An ultra-broadband optical absorber based on multi-layer transition metal layers

Abstract

The present application discloses an ultra-wideband optical absorber based on a multi-layer transition metal layer. The working band of the ultra-wideband optical absorber is respectively the visible-near infrared band or the mid-infrared band; a high-reflection metal film layer, a transition metal film layer, and a dielectric film layer are sequentially stacked on a substrate; the high-reflection metal film layer, the multi-layer transition metal film layer, and the dielectric film layer form a planar multi-layer structure, and the high-reflection metal film layer is used to prevent light from passing through. The combination of the multi-layer transition metal film layer and the dielectric film layer in the absorber reduces reflection, thereby achieving the effect of ultra-wideband efficient optical absorption. The optical absorber can achieve an average absorption rate of more than 92% in the visible-near infrared band of 400 to 2500nm; and an average absorption rate of more than 80% in the mid-infrared band of 3 to 16μm. The absorber is insensitive to the incident angle and the polarization of light, has a simple structure and process, and the processing error of the film layer has little effect on the performance, with a high yield rate, and is suitable for large-area preparation.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to an ultra-wideband optical absorber based on multiple transition metal layers and operating in the visible to infrared band. Background Art

[0002] Ultra-broadband optical absorbers operating in the visible-infrared band have a wide range of applications. Depending on the specific wavelengths of light they absorb, optical absorbers can be applied in a wide range of fields, including communications, sensing, military, environmental monitoring, medical treatment, and basic research.

[0003] When light (electromagnetic waves) is incident on metal, dielectric, and semiconductor materials, dielectric loss, hysteresis loss, and resistive loss occur, causing the electromagnetic energy incident on the object to be converted into other forms of energy and consumed. A common optical absorber structure utilizes the Fabry-Perot resonant cavity principle, whose optical path is one-quarter of the wavelength of the electromagnetic wave. By utilizing the principle of multi-beam interference caused by multiple reflections of electromagnetic waves, the electromagnetic waves interfere with each other and are destructively absorbed. The thickness of this absorber is usually an odd multiple of one-quarter wavelength. It is extremely sensitive to changes in the incident angle and polarization state of light, and its operating bandwidth is also very narrow. Another common metamaterial absorber is designed by designing a subwavelength patterned structure on the top layer to absorb specific wavelengths. This metamaterial absorber can greatly reduce the thickness of the film, but requires technical means such as photolithography, making the preparation cost expensive, limiting the sample area, and also subjecting the operating bandwidth to certain restrictions.

[0004] The visible-infrared band is an important band with wide applications in many fields. How to effectively improve the structural design and preparation methods of the absorber to achieve the expansion of the optical absorber bandwidth, reduction in size, reduction in cost and large-area preparation is of significant significance to the absorber field. Summary of the Invention

[0005] To address the aforementioned drawbacks of absorbers, such as narrow absorption bands, low absorption efficiency, and complex structures, this application aims to propose an ultra-wideband optical absorber based on multiple transition metal layers that is insensitive to incident angle. This ultra-wideband optical absorber has the advantages of an extremely wide absorption band, a simple structure, the ability to fabricate over large and flexible areas, and insensitivity to structural dimensional errors.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] An ultra-wideband optical absorber based on a multi-layer transition metal layer, operating in the visible-near infrared band or the mid-infrared band, characterized by:

[0008] It includes: a substrate, a planar multilayer structure arranged on the substrate,

[0009] The planar multilayer structure includes a high-reflection metal film layer and at least three light-absorbing thin film structures disposed on the high-reflection metal film layer. Each light-absorbing thin film structure includes a transition metal film layer and a dielectric film layer, and the thickness of the transition metal film layer in each layer is less than the thickness of the dielectric film layer.

[0010] The thickness of the ultra-wideband optical absorber is less than 3000 nm.

[0011] Preferably, the material of the transition metal film layer is selected from at least one of titanium, chromium and platinum.

[0012] Preferably, the material of the dielectric film layer is selected from magnesium fluoride or silicon oxide.

[0013] Preferably, the material of the high reflective metal film layer is selected from at least one of gold, aluminum and chromium, and the thickness is greater than 50 nm.

[0014] Preferably, the ultra-wideband optical absorber has an operating band of visible-near infrared and a thickness of less than 500 nm.

