LU504559B1

LU504559B1 - A Low-Reflectance Neutral Density Filter and Its Preparation Method

Info

Publication number: LU504559B1
Application number: LU504559A
Authority: LU
Inventors: Yuanqiang Zhu; Shenhang Ye; Gang Chen
Original assignee: Fujian Foctek Photonics Co Ltd
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2023-12-21

Abstract

The present invention relates to the field of optical film coatings, particularly to a low- reflectance neutral density filter and its preparation method. The neutral density filter comprises a glass substrate, a metal absorption layer, and a dielectric antireflection layer sequentially stacked. The dielectric antireflection layer includes a first TiO2 layer, a first MgF2 layer, a second TiO2 layer, a second MgF2 layer, a third TiO2 layer, and a third MgF2 layer, which are sequentially stacked. The first TiO2 layer is in contact with the metal absorption layer on the side away from the first MgF2 layer. By adding a dielectric antireflection layer on the surface of the metal absorption layer located on the glass substrate and using specific dielectric materials and parameters, the reflectance of the metal absorption layer is reduced without affecting its absorption performance.

Description

A Low-Reflectance Neutral Density Filter and Its Preparation Method

LU504559

TECHNICAL FIELD

The present invention relates to the field of optical film coating technology, particularly to a low-reflectance neutral density filter and its preparation method.

BACKGROUND

The commonly used absorbing material is a metal material, which involves depositing a certain thickness of metal on a transparent glass substrate to achieve a specific level of light absorption or attenuation. However, metal materials exhibit strong absorption characteristics along with significant reflection properties. For instance, in certain optical systems, strong reflection can have negative effects such as increased signal noise and ghosting in imaging.

SUMMARY

The technical problem to be solved by the present invention is to provide a low reflectance neutral density filter and its preparation method, which reduces the reflectance of the metal absorption layer without affecting its absorption performance.

In order to solve the above-mentioned technical problem, the first technical solution adopted by the present invention is as follows:

A low reflectance neutral density filter comprises sequentially stacked layers of a glass substrate, a metal absorption layer, and a dielectric anti-reflection layer. The dielectric anti- reflection layer includes sequentially stacked layers of the first TiO; dielectric layer, the first

MgF- dielectric layer, the second TiO. dielectric layer, the second MgF- dielectric layer, the third

TiO; dielectric layer, and the third MgF> dielectric layer. The first TiO dielectric layer is in contact with the metal absorption layer on the side away from the first MgF2 dielectric layer.

The glass substrate has a refractive index of 1.52 at a wavelength of 550 nm. The metal absorption layer has a refractive index of 3.17 at a wavelength of 550 nm. The refractive indices of the first, second, and third TiO. dielectric layers at a wavelength of 550 nm are all 2.3. The refractive indices of the first, second, and third MgFz dielectric layers at a wavelength of 550 nm are all 1.38.

The thickness of the metal absorption layer is 7.1nm, the thickness of the first TiO. dielectric layer is 38.1nm, the thickness of the first MgF dielectric layer is 197.8nm, the thickness of the second TiO. dielectric layer is 24.1nm, the thickness of the second MgF2 dielectric layer is 37.9nm, the thickness of the third TiO; dielectric layer is 25.1nm, and the thickness of the third MgF: dielectric layer is 109nm.

The second technical solution adopted by the present invention is as follows:

A low reflectance neutral density filter comprises sequentially stacked layers of a glass substrate, a metal absorption layer, and a dielectric anti-reflection layer. The dielectric anti-

reflection layer includes interleaved layers of TiO, and MgF». The TiO; dielectric layers are in LU504559 contact with the metal absorption layer on the side away from the MgF2 dielectric layer ;

The glass substrate has a refractive index of 1.52 at a wavelength of 550 nm. The metal absorption layer has a refractive index of 3.17 at a wavelength of 550 nm. The refractive index of the TiO; dielectric layer at a wavelength of 550 nm is 2.3. The refractive index of the MgF2 dielectric layer at a wavelength of 550 nm is 1.38 ;

The thickness of the metal absorption layer is 10.2nm, the thickness of the TiO; dielectric layer is 34.2nm, and the thickness of the MgF dielectric layer is 78.8nm.

