WO2022041312A1 - 低偏振高衍射效率金属反射浸没光栅及光学系统 - Google Patents

低偏振高衍射效率金属反射浸没光栅及光学系统 Download PDF

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WO2022041312A1
WO2022041312A1 PCT/CN2020/113661 CN2020113661W WO2022041312A1 WO 2022041312 A1 WO2022041312 A1 WO 2022041312A1 CN 2020113661 W CN2020113661 W CN 2020113661W WO 2022041312 A1 WO2022041312 A1 WO 2022041312A1
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layer
grating
dielectric layer
metal reflection
diffraction efficiency
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潘俏
沈为民
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Suzhou University
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Suzhou University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials

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  • the invention relates to the technical field of gratings, in particular to a metal reflection immersion grating with low polarization and high diffraction efficiency and an optical system.
  • grating-type hyperspectral imaging instruments especially for spectrometers used for atmospheric composition detection
  • gratings with low polarization, high diffraction efficiency, and high dispersion characteristics are one of the core components for the instrument to achieve high-precision detection and inversion.
  • the volume and mass of the system increase dramatically.
  • E.Hulthén proposed the concept of immersion grating (see E.Hulthén, and H.Neuhaus, Nature, 1954, 173(4401):442-443.), when the grating surface is immersed in a medium with a refractive index of n, its spectrum The resolving power is n-fold higher than without immersion.
  • the linear dimension of the immersion grating will be reduced by a factor of n, and the size of other optical components in the spectrometer will also be reduced, which greatly reduces the overall size of the grating. size and mass of the machine.
  • metal reflection gratings can achieve high diffraction efficiency in a wide wavelength range.
  • the grating groove shape can achieve both low polarization and high diffraction efficiency only if the grating groove shape meets the conditions of large duty cycle and high depth period ratio.
  • the groove tolerance of the grating has a great influence, which poses a great challenge to the processing and manufacturing process of the grating. Therefore, it is of research significance and application value to design an easy-to-implement low-polarization and high-diffraction-efficiency metal reflective immersion grating.
  • the technical problem to be solved by the present invention is to provide a metal reflection immersion grating with low polarization and high diffraction efficiency and an optical system, which can realize low polarization and high diffraction efficiency, reduce the difficulty of the manufacturing process, and have important applications in the field of high-resolution atmospheric detection. value.
  • the present invention provides a low-polarization and high-diffraction-efficiency metal reflection immersion grating, which includes a grating layer, and the grating layer includes a plurality of first grooves arranged in an array;
  • a dielectric layer covering the surface of the grating layer with an equal thickness, the thickness of the dielectric layer is less than the groove depth of the grating layer, and a second groove body is formed on the surface of the dielectric layer;
  • a metal reflective layer which is located on the side of the dielectric layer away from the grating layer, and one side of the metal reflective layer fills the second groove body;
  • a first interface is formed between the grating layer and the dielectric layer, and a second interface is formed between the dielectric layer and the metal reflection layer;
  • the incident light is incident toward the first interface through the interior of the grating layer, and a diffraction effect occurs between the first interface, the dielectric layer and the second interface to generate diffracted light, and the diffracted light is
  • the metal reflective layer reflects and emerges from the interior of the grating layer.
  • the thickness a of the dielectric layer, the duty cycle f of the grating layer, and the duty cycle t of the metal reflective layer satisfy the constraints:
  • the period d of the grating layer is 700-1050 nm
  • the groove depth-to-period ratio h of the grating layer is 0.7-0.9
  • the duty cycle f of the grating layer is in the range of 0.2-0.4
  • the The duty ratio t of the metal reflective layer is 0.2-0.45
  • the thickness a of the dielectric layer is 80-250 nm.
  • the groove density of the grating layer is 950-1430 line pairs/mm.
  • the grating layer is made of fused silica optical glass.
  • the dielectric layer is made of oxide material, and the real part of the complex refractive index of the dielectric layer ranges from 1.6 to 2.5, and the imaginary part ranges from 0 to 1*10 -2 .
  • the dielectric layer is Al 2 O 3 , HfO 2 , Ta 2 O 5 or TiO 2 .
  • the material of the metal reflective layer is gold, silver or aluminum.
  • the present invention also discloses an optical system, comprising the above-mentioned immersion grating, characterized in that the incident angle of the incident light is 40°-50°.