[0015] The planar multilayer structure includes three sequentially stacked light-absorbing thin film structures, and is configured to be sequentially stacked with a high-reflection metal film layer, a first transition metal film layer, a first dielectric film layer, a second transition metal film layer, a second dielectric film layer, a third transition metal film layer, and a third dielectric film layer;

[0016] The thickness of the first transition metal film layer is greater than the thickness of the second transition metal film layer and greater than the thickness of the third transition metal film layer, the ultra-wideband optical absorber.

[0017] Preferably, in the ultra-wideband optical absorber based on multiple transition metal layers,

[0018] The material of the first transition metal film layer is Ti, and its thickness is between 40 and 70 nm;

[0019] The first dielectric film layer is made of MgF2 and has a thickness between 90 and 110 nm.

[0020] The material of the second transition metal film layer is Ti, and its thickness is between 10 and 13 nm;

[0021] The second dielectric film layer is made of MgF2 and has a thickness between 110 and 130 nm.

[0022] The material of the third transition metal film layer is Ti, and its thickness is between 4 and 7 nm;

[0023] The material of the third dielectric film layer is MgF2, and the thickness thereof is between 90 nm and 110 nm.

[0024] Preferably, the ultra-wideband optical absorber has an operating wavelength in the mid-infrared band and a thickness of less than 3000 nm.

[0025] The planar multilayer structure includes three layers of light-absorbing thin film structures, and is configured to be stacked in sequence: a high-reflective metal film layer, a seventh dielectric film layer, a fourth light-absorbing thin film structure, an eighth dielectric film layer, a fifth light-absorbing thin film structure, a sixth light-absorbing thin film structure, and a ninth dielectric film layer.

[0026] Preferably, in the ultra-wideband optical absorber based on multiple transition metal layers,

[0027] The first dielectric film layer is made of MgF2 and has a thickness of 850 to 910 nm.

[0028] The material of the first transition metal film layer is Ti, and its thickness is 15 to 20 nm;

[0029] The material of the second dielectric film layer is MgF2, and its thickness is 900-1000nm;

[0030] The third dielectric film layer is made of Ta2O5 with a thickness of 120 to 160 nm.

[0031] The material of the second transition metal film layer is Ti, and its thickness is 15 to 20 nm;

[0032] The fourth dielectric film is made of Ta2O5 and has a thickness of 600-650 nm.

[0033] The material of the third transition metal film layer is Ti, and its thickness is 4 to 5 nm;

[0034] The material of the fifth dielectric film layer V is Si3N4, and its thickness is 750-850nm;

[0035] The sixth dielectric film layer is made of MgF2 and has a thickness of 800-900 nm.

[0036] Preferably, the substrate is selected from silicon wafer, SiO2 glass, polished Al wafer or PET plastic.

[0037] Preferably, when designing the ultra-wideband optical absorber based on multiple transition metal layers,

[0038] The optimization goal is to make the equivalent optical admittance of the planar multilayer structure equal to the optical admittance of air. The materials and thicknesses of each layer in the planar multilayer structure are designed. The planar multilayer structure is deposited on the substrate surface by vacuum coating. The absorptivity formula of the ultra-wideband optical absorber based on multilayer transition metal layers is: A = 1-RT, and the reflectivity formula is described by optical admittance.

[0039] Among them, Y0 and Yend are the optical admittance values ​​of air and absorber, Y end =H a / E a , H a For and E a are the magnetic field component and electric field component at the interface between air and absorber, respectively. The bottom layer is highly reflective metal with transmittance T=0.

[0040] Therefore, the absorber's equivalent optical admittance should be as close as possible to that of air. When designing an ultra-wideband optical absorber based on multilayer transition metal layers, the optimization goal is to achieve an equivalent optical admittance of the planar multilayer structure equal to that of air. The materials and thicknesses of each layer in the planar multilayer structure are then designed. The ultra-wideband optical absorber is then obtained by depositing the planar multilayer structure on a substrate using vacuum coating.

[0041] Beneficial effects:

[0042] The ultra-wideband optical absorber proposed in the embodiments of this application exhibits excellent ultra-broadband absorption performance. The ultra-wideband optical absorber in the visible-to-near-infrared band has an average absorptivity exceeding 92% at wavelengths between 400 and 2500 nm, and the average absorptivity remains above 84% at angles of incidence greater than 68°. The ultra-wideband optical absorber in the mid-infrared band has an average absorptivity exceeding 80% at wavelengths between 3 and 16 μm.

