Patent Publication Number: US-11656407-B2

Title: Flexible ceramic waveguides for terahertz applications and use as on-board interconnects

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/842,871 filed Apr. 8, 2020, which claims the priority benefit of U.S. Application No. 62/895,200 filed Sep. 3, 2019, both of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Optical communication systems typically operate at the near-infrared bands of the electromagnetic spectrum having wavelengths on the order of 800 nm to 2000 nm. Other types of communication systems such as cell phone systems operate at radio-wave band of the electromagnetic (EM) spectrum from about 3 KHz to 60 GHz, with plans to extend this range into the microwave and millimeter bands, which extend up to about 300 GHz. The move to higher and higher RF and microwave frequencies has been enabled in part by developments in state of the art complementary metal-oxide-semiconductor (“CMOS”)-based EM radiation sources and receivers that can operate at frequencies greater than 100 GHz. 
     The terahertz wavelength range of the EM spectrum is generally considered to range from 0.1 THz (=100 GHz) to 10 THz (10,000 GHz), where the corresponding free-space wavelength is denoted λ0 and is in the range from 3 mm to 0.03 mm. In a dielectric material with the real part of the dielectric constant c′, the wavelength λ, is given by λ=λ0/(ε′) 1/2 . More generally, the dielectric constant is expressed as ε=ε′+iε″ where ε″ is the imaginary or lossy part of the dielectric constant. Terahertz (“THz”) waveguides can be formed from a guiding structure in which the real part of the dielectric constant is higher than that of the surrounding material or space. Such waveguides can be used to confine and transport a THz optical signal from a source location to a receiver location. 
     The sub-mm wave or THz band (i.e., having a wavelength between 0.1 mm-1 mm) is one of the least explored sections of the electromagnetic spectrum. This is due to the historical cost of sources and detectors and a lack of a low-loss guiding structures, equivalent to an optical fiber that may be used with visible and infrared wavelengths. Traditional microstrip line circuits, or metallic waveguides at microwave frequencies are generally insufficient to support low loss THz band propagation because high-frequency signals may be absorbed by the materials. Similarly dielectric waveguide for millimeter waves have generally been lossy due to radiation and/or subject to dispersion and have been difficult to costly to use. Even the modern surface plasmon polariton waveguides are too lossy for long-distance transmission in THz bands. Lossy means having or involving the dissipation of electrical or electromagnetic energy. 
     Most THz waveguides are made of a metal or a plastic and are not made of ceramic materials. While fused silica glass has relatively good transmission at THz frequencies, it is relatively fragile as compared to metal and plastic and therefore makes it difficult to form a commercially viable THz waveguide product. Said differently, a commercially viable THz waveguide product needs to have both sufficiently low loss in the THz frequency range and be mechanically robust so that it can be handled for manufacturing and operate for extended periods of time in a wide range of environments. 
     Yeh et al. has proposed a concept for overcoming this drawback and describes a new family of an ultra-low-loss rectangular single-mode waveguide structure for propagating THz signals, which has an attenuation constant more than 100× less than that of a conventional dielectric or metallic waveguide. Cavour Yeh et al.,  Low - Loss Terahertz Ribbon Waveguides,  44 APPLIED OPTICS 28, 5937 (2005); Cavour Yeh et al.,  Communication at Millimetre - Submillimetre Wavelengths Using a Ceramic Ribbon,  404 NATURE 584 (2000). The material Yeh et al. uses is a high purity alumina “rectangular rod” (99.8% purity, 10:1 aspect ratio with 0.635 mm in thickness, 6.35 mm in width and 910 mm in length), operated in 30-40 GHz. However, the thickness of the rectangular rod limits its application in higher frequency signals and its flexibility. 
     For high speed interconnects, optical transceivers can be co-packaged with an integrated package carrying basic components and common functionalities for a programmable logic circuit (“PL IC”) or an application-specific integrated circuit customized for a particular use (“ASIC”) on the same substrate to reduce the length of electrical interconnects to a few millimeters for 112 GB/s and above electrical signal links. The reduced length between electrical interconnects is required because of high loss of electrical signals at higher frequencies and an increase in power consumption. Power and costs can be saved when transceivers are close to the integrated circuit (“IC”) and optically interconnected with the fiber network of the building (e.g. datacenter) or between buildings. Today, fiber array units (FAU) are a fiber assembly with an array of fibers aligned in a V-groove and end-face polished. The FAU is actively aligned to electronic integrated circuits (PIC) and permanently attached to provide a connector interface to the transceiver. The fiber length can be short for pluggable transceivers or customized in length for other applications. 
     In some aspects, waveguides may be used as a transmission line to guide electromagnetic waves. For example, waveguides may confine electromagnetic waves to propagate in one dimension such that the waves lose a reduced amount of power as it propagates during transmission. Waveguides may be configured for the transmission of electromagnetic waves at different wavelengths. For example, waveguides may be configured to transmit electromagnetic wavelengths within the visible, infrared, radio, microwave, or terahertz bands of the electromagnetic spectrum though the useful range of operation of a particular waveguide technology is typically limited. Waveguides may be designed to minimize loss (e.g., dissipation of energy) while maintaining flexibility, specific dimensions, shape, or the other properties for the desired end use. In some examples, waveguides configured to guide electromagnetic waves within a certain band of the electromagnetic spectrum may be different than waveguides configured to guide electromagnetic waves within a different band of the electromagnetic spectrum. In this way, waveguides may be designed (e.g., shape, dimensions, material, or the like) to optimize performance based on the wavelengths of the electromagnetic spectrum the waveguide is intended to transmit. 