The third technical solution adopted by the present invention is as follows:

A method for preparing a low reflectance neutral density filter includes the following steps:

S1, Prepare a glass substrate;

S2, Use physical vapor deposition technology to sequentially form a metal absorption layer and a dielectric anti-reflection layer on the surface of the glass substrate.

In the formation of the dielectric anti-reflection layer, specifically:

On one side of the metal absorption layer, away from the glass substrate, sequentially form the first TiO, dielectric layer, the first MgF> dielectric layer, the second TiO. dielectric layer, the second MgF dielectric layer, the third TiO. dielectric layer, and the third MgF. dielectric layer.

The glass substrate has a refractive index of 1.52 at a wavelength of 550 nm. The metal absorption layer has a refractive index of 3.17 at a wavelength of 550 nm. The first TiO» dielectric layer, the second TiO: dielectric layer, and the third TiO. dielectric layer all have a refractive index of 2.3 at a wavelength of 550 nm. The first MgF2 dielectric layer, the second

MgFz2 dielectric layer, and the third MgF2 dielectric layer all have a refractive index of 1.38 at a wavelength of 550 nm.

The metal absorption layer has a thickness of 7.1nm. The first TiO dielectric layer has a thickness of 38.1nm. The first MgFz dielectric layer has a thickness of 197.8nm. The second

TiO, dielectric layer has a thickness of 24.1nm. The second MgF- dielectric layer has a thickness of 37.9nm. The third TiO. dielectric layer has a thickness of 25.1nm. The third MgF2 dielectric layer has a thickness of 109nm.

The fourth technical solution adopted by the present invention is as follows:

S1. Prepare a glass substrate.

S2. Utilize physical vapor deposition technique to sequentially form a metal absorption layer and a dielectric antireflection layer on the surface of the glass substrate.

Specifically, to form the dielectric antireflection layer:

On the side of the metal absorption layer facing away from the glass substrate, sequentially deposit TiO, dielectric layers and MgF- dielectric layers.

Wherein, the glass substrate has a refractive index of 1.52 at a wavelength of 550 nm. The metal absorption layer has a refractive index of 3.17 at a wavelength of 550 nm. The TiO:

dielectric layers have a refractive index of 2.3 at a wavelength of 550 nm. The MgF: dielectric LU504559 layers have a refractive index of 1.38 at a wavelength of 550 nm.

The metal absorption layer has a thickness of 10.2nm, and the TiO: dielectric layer has a thickness of 34.2nm, while the MgF2 dielectric layer has a thickness of 78.8nm.

The advantageous effect of the present invention is as follows:

The present invention provides a low-reflectivity neutral density filter and its preparation method. By adding a dielectric antireflection layer on the surface of the metal absorption layer located on the glass substrate, and utilizing specific dielectric layers and parameter configurations, the reflectivity of the metal absorption layer is reduced without affecting its absorption efficiency.

DESCRIPTION OF DRAWINGS

Figure 1: Schematic diagram of the structure of a low reflectance neutral density filter, an embodiment of the present invention (Example 1).

Figure 2: Schematic diagram of the reflectance of the existing metal absorption layer in

Example 1 of the present invention.

Figure 3: Schematic diagram of the transmittance of the existing metal absorption layer in

Example 1 of the present invention.

Figure 4: Schematic diagram of the reflectance of the metal absorption layer in Example 1 of the present invention.

Figure 5: Schematic diagram of the transmittance of the metal absorption layer in Example 1 of the present invention.

Label Explanation: 1. Glass substrate; 2. Metal absorption layer; 3. Dielectric antireflection layer; 31. First TiO» dielectric layer; 32. First MgF> dielectric layer; 33. Second TiO. dielectric layer; 34. Second

MgF- dielectric layer; 35. Third TiO. dielectric layer; 36. Third MgF2 dielectric layer; 4. Glass substrate; 5. Metal absorption layer; 6. Dielectric antireflection layer; 61. TiO. dielectric layer; 62. MgF: dielectric layer

DETAILED DESCRIPTION

In order to provide a detailed explanation of the technical content, objectives, and achieved effects of the present invention, the following embodiments will be described in conjunction with the accompanying drawings.

