CN104880754B - Sub-wavelength three-dimensional spiral circular polarization filter and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of sub-wavelength three-dimensional spiral circular polarization filter and preparation method thereof, the preparation method of the circular polarization filter comprises the following steps：（1）The spin coating photoresist in silicon dioxide substrates；（2）Directly write out three-dimensional spiral nanometer rod structure on a photoresist using laser direct writing system and developed；（3）Oxygen is passed through, is performed etching using reactive ion beam, remove residual photoresist；（4）Metal film layer is plated using magnetically controlled sputter method on silicon dioxide substrates and three-dimensional spiral the nanometer rod structure for having shifted.The present invention can realize the differentiation to left-right rotary circularly polarized light, and with simple structure, it is easy to the characteristics of making.

Description

Sub-wavelength three-dimensional spiral circular polarizing filter and manufacturing method thereof

technical field

The invention relates to a filter, in particular to a sub-wavelength three-dimensional spiral circular polarization filter and a manufacturing method thereof.

Background technique

In imaging technology, because polarization imaging technology can perform long-distance image acquisition operations in harsh environments, it has absolute advantages in suppressing background noise, improving detection distance, obtaining detailed features, and identifying target camouflage. Therefore, it has a very wide range of applications, for example: it can detect hidden or camouflaged targets; it can realize the detection and identification of sea surface and underwater targets; it can realize navigation under smoky weather conditions; It can distinguish real targets in objects; it can perform medical diagnosis such as cancer and burns; it can identify object characteristics (such as fingerprints, etc.); it can realize spaceborne or airborne remote sensing; it can also be combined with other technologies, such as multispectral polarization infrared imaging , hyperspectral polarized infrared imaging, etc. In polarized light imaging technology, circular polarization imaging has been widely valued because of its unique advantages in large particle scattering media. For example, the imaging quality of circularly polarized light is better than that of linearly polarized light in underwater, smog, cloud and biological tissues. In 2005, S.A. Kartazayeva et al inserted the chrome-plated 2951USAF ladder template into deionized water dissolved with polystyrene particles (d=10.143um) as the detection target. Active imaging was performed using linearly polarized and circularly polarized light as excitation sources, respectively. The results prove that the imaging effect of circularly polarized light is better than that of linearly polarized light in large particle turbid media.

It is extremely important to distinguish circular polarization from left-handed to right-handed in optical imaging techniques. The traditional method of distinguishing left and right circularly polarized light is generally to use a quarter-wave plate to convert circular polarization into linearly polarized light with different polarization directions, and then select an analyzer to filter according to the required polarization direction. However, the applicable wave band of this method is limited by the bandwidth of the wave plate and is not conducive to the miniaturization and integration of components. In recent years, as an emerging discipline, subwavelength structural devices and technologies based on surface plasmon waves have many potential applications in many fields, so they have attracted more and more attention. At present, many research groups have done a lot of research work on the use of nanostructures to distinguish left and right circularly polarized light. In 2009, Justyna K. Gansel and others proposed and produced a broadband circular polarizing filter, that is, periodically placing spiral metal gold wires on the dielectric substrate, by controlling the rotation direction of the helix, the left-handed polarization can be achieved. and selective transmission of right-handed circularly polarized light. They first deposited a very thin layer (25nm) of indium tin oxide (ITO) on the glass substrate as the cathode of electrochemical deposition, then coated with positive photoresist, and carved the spiral air line through the 3D laser direct writing system. , and then put it into a gold-containing electrolyte and use electrochemical deposition to fill the gaps with gold, and finally remove the photoresist to obtain a broadband circular polarizer with an average circular dichroism of 0.7 at 4um-8um. This structure process is complex and difficult to manufacture. In 2013, A. Alù et al. designed a circular polarizing polarizer in the visible light band by using the metal sheet space rotation stacked structure. They sequentially plated Au, SiO ₂ and photoresist on the glass substrate, and then used electron beam direct and reactive ion beam etching to obtain 55nm grooves on SiO ₂ , and then used electron beam evaporation to plate 5nm Ti, and finally used photolithography The glue stripping process is used to plate 50nm Au to obtain metal sheets in the grooves. Through such a process, multiple layers are stacked and stacked to obtain a metal sheet structure that is rotated and stacked in space. In 500nm-800mn, the average circular dichroism is 0.3 and the function of the circular polarizer is realized. In 2014, Wenshan Cai et al. designed and produced a double-layer arc-shaped metal (Ag) structure, and experimentally obtained a maximum circular dichroism of 0.35 at 1.4um. In 2014, E.-B. Kley et al., produced 2-D and 3-D starfish-shaped metal (Au) structures were developed, where the three-dimensional structure obtained a circular dichroism of 0.4 at 660 nm. To sum up, the prior art has the problems of complex structure and process, high manufacturing difficulty, or low degree of differentiation.

Contents of the invention

The object of the present invention is to provide a sub-wavelength three-dimensional spiral circular polarizing filter and its manufacturing method, which can distinguish left and right circular polarized light, and has the characteristics of simple structure and easy manufacture.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is: a sub-wavelength three-dimensional spiral circular polarizing filter, including a silicon dioxide substrate, a three-dimensional spiral nano-column on the silicon dioxide The silicon substrate and the metal film layer on the surface of the three-dimensional helical nanocolumn, the radius of the three-dimensional helical nanocolumn is 0.7-1.1um, the height is 1.8～3um, and the period of each three-dimensional helical nanocolumn is 1.4～2.2um. The thickness of the metal thin film layer is 0.05-0.15um.

