A space-time anti-reflection film and anti-reflection system

Abstract

The present invention discloses a space-time anti-reflection film and an anti-reflection system. The space-time anti-reflection film of the present invention comprises: a nonlinear medium, the nonlinear medium produces a shift change in refractive index under the oblique irradiation of a target light source, and realizes a dynamic interface to reduce the reflection of an incident wave when it is incident from an incident medium to a transmission medium. The space-time anti-reflection film of the present invention causes the nonlinear medium to produce a shift change in refractive index by obliquely irradiating the nonlinear medium with a target light source, thereby forming a space-time metamaterial with a dynamic interface to reduce the reflection of an incident wave when it is incident from an incident medium to a transmission medium. The present invention extends the non-reflection from pure space and pure time to the space-time domain, and uses space-time to break the translational symmetry of space and time to realize the regulation of frequency wave vectors.

Description

Technical Field

[0001] The invention relates to the field of optical materials, in particular to a space-time anti-reflection film and an anti-reflection system. Background Art

[0002] When light propagates at the interface between two different media, reflection occurs. Suppressing reflection is of great significance for practical applications of information conversion and transmission, such as resonators, antennas, filters and lenses. At present, technologies such as Brewster effect and material coating have been widely used to suppress reflection phenomena at pure space or pure time interfaces. Anti-reflection film is one of the key technologies to reduce space or time reflection during light-matter interaction. In the dimension of space and time, the space-time interface between different media will naturally produce reflection, which is not conducive to the propagation of information. How to eliminate reflection at the space-time interface is still extremely difficult.

[0003] Reflection of light refers to the phenomenon that when light interacts with matter, the propagation direction of light changes and returns to the original medium due to the impedance mismatch of the media on both sides of the interface. In many optical systems, it is very necessary to reduce reflection. Traditional optical reflection reduction is achieved by using single-layer or multi-layer dielectric films and gradient refractive index surface structures in different wavelength ranges. These methods not only require non-planar surfaces, but also involve complex manufacturing processes and integrated devices. Therefore, a new anti-reflection solution is needed to solve the above problems. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a time-space anti-reflection film with a reasonable structure.

[0005] In order to solve the above technical problems, the present invention provides a space-time anti-reflection film, which is used to be arranged between an incident medium and a transmission medium. The space-time anti-reflection film includes:

[0006] A nonlinear medium generates a movement change of the refractive index under the oblique illumination of a target light source, forming a space-time metamaterial with a dynamic interface to reduce the reflection of an incident wave when it is incident from an incident medium to the transmission medium.

[0007] In one embodiment of the present invention, after the incident wave is incident on the space-time metamaterial from the incident medium, it is transmitted to the transmission medium.

[0008] In one embodiment of the present invention, after the incident wave is incident on the space-time metamaterial from the incident medium and then transmitted to the transmission medium, the space-time metamaterial satisfies the following conditions:

[0009]

[0010] Among them, n2 is the refractive index of the space-time metamaterial, n1 is the refractive index of the incident medium, n3 is the refractive index of the transmission medium, a is an odd number, Δx is the thickness of the nonlinear medium in the spatial domain, λ is the wavelength of the incident wave, and β is the normalized dynamic interface velocity.

[0011] In one embodiment of the present invention, when the nonlinear medium is irradiated obliquely by the target light source, a refractive index shift change Δn is generated, satisfying:

[0012] Δn = NI

[0013] Among them, N is the refractive index coefficient of the nonlinear medium, and I is the light intensity of the target light source.

[0014] In one embodiment of the present invention, the incident angle of the target light source on the nonlinear medium is m, and m satisfies: 0° < m < 90°.

[0015] In one embodiment of the present invention, the dynamic interface is a superluminal dynamic interface or a subluminal dynamic interface.

[0016] In one embodiment of the present invention, the target light source is a pump light source.

[0017] In one embodiment of the present invention, the nonlinear medium is indium tin oxide.

