All-dielectric optical microwave spectrum splitting and frequency dividing element

Abstract

The application discloses a full-dielectric optical microwave light splitting and frequency splitting element, which comprises a one-dimensional photonic crystal optical reflection film and a wave-transparent substrate. The one-dimensional photonic crystal optical reflection film is an alternating film system structure composed of two high and low refractive index dielectrics, and the film system structure comprises a visible light reflection film system structure and an infrared reflection film system structure, which can efficiently reflect visible light and infrared light. The wave-transparent substrate is a microwave non-destructive dielectric substrate, which can ensure efficient transmission of microwaves. The visible light reflection film system structure and the infrared reflection film system structure are grown on the wave-transparent substrate from bottom to top. The light splitting and frequency splitting element separates the signals of light waves and microwaves through reflection of light waves and transmission of microwaves, and can be applied to the optical SAR integrated co-time phase detection field, realizes efficient reflection of visible light and infrared light in a large field of view, and effectively improves the light splitting and frequency splitting efficiency.

Description

Technical Field

[0001] This invention relates to the field of microwave-optical wave fusion, and in particular to an all-dielectric optical microwave beam splitter and frequency divider. Background Technology

[0002] Optical SAR integrated simultaneous phase detection combines the advantages of optical remote sensing imaging, such as good concealment, high resolution, good image quality, and resistance to electronic interference, with the advantages of SAR imaging, such as all-weather and all-time detection, strong penetration capability, and ability to detect and identify camouflaged targets, greatly improving the ability to accurately detect various targets. The design and fabrication of its core component, the beam splitting and frequency division element, can provide support for the development of optical SAR integrated imaging systems and urgently needs to be studied.

[0003] In the design and development of optical / microwave beam splitting and frequency division, the main technical approaches are dielectric reflective films, frequency selective surfaces, and diffractive optical devices. The infrared reflectivity and radar transmittance of frequency selective surfaces are both related to the unit structure, exhibiting mutual constraints. Diffractive optical elements are characterized by small size, high efficiency, high design flexibility, and easy integration; however, the fabrication of dichroic mirrors is still in the exploratory stage, and they do not have no impact on the polarization state of millimeter waves, and the element size cannot be scaled up. Depositing dielectric reflective films on dielectric substrates is a relatively mature technology, enabling effective reflection of light waves in the target wavelength band, while the dielectric material has good microwave transmittance characteristics. However, the reflection efficiency of dielectric reflective films drops sharply under large field of view. Summary of the Invention

[0004] The technical problem solved by this invention is to solve the technical problem of large field of view and high efficiency of optical microwave beam splitting and frequency division, and to provide an all-dielectric optical microwave beam splitting and frequency division element.

[0005] The technical solution of this invention is: an all-dielectric optical microwave beam splitter and frequency divider, comprising a wave-transparent substrate, on one side of which an infrared light reflective film structure and a visible light reflective film structure are sequentially deposited. Both the infrared light reflective film structure and the visible light reflective film structure are multilayer alternating film structures composed of two media with different refractive indices. The infrared light reflective film structure includes a second infrared photonic crystal and a first infrared photonic crystal in sequence along the direction away from the wave-transparent substrate, and the visible light reflective film structure includes a second visible light photonic crystal and a first visible light photonic crystal in sequence along the direction away from the wave-transparent substrate. The refractive indices of the two media in the second infrared photonic crystal are the same as those in the first infrared photonic crystal, but their lattice constants are different. The refractive indices of the two media in the second visible light photonic crystal are the same as those in the first visible light photonic crystal, but their lattice constants are different.

[0006] Furthermore, the first and second visible light photonic crystals, starting from the side furthest from the transparent substrate, have refractive index values ​​of n...1a and n 1b Two types of lossless dielectric materials for the visible light band are used to alternately form reflective films, n 1a >n 1b ;

[0007] The first infrared photonic crystal and the second infrared photonic crystal, starting from the side furthest from the transparent substrate, are composed of refractive index values ​​n and n, respectively. 2a and n 2b The reflective films, made of two types of non-destructive dielectric materials in the infrared band, are alternately arranged in sequence, n 2a >n 2b .

[0008] Furthermore, the first visible light photonic crystal has a lattice constant of 110-150 nm and 6-12 layers, while the second visible light photonic crystal has a lattice constant of 160-190 nm and 6-12 layers.

