WO2023134248A1 - 基于超构光栅的多功能高效分束器 - Google Patents

基于超构光栅的多功能高效分束器 Download PDF

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WO2023134248A1
WO2023134248A1 PCT/CN2022/126123 CN2022126123W WO2023134248A1 WO 2023134248 A1 WO2023134248 A1 WO 2023134248A1 CN 2022126123 W CN2022126123 W CN 2022126123W WO 2023134248 A1 WO2023134248 A1 WO 2023134248A1
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beam splitter
grating
air
super
polarized light
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PCT/CN2022/126123
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French (fr)
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徐亚东
孙宝印
曹燕燕
金霞
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苏州大学
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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
    • 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
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials

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  • the invention belongs to the technical field of light beam transmission, and in particular relates to a multifunctional high-efficiency beam splitter based on a superstructured grating.
  • LBS Light Beam Splitters
  • PGMs optical phase-gradient metasurfaces
  • EM electromagnetic waves
  • the object of the present invention is to provide a multifunctional and efficient beam splitter based on a metagrating.
  • a multifunctional high-efficiency beam splitter based on a super-grating includes a number of periodically distributed super-gratings, the super-gratings include a number of dielectric layers distributed at intervals, and a plurality of The air slit, the thickness of the medium layer and the air slit are equal, the medium layer has different widths, the air slits have different widths, the phase delay of each supergrating spans a phase range of 2 ⁇ , and the distance between adjacent air slits The phase difference ⁇ is equal.
  • the beam splitter is used to realize the polarization splitting of the incident light beam, the incident light beam includes transverse electric polarized light and transverse magnetic polarized light, and the beam splitter can realize the total reflection of transverse electric polarized light and the diffraction order of transverse magnetic polarized light The lowest number of negative refractions.
  • the transverse magnetically polarized light only has a fundamental mode in the air slit, and satisfies:
  • ⁇ i is the propagation constant
  • the real part represents the propagating wave vector
  • the imaginary part represents the dissipation of surface plasmons in the air slit
  • ⁇ is the incident beam wavelength
  • ⁇ m is the dielectric constant of the dielectric layer
  • phase delay ⁇ i of the i-th air slit is:
  • ⁇ is the additional phase due to multiple reflections at the interface between the grating and air.
  • the material of the dielectric layer is silver
  • the dielectric constant ⁇ m -17.36+0.715i
  • the metagrating includes 5 air slits with widths of w 1 , w 2 , w 3 , w 4 , and w 5 respectively
  • the wavelength ⁇ of the incident light beam is 590 nm ⁇ 668 nm, and the incident angle is ⁇ i ⁇ (-74°, -7°).
  • the incident angle and reflection angle of the transverse magnetically polarized light on the meta-grating satisfy:
  • the reflection extinction ratio ERTE of the transverse electric polarized light is greater than 10 dB
  • the transmission extinction ratio ERTM of the transverse magnetic polarization light is greater than 132 dB.
  • the beam splitter of the present invention is based on the diffraction mechanism of the superstructured grating, can simultaneously realize high-efficiency beam splitting of energy and polarization, has broadband response, and is suitable for imaging systems and optical communication fields.
  • FIG. 1 is a schematic structural diagram of a multifunctional high-efficiency beam splitter based on a metagrating according to the present invention.
  • FIG. 2 is a graph showing the relationship between the phase delay ⁇ i and the air slit width w i in an embodiment of the present invention.
  • Fig. 3 a is the corresponding relationship graph between the incident angle of transverse magnetic polarized light (TM) and the diffraction efficiency of each diffraction order in one embodiment of the present invention
  • Fig. 3b is a graph of the corresponding relationship between the incident angle of transversely electrically polarized light (TE) and the diffraction efficiency of each diffraction order in an embodiment of the present invention
  • Figure 3c is a magnetic field simulation diagram of transverse magnetic polarization (TM) in an embodiment of the present invention.
  • Fig. 3d is a magnetic field simulation diagram of transverse electrically polarized light (TE) in an embodiment of the present invention.