[0018] In one embodiment of the present invention, a deceleration medium is provided on the nonlinear medium, and the target light source is irradiated onto the nonlinear medium by the deceleration medium to reduce the speed of the dynamic interface.

[0019] The present invention provides an antireflection system, which includes the space-time antireflection film described in any one of the above and the target light source; when the nonlinear medium is irradiated obliquely by the target light source, a refractive index shift change is generated to form a space-time metamaterial with a dynamic interface, so as to reduce the reflection when the incident wave is incident from the incident medium to the transmission medium.

[0020] The above technical solutions of the present invention have the following advantages compared with the prior art:

[0021] The space-time antireflection film of the present invention irradiates the nonlinear medium obliquely by the target light source, so that the nonlinear medium generates a refractive index shift change to form a space-time metamaterial with a dynamic interface, so as to reduce the reflection when the incident wave is incident from the incident medium to the transmission medium. The present invention extends non-reflection from the pure space and pure time to the space-time domain, and uses space-time to break the translational symmetry of space and time to achieve the regulation of the frequency wave vector.

[0022] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following specifically cites a preferred embodiment and describes it in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0024] Figure 1 It is a schematic diagram of the scattering behavior of waves in subluminal interface media and superluminal interface media in a space-time system;

[0025] Figure 2 This is a diagram showing the influence of a hollow anti-reflection film on the field distribution of plane wave excitation in one embodiment of the present invention;

[0026] Figure 3 is a diagram showing the effect of a spatiotemporal antireflection film on the magnetic field distribution excited by a narrowband pulse in one embodiment of the present invention;

[0027] Figure 4 It is a structural diagram of a space-time anti-reflection film realizing space-time non-reflection in one embodiment of the present invention;

[0028] Figure 5 This is the result of implementing the space-time anti-reflection film on the ITO (indium tin oxide) material in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0030] Reference Figure 1 , where (a) and (b) are schematic diagrams of the scattering behavior of subluminal interface media in the space-time system, and (c) and (d) are schematic diagrams of the scattering behavior of waves in superluminal interface media. The horizontal axis x is the space domain, the vertical axis ct is the time domain, and the grid area, gray area, and dot area correspond to media with refractive indices n1, n2, and n3, respectively. The incident wave, reflected wave, and transmitted wave are represented by Ψ inc , - , + Mark. The thickness of the space-time anti-reflection film is Δx in the spatial domain and d in the space-time domain.

[0031] Since time-varying media can generally be divided into two types, namely, moving interface media and moving material media, although the electromagnetic responses of these two configurations are different, they can be switched to each other after appropriate Lorentz transformation. In order to facilitate practical implementation, this paper mainly discusses moving material media. Without loss of generality, we consider the dynamic interface between two media with refractive indices n1 and n3 respectively. The dynamic interface moves along the x-axis at a speed v b The incident light propagates along the x-axis and interacts with the dynamic interface.

[0032] Different refractive indices lead to impedance mismatch between the two media, which inevitably produces reflection. For the sake of completeness, we consider two classic dynamic interfaces here, namely subluminal and superluminal interfaces. For subluminal interfaces, the reflected and transmitted waves are on both sides of the dynamic interface (such as Figure 1 For a superluminal interface, due to causality, the reflected wave and the transmitted wave coexist on the same side of the dynamic interface (as shown in (a)). Figure 1 Adding space-time metamaterials to the dynamic interface (as shown in (c) Figure 1 (b) and (d) in the figure, the above scattering characteristics will change significantly. The space-time thickness of the metamaterial is d, and the projection of thickness d in the space domain is Δx. When d and n are carefully designed, the reflected wave disappears. We define such a metamaterial as a space-time anti-reflection film. Due to the destruction of translational symmetry in space and time, different modulation speeds will lead to the dispersion of modes (ω=ck / n1, ). In a uniform moving interface medium, kv b -ω is always a conserved quantity. Therefore, the frequency relationship between incident and transmitted is as follows:

[0033]

[0034] In the formula, ω inc ,ω + are the incident frequency and the transmitted frequency respectively, β=v b / c is the interface velocity β normalized to the speed of light in vacuum sub , β sup The modulation speed changes the frequency of the transmitted wave to However, because the scattering of light in space (time) artificial media must obey the conservation of frequency (momentum), it is difficult to achieve flexible transitions in pure space or time artificial media.

