WO2016179869A1 - 一种锥形波导及硅基芯片 - Google Patents

一种锥形波导及硅基芯片 Download PDF

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Publication number
WO2016179869A1
WO2016179869A1 PCT/CN2015/080909 CN2015080909W WO2016179869A1 WO 2016179869 A1 WO2016179869 A1 WO 2016179869A1 CN 2015080909 W CN2015080909 W CN 2015080909W WO 2016179869 A1 WO2016179869 A1 WO 2016179869A1
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Prior art keywords
waveguide
tapered
shallow etched
etched strip
length
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PCT/CN2015/080909
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English (en)
French (fr)
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赵飞
李明
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华为技术有限公司
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Priority to CN201580077733.8A priority Critical patent/CN107924024B/zh
Priority to EP15891572.8A priority patent/EP3287821B1/en
Publication of WO2016179869A1 publication Critical patent/WO2016179869A1/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
    • 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
    • G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
    • 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
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12097—Ridge, rib or the like
    • 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
    • G02B2006/121—Channel; buried or the like

Definitions

  • the invention relates to the technical field of communication, in particular to a tapered waveguide and a silicon-based chip.
  • silicon-based photoelectrons uniformly fabricate devices such as lasers, modulators, detectors, and optical switches onto silicon-on-insulator (SOI) materials, which are silicon-based chips.
  • SOI silicon-on-insulator
  • Waveguides are the most basic structure in silicon-based chips for connecting and forming various devices.
  • the waveguide is composed of a core layer composed of a high refractive index material, and a substrate and a cladding layer composed of a low refractive index material, and the substrate of the chip is usually a silicon substrate.
  • Rectangular waveguides and ridge waveguides are two types of waveguides commonly found in silicon-based chips: rectangular waveguides have a rectangular core section, as shown in Figure 2, which is used to connect various devices; ridge waveguides are made of higher-height central waveguides 1 And shallow etched strip waveguide 2 with low height on both sides, as shown in Figure 3, mostly used in functional devices, in MMI, DC (directional coupler), PBS (polarization beam splitter), PR (polarization converter) ), optical switches, modulators (PN junction waveguides are ridge waveguides) may appear.
  • MMI directional coupler
  • PBS polarization beam splitter
  • PR polarization converter
  • modulators PN junction waveguides are ridge waveguides
  • a tapered waveguide In order to connect a rectangular waveguide and a ridge waveguide, a tapered waveguide is required, so the tapered waveguide is also a basic device widely used in a silicon-based chip.
  • the existing tapered waveguide connecting the rectangular waveguide and the ridge waveguide adopts a linear structure: a cone
  • the width of the shaped waveguide increases uniformly with length.
  • the linear tapered waveguide is shown in Figure 1. It comprises a substrate 4, a substrate 3 disposed on the substrate 4, a central waveguide 1 and a shallow etched strip waveguide 2, and a cladding layer 5 encasing the central waveguide 1 and the shallow etched strip waveguide 2, wherein the shallow etched strip
  • the waveguide 2 is symmetrically disposed on both sides of the center waveguide, and the tapered waveguide width is equal to the sum of the widths of the side ridge waveguides and the width of the center waveguide.
  • the width of the shallow etched strip waveguide and the length of the tapered waveguide satisfy the linear relationship, and the effective refractive index of the waveguide and the width of the shallow etched strip waveguide do not satisfy the linear relationship, so the waveguide The effective refractive index and the length of the tapered waveguide also do not satisfy the linear relationship.
  • a tapered waveguide with a linear structure the region of which the shallow etched strip waveguide has a small width (for example, 0-0.3 um) occupies a relatively low overall length, but the corresponding effective refractive index change is relatively large, resulting in insertion loss. Larger; the shallow etched strip waveguide has a larger width (for example, 0.3-1 um), which is higher in the overall length, but the effective refractive index does not change much, and the insertion loss of the device cannot be reduced, but the length of the device is increased.
  • Disadvantage 1 The shallow etched strip has a relatively small width corresponding to a short length, and the effective refractive index changes drastically, resulting in a relatively large insertion loss of the device.
  • Disadvantage 2 The area of the shallow etched strip waveguide has a relatively long length, but the effective refractive index does not change significantly, and its effect on reducing the loss is not obvious, but the overall length of the device is relatively long.
  • the present invention provides a tapered waveguide and a silicon-based chip for reducing the loss of the tapered waveguide and reducing the length of the tapered waveguide.
  • a tapered waveguide including a center waveguide and a shallow etched strip waveguide disposed on both sides of the central waveguide, wherein each shallow etched strip waveguide is a structure having a width gradation,
  • the outline line of the shallow etched strip waveguide along a side of the length direction away from the center waveguide is a concave curved shape.
