System and method for terahertz amplification by wavelength injection of a resonant tunneling diode oscillator

Abstract

To provide a device that can improve the robustness of communication systems. [Solution] The device includes a waveguide resonant tunnel diode (RTD) that oscillates at a terahertz (THz) frequency, a DC power supply electrically coupled to the RTD and providing a DC bias voltage to the RTD, and a waveguide isolation element operably connected to the RTD. When the RTD is injected and locked to an externally incident radiated signal having a first frequency, it generates and radiates an output radiated signal having a second frequency.

Description

Technical Field

[0001] [Priority Claim] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 779,637, filed on March 28, 2025, which is hereby incorporated by reference in its entirety into the present specification.

[0002] The present application relates to an amplification apparatus for terahertz radiation (for example, 100 GHz to 10 THz).

Background Art

[0003] Resonant tunneling diodes (RTDs) have been developed and demonstrated as low-cost, energy-efficient means for generating terahertz frequency radiation (for example, 100 GHz to 10 THz). See, for example, M. Asada and S. Suzuki, "J Infrared Milli Terahz Waves, vol. 37, no. 12, pp. 1185-1198, Dec. 2016", U.S. Patent No. 10205242B2, and U.S. Patent No. 8436382B2. One area of application for such devices is in next-generation wireless communications characterized by terahertz carrier frequencies (see, for example, T. Schneider et al., "IEEE Transactions on Terahertz Science and Technology, vol. 2, no. 2, pp. 250-256, 2012"). RTDs have demonstrated both the tuning range and output power that are utilized in such applications. However, a remaining challenge is the spectral purity of terahertz radiation. The quality of this radiation, characterized by amplitude and phase noise, directly affects the amount of data that can be encoded, transmitted, carried, demodulated, and ultimately detected wirelessly. Furthermore, the frequency drift of these devices affects the channelization of future wireless communication systems.

[0004] One candidate for such high-purity radiation is an optical mixing light source that has demonstrated state-of-the-art spectral purity and tuning. Such light sources have also been directly used in 300 GHz wireless communication demonstrations. However, optical mixing technology can lose power dramatically as the carrier frequency increases beyond 300 GHz. This challenge can be overcome by amplification. However, commercially available amplifiers have a maximum frequency of around 300 GHz and a maximum gain of only 25 dB.

[0005] Injecting low-power, high-quality radiation can significantly improve the spectral purity of any oscillator (see, e.g., R. Adler, "Proceedings of the IEEE, vol. 61, no. 10, pp. 1380-1385, 1973"). In the case of RTDs, injection can also effectively mitigate drift, as demonstrated by utilizing the optical mixing source of terahertz radiation and free-space isolators, as well as the reflection geometry of the injection, by locking the frequency to a microwave reference (see, e.g., T. Hiraoka et al., "APL Photonics, vol. 6, no. 2, p. 021301, Feb. 2021"). While spectral purity improved dramatically, the free-space isolators resulted in enormous power losses. The direct output of the optical mixer was greater than the resulting injected radiation.

[0006] Another injection demonstration by RTD showed that they could act as harmonic frequency multipliers (see, e.g., K. Arzi et al., "IEEE Transactions on Terahertz Science and Technology, vol. 10, no. 2, pp. 221-224, 2020"), where an amplifier multiplier chain (AMC) was used as an external source of terahertz radiation and a transmission injection geometry was utilized. Again, the power resulting from the multiplied radiation was lower than that achievable through direct generation of AMCs. Furthermore, both injection demonstrations suffered from free-space alignment of all components involved. Free-space configuration can lead to a lack of robustness desired for widely deployed commercial applications.

[0007] Free-space power loss can be mitigated by utilizing waveguide components. RTDs have been incorporated into waveguide packaging for several practical demonstrations, including terahertz detectors (see, e.g., Y. Takida et al., "Applied Physics Letters, vol. 117, no. 2, p. 021107, 2020"), communications (see, e.g., X. Yu et al., "Electronics Letters, vol. 56, no. 7, pp. 342-344, 2020"), and imaging (see, e.g., J. Wang et al., "Applied Sciences, vol. 12, no. 8, Art. no. 8, 2022"). None of these waveguide RTD demonstrations have so far achieved spectral purification via injection of terahertz radiation from an external source.

[0008] Mutual injection of RTD arrays has also been demonstrated (see, for example, Y. Koyama et al., "IEEE Trans. THz Sci. Technol., vol. 12, no. 5, pp. 510-519, 2022"), which reduces phase noise by a factor of √N, where N is the number of RTD elements. Mutual injection can also increase the output power of the device. These devices can also be set up to benefit from external injection of terahertz radiation, as mutual injection reduces the power from an external source required to synchronize the collective oscillation.

[0009] An alternative method for reducing the phase noise of RTDs is direct phase locking to a microwave reference, utilizing a fast cavity tuning element; such varactor diodes are mounted in slot antennas. Research has successfully used this method to dramatically reduce the phase noise of RTDs (see, e.g., K. Ogino, S. Suzuki and M. Asada, "J Infrared Milli Terahz Waves, vol. 38, no. 12, pp. 1477-1486, 2017"). However, phase-locked loops (PLLs) are inherently limited in bandwidth by the loop filter (e.g., electronics) used. External injection locking can achieve much larger bandwidths than PLLs without any external electronics. This attribute can be particularly important in the context of wireless communications, as wireless signals are typically encoded (e.g., modulated) far from the carrier. Thus, an insufficiently fast PLL will erase any data encoded on noise-reduced terahertz radiation. [Overview of the project] [Problems that the invention aims to solve]

[0010] In some embodiments, the device comprises a waveguide resonant tunneling diode (RTD) oscillating at a terahertz (THz) frequency, a DC power supply electrically coupled to the RTD and supplying a DC bias voltage to the RTD, and a waveguide isolation element operably connected to the RTD. When the RTD is injected and locked to an externally incident radiated signal having a first frequency, it generates and radiates an output radiated signal having a second frequency.

[0011] In some embodiments, a method is provided for injection locking a waveguide RTD and characterizing the absolute phase noise of the resulting terahertz radiation. The method comprises the step of injecting a first reference terahertz radiation signal into the waveguide RTD. The method further comprises the step of applying a DC bias voltage to the RTD to tune the oscillation frequency of the RTD and establish injection lock with the first reference terahertz signal. The method further comprises the step of mixing the amplified RTD output signal from the RTD with a second terahertz reference signal to form an intermediate frequency (IF) output signal in response to the mixing of the amplified RTD output signal and the second terahertz reference signal. The method further comprises the step of measuring the absolute phase noise of the first reference terahertz radiation signal.

[0012] In some embodiments, a method is provided for injecting and locking a waveguide RTD and characterizing the residual phase noise of the waveguide RTD. The method comprises the steps of generating a terahertz reference signal and dividing the terahertz reference signal into a first part and a second part. The method further comprises applying a frequency shift to the second part using a frequency synthesizer. The method further comprises injecting a waveguide RTD with the first part of the terahertz reference signal. The method further comprises mixing the amplified RTD output signal from the waveguide RTD with the frequency-shifted second part in a waveguide mixer. The method further comprises analyzing the IF signal obtained from the waveguide mixer using a phase noise analyzer synchronized with the frequency synthesizer to determine the residual phase noise introduced by injecting the waveguide RTD with the first part of the terahertz reference signal. [Brief explanation of the drawing]