[0035] In order to realize the anti-reflection film in space and time, we studied the reflection coefficient of the reflected wave scattered by the moving interface medium. By applying a one-dimensional space-time boundary condition:

[0036]

[0037] Among them, are the electric field, electric displacement, magnetic flux density, and magnetic field respectively, is the unit vector from medium j to medium i. In the one-dimensional case, it is assumed that the electric field and electric displacement are polarized along the y-axis, that is, while the magnetic flux density and magnetic field are polarized along the z-axis, that is, and If no spacetime metamaterial is added, the reflection coefficient of this structure is:

[0038]

[0039] Regardless of the modulation speed, the reflection coefficients of the reflected waves at the sub-light-speed and super-light-speed interfaces cannot be zero. However, in the presence of a spacetime metamaterial with a refractive index of n2, the reflection coefficient of this structure is:

[0040]

[0041] If the reflection coefficients in the media at the sub-light-speed interface and the super-light-speed interface are to be reduced to zero, the following conditions need to be met:

[0042]

[0043] Among them, n2 is the refractive index of the spacetime metamaterial, n1 is the refractive index of the incident medium, n3 is the refractive index of the transmitted medium, a is an odd number, Δx is the thickness of the nonlinear medium in the spatial domain, λ is the wavelength of the incident wave, and β is the normalized dynamic interface velocity.

[0044] Based on the above theory, the present invention discloses a spacetime antireflection film for being disposed between an incident medium and a transmitted medium, which includes:

[0045] A nonlinear medium, which generates a moving change in the refractive index under the oblique irradiation of a target light source to form a spacetime metamaterial with a dynamic interface, so as to reduce the reflection when an incident wave is incident from the incident medium to the transmitted medium. Further, after the incident wave is incident on the dynamic interface from the incident medium, it is transmitted to the transmitted medium. Among them, the incident angle of the target light source on the nonlinear medium is m, and m satisfies: 0 degree < m < 90 degrees.

[0046] In order to verify the effectiveness of the present invention, in a specific embodiment, a plane wave is used as the incident wave to examine the influence of the spacetime antireflection film on the magnetic field distribution. Here, the refractive indices of the three media in the present invention are respectively set to n1, n3, and The thickness of the spacetime antireflection film is set to a = 1, the sub-light-speed interface is set to β = 0.2, and the super-light-speed interface is set to β = 1.25. When no spacetime antireflection film is added, the reflected wave is clearly visible in the sub-light-speed system (super-light-speed system) (such as Figure 2(a), (d) and the top of (c), (f). When the designed space-time anti-reflection film is placed on a dynamic interface, Figure 2 The disappearance of the interference pattern in the middle (b), (e) and at the bottom of (c) and (f) shows that the reflected wave is completely eliminated. Figure 2 In the figure, (a) and (b) are the space-time field distributions when β = 0.2 without / with anti-reflection film; (c) is the field distribution at β = 0.2 and ct = 1 μm (as shown in Figure 2 (a) and (b) are black solid lines; (d) and (e) are the space-time field distributions without and with anti-reflection film when β = 1.25; (f) is the field distribution at β = 1.25 and x = 5μm (indicated by the black solid lines in (d) and (e)). The black dotted lines represent the dynamic interfaces between different media, and the grid area, gray area, and dot area correspond to media with refractive indices of n1, n2, and n3, respectively. The gray areas in (c) and (f) correspond to the space-time anti-reflection film.