  • the bandwidth of the incident light is 10-120 nm, and the wavelength of the incident light is 1550-2400 nm.
  • the -1st order diffraction efficiency of the immersion grating TE polarization and TM polarization of the present invention is higher than 80% in the entire working bandwidth, the relative linear polarization degree is less than 1.5%, and the diffraction efficiency is higher than 85% at the central wavelength of the working bandwidth.
  • the degree of linear polarization is less than 1%.
  • the immersion grating of the present invention can achieve low polarization and high diffraction efficiency in a wide bandwidth (10-120 nanometers).
  • the immersion grating of the present invention effectively reduces the duty ratio of the grating under the conditions of high groove density and large incident angle, reduces the difficulty of the manufacturing process, and has important application value in the field of high-resolution atmospheric detection.
  • Fig. 1 is the structural representation of the present invention
  • Fig. 2 is the variation curve of the average diffraction efficiency at the center wavelength of the working band in the first embodiment with the thickness a of the dielectric layer;
  • Fig. 3 is the variation curve of the relative linear polarization degree DP at the center wavelength of the working band in the first embodiment with the thickness a of the dielectric layer;
  • Fig. 4 is the diffraction efficiency and relative linear polarization curve of the immersion grating that a is 115nm in embodiment one;
  • Fig. 5 is the variation trend of the average diffraction efficiency at the center wavelength of the working band in the second embodiment with the thickness a of the dielectric layer and the duty cycle f of the grating layer;
  • Fig. 7 is the diffraction efficiency and relative linear polarization curve of the immersion grating when f is 0.2 and a is 180 nm in Example 2;
  • Fig. 10 is the curve of the diffraction efficiency and the relative linear polarization degree of the immersion grating when f is 0.25 and a is 192 nm in Example 3.
  • the present invention discloses a metal reflection immersion grating with low polarization and high diffraction efficiency, which includes a grating layer 3 , a dielectric layer 4 and a metal reflection layer 5 .
  • the grating layer 3 includes a plurality of first groove bodies arranged in an array, and the first groove bodies are rectangular grooves.
  • the grating structure is directly etched on the surface of the base material where the grating layer 3 is located.
  • the dielectric layer 4 covers the surface of the grating layer 3 with an equal thickness, and the thickness of the dielectric layer 4 is smaller than the groove depth of the grating layer 3, that is, the dielectric layer 4 does not fill the first groove of the grating layer 3. In this way, the surface of the dielectric layer 4 forms
  • the second groove body has the same shape as the first groove body, and the dimensions are different.
  • the metal reflective layer 5 is located on the side of the dielectric layer 4 away from the grating layer 3, and the side of the metal reflective layer 5 fills the second groove.
  • the metal reflective layer 5 is generally thicker, so as to ensure that diffracted light can be reflected. In this way, the metal reflective layer 5 forms the inverse structure of the dielectric layer 4 .
  • a first interface 6 is formed between the grating layer 3 and the dielectric layer 4
  • a second interface 7 is formed between the dielectric layer 4 and the metal reflection layer 5 .
  • the incident light enters the direction of the first interface 6 through the interior of the grating layer 3, and a diffraction effect occurs between the first interface 6, the dielectric layer 4 and the second interface 7 to generate diffracted light, and the diffracted light passes through the metal reflective layer. 5 is reflected and emerges from the interior of the grating layer 3 .
  • ⁇ is the incident angle of the light beam
  • d is the period of the grating layer 3
  • the corresponding groove density is 1/d
  • a is the thickness of the dielectric layer 4 .
  • the thickness a of the dielectric layer 4, the duty cycle f of the grating layer 3 and the duty cycle t of the metal reflective layer 5 satisfy the constraints:
  • the TE polarized incident photoelectric field vector vibration direction is perpendicular to the incident plane, and the diffraction efficiency is ⁇ TE .
  • the vibration direction of the magnetic field vector of the TM polarized incident light is perpendicular to the incident plane, and the diffraction efficiency is ⁇ TM .
  • the relative linear polarization degree DP is defined as follows:
  • the period d of the grating layer 3 is 700-1050 nm, the groove depth to period ratio h of the grating layer 3 is 0.7-0.9, the duty cycle f of the grating layer 3 is in the range of 0.2-0.4; the duty cycle t of the metal reflective layer 5 is 0.2-0.45; the thickness a of the dielectric layer 4 is 80-250 nm.
