Thz frequency multiplier devices based on a dielectric waveguide inserted in metallic waveguides

Abstract

A terahertz (THz) frequency multiplier device is disclosed. The device includes a first metallic waveguide that receives, in its first interior space, an input electromagnetic field oscillating at an input frequency. A dielectric waveguide extends partly within the first interior space and is terminated with an output port located outside the first interior space. A nonlinear circuit element is coupled to the dielectric waveguide in the first interior space. The element is excited by the input field to generate an electrical current containing harmonics of the input field and inducing an output electromagnetic field within the dielectric waveguide at an output THz frequency corresponding to one of the harmonics. A second metallic waveguide receives a portion of the dielectric waveguide extending outside the first interior space, the second waveguide being configured to impede propagation of the input field while allowing propagation of the output field toward the output port.

Description

THZ FREQUENCY MULTIPLIER DEVICES BASED ON A DIELECTRIC WAVEGUIDE INSERTED IN METALLIC WAVEGUIDESRELATED PATENT APPLICATION

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 676,021 filed on July 26, 2024, the disclosure of which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The technical field generally relates to sources of terahertz (THz) electromagnetic radiation, and more particularly to THz frequency multiplier devices based on a dielectric waveguide inserted in metallic waveguides.BACKGROUND

[0003] Numerous types of THz radiation sources and frequency multiplier devices exist, their operation being based on various emission mechanisms, technologies, and processes. Terahertz radiation typically refers to electromagnetic radiation with frequency ranging from about 0.1 THz to about 10 THz, corresponding to a wavelength ranging from about 30 pm to about 3000 pm. THz radiation can penetrate materials that are opaque to visible light while remaining safe for humans and animals, unlike X-ray radiation. Optical sensing and imaging systems that employ THz radiation can perform see-through imaging for various commercial and industrial applications including security screening and inspection, industrial quality control, medicine, communications, and spectroscopy. However, the development of these applications has been impeded by the lack of reliable, compact, and affordable THz sources and detectors, a deficiency often referred to as the “THz gap”. Despite ongoing efforts to develop new devices for generation and detection of THz radiation, various challenges remain in this field.SUMMARY

[0004] The present description generally relates to THz frequency multiplier devices that use nonlinear circuit elements, such as diodes, coupled to a dielectric waveguide disposed within metallic waveguides.

[0005] In accordance with an aspect, there is provided a THz frequency multiplier device, including: a first metallic waveguide extending longitudinally between a first end and a second end, the first end serving as an input port of the device, the first metallic waveguide defining afirst interior space configured to support an input electromagnetic field oscillating at an input frequency and received via the input port; a dielectric waveguide extending longitudinally between a first end disposed within the first interior space and a second end disposed outside the first interior space, the second end serving as an output port of the device; a frequency-multiplying circuit disposed within the first interior space, the frequencymultiplying circuit including at least one nonlinear circuit element configured to be excited by the input electromagnetic field to generate an electrical current including higher harmonics of the input electromagnetic field, the frequency-multiplying circuit being coupled to the dielectric waveguide such that the electrical current induces an output electromagnetic field within the dielectric waveguide, the output electromagnetic field oscillating at an output frequency in the THz frequency range, the output frequency corresponding to one of the higher harmonics; and a second metallic waveguide extending longitudinally between a first end and a second end, the first end of the second metallic waveguide being coupled to the second end of the first metallic waveguide, the second metallic waveguide defining a second interior space configured to receive a portion of the dielectric waveguide that extends outside the first interior space, the second metallic waveguide having a cutoff frequency lying between the input frequency and the output frequency, thereby allowing the output electromagnetic field induced within the dielectric waveguide to reach the output port while impeding propagation of the input electromagnetic field within the second metallic waveguide.

[0006] In some embodiments, the output frequency corresponds to the second or third harmonic of the input electromagnetic field.

[0007] In some embodiments, the output frequency ranges from about 100 GHz to about 1000 GHz.

[0008] In some embodiments, the dielectric waveguide is made of silicon.

[0009] In some embodiments, the dielectric waveguide has a rectangular or a square crosssection.

[0010] In some embodiments, the first metallic waveguide is configured to receive the input electromagnetic field via waveguide coupling from an electromagnetic energy source.

[0011] In some embodiments, each of the first and second metallic waveguides has a circular or a rectangular cross-section.

[0012] In some embodiments, the output port is designed as a THz antenna configured to radiate the output electromagnetic field.

[0013] In some embodiments, the at least one nonlinear circuit element includes a Schottky diode.

