KR102826138B1 - Fabry-Perot wide angle resonator - Google Patents

Abstract

A Fabry-Perot wide-angle resonator according to one aspect of the present invention comprises a first reflective surface and a second reflective surface, further comprising: at least one negative refractive layer exhibiting negative refractive index between the first reflective surface and the second reflective surface; and at least one positive refractive layer exhibiting positive refractive index between the first reflective surface and the second reflective surface; and is characterized in that it resonates over a wide incident angle range in a predetermined wavelength region.

Description

Fabry-Perot wide angle resonator

The present invention relates to a Fabry-Perot wide-angle resonator, and more particularly, to a Fabry-Perot wide-angle resonator having nearly the same resonant frequency for a wide incident or emission angle.

The Fabry-Perot resonance wavelength is the wavelength at which constructive interference occurs when two mirrors are placed facing each other at a certain distance and light is repeatedly reflected between the two mirrors, so that the length of the round-trip path of the light is an integer multiple of the wavelength of the light.

At this time, the two mirrors can each have a phase delay, and the phase delay of the light repeatedly reflected in three-dimensional space can have a phase delay in the direction parallel to the mirrors (longitudinal resonance mode), and can also have a phase delay for two directions perpendicular to the direction parallel to the mirrors (transverse resonance mode). Typically, since the different vertical resonance modes of the Fabry-Perot resonator have different resonance wavelengths, physical phenomena such as the improvement of absorption efficiency due to resonance or the improvement of spontaneous emission efficiency appear at different wavelengths.

For example, in a mode where the intensity in the vertical direction is constant but the phase is delayed proportionally with distance, in the case of an absorptive element, the light can be excited with an inclined incident light with respect to the normal direction of the mirror from outside the resonator, and in the case of a light-emitting element, the inclined emission light can be excited. In this case, since the resonance wavelength is different depending on the inclined angle, there is a problem that the performance of the element is degraded.

For example, in OLED-based display devices, there is a problem that when the viewing angle increases, the light intensity decreases or the color of the light appears different. A Fabry-Perot wide-angle resonator that has almost the same resonance wavelength regardless of the incident or emission angle and regardless of the vertical resonance mode is required.

The present invention aims to solve the above-mentioned problem by providing a Fabry-Perot wide-angle resonator that operates regardless of the angle of incidence.

The purpose of the present invention is not limited to the purposes mentioned above, and other purposes not mentioned will be clearly understood by those skilled in the art from the description below.

According to one aspect of the present invention for achieving the above-mentioned object, a Fabry-Perot wide-angle resonator comprises a first reflective surface and a second reflective surface, further comprising: at least one negative refractive layer exhibiting negative refractive index between the first reflective surface and the second reflective surface; and at least one positive refractive layer exhibiting positive refractive index between the first reflective surface and the second reflective surface; and is characterized in that it resonates in a wide incident angle range in a predetermined wavelength region.

According to the present invention, a Fabry-Perot wide-angle resonator in which a plurality of perpendicular modes in a specific parallel directional mode have almost the same resonant frequency has little change in resonant frequency depending on the incident angle or the emission angle, and therefore can be usefully used in solar cells, light-emitting diode (LED) displays, organic light-emitting diode (OLED) displays, lasers, and the like, and can also be used for electromagnetic waves other than visible light such as microwaves as well as sound waves.

Figure 1 is a structural diagram of a Fabry-Perot wide-angle resonator according to the present invention.
FIG. 2 is an exemplary diagram showing a photonic crystal structure for explaining a method of forming a negative refractive layer using a photonic crystal according to a partial embodiment of the present invention.
FIG. 3 is an exemplary diagram illustrating a metamaterial having an indefinite effective permittivity tensor according to a partial embodiment of the present invention.
FIG. 4 is an exemplary diagram illustrating a metasurface exhibiting negative refractive index according to a partial embodiment of the present invention.

