A tunable nonlinear metasurface device and a mid-to-far-infrared single-photon detection device

Abstract

This invention provides a tunable nonlinear metasurface device and a mid-to-far-infrared single-photon detection device. The tunable nonlinear metasurface device includes electrodes, a substrate, a tuning dielectric layer, and a metamaterial array structure layer. The electrodes generate an electric field; the tuning dielectric layer changes its dielectric properties under the influence of the electric field to tune the resonant wavelength of the metamaterial array structure layer; the metamaterial array structure layer simultaneously resonates with both the signal light to be converted and the pump light, resulting in a nonlinear sum-frequency interaction between the light and the material, generating parametric upconversion light; the structural parameters of the metamaterial array structure layer are smaller than the coherent wavelength; the substrate transmits the parametric upconversion light. This invention reduces the requirements for phase matching conditions during the conversion process, uses the electro-optic effect as the tuning mechanism for the signal light to be converted, achieves broadband upconversion detection of mid-to-far-infrared light at room temperature, and has the advantages of high integration and miniaturization.

Description

Technical Field

[0001] This invention relates to the field of mid-infrared light detection technology, and in particular to a tunable nonlinear metasurface device and a mid-to-far-infrared single-photon detection device. Background Technology

[0002] Single-photon detection is of great significance in fields such as quantum information processing, quantum secure communication, security monitoring, biomedicine, and military reconnaissance. Taking quantum communication as an example, the mid-infrared band has significant advantages over the near-infrared and visible light bands. On the one hand, the Rayleigh scattering cross section in the mid-infrared region is greatly reduced, and it has an atmospheric transparency window. On the other hand, during the day, the combined effect of mid-infrared radiation and solar background radiation is only one-third that of the near-infrared 1550nm telecommunication band. These advantages greatly promote the application demand for mid-infrared single-photon sensitivity detection technology. Compared to photodetectors with single-photon sensitivity in the near-infrared and visible light bands, direct detectors in the mid-infrared band often have lower sensitivity, and ultra-high sensitivity often relies on cryogenic cooling, making it impossible to achieve single-photon levels.

[0003] By utilizing optical nonlinear effects, the frequency of the mid-infrared wave to be measured is upconverted to the easily detectable visible and near-infrared bands. Then, using a single-photon detector in the upconverted optical band, single-photon-level detection of the mid-infrared light field can be achieved. This parametric upconversion detection method can not only be performed at room temperature but also retains the temporal and spectral information of the mid-infrared light field, making it a mid-infrared single-photon detection technique with significant advantages.

[0004] However, the occurrence of optical nonlinear effects requires consideration of phase matching conditions. Existing methods for parametric upconversion detection using nonlinear crystals have very limited bandwidth for mid-infrared light. Achieving narrowband tuning often requires precise control of certain properties of the optical path or optical devices, making the tuning of the converted signal wavelength extremely difficult. Therefore, reducing the requirements for phase matching conditions during the conversion process and achieving tunable conversion over a wider spectral range has become a key technical problem that needs to be solved. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a tunable nonlinear metasurface device and a mid-to-far infrared single-photon detection device, which can reduce the requirements for phase matching conditions during the conversion process. It uses the electro-optic effect as the tuning mechanism of the signal light to be converted, and realizes broadband upconversion detection of mid-to-far infrared light at room temperature. It also has the advantages of high integration and miniaturization.

[0006] This invention provides a tunable nonlinear metasurface device, comprising: an electrode for generating an electric field; a metamaterial array structure layer formed on a tuning dielectric layer for simultaneously resonating with incident signal light to be converted and pump light, wherein the light and the material undergo nonlinear sum-frequency interaction to generate parametric upconversion light; the structural parameters of the metamaterial array structure layer are smaller than the coherent wavelength; the signal light to be converted includes mid- to far-infrared light; the tuning dielectric layer formed on a substrate for changing the dielectric properties under the action of the electric field to tune the resonant wavelength of the metamaterial array structure layer; and the substrate for transmitting the parametric upconversion light.