[0009] Furthermore, the two combinations of lossless dielectric materials in the visible light band are TiO2 and SiO2, TiO2 and Al2O3, or Al2O3 and SiO2.

[0010] Furthermore, the first infrared photonic crystal has a lattice constant of 800-1150 nm and 6-12 layers, while the second infrared photonic crystal has a lattice constant of 1170-1300 nm and 6-12 layers.

[0011] Furthermore, the two combinations of non-destructive dielectric materials in the infrared band are TiO2 and SiO2, ZnS and HfO2, or ZnSe and YiF3.

[0012] Furthermore, the first visible light photonic crystal, the second visible light photonic crystal, the first infrared light photonic crystal, and the second infrared light photonic crystal are all composed of reflective films made of TiO2 and SiO2 alternately. The refractive indices of TiO2 and SiO2 in the first and second visible light photonic crystals are 2.43 and 1.46, respectively, and the refractive indices of TiO2 and SiO2 in the first and second infrared light photonic crystals are 2.18 and 1.39, respectively. The lattice constants are 122 nm, 165 nm, 897 nm, and 1208 nm, respectively. The thicknesses of the TiO2 and SiO2 dielectric films are 43 nm and 79 nm, 59 nm and 106 nm, 343 nm and 554 nm, and 465 nm and 743 nm, respectively, and the number of layers are 10, 10, 8, and 8, respectively.

[0013] Furthermore, the microwave-transparent substrate is a microwave-free dielectric substrate with a thickness of 2mm-10mm, a shape of a plane mirror, a double concave mirror, or a double convex mirror, and a material of quartz glass or sodium calcium glass.

[0014] The advantages of this invention compared to the prior art are:

[0015] (1) The technical solution proposed in this invention can achieve efficient reflection of visible light and infrared light within a large field of view (incident angle within 45 degrees).

[0016] (2) The optical splitting and frequency division element of the present invention can achieve an optical splitting and frequency division efficiency of ≥95% in the target band. Attached Figure Description

[0017] Figure 1 A schematic diagram showing the structure of a beam splitter / frequency divider element according to one embodiment of the present invention;

[0018] Figure 2 This indicates the relationship between the refractive index values ​​of TiO2 and SiO2 and wavelength.

[0019] Figure 3 This represents the reflection spectrum of a heterogeneous photonic crystal structure according to one embodiment of the present invention for TE-polarized visible light (P-light) incident conditions;

[0020] Figure 4 This represents the reflection spectrum of a heterogeneous photonic crystal structure according to one embodiment of the present invention under the condition of TE-polarized infrared light (P-light) incident.

[0021] Figure 5 This represents the reflection spectrum of a heterogeneous photonic crystal structure according to one embodiment of the present invention for incident TM-polarized visible light (S-ray);

[0022] Figure 6 This represents the reflection spectrum of a heterogeneous photonic crystal structure according to one embodiment of the present invention under the condition of incident TM polarized infrared light (S-ray);

[0023] Figure 7 This indicates the microwave transmittance of the beam splitter / frequency divider element according to one embodiment of the present invention. Detailed Implementation

[0024] To better understand the technical solution of the present invention, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] A fully dielectric optical microwave beam splitter / frequency divider includes a transparent substrate 3 and a one-dimensional photonic crystal optical reflective film. The film is an alternating film structure composed of two media with different refractive indices, including a visible light reflective film structure 1 and an infrared reflective film structure 2. The visible light reflective film structure 1 is composed of a first visible light photonic crystal 11 and a second visible light photonic crystal 12. The infrared reflective film structure 2 is composed of a first infrared photonic crystal 21 and a second infrared photonic crystal 22. The transparent substrate 3 is a microwave-free dielectric substrate. The visible light reflective film structure 1 and the infrared reflective film structure 2 are grown on the transparent substrate 3 from bottom to top, where "bottom" refers to the side furthest from the transparent substrate.

[0026] The first visible light photonic crystal 11 and the second visible light photonic crystal 12 are composed of refractive indices n1 and n2, respectively. a and n1 b It consists of an alternating film structure of two types of lossless dielectric materials in the visible light band, n1 a >n1 b The material combinations can be, but are not limited to, TiO2 / SiO2, TiO2 / Al2O3, Al2O3 / SiO2, etc.

