Terahertz direct modulator with low insertion loss

Abstract

The invention discloses a low-insertion-loss terahertz direct modulator, relates to the technical field of terahertz communication, and solves the technical problem that low insertion loss and large modulation depth are difficult to realize on the terahertz direct modulator at the same time due to the fact that the prior art is limited by the influence of the performance and parasitic parameters of a transistor. The antenna comprises a transmission waveguide and a feed-in resonance structure, the feed-in resonance structure penetrates through the long edge of the transmission waveguide in the direction perpendicular to the two ends of the transmission waveguide, and the feed-in resonance structure comprises a substrate, feed-in units arranged at the two ends of the substrate and a resonance unit arranged between the feed-in units. The resonance unit comprises a fin line structure, semiconductor regulation and control devices and metal resonance structures, the semiconductor regulation and control devices are nested at two sides of the fin line structure, and the metal resonance structures are arranged at two sides of the fin line structure and are used for adjusting a resonance mode into a required mode and restraining a surrounding field near a fin line; according to the invention, low insertion loss and large modulation depth can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz communication, and in particular to a low-insertion-loss terahertz direct modulator. Background Art

[0002] In recent years, with the gradual maturity of the fifth generation mobile communication technology (5G) and the widespread promotion and use of commercial applications. A large number of applications with extremely high latency performance requirements have emerged, which far exceeds the support capacity of 5G. It is expected that the capacity of 5G technology will reach its limit by 2030 and beyond. Therefore, it is urgent to develop the sixth generation mobile communication system (6G) with higher transmission rate, ultra-low latency, high spectrum efficiency, high coverage, and high mobility. Terahertz waves have become an important choice for high-speed communication carriers for the next generation of 6G mobile communications due to their ultra-high bandwidth and high-speed transmission capabilities. Terahertz direct modulation technology has been proven to be an effective, minimalist, low-power, high-rate modulation method without AD / DA. The modulation type currently targeted by terahertz direct modulation technology is OOK modulation, so the modulation depth and insertion loss of the device directly affect the modulation effect and power consumption of the modulator. However, the existing terahertz direct modulator is limited by the performance of the transistor itself and the influence of parasitic parameters, and it is difficult to achieve low insertion loss and large modulation depth at the same time, which makes the insertion loss of the current waveguide terahertz modulator generally greater than 3dB and the modulation depth less than 99%. Summary of the invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a low insertion loss terahertz direct modulator to solve the technical problem that the prior art is limited by the performance of the transistor itself and the influence of parasitic parameters, and it is difficult to achieve low insertion loss and large modulation depth on the terahertz direct modulator at the same time.

[0004] The present invention realizes the regulation of Schottky diodes through voltage changes, forms a strong resonance state on the transmission structure, and achieves the effect of amplitude modulation of terahertz waves. By overall designing the resonance structure, transmission structure, and filtering structure, a composite resonance structure is formed, and extremely low insertion loss and extremely high modulation depth are achieved at the same time. The terahertz amplitude direct modulator designed based on this principle can work under normal temperature, normal pressure and non-vacuum conditions. The portability of the working frequency band is high and the device packaging is relatively easy, so it can be widely used in various scenarios.

[0005] A low insertion loss terahertz direct modulator comprises a transmission waveguide and a feeding resonant structure, wherein the feeding resonant structure penetrates the wide side of the transmission waveguide in a direction perpendicular to the waveguide mouth surface, the feeding resonant structure comprises a substrate, feeding units arranged at both ends of the substrate, and a resonant unit arranged between the feeding units, the resonant unit comprises a fin line structure, a semiconductor control device and a metal resonant structure, the semiconductor control device is nested on the fin line structure, the metal resonant microstructure is designed on both sides of the fin line structure to adjust the resonant mode to a required mode, and constrain the surrounding field near the fin line, and the metal resonant microstructure also realizes impedance matching between the part of the fin line after the semiconductor control device is loaded and the filter part, the fin line structure, the semiconductor control device and the metal resonant microstructure together constitute a modulation unit, the switch of the semiconductor control device realizes the mode conversion of the modulation part, and performs amplitude modulation on the terahertz wave coupled to the modulation unit.

