CN114442211A

CN114442211A - RGB (red, green and blue) -based wide-spectrum high-efficiency polarization-independent inclined double-layer grating

Info

Publication number: CN114442211A
Application number: CN202011221276.4A
Authority: CN
Inventors: 刘炜程; 周常河; 金戈; 贾伟
Original assignee: Jinan University
Current assignee: Jinan University
Priority date: 2020-11-03
Filing date: 2020-11-03
Publication date: 2022-05-06

Abstract

The invention discloses an RGB (red, green and blue) -based wide-spectrum high-efficiency polarization-independent inclined double-layer grating, wherein a substrate of the grating is quartz, and a first layer of material is MgF₂Depth of h₁The second layer is made of quartz with a depth h₂. The period d of the grating is 706-727 nanometers, the ridge width b is 396-418 nanometers, the inclination angle theta is 18-19 degrees, and h₁Is 452 to 504 nanometers, h₂691-743 nm, the grating structure has a wavelength bandwidth of 454-630 nm under normal incidence. The invention is a high-efficiency polarization-independent oblique double-layer grating suitable for RGB three primary colors (the central wavelength is 460 nm, 526 nm and 620 nm of blue light, green light and red light), which is processed by combining an electron beam direct writing device with a microelectronic deep etching process, has the advantages of convenient material acquisition, simple structure, large tolerance and low manufacturing cost, can be produced in large batch, and can be applied to three-dimensional imaging display technologies such as AR, VR and the like.

Description

RGB (red, green and blue) -based wide-spectrum high-efficiency polarization-independent inclined double-layer grating

Technical Field

The invention relates to the technical field of transmission gratings, in particular to an oblique double-layer grating based on RGB (red, green and blue) three-primary-color wide spectrum high-efficiency polarization independence under a normal incidence condition.

Background

With the continuous improvement of the living standard of people, the requirements of people on visual experience are higher and higher, so that the people hope to bring more real feeling, and the 3D display technology can just meet the requirement. Binocular parallax is the basic principle of naked eye technology, and the left eye and the right eye can achieve the three-dimensional effect after seeing object images at different angles and being processed and synthesized by human brain. The traditional realization method realizes two viewpoints by using parallax barrier and cylindrical lens technology, and the design is easy to form ghost images and blur, and can only be viewed at a specific position and angle, so that the experience is very poor. However, multiple viewpoints and continuous parallax can be realized through the grating array, and a very good user experience can be provided. Therefore, the RGB-based wide-spectrum high-efficiency polarization-independent oblique double-layer grating has very important research prospects and practical values in the fields of three-dimensional screen display technology and the like.

The three-dimensional display technology has very important application prospect as the very popular screen display technology at present. The holographic technology can only be made in a smaller area, and compared with the holographic technology, the inclined grating can be made in a very large area, so that the inclined double-layer grating which can efficiently transmit RGB (red, green and blue) three primary colors and has an asymmetric structure plays an important role in the three-dimensional display technology. Fused silica and MgF₂As ideal grating materials, the grating materials have very high optical quality, stable performance, higher damage threshold and very wide transmission spectrum, and the high-efficiency inclined double-layer grating designed in the way has the advantages of simple structure, simple and convenient process flow and easy large-size manufacturing and processing. Therefore, the etching of the high-density deep etching grating has very wide application prospect for the three-dimensional display technology. For high density gratings, one common mode of incidence is normal incidence, i.e., the angle of incidence is zero degrees.

Changhe Zhou et al have designed a-1 level high-efficiency transmission slanted double-layer grating under the vertical incidence [ fuchanghe, li shu, high-efficiency slanted double-layer grating, CN103675969B ], which has a large wavelength bandwidth and a large incident angle bandwidth, but because the slant angle is large (68-69 degrees), the processing is not easy, and therefore it is urgently needed to design a slanted double-layer grating convenient to process. The oblique double-layer grating is based on a rectangular transmission type grating which is vertically incident, when light beams vertically irradiate the oblique double-layer grating, due to the fact that the oblique double-layer grating has asymmetric characteristics in structure, transmitted light energy can be asymmetrically distributed, meanwhile, the oblique double-layer grating has more variables, the oblique double-layer grating has more design freedom, and-1-level high-efficiency transmission of three wave bands of RGB three primary colors can be achieved under the same grating structure.

