WO2021129237A1 - 薄膜光波导及其制备方法 - Google Patents

薄膜光波导及其制备方法 Download PDF

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WO2021129237A1
WO2021129237A1 PCT/CN2020/129664 CN2020129664W WO2021129237A1 WO 2021129237 A1 WO2021129237 A1 WO 2021129237A1 CN 2020129664 W CN2020129664 W CN 2020129664W WO 2021129237 A1 WO2021129237 A1 WO 2021129237A1
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optical waveguide
thin film
lattice
silicon
refractive index
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PCT/CN2020/129664
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English (en)
French (fr)
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陈亦凡
黄萌
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苏州易锐光电科技有限公司
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Priority to US17/632,808 priority Critical patent/US20220268993A1/en
Publication of WO2021129237A1 publication Critical patent/WO2021129237A1/zh

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/124—Geodesic lenses or integrated gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/12038—Glass (SiO2 based materials)
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/1204—Lithium niobate (LiNbO3)
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/12061—Silicon
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/12069—Organic material
    • G02B2006/12076—Polyamide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/1213—Constructional arrangements comprising photonic band-gap structures or photonic lattices
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12166—Manufacturing methods

Definitions

  • the invention relates to a thin film optical waveguide and a preparation method thereof.
  • optical waveguides based on sub-wavelength grating structures have received widespread attention due to their advantages such as low loss and adjustable effective refractive index.
  • the two-dimensional lattice sub-wavelength thin film waveguide structure has a higher degree of parameter freedom than the one-via wavelength grating structure, and can design the effective refractive index of the optical waveguide in a large range and accurately, so it has a wide range of application prospects.
  • the effective refractive index of an optical waveguide is one of the important parameters that characterize its performance, and has a huge impact on various optoelectronic devices, so it is an important index that determines the material and structure of the optical waveguide.
  • the effective refractive index of light propagating in different directions is different, which has an impact on the performance of some specific optical devices.
  • the anisotropic effective refractive index is also a challenge for design and process. Taking the micro-ring resonator as an example, in order to ensure that the light propagates in the curved optical waveguide with the same effective refractive index, it is necessary to continuously change the direction of the two-dimensional lattice during the design process.
  • the purpose of the present invention is to provide a two-dimensional lattice sub-wavelength structure whose effective lattice constant and duty cycle are approximately the same in all directions, so as to obtain a thin film optical waveguide with an effective refractive index approximately isotropic.
  • a thin film optical waveguide includes a silicon-based substrate, a cladding layer provided on the silicon-based substrate, and an optical waveguide core provided on the silicon-based substrate
  • the optical waveguide core layer is arranged in the cladding layer and the refractive index of the optical waveguide core layer is higher than the refractive index of the cladding layer.
  • the optical waveguide core layer includes a double-layer optical waveguide dielectric film and
  • the thin film material interlayer between the double-layer optical waveguide dielectric films, the thin film material interlayer is a two-dimensional lattice sub-wavelength structure, and the effective lattice constant and the duty cycle of the two-dimensional lattice sub-wavelength structure are in each The propagation direction is approximately the same.
  • the two-dimensional lattice sub-wavelength structure includes lattice points, and the effective lattice constant and the duty cycle are determined by the shape and the length and width of the lattice points.
  • the lattice points are one of an ellipse, a cross, a hexagon, and an octagon.
  • the two-dimensional lattice sub-wavelength structure is a Bravais lattice structure or a quasi lattice structure.
  • the Bravais lattice includes square or hexagonal shapes.
  • the quasi-lattice structure is octagonal, decagonal or dodecagonal.
  • the interlayer of the thin film material is one of silicon, doped silicon dioxide, lithium niobate, titanium dioxide, zinc oxide, and magnesium doped zinc oxide.
  • optical waveguide dielectric film is doped silicon dioxide.
  • the doped silica is 2% germanium doped silica.