  • the groove density of the grating layer 3 is 950-1430 line pairs/mm.
  • the grating layer 3 is made of fused silica optical glass.
  • the dielectric layer 4 is made of oxide material, the real part of the complex refractive index of the dielectric layer 4 ranges from 1.6 to 2.5, and the imaginary part ranges from 0 to 1*10 -2 .
  • the dielectric layer 4 is Al 2 O 3 , HfO 2 , Ta 2 O 5 or TiO 2 .
  • the material of the metal reflection layer 5 is gold, silver or aluminum.
  • the present invention also discloses an optical system, comprising the above-mentioned immersion grating, the incident angle of the incident light is 40°-50°; the bandwidth of the incident light is 10-120nm, and the wavelength of the incident light is 1550-2400nm .
  • the present invention can obtain immersion gratings with different diffraction efficiencies and relative linear polarization degrees by changing the film layer structure and film layer material of the immersion grating, which will be explained and described below with reference to specific embodiments.
  • the material of the grating layer 3 is fused silica optical glass, the material of the dielectric layer 4 is TiO 2 , the metal reflective layer 5 is silver, the period d of the grating layer 3 is 690 nanometers, the groove depth to period ratio h of the grating layer 3 is 0.8, The duty ratio f of the grating layer 3 is 0.3, and the duty ratio t of the metal reflective layer 5 is 0.37.
  • the incident angle ⁇ of the incident light in the grating layer 3 is 47°.
  • FIG. 2 it is the variation curve of the average diffraction efficiency at the center wavelength of the working band with the thickness a of the dielectric layer 4 .
  • Fig. 3 is the change curve of the relative linear polarization degree DP at the central wavelength of the working band with the thickness a of the dielectric layer 4; it can be seen from Fig. 2 and Fig. 3 that when the thickness a of the dielectric layer is 115 nm, the immersion grating has better performance Diffraction efficiency and relative linear polarization degree.
  • FIG. 4 which is the diffraction efficiency and relative linear polarization degree curves of the immersion grating with the thickness a of the dielectric layer 4 of 115 nm in the present embodiment as a function of wavelength.
  • the -1st order diffraction efficiency of TE polarization and TM polarization are both higher than 80%
  • the relative linear polarization degree is less than 1%
  • the diffraction efficiency of TE polarization and TM polarization at the central wavelength is higher than 85% %
  • the relative linear polarization degree is close to 0.
  • the grating layer 3 is made of fused silica optical glass
  • the dielectric layer 4 is Al 2 O 3
  • the metal reflective layer 5 is silver
  • the period d of the grating layer 3 is 690 nm
  • the groove depth to period ratio h of the grating layer 3 is 0.8
  • the duty ratio t of the metal reflection layer 5 is 0.2.
  • the incident angle ⁇ of the incident light in the grating layer 3 is 48°.
  • Fig. 5 is the variation trend of the average diffraction efficiency at the center wavelength of the working band with the thickness a of the dielectric layer 4 and the duty cycle f of the grating layer 3 in the second embodiment
  • Fig. 6 is the relative linear polarization degree DP at the center wavelength of the working band
  • the colors in the figure represent the average diffraction efficiency and the relative linear polarization degree. 5 and 6, it can be seen that the duty cycle f of the grating layer 3 is 0.2, the thickness a of the dielectric layer 4 is 180 nm, and the immersion grating has better diffraction efficiency and relative linear polarization degree.
  • the duty ratio f of the grating layer 3 is 0.2, and the thickness a of the dielectric layer 4 is 180 nm
  • the diffraction efficiency and relative linear polarization degree curves of the immersion grating are shown.
  • the working band of the grating is 1595-1625 nanometers. In the range of 1595-1625 nanometers, the -1 order diffraction efficiencies of TE polarization and TM polarization are both higher than 85%, and the relative linear polarization degree is less than 1%.
  • the material of the grating layer 3 is fused silica optical glass, the medium layer 4 is TiO 2 , the metal reflective layer 5 is silver, the period d of the grating layer 3 is 1010 nm, the groove depth to period ratio h of the grating layer 3 is 0.8, and the metal reflective layer is The duty cycle t of 5 is 0.4.