[0043] Furthermore, the ultra-wideband optical absorber proposed in the embodiments of this application has a simple structure, eliminating the need for complex photolithography techniques. The fabricated device area depends solely on the size of the vacuum coating chamber, and device performance is minimally affected by machining precision, making it practical for large-scale fabrication. Optical absorbers fabricated using planar multilayer thin-film structures are insensitive to polarization and incident angle. They also require low process precision and can utilize smooth, clean, flexible materials, potentially enabling the fabrication of flexible optical absorbers. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a structural cross-sectional view of the visible-near-infrared band ultra-wideband optical absorber according to an embodiment of the present application, wherein: 1. substrate; 2. highly reflective metal film layer; 3. first transition metal film layer; 4. first dielectric film layer; 5. second transition metal film layer; 6. second dielectric film layer; 7. third transition metal film layer; 8. third dielectric film layer.

[0045] Figure 2 This is a cross-sectional view of the structure of the mid-infrared ultra-wideband optical absorber according to an embodiment of the present application.

[0046] Figure 3 This is an experimental absorption spectrum diagram of the visible-near-infrared ultra-wideband optical absorber according to an embodiment of the present application under vertical light incidence.

[0047] Figure 4 This is an experimental absorption spectrum diagram of the visible-near-infrared ultra-wideband optical absorber according to an embodiment of the present application when the incident light angle changes.

[0048] Figure 5 This is an experimental absorption spectrum diagram of the mid-infrared ultra-wideband optical absorber of an embodiment of the present application under vertical light incidence. DETAILED DESCRIPTION

[0049] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the present application and are not intended to limit the scope of the present application. The implementation conditions used in the examples can be further adjusted according to the conditions of the specific manufacturer. The implementation conditions not specified are generally those used in routine experiments.

[0050] The present invention proposes an ultra-wideband optical absorber based on a multilayer transition metal layer, operating in the visible-near-infrared or mid-infrared band. The absorber comprises a substrate and a planar multilayer structure disposed on the substrate. The planar multilayer structure comprises a highly reflective metal film layer and at least three light-absorbing thin-film structures disposed on the highly reflective metal film layer. Each light-absorbing thin-film structure comprises a transition metal film layer and a dielectric film layer, and the thickness of each transition metal film layer is less than that of the dielectric film layer. The thickness of the ultra-wideband optical absorber is less than 3000 nm. This design effectively improves the absorber's structural design and fabrication methods, achieving an expansion of the optical absorber's bandwidth, a reduction in cost, and large-scale fabrication, which is of significant significance in the absorber field.

[0051] Example 1

[0052] like Figure 1 The figure shows an ultra-wideband optical absorber based on a multi-layer transition metal layer proposed in this application. The working band of the ultra-wideband optical absorber is the visible-near infrared band.

[0053] The ultra-wideband optical absorber includes three light-absorbing film structures, namely a first light-absorbing film structure, a second light-absorbing film structure and a third light-absorbing film structure. The first light-absorbing film structure includes: a first transition metal film layer and a first dielectric film layer; the second light-absorbing film structure includes: a second transition metal film layer and a second dielectric film layer; and the third light-absorbing film structure includes: a third transition metal film layer and a third dielectric film layer.

[0054] The ultra-wideband optical absorber is configured as a planar multilayer structure, which includes a substrate 1, a high-reflection metal film layer 2, a first transition metal film layer 3, a first dielectric film layer 4, a second transition metal film layer 5, a second dielectric film layer 6, a third transition metal film layer 7, and a third dielectric film layer 8 stacked in sequence.

[0055] In actual preparation, the substrate 1 is a 500 μm thick silicon (Si) wafer (e.g., a 2-inch polished silicon (Si) wafer). Then, a certain thickness (e.g., 80 nm thick) of Au highly reflective metal film layer, a certain thickness (e.g., 62 nm thick) of Ti as a first transition metal film layer, a certain thickness (e.g., 98 nm thick) of MgF2 as a first dielectric film layer, a certain thickness (e.g., 11.2 nm thick) of Ti as a second transition metal film layer, a certain thickness (e.g., 118 nm thick) of MgF2 as a second dielectric film layer, a certain thickness (e.g., 5.4 nm thick) of Ti as a third transition metal film layer, and a certain thickness (e.g., 102 nm thick) of MgF2 as a third dielectric film layer are sequentially deposited on the substrate 1 from bottom to top. In this embodiment, the substrate is a silicon wafer. In other embodiments, the substrate can be SiO2 glass, a polished Al wafer, or PET plastic.