[0007] According to the present invention, a tunable nonlinear metasurface device is provided, wherein the metamaterial array structure layer comprises a plurality of array units; each array unit comprises a first coupler, a waveguide-like structure, and a second coupler arranged sequentially; the first coupler is used to enhance the coupling of the signal light to be converted, to obtain enhanced coupled signal light and residual signal light; the second coupler is used to enhance the coupling of the pump light, to obtain enhanced coupled pump light and residual pump light; and is also used to enhance the quasi-bound state of the coupled parametric upconversion light; the waveguide-like structure is used to resonate the enhanced coupled signal light and the enhanced coupled pump light, to generate the parametric upconversion light through nonlinear sum-frequency effects.

[0008] According to the present invention, a tunable nonlinear metasurface device is provided, wherein the first coupler is shaped as a set of double cylinders, the waveguide-like shape is cuboid, and the second coupler is shaped as multiple sets of double cylinders.

[0009] According to the present invention, a tunable nonlinear metasurface device is provided in which the refractive index of the substrate material is lower than the refractive index of the tuning dielectric layer and the refractive index of the metamaterial array structure layer.

[0010] According to the present invention, a tunable nonlinear metasurface device is provided, wherein the thickness of the metamaterial array structure layer is less than the thickness of the tuning dielectric layer, and the thickness of the tuning dielectric layer is less than the thickness of the substrate.

[0011] According to the present invention, a tunable nonlinear metasurface device is provided, wherein the substrate is made of MgF2, CaF2 or BaF2; the tuning dielectric layer is made of LiNbO3; and the metamaterial array structure layer is made of GaAs, GaP or GaSe.

[0012] The present invention also provides a mid-to-far infrared single-photon detection device, comprising: a pulsed light source for generating pump light; a semi-transparent mirror disposed on the pump light output side of the pulsed light source for combining the pump light with the signal light to be converted and then incident on the tunable nonlinear metasurface device as described above; the tunable nonlinear metasurface device disposed on the side of the semi-transparent mirror away from the pulsed light source for generating parametric upconversion light according to the pump light and the signal light to be converted; a voltage source for providing voltage to the electrodes of the tunable nonlinear metasurface device to generate an electric field; a filter disposed on the side of the tunable nonlinear metasurface device away from the semi-transparent mirror for filtering noise in the frequency band of the non-parametric upconversion light; and a single-photon detector disposed on the side of the filter away from the tunable nonlinear metasurface device for detecting photons of the upconversion light.

[0013] According to the present invention, a mid-to-far infrared single-photon detection device is provided, wherein the center frequency of the pulsed light source is located in the near-infrared or visible light band, the pulse width is less than 500 fs, and the peak power is greater than 10. 7 W.

[0014] According to the present invention, the material of the semi-transparent and semi-reflective mirror is a fluoride.

[0015] According to the present invention, a mid-to-far infrared single-photon detection device is provided, wherein the single-photon detector is an avalanche photodetector made of silicon material or InGaAs / InP material.

[0016] This invention provides a tunable nonlinear metasurface device and a mid-to-far-infrared single-photon detection device. The tunable nonlinear metasurface device includes electrodes, a substrate, a tuning dielectric layer, and a metamaterial array structure layer. The electrodes generate an electric field; the tuning dielectric layer changes its dielectric properties under the influence of the electric field to tune the resonant wavelength of the metamaterial array structure layer; the metamaterial array structure layer simultaneously resonates with both the signal light to be converted and the pump light, resulting in a nonlinear sum-frequency interaction between the light and the material, generating parametric upconversion light; the structural parameters of the metamaterial array structure layer are smaller than the coherent wavelength; the substrate transmits the parametric upconversion light. This invention reduces the requirements for phase matching conditions during the conversion process, uses the electro-optic effect as the tuning mechanism for the signal light to be converted, achieves broadband upconversion detection of mid-to-far-infrared light at room temperature, and has the advantages of high integration and miniaturization. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a side view schematic diagram of a tunable nonlinear metasurface device provided by the present invention.

[0019] Figure 2 This is a top view schematic diagram of a tunable nonlinear metasurface device provided by the present invention.

[0020] Figure 3 This is a top view of the array unit provided by the present invention.

[0021] Figure 4 This invention provides the transmission spectrum of a tunable nonlinear metasurface device in the 1.2-1.8 μm band.

[0022] Figure 5 This invention provides the transmission spectrum of a tunable nonlinear metasurface device in the 3.8-4.8 μm band.

