Superconducting tunnel junction mixer local oscillation noise suppression device

Abstract

The invention provides a local oscillation noise suppression device for a superconductive tunnel junction mixer, and belongs to the technical field of terahertz detection. The device comprises a local oscillator signal source, a local oscillator light path, a superconductive tunnel junction mixer and a quasi-optical filter. The local oscillator signal source provides a local oscillator signal to the superconductive tunnel junction mixer through a local oscillator light path; the quasi-optical filter is located between the local oscillator signal source and the local oscillator light path and used for attenuating local oscillator power and reducing reflection of signals in the local oscillator light path. The quasi-optical filter is formed by machining an integrated metal plate, circular grooves are formed in the symmetrical positions of the two sides of the metal plate, and through holes are formed in the centers of the grooves and serve as attenuation windows. The environment adaptability is high, and normal-temperature / low-temperature stable work is supported; signal reflection and sideband noise are effectively suppressed by the composite design of the conical structure and the black body absorbing coating; and realizing accurate power matching based on a Gaussian beam theory.

Description

Technical Field

[0001] This invention belongs to the field of terahertz detection technology, specifically relating to a local oscillator noise suppression device for a superconducting tunnel junction mixer. Background Technology

[0002] A superconductor-insulator-superconductor (SIS) mixer is a quantum-limited sensitivity coherent detector widely used in astronomical detection, space remote sensing, and deep space exploration, ranging from millimeter waves to terahertz waves. This mixer requires a local oscillator (LO) signal source to provide a highly stable reference signal, and its sensitivity is typically characterized by the equivalent noise temperature.

[0003] Early superconducting SIS mixers typically employed a local oscillator (LO) signal source based on a Gunn oscillator and frequency multiplier architecture. Its sideband noise was minimal and negligible in practical applications. However, such LO signal sources suffer from narrow bandwidth, limited output power, and reliance on mechanical tuning, restricting their application in complex interferometric array systems. In recent years, a new generation of LO signal sources, consisting of a microwave reference source, frequency multiplier, and power amplifier, has gradually become mainstream. While this architecture offers advantages such as large bandwidth, high power, no need for mechanical tuning, and ease of use, it also introduces more significant LO sideband noise. This noise is down-converted to the intermediate frequency during mixing, directly affecting the system's detection sensitivity.

[0004] The formation mechanism of this type of noise is complex, mainly influenced by factors such as the phase noise of the reference signal, the operating state of the power amplifier, and the nonlinearity and efficiency of the frequency multiplier. Furthermore, research has found that the reflected signal generated by optical devices in the local oscillator optical path system causes some of the local oscillator energy to be recoupled to the signal link, thus significantly exacerbating the sideband noise level. These problems have become factors that cannot be ignored in practical applications.

[0005] Currently, common methods for suppressing local oscillator noise mainly include: 1. Placing the local oscillator signal source in a low-temperature environment, which can suppress local oscillator thermal noise, but will significantly increase system complexity, power consumption and size, and the overall sideband noise suppression effect is limited; 2. Power amplifiers can reduce the noise they introduce by operating in the drive saturation region, but when the sideband noise of the microwave reference source is high, its noise will deteriorate the sideband noise of the final output signal after passing through the power amplifier and the frequency multiplier link, resulting in an unsatisfactory suppression effect; 3. Introducing a narrowband tunable filter at the output of the microwave reference source, which can effectively suppress out-of-band noise, also faces two major problems: First, it will introduce a large insertion loss, weakening the input drive capability of the frequency multiplier; second, as an active device, it has high control difficulty and circuit complexity, and may change its frequency characteristics due to temperature drift during long-term operation, thereby increasing the overall stability risk of the system.