  • Figure 4a is a graph showing the relationship between the reflection extinction ratio ER TE and the incident angle in an embodiment of the present invention
  • Fig. 4b is a graph showing the relationship between the transmission extinction ratio ER TE and the incident angle in an embodiment of the present invention
  • Fig. 5a is a graph of incident angle and T -1 order diffraction efficiency under different thicknesses in an embodiment of the present invention
  • Fig. 5b is a graph of incident angle and R 0 order diffraction efficiency under different thicknesses in an embodiment of the present invention
  • Figure 5c is a graph showing the relationship between absorption efficiency and thickness in an embodiment of the present invention.
  • PGMs are periodic gratings with supercells containing m cells with different optical responses that discretely introduce abrupt phase shifts (APS) that fully cover 2 ⁇ .
  • APS phase shifts
  • the introduced APS produces phase gradients (ie additional wave vectors) that alter the fundamental laws of reflection and refraction of light that occur at interfaces.
  • Diffraction effects are ubiquitous in PGMs, and higher-order diffractions are described by parity-dependent diffraction laws. Therefore, free control of the diffraction effect and its efficiency in PGMs is the key to improving the performance of PGM-based devices including beam splitters.
  • the LBS of the present invention is a pure plasmon PGM, and the required APS along the transport interface is introduced by adjusting the width of the air slit, which determines the propagating wave vector of the surface plasmon passing through it. It is demonstrated that the designed LBS can simultaneously achieve efficient beam splitting of energy and polarization with broadband and wide-angle response.
  • the ohmic loss of the metal plays an important role in determining the diffraction efficiency of each diffraction order on both the reflection and transmission sides of the TM polarization.
  • the LBS can also uniformly transfer the TM-polarized incident energy to the reflection and refraction sides.
  • the invention has fundamental significance for the research of PGM-based LBS, and the proposed design shows great application potential in the fields of integrated optical communication or optical measurement.
  • the beam splitter includes several periodically distributed super-gratings, and the structure of a single period super-grating is shown in Figure 1, the super-structure
  • the grating includes a number of dielectric layers 10 distributed at intervals, a plurality of air slits 20 are formed between the dielectric layers 10, the thickness of the dielectric layer and the air slits are equal, the dielectric layers have different widths, and the air slits have different widths.
  • the phase delay of each supergrating spans a phase range of 2 ⁇ , and the phase difference ⁇ between adjacent air slits is equal.
  • the beam splitter is used to realize the polarization splitting of the incident beam.
  • the incident beam includes transverse electric polarized light (TE) and transverse magnetic polarized light (TM).
  • the beam splitter can realize the total reflection of transverse electric polarized light and the diffraction order of transverse magnetic polarized light. Lowest negative refraction.
  • the metagrating in this embodiment includes five air slits with widths w 1 , w 2 , w 3 , w 4 , and w 5 , and the material of the dielectric layer is metallic silver.
  • Transverse magnetically polarized light only exists in the fundamental mode in the air slit, and satisfies:
  • ⁇ i is the propagation constant
  • the real part represents the propagating wave vector
  • the imaginary part represents the dissipation of surface plasmons in the air slit
  • ⁇ is the incident beam wavelength
  • ⁇ m is the dielectric constant of the dielectric layer
  • ⁇ is the additional phase generated by multiple reflections at the interface between the grating and air, and the value of ⁇ is the same for all air slits.
  • the phase delay of each metagrating spans a phase range of 2 ⁇ , and the phase difference ⁇ between adjacent air slits is equal. Therefore, by adjusting the width w i of each air slit, the desired phase shift can be achieved discretely.
  • the corresponding relationship between the phase delay ⁇ i and the width w i of the air slit is shown in Figure 2, in order to ensure the distance between adjacent air slits
  • Transversely magnetically polarized light incident on the transmitted side introduces a phase gradient It will control the direction of the outgoing light.
  • the angle of incidence and angle of reflection satisfy:
  • the critical angle ⁇ i 0°
  • Figure 3a shows the relationship between the incident angle of transverse magnetically polarized light (TM) and the diffraction efficiency of each diffraction order.
