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 particularly to a polarization beam splitter based on a two-dimensional grating. Background Art

[0002] The function of a polarization beam splitter is to split incident light with orthogonal polarization states into two different polarized (TE and TM) light beams propagating in different directions. As a basic type of 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 optical engine system.

[0003] Traditional polarization beam splitters are realized based on birefringent materials. Generally, a sufficiently long optical propagation distance is required to achieve the spatial separation of polarized light beams. Therefore, the device has a large volume and is difficult to integrate, seriously hindering the miniaturization and integration of optical systems. For a polarization beam splitter based on a one-dimensional diffraction grating, although a small size can be achieved, it can only perform polarization beam splitting of incident light in a one-dimensional plane. Summary of the Invention

[0004] To solve the above technical deficiencies, the object of the present invention is to provide a polarization beam splitter based on a two-dimensional grating, which solves the defects that traditional polarization beam splitting devices have a large volume and are difficult to integrate or can only perform polarization beam splitting in a one-dimensional plane.

[0005] To achieve the above object, the present invention adopts the following technical solution: A polarization beam splitter based on a two-dimensional grating includes a substrate medium. A two-dimensional grating is constructed at the bottom of the substrate medium. The two-dimensional grating is composed of first nanocolumns and second nanocolumns that are both arranged in a square period. The first nanocolumns and the second nanocolumns are cubic columns with different sizes. The periodic arrangements formed by the first nanocolumns and the second nanocolumns are offset 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 located at the four vertex positions surrounding the second nanocolumn as the center of the square. For the constructed two-dimensional grating, when light with orthogonal polarization states is perpendicularly incident on the polarization beam splitter, TE-polarized light propagates to the (0, ±1) orders, and TM-polarized light diffracts to the (±1, 0) orders. Vice versa, and at the same time, the zero-order (0, 0) transmission is suppressed, realizing the spatial beam splitting of polarized light and a high extinction ratio.

[0006] Furthermore, the sizes of the first nanocolumns and the second nanocolumns can also be the same in terms of the cross-sectional side length, but different in height.

[0007] The first nanocolumns and / or the second nanocolumns can also be set as cylindrical, frustum-shaped, triangular cross-section columns, or columns with any other cross-sectional shape.

[0008] The first nanocolumns and the second nanocolumns can also be the same in size and shape, but different in refractive index or dielectric constant.

[0009] A two-dimensional grating is constructed at the bottom of the substrate medium. The two-dimensional grating is composed of two types of nano-columns with different sizes embedded in the substrate. Each type of nano-columns with the same size is arranged in a square period, and the two formed periodic arrays are offset by half a period in the horizontal direction.

[0010] The beneficial effects of the present invention are as follows: The constructed two-dimensional grating has a large design freedom to flexibly adjust the transmission efficiency of each diffraction order, and has the advantages of high extinction ratio, small volume and easy integration, and polarization beam splitting in two orthogonal planes. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The structure and technical features of the present invention will be further described below in conjunction with the drawings and embodiments.

[0012] Figure 1 It is a schematic structural diagram of the present invention.

[0013] Figure 2 is Figure 1 A plan view of the two-dimensional grating in (the part within the dashed box).

[0014] 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 of the present invention.

[0015] 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 of the present invention.

[0016] Attached Figure 1-2 In, 1. Substrate medium, 2. First nano-column, 3. Second nano-column.

[0017] P represents the cell period, h represents the height of the first nano-column and the second nano-column, H represents the height of the substrate medium layer, D1 represents the side length of the second nano-column, and D2 represents the side length of the first nano-column. DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to the attached Figure 1-2 It is an embodiment of the present invention, which discloses a polarization beam splitter based on a two-dimensional grating, including a substrate medium 1. A two-dimensional grating is constructed at the bottom of the substrate medium 1. The two-dimensional grating is composed of a first nano-column 2 and a second nano-column 3 arranged in a square period. The first nano-column 2 and the second nano-column 3 are cubic columns with different sizes, and the periodic arrangements formed by the first nano-column 2 and the second nano-column 3 are offset by half a period in the horizontal direction. In a square cell of the two-dimensional grating, four first nano-columns 2 are provided, surrounding the four vertex positions with the second nano-column 3 as the square center.