[0014] In some embodiments, the at least one nonlinear circuit element is provided on a dielectric substrate integrated within or serving as the dielectric waveguide.

[0015] In some embodiments, the dielectric waveguide is dimensioned to fit snugly within the interior space of the second metallic waveguide.

[0016] In some embodiments, the THz frequency multiplier device further includes a waveguide holder configured to support a portion of the dielectric waveguide that projects longitudinally beyond the second end of the second metallic waveguide.

[0017] In some embodiments, the waveguide holder is affixed to the second end of the second metallic waveguide.

[0018] In some embodiments, the waveguide holder is affixed to the second metallic waveguide using glue.

[0019] In some embodiments, the waveguide holder includes an opening formed therein through which the dielectric waveguide extends.

[0020] In some embodiments, the dielectric waveguide is configured to fit snugly within the opening of the waveguide holder.

[0021] In some embodiments, the waveguide holder is made of a dielectric material having a refractive index lower than a refractive index of the dielectric waveguide at the output frequency.

[0022] In some embodiments, the output port of the dielectric waveguide is located outside the waveguide holder.

[0023] Other features and advantages of the present description will become more apparent upon reading the following non-restrictive description of specific embodiments, provided by way ofexample only, with reference to the appended drawings. Although specific features described in the above summary and the following detailed description may be associated with particular embodiments or aspects, these features can be combined with one another unless stated otherwise.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Fig. 1 is a schematic perspective view of an embodiment of a THz frequency multiplier device.

[0025] Fig. 2 is a schematic cross-sectional perspective view of the THz frequency multiplier device shown in Fig. 1 , taken along line ll-ll.

[0026] Fig. 3 is a schematic front elevation view of the THz frequency multiplier device of Fig. 1.

[0027] Fig. 4 is an enlarged schematic view showing details of the dielectric waveguide and the frequency-multiplying circuit of the THz frequency multiplier device of Fig. 1 .

[0028] Fig. 5 is a schematic perspective view of another embodiment of a THz frequency multiplier device.

[0029] Fig. 6 is a schematic cross-sectional perspective view of the THz frequency multiplier device shown in Fig. 5, taken along line VI-VI.

[0030] Fig. 7 is a schematic partially exploded perspective view of the THz frequency multiplier device of Fig. 5.DETAILED DESCRIPTION

[0031] The present description generally relates to THz frequency multiplier devices that use nonlinear circuit elements, such as diodes, coupled to a dielectric waveguide positioned within metallic waveguides.

[0032] Throughout the present description, similar features in the drawings have been given similar reference numerals. To avoid cluttering certain figures, some elements may not be indicated if previously identified in preceding figures. Elements in drawings are not necessarily depicted to scale, emphasis being on clearly illustrating elements and structures of disclosed embodiments. Positional descriptors indicating the location or orientation of one element relative to another are used for ease and clarity of description. Unless indicated otherwise, these descriptors should be understood in the context of the figures and should not be consideredlimiting. Such spatially relative terms are intended to encompass different orientations in use or operation of disclosed embodiments, in addition to orientations exemplified in the figures. Furthermore, when a first element is referred to as being “on”, “above”, “below”, “over”, or “under” a second element, the first element can be directly or indirectly on, above, below, over, or under the second element, respectively, such that one or multiple intervening elements may be disposed between the first element and the second element.

[0033] The terms “a”, “an”, and “one” are defined herein to mean “at least one”, and do not exclude a plural number of elements, unless stated otherwise.

[0034] The term “or” is defined herein to mean “and / or”, unless stated otherwise.

[0035] Terms such as “substantially”, “generally”, and “about”, which modify a value, condition, or characteristic of a feature of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within tolerances that are acceptable for the proper operation of this exemplary embodiment for its intended application, or that fall within an acceptable range of experimental error. In particular, the term “about” generally refers to a range of numbers that one skilled in the art would consider equivalent to the stated value (e.g., having the same or nearly the same function or result). In some instances, the term “about” means a variation of ±10% of the stated value. It is noted that all numerical values used herein are assumed to be modified by the term “about”, unless stated otherwise.

[0036] The term “based on” as used herein is intended to mean “based at least in part on”, whether directly or indirectly, and to encompass both “based solely on” and “based partly on”. In particular, the term “based on” may also be understood as meaning “depending on”, “representative of”, “indicative of”, “associated with”, “relating to”, and the like.

[0037] The terms “match”, “matching”, and “matched” refer herein to a condition in which two or more elements are either the same or within some predetermined tolerance of one another. These terms are meant to encompass not only “exactly” or “identically” matching the two or more elements, but also “substantially”, “approximately”, or “subjectively” matching the elements, as well as providing a higher or best match among a plurality of matching possibilities.

