A chip-based spectrometer based on metamaterials

Abstract

The present invention discloses a chip-type spectrometer based on metamaterials. The chip-type spectrometer includes at least one metamaterial detection unit, and the more metamaterial detection units there are, the more frequency points that can be analyzed. The metamaterial detection unit includes a frequency selection structure and a photoelectric conversion structure. When performing spectral analysis, the frequency selection structure in each metamaterial detection unit responds to a specific frequency in the target signal and generates a local electric field and a magnetic field; the free carriers in the photoelectric conversion structure placed in the local field are directionally deflected due to the Lorentz force, thereby forming a DC potential difference at its boundary. Each metamaterial detection unit corresponds to its own frequency, so that the correspondence between a specific optical frequency and a specific electrical signal is achieved, and the spectrum analysis is completed. The chip-type spectrometer of the present invention realizes the integration of frequency resolution and photoelectric detection, and has the advantages of simple structure, fast response speed, small size, easy integration, and a large response band range.

Description

Technical Field

[0001] The invention relates to a chip-type spectrometer based on metamaterials, and belongs to the field of optical electronic devices. Background Art

[0002] As a tool for analyzing spectral components, spectrometers are widely used in food component analysis, biological detection sensing, medical health detection, image spectrum analysis, etc., which mainly include spectral resolution and photoelectric detection. There are two main types of spectrometer technologies currently used. The first type is a spectrometer based on the principle of grating spectroscopy combined with photodetectors. It mainly uses optical devices to converge different frequency components of the spectrum to different spatial positions, and then uses photodetectors to capture the spectral components of different spatial positions to complete spectral analysis; the second type is a spectrometer based on Fourier transform, which mainly includes a movable Michelson interferometer. It uses the principle of interference to collect equivalent time domain signals, and then converts them into photoelectric signals, and uses computers to complete Fourier transform to obtain spectral information. The spectral resolution and photoelectric detection of existing spectrometers are independent, so they contain more components, making the spectrometer larger and not conducive to integration. At the same time, based on the existing detection principle, the frequency band covered is limited. The same spectrometer only works in a narrow frequency range and does not have wide-band versatility.

[0003] Metamaterials have developed rapidly in recent years due to their unique electromagnetic wave response characteristics. Spectral resolution can be achieved by utilizing the sub-wavelength structural characteristics of metamaterials and their frequency selection of electromagnetic waves. At the same time, combined with new photoelectric detection theories, we can try to use them to build a new photoelectric spectrometer to achieve spectral resolution and photoelectric conversion integration, thereby overcoming the shortcomings of existing spectrometers such as large size, difficulty in integration, limited operating frequency, and long sampling time. Summary of the invention

[0004] The purpose of the present invention is to provide a chip-type spectrometer based on metamaterials, which can realize the integration of frequency resolution and photoelectric detection, and has the advantages of simple structure, fast response speed, small size, easy integration, and wide response band range.

[0005] The metamaterial-based chip spectrometer provided by the present invention comprises at least one metamaterial detection unit;

[0006] The metamaterial detection unit includes a frequency selection structure and a photoelectric conversion structure, and the photoelectric conversion structure is located in a local electromagnetic field formed by the resonance of the frequency selection structure and the target electromagnetic wave. In addition, there is no special restriction on the geometric relationship between them. The photoelectric conversion structure is used for converting the target electromagnetic wave (light) into an electrical signal.

[0007] The metamaterial detection unit is entirely arranged on a low-loss substrate.

[0008] When the metamaterial detection unit is working, the frequency selection structure generates a resonant response to electromagnetic waves in the target frequency range, and generates a local electric field and a magnetic field inside the frequency selection structure, and the local electric field and magnetic field strengths are enhanced compared to the electric field and magnetic field strengths of the incident electromagnetic wave. Electromagnetic waves outside the target frequency range do not generate a resonant response with the frequency selection structure, so no local electric field and magnetic field enhancement are generated. The photoelectric conversion structure is placed within the local electric field and magnetic field region of the frequency selection structure. Under the joint action of the aforementioned local electric field and magnetic field, the free carriers in the photoelectric conversion structure will move due to the Lorentz force, and its motion component includes a DC component. Under the action of the DC component, the free carriers in the photoelectric conversion structure will move in a directional manner, thereby forming an accumulation of opposite-sign charges at the two end boundaries of the photoelectric conversion structure, generating a DC potential difference. By directly recording the DC potential difference, the electric field strength of the electromagnetic wave of the frequency selected by the frequency selection structure can be calculated, thereby realizing the detection of the electromagnetic wave of the frequency.