[0019] When the constructed two-dimensional grating is irradiated by light with orthogonal polarization states perpendicularly incident on a polarization beam splitter, the TE polarized light propagates to the (0, ±1) orders, and the TM polarized light diffracts to the (±1, 0) orders, and vice versa. At the same time, the transmission of the zero-order (0, 0) is suppressed, realizing the spatial beam splitting of polarized light and a high extinction ratio.

[0020] The polarization beam splitter designed according to the present invention, as Figure 1 shown, when perpendicularly incident, the TE (E y , H x , H z ) polarized light propagates to the (0, ±1) orders, and the TM (H y , E x , E z ) polarized light diffracts to the (±1, 0) orders, realizing the spatial beam splitting of polarized light and a high extinction ratio.

[0021] In this embodiment, taking the square column grating arranged in a two-dimensional square array as an example, for the orthogonally polarized incident light with a wavelength of 1.55 μm, the cell period of the constructed polarization beam splitter is P (1.675 μm), the dielectric substrate is silicon dioxide SiO2 (refractive index is 1.440), the height is H (7.31 μm), and the bottom two-dimensional grating is formed by alternately arranging two kinds of silicon Si (refractive index is 3.478) nanocolumns with different sizes embedded in the substrate in a square shape. Each square arrangement period is P (1.675 μm), and the side lengths of the two kinds of nanosquare columns are D1 (0.543 μm) and D2 (0.911 μm) respectively. The alternating misalignment distances in the (x, y) directions are P / 2 (0.8375 μm), and their heights are both h (2.11 μm).

[0022] For the bottom two-dimensional grating, here the grating is exemplified by square columns arranged in a square shape. In fact, it can also be cylindrical columns, or columns with octagonal (12-sided, 16-sided...) cross-sections, etc., as well as their combined symmetric shapes. In addition, these columns can be protruding columns or recessed air holes. They can be embedded in the substrate or in the air layer on the substrate surface. In addition, here the incident light with a wavelength of 1550 nm is taken as an example, and the corresponding designed structural parameters, such as refractive index, period, radius, height, etc. are all relatively optimal values, not the only values.

[0023] When the TE polarized light is perpendicularly incident, it can be calculated by the rigorous coupled-wave analysis method (software RETICOLO) that Figure 3 shown, there are a total of five transmission orders. Among them, the transmission efficiency T0 of the zero-order (0, 0) light is 0.46%, and the total transmission efficiency T of the (0, ±1) light te is a total of 71.32%, and the total transmission efficiency T of the (±1, 0) light tmThe total is 0.72%. Define the polarization extinction ratio E of the polarization beam splitter te = 10·log 10 (T te / T tm ). It can be known that the extinction ratio is 19.97 dB.

[0024] When the TM polarized light is incident vertically, the efficiency distribution diagrams of each order as shown in Figure 4 can be obtained. Among them, the transmission efficiency T0 of the zero-order (0, 0) light is 0.46%, and the total transmission efficiency T te of the (0, ±1) light is 0.72% in total, and the total transmission efficiency T tm of the (±1, 0) light is 71.32% in total. It can be known that its extinction ratio E tm = 10·log 10 (T tm / T te ) is 19.97 dB.

[0025] It can be seen from this that the proposed polarization beam splitter can split the incident light with orthogonal polarization states into two types of different polarized (TE and TM) light 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; different from the polarization beam splitter based on one-dimensional diffraction gratings that splits light in the same propagation plane, the proposed polarization beam splitter splits TE and TM polarized light in two orthogonal propagation planes, enriching the polarization beam splitting and regulation ability.

[0026] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For the two-dimensional grating of the present invention, in addition to the square columns arranged in a square, it can also be cylindrical, frustum-shaped, columns with triangular cross-sections, or columns with any other cross-sectional shape. In addition, these columns can be protruding columns or recessed air holes. They can be embedded in the substrate or in the air layer on the surface of the substrate. The embodiments of the present invention take the incident light with a wavelength of 1.55 μm as an example, and the corresponding designed structural parameters, such as period, radius, height, etc. are all relatively optimal values, not the only values. For those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall 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 index or dielectric constant.

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