  • the width of the shallow etched strip waveguide of the tapered waveguide satisfies the relationship of the length of the tapered waveguide to the uniform variation of the effective refractive index of the tapered waveguide. law.
  • the width of the shallow etched strip waveguide of the tapered waveguide satisfies the parabolic equation as a function of length.
  • the width of the shallow etched strip waveguide of the tapered waveguide satisfies the elliptic equation as a function of length.
  • the method further includes a substrate carrying the central waveguide and the shallow etched strip waveguide, and a cladding layer encapsulating the central waveguide and the shallow etched strip waveguide, and each of the substrate and the cladding layer has a refractive index Lower than the refractive index of the central waveguide and the shallow etched strip waveguide.
  • the central waveguide and the shallow etched strip waveguide are fabricated from silicon, silicon nitride, a polymer, or a semiconductor material.
  • the substrate and the cladding layer are made of silicon dioxide, silicon nitride, boron-doped, phosphorous or antimony-doped glass. Made of materials.
  • the center waveguide height is higher than the shallow etched strip waveguide.
  • a silicon-based chip comprising the tapered waveguide of any of the above.
  • the silicon-based chip provided by the second aspect in the present invention, is optimized for the structure of the tapered waveguide, using a rectangular central waveguide and a concave shallow etched strip waveguide,
  • the length of the shallow etched strip waveguide is relatively long, so that the effective refractive index changes relatively slowly, which can effectively reduce the device insertion loss.
  • the length of the shallow etched strip waveguide is relatively short, but The effective refractive index does not change much, and does not increase the insertion loss of the device, but effectively reduces the length of the device.
  • FIG. 1 is a top plan view of a tapered waveguide in the prior art
  • FIG. 2 is a schematic cross-sectional view of a rectangular waveguide
  • Figure 3 is a schematic cross-sectional view of a ridge waveguide
  • FIG. 4 is a schematic structural diagram of a tapered waveguide according to an embodiment of the present invention.
  • FIG. 5 is a schematic structural diagram of a tapered waveguide according to Embodiment 1 of the present invention.
  • FIG. 6 is a schematic structural view of a tapered waveguide according to Embodiment 2 of the present invention.
  • FIG. 7 is a schematic structural diagram of a tapered waveguide according to Embodiment 3 of the present invention.
  • Figure 8 is a diagram showing the relationship between the width of the shallow etched strip waveguide and the effective refractive index
  • FIG. 9 is a comparison diagram of the loss of the tapered waveguide provided by the present invention and the waveguide of the prior art.
  • FIG. 4 shows a tapered waveguide provided by the present invention
  • FIGS. 5, 6, and 7 show different tapered structures provided by the present embodiment.
  • Shaped waveguide the shallow etched strip waveguide provided in this embodiment may also be called a shallow etched waveguide, a shallow etched strip waveguide, a shallow etched thin film waveguide, and a shallow etched slab waveguide.
  • the English names of other waveguides in this embodiment are as follows: ridge waveguide, rib waveguide, center waveguide (core Waveguide), shallow slab waveguide. Over cladding, buried cladding.
  • the embodiment of the present invention provides a tapered waveguide 50 including a central waveguide 10 and a shallow etched strip waveguide 20 disposed on both sides of the central waveguide 10, wherein each shallow etched strip waveguide 20
  • the outline line of the shallow etched strip waveguide 20 away from the center waveguide 10 along its length direction is a concave curved shape without abrupt changes.
  • the wider end of the tapered waveguide is connected to the rectangular waveguide 30, and the narrower end is connected to the ridge waveguide 40.
  • the recess in the concave curved shape in the above means that it is recessed toward the inside of the waveguide itself.
  • the structure of the tapered waveguide includes a central waveguide 10, a shallow etched strip waveguide 20, and a substrate further including a central waveguide 10 and a shallow etched strip waveguide 20, and a package enclosing the central waveguide 10 and the shallow etched strip waveguide 20.
  • the cladding layer and the refractive index of each of the substrate and the cladding layer are lower than the refractive indices of the central waveguide 10 and the shallow etched strip waveguide 20.
  • the refractive index for the present embodiment refers to the characteristics of the material itself, that is, the change in the refractive index of the light of the same wavelength.
  • the central waveguide 10 and the shallow etched strip waveguide 20 are made of a material having a high refractive index
  • the substrate and the cladding layer are made of a material having a low refractive index
  • the center waveguide 10 and the shallow are specifically fabricated.
  • the etched strip waveguide 20 can be fabricated from silicon, silicon nitride, polymer or semiconductor materials.
  • the substrate and the cladding layer may be made of a glass material of silicon dioxide, silicon nitride, or boron, phosphorus or antimony. The fraction of boron, phosphorus and antimony doped in the glass material may be a fraction already existing in the prior art, which is not limited herein.