[0009] Different frequency selection structures in different metamaterial detection units select different frequency components, and realize the conversion of electromagnetic waves into DC potential difference through their respective photoelectric conversion structures. Combining multiple different metamaterial detection units can perform spectrum analysis and record of light waves containing multiple frequency components.

[0010] The frequency selective structure generates a resonant response to electromagnetic waves of a specific polarization and a specific frequency, and has a sub-wavelength size. It has two functions: one is to selectively respond to a specific frequency band among many frequencies to complete the frequency selection; the other is to generate the required local electric field and magnetic field. The shape of the frequency selective structure is not unique, and can be geometrically continuous or a combination of multiple discrete shapes. Specifically, Figure 1 As shown in (a), the frequency selection structure is an open ring resonant structure, a local electric field and a magnetic field are formed inside the open ring resonant structure, and the photoelectric conversion structure is placed inside the open ring resonant structure.

[0011] The constituent materials of the frequency selective structure only need to meet the basic requirements of electromagnetic wave resonance for materials, without any additional restrictions; it can be a good conductor metal material such as Al, Au, Ag, Cu, Ni, or a dielectric material such as TiO2, SiO2, BaTiO3, GaF2, MgF2, MgO, etc.; it can also be a heavily doped or undoped semiconductor such as GaAs, Si, Ge, Se, ZnS, CdTe, HgTe, etc., and the elements doped in the heavily doped or undoped semiconductor include boron, phosphorus, arsenic, antimony, etc.; it can be a polymer material such as polyethylene, polypropylene, polystyrene, epoxy resin, phenolic resin, etc.; it can also be a conductive polymer material filled with conductive fillers such as carbon black, carbon nanotubes, graphene, metal, etc.

[0012] The photoelectric conversion structure is used to convert optical signals into electrical signals and needs to be located within the local electric and magnetic fields generated by the frequency selection structure. The shape of the photoelectric conversion structure is not particularly limited and can be a continuous structure or a discrete structure. The specific shape is related to the wiring method of the spectrometer electrical signal.

[0013] The photoelectric conversion structure is composed of a material with free carriers, which may be a semi-metal material such as Bi, Cd3As2, CrO2, CoS2; it may also be an n-type or p-type doped semiconductor material such as Si, Ge, Se, InP; it may also be a two-dimensional material such as graphene, black phosphorus, MoS2, etc.

[0014] The low-loss substrate refers to a material with low loss to the target electromagnetic wave, such as Teflon, FR-4, etc. in the microwave band, high-purity Si, high-purity GaAs, high-purity Ge, etc. in the terahertz band, glass, quartz, etc. in the visible light band. The specific choice depends on the working band of the chip-based spectrometer based on the metamaterial.

[0015] The metamaterial detection unit can be used alone to complete single frequency band detection; metamaterial detection units of different sizes can be used together to complete multiple frequency band detection; or they can be used in conjunction with other equipment to complete imaging analysis, security inspection and other functions.

[0016] The present invention has the following beneficial effects:

[0017] 1) The metamaterial detection unit used in the present invention is of sub-wavelength size, and the overall structure can be prepared by conventional semiconductor processing technology, which is a small-sized, easily integrated chip-type spectrometer;

[0018] 2) The metamaterial detection unit used in the present invention simultaneously completes the spectral resolution and photoelectric conversion process, without the need for additional spectral resolution optical elements such as gratings and interferometers, and also without the need for additional photoelectric detectors. The overall device is small and easy to carry;

[0019] 3) The metamaterial detection unit used in the present invention has complete design freedom for the response wavelength, covering from the radio frequency band to the visible light band (the wavelength range may include 400nm to 4m);

[0020] 4) The chip-type spectrometer provided by the present invention directly drives the movement of carriers to achieve photoelectric conversion based on the Lorentz force, and therefore has an ultra-fast response speed of picoseconds. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 (a) is a schematic diagram of a metamaterial detection unit of a metamaterial-based chip spectrometer in Example 1 of the present invention; wherein 1 represents a photoelectric conversion structure, 2 represents a frequency selection structure, and 3 represents a low-loss substrate;

[0022] Figure 1 (b) is a schematic diagram of the spectral response of the metamaterial detection unit 1 of the metamaterial-based chip spectrometer in Example 1 of the present invention.

[0023] Figure 2 (a) is the frequency response selection characteristic of the metamaterial detection unit 1 in the terahertz band in Example 1 of the present invention; Figure 2 (b) is the photoelectric conversion result of the metamaterial detection unit 1 in Example 1 of the present invention under the irradiation of a single-frequency electromagnetic wave.