[0013] [Figure 1A] Figure 1A shows exemplary devices (e.g., injection amplifiers) that utilize reflective geometry according to some embodiments described herein. [Figure 1B] Figure 1B shows an exemplary device (e.g., an injection amplifier) ​​that utilizes transmit geometry according to some embodiments described herein. [Figure 2A] Figure 2A shows exemplary devices that utilize reflective geometry (e.g., injection multipliers) according to some embodiments described herein. [Figure 2B] Figure 2B shows exemplary devices that utilize transmission geometry (e.g., injection multipliers) according to some embodiments described herein. [Figure 3A] Figure 3A is a schematic diagram of an exemplary device (e.g., a tracking oscillator) that utilizes reflective geometry according to some embodiments described herein. [Figure 3B] Figure 3B is a schematic diagram of an exemplary device (e.g., a tracking oscillator) that utilizes transmit geometry, according to some embodiments described herein. [Figure 4A] Figure 4A is a schematic diagram of an exemplary wireless communication system utilizing an exemplary device (e.g., a terahertz repeater) according to some embodiments described herein. [Figure 4B] Figure 4B is a schematic diagram of an exemplary wireless communication system utilizing an exemplary device (e.g., a terahertz repeater) according to some embodiments described herein. [Figure 5] Figure 5 is a schematic diagram of an exemplary device (e.g., a subharmonic mixer) according to some embodiments described herein. [Figure 6] Figure 6 is a schematic diagram of an exemplary system (e.g., a demultiplexing system) in the context of a multiplexed wireless communication system according to some embodiments described herein. [Figure 7]Figure 7 is a schematic diagram of an exemplary system (e.g., an optical mixing multiplexer) in accordance with some embodiments described herein. [Figure 8] Figure 8 is a schematic diagram of an exemplary system (e.g., comprising a wireless link) in accordance with some embodiments described herein. [Figure 9A] Figure 9A is a schematic diagram of an exemplary system (e.g., utilizing absolute injection PN) in accordance with some embodiments described herein. [Figure 9B] Figure 9B is a flow diagram of an exemplary method in accordance with some embodiments described herein. [Figure 9C] Figure 9C is a plot of phase noise power spectral density (PSD) for a free-running RTD (upper trace), a dual-wavelength Brillouin laser (DWBL) (lower trace), and the injected RTD and several injection powers for the exemplary system according to Figure 9A. [Figure 9D] Figure 9D is a plot of the variation of the RTD injection locking frequency range with the injection power ratio for the exemplary system according to Figure 9A. [Figure 10A] Figure 10A is a schematic diagram of an exemplary system (e.g., utilizing residual injection PN) in accordance with some embodiments described herein. [Figure 10B] Figure 10B is a flow diagram of an exemplary method in accordance with some embodiments described herein. [Figure 11A] Figure 11A schematically illustrates an exemplary device (e.g., a high-speed voltage-controlled phase modulator) in accordance with some embodiments described herein. [Figure 11B] Figure 11B schematically illustrates an exemplary device (e.g., a high-speed voltage-controlled phase modulator) in accordance with some embodiments described herein. [Figure 12A] Figure 12A schematically illustrates an exemplary device (e.g., a high-speed voltage-controlled intensity modulator) in accordance with some embodiments described herein. [Figure 12B]Figure 12B schematically shows exemplary devices according to some embodiments described herein (e.g., high-speed voltage-controlled intensity modulators). [Modes for carrying out the invention]

[0014] Some embodiments described herein involve amplification of terahertz radiation via injection of external terahertz radiation into a waveguide RTD. External terahertz radiation can be incident on the waveguide RTD, and the waveguide RTD can be tuned by a DC bias voltage to oscillate at the incident frequency. Once the frequency is tuned, injection lock can occur, and the RTD can synchronize with the incident radiation. The radiation from the RTD can then be an amplified copy of the incident radiation. The bandwidth of the injection lock, and therefore the bandwidth of the amplifier, can be explained by injection lock theory, i.e., determined by the ratio of the incident externally radiated power to the power radiated by the waveguide RTD. By utilizing waveguide isolation elements such as circulators or isolators, the formation of an external cavity with the RTD can be prevented, thus ensuring synchronization between the incident radiation and the RTD oscillation. By using only waveguide components, power loss can be reduced (e.g., minimized), and robustness can be improved to the point where practical communication systems can be realized.

[0015] The injection locking of RTDs into an external terahertz source can be achieved with two geometries: reflective geometry (e.g., utilizing a waveguide circulator) and transmissive geometry (e.g., utilizing only an isolator). Both geometries are compatible with waveguide RTDs and can result in a functional amplifier.

[0016] In the case of a reflective geometry, a weak terahertz signal can be injected into the input of a 3-port waveguide circulator (e.g., port 1). A waveguide RTD can be fixed to port 2 of the circulator, and the RTD can be biased by a DC power supply. The voltage from the DC power supply can be varied so that the RTD oscillates at a frequency very close to the input terahertz signal frequency. Once tuned, the RTD can synchronize with the input radiation and be injection-locked. The output of the circulator (e.g., port 3) can be an injected RTD with more power than that injected into the input. Thus, amplification of the input signal can be achieved through injection locking of the waveguide RTD.

[0017] In the case of a transparent geometry, a weak terahertz signal can be incident on the rear surface of a waveguide RTD, and the RTD can be biased by a DC power supply. The voltage from the DC power supply can be varied so that the RTD oscillates at a frequency very close to the input terahertz signal frequency. Once tuned, the RTD can synchronize with the input radiation transmitted through the rear surface of the RTD, and the RTD can be injection-locked. The output of the waveguide RTD can be transmitted through a waveguide isolator. The output of the waveguide isolator can be an injected RTD with more power than that incident on the input. Thus, amplification of the input signal can be achieved through injection locking of the waveguide RTD.

[0018] In both the reflective and transmitted geometry, the isolation component may be the final element before the output, which can prevent reflected radiation that could interfere with weak incident signals and RTD synchronization from entering the amplifier.

[0019] [Various exemplary embodiments] The various exemplary terahertz devices and derivatives described herein are illustrative and not limiting. Various alternative embodiments, examples, and operating techniques are also compatible with some of the embodiments described herein.

[0020] [Example 1: Waveguide RTD Injection Amplifier] Figures 1A and 1B schematically show exemplary devices 100 (e.g., waveguide RTD injection amplifiers) according to some embodiments described herein. In Figure 1A, the exemplary device 100 has a reflective geometry, and in Figure 1B, the exemplary device 100 has a transmissive geometry. The exemplary device 100 comprises a waveguide resonant tunnel diode (RTD) 110 configured to oscillate at a terahertz frequency, and a DC power supply 120 electrically coupled to the RTD 110 and configured to supply a DC bias voltage to the RTD 110. The device 100 further comprises waveguide isolation elements 130 (e.g., a circulator 132 in Figure 1A, an isolator 136 in Figure 1B) operably connected to the RTD 110. When the RTD 110 is injected and locked to an externally incident radiated signal 140 having a first frequency, it generates and radiates an output radiated signal 150 having a second frequency. As described herein with respect to Figures 1A and 1B, the device 100 can operate as an injection amplifier (for example, the first frequency of the external incident radiated signal 140 can be a terahertz frequency, the second frequency of the output radiated signal 150 can be substantially equal to the first frequency, and the output radiated signal 150 can be amplified compared to the external incident radiated signal 140).

[0021] As shown in Figure 1A, the waveguide isolation element 130 comprises a three-port waveguide circulator 132 having a first port 133 (e.g., an input port) configured to receive an external incident radiation signal 140, a second port 134 (e.g., a first output port) for optical communication with the RTD 110, and a third port 135 (e.g., a second output port) configured to emit an output radiation signal 150. As shown in Figure 1B, the waveguide isolation element 130 comprises an optical isolator 136, and the RTD 110 comprises an input port 112 (e.g., an input port of device 100) configured to receive an external incident radiation signal 140, and an output port 114 for optical communication with the optical isolator 136. The RTD 110 can be configured (e.g., mounted in a waveguide package) so that radiation from both the input port 112 and the output port 114 (e.g., waveguide radiation) interacts with the oscillating portion of the RTD 110. The optical isolator 136 may include an input port 137 that communicates optically with the output port 114 of the RTD 110, and an output port 138 (for example, the output port of device 100) configured to emit an output radiated signal 150.