[0038] The terms “connected” and “coupled”, and derivatives and variants thereof, refer herein to any connection or coupling, either direct or indirect, between two or more elements, unless stated otherwise.

[0039] The terms “light” and “optical”, and variants and derivatives thereof, refer herein to radiation in any appropriate region of the electromagnetic spectrum. These terms are not limited to visible light but may also include, without being limited to, the infrared, terahertz, millimeterwave, and centimeter-wave regions.

[0040] The term “terahertz radiation” generally refers herein to electromagnetic radiation having a center frequency ranging from about 0.1 THz to about 10 THz, corresponding to a center wavelength ranging from about 30 pm to about 3000 pm. The definition of “terahertz radiation” with reference to a particular spectral range may vary depending on the technical field or standard under consideration and is not meant to limit the scope of application of the present techniques. Although various embodiments described herein operate with THz radiation, other embodiments could additionally or alternatively operate with radiation lying in other regions of the electromagnetic spectrum. Examples of such regions are the millimeter- wave region (i.e., electromagnetic radiation with a center frequency ranging from about 30 GHz to about 300 GHz, corresponding to a center wavelength ranging from about 1 mm to about 10 mm) and the centimeter-wave region (i.e., electromagnetic radiation with a center frequency ranging from about 3 GHz to about 30 GHz, corresponding to a center wavelength ranging from about 1 cm to about 10 cm). According to the above definitions, the upper part of the millimeter- wave region overlaps with the lower part of the THz region.

[0041] Certain conventional THz frequency multipliers utilize a split-block technique relying on interconnected metal block circuits, cavities, and waveguides. While these metal-based devices offer some advantages, they also come with drawbacks and limitations, particularly at operation wavelengths shorter than about 1 mm (i.e., for frequencies higher than about 0.3 THz). The challenges encountered with these devices include increased ohmic losses in metal components at higher THz frequencies and difficulties in scaling down the manufacturing of metal components to submillimeter size with high precision, low cost, and high yield. Various embodiments of the present techniques aim to address or mitigate these challenges by providing compact, higher- power, and lower-cost devices for THz frequency multiplication.

[0042] The present techniques have potential use in various commercial and industrial applications that may benefit from enhanced or improved sources of THz radiation. Examples include quality control (e.g., non-destructive inspection), security screening (e.g., concealed object detection), medicine (e.g., health diagnosis), imaging, spectroscopy, sensing, communications, and fundamental research.

[0043] Various aspects, features, and implementations of the present techniques are described below with reference to the figures.

[0044] Referring to Figs. 1 to 3, schematic views of an embodiment of a THz frequency multiplier device 100 are depicted. The term “frequency multiplier device”, or simply “frequency multiplier”, refers herein to a device configured to receive an input electromagnetic field and, using a nonlinear circuit element such as a diode, generate an output electromagnetic field that is a higher harmonic of the input field. Specifically, the frequency nfa of the output electromagnetic field is a multiple of the frequency fa of the input field, where n is a positive integer greater than one. In this context, the input field corresponds to the first harmonic (also referred to as the fundamental) of the harmonic series.

[0045] The THz frequency multiplier device 100 includes a first metallic waveguide 102, a second metallic waveguide 104, a dielectric waveguide 106, and a frequency-multiplying circuit 108. The THz frequency multiplier device 100 operates in combination with an electromagnetic energy source 110 coupled to the first metallic waveguide 102.

[0046] The first metallic waveguide 102 extends longitudinally along a first waveguide axis, between a first end 112 and a second end 114, with the first end 112 serving as the input port of the device 100. The first metallic waveguide 102 has a hollow interior that forms a first interior space 116 configured to support an input electromagnetic field 118 received from the electromagnetic energy source 110 via the first end 112. The input field 118 oscillates at an input frequency fa (e.g., a center frequency) within a certain spectral band.

[0047] The dielectric waveguide 106 extends longitudinally along a dielectric waveguide axis, between a first end 120 disposed within the first interior space 116 and a second end 122 disposed outside the first interior space 116. The second end 122 serves as the output port of the frequency multiplier device 100. In the depicted embodiment, the dielectric waveguide axis coincides with the first waveguide axis, although this is not a requirement. The dielectric waveguide 106 includes a first longitudinal portion 124 extending within the first interior space 116 from the first end 120 to an intermediate position 126. The dielectric waveguide 106 also includes a second longitudinal portion 128 extending outside the first interior space 116 from the intermediate position 126 to the second end 122.