[0024] Figure 3 (a) is a schematic diagram of a combination of four metamaterial detection units of different sizes in Example 1 of the present invention; Figure 3 (b) is the frequency response selection characteristic of the four metamaterial detection units of different sizes in Example 1 of the present invention in the terahertz band, and the central operating frequencies are 0.6 THz, 0.8 THz, 1.0 THz and 1.2 THz respectively.

[0025] Figure 4 This is the dependence of the DC voltage and power density generated by the four metamaterial detection units of different sizes in Example 1 of the present invention.

[0026] Figure 5 Schematic diagram of spectrum analysis results of a chip-based spectrometer based on metamaterials in Example 1 of the present invention.

[0027] Figure 6 for Figure 1 The working concept diagram of a chip-based spectrometer composed of individual metamaterial detection units is shown. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified, the experimental methods involved in the following embodiments are all conventional methods.

[0030] Unless otherwise specified, the materials, reagents, etc. involved in the following examples can be obtained from commercial sources.

[0031] The present invention provides a metamaterial-based chip spectrometer that can distinguish four frequencies, which are 0.6THz, 0.8THz, 1.0THz and 1.2THz respectively. The metamaterial detection unit structure can be prepared by ultraviolet lithography or laser direct writing technology.

[0032] The metamaterial detection unit provided by the present invention is composed of the following parts:

[0033] Figure 1 The mark 1 in (a) indicates a photoelectric conversion structure, the specific material is n-type doped GaAs, and the dimensions are as follows: metamaterial detection unit 1 is 14μm×14μm, with a thickness of 300nm; metamaterial detection unit 2 is 9μm×9μm, with a thickness of 300nm; metamaterial detection unit 3 is 7μm×7μm, with a thickness of 300nm; metamaterial detection unit 4 is 5μm×5μm, with a thickness of 300nm. The specific arrangement is shown in Figure 3 (a).

[0034] Figure 1 The mark 2 in (a) indicates a frequency selective structure, the specific material is gold, and the dimensions are as follows: the line width of metamaterial detection unit 1 is 6μm, the outer length is 31μm, the gap width is 2μm, and the gold layer thickness is 300nm; the line width of metamaterial detection unit 2 is 6μm, the outer length is 25μm, the gap width is 2μm, and the gold layer thickness is 300nm; the line width of metamaterial detection unit 3 is 4μm, the outer length is 19.5μm, the gap width is 2μm, and the gold layer thickness is 300nm; the line width of metamaterial detection unit 4 is 4μm, the outer length is 17μm, the gap width is 2μm, and the gold layer thickness is 300nm. See the specific arrangement. Figure 3 (a).

[0035] Figure 1 Mark 3 in (a) indicates a substrate with low loss in the terahertz band, and the specific material is high-purity GaAs (corrosion defect density is 1500-5000cm 2 ), with a thickness of 10μm and a relative dielectric constant of 12.9 in the terahertz band; the four metamaterial detection units are combined together, with an overall size of 160μm×160μm.

[0036] Figure 1(b) is the overall frequency response curve of the metamaterial detection unit 1. The incident wave adopts plane wave normal incidence, and the resonant frequency is designed to be 0.6THz. The calculation result is consistent with the design. It can be seen that near 0.6THz, the metamaterial detection unit 1 has a resonant response with a narrow peak shape. At frequencies far away from 0.6THz, the metamaterial detection unit 1 does not show resonant characteristics, so the metamaterial detection unit 1 can be used to select the 0.6THz frequency component in the incident spectrum.

[0037] Figure 2 (a) is the normalized electromagnetic responsivity of the metamaterial detection unit 1. It can be seen that a response curve with frequency selection characteristics is shown near 0.6 THz;

[0038] Figure 2 (b) is the photoelectric conversion response of the metamaterial detection unit 1 to 0.6THz electromagnetic wave irradiation. The electric field strength of the incident terahertz wave is 10 7 V / m, an integrated DC voltage of 35mV can be obtained across the photoelectric conversion structure in the metamaterial detection unit 1. It can be seen that after the frequency selection structure in the metamaterial detection unit 1 selects the 0.6THz frequency, the photoelectric conversion structure in the metamaterial detection unit 1 can complete the conversion of electromagnetic waves into electrical signals. Therefore, no additional optical spectrometer and photoelectric detector are required, and the metamaterial detection unit 1 can complete frequency selection and photoelectric conversion.