  • the present invention also provides a preparation method for preparing the thin film optical waveguide, and the preparation method is as follows:
  • a silicon-based substrate is provided, and a lower optical waveguide dielectric film is formed on the silicon-based substrate;
  • the beneficial effect of the present invention is that the effective lattice constant and the duty cycle of the two-dimensional lattice sub-wavelength structure of the thin film optical waveguide provided by the present invention are approximately the same in each propagation direction, so that the effective refractive index of the thin film optical waveguide is Approximately isotropic, which overcomes the problem of complex structure and process errors in the design of thin film optical waveguides with a two-dimensional lattice sub-wavelength structure whose effective refractive index is approximately isotropic. It does not require additional structural design and changing the direction of the two-dimensional lattice. The structure of the thin film optical waveguide is simplified and the performance of the thin film optical waveguide is ensured.
  • FIG. 1 is a schematic diagram of the structure of a two-dimensional lattice sub-wavelength thin film optical waveguide in an embodiment of the present invention
  • FIG. 2 is a schematic diagram of the structure of incident light entering the two-dimensional lattice sub-wavelength thin film optical waveguide of FIG. 1 in the direction of 0°;
  • Fig. 3 is a schematic diagram of the structure of the cross lattice points in Fig. 1;
  • FIG. 4 is a schematic structural diagram of incident light entering the two-dimensional lattice sub-wavelength thin film optical waveguide of FIG. 1 in the direction of 45°;
  • Fig. 5 is the effective refractive index in each direction of the two-dimensional lattice sub-wavelength optical waveguide of the planar square Bravais lattice;
  • Fig. 6 is a diagram showing the relationship between the difference in effective refractive index of incident light in the two directions of 0° and 45° and the length L of the cross-shaped lattice point;
  • Fig. 7 is a graph showing the relationship between the difference in effective refractive index of incident light in the two directions of 0° and 45° and the width D of the cross-shaped lattice point.
  • the thin-film optical waveguide shown in an embodiment of the present invention includes a silicon-based substrate 1, an optical waveguide core layer 2 provided on the silicon-based substrate 1, and an optical waveguide core layer 2 provided on the silicon-based substrate 1.
  • a cladding layer (not shown) on the base substrate 1, the optical waveguide core layer 2 is provided in the cladding layer, and the refractive index of the optical waveguide core layer 2 is higher than the refractive index of the cladding layer.
  • the optical waveguide core layer 2 includes a double-layer optical waveguide dielectric film 21 with the same thickness and a film material interlayer 22 arranged between the double-layer optical waveguide dielectric films 21.
  • the optical waveguide dielectric film 21 generally uses doped silicon dioxide.
  • the thin film material interlayer 22 is generally one of silicon, doped silicon dioxide, and lithium niobate common materials, or titanium dioxide, zinc oxide, and magnesium-doped zinc oxide negative thermo-optical coefficient materials.
  • the thin film material interlayer 22 has a two-dimensional lattice sub-wavelength structure, and the effective lattice constant and duty cycle of the two-dimensional lattice sub-wavelength structure are approximately the same in each propagation direction.
  • the two-dimensional lattice sub-wavelength structure is a Bravais lattice structure or a quasi-lattice structure, the Bravais lattice is a square or a hexagon, and the quasi-lattice structure is an octagon or a decagon Or dodecagon. Please refer to Fig. 2.
  • the two-dimensional lattice array is an abstract image.
  • the lattice point 221 is the position of the center of mass of the unit cell.
  • the lattice constant ⁇ is the side length of the unit cell. In Fig. 2, it can be regarded as two adjacent crystals. The distance between grid points 221.
  • the lattice point 211 is one of an ellipse, a cross, a hexagon, and an octagon.
  • the thin-film optical waveguide is prepared from a silicon dioxide substrate 1, a 2% germanium-doped silicon dioxide double-layer optical waveguide dielectric film 21, a titanium dioxide thin film material interlayer 22, and a silicon dioxide cladding layer, wherein the titanium dioxide film
  • the material interlayer 22 uses a two-dimensional lattice sub-wavelength structure of a square Bravais lattice, and the lattice points 221 are cross-shaped.