[0048] The frequency-multiplying circuit 108 is positioned within the first interior space 116 and mounted somewhere on the outer surface of the first longitudinal portion 124 of the dielectricwaveguide 106. Incorporating at least one nonlinear circuit element 130 such as a Schottky diode, the frequency-multiplying circuit 108 is configured to be excited by the input electromagnetic field 118. The term “nonlinear circuit element” refers herein to an electronic component that exhibits a nonlinear current-voltage (l-V) characteristic at least within a portion of its range of operation. The nonlinear response of the element 130 produces an output signal that scales nonlinearly with the input signal, thus leading to the generation of harmonics. Upon excitation by the input field 118, the nonlinear circuit element 130 produces an electrical current having a spectrum that contains higher harmonics. Through electromagnetic coupling of the frequencymultiplying circuit 108 with the dielectric waveguide 106, the electrical current generates an output electromagnetic field 132 that propagates within the dielectric waveguide 106. This output field 132 has an output frequency / out (e.g., a center frequency) lying within the THz frequency range, corresponding to one of the higher harmonics of the input field 118, that is, / out = nfm, where n = 2, 3, 4, ... is a positive integer greater than one. In some embodiments, the output frequency / out can range from about 100 GHz to about 1000 GHz. In practice, the lower-frequency limit is set by the available millimeter-wave radiation sources while the higher-frequency limit is set by the fabrication precision of the dielectric and metallic waveguides.

[0049] The second metallic waveguide 104 extends longitudinally along a second waveguide axis between a first end 134 and a second end 136, with the first end 134 being coupled to the second end 114 of the first metallic waveguide 102. In the depicted embodiment, the second waveguide axis coincides with the first waveguide axis, although this is not a requirement. The second metallic waveguide 104 has a hollow interior that forms a second interior space 138 that receives the dielectric waveguide 106 over at least part of the second longitudinal portion 128 of the waveguide 106. The second metallic waveguide 104 is designed to have a cutoff frequency lying between the input frequency and the output frequency. The term “cutoff frequency” refers herein to the lowest frequency that can propagate within a waveguide. This cutoff frequency can be achieved by providing the second metallic waveguide 104 with transverse dimensions smaller than those of the first metallic waveguide 102. Consequently, this configuration enables the output field 132, induced within the dielectric waveguide 106, to propagate toward the output port of the device 100 while preventing the input field 118 from entering the second metallic waveguide 104. The second metallic waveguide 104 thus acts, for the input field 118, as a reflective termination located at the second end 114 of the first metallic waveguide 102. This design allows the input field 118 to establish a longitudinal standing-wave pattern within the first interior space 116.

[0050] Further details on the structure, configuration, and operation of these and other possible components associated with the THz frequency multiplier device 100 are provided in the following description. The schematic representations illustrated in Figs. 1 to 3 and in subsequent figures aim to illustrate a limited number of components and features associated with the THz frequency multiplier device 100. Therefore, additional components and features useful for practical operation of the device 100 may not be specifically depicted. For illustration, the THz frequency multiplier device 100 depicted in Figs. 1 to 3 will be described below as an exemplary frequency doubler that operates with an input frequencyof 150 GHz and an output frequency / out of 300 GHz.

[0051] The electromagnetic energy source 110 can be any suitable device or combination of devices configured to generate the input field 118 oscillating at the input frequencyExamples include vacuum electronic sources and solid-state electronic sources. The theory, configuration, implementation, and operation of such electromagnetic energy sources are well established in the art and need not be detailed herein beyond facilitating an understanding of the present techniques. In some embodiments, the input frequencycan range from about 40 GHz to about 150 GHz. It is noted that this exemplary frequency range extends partly below the typical THz frequency range from 0.1 to 10 THz referenced earlier. This implies that, in certain embodiments, the THz frequency multiplier device 100 disclosed herein can generate a THz output field 132 having an output frequency / out higher than 0.1 THz from a sub-THz input field 118 having an input frequency lower than 0.1 THz.

