Thin-film narrow-band-pass filter, preparation method and application

Abstract

The invention discloses a thin-film narrow-band-pass filter, a preparation method and application. The filter is based on the Fabry-Perot cavity theory and sequentially comprises a substrate layer, a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer from bottom to top. The refractive index of the top metal reflector layer and the bottom metal reflector layer is higher than that of the dielectric layer. The filter is based on the Fabry-Perot cavity theory, excellent spectral selectivity is achieved through the accurately-designed multi-layer film structure, the filter is particularly suitable for a multi-spectral imaging system, the filter can keep high transmissivity and achieve narrow-band transmission within the required wavelength range at the same time by optimizing selection and layer thickness of film materials, and the filter is suitable for large-scale popularization and application. And the requirements of a multispectral imaging system are met. The thin-film narrow-band-pass filter is simple in structure and easy to manufacture, and large-scale production can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical filters, in particular to a thin film narrow bandpass filter based on Fabry-Perot cavity theory and a preparation method thereof. The filter is suitable for a multi-spectral imaging system. Background Art

[0002] In the field of multispectral imaging technology, narrowband filters are one of the key components to achieve image capture. They are able to allow light in a specific wavelength range to pass through while reflecting or absorbing light of other wavelengths, thereby achieving selective transmission of a specific spectral region. Traditional narrowband filters usually use complex optical systems such as diffraction gratings, prisms, etc., which are not only bulky but also expensive. With the development of micro-nano processing technology, thin film filters achieve spectral selection by depositing multiple layers of thin films on a substrate, which can be metal, dielectric or a combination of them. Thin film filters have the advantages of small size, light weight, low cost and flexible design, making them have a wide range of application potential in multispectral imaging systems. Therefore, it is of great practical significance to develop a narrow bandpass filter with simple structure, low cost and excellent performance. Summary of the invention

[0003] The purpose of the present invention is to provide a thin film narrow bandpass filter, a preparation method and an application thereof in view of the deficiencies of the prior art. The filter of the present invention is based on the Fabry-Perot cavity theory and achieves excellent spectral selectivity through a precisely designed multilayer thin film structure. The filter is particularly suitable for multi-spectral imaging systems. By optimizing the selection of thin film materials and layer thickness, the filter can achieve narrowband transmission in the required wavelength range while maintaining high transmittance, meeting the requirements of multi-spectral imaging systems.

[0004] The objective of the present invention is achieved through the following technical solutions: a thin film narrow band pass filter, which is based on the Fabry-Perot cavity theory and comprises, from bottom to top, a substrate layer, a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer; the refractive index of the top metal reflector layer and the bottom metal reflector layer is higher than that of the dielectric layer; the dielectric layer is used to form a narrow band transmission peak; the top metal reflector layer and the bottom metal reflector layer work together to form a Fabry-Perot resonant cavity, so that light of a specific wavelength is resonated, enhanced and transmitted in the resonant cavity.

[0005] Furthermore, the peak wavelength λ of the filter is given by λ=2n1d1 / m, where n1 is the refractive index of the dielectric layer, d1 is the thickness of the dielectric layer, and m is the diffraction order. By precisely controlling the thickness and refractive index of the dielectric layer, the peak wavelength of the filter can be precisely tuned to meet the needs of specific applications.

[0006] Furthermore, the refractive index n2 of the bottom metal reflector layer is equal to the refractive index n3 of the top metal reflector layer; the thickness d2 of the bottom metal reflector layer is equal to the thickness d3 of the top metal reflector layer, and d2=n1d1 / n2.

[0007] Furthermore, the top metal reflector layer and the bottom metal reflector layer are made of gold material, which has high reflectivity and good conductivity, and can effectively support a resonance wavelength of less than 500nm; at the same time, the thickness of the gold layer is adjusted according to specific design requirements to optimize the overall filtering transmittance.

[0008] Furthermore, the dielectric layer serves as a dielectric cavity of the filter, and its material is SiO2, which has good optical properties and chemical stability, and can achieve high refractive index and narrow bandpass characteristics.

[0009] Furthermore, the adhesion is improved by depositing an adhesion layer, which helps to improve the mechanical stability and durability of the filter. The material of the adhesion layer is TiO2. The thickness of the four adhesion layers is the same, between 9nm and 11nm.

[0010] Furthermore, the material of the protective layer and the base layer is SiO2.

[0011] The present invention also provides a method for preparing the above-mentioned thin film narrow bandpass filter, which specifically comprises: preparing a base layer, and sequentially depositing a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer on the base layer.

[0012] Furthermore, during the preparation process, an electron beam evaporator was used to deposit each thin film layer, wherein the deposition rate of the dielectric layer and the adhesion layer was The deposition rate of the metal mirror layer changes from Gradually increase to This approach ensures uniformity and stability of the film, thereby improving filter performance.