  • the center waveguide 10 is higher in height than the shallow etched strip waveguide 20. And the center waveguide 10 is located at the center line of the tapered waveguide 50, and the structure of the shallow etched strip waveguide 20 on both sides of the center waveguide 10 is centrally symmetrical.
  • the effective refractive index is an important and commonly used parameter in the optical waveguide. Its value is related to the cross-sectional shape of the waveguide and the refractive index of the waveguide material. Once the cross-sectional shape and material of the waveguide are determined, the effective refractive index of the waveguide will also be determined. The value can be calculated by simulation software.
  • the effective refractive index value is related to the mode of the waveguide, and the different modes correspond to different effective refractive indices. Effective in this patent
  • the refractive index refers to the effective refractive index of the fundamental mode of the tapered waveguide.
  • the fundamental mode of the waveguide refers to the TE zero-order mode in the waveguide, referred to as TE0.
  • the effective refractive index refers to an effective refractive index corresponding to the working wavelength of the tapered waveguide.
  • FIG. 8 shows a correspondence diagram between the width of the shallow etched strip waveguide and the effective refractive index, and the corresponding center waveguide width is 0.5 um. From FIG. 8, it can be found that the shallow etched strip waveguide width When the effective refractive index is changed, the smaller the width of the shallow etched strip waveguide 20 is, the larger the variation is. When the width of the shallow etched strip waveguide 20 is greater than about 0.5 to 1 um, the effective refractive index of the waveguide does not change significantly.
  • the loss of the tapered waveguide is mainly due to the mode mismatch of the light transmitted in the waveguide, the surface roughness of the silicon waveguide, and the absorption loss of the waveguide.
  • the latter two are determined by the manufacturing process and the waveguide material, and are independent of the structure of the tapered waveguide itself.
  • the structural shape of the tapered waveguide can be optimized for mode mismatch, reducing insertion loss. Therefore, in the tapered waveguide provided in this embodiment, the structure of the shallow etched strip waveguide 20 is optimized, and the length of the shallow etched strip waveguide 20 is used. The length of the effective refractive index is relatively slow, which can effectively reduce the insertion loss of the device.
  • the length of the shallow etched strip waveguide is relatively short (that is, the length of the wider portion of the shallow etched strip waveguide is smaller than the shallow The length of the narrower portion of the etched waveguide), but the effective refractive index does not change much, does not increase the insertion loss of the device, but effectively reduces the length of the device, facilitating the development of miniaturization.
  • the function f(x) w of the shallow etched strip waveguide width w and the length x in this embodiment satisfies f"(x)>0 (the second derivative of the function is greater than 0).
  • the shallow engraving is provided. The understanding of the etched waveguide will be described in detail below with reference to the accompanying drawings.
  • the structure of the tapered waveguide provided in this embodiment includes a central waveguide 10, a shallow etched strip waveguide 21, and a substrate and a cladding layer surrounding the central waveguide 10 and the shallow etched strip waveguide 21, the material and positional relationship of each part and the total The same is true for the tapered waveguide provided in the embodiment, and will not be further described herein.
  • the width of the shallow etched strip waveguide 21 in the tapered waveguide provided by the present embodiment is long.
  • the degree change relationship satisfies the law that the effective refractive index of the waveguide changes uniformly with the length.
  • the effective refractive indices of the ridge waveguide 40 and the rectangular waveguide 30 are n1 and n2, respectively.
  • the effective refractive index at any length x (from the end of the tapered waveguide 50 connected to the rectangular waveguide 30) can be found to be n2+x/L*(n1-n2);
  • the refractive index varies with the width of the shallow etched strip waveguide 21 (as shown in Fig. 8, which can be obtained using simulation software), and the width of the corresponding shallow etched strip waveguide 21 can be obtained, thereby obtaining a shallow etched strip waveguide 21 along the tapered waveguide. Line type on both sides in the length direction.
  • the inverse function g(neff) of the effective refractive index and the width of the shallow etched strip waveguide 21 can be calculated.
  • w both numerical solution and analytical solution are possible
  • the central waveguide 10 has a width Wc
  • the shallow etched strip waveguides 20 on both sides have a width w (ie, a width of the tapered waveguide 50 on the side of the central waveguide 10, the value of which varies with length), and a cone
  • the total width of the waveguide is Wc+w*2, and the length of the tapered waveguide is L.
  • the two ends of the tapered waveguide are respectively connected to the rectangular waveguide 30 and the ridge waveguide 40.
  • the width of the rectangular waveguide 30 is Wc
  • the width of the ridge waveguide 40 is Wc+Ws*2 (the width of the shallow etched strip waveguide on both sides is Ws, the center waveguide width For Wc).
