Tunable nonlinear metasurface device and middle and far infrared single photon detection device

Abstract

The invention provides a tunable nonlinear metasurface device and a middle and far infrared single photon detection device. The tunable nonlinear metasurface device comprises an electrode, a substrate, a tuning dielectric layer and a metamaterial array structure layer. The electrode generates an electric field; the dielectric property of the tuning dielectric layer is changed under the action of an electric field so as to tune the resonant wavelength of the metamaterial array structure layer; the metamaterial array structure layer resonates with the signal light to be converted and the pump light at the same time, the light and a substance generate a nonlinear sum frequency effect, and parametric up-conversion light is generated; the structural parameter of the metamaterial array structural layer is smaller than the coherent wavelength; the substrate transmits parametric upconversion light. The requirement for phase matching conditions in the conversion process can be lowered, the electro-optical effect serves as the tuning mechanism of signal light to be converted, broadband up-conversion detection of middle and far infrared light is achieved at the room temperature, and the device has the advantages of being high in integration and small in size.

Description

Technical Field

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

[0002] Single-photon detection is of great significance in the fields of quantum information processing, quantum secure communication, security monitoring, biomedicine, military reconnaissance, etc. Taking quantum communication as an example, the mid-infrared band has huge 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 transparent window. On the other hand, during the day, the combined effect of mid-infrared and solar background radiation is only one-third of that in the near-infrared 1550nm telecommunications band. These advantages have greatly promoted the application demand for mid-infrared single-photon sensitivity detection technology. Compared with photoelectric detectors 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 low-temperature refrigeration, which cannot reach the single-photon level.

[0003] Through the optical nonlinear effect, the frequency of the mid-infrared wave to be measured is up-converted to the visible and near-infrared bands that are easy to detect, and then the single-photon level detection of the mid-infrared light field can be achieved by using a single-photon detector in the up-converted light band. This parametric up-conversion detection method can not only be carried out at room temperature, but also retain the time domain and spectrum information of the mid-infrared light field. It is a mid-infrared single-photon detection technology with significant advantages.

[0004] However, the occurrence of optical nonlinear effects requires consideration of phase matching conditions. The existing bandwidth of infrared light detection by parametric up-conversion based on nonlinear crystals is very limited. The realization of narrowband tuning often requires precise control of the optical path or certain properties of optical devices, which makes the tuning conversion of the signal light wavelength very difficult. Therefore, how to reduce the requirements for phase matching conditions during the conversion process and realize tunable conversion over a larger spectrum range has become a technical problem that needs to be solved. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a tunable nonlinear metasurface device and a mid- and far-infrared single-photon detection device, which can reduce the requirements for phase matching conditions in the conversion process, use the electro-optic effect as the tuning mechanism of the signal light to be converted, and realize broadband up-conversion detection of mid- and far-infrared light at room temperature, and has the advantages of high integration and miniaturization.

[0006] The present invention provides a tunable nonlinear metasurface device, comprising: an electrode for generating an electric field; a metamaterial array structure layer formed on a tuning medium layer and used for simultaneously resonating with incident signal light to be converted and pump light, so that light and matter undergo nonlinear and frequency-scaling effects to generate parametric up-conversion light; a structural parameter of the metamaterial array structure layer is smaller than a coherent wavelength; the signal light to be converted includes mid- and far-infrared light; the tuning medium layer is formed on a substrate and used for changing dielectric properties under the action of the electric field to tune the resonant wavelength of the metamaterial array structure layer; and the substrate is used for transmitting the parametric up-conversion light.

[0007] According to a tunable nonlinear metasurface device provided by the present invention, the metamaterial array structure layer includes a plurality of array units; each array unit includes a first coupler, a waveguide-like and a second coupler arranged in sequence; 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 coupled parametric up-conversion light; the waveguide-like is used to make the enhanced coupled signal light and the enhanced coupled pump light resonate, and generate the parametric up-conversion light through the nonlinear sum-frequency effect.

[0008] According to a tunable nonlinear metasurface device provided by the present invention, the first coupler is shaped like a group of double cylinders, the waveguide-like device is shaped like a rectangular parallelepiped, and the second coupler is shaped like a plurality of groups of double cylindrical bodies.