  • the cross-shaped lattice point 211 has a length L and a width D.
  • the optical waveguide dielectric film 21 in the thin-film optical waveguide is the main optical waveguide structure, which ensures the single-mode operating mode of the thin-film optical waveguide.
  • the two-dimensional lattice sub-wavelength structure formed in the thin film material interlayer 22 can be regarded as a single-mode optical waveguide structure of a uniform medium.
  • this embodiment uses the scalar Heimholtz formula as a guide, namely:
  • ⁇ can be any field component
  • k 0 is the vacuum wave number
  • n is the refractive index
  • the z direction is the propagation direction
  • x and y are the vertical and parallel directions of the cross section.
  • F and G are mode distributions
  • n eff is the effective refractive index
  • ⁇ is the propagation constant.
  • the reason for the effective refractive index anisotropy of the two-dimensional lattice sub-wavelength thin film optical waveguide is that the effective lattice constant and the effective lattice constant seen by light propagating in different directions
  • the duty cycle is different, resulting in a different effective refractive index.
  • quasi-crystalline structures such as octagonal, decagonal or dodecagonal can reduce the degree of anisotropy within a certain range, but the limited width of the optical waveguide makes the quasi-crystalline structure unable to achieve further isotropy.
  • the shape and length and width of the lattice points 221 are adjusted to make the effective lattice of the two-dimensional lattice sub-wavelength structure
  • the constant and the duty cycle are approximately the same in each propagation direction, so that the effective refractive index of the thin-film optical waveguide is approximately isotropic.
  • the wavelength of the incident light is selected to be 1550 nm.
  • the square Bravais lattice only needs to consider the effective refractive index in the propagation direction of 0°-45° due to its symmetry.
  • Figure 5 through the simulation of the effective refractive index of the two-dimensional lattice sub-wavelength optical waveguide of the planar square Bravais lattice in each direction, it can be seen that the effective refractive index of the two-dimensional lattice optical waveguide is equal to 0° and 45°. The biggest difference is in each direction. Therefore, in this embodiment, it is only necessary to consider the effective refractive index in the two directions of 0° and 45°.
  • the length L of the cross-shaped lattice point 211 is fine-tuned, and the relationship between the effective refractive index difference of the incident light in the two directions of 0° and 45° and the length L of the cross-shaped lattice point is shown in Fig. 6 ; Fine-tune the width D of the cross-shaped lattice point 211, the relationship between the effective refractive index difference of the incident light in the two directions of 0° and 45° and the width D of the cross-shaped lattice point 211 is shown in Figure 7 Shown.
  • the maximum difference of the effective refractive index in the two directions of 0° and 45° is less than 0.0002.
  • the symmetry of the square Bravais lattice shows that the effective refractive index in all directions is approximately the same, and the effective refractive index is approximately all directions. Same-sex requirements.
  • the present invention optimizes the length and width of the lattice points in the two-dimensional lattice, and uses the symmetry of the two-dimensional lattice to make the effective refractive index difference of the two incident directions with the largest difference in effective refractive index in the two-dimensional lattice approximately the same. At this time, the effective lattice constant and duty cycle of light in different propagation directions remain approximately the same, meeting the requirements of approximately isotropy.
  • This method can be applied to any symmetrical two-dimensional lattice structure (hexagon, octagon, decagon, dodecagon, etc.) and related lattice points (hexagon, octagon, etc.)
  • the present invention also provides a preparation method for preparing the above-mentioned thin-film optical waveguide, and the preparation method is as follows:
  • a silicon-based substrate 1 specifically a silicon dioxide substrate 1, on which a plasma-enhanced chemical vapor deposition (PECVD) method is used to coat the doped silicon dioxide material to form a lower optical waveguide Dielectric film, wherein the doped silicon dioxide material is 2% germanium doped silicon dioxide;
  • PECVD plasma-enhanced chemical vapor deposition
  • the titanium dioxide thin film material interlayer is prepared into the two-dimensional lattice subwavelength structure by nanoimprinting (NIL) or electron beam lithography or optical lithography, wherein The effective lattice constant and duty cycle of the two-dimensional lattice sub-wavelength structure are approximately the same in all directions;
  • PECVD plasma-enhanced chemical vapor deposition
  • a silicon dioxide cladding is prepared on the outer circumference of the double-layer optical waveguide dielectric film 21 and the film material interlayer 22.
