Tunable narrow-band filtering device, optical spectrometer and spectral detection system

Abstract

The application relates to the technical field of spectral detection, in particular to a tunable narrow-band filter device, a spectrometer and a spectral detection system. The tunable narrow-band filter device comprises a resonant metasurface, which has a metasurface structure and is used for generating a narrow-band resonant response for light incident thereon, the narrow-band resonant response is characterized by a narrow-band transmission peak and / or a transmission valley with a center wavelength in the spectrum; a refractive index tunable medium layer covering the resonant metasurface, the refractive index of the refractive index tunable medium layer is continuously adjustable under the action of an external electric field, so as to change the equivalent refractive index of the surrounding environment of the resonant metasurface through the change of the refractive index; and an electrode array connected with the refractive index tunable medium layer and used for applying an external electric field to the refractive index tunable medium layer to adjust the refractive index. Through the technical scheme, miniaturization can be met, high resolution and large working bandwidth can be realized.

Description

Technical Field

[0001] This application relates to the field of spectral detection technology, and in particular to a tunable narrowband filter device, a spectrometer, and a spectral detection system. Background Technology

[0002] Narrowband filters are the core components in optical systems that enable wavelength selective transmission or blocking, and are widely used in fields such as spectral analysis, optical communication, laser frequency selection, and biosensing.

[0003] Currently, common narrowband filtering devices mainly include thin-film interference filters, diffraction gratings, and Fabry-Perot etalons. Thin-film interference filters achieve narrowband filtering based on the interference effect of multilayer dielectric films, but their center wavelength is fixed after fabrication and lacks dynamic tuning capability. While Fabry-Perot etalons can achieve wavelength tuning within a certain range by mechanically changing the cavity length, their precision is limited by the flatness and mechanical stability of the mirrors. There is an inherent constraint between the tuning range and the filter linewidth, making it difficult to maintain an extremely narrow filter linewidth over a large wavelength tuning range. Tunable filters based on acousto-optic or electro-optic effects support electrically controlled tuning, but their filter linewidth is typically wide, resulting in limited spectral resolution.

[0004] Existing narrowband filtering devices struggle to simultaneously achieve extremely narrow filter linewidths and large wavelength tuning ranges within a compact size. This issue is particularly prominent in applications such as chip-scale miniaturized spectrometers, which rely on tunable narrowband filtering devices as core frequency selection components. The linewidth and tuning range of these devices directly determine the spectrometer's resolution and operating bandwidth. The limitations of existing filtering device performance have become a bottleneck restricting the overall performance of miniaturized spectrometers. Summary of the Invention

[0005] This application provides a tunable narrowband filter device, a spectrometer, and a spectral detection system to at least partially solve the above-mentioned technical problems.

[0006] To achieve the above objectives, according to a first aspect of this application, a tunable narrowband filter device is provided, comprising: A resonant metasurface has a metasurface structure and is used to generate a narrowband resonant response to light incident on it. The narrowband resonant response is characterized by a narrowband transmission peak and / or transmission valley with a center wavelength in the spectrum. A refractive index tunable dielectric layer is covered on the resonant metasurface. The refractive index of the refractive index tunable dielectric layer is continuously adjustable under the action of an external electric field, so as to change the equivalent refractive index of the surrounding environment of the resonant metasurface by changing the refractive index. An electrode array, connected to the refractive index tunable dielectric layer, is used to apply the external electric field to the refractive index tunable dielectric layer to adjust the refractive index.

[0007] Furthermore, the resonant metasurface includes a plurality of pixels arranged in an array, each pixel containing at least one resonant unit, and the resonant units contained in different pixels are used to enable different pixels to have different resonant wavelengths, wherein the filtering windows of each pixel collectively cover a continuous or quasi-continuous spectral band.

[0008] Furthermore, the resonant unit is asymmetric, so that by introducing asymmetric perturbation, the resonant energy of the resonant unit leaks into free space, thereby generating the narrowband resonant response.

[0009] Furthermore, the asymmetry is formed in at least one of the following ways: The resonant unit includes at least one irregular structure to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis and are rotated by a preset angle to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the two substructures have a size difference in at least one of length, width or height, so as to break the mirror symmetry and rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis. The two substructures are made of dielectric materials with different dielectric constants to break the dielectric constant symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the refractive indices of the medium in which the two substructures are located differ, thereby breaking the dielectric constant symmetry of the resonant unit.

[0010] Furthermore, the two substructures are two rectangular pillars of different lengths, so that the resonant unit constitutes the asymmetry; or The two substructures are two elliptical cylinders, which are rotated together relative to the axis by a predetermined angle so that the resonant unit constitutes the asymmetry.

[0011] Furthermore, the aspect ratio of the rectangular pillar is greater than a preset ratio, so that when the refractive index adjustable medium layer is oriented on one side, the molecules in the refractive index adjustable medium layer near the surface of the resonant metasurface are arranged in an orderly manner along the sidewall direction of the rectangular pillar.

[0012] According to a third aspect of this application, a spectrometer is proposed, comprising the tunable narrowband filter device as described above.

[0013] Furthermore, the spectrometer also includes: A polarization control unit is disposed before the tunable narrowband filter device, used to control the polarization state of the incident light and guide the polarized light to the tunable narrowband filter device. The detector is disposed in the output optical path of the tunable narrowband filter device and is used to receive the optical signal output after being filtered by the tunable narrowband filter device and convert the light intensity of the optical signal into a light intensity detection value. A computing unit, connected to the detector, is used to obtain the spectral information of the incident light based on the pre-calibrated transmission matrix and the light intensity detection value output by the detector.

