Polarization beam splitter based on two-dimensional grating

Abstract

The invention discloses a polarization beam splitter based on a two-dimensional grating, which comprises a substrate medium, the two-dimensional grating is constructed at the bottom of the substrate medium, the two-dimensional grating is composed of a first nano-column and a second nano-column which are periodically arranged in a square shape, the first nano-column and the second nano-column are cubic columns with different sizes, and the first nano-column and the second nano-column are rectangular columns with different sizes. The first nano-columns and the second nano-columns are arranged in a square cell of the two-dimensional grating, periods formed by the first nano-columns and the second nano-columns respectively are arranged in the horizontal direction and deviate from each other by a half period, and the four first nano-columns are arranged in the square cell of the two-dimensional grating and surround four vertex positions with the second nano-columns as the center of the square; according to the constructed two-dimensional grating, when light with an orthogonal polarization state vertically enters a polarization beam splitter, TE polarized light is propagated to the (0, + / -1) level, and TM polarized light is diffracted to the (+ / -1, 0) level, otherwise, zero-level (0, 0) transmission can be restrained at the same time, and spatial beam splitting and high extinction ratio of polarized light are achieved.

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 two-dimensional grating. Background Art

[0002] The function of a polarization beam splitter is to split the 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 display, optical communication and optical sensing. A typical example is the LCoS optomechanical system.

[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 two-dimensional grating 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 two-dimensional grating, comprising a substrate medium, a two-dimensional grating is constructed at the bottom of the substrate medium, the two-dimensional grating is composed of a first nanocolumn and a second nanocolumn arranged in a square period, wherein the first nanocolumn and the second nanocolumn are cubic columns of different sizes, and the periodic arrangement formed by the first nanocolumn and the second nanocolumn are offset from each other by half a period in the horizontal direction, and in a square cell of the two-dimensional grating, there are four first nanocolumns, which are surrounded by four vertex positions with the second nanocolumn as the center of the square; when light with orthogonal polarization states is vertically incident on the polarization beam splitter, the constructed two-dimensional grating propagates to the (0, ±1) order, and the TM polarized light is diffracted to the (±1, 0) order, or vice versa, while suppressing the zero-order (0, 0) transmission, thereby realizing spatial beam splitting and high extinction ratio of polarized light.

[0006] Furthermore, the first nanocolumn and the second nanocolumn may have the same cross-sectional length but different heights.

[0007] The first nanorod and the second nanorod can also be configured as cylindrical, truncated cone, or triangular cross-section columns.

[0008] The first nanorod and the second nanorod may also have the same size and shape but different refractive indices.

[0009] 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

[0010] The structure and technical features of the present invention are further described below in conjunction with the accompanying drawings and embodiments.

[0011] Figure 1 It is a structural schematic diagram of the present invention.

[0012] Figure 2 yes Figure 1 Schematic diagram of the two-dimensional grating in the figure (the dotted box part).

[0013] Figure 3 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.

[0014] Figure 4 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.

[0015] Attached Figure 1-2 In the figure, 1. substrate medium, 2. first nanocolumn, 3. second nanocolumn.

[0016] P represents the cell period, h represents the height of the first nanocolumn and the second nanocolumn, H represents the height of the substrate dielectric layer, D 1 represents the side length of the first nanorod, D 2 Represents the side length of the second nanorod. DETAILED DESCRIPTION

[0017] See attached Figure 1-2 An embodiment of the present invention discloses a polarization beam splitter based on a two-dimensional grating, including a substrate medium 1, at the bottom of which a two-dimensional grating is constructed. The two-dimensional grating is composed of first nanopillars 2 and second nanopillars 3 arranged in a square periodic pattern, wherein the first nanopillars 2 and the second nanopillars 3 are cubic pillars of different sizes, and the periodic arrangements formed by the first nanopillars 2 and the second nanopillars 3 are offset from each other by half a period in the horizontal direction. In a square cell of the two-dimensional grating, there are four first nanopillars 2, which are arranged around four vertex positions with the second nanopillars 3 as the center of the square.

[0018] The constructed two-dimensional grating, 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.

[0019] 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.

[0020] This embodiment takes a two-dimensional square column grating as an example. For orthogonal polarized incident light with a wavelength of 1.55 nm, the cell period of the polarization beam splitter is P (1.675 nm), and the dielectric substrate is silicon dioxide SiO 2 (refractive index is 1.440), height is H (7.31nm), the bottom two-dimensional grating is formed by two different sizes of silicon Si (refractive index is 3.478) nanocolumns embedded in the substrate and arranged alternately in a square shape. The period of each square arrangement is P (1.675nm), the side lengths of the two nano square columns are D1 (0.543nm) and D2 (0.911nm), the alternating misalignment distances in the (x, y) direction are P / 2 (0.8375nm), and the height of both is h (2.11nm).

[0021] When TE polarized light is incident vertically, the rigorous coupled wave analysis method (software RETICOLO) can be used to calculate Figure 3 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 0.46%. te The total transmission efficiency of (±1, 0) light is 71.32%. tm The total is 0.72%. 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 19.97dB.

[0022] When TM polarized light is incident vertically, we can get Figure 4 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 0.46%. te The total transmission efficiency of light is 0.72% (±1, 0). tm The total is 71.32%. It can be seen that the extinction ratio E tm =10·log 10 (T tm / T te ) is 19.97dB.

[0023] 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.

[0024] 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 two-dimensional grating, characterized in that: The invention comprises a substrate medium, at the bottom of which a two-dimensional grating is constructed. The two-dimensional grating is composed of a first nanocolumn and a second nanocolumn arranged in a square period, wherein the first nanocolumn and the second nanocolumn are cubic columns of different sizes, and the periodic arrangement formed by the first nanocolumn and the second nanocolumn is offset from each other by half a period in the horizontal direction. In a square unit cell of the two-dimensional grating, there are four first nanocolumns, which are arranged around four vertex positions with the second nanocolumn as the center of the square. When light with orthogonal polarization states is vertically incident on a polarization beam splitter, the constructed two-dimensional grating propagates TE polarized light to the (0, ±1) order, and TM polarized light is diffracted to the (±1, 0) order, or vice versa, and at the same time, the zero-order (0, 0) transmission is suppressed, thereby realizing spatial beam splitting and high extinction ratio of polarized light.

2. The polarization beam splitter based on a two-dimensional grating according to claim 1, characterized in that: The first nanocolumn and the second nanocolumn may have the same cross-sectional length but different heights.

3. The polarization beam splitter based on a two-dimensional grating according to claim 1, characterized in that: The first nanorod and / or the second nanorod can also be configured as a cylindrical, truncated cone, triangular cross-section column, or any other cross-sectional shape column.

4. The polarization beam splitter based on a two-dimensional grating according to claim 1, characterized in that: The first nanorod and the second nanorod may also have the same size and shape but different refractive indices (or dielectric constants).

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