[0027] The first visible light photonic crystal 11 and the second visible light photonic crystal 12 have a lattice constant of 110-150 nm and 6-12 layers, respectively; the latter have a lattice constant of 160-190 nm and 6-12 layers.

[0028] The first infrared photonic crystal 21 and the second infrared photonic crystal 22 have refractive index values ​​of n respectively. 2a and n 2b It consists of an alternating film structure of two types of non-destructive dielectric materials in the infrared band, n 2a >n 2b The material combination can be TiO2 / SiO2, ZnS / HfO2, ZnSe / YiF3, etc.

[0029] The first infrared photonic crystal 21 and the second infrared photonic crystal 22 have a lattice constant of 800-1150 nm and 6-12 layers, respectively, and a lattice constant of 1170-1300 nm and 6-12 layers, respectively.

[0030] The substrate is made of microwave-free material, which can efficiently transmit microwaves. The thickness can be 2mm-10mm, and the shape can be a plane mirror, a double concave mirror, a double convex mirror, etc. The material can be quartz glass, sodium silicate glass, etc.

[0031] The following is a specific embodiment of the present invention:

[0032] Based on the transfer matrix method and the angular frequency domain superposition method, a heterogeneous photonic crystal structure with high reflectivity in both the visible and mid-infrared bands was designed using TiO2 and SiO2 as dielectric materials.

[0033] The structure of photonic crystal reflective film systems grown on quartz glass substrates is shown in the figure. Figure 1 The refractive indices of TiO2 and SiO2 are as follows: Figure 2 As shown, the extinction coefficients of these two dielectric materials are negligible in the visible and mid-infrared bands. Both materials are dispersive, and their refractive indices decrease with increasing wavelength. When designing the film thickness of the photonic crystal structure in the optical band, the refractive indices of TiO2 and SiO2 are taken as 2.43 and 1.46 (550nm), respectively, for calculation; while in the mid-infrared band, the refractive indices of TiO2 and SiO2 are taken as 2.18 and 1.39 (4μm), respectively, for calculation.

[0034] Four photonic crystals with different lattice constants were designed, from top to bottom: second infrared photonic crystal 22 (denoted as infrared photonic crystal d), first infrared photonic crystal 21 (denoted as infrared photonic crystal c), second visible light photonic crystal (denoted as visible light photonic crystal b), and first visible light photonic crystal (denoted as visible light photonic crystal a). These were grown on a quartz glass substrate in this order. The lattice constants for each crystal are L... a =122nm, L b =165nm, L c =897nm, L d =1208nm. The thicknesses of the two dielectric films, TiO2 and SiO2, are as follows: visible light photonic crystal a: 43nm and 79nm; visible light photonic crystal b: 59nm and 106nm; infrared photonic crystal c: 343nm and 554nm; and infrared photonic crystal d: 465nm and 743nm. The number of layers are 10, 10, 8, and 8, respectively. The 10 layers represent 5 layers of TiO2 and 5 layers of SiO2 overlapping each other.

[0035] The reflection characteristics of the heterogeneous photonic crystal structure with dual reflection bands based on the above structural parameters are as follows: Figure 3 As shown in Figure 6. Figure 3 and 4 The reflectance spectra of the heterogeneous photonic crystal structure for TE-polarized light incident in the 400–700 nm and 3–5 μm bands are presented respectively. Within a 45° field of view, the heterogeneous photonic crystal exhibits near total internal reflection of incident light, with a theoretical reflection efficiency greater than 99% across the entire target wavelength range. Figure 5 and 6The reflectance spectra of the heterogeneous photonic crystal structure for TM-polarized light incident in the 400–700 nm and 3–5 μm bands are presented respectively. Within a 30° incident angle, its reflection efficiency is essentially the same as that for TE-polarized light. However, at a 45° angle, the heterogeneous photonic crystal structure exhibits poor reflectance at a few wavelengths within the target band, but the overall reflectance remains greater than 95%. Based on the above simulation results, it can be concluded that the designed heterogeneous photonic crystal structure has a theoretical reflectance greater than 95% for both modes of polarized light within the target bands of 400 nm–700 nm and 3–5 μm at a 45° oblique incident angle.