The inclined double-layer grating can be processed into a double-layer grating with an inclined groove shape on a quartz substrate by utilizing a microelectronic deep etching process. Since high density tilted gratings cannot be interpreted analytically simply using the formula of scalar grating diffraction theory, we need to use the formula of vector diffraction theory for interpretation. Through maxwell equations in vector form and combining with the boundary conditions of the grating, a computer code program is written for accurate and rapid calculation, and optimization is performed by using a simulated annealing algorithm [ w.goffe et al, j.economics 60,65-99(1994) ] so as to obtain an ideal result. The diffraction problem of this type of high density grating is best solved by the rigorous coupled wave analysis method (RCWA) by Moharam et al [ M.G.Moharam et al.J.Opt.Soc.Am.A., 12,1077(1995) ]. At present, as known from the research of the prior art, no design for realizing vertical incidence lower-1 level high-efficiency transmission by using the same grating structure according to the wavelengths of RGB three primary colors (the central wavelengths are respectively 420 nanometers of blue light, 526 nanometers of green light and 620 nanometers of red light) exists.

Disclosure of Invention

The invention aims to solve the defects in the prior art and provides an efficient polarization-independent tilted double-layer grating based on RGB three-primary-color wide spectrum. The inclined double-layer grating structure can be simultaneously suitable for the wavelengths of RGB (red, green and blue) three primary colors, polarization independence is realized during vertical incidence, energy is mainly distributed on-1-level transmission light, the diffraction efficiency of the-1-level transmission light of the RGB three primary colors is greater than 80% within the wavelength bandwidth of 454-630 nanometers, the highest efficiency can reach 97%, and the 0-level transmission efficiency is about 10%.

The purpose of the invention can be achieved by adopting the following technical scheme:

the high-efficiency polarization-independent oblique double-layer grating based on RGB (red, green and blue) three-primary-color wide spectrum is suitable for high-efficiency polarization-independent oblique double-layer gratings with central wavelengths of 460 nanometers, 526 nanometers and 620 nanometers of blue light, and the substrate of the oblique double-layer grating is quartzOne layer of material is MgF₂Depth of h₁The second layer is made of quartz with a depth h₂The grating layer formed by the first layer material and the second layer material is a grating structure with a certain inclination angle, the grating structure has a wavelength bandwidth of 454-630 nanometers under the normal incidence condition, the period d of the inclined double-layer grating is 706-727 nanometers, the ridge width b is 396-418 nanometers, the inclination angle theta is 18-19 degrees, and the grating depth h is₁Is 452 to 504 nanometers, and the grating depth h₂691 to 743 nm.

Furthermore, the period d of the inclined double-layer grating is 726.1 nanometers, the ridge width b is 416.9 nanometers, the inclination angle theta of the grating is 18.2 degrees, and the grating depth h is₁484.6 nm, grating depth h₂723.7 nm.

Compared with the prior art, the invention has the following advantages and effects:

the invention discloses a diagonal double-layer grating which has the grating period d of 726.1 nanometers, the ridge width b of 574.2 degrees, the grating inclination angle theta of 18.2 degrees and the first layer grating depth h₁484.6 nm, second layer grating depth h₂723.7 nm, the diffraction efficiency for the-1 st order transmitted light is TE blue (460 nm): 85.16%, TE green light (526 nm): 92.55%, TE Red (620 nm): 89.36 percent; TM blue light (460 nm): 87.87%, TM green light (526 nm): 95.60%, TM red (620 nm): 88.94 percent, and the 0-level transmission efficiency is less than 9 percent. The invention has the advantages of flexible use, high diffraction efficiency, good uniformity and the like, is an ideal diffraction optical element with very wide applicability, can be processed and manufactured by an electron beam direct writing technology and a microelectronic deep etching process, can realize large-scale and large-area manufacturing, has low production cost, and has very stable and reliable performance of the etched grating, thereby having very important application prospect.

Drawings

FIG. 1 is a schematic diagram of a geometry of a high efficiency polarization independent slanted double layer grating based on RGB three primary color bands at normal incidence as disclosed in an embodiment of the present invention;

in FIG. 1, 1-represents the incident beam, 2-the emergent beam, and 3-the refractive indexIs n ₁1 uniform air layer, 4-for the second layer grating region (refractive index n)_r2) And 5-represents the grating region of the first layer (refractive index n)_r1) 6-represents a refractive index of n₂1.45 uniform quartz area, d-represents the grating period, b-represents the grating ridge width, θ -represents the tilt angle of the grating, h₁-represents a refractive index n of the medium_r1Depth of grating of h₂-represents a refractive index n of the medium_r2The grating depth of (a);