[0014] Furthermore, the transfer matrix is ​​obtained by calibrating the spectral response of the tunable narrowband filter device, the spectral response calibration including: Monochromatic light of different wavelengths is sequentially output from a calibrated light source, and after passing through the polarization control unit, it is incident on the tunable narrowband filter device; Different driving voltages are sequentially applied to the tunable narrowband filter device to change the refractive index of the refractive index-tunable medium layer, and the light intensity response of each pixel is collected under different driving voltages and different wavelengths. The transmission matrix is ​​constructed based on the light intensity response.

[0015] According to a third aspect of this application, a spectral detection system is proposed, comprising a tunable narrowband filter device as described above, or a spectrometer as described above.

[0016] The tunable narrowband filter device in this embodiment generates a narrowband resonant response through a resonant metasurface. By utilizing the characteristic that the refractive index of the resonant metasurface is continuously adjustable under the drive of an external electric field, the equivalent refractive index of the environment surrounding the resonant metasurface is changed, thereby causing a continuous shift in the center wavelength of the narrowband resonant response. While maintaining a small chip-level volume, an electrically tunable narrowband filtering function is achieved. This enables high resolution and a large operating bandwidth while meeting miniaturization requirements, providing a miniaturized hardware foundation for high-resolution, large-bandwidth spectral analysis devices.

[0017] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a tunable narrowband filter device provided in one embodiment of this application; Figure 2 This is a schematic diagram of the optical path of the spectrometer provided in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a resonant unit in the form of a double elliptical cylinder in one embodiment of this application; Figure 4 This is a schematic diagram of the pixelated design of a resonant metasurface in one embodiment of this application; Figure 5 The image shows the tuning filter spectrum of a single pixel in a tunable narrowband filter device in the form of a double elliptical cylinder according to an embodiment of this application. Figure 6 This is a schematic diagram of the structure of a resonant unit in the form of a double rectangular column in one embodiment of this application; Figure 7 This is a schematic diagram of a single-sided orientation scheme of a tunable narrowband filter device in one embodiment of this application; Figure 8 The tuning filter spectrum of pixel 1 in a tunable narrowband filter device in the form of a double rectangular column in one embodiment of this application; Figure 9 The tuning filter spectrum of pixel 2 in a tunable narrowband filter device in the form of a double rectangular column in one embodiment of this application; Figure 10 The image shows the notch filtering effect of a tunable narrowband filter device in one embodiment of this application. Figure 11 The tunable notch filter spectrum of a tunable narrowband filter device based on a double elliptic cylinder structure in one embodiment of this application is shown. Figure 12 This is a tunable notch filter spectrum of a tunable narrowband filter device based on a double rectangular pillar structure in one embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 10, tunable narrowband filter device; 100, resonant metasurface; 200, refractive index tunable dielectric layer; 300, electrode array; 20, detector; 30, beam splitter; 40, polarization control unit. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0021] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] Reference Figure 1 As shown, according to a first aspect of this application, this application provides a tunable narrowband filter device 10, comprising: The resonant metasurface 100 has a metasurface structure for generating a narrowband resonant response to light incident thereon, the narrowband resonant response being characterized by a narrowband transmission peak and / or transmission valley with a center wavelength in the spectrum. A refractive index adjustable dielectric layer 200 is applied to the resonant metasurface 100. The refractive index of the refractive index adjustable dielectric layer 200 is continuously adjustable under the action of an external electric field, so as to change the equivalent refractive index of the surrounding environment of the resonant metasurface 100 by changing the refractive index. The electrode array 300 is connected to the refractive index adjustable dielectric layer 200 and is used to apply the external electric field to the refractive index adjustable dielectric layer 200 to adjust the refractive index.

[0023] Specifically, the resonant metasurface 100 is a structure formed by arranging multiple structural units according to a predetermined period, capable of generating a resonant response to incident light of a specific wavelength. When incident light irradiates the resonant metasurface 100, it resonates at a specific wavelength, corresponding to a transmission peak and / or transmission valley with extremely narrow linewidth in the spectrum. The extremely narrow linewidth of this resonant response (i.e., the full width at half maximum (FWHM) of the resonance peak is extremely small, and the Q factor is extremely high) means that a very small wavelength shift can be resolved in the spectrum, which can significantly improve the resolution of spectral detection.

[0024] The refractive index of the tunable dielectric layer 200 can be continuously and tunably changed under the action of an external electric field. When the refractive index of the tunable dielectric layer 200 changes, the equivalent refractive index of the surrounding environment of the resonant metasurface 100 changes accordingly, which in turn causes the center wavelength of the narrowband resonant response generated by the resonant metasurface 100 to shift.

[0025] The position of the resonant wavelength of the narrowband resonant response generated by the resonant metasurface 100 has a good linear relationship with the equivalent refractive index of the environment surrounding the resonant metasurface 100 (that is, there is a good linear relationship between the amount of refractive index change of the refractive index tunable medium layer 200 and the amount of offset of the resonant center wavelength).

[0026] In an optional embodiment of this application, the refractive index tunable dielectric layer 200 can be made of liquid crystal material. Under the influence of an external electric field, the liquid crystal molecules deflect, and the change in their direction of orientation causes a continuous change in the equivalent refractive index of the liquid crystal layer in the polarization direction of the incident light. Optionally, the refractive index tunable dielectric layer 200 can also be made of electro-optic crystal material, electro-refractive polymer material, or other materials whose refractive index can be continuously changed under the influence of an electric field.

[0027] An electrode array 300 is connected to the refractive index tunable dielectric layer 200 and is used to apply the external electric field to the refractive index tunable dielectric layer 200 to adjust the refractive index. The electrode array 300 can be made of a transparent conductive material, such as indium tin oxide or other transparent conductive oxides, to ensure that incident light can pass through the electrode array 300 and enter the refractive index tunable dielectric layer 200 and the resonant metasurface 100. By applying different driving voltages to different electrode units in the electrode array 300, the local refractive index of each region of the refractive index tunable dielectric layer 200 can be independently adjusted, thereby causing a continuous shift in the center wavelength of the narrowband resonant response.