[0056] Next, the preparation method of the above-mentioned visible-near infrared optical absorber is described. The preparation process is as follows:

[0057] 1) Deposit an adhesion layer on the substrate, and then deposit a highly reflective Au metal film on the adhesion layer. In this process, a polished Si wafer, SiO2 glass, polished Al wafer, or PET plastic, cleaned ultrasonically with acetone, ethanol, and deionized water, is selected as the substrate. Using thermal evaporation, a 5nm thick layer of Ti is first deposited as the adhesion layer, followed by a highly reflective Au metal film with a thickness greater than 80nm (film thickness is monitored using a quartz crystal oscillator thickness gauge). The deposition vacuum is 5×10 -4 Pa; preferably, the thickness of the high reflective metal film is between 80 and 100 nm.

[0058] 2) Then, a Ti transition metal layer with a thickness of 62 nm was deposited on the high reflective metal film layer using ion beam sputtering technology. Before film deposition, a 5-minute pre-sputtering was performed, and the deposition vacuum was 5×10 -4 Pa, the parameters of ion beam sputtering include: target material is Ti target, ion energy is 800eV, ion beam current is 70mA, argon gas is introduced during sputtering, and the chamber pressure is 0.02Pa;

[0059] 2) Then, ion beam sputtering technology was used to deposit a first dielectric film layer of MgF2 on the highly reflective metal film layer with a thickness of 97.8 nm. Before film deposition, a 5-minute pre-sputtering was performed and the deposition vacuum was 5×10 -4 Pa, the parameters of ion beam sputtering include: target material is MgF2 target, ion energy is 800eV, ion beam current is 70mA, neutralization current is 90mA, argon gas is introduced during sputtering, and the chamber pressure is 0.02Pa;

[0060] 3) Depositing a second transition metal film layer on the first dielectric film layer, wherein the deposited Ti transition metal layer has a thickness of 11.2 nm, preferably, by using ion beam sputtering technology.

[0061] 4) Depositing a second dielectric film layer on the second transition metal film layer, wherein the deposited MgF2 dielectric film layer has a thickness of 118 nm, preferably, by using ion beam sputtering technology.

[0062] 5) Depositing a third transition metal film layer on the second dielectric film layer, wherein the deposited Ti transition metal film layer has a thickness of 5.4 nm. Preferably, the deposition is performed using ion beam sputtering technology.

[0063] 6) Depositing a third dielectric film layer on the third transition metal film layer, wherein the deposited MgF2 dielectric film layer has a thickness of 102 nm, preferably, by using ion beam sputtering technology.

[0064] The absorption spectrum of the ultra-broadband optical absorber in the visible-near infrared band is shown in Figure 3 ,from Figure 3 It can be seen that when the incident light is incident normally on the ultra-wideband optical absorber in the visible-near infrared band, the average absorption rate at a wavelength of 400 to 2500 nm is greater than 92%.

[0065] The absorption spectrum of ultra-broadband optical absorbers in the visible-near infrared band changes with the incident light angle. Figure 4 ,from Figure 4 It can be seen that when the incident angle of the incident light increases from 0° to 68°, the average absorption rate at a wavelength of 400 to 2500 nm is >84%.

[0066] Example 2

[0067] An ultra-broadband optical absorber based on multi-layer transition metal layers, which operates in the visible-near infrared band. Figure 1 As shown, it is the same as Example 1, except that the material of the Au high-reflection metal film layer is Cr, and the preparation method of the Cr high-reflection metal film layer can be selected from electron beam evaporation, magnetron sputtering, or ion beam sputtering. The preparation method of the remaining steps of the visible-near-infrared band ultra-wideband optical absorber refers to Example 1.

[0068] Example 3

[0069] An ultra-broadband optical absorber based on multi-layer transition metal layers, which operates in the visible-near infrared band. Figure 1As shown, it is the same as Example 1, except that the material of the Au high-reflection metal film layer is Al, and the preparation method of the Al high-reflection metal film layer can be selected from electron beam evaporation, magnetron sputtering or ion beam sputtering. The preparation method of the remaining steps of the visible-near-infrared band ultra-wideband optical absorber refers to Example 1.