[0047] Figure 3 It is shown that the proposed space-time anti-reflection film is also suitable for narrow-band pulses. The field distribution of Gaussian pulse excitation is calculated using the time-domain finite difference method. Among them, the space-time anti-reflection film is applied to the sub-light speed system ( Figure 3 (b)) or superluminal system ( Figure 3 In (d), the reflection is significantly suppressed. In contrast, without the use of a spatiotemporal anti-reflection film, the reflected wave in the sub-light speed system ( Figure 3 (a)) and superluminal system ( Figure 2 The interface in (c) can be clearly distinguished.

[0048] Figure 3 Figures (e)-(h) also prove that the scheme proposed by the present invention can also achieve efficient frequency and wave vector conversion. In the sub-light speed system with β = 0.2, the transmission frequency and wave vector become 1.33f inc and 2.67k inc (like Figure 3 In the superluminal system, the transmission frequency and wave vector become 0.17f respectively. inc and 0.33k inc (See Figure 3 (h)). Note here that the intensity of the converted signal is much higher than that of the incident signal, but it is very challenging to achieve such efficient frequency and wave vector conversion using conventional techniques. Figure 3In the figure, (a) and (b) are the space-time field distribution with and without anti-reflection film when β = 0.2; (c) and (d) are the space-time field distribution with and without anti-reflection film when β = 1.25; (e)-(h) are the intensity distribution of the field in the reciprocal domain (a)-(d), and the dotted line below is the dispersion curve of the corresponding situation. The circular, triangular and square points represent the intensity of the incident wave, reflected wave and transmitted wave, respectively.

[0049] In order to prove the feasibility of the space-time anti-reflection film of the present invention, the present invention realizes it in a nonlinear medium, indium tin oxide (ITO). In a nonlinear medium, due to the Kerr effect, under the irradiation of a pump beam of appropriate intensity, a shift change of the refractive index Δn (Δn=NI, where N is the refractive index coefficient of the nonlinear medium and I is the light intensity of the target light source) can be caused, thereby achieving a speed of v b = -c / cosθ interface motion. When the pump light is incident on the indium tin oxide (ITO) surface at a certain angle, the dynamic interface can achieve superluminal motion, that is, β = -1 / cosθ. Figure 4 As shown, the pump light has an incident angle of m = 90°-θ and an intensity of I pump,1 (t), I pump,2 (t) is incident on the indium tin oxide (ITO) plate (n1), achieving and superluminal dynamic interface. When the spatial thickness Δx of the space-time anti-reflection film (n2) is adjusted to an appropriate value, the reflection can be completely suppressed. Here, we set θ to 60°, then β = -2. Because the refractive index coefficient of the nonlinear material reaches ~10 -10 m 2 / W, the intensity of the pump light is ~10 9 W / m 2 , then n2=1.2497+0.01i, n3=1.5845+0.01i. Figure 5 As shown in (b), when the thickness of the anti-reflection film is adjusted to Figure 5 When the value of A in (a) is Δx = 3.1622 μm, the reflection is fully suppressed. The frequency and wave vector generated by the incident wave after passing through the structure are 0.0426f inc and 0.5871k inc In summary, while achieving space-time non-reflection by using a space-time anti-reflection film (indium tin oxide (ITO)), efficient frequency-wave-vector conversion can also be achieved.

[0050] Furthermore, the dynamic interface is a superluminal dynamic interface or a subluminal dynamic interface. When the pump light is directly incident on the indium tin oxide (ITO) surface at a certain angle, the dynamic interface can achieve superluminal motion. When it is necessary to reduce the speed of the dynamic interface to achieve a subluminal dynamic interface, a deceleration medium can be set on the nonlinear medium, and the target light source is irradiated from the deceleration medium to the nonlinear medium to reduce the speed of the dynamic interface.