  • the effective lattice constant and duty cycle of the two-dimensional lattice sub-wavelength structure of the thin film optical waveguide provided by the present invention are approximately the same in each propagation direction, the effective refractive index of the thin film optical waveguide is approximately isotropic.
  • the structure of the waveguide ensures the performance of the thin film optical waveguide.

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
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Abstract

一种薄膜光波导，包括硅基衬底（1）、设置在硅基衬底（1）上的包层以及设置在硅基衬底（1）上的光波导芯层（2），光波导芯层（2）设于包层之中并且光波导芯层（2）折射率高于包层的折射率，光波导芯层（2）包括双层光波导介质薄膜（21）以及设置于双层光波导介质薄膜（21）之间的薄膜材料夹层（22），薄膜材料夹层（22）为二维晶格亚波长结构，二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同，以使薄膜光波导的有效折射率近似各向同性。克服了有效折射率近似各向同性的二维晶格亚波长结构的薄膜光波导设计结构复杂和工艺误差的问题，不需要额外的结构设计和改变二维晶格方向，简化了薄膜光波导的结构并保证了薄膜光波导的性能。

Description

薄膜光波导及其制备方法
本申请要求了申请日为2019年12月25日，申请号为201911360478.4的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及一种薄膜光波导及其制备方法。
背景技术
目前在光通信领域中，基于亚波长光栅结构的光波导由于其低损耗、有效折射率可调等优势被广泛关注。其中，二维晶格亚波长薄膜波导结构相比一维亚波长光栅结构具有更高的参数自由度，可大范围、准确的设计光波导的有效折射率，因此具有广泛的应用前景。光波导的有效折射率是表征其性能的重要参数之一，对各种光电器件的影响巨大，因此是决定光波导材料和结构的重要指标。对于二维晶格亚波长薄膜波导结构，光在不同方向传播的有效折射率都有所不同，这对于某些特定光学器件的工作性能产生影响。同时，对于有弯曲波导结构的光学器件，如微环共振器，各向异性的有效折射率对于设计和工艺也是一种挑战。以微环共振器为例，为保证光在弯曲的光波导传播具有相同的有效折射率，需要在设计过程中不断改变二维晶格的方向。同时，由于微环共振器的内径和外径的差异，还需要在靠近内径一侧和靠近外径一侧不断改变二维晶格的晶格常数和占空比，以保持相同的有效折射率。这种设计方式不但设计上的复杂度，在制备过程中，工艺误差也可能会对器件性能产生巨大影响。
发明内容
本发明的目的在于提供一种二维晶格亚波长结构的有效晶格常数和占空比在各个方向近似相同，以得到有效折射率近似各向同性的薄膜光波导。
为达到上述目的，本发明提供如下技术方案：一种薄膜光波导包括硅基衬底、设置在所述硅基衬底上的包层、以及设置在所述硅基衬底上的光波导芯层，所述光波导芯层设于所述包层之中并且所述光波导芯层折射率高于所述包层的折射率，所述光波导芯层包括双层光波导介质薄膜以及设置于所述双层光波导介质薄膜之间的薄膜材料夹层，所述薄膜材料夹层为二维晶格亚波长结构，所 述二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同。