[0022] In the exemplary device 100 shown in Figures 1A and 1B, the bias voltage of the DC power supply 120 can be adjusted to control the frequency of the output radiated signal 150 emitted by the device 100. When the frequency is tuned within the injection lock bandwidth of the incident radiated signal 140, injection lock can occur. The emitted output radiated signal 150 may be an amplified copy of the incident radiated signal 140 within the injection lock bandwidth (e.g., the output radiated signal 150 is amplified compared to the externally incident radiated signal 140). In some embodiments, waveguide isolation elements 130 (e.g., circulator 133, optical isolator 136) prevent radiation incident on the output of the device 100 (e.g., the third port 135 in Figure 1A, the output port 138 in Figure 1B) from interfering with the injection process, thereby allowing the waveguide RTD 110 to provide a stable injection-based amplifier (e.g., reflected geometry in Figure 1A, transmitted geometry in Figure 1B).

[0023] In certain other examples described herein, device 100 (e.g., injection amplifier) ​​in either a reflective geometry (e.g., Figure 1A) or a transmissive geometry (e.g., Figure 1B) serves as a basic component. Both geometries are functionally equivalent and can be considered interchangeable.

[0024] In some embodiments, the injection lock range of the RTD 110 is a function of the power ratio of the incident power to the radiated power. The effective bandwidth of device 100 can be estimated from this lock range. For example, using a 260 GHz wave, a 1 GHz bandwidth results from a power ratio of 0.1. The inverse power ratio can also be a measure of the amplification factor. Without active tuning of the RTD bias voltage, a 40 dB amplification may result in a 10 MHz bandwidth. Active tracking methods for the RTD bias voltage can enable even larger amplification factors and narrower bandwidths.

[0025] In some embodiments, utilizing an array of devices 100 (e.g., in a waveguide) can effectively increase the quality factor of the RTD 110. The impact on injection may be an improvement in amplification and a narrower lock range / bandwidth.

[0026] [Example 2: Waveguide RTD Injection Frequency Multiplier] Figures 2A and 2B schematically show another exemplary device 200 (e.g., an amplification frequency multiplier) according to some embodiments described herein. The exemplary device 200 in Figure 2A has the same components as the exemplary device 100 in Figure 1A arranged in reflective geometry, and the exemplary device 200 in Figure 2B has the same components as the exemplary device 100 in Figure 1B arranged in transmissive geometry. The difference between the exemplary device 100 in Figures 1A and 1B and the exemplary device 200 in Figures 2A and 2B is that the RTD 110 in Figures 2A and 2B is tuned to a first harmonic multiple of the frequency of the externally incident radiated signal 140. When tuned within the injection lock range, harmonic injection can occur, resulting in synchronization between the externally incident radiated signal 140 and the output radiated signal 150 radiated by the RTD 110 at a second frequency that is an integer multiple of the first frequency. For example, an external source of terahertz radiation can be frequency multiplied and emitted from the output so that device 200 operates as a terahertz harmonic frequency multiplier device.

[0027] In some embodiments of the exemplary device 200 in Figures 2A and 2B, the RTD 110 is mounted in a waveguide package (not shown), which comprises an input port and an output port. The waveguide size in the components of Figures 2A and 2B can be adapted to the expected frequency range at both the input and output ports. Smaller waveguides may be better for higher frequencies, leading to improved multiplier performance in terms of power loss and conversion efficiency. The input port may have a larger waveguide dimension than the output port waveguide, and thus the package can be configured to adapt to higher input frequencies and facilitate harmonic locking. In some embodiments of the exemplary device 200 in Figures 2A and 2B, filtering of the externally incident radiated signal can also be achieved by the waveguide at the output port, and waveguide isolation elements 130 (e.g., circulator 132, optical isolator 136) can isolate only the radiation at the designed harmonic multi-frequency. Since higher frequencies propagate within larger waveguides, this waveguide size matching is not required. When waveguide size matching is omitted, a larger bandwidth waveguide isolation element 130 can be used to provide separation at input and output frequencies.

[0028] [Example 3: Waveguide RTD Injection Tracking Oscillator] The exemplary device 100 schematically illustrated by Figures 1A and 1B can be a component of a tracking oscillator, such that the device 100 tracks any frequency drift of an externally incident radiation signal 140, provided that the drift remains within the bandwidth of the injection lock. Another feature of a tracking oscillator is the tuning of the tracking bandwidth. In the exemplary device 100 of Figures 1A and 1B, the power ratio adjusts the injection amplification lock range, and therefore the amplifier bandwidth. Figures 3A and 3B schematically illustrate another exemplary device 300 (having reflective and transmitted geometries, respectively), which further comprises a variable terahertz power attenuator 310 according to several embodiments described herein. The power attenuator 310 can be configured to control the amplitude of the externally incident radiation signal 140. Examples of the power attenuator 310 include, but are not limited to, manually adjustable power attenuators, voltage adjustable power attenuators, and power attenuators available from Eravant of Torrance CA. The tracking bandwidth of the RTD110 can be determined by the ratio of the input power of the external incident radiated signal 140 to the oscillation power of the RTD110, enabling frequency tracking within the injection lock frequency range. In Figure 3A, the power attenuator 310 communicates optically with the first port 133 of the circulator 132, and the power attenuator 310 communicates optically with the input port 112 of the RTD110.

[0029] Device 300 (e.g., a tracking oscillator based on waveguide RTD injection) may also be a tunable amplified terahertz filter. The center frequency can be adjusted by a DC bias voltage on the RTD 110, and the filter bandwidth can be adjusted by a variable power attenuator 310. An extremely wide bandwidth (e.g., less than 10 MHz to more than 1 GHz) and a range of center frequencies across the terahertz band can be achieved.

[0030] [Example 4: Waveguide RTD Injection Wireless Repeater] In some embodiments, a wireless communication system 400 utilizing device 100 can balance a desired data transmission rate with link directivity and link distance. Figures 4A and 4B schematically show exemplary wireless communication systems 400 according to some embodiments described herein. Operating at terahertz carrier frequencies may present further challenges of atmospheric absorption, which can limit the practical link range and data rates for various bands of terahertz wireless communication. Wireless repeaters are devices that act as intermediate receiver stations extending the total distance of wireless transmissions. The exemplary system 400 in Figures 4A and 4B includes an exemplary wireless repeater 410 (e.g., a terahertz injection wireless repeater) in the context of a typical terahertz wireless communication link according to some embodiments described herein. A terahertz transmitter 420 (e.g., a wireless transmitter) may include a terahertz emitter 422 and a first antenna / feed horn 422 configured to radiate a first terahertz wave 430 that carries encoded data across free space. An exemplary wireless repeater 410 may further include a second antenna / feed horn 412 configured to receive at least a portion of a terahertz wave 430 (e.g., input, external incident radiated signal 140) and allow the received portion to propagate through a waveguide to a waveguide separation element 130 (e.g., circulator 132 in Figure 4A, optical isolator 136 in Figure 4B), and a third antenna / feed horn 414 configured to receive an output radiated signal 150 from the waveguide separation element 130 and emit the output radiated signal 150 as a second terahertz wave 440 (e.g., amplified terahertz wave) having encoded information. The exemplary system 400 may further include a terahertz receiver 450 (e.g., a terahertz wireless receiver) comprising a fourth antenna / feed horn 452 configured to receive at least a portion of the second terahertz wave 440 and allow the received portion to propagate through a waveguide to a terahertz detector 454.Using the device 100 (e.g., an injected waveguide RTD amplifier) ​​in either a reflective geometry (Figure 4A) or a transmitted geometry (Figure 4B), the exemplary wireless repeater 410 in Figures 4A and 4B can radiate amplified terahertz waves along with encoded information to a terahertz wireless receiver 450.