     Applicant&#39;s cutting-edge technology, continuous firing process, and ribbon ceramics products offers the manufacturing of an ultra-high purity alumina ribbon waveguide with an extremely thin form factor and long length. The attributes of Applicant&#39;s waveguides provide for an ideal solution for THz communication and could address the drawbacks mentioned above. These attributes include, but are not limited to, an ultrahigh purity alumina that enables great dielectric performance, a fine grain size that provides for excellent flexibility and mechanical strength, a thin form factor, and a long length. Applicants have developed a new way to cost effectively fabricate an attractive material into a form factor that is beneficial for the microwave/mmWave applications and configurations to make use of such a material. 
     SUMMARY 
     The present disclosure relates to the use of ceramic dielectric waveguides resulting in the low loss propagation of high-frequency signals in or on printed circuit boards. One aspect of the present disclosure is an assembly, comprising: a printed circuit board (PCB) assembly comprising opposite first and second ends and at least one PCB layer wherein the at least one PCB layer comprises at least one conductive element, an integrated circuit (IC) operably disposed on the top surface of the PCB assembly by I/O pads, the IC having at least one IC device, a at least one coupling element, a ceramic dielectric terahertz (THz) waveguide for guiding signals having a THz frequency in the range from about 0.1 THz to about 10 THz comprising a ceramic core comprising an alumina ribbon wherein the alumina ribbon has a dielectric constant (Dk1) and a cladding surrounding the ceramic core, wherein the cladding has a dielectric constant (Dk2) such that Dk2&lt;Dk1, and a major surface and an access aperture wherein the major surface is disposed between the first end and second end, and the ceramic dielectric waveguide is mounted to the top surface of at least one PCB layer, the ceramic dielectric terahertz (THz) waveguide comprising a first-end section with an end face accessible through the access aperture. In another aspect, the printed circuit board is an optical-electrical printed circuit board (OE-PCB). 
     In another aspect, the ceramic core is surrounded on two parallel sides by at least one cutout. In a further aspect, the at least one cutout is empty. In an alternative aspect, the at least one cutout is filled with a dielectric material having a dielectric constant lower than the dielectric constant that of the ceramic core. In a further aspect, the dielectric material is polymer, glass, or silicon dioxide. In yet a further aspect, the polymer is selected from the group consisting of polytetrafluoroethylene (PTFE), SU-8, fluoropolymers, and polystyrene, polyimide (Kapton or Cirlex), parylene-N, high-density polyethylene (HDPE), polypropylene (PP) and polyethylene cyclic olefin copolymer (Topas), polybenzoxazole (PBO), benzocyclobutene (RCB), and liquid crystal polymers. 
     In another aspect, the at least one cutout has a bending angle of at least 10 degrees, alternatively at least 20 degrees, alternatively at least 30 degrees, alternatively at least 40 degrees, alternatively at least 45 degrees, alternatively at least 50 degrees, alternatively at least 60 degrees, alternatively at least 70 degrees, alternatively at least 80 degrees, or alternatively at least 90 degrees. In another aspect, the at least one cutout progressively tapers along the propagation direction. In yet another aspect, the cutout comprises an array of holes. In a further aspect, the array of holes creates an electronic bandgap cladding layer. In a further aspect, the holes are uniform in shape, size, and/or linear placement. In yet a further aspect, the holes vary in size along the propagation direction. 
     In another aspect, the electronic assembly further comprises a cavity for a source component and a cavity for a detector component on opposite terminal ends of the ceramic dielectric terahertz (THz) waveguide. In another aspect, the source component is a transmitter or transceiver. In yet another aspect, the detector component is a receiver or receive side of a transceiver. Transceiver it is device with a transmitter and receiver and is used in most bidirectional communication applications. 
     In another aspect, the electronic assembly further comprises a strut, wherein the strut consists of an alumina ribbon, and wherein the strut is at the terminal ends of the ceramic dielectric terahertz (THz) waveguide. In another aspect, the electronic assembly further comprises a least one strut, wherein the strut is transverse to the ceramic dielectric terahertz (THz) waveguide. 
     In another aspect, the ceramic dielectric terahertz (THz) waveguide is fully or partially embedded within the printed circuit board (PCB) assembly. In yet another aspect, the ceramic dielectric terahertz (THz) waveguide is disposed between at least two PCB layers. In yet another aspect, the ceramic dielectric terahertz (THz) waveguide is mounted directly on the top surface of the printed circuit board (PCB) assembly. 
     In another aspect, the coupling element is located on the top, the bottom, or the first or the second end of the printed circuit board (PCB) assembly. In yet another aspect, the coupling element acts as an antenna. A coupling element can be used to launch the signal from a conducting/metallic waveguide into the dielectric waveguide. Such a coupling element may be referred to as an ‘antenna’, but a human or computer designed/optimized coupling element does not need to look like a conventional antenna. 
     In another aspect, at least one end of the ceramic dielectric terahertz (THz) waveguide is tapered. In a further aspect, the coupling element runs along the tapered edge to the top surface of the printed circuit board (PCB) assembly. In another aspect, the coupling element is connected directly to at least one PCB layer. In another aspect, the coupling element is connected to at least one PCB layer through at least one conductive via. In yet another aspect, the coupling element couples a conductive transmission waveguide to a dielectric waveguide. 
     In another aspect, the electronic assembly further comprises a glass substrate mounted on the top surface of the printed circuit board (PCB) assembly. In yet another aspect, the ceramic dielectric terahertz (THz) waveguide is mounted on the top surface of the glass substrate. 
     In another aspect, the electronic assembly further comprises a port/interface component. In a further aspect, the port/interface component is mounted on each source and detector component. 