  • the material and the positional relationship of the substrate and the cladding layer, the center waveguide 10 and the shallow etched strip waveguide 22 in the structure of the tapered waveguide provided in this embodiment are the same as the tapered waveguide provided in the general embodiment. The same, no longer repeat them here.
  • the linearity of the shallow etched strip waveguide 22 of the tapered waveguide provided by the present embodiment is changed.
  • the width of the shallow etched strip waveguide 22 varies with length to satisfy the parabolic equation.
  • the relationship between the tapered waveguide line type and the parabola is shown in Fig. 6.
  • the relationship between the width w of the shallow etched strip waveguide 22 and the length x of the waveguide can be determined as follows:
  • L is the total length of the tapered waveguide 50 and Ws is the maximum width of the shallow etched strip waveguide 22 of the tapered waveguide (equal to the width of the shallow etched strip on either side of the ridge waveguide to which it is connected).
  • Wo is the vertical distance from the wider end of the tapered waveguide 50 to the centerline of the parabola of the outer line shape of the shallow etched strip waveguide 22.
  • the material and the positional relationship of the substrate and the cladding layer, the center waveguide 10 and the shallow etched strip waveguide 23 in the structure of the tapered waveguide provided in this embodiment are the same as the tapered waveguide provided in the general embodiment. The same, no longer repeat them here.
  • the linear shape of the shallow etched strip waveguide 23 of the tapered waveguide provided by the present embodiment is changed.
  • the width of the shallow etched strip waveguide 23 satisfies the elliptic equation as a function of length.
  • the relationship between the tapered waveguide line type and the ellipse is shown in Figure 7! The reference source was not found.
  • the relationship between the width w of the shallow etched strip waveguide 23 and the length x of the waveguide can be determined as follows:
  • L is the total length of the tapered waveguide 50
  • Ws is the maximum width of the shallow etched strip waveguide 23 (equal to the width of the shallow etched strip on either side of the ridge waveguide connected thereto).
  • Wo is the vertical distance from the wider end of the tapered waveguide 50 to the center line of the long axis of the ellipse of the shallow etched strip waveguide 23.
  • the linear shape of the shallow etched strip waveguide in the tapered waveguide provided in this embodiment may adopt different concave curved lines, and the specific linear shape is not limited to the specific embodiment 1.
  • the linear shapes provided in Embodiment 2 and Embodiment 3 can also adopt other shapes.
  • the present embodiment compares the insertion loss of three different linear structures of the tapered waveguide, and the result is shown in FIG.
  • the linear type is a structure of a tapered waveguide used in the prior art, wherein the concave type is a structure of a tapered waveguide provided according to the present invention, and the concave type 1 and the concave type 2 are different in that the concave line shape is different.
  • the line shape note that it does not correspond to Embodiments 1, 2.
  • the convex shape is a structure similar to the tapered waveguide provided by the embodiment, and the difference is that the linear shape of the shallow etched strip waveguide adopts an outwardly convex shape, and the difference between the outer convex shape 1 and the outer convex shape 2 is The difference in the convex arc.
  • the tapered waveguide invention provided by the embodiment can significantly reduce the insertion loss of the device. And significantly reduce the length of the device, increasing the integration of the chip.
  • the device of the tapered waveguide provided by the embodiment is simple in structure, compatible with the CMOS process, and easy to integrate. And the process requirements are lower, and the process error has a higher tolerance.
  • the embodiment of the invention further provides a silicon-based chip comprising the tapered waveguide of any of the above.
  • the tapered waveguide of any of the above is included, and therefore, the tapered waveguide structure and the effect are adopted, that is, a rectangular center waveguide and a concave shallow etched strip waveguide are used.
  • the length of the region where the width of the etched strip waveguide is small is relatively long, so that the effective refractive index changes relatively slowly, which can effectively reduce the insertion loss of the device; at the same time, the length of the region where the shallow etched strip waveguide has a large width is relatively short, but effective The change in refractive index is not large, and the insertion loss of the device is not increased, but the length of the device is effectively reduced, and the miniaturization is facilitated.