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

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

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

[0012] The present invention also provides a mid- and far-infrared single-photon detection device, comprising: a pulse light source for generating pump light; a semi-transparent and semi-reflective mirror, arranged at the pump light output side of the pulse 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, arranged on a side of the semi-transparent and semi-reflective mirror away from the pulse light source, for generating parametric up-conversion light according to the pump light and the signal to be converted; a voltage source, for providing a voltage to the electrodes of the tunable nonlinear metasurface device so that the electrodes generate an electric field; a filter, arranged on a side of the tunable nonlinear metasurface device away from the semi-transparent and semi-reflective mirror, for filtering out noise in a frequency band other than the parametric up-conversion light; and a single-photon detector, arranged on a side of the filter away from the tunable nonlinear metasurface device, for detecting photons of the up-conversion light.

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

[0014] According to a mid- and far-infrared single-photon detection device provided by the present invention, the material of the semi-transparent and semi-reflective mirror is fluoride.

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

[0016] The present invention provides a tunable nonlinear metasurface device and a mid-to-far infrared single photon detection device, wherein the tunable nonlinear metasurface device includes an electrode, a substrate, a tuning dielectric layer, and a metamaterial array structure layer. The electrode generates an electric field; the tuning dielectric layer changes the dielectric properties under the action of the electric field to tune the resonant wavelength of the metamaterial array structure layer; the metamaterial array structure layer resonates with the signal light to be converted and the pump light at the same time, and the light and the material undergo nonlinear and frequency interactions to generate parametric up-conversion light; the structural parameters of the metamaterial array structure layer are less than the coherent wavelength; and the substrate transmits the parametric up-conversion light. The present invention can reduce the requirements for phase matching conditions during the conversion process, use the electro-optical effect as the tuning mechanism of the signal light to be converted, realize broadband up-conversion detection of mid-to-far infrared light at room temperature, and has the advantages of high integration and miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

[0020] Figure 3 It is a schematic diagram of the top view structure of the array unit provided by the present invention.

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

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

[0023] Figure 6 It is a structural schematic diagram of the mid- and far-infrared single-photon detection device provided by the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Please refer to Figure 1 , Figure 1 A schematic diagram of the side structure of a tunable nonlinear metasurface device provided by the present invention.

[0026] The present invention provides a tunable nonlinear metasurface device 7, comprising: an electrode 4, used for generating an electric field; a metamaterial array structure layer 3, formed on a tuning medium layer 2, used for simultaneously resonating with incident signal light to be converted and pump light, so that light and matter undergo nonlinear and frequency interaction to generate parametric up-conversion light; a structural parameter of the metamaterial array structure layer 3 is smaller than a coherent wavelength; the signal light to be converted includes mid- and far-infrared light; the tuning medium layer 2, formed on a substrate 1, used for changing dielectric properties under the action of an electric field to tune the resonant wavelength of the metamaterial array structure layer 3; and a substrate 1, used for transmitting the parametric up-conversion light.

[0027] The present 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, and the electric field is used to regulate 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 (smaller than the material refractive index of the metamaterial array structure layer 3) in the mid- and far-infrared bands. The substrate 1 enhances the structural strength of the entire device and can transmit parametric up-conversion light and unconverted part of the signal light and pump light. The tuning dielectric layer 2 disposed on the substrate 1 can be selected from a material with a strong electro-optical effect, such as LiNbO3. When the electrode 4 generates an electric field, the dielectric properties of the tuning dielectric layer 2 will change accordingly. According to the electro-optical effect, the change in refractive index can be expressed as: in, E is the strength of the external electric field, r is the electro-optic coefficient tensor, n 0 is the refractive index of the material in the absence of an electric field.

[0028] By adjusting the voltage between the electrodes 4, the change of the refractive index can be precisely controlled, thereby tuning the resonant wavelength of the metamaterial array structure layer 3 to be converted. The metamaterial array structure layer 3 is arranged on the tuning medium layer 2, and its structural parameters (such as the length L and width D of the array unit) are smaller than the coherent wavelength, thereby allowing the metamaterial array structure layer 3 to resonate simultaneously with the incident signal light (4-14μm) and pump light (1.52-1.57μm) to be converted. This design allows the nonlinear sum frequency interaction between light and matter to occur, generating detectable parametric up-conversion light. The design of the metamaterial array structure layer 3 allows continuous tuning over a wide bandwidth, is not limited by phase matching conditions, and does not need to consider the phase mismatch problem caused by the change in the refractive index of the material. The frequency of the up-conversion light is higher than that of the pump light and the signal light, and is easily detected by the single-photon detector 10, realizing broadband tunable and effective detection of mid- and far-infrared light. The electro-optic effect is used as the tuning mechanism of the resonant wavelength of the metamaterial array structure layer 3, which can be controlled in a convenient way through the voltage source 8, without the need to use precise means to control the optical path or device, and achieves continuous, high spectral resolution tuning in a broadband range, high stability, simple mechanism, easy to achieve miniaturization and high integration of devices, and can be processed and manufactured with existing technology and devices at low cost. The use of parametric up-conversion for detection not only has higher single-photon sensitivity, but the system can also work at room temperature, and has a wider range of applications.