[0028] Reference Figure 1 and Figure 7 As shown, the electrode array 300 includes an indium tin oxide layer, which is connected to the refractive index adjustable dielectric layer 200 (liquid crystal layer) to achieve driving.

[0029] The tunable narrowband filter device 10 in this embodiment generates a narrowband resonant response through a resonant metasurface 100. By utilizing the characteristic that the refractive index of the resonant metasurface 100 is continuously adjustable under the drive of an external electric field, the equivalent refractive index of the environment surrounding the resonant metasurface 100 is changed, thereby causing a continuous shift in the center wavelength of the narrowband resonant response. While maintaining a small chip-level volume, an electrically tunable narrowband filtering function is achieved. This enables miniaturization while achieving high resolution and a large operating bandwidth, providing a miniaturized hardware foundation for high-resolution, large-bandwidth spectral analysis devices.

[0030] In an optional embodiment of this application, the resonant metasurface 100 includes a plurality of pixels arranged in an array, each pixel containing at least one resonant unit, the resonant units contained in different pixels being used to enable different pixels to have different resonant wavelengths, and the filtering windows of each pixel collectively cover a continuous or quasi-continuous spectral band.

[0031] Specifically, the resonant units have different geometric parameters and / or material parameters so that different pixels have different resonant wavelengths. In this embodiment, a pixel refers to a region in the resonant metasurface 100 that has a set of resonant units. The resonant units of different pixels are designed to have different geometric parameters (e.g., different shapes, sizes, or rotation angles) and / or material parameters (e.g., different refractive indices and different dielectric constants, etc.). Since these parameters of the resonant units determine the wavelength position of the resonance they produce, the resonant units of different pixels correspond to different resonant wavelengths. The resonant wavelength of each pixel can be continuously scanned and moved within a wavelength range by adjusting the refractive index of the refractive index-tunable dielectric layer 200 covering it. This scanning range is the filtering window of the pixel. The filtering windows of each pixel can be connected end to end or have a certain overlapping area, jointly splicing together to cover a continuous or quasi-continuous broadband band.

[0032] In an optional embodiment, the resonant metasurface 100 may include an M-row × N-column pixel array (M and N are both integers greater than or equal to 1). Each pixel is pre-assigned a different target resonant wavelength during the design phase. By designing the resonant units within each pixel, the resonant center wavelengths of each pixel are distributed sequentially from short-wavelength to long-wavelength or from long-wavelength to short-wavelength. Figure 4 Taking the pixelated resonant metasurface 100 design as an example, pixels in different rows and / or columns are configured with different parameters of the resonant units. Combined with the refractive index tuning capability of the refractive index tunable dielectric layer 200 covering it, the filter windows of each pixel are connected in sequence to achieve full coverage of the predetermined spectral band.

[0033] Taking the resonant metasurface 100 based on a double rectangular prism structure as an example, by configuring different rectangular prism length parameters for the resonant units of different pixels, the initial resonant wavelengths of each pixel are distributed at different wavelength positions. Under the refractive index tuning effect of the refractive index tunable dielectric layer 200, the center wavelength of each pixel can be continuously scanned within a predetermined range. For example, the filtering window of a single pixel can reach the range of 14nm to 60nm, and only two to nine pixels are needed to cover a spectral range of more than 100nm. Taking the resonant metasurface 100 based on a double elliptical prism structure as an example, the pixelated design can achieve a wide-spectrum detection capability covering the 1530nm to 1641nm band (approximately 111nm bandwidth).

[0034] It should be noted that the pixelated array structure provided in this embodiment is an optional implementation of the resonant metasurface 100. In other embodiments, the resonant metasurface 100 can also adopt a non-pixelated continuous gradient structure or other methods to achieve multi-wavelength coverage. This application does not limit this.

[0035] The tunable narrowband filter device 10 in this embodiment of the application, by designing the resonant metasurface 100 into a pixel-like array structure, distributes the resonant wavelengths of different pixels at different positions in the spectral band. The filtering windows of each pixel are interconnected to jointly cover a continuous or quasi-continuous wide spectral band. With each pixel only needing to undertake the task of covering a small band, a large bandwidth spectral coverage is achieved through multi-pixel collaboration. In addition, each pixel undertakes a different spectral band, and combined with the electronically controlled tuning effect of the liquid crystal refractive index, the device can achieve continuous and accurate scanning and coverage in a wide spectral range by means of electrical modulation without the need for mechanical moving parts. It can also flexibly address according to different target bands.

[0036] Furthermore, the pixelated array scheme in this embodiment possesses strong fault tolerance and self-calibration capabilities: the presence of liquid crystal material provides a means of compensating for geometric errors generated during processing, allowing each pixel to reserve a certain overlap area during design. By precisely adjusting the refractive index of the tunable dielectric layer 200, the resonant peak shift caused by processing errors can be corrected, ensuring full spectral connectivity of multiple pixels. Thus, the fully planar metasurface architecture is compatible with existing semiconductor processing techniques, significantly reducing the size and weight of the optical system.

[0037] In an optional embodiment of this application, the resonant unit is asymmetric, so that by introducing asymmetric perturbation, the resonant energy of the resonant unit leaks into free space, thereby generating the narrowband resonant response.