The advantages and features of the present invention, and the methods for achieving them, will become clear with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments are provided to make the disclosure of the present invention complete, and to fully inform a person having ordinary skill in the art to which the present invention belongs of the scope of the invention, and the present invention is defined only by the scope of the claims. Meanwhile, the terminology used in this specification is for the purpose of describing the embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated in the phrase. The terms "comprises" and/or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations, and/or elements mentioned.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

The Fabry-Perot resonance wavelength is the wavelength at which constructive interference occurs when two mirrors are placed facing each other at a certain distance and light is repeatedly reflected between the two mirrors, so that the length of the round-trip path of the light is an integer multiple of the wavelength of the light.

The Fabry-Perot resonance condition can be described using the following equation.

When a medium having a refractive index other than vacuum is included inside the resonator, the wavelength inside the medium is different from the wavelength in vacuum due to the refractive index of the medium, so the above mathematical formula is written using wave numbers rather than wavelengths, and the resonance condition is when m is an integer.

If one or both of the two mirrors used in a Fabry-Perot resonator have a reflectivity of less than 100% and a transmittance of greater than 0%, light reaching the resonator from the outside may be absorbed into the resonator (a light-absorbing element such as a solar cell), or light generated inside the resonator may be emitted to the outside (a light-emitting element such as an LED).

When the wavelength of light incident on the inside of the resonator is similar to the resonant wavelength, the absorption element absorbs more light through the resonance phenomenon, thereby increasing the absorption efficiency.

When the emission wavelength of the light-emitting element matches the resonant wavelength of the resonator, the spontaneous emission rate increases due to the Purcell effect, which can increase the light emission efficiency. When the amount of light supplied from the light-emitting element is sufficient compared to the amount absorbed or emitted outside the resonator, a laser can be implemented by the stimulated emission phenomenon.

Instead of using two mirrors as described above, the Fabry-Perot resonator can use the boundary of two media instead of mirrors, or can use a grating structure or a photonic crystal structure. That is, the mirror can be viewed as a boundary with a reflectivity greater than 0% and less than 100%.

In particular, if one reflective surface (mirror) is a phase retardation reflector whose phase is changed by 180 degrees, and the other reflective surface (mirror) is a mirror whose phase is not changed, constructive interference occurs when the round trip distance is wavelength x (integer + 0.5). In general terms, if the phase retardations of each reflective surface are Φ ₁ and Φ ₂ , the following equation applies.

The Fabry-Perot wide-angle resonator according to the present invention can have nearly identical resonance wavelengths for multiple vertical resonance modes.

The Fabry-Perot wide-angle resonator according to the present invention implements a wide-angle resonator using a normal medium and a medium exhibiting negative refractive index. In this case, the ‘medium having a negative refractive index’ and the ‘medium exhibiting negative refractive index’ are different concepts.

A Fabry-Perot wide-angle resonator according to the present invention includes a positive refractive layer and a negative refractive layer. According to the present invention, it has almost the same resonance wavelength for a plurality of vertical resonance modes. In other words, it has almost the same resonance wavelength for a wide range of incident or emission angles. The phase retardation in a normal medium exhibiting positive refractive index and the phase retardation in a medium exhibiting negative refractive index should have opposite signs, and considering that partial reflection may occur due to the impedance difference at the boundary between the medium exhibiting positive refractive index and the medium exhibiting negative refractive index, the entire round-trip phase retardation should be designed so that the resonance condition is satisfied at the same wavelength.

Figure 1 shows a structural diagram of a Fabry-Perot wide-angle resonator according to the present invention.

A Fabry-Perot wide-angle resonator according to the present invention comprises a first reflective surface, a second reflective surface, a negative refractive layer and a positive refractive layer.

The above first and second reflective surfaces may be any one of ① a mirror made of a conductive metallic material, ② a mirror made of a grating structure or a photonic crystal structure, and ③ a mirror that uses the boundary of two media with different impedances as a reflective surface.