[0070] Example 4

[0071] like Figure 2 Shown is another embodiment of the present application of an ultra-wideband optical absorber in the mid-infrared band. The ultra-wideband optical absorber is configured as a planar multilayer structure, having three light-absorbing thin film structures (a fourth light-absorbing thin film structure, a fifth light-absorbing thin film structure, and a sixth light-absorbing thin film structure). The fourth light-absorbing thin film structure includes: a fourth transition metal film layer and a fourth dielectric film layer, the fifth light-absorbing thin film structure includes: a fifth transition metal film layer and a fifth dielectric film layer, and the sixth light-absorbing thin film structure includes: a sixth transition metal film layer and a sixth dielectric film layer.

[0072] The ultra-broadband optical absorber is composed of a planar multilayer structure.

[0073] The planar multilayer structure is composed of a substrate 11; a highly reflective metal film layer 12; a seventh dielectric film layer 13; a fourth transition metal film layer 14; a fourth dielectric film layer 15; an eighth dielectric film layer 16; a fifth transition metal film layer 17; a fifth dielectric film 18; a sixth transition metal film layer 19; a sixth dielectric film layer 20; and a ninth dielectric film layer 21.

[0074] During actual preparation, a 500 μm thick Si wafer (such as a 2-inch polished Si wafer) is used as the substrate. On a polished Si wafer substrate, a Ti adhesion layer of a certain thickness (e.g., 5 nm thick), an Au high-reflection metal film layer of a certain thickness (e.g., 80 nm thick), a first MgF2 dielectric film layer of a certain thickness (e.g., 887 nm thick), a first Ti transition metal film layer of a certain thickness (e.g., 18.4 nm thick), a second MgF2 dielectric film layer of a certain thickness (e.g., 946 nm thick), a third Ta2O5 dielectric film layer of a certain thickness (e.g., 140 nm thick), a second Ti transition metal film layer of a certain thickness (e.g., 18.3 nm thick), a fourth Ta2O5 dielectric film of a certain thickness (e.g., 630 nm thick), a third Ti transition metal film layer of a certain thickness (e.g., 4.5 nm thick), a fifth Si3N4 dielectric film layer of a certain thickness (e.g., 811 nm thick), and a sixth MgF2 dielectric film layer of a certain thickness (e.g., 833 nm thick) are deposited in sequence from bottom to top using a vacuum coating method.

[0075] Next, a method for preparing the ultra-wideband optical absorber (operating in the mid-infrared band) based on a multi-layer transition metal layer is described. The preparation method is as follows:

[0076] 1) Depositing an adhesion layer on the substrate, and then depositing an Au highly reflective metal film layer 12 on the adhesion layer, or directly depositing an Al or Cr highly reflective metal film layer 12 on the substrate. In this process, a polished Si wafer, SiO2 glass, polished Al wafer, or PET plastic, which has been ultrasonically cleaned in acetone, ethanol, and deionized water, is selected as the substrate. Using vacuum coating technology, a 5nm thick layer of Ti is first deposited as the adhesion layer, followed by the Au highly reflective metal film layer. Preferably, the thickness of the highly reflective metal film layer is between 80 and 100nm.

[0077] 2) Then, a seventh dielectric film layer of MgF2 is deposited on the Au high-reflection metal film layer using a vacuum coating technique, with a thickness of 887 nm.

[0078] 3) Then, a Ti fourth transition metal film layer is deposited on the MgF2 seventh dielectric film layer using a vacuum coating technique, with a thickness of 18.4 nm.

[0079] 4) Then, a MgF2 fourth dielectric film layer is sequentially deposited on the Ti fourth transition metal film layer using a vacuum coating technique, with a thickness of 946 nm.

[0080] 5) Then, a Ta2O5 eighth dielectric film layer is deposited on the MgF2 fourth dielectric film layer using a vacuum coating technique, with a thickness of 140 nm.

[0081] 6) A Ti fifth transition metal film layer is then deposited on the Ta2O5 eighth dielectric film layer using a vacuum coating technique, with a thickness of 18.3 nm.

[0082] 7) Then, a Ta2O5 fifth dielectric film with a thickness of 630 nm is deposited on the Ti fifth transition metal film layer using a vacuum coating technique.

[0083] 8) A Ti sixth transition metal film layer is then deposited on the Ta2O5 fifth dielectric film using a vacuum coating technique, with a thickness of 4.5 nm.