[0023] Figure 6 This is a schematic diagram of the structure of the mid- and far-infrared single-photon detection device provided by the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Please refer to Figure 1 , Figure 1 This is a side view of a tunable nonlinear metasurface device provided by the present invention.

[0026] This invention provides a tunable nonlinear metasurface device 7, comprising: an electrode 4 for generating an electric field; a metamaterial array structure layer 3 formed on a tuning dielectric layer 2 for simultaneously resonating with incident signal light to be converted and pump light, wherein the light and the material undergo nonlinear sum-frequency interaction to generate parametric upconversion light; the structural parameters of the metamaterial array structure layer 3 are smaller than the coherent wavelength; the signal light to be converted includes mid- and far-infrared light; the tuning dielectric layer 2 formed on a substrate 1 for changing the dielectric properties under the action of an electric field to tune the resonant wavelength of the metamaterial array structure layer 3; and the substrate 1 for transmitting parametric upconversion light.

[0027] This invention provides a tunable nonlinear metasurface device 7, comprising an electrode 4, a substrate 1, a tuning dielectric layer 2, and a metamaterial array structure layer 3. An electric field is generated by the electrode 4, which is used to modulate the dielectric properties of the tuning dielectric layer 2. The substrate 1 can be made of a high-transmittance material, such as CaF2. The substrate 1 material has a low absorptivity (<10%) and a small refractive index (less than the refractive index of the material in the metamaterial array structure layer 3) in the mid-to-far infrared band. The substrate 1 enhances the structural strength of the entire device, allowing transmission of parametric upconverted light and unconverted portion of the signal light and pump light. The tuning dielectric layer 2 disposed on the substrate 1 can be selected from materials with strong electro-optic effects, such as LiNbO3. When the electrode 4 generates an electric field, the dielectric properties of the tuning dielectric layer 2 change accordingly. According to the electro-optic effect, the change in refractive index can be expressed as:

[0028]

[0029] in, E For the applied electric field strength, r For the electro-optic coefficient tensor, n 0 represents the refractive index of the material in the absence of an electric field.

[0030] By adjusting the voltage between electrodes 4, the refractive index change can be precisely controlled, thereby tuning the resonant wavelength of the metamaterial array structure layer 3. The metamaterial array structure layer 3 is positioned above the tuning medium layer 2, and its structural parameters (such as the length L and width D of the array units) are smaller than the coherent wavelength, allowing the metamaterial array structure layer 3 to resonate simultaneously with the incident signal light (4-14 μm) and pump light (1.52-1.57 μm). This design enables nonlinear sum-frequency interactions between light and matter, generating detectable parametric upconversion light. The design of the metamaterial array structure layer 3 allows for broadband continuous tuning, unrestricted by phase-matching conditions, and without considering phase mismatch issues caused by changes in the material's refractive index. The upconversion light has a higher frequency than both the pump light and the signal light and is easily detected by the single-photon detector 10, achieving broadband tunable and effective detection of mid- and far-infrared light. Using the electro-optic effect as the tuning mechanism for the resonant wavelength of the metamaterial array structure layer 3, it can be conveniently controlled by a voltage source 8 without the need for precise control of the optical path or devices. This achieves continuous, high spectral resolution tuning over a wide range, exhibiting high stability, a simple mechanism, and ease of miniaturization and high integration of the device. It can be fabricated using existing technologies and devices at low cost. Employing parametric upconversion for detection not only provides higher single-photon sensitivity but also allows the system to operate at room temperature, broadening its application range.

[0031] Electrode 4 can be disposed on both sides of substrate 1, tuning dielectric layer 2 and metamaterial array structure layer 3, or disposed at other locations that facilitate the formation of an electric field. This invention does not impose any particular limitation on these locations.

[0032] The material selected for the metamaterial array structure layer 3 must exhibit second-order nonlinear effects and have a low absorption rate in the mid- and far-infrared bands. The thickness of the metamaterial array structure layer 3 and the diameter of the cylinder should be smaller than the wavelength of the signal light within the metamaterial to ensure that the effects caused by phase matching conditions are negligible.

[0033] The tuning dielectric layer 2 is made of a material with a strong electro-optic effect.

