WO2022012434A1 - 一种高密度集成光波导 - Google Patents

一种高密度集成光波导 Download PDF

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WO2022012434A1
WO2022012434A1 PCT/CN2021/105519 CN2021105519W WO2022012434A1 WO 2022012434 A1 WO2022012434 A1 WO 2022012434A1 CN 2021105519 W CN2021105519 W CN 2021105519W WO 2022012434 A1 WO2022012434 A1 WO 2022012434A1
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waveguide
curved
waveguides
straight
coupling
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French (fr)
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李涛
宋万鸽
祝世宁
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Nanjing University
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Nanjing University
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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
    • 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
    • G02B6/125—Bends, branchings or intersections
    • 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
    • G02B2006/12119—Bend

Definitions

  • the invention relates to the field of integrated photonics, in particular to a high-density integrated optical waveguide.
  • Silicon-on-insulator has become one of the most widely used platforms in integrated photonics, and based on this, many photonic devices with a wide range of applications have been developed, such as waveguides, directional couplers, etc.
  • SOI Silicon-on-insulator
  • the existence of the diffraction limit increases the crosstalk between components, thus limiting the further improvement of the chip integration degree.
  • these integrated photonic devices generally exhibit structure and wavelength sensitivity. Therefore, how to realize crosstalk-free transmission and broadband coupling of signals in a high-density integrated chip in a wide band is an urgent problem to be solved in the current chip industry.
  • the first is to adjust the width of the waveguide to increase the mode mismatch to reduce the crosstalk.
  • This method requires the width of the waveguide to be designed; the second is to adjust the width of the waveguide.
  • Several auxiliary small waveguides are inserted between them to reduce the crosstalk by reducing the width of the waveguide mode. Since the size of the auxiliary waveguides is often small, it is also a challenge for large-scale processing.
  • broadband coupling there are currently two mainstream schemes. One is to introduce the compensation process of the Mach-Zehnder interferometer, which can adjust the phase on one arm of the interferometer through thermal effects, electro-optic effects, etc., so as to realize the dynamic modulation of the coupling distance.
  • the purpose of the present invention is to provide a high-density integrated optical waveguide to solve the problem that the current integrated chip mainly based on straight waveguides cannot get rid of the sensitivity and dependence on parameters such as waveguide spacing and wavelength under high-density integration.
  • the present invention provides the following scheme:
  • a high-density integrated optical waveguide the optical waveguide is arranged on a waveguide substrate, comprising: a plurality of curved waveguides;
  • a rectangular coordinate system is established with the bending direction of the curved waveguide as the y-axis and the propagation direction of the light as the x-axis; and based on the rectangular coordinate system, the curved waveguide is periodic along the propagation direction in the bending direction sexual bending;
  • a plurality of curved waveguides are arranged in parallel along the y-axis direction, and the curved waveguides are perpendicular to the y-axis direction to form a curved waveguide array; the optical waveguide is realized by adjusting the coupling coefficient between the curved waveguides Optical waveguide signal transmission function or optical waveguide directional coupling function.
  • the coupling coefficient is adjusted according to the bending amplitude of the bending waveguide, the bending period, the incident wavelength of the incident light, the refractive index of the waveguide substrate, and the period interval of the bending waveguide.
  • c is the coupling coefficient between the curved waveguides
  • c 0 is the coupling coefficient between straight waveguides, c 0 >0, the straight waveguide is the first straight waveguide or the second straight waveguide
  • A is the bending amplitude
  • P is the bending period
  • ⁇ is the incident wavelength
  • n 0 is the substrate refractive index.
  • the optical waveguide further includes: a first straight waveguide array and a second straight waveguide array;
  • the first straight waveguide array includes a plurality of first straight waveguides arranged in parallel along the y-axis;
  • the second straight waveguide array includes a plurality of second straight waveguides arranged in parallel along the y-axis; the The coupling coefficient between the first straight waveguides is equal to the coupling coefficient between the second straight waveguides, and the coupling coefficient between the first straight waveguides and the coupling coefficient between the second straight waveguides are both greater than 0;