  • TM transverse magnetically polarized light
  • Fig. 3c and Fig. 3d are the magnetic field simulation diagrams of transverse magnetic polarized light (TM) and transverse electric polarized light (TE) respectively, it can be seen that efficient negative refraction occurs in TM and perfect reflection occurs in TE, therefore, the metagrating of the present invention can realize Efficient polarization beam splitting.
  • the extinction ratio is usually an important parameter to evaluate the performance of the polarization beam splitter, and the extinction ratio is divided into the reflection extinction ratio ER TE and the transmission extinction ratio ER TM , namely:
  • the reflection extinction ratio ER TE refers to the ratio of the reflection efficiency of transverse electrical polarization (TE) to transverse magnetic polarization (TM)
  • the transmission extinction ratio ER TM refers to the ratio of transverse magnetic polarization (TM) to transverse electrical polarization (TE) ratio of transmission efficiency.
  • Figure 4a shows the relationship between the reflection extinction ratio ER TE and the incident angle in this embodiment.
  • the incident angle ⁇ i ⁇ (-74°, -7°)
  • the reflection extinction ratio ER TE is above 10dB
  • ⁇ When i -62°
  • the reflection extinction ratio ER TE is the highest, reaching 18dB.
  • Fig. 4b shows the relationship between the transmission extinction ratio ER TE and the incident angle in this embodiment, in the whole angle range, the transmission extinction ratio ER TM is relatively high (ER TE >130dB).
  • the metagrating in the present invention has wide-angle response characteristics.
  • ER TE >10dB the bandwidth is about 78nm
  • the wavelength ⁇ is 590nm-668nm
  • the ER TM is greater than 132dB.
  • the metagrating in this embodiment can also realize the energy splitting of only transverse magnetic polarization (TM), as shown in Figure 3a or Figure 3c, the incident energy is divided into three parts, corresponding to R 0 , T 0 and T - 1st order diffraction.
  • the energy splitting can be controlled by controlling the thickness of the grating due to the interaction between the losses of the two metal structures themselves and the surface plasmons passing through the air slit, thus determining the diffraction efficiency of each diffraction order.
  • the absorption efficiency of the whole structure increases gradually with the increase of the thickness, because the decrease of the thickness will narrow the width of the air slit, and the duty cycle of the metal in the grating will increase accordingly, which will lead to Transmission decreases and reflection increases.
  • the thickness should not be too large. This is because when the incident beam propagates in the air slit, the increase in thickness will cause more loss, so the absorption efficiency will increase and the corresponding transmission efficiency will decrease, therefore, there is a critical thickness for transmission due to loss.
  • Fig. 5d is the corresponding magnetic field simulation diagram, it can be clearly seen that the incident light is divided into two beams (reflected light and transmitted light), and the two beams of light are in a straight line. Therefore, the designed grating can realize various spectroscopic functions.
  • the present invention has the following advantages:
  • the beam splitter of the present invention is based on the diffraction mechanism of the superstructured grating, can simultaneously realize high-efficiency beam splitting of energy and polarization, has broadband response, and is suitable for imaging systems and optical communication fields.