[0034] In a preferred embodiment, the metamaterial array structure layer 3 includes several array units; each array unit includes a first coupler, a waveguide-like structure, and a second coupler arranged sequentially; the first coupler is used to enhance the coupling of the signal light to be converted, resulting in enhanced coupled signal light and residual signal light; the second coupler is used to enhance the coupling of the pump light, resulting in enhanced coupled pump light and residual pump light; it is also used to enhance the quasi-bound state of the coupled parametric upconversion light; the waveguide-like structure is used to make the enhanced coupled signal light and the enhanced coupled pump light resonate, generating parametric upconversion through nonlinear sum-frequency effects.

[0035] Please refer to Figure 2 , Figure 2This is a top view schematic diagram of a tunable nonlinear metasurface device provided by the present invention.

[0036] Please refer to Figure 3 , Figure 3 This is a top view of the array unit provided by the present invention.

[0037] In this embodiment, the metamaterial array structure layer 3 may include several array units, each of which may be rectangular or other geometric shapes (triangular, circular, hexagonal, or irregular). Each array unit includes a first coupler, a waveguide-like structure, and a second coupler arranged sequentially. The first coupler is used to enhance the coupling of the signal light to be converted, resulting in enhanced coupled signal light and residual signal light. By optimizing the geometry and material properties of the first coupler, the intensity of the coupled signal light can be maximized while minimizing the loss of residual signal light. The second coupler is used to enhance the coupling of the pump light, resulting in enhanced coupled pump light and residual pump light. The waveguide-like structure is located between the first and second couplers, and its function is to enable the enhanced coupled signal light and enhanced coupled pump light to resonate within it, generating a quasi-bound state of the parametric upconversion light. By precisely controlling the size and refractive index of the waveguide-like structure, it can be ensured that the signal light to be converted and the pump light resonate effectively within the waveguide-like structure, thereby generating parametric upconversion light. Furthermore, the second coupler is also responsible for enhancing the quasi-bound state of the coupled parametric upconversion light, which is crucial for improving upconversion efficiency.

[0038] The length and width of the rectangular array unit are optimized according to the wavelengths of the signal light to be converted and the pump light. The length L ranges from 1800nm ​​to 6600nm, for example, 2010nm, and the width D ranges from 1750nm to 6550nm, for example, 2000nm. This invention does not impose any special limitations on these values.

[0039] In a preferred embodiment, the first coupler is a set of double cylinders, the waveguide-like shape is a cuboid, and the second coupler is a set of multiple double cylinders.

[0040] In this embodiment, the first coupler is shaped like a set of two cylinders, a design particularly suitable for enhancing the coupling of the signal light to be converted. The double-cylinder structure provides efficient light wave guidance and localization, thereby enhancing the coupling efficiency between the light wave and the waveguide-like structure. The dimensions and spacing of the two cylinders of the first coupler are designed (the radius R1 of the smaller circle ranges from 200-350 nm, for example, 270 nm; the radius R2 of the larger circle ranges from 230-420 nm, for example, 320 nm; the center-to-center distance l1 of the two circles ranges from 600-1000 nm, for example, 850 nm; and the distance d1 between the center of the two circles and the left side of the waveguide-like structure ranges from 300-800 nm, for example, 560 nm) to match the wavelength and polarization state of the signal light to be converted, thereby maximizing the coupling efficiency. The waveguide-like structure is cuboid in shape, which helps to restrict the propagation of the light wave in two directions, forming a two-dimensional waveguide mode. The width and length of the waveguide-like structure can be optimized according to the wavelengths of the signal light to be converted and the pump light. The width w ranges from 500 to 2000 nm, for example, 600 nm, and the length is, for example, 2000 nm to achieve the best resonance conditions. The second coupler is shaped like multiple sets of two-sided pillars. This design helps to enhance the quasi-bound state of the coupled pump light and the parametric upconversion light. The arrangement and dimensions of the two pillars (the side length w1 of the small square ranges from 120-240 nm, for example, 180 nm; the side length w2 of the large square ranges from 130-270 nm, for example, 200 nm; the distance l2 between the centers of the two large pillars ranges from 500-800 nm, for example, 600 nm; the distance l3 between the centers of the large and small pillars ranges from 200-280 nm, for example, 245 nm; and the distance d2 between the centers of the large and small pillars and the right side of the waveguide-like structure ranges from 80-160 nm, for example, 120 nm) are optimized to match the characteristics of the pump light and the upconversion light, ensuring that the light wave can be effectively coupled out of the waveguide-like structure. This embodiment achieves simultaneous resonance of quasi-bound states with large wavelength difference, enabling upconversion detection in the long-wavelength mid-far-infrared band (4-14 μm).