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Abstract

一种锥形波导，包括中心波导（10）以及设置在该中心波导两侧的浅刻蚀条波导（20），其中，每个浅刻蚀条波导（20）为宽度渐变的结构，浅刻蚀条波导（20）沿其长度方向远离中心波导（10）的外形线为没有突变的内凹弧形。该锥形波导的有效折射率变化相对缓慢，有效减小了器件插损；同时，在浅刻蚀条波导宽度较大的区域长度比较短，有效减小了器件长度，有利于器件的小型化。还披露了一种硅基芯片。

Description

一种锥形波导及硅基芯片 技术领域
本发明涉及到通讯的技术领域，尤其涉及到一种锥形波导及硅基芯片。
背景技术
随着互联网的发展，特别是云计算、云存储、移动互联网的兴起，对于通信网络的传输速率和通信质量提出了更高的要求，现有的电交换由于背板、能耗等技术的限制已经不能满足交换容量持续增长的需求。全光交换和全光信号处理具有低能耗，大容量等优点，是未来宽带通信的发展方向。
硅基光电子作为全光信号处理中的一种主流技术，将激光器、调制器、探测器和光开关等器件统一制作到绝缘体硅(SOI)材料上，即为硅基芯片。硅基光芯片具有高带宽、低功耗、与现有的CMOS工艺兼容的优点，是未来全光交换的发展方向和关键技术。
波导是硅基芯片中最基础的一种结构，用于连接和构成各种器件。波导由高折射率材料组成的芯层，以及低折射率材料组成的衬底和包覆层构成，芯片的基底通常是硅基。
矩形波导和脊形波导是硅基芯片中常见的两种波导：矩形波导的芯层截面为矩形，如图2所示，多用于连接各种器件；脊形波导由高度较高的中心波导1和两侧高度较低的浅刻蚀条波导2组成，如图3所示，多用于功能器件中，在MMI，DC(定向耦合器)、PBS(偏振分束器)、PR(偏振转换器)、光开关、调制器(PN结波导是脊形波导)中都可能出现。
为了连接矩形波导和脊形波导，就需要使用锥形波导，所以锥形波导也是硅基芯片中应用十分广泛的一种基础器件。
现有的连接矩形波导和脊形波导的锥形波导采用的均是直线型结构：即锥 形波导的宽度随长度均匀增加。直线型锥形波导如图1所示。其包含基底4，设置在基底4上的衬底3、中心波导1及浅刻蚀条波导2，以及包裹中心波导1及浅刻蚀条波导2的包覆层5，其中，浅刻蚀条波导2对称设置在中心波导的两侧，锥形波导宽度等于两侧脊波导宽度与中心波导宽度之和。
对于直线型的锥形波导，浅刻蚀条波导的宽度与锥形波导的长度满足线型变化关系，而波导的有效折射率与浅刻蚀条波导的宽度不满足线型变化关系，因而波导的有效折射率与锥形波导的长度也不满足线型变化关系。
采用直线型结构的锥形波导，其浅刻蚀条波导宽度较小(例如0-0.3um)的区域在整体长度中占比较低，然而其对应的有效折射率变化又比较大，导致插损较大；其浅刻蚀条波导宽度较大(例如0.3-1um)的区域在整体长度中占比较高，但有效折射率变化不大，不能降低器件的插损，反而增加了器件的长度。
缺点一：浅刻蚀条波导宽度较小的区域对应长度比较短，有效折射率变化剧烈，导致器件的插损比较大。
缺点二：浅刻蚀条波导宽度较大的区域长度比较长，但有效折射率没有明显变化，其对于降低损耗作用不明显，却导致器件整体长度比较长。
发明内容
本发明提供了一种锥形波导及硅基芯片，用以降低锥形波导的耗损，并降低锥形波导的长度。
第一方面，提供了一种锥形波导，该锥形波导包括中心波导以及设置在所述中心波导两侧的浅刻蚀条波导，其中，每个浅刻蚀条波导为宽度渐变的结构，所述浅刻蚀条波导沿其长度方向的远离所述中心波导的一侧的外形线为内凹弧形。
结合上述第一方面，在第一种可能的实现方式中，所述锥形波导的浅刻蚀条波导宽度随长度变化关系满足锥形波导的有效折射率随长度均匀变化的规 律。
结合上述第一方面，在第二种可能的实现方式中，所述锥形波导的浅刻蚀条波导宽度随长度变化关系满足抛物线方程。
结合上述第一方面，在第三种可能的实现方式中，所述锥形波导的浅刻蚀条波导的宽度随长度变化关系满足椭圆方程。
结合上述第一方面、第一方面的第一种可能的实现方式、第一方面的第二种可能的实现方式、第一方面的第三种可能的实现方式，在第四种可能的实现方式中，还包括承载所述中心波导及浅刻蚀条波导的衬底，以及包裹所述中心波导及浅刻蚀条波导的包覆层，且所述衬底和包覆层各自的折射率均低于所述中心波导及浅刻蚀条波导的折射率。