[0036] Quartz glass was chosen as the substrate material, with a refractive index of approximately 3.75 in the microwave band, resulting in negligible microwave loss. In the beam splitting and frequency division optical path structure, to meet the imaging requirements of the optical band, one side of the quartz substrate to be coated with a photonic crystal reflective film needs to be designed as convex, while the other side is designed as concave. The substrate has a uniform thickness throughout to reduce the influence on the microwave phase. The diameter of the quartz substrate is 25.4 mm (one inch), and the radius of curvature is 78.4 mm. The wave transmittance performance of the quartz substrate was simulated using CST STUDIOSUITE software. A time-domain solver was used, with X, Y, and Z all set as electric walls in the boundary conditions, and the environment set as a perfect electric conductor. The incident port was a waveguide. After optimization, the microwave transmittance in the target band was optimal when the thickness of the quartz substrate was 4.4 mm. Figure 7 As shown, the microwave transmittance is above 90% in the 32-38 GHz range and above 95% in the 34-36 GHz range. Simulations at thicknesses of 4.3 mm and 4.4 mm show that the microwave transmittance of the quartz substrate is greater than 90% in the target wavelength band (34-36 GHz), indicating that the transmittance of the quartz substrate can meet the requirements within a certain processing error range.

[0037] In summary, the beam splitting and frequency division prototype designed in this invention can efficiently split optical and microwave signals with a splitting efficiency greater than 95%.

[0038] It is understood that this invention has been described through embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific circumstances without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this invention.

[0039] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A full dielectric optical microwave spectrum splitting and frequency splitting element, characterized in that: it comprises a wave-transparent substrate (3), on one side of which an infrared light reflection film system structure (2) and a visible light reflection film system structure (1) are sequentially coated, the infrared light reflection film system structure and the visible light reflection film system structure are both a multilayer alternating film system structure composed of two media with different refractive indexes; the infrared light reflection film system structure (2) comprises a second infrared light photonic crystal (22) and a first infrared light photonic crystal (21) in sequence away from the wave-transparent substrate, and the visible light reflection film system structure (1) comprises a second visible light photonic crystal (12) and a first visible light photonic crystal (11) in sequence away from the wave-transparent substrate; the refractive indexes of the two media in the second infrared light photonic crystal (22) are consistent with those in the first infrared light photonic crystal (21), and the lattice constants are different; the refractive indexes of the two media in the second visible light photonic crystal (12) are consistent with those in the first visible light photonic crystal (11), and the lattice constants are different; the first visible light photonic crystal (11), the second visible light photonic crystal (12), the first infrared light photonic crystal (21) and the second infrared light photonic crystal (22) are all composed of TiO2 and SiO2 reflection films alternately, the refractive indexes of TiO2 and SiO2 in the first visible light photonic crystal (11) and the second visible light photonic crystal (12) are 2.43 and 1.46 respectively, the refractive indexes of TiO2 and SiO2 in the first infrared light photonic crystal (21) and the second infrared light photonic crystal (22) are 2.18 and 1.39 respectively, the lattice constants are 122 nm, 165 nm, 897 nm and 1208 nm in sequence, the thicknesses of the two media films of TiO2 and SiO2 are 43 nm and 79 nm, 59 nm and 106 nm, 343 nm and 554 nm, and 465 nm and 743 nm respectively, and the number of layers is 10, 10, 8 and 8 in sequence. The wave-transparent substrate (3) is a microwave lossless dielectric substrate, the thickness can be 2 mm-10 mm, the shape is a plane mirror, a double-concave mirror or a double-convex mirror, and the material is quartz glass or calcium-sodium glass. The first visible light photonic crystal (11) and the second visible light photonic crystal (12) are made of two visible light waveband lossless dielectric materials with refractive index values of n 1a and n 1b respectively, and are alternately composed of reflective films in sequence, n 1a >n 1b ; The first infrared light photonic crystal (21) and the second infrared light photonic crystal (22) are made of two kinds of infrared light wave band non-destructive dielectric materials with refractive index values of n 2a and n 2b respectively, and are alternately composed of reflective films in sequence, n 2a >n 2b ; ​ 2. The all-dielectric optical microwave frequency spectrometer frequency-division element according to claim 1, characterized in that: ​

Images