The negative refractive layer and the positive refractive layer exist between the first reflective surface and the second reflective surface, and the first reflective surface can be formed by a first medium adjacent to the negative refractive layer, and the second reflective surface can be formed by a second medium adjacent to the positive refractive layer.

There may be two or more layers present between the first reflective surface and the second reflective surface.

FIG. 1(b) shows a Fabry-Perot wide-angle resonator laminated in the order of a second reflective surface, a negative refractive layer, a positive refractive layer, a negative refractive layer, and a first reflective surface, FIG. 1(c) shows a Fabry-Perot wide-angle resonator laminated in the order of a second reflective surface, a positive refractive layer, a negative refractive layer, a positive refractive layer, and a first reflective surface, and FIG. 1(d) shows a Fabry-Perot wide-angle resonator laminated in the order of a second reflective surface, a positive refractive layer, a negative refractive layer, a positive refractive layer, a negative refractive layer, and a first reflective surface. The above-described stacking order and the number of stacked layers are exemplary and do not limit the scope of the invention.

In addition, the positive refractive layer and the negative refractive layer may each have a multi-layered structure. For example, the positive refractive layer and the negative refractive layer may have a structure in which different semiconductor materials having different band gaps are laminated. In particular, the negative refractive layer (a layer exhibiting negative refractive index) may be formed using a photonic crystal structure, a three-dimensional metamaterial, and a metasurface.

FIG. 2 shows the reciprocal lattice space of a photonic crystal structure for explaining a method of forming a negative refractive layer using a photonic crystal according to a partial embodiment of the present invention.

A photonic crystal is a composite structural medium in which a three-dimensional structure is formed by repeating at a period of half the wavelength of the target wavelength, and which exhibits unique optical properties due to destructive interference and constructive interference of light scattered from each unit structure. The negative refraction phenomenon occurs in this photonic crystal structure. There is a negative refraction phenomenon that appears near a specific band edge and a negative refraction phenomenon that appears near the band center (gamma point) in the upper band.

Figure 2 illustrates the Brillouin zone in the reciprocal lattice space of the lattice structure. At the point farthest from the central gamma point, for example, near R in a cubic crystal in Figure 2(a), near H in a body-centered cubic crystal, or near X in a face-centered cubic crystal, the modes of the first and second bands exhibit negative refraction, which is called the negative refraction phenomenon near the band edge.

In the first band and the second band, which are the lower bands described above, the negative refraction phenomenon appears near the point farthest from the gamma point, but in the upper band (e.g., the third band), the negative refraction phenomenon can appear near the gamma point. In the cubic crystal, the body-centered cubic crystal, and the face-centered cubic crystal illustrated in Fig. 2, the negative refraction phenomenon appears near the gamma point of the third band.

When a three-dimensional structure is repeated periodically or aperiodically at intervals smaller than half a wavelength of a specific wavelength, and each unit structure has a resonance phenomenon at a specific wavelength, the composite medium that exhibits unique optical properties near the resonance wavelength or at other wavelengths is called a metamaterial, and a negative refractive layer can be formed using a metamaterial.

Specifically, a negative refractive layer can be formed using a negative sign metamaterial in which the sign of the permittivity or permeability changes depending on the direction of the electromagnetic field, and a negative refractive layer can be formed using a double negative metamaterial in which both the permittivity and permeability have negative values.

FIG. 3 is an exemplary diagram illustrating a metamaterial having an indefinite effective permittivity tensor according to a partial embodiment of the present invention.

The effective dielectric of a metamaterial is generally a two-dimensional tensor. When this is expressed as a matrix, if the matrix becomes a negated matrix, it is called a negated metamaterial.