  • the incident angle ⁇ of the incident light in the grating layer 3 is 43°.
  • Fig. 8 is the variation trend of the average diffraction efficiency at the center wavelength of the working band in Example 3 with the thickness a of the dielectric layer 4 and the duty cycle f of the grating layer 3; the relative linear polarization DP at the center wavelength of Fig. 9 varies with the dielectric layer
  • the changing trend of the thickness a of 4 and the duty cycle f of the grating layer 3, the colors in the figure represent the average diffraction efficiency and the relative linear polarization degree. 8 and 9, when the duty cycle of the grating layer 3 is 0.25 and the thickness a of the dielectric layer 4 is 192 nm, the immersion grating has better diffraction efficiency and relative linear polarization degree.
  • the diffraction efficiency and relative linear polarization degree curves of the immersion grating are shown.
  • the working band of the grating is 2250-2350 nanometers. In the range of 2250-2350 nm, the -1st order diffraction efficiency of TE polarization and TM polarization are both higher than 82%, the relative linear polarization degree is less than 1.5%, and the diffraction efficiency of TE polarization and TM polarization at the central wavelength is higher than 85%, The relative linear polarization degree is close to 0.

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Abstract

本发明公开了一种低偏振高衍射效率金属反射浸没光栅及光学系统，包括：光栅层，光栅层包括多个阵列排布的第一槽体；介质层，其等厚度覆盖在光栅层表面，介质层的厚度小于光栅层的槽深，介质层表面形成第二槽体；金属反射层，其位于介质层远离光栅层的一侧，金属反射层的一侧填覆第二槽体；光栅层与介质层之间形成第一交界面，介质层与金属反射层之间形成第二交界面；入射光经光栅层的内部朝向第一交界面方向入射，并在第一交界面、介质层和第二交界面之间发生衍射效应以产生衍射光，衍射光经金属反射层反射并从光栅层的内部出射。其能实现低偏振和高衍射效率，降低制造工艺难度，在高分辨率大气探测领域具有重要的应用价值。

Description

低偏振高衍射效率金属反射浸没光栅及光学系统 技术领域
本发明涉及光栅技术领域，具体涉及一种低偏振高衍射效率金属反射浸没光栅及光学系统。
背景技术