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Abstract

一种基于超构光栅的多功能高效分束器，分束器包括若干周期性分布的超构光栅，超构光栅包括若干间隔分布的介质层（10），介质层（10）之间形成有多个空气狭缝（20），介质层（10）与空气狭缝（20）的厚度相等，介质层（10）具有不同的宽度，空气狭缝（20）具有不同的宽度，每个超构光栅的相位延迟跨越2π的相位范围，相邻空气狭缝（20）之间的相位差ΔΦ相等。分束器基于超构光栅的衍射机制，能同时实现能量和偏振的高效率光束分裂，并具有宽带响应，能够适用于成像系统及光通信领域。

Description

基于超构光栅的多功能高效分束器
本发明要求2022年01月11日向中国专利局提交的、申请号为202210027490.9、发明名称为“基于超构光栅的多功能高效分束器”的中国专利申请的优先权，该申请的全部内容通过引用结合在本文中。
技术领域
本发明属于光束传输技术领域，具体涉及一种基于超构光栅的多功能高效分束器。
背景技术
分束器(Light Beam Splitters，LBS)可以将入射光束分为两部分，是现代先进光学技术中不可或缺的光学元件，在许多应用和各种光学设备中发挥着重要作用，如光学开关、光偏振仪、量子光子学集成电路和通信设备等，LBS通常为光栅或半反射镜面，其重量大，难以集成到紧凑型光学器件中。
随着集成光子学的发展，人们迫切需要紧凑高效的LBS，这促使人们以各种方式努力实现这一目标。纳米光子学中出现的光学相位梯度超表面(PGM)为我们提供了一种设计紧凑、平坦、高性能的LBS的新范例。PGM是亚波长元原子的周期性排列，通过适当设计光与元原子之间的相互作用，可以有效地操纵电磁波(EM)的振幅、相位和偏振特性，从而产生各种功能，如超薄隐形、超透镜、回射和不对称传播等。
然而，对于目前报道的大多数基于亚表面的LBS，对于固定偏振光，它们只能实现偏振分裂或能量分离，很少有研究报道在一个设计中同时实现上述两个功能。光子集成系统具有灵活多样的光流控制能力，因此需要多功能、高效率的LBS。
因此，针对上述技术问题，有必要提供一种基于超构光栅的多功能高效分束器。
发明内容
有鉴于此，本发明的目的在于提供一种基于超构光栅的多功能高效分束器。
为了实现上述目的，本发明一实施例提供的技术方案如下：
一种基于超构光栅的多功能高效分束器，所述分束器包括若干周期性分布的超构 光栅，所述超构光栅包括若干间隔分布的介质层，介质层之间形成有多个空气狭缝，介质层与空气狭缝的厚度相等，介质层具有不同的宽度，空气狭缝具有不同的宽度，每个超构光栅的相位延迟跨越2π的相位范围，相邻空气狭缝之间的相位差ΔΦ相等。
一实施例中，所述分束器用于实现入射光束的偏振分裂，入射光束包括横向电偏振光和横向磁偏振光，分束器能够实现横向电偏振光的全反射及横向磁偏振光衍射阶数最低的负折射。
一实施例中，所述超构光栅包括m个空气狭缝，超构光栅的周期宽度为p，介质层与空气狭缝的厚度为d，空气狭缝的宽度为w i，i＝1～m，相邻空气狭缝之间的中心距离为a＝p/m，相邻空气狭缝之间的相位差ΔΦ＝2π/m。
一实施例中，横向磁偏振光在所述空气狭缝中仅存在基本模式，且满足：
Figure PCTCN2022126123-appb-000001
其中，β i为传播常数，其实部表示传播波矢量，虚部表示表面等离子体激元在空气狭缝中的耗散，k 0＝2π/λ为真空中的波矢量，λ为入射光束的波长，ε m为介质层的介电常数；
第i个空气狭缝的相位延迟Φ i为：
Φ i＝β i*d-δ；
其中，δ为光栅和空气之间的界面处多次反射而产生的附加相位。
一实施例中，所述介质层的材料为银，介电常数ε m＝-17.36+0.715i，超构光栅的周期宽度为p＝λ，介质层与空气狭缝的厚度为d＝0.6λ～2.4λ，超构光栅包括5个空气狭缝，宽度分别为w 1、w 2、w 3、w 4、w 5，相邻空气狭缝之间的相位差ΔΦ＝2π/5。