The wire (Fig. 3(a)), thin film (Fig. 3(b)), and elliptical solid of revolution (Fig. 3(c)) portions illustrated in Fig. 3 are conductive portions whose real part of permittivity is negative, and the surrounding area means a dielectric portion whose real part of permittivity is positive. When the absolute value of the real part of the permittivity of the conductive material is much larger than the absolute value of the real part of the permittivity of the dielectric material, the conductive wire shape of Fig. 3(a) can have an effective permittivity that is negative for an electric field in a direction parallel to the wire, and an effective permittivity that is positive for an electric field in a plane perpendicular to the wire. When the wires are arranged perpendicular to a mirror surface, a negative refraction phenomenon occurs.

When the absolute value of the real part of the permittivity of the conductive material is not significantly larger than the absolute value of the real part of the permittivity of the dielectric material, the effective permittivity may differ in the direction depending on the volume ratio of the conductive material and the dielectric material and the shape of the conductive material. In particular, the effective permittivity may be positive for an electric field parallel to the wire, and negative for an electric field in a plane perpendicular to the wire. As described above, when the absolute value of the real part of the permittivity of the conductive material is small, a thin film (Fig. 3(b)) laminated structure parallel to the reflective surface can be used instead of the wire to cause the negative refractive phenomenon in the desired direction.

FIG. 3(c) shows an elliptical body of revolution arranged in a direction perpendicular to a reflective surface instead of a wire and a thin film, but this may be an elliptical column, a square column, or a hexagonal column, and does not limit the scope of the invention.

In the structure of Fig. 3(c), since the real part of the permittivity may be negative at a wavelength shorter than the resonant wavelength in the vertical direction of the reflective surface depending on the length of the conductor, a negative refraction phenomenon may occur.

By using a metamaterial with a mesh structure, it is possible to create a medium in which the real part of the effective permeability is negative in the visible light range and the real part of the effective permittivity is also negative. In this way, a negative refraction phenomenon can be exhibited by using a double negative metamaterial in which the real parts of both the permeability and the permittivity are negative. The above double negative material can also be implemented using a structure other than the above mesh structure.

A metasurface is a composite surface in which a structure having a height smaller than a specific wavelength is repeated periodically or non-periodically on a plane at an interval smaller than half a wavelength of the specific wavelength, and a resonance phenomenon occurs due to the shape and repeating period of the structure, and unique optical properties are exhibited around the resonance wavelength or at other wavelengths. The negative refraction phenomenon can be implemented using a metasurface.

Since the metasurface has a surface structure with a height smaller than the wavelength, it is difficult to see the path of light due to its thin thickness, and it may be difficult to easily observe the usual 'refractive index', so the negative refraction in the metasurface is strictly defined as described below.

Consider the situation where an incident wave that reaches the metasurface in the direction of the incident angle θ (0≤?<90°) from the surface normal direction passes through the surface and becomes a transmitted wave. In the case of a metasurface in which unit structures smaller than half a wavelength are uniformly arranged, if the incident wave is a uniform plane wave, the transmitted wave also becomes a uniform plane wave.

FIG. 4 is an exemplary diagram illustrating a metasurface exhibiting negative refractive index according to a partial embodiment of the present invention.

Among the points on the metasurface, there is a point A located on the incident wave side and a point B located perpendicular to the surface and separated from the point A by the thickness of the metasurface. The value obtained by subtracting the phase of the incident wave at point A from the phase of the transmitted wave at point B is called the “phase lag on the metasurface.” If the phase lag decreases as the incident angle increases, it is called a positive refractive metasurface, and if the phase lag increases as the incident angle increases, it is called a negative refractive metasurface.

The resonance conditions of a Fabry-Perot wide-angle resonator in which N layers including at least one negative refractive layer and one positive refractive layer are inserted into the first reflective surface and the second reflective surface are as follows.

means the wavenumber in the p layer, represents the height of the p layer. N is the total number of layers.

As described above, the wavenumber depends on the angle of incidence θ. changes, and this is determined by the optical properties of the negative or positive refractive layer, so it depends on the angle of incidence. Wow height By controlling it layer by layer, regardless of the angle of incidence θ, Fabry-Perot wide-angle resonators can be designed so that the values are constant.