在光栅型高光谱成像仪器中，特别是针对用于大气成分探测的光谱仪，具有低偏振、高衍射效率、高色散特点的光栅是仪器实现高精度探测和反演的核心元件之一。随着仪器光谱分辨率要求提高，系统的体积和质量急剧增加。E.Hulthén提出浸没光栅的概念(参见E.Hulthén,and H.Neuhaus,Nature,1954,173(4401):442-443.)，当光栅面浸没在折射率为n的介质中时，其光谱分辨能力比未浸没时增加n倍。这就意味着，相比于具有同等色散能力的非浸没光栅，浸没光栅的线度尺寸将减小n倍，光谱仪中与之匹配的其他光学器件尺寸也随之减小，从而大大降低了整机的体积和质量。此外，金属反射光栅可以在较宽的波段范围内实现高衍射效率。然而，对于大角度入射的高槽密度金属反射浸没光栅，光栅槽形只有满足大占空比和高深周期比的条件，才能同时实现低偏振和高衍射效率，并且此时偏振度和衍射效率受光栅的槽形公差影响较大，这对光栅的加工制造工艺提出了极大的挑战。为此，设计一种易于实现的低偏振高衍射效率金属反射浸没光栅是具有研究意义和应用价值的。
发明内容
本发明要解决的技术问题是提供一种低偏振高衍射效率金属反射浸没光栅及光学系统，其能实现低偏振和高衍射效率，降低制造工艺难度，在高分辨率 大气探测领域具有重要的应用价值。
为了解决上述技术问题，本发明提供了一种低偏振高衍射效率金属反射浸没光栅，包括光栅层，所述光栅层包括多个阵列排布的第一槽体；
介质层，其等厚度覆盖在所述光栅层表面，所述介质层的厚度小于所述光栅层的槽深，所述介质层表面形成第二槽体；
金属反射层，其位于所述介质层远离所述光栅层的一侧，所述金属反射层的一侧填覆所述第二槽体；
所述光栅层与所述介质层之间形成第一交界面，所述介质层与所述金属反射层之间形成第二交界面；
入射光经所述光栅层的内部朝向所述第一交界面方向入射，并在所述第一交界面、介质层和第二交界面之间发生衍射效应以产生衍射光，所述衍射光经所述金属反射层反射并从光栅层的内部出射。
作为优选的，所述介质层的厚度a、所述光栅层的占空比f和所述金属反射层的占空比t满足约束条件：
Figure PCTCN2020113661-appb-000001
且
Figure PCTCN2020113661-appb-000002
作为优选的，所述光栅层的周期d为700-1050nm，所述光栅层的槽深与周期比h为0.7-0.9，所述光栅层的占空比f的范围为0.2-0.4；所述金属反射层的占空比t为0.2-0.45；所述介质层的厚度a为80-250nm。
作为优选的，所述光栅层的槽密度为950-1430线对/毫米。
作为优选的，所述光栅层由熔融石英光学玻璃制备。
作为优选的，所述介质层为氧化物材料制备，所述介质层的复折射率实部范围为1.6-2.5，虚部范围为0-1*10 -2。
作为优选的，所述介质层为Al 2O 3、HfO 2、Ta 2O 5或TiO 2。
作为优选的，所述金属反射层的材料为金、银或铝。
本发明还公开了一种光学系统，包括上述的浸没光栅，其特征在于，所述入射光的入射角为40°-50°。
作为优选的，所述入射光的带宽为10-120nm，所述入射光波长在1550-2400nm。
本发明的有益效果：
1、本发明的浸没光栅TE偏振和TM偏振的-1级衍射效率在整个工作带宽内高于80％，相对线偏振度小于1.5％，在工作带宽中心波长处衍射效率高于85％，相对线偏振度小于1％。
2、本发明的浸没光栅在较宽带宽(10～120纳米)均能实现低偏振和高衍射效率。
3、本发明的浸没光栅有效降低高槽密度、大入射角条件下的光栅占空比，降低制造工艺难度，在高分辨率大气探测领域具有重要的应用价值。
附图说明
图1为本发明的结构示意图；
图2为实施例一中工作波段中心波长处的平均衍射效率随介质层的厚度a的变化曲线；
图3为实施例一中工作波段中心波长处的相对线偏振度DP随介质层的厚度a的变化曲线；
图4为实施例一中a为115nm的浸没光栅的衍射效率和相对线偏振度曲线；
图5为实施例二中工作波段中心波长处的平均衍射效率随介质层的厚度a和光栅层的占空比f的变化趋势；
图6为实施例二中工作波段中心波长处的相对线偏振度DP随介质层的厚度a和光栅层的占空比f的变化趋势；
图7为实施例二中f为0.2和a为180nm时，浸没光栅的衍射效率和相对线偏振度曲线；
图8为实施例三中工作波段中心波长处的平均衍射效率随介质层的厚度a和光栅层的占空比f的变化趋势；
图9为实施例三中中心波长处的相对线偏振度DP随介质层的厚度a和光栅层的占空比f的变化趋势；
图10为实施例三中f为0.25，a为192nm时，浸没光栅的衍射效率和相对线偏振度曲线。
图中标号说明：1、入射光；2、衍射光；3、光栅层；4、介质层；5、金属反射层；6、第一交界面；7、第二交界面。
具体实施方式
下面结合附图和具体实施例对本发明作进一步说明，以使本领域的技术人员可以更好地理解本发明并能予以实施，但所举实施例不作为对本发明的限定。
参照图1所示，本发明公开了一种低偏振高衍射效率金属反射浸没光栅，包括光栅层3、介质层4和金属反射层5。