[0006] In summary, while existing methods can suppress sideband noise to some extent, they all have significant performance limitations or high system costs. Therefore, there is an urgent need for a local oscillator sideband noise suppression device for superconducting tunnel junction mixers. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a local oscillator noise suppression device for superconducting tunnel junction mixers, which is suitable for suppressing local oscillator sideband noise and optimizing system performance in high-sensitivity superconducting tunnel junction mixers.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A local oscillator noise suppression device for a superconducting tunnel junction mixer includes: a local oscillator signal source, a local oscillator optical path, a superconducting tunnel junction mixer, and a quasi-optical filter; the local oscillator signal source provides the local oscillator signal to the superconducting tunnel junction mixer through the local oscillator optical path; the quasi-optical filter is located between the local oscillator signal source and the local oscillator optical path, and is used to attenuate the local oscillator power and reduce the reflection of the signal in the local oscillator optical path; the quasi-optical filter is made of an integrated metal plate, and circular grooves are provided symmetrically on both sides of the metal plate, with a through hole in the center of the groove as an attenuation window.

[0009] Optionally, the area outside the through holes in the grooves on both sides of the metal plate is symmetrically provided with a conical structure array, which is composed of multiple cone arrays and coated with a blackbody absorbing material.

[0010] Optionally, the metal plate is an aluminum plate.

[0011] Optionally, the radius of the groove Satisfy the following formula:

[0012] In the formula, for a base film Gaussian beam propagating along the z-axis, the beam waist is located at... Place, Indicates the beam radius. Indicates the transmission distance. Indicates wavelength. This indicates the initial waist radius of the signal.

[0013] Optionally, the through hole is in Cut off at point, through hole radius Satisfy the following formula:

[0014] In the formula, Power transmittance is equal to the power of the signal after attenuation through the via. With original power The ratio of .

[0015] Optionally, the height of the vertebral body Satisfy the following formula:

[0016] In the formula, This represents the low-frequency cutoff frequency of the blackbody absorbing material. At the speed of light, The relative permittivity of the blackbody absorbing material; The base width of the cone With height The ratio is 0.7 to 1.2; the distance between two adjacent vertebrae. , The wavelength corresponding to the highest frequency of the target.

[0017] Optionally, the blackbody absorbing material uses silicon carbide particles as the absorbent, and the silicon carbide particles are uniformly dispersed in a mixed matrix of Stycast epoxy resin and Catalyst 9 curing agent, and cured to form a composite microwave absorbing structure.

[0018] Optionally, the particle size of the silicon carbide particles... Based on the target operating frequency The design principles are given by the following formula:

[0019] In the formula, At the speed of light, This represents the relative permittivity of silicon carbide in the terahertz frequency band.

[0020] The beneficial effects of this invention are: 1. Strong environmental adaptability, supporting stable operation at both room temperature and low temperature: The quasi-optical filter has dual environmental adaptability at both room temperature and low temperature, supports flexible switching at room temperature, is easy to operate, and does not require the integration of a low temperature system, which greatly reduces system complexity and cost.

[0021] 2. The composite design of the conical structure and blackbody absorption coating effectively suppresses signal reflection and sideband noise: A conical array structure is designed at the symmetrical center position in the grooves on both sides of the aluminum plate (excluding the signal through-hole area), and a special blackbody absorption coating is coated on its surface, which can efficiently absorb signals and thus significantly suppress signal reflection.

[0022] 3. Achieving precise power matching based on Gaussian beam theory: Combining Gaussian beam propagation theory, the optimal attenuation aperture is calculated and selected based on the required local oscillator power, thereby flexibly and accurately adjusting the local oscillator power to the optimal operating point of the superconducting tunnel junction mixer, achieving optimal matching between power attenuation and sideband noise.

[0023] In summary, the device has a simple overall structure, low cost, and strong versatility. It can effectively solve the problem of local oscillator sideband noise degradation caused by excessive local oscillator power and signal reflection. It is suitable for local oscillator sideband noise suppression and system performance optimization of high-sensitivity superconducting tunnel junction mixers. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a local oscillator noise suppression device for a superconducting tunnel junction mixer.

[0025] Figure 2 This is a design model diagram of a quasi-optical filter.

[0026] Figure 3 This is a schematic diagram of a cone-shaped array.