[0051] Among them, Figure 4 Indium tin oxide (ITO) is the main material with a strength of I pump,1 (t), I pump,2 The pump beam (t) irradiates ITO at an oblique incidence of 90°-θ to generate new refractive indices n2 and n3, respectively, where The spatial thickness of the spatiotemporal antireflection film is Δx. The incident wave, reflected wave and transmitted wave are represented by Ψ inc ,Ψ - ,Ψ + mark.

[0052] Among them, Figure 5 In (a), the relationship between the reflection coefficient and the spatial thickness is shown. The inset shows the schematic diagram of the experimental setup. Two pump lights are incident from free space on the ITO at an angle of 90°-θ. The two beams correspond to intensities I pump,1 and I pump,2 The position of point A corresponds to |R| = 0; (b) is the spatiotemporal field distribution of narrowband pulse excitation. The inset shows the simplified diagram of the time-varying dielectric constant and intensity distribution of the pump light at a fixed position x0. The pump light has θ = 60° and the incident wavelength is 1 μm.

[0053] The space-time anti-reflection film of the present invention causes the nonlinear medium to produce a shift change in the refractive index through the oblique illumination of the target light source, thereby forming a space-time metamaterial with a dynamic interface to reduce the reflection of the incident wave when it enters the transmission medium from the incident medium. The present invention extends the non-reflection from pure space and pure time to the space-time domain, and uses space-time to break the translational symmetry of space and time to achieve the regulation of the frequency wave vector.

[0054] An embodiment of the present invention also provides an anti-reflection system, which includes the space-time anti-reflection film described in the above embodiment and the target light source; the nonlinear medium produces a movement change in refractive index under the oblique illumination of the target light source and realizes a dynamic interface to reduce the reflection of the incident wave when it is incident from the incident medium to the transmission medium.

[0055] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A space-time anti-reflection film, used to be arranged between an incident medium and a transmission medium, characterized in that: Comprising: A nonlinear medium which generates a moving change in refractive index under the oblique illumination of a target light source to form a spatio-temporal metamaterial with a dynamic interface, so as to reduce the reflection when an incident wave enters from an incident medium into the transmission medium; After the incident wave enters the spatio-temporal metamaterial from the incident medium, it is transmitted to the transmission medium; When the incident wave enters the spatio-temporal metamaterial from the incident medium and is transmitted to the transmission medium, the spatio-temporal metamaterial satisfies the following conditions: Wherein, n2 is the refractive index of the spatio-temporal metamaterial, n1 is the refractive index of the incident medium, n3 is the refractive index of the transmission medium, a is an odd number, Δx is the thickness of the nonlinear medium in the spatial domain, λ is the wavelength of the incident wave, and β is the normalized dynamic interface velocity; The nonlinear medium generates a moving change in refractive index Δn under the oblique illumination of the target light source, satisfying: Δn = NI Wherein, N is the refractive index coefficient of the nonlinear medium, and I is the light intensity of the target light source.

2. The space-time anti-reflection film according to claim 1, characterized in that: The incident angle of the target light source on the nonlinear medium is m, and m satisfies: 0° < m < 90°.

3. The spatiotemporal anti-reflection film according to claim 1, characterized in that: The dynamic interface is a superluminal dynamic interface or a subluminal dynamic interface.

4. The temporal-spatial anti-reflection film according to claim 1, characterized in that: The target light source is a pump light source.

5. The temporal-spatial anti-reflection film according to claim 1, characterized in that: The nonlinear medium is indium tin oxide.

6. The temporal-spatial anti-reflection film according to claim 1, characterized in that: A deceleration medium is arranged on the nonlinear medium, and the target light source irradiates the nonlinear medium through the deceleration medium to reduce the speed of the dynamic interface.

7. An anti-reflection system, characterized in that: Comprising the spatio-temporal antireflection film according to any one of claims 1-6 and the target light source; the nonlinear medium generates a moving change in refractive index under the oblique illumination of the target light source to form a spatio-temporal metamaterial with a dynamic interface, so as to reduce the reflection when an incident wave enters from an incident medium into the transmission medium.

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