结合上述第一方面的第五种可能的实现方式，在第六种可能的实现方式中，所述中心波导及浅刻蚀条波导由硅、氮化硅、聚合物或半导体材料制作而成。
结合上述第一方面的第五种可能的实现方式，在第七种可能的实现方式中，所述衬底和包覆层由二氧化硅、氮化硅、掺杂硼、磷或锗的玻璃材料制作而成。
结合上述第一方面的第五种可能的实现方式，在第八种可能的实现方式中，所述中心波导高度高于所述浅刻蚀条波导。
第二方面，提供了一种硅基芯片，该硅基芯片包括上述任一项所述的锥形波导。
根据第一方面提供的锥形波导，第二方面提供的硅基芯片，在本发明中，针对锥形波导的结构进行了优化，采用矩形的中心波导及内凹形的浅刻蚀条波导，浅刻蚀条波导宽度较小的区域长度比较长，使得有效折射率变化相对缓慢，可以有效地减小器件插损；同时，在浅刻蚀条波导宽度较大的区域长度比较短，但由于有效折射率变化不大，没有增大器件的插损，但有效减小了器件的长度， 便于小型化发展。
附图说明
图1为现有技术中的锥形波导的俯视图；
图2为矩形波导截面示意图；
图3为脊形波导截面示意图；
图4为本发明实施例提供的锥形波导的结构示意图；
图5为本发明实施例一提供的锥形波导的结构示意图；
图6为本发明实施例二提供的锥形波导的结构示意图；
图7为本发明实施例三提供的锥形波导的结构示意图；
图8为浅刻蚀条波导的宽度与有效折射率的对应关系图；
图9为本发明提供的锥形波导与现有技术中波导的耗损对比图。
附图标记：
1-中心波导    2-浅刻蚀条波导    3-衬底
4-基底    5-包覆层    10-中心波导
20-浅刻蚀条波导    21-浅刻蚀条波导
22-浅刻蚀条波导    23-浅刻蚀条波导
30-矩形波导    40-脊形波导    50-锥形波导
具体实施方式
以下结合附图对本发明的具体实施例进行详细说明。应当理解的是，此处所描述的具体实施方式仅用于说明和解释本发明，并不用于限制本发明。
如图4、图5、图6及图7所示，图4示出了本发明提供的供的锥形波导，图5、图6及图7示出了本实施例提供的不同结构的锥形波导。为了方便理解，本实施例提供的浅刻蚀条波导也可以叫浅刻蚀波导、浅刻蚀条形波导，浅刻蚀薄膜波导，浅刻蚀平板波导。此外，本实施例中其他的波导对应的英文名称如下：矩形波导(ridge waveguide)、脊形波导(rib waveguide)，中心波导(core  waveguide)，浅刻蚀条波导(slab waveguide)。包覆层(upper cladding)，衬底(buried cladding)。
本发明实施例提供了一种锥形波导50，该锥形波导50包括中心波导10以及设置在所述中心波导10两侧的浅刻蚀条波导20，其中，每个浅刻蚀条波导20为宽度渐变的结构，浅刻蚀条波导20沿其长度方向的远离中心波导10的外形线为没有突变的内凹弧形。锥形波导较宽的一端与矩形波导30连接，较窄的一端与脊形波导40连接。
在本实施例中，上述中的内凹弧形中的内凹是指朝向波导本身内部凹陷。锥形波导的结构包括中心波导10、浅刻蚀条波导20以及还包括承载中心波导10及浅刻蚀条波导20的衬底，以及包裹所述中心波导10及浅刻蚀条波导20的包覆层，且所述衬底和包覆层各自的折射率均低于中心波导10及浅刻蚀条波导20的折射率。针对本实施例中的折射率所指的是材料本身的特性，即针对同一波长的光线的折射率的变化情况。具体的，中心波导10及浅刻蚀条波导20由高折射率的材料制备而成，而衬底和包覆层由低折射率的材料制作而成，在具体制作时，中心波导10及浅刻蚀条波导20可以采用硅、氮化硅、聚合物或半导体材料制作而成。衬底和包覆层可以采用二氧化硅、氮化硅、掺杂硼、磷或锗的玻璃材料制作而成。其中，玻璃材料中掺杂的硼、磷及锗元素的分数可以采用现有技术中已有的分数，在此不进行限定。此外，在制作成的锥形波导中，中心波导10高度高于浅刻蚀条波导20。并且中心波导10位于锥形波导50的中心线处，位于中心波导10两侧的浅刻蚀条波导20的结构呈中心对称。
