CN101782666A - Helical metal wire grating circuit polarizer - Google Patents

Abstract

The invention discloses a helical metal wire grid circular polarizer, which belongs to an optical device, and aims to make it have a wider working wavelength in the visible light band, and the device has a small size, a compact structure, and is easy to integrate. In the circular polarizer of the present invention, N evenly distributed helical aluminum metal wire grids are deposited on the quartz glass substrate, the metal wire grids have a diameter of 40-60 nanometers, and the number of helical helical periods is greater than or equal to 2 weeks. The pitch of the metal wire grid is 190-290 nanometers, the pitch of the helix is 150-400 nanometers, the diameter of the helix is 100 nanometers, and N≥10 ⁶ . The invention can work in the visible light spectrum range, the working wavelength range can reach 580-730 nanometers, the polarization extinction ratio is greater than 8.8:1, the polarized light transmittance is greater than 67%, and the device is small in size, compact in structure and easy to integrate, and is suitable for polarization Spectroscopy, color display, laser technology and other fields.

Description

A spiral metal wire grid circular polarizer

technical field

The invention belongs to optical devices, in particular to a spiral metal wire grid circular polarizer.

Background technique

Circular polarizer is an important polarizing component in the field of optics. It has been widely used in polarization splitting, color display, laser technology and other fields. At present, in the field of optics, it is common practice to use two separate components, a linear polarizer and a quarter-wave plate, to form a circular polarizer. The angle is passed through a quarter-wave plate, and circularly polarized light is finally obtained. The disadvantages of this structure are very obvious: 1. The working wavelength range is narrow, mainly because the working wavelength range of the quarter-wave plate is narrow, so this structure cannot obtain circularly polarized light with a wide wavelength range; 2. The structure Two separate optical components are used, so the device size is large and not easy to integrate.

Obtaining circularly polarized light using a helical metal wire grid was first discovered by researchers at the University of Karlsruhe in Germany in September 2009, see Justyna K.Gansel, et al. "Circular Polarizer Gold Helix Photonic Metamaterial as Broadband," Science 325 , 1513 (2009). But their research scope is limited to the following two aspects: 1. The metal wire grid material is gold; 2. The working wavelength range is in the infrared band of 3-6 microns. Since the optical properties of the gold they used in the visible light range are far inferior to the aluminum material, and the helical metal wire grid they proposed is too large, it cannot be applied to the visible light band at all. In addition, they did not propose the structure of circular polarizers suitable for other wavelength bands, nor did they discuss other metal materials.

Contents of the invention

The invention proposes a helical metal wire grid circular polarizer with the purpose of making it have a wider working wavelength range in the visible light band, and the device has a small size, a compact structure and is easy to integrate.

A spiral metal wire grid circular polarizer of the present invention has N uniformly distributed spiral metal wire grids deposited on the substrate, and is characterized in that:

The substrate is quartz glass; the material of the metal wire grid is metal aluminum, the diameter of the metal wire grid is 40-60 nanometers, the number of helical helical periods is greater than or equal to 2, and the pitch of the helical metal wire grid is 190-290 nanometers. The helical periodic pitch is 150-400 nanometers, the helical diameter is 100 nanometers, and N≥10 ⁶ .

The preparation method of the spiral metal wire grid circular polarizer of the present invention comprises the following steps:

(1). Deposit a conductive film on the surface of the substrate;

(2). Spin-coat photoresist on the conductive film;

(3). Through deep ultraviolet coherent etching, N uniformly distributed helical air gaps on the order of tens of nanometers are formed in the photoresist;

(4). By electrochemical deposition, metal materials are deposited in N uniformly distributed spiral air gaps to form a spiral metal wire grid;

(5). Remove the photoresist between the spiral metal wire grids.