[0038] Specifically, in a perfectly symmetrical resonant structure, various radiating multipoles (such as electric dipoles and magnetic dipoles) produce destructive interference in the far field, resulting in zero total radiation intensity and the quality factor Q (the ratio of the center wavelength to the full width at half maximum) tending to infinity (i.e., the resonant linewidth approaches zero, and the resonant energy is completely confined within the structure, unable to radiate outwards), forming a symmetry-protected bound states in the continuous (BIC) mode. In the BIC mode, the resonant energy is completely confined within the structure and cannot couple with the optical field in free space, thus making it difficult to be excited and utilized by external incident light.

[0039] In this embodiment, when the resonant unit is asymmetric, the geometric symmetry of the originally perfectly symmetrical resonant structure is artificially broken, introducing an asymmetric perturbation. This perturbation causes the originally fully confined BIC mode to degenerate into a symmetry-breaking induced quasi-Bound States in the Continuum (q-BIC) mode (i.e., degenerates from an ideal BIC mode to a q-BIC mode with controlled radiative leakage). In the q-BIC mode, the originally confined resonant energy leaks into free space at a controlled rate, resulting in an ultra-narrowband resonant spectrum with an extremely high Q value. Since this resonant response only allows light within a very narrow range near a specific wavelength to effectively interact with the metasurface, it is equivalent to narrowband filtering of the incident light. By designing the degree of asymmetry of the resonant unit (e.g., adjusting the size of the rotation angle or the size difference), the rate at which the resonant energy leaks into free space can be controlled, thereby controlling the linewidth of the narrowband resonant response.

[0040] The tunable narrowband filter device 10 in this embodiment introduces asymmetric disturbances by making the resonant unit asymmetric. The resonant energy leaks in a controlled manner and forms a resonant response with an extremely narrow linewidth in the spectrum, thus realizing the narrowband filtering function. At the same time, the flexible control of the filter linewidth is achieved by adjusting the degree of asymmetry.

[0041] In an optional embodiment of this application, the asymmetry is formed by at least one of the following methods: The resonant unit includes at least one irregular structure to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis and are rotated by a preset angle to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the two substructures have a size difference in at least one of length, width or height, so as to break the mirror symmetry and rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis. The two substructures are made of dielectric materials with different dielectric constants to break the dielectric constant symmetry of the resonant unit.

[0042] The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the refractive indices of the medium in which the two substructures are located differ, thereby breaking the dielectric constant symmetry of the resonant unit.

[0043] In an optional embodiment of this application, the resonant unit may be a single irregular structure that disrupts the inherent symmetry of the unit by changing its own shape, such as a convex shape, in order to break the mirror symmetry or rotational symmetry of the resonant unit.

[0044] In another optional embodiment of this application, the resonant unit is composed of at least two substructures, each substructure being a component of the resonant unit with a specific geometry. The material of the substructures can be selected from dielectric materials with high refractive indices, such as silicon (Si), silicon nitride (Si3N4), and titanium dioxide (TiO2). The two substructures have geometric asymmetry, specifically: In the first approach, two substructures are located on either side of a central axis (the axis of symmetry passing through the geometric center of the resonant unit; when the angles and dimensions of the two substructures are not adjusted, the two substructures are mirror-symmetric about this central axis and rotationally symmetric about the geometric center), and each substructure is rotated by a preset angle. Because the orientation of the originally anisotropic substructures (e.g., rectangular or elliptical cylinders) is rotated as a whole, the mirror symmetry of the two substructures in the resonant unit with respect to the central axis is broken (when the two substructures rotate a preset angle in the same direction), or the rotational symmetry of the two substructures with respect to the geometric center is broken (when the two substructures rotate a preset angle together towards the central axis, such as...). Figure 3 (The rotation direction is shown). The magnitude of the rotation angle determines the strength of the geometric asymmetry. The larger the preset rotation angle, the stronger the geometric asymmetry disturbance, the more resonant energy leaks into free space, and the larger the resonant linewidth. The preset angle can be determined through simulation or experiment based on the required filter linewidth for the actual application.

[0045] In the second approach, the two substructures are located on opposite sides of a central axis, and the two substructures differ in size in at least one dimension of length, width, or height (e.g., Figure 6 The length difference ΔL between the two rectangular silicon pillars shown is illustrated. Because the dimensional relationship between the substructures, which should have maintained equal dimensions on both sides of the axis, is no longer symmetrical, the mirror symmetry and rotational symmetry of the resonant unit are simultaneously broken. The dimensional difference (e.g., length or width difference) determines the strength of the geometric asymmetry; the greater the dimensional difference, the stronger the geometric asymmetry disturbance. The value of the dimensional difference can also be determined based on the required filter linewidth for the actual application.

[0046] In another optional embodiment of this application, the resonant unit includes at least two substructures, each located on opposite sides of a central axis, and the two substructures are made of different materials to achieve asymmetry. Specifically: In the first approach, the two substructures are made of dielectric materials with different dielectric constants, such as silicon and titanium dioxide, silicon and indium arsenide / gallium, silicon and indium phosphide, etc., which break the dielectric constant symmetry of the resonant unit while maintaining the geometric symmetry.

[0047] In the second approach, the refractive indices of the two substructures in the medium environment are different. For example, a dielectric layer can be used to wrap one of the substructures, such as using a silicon dioxide cladding layer, to break the dielectric constant symmetry of the resonant unit while maintaining the geometric symmetry.

[0048] The above-mentioned methods can be used individually or in combination. For example, the two substructures of the resonant unit can have both rotation angle and size differences, or only rotation angle or only size differences, to achieve geometric asymmetry. In other embodiments, asymmetry can also be achieved by combining geometric asymmetry with material differences, all of which can generate narrowband resonant responses.

[0049] The tunable narrowband filter device 10 in this embodiment breaks the symmetry of the resonant unit by introducing asymmetric disturbances, thereby generating a narrowband resonant response. The degree of asymmetry can be flexibly controlled by the rotation angle and / or size difference, and the structural shape can be changed or different materials can be selected to form it, providing controllable design freedom for the linewidth of the narrowband filter response.

