阅读说明：本技术 一种透射滤光片 (Transmission filter ) 是由 季陈纲 于 2018-07-11 设计创作，主要内容包括：本申请公开一种透射滤光片,该透射滤光片包括衬底基板以及依次位于所述衬底基板上的第一金属层、吸收介质层和第二金属层,所述第一金属层、所述吸收介质层以及所述第二金属层组成光学谐振腔,用以选择性的透射不同波长的光,其中,所述第一金属层和第二金属层的厚度相同。通过上述方式,本申请能够显著增强透射光的色纯度,提高透射滤光片的角度不敏感特性。(The application discloses transmission filter, this transmission filter include the substrate base plate and be located in proper order first metal level, absorbing dielectric layer and second metal level on the substrate base plate, first metal level absorbing dielectric layer and the optical resonator is constituteed to the second metal level for the light of the different wavelength of selective transmission, wherein, the thickness of first metal level and second metal level is the same. Through the mode, the color purity of the transmission light can be obviously enhanced, and the angle insensitivity of the transmission filter is improved.)

1. A transmission optical filter is characterized by comprising a substrate base plate, a first metal layer, an absorption medium layer and a second metal layer, wherein the first metal layer, the absorption medium layer and the second metal layer are sequentially arranged on the substrate base plate, and form an optical resonant cavity for selectively transmitting light with different wavelengths.

2. The transmission filter of claim 1, wherein the absorbing medium layer is made of a material selected from the group consisting of amorphous silicon, crystalline silicon, amorphous germanium, ferric oxide, titanium nitride, copper oxide, cuprous oxide, zinc sulfide, selenium sulfide, titanium oxide, niobium oxide, zirconium oxide, zinc oxide, tungsten oxide, aluminum oxide, and silicon oxide.

3. The transmission filter according to claim 2, wherein the thickness of the absorption medium layer is correlated with the wavelength of the transmitted light, and the absorption capacity is equal to or less thanWherein c is the speed of light, ε₀Is the dielectric constant of free space, n is the real part of the refractive index,

4. The transmission filter according to claim 1, wherein the first metal layer and the second metal layer are made of the same material and include at least one of silver, gold, copper, aluminum, chromium, thallium, tungsten, nickel, molybdenum, titanium, niobium, cobalt, palladium, and vanadium.

5. The transmission filter according to claim 4, wherein the first metal layer and the second metal layer have a thickness of 5-50nm for allowing incident light to penetrate the second metal layer and enter the optical resonator for resonance.

6. The transmission filter of claim 1, further comprising a dielectric coating disposed over the second metal layer and/or between the substrate base plate and the first metal layer for improving transmittance efficiency of incident light.

7. The transmission filter according to claim 6, wherein the dielectric coating has a thickness of 10-100 nm;

the dielectric coating is made of one of tungsten oxide, titanium oxide, niobium oxide, zirconium oxide, zinc oxide, aluminum oxide and silicon oxide.

8. The transmission filter of claim 1, further comprising a wetting layer between the second metal layer and the absorbing medium layer, wherein the wetting layer is configured to facilitate film formation of the second metal layer and reduce structural scattering.

9. The transmission filter according to claim 8, wherein the wetting layer is made of at least one of PTCBI, ge, cu, and al, which are organic materials, and has a thickness of 2-10 nm.

10. The reflective filter according to claim 3, wherein said absorbing medium layer has thickness values of 28nm, 15nm and 9nm for red, green and blue colors, respectively.

Technical Field

The application relates to the field of optical filters, in particular to a transmission optical filter.

Background

Optical resonators are widely used in various application fields such as filters, lasers, sensors, and modulators. Conventional fabry-perot (F-P) type resonators are composed of a transparent or low absorption medium with a thickness in the wavelength scale range of visible light, which allows light to interfere without large losses, resulting in longer photon lifetime (i.e., high quality factor, q-factor).

