Polarization beam splitter based on super-structure grating

Abstract

The polarization beam splitter comprises a uniform two-dimensional grating layer, a substrate dielectric layer and a non-uniform two-dimensional grating layer which are stacked in sequence, and the uniform two-dimensional grating layer is formed by periodically and uniformly arranging a plurality of nano columns with the same size in a square shape. The uniform two-dimensional grating period is equal to half of the super-structure grating period; the uniform two-dimensional grating layer is formed by distributing nine nano-columns on the outer surface of a cubic cell of the super-structure grating, and the nine nano-columns comprise first nano-columns located at four vertexes of a square, middle points of four side lengths of the square and the center of the square; the non-uniform two-dimensional grating layer is constructed on the substrate dielectric layer and is formed by periodically arranging a plurality of nano columns with different sizes in a square shape, the periodic arrangement formed by each nano column is mutually shifted by a half period in the horizontal direction, and the period of the non-uniform two-dimensional grating layer is equal to the period of the super-structure grating. Compared with the prior art, the two-dimensional grating constructed by the invention has a large design freedom degree so as to flexibly adjust the transmission efficiency of each diffraction order, and has the advantages of high extinction ratio, small volume, easiness in integration, polarized light beam splitting on two orthogonal planes and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polarization beam splitters, and in particular to a polarization beam splitter based on a metagrating. Background Art

[0002] The function of a polarization beam splitter is to split incident light with orthogonal polarization states into two different polarization beams (TE and TM) propagating in different directions. As a basic optical device, it has a wide range of applications in many fields such as optical communications, optical sensing and optical display.

[0003] Traditional polarization beam splitters are based on birefringent materials and generally require a sufficiently long light propagation distance to achieve spatial separation of polarized light beams. As a result, the devices are large and difficult to integrate, which seriously hinders the miniaturization and integration of optical systems. Polarization beam splitters based on one-dimensional diffraction gratings can only polarize incident light in a one-dimensional plane, although they can be small in size. Summary of the invention

[0004] In order to solve the above technical defects, the purpose of the present invention is to provide a polarization beam splitter based on a metagrating to solve the defects of traditional polarization beam splitting devices that are large in size and difficult to integrate or can only perform polarization splitting in a one-dimensional plane.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a polarization beam splitter based on a meta-grating, comprising a uniform two-dimensional grating layer, a substrate dielectric layer and a non-uniform two-dimensional grating layer stacked in sequence, wherein the uniform two-dimensional grating layer is composed of a plurality of nano-pillars of the same size arranged uniformly in a square periodic pattern, and the period of the uniform two-dimensional grating is equal to half of the period of the meta-grating; The non-uniform two-dimensional grating layer is constructed on the substrate dielectric layer, and is composed of a plurality of nanocolumns of different sizes arranged in a square periodic pattern. The periodic arrangement formed by each nanocolumn is offset from each other by half a period in the horizontal direction, and the non-uniform two-dimensional grating period is equal to the superstructure grating period.

[0006] Furthermore, the uniform two-dimensional grating layer is formed by distributing 9 nanocolumns on the outer surface of a cubic cell of the metagrating, and the above 9 nanocolumns include a first nanocolumn located at the four vertices of the square, at the midpoints of the four sides of the square and at the center of the square.

[0007] The non-uniform two-dimensional grating layer is formed by distributing five nanocolumns on the inner bottom surface of a cubic cell of the meta-grating. The five nanocolumns include a second nanocolumn located at the center of the square and a third nanocolumn located at the four vertices of the square.

[0008] The constructed metagrating, when light with orthogonal polarization states is vertically incident on the polarization beam splitter, TE polarized light propagates to the (0, ±1) order, TM polarized light diffracts to the (±1, 0) order, and vice versa, while suppressing the zero-order (0, 0) transmission, achieving spatial beam splitting of polarized light and a high extinction ratio.

[0009] The second nanorod and the third nanorod in the non-uniform two-dimensional grating have different cross-sectional side lengths but the same heights, or have the same cross-sectional side lengths but different heights.

[0010] The second and third nanorods in the non-uniform two-dimensional grating have exactly the same size and shape, but different refractive indices.

[0011] The shapes of the nanorods in the uniform two-dimensional grating layer and the non-uniform two-dimensional grating layer are square, rectangular, cylindrical, truncated cone, or triangular cross-section columns.