In the preparation process, step (3) and step (4) are two more important steps. Forming a structure with a line width of tens of nanometers is difficult for general lithography. In 2007, a research team in the United States successfully used the method of deep ultraviolet coherent etching to obtain a large-scale metal wire grid structure with a line width of less than 40 nanometers. See J.J.Wang, F.Walters, X.M.Liu, P.Sciortino, and X.G.Deng, "High-performance, large area, deep ultraviolet to infrared polarizers based on 40nm line/78nm spacenanowire grids," Appl.Phys.Lett.90, 61104 (2007); this provides a basis for the implementation of step (3). In addition, it is completely feasible to deposit metal materials in a helical structure by electrochemical deposition, see Justyna K. Gansel, et al. "Circular Polarizer Gold Helix Photonic Metamaterialas Broadband," Science 325, 1513 (2009).

Compared with the existing helical circular polarizer, by adjusting and optimizing the parameters of the helical metal nanowire grid (such as: wire grid diameter, number of helical periods, etc.), the present invention can work in the visible light spectrum range with a shorter wavelength, and its The working wavelength range can reach 580-730 nanometers, the polarization extinction ratio is greater than 8.8:1, and the polarized light transmittance is greater than 67%, which is superior to existing visible light polarizers, and the device is small in size, compact in structure, easy to integrate, and suitable for polarization Spectroscopy, color display, laser technology and other fields.

Description of drawings

Fig. 1 (a) is the structural representation of the present invention;

Fig. 1 (b) is the top view of the present invention;

Fig. 1 (c) is the side view of the present invention;

Fig. 2 (a) is the distribution diagram of the light field at different times when the FDTD algorithm is used to simulate left-handed circularly polarized light passing through the present invention;

Fig. 2 (b) is for using the FDTD algorithm to simulate right-handed circularly polarized light passing through the present invention, the distribution diagram of the light field at different times;

Fig. 3 is the optical characteristic curve of embodiment 1;

Fig. 4 is the optical characteristic curve of embodiment 2;

Fig. 5 is the optical characteristic curve of embodiment 3;

Fig. 6 is the optical characteristic curve of embodiment 4;

Fig. 7 is the optical characteristic curve of embodiment 5;

Fig. 8 is the optical characteristic curve of embodiment 6;

Fig. 9(a) to Fig. 9(e) are process flow diagrams of the preparation method of the present invention.

Detailed ways

As shown in Fig. 1 (a) ~ Fig. 1 (c), the present invention is deposited with N uniformly distributed spiral metal wire grids 2 on the substrate 1, and the substrate is quartz glass; the material of the metal wire grids It is metal aluminum, the diameter SD of the metal wire grid is 40-60 nanometers, the number of helical helical periods CN is greater than or equal to 2, the spacing CW of the helical metal wire grid is 190-290 nanometers, and the helical period spacing CS is 150-400 nanometers, The helix diameter CD is 100 nm, N≥10 ⁶ .

Fig. 2 (a) is the distribution diagram of the light field at different times when simulating left-handed circularly polarized light with the FDTD algorithm passes through the present invention; It can be seen from the figure that most of the energy of the left-handed circularly polarized light is reflected after passing through the polarizer, while most of the energy of the right-handed circularly polarized light can pass through the polarizer smoothly.

Embodiment 1: 10 ⁶ evenly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the metal wire grid diameter SD is 40 nanometers, the helical helical cycle number CN is equal to 2, and the helical metal wires The grid spacing CW is 190 nanometers, the helix periodic spacing CS is 200 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 3 shows the optical characteristic curve of embodiment 1, among the figure, the curve that hollow rectangular frame depicts is right-handed circularly polarized light transmittance, and the curve that hollow triangular frame depicts is left-handed circularly polarized light transmittance, black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.5-0.75 μm, 73%, and 19.7:1, respectively.