[0031] In some embodiments, the wireless repeater 410 may have a sufficiently large amplification ratio (e.g., 40 dB) configured to address the challenges of atmospheric absorption for terahertz wireless communication systems. In contrast, a commercially available waveguide amplifier operating at approximately 260 GHz may provide a gain of approximately 25 dB.

[0032] In some embodiments, the wireless repeater 410 is configured for other types of terahertz wireless links besides communication. For example, a terahertz signal derived from an optical atomic clock can be used to wirelessly synchronize its position to the world's most accurate frequency standard. The exemplary wireless repeater 410 in Figures 4A and 4B (e.g., a waveguide RTD injection repeater) may be configured to boost power and therefore boost the link distance of such wireless clock signals.

[0033] In some embodiments, the wireless repeater 410 is configured for radio astronomy. Very faint signals from long distances in our world can be detected over long periods by large terahertz arrays (e.g., ALMA collaboration). The wireless repeater 410 in Figures 4A and 4B may be configured to boost interstellar signals, resulting in a higher signal-to-noise ratio and therefore a shorter averaging time (e.g., observation time) to achieve desired measurement accuracy.

[0034] [Example 5: Waveguide RTD Injection Subharmonic Mixer] Figure 5 schematically shows another exemplary device 500 (e.g., a terahertz subharmonic mixer) according to some embodiments described herein. The exemplary device 500 comprises a device 200 (e.g., a waveguide RTD injection multiplier) as schematically illustrated by Figure 2B and a basic mixer 510 (e.g., a subharmonic mixer). The LO input 520 of the exemplary device 500 can be connected to the input port 112 of the device 200, the output port 138 of the device 200 can optically communicate with the first input port 512 (e.g., the LO port) of the mixer 510, and the second input port 514 (e.g., the RF input port) can be configured to receive external terahertz radiation 530 (e.g., the RF input) and couple the external terahertz radiation 530 to the mixer 510. The mixer 510 may further include an output port 514 configured to emit a mixed signal 540 (e.g., an intermediate frequency or IF) which is a mixture of external terahertz radiation 530 received by a second input port 514 and a harmonic multiple of the LO input 520 received at input port 112. In some embodiments, the RTD 110 is configured to generate a coherent reference signal local oscillator for phase-sensing detection. Device 200 (e.g., a frequency multiplier) may be a component of the subharmonic mixer. Coherence of the reference signal is not required to realize the subharmonic mixer. However, if the reference signal is coherent, device 500 may be a phase-sensing detector.

[0035] In some embodiments, injection multiplication can be significantly more power-efficient than nonlinear harmonic generation. Only one harmonic is generated, determined by the DC bias voltage 120 of the RTD110. Harmonic injection can occur with a large power ratio, as long as the resulting bandwidth is sufficient. As a result, the sub-harmonic mixer 500 in Figure 5 can have significantly lower conversion losses than a terahertz sub-harmonic mixer that relies on nonlinear harmonic generation.

[0036] Figure 5 schematically illustrates a device 500 having a transparent geometry, but in some other embodiments, the device 500 may have a reflective geometry.

[0037] [Example 6: Terahertz Wireless Communication Demultiplexer] Figure 6 schematically shows an exemplary system 600 (e.g., a terahertz demultiplexing system) comprising a plurality of devices 300 (e.g., tracking oscillators) according to some embodiments described herein. The exemplary system 600 described herein may be configured to significantly increase the number of simultaneous wireless devices 300 to utilize many frequency channels. In such high-frequency multiplexed scenarios, the system 600 may be configured to isolate multiple wireless signals from one another. In some embodiments, the system 600 is configured to adjust the bandwidth of the devices 300 (e.g., amplify the filters) by controlling the DC bias voltage 120 to change the center frequency of the devices 300. In some embodiments, the system 600 may comprise a plurality of terahertz detectors (not shown), each of which communicates optically with a corresponding device 300 among the plurality of devices 300, and the system 600 is configured to demultiplex the plurality of terahertz communication signals to the plurality of terahertz detectors.

[0038] As schematically shown in Figure 6, an exemplary system 600 comprises a waveguide power splitter 610 having an input 612 (e.g., a receiver antenna / feed horn) configured to wirelessly receive a plurality of terahertz communication signals 620 having different frequencies (e.g., f1, f2, f3). The power splitter 610 further comprises a plurality of outputs 614 (e.g., output ports), which are configured to separate the terahertz communication signals 620 received at the input 612 and transmit them to the plurality of outputs 614, each output 614 receiving the corresponding terahertz communication signal 620 from the plurality of terahertz communication signals 620. The system 600 further comprises a plurality of devices 300 (e.g., waveguide RTD injection tracking oscillators) as described herein with respect to Figures 3A and 3B. Each device 300 of the plurality of devices 300 optically communicates with the corresponding output 614 from the plurality of outputs 614. For example, as schematically shown in Figure 6, the multiple terahertz communication signals 620 comprise three terahertz communication signals 620a to 620c, and the multiple devices 300 comprise three devices 300a to 300c arranged in parallel with each other. Each device 300 communicates optically with the corresponding outputs 614a to 614c of the power splitter 610, and the power splitter 610 separates and transmits the multiple terahertz communication signals 620a to 620c so that each output 614a to 614c receives the corresponding terahertz communication signals 620a to 620c, and each device 300a to 300c receives the corresponding terahertz communication signals 620a to 620c.

[0039] In some embodiments, as schematically shown in Figure 6, the corresponding bias voltages 120a to 120c of a plurality of devices 300 can be tuned to resonate at a predetermined carrier frequency to be filtered, so that each device 300a to 300c emits a corresponding one of a plurality of external terahertz wireless communication signals 620a to 620c. The variable attenuator 310 of the plurality of devices 300 can be adjusted to ensure a sufficiently narrow bandwidth so that only one frequency is filtered. Although the devices 300 are shown with reflective geometry in Figure 6, in some other embodiments, one or more of the devices 300 may have transmissive geometry.

[0040] In some embodiments, as schematically shown in Figure 6, the injection properties of device 300 (e.g., a tracking oscillator) allow the input wireless signal 620 to be made very weak, and a simple power splitter can be sufficient to separate the input wireless signal 620 to various devices 300 for subsequent detection (not shown). For example, the devices 300 in Figures 3A and 3B can be configured for a 10 MHz bandwidth with 40 dB injection amplification, which can enable frequency multiplexing of 5000 simultaneous wireless connections in a 50 GHz bandwidth corresponding to an absorption window in the carrier frequency range of 250-300 GHz.

[0041] In some embodiments, device 300 is a sub-component of system 600 and provides spectral filtering (e.g., frequency) and gain (e.g., power) of the RTD 110 via an injection-lock mechanism. Device 300, like device 100 (e.g., an injection-lock amplifier), can track the input frequency and output more power than the input. The power splitter 610 can send all three frequencies to all three output ports, thus reducing the amplitude entering each device 300. The amplitude can be further reduced by an attenuator to adjust the tracking bandwidth (e.g., via an injection-lock range). Since the output power of the RTD 110 is independent of the input power, amplification can occur to recover input power losses.

[0042] [Example 7: Multiplexed terahertz oscillator via optical mixing] Figure 7 schematically shows an exemplary system 700 configured for coherent detection of terahertz waves at harmonic frequencies according to several embodiments described herein. System 700 detects multiple terahertz frequencies that are different from each other (e.g., f a ,f b ,...,f N The system comprises multiple optically carried terahertz frequency sources 710 (e.g., optical terahertz sources 710a, 710b, ..., 710N) operating in a manner in which each terahertz frequency source 710 is configured to emit an optical signal at a corresponding terahertz frequency.

[0043] In some embodiments, the system 700 further comprises an optical coupler (not shown) configured to receive and merge optical signals from multiple terahertz frequency sources 710. For example, the optical coupler may include a multiplexer configured to multiplex the optical signals received from the multiple terahertz frequency sources 710 to generate multiple terahertz waves.