     In another aspect, the ceramic core has a circular, elliptical or rectangular cross-sectional shape. In another aspect, the ceramic dielectric terahertz (THz) waveguide is non-planar. In yet another aspect, the ceramic dielectric terahertz (THz) waveguide is planar and the ceramic core has opposite first and second planar surfaces and a thickness in the range from 10 μm to 500 μm; and the cladding is defined by first and second planar layers respectively disposed immediately adjacent the first and second planar surfaces of the ceramic core, the first and second layers having dielectric constants (Dk2 and Dk3) such that Dk2&lt;Dk1 and Dk3&lt;Dk1. 
     One aspect of the present disclosure is a ceramic dielectric terahertz (THz) waveguide for guiding signals having a THz frequency in the range from about 0.1 THz to about 10 THz comprising a ceramic core comprising an alumina ribbon wherein the alumina ribbon has a dielectric constant (Dk1), wherein the ceramic core is surrounded on at least two parallel sides by at least one cutout, wherein the at least one cutout create an electronic bandgap cladding layer, and wherein the electronic bandgap cladding layer has a dielectric constant (Dk2) such that Dk2&lt;Dk1. 
     In another aspect, the at least one cutout is empty. In an alternative aspect, the at least one cutout is filled with a dielectric material having a dielectric constant lower than the dielectric constant that of the ceramic core. In a further aspect, the dielectric material is polymer, glass, or silicon dioxide. In yet a further aspect, the polymer is selected from the group consisting of polytetrafluoroethylene (PTFE), SU-8, fluoropolymers, and polystyrene, polyimide (Kapton or Cirlex), parylene-N, high-density polyethylene (HDPE), polypropylene (PP) and polyethylene cyclic olefin copolymer (Topas), polybenzoxazole (PBO), benzocyclobutene (BCB), and liquid crystal polymers. 
     In another aspect, the at least one cutout has a bending angle of at least 10 degrees, alternatively at least 20 degrees, alternatively at least 30 degrees, alternatively at least 40 degrees, alternatively at least 45 degrees, alternatively at least 50 degrees, alternatively at least 60 degrees, alternatively at least 70 degrees, alternatively at least 80 degrees, or alternatively at least 90 degrees. In another aspect, the at least one cutout progressively tapers along the propagation direction. In an alternative aspect, the at least one cutout comprises an array of holes. In a further aspect, the holes are uniform in shape, size, and/or linear placement. In a further alternative aspect, the holes vary in size along the propagation direction. 
     The presently described and claimed technology has numerous advantages, including, but not limited to, (1) reducing manufacturing costs for parallel links in a circuit; (2) simplifying alignment of a transmitter or receiver by precisely creating patterns in a sheet of ceramic material due to its rigid structure; (3) saving power within the circuit due to no longer needing to convert from electrical to optical signals or optical to electrical signals; (4) simplifying transmitter and/or receiver assembly; (5) having lower loss than conventional conductive waveguides at mm wave frequencies because mm waves can be excited directly in dielectric THz waveguides without costly and high-loss lasers and photodetectors; (6) industrializing known waveguide fabrication techniques that provide high quality waveguides, e.g., laser hole formation or singulation, dielectric dip-coating or coating die; (7) more easily creating interconnects through the use of waveguides embedded as a sheet of ceramic material; (8) using effective index cladding material allowing for fine tuning of the confinement of the guided electromagnetic radiation and the number of propagating modes; (9) creating transitions in that confinement that can more easily be made in effective index material, such as soot by localized heating and sintering of the silica particles along the propagation direction; and (10) creating THz waveguides with different rigid geometries making coupling more efficient. providing a millimeter wave waveguiding technology that can be readily incorporated into established electronic circuit board fabrication and assembly techniques 
     These and other advantages and novel features of the present invention, as well as details of illustrated aspects thereof will be more fully understood from the following description and from the figures. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       These as well as other features of the present invention will become more apparent upon reference to the drawings wherein: 
         FIG.  1    illustrates a cross-section view of multiple alumina waveguides surrounded by a dielectric material embedded within a printed circuit board. 
         FIG.  2    illustrates a cross-section view of multiple alumina waveguides directly on a common dielectric substrate all surrounded by a different dielectric material embedded within a printed circuit board. 
         FIG.  3    illustrates a cross-section view of a wire bond link between a transmitter and receiver mounted directly on top of a printed circuit board wherein the ribbon is made of alumina and may be encapsulated by a dielectric material or air. 
         FIG.  4    illustrates a cross-section view of a sample configuration of an electronic circuit board assembly and a waveguide coupling element embedded within the printed circuit board (PCB) assembly to couple the electrical transmission signal to the mounted ceramic dielectric terahertz (THz) waveguide. 
         FIG.  5    illustrates a cross-section view of a sample configuration of assembly and multiple coupling elements embedded within the printed circuit board (PCB) assembly to couple the electrical transmission signal to the embedded ceramic dielectric terahertz (THz) waveguide. 
         FIG.  6    illustrates a cross-section view of a sample configuration of a assembly with a ceramic dielectric terahertz (THz) waveguide tapered on one end and mounted on the printed circuit board (PCB) assembly and a conductive element running along the tapered end to a conductive pathway (“via”) where the via intersects with PCB layers embedded within the printed circuit board (PCB). 
         FIG.  7    illustrates a cross-section view of a sample configuration of a assembly with a ceramic dielectric terahertz (THz) waveguide tapered on one end and mounted on a printed circuit board (PCB) assembly and a coupling element running along the tapered end to a PCB layer within the electronic assembly. 
         FIG.  8    illustrates a cross-section view of a sample configuration of an assembly with a mounted dielectric material encompassing a glass substrate used to support a ceramic dielectric terahertz (THz) waveguide and a coupling element which connects to a via where the via intersects with a PCB layer embedded within the printed circuit board (PCB) assembly 
         FIG.  9 A  illustrates a top view of alumina ribbon cut out in regions to create straight pathways that run along the x-axis.  FIG.  9 B  illustrates a top view of alumina ribbon cut out in regions to create a 90 degree waveguide bend. 