In recent years, researchers have found that there is a strong interference phenomenon of reflected light in a resonant cavity composed of an ultra-thin semiconductor material deposited on a metal substrate in the optical frequency range, that is, strong absorption of a semiconductor at a metal-semiconductor interface and an extraordinary reflection phase shift (neither 0 nor pi) cause strong absorption resonance in the semiconductor in the nanometer thickness range, and thus, the thickness of the resonant cavity can be significantly reduced by using this characteristic. However, in many practical applications, the ability to create transmission resonances is favored over strong absorption characteristics.

Color filters play a key role in many areas such as Liquid Crystal Displays (LCDs), Complementary Metal Oxide Semiconductor (CMOS) image sensors, and the like. Typical color filtering techniques rely on chemical pigment pigments that are susceptible to degradation under high temperature or continuous Ultraviolet (UV) radiation. To overcome the above challenges, researchers have developed color filters with sub-wavelength gratings based on Guided Mode Resonance (GMR) and using metal nanostructures as an alternative surface plasmon filter. However, since these structures excite Surface Plasmon Polariton (SPP) or waveguide photon mode using grating coupling, their optical properties inevitably depend on the incident angle according to the momentum matching condition.

Disclosure of Invention

The application provides a transmission filter, can show the colour purity that strengthens the transmitted light, improves transmission filter's angle insensitive characteristic.

In order to solve the technical problem, the application adopts a technical scheme that: the transmission optical filter comprises a substrate, and a first metal layer, an absorption medium layer and a second metal layer which are sequentially arranged on the substrate, wherein the first metal layer, the absorption medium layer and the second metal layer form an optical resonant cavity for selectively transmitting light with different wavelengths.

The beneficial effect of this application is: the transmission filter is characterized in that an optical resonant cavity is formed by clamping an absorption medium layer between a first metal layer and a second metal layer, and by utilizing the strong interference effect of the optical resonant cavity, the ultra-thin visible light transmission type filter can be realized, the propagation phase shift of light in the ultra-thin absorption medium layer can be ignored, and the angle insensitivity of the transmission filter can be improved.

Drawings

FIG. 1 is a schematic cross-sectional view of a first embodiment of a transmission filter according to the present application;

FIG. 2 is a schematic cross-sectional view of a second embodiment of the transmission filter of the present application;

FIG. 3 is a schematic cross-sectional view of a third embodiment of the transmission filter of the present application;

FIG. 4 is a graph comparing calculated and measured transmission spectra for one embodiment of a transmission filter for normal light incidence within a particular wavelength range of the present application;

FIG. 5 is a schematic diagram illustrating the reflection phase shift of incident light propagating at different interfaces according to the present application versus the incident angle;

FIG. 6 is a schematic diagram of transmission spectra obtained by calculation of polarized light at different incident angles;

FIG. 7 is a schematic diagram of transmission spectra measured at different incident angles for polarized light according to the present application;

FIG. 8 is a graph comparing calculated and measured transmission spectra for different media coating thicknesses in a transmission filter according to the present application;

FIG. 9 is a schematic illustration of admittance at various media coating thicknesses according to the present application.

Detailed Description

The technical solutions of the various exemplary embodiments provided in the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. The various embodiments described below and the features of the embodiments can be combined with each other without conflict. Furthermore, directional terms such as "upper" and "lower" are used throughout the present application to better describe the technical solutions of the embodiments, and are not used to limit the protection scope of the present application.

As shown in fig. 1, fig. 1 is a schematic cross-sectional view of a structure of an embodiment of a transmission filter according to the present application. As shown in fig. 1, the transmission filter 100 provided in the present application includes a substrate 110, and a first metal layer 120, an absorption medium layer 130, and a second metal layer 140 sequentially disposed on the substrate 110.

The first metal layer 120, the absorbing medium layer 130 and the second metal layer 140 form an optical resonant cavity for selectively transmitting light with different wavelengths.

The substrate 110 may be made of a transparent material, and may specifically be any type of substrate such as glass, a ceramic substrate, or transparent plastic, which is not limited in this application.