[0052] The electromagnetic energy source 110 includes an output port 140 optically coupled to the first end 112 of the first metallic waveguide 102. In some embodiments, the electromagnetic energy source 110 is coupled to the first metallic waveguide 102 via waveguide coupling. For example, in the configuration depicted in Figs. 1 to 3, the output port 140 is configured as a waveguide port featuring a waveguide flange connectable to a corresponding waveguide flange located at the first end 112 of the first metallic waveguide 102. These flanges, such as UG-387 / U- M circular flanges, are typically bolted together. It is noted that the figures show simplified, schematic representations of the various flanges that can be used in the device 100 as the mounting hardware and certain features of the flanges are not illustrated. Using a flange-to-flange connection can ensure secure and efficient transmission of energy from the electromagnetic energy source 110 to the first metallic waveguide 102. Alternatively, the output port 140 of the electromagnetic energy source 110 may be coupled to the first metallic waveguide 102 via free- space optics. For example, the electromagnetic energy source 110 may radiate directly into freespace using an antenna. Various antenna designs can be used, including horn antennas, bowtie antennas, dipole antennas, log-periodic antennas, and Vivaldi antennas.

[0053] Both the first metallic waveguide 102 and the second metallic waveguide 104 can be formed from any suitable type of metallic waveguide. The term “metallic waveguide” refers herein to a hollow structure with electrically conducting walls designed to confine and support electromagnetic waves in one or multiple transverse modes by reflecting the waves off the inner wall surface. The specific modes supported by the waveguide, such as transverse electric (TE) or transverse magnetic (TM), depend on its cross-sectional geometry and transverse dimensions. The term “metallic waveguide” encompasses not only hollow-core structures with metallic walls for electromagnetic energy transmission, but also resonant cavities and other enclosed structures made of electrically conducting materials and designed to support standing waves oscillating at specific frequencies. Various materials, including pure metals and alloys, can be used for metallic waveguides operating at or near THz frequencies, such as copper, aluminum, silver, and brass. In some cases, metallic waveguides may be fabricated from lower-conductivity bulk materials provided their inner walls are coated with an electrically conducting metal.

[0054] Each of the first 102 and second 104 metallic waveguides may have various cross- sectional shapes including rectangular, circular, elliptical, square, and others. For instance, in the illustrated embodiment the first metallic waveguide 102 has a rectangular cross-section while the second metallic waveguide 104 has a circular cross-section. These two waveguides 102, 104 can be connected by using flanges (e.g., UG-387 / U-M circular flanges) and secured with fasteners like bolts and nuts. Using standard and commercially available waveguides 102, 104 can streamline fabrication of the THz frequency multiplier device 100 and reduce its manufacturing costs.

[0055] The transverse dimensions of the first and second waveguides 102, 104 are selected based on the frequencies of the electromagnetic fields each waveguide is intended to support. For instance, the first metallic waveguide 102 is designed with dimensions that ensure that its cutoff frequency is lower than the input frequencyenabling effective support of the input field 118 received from the electromagnetic energy source 110. Meanwhile, the second metallic waveguide 104 is dimensioned so that its cutoff frequency lies between the input frequency and the output frequency / out to selectively permit propagation of the output field 132 while blocking the input field 118. In some implementations, the first metallic waveguide 102 may have transverse dimensions ranging from about 0.5-1 mm at higher input frequencies to about 5-10 mmat lower input frequencies, although values outside these ranges are also considered. The transverse dimensions of the second metallic waveguide 104 are typically approximately n times smaller, where n represents the integer ratio of the output frequency / out to the input frequency For example, with= 150 GHz and / out = 300 GHz, the first metallic waveguide 102 may be a WR6 rectangular waveguide measuring 1.651 x0.826 mm2and designed for operation at frequencies ranging from 110 GHz to 170 GHz, while the second metallic waveguide 104 may be a circular waveguide with an internal diameter of about 0.4 mm. The present techniques are adaptable to operate within other frequency ranges and accommodate harmonics higher than the second one. This is achievable, in first approximation, by scaling the transverse dimensions of the first 102 and second 104 metallic waveguides proportionally to the wavelengths of the input 118 and output 132 fields.

[0056] The dielectric waveguide 106 can be of any suitable type. The term “dielectric waveguide” refers herein to a waveguiding structure made primarily, though not necessarily exclusively, of a dielectric material and designed to confine and support electromagnetic waves in one or multiple guided modes. Various dielectric materials are suitable for operation at or near THz frequencies, including crystalline materials (e.g., silicon, germanium, sapphire, quartz), glass materials (e.g., fused silica), and polymer materials (e.g., polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE)). The dielectric material may be selected for its high refractive index and low absorption at THz frequencies. For instance, the dielectric waveguide 106 can be made of silicon, and more specifically of monocrystalline, high-purity, high-resistivity silicon (HR-Si), which has a refractive index of about 3.4, favorable thermomechanical properties, and low absorption losses at THz frequencies.