[0044] In some embodiments, the system 700 further comprises a waveguide photomixer 720 configured to receive merged optical signals from an optical coupler and convert the merged optical signals into terahertz radiated signals. As schematically shown in Figure 7, optical signals from multiple terahertz frequency sources 710 can be coupled in the optical domain and coupled to a single terahertz photomixer 720. The terahertz photomixer 720 can radiate terahertz frequencies of any frequency difference between optical lines within its bandwidth.

[0045] In some embodiments, the system 700 further comprises a waveguide power splitter 730 having an input port that optically communicates with the output of a photomixer 720, and the power splitter 730 further comprises a plurality of output ports. In some embodiments, the system 700 further comprises a plurality of devices 300 (e.g., waveguide RTD injection tracking oscillators), each device 300 optically communicating with a corresponding output port of the power splitter 730. Each device 300 (e.g., tracking oscillator) can be configured to filter and amplify a predetermined frequency component of terahertz radiation from a plurality of terahertz frequency sources 710. For example, each device 300 can be tuned to a corresponding center frequency and bandwidth by the corresponding DC bias voltage 120 of the device 300 and a variable terahertz attenuator 310.

[0046] In some embodiments, the photomixer 720 is configured to divide the radiated output power among many terahertz waves when multiplexed. Amplifying filters in device 300 (e.g., waveguide-injected terahertz tracking oscillators) can make multiplexing practical. In addition, device 300 can isolate and / or reject incident terahertz waves generated by optical mixing of optical frequencies from a separate terahertz frequency source 710. Although device 300 is depicted in Figure 7 as having a transmission injection geometry, in some other embodiments, one or more of the devices 300 have a reflection geometry.

[0047] [Example 8: Multiple Terahertz Wireless Communication System] Figure 8 schematically shows an exemplary system 800 (e.g., a frequency-multiplexed terahertz wireless communication system) according to some embodiments described herein. By constructing other devices and systems disclosed herein, exemplary system 800 can represent one of many possible configurations for a terahertz wireless communication system. Exemplary system 800 can utilize many of the exemplary devices described herein and can demonstrate the modularity of device 100 (e.g., an injected waveguide RTD amplifier).

[0048] System 800 uses multiple terahertz frequencies that are different from each other (for example, f a ,f b ,f c The system comprises multiple optically carried terahertz frequency sources 810 (e.g., optical terahertz sources 810a-810c) operating at a specific terahertz frequency, and the optical signal from each terahertz frequency source 810 is modulated (e.g., by modulators 820a-822c) in the corresponding data streams 822a-822c. For example, the exemplary system 800 in Figure 8 includes multiple optically carried terahertz sources 810a-810c, each operating at a specific terahertz frequency. The multiple terahertz frequency sources 810 may comprise multiple photomixer-based terahertz generators, each terahertz generator configured to produce two optical tones that are applied to a single mobile carrier photodiode. The optical signals from the terahertz frequency sources 810a-810c may be modulated to encode separate data streams 822a-822c.

[0049] In some embodiments, the system 800 further comprises a plurality of waveguide photomixers 830, each photomixer 830 configured to convert an optical signal from a corresponding terahertz frequency source 810 among a plurality of terahertz frequency sources 810 into terahertz radiation accompanied by a corresponding encoded data stream. For example, a photomixer 830 can be used to convert an optically carried terahertz wave and encoded information into terahertz radiation. The system 800 further comprises a plurality of devices 100, each device 100a to 100c configured to receive terahertz radiation from a corresponding photomixer 830 among the plurality of waveguide photomixers 830. The radiation from each photomixer 830 can be amplified by the corresponding devices 100a to 100c (e.g., waveguide RTD injection amplifiers) as described herein with respect to Figures 1A and 1B. The bias voltage 120 of each device 100a to 100c can be adjusted so that devices 100a to 100c are amplified at the carrier frequency of the respective optical terahertz operating frequency of the corresponding data channel. Although device 100 is depicted in Figure 8 as having a reflective geometry, in some other embodiments one or more devices 100 may have a transmissive geometry.

[0050] In some embodiments, the system 800 further comprises a waveguide power coupler 840 configured to couple amplified radiation from a plurality of devices 100, and a transmitting antenna / feed horn 842 configured to emit the coupled amplified radiation 850. The combined elements of the photomixer 830, the devices 100 (e.g., injection amplifiers), and the power coupler 840 can constitute a terahertz wireless communication frequency multiplexer.

[0051] The coupled amplified radiation 850 from the transmitting feedhorn / antenna 842 can propagate through free space (e.g., a multiplexed wireless link) to the receiver feedhorn / antenna 610 of system 600 (e.g., a terahertz wireless communication frequency demultiplexer), as described herein. The separated frequency channels can be connected to individual terahertz detectors 860, which can read out the corresponding data streams 822a-822c carried on each terahertz wave. The entire implementation of system 800 can constitute a frequency-multiplexed terahertz wireless communication network. The wireless link 850 of system 800 can operate within the 250 GHz-350 GHz atmospheric transmission window.

[0052] [Example 9: Waveguide RTD injection and absolute phase noise characterization method] Figure 9A schematically shows exemplary systems 900 (e.g., utilizing absolute injection PN) according to several embodiments described herein. Each exemplary system 900 utilizes a first terahertz frequency and a second terahertz frequency (e.g., f a ,f bThe system 900 further comprises first and second optically carried terahertz frequency sources 910a, 910b (e.g., optical terahertz sources) operating in a manner where the first and second terahertz frequencies are different from each other. The system 900 further comprises first and second waveguide photomixers 920a, 920b, the first photomixer 920a is configured to receive a first optical signal 912a from the first terahertz frequency source 910a and convert it into a first terahertz radiation, and the second photomixer 920b is configured to receive a second optical signal 912b from the second terahertz frequency source 910b and convert it into a second terahertz radiation. The system 900 further comprises devices 100, 200 comprising waveguide RTD 110, the devices 100, 200 are configured to receive the first terahertz radiation 912a and output amplified terahertz radiation. System 900 further comprises a mixer 930 (e.g., mixer 510) configured to receive amplified terahertz radiation and second terahertz radiation and emit an intermediate frequency (IF) output signal 932 in response to a mixture of the amplified terahertz radiation and second terahertz radiation. System 900 further comprises a phase noise analyzer 940 configured to receive the IF output signal 932 and generate information about the phase noise of the amplified terahertz radiation from devices 100, 200.

[0053] In some embodiments, the exemplary system 900 performs injection locking of the waveguide RTD 110 and method 950 for characterizing the absolute phase noise of the amplified terahertz radiation, according to some embodiments described herein. The injection amplification process is not the same as broadband amplification. As a result, residual noise can be imparted to the amplified terahertz radiation from the RTD 110.

[0054] Figure 9B is a flowchart of an exemplary method 950 according to some embodiments described herein. In operation block 952, method 950 includes injecting a first reference terahertz radiation signal into waveguide RTD 110. For example, a first optically carried terahertz frequency source 910a can optically communicate with a first photomixer 920a that can generate the first reference terahertz radiation signal. The RTD injection can be locked onto the first optically carried terahertz frequency source 910a.

[0055] In operation block 954, method 950 further includes applying a DC bias voltage 112 to the RTD 110 to adjust the oscillation frequency of the RTD 110 and establish an injection lock with a first reference terahertz radiation signal. For example, the first photomixer 920a can inject a first reference terahertz radiation signal into the waveguide RTD 110 (in the same manner as described, for example, with respect to the exemplary device 100 and Figure 1A). The DC bias voltage 112 of the waveguide RTD 110 can be adjusted to match the RTD frequency with the frequency of the first terahertz radiation generated by the first photomixer 920a.