Alternatively, the first metal layer 120 and the second metal layer 140 in the present application have the same thickness, and the first metal layer 120 and the second metal layer 140 are made of the same material, and each of the first metal layer 120 and the second metal layer 140 may be made of one of silver, gold, copper, aluminum, chromium, thallium, tungsten, nickel, molybdenum, titanium, niobium, cobalt, palladium, and vanadium. In this embodiment, the metal silver with low absorption rate and high reflectivity is selected to reflect the incident light. In a specific embodiment, the first metal layer 120 and the second metal layer 140 may be formed on the substrate base 110 and the absorption medium layer 130 respectively by means of superheated evaporation. In addition, in the present application, the first metal layer 120 and the absorption medium layer 130 may form an optical resonance, and the second metal layer 140 may enhance the reflection of light in the optical resonance cavity while ensuring that incident light enters the transmission filter 100, so as to further enhance the color purity of the transmitted light color.

Optionally, the thickness of the first metal layer 120 and the second metal layer 140 in this application are the same, and the thickness of the first metal layer 120 and the second metal layer 140 is in a range of 5-50nm, specifically, 5nm, 18nm, 50nm, and the like, and is not further limited herein. In a specific application scenario of the present application, the thicknesses of the first metal layer 120 and the second metal layer 140 may be specifically 18nm, that is, strong optical resonance is ensured in the optical resonance cavity while incident light is allowed to enter the transmission filter 100, and color purity of transmitted light may be significantly improved.

Optionally, the thicknesses of the first metal layer 120 and the second metal layer 140 in this embodiment cannot be selected at will, and in practical applications, it is found that as the thicknesses of the first metal layer 120 and the second metal layer 140 increase, the absorption spectrum bandwidth of the transmission filter 100 becomes narrower, the color purity of the transmitted light is improved, but as the thickness of the metal layer increases, the absorption rate of the incident light decreases, which affects the color purity of the transmitted light to be worse, so in this embodiment, the first metal layer 120 and the second metal layer 140 have an optimal thickness, that is, 18 nm. The research in the prior art is focused on narrowing the bandwidth, and generally, the decrease of the absorption efficiency is not concerned about causing adverse effects, and the application finds the existence of the above rule for the first time, so that when the thicknesses of the first metal layer 120 and the second metal layer 140 are determined to be 18nm, the absorption rate of the first metal layer to the incident light is the highest, and the absorption bandwidth is the narrowest.

An absorbing dielectric layer 130 is formed on the first metal layer 120 to form an optical resonant cavity. The imaginary refractive index of the absorption medium layer 130 is smaller than the imaginary refractive index of germanium, and the thickness of the absorption medium layer 130 is related to the wavelength of the transmitted light, specifically, the light absorption capacity (absorption of light intensity) of the absorption medium layer 130 is smaller than or equal to:

wherein c is the speed of light, ε₀Which is the dielectric constant of free space, n is the real part of the refractive index of the absorbing medium layer 130,

in order to obtain the extinction coefficient, α is the absorption coefficient of the absorption medium layer 130, E (x, λ) represents that the electric field E is a function of x and the wavelength λ of incident light, x represents the position of the absorption medium layer 130 along the thickness direction, and λ represents the wavelength of incident light.

Alternatively, the incident light penetrates through the second metal layer 140 and is incident on the absorption medium layer 130, and the absorption medium layer 130 generates plasmons (or photons) under the light irradiation, and the plasmons are reflected back and forth in the optical resonant cavity to form resonance. In this embodiment, the larger the imaginary part of the refractive index of the absorption medium layer 130 is, the larger the light absorption coefficient is, the stronger the light absorption capability thereof is, and the larger the Q factor (quality factor) of the optical resonator is. Further, the more light is transmitted by the absorption medium layer 130, so that the purity of the color of the transmitted light can be significantly enhanced.

The material for manufacturing the absorption dielectric layer 130 may specifically include one of amorphous silicon (a-Si), crystalline silicon, amorphous germanium, iron sesquioxide, titanium nitride, copper oxide, cuprous oxide, zinc sulfide, selenium sulfide, titanium oxide, niobium oxide, zirconium oxide, zinc oxide, aluminum oxide, and silicon oxide. In this embodiment, amorphous silicon having a high light absorption coefficient in the visible light range is selected for specific description. Of course, in other embodiments, the material of the absorption medium layer 130 may be any one of the materials listed above, and is not limited herein. In the preparation process, a Plasma Enhanced Chemical Vapor Deposition (PECVD) manner may be adopted for Deposition.