In a preferred technical solution, the radius of the three-dimensional helical nanocolumn is 0.95um, the height is 2um, and the period of each three-dimensional helical nanocolumn is 1.9um.

In a preferred technical solution, the thickness of the metal thin film layer is 0.1um.

In the above technical solution, the material of the metal thin film layer may be gold, silver, aluminum, copper or titanium nitride.

A method for manufacturing a sub-wavelength three-dimensional spiral circular polarizing filter, comprising the steps of:

(1) Spin-coat photoresist on a silicon dioxide substrate;

(2) Using a laser direct writing system to directly write a three-dimensional helical nanocolumn structure on the photoresist and develop it;

(3) Oxygen is introduced, and reactive ion beam is used for etching to remove residual photoresist;

(4) The transferred silicon dioxide substrate and the three-dimensional helical nanocolumn structure are plated with a metal thin film by magnetron sputtering.

The principle of the present invention is: since the spatial metal three-dimensional chiral structure has the characteristics of circular dichroism, in order to realize the distinction between left and right circularly polarized light, the present invention designs a three-dimensional helical nano-column structure and coats a layer of metal on the surface of the structure. The thin film layer, due to the plasmon effect on the metal surface of the chiral structure, makes the structure have strong circular dichroism. The selective transmission of left and right circularly polarized light can be realized by designing different helical structures. By rationally optimizing the period, height and thickness of the metal layer of the structure, the distinction between left and right circularly polarized light can be realized. Among them, the larger the period, the longer the applicable wavelength range, and the smaller the period, the shorter the applicable wavelength range and the higher the height. The wider the range of bands to adapt to, the more difficult it is to make.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

The invention designs a three-dimensional helical nanocolumn structure and coats a layer of metal thin film on the surface of the structure. Due to the plasma effect on the metal surface of the chiral structure, the structure has strong circular dichroism, thereby realizing the function of a circular polarization filter , its circular dichroism is above 0.7 on average in the 3um-5um band, and has the advantages of simple structure and easy fabrication.

Description of drawings

Fig. 1 is a structural schematic diagram of a unit of the three-dimensional helical nanocolumn of the present invention in Example 1.

Fig. 2 is a graph of the transmittance of left and right circularly polarized light incident from the substrate through the circular polarizing filter of the present invention in the first embodiment.

Among them: 1. Silica substrate; 2. Three-dimensional helical nanocolumn; 3. Metal thin film layer.

detailed description

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment one: referring to shown in Fig. 1, a kind of sub-wavelength three-dimensional helical circular polarizing filter comprises a silicon dioxide substrate 1, a three-dimensional helical nanocolumn 2 that is located on the silicon dioxide substrate and covers the silicon dioxide substrate sheet and the metal thin film layer 3 on the surface of the three-dimensional helical nanocolumn, the radius of the three-dimensional helical nanocolumn is r=0.95um, the height is H ₁ =2um, and the period of each three-dimensional helical nanocolumn is P=1.9um. The thickness of the metal thin film layer is H ₂ =0.1um.

In this embodiment, the material of the metal thin film layer may be gold, silver, aluminum, copper or titanium nitride.

A method for manufacturing a sub-wavelength three-dimensional spiral circular polarizing filter, comprising the steps of:

(1) Spin-coat photoresist on a silicon dioxide substrate;

(2) Using a laser direct writing system to directly write a three-dimensional helical nanocolumn structure on the photoresist and develop it;

(3) Oxygen is introduced, and reactive ion beam is used for etching to remove residual photoresist;

(4) The transferred silicon dioxide substrate and the three-dimensional helical nanocolumn structure are plated with a metal thin film by magnetron sputtering.

As shown in Figure 2, the average circular dichroism in the 3um-5um band is above 0.7.

Claims (4)

1. a kind of sub-wavelength three-dimensional spiral circular polarization filter, it is characterised in that：Including silicon dioxide substrates, located at silica Three-dimensional spiral nano-pillar on substrate and the metal film layer of silicon dioxide substrates and three-dimensional spiral nano-pillar surface is overlying on, it is described The radius of three-dimensional spiral nano-pillar is 0.7~1.1um, a height of 1.8~3um, cycle of each three-dimensional spiral nano-pillar for 1.4~ 2.2um, the metal film layer thickness is 0.05~0.15um.

2. a kind of sub-wavelength three-dimensional spiral circular polarization filter according to claim 1, it is characterised in that：The three-dimensional spiral shell The radius for revolving nano-pillar is 0.95um, a height of 2um, and the cycle of each three-dimensional spiral nano-pillar is 1.9um.

3. a kind of sub-wavelength three-dimensional spiral circular polarization filter according to claim 1, it is characterised in that：The metal foil Thicknesses of layers is 0.1um.

4. a kind of preparation method of sub-wavelength three-dimensional spiral circular polarization filter, it is characterised in that comprise the following steps：

（1）The spin coating photoresist in silicon dioxide substrates；

（2）Directly write out three-dimensional spiral nanometer rod structure on a photoresist using laser direct writing system and developed；

（3）Oxygen is passed through, is performed etching using reactive ion beam, remove residual photoresist；

（4）Metal foil is plated using magnetically controlled sputter method on silicon dioxide substrates and three-dimensional spiral the nanometer rod structure for having shifted Film layer.