[0057] In the embodiment illustrated in Figs. 1 to 3, the dielectric waveguide 106 is an elongated solid piece of dielectric material with a square cross-section. A dielectric waveguide 106 shaped this way can be referred to as a “dielectric ribbon waveguide” (DRW). However, different configurations can be used in other embodiments, including waveguides with non-square crosssections (e.g., rectangular or circular), waveguides with cladding, effective-medium-cladding waveguides, hollow-core waveguides, ridge waveguides, rib waveguides, optical fibers, and the like. Providing the dielectric waveguide 106 as a DRW, specifically an HR-Si ribbon waveguide, offers advantages such as manufacturing at low-cost using microfabrication techniques of common use in the monolithic microwave integrated circuit (MMIC) industry.

[0058] The transverse dimensions of the dielectric waveguide 106 are selected according to the frequency of the electromagnetic field it is designed to support. For example, with / out = 300 GHz, and considering the transverse dimensions specified above for the first 102 and second 104 metallic waveguides, the dielectric waveguide 106 may have a square cross-section with a side length of about 0.283 mm. This corresponds to a diagonal dimension of about 0.4 mm, closely matching the diameter of the second interior space 138 of the second metallic waveguide 104, as shown in Fig. 3. This snug fit ensures that the dielectric waveguide 106 is held in place by the second metallic waveguide 104 along a length of the second longitudinal portion 128 of the waveguide 106. Conversely, the first longitudinal portion 124 of the dielectric waveguide 106 is suspended in a cantilevered configuration within the first interior space 116 of the first metallic waveguide 102, as illustrated in Fig. 2. Various combinations of cross-sectional shapes for both the second metallic waveguide 104 and the dielectric waveguide 106 can be employed to achieve this support arrangement.

[0059] In one embodiment, the nonlinear circuit element 130 is implemented as a Schottky diode. Such diodes are commonly used in THz frequency multipliers due to their ease of fabrication and high efficiency. An example is the GaN THz Nano-Schottky Diode available from Teledyne Technologies Inc. (Thousand Oaks, CA, USA). Other types of diodes, such as varactor diodes, or any currently available or future nonlinear semiconductor devices with suitable current-voltage characteristics can also be considered for use in other embodiments. In some cases, the Schottky diode can be fabricated on a dielectric substrate 142 made of a material such as SiC. This substrate 142 may then be processed and integrated within the dielectric waveguide 106, as shown in Fig. 4. Alternatively, the dielectric substrate 142 can serve as the dielectric waveguide 106 itself, particularly at higher output frequencies (e.g., / out higher than 400 GHz).

[0060] The frequency-multiplying circuit 108 shown in Figs. 2 and 4 includes metal electrodes 144 of appropriate length and design, connected to both terminals of the Schottky diode 130. In some embodiments, the frequency-multiplying circuit 108 may also incorporate a power supply (e.g., a constant-voltage source) to bias the Schottky diode 130 at a specific set point on its current-voltage characteristic. Alternatively, unbiased operation is possible and allows for the electrical current to be generated solely from energy received from the input electromagnetic field 118. In such cases, the THz frequency multiplier device 100 can function effectively as a passive device.

[0061] Although the frequency-multiplying circuit 108 depicted in Figs. 2 and 4 includes a single nonlinear circuit element 130, other implementations can include a plurality of nonlinear circuit elements, such as multiple diodes connected in parallel or in series, integrated on the dielectric waveguide 106. These configurations can reduce the voltage or current per diode, allowing for more power from the input field 118 to be coupled to the diodes, thereby potentially leading to a more powerful output THz field 132.

[0062] The operation of the THz frequency multiplier device 100 illustrated in Figs. 1 to 3 is detailed below.

[0063] The electromagnetic energy source 110 generates the input electromagnetic field 118 oscillating at the input frequencywhich is coupled to the first end 112 of the first metallic waveguide 102. The second metallic waveguide 104, having a cutoff frequency higher than acts as a reflective termination located at the second end 114 of the first metallic waveguide 102. This arrangement allows the input field 118 to form a longitudinal standing-wave pattern within the first interior space 116 of the first metallic waveguide 102. The standing wave excites the frequency-multiplying circuit 108 located on the dielectric waveguide 106. Due to its nonlinear current-voltage characteristic, the nonlinear circuit element 130 generates an electrical current having a frequency spectrum that includes the fundamental frequency and higher harmonics nfm, where n = 2, 3, 4, ... are positive integers greater than one. Positioning the nonlinear circuit element 130 close to a node of the standing-wave pattern can enhance this excitation, resulting in a higher electrical current. For instance, the nonlinear circuit element 130 can be positioned on the dielectric waveguide 106 so that its longitudinal distance from the second end 114 of the first metallic waveguide 102 corresponds to a half wavelength of the input field 118 (e.g., about 1 mm for fin = 150 GHz). However, this specific positioning is not mandatory, and certain embodiments may operate effectively even if the nonlinear circuit element 130 does not coincide exactly with a node of the standing-wave pattern.