Alternatively, the thickness of the absorption medium layer 130 in the present application is related to the wavelength of the light that needs to be transmitted by the transmission filter, i.e., the thickness of the absorption medium layer 130 varies with the wavelength of the light that needs to be transmitted. In one embodiment, the thicknesses of the absorption medium layer 130 may be 28nm, 15nm and 9nm for red, green and blue colors, respectively. In this embodiment, the material of the absorption medium layer 130 may include amorphous silicon with a high absorption coefficient, and a strong interference effect exists in the optical resonant cavity formed by the absorption medium layer 130 and the first metal layer 120, so that the quality factor Q of the optical resonant cavity may be further improved.

Optionally, the transmission filter 100 in the present application further includes a dielectric coating 150, and the dielectric coating 150 may be disposed above the second metal layer 140 and/or between the substrate base plate 110 and the first metal layer 120. Referring to fig. 1, the dielectric coating 150 is disposed above the second metal layer 140, in other embodiments, the dielectric coating 150 may also be disposed between the substrate 110 and the first metal layer 120 as shown in fig. 2, and of course, the dielectric coating 150 may also be disposed between the substrate 110 and the first metal layer 120 and above the second metal layer 140 at the same time to improve the transmittance of the transmission filter, as shown in fig. 3.

Optionally, the material of the dielectric coating 150 may be one of tungsten oxide, titanium oxide, niobium oxide, zirconium oxide, zinc oxide, aluminum oxide, and silicon oxide, and the thickness of the one of the two materials is in a range of 10 to 100nm, and specifically may be 10nm, 55nm, 100nm, and the like, which is not further limited herein. The dielectric coating 150 in this embodiment is tungsten oxide (WO)₃). The contrast between the optical constants of the air medium and the medium coating 150 is smaller than the contrast between the optical constants of the air and the second metal layer 140, so that the transmission efficiency of the transmission filter 100 to the incident light can be further improved, and the reflection to the incident light is reduced, so that more incident light enters the transmission filter 100.

Optionally, the transmission filter 100 of the present application further includes a wetting layer 160 disposed between the second metal layer 140 and the absorption medium layer 130, wherein the wetting layer 160 is used to promote the formation of the second metal layer, ensure the flatness of the second metal layer 140, and reduce the scattering loss of the incident light. The material of the wetting layer 160 in the present application may be selected from organic materials, such as perylene tetracarboxylic bisbenzimidazole (PTCBI), semiconductor materials, such as germanium, and metal materials, such as at least one of copper and aluminum. In the embodiment, it is found that the scattering loss of the transmission filter 100 widens the absorption bandwidth of the transmission filter 100, so the thickness of the wetting layer 160 may be in a range of 2-10nm, specifically, 2nm, 5nm, 10nm, and the like, which is not limited herein. Of course, in the embodiment, the wetting layer 160 is selected to have a thickness of 5nm, which has the most significant effect of reducing the scattering loss of the transmission filter 100. Alternatively, in embodiments, the wetting layer 160 may be prepared by superheated evaporation.

In addition, the preparation of each lamination structure of the transmission optical filter in the application adopts a simple coating process, so that the processing of different structural colors can be realized, and compared with a nanometer groove or a grating depending on a sub-wavelength, the method uses a more complex manufacturing technology including nanometer-scale pattern processing and etching, the application can simplify the manufacturing process, and creates possibility for the prospect of large-area use of optical structural colors.

Compared with the optical filter in the prior art, the position of a transmission band generally changes along with the change of an incident angle, so that the color seen at different incident angles or different observation angles has deviation, and the display effect is influenced.

In the above embodiment, the optical resonant cavity is formed by interposing the absorbing medium layer between the first metal layer and the second metal layer, and by using the strong interference effect of the optical resonant cavity, the color purity of the ultra-thin visible light transmission type optical filter and the light required for selective transmission can be enhanced, and the angle insensitivity of the transmission optical filter can be improved.