[0041] In a preferred embodiment, the refractive index of the substrate 1 is lower than that of the tuning medium layer 2 and the metamaterial array structure layer 3.

[0042] In this embodiment, the refractive index of the substrate 1 is lower than that of the tuning dielectric layer 2 and the metamaterial array structure layer 3. The low refractive index of the substrate 1 helps reduce the reflection and scattering of the parametric upconversion light within the device, thereby improving the transmission efficiency of the light wave and the overall performance of the device. The high refractive index of the tuning dielectric layer 2 helps to generate a significant refractive index change under the action of an applied electric field, thereby achieving precise tuning of the wavelength of the light to be converted. The material of the metamaterial array structure layer 3 is chosen to be a medium with second-order nonlinear effects. The refractive index of the metamaterial array structure layer 3 is higher than that of the substrate 1 and the tuning dielectric layer 2, which helps to achieve localization of the light wave and enhance the nonlinear effects in the metamaterial array structure layer 3.

[0043] In a preferred embodiment, the thickness of the metamaterial array structure layer 3 is less than the thickness of the tuning medium layer 2, and the thickness of the tuning medium layer 2 is less than the thickness of the substrate 1.

[0044] In this embodiment, the thickness of the metamaterial array structure layer 3 (600 nm in this embodiment, with a range of 400-2000 nm) is greater than the thickness of the substrate 1 but less than the thickness of the tuning medium layer 2. This ensures that the metamaterial array structure layer 3 effectively interacts nonlinearly with light waves while maintaining sufficient structural strength. The thickness of the tuning medium layer 2 (2000 nm in this embodiment, with a range of 1600-4000 nm) is designed to be greater than the thickness of the metamaterial array structure layer 3 but less than the thickness of the substrate 1. This design allows the tuning medium layer 2 to generate sufficient refractive index change under the action of an applied electric field to achieve effective tuning of light waves. The thickness of the substrate 1 (e.g., 200-2000 μm) is designed to be maximum to provide sufficient support and stability while minimizing the propagation loss of light waves in the substrate 1.

[0045] In a preferred embodiment, the substrate 1 is made of MgF2, CaF2 or BaF2; the tuning dielectric layer 2 is made of LiNbO3; and the metamaterial array structure layer 3 is made of GaAs, GaP or GaSe.

[0046] Please refer to Figure 4 , Figure 4 The transmission spectrum of a tunable nonlinear metasurface device in the 1.2-1.8 μm band is provided by the present invention.

[0047] Please refer to Figure 5 , Figure 5 The transmission spectrum of a tunable nonlinear metasurface device in the 3.8-4.8 μm band is provided by the present invention.

[0048] In this embodiment, the substrate 1 is made of CaF2, the tuning dielectric layer 2 is made of LiNbO3, and the metamaterial array structure layer 3 is made of GaAs. The LiNbO3 tuning dielectric layer 2 is disposed between the CaF2 substrate 1 and the GaAs material array structure. It exhibits an electro-optic effect, and the refractive index of the material changes with the direction and magnitude of the electric field. The applied electric field is generated by the potential difference between the two microelectrodes 4. By adjusting the voltage values ​​of the two electrodes 4, the refractive index of the LiNbO3 material is changed, thereby affecting the resonant response of the metasurface structure, causing the resonant frequency of the metasurface device to drift, and the corresponding conversion wavelength is tuned. The larger r in the electro-optic coefficient tensor of the LiNbO3 material is used as the reference value. 33 The component serves as the source of electro-optic modulation. The transmission spectra of this embodiment in the near-infrared 1.2-1.8 μm band and mid-infrared 3.8-4.8 μm band were simulated using the finite-difference time-domain method. It can be seen that, without an external electric field, the metasurface exhibits strong resonances near 1540 nm in the near-infrared and 4250 nm in the mid-infrared, suitable as resonance modes for pump light and signal light, respectively. By changing the intensity and direction of the external electric field, the resonance spectrum of the metasurface can be shifted. When the external electric field is ±2 × 10⁻⁶, the resonance spectrum of the metasurface can be shifted. 8 The metasurface transmission spectrum at V / m allows for continuous tuning of the signal light with a bandwidth exceeding 100 nm within this applied electric field range. Simultaneously, the resonant peak of the signal mode remains within the 1520-1570 nm communication band, a band with commercially available high-power, tunable femtosecond light sources, facilitating nonlinear parametric conversion.