Embodiment 2: 10 ⁶ evenly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the metal wire grid diameter SD is 60 nanometers, the helical helical cycle number CN is equal to 2, and the helical metal wires The grid spacing CW is 190 nanometers, the helix periodic spacing CS is 200 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 4 shows the optical characteristic curve of embodiment 2, among the figure, the curve that hollow rectangular frame depicts is right-handed circularly polarized light transmittance, and the curve that hollow triangular frame depicts is left-handed circularly polarized light transmittance, black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.4-0.77 μm, 69%, and 26.3:1, respectively.

Embodiment 3: 10 ⁶ evenly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the metal wire grid diameter SD is 40 nanometers, the helical helical cycle number CN is equal to 4, and the helical metal wires The grid spacing CW is 190 nanometers, the helix periodic spacing CS is 200 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 5 shows the optical characteristic curve of embodiment 3, among the figure, the curve that the hollow rectangular frame depicts is the right-handed circularly polarized light transmittance, the curve that the hollow triangular frame depicts is the left-handed circularly polarized light transmittance, and the black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.42-0.83 μm, 58%, and 46.3:1, respectively.

Embodiment 4: 10 ⁶ uniformly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the metal wire grid diameter SD is 40 nanometers, the number of helical helical periods CN equals 2, and the helical metal wires The grid spacing CW is 290 nanometers, the helix periodic spacing CS is 200 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 6 shows the optical characteristic curve of embodiment 4, among the figure, the curve that hollow rectangular frame depicts is right-handed circularly polarized light transmittance, the curve that hollow triangular frame depicts is left-handed circularly polarized light transmittance, black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.55-0.73 μm, 85%, and 8.8:1, respectively.

Embodiment 5: 10 ⁶ uniformly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the metal wire grid diameter SD is 40 nanometers, the number of helical helical periods CN equals 2, and the helical metal wires The grid spacing CW is 190 nanometers, the helix periodic spacing CS is 150 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 7 shows the optical characteristic curve of embodiment 5, among the figure, the curve that hollow rectangular frame depicts is right-handed circularly polarized light transmittance, the curve that hollow triangular frame depicts is left-handed circularly polarized light transmittance, black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.39-0.79 μm, 67%, and 12.1:1, respectively.

Embodiment 6: 10 ⁶ evenly distributed helical aluminum metal wire grids 2 are deposited on the quartz glass substrate 1, the diameter SD of the metal wire grid is 40 nanometers, the helical helical cycle number CN is equal to 2, and the helical metal wires The grid spacing CW is 190 nanometers, the helix periodic spacing CS is 400 nanometers, and the helix diameter CD is 100 nanometers;

Fig. 8 shows the optical characteristic curve of embodiment 6, among the figure, the curve that the hollow rectangular frame depicts is the right-handed circularly polarized light transmittance, the curve that the hollow triangular frame depicts is the left-handed circularly polarized light transmittance, and the black solid frame The curve depicted is the extinction ratio;

In this embodiment, the working wavelength range, average transmittance, and average extinction ratio are 0.58-0.75 μm, 78%, and 138:1, respectively.

Figure 9(a) to Figure 9(e) show the process flow chart of the preparation method of the present invention. Figure 9(a). Deposit a conductive film on the surface of the substrate; Figure 9(b). Spin-coat photoresist on the conductive film; Figure 9(c). Form tens of N uniformly distributed helical air gaps at the nanoscale; Figure 9(d). Metal aluminum materials are deposited in N uniformly distributed helical air gaps by electrochemical deposition to form a helical metal wire grid; Figure 9 (e). Removing the photoresist between the helical metal wire grids to finally form a helical metal wire grid circular polarizer.

Claims (1)

1. A spiral metal wire grid circular polarizer is deposited with N uniformly distributed spiral metal wire grids on the substrate, characterized in that: The substrate is quartz glass; the material of the metal wire grid is metal aluminum, the diameter of the metal wire grid is 40-60 nanometers, the number of helical helical periods is greater than or equal to 2, and the pitch of the helical metal wire grid is 190-290 nanometers. The helical periodic pitch is 150-400 nanometers, the helical diameter is 100 nanometers, and N≥10 ⁶ .

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