Example 1 (Neutral Density Filter with 50% Transmittance)

Referring to Figures 1 to 5, the present invention provides a low reflectance neutral density filter. It includes a glass substrate 1, a metal absorption layer 2, and a dielectric anti-reflection layer 3 arranged in a stacked configuration. The dielectric anti-reflection layer 3 comprises sequentially stacked layers: a first TiO. dielectric layer 31, a first MgF2 dielectric layer 32, a second TiO; dielectric layer 33, a second MgF dielectric layer 34, a third TiO, dielectric layer LU504559 35, and a third MgF2 dielectric layer 36. The first TiO. dielectric layer 31 is in contact with the metal absorption layer 2 on the side opposite to the first MgF2 dielectric layer 32. In this embodiment, the metal absorption layer 2 is made of chromium (Cr). The glass substrate 1 is made of commonly used K9 glass.

The refractive indices at a wavelength of 550 nm are as follows: the glass substrate has a refractive index of 1.52, the metal absorption layer has a refractive index of 3.17, the first, second, and third TiO; dielectric layers have a refractive index of 2.3, and the first, second, and third MgF dielectric layers have a refractive index of 1.38.

The thicknesses of the layers are as follows: the metal absorption layer has a thickness of 7.1 nm, the first TiO dielectric layer has a thickness of 38.1 nm, the first MgF2 dielectric layer has a thickness of 197.8 nm, the second TiO; dielectric layer has a thickness of 24.1 nm, the second MgF dielectric layer has a thickness of 37.9 nm, the third TiO, dielectric layer has a thickness of 25.1 nm, and the third MgF2 dielectric layer has a thickness of 109 nm.

The advantageous effects of the present invention are as follows:

By adding a dielectric anti-reflection layer on the surface of the metal absorption layer on the glass substrate and using specific dielectric layers with specific parameters, the reflectance of the metal absorption layer can be reduced without affecting its absorption properties. With the specified parameter configuration, the reflectance of the metal absorption layer at wavelengths from 380 nm to 780 nm can be reduced from 18.1% to 1%.

Referring to Figures 2 and 3, for a neutral density filter with only a metal absorption layer and 50% transmittance (ND = 50%), although the chromium (Cr) film thickness is only 4.6 nm, its reflectance is as high as Rave = 18.1% at 380-780 nm, and transmittance is Tave = 50.5% at 380-780 nm. With the design of this invention, as shown in Figures 4 and 5, the measured reflectance is Rave = 1.0% at 380-780 nm, and transmittance is Tave = 50.1% at 380-780 nm. It can be clearly seen that the reflectance of the metal absorption layer is reduced without affecting its absorption properties. The reflectance of the metal absorption layer at wavelengths from 380 nm to 780 nm is reduced from 18.1% to 1%.

The present invention also provides a method for manufacturing a low reflectance neutral density filter, including the following steps:

S1. Prepare a glass substrate.

S2. Utilize physical vapor deposition techniques, specifically magnetron sputtering or electron beam evaporation, to sequentially form a metal absorption layer and a dielectric anti- reflection coating on the surface of the glass substrate.

The dielectric anti-reflection coating is formed as follows:

On the side of the metal absorption layer facing away from the glass substrate, sequentially form the first TiO, dielectric layer, the first MgF dielectric layer, the second TiO. dielectric layer,

the second MgF dielectric layer, the third TiO. dielectric layer, and the third MgF> dielectric LU504559 layer.

The glass substrate has a refractive index of 1.52 at a wavelength of 550 nm. The metal absorption layer has a refractive index of 3.17 at a wavelength of 550 nm. The first, second, and 5 third TiO: dielectric layers have a refractive index of 2.3 at a wavelength of 550 nm. The first, second, and third MgF2 dielectric layers have a refractive index of 1.38 at a wavelength of 550 nm.