[0027] Figure 4 This is a schematic diagram of the planar structure of a quasi-optical filter. Detailed Implementation

[0028] The invention will now be described in further detail with reference to the accompanying drawings.

[0029] This invention provides a local oscillator noise suppression device for a superconducting tunnel junction mixer. For example... Figure 1 As shown, the device mainly consists of a local oscillator signal source, a quasi-optical filter, a local oscillator optical path, and a superconducting tunnel junction mixer. The quasi-optical filter is located between the local oscillator signal source and the local oscillator optical path to attenuate excessive local oscillator power and reduce signal reflection in the optical path.

[0030] The quasi-optical filter is fabricated from a single aluminum plate and integrates a set of quasi-optical filter units with through holes of different radii. For example... Figure 2 and Figure 3As shown, each unit has a radius of [missing information] at symmetrical positions on both sides of the aluminum plate. mm, depth is A groove of mm in diameter, with a variable radius opening at the center of the groove. The through-hole (mm) serves as an attenuation window, and the local oscillator power can be precisely adjusted by flexibly matching the through-hole radius; a conical array of structures is symmetrically arranged on both sides of the aluminum plate, and its surface is coated with a special blackbody absorbing material, which can simultaneously achieve efficient absorption of electromagnetic waves and suppression of signal reflection.

[0031] Next, regarding the main body of the device, we will examine its groove radius separately. With the radius of the through hole The calculation, conical structure design, and blackbody coating production are explained in detail.

[0032] (1) Groove radius With the radius of the through hole calculate The planar structure of the quasi-optical filter is shown in the diagram below. Figure 4 As shown, it uses a size of X mm × Y Made from a small aluminum plate (mm), with symmetrically placed radius [missing information] positions on both sides of the aluminum plate. mm, deep A groove of mm is designed at the bottom of this groove. mm (wherein) The through-hole is used as a window for signal transmission to achieve local oscillator power attenuation.

[0033] Assume the initial beam waist radius of the signal is (Unit: mm) This radius is defined as the radius at which the light intensity (power density) decreases to the center value. The lateral radius at that time. The vertical distance between the waist position and the quasi-optical filter is... Let the original power be... The output power after attenuation is (Unit: dBm), then the required groove radius for the optical filter With the radius of the through hole It can be calculated using the following method: For a base-film Gaussian beam propagating along the z-axis, the beam waist is located at... At, at wavelength Under these conditions, the propagation distance After that, beam radius It can be represented as: (1-1) To ensure that the entire signal transmission area is covered by a radius of The circular groove must be covered to meet the following conditions: .

[0034] exist At this point, the radius is [missing information]. If a through-hole is used, the power of the signal will be attenuated after passing through the through-hole. With original power ratio A It can be represented as: (1-2) in, A Power transmittance ( ; The aperture radius of the quasi-optical filter. Based on the target power transmittance. A The required through-hole radius for: (1-3) therefore, The size needs to be larger than the beam radius To ensure complete signal coverage; simultaneously, attenuation via radius The smaller the value, the more significant the beam-blocking effect, the stronger the attenuation, and the lower the final output power.

[0035] (2) Conical structure design To better suppress sideband noise exacerbated by signal reflection in the local oscillator optical path, a conical array structure was designed at the symmetrical center position within the grooves on both sides of the aluminum plate (excluding the signal via area) (see...). Figure 2 and Figure 3 (Illustrative diagram), and its surface is coated with a special blackbody absorbing coating. This conical structure can effectively suppress the direct reflection of incident waves; at the same time, electromagnetic waves are reflected and scattered multiple times between the cones, which greatly extends their propagation path in the coating material, so that electromagnetic energy can be fully dissipated and converted into heat energy, thereby achieving the expected high absorption rate in the target frequency band.

[0036] The key design parameters for the tapered structure are as follows: Height (H): This parameter directly determines the low-frequency cutoff frequency of the absorber. The low-frequency cutoff frequency is approximately inversely proportional to the height. An empirical formula is: Where c is the speed of light. Given the relative permittivity of the substrate material, the cone height H can be calculated. Therefore, to absorb lower frequency electromagnetic waves, the cone height needs to be increased accordingly.