[0039] Figure 3 (a) is a schematic diagram of a combination of four metamaterial detection units of different sizes, namely metamaterial detection unit 1, metamaterial detection unit 2, metamaterial detection unit 3 and metamaterial detection unit 4;

[0040] Figure 3 (b) shows the frequency response selection characteristics of four metamaterial detection units of different sizes in the terahertz band, with central operating frequencies of 0.6THz, 0.8THz, 1.0THz, and 1.2THz, respectively. It can be seen that different metamaterial detection units have selection characteristics for different frequencies. Combined with the photoelectric conversion structure in each metamaterial detection unit, the selection and recording of different frequencies in the spectrum can be completed, thus completing the spectrum analysis process, indicating that the device has the function of a spectrometer.

[0041] Figure 4 The dependence of the DC voltage and power density generated by four metamaterial detection units of different sizes. As can be seen from the figure, under the incident power density, the DC voltage obtained by each metamaterial detection unit is proportional to the incident electromagnetic wave power density, and the linearity is good. Therefore, by testing and recording the DC voltage of each metamaterial detection unit, the intensity corresponding to each frequency of the incident electromagnetic wave can be calculated by mathematical deduction.

[0042] Figure 5 An example of a spectrometer actually reconstructing the intensity of electromagnetic waves. Figure 5 (a) shows the DC voltages at both ends of the four metamaterial detection units obtained by theoretical calculation. The field strengths of each frequency are reconstructed using their respective DC voltages. The reconstruction results are shown in Figure 5 (b), it can be seen that the relative error between the reconstructed field intensity completed by the spectrometer and the actual incident field intensity is within 1%, indicating that the spectrometer of the present invention has good frequency analysis performance.

[0043] Figure 6 for Figure 1 The working concept diagram of a chip-type spectrometer composed of a combination of single metamaterial detection units is shown. The more metamaterial detection units the chip-type spectrometer based on metamaterials contains, the more spectral frequency points can be analyzed. When the electromagnetic wave to be measured is irradiated onto the spectrometer, the metamaterial detection unit of the corresponding frequency generates a direct current. By recording and calculating the direct current signal, the spectrum information of the electromagnetic wave to be analyzed can be obtained.

[0044] In the metamaterial-based chip spectrometer provided by the present invention, the frequency selection structure in the metamaterial detection unit can complete the detection and selection of spectral frequencies, and the photoelectric conversion structure completes the conversion of optical signals into electrical signals. Therefore, there is no need for additional gratings and other optical splitting devices and photoelectric test devices such as photodetectors. The size of a single detection unit is as low as sub-wavelength level, and spectral resolution and photoelectric conversion are integrated, which can greatly reduce the number and volume of components of the spectrometer and facilitate integration and carrying. At the same time, the frequency selection characteristics are completely determined by the metamaterial structure, and in theory, it can be applied from the microwave band to the visible light band (the wavelength range may include 400nm~4m).

Claims

1. A metamaterial-based chip spectrometer, comprising at least one metamaterial detection unit; The metamaterial detection unit includes a frequency selection structure and a photoelectric conversion structure, and the photoelectric conversion structure is located in a local electromagnetic field formed by the resonance of the frequency selection structure and the target electromagnetic wave, and the photoelectric conversion structure is used to convert the target electromagnetic wave into an electrical signal; The metamaterial detection unit is disposed as a whole on a low-loss substrate; The frequency selective structure selects a specific frequency of the incident spectrum and generates a local electromagnetic field; The frequency selective structure is a geometrically continuous structure or a structure formed by a plurality of discrete shapes.

2. The chip-type spectrometer according to claim 1, characterized in that: The constituent material of the frequency selection structure is selected from any one of the following: good conductor metal material, dielectric material, heavily doped or undoped semiconductor and conductive polymer material.

3. The chip-type spectrometer according to claim 1 or 2, characterized in that: The photoelectric conversion structures are in the form of individual structures separated from each other or continuous geometric structures.

4. The chip-type spectrometer according to claim 1 or 2, characterized in that: The photoelectric conversion structure is composed of a material with free carriers, selected from any one of the following: n-type or p-type doped semiconductor materials, semi-metal materials and two-dimensional materials.

5. The chip-type spectrometer according to claim 1 or 2, characterized in that: The low-loss substrate is a receiving platform, and the material is Teflon, FR-4, high-purity Si, high-purity GaAs, high-purity Ge, glass or quartz.

6. The chip-type spectrometer according to claim 1 or 2, characterized in that: The chip-type spectrometer may include a plurality of the metamaterial detection units; A plurality of the metamaterial detection units are arranged in combination in the form of a planar array, nesting, random and / or longitudinal stacking.

Images