一实施例中，所述入射光束的波长λ为590nm～668nm，入射角为θ i∈(-74°,-7°)。
一实施例中，所述入射光束的波长λ＝650nm，且d＝1.5λ时，空气狭缝的宽度分别为w 1＝120nm、w 2＝68nm、w 3＝46nm、w 4＝34nm、w 5＝27nm。
一实施例中，横向磁偏振光在所述超构光栅的入射角和反射角满足：
k 0sinθ i＝k 0sinθ t+nG；
其中，
Figure PCTCN2022126123-appb-000002
为相位梯度，θ i和θ t分别为入射角和折射角，G＝2π/p为倒格矢，n为衍射级次，且ζ＝G。
一实施例中，n＝-1为横向磁偏振光的最低衍射级次；
当入射角小于临界角时，折射光遵循n＝-1的衍射级次；
当入射角大于临界角时，折射光遵循n＝1的衍射级次。
一实施例中，所述横向电偏振光的反射消光比ERTE大于10dB，所述横向磁偏振光的透射消光比ERTM大于132dB。
本发明具有以下有益效果：
本发明的分束器基于超构光栅的衍射机制，能同时实现能量和偏振的高效率光束分裂，并具有宽带响应，能够适用于成像系统及光通信领域。
附图说明
图1为本发明基于超构光栅的多功能高效分束器的结构示意图。
图2为本发明一实施例中相位延迟Φ i与空气狭缝宽度w i的对应关系曲线图。
图3a为本发明一实施例中横向磁偏振光(TM)的入射角和每个衍射级的衍射效率之间的对应关系曲线图；
图3b为本发明一实施例中横向电偏振光(TE)的入射角和每个衍射级的衍射效率之间的对应关系曲线图；
图3c为本发明一实施例中横向磁偏振光(TM)的磁场模拟图；
图3d为本发明一实施例中横向电偏振光(TE)的磁场模拟图。
图4a为本发明一实施例中反射消光比ER TE和入射角之间的关系曲线图；
图4b为本发明一实施例中透射消光比ER TE和入射角之间的关系曲线图；
图4c为本发明一实施例中入射角θ i＝-30°时横向电偏振光(TE)的频率响应曲线图；
图4d为本发明一实施例中入射角θ i＝-30°时横向磁偏振光(TM)的频率响应曲线图。
图5a为本发明一实施例中不同厚度下入射角与T -1级衍射效率的曲线图；
图5b为本发明一实施例中不同厚度下入射角与R 0级衍射效率的曲线图；
图5c为本发明一实施例中吸收效率与厚度的关系曲线图；
图5d为本发明一实施例中入射角θ i＝-30°时的磁场模拟图。
具体实施方式
为了使本技术领域的人员更好地理解本发明中的技术方案，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例， 本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都应当属于本发明保护的范围。
基于PGM的概念，通过探索和操纵其衍射特性，本发明设计了一种在光学区域工作的基于PGM的多功能分束器(LBS)。众所周知，PGMs是具有超单元的周期光栅，超单元包含具有不同光学响应的m个单元，这些单元离散地引入完全覆盖2π的突变相移(APS)。引入的APS产生相位梯度(即附加波矢量)，其改变了发生在界面处的光的反射和折射的基本定律。衍射效应在PGMs中普遍存在，高阶衍射由奇偶依赖衍射定律描述。因此，自由控制PGM中的衍射效应及其效率是提高包括分束器在内的PGM基器件性能的关键。
本发明的LBS是一种纯等离激元PGM，通过调整空气狭缝的宽度来引入沿传输界面所需的APS，空气狭缝决定了通过它的表面等离激元的传播波矢量。经过证明，所设计的LBS可以同时实现能量和偏振的高效光束分裂，并且具有宽带和广角响应。例如，当横向电偏振光(TE)和横向磁偏振光(TM)以θ i＝-30°的入射角同时入射时，LBS可以使横向电偏振光(TE)完全反射，反射角为θ r＝-30°，即发生完美的镜面反射；而对于横向磁偏振光(TM)，由于PGM中的衍射效应，在LBS中可以看到衍射阶数最低的高效负折射，并且折射角为θ t＝30°。通过这种方式，可以获得偏振分裂。此外，金属的欧姆损耗在决定TM偏振的反射侧和透射侧各衍射级的衍射效率方面起着重要作用。有了这些物理原理，LBS还可以将TM偏振的入射能量均匀地传递到反射侧和折射侧。本发明对基于PGM的LBS的研究具有基础性意义，所提出的设计在集成光通信或光测量等领域显示出巨大的应用潜力。