The theoretical study of the transmission filter is verified in combination with simulation calculations as follows:

referring to fig. 4, fig. 4 is a graph illustrating the calculated and measured transmittance spectrum contrast of one embodiment of the transmission filter under the incidence of vertical light within a specific wavelength range according to the present application. Fig. 4 a) is a calculated transmission spectrum diagram of the transmission filter in which light of the present application vertically enters, wherein the calculated transmission spectrum diagram includes transmittance spectrum lines of red (R), green (G) and blue (B) primary colors of light respectively. b) The transmission spectrum line measured by the transmission filter is a transmission spectrum line diagram in which light vertically enters, wherein the transmission spectrum line diagram respectively comprises the transmittance spectrum lines of red (R), green (G) and blue (B) primary colors.

Wherein the wavelength ranges in a) and b) can be 300-900nm, and the calculation of the transmission filter model can be obtained by using a Fourier Model Method (FMM). The calculation method converts Maxwell equations into algebraic eigenvalue equations in a spatial frequency domain, and the distribution of an electromagnetic field is described by a Bloch characteristic mode. A complete set of optical structural signature modes spans all possible optical fields in a finite dimensional numerical framework, and in FMM simulations, material parameters such as dielectric constant are expressed in tensor form. Alternatively, the experimental data of the transmission spectrum of the transmission filter is measured by a spectrometer (model HR4000CG, ocean optics), and the experimental measurement value of the transmission filter obtained by comparing the two is matched with the result of the simulation calculation.

Referring further to fig. 5, fig. 5 is a schematic diagram illustrating a reflection phase shift of incident light propagating through different interfaces according to the present application in comparison with a change of an incident angle. As shown in fig. 5, the resonance wavelengths in diagrams a), b) and c) correspond to 454nm, 508nm and 614nm, respectively, and correspond to blue light, green light and red light, respectively. Wherein, four curves A, B, C, D in the graphs a), b) and c) represent the variation of the reflection phase shift when the incident light propagates at different interfaces. Wherein, curve a represents the phase shift curve of the incident light when reflected by the first metal layer 120, curve B represents the phase shift curve of the incident light when reflected by the second metal layer 140, curve C represents the phase shift curve of the incident light when transmitted by the amorphous silicon layer (absorption medium layer), and curve D represents the phase shift curve of the incident light when transmitted by the transparent medium (silicon dioxide).

In this embodiment, silicon dioxide is used as the absorption medium layer, and amorphous silicon is used as the absorption medium layer in this application for comparison. The refractive index of the silicon dioxide can be 1.45, and in a specific structure, the materials and thicknesses of the first metal layer and the second metal layer which take the silicon dioxide as the absorption medium layer are the same, namely the metal silver, the thickness of the metal silver is set to be 18nm, the thicknesses of the silicon dioxide relative to three primary colors of red, green and blue are respectively 152nm,114nm and 95nm, and the corresponding resonance wavelengths are respectively 614nm, 508nm and 454 nm.

As shown in the above figures a), b) and C), the phase shift of the propagation of the light of the three primary colors in the resonator structure of the present application (curve C) is significantly smaller than the propagation of light in the resonator using the conventional transparent medium (curve D) compared to the resonator using the conventional transparent medium. In addition, when the incident light angle is increased, the reflection phase shift of light on the surfaces of the absorption medium layer and the first metal layer (a-Si/Ag) has a special compensation effect on the propagation phase of light in the absorption medium layer (a-Si). These two effects combine to improve the characteristic of the transmission filter that is not angle sensitive.

In an embodiment, in order to verify the angle-insensitive property of the transmission filter provided in the present application, the present application further obtains refractive index data of the absorption medium layer (a-Si) and the first metal layer (Ag) using a spectrophotometry method, and performs a numerical simulation using a transmission matrix method, which is described in detail as follows:

referring to fig. 6 and 7, fig. 6 is a schematic diagram of a transmission spectrum obtained by calculation of the polarized light of the present application at different incident angles, and fig. 7 is a schematic diagram of a transmission spectrum obtained by measurement of the polarized light of the present application at different incident angles. The wavelength dynamic range of the experiment is the wavelength range of visible light, Transverse Magnetic (TM) polarized light is selected as the polarized light, and the incident angle range of the incident light is 0-70 degrees. Referring to fig. 6 and 7, it can be seen that the transmission spectrum obtained by experimental measurement and the result obtained by simulation calculation match each other, and the position of the transmission peak does not change with the change of the incident angle.