[0050] In one optional embodiment of this application, the two substructures are two rectangular pillars of different lengths, so that the resonant unit constitutes the geometric asymmetry; or the two substructures are two elliptical pillars, which are rotated together relative to the axis by a preset angle, so that the resonant unit constitutes the geometric asymmetry.

[0051] Specifically, this application provides two specific implementations of substructure shapes.

[0052] For the rectangular column scheme, refer to... Figure 6 The resonant unit shown has two rectangular pillars made of silicon, and the substrate material is silicon dioxide. Figure 6 To omit the view of the electrode array 300 (indium tin oxide layer) between the resonant unit and the substrate, in practical applications, such as... Figure 1 and Figure 7As shown, there is an electrode array 300 between the two. The two rectangular pillars have the same width, w; the same height, H; and the same period, p, in both the x and y directions. The lengths of the two rectangular pillars are L1 and L2, respectively, and L1 ≠ L2. The length difference ΔL = L1 - L2 constitutes a geometrically asymmetric perturbation. Due to the difference in length between the two rectangular pillars, the original symmetrical geometric relationship is broken, and the resonant unit forms a geometrically asymmetric structure, generating a narrowband resonant response.

[0053] For the rectangular pillar scheme, by adjusting the length parameter of the rectangular pillars in different pixels, the initial resonant wavelength of each pixel is distributed at different wavelength positions. Combined with the continuous refractive index tuning of the refractive index tunable dielectric layer 200 (e.g., the liquid crystal refractive index changes from n1 to n2), the filtering window of each pixel can cover a wavelength range. Taking a filtering bandwidth of approximately 60nm per pixel as an example, only two pixels are needed to cover a continuous spectral range exceeding 100nm. Figure 8 and Figure 9 The filtered spectra of these two pixels under refractive index tuning of a 200-fold refractive index tunable dielectric layer are shown. This scheme has the advantages of large single-pixel bandwidth and a small number of required pixels.

[0054] For the elliptical cylinder scheme, refer to... Figure 3 The resonant unit shown has two elliptical cylinders made of silicon, and the substrate material is silicon dioxide (same as above). Figure 3 To omit the view of the electrode array 300 (indium tin oxide layer) between the resonant unit and the substrate, in practical applications, such as... Figure 1 and Figure 7 As shown, there is an electrode array 300 between the two elliptical cylinders. The minor axis of the elliptical cylinder is 2a, and the major axis is 2b. The period in the x-direction is px, and the period in the y-direction is py. The height of the elliptical cylinder is H. The two elliptical cylinders are symmetrically arranged about a central axis. The two elliptical cylinders rotate together about this axis by an angle θ (i.e., ... Figure 3 The rotation angle θ (marked in the image) constitutes a geometrically asymmetric perturbation, causing the resonant unit to form a geometrically asymmetric structure (rotational symmetry is broken), resulting in a narrowband resonant response. The rotation angle θ can be designed based on the target filter linewidth and Q-factor requirements.

[0055] For the elliptical cylinder scheme, by configuring different elliptical cylinder geometric parameters (e.g., minor axis a, major axis b, and periods px, py, etc.) for different pixels, the initial resonant wavelength of each pixel is distributed at different wavelength positions. Combined with the refractive index tuning capability of the refractive index tunable dielectric layer 200, the pixelated array can cover a spectral range of approximately 1530nm to 1641nm (approximately 111nm). Figure 4 A design example of the pixelated resonant metasurface 100 is shown. Figure 5The filter spectrum of a single pixel under refractive index tuning of the refractive index tunable medium layer 200 is shown. The filter window of this pixel can cover the range of approximately 1579nm to 1583nm, and the bandwidth of a single pixel is approximately 14nm. The filter windows of the nine pixels are stitched together to cover the aforementioned wide band of 111nm.

[0056] The two schemes described above can be selected independently based on the application scenario. For example, the rectangular cylinder scheme can be used in applications requiring high single-pixel bandwidth, while the elliptical cylinder scheme can be used in scenarios with ample pixel count and greater design freedom. Both schemes can effectively generate narrowband resonant responses, and both can achieve continuous shift of the center wavelength by cooperating with the refractive index tuning of the refractive index tunable dielectric layer 200. In addition, this application can achieve a larger spectral coverage range by designing different resonant unit geometries while keeping the Q value (i.e., resonant linewidth) almost unchanged, using more pixels.

[0057] In an optional embodiment of this application, the aspect ratio of the rectangular column is greater than a preset ratio, so that when the refractive index adjustable medium layer 200 is oriented on one side, the molecules in the refractive index adjustable medium layer 200 near the surface of the resonant metasurface 100 are arranged in an orderly manner along the sidewall direction of the rectangular column.

[0058] Specifically, since this system contains a metasurface structure, the typical two-sided orientation (with an orientation layer on each side of the refractive index tunable dielectric layer 200) would disrupt the metasurface structure. Therefore, in this embodiment, during device packaging, a one-sided orientation method is adopted for the refractive index tunable dielectric layer 200 (i.e., orientation control is applied only from the side of the refractive index tunable dielectric layer 200 away from the metasurface, and no orientation layer is set on the metasurface side). Because the surface morphology of the metasurface has a certain influence on the orientation of the molecules in the refractive index tunable dielectric layer 200, in a system with one-sided orientation, molecules near the surface of the metasurface will exhibit orientation disorder, which is detrimental to the control of the refractive index tunable dielectric layer 200. This embodiment employs a rectangular pillar design, which can achieve good molecular orientation under the condition that the rectangular pillar meets a specific aspect ratio. That is, by designing the aspect ratio of the rectangular pillar to be greater than a preset value, the molecules near the surface of the metasurface are arranged in an orderly manner along the sidewall direction of the rectangular pillar, thereby solving the one-sided orientation problem existing in the liquid crystal metasurface system.