进一步地，所述二维晶格亚波长结构包括晶格点，所述有效晶格常数和所述占空比由所述晶格点的形状以及长宽确定。
进一步地，所述晶格点为椭圆形、十字交叉形、六角形以及八角形中的一种。
进一步地，所述二维晶格亚波长结构为布拉维晶格结构或准晶格结构。
进一步地，所述布拉维晶格为包括正方形或六角形。
进一步地，所述准晶格结构为八边形或十边形或十二边形。
进一步地，所述薄膜材料夹层为硅、掺杂二氧化硅、铌酸锂、二氧化钛、氧化锌以及镁掺杂氧化锌中的一种。
进一步地，所述光波导介质薄膜为掺杂二氧化硅。
进一步地，所述掺杂二氧化硅为2％锗掺杂二氧化硅。
本发明还提供了一种用以制备所述薄膜光波导的制备方法，所述制备方法如下：
S1、提供硅基衬底，在所述硅基衬底上形成下层光波导介质薄膜；
S2、制备薄膜材料夹层；
S3、将所述薄膜材料夹层制备成所述二维晶格亚波长结构，其中，所述二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同；
S4、制备上层光波导介质薄膜，所述下层光波导介质薄膜和所述下层光波导介质薄膜形成所述双层光波导介质薄膜；
S5、制备所述包层。
本发明的有益效果在于：由于本发明所提供的薄膜光波导的二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同，以使薄膜光波导的有效折射率近似各向同性，其克服了有效折射率近似各向同性的二维晶格亚波长结构的薄膜光波导设计结构复杂和工艺误差的问题，不需要额外的结构设计和改变二维晶格方向，简化了薄膜光波导的结构并保证了薄膜光波导的性能。
上述说明仅是本发明技术方案的概述，为了能够更清楚了解本发明的技术 手段，并可依照说明书的内容予以实施，以下以本发明的较佳实施例并配合附图详细说明如后。
附图说明
图1为本发明一实施例中二维晶格亚波长薄膜光波导的结构示意图；
图2为入射光在0°方向上进入图1的二维晶格亚波长薄膜光波导的结构示意图；
图3为图1中十字交叉晶格点的结构示意图；
图4为入射光在45°方向上进入图1的二维晶格亚波长薄膜光波导的结构示意图；
图5为平面型正方形布拉维晶格的二维晶格亚波长光波导在各方向的有效折射率；
图6为入射光在0°和45°两个方向上的有效折射率的差值与十字交叉形晶格点的长L的关系图；
图7为入射光在0°和45°两个方向上的有效折射率的差值与十字交叉形晶格点的宽D的关系图。
具体实施方式
下面将结合附图对本发明的技术方案进行清楚、完整地描述，显然，所描述的实施例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，都属于本发明保护的范围。
在本发明的描述中，需要说明的是，术语“中心”、“上”、“下”、“左”、“右”、“竖直”、“水平”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的机构或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，术语“第一”、“第二”、“第三”仅用于描述目的，而不能理解为指示或暗示相对重要性。
在本发明的描述中，需要说明的是，除非另有明确的规定和限定，术语“安 装”、“相连”、“连接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以具体情况理解上述术语在本发明中的具体含义。
此外，下面所描述的本发明不同实施方式中所涉及的技术特征只要彼此之间未构成冲突就可以相互结合。
请参见图1和图2，本发明一实施例所示的薄膜光波导，包括硅基衬底1、设置在所述硅基衬底1上的光波导芯层2、以及设置在所述硅基衬底1上的包层(未图示)，所述光波导芯层2设于所述包层之中并且所述光波导芯层2折射率高于所述包层的折射率。具体的，所述光波导芯层2包括厚度相同的双层光波导介质薄膜21以及设置于所述双层光波导介质薄膜21之间的薄膜材料夹层22。所述光波导介质薄膜21一般使用掺杂二氧化硅。所述薄膜材料夹层22一般为硅、掺杂二氧化硅以及铌酸锂常见材料或者二氧化钛、氧化锌以及镁掺杂氧化锌负热光系数材料中的一种。
