CN111596390A - Plane grating with light splitting and focusing capabilities - Google Patents

Abstract

The invention discloses a plane grating with light splitting and focusing capabilities, which is provided with a vertical incident structure for parallel light, light of different wavelengths will be focused at different positions, and includes a plurality of substructures, each substructure includes a microstructure and supports the microstructure. The base of the structure, the bases of all the substructures together constitute the base of the overall structure, and all the substructures together constitute the overall grating structure; the phase corresponding to the center of each substructure in the grating array can be determined by the design wavelength, design focal length, focus The offset angle and the position corresponding to the center of the substructure are determined. The corresponding phase at the center of each substructure determines the size parameter of the substructure. The grating can make incident light of different wavelengths pass through the grating and converge at different focal points. , so as to realize the functions of light splitting and focusing.

Description

A plane grating with beam splitting and focusing capabilities

technical field

The invention relates to a plane grating with both light splitting and focusing capabilities. As a light splitting device, it can be used in a monochromator and a spectrometer, and belongs to the fields of geometric optics and micro-nano optics.

Background technique

The traditional grating is a flat glass or metal sheet engraved with a large number of parallel equal-width and equal-distance slits (scribed lines), which only have the function of dispersive light splitting. When used in a spectrometer, an additional focusing lens is required, which is not conducive to the simplification of the optical path. . The concave grating is a reflective grating composed of a series of parallel scribed lines on the concave surface of a highly reflective metal. It has light splitting and focusing capabilities, but has serious astigmatism problems, low diffraction efficiency, and difficult mechanical scribing, so it has not been widely used. .

A metasurface is an ultrathin two-dimensional surface composed of a series of subwavelength structures, which can effectively control the amplitude, phase, and polarization state of the incident beam. Diffraction grating makes the phase of incident light subject to periodic spatial modulation through a regular structure. When polychromatic light passes through the grating, spectral lines of different wavelengths appear at different positions to form a spectrum. Therefore, the grating can also be regarded as a metasurface. element. Due to the small size and high integration of metasurfaces, optical components designed using metasurfaces have received extensive attention.

SUMMARY OF THE INVENTION

1. Purpose of the present invention

The purpose of the present invention is to provide a plane grating with both beam splitting and focusing capabilities, so as to simplify the optical path.

2. The technical solution adopted in the present invention

The invention discloses a plane grating with light splitting and focusing capabilities, which is provided with a vertical incident structure for parallel light, and light of different wavelengths can be focused at different positions; it includes a plurality of substructures, each substructure includes a microstructure and supports the microstructure. The base of the structure, the width of the substructure is T, the microstructure is a cuboid, the width of the microstructure is L, the height is H, the bases of all the substructures together form the base of the overall structure, and all the substructures together constitute the whole grating structure;

By adjusting the size parameters of each substructure (such as duty cycle, width T), the phase of the outgoing light can be changed differently;

According to the focusing requirements, the phase distribution of the grating surface is determined by the following formula, so as to determine the size parameters of each substructure;

Where, with the grating surface as the origin at the center, φ _(x) is the phase at the coordinate point (x), λ is the designed wavelength of incident light, f is the distance from the focus to the center of the grating, α is the angle at which the focus deviates from the axis, m For any integer, the parameters of each cuboid microstructure unit are determined by setting the phase φ _(x) of each different position on the grating surface; by changing the size parameter of each substructure, the phase distribution of the entire grating is adjusted, so as to realize the grating’s phase distribution. Focus function.

Furthermore, the substructure width T ranges from 300 nm to 1000 nm, and different phases can be obtained by adjusting the width or duty ratio of the substructure.

In order to improve the phase modulation capability and transmittance of the microstructure, the cuboid composition material of the microstructure is silicon or titanium dioxide.

Furthermore, the cuboid width L of the microstructure ranges from 30 nm to 800 nm, the height H is 1000-5000 nm, and the duty ratio of the substructure is defined as L/T. Different phases can also be obtained by adjusting the duty ratio of the substructure.

Furthermore, the applicable spectral range of the grating is the infrared band and the visible light band.

In order to improve the transmittance of the grating, the constituent material of the substrate is silicon dioxide.

Furthermore, when the height of the microstructure is H=1500nm, and the duty cycle of the substructure varies between 0.1 and 0.7, the phase coverage of 2π is achieved.

Furthermore, the boundary condition of the microstructure in the X direction is set as the periodic boundary condition, and the boundary condition in the propagation direction of the incident light, that is, the Y direction, is set as the PML boundary condition, and the transmittance and phase change of the incident light are obtained, respectively. The relationship of structure size (such as duty cycle, width).

Furthermore, gratings are not polarization sensitive, ie for incident light of any polarization direction, the position of the focal point is the same.

3. Beneficial effects adopted by the present invention

(1) The grating provided by the present invention is composed of a substrate and cuboid microstructures arranged on the substrate. By adjusting the size parameters of the substructures, a phase modulation of 0 to 2π can be achieved for incident light.

(2) By setting reasonable parameters of wavelength, focal length and angle in the present invention, a plane grating with light splitting and focusing ability can be realized.