[0056] In operation block 956, method 950 further includes mixing the amplified RTD output signal from RTD 110 (e.g., amplified terahertz radiation) with a second terahertz reference signal to form an intermediate frequency (IF) output signal in response to the mixing of the amplified RTD output signal and the second terahertz reference signal. For example, the amplified terahertz radiation output from device 100 can be input to the RF input of mixer 930 (e.g., a terahertz waveguide mixer), and the second terahertz radiation from a second photomixer 920b can be input to the LO input of mixer 930. The second terahertz radiation may be generated by a second photomixer 920b driven by a second optically carried terahertz frequency source 910b, which is frequency-shifted from a first optically carried terahertz frequency source 910a.

[0057] In operation block 958, method 950 further includes measuring the absolute phase noise of a first reference terahertz radiated signal. For example, mixing the amplified RTD output signal with a second terahertz reference signal can be done using mixer 930, and measuring the absolute phase noise of the first reference terahertz radiated signal may include inputting the IF output signal 932 from mixer 930 to phase noise analyzer 940. Phase noise analyzer 940 may include a dual-channel heterodyne detection system for cross-correlation.

[0058] In some embodiments, the resulting phase noise measured by the phase noise analyzer 940 may be a combination of the relative phase noise of the two optically carried terahertz sources 910a and 910b and the residual phase noise of the injection process. If the two optically carried terahertz sources 910a and 910b have similar phase noises, the absolute phase noise of the injected terahertz wave can be accurately measured by the phase noise analyzer 940.

[0059] This exemplary method 900 can be broadly applied not only to optical mixing sources but also to other terahertz oscillator sources. The reference oscillator (e.g., a second source 910b) may have a phase noise similar to or lower than that of the injection oscillator (e.g., a first source 910a). Furthermore, the geometry of the terahertz injection can be either transmitted or reflected, although only the reflected geometry is shown in Figure 9A.

[0060] Figure 9C plots the phase noise power spectral density (PSD) for an injected RTD and some injected power for a free-running RTD (upper trace), a dual-wavelength Brillouin laser (DWBL) (lower trace), and an exemplary system 900 as shown in Figure 9A. The injection reduces the phase noise of the free-running RTD but does not perfectly track the DWBL source. The resulting phase noise is residual injected noise that decreases with the injected power and offset frequency.

[0061] Figure 9D is a plot of the variation in the RTD injection lock frequency range with respect to the injection power ratio for the exemplary system 900 shown in Figure 9A. The reciprocal of the injection power ratio is the amplification ratio in logarithmic units. The white circles represent the lock range data confirmed from phase noise measurements. The solid line is a fit to the data excluding the maximum injection power ratio.

[0062] [Example 10: Waveguide RTD injection and residual phase noise characteristic evaluation method] Figure 10A is a schematic diagram of an exemplary system 1000 (e.g., utilizing residual injection PN) according to some embodiments described herein. The exemplary system 1000 comprises an optically carried terahertz frequency source 1010 (e.g., an optical terahertz source) which operates at terahertz frequencies and is configured to generate an optical signal 1012 at terahertz frequencies. The exemplary system 1000 further comprises an optical splitter 1013 configured to receive the optical signal 1012 from the terahertz frequency source 1010 and split it into a first portion 1012a and a second portion 1012b. The system 1000 further comprises first and second waveguide photomixers 1020a, 1020b, the first photomixer 1020a configured to receive the first portion 1012a of the optical signal 1012 from the terahertz frequency source 1010 and convert it into a first terahertz radiation. The system 1000 further comprises a frequency shifter 1025 configured to receive a second portion 1012b of an optical signal 1012 from a terahertz frequency source 1010, frequency shift the second portion 1012b, and transmit the frequency-shifted second portion 1012b to a second photomixer 1020b configured to receive the frequency-shifted second portion 1012b and convert it into a second terahertz radiation.

[0063] System 1000 further comprises devices 100, 200, each having a waveguide RTD 110, configured to receive a first terahertz radiation and output amplified terahertz radiation. System 1000 further comprises a mixer 1030 (e.g., mixer 510) configured to receive the amplified terahertz radiation and a second terahertz radiation and to emit an intermediate frequency (IF) output signal 1032 (e.g., data under test or DUT) in response to a mixture of the amplified terahertz radiation and the second terahertz radiation. System 1000 further comprises a phase noise analyzer 1040 configured to receive the IF output signal 1032 and generate a reference signal 1042 indicating the residual phase noise of the amplified terahertz radiation from devices 100, 200. System 1000 further comprises a synthesizer 1045 configured to receive the reference signal 1042 and transmit a control signal to a frequency shifter 1025.

[0064] In some embodiments, the exemplary system 1000 performs injection locking of the waveguide RTD 110 and method 1050 for characterizing the residual phase noise of the waveguide RTD 110, according to some embodiments described herein. The injection amplification process is not the same as broadband amplification. As a result, residual noise can be imparted to the terahertz radiated signal amplified from the RTD 110.

[0065] Figure 10B is a flowchart of an exemplary method 1050 according to several embodiments described herein. In operation block 1052, method 1050 includes generating a terahertz reference signal 1012. In operation block 1054, method 1050 further includes splitting the terahertz reference signal into a first part 1012a and a second part 1012b. In operation block 1056, method 1050 further includes applying a frequency shift to the second part 1012b using a frequency synthesizer 1045 (e.g., using a frequency shifter 1025 and a frequency synthesizer 1045). The frequency shifter 1045 may comprise a direct digital synthesizer (DDS) driven by a microwave clock.

[0066] In operation block 1058, method 1050 further includes injecting an unshifted first portion 1012a of the terahertz reference signal 1012 into the waveguide RTD 110. For example, an optically carried terahertz frequency source 1010 can optically communicate with a first photomixer 1020a that can generate terahertz radiation to inject into the waveguide RTD 110 (in the same manner as described herein with respect to exemplary device 100 and Figure 1A).

[0067] In operation block 1060, method 1050 further includes mixing the amplified RTD output signal from waveguide RTD 110 with a frequency-shifted second section 1012b in the terahertz waveguide mixer 1030. The LO input of the terahertz waveguide mixer 1030 can be connected to a second terahertz photomixer 1020b, which can be driven by the frequency-shifted second section 1012b.

[0068] In operation block 1062, method 1050 further includes analyzing the resulting IF signal 1032 from mixer 1030 using a phase noise analyzer 1040 synchronized with frequency synthesizer 1045 to determine the residual phase noise introduced by injecting the unshifted first portion of the terahertz reference signal into waveguide RTD 110. For example, phase noise analyzer 1040 may refer to the same optical terahertz frequency source 1010 that drives the optically carried terahertz frequency shifter 1025. The DC bias voltage 112 of waveguide RTD 110 can be adjusted to match the RTD frequency with the input terahertz radiation frequency generated by the first photomixer 1020a. The RTD injection can be locked onto optical terahertz frequency source 1010. The resulting phase noise measured by phase noise analyzer 1040 may be the residual phase noise of the injection process. This exemplary method can be broadly applied to other terahertz oscillator sources as well as optically mixed ones. Furthermore, the geometry of the terahertz injection can be either transmitted or reflected, even if only reflection is shown in Figure 10.

[0069] [Example 11: Waveguide RTD injection and high-speed phase modulation] Figures 11A and 11B schematically show exemplary devices 1100 (e.g., a high-speed voltage-controlled phase modulator) according to some embodiments described herein. Device 1100 comprises a device 100 having a waveguide RTD 110 (e.g., as described herein in relation to Figures 1A and 1B), the device 100 is configured to receive an input signal 1110 and emit an output signal 1120. Device 1100 further comprises a bias T 1130 configured to receive a modulated signal 1142 from an arbitrary modulation source 1140, receive a DC signal 1152 from an independent DC power supply 1150, emit an AC bias voltage 1132, and transmit the AC bias voltage 1132 to the RTD 110.