本发明一具体实施例中基于超构光栅的多功能高效分束器(LBS)，分束器包括若干周期性分布的超构光栅，单个周期超构光栅的结构参图1所示，超构光栅包括若干间隔分布的介质层10，介质层10之间形成有多个空气狭缝20，介质层与空气狭缝的厚度相等，介质层具有不同的宽度，空气狭缝具有不同的宽度，每个超构光栅的相位延迟跨越2π的相位范围，相邻空气狭缝之间的相位差ΔΦ相等。
分束器用于实现入射光束的偏振分裂，入射光束包括横向电偏振光(TE)和横向磁偏振光(TM)，分束器能够实现横向电偏振光的全反射及横向磁偏振光衍射阶数最低的负折射。
其中，超构光栅包括m个空气狭缝，超构光栅的周期宽度为p，介质层与空气狭缝的厚度为d，空气狭缝的宽度为w i，i＝1～m，相邻空气狭缝之间的中心距离为a＝p/m， 相邻空气狭缝之间的相位差ΔΦ＝2π/m，且w i具有亚波长尺寸，满足w i<<λ。
具体地，本实施例中超构光栅包括5个空气狭缝，宽度分别为w 1、w 2、w 3、w 4、w 5，介质层的材料为金属银。
横向磁偏振光在空气狭缝中仅存在基本模式，且满足：
Figure PCTCN2022126123-appb-000003
其中，β i为传播常数，其实部表示传播波矢量，虚部表示表面等离子体激元在空气狭缝中的耗散，k 0＝2π/λ为真空中的波矢量，λ为入射光束的波长，ε m为介质层的介电常数；
当入射光束通过第i个空气狭缝并到达传输界面时，总的相位延迟Φ i为：
Φ i＝β i*d-δ；
其中，δ为光栅和空气之间的界面处多次反射而产生的附加相位，对于所有的空气狭缝，δ的值均相同。
根据PGM的概念，每个超构光栅的相位延迟跨越2π的相位范围，相邻空气狭缝之间的相位差ΔΦ相等。因此，通过调整每个空气狭缝的宽度w i，可以离散地实现所需的相移。
本实施例中，设置入射光束的波长λ＝650nm，介质层的介电常数ε m＝-17.36+0.715i，超构光栅包括5个空气狭缝(即m＝5)，超构光栅的周期宽度为p＝λ，介质层与空气狭缝的厚度为d＝1.5λ，相位延迟Φ i与空气狭缝宽度w i的对应关系如图2所示，为了保证相邻空气狭缝之间的相位差ΔΦ相等，本实施例中空气狭缝的宽度分别为w 1＝120nm、w 2＝68nm、w 3＝46nm、w 4＝34nm、w 5＝27nm。
横向磁偏振光入射时，在透射侧会引入一个相位梯度
Figure PCTCN2022126123-appb-000004
它将控制出射光的方向。入射角和反射角满足：
k 0sinθ i＝k 0sinθ t+nG；
其中，
Figure PCTCN2022126123-appb-000005
为相位梯度，θ i和θ t分别为入射角和折射角，G＝2π/p为倒格矢，n为衍射级次，n＝v-1，且ζ＝G。
v＝0(即n＝-1)为横向磁偏振光的最低衍射级次，它预测了出现高阶衍射的临界角θ i＝0°。当入射角小于临界角时(θ i＜0°)，折射光遵循n＝-1的衍射级次；当入射角大于临界角时(θ i＞0°)，折射光遵循n＝1的衍射级次。
另一方面，对于横向电偏振光，由于亚波长空气狭缝的存在，它将被超构光栅完全反射。
接下来分析入射光束如何在超构光栅中实现偏振分裂。
图3a为横向磁偏振光(TM)的入射角和每个衍射级的衍射效率之间的关系。当θ i＜0°时，最低衍射级的透射占主导地位(即n＝-1)，入射角θ i＝30°时，透射效率约为70％。当θ i＞0°时，衍射主要由高阶n＝1的反射控制，这是由于m(此处m＝5)的奇偶校验造成的，入射光将有效地耦合到n＝1阶的反射光，这意味着在这种情况下会发生反向反射，特别是入射角θ i＝30°时，θ r＝-30°，R -1≈40％。在高阶衍射中，更多的耗散或更低的衍射效率是由光栅内部的多次反射引起的。