[0059] The specific value of the preset ratio can be determined through simulation calculation or experimental testing based on factors such as the material type of the resonant metasurface 100, the material type of the rectangular column, and the material type of the refractive index adjustable dielectric layer 200, and is not limited here.

[0060] Figure 7This illustration shows the molecular orientation state of the refractive index adjustable dielectric layer 200 (liquid crystal layer) near the metasurface (silicon metasurface, i.e., the metasurface structure of the resonant metasurface) in the single-sided orientation scheme of this embodiment. On the side away from the resonant metasurface 100, orientation force is applied through a conventional orientation layer, while on the side closer to the metasurface, the orderly arrangement of molecules is achieved by relying on the sidewalls of rectangular pillars. Thus, the problem of chaotic molecular orientation on the surface of the single-sided orientation system is solved without adding an additional orientation layer or destroying the metasurface structure.

[0061] The tunable narrowband filter device 10 in this embodiment adopts a rectangular pillar design. Under the condition that the rectangular pillar meets a specific aspect ratio, the molecules near the surface of the metasurface in the system with unilateral orientation are arranged in an orderly manner along the sidewall direction of the rectangular pillar. This solves the unilateral orientation problem existing in the liquid crystal metasurface system and ensures the uniformity of refractive index tuning and the stability of the device's filtering performance.

[0062] A second aspect of this application provides a spectrometer including a tunable narrowband filter device 10 as described in any of the foregoing embodiments.

[0063] Specifically, the spectrometer uses the aforementioned tunable narrowband filter device 10 as the core spectral encoding element. Utilizing its narrowband filtering and electronically tunable characteristics, it encodes the spectral information of different wavelengths in the incident light into light intensity signals that can be read by the detector 20, and then restores the complete spectral information through subsequent calculations and processing.

[0064] The tunable narrowband filter device 10 receives incident light after polarization state control. Under the electrical tuning of the refractive index of the refractive index-tunable dielectric layer 200, the center wavelength of its narrowband resonant response is progressively scanned across the entire operating band of the spectrometer according to a preset sequence. At each center wavelength position, the tunable narrowband filter device 10 only allows spectral components within the narrowband range to pass through and reach the detector 20; spectral components in other bands are reflected or filtered out. The detector 20 converts the light intensity of the received narrowband filtered light signal into a detected value in the form of an electrical signal. By jointly calculating the light intensity detected values ​​obtained by the same pixel at multiple different center wavelength positions, the complete spectral information of the incident light in the corresponding band can be reconstructed.

[0065] The spectrometer in this embodiment achieves dynamic scanning of the center wavelength through electronic tuning, converting spectral information into a measurable sequence of light intensity changes. It realizes spectral analysis function within a chip-scale, eliminating the need for mechanical moving parts or dispersive optical paths. This significantly reduces the physical size and system complexity of the spectrometer, making it suitable for applications such as portable terminals and in-situ detection.

[0066] Reference Figure 2 As shown, in an optional embodiment of this application, the spectrometer further includes: A polarization control unit 40 is disposed before the tunable narrowband filter device 10 and is used to control the polarization state of the incident light and guide the polarized light to the tunable narrowband filter device 10. The detector 20 is disposed in the outgoing optical path of the tunable narrowband filter device 10, and is used to receive the optical signal output after being filtered by the tunable narrowband filter device 10, and convert the light intensity of the optical signal into a light intensity detection value. The computing unit, connected to the detector 20, is used to obtain the spectral information of the incident light based on the pre-calibrated transmission matrix and the light intensity detection value output by the detector 20.

[0067] Specifically, the polarization control unit 40 is located at the optical path front end of the spectrometer and is used to control the polarization state of the incident light. The polarization control unit 40 can be a polarizer, used to convert the incident light into linearly polarized light with a defined polarization direction and guide it to the tunable narrowband filter device 10. Because the rotational symmetry is broken, the tunable narrowband filter device 10 is sensitive to the polarization state of the incident light. By unifying the polarization state of the incident light through the polarization control unit 40, the consistency and accuracy of subsequent filtering and detection can be guaranteed.

[0068] Detector 20 is positioned in the output optical path of the tunable narrowband filter device 10 to receive the optical signal output after filtering by the tunable narrowband filter device 10. Detector 20 converts the light intensity of the received optical signal into a light intensity detection value in the form of an electrical signal. Detector 20 can be, but is not limited to, a photodiode (PD), a charge-coupled device (CCD), a complementary metal-oxide-semiconductor (CMOS), or other photoelectric conversion devices. The spectral response range of detector 20 should cover the designed operating wavelength range of the spectrometer.

[0069] The computing unit (not shown in the figure) is electrically connected to the detector 20 and is used to receive light intensity detection values ​​from the detector 20 and calculate and reconstruct the spectral information of the incident light based on the pre-calibrated transmission matrix and the detection values. The computing unit can be implemented in hardware such as, but not limited to, a microprocessor (MPU), a digital signal processor (DSP), a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC), or it can be implemented by a software module running on a general-purpose computer or embedded platform.

[0070] Furthermore, the optical path of the spectrometer also includes a beam splitter 30, which is disposed between the polarization control unit 40 and the tunable narrowband filter device 10. The beam splitter 30 is used to guide the polarization-controlled incident light to the tunable narrowband filter device 10 and guide the filtered light reflected back by the tunable narrowband filter device 10 to the detector 20. Figure 2 A schematic diagram of the optical path of a spectrometer based on a pixelated tunable narrowband filter device 10 is shown. Incident light emitted from the laser passes through a polarization control unit 40 and a beam splitter 30 before illuminating the surface of the tunable narrowband filter device 10. The filtered reflected light is then guided to the detector 20 by the beam splitter 30. This reflective optical path structure is advantageous for reducing the optical path size and is suitable for miniaturized integration.