所述薄膜材料夹层22为二维晶格亚波长结构，二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同。所述二维晶格亚波长结构为布拉维晶格结构或准晶格结构，所述布拉维晶格为包括正方形或六角形，所述准晶格结构为八边形或十边形或十二边形。请参见图2，二维晶格阵列为抽象图，晶格点221为晶胞质心所在的位置，晶格常数Λ为晶胞的边长，在图2中，可视为两个相邻晶格点221之间的距离。所述晶格点211为椭圆形、十字交叉形、六角形以及八角形中的一种。
本实施例中，薄膜光波导由二氧化硅衬底1、2％锗掺杂二氧化硅的双层光波导介质薄膜21、二氧化钛薄膜材料夹层22、以及二氧化硅包层制备，其中二氧化钛薄膜材料夹层22使用正方形布拉维晶格的二维晶格亚波长结构，晶格点221为十字交叉形。
下面以晶格点221为十字交叉形为例进行详细说明如何得到效晶格常数和占空比在各个传播方向上近似相同，以使薄膜光波导的有效折射率近似各向同 性。请参见图3，十字交叉形晶格点211具有长度L和宽度D。
薄膜光波导中的所述光波导介质薄膜21是主要的光波导结构，保证薄膜光波导的单模工作模式。薄膜材料夹层22中形成的二维晶格亚波长结构，可以被视为均匀介质的单模光波导结构。
在对薄膜光波导结构的设计中，本实施例以标量海姆霍兹公式作为指导，即：
Figure PCTCN2020129664-appb-000001
其中Ψ可为任何场分量，k 0为真空波数，n为折射率，z方向为传播方向，x、y为横截面的竖直、平行方向。为得到此方程的解，可通过有效折射率法简化为：
Figure PCTCN2020129664-appb-000002
Figure PCTCN2020129664-appb-000003
其中F、G为模分布，n eff为有效折射率，β为传播常数。通过此方法，可以计算得出光波导的传播常数和有效折射率。
以正方形布拉维晶格结构，圆形晶格点为例，二维晶格亚波长薄膜光波导有效折射率各向异性的原因在于，光在不同方向上传播所见的有效晶格常数和占空比均不同，从而造成有效折射率不同。使用准晶体结构如八边形，十边形或十二边形等可在一定范围内降低各向异性的程度，但是光波导的有限宽度使得准晶体结构不能更进一步达到各向同性。
因有效晶格常数和所述占空比由所述晶格点221的形状以及长宽确定，故通过调整晶格点221的形状以及长宽，使得二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同，以使薄膜光波导的有效折射率近似各向同性。现以本实施例所示薄膜光波导为例，入射光波长选择为1550nm。
正方形布拉维晶格因其对称性只需考虑0°-45°的传播方向上的有效折射率。请参见图5，通过对平面型正方形布拉维晶格的二维晶格亚波长光波导在各方向的有效折射率仿真可知，二维晶格光波导有效折射率与0°和45°两个方向上差别最大。因此，本实施例中，仅需考虑0°和45°两个方向上有效折射 率即可。
请参见图2和图4，为入射光在0°和45°两个方向上进入薄膜光波导中遇到的正方形布拉维晶格十字交叉形晶格点的方向位置是不同的，相应的有效晶格常数和占空比则不同。
对十字交叉形晶格点211的长L进行微调，入射光在0°和45°两个方向上的有效折射率的差值与十字交叉形晶格点的长L的关系如图6所示；对十字交叉形晶格点211的宽D进行微调，入射光在0°和45°两个方向上的有效折射率的差值与十字交叉形晶格点211的宽D的关系如图7所示。在0°和45°两个方向上的有效折射率的最大差别小于0.0002，由正方形布拉维晶格的对称性可知，在各个方向上的有效折射率近似相同，达到有效折射率近似各向同性的要求。
本发明通过优化二维晶格中晶格点的长宽，通过二维晶格的对称性以使二维晶格中有效折射率差别最大的两个入射方向的有效折射率差值近似相同，此时光在不同传播方向上的有效晶格常数和占空比维持大致相同，达到近似各向同性的要求。此方法可以应用到任一一个具有对称性的二维晶格结构(六边形，八边形，十边形，十二边形等)和相关的晶格点(六角形，八角形，十角形、十二角形等)形状形成的薄膜光波导。