[0013] The present invention also provides an application method of the thin film narrow bandpass filter, wherein the thin film narrow bandpass filter is integrated into a multi-spectral imaging system; the multi-spectral imaging system comprises P thin film narrow bandpass filters, and the corresponding peak wavelengths are λ1, ..., λ P , and a black-and-white image sensor, all thin-film narrow bandpass filters work in conjunction with the black-and-white image sensor to simultaneously capture image data for P spectral channels. This integration provides a simple, compact, and cost-effective multispectral imaging solution.

[0014] Furthermore, P thin-film narrow bandpass filters are formed into an integrated filter array through a UV photolithography machine, a mask plate and a coating device, and the P thin-film narrow bandpass filters and the black-and-white image sensor are calibrated at the pixel level through a flip-chip welding machine. Each thin-film narrow bandpass filter serves as a pixel, which is integrated into a multi-spectral imaging system by spin coating and bonding with optically transparent glue.

[0015] Furthermore, the optically transparent glue is prepared by mixing PMMA powder and anisole.

[0016] Furthermore, the preparation method of the integrated filter array includes: preparing a base layer, and periodically arranging P square first adhesion layers on the base layer by using an ultraviolet photolithography machine and a mask; depositing a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer in sequence on each first adhesion layer to form P thin film narrow bandpass filters.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] 1. The thin film narrow bandpass filter of the present invention has a simple structure, is easy to manufacture, and can be mass-produced;

[0019] 2. The thin film narrow bandpass filter of the present invention has high spectral selectivity and is suitable for multi-spectral imaging systems;

[0020] 3. The thin film narrow bandpass filter of the present invention is low-cost and can replace the traditional complex optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 A schematic cross-sectional structure diagram of a thin film narrow bandpass filter provided by an embodiment of the present invention;

[0023] Figure 2 The transmittance of the thin film narrow bandpass filter at different wavelengths provided by the embodiment of the present invention;

[0024] Figure 3 A schematic diagram of an integrated filter array when P=6 provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0026] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0028] like Figure 1 As shown, an embodiment of the present invention provides a thin film narrow bandpass filter, which is designed based on a multilayer structure of the Fabry-Perot cavity theory, and comprises, from bottom to top, a parallel substrate layer, a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer; the refractive index of the top metal reflector layer and the bottom metal reflector layer is higher than that of the dielectric layer. The dielectric layer is composed of a dielectric material with a high refractive index, and is used to realize multiple reflections and interference of light of a specific wavelength in the dielectric layer, thereby forming a narrow-band transmission peak. The top metal reflector layer and the bottom metal reflector layer work together to form a Fabry-Perot resonant cavity, so that light of a specific wavelength resonates and is enhanced in the resonant cavity and transmitted out.

[0029] Furthermore, the peak wavelength λ of the filter is determined by the formula λ=2n1d1 / m, where n1 is the refractive index of the dielectric layer, d1 is the thickness of the dielectric layer, and m is the diffraction order. In this embodiment, m=1. By precisely controlling the thickness and refractive index of the dielectric layer, the peak wavelength of the filter can be precisely tuned to meet the needs of specific applications.

[0030] Further, the refractive index n2 of the bottom metal reflector layer is equal to the refractive index n3 of the top metal reflector layer. The thickness d2 of the bottom metal reflector layer is equal to the thickness d3 of the top metal reflector layer, and d2=n1d1 / n2.

[0031] Furthermore, the two metal reflector layers are made of gold material, which has high reflectivity and good conductivity, and can effectively support resonance wavelengths less than 500nm. At the same time, the thickness of the gold layer is adjusted according to specific design requirements to optimize the overall filtering transmittance.

[0032] Furthermore, the dielectric layer serves as a dielectric cavity of the filter, and its material is SiO2, which has good optical properties and chemical stability, and can achieve high refractive index and narrow bandpass characteristics.

[0033] Furthermore, depositing four adhesion layers to improve adhesion helps to improve the mechanical stability and durability of the filter. The thickness of the four adhesion layers is the same, between 9nm and 11nm. The material of the adhesion layer in this embodiment is TiO2, and the thickness of each layer is 10nm.

[0034] Furthermore, the material of the protective layer is the same as that of the base layer. In this embodiment, both the protective layer and the base layer are made of SiO2.

[0035] The preparation method of the thin film narrow bandpass filter in this embodiment is specifically: prepare a base layer, and then deposit a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer on the base layer in sequence.

[0036] Preferably, an electron beam evaporator is used to deposit each thin film layer during the preparation process, wherein the deposition rate of the dielectric layer and the adhesion layer is The deposition rate of the metal in the metal reflector layer changes from Gradually increase to This approach ensures uniformity and stability of the film, thereby improving filter performance.

[0037] like Figure 2 FIG. 1 shows the overall (normalized) transmittance curves of a single thin film narrow bandpass filter, which show the light transmission performance of the filter at different wavelengths. The use of thin film narrow bandpass filters successfully filters out unwanted peaks in the visible light region.

[0038] In another embodiment, an application method of the thin film narrow bandpass filter is provided, wherein the thin film narrow bandpass filter is integrated into a multi-spectral imaging system. The multi-spectral imaging system comprises P thin film narrow bandpass filters, and the corresponding peak wavelengths are λ1, ..., λ P , and a black-and-white image sensor, all thin-film narrow bandpass filters work in conjunction with the black-and-white image sensor to simultaneously capture image data for P spectral channels. This integration provides a simple, compact, and cost-effective multispectral imaging solution.