[0006] Furthermore, the transmission waveguide includes a standard waveguide and a reduced height waveguide, wherein the standard waveguide is arranged at both ends of the reduced height waveguide, and the standard waveguide is used to match the size of the front-stage source and the rear-stage demodulation waveguide, so that the terahertz wave therein is mainly in the form of TE 10 Mode TE in the rectangular waveguide main mode 10 The TE mode is the most important mode in a rectangular waveguide. This mode has the characteristics of fixed and stable polarization direction. The field is only related to the coordinate x and has nothing to do with the coordinate y, that is, it has nothing to do with the narrow side dimension b. Therefore, by reducing b, materials can be saved and weight can be reduced; TE 10 The mode is the lowest mode in the rectangular waveguide, also called the main mode, with the lowest cutoff frequency. Single-mode transmission can be achieved by designing the waveguide size. The height of the waveguide is reduced to match the impedance of the standard waveguide and the feeding resonant structure, so that the terahertz wave can be better transformed from the waveguide mode to the on-chip transmission mode.

[0007] Furthermore, when the semiconductor control device is a diode, the cathode and anode of the diode are respectively placed on the metal on both sides of the fin line structure, with a total number of M, M≥2, and the anodes of the multiple diodes are on the same side, and the cathodes are on the same side, in a parallel connection mode. The number of diodes and the distance between each diode can be adjusted to better adjust the amplitude to meet the design requirements.

[0008] Furthermore, the semiconductor control device is any one of a GaAs Schottky diode, a PIN diode, and a metal oxide semiconductor.

[0009] Furthermore, the feeding unit is a low-pass filter circuit, which realizes the input of the intermediate frequency modulation signal and suppresses the leakage of the high-frequency terahertz wave. The external modulation signal is input by the feeding filter structure and loaded into the diode in the modulation unit through the feeding-filter structure.

[0010] Furthermore, the low-pass filter of the feeding unit is a compact microstrip resonant CMRC filter.

[0011] Furthermore, the material of the substrate is any one of sapphire, silicon dioxide, high-resistance silicon, gallium arsenide or silicon carbide.

[0012] Furthermore, the metal material involved is Au, Ag, Cu, or Al.

[0013] Working mechanism and design method of the present invention:

[0014] By designing the resonant unit to construct resonant states with different mode characteristics, the switching of conduction / isolation of terahertz waves is realized with the participation of Schottky diodes. During the design process, the port comprehensive optimization of the unit structure is carried out through the field-circuit fusion method, and the metal resonant microstructure is optimized according to the design goals. Finally, extremely low insertion loss transmission and high-speed conversion between high-Q value resonances are achieved in controllable elements such as fin-line structures, metal resonant microstructures and Schottky diodes.

[0015] The terahertz wave is input through a standard waveguide, and after the impedance matching of the height-reducing waveguide is used for mode conversion, the terahertz wave is converted from the waveguide mode to the quasi-TEM mode in the fin line. The terahertz wave mainly passes through the fin line gap. Diodes are loaded on both sides of the fin line, and a metal resonant microstructure is designed outside the fin line structure. At this time, the diode, the fin line structure, and the metal resonant microstructure together constitute a modulation unit, and the diode is controlled on and off by an external voltage:

[0016] When the diode is in the off state, the terahertz wave is transmitted from the fin line gap, and the terahertz wave is transmitted through the height-reduced waveguide and the standard waveguide at the output end;

[0017] When the diode is in the on state, the diode and the fin structure form an "H"-shaped microstructure, and the metal resonant microstructure outside the fin structure also participates in the resonance. A strong resonance is formed between the two, and the terahertz wave cannot pass through. Based on this, the amplitude of the terahertz wave can be controlled by controlling the on and off of the diode through voltage. In this process, the modulation signal is always loaded onto the diode through feeding, filtering, and the metal resonant microstructure and modulated by the terahertz carrier. At the same time, the impedance matching of the feeding-filtering part and the diode-fin part is achieved by adjusting the metal resonant microstructure, thereby ensuring the integrity of the fed modulation signal and ultimately achieving high-speed direct amplitude modulation.