[0070] When a source injects RTD110 (regardless of the injection geometry), a phase lock occurs between the source and the RTD radiation. The phase difference between the source and the RTD radiation can be controlled by adjusting the bias voltage 1132 of RTD110. A phase difference (e.g., up to ±π / 2) can be generated during the injection lock. Therefore, fast modulation of the RTD bias voltage 1132 can generate fast modulation of the output phase of the RTD radiation. Large modulation depths (e.g., up to π radians) can be achieved without breaking the injection lock. The modulation bandwidth can be limited by the RTD response, which is electrically equal to the radiation frequency (e.g., greater than 100 GHz). The realized phase modulator can be independent of the injection source and therefore general-purpose. Figures 11A and 11B schematically show the device 1100 (e.g., an injection phase modulator) in reflection and transmission geometry, respectively. Bias T1130 can be used to provide the bias voltage 1132 to RTD110. DC power supply 1150 provides slow control over the RTD bias voltage 1132 to maintain injection lock and adjust the overall phase shift between the source and RTD radiation at output 1120. Modulation source 1140 can be coupled to RTD 110 via the RF port of bias T1130, and modulation signal 1142 can provide modulation to be written to the RTD radiation.

[0071] [Example 12: Waveguide RTD injection and high-speed intensity modulation] Figures 12A and 12B schematically show an exemplary device 1200 (e.g., a high-speed voltage-controlled intensity modulator) according to some embodiments described herein. Device 1200 includes a device 1100 located on one arm of a Mach-Zehnder interferometer 1210. The interferometer 1210 includes a waveguide power splitter 1212 (e.g., 50:50) configured to receive and split an input signal 1110, with a first portion of the input signal 1110 propagating through the first arm of the interferometer 1210 and acquiring a phase shift by device 1100, and a second portion of the input 1110 propagating through the second arm of the interferometer 1210 without acquiring a phase shift. The interferometer 1210 further includes a 50:50 power coupler 1214 configured to recombine the first and second portions to produce an output signal 1220. In recombination, the first and second parts interfere to generate amplitude modulation of the original input 1110. The amplitude modulation is written to the RTD 110 via the modulation signal 1142 from the modulation source 1140, and the bias voltage 1132 from the bias T 1130 is supplied to the RTD 110. The DC voltage 1152 from the DC power supply 1150 maintains injection and phase difference so that amplitude modulation of output 1220 occurs. The realized intensity modulator, like the realized phase modulator in Figures 11A and 11B, is versatile in terms of source compatibility and can be fast in terms of bandwidth. Figures 12A and 12B show the device 1200 (e.g., the injection intensity modulator) in reflective and transmitted geometry, respectively.

[0072] Exemplary, non-limiting experimental data are included herein to illustrate the results achievable by various embodiments of the systems and methods described herein. All data ranges shown in the figures or described in the specification, and all values ​​within such data ranges, are expressly included in this disclosure. Exemplary experiments, experimental data, tables, graphs, plots, figures, and processing and / or operating parameters (e.g., values ​​and / or ranges) described herein are intended to be illustrative of the operating conditions of the disclosed systems and methods, and are not intended to limit the range of operating conditions for various embodiments of the methods and systems disclosed herein. In addition, the experiments, experimental data, computational data, tables, graphs, plots, figures, and other data disclosed herein demonstrate various regimes in which embodiments of the disclosed systems and methods may operate effectively to produce one or more desired results. Such operating regimes and desired results are not limited to, for example, specific values ​​of operating parameters, conditions, or results shown in tables, graphs, plots, or figures, but also include preferred ranges that include or extend to these specific values. Accordingly, the values ​​disclosed herein include ranges of values ​​between any of the values ​​listed or shown in tables, graphs, plots, figures, etc. In addition, the values ​​disclosed herein include a range of values ​​above or below any of the values ​​listed or shown in tables, graphs, plots, figures, etc., as can be demonstrated by other values ​​listed or shown in tables, graphs, plots, figures, etc. Also, while the data disclosed herein may establish one or more effective operating ranges and / or one or more desired results for a particular embodiment, it should be understood that not all embodiments are required to be operable within their respective such operating ranges or to produce their respective such desired results. Furthermore, other embodiments of the disclosed systems and methods may operate in and / or produce other operating regimes other than those shown and described herein with reference to exemplary experiments, experimental data, tables, graphs, plots, figures, and other data herein.

[0073] The present invention has been described in several non-limiting embodiments. It should be understood that the embodiments are not mutually exclusive, and elements described in relation to one embodiment can be combined with, rearranged from, or excluded from other embodiments in a manner suitable for achieving the desired design objective. A single feature or group of features may or may not be required in each embodiment. Those skilled in the art can conceive of various modifications and applications without departing from the true spirit and scope of the invention. Therefore, for example, in any method or process disclosed herein, the actions or operations constituting the method / process may be performed in any preferred order, and are not necessarily limited to any particular disclosed order. Features or elements from the various embodiments and examples described above can be combined with each other to produce alternative configurations suitable for the embodiments disclosed herein.

[0074] For the purpose of summarizing the present invention, several aspects, advantages, and novel features of the present invention are described herein. However, it should be understood that not all such advantages are necessarily achieved according to any particular embodiment. Thus, the present invention may be embodied or performed to achieve one or more advantages without necessarily achieving other advantages that may be taught or suggested herein.

[0075] As used herein, any reference to “one embodiment” or “several embodiments” or “embodiment” or “several embodiments” means that a particular element, feature, structure, or characteristic described in relation to an embodiment is included in at least one embodiment. Occurrences of the phrase “in one embodiment” or “in several embodiments” in various places herein do not necessarily all refer to the same embodiment. In particular, conditional language used herein, such as “can,” “could,” “might,” “may,” and “eg,” is generally intended to convey that some embodiments include certain features, elements, and / or steps, while others do not, unless otherwise specifically stated or understood differently in the context in which they are used. Furthermore, the articles “a,” “an,” or “the” used in this application and the appended claims should be interpreted as meaning “one or more” or “at least one,” unless otherwise specified.

[0076] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof are non-restrictive terms intended to include non-exclusive inclusions. For example, a process, method, article, or apparatus comprising a list of elements is not necessarily limited to those elements alone and may include other elements not expressly enumerated or specific to such process, method, article, or apparatus. Furthermore, unless the opposite is expressly stated, “or” means neither inclusive nor exclusive. For example, condition A or condition B is satisfied by either A being true (or existing) and B being false (or not existing), A being false (or not existing) and B being true (or existing), or both A and B being true (or existing). As used herein, the phrase “at least one of” in a list of items refers to any combination of those items, including a single member. For example, “at least one of A, B, or C” is intended to include A, B, C, A and B, A and C, B and C, and A, B and C. Connecting language such as “at least one of X, Y, and Z” is understood separately in contexts where it is commonly used to indicate that an item, term, etc., may be at least one of X, Y, or Z, unless otherwise specified. Thus, such connecting language is generally not intended to imply that a particular embodiment requires the presence of at least one of X, at least one of Y, and at least one of Z, respectively.

[0077] Words of degree as used herein, such as “approximately,” “about,” “roughly,” and “substantially,” describe a value, quantity, or characteristic that is close to the stated value, quantity, or characteristic that still performs the desired function or achieves the desired result. For example, the terms “approximately,” “about,” “roughly,” and “substantially” may refer to a quantity that is within ±10%, ±5%, ±2%, ±1%, or ±0.1% of the stated quantity. The scope disclosed herein also includes any overlap, sub-scopes, and combinations thereof. Words such as “maximum,” “at least,” “greater than,” “less than,” and “between” include the listed numbers. Where used herein, the meanings of “a,” “an,” and “said” include multiple references unless the context explicitly indicates otherwise. Structures and / or methods are discussed herein with respect to elements labeled by ordinal numbers (e.g., 1st, 2nd, etc.), but ordinal numbers are used only as labels to distinguish one element from another, and are not used to indicate the order of these elements or their use.