[0071] The spectrometer in this embodiment sets a polarization control unit 40 and a detector 20 before and after the tunable narrowband filter device 10, respectively, and introduces a calculation unit to perform spectral reconstruction. The spectral information of the incident light is encoded into a light intensity signal sequence by electronically controlled scanning and then reconstructed by calculation. This realizes a complete spectral analysis link from spectral encoding to photoelectric detection and then to calculation and analysis, and completes the acquisition of spectral information without mechanical moving parts and free space dispersive optical path.

[0072] In an optional embodiment of this application, the transfer matrix is ​​obtained by calibrating the spectral response of the tunable narrowband filter device 10, wherein the spectral response calibration includes: Monochromatic light of different wavelengths is sequentially output from a calibrated light source, and after passing through the polarization control unit 40, it is incident on the tunable narrowband filter device 10; Different driving voltages are sequentially applied to the tunable narrowband filter device 10 to change the refractive index of the refractive index tunable dielectric layer 200, and the light intensity response of each pixel under different driving voltages and different wavelengths is collected. The transmission matrix is ​​constructed based on the light intensity response.

[0073] Specifically, before the spectrometer performs actual spectral measurements, the tunable narrowband filter device 10 needs to be calibrated for its spectral response in order to obtain the transfer matrix characterizing the spectral response properties of the spectrometer system. T(λ, V i ) The transfer matrix quantitatively describes the mapping relationship between the spectral information of the incident light and the light intensity detection value output by the detector 20.

[0074] The calibration light source is used to provide standard monochromatic light of known wavelengths. The calibration light source can be, but is not limited to, a monochromator or a tunable laser. The calibration light source outputs wavelengths ranging from λ1 to λ... n Standard monochromatic light, after polarization control, is incident perpendicularly onto a tunable narrowband filter device 10. The control system sequentially applies different driving voltages to the refractive index-tunable dielectric layer 200 in the tunable narrowband filter device 10. V 1 -V i By changing its refractive index, the filtering peak of the device will also change accordingly. The detector 20 synchronously acquires the light intensity response of each pixel unit under different voltages and wavelengths; based on the acquired light intensity data, the spectral response curve corresponding to each pixel unit is extracted and established, and finally, a transfer matrix characterizing the spectral response properties of the system is constructed. T(λ, V i ) After calibration, the light to be measured can be measured and its spectrum restored: the light to be measured, containing spectral information, passes through the optical system and is incident perpendicularly onto the tunable narrowband filter device 10, according to the voltage sequence established during calibration. V 1 -V i The refractive index of the dynamically adjustable dielectric layer 200 is adjusted to change the position of the metasurface resonance peak. Simultaneously, the intensity of the light after filtering by the tunable narrowband filter device 10 is recorded using detector 20, denoted as . I(λ, V i ) .

[0075] Within a single pixel, the light intensity information obtained by detector 20 is the incident light spectrum. S(λ) With system response matrix T(λ, V i ) The convolution of can be represented by a set of linear equations: ; in, S(λ) The spectral information representing the light to be measured, and the transfer matrix obtained from the aforementioned calibration process. T(λ, V i) The light intensity obtained from detector 20 I(λ, V i ) Spectral information can be obtained using algorithms. S(λ) By solving for the detection values ​​of multiple pixels, the complete spectral information of the light under test can be reconstructed. The solution algorithm can employ, but is not limited to, numerical optimization methods such as least squares, Tikhonov regularization, and compressed sensing reconstruction algorithms.

[0076] The spectrometer in this embodiment calibrates the spectral response of the tunable narrowband filter device 10 pixel by pixel and voltage by voltage, constructs a transmission matrix, and quantifies the spectral response characteristics of the entire spectrometer system into a computable mathematical model. During measurement, the spectral information is restored by solving a system of linear equations, transforming the spectral measurement problem into a mathematical problem. The computational power replaces the bulky dispersive optical path in traditional spectrometers, and wide-band, high-resolution spectral analysis is completed within a small device size.

[0077] In a third aspect, this application provides a spectral detection system, including a tunable narrowband filter device 10 as described in any of the foregoing embodiments, or including a spectrometer as described in any of the foregoing embodiments.

[0078] Specifically, this spectral detection system can be integrated into portable medical diagnostic terminals, such as handheld skin spectrometers and non-invasive blood glucose monitoring devices, utilizing the small size and low power consumption of chip-level spectrometers to achieve in-situ real-time spectral detection and material composition analysis; it can also be integrated into vehicle-mounted intelligent sensing systems, such as vehicle exhaust gas monitoring sensors or road environment spectral monitoring devices, utilizing the large bandwidth and high resolution advantages of spectrometers to achieve simultaneous detection and identification of multi-component gases; it can also be integrated into food safety testing equipment, such as handheld food component analyzers or pesticide residue detection devices; it can also be integrated into industrial process monitoring devices, such as online spectral monitoring instruments for chemical reaction processes or online thin film thickness measurement devices; and it can also be integrated into optical communication modules as a component of wavelength monitoring or channel power equalization.

[0079] The spectral detection system in this application embodiment integrates a tunable narrowband filter device 10 or a spectrometer based on the device, which can encapsulate wide-spectrum, high-resolution spectral analysis capabilities in a chip-level device. It is suitable for various miniaturized application scenarios such as portable medical devices, automotive sensing, food safety, industrial monitoring, and optical communication, and gives intelligent terminal devices in-situ, real-time spectral detection capabilities.