With further reference to fig. 8, fig. 8 is a graph comparing calculated and measured transmission spectra for different thicknesses of the dielectric coating in the transmission filter of the present application.

As represented by a) in fig. 8 is the transmission spectrum calculated when the thickness of the different medium coating layers is calculated, and b) is the transmission spectrum measured when the thickness of the different medium coating layers is calculated. The curves represented in the graphs a) and B) are respectively a green light spectrum G, a red light spectrum R and a blue light spectrum B, and the thicknesses of the dielectric coatings respectively disposed on the second metal layer 140 are respectively 15nm, 30nm and 0 nm. From the results of the simulation and measurement of the graphs a) and b), it can be seen that the dielectric coating thicknesses of 15nm and 30nm had higher transmission efficiencies than the transmission filter without the dielectric coating, the reason for which is attributable to the air and the dielectric coating (tungsten oxide WO is used in the present example)₃) Is smaller than that caused by the large contrast between the air and the first metal layer Ag.

To confirm this conclusion, the following experiments were also performed to further verify:

referring further to fig. 9, fig. 9 is a schematic diagram of admittance at different dielectric coating thicknesses according to the present application. As shown in fig. 9, where admittance refers to the inverse of impedance, in this embodiment, admittance of the whole structure of the transmission filter starts from the substrate, in this embodiment, glass is used as the substrate, the admittance point is (1.45, 0), and the track of the transmission filter depends on the thickness of the material and the optical constants. In order to reduce the reflection of the overall structure, it is necessary to minimize the distance between the total admittance (i.e., the admittance end point of the overall structure) and the corresponding admittance point (1, 0) of the air.

Alternatively, for the optical filter without the dielectric coating WO3 added above the second metal layer, the admittance end points (1.311, 1.646) of the structure as shown in fig. 9 a) are far from the air admittance point, resulting in a rather strong reflection, and the reflectivity of the incident light can reach 35%. As in fig. 9 b) in the filter of WO3 with a dielectric coating of 15nm thickness, the admittance ends at (0.842, 0.799), which is closer to (1, 0) than in the case of WO3 without dielectric coating, but still produces high reflection, with a reflectivity of the incident light of up to 17%. As in fig. 9 c) for a filter with a dielectric coating of 30nm thickness, the admittance end-point is (0.736, 0.106), which is closer to air (1, 0) than in the first two cases, so that the reflection of the incident light can be suppressed, in which case the reflectivity of the incident light is only 2%.

Alternatively, in other embodiments, the same dielectric coating may be introduced on the substrate base plate before the deposition of the first metal layer, to achieve the same effect, as shown in fig. 2. In addition, a dielectric coating may be introduced over the second metal layer and on the substrate simultaneously to achieve the purpose of further improving the transmission efficiency, as shown in fig. 3, and the specific implementation principle is similar to that of the first embodiment of the transmission filter of the present application, and is not further limited herein.

In the above embodiment, the optical resonant cavity is formed by interposing the absorption medium layer between the first metal layer and the second metal layer, and by using the strong interference effect of the optical resonant cavity, the ultra-thin visible light transmission type optical filter can be realized, the propagation phase shift of light in the ultra-thin absorption medium layer can be ignored, and the angle insensitivity of the transmission optical filter can be improved.

In summary, it is easily understood by those skilled in the art that the present application provides a transmission filter, in which an optical resonant cavity is formed by interposing an absorption medium layer between a first metal layer and a second metal layer, and a strong interference effect of the optical resonant cavity is utilized, so that an ultra-thin visible light transmission type filter can be implemented, a propagation phase shift of light in the ultra-thin absorption medium layer can be negligible, and an angle insensitivity of the transmission filter can be improved.

The above-mentioned embodiments are only examples of the present application, and not intended to limit the scope of the present application, and all equivalent structures or equivalent flow transformations made by the contents of the specification and the drawings, such as the combination of technical features between the embodiments and the direct or indirect application to other related technical fields, are also included in the scope of the present application.