有效折射率是光波导中的一个重要和常用的参数，其数值与波导的截面形状和波导材料的折射率有关，一旦波导的截面形状和材料确定，波导的有效折射率也将确定，具体的数值可以通过仿真软件进行计算得到。有效折射率数值与波导的模式相关，不同的模式对应的有效折射率不同。本专利中提到的有效 折射率是指锥形波导基模的有效折射率。波导的基模是指波导中的TE零阶模，简称TE0。其中，有效折射率是指锥形波导工作波长对应的有效折射率。
如图8所示，图8示出了浅刻蚀条波导宽度与有效折射率之间的对应关系图，对应的中心波导宽度为0.5um，由图8可以发现随着浅刻蚀条波导宽度增加，有效折射率会发生变化，而且浅刻蚀条波导20宽度越小时，变化越大，浅刻蚀条波导20宽度大于0.5～1um左右时，波导的有效折射率不再发生明显变化。锥形波导的损耗主要来源于光在波导中传输时的模式不匹配、硅波导表面粗糙度、波导吸收损耗，后两项由制造工艺和波导材料决定，与锥形波导本身的结构无关，所以可以针对模式不匹配对锥形波导的结构形状进行优化，降低插损。因此，在本实施例提供的锥形波导中，针对浅刻蚀条波导20的结构进行了优化，采用内凹形的浅刻蚀条波导20，浅刻蚀条波导宽度较小的区域长度比较长，使得有效折射率变化相对缓慢，可以有效地减小器件插损；同时，在浅刻蚀条波导宽度较大的区域长度比较短(即浅刻蚀条波导较宽部分的长度小于浅刻蚀条波导较窄部分的长度)，但由于有效折射率变化不大，没有增大器件的插损，但有效减小了器件的长度，便于小型化发展。
本实施例中的浅刻蚀条波导宽度w与长度x的函数f(x)＝w满足f”(x)>0(函数的二次导数大于0)。为了方便对本实施例提供的浅刻蚀条波导的理解，下面结合附图对其结构进行详细的说明。
实施例1
本实施例提供的锥形波导的结构包括中心波导10、浅刻蚀条波导21以及包围中心波导10及浅刻蚀条波导21的衬底和包覆层，各部分的材料以及位置关系与总实施例中提供的锥形波导的相同，在此不再一一赘述。
继续参考图5，本实施例提供的锥形波导中的浅刻蚀条波导21的宽度随长 度变化关系满足波导的有效折射率随长度均匀变化的规律。
脊形波导40和矩形波导30的有效折射率分别为n1、n2。
由于有效折射率随长度均匀变化，可以求出任意长度x处(从锥形波导50连接矩形波导30的一端算起)的有效折射率为n2+x/L*(n1-n2)；根据有效折射率随浅刻蚀条波导21宽度变化关系(如图8，可以使用仿真软件求出)，可以得到对应的浅刻蚀条波导21宽度，从而得到锥形波导的浅刻蚀条波导21沿长度方向的两侧的线型。
一般地，若有效折射率neff与浅刻蚀条波导21宽度w的函数关系为f(w)＝neff，由此可以算出有效折射率与浅刻蚀条波导21宽度的反函数g(neff)＝w(数值解和解析解都可以)，则有效折射率均匀变化的锥形波导的浅刻蚀条波导21的宽度w与波导长度x的关系为：h(x)＝g(n2+x/L*(n1-n2))＝w。
如图4所示，设中心波导10宽度为Wc，两侧的浅刻蚀条波导20宽度为w(即锥形波导50中位于中心波导10一侧的宽度，其数值随长度变化)，锥形波导的总宽度为Wc+w*2，锥形波导的长度为L。锥形波导两端分别与矩形波导30和脊形波导40连接，矩形波导30宽度为Wc，脊形波导40宽度为Wc+Ws*2(两侧浅刻蚀条波导宽度为Ws，中心波导宽度为Wc)。
实施例2
如图6所示，本实施例提供的锥形波导的结构中的衬底和包覆层、中心波导10及浅刻蚀条波导22的材料以及位置关系与总实施例中提供的锥形波导的相同，在此不再一一赘述。与实施例1相比，本实施例提供的锥形波导的浅刻蚀条波导22的线性发生了改变。
具体的，浅刻蚀条波导22宽度随长度变化关系满足抛物线方程。锥形波导线型与抛物线关系如图6所示，抛物线方程为y＝ax2，a>0，w0≥0。可以求得浅刻蚀条波导22的宽度w与波导长度x的关系为：
Figure PCTCN2015080909-appb-000001
其中，L为锥形波导50的总长度，Ws为锥形波导的浅刻蚀条波导22的最大宽度(等于与之连接的脊形波导两侧的浅刻蚀条宽度)。Wo为锥形波导50较宽的一端到浅刻蚀条波导22的外线形所在抛物线的中心线的垂直距离。
实施例3
如图7所示，本实施例提供的锥形波导的结构中的衬底和包覆层、中心波导10及浅刻蚀条波导23的材料以及位置关系与总实施例中提供的锥形波导的相同，在此不再一一赘述。与实施例1相比，本实施例提供的锥形波导的浅刻蚀条波导23的线形发生了改变。