[0018] The beneficial effects of the present invention include:

[0019] (1) The composite resonant structure adopted in the present invention can effectively achieve overall matching between the modulation feed unit and the modulation unit, thereby reducing the loss while improving the resonant Q value, and achieving low insertion loss and large modulation depth;

[0020] (2) The feed-in resonant structure of the present invention effectively realizes the construction of input field distribution, and can be combined with GaAs Schottky diodes to achieve efficient and high-speed direct modulation;

[0021] (3) The comprehensive matching design method of the resonant unit and the feeding unit adopted in the present invention reduces the influence of parasitic parameters on the transmission of terahertz waves, reduces the loss of terahertz wave transmission, and effectively ensures the high Q value and low loss characteristics of the resonant unit;

[0022] (4) The present invention has strong plasticity, and the position of the strong resonance frequency band can be effectively adjusted by adjusting the spacing, position, and size of the fin line structure of each diode;

[0023] (5) The two-dimensional planar structure used in the present invention can be realized by micro-machining, and the process is mature and easy to manufacture;

[0024] (6) The present invention works by electronic control without the need for external excitation such as light or temperature, and the feeding method can directly use a coaxial interface for feeding, which is conducive to the miniaturization, practicality and production of the device;

[0025] (7) The present invention is directed to waveguide propagation of terahertz electromagnetic waves, can operate under normal temperature, normal pressure, and non-vacuum conditions, and is easy to package and convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a structural diagram of a low insertion loss terahertz direct modulator involved in an embodiment of the present application.

[0027] Figure 2 This is a top view of a low insertion loss terahertz direct modulator involved in an embodiment of the present application.

[0028] Figure 3 The test result S in the conduction / isolation state involved in the embodiment of the present application 21 Parameter diagram.

[0029] Figure 4 This is a graph of single-tone test results at 1 GHz, 10 GHz, 20 GHz and 25 GHz involved in the embodiments of the present application.

[0030] Figure 5 This is the 141 GHz eye diagram test result involved in the embodiments of the present application.

[0031] Figure 6 This is the schematic diagram of OOK modulation.

[0032] Reference numerals

[0033] 1-standard waveguide, 2-resonance unit, 21-fin line structure, 22-semiconductor control device, 23-metal resonant microstructure, 3-feeding unit, 4-reduced height waveguide. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0035] Example 1

[0036] The modulation type currently targeted by terahertz direct modulation technology is OOK modulation, so the modulation depth and insertion loss of the device directly affect the modulation effect and power consumption of the modulator. OOK (On-Of Keying), on-off keying. Figure 6 As shown in the figure, Vm(t) is the digital signal to be sent, Acos(2mfct) is the unmodulated carrier, and VAM(t) is the carrier signal modulated by OOK. The modulation principle of OOK is to control one amplitude to be 0 and the other amplitude to be non-zero, which is OOK. Also known as binary amplitude keying (2ASK), it uses a unipolar non-return-to-zero code sequence to control the opening and closing of the sinusoidal carrier.

[0037] The present invention realizes the regulation of Schottky diodes through voltage changes, forms a strong resonance state on the transmission structure, and achieves the effect of amplitude modulation of terahertz waves. By overall designing the resonance structure, transmission structure, and filtering structure, a composite resonance structure is formed, and extremely low insertion loss and extremely high modulation depth are achieved at the same time. The terahertz amplitude direct modulator designed based on this principle can work under normal temperature, normal pressure and non-vacuum conditions. The portability of the working frequency band is high and the device packaging is relatively easy, so it can be widely used in various scenarios.