The thickness of the metal absorption layer is 7.1nm. The thickness of the first TiO; dielectric layer is 38.1nm. The thickness of the first MgF dielectric layer is 197.8nm. The thickness of the second TiO; dielectric layer is 24.1nm. The thickness of the second MgF dielectric layer is 37.9nm. The thickness of the third TiO. dielectric layer is 25.1nm. The thickness of the third

MgFz2 dielectric layer is 109nm.

By employing the aforementioned fabrication method, the aforementioned neutral density filter can be obtained, thereby achieving the claimed technical effects.

Claims

1. Alow-reflectance neutral density filter comprises a glass substrate, a metal absorption layer, and a dielectric antireflection layer sequentially stacked, wherein: — the dielectric antireflection layer includes a first TiO. layer, a first MgFa layer, a second TiO layer, a second MgF layer, a third TiO. layer, and a third MgF. layer, which are sequentially stacked:; — the first TiO, layer is in contact with the metal absorption layer on the side away from the first MgFz layer; — the glass substrate has a refractive index of 1.52 measured at a wavelength of 550 nm; — the metal absorption layer has a refractive index of 3.17 measured at a wavelength of 550 nm: — the first, second, and third TiO, layers have refractive indices of 2.3 measured at a wavelength of 550 nm; — the first, second, and third MgFa layers have refractive indices of 1.38 measured at a wavelength of 550 nm; — the thickness of the metal absorption layer is 7.1nm, the thickness of the first TiO. layer is 38.1 nm, the thickness of the first MgF2 layer is 197.8 nm, the thickness of the second

TiO. layer is 24.1 nm, the thickness of the second MgF- layer is 37.9 nm, the thickness of the third TiO: layer is 25.1 nm, and the thickness of the third MgF layer is 109 nm; — the dielectric antireflection layer includes interleaved TiO: layers and MgFz layers; — the TiO: layers are in contact with the metal absorption layer on the side away from the MgFz layers; — the glass substrate has a refractive index of 1.52 measured at a wavelength of 550 nm; — the metal absorption layer has a refractive index of 3.17 measured at a wavelength of 550 nm; — the TiO; layers have refractive indices of 2.3 measured at a wavelength of 550 nm; — the MgFz layers have refractive indices of 1.38 measured at a wavelength of 550 nm; — the thickness of the metal absorption layer is 10.2 nm, the thickness of the TiO: layer is

34.2 nm, and the thickness of the MgF- layer is 78.8 nm.

2. The low-reflectance neutral density filter according to claim 1, wherein the metal absorption layer is made of chromium.

3. The low-reflectance neutral density filter according to claim 1, wherein the glass substrate is made of K9 glass.

4. A method for preparing a low-reflectance neutral density filter, comprising the following steps: S1: preparing of a glass substrate. S2: applying physical vapor deposition technology to sequentially form a metal absorption layer and a dielectric antireflection layer on the surface of the glass substrate, wherein the formation of the dielectric antireflection layer comprises sequentially forming the first TiO2 layer, the first MgF> layer, the second TiO. layer, the second MgF- layer, the third TiO> layer, and the third MgFz layer on the side of the metal absorption layer away from the glass substrate, wherein — the glass substrate having a refractive index of 1.52 measured at a wavelength of 550 nm; — the metal absorption layer has a refractive index of 3.17 measured at a wavelength of 550 nm; — the first, second, and third TiO. layers have refractive indices of 2.3 measured at a wavelength of 550 nm; — the material of the metal absorption layer is chromium; and — the glass substrate is a K9 glass substrate.

5. A method for preparing a low reflectance neutral density filter of claim 4, comprising the step of forming a TiO. dielectric layer and an MgF: dielectric layer sequentially on one side of the metal absorption layer, away from the glass substrate, wherein — the glass substrate has a refractive index of 1.52 measured at a wavelength of 550 nm; — the metal absorption layer has a refractive index of 3.17 measured at a wavelength of 550 nm; — the TiO» dielectric layer has a refractive index of 2.3 measured at a wavelength of 550 nm; — the MgF: dielectric layer has a refractive index of 1.38 measured at a wavelength of 550 nm; — the material of the metal absorption layer is chromium; and — the glass substrate is a K9 glass substrate.