  • the output end of the first straight waveguide array is butted with the input end of the curved waveguide array
  • the output end of the curved waveguide array is butted with the input end of the second straight waveguide array
  • the first straight waveguide array The curved waveguide array and the second straight waveguide array form a three-level cascade structure; the incident light enters the three-level cascade structure from the input end of the first straight waveguide array, and the incident light is in the three-level cascade structure.
  • the first straight waveguide array diverges due to coupling, and the curved waveguide array re-converges the divergent light to the second straight waveguide array due to negative coupling.
  • the negative coupling strength is matched to realize the optical waveguide signal transmission function of broadband and low crosstalk.
  • the optical waveguide includes a plurality of the three-stage cascade structures; and the plurality of the three-stage cascade structures are arranged in parallel in the x-axis direction.
  • the coupling coefficient is less than 0, and the curved coupling array specifically includes two curved waveguides; the two curved waveguides are along the y-axis direction Arranged in parallel to realize the directional coupling function of optical waveguides in a wide band.
  • the periodic bending expression of the curved waveguide is:
  • y(x) is the periodic bending function of the bending waveguide; A is the bending amplitude; P is the bending period; It is the initial phase of bending.
  • the present invention discloses the following technical effects: the present invention provides a high-density integrated optical waveguide, a plurality of curved waveguides are arranged on a waveguide substrate to form a curved waveguide array, and the curved waveguides are adjusted by adjusting the curved waveguides.
  • the coupling coefficient between the waveguides realizes the optical waveguide signal transmission function or the optical waveguide directional coupling function of the optical waveguides.
  • the invention utilizes the regulation of the coupling by the curved waveguide, realizes the broadband low crosstalk transmission and robust coupling under high-density integration, exhibits quite good robustness to structural deviation and wavelength change, and improves the processing error tolerance, thereby Save processing costs.
  • the optical waveguide provided by the present invention does not require further adjustment and correction after processing, thereby avoiding additional energy consumption and loss; it is fully compatible with the current manufacturing process, does not bring additional processing difficulties, and is easy to scale Production requires low production accuracy.
  • FIG. 1 is a schematic diagram of a cascaded positive-coupling straight waveguide array and a negative-coupling curved waveguide array for realizing broadband low-crosstalk optical waveguide transmission;
  • FIG. 2 is a schematic diagram of a zero-coupling curved waveguide array for realizing broadband low-crosstalk optical waveguide transmission
  • FIG. 3 is a schematic diagram of a negatively coupled curved waveguide for realizing directional coupling of broadband robust optical waveguides
  • FIG. 4 is a schematic diagram of a straight waveguide array of N waveguides and a curved waveguide array of N waveguides;
  • FIG. 5 is a schematic diagram of a three-stage cascade structure formed by cascading two straight waveguide arrays and a curved waveguide array together;
  • Figure 6 shows the initial phase of the curved waveguide and the first phase Schematic diagram of connection with straight waveguide in two cases
  • FIG. 9 is a schematic diagram of the propagation of the optical field in the waveguide at 100 ⁇ m and 200 ⁇ m under the corresponding different wavelengths in the cascade structure;
  • FIG. 11 is a schematic diagram of the propagation of the corresponding optical field at different wavelengths by 100 ⁇ m in the cascade structure
  • Fig. 14 is a schematic diagram of the propagation of the optical field in the waveguide of 100 ⁇ m at different wavelengths corresponding to the zero-coupling curved waveguide;
  • Fig. 16 is a schematic diagram of the propagation of the corresponding optical field of 100 ⁇ m under different wavelengths of the zero-coupling curved waveguide;
  • 17 is a graph showing the relationship between the coupling coefficient c between the waveguides as a function of wavelength under the condition of different bending amplitudes A;
  • Figure 18 is a graph showing the variation of coupling degree with wavelength
  • Figure 19 is a graph showing the variation of isolation with wavelength
  • Figure 20 is a graph showing the change of directivity with wavelength
  • Figure 21 is a schematic diagram of the propagation of the optical field in the waveguide under different wavelengths of the straight waveguide
  • 22 is a schematic diagram of the propagation of the optical field in the waveguide under different wavelengths of the curved waveguide;
  • FIG. 23 is a graph showing the relationship between the coupling coefficient c