图3b为横向电偏振光(TE)的入射角和每个衍射级的衍射效率之间的关系。只有n＝0阶的反射是左反射且占主导地位，这是由于亚波长空气狭缝远低于TE通过的截止频率。对于TE入射光束会发生镜面反射，θ i＝θ r。当入射角θ i＝30°时，反射效率为R 0＝96％。
图3c和图3d分别为横向磁偏振光(TM)和横向电偏振光(TE)的磁场模拟图，可见，TM发生高效负折射，TE出现完美反射，因此，本发明的超构光栅可以实现高效的偏振分束。
消光比通常是评价偏振分束器性能的一个重要参数，消光比分为反射消光比ER TE和透射消光比ER TM，即：
Figure PCTCN2022126123-appb-000006
反射消光比ER TE是指横向电偏振光(TE)与横向磁偏振光(TM)的反射效率之比，透射消光比ER TM是指横向磁偏振光(TM)与横向电偏振光(TE)的透射效率之比。
图4a为本实施例中反射消光比ER TE和入射角之间的关系，当入射角θ i∈(-74°,-7°)时，反射消光比ER TE都在10dB以上，而当θ i＝-62°时，反射消光比ER TE最高，达到18dB。图4b为本实施例中透射消光比ER TE和入射角之间的关系，在整个角度范围内，透射消光比ER TM相对较高(ER TE>130dB)。通常，当入射角θ i∈(-74°,-7°)时，反射消光比ER TE和透射消光比ER TM均大于10dB，该器件被认为具有良好的偏振分束效果。因此，本发明中的超构光栅具有广角响应特性。
另外，图4c和图4d分别本实施例中入射角θ i＝-30°的频率响应曲线，尽管上述实施例中的波长λ以650nm为例进行说明，但由于PGM设计中的公差，其仍然具有偏振分裂的宽带响应。ER TE>10dB时，带宽约为78nm，波长λ为590nm～668nm，其中ER TM大于132dB。
此外，本实施例中的超构光栅还可以实现仅横向磁偏振光(TM)的能量分裂，参图3a或图3c所示，入射能量分为三部分，分别对应于R 0、T 0和T -1级衍射。由于两个金属结构本身的损耗和穿过空气狭缝的表面等离激元之间的相互作用，通过控制光栅的厚度可以控制能量分裂，从而确定每个衍射级次的衍射效率。图5a及图5b分别为不同厚度下入射角与T -1和R 0级衍射效率的曲线图，厚度分别为d＝0.6λ、d＝λ、d＝1.5λ、d＝2.4λ，在上述情况下，相位梯度
Figure PCTCN2022126123-appb-000007
保持不变。随着厚度的变化，传播常数β i(w)随之变化以获得不变的APS(即φ i＝β i(w)d-δ)，这可以通过选择合适的空气狭缝宽度来满足。如图5a、5b所示，随着d从0.6λ增加到2.4λ，T -1级衍射效率先增加后降低，R 0级衍射效率逐渐降低。
参图5c所示，整个结构的吸收效率随着厚度的增加而逐渐增加，这是因为厚度的减小将缩小空气狭缝的宽度，并且光栅中金属的占空比将相应增加，这将导致透射降低和反射增加。但是，另一方面，厚度不能太大。这是因为当入射光束在空气狭缝中传播时，厚度的增加将导致更多的损失，因此吸收效率将增加，相应的传输效率将降低，因此，由于损耗存在传输的临界厚度。当d＝0.6λ且θ i＝-30°时，n＝1阶的传输效率几乎等于n＝0阶的反射效率，其分别为43％和39％。图5d为相应的磁场模拟图，可以清楚地看到，入射光分为两束(反射光和透射光)，两束光呈直线。因此，所设计的光栅可以实现多种分光功能。
由以上技术方案可以看出，本发明具有以下优点：
本发明的分束器基于超构光栅的衍射机制，能同时实现能量和偏振的高效率光束分裂，并具有宽带响应，能够适用于成像系统及光通信领域。
对于本领域技术人员而言，显然本发明不限于上述示范性实施例的细节，而且在不背离本发明的精神或基本特征的情况下，能够以其他的具体形式实现本发明。因此，无论从哪一点来看，均应将实施例看作是示范性的，而且是非限制性的，本发明的范围由所附权利要求而不是上述说明限定，因此旨在将落在权利要求的等同要件的含义和范围内的所有变化囊括在本发明内。不应将权利要求中的任何附图标记视为限制所涉及的权利要求。