[0038] A low insertion loss terahertz direct modulator, such as Figure 1-2As shown in the figure, it includes a transmission waveguide and a feeding resonant structure. The feeding resonant structure penetrates the wide side of the transmission waveguide in a direction perpendicular to the waveguide port surface. The feeding resonant structure includes a substrate, feeding units 3 provided at both ends of the substrate, and resonant units 2 provided between the feeding units 3. The resonant unit 2 includes a finline structure 21, a semiconductor control device 22, and a metal resonant structure. The semiconductor control device 22 is nested on the finline structure 21. Metal resonant microstructures 23 are designed on both sides of the finline structure 21 to adjust the resonant mode to the required mode, and to confine the surrounding field near the finline. At the same time, the metal resonant microstructures 23 also achieve impedance matching between the part after the finline is loaded with the semiconductor control device 22 and the filter part. The finline structure 21, the semiconductor control device 22, and the metal resonant microstructures 23 together constitute a modulation unit. The switching of the semiconductor control device 22 realizes the mode conversion of the modulation part, and amplitude-modulates the terahertz wave coupled to the modulation unit. Specifically, the metal resonant microstructures 23 are cross-shaped, and the overall structure presents a shape similar to the character "丰" (Feng). This design method provides more dimensions for the matching of terahertz frequency and intermediate frequency, and can achieve lower insertion loss and higher switching ratio.

[0039] The transmission waveguide includes a standard waveguide 1 and a height-reduced waveguide 4. The standard waveguide 1 is provided at both ends of the height-reduced waveguide 4. The standard waveguide 1 is used to match the sizes of the pre-stage source and the post-stage demodulation waveguide, so that the terahertz wave in it mainly propagates in the TE10 mode in the rectangular waveguide main mode. The TE10 mode is the most important mode in the rectangular waveguide. This mode has the characteristics of a fixed and stable polarization direction. And the field is only related to the coordinate x and has nothing to do with the coordinate y, that is, it has nothing to do with the narrow-side dimension b. Therefore, materials can be saved and the weight can be reduced by reducing b; the TE10 mode is the lowest mode in the rectangular waveguide, also known as the main mode, and has the lowest cut-off frequency. Single-mode transmission can be achieved through the design of the waveguide size. The height-reduced waveguide 4 performs impedance matching on the standard waveguide 1 and the feeding resonant structure, so that the terahertz wave is better transformed from the waveguide mode to the on-chip transmission mode.

[0040] In the coplanar waveguide modulation, the side resonant feeder of the coplanar waveguide is grounded through a metal block, and the central feeder is connected to the feeding filter area through a metal wire to feed the control signal.

[0041] The semiconductor control device 22 is a diode. The cathode and anode of the diode are respectively placed on the metals on both sides of the finline structure 21, with a total of M, M≥2. The anodes of multiple diodes are on the same side, and the cathodes are on the same side, and are connected in parallel. The number of diodes and the distance between each diode are adjustable to better adjust the amplitude to meet the design requirements.

[0042] The diode is a GaAs Schottky diode.

[0043] The feeding unit 3 is a low-pass filter circuit, which realizes the input of low-frequency debugging signals and suppresses the leakage of high-frequency terahertz waves. The external modulation signal is input by the feeding filter structure and loaded into the diode in the modulation unit through the feeding-filter structure.

[0044] The low-pass filter of the feeding unit 3 is a compact microstrip resonant CMRC filter.

[0045] The material of the substrate is sapphire.

[0046] The metal material involved is Au, Ag, Cu, or Al.

[0047] The working mechanism and design method of the present invention are as follows: by designing the resonance unit 2 to construct a resonance state with different mode characteristics, with the participation of the Schottky diode, the switching of the conduction / isolation of the terahertz wave is realized, and during the design process, the port comprehensive optimization of the unit structure is carried out through the field-circuit fusion method, and the metal resonant microstructure 23 is optimized according to the design goal. Finally, extremely low insertion loss transmission and high-speed conversion between high-Q value resonances are realized in controllable elements such as the fin line structure 21, the metal resonant microstructure 23 and the Schottky diode. The terahertz wave is input through the standard waveguide 1, and the mode conversion is performed through the impedance matching of the height-reduced waveguide 4. The terahertz wave is converted from the waveguide mode to the quasi-TEM mode in the fin line. The terahertz wave mainly passes through the fin line gap. Schottky diodes are loaded on both sides of the fin line. A metal resonant microstructure 23 is designed outside the fin line structure 21. At this time, the Schottky diode, the fin line structure 21, and the metal resonant microstructure 23 together constitute a modulation unit. The on and off of the Schottky diode are controlled by an external voltage. When the Schottky diode is in the off state, the terahertz wave is transmitted from the fin line gap, and the terahertz wave is transmitted through the height-reduced waveguide 4 and the standard waveguide 1 at the output end; when the Schottky diode is in the on state, the Schottky diode The Schottky diode and the fin line structure 21 form an "H"-shaped microstructure, and the metal resonant microstructure 23 outside the fin line structure 21 also participates in the resonance. A strong resonance is formed between the two through the action, and the terahertz wave cannot pass through. Based on this, the amplitude of the terahertz wave can be controlled by controlling the on and off of the Schottky diode by voltage. In this process, the modulation signal is always loaded onto the Schottky diode through feeding, filtering, and the metal resonant microstructure 23 to be modulated by the terahertz carrier. At the same time, the impedance matching of the feeding-filtering part and the Schottky diode-fin line part is achieved by adjusting the metal resonant microstructure 23, thereby ensuring the integrity of the fed modulation signal, and finally realizing high-speed OOK direct modulation.