[0012] The beneficial effects of the present invention are: the constructed two-dimensional grating has a large design freedom to flexibly adjust the transmission efficiency of each diffraction order, has the advantages of high extinction ratio, small size and easy integration, and polarized light splitting on two orthogonal planes. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The structure and technical features of the present invention are further described below in conjunction with the accompanying drawings and embodiments.

[0014] Figure 1 It is a structural schematic diagram of the present invention.

[0015] Figure 2 yes Figure 1 Schematic diagram of the uniform two-dimensional grating layer in the figure (the dotted box part).

[0016] Figure 3 yes Figure 1 Schematic diagram of the non-uniform two-dimensional grating layer in the figure (dashed box part).

[0017] Figure 4 It is a schematic diagram of the efficiency distribution of each transmission order when TE polarized light is incident on the polarization beam splitter in the present invention.

[0018] Figure 5 It is a schematic diagram of the efficiency distribution of each transmission order when TM polarized light is incident on the polarization beam splitter in the present invention.

[0019] Attached Figure 1-3 In the figure, 1. first nanocolumn, 2. substrate dielectric layer, 3. second nanocolumn, 4. third nanocolumn; Psc represents the Yuanbao cycle, h 2 Represents the height of the substrate dielectric layer, h 1 represents the first nanocolumn height, h 3represents the second nanopillar height, D 1 represents the side length of the first nanorod, D 2 represents the side length of the second nanorod, D 3 Represents the side length of the third nanorod. DETAILED DESCRIPTION

[0020] See attached Figure 1-3 An embodiment of the present invention discloses a polarization beam splitter based on a metagrating, including a three-layer structure stacked in sequence: the first layer is a uniform two-dimensional grating, which is composed of first nanocolumns 1 of the same size that are periodically and uniformly arranged in a square shape; the period of the uniform two-dimensional grating is equal to half of the period of the metagrating; on the upper top surface of a cubic cell of the metagrating, there are nine uniformly distributed first nanocolumns 1, which are respectively located at the four vertices of the square, the midpoints of the four sides and the center of the square; the second layer is a substrate dielectric layer 2.

[0021] The third layer is a non-uniform two-dimensional grating constructed at the bottom of the substrate dielectric layer 2, which is composed of second nanopillars 3 and third nanopillars 4 arranged in a square period, wherein the second nanopillars 3 and the third nanopillars 4 are cubic pillars of different sizes, and the periodic arrangement formed by the second nanopillars 3 and the third nanopillars 4 are offset from each other by half a period in the horizontal direction; the non-uniform two-dimensional grating period is equal to the meta-grating period; on the inner bottom surface of a cubic cell of the meta-grating, there are four third nanopillars 4, surrounding the four vertex positions with the second nanopillar 3 as the center of the square. When light with orthogonal polarization states is vertically incident on the polarization beam splitter, the TE polarized light propagates to the (0, ±1) order, and the TM polarized light diffracts to the (±1, 0) order, or vice versa, while suppressing the zero-order (0, 0) transmission, achieving spatial beam splitting and high extinction ratio of polarized light.

[0022] The polarization beam splitter designed according to the present invention, such as Figure 1 As shown, at vertical incidence, TE (E y , H x , H z ) Polarized light propagates to the (0, ±1) order, TM (H y , E x , E z ) The polarized light is diffracted to the (±1, 0) order, achieving spatial beam splitting and high extinction ratio of polarized light.

[0023] In this embodiment, a cubic grating arranged in a square is taken as an example. For an orthogonally polarized incident light with a wavelength of 1.55 nm, the cell period of the polarization beam splitter is P sc (1.675nm), the substrate dielectric layer 2 is silicon dioxide SiO 2(refractive index is 1.440), with a height of h2 (5.2nm), and the top two-dimensional grating is composed of Si (refractive index is 3.478) cubic columns uniformly arranged in air on the substrate surface, with a height of h1 (0.547nm) and a period of P=P sc / 2 (0.8375nm), the side lengths of the square sections of the nanocubic columns are D1 (0.576nm), and the bottom two-dimensional grating is formed by two different sizes of silicon Si (refractive index 3.478) nanocolumns embedded in the substrate and arranged alternately in a square shape. The period of each square arrangement is P sc (1.675nm), the side lengths of the square sections of the two nanocubic columns are D2 (0.543nm) and D3 (0.911nm), and the alternating misalignment distances in the (x, y) direction are P sc / 2 (0.8375nm), and the heights of both are h3 (2.11nm).