FIG. 2 shows a-1-grade high-efficiency tilted double-layer grating (refractive index of quartz 1.45, MgF) with a wavelength of 454-630 nm₂Refractive index of 1.379), grating period d of 726.1 nm, ridge width b of 574.2, grating inclination angle theta of 18.2 degrees, and grating depth h₁484.6 nm, grating depth h₂A graphical representation of diffraction efficiency at 723.7 nm as a function of wavelength.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples

Referring to fig. 1, fig. 1 is a geometric structure diagram of a high-efficiency polarization-independent slanted double-layer grating based on RGB three-primary-color bands according to an embodiment of the present invention. In FIG. 1, 1-represents the incident beam, 2-the emergent beam, and 3-the refractive index n ₁1 uniform air layer, 4-for the second layer grating region (refractive index n)_r2) 5-represents the first layer grating region (refractive index n)_r1) 6-represents a refractive index of n₂1.45 uniform quartz area. d represents the grating period, b represents the grating ridge width, theta is the tilt angle of the grating, h₁Representing a medium with a refractive index n_r1Depth of grating of h₂Representative of a refractive index of the medium ofn_r2The grating depth of (a). As can be seen from the figure, the grating is used for the inclined double-layer grating which has high-efficiency diffraction and is irrelevant to polarization and has three primary colors of RGB (red, green and red light) under the condition of vertical incidence, the period d of the grating is 706-727 nanometers, the ridge width b is 396-418 nanometers, the inclination angle theta is 18-19 degrees, and the grating depth h is₁Is 452 to 504 nanometers, and the grating depth h₂691-743 nm, the wavelength bandwidth of the polarization-independent grating is 454-630 nm.

Under the oblique double-layer grating structure shown in fig. 1, the diffraction efficiency of the oblique double-layer grating in the central wavelength band of the RGB three primary colors is calculated by the strict coupled wave theory [ prior art 3 ]; and then, optimizing by adopting a simulated annealing algorithm (prior art 2) so as to obtain the-1-level high-efficiency diffraction inclined double-layer grating structure.

FIG. 2 is a graph of the diffraction efficiency of the-1 st order transmitted light of the present invention as a function of wavelength over the red, green, and blue bands.

The-1-level high-efficiency oblique double-layer grating based on the polarization-independent vertical incidence of the RGB three-primary-color wave band disclosed by the embodiment has the advantages of flexibility in use, high diffraction efficiency, good uniformity and the like, is an ideal diffractive optical element with very wide applicability, can be manufactured in a large scale and in a large area through an electron beam direct writing technology and a microelectronic deep etching process, is low in production cost, and has very important application prospects, and the performance of the etched grating is very stable and reliable.

Table 1 shows a series of examples of the present invention, where d is the grating period, b is the grating ridge width, θ is the tilt angle of the grating, and h₁A medium having a refractive index n_r1Depth of grating of h₂Is a medium with a refractive index n_r2η is the diffraction efficiency of the emergent light. In the process of manufacturing the high-efficiency polarization-independent inclined double-layer grating for the RGB three-primary-color waveband, the period d, the ridge width b, the inclination angle theta and the grating depth h of the grating are selected properly₁And grating depth h₂High efficiency diffraction can be obtained within a certain bandwidth.

TABLE 1 diffraction efficiency numerical table for different parameters of tilted bilayer grating

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. The high-efficiency polarization-independent oblique double-layer grating based on RGB (red, green and blue) three-primary-color wide spectrum is suitable for high-efficiency polarization-independent oblique double-layer gratings with central wavelengths of 460 nanometers, 526 nanometers and 620 nanometers of green light, and is characterized in that the substrate of the oblique double-layer grating is quartz, and the first layer is made of MgF (magnesium fluoride) and is made of MgF (magnesium fluoride)₂Depth of h₁The second layer is made of quartz with a depth h₂The grating layer formed by the first layer material and the second layer material is a grating structure with a certain inclination angle, the grating structure has a wavelength bandwidth of 454-630 nanometers under the normal incidence condition, the period d of the inclined double-layer grating is 706-727 nanometers, the ridge width b is 396-418 nanometers, the inclination angle theta is 18-19 degrees, and the grating depth h is₁Is 452 to 504 nanometers, and the grating depth h₂691 to 743 nm.

2. The RGB three primary color-based wide-spectrum high-efficiency polarization-independent slanted double-layered grating according to claim 1,the period d of the inclined double-layer grating is 726.1 nanometers, the ridge width b is 416.9 nanometers, the inclination angle theta of the grating is 18.2 degrees, and the depth h of the grating is₁484.6 nm, grating depth h₂723.7 nm.