光栅层3包括多个阵列排布的第一槽体，第一槽体为矩形槽。光栅结构直接刻蚀在光栅层3所在基底材料的表面。
介质层4等厚度覆盖在所述光栅层3表面，介质层4的厚度小于光栅层3的槽深，即介质层4未填满光栅层3的第一槽体，如此，介质层4表面形成第二槽体，第二槽体与第一槽体的形貌相同，尺寸不一。
金属反射层5位于介质层4远离光栅层3的一侧，金属反射层5的一侧填 覆第二槽体。金属反射层5一般设置的较厚，从而保证能够反射衍射光。如此，金属反射层5形成了介质层4的反结构。
光栅层3与介质层4之间形成第一交界面6，介质层4与金属反射层5之间形成第二交界面7。入射光经光栅层3的内部朝向第一交界面6方向入射，并在第一交界面6、介质层4和第二交界面7之间发生衍射效应以产生衍射光，衍射光经金属反射层5反射并从光栅层3的内部出射。
通过上述的这种浸没光栅，在较宽带宽(10-120纳米)均能实现低偏振和高衍射效率，其有效降低高槽密度、大入射角条件下的光栅占空比，降低制造工艺难度，在高分辨率大气探测领域具有重要的应用价值。
结合图1，定义如下参数：
θ为光束入射角，d为光栅层3的周期，对应的槽密度为1/d，a为介质层4的厚度。h d为第一槽体的深度，光栅层3的槽深与周期比h满足条件：h d＝h*d。
f d为光栅层3的第一槽体的宽度，光栅层3的占空比f满足条件：f d＝f*d。
t d为金属反射层5内金属槽的宽度，金属槽的的占空比t满足条件：t d＝t*d，如此t d＝f d-2*a。
本发明中，介质层4的厚度a、光栅层3的占空比f和金属反射层5的占空比t满足约束条件：
Figure PCTCN2020113661-appb-000003
且
Figure PCTCN2020113661-appb-000004
TE偏振的入射光电场矢量振动方向垂直入射面，衍射效率为η TE。TM偏振的入射光磁场矢量振动方向垂直入射面，衍射效率为η TM。那么，相对线偏振度DP的定义如下：
Figure PCTCN2020113661-appb-000005
光栅层3的周期d为700-1050nm，光栅层3的槽深与周期比h为0.7-0.9，光栅层3的占空比f的范围为0.2-0.4；金属反射层5的占空比t为0.2-0.45；介质层4的厚度a为80-250nm。光栅层3的槽密度为950-1430线对/毫米。
光栅层3由熔融石英光学玻璃制备。
介质层4为氧化物材料制备，介质层4的复折射率实部范围为1.6-2.5，虚部范围为0-1*10 -2。介质层4为Al 2O 3、HfO 2、Ta 2O 5或TiO 2。
金属反射层5的材料为金、银或铝。
本发明还公开了一种光学系统，包括上述的浸没光栅，所述入射光的入射角为40°-50°；所述入射光的带宽为10-120nm，所述入射光波长在1550-2400nm。
本发明通过改变浸没光栅的膜层结构及膜层材料，可以获取不同的衍射效率和相对线偏振度的浸没光栅，以下结合具体的实施例来解释与说明。
实施例一
光栅层3的材料为熔融石英光学玻璃，介质层4的材料为TiO 2，金属反射层5为银，光栅层3的周期d为690纳米，光栅层3的槽深与周期比h为0.8，光栅层3的占空比f为0.3，金属反射层5的占空比t为0.37。入射光在光栅层3内的入射角θ为47°。
参见图2所示，为工作波段中心波长处的平均衍射效率随介质层4的厚度a的变化曲线。图3是工作波段中心波长处的相对线偏振度DP随介质层4的厚度a的变化曲线；结合图2和图3可以看出，在介质层厚度a为115纳米时，浸没光栅具有较好的衍射效率和相对线偏振度。
参照图4所示，其为本实施例中介质层4的厚度a为115纳米的浸没光栅随波长变化的衍射效率和相对线偏振度曲线。其中，在1570～1635纳米范围内， TE偏振和TM偏振的-1级衍射效率均高于80％，相对线偏振度小于1％，在中心波长处TE偏振和TM偏振的衍射效率高于85％，相对线偏振度接近0。
实施例二
光栅层3的材料为熔融石英光学玻璃，介质层4为Al 2O 3，金属反射层5为银，光栅层3的周期d为690纳米，光栅层3的槽深与周期比h为0.8，金属反射层5的占空比t为0.2。入射光在光栅层3内的入射角θ为48°。
图5是实施例二中工作波段中心波长处的平均衍射效率随介质层4的厚度a和光栅层3的占空比f的变化趋势；图6是工作波段中心波长处的相对线偏振度DP随介质层4的厚度a和光栅层3的占空比f的变化趋势，图中颜色表示平均衍射效率和相对线偏振度的大小。结合图5和图6所示，可以看出光栅层3的占空比f为0.2，介质层4的厚度a为180纳米，浸没光栅具有较好的衍射效率和相对线偏振度。