具体的，浅刻蚀条波导23的宽度随长度变化关系满足椭圆方程。锥形波导线型与椭圆关系如图7错误！未找到引用源。所示，椭圆方程为x2/a2+y2/b2＝0，a>0，b>0，w0≥0。可以求得浅刻蚀条波导23的宽度w与波导长度x的关系为：
Figure PCTCN2015080909-appb-000002
其中，L为锥形波导50的总长度，Ws为浅刻蚀条波导23的最大的宽度，(等于与之连接的脊形波导两侧的浅刻蚀条宽度)。Wo为锥形波导50较宽的一端到浅刻蚀条波导23的外线形所在椭圆长轴的中心线的垂直距离。
通过上述具体的实施例可以看出，本实施例提供的锥形波导中的浅刻蚀条波导的线形可以采用不同的内凹形的弧形线形，具体的线形不局限在具体实施例1、实施例2及实施例3提供的线形形状，还可以采用其他的形状。
为了方便对本实施例提供的锥形波导的效果有更佳清晰的理解，本实施例将三种不同线形结构的锥形波导的插入损耗进行了实验对比，其结果如图9所 示，其中直线型为现有技术中采用的锥形波导的结构，其中的内凹型为根据本发明提供的锥形波导的结构，内凹型1及内凹型2的区别在于内凹的线形采用不同的线形，注意其不对应实施例1、2。其中的外凸型为类似本实施例提供的锥形波导的结构，其区别在于浅刻蚀条波导的线形采用向外凸出的形状，并且外凸形1与外凸形2的区别在与凸出的弧形的不同。通过对比上述直线型、内凹型1、内凹型2、外凸形1及外凸型2的实验结果可以看出，采用内凹型结构的锥形波导损耗普遍小于直线型，外凸型锥形波导损耗最大，与之前的分析结果相同。对于同样长度的锥形波导，采用内凹型结构，损耗可大幅降低。因此，本实施例提供的锥形波导发明能够明显减小器件的插损。并且明显减小器件的长度，增加芯片的集成度。此外，本实施例提供的锥形波导的器件结构简单，与CMOS工艺相容，容易集成。并且工艺要求较低，工艺误差有较高的容忍度。
本发明实施例还提供了一种硅基芯片，该硅基芯片包括上述任一项所述的锥形波导。
在本实施例提供的硅基芯片中，包含上述任一种的锥形波导，因此，具有上述锥形波导结构及效果，即采用矩形的中心波导及内凹形的浅刻蚀条波导，浅刻蚀条波导宽度较小的区域长度比较长，使得有效折射率变化相对缓慢，可以有效地减小器件插损；同时，在浅刻蚀条波导宽度较大的区域长度比较短，但由于有效折射率变化不大，没有增大器件的插损，但有效减小了器件的长度，便于小型化发展。
显然，本领域的技术人员可以对本发明进行各种改动和变型而不脱离本发明的精神和范围。这样，倘若本发明的这些修改和变型属于本发明权利要求及其等同技术的范围之内，则本发明也意图包含这些改动和变型在内。

Claims (9)

  1. 一种锥形波导，包括中心波导以及设置在所述中心波导两侧的浅刻蚀条波导，其特征在于，每个浅刻蚀条波导为宽度渐变的结构，所述浅刻蚀条波导沿其长度方向的远离所述中心波导的一侧的外形线为内凹弧形。
  2. 如权利要求1所述的锥形波导，其特征在于，所述浅刻蚀条波导宽度随长度变化关系满足锥形波导的有效折射率随长度均匀变化的规律。
  3. 如权利要求1所述的锥形波导，其特征在于，所述浅刻蚀条波导宽度随长度变化关系满足抛物线方程。
  4. 如权利要求1所述的锥形波导，其特征在于，所述浅刻蚀条波导的宽度随长度变化关系满足椭圆方程。
  5. 如权利要求1～4任一项所述的锥形波导，其特征在于，还包括承载所述中心波导及浅刻蚀条波导的衬底，以及包裹所述中心波导及浅刻蚀条波导的包覆层，且所述衬底和包覆层各自的折射率均低于所述中心波导及浅刻蚀条波导的折射率。
  6. 如权利要求5所述的锥形波导，其特征在于，所述中心波导及浅刻蚀条波导由硅、氮化硅、聚合物或半导体材料制作而成。
  7. 如权利要求5所述的锥形波导，其特征在于，所述衬底和包覆层由二氧化硅、氮化硅、掺杂硼、磷或锗的玻璃材料制作而成。
  8. 如权利要求5所述的锥形波导，其特征在于，所述中心波导高度高于所述浅刻蚀条波导。
  9. 一种硅基芯片，其特征在于，包括如权利要求1～8任一项所述的锥形波导。
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