此外，应当理解，虽然本说明书按照实施方式加以描述，但并非每个实施方式仅包含一个独立的技术方案，说明书的这种叙述方式仅仅是为清楚起见，本领域技术人员应当将说明书作为一个整体，各实施例中的技术方案也可以经适当组合，形成本领域技术人员可以理解的其他实施方式。

Claims (10)

  1. 一种基于超构光栅的多功能高效分束器，其特征在于，所述分束器包括若干周期性分布的超构光栅，所述超构光栅包括若干间隔分布的介质层，介质层之间形成有多个空气狭缝，介质层与空气狭缝的厚度相等，介质层具有不同的宽度，空气狭缝具有不同的宽度，每个超构光栅的相位延迟跨越2π的相位范围，相邻空气狭缝之间的相位差ΔΦ相等。
  2. 根据权利要求1所述的基于超构光栅的多功能高效分束器，其特征在于，所述分束器用于实现入射光束的偏振分裂，入射光束包括横向电偏振光和横向磁偏振光，分束器能够实现横向电偏振光的全反射及横向磁偏振光衍射阶数最低的负折射。
  3. 根据权利要求1所述的基于超构光栅的多功能高效分束器，其特征在于，所述超构光栅包括m个空气狭缝，超构光栅的周期宽度为p，介质层与空气狭缝的厚度为d，空气狭缝的宽度为w i，i＝1～m，相邻空气狭缝之间的中心距离为a＝p/m，相邻空气狭缝之间的相位差ΔΦ＝2π/m。
  4. 根据权利要求3所述的基于超构光栅的多功能高效分束器，其特征在于，横向磁偏振光在所述空气狭缝中仅存在基本模式，且满足：
    Figure PCTCN2022126123-appb-100001
    其中，β i为传播常数，其实部表示传播波矢量，虚部表示表面等离子体激元在空气狭缝中的耗散，k 0＝2π/λ为真空中的波矢量，λ为入射光束的波长，ε m为介质层的介电常数；
    第i个空气狭缝的相位延迟Φ i为：
    Φ i＝β i*d-δ；
    其中，δ为光栅和空气之间的界面处多次反射而产生的附加相位。
  5. 根据权利要求4所述的基于超构光栅的多功能高效分束器，其特征在于，所述介质层的材料为银，介电常数ε m＝-17.36+0.715i，超构光栅的周期宽度为p＝λ，介质层与空气狭缝的厚度为d＝0.6λ～2.4λ，超构光栅包括5个空气狭缝，宽度分别为w 1、w 2、w 3、w 4、w 5，相邻空气狭缝之间的相位差ΔΦ＝2π/5。
  6. 根据权利要求5所述的基于超构光栅的多功能高效分束器，其特征在于，所述入射光束的波长λ为590nm～668nm，入射角为θ i∈(-74°,-7°)。
  7. 根据权利要求5所述的基于超构光栅的多功能高效分束器，其特征在于，所述入射光束的波长λ＝650nm，且d＝1.5λ时，空气狭缝的宽度分别为w 1＝120nm、w 2＝68nm、 w 3＝46nm、w 4＝34nm、w 5＝27nm。
  8. 根据权利要求6或7所述的基于超构光栅的多功能高效分束器，其特征在于，横向磁偏振光在所述超构光栅的入射角和反射角满足：
    k 0sinθ i＝k 0sinθ t+nG；
    其中，
    Figure PCTCN2022126123-appb-100002
    为相位梯度，θ i和θ t分别为入射角和折射角，G＝2π/p为倒格矢，n为衍射级次，且ζ＝G。
  9. 根据权利要求8所述的基于超构光栅的多功能高效分束器，其特征在于，n＝-1为横向磁偏振光的最低衍射级次；
    当入射角小于临界角时，折射光遵循n＝-1的衍射级次；
    当入射角大于临界角时，折射光遵循n＝1的衍射级次。
  10. 根据权利要求6所述的基于超构光栅的多功能高效分束器，其特征在于，所述横向电偏振光的反射消光比ERTE大于10dB，所述横向磁偏振光的透射消光比ERTM大于132dB。
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