[0064] Among the generated higher harmonics, one at THz frequency fiout corresponds to a mode guided by the dielectric waveguide 106, determined by its cross-sectional dimensions. Through electromagnetic coupling, the electrical current component at fiout generated within the frequencymultiplying circuit 108 excites an output electromagnetic field 132 at this frequency within the dielectric waveguide 106. In the illustrated embodiment, the first end 120 of the dielectric waveguide 106 includes a film made up of an electrically conducting material, thus providing a reflective termination. This reflective termination allows the dielectric waveguide 106 to support astanding wave between its first end 120 and the position of the nonlinear circuit element 130 while supporting a traveling wave along the remainder of its length. This traveling wave is guided through the portion 128 of the dielectric waveguide 106 inserted within the second metallic waveguide 104 toward the second end 122, where the output field 132 exits the device 100.

[0065] Proper positioning of the nonlinear circuit element 130 along the dielectric waveguide 106 can ensure efficient excitation of the THz output field 132 oscillating at / out within the dielectric waveguide 106. In some embodiments, the nonlinear circuit element 130 is advantageously placed close to a node of the longitudinal standing-wave pattern at / out established within the dielectric waveguide 106. For example, in the illustrated embodiment, the nonlinear circuit element 130 is positioned at a distance of about 2 mm from the first end 120 of the dielectric waveguide 106. However, this specific positioning is not strictly necessary.

[0066] In some embodiments, the second end 122 of the dielectric waveguide 106 functions as a THz antenna configured to radiate the output field 132. This is illustrated in Figs. 1 and 2, where the second end 122 has a tapered configuration. The geometry of this antenna (e.g., taper angle, cross-sectional shape and size of the tapered tip) can be designed to achieve the desired antenna characteristics (e.g., emission frequency, radiation pattern, polarization state and direction). Alternatively, the second end 122 may be coupled to another waveguide or optical component configured to receive the output field 132 generated by the device 100.

[0067] In some embodiments, the second metallic waveguide 104 may also act as a heat sink to dissipate any heat load generated by the nonlinear circuit element 130 and to maintain its temperature stable. Alternatively, the second metallic waveguide 104 may be connected to a dedicated heat sink component.

[0068] Referring to Figs. 5 to 7, another embodiment of the THz frequency multiplier device 100 is depicted. This embodiment shares several features with the one shown in Figs. 1 to 3, which will not be detailed again, except to highlight the differences. In the embodiment of Figs. 5 to 7, the THz frequency multiplier device 100 includes a waveguide holder 146 specifically designed to mechanically support the dielectric waveguide 106 and put it in correct placement within the assembly. Eliminating the need for the second metallic waveguide 104 to act as a support can avoid potential manufacturing and assembly challenges related to the snug fitting of the dielectric waveguide 106 to the second metallic waveguide 104. Additionally, the second metallic waveguide 104 can be made shorter without compromising the stable positioning of the dielectric waveguide 106.

[0069] The holder 146 is a solid piece of material with an opening 148 formed through it. The holder 146 may be made from an elastic dielectric material, such as PTFE, or from other materials with suitable properties. The opening 148 is sized and shaped to snugly receive a portion of the dielectric waveguide 106 that projects longitudinally beyond the second end 136 of the second metallic waveguide 104. The holder 146 extends longitudinally between a first end 150 and a second end 152. The first end 150 of the holder 146 may be affixed to the second end 136 of the second metallic waveguide 104 using appropriate fixing means, such as glue or other adhesive material. The dielectric waveguide 106 may also project longitudinally beyond the second end 152 of the holder 146. The longitudinal extent of the holder 146 should be sufficient to provide stable and adequate support to the dielectric waveguide 106, considering its length. For better efficiency, the holder 146 should not hinder the propagation of the output field 132 within the dielectric waveguide 106, for example, through radiation losses. This can be prevented by selecting a holder material having a refractive index lower than that of the dielectric waveguide material at THz frequencies.