[0049] The mid- and far-infrared single-photon detection device provided by the present invention is described below. The mid- and far-infrared single-photon detection device described below can be referred to in correspondence with the tunable nonlinear metasurface device 7 described above.

[0050] Please refer to Figure 6 , Figure 6 This is a schematic diagram of the structure of the mid- and far-infrared single-photon detection device provided by the present invention.

[0051] The present invention also provides a mid-to-far infrared single-photon detection device, comprising: a pulsed light source 5 for generating pump light; a semi-transparent mirror 6 disposed on the pump light output side of the pulsed light source 5 for combining the pump light and the signal light to be converted and then incident on the tunable nonlinear metasurface device 7 as described above; the tunable nonlinear metasurface device 7 disposed on the side of the semi-transparent mirror 6 away from the pulsed light source 5 for generating parametric upconversion light according to the pump light and the signal light to be converted; a voltage source 8 for providing voltage to the electrodes 4 of the tunable nonlinear metasurface device 7 to generate an electric field on the electrodes 4; a filter disposed on the side of the tunable nonlinear metasurface device 7 away from the semi-transparent mirror 6 for filtering noise in the nonparametric upconversion light frequency band; and a single-photon detector 10 disposed on the side of the filter away from the tunable nonlinear metasurface device 7 for detecting photons of the upconversion light.

[0052] This invention also provides a mid-to-far-infrared single-photon detection device, including key components such as a pulsed light source 5, a semi-transparent mirror 6, a tunable nonlinear metasurface device 7, a voltage source 8, a filter, and a single-photon detector 10. The near-infrared pulsed light source 5 generates pump light, the center frequency of which is selected according to the characteristics of the signal light to be converted, to ensure effective nonlinear interaction. The pulse width and peak power of the pump light are adjusted as needed to optimize the upconversion efficiency. The semi-transparent mirror 6 is located on the pump light output side of the pulsed light source 5. After the signal light to be converted (mid-infrared signal light) enters the detection device, it is combined with the pump light through the semi-transparent mirror 6 and incident together on the tunable nonlinear metasurface device 7. Subsequently, the light and matter undergo nonlinear sum-frequency interaction, generating parametric upconverted light with a frequency equal to the sum of the frequencies of the signal light and the pump light. Then, the remaining signal light, remaining pump light, and parametric upconverted light are transmitted from the nonlinear metasurface. A filter is positioned on the side of the nonlinear metasurface device away from the semi-transparent mirror 6 to filter noise in the nonparametric upconversion light frequency band and improve the signal-to-noise ratio. The remaining signal light, remaining pump light, and parametric upconversion light are filtered by the filter 9, leaving only the upconverted light in the visible or near-infrared band, which is then incident on the single-photon detector 10 and detected. The single-photon detector 10 is positioned on the side of the filter away from the nonlinear metasurface device. The output voltage of the voltage source 8 is adjustable; its voltage output resolution and range determine the tuning resolution and range of the conversion wavelength, respectively. The voltage output from the voltage source 8 is connected to the electrode 4 on the nonlinear metasurface device. By controlling the magnitude of the output voltage, the electric field strength of the space where the nonlinear metasurface device is located is changed, thereby achieving tuning of the structural resonant frequency and changing the wavelength of the signal light to be converted.

[0053] In a preferred embodiment, the center frequency of the pulsed light source 5 is located in the near-infrared or visible light band, the pulse width is less than 500 fs, and the peak power is greater than 10. 7 W.

[0054] In this embodiment, the pulsed light source 5 is designed with a center frequency in the near-infrared or visible light band to ensure effective nonlinear interaction between the pump light and the mid-to-far-infrared signal light to be converted. The pulse width of the pulsed light source 5 is optimized to be less than 500 fs to provide high peak power and time resolution. The peak power of the pulsed light source 5 is designed to be greater than 10. 7 W is used to ensure sufficient energy input during the nonlinear process.

[0055] In a preferred embodiment, the material of the semi-transparent mirror 6 is a fluoride.