[0039] P thin film narrow bandpass filters are formed into an integrated filter array through a UV lithography machine, a mask plate and a coating device, and the P thin film narrow bandpass filters and a black and white image sensor are calibrated at the pixel level through a flip welding machine, each thin film narrow bandpass filter is used as a pixel, and combined with optically transparent glue, spin coating and bonding to form a multi-spectral imaging system. Preferably, the optically transparent glue is prepared by mixing PMMA powder and anisole.

[0040] The method for preparing the above integrated filter array specifically comprises the following steps:

[0041] (1) preparing a base layer;

[0042] (2) periodically arranging P square first adhesion layers on the substrate layer using an ultraviolet photolithography machine and a mask;

[0043] (3) A bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer are sequentially deposited on each first adhesion layer to form P thin film narrow bandpass filters.

[0044] Preferably, each thin film layer is deposited by an electron beam evaporator, wherein the deposition rate of the dielectric layer and the adhesion layer is The deposition rate of the metal in the metal reflector layer changes from Gradually increase to This approach ensures uniformity and stability of the film, thereby improving filter performance.

[0045] like Figure 3 As shown, it is a schematic diagram of the integrated filter array structure when P=6.

[0046] Through the above manufacturing method, a thin film narrow bandpass filter with excellent spectral selectivity can be manufactured efficiently and accurately to meet the needs of multi-spectral imaging systems.

[0047] The above is only a preferred embodiment of the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, all belong to the scope of protection of the technical solution of the present invention.

Claims

1. A thin film narrow bandpass filter, characterized in that: The filter is based on the Fabry-Perot cavity theory, and comprises, from bottom to top, a substrate layer, a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer; the refractive index of the top metal reflector layer and the bottom metal reflector layer is higher than that of the dielectric layer; the dielectric layer is used to form a narrow-band transmission peak; the top metal reflector layer and the bottom metal reflector layer work together to form a Fabry-Perot resonant cavity, so that light of a specific wavelength is resonated, enhanced and transmitted in the resonant cavity.

2. The thin film narrow bandpass filter according to claim 1, characterized in that: The formula for the peak wavelength λ of the filter is λ=2n1d1 / m, where n1 is the refractive index of the dielectric layer, d1 is the thickness of the dielectric layer, and m is the diffraction order.

3. The thin film narrow bandpass filter according to claim 2, characterized in that: The refractive index n2 of the bottom metal reflector layer is equal to the refractive index n3 of the top metal reflector layer; the thickness d2 of the bottom metal reflector layer is equal to the thickness d3 of the top metal reflector layer, and d2=n1d1 / n2.

4. The thin film narrow bandpass filter according to claim 1, characterized in that: The top metal reflector layer and the bottom metal reflector layer are made of gold material; the dielectric layer serves as the dielectric cavity of the filter, and its material is SiO2.

5. The thin film narrow bandpass filter according to claim 1, characterized in that: The material of the four adhesion layers is TiO2, and the thickness is the same, ranging from 9nm to 11nm.

6. A method for preparing a thin film narrow bandpass filter according to any one of claims 1 to 5, characterized in that: The method specifically comprises: preparing a base layer, and sequentially depositing a first adhesion layer, a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer on the base layer.

7. The preparation method according to claim 6, characterized in that: Each thin film layer was deposited using an electron beam evaporator, where the deposition rate of the dielectric layer and the adhesion layer was The deposition rate of the metal mirror layer changes from Gradually increase to 8. An application method of the thin film narrow bandpass filter according to any one of claims 1 to 5, characterized in that: The thin film narrow bandpass filter is integrated into a multi-spectral imaging system; the multi-spectral imaging system comprises P thin film narrow bandpass filters, and the corresponding peak wavelengths are λ1, ..., λ P , and a black-and-white image sensor, all of the thin film narrow bandpass filters are used in conjunction with the black-and-white image sensor to simultaneously capture image data of P spectral channels.

9. The application method of the thin film narrow bandpass filter according to claim 8, characterized in that: P thin-film narrow bandpass filters are formed into an integrated filter array through a UV photolithography machine, a mask plate and a coating device. The P thin-film narrow bandpass filters and the black-and-white image sensor are calibrated at the pixel level through a flip-chip welding machine. Each thin-film narrow bandpass filter is used as a pixel, which is combined with optically transparent glue by spin coating and bonding to form an integrated multi-spectral imaging system.

10. The application method of the thin film narrow bandpass filter according to claim 9, characterized in that: The preparation method of the integrated filter array includes: preparing a base layer, and periodically arranging P square first adhesion layers on the base layer by using an ultraviolet photolithography machine and a mask; and sequentially depositing a bottom metal reflector layer, a second adhesion layer, a dielectric layer, a third adhesion layer, a top metal reflector layer, a fourth adhesion layer and a protective layer on each first adhesion layer to form P thin film narrow bandpass filters.

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