[0084] 9) A sixth dielectric film layer comprising Si 3 N 4 is then deposited on the Ti sixth transition metal film layer using a vacuum coating technique, with a thickness of 811 nm.

[0085] 10) A ninth dielectric film layer of MgF2 is then deposited on the sixth dielectric film layer comprising Si3N4 using a vacuum coating technique, with a thickness of 833 nm.

[0086] The preparation method of the Au high-reflection metal film layer, the Ti adhesion layer, the Ti transition metal film layer, the MgF2 dielectric film layer, and the Ta2O5 dielectric film layer can be selected from electron beam evaporation, magnetron sputtering, or ion beam sputtering, and the preparation method of the Si3N4 dielectric film layer can be selected from plasma enhanced chemical vapor deposition or inductively coupled plasma chemical vapor deposition.

[0087] The absorption spectrum of the final ultra-broadband mid-infrared optical absorber is shown in Figure 5 When the incident light is incident on the mid-infrared band ultra-wideband optical absorber, the average absorption rate at the wavelength of 3 to 16 μm is greater than 80%.

[0088] Example 5

[0089] An ultra-broadband optical absorber based on multi-layer transition metal layers, whose operating band is the mid-infrared band, its structure is shown in Figure 2 As shown, it is the same as Example 1, except that the material of the Au high-reflection metal film layer is changed to Cr, and the preparation method of the Cr high-reflection metal film layer can be selected from electron beam evaporation, magnetron sputtering or ion beam sputtering. The preparation method of the remaining steps of the mid-infrared band ultra-wideband absorber refers to Example 4.

[0090] Example 6

[0091] An ultra-broadband optical absorber based on multi-layer transition metal layers, which operates in the mid-infrared band. Figure 2 As shown, it is the same as Example 4, except that the material of the Au high-reflection metal film layer is changed to Al, and the preparation method of the Al high-reflection metal film layer can be selected from electron beam evaporation, magnetron sputtering or ion beam sputtering. The preparation method of the remaining steps of the mid-infrared band ultra-wideband absorber refers to Example 4.

[0092] The above are only preferred embodiments of the present application. Of course, the present application may have many other embodiments. Without departing from the spirit and essence of the present application, technicians familiar with the field can make various corresponding changes and deformations based on the present application, such as changing the size, shape or material, etc., but these corresponding changes and deformations should all fall within the scope of protection of the present application.

Claims

1. An ultra-wideband optical absorber based on a multi-layer transition metal layer, operating in the visible-near infrared band or the mid-infrared band, characterized by: include: a substrate, a planar multilayer structure disposed on the substrate, The planar multilayer structure includes a high-reflection metal film layer and at least three light-absorbing thin film structures disposed on the high-reflection metal film layer. Each light-absorbing thin film structure includes a transition metal film layer and a dielectric film layer, and the thickness of the transition metal film layer in each layer is less than the thickness of the dielectric film layer. The thickness of the ultra-wideband optical absorber is less than 3000 nm; The planar multilayer structure includes three sequentially stacked light-absorbing thin film structures, and is configured to be sequentially stacked with a high-reflection metal film layer, a first transition metal film layer, a first dielectric film layer, a second transition metal film layer, a second dielectric film layer, a third transition metal film layer, and a third dielectric film layer; The thickness of the first transition metal film layer is greater than the thickness of the second transition metal film layer and greater than the thickness of the third transition metal film layer; The material of the first transition metal film layer is Ti, and its thickness is between 40 and 70 nm; The first dielectric film layer is made of MgF2 and has a thickness between 90 and 110 nm. The material of the second transition metal film layer is Ti, and its thickness is between 10 and 13 nm; The second dielectric film layer is made of MgF2 and has a thickness between 110 and 130 nm. The third transition metal film layer is made of Ti, and its thickness is between 4 and 7 nm. The third dielectric film layer is made of MgF2 and has a thickness between 90 and 110 nm. Taking the equivalent optical admittance of the planar multilayer structure equal to the optical admittance of air as the optimization goal, the material and thickness of each layer in the planar multilayer structure are designed; the planar multilayer structure is deposited on the surface of the substrate by vacuum coating.

2. The ultra-wideband optical absorber based on multi-layer transition metal layers according to claim 1, characterized in that: The substrate is selected from silicon wafer, SiO2 glass, polished Al wafer or PET plastic.

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