[0080] In other embodiments of this application, the tunable narrowband filter device 10, besides being used in a spectrometer, can also be used as a standalone wavelength-tunable notch filter. In a transmission-type operating system architecture, the tunable narrowband filter device 10 generates an extremely narrow transmission valley at the resonance point, which can precisely filter out or block unwanted spectral components from the complex incident spectrum. Taking the tunable narrowband filter device 10 based on a double elliptical cylinder structure as an example... Figure 10 It demonstrates the notch filtering effect of a single pixel, with a full width at half maximum (FWHM) of approximately 1.97 nm, and spectral lines exhibiting extremely high out-of-band transparency and extremely steep cutoff edges. Figure 11 The notch filter spectrum of this structure under refractive index tuning of the refractive index tunable dielectric layer 200 is shown. By array-based addressing control of multiple pixels, combined with refractive index tuning of the refractive index tunable dielectric layer 200, free switching of the center wavelength within a bandwidth of over one hundred nanometers can be achieved. Taking the tunable narrowband filter device 10 based on a dual rectangular pillar structure as an example, a single pixel has a larger tuning bandwidth, and its tuning filter spectrum is as follows: Figure 12 As shown.

[0081] The wavelength-tunable notch filter in this application embodiment solves the limitations of traditional notch filters, such as fixed operating wavelength, inability to be dynamically tuned, or limited tuning range. It can be applied to scenarios such as filtering background excitation light in fluorescence microscopy imaging equipment, suppressing Rayleigh scattering light in Raman spectroscopy analysis equipment, suppressing crosstalk signals of specific wavelengths in optical communication systems, and filtering out interfering spectral components in biochemical molecular sensing.

[0082] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0083] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0084] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A tunable narrowband filter device, characterized in that, include: A resonant metasurface has a metasurface structure and is used to generate a narrowband resonant response to light incident on it. The narrowband resonant response is characterized by a narrowband transmission peak and / or transmission valley with a center wavelength in the spectrum. A refractive index tunable dielectric layer is covered on the resonant metasurface. The refractive index of the refractive index tunable dielectric layer is continuously adjustable under the action of an external electric field, so as to change the equivalent refractive index of the surrounding environment of the resonant metasurface by changing the refractive index. An electrode array, connected to the refractive index tunable dielectric layer, is used to apply the external electric field to the refractive index tunable dielectric layer to adjust the refractive index.

2. The tunable narrowband filter device according to claim 1, characterized in that, The resonant metasurface includes a plurality of pixels arranged in an array, each pixel containing at least one resonant unit, and the resonant units contained in different pixels are used to enable different pixels to have different resonant wavelengths, wherein the filtering windows of each pixel collectively cover a continuous or quasi-continuous spectral band.

3. The tunable narrowband filter device according to claim 2, characterized in that, The resonant unit is asymmetric, so that by introducing asymmetric perturbation, the resonant energy of the resonant unit leaks into free space, thereby generating the narrowband resonant response.

4. The tunable narrowband filter device according to claim 3, characterized in that, The asymmetry is formed in at least one of the following ways: The resonant unit includes at least one irregular structure to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis and are rotated by a preset angle to break the mirror symmetry or rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the two substructures have a size difference in at least one of length, width or height, so as to break the mirror symmetry and rotational symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis. The two substructures are made of dielectric materials with different dielectric constants to break the dielectric constant symmetry of the resonant unit. The resonant unit includes at least two substructures, which are located on opposite sides of a central axis, and the refractive indices of the medium in which the two substructures are located differ, thereby breaking the dielectric constant symmetry of the resonant unit.

5. The tunable narrowband filter device according to claim 4, characterized in that, The two substructures are two rectangular pillars of different lengths, so that the resonant unit constitutes the asymmetry; or The two substructures are two elliptical cylinders, which are rotated together relative to the axis by a predetermined angle so that the resonant unit constitutes the asymmetry.

6. The tunable narrowband filter device according to claim 5, characterized in that, The aspect ratio of the rectangular pillar is greater than a preset ratio, so that when the refractive index adjustable medium layer is oriented on one side, the molecules in the refractive index adjustable medium layer near the surface of the resonant metasurface are arranged in an orderly manner along the sidewall direction of the rectangular pillar.

7. A spectrometer, characterized in that, Includes the tunable narrowband filter device as described in any one of claims 1-6.

8. The spectrometer according to claim 7, characterized in that, Also includes: A polarization control unit is disposed before the tunable narrowband filter device to control the polarization state of the incident light and guide the polarized light to the tunable narrowband filter device. The detector is disposed in the output optical path of the tunable narrowband filter device and is used to receive the optical signal output after being filtered by the tunable narrowband filter device and convert the light intensity of the optical signal into a light intensity detection value. A computing unit, connected to the detector, is used to obtain the spectral information of the incident light based on the pre-calibrated transmission matrix and the light intensity detection value output by the detector.

9. The spectrometer according to claim 8, characterized in that, The transmission matrix is ​​obtained by calibrating the spectral response of the tunable narrowband filter device, and the spectral response calibration includes: Monochromatic light of different wavelengths is sequentially output from a calibrated light source, and after passing through the polarization control unit, it is incident on the tunable narrowband filter device; Different driving voltages are sequentially applied to the tunable narrowband filter device to change the refractive index of the refractive index-tunable medium layer, and the light intensity response of each pixel is collected under different driving voltages and different wavelengths. The transmission matrix is ​​constructed based on the light intensity response.

10. A spectral detection system, characterized in that, It includes the tunable narrowband filter device as described in any one of claims 1-6, or the spectrometer as described in any one of claims 7-9.

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