[0037] Aspect ratio (W / H): This is the ratio of the width (W) of the cone's base to its height (H), and it is a core parameter for balancing performance and manufacturability. A smaller ratio generally indicates better absorption performance and bandwidth, but at the cost of reduced mechanical stability and increased manufacturing complexity. In engineering, it is typically optimized within the range of 0.7 to 1.2. Considering both mechanical stability and manufacturing difficulty, the ratio of the cone's base width (W) to its height (H) is set to 1.

[0038] Period (P): refers to the distance between the centers of two adjacent cones in the array. To avoid performance degradation due to grating lobes caused by diffraction effects, the design requires... ( (The wavelength corresponding to the highest frequency of the target).

[0039] (3) Blackbody coating preparation The blackbody absorbing coating uses silicon carbide particles as the absorber, and their particle size is optimized and determined based on the electromagnetic resonance characteristics of the target frequency band. Specifically, it is designed for the target operating frequency. Through the formula: (1-4) By combining the dielectric properties of the material in the terahertz band with comprehensive calculations, the particle size of silicon carbide was determined to be... D μ Silicon carbide particles are uniformly dispersed in a mixed matrix of Stycast epoxy resin and Catalyst 9 curing agent, and cured to form a composite absorbing structure. This absorbing coating achieves excellent electromagnetic wave absorption performance and extremely low reflectivity in the terahertz frequency band, thereby significantly suppressing the sideband noise enhancement caused by optical path reflection.

[0040] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A local oscillator noise suppression device for a superconducting tunnel junction mixer, characterized in that, include: Local oscillator signal source, local oscillator optical path, superconducting tunnel junction mixer and quasi-optical filter; The local oscillator signal source provides the local oscillator signal to the superconducting tunnel junction mixer through the local oscillator optical path; The quasi-optical filter is located between the local oscillator signal source and the local oscillator optical path, and is used to attenuate the local oscillator power and reduce the reflection of the signal in the local oscillator optical path. The quasi-optical filter is made of an integrated metal plate, and circular grooves are provided on both sides of the metal plate. A through hole is opened in the center of the groove as an attenuation window.

2. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 1, characterized in that: The metal plate has a symmetrical array of conical structures arranged in the grooves on both sides, except for the through holes. The array of conical structures is composed of multiple cone-shaped arrays and is coated with a blackbody absorbing material.

3. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 1, characterized in that: The metal plate is an aluminum plate.

4. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 1, characterized in that: The radius of the groove Satisfy the following formula: In the formula, for a base film Gaussian beam propagating along the z-axis, the beam waist is located at... Place, Indicates the beam radius. Indicates the transmission distance. Indicates wavelength. This indicates the initial waist radius of the signal.

5. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 4, characterized in that: The through hole is in Cut off at point, through hole radius Satisfy the following formula: In the formula, Power transmittance is equal to the power of the signal after attenuation through the via. With original power The ratio of .

6. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 2, characterized in that: The height of the vertebral body Satisfy the following formula: In the formula, This represents the low-frequency cutoff frequency of the blackbody absorbing material. At the speed of light, The relative permittivity of the blackbody absorbing material; The base width of the cone With height The ratio is 0.7 to 1.2; the distance between two adjacent vertebrae. , The wavelength corresponding to the highest frequency of the target.

7. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 2, characterized in that: The blackbody absorbing material uses silicon carbide particles as the absorbent. The silicon carbide particles are uniformly dispersed in a mixed matrix of Stycast epoxy resin and Catalyst 9 curing agent, and then cured to form a composite microwave absorbing structure.

8. The local oscillator noise suppression device for a superconducting tunnel junction mixer as described in claim 7, characterized in that: The particle size of the silicon carbide particles Based on the target operating frequency The design principles are given by the following formula: In the formula, At the speed of light, This represents the relative permittivity of silicon carbide in the terahertz frequency band.

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