(3) Planar gratings with both spectroscopic and focusing capabilities have potential applications in the miniaturization and integrated design of spectrometers, monochromators and other instruments, and have very important research significance.

Description of drawings

FIG. 1 is a schematic diagram of an overall grating structure according to an exemplary embodiment of the present invention;

FIG. 2 is a front view of an integral grating and a front view of a single substructure structure according to an exemplary embodiment of the present invention;

FIG. 3 is a front view of the overall structure of a grating according to an exemplary embodiment of the present invention;

Fig. 4 is the schematic diagram of the incident light splitting and focusing after passing through the grating under different wavelengths;

Figure 5 is a schematic diagram showing the relationship between the transmittance and phase change of the outgoing light and the duty ratio (L/T) and height (H) under the condition that the wavelength of the incident light is 1500 nm;

Figure 6 is a schematic diagram of the phase response of the complete grating distribution to linearly polarized light with TE polarization (left) and TM polarization (right);

Figure 7 is a field intensity distribution diagram of TE polarized linearly polarized light of different wavelengths incident along the Y-axis, and the dotted line is the determined focal plane position;

Fig. 8 is a field intensity distribution diagram of TM-polarized linearly polarized light of different wavelengths incident along the Y-axis, and the dotted line is the determined focal plane position;

Figure 9 is the field intensity distribution of light of different wavelengths on the focal plane, the abscissa represents the position on the focal plane, the ordinate represents the magnitude of the electric field intensity, and each line represents a different wavelength;

Figure 10 shows the field intensity distribution of light of different wavelengths on the focal plane, the abscissa represents the wavelength, the ordinate represents the position on the focal plane, and the color scale represents the magnitude of the electric field intensity;

Figure 11 shows the relationship between the transmittance and phase change of the outgoing light and the width T of the substructure under the condition that the wavelength of the incident light is 532 nm;

FIG. 12 is a field intensity distribution diagram of TE-polarized linearly polarized light with different wavelengths incident along the Y-axis, and the dotted line is the determined focal plane position.

Detailed ways

The technical solutions in the examples of the present invention will be clearly and completely described below with reference to the drawings in the examples of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.

The examples of the present invention will be described in further detail below with reference to the accompanying drawings.

Example 1

Please refer to FIG. 1, a plane grating with both light splitting and focusing capabilities, comprising a plurality of substructures, each substructure includes a microstructure 1 and a part of the substrate supporting the microstructure, and the part of the substrate of each substructure together constitutes the substrate of the grating 2. The microstructures of all substructures constitute a grating array. The grating can make incident light with different wavelengths pass through the grating and then converge on different focal points, thereby realizing the functions of light splitting and focusing. In the present invention, each cuboid microstructure unit in the grating is equivalent to a phase shifter. After the incident light passes through the phase shifter, an additional phase difference is added. The size of the additional phase difference is related to the parameters of the structure. The design parameters of 0 to 2π can achieve a phase shift of 0 to 2π and obtain a higher transmittance.

As shown in FIG. 2 , any microstructure and a part of the substrate supporting it can be referred to as substructures of a grating, and each substructure is arranged to form a grating. The length of the substructure in the X direction is T, the height of the microstructure is H, the width is L, and the duty cycle of the substructure is defined as L/T.

According to the actual focusing requirements, the phase distribution of the grating surface can be determined by the following formula, and then the size parameters of each substructure can be determined according to the simulated data (the relationship between the substructure size parameters and the phase, Figure 5).

Where, with the grating surface as the origin at the center, φ _(x) is the phase at the coordinate point (x), λ is the designed wavelength of incident light, f is the distance from the focus to the center of the grating, α is the angle at which the focus deviates from the axis, m is any integer, as shown in Figure 3. The size parameters (L, T, H) of each sub-structural unit are determined by determining the phase φ _(x) of each different position on the grating surface.

In order to improve the transmittance of the grating, the base material is preferably silicon dioxide. In order to improve the phase modulation capability and transmittance of the microstructure, the microstructure material is preferably silicon or titanium dioxide. In order to ensure the high transmittance of the grating and realize the phase control of 0-2π, the finite difference time domain (FDTD) method can be used to simulate and numerically analyze the substructure of the grating.

The cuboid microstructure material is set to silicon with a refractive index of 3.48, the substrate is set to silicon dioxide with a refractive index of 1.45 and a thickness of 1000 nm, the length (T) of the substructure is fixed at 300 nm, and the incident light wavelength is 1500 nm, The boundary conditions of the microstructure in the X direction are set as periodic boundary conditions, and the boundary conditions in the propagation direction (Y direction) of the incident light are set as PML boundary conditions. The incident light mentioned here is TE polarized linearly polarized light. (See Figure 4 for the definition of polarized light). After simulation, the relationship between the transmittance of incident light and the duty ratio (L/T) and height (H) is obtained, as shown in Figure 5.

In addition, the relationship between the phase change of the incident light (the phase when the duty ratio (L/T) is 0.1 is taken as 0, the unit is rad) and the duty ratio (L/T) and high (H) are obtained.