[0024] When TE polarized light is incident vertically, the rigorous coupled wave analysis method (software RETICOLO) can be used to calculate Figure 4 As shown, there are five transmission orders, among which the zero-order (0, 0) light transmission efficiency T 0 The total transmission efficiency of (0, ±1) light is 0.0008812%. te The total transmission efficiency of light is 99.36% (±1, 0). tm The total is 0.00004%. Define the polarization extinction ratio E of the polarization beam splitter te =10·log 10 (T te / T tm ), we can see that the extinction ratio is 63.9dB.

[0025] When TM polarized light is incident vertically, we can get Figure 5 The efficiency distribution diagram of each level is shown, where the zero-order (0, 0) light transmission efficiency T 0 The total transmission efficiency of (0, ±1) light is 0.000871%. te The total transmission efficiency of light is 0.000039% (±1, 0). tm The total is 99.36%. It can be seen that the extinction ratio E tm =10·log 10 (T tm / T te ) is 63.9dB.

[0026] It can be seen that the proposed polarization beam splitter can split the incident light with orthogonal polarization states into two types of different polarization (TE and TM) beams propagating in different directions. Compared with the polarization beam splitter based on birefringent materials, the proposed polarization beam splitter is small in size and easy to integrate; unlike the polarization beam splitter based on one-dimensional diffraction grating that polarizes light in the same propagation plane, the proposed polarization beam splitter splits TE and TM polarized light into two orthogonal propagation planes, enriching the polarization beam splitting control capability.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For the two-dimensional grating of the present invention, in addition to square columns arranged in a square, it can also be cylindrical, truncated cone, triangular cross-section columns, or columns of any other cross-sectional shape. In addition, these columns can be raised columns or recessed air holes. They can be embedded in the substrate or in the air layer on the surface of the substrate. The embodiment of the present invention takes the incident light with a wavelength of 1.55nm as an example. The corresponding designed structural parameters, such as period, radius, height, etc., are all relatively optimal values, not unique values. For those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A polarization beam splitter based on a metagrating, characterized in that: It comprises a uniform two-dimensional grating layer, a substrate medium layer and a non-uniform two-dimensional grating layer stacked in sequence, wherein the uniform two-dimensional grating layer is composed of a plurality of nano-pillars of the same size arranged uniformly in a square periodic pattern, and the uniform two-dimensional grating period is equal to half of the superstructure grating period; The non-uniform two-dimensional grating layer is constructed on the substrate dielectric layer, and is composed of a plurality of nanocolumns of different sizes arranged in a square periodic pattern. The periodic arrangement formed by each nanocolumn is offset from each other by half a period in the horizontal direction, and the non-uniform two-dimensional grating period is equal to the superstructure grating period.

2. The polarization beam splitter based on a metagrating according to claim 1, characterized in that: The uniform two-dimensional grating layer is formed by distributing 9 nanocolumns on the outer surface of a cubic cell of the metagrating, wherein the 9 nanocolumns include a first nanocolumn located at the four vertices of the square, at the midpoints of the four sides of the square and at the center of the square.

3. The polarization beam splitter based on a metagrating according to claim 1, characterized in that: The non-uniform two-dimensional grating layer is formed by distributing five nanocolumns on the inner bottom surface of a cubic cell of the meta-grating. The five nanocolumns include a second nanocolumn located at the center of the square and a third nanocolumn located at the four vertices of the square.

4. The polarization beam splitter based on a metagrating according to claim 1, characterized in that: The constructed metagrating, when light with orthogonal polarization states is vertically incident on the polarization beam splitter, TE polarized light propagates to the (0, ±1) order, TM polarized light diffracts to the (±1, 0) order, and vice versa, while suppressing the zero-order (0, 0) transmission, achieving spatial beam splitting of polarized light and a high extinction ratio.

5. The polarization beam splitter based on a metagrating according to claim 3, characterized in that: The second nanorod and the third nanorod in the non-uniform two-dimensional grating have different cross-sectional side lengths but the same heights, or have the same cross-sectional side lengths but different heights.

6. The polarization beam splitter based on a metagrating according to claim 3, characterized in that: The second and third nanorods in the non-uniform two-dimensional grating have exactly the same size and shape, but different refractive indices.

7. The polarization beam splitter based on a metagrating according to claim 1, characterized in that: The shapes of the nanorods in the uniform two-dimensional grating layer and the non-uniform two-dimensional grating layer are square, rectangular, cylindrical, truncated cone, or triangular cross-section columns.

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