The Fabry-Perot wide-angle resonator according to the present invention has reflections at the boundaries of each layer and according to the angle of incidence θ. Since the values of can appear in various ways, the structure selection and thickness selection of the negative or positive refractive layer cannot be simply obtained, and an appropriate structure can be selected by the transfer matrix method or the finite difference time-domain method.

Above, the configuration of the present invention has been described in detail with reference to the attached drawings, but this is only an example, and it is obvious that those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and changes within the scope of the technical idea of the present invention. Therefore, the protection scope of the present invention should not be limited to the above-described embodiments, but should be determined by the description of the following patent claims.

Claims (8)

In a Fabry-Perot wide-angle resonator comprising a first reflective surface and a second reflective surface,
One or more negative refractive layers exhibiting negative refractive index between the first reflective surface and the second reflective surface; and
At least one bi-refractive layer exhibiting positive refraction between the first reflective surface and the second reflective surface;
Including
A Fabry-Perot wide-angle resonator that resonates over a wide range of incidence angles in a given wavelength range.
The above-mentioned negative refractive layer is formed using at least one selected from a photonic crystal structure, a three-dimensional metamaterial, and a meta surface.
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above first and second reflective surfaces are,
A reflective surface made of a grating structure or a photonic crystal structure
Fabry-Perot wide-angle resonator.
In the first paragraph,
A first reflective layer present on the first reflective surface; and
A second reflective layer present beneath the second reflective surface;
Including more,
The above first reflective layer is,
Having a different impedance from the layer existing directly below the first reflective surface,
The above second reflective layer is,
It has a different impedance from the layer existing directly above the second reflective surface,
The above first reflective surface is,
The boundary surface between the first reflective layer and the layer existing directly below the first reflective surface,
The above second reflective surface is,
The boundary surface between the second reflective layer and the layer existing directly above the second reflective surface
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above negative refractive layer is,
It is composed of a three-dimensional photonic crystal structure,
The above photonic crystal structure is,
The unit structure is a crystal formed by repeating a cycle at the level of a half wavelength of a specific wavelength,
The above unit structure is,
Containing at least one of a cubic crystal structure, a body-centered cubic crystal structure, and a face-centered cubic crystal structure
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above negative refractive layer is,
A three-dimensional metamaterial in which a wire made of a conductive material arranged in a direction perpendicular to the second reflective surface and a portion of the negative refractive layer excluding the wire is filled with a dielectric having a positive real part of the permittivity,
The real part of the permittivity of the above conductive material is negative,
characterized in that the absolute value of the real part of the conductive material is greater than the absolute value of the real part of the permittivity of the dielectric.
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above negative refractive layer is,
A three-dimensional metamaterial comprising a thin film made of a conductive material arranged in a direction parallel to a second reflective surface, and a negative refractive layer portion excluding the thin film filled with a dielectric having a positive real part of permittivity,
The real part of the permittivity of the above conductive material is negative,
characterized in that the absolute value of the real part of the conductive material is smaller than the absolute value of the real part of the permittivity of the dielectric.
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above negative refractive layer is,
A three-dimensional metamaterial comprising a plurality of wires made of a conductive material arranged in a direction perpendicular to the second reflective surface, and a portion of the negative refractive layer excluding the wires filled with a dielectric having a positive real part of the permittivity,
The real part of the permittivity of the above conductive material is negative,
The above wire,
Within the above-mentioned negative refractive layer, two or more are arranged in a straight line in a direction perpendicular to the second reflective surface, and their lengths are shorter than the resonant wavelength.
characterized in that the absolute value of the real part of the conductive material is greater than the absolute value of the real part of the permittivity of the dielectric.
Fabry-Perot wide-angle resonator.
In the first paragraph,
The above negative refractive layer is one,
The above refractive layer is one,
Calculate the product of wavenumber and height for the angle of incidence θ at each layer.
It is characterized by determining the height of each layer so that the sum of the products produced is constant.
Fabry-Perot wide-angle resonator.