It can be seen from Figure 5 that when the height of the microstructure is H=1500nm, and the duty cycle of the substructure varies between 0.1 and 0.7, the phase coverage of 2π can be better achieved, and its transmittance to incident light is generally higher. high.

Based on the above simulation results and numerical analysis, a complete grating can be designed. The focal length f of the grating can be set to 30 mm, the angle is set to 15 degrees, and the design wavelength is set to 1500 nm. Figure 6 shows the phase response of the complete grating distribution to linearly polarized light with TE polarization (left) and TM polarization (right).

The effect of incident light passing through the grating can be obtained through simulation. Figure 7 shows the field intensity distribution of TE-polarized linearly polarized light with different wavelengths incident along the Y-axis, and the dotted line is the determined focal plane position. FIG. 8 is a field intensity distribution diagram of TM-polarized linearly polarized light with different wavelengths incident along the Y-axis, and the dotted line is the determined focal plane position.

It can be seen from Figure 7 and Figure 8 that after passing through the grating, light of different wavelengths is focused at different positions respectively, realizing the functions of light splitting and focusing.

Figures 9 and 10 show the field intensity distribution of incident light of different wavelengths along the focal line direction. Each line in Figure 9 represents incident light of different wavelengths, and it can be seen that there is an obvious spectroscopic effect.

Example 2

The difference between the design scheme of the plane grating with light splitting and focusing capabilities in this embodiment is that the material of the microstructure is titanium dioxide, the applicable spectral range of the grating is the visible light band, and the phase change generated by the substructure is generated by Produced by adjusting the width (T) of the substructure.

In this example, the cuboid microstructure material is set to titanium dioxide with a refractive index of 2.5, the substrate is set to silicon dioxide with a refractive index of 1.45 and a thickness of 1000 nm, the width L of the substructure is fixed to 50 nm, and the height H is set to 50 nm. is 3000nm, the wavelength of the incident light is 532nm, the boundary conditions of the microstructure in the X direction are set as periodic boundary conditions, and the boundary conditions in the propagation direction of the incident light (Y direction) are set as the PML boundary conditions, mentioned here The incident light is linearly polarized light with TE polarization (see Figure 4 for the definition of polarized light). After simulation, the relationship between the transmittance and phase change of the outgoing light (the phase when the lateral dimension (T) of the structure is 300 nm is defined as 0, the unit is rad) and the width of the substructure (T) are obtained, as shown in Figure 11.

Based on the above simulation results and numerical analysis, a complete grating can be designed. The focal length f of the grating can be set to 30 mm, the angle is set to 5 degrees, and the design wavelength is set to 532 nm.

The effect of the incident light after passing through the above grating can be obtained by simulation. Figure 12 shows the field intensity distribution of TE polarized linearly polarized light with different wavelengths incident along the Y-axis. The dotted line is the determined focal plane position. It can be seen that the designed The wavelength also has a good effect in the visible light band, realizing the splitting and focusing of the incident light.

The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of changes or Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (9)

1. A planar grating having beam splitting and focusing capabilities, comprising: a parallel light vertical incidence structure is arranged, and light with different wavelengths is focused at different positions; the grating structure comprises a plurality of substructures, wherein each substructure comprises a microstructure and a substrate for supporting the microstructure, the width of the substructure is T, the microstructure is a cuboid, the width of the microstructure is L, the height of the microstructure is H, the substrates of all the substructures form the substrate of the integral structure together, and all the substructures form the integral grating structure together;

determining the phase distribution of the grating surface according to the focusing requirement by the following formula, thereby determining the size parameter of each substructure;

wherein, the surface of the grating is used as the origin with the center as phi_(x)Is the phase at the coordinate point (x), λ is the designed incident light wavelength, f is the distance from the focal point to the center of the grating, α is the angle of the focal point from the axis, m is any integer, and the phase phi of each different position on the grating surface is obtained by reasonable setting parameters_(x)Thereby determining each of the sub-structural unit dimension parameters.

2. The planar grating structure of claim 1, wherein the sub-structure width T ranges from 300nm to 1000nm, and different phases can be obtained by adjusting the width or duty cycle of the sub-structure.

3. The planar grating structure of claim 1, wherein: the microstructure is silicon or titanium dioxide.

4. The planar grating structure of claim 1, wherein: the width L of the cuboid of the microstructure is 30nm to 800nm, and the height H is 1000-5000 nm.

5. The planar grating structure of claim 1, wherein: the applicable spectral range is visible light wave band and infrared wave band.

6. The planar grating structure of claim 1 wherein the substrate component material is silicon dioxide.

7. The planar grating structure of claim 1, wherein: the microstructure height H is 1500nm and the duty cycle of the substructure varies between 0.1 and 0.7, achieving a phase coverage of 2 pi.

8. The planar grating structure of claim 1, wherein the boundary condition of the microstructure in the X direction is set as a periodic boundary condition, and the boundary condition in the propagation direction of the incident light, i.e., the Y direction, is set as a PML boundary condition, whereby the relationship between the transmittance of the outgoing light, the phase change, and the size of the substructure, respectively, is obtained.

9. The planar grating structure of claim 1, wherein: the position of the focal point is the same for incident light of any polarization direction.

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