[0029] The electrodes 4 may be disposed on both sides of the substrate 1 , the tuning medium layer 2 and the metamaterial array structure layer 3 , or at other locations that are convenient for forming an electric field, and the present invention does not make any particular limitation thereto.

[0030] The material selected for the metamaterial array structure layer 3 must have a second-order nonlinear effect and a low absorptivity 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 in the metamaterial to ensure that the influence caused by the phase matching condition can be ignored.

[0031] The tuning medium layer 2 is made of a material having a strong electro-optical effect.

[0032] As a preferred embodiment, the metamaterial array structure layer 3 includes a plurality of array units; each array unit includes a first coupler, a waveguide-like and a second coupler arranged in sequence; the first coupler is used to enhance the coupling of the signal light to be converted to obtain enhanced coupling signal light and residual signal light; the second coupler is used to enhance the coupling of the pump light to obtain enhanced coupling pump light and residual pump light; and is also used to enhance the quasi-bound state of the coupled parametric up-conversion light; the waveguide-like is used to make the enhanced coupling signal light and the enhanced coupling pump light resonate, and generate parametric up-conversion through the nonlinear sum-frequency effect.

[0033] Please refer to Figure 2 , Figure 2A schematic diagram of the top-down structure of a tunable nonlinear metasurface device provided by the present invention.

[0034] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the top view of the array unit provided by the present invention.

[0035] In this embodiment, the metamaterial array structure layer 3 may include a plurality of array units, each of which may be in the shape of a rectangle or other geometric shapes (triangle, circle, hexagon or irregular shape), and each of which includes a first coupler, a quasi-waveguide and a second coupler arranged in sequence. 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. By optimizing the geometric shape and material properties of the first coupler, the intensity of the coupled signal light can be maximized while reducing the loss of the 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. The quasi-waveguide is located between the first and second couplers, and its function is to make the enhanced coupled signal light and the enhanced coupled pump light resonate therein to generate a quasi-bound state of parametric up-conversion light. By precisely controlling the size and refractive index of the quasi-waveguide, it can be ensured that the signal light to be converted and the pump light effectively resonate in the quasi-waveguide, thereby generating parametric up-conversion light. In addition, the second coupler is also responsible for enhancing the quasi-bound state of the coupled parametric up-conversion light, which is crucial to improving the up-conversion efficiency.

[0036] The length and width of the rectangular array unit are optimized according to the wavelengths of the signal light and pump light to be converted. The length L ranges from 1800nm ​​to 6600nm, such as 2010nm, and the width D ranges from 1750nm to 6550nm, such as 2000nm. The present invention does not make any special limitation here.

[0037] As a preferred embodiment, the first coupler is shaped as a group of double cylinders, the waveguide-like shape is a rectangular parallelepiped, and the second coupler is shaped as a plurality of groups of double cylinders.

