawing the waveguide core through the container of the liquid including the conductive material. 
     Example 18 includes subject matter (such as a system), or can optionally be combined with one or any combination of Examples 1-17 to include such subject matter, comprising a first server and a second server, wherein the first and second servers each include a plurality of ports; and a waveguide operatively coupled to a first port of the first server and a first port of the second server, wherein the waveguide includes an elongate waveguide core including a dielectric material, wherein the waveguide core includes at least one space arranged lengthwise along the waveguide core that is void of the dielectric material; and a metal layer arranged around the waveguide core. 
     In Example 19, the subject matter of Example 18 optionally includes the waveguide operatively coupled to the first port of the first server using a first waveguide transceiver circuit and a first waveguide launcher, and wherein the waveguide is operatively coupled to the first port of the second server using a second waveguide transceiver circuit and a second waveguide launcher. 
     In Example 20, the subject matter of one or both of Examples 18 and 19 optionally includes the elongate waveguide core including multiple spaces arranged lengthwise through the wave guide core that are void of the dielectric material. 
     These non-limiting examples can be combined in any permutation or combination. 
     The Abstract is provided to allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.