         FIG.  10 A  illustrates a top view of alumina ribbon cut out in regions to create an adiabatic taper for mode conversion.  FIG.  10 B  illustrates a top view of alumina ribbon cut out in regions to create a splitter/combiner. 
         FIG.  11 A  illustrates a top view of alumina ribbon wherein a ceramic dielectric terahertz (THz) waveguide is terminated by cutouts.  FIG.  11 B  illustrates a top view of alumina ribbon with periodic cross braces wherein a waveguide is terminated. 
         FIG.  12    illustrates a side view of a multi-layer stack of waveguides. 
         FIG.  13 A  illustrates a ceramic dielectric terahertz (THz) waveguide with an array of hole creating a uniform electronic bandgap cladding layer.  FIG.  13 B  illustrates a ceramic dielectric terahertz (THz) waveguide with an array of hole creating a tapered electronic bandgap cladding layer. 
     
    
    
     The foregoing summary, as well as the following detailed description of certain features of the present application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustration, certain features are shown in the drawings. It should be understood, however, that the claims are not limited to the arrangements shown in the attached drawings. 
     DETAILED DESCRIPTION 
     Referring generally to the figures, aspects of the present disclosure relate to the use of a ceramic dielectric waveguide to couple an electrical transmission line signal with that of a printed circuit board. Advantageously, the shape and position of the ceramic dielectric waveguide with respect to the printed circuit board adjusts how the electromagnetic field of the waveguide couples with that of the conductive structures within the printed circuit board, creating opportunities to make propagation of THz waves more efficient and less lossy. Also advantageously, the potential addition coupling elements such as antenna elements creates more opportunities for the same. Some potential shapes and positions of the ceramic dielectric waveguide, along with the potential addition of antenna or coupling elements, will be discussed in the following sections. The aspects described herein are for the purposes of illustration and should not be considered limiting. 
     Waveguide Creation 
     The present disclosure relates to waveguides configured to transmit electromagnetic waves within the THz range that include a ceramic core and an optional dielectric material cladding. Amongst other factors, propagation of an electromagnetic wave is influenced by the size and shape of the waveguide. In some aspects, a ceramic core with smaller cross-sectional dimensions may be more suitable for transmitting waves in the THz range than a core with larger cross-sectional dimensions. The ceramic core may have a cross-sectional dimension in the range of about 10 microns to about 500 microns (μm), preferably about 20 μm. The cross sectional dimension is not limited to rectangular cross-sectional shapes but may be applied interchangeably to circular, elliptical, or other cross-sectional shapes. 
     The ceramic core may be comprised of any suitable ceramic material and may be rectangular or ribbon-shaped. Electromagnetic waves propagate within the confines of the walls of a waveguide, with the walls acting as boundaries. Therefore, some cross-sectional shapes may be more suitable for transmitting waves in the THz range than other cross-sectional shapes. 
     In some aspects, the THz waveguide may have a long form factor. In these aspect, the THz waveguide  10  may have a length  12  of about 3 centimeters (cm) or greater. A longer form factor may be more suitable for transmitting waves in the THz range than a shorter form factor. Similarly, a longer form factor may be more suitable for transmitting waves over a longer distance than a shorter form factor that transmits waves over a shorter distance. 
     In other aspects, the THz waveguide may also be thin. For example, it may have a rectangular cross-section of a THz waveguide having a width and a height. In this aspect, the ceramic core may have a width or height in the range of about 20 μm to about 500 μm, preferably about 20 μm. A ceramic core with a smaller width and/or height may be more suitable for transmitting waves in the THz range than a ceramic core with a larger width and/or height. Similarly, a ceramic core with a smaller width and/or height may be more suitable for THz applications requiring smaller waveguides, e.g. inter-chip interconnects or chip-to-chip communication. 
     In some aspects, the THz waveguides may transmit signals in the frequency range of about 0.1 THz to about 10 THz with a ceramic core comprised of alumina. In other aspects, an alumina core may be comprised of ultra-high purity alumina with a purity level of about 99% or higher, about 99.5% or higher, about 99.75% or higher, about 99.9%, about 99.95% or higher, about 99.96% or higher, or about 99.99% or higher. In yet a further aspect, the alumina has a purity of about 99.96% or higher. In these aspects, an alumina core with a high purity level enables greater dielectric performance than an alumina core with lower purity level. In one aspect, the core may have a Dk in the range of 10-1000 and a dissipation factor (“Df”) in the range of less than 1×10 −3 , preferably a Dk=10 and a Df&lt;=1×10 −4 , respectively. In view of the present aspects, a waveguide comprised of a high purity alumina core can effectively transmit signals within the THz range while still having low transmission loss. 
     In other aspects, the alumina ceramic core may have a Dk of ε r , surrounded by air. A high dielectric constant can enable single mode operation in a wide frequency window. Waveguide propagation modes depend on the operating wavelength and polarization, along with the shape and size of the waveguide. For the rectangular waveguide shown in  FIG.  1 A , normalized frequency parameters are provided below: 
     
       
         
           
             
               
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     For single mode operation in both the x and y directions, V x =π, and V y =π. The cutoff frequency for single mode operation can be determined by the following equations: 
     
       
         
           
             
               
                 
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     Depending on the form factor of the waveguide and its dielectric properties, a waveguide can permit single mode operation at a high cut-off frequency. Single mode operation can be achieved if the waveguide dimensions width (w) and height (h) satisfy the above equations. For material with a high dielectric constant, the waveguide dimensions can be reduced for single mode operation. Small waveguide dimensions increase the waveguide density for waveguide arrays used in interconnects and improve the mechanical flexibility. For a suitably dimensioned alumina ceramic ribbon waveguide having low-loss and a high dielectric constant, the waveguide can exhibit an attenuation coefficient of less than 10 dB/cm. 