[0038] In this embodiment, the first coupler is in the shape of a group of double cylinders, and this design is particularly suitable for enhancing the coupling of the signal light to be converted. The double cylinder structure can provide efficient light wave guidance and localization, thereby enhancing the coupling efficiency between the light wave and the waveguide-like. The design of the size and spacing of the double cylinders of the first coupler (the value range of the radius R1 of the small circle is 200-350nm, for example, 270nm, the value range of the radius R2 of the large circle is 230-420nm, for example, 320nm, the value range of the center distance l1 of the two circles is 600-1000nm, for example, 850nm, and the value range of the distance d1 between the center of the two circles and the left side of the waveguide-like is 300-800nm, for example, 560nm) is to match the wavelength and polarization state of the signal light to be converted, thereby maximizing the coupling efficiency. The shape of the waveguide-like is a rectangular parallelepiped, and this structure helps to limit the propagation of light waves in two directions, forming a two-dimensional optical waveguide mode. The width and length of the waveguide-like structure can be optimized according to the wavelength of the signal light to be converted and the pump light, and the width w is in the range of 500-2000nm, for example 600nm, and the length is, for example, 2000nm to achieve the best resonance condition. The shape of the second coupler is a plurality of groups of square cylinders, and this design helps to enhance the quasi-bound state of the coupled pump light and the parametric up-converted light. The arrangement and size of the two square columns (the side length w1 of the small square is in the range of 120-240nm, for example, 180nm, the side length w2 of the large square is in the range of 130-270nm, for example, 200nm, the distance l2 between the centers of the two large square columns is in the range of 500-800nm, for example, 600nm, the distance l3 between the centers of the large and small square columns is in the range of 200-280nm, for example, 245nm, and the distance d2 between the centers of the large and small square columns and the right side of the quasi-waveguide is in the range of 80-160nm, for example, 120nm) are optimized to match the characteristics of the pump light and the up-conversion light, ensuring that the light wave can be effectively coupled out of the quasi-waveguide. This embodiment realizes the simultaneous resonance of the quasi-bound state with a large wavelength difference, and can realize up-conversion detection in the long-wave mid-infrared band (4-14μm).

[0039] As a preferred embodiment, the material refractive index of the substrate 1 is smaller than the material refractive index of the tuning medium layer 2 and the material refractive index of the metamaterial array structure layer 3 .

[0040] In this embodiment, the material refractive index of the substrate 1 is less than the material refractive index of the tuning medium layer 2 and the material refractive index of the metamaterial array structure layer 3. The low refractive index of the substrate 1 helps to reduce the reflection and scattering of the light waves of the parametric up-conversion light inside the device, thereby improving the transmission efficiency of the light waves and the overall performance of the device. The high refractive index of the tuning medium layer 2 helps to produce a significant refractive index change under the action of an external electric field, thereby achieving precise tuning of the light wavelength of the signal light to be converted. The material of the metamaterial array structure layer 3 is selected as a medium with a second-order nonlinear effect, and the material refractive index of the metamaterial array structure layer 3 is higher than the material refractive index of the substrate 1 and the tuning medium layer 2, which helps to achieve localization of light waves and enhanced nonlinear effects in the metamaterial array structure layer 3.

[0041] As a preferred embodiment, the thickness of the metamaterial array structure layer 3 is smaller than the thickness of the tuning medium layer 2 , and the thickness of the tuning medium layer 2 is smaller than the thickness of the substrate 1 .

[0042] In this embodiment, the thickness of the metamaterial array structure layer 3 (600nm in this embodiment, set in the range of 400-2000nm) is greater than the thickness of the substrate 1 but less than the thickness of the tuning medium layer 2, which can ensure that the metamaterial array structure layer 3 effectively interacts with the light wave in a nonlinear manner while maintaining sufficient structural strength. The thickness of the tuning medium layer 2 (2000nm in this embodiment, set in the range of 1600-4000nm) 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 produce sufficient refractive index changes under the action of an external electric field to achieve effective tuning of the light wave. The thickness of the substrate 1 (e.g., 200-2000μm) is designed to be the maximum to provide sufficient support and stability while minimizing the propagation loss of the light wave in the substrate 1.

[0043] As a preferred embodiment, the material of the substrate 1 includes MgF2, CaF2 or BaF2; the material of the tuning medium layer 2 is LiNbO3; and the material of the metamaterial array structure layer 3 includes GaAs, GaP or GaSe.

[0044] Please refer to Figure 4 , Figure 4 The invention provides a transmission spectrum of a tunable nonlinear metasurface device in the 1.2-1.8 μm band.

[0045] Please refer to Figure 5 , Figure 5 The invention provides a transmission spectrum of a tunable nonlinear metasurface device in the 3.8-4.8 μm band.