[0070] In the embodiment shown in Figs. 5 to 7, the second metallic waveguide 104 is a rectangular waveguide with cross-sectional dimensions smaller than those of the first metallic waveguide 102. For example, the first metallic waveguide 102 may be a WR6 rectangular waveguide measuring 1.651 x0.826 mm2and designed for operation at frequencies between 110 and 170 GHz. In turn, the second metallic waveguide 104 may be a WR3 rectangular waveguide measuring 0.864x0.432 mm2and designed for operation at frequencies between 220 and 330 GHz. This WR3 rectangular waveguide has a cutoff frequency of about 174 GHz for the lowest-order TE mode, effectively blocking the propagation of the input field 118 oscillating at fm = 150 GHz. It also easily accommodates the dielectric waveguide 106, which can have a square cross-section with a side length of about 0.283 mm.

[0071] Numerous modifications could be made to the embodiments described above without departing from the scope of the appended claims.

Claims

CLAIMS1. A THz frequency multiplier device, comprising: a first metallic waveguide extending longitudinally between a first end and a second end, the first end serving as an input port of the device, the first metallic waveguide defining a first interior space configured to support an input electromagnetic field oscillating at an input frequency and received via the input port; a dielectric waveguide extending longitudinally between a first end disposed within the first interior space and a second end disposed outside the first interior space, the second end serving as an output port of the device; a frequency-multiplying circuit disposed within the first interior space, the frequencymultiplying circuit comprising at least one nonlinear circuit element configured to be excited by the input electromagnetic field to generate an electrical current comprising higher harmonics of the input electromagnetic field, the frequency-multiplying circuit being coupled to the dielectric waveguide such that the electrical current induces an output electromagnetic field within the dielectric waveguide, the output electromagnetic field oscillating at an output frequency in the THz frequency range, the output frequency corresponding to one of the higher harmonics; and a second metallic waveguide extending longitudinally between a first end and a second end, the first end of the second metallic waveguide being coupled to the second end of the first metallic waveguide, the second metallic waveguide defining a second interior space configured to receive a portion of the dielectric waveguide that extends outside the first interior space, the second metallic waveguide having a cutoff frequency lying between the input frequency and the output frequency, thereby allowing the output electromagnetic field induced within the dielectric waveguide to reach the output port while impeding propagation of the input electromagnetic field within the second metallic waveguide.

2. The THz frequency multiplier device of claim 1 , wherein the output frequency corresponds to the second or third harmonic of the input electromagnetic field.

3. The THz frequency multiplier device of claim 1 or 2, wherein the output frequency ranges from about 100 GHz to about 1000 GHz.

4. The THz frequency multiplier device of any one of claims 1 to 3, wherein the dielectric waveguide is made of silicon.

5. The THz frequency multiplier device of any one of claims 1 to 4, wherein the dielectric waveguide has a rectangular or a square cross-section.

6. The THz frequency multiplier device of any one of claims 1 to 5, wherein the first metallic waveguide is configured to receive the input electromagnetic field via waveguide coupling from an electromagnetic energy source.

7. The THz frequency multiplier device of any one of claims 1 to 6, wherein each of the first and second metallic waveguides has a circular or a rectangular cross-section.

8. The THz frequency multiplier device of any one of claims 1 to 7, wherein the output port is designed as a THz antenna configured to radiate the output electromagnetic field.

9. The THz frequency multiplier device of any one of claims 1 to 8, wherein the at least one nonlinear circuit element comprises a Schottky diode.

10. The THz frequency multiplier device of any one of claims 1 to 9, wherein the at least one nonlinear circuit element is provided on a dielectric substrate integrated within or serving as the dielectric waveguide.

11. The THz frequency multiplier device of any one of claims 1 to 10, wherein the dielectric waveguide is dimensioned to fit snugly within the interior space of the second metallic waveguide.

12. The THz frequency multiplier device of any one of claims 1 to 10, further comprising a waveguide holder configured to support a portion of the dielectric waveguide that projects longitudinally beyond the second end of the second metallic waveguide.

13. The THz frequency multiplier device of claim 12, wherein the waveguide holder is affixed to the second end of the second metallic waveguide.

14. The THz frequency multiplier device of claim 13, wherein the waveguide holder is affixed to the second metallic waveguide using glue.

15. The THz frequency multiplier device of any one of claims 12 to 14, wherein the waveguide holder comprises an opening formed therein through which the dielectric waveguide extends.

16. The THz frequency multiplier device of claim 15, wherein the dielectric waveguide is configured to fit snugly within the opening of the waveguide holder.

17. The THz frequency multiplier device of any one of claims 12 to 16, wherein the waveguide holder is made of a dielectric material having a refractive index lower than a refractive index of the dielectric waveguide at the output frequency.

18. The THz frequency multiplier device of any one of claims 12 to 17, wherein the output port of the dielectric waveguide is located outside the waveguide holder.

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