参见附图7，为光栅层3的占空比f为0.2，介质层4的厚度a为180纳米时，浸没光栅的衍射效率和相对线偏振度曲线。该光栅的工作波段为1595～1625纳米，在1595～1625纳米范围内，TE偏振和TM偏振的-1级衍射效率均高于85％，相对线偏振度小于1％。
实施例三
光栅层3的材料为熔融石英光学玻璃，介质层4为TiO 2，金属反射层5为银，光栅层3周期d为1010纳米，光栅层3的槽深与周期比h为0.8，金属反射层5的占空比t为0.4。入射光在光栅层3内的入射角θ为43°。
图8是实施例三中工作波段中心波长处的平均衍射效率随介质层4的厚度a和光栅层3的占空比f的变化趋势；图9中心波长处的相对线偏振度DP随介质层4的厚度a和光栅层3的占空比f的变化趋势，图中颜色表示平均衍射效 率和相对线偏振度的大小。结合图8和图9所示，光栅层3的占空比为0.25，介质层4的厚度a为192纳米时，浸没光栅具有较好的衍射效率和相对线偏振度。
参见附图10所示，为光栅层3的占空比为0.25，介质层4的厚度a为192纳米时，浸没光栅的衍射效率和相对线偏振度曲线。该光栅的工作波段为2250～2350纳米。在2250～2350纳米范围内，TE偏振和TM偏振的-1级衍射效率均高于82％，相对线偏振度小于1.5％，在中心波长处TE偏振和TM偏振的衍射效率高于85％，相对线偏振度接近0。
以上所述实施例仅是为充分说明本发明而所举的较佳的实施例，本发明的保护范围不限于此。本技术领域的技术人员在本发明基础上所作的等同替代或变换，均在本发明的保护范围之内。本发明的保护范围以权利要求书为准。

Claims (10)

  1. 一种低偏振高衍射效率金属反射浸没光栅，其特征在于，包括：
    光栅层，所述光栅层包括多个阵列排布的第一槽体；
    介质层，其等厚度覆盖在所述光栅层表面，所述介质层的厚度小于所述光栅层的槽深，所述介质层表面形成第二槽体；
    金属反射层，其位于所述介质层远离所述光栅层的一侧，所述金属反射层的一侧填覆所述第二槽体；
    所述光栅层与所述介质层之间形成第一交界面，所述介质层与所述金属反射层之间形成第二交界面；
    入射光经所述光栅层的内部朝向所述第一交界面方向入射，并在所述第一交界面、介质层和第二交界面之间发生衍射效应以产生衍射光，所述衍射光经所述金属反射层反射并从光栅层的内部出射。
  2. 如权利要求1所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述介质层的厚度a、所述光栅层的占空比f和所述金属反射层的占空比t满足约束条件：
    Figure PCTCN2020113661-appb-100001
    且
    Figure PCTCN2020113661-appb-100002
    其中，d为光栅层的周期。
  3. 如权利要求2所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述光栅层的周期d为700-1050nm，所述光栅层的槽深与周期比h为0.7-0.9，所述光栅层的占空比f的范围为0.2-0.4；
    所述金属反射层的占空比t为0.2-0.45；
    所述介质层的厚度a为80-250nm。
  4. 如权利要求3所述的低偏振高衍射效率金属反射浸没光栅，其特征在于， 所述光栅层的槽密度为950-1430线对/毫米。
  5. 如权利要求1所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述光栅层由熔融石英光学玻璃制备。
  6. 如权利要求1所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述介质层为氧化物材料制备，所述介质层的复折射率实部范围为1.6-2.5，虚部范围为0-1*10 -2。
  7. 如权利要求1所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述介质层为Al 2O 3、HfO 2、Ta 2O 5或TiO 2。
  8. 如权利要求1所述的低偏振高衍射效率金属反射浸没光栅，其特征在于，所述金属反射层的材料为金、银或铝。
  9. 一种光学系统，包括权利要求1-8任一项所述的浸没光栅，其特征在于，所述入射光的入射角为40°-50°。
  10. 如权利要求9所述的一种光学系统，其特征在于，所述入射光的带宽为10-120nm，所述入射光波长在1550-2400nm。
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