[0046] In this embodiment, the material of the substrate 1 is CaF2, the material of the tuning dielectric layer 2 is LiNbO3, and the material of the metamaterial array structure layer 3 is GaAs. The LiNbO3 tuning dielectric layer 2 is arranged between the CaF2 substrate 1 and the GaAs material array structure. It has an electro-optical effect. The refractive index of the material changes with the direction and magnitude of the electric field. The external electric field is generated by the potential difference of the microelectrodes 4 on both sides. By adjusting the voltage value of the two electrodes 4, the refractive index of the LiNbO3 material is changed to affect the resonant response of the metasurface structure, so that the resonant frequency of the metasurface device drifts, and the corresponding conversion wavelength is tuned. With the larger r in the electro-optic coefficient tensor of the LiNbO3 material 33 The component is used as the source of electro-optical modulation, and the transmission spectrum of this embodiment in the near-infrared 1.2-1.8μm band and the mid-infrared 3.8-4.8μm band is simulated and calculated by the time-domain finite difference method. It can be seen that in the absence of an external electric field, the metasurface has a strong resonance near the near-infrared 1540nm and the mid-infrared 4250nm, which are suitable as the resonance modes of 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 drifted. When the external electric field is ±2×10 8 The metasurface transmission spectrum at 200 V / m can achieve continuous tuning of the signal light with a bandwidth exceeding 100 nm within this range of applied electric field values. At the same time, the resonance peak of the signal mode has always been located in the communication band of 1520-1570 nm, in which there are commercial high-power, center-frequency adjustable femtosecond light sources, which are easy to realize nonlinear parameter conversion.

[0047] The mid-infrared and far-infrared single-photon detection device provided by the present invention is described below. The mid-infrared and far-infrared single-photon detection device described below and the tunable nonlinear metasurface device 7 described above can be referenced to each other.

[0048] Please refer to Figure 6 , Figure 6 This is a schematic structural diagram of the mid- and far-infrared single-photon detection device provided by the present invention.

[0049] The present invention also provides a mid-to-far infrared single-photon detection device, comprising: a pulse light source 5, used to generate pump light; a semi-transparent and semi-reflective mirror 6, arranged at the pump light output side of the pulse light source 5, used to combine the pump light with the signal light to be converted and then incident on the tunable nonlinear metasurface device 7 as mentioned above; the tunable nonlinear metasurface device 7, arranged on the side of the semi-transparent and semi-reflective mirror 6 away from the pulse light source 5, used to generate parametric up-conversion light according to the pump light and the signal to be converted; a voltage source 8, used to provide a voltage to the electrode 4 of the tunable nonlinear metasurface device 7 so that the electrode 4 generates an electric field; a filter, arranged on the side of the tunable nonlinear metasurface device 7 away from the semi-transparent and semi-reflective mirror 6, used to filter out noise in the non-parametric up-conversion light frequency band; a single-photon detector 10, arranged on the side of the filter away from the tunable nonlinear metasurface device 7, used to detect photons of the up-conversion light.

[0050] The present invention also provides a mid-infrared single-photon detection device, including key components such as a pulse light source 5, a semi-transparent and semi-reflective mirror 6, a tunable nonlinear metasurface device 7, a voltage source 8, a filter and a single-photon detector 10. The near-infrared pulse light source 5 is used to generate pump light, and the center frequency of the pump light 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 up-conversion efficiency. The semi-transparent and semi-reflective mirror 6 is arranged at the pump light output side of the pulse 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 and semi-reflective mirror 6 and incident on the tunable nonlinear metasurface device 7 together. Subsequently, the light and the material undergo nonlinear sum-frequency action to generate parametric up-conversion light whose optical frequency is equal to the sum of the signal light and the pump light frequency. Then, the remaining signal light, the remaining pump light and the parametric up-conversion light are transmitted from the nonlinear metasurface. The filter is arranged on the side of the nonlinear metasurface device away from the semi-transparent and semi-reflective mirror 6, and is used to filter out the noise in the non-parametric up-conversion light frequency band to improve the signal-to-noise ratio. The remaining signal light, the remaining pump light and the parametric up-conversion light are filtered by the filter 9, and the up-conversion light in the visible light or near-infrared band is left, and finally incident on the single-photon detector 10 and detected. The single-photon detector 10 is arranged on the side of the filter away from the nonlinear metasurface device. The output voltage of the voltage source 8 is adjustable, and its voltage output resolution and range respectively determine the tuning resolution and range of the conversion wavelength. The voltage output by 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 in the space where the nonlinear metasurface device is located is changed, the structural resonance frequency is tuned, and the wavelength of the signal light to be converted is changed.