[0056] In this embodiment, the semi-transparent and semi-reflective mirror 6 needs to be able to operate simultaneously in the signal light and pump light bands. It is selected as a fluoride, such as MgF2, CaF2 or BaF2, because of its excellent transmittance and low absorption rate in the mid- and far-infrared bands, and at the same time, it has good mechanical properties and chemical stability.

[0057] As a preferred embodiment, the single-photon detector 10 is an avalanche photodetector made of silicon or InGaAs / InP material.

[0058] In this embodiment, the single-photon detector 10 is determined according to the wavelength of the upconversion light. For example, avalanche photodetectors made of silicon can be used for 350-1100nm, and avalanche photodetectors made of InGaAs / InP can be used for 900-1700nm.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tunable nonlinear metasurface device, characterized in that, include: Electrodes are used to generate an electric field; The metamaterial array structure layer, formed on the tuning medium layer, is used to resonate simultaneously with the incident signal light to be converted and the pump light. The light and the matter undergo nonlinear sum-frequency interaction to generate parametric upconversion light. The structural parameters of the metamaterial array structure layer are smaller than the coherent wavelength; The signal light to be converted includes mid- and far-infrared light; The tuning dielectric layer, formed on the substrate, is used to change the dielectric properties under the action of the electric field in order to tune the resonant wavelength of the metamaterial array structure layer. The substrate is used to transmit the parametric upconversion light; The metamaterial array structure layer includes several array units; each array unit includes a first coupler, a waveguide-like structure, and a second coupler arranged sequentially. The first coupler is used to enhance the coupling of the signal light to be converted, resulting in enhanced coupled signal light and residual signal light; The second coupler is used to enhance the coupling of the pump light, resulting in enhanced coupled pump light and residual pump light; It is also used to enhance the quasi-bound state of coupled parametric upconversion light; The waveguide-like structure is used to resonate the enhanced coupled signal light and the enhanced coupled pump light, generating the parametric upconversion light through nonlinear sum-frequency effects; The first coupler is a set of double cylinders, the waveguide-like shape is a cuboid, and the second coupler is a set of multiple double cylinders.

2. The tunable nonlinear metasurface device according to claim 1, characterized in that, The refractive index of the substrate material is lower than that of the refractive index of the tuning medium layer and the refractive index of the metamaterial array structure layer.

3. The tunable nonlinear metasurface device according to claim 1, characterized in that, The thickness of the metamaterial array structure layer is less than the thickness of the tuning medium layer, and the thickness of the tuning medium layer is less than the thickness of the substrate.

4. The tunable nonlinear metasurface device according to any one of claims 1 to 3, characterized in that, The substrate material includes MgF2, CaF2 or BaF2; the tuning medium layer material is LiNbO3; the metamaterial array structure layer material includes GaAs, GaP or GaSe.

5. A mid-to-far-infrared single-photon detection device, characterized in that, include: A pulsed light source is used to generate pump light; A semi-transparent and semi-reflective mirror is disposed on the pump light output side of the pulsed light source, and is used to combine the pump light and the signal light to be converted and then incident it onto the tunable nonlinear metasurface device as described in any one of claims 1 to 4. The tunable nonlinear metasurface device is disposed on the side of the semi-transparent mirror away from the pulsed light source, and is used to generate parametric upconversion light according to the pump light and the signal to be converted; A voltage source is provided to supply voltage to the electrodes of the tunable nonlinear metasurface device so as to generate an electric field on the electrodes; A filter is disposed on the side of the tunable nonlinear metasurface device away from the semi-transparent and semi-reflective mirror, and is used to filter out noise in the non-parametric upconversion optical frequency band; A single-photon detector is disposed on the side of the filter away from the tunable nonlinear metasurface device, and is used to detect photons of the upconverted light.

6. The mid-to-far infrared single-photon detection device according to claim 5, characterized in that, The pulsed light source has a center frequency in the near-infrared or visible light band, a pulse width of less than 500 fs, and a peak power greater than 10. 7 W.

7. The mid-to-far infrared single-photon detection device according to claim 5, characterized in that, The material of the semi-transparent and semi-reflective mirror is fluoride.

8. The mid-to-far infrared single-photon detection device according to any one of claims 5 to 7, characterized in that, The single-photon detector is an avalanche photodetector made of silicon or InGaAs / InP material.

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