     A THz waveguide needs to have both low transmission loss in the THz frequency and a wide range of mechanical properties that allow for operation in a variety of environmental conditions. In one aspect, the ceramic core comprises alumina and may have a grain size of at least about 0.5 μm. A ceramic core that comprises alumina with a smaller grain size can be denser and may exhibit more flexibility than a ceramic core with a larger grain size. In some aspects, ceramic core that comprises alumina with a grain size of at least about 0.5 μm may have variable flexibility, e.g. a bending radius of about 17 mm for a form factor with a thickness in the range from about 10 μm to about 200 μm. In view of the present aspects, a waveguide comprised of a ceramic core that comprises alumina can effectively transmit signals within the THz range while still having low transmission loss and improved flexibility. 
     Conventional waveguides that exhibit flexibility may still fracture or shatter when exposed to a variety environmental conditions. Therefore, a THz waveguide that has greater mechanical strength but remains flexible, pliable, or supple, may be more suitable for terahertz applications. As discussed above, a ceramic core that comprises alumina with a smaller grain size can be denser and may exhibit more flexibility, and mechanical strength, than a ceramic core that comprises alumina with a larger grain size. In some aspects, a ceramic core that comprises alumina with a grain size of at least about 0.5 μm may have a mechanical strength of at least 700 MPa when undergoing a 2 pt flexural bending strength test. In view of the present aspects, a waveguide comprised of a ceramic core that comprises alumina can effectively transmit signals within the THz range while still having low transmission loss and improved strength. 
     In other aspects, the ceramic core material is not limited to alumina; core material may also include, for example, silica (Dk˜4), mullite (Dk˜6), magnesium titinate (Dk˜15-20), zirconium tin titinate (Dk˜37), titania (Dk˜100), or barium titinate (Dk&gt;1000). Other core materials are contemplated that similarly transmit signals in the frequency range of 0.1 THz to 10 THz but provide for a high Dk. 
     In some aspects, a THz waveguide may have a cladding disposed around a ceramic core that comprises alumina. A cladding serves as a protective gliding material for a ceramic core thereby enabling propagation in the THz range with low transmission loss. In addition, a cladding may inhibit any potential interactions between a propagating wave and the surrounding environment. 
     A cladding can be disposed around a ceramic. In some aspects, it may be preferable for cladding to have a lower dielectric constant than the dielectric constant of core. In other aspects, it may be preferable for cladding to have a Df less than 1×10 −3 . As a result, cladding may assist in confining an electromagnetic wave inside the ceramic core structure so that it limits how much the fields spread out, and losses resulting from this effect are eliminated. It is advantageous for cladding to have a similar loss tangent in the THz range as the ceramic core (though it can be somewhat higher because the total loss is less sensitive to the cladding), as well as a low dielectric constant so to minimize transmission loss and the size of the structure formed as part of the waveguide. In some aspects, cladding may have a dielectric constant within the range of 10-1000. 
     Cladding 25 can be made of air, glass, silicon dioxide (silica glass), or polymers. In aspects where cladding 25 is made of a polymer, polymers may include, for example, SU-8, polytetrafluoroethylene (Teflon), or other fluoropolymers that have low loss properties in the frequency range of 100 GHz-1000 GHz. Other suitable materials for the cladding 18 may be any combination thereof. 
     As discussed above,  FIG.  1 D  shows an aspect where a THz waveguide may have a planar configuration. In this aspect, the ceramic core  21  may be comprised of opposite first  22  and second  23  planar surfaces.  FIG.  5    shows one aspect where a cladding is defined by a first  27  and second  28  planar layer that may be respectively disposed immediately adjacent to the first  29  and second  30  planar surfaces of the ceramic core. 
     In some aspects, it may be preferable for the first planar  27  layer of the cladding to have a lower dielectric constant than the dielectric constant of ceramic core. In other aspects, it may be preferable for the second  28  planar layer of the cladding to have a lower dielectric constant than the dielectric constant of the ceramic core. In other aspects, it may be preferable for both the first  27  and second  28  planar layers of the cladding to have lower dielectric constants than the dielectric constant of the ceramic core. As a result, the first  27  and second  28  planar layers of the cladding may assist in confining an electromagnetic wave inside the ceramic core structure so that it does not spread out, and losses resulting from this effect are eliminated. It is advantageous for the first and second planar layers of the cladding to have a similar loss tangent in the THz range as the ceramic core, as well as a low Dk so to minimize transmission loss and the size of the structure formed as part of the waveguide. 
     In yet another aspect, it may be preferable for the first planar  27  layer of the cladding to have a Df less than 1×10 −3 . In other aspects, it may be preferable for the second  28  planar layer of the cladding to have a Df less than 1×10 −3 . In other aspects, it may be preferable for both the first  27  and second  28  planar layers of the cladding to have a Df less than 1×10 −3 . As a result, the first  27  and second  28  planar layers of the cladding may assist in confining an electromagnetic wave inside the ceramic core structure so that it does not spread out, and losses resulting from this effect are eliminated. It is advantageous for the first and second planar layers of the cladding to have a similar loss tangent in the THz range as the core, as well as a low DF so to minimize transmission loss and the size of the structure formed as part of the waveguide. 