[0051] As a preferred embodiment, the center frequency of the pulse light source 5 is 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.

[0052] In this embodiment, the pulse light source 5 is designed to have a center frequency in the near infrared or visible light band to ensure effective nonlinear interaction between the pump light and the mid- and far-infrared signal light to be converted. The pulse width of the pulse light source 5 is optimized to be less than 500 fs to provide high peak power and time resolution. The peak power of the pulse light source 5 is designed to be greater than 10 7 W, to ensure sufficient energy input in the nonlinear process.

[0053] As a preferred embodiment, the material of the semi-transparent and semi-reflective mirror 6 is fluoride.

[0054] In this embodiment, the semi-transparent and semi-reflective mirror 6 needs to be able to work in the signal light and pump light bands at the same time, and is selected to be a fluoride, such as MgF2, CaF2 or BaF2, because of their excellent transmittance and low absorption rate in the mid- and far-infrared bands, and they have good mechanical properties and chemical stability.

[0055] As a preferred embodiment, the single photon detector 10 is an avalanche photodetector made of silicon material or InGaAs / InP material.

[0056] In this embodiment, the single photon detector 10 is determined according to the wavelength of the up-converted light. For example, a silicon avalanche photodetector can be used for 350-1100 nm, and an InGaAs / InP avalanche photodetector can be used for 900-1700 nm.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions 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 for generating an electric field; The metamaterial array structure layer is formed on the tuning medium layer and is used to simultaneously resonate with the incident signal light to be converted and the pump light, so that the light and the material undergo nonlinear sum-frequency interaction to generate parametric up-conversion light; The structural parameter of the metamaterial array structure layer is smaller than the coherence wavelength; The signal light to be converted includes mid-infrared and far-infrared light; The tuning dielectric layer is formed on the substrate and is used to change the dielectric properties under the action of the electric field to tune the resonant wavelength of the metamaterial array structure layer; The substrate is used to transmit the parametric up-conversion light.

2. The tunable nonlinear metasurface device according to claim 1, characterized in that: The metamaterial array structure layer includes a plurality of array units; each array unit includes a first coupler, a waveguide-like device, and a second coupler which are sequentially arranged; The first coupler is used for enhancing the coupling of the signal light to be converted to obtain enhanced coupled signal light and residual signal light; The second coupler is used for enhancing the coupling of the pump light to obtain enhanced coupled pump light and residual pump light; It is also used to enhance the quasi-bound states of coupled parametric upconversion light; The waveguide-like light is used to make the enhanced coupling signal light and the enhanced coupling pump light resonate, and generate the parametric up-conversion light through the nonlinear sum-frequency effect.

3. The tunable nonlinear metasurface device according to claim 2, characterized in that: The first coupler is in the shape of a group of double cylinders, the waveguide-like shape is a rectangular parallelepiped, and the second coupler is in the shape of a plurality of groups of double cylindrical bodies.

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

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

6. The tunable nonlinear metasurface device according to any one of claims 1 to 5, characterized in that: The material of the substrate includes MgF2, CaF2 or BaF2; the material of the tuning medium layer is LiNbO3; and the material of the metamaterial array structure layer includes GaAs, GaP or GaSe.

7. A mid-to-far infrared single-photon detection device, characterized in that: include: A pulse light source for generating pump light; A semi-transparent and semi-reflective mirror, arranged at the pump light output side of the pulse light source, used to combine the pump light with the signal light to be converted and then inject it into the tunable nonlinear metasurface device according to any one of claims 1 to 6; The tunable nonlinear metasurface device is arranged on a side of the semi-transparent and semi-reflective mirror away from the pulse light source, and is used to generate parametric up-conversion light according to the pump light and the signal to be converted; A voltage source, used for providing a voltage to the electrodes of the tunable nonlinear metasurface device so that the electrodes generate an electric field; A filter, arranged on a side of the tunable nonlinear metasurface device away from the semi-transparent and semi-reflective mirror, for filtering out noise in a frequency band other than the parametric up-conversion optical frequency band; A single-photon detector is arranged on a side of the filter away from the tunable nonlinear metasurface device and is used to detect photons of the up-converted light.

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

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

10. The mid-to-far infrared single photon detection device according to any one of claims 7 to 9, characterized in that: The single-photon detector is an avalanche photodetector made of silicon material or InGaAs / InP material.

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