[0078] Therefore, although only specific embodiments have been described herein, it will be apparent that numerous modifications can be made without departing from the spirit and scope of the invention. Furthermore, acronyms are used solely to enhance the readability of the specification and claims. It should be noted that these acronyms are not intended to diminish the generality of the terminology used, and the claims should not be construed as limiting them to the embodiments described herein.

Claims

1. A waveguide resonant tunnel diode (RTD) that oscillates at terahertz (THz) frequencies, A DC power supply electrically coupled to the RTD and providing a DC bias voltage to the RTD, The RTD is operably connected to a waveguide isolation element, The RTD is a device characterized by generating and emitting an output radiation signal having a second frequency when it is injected and locked onto an externally incident radiation signal having a first frequency.

2. The device according to claim 1, characterized in that the RTD operates within a frequency range of 100 GHz to 1 THz.

3. The device according to claim 1, characterized in that the waveguide separation element is a three-port circulator comprising an injection port for receiving the external incident radiation signal and an output port for directing the output radiation signal away from the injection port.

4. The device according to claim 1, characterized in that the waveguide isolation element is an optical isolator comprising an input port for receiving a radiated signal from the RTD and an output port for emitting the output radiated signal.

5. The device according to claim 1, characterized in that the RTD is mounted in a waveguide package that maximizes power extraction efficiency.

6. The device according to claim 1, characterized in that the DC bias voltage is adjusted to adjust the oscillation frequency of the RTD, the RTD prevents undesirable feedback and maintains injection lock stability, and the output radiated signal is amplified compared to the externally incident radiated signal.

7. The device according to claim 1, characterized in that the DC bias voltage is adjusted so that the RTD oscillates at an integer multiple of the first frequency, thereby generating harmonic frequency signals of the external incident radiation signal.

8. The device according to claim 7, characterized in that the DC bias voltage is adjusted so that the RTD generates a second harmonic signal of the external incident radiation signal.

9. The device according to claim 7, wherein the RTD is mounted within a waveguide package, the package comprising an input port and an output port, the input port having a waveguide dimension larger than the waveguide dimension of the output port, and the package is adapted to higher input frequencies and facilitates harmonic locking.

10. The RTD is further operably coupled to a variable power attenuator that controls the amplitude of the external incident radiation signal, The device according to claim 1, characterized in that the tracking bandwidth of the RTD is determined by the ratio of the input power of the external incident radiated signal to the oscillation power of the RTD, enabling frequency tracking within the injection lock frequency range.

11. THz radiation source and THz emission detector and The device according to claim 1, A first wireless link between the THz radiation source and the device, A wireless communication system comprising a second wireless link between the device and the THz radiation detector, The aforementioned RTD functions as a THz repeater, receiving, amplifying, and retransmitting THz signals from a THz radiation source, thereby extending the communication range of the system.

12. The device according to claim 1, A device characterized by comprising a waveguide mixer that receives and processes the subharmonic multiples of the incident radiated signal.

13. Waveguide power splitter, An input section that wirelessly receives multiple THz communication signals having different frequencies, A waveguide power splitter having multiple outputs, each output having a THz communication signal received at the input, which is separated and transmitted to the multiple outputs, and each output of the multiple outputs receives the corresponding THz communication signal from the multiple THz communication signals, A system comprising a plurality of devices according to claim 3, wherein each of the plurality of devices comprises a device that optically communicates with a corresponding output among the plurality of outputs and tracks and amplifies the respective THz frequency channel.

14. The system according to claim 13, comprising a plurality of THz detectors, each of the plurality of THz detectors further comprising a plurality of THzs that optically communicate with a corresponding device among the plurality of devices, wherein the system demultiplexes the plurality of THz communication signals to the plurality of THz detectors.

15. A plurality of THz frequency sources operating at multiple different THz frequencies, wherein each of the plurality of THz frequency sources emits an optical signal at the corresponding THz frequency, An optical coupler configured to receive and merge optical signals from multiple THz frequency sources, A waveguide photomixer that receives the merged optical signal and converts the merged optical signal into a THz radiated signal, A waveguide power splitter having an input port for optical communication with the output of the photomixer, the power splitter further having a plurality of output ports, A system comprising a plurality of devices according to claim 3, wherein each of the plurality of devices communicates optically with a corresponding output port of the power splitter and filters and amplifies predetermined frequency components of THz radiation from a plurality of THz frequency sources.

16. A plurality of terahertz frequency sources operating at multiple different THz frequencies, wherein the optical signals from each of the plurality of THz frequency sources are modulated by a corresponding data stream, A plurality of waveguide photomixers, each photomixer of the plurality of waveguide photomixers converts the optical signal from a corresponding THz frequency source among the plurality of THz frequency sources into a THz radiation having a corresponding encoded data stream, A system comprising a plurality of devices according to claim 1, wherein each of the plurality of devices is tuned to amplify at the corresponding carrier frequency of the corresponding data channel.

17. The system according to claim 16, wherein the plurality of THz frequency sources comprises a plurality of photomixer-based THz generators, each THz generator generating two optical tones that are applied to a single mobile carrier photodiode.

18. The system according to claim 16, further comprising a wireless link operating within a 250 GHz to 350 GHz atmospheric transmission window.

19. A method for injecting and locking a waveguide RTD and characterizing the absolute phase noise of the resulting THz radiation, The steps include injecting a first reference THz radiated signal into a waveguide RTD, The steps include applying a DC bias voltage to the RTD to adjust the oscillation frequency of the RTD and establishing an injection lock with the first reference THz signal, The steps include: mixing the amplified RTD output signal from the RTD with a second THz reference signal to form an intermediate frequency (IF) output signal in response to the mixing of the amplified RTD output signal and the second THz reference signal; A method characterized by comprising the step of measuring the absolute phase noise of the first reference THz radiated signal.

20. The method according to 19, characterized in that the step of mixing the amplified RTD output signal with the second THz reference signal is performed using a mixer, and the step of measuring the absolute phase noise of the first reference THz radiated signal is performed by inputting the IF output signal from the mixer to a phase noise analyzer.

21. The method according to 20, characterized in that the phase noise analyzer includes a dual-channel heterodyne detection system for cross-correlation.

22. A method for injecting and locking a waveguide RTD and characterizing the residual phase noise of the waveguide RTD, The steps include generating a THz reference signal and The steps include dividing the THz reference signal into a first part and a second part, The steps include applying a frequency shift to the second portion using a frequency synthesizer, The steps include injecting a waveguide RTD into the first portion of the THz reference signal, The steps include mixing the amplified RTD output signal from the waveguide RTD with the second portion that has been frequency-shifted in the waveguide mixer, A method characterized by comprising the step of analyzing the IF signal obtained from the waveguide mixer using a phase noise analyzer synchronized with the frequency synthesizer, and determining the residual phase noise introduced by injecting the first portion of the THz reference signal into the waveguide RTD.

23. The method according to 22, characterized in that the step of applying the frequency shift comprises the step of using a frequency synthesizer.

24. The method according to 23, characterized in that the frequency synthesizer is a direct digital synthesizer (DDS) driven by a microwave clock.

25. A device according to claim 1 that receives an input signal and emits an output signal, A device comprising a bias T that receives a modulated signal from a modulation source and a DC signal from a DC power supply, emits a bias voltage, and transmits an AC bias voltage to the RTD of the device, wherein the AC bias voltage generates phase modulation in the output signal.

26. The device according to claim 25, The device comprises a Mach-Zehnder interferometer having a first arm and a second arm, wherein the device is incorporated inside the first arm. The aforementioned interferometer is A waveguide power splitter that receives the input signal and splits the input signal into a first part and a second part, wherein the first part propagates through the first arm and acquires a phase shift, and the second part propagates through the second arm and does not acquire a phase shift, A device characterized by comprising a waveguide power coupler that recombines the first part and the second part to generate an output signal.

Images