[0048] from Figure 3-5It can be seen that this example achieves a minimum insertion loss of 0.9db and a maximum switch ratio of 30db, that is, the minimum insertion loss is better than 1db and the switch ratio is greater than 29db. At the same time, it achieves a single-tone signal (sinusoidal signal) dynamic response of up to 25GHz and an OOK modulation rate of 30Gbps.

[0049] Example 2

[0050] The difference between this embodiment and Embodiment 1 is that the semiconductor control device 22 adopts any one of a PIN diode and a metal oxide semiconductor.

[0051] Example 3

[0052] The difference between this embodiment and embodiment 1 is that the material of the substrate is any one of silicon dioxide, high-resistance silicon, gallium arsenide or silicon carbide.

[0053] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A low insertion loss terahertz direct modulator, characterized in that: It includes a transmission waveguide and a feeding resonance structure, wherein the feeding resonance structure penetrates the wide side of the transmission waveguide in a direction perpendicular to the waveguide mouth surface, the feeding resonance structure includes a substrate, feeding units arranged at both ends of the substrate, and a resonance unit arranged between the feeding units, the resonance unit includes a fin line structure, a semiconductor control device and a metal resonance structure, the semiconductor control device is nested on the fin line structure, and the metal resonance microstructure is arranged on both sides of the fin line structure, and is used to adjust the resonance mode to the required mode and constrain the surrounding field near the fin line.

2. A low insertion loss terahertz direct modulator according to claim 1, characterized in that: The transmission waveguide includes a standard waveguide and a reduced height waveguide. The standard waveguide is arranged at both ends of the reduced height waveguide. The feeding resonance structure is arranged on the reduced height waveguide. The standard waveguide is used to match the size of the front-stage source and the rear-stage demodulation waveguide. The reduced height waveguide performs impedance matching on the standard waveguide and the modulation chip, so that the terahertz wave is transformed from a waveguide mode to an on-chip transmission mode.

3. The low insertion loss terahertz direct modulator according to claim 1, characterized in that: When the semiconductor control device is a diode, the cathode and anode of the diode are placed on the metal on both sides of the fin line structure, with a total number of M, M≥2, and the anodes and cathodes of the multiple diodes are on the same side and the same side, and are connected in parallel.

4. The low insertion loss terahertz direct modulator according to claim 3, characterized in that: The diode is any one of a GaAs Schottky diode, a PIN diode, and a metal oxide semiconductor.

5. The low insertion loss terahertz direct modulator according to claim 1, characterized in that: The feeding unit includes a low-pass filter circuit.

6. The low insertion loss terahertz direct modulator according to claim 5, characterized in that: The low-pass filter of the feeding unit is a compact microstrip resonant CMRC filter.

7. The low insertion loss terahertz direct modulator according to claim 1, characterized in that: The material of the substrate is any one of sapphire, silicon dioxide, high-resistance silicon, gallium arsenide or silicon carbide.

8. The low insertion loss terahertz direct modulator according to claim 1, characterized in that: The metal material involved is Au, Ag, Cu, or Al.

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