本发明还提供了一种用以制备上述薄膜光波导的制备方法，所述制备方法如下：
S1、提供硅基衬底1，具体为二氧化硅衬底1，在二氧化硅衬底1上使用等离子体增强化学气相沉积法(PECVD)将掺杂二氧化硅材料进行镀膜形成下层光波导介质薄膜，其中掺杂二氧化硅材料为2％锗掺杂二氧化硅；
S2、使用原子层沉积法(ALD)将二氧化钛材料制备薄膜材料夹层22；
S3、将二氧化钛薄膜材料夹层通过纳米压印(NIL)或电子束光刻技术(electron beam lithography)或光学光刻技术(optical lithography)制备成所述二维晶格亚波长结构，其中，所述二维晶格亚波长结构的有效晶格常数和占空比在各个方向近似相同；
S4、使用等离子体增强化学气相沉积法(PECVD)将2％锗掺杂二氧化硅材料进行镀膜制备上层光波导介质薄膜，所述下层光波导介质薄膜和所述下层光波导介质薄膜形成所述双层光波导介质薄膜21；
S5、在双层光波导介质薄膜21和薄膜材料夹层22外圆周制备二氧化硅包层。
综上，由于本发明所提供的薄膜光波导的二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同，以使薄膜光波导的有效折射率近似各向同性，其克服了有效折射率近似各向同性的二维晶格亚波长结构的薄膜光波导设计结构复杂和工艺误差的问题，不需要额外的结构设计和改变二维晶格方向，简化了薄膜光波导的结构并保证了薄膜光波导的性能。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。

Claims (10)

  1. 一种薄膜光波导，包括硅基衬底以及设置在所述硅基衬底上的包层，其特征在于，所述薄膜光波导还包括设置在所述硅基衬底上的光波导芯层，所述光波导芯层设于所述包层之中并且所述光波导芯层折射率高于所述包层的折射率，所述光波导芯层包括双层光波导介质薄膜以及设置于所述双层光波导介质薄膜之间的薄膜材料夹层，所述薄膜材料夹层为二维晶格亚波长结构，所述二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同。
  2. 如权利要求1所述的薄膜光波导，其特征在于，所述二维晶格亚波长结构包括晶格点，所述有效晶格常数和所述占空比由所述晶格点的形状以及长宽确定。
  3. 如权利要求1所述的薄膜光波导，其特征在于，所述晶格点为椭圆形、十字交叉形、六角形以及八角形中的一种。
  4. 如权利要求1所述的薄膜光波导，其特征在于，所述二维晶格亚波长结构为布拉维晶格结构或准晶格结构。
  5. 如权利要求4所述的薄膜光波导，其特征在于，所述布拉维晶格为包括正方形或六角形。
  6. 如权利要求4所述的薄膜光波导，其特征在于，所述准晶格结构为八边形或十边形或十二边形。
  7. 如权利要求1所述的薄膜光波导，其特征在于，所述薄膜材料夹层为硅、掺杂二氧化硅、铌酸锂、二氧化钛、氧化锌以及镁掺杂氧化锌中的一种。
  8. 如权利要求1所述的薄膜光波导，其特征在于，所述光波导介质薄膜为掺杂二氧化硅。
  9. 如权利要求8所述的薄膜光波导，其特征在于，所述掺杂二氧化硅为2％锗掺杂二氧化硅。
  10. 一种用以制备权利要求1至9项中任一项所述的薄膜光波导的制备方法，其特征在于，所述制备方法如下：
    S1、提供硅基衬底，在所述硅基衬底上形成下层光波导介质薄膜；
    S2、制备薄膜材料夹层；
    S3、将所述薄膜材料夹层制备成所述二维晶格亚波长结构，其中，所述二维晶格亚波长结构的有效晶格常数和占空比在各个传播方向上近似相同；
    S4、制备上层光波导介质薄膜，所述下层光波导介质薄膜和所述下层光波导介质薄膜形成所述双层光波导介质薄膜；
    S5、制备所述包层。
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