     The first and second planar layers of the cladding can be made of air, glass, silicon dioxide (silica glass), or polymers. In aspects where the first and second planar layers of the cladding are made of a polymer, polymers may include, for example, SU-8, polytetrafluoroethylene (Teflon), or other fluoropolymers that have low loss properties in the frequency range of 100 GHz-1000 GHz. Other suitable materials for the cladding 18 may be glass, air, polymer and any combination thereof. 
     In aspects where a cladding is disposed around a ceramic core, the waveguide may become stiff, inflexible, or fragile. In addition, disposing a cladding around a ceramic core may increase the overall size of the waveguide. Therefore, the thickness of a cladding may influence the flexibility, durability, and size of a waveguide. In one aspect, the cladding comprises a thickness  31  in the range from 0.1 mm to 10 mm. In another aspect, the first and second planar layers of a cladding comprises a thickness in the range of 0.1 mm to 10 mm. Because of the thickness of a cladding, a THz waveguide may remain flexible with the added benefit of reducing the overall size of the waveguide structure. 
       FIG.  9 A  illustrates a top view of a ceramic ribbon  40  cut out in regions  42  to create an array of THz waveguides  14 . Each ceramic ribbon  40  may range from 1 mm to 100 mm in width. Each cutout  42  may range from 10 um to 5 mm in width. Each waveguide  14  may range from 100 nm to 1 mm in width. Each cutout  42  may be created by laser cutting, ablation, perforation and separation process, or any similar process. 
     A cutout  42  may be filled with air, forming a cladding layer between each waveguide  14 . Cladding material can be composed of two materials of differing dielectric constants acting as an effective index material such that they retain their distinct composition in local regions upon combination, the size of these distinct regions being much less than the THz operating wavelength, and on average the dielectric constant of the cladding material is lower than the dielectric constant of the THz waveguide  14 . An example of cladding material could be a fluoropolymer where it is made porous with air bubbles to lower the dielectric constant and the pore size is much less than the THz operating wavelength. Another example of cladding material could be silica soot deposited as a cladding. Pore size as deposited is small enough that silica soot need not be consolidated. Localized heating and consolidation can be done to create transitions in the THz waveguide effective index that can be useful for mode field conversion. Alternatively, any or all cutouts  42  may also be filled with a dielectric material, for example a polymer, having a lower dielectric constant than a THz waveguide  14 . Each cutout  42  shown runs in a straight line, but it is also contemplated within the scope of the present invention that it may contain a bend, for example a cutout curved by somewhere between 0-90 degrees (see  FIG.  9 B ). 
       FIG.  10 A  illustrates a top view of a ceramic ribbon  40  cut out in regions  42  to create an adiabatic taper for THz waveguide mode conversion along the propagation direction. This allows for coupling between a THz waveguide with a relatively wide width to a THz waveguide with a relatively narrow width, or vice versa depending on the direction of propagation. Each ceramic ribbon  40  may range from 1 to 100 mm in width. Each cutout  42  may range from 10 um to 5 mm in width. Each waveguide  14  may range from 100 nm to 1 mm in width before the taper and from 1 um to 1 mm in width after the taper. Each cutout  42  may be created by laser cutting, ablation, perforation and separation process, or any similar process. A cutout  42  may be filled with air, forming a cladding layer between waveguides  14 . Alternatively, any or all cutouts  42  may also be filled with a dielectric material, for example a polymer, having a lower dielectric constant than a THz waveguide  14 . Rather than an adiabatic taper, a ceramic ribbon  40  may be cut out in regions  42  to create a splitter or combiner, depending on the propagation direction (see  FIG.  10 B ). The splitter shown has a waveguide  14  splitting in to two separate waveguides  14 , but it is also contemplated within the scope of the present invention that a waveguide  14  may split in to two or more parts. Likewise, the combiner shown has two separate waveguides  14  combining into one waveguide  14 , but it is within the scope of the present invention that a combiner may combine two or more separate waveguides  14 . 
       FIG.  11 A  illustrates a top view of a ceramic ribbon  40  cut out in regions  42  to create a THz waveguide  14 . A cutout  42  exists near each end of the waveguide  14  allowing space for a transmitter  44  and receiver  46 . Each cutout  42  may be created by laser cutting, ablation, perforation and separation process, or any similar process. Between the THz waveguide  14  and the space for a transmitter  44  or receiver  46  is at least one strut, which comprises a strip of ceramic ribbon,  48  with a width much less than a single THz frequency wavelength. The narrow width of the strut  48  between the THz waveguide  14  creates edge coupling of THz electromagnetic radiation into or out of the waveguide  14  from a source  20  or detector  22 , respectively. To add more mechanical support to the THz waveguide  14 , struts  48  may be added transverse to the ceramic dielectric terahertz waveguide, creating smaller cutout regions  42  (see  FIG.  11 B ). 
       FIG.  12    illustrates a side view of multiple layers of ceramic ribbon  40  separated from each other by layers of dielectric material  50  having a lower dielectric constant than the THz waveguide  14 . Each layer of ceramic ribbon  42  may have embedded within it one or more THz waveguides  14 , one or more waveguide devices, one or more sources (e.g., transmitters)  20 , and/or one or more detectors (e.g. receivers)  22 . Each layer of dielectric material  50  acts as a waveguide material and may be a polymer or other suitable material with a dielectric constant lower than that of the THz waveguide  14 . The layers shown are singular (i.e., alternating one layer of dielectric material with one layer of ceramic ribbon), but it is within the scope of the present invention that there may be one or more layers of dielectric material  50  between each layer of ceramic ribbon  40 . It is also within the scope of the present invention that there may be one or more layers of ceramic ribbon  40  between each layer of dielectric material  50 . 
       FIG.  13 A  illustrates a top view of a ceramic ribbon  40  cut out in an array of circular holes  54  uniform in shape, size, and placement in the region adjacent to the THz waveguide  14  to create a electronic bandgap cladding layer for a THz waveguide  14 . Advantageously, light cannot propagate in a electronic bandgap, so light propagation is bound to the core region (i.e., the THz waveguide  14 ). Each ceramic ribbon  40  may range from 1 to 100 mm in width. Each cutout  54  may range from 10 um to 5 mm in diameter, and are preferably created with a laser. Each waveguide  14  may range from 100 nm to 1 mm in width. A cutout  54  may be filled with air, forming a electronic bandgap cladding layer for a THz waveguide  14 . Alternatively, any or all cutouts  54  may be filled with a dielectric material, for example a polymer, having a lower dielectric constant than a THz waveguide  14 . The cutouts  54  in the ceramic ribbon  40  provide mechanical support for the THz waveguide  14  without disrupting coupling or propagation or creating excess loss. The cutouts  54  shown are identical, but it is within the scope of the present invention that each cutout  54  may be a shape other than circular, for example, square, rectangular, triangular, or any other polygonal or non-polygonal shape. It is also within the scope of the present invention that the placement of each cutout  54  may be sporadic and not uniform in placement. It is also within the scope of the present invention that the size of each cutout  54  may differ.  FIG.  13 B , for example, illustrates a top view of a ceramic ribbon  40  cut out in an array of circular holes  54  moving from largest in diameter to smallest in diameter. Variation in the size of the array of holes along the propagation direction creates a taper by varying properties of the THz frequency wave propagating through the THz waveguide  14 . 
     Wire Bonds 
       FIG.  3    illustrates a cross-section of a printed circuit board  10  having assembled on its top surface at least one transmitter component  20  and at least one receiver component  22 . Each transmitter component  20  and receiver component  22  includes a connecting port/interface  24  where a ceramic alumina wire  56  may be placed post-assembly thereby connecting the port/interface  24  of the two components  20 ,  22 . Post-assembly placement of the ceramic alumina wire  56  may enable embedded interconnects for surface mount assembly and interconnect of a transmitter  20  or receiver  22  to the THz waveguide  14 . Advantageously, this allows flexibility in pick and place assembly of each transmitter  20  and receiver  22 , solder reflow, and/or adhesive bonding. The ceramic alumina wire  56  is flexible enough so that it may be coiled. If coiled, the ceramic alumina wire  56  is compact enough that it may be readily unreeled during wire bonding. Advantageously, this allows for each wire bond to be created within seconds. Also advantageously, gold ball wire bonding processes and other state-of-the-art wire bonding tools may be used. Additionally, UV curable adhesives may be used where the ceramic alumina wire  56  is attached to a port/interface  24 . UV curable adhesive has the dielectric property of being low loss and may have a dielectric constant lower than that of the ceramic alumina wire  56 . The length of the ceramic alumina wire  56  may range from 10 cm to 100 m. Each ceramic alumina wire  56  may have a ceramic alumina core  14  coated in a dielectric material having a dielectric constant lower than that of the ceramic alumina core  14 , for example a polymer or any other suitable substance. The dielectric material coating the ceramic alumina core  14  provides a cladding layer for the ceramic alumina core  14 . The ceramic alumina wire  56  may have a protective or shielding layer (e.g., a metal). After the ceramic alumina wire  56  is connected to a port/interface  24 , it may be embedded in a dielectric material having a lower dielectric constant than that of the ceramic alumina wire  56 , for example a polymer, air, or any other suitable material. 
     Planar Ceramic Dielectric Waveguide 
       FIG.  1    illustrates a cross-section of a printed circuit board  10  having a ceramic dielectric waveguide  16  embedded within its circuit substrate and extending along the z-axis. The printed circuit board  10  may be comprised of one or more layers of ceramic, glass, or other suitable materials. The ceramic dielectric waveguide  16  may be comprised of at least one ceramic core  14 , for example alumina, zirconia, titania, silica, or any other suitable material, embedded within another dielectric  12 , for example a polymer, glass, or any other suitable material. The surrounding dielectric  12  becomes a cladding so that the strip(s) of ceramic dielectric become the core for guiding THz frequency waves. The surrounding dielectric  12  has a lower dielectric constant than the ceramic core  14  to ensure the THz wave propagates through the waveguide efficiently. The ceramic dielectric waveguide  16  shown has a rectangular configuration, but it is also contemplated within the scope of the present invention that it may have a configuration other than rectangular, for example circular, elliptical, triangular, or any other polygonal or non-polygonal shape. The ceramic core  14  is likewise shown having a rectangular configuration, but it is also contemplated within the scope of the present invention that it may have a configuration other than rectangular, for example circular, elliptical, triangular, or any other polygonal or non-polygonal shape. 
     Also embedded within the ceramic dielectric waveguide  16  may be a ceramic support structure  18  (see  FIG.  2   ), where the ceramic support structure  18  is comprised of the same material as the ceramic core and runs perpendicular to the ceramic core  14  along the x-axis. When the ceramic support structure  18  is present at least one ceramic dielectric waveguide  14  can rest directly on top of the ceramic support structure  18 . 
       FIG.  4    illustrates a cross-section of a printed circuit board  10  having a ceramic dielectric waveguide  16  mounted directly on the top surface of the circuit substrate. Along a portion of the top surface of the circuit substrate, below the ceramic dielectric waveguide  16 , may run an antenna or coupling element  30 . The antenna or coupling element  30  may couple the electrical transmission line signal from the integrated circuit (IC)  26  to the ceramic dielectric waveguide  16  containing a ceramic core  14 . The IC  26  drives the electrical signal through the printed circuit board  10 . The IC  26  may be connected to the printed circuit board  10  by metal input/output (I/O) pads  28  that conduct signals in and out of the integrated circuit. The electrical signal generated by the IC  26  may be propagated through vias  32  to PCB conductive layers  34  embedded within the printed circuit board  10 . The same electrical signal may further be propagated through PCB conductive layers  34  and/or more vias  32  to the antenna or coupling element  30  which may couple the signal to the ceramic dielectric waveguide  16 . The antenna or coupling element  30  shown runs horizontally along the bottom of the ceramic dielectric waveguide  16 , but it is also contemplated within the scope of the present invention that it may run vertically along the end surface of the ceramic dielectric waveguide  16 . The mixture of vertical and horizontal coupling elements can be used to optimize the coupling to individual modes guided within the dielectric waveguide. 
       FIG.  5    illustrates a cross-section of a printed circuit board  10  having a ceramic dielectric waveguide  16  embedded within its circuit substrate. Along portions of the top and the bottom surfaces of the ceramic dielectric waveguide  16  may be antennas or coupling elements  30  which may act as a conductive transmission line waveguide to couple the electrical transmission line signal from the IC  26  to the ceramic dielectric waveguide  16 . The antenna or coupling elements  30  may connect to embedded conductive layers  34  within the printed circuit board  10  either directly or through one or more vias  32 . The antenna or coupling elements may connect to the IC  26  either directly or through embedded conductive layers  34  and vias  32 . The antenna or coupling elements  30  shown run horizontally along a portion of the top and the bottom surfaces of the ceramic dielectric waveguide  16 , but it is also contemplated within the scope of the present invention that it may run horizontally along a portion of only the top surface of the ceramic dielectric waveguide  16  or along a portion of only the bottom surface of the ceramic dielectric waveguide  16 . It is also contemplated within the scope of the present invention that the antenna or coupling element  30  may run vertically along the end surface of the ceramic dielectric waveguide  16 . It is also contemplated within the scope of the present invention that the antenna or coupling element  30  may run in a combination of these orientations, including but not limited to, horizontally along the bottom surface and vertically along the end surface of the ceramic dielectric waveguide  16 , horizontally along the top surface and vertically along the end surface of the ceramic dielectric waveguide  16 , and horizontally along the bottom and top surfaces and vertically along the end surface of the ceramic dielectric waveguide  16 . 
       FIG.  6    illustrates a cross-section of a printed circuit board  10  having a ceramic dielectric waveguide  16  mounted directly on the top surface of the circuit substrate. The ceramic dielectric waveguide  16  may have a linearly tapered left edge, along which may run an antenna or coupling element  30 . The taper or other transition regions increase coupling from the antenna or coupling element  30  which launches the signal into the ceramic dielectric waveguide  16 . When the ceramic dielectric waveguide  16  is on the same plane as the IC  26 , the antenna or coupling element  30  running along the tapered edge of the ceramic dielectric waveguide  16  may connect to embedded conductive layers  34  within the printed circuit board  10  through a via  32 . When the ceramic dielectric waveguide  16  is on a lower plane than the IC  26  (see  FIG.  7   ), the antenna or coupling element  30  running along the tapered edge of the ceramic dielectric waveguide  16  may directly connect to embedded conductive layers  34  within the printed circuit board  10 . If the IC  26  is on a higher plane than the ceramic dielectric waveguide  16 , the IC may still connect to the embedded conductive layers  34  through a via  32 . The ceramic dielectric waveguide  16  is shown having a linearly tapered left edge surface, but it is also contemplated within the scope of the present invention that any edge may be linearly tapered. It is also contemplated within the scope of the present invention that the ceramic dielectric waveguide  16  may have an exponential taper, logarithmic taper, or any other curved taper creating a non-vertical edge. The ceramic dielectric waveguide  16  is shown on the same plane (see  FIG.  6   ) or lower plane (see  FIG.  7   ) compared to the IC  26 , but it is contemplated within the scope of the present invention that the ceramic dielectric waveguide  16  may be on a higher plane compared to the IC  26 . 
       FIG.  8    illustrates a cross-section of a printed circuit board  10  having a glass substrate  36  mounted directly on the top surface of the circuit substrate. The glass substrate  36  may support the ceramic dielectric waveguide  16  which rests directly on top of the glass substrate  36 . Encompassing the glass substrate  36  and the ceramic dielectric waveguide  16  may be a dielectric material  12 , for example a polymer or any other suitable substance with a dielectric constant lower than that of the ceramic dielectric waveguide  16 . The dielectric material  12  encompassing the glass substrate  36  and ceramic dielectric waveguide  16  is shown, but it is also contemplated within the scope of the present invention that the dielectric material  12  is an optional element. Encompassed by the glass substrate  36  and connected to the ceramic dielectric waveguide  16  may be an antenna or coupling element  30 . The glass substrate  36  supporting the ceramic dielectric waveguide  16  provides a low loss substrate for the antenna or coupling element  30  to launch an electric signal into the ceramic dielectric waveguide  16 . The antenna or coupling element  30  may be connected to a via  32  which may intersect between the glass substrate  36  and the circuit substrate of the printed circuit board  10 . The via  32  may further intersect with one or more embedded conductive layers  34  within the printed circuit board  10 . 
     In the present disclosure, use of the singular includes the plural except where specifically indicated. 
     The present described technology is now described in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains to practice the same. It is to be understood that the foregoing described preferred aspects of the technology and that modification may be made therein without departing from the spirit of scope of the invention as set forth in the appended claims. The scope of the following claims is to be accorded the broadest interpretation to encompass all such modifications and equivalent structures and functions. Therefore, it is intended that the application not be limited to the particular aspects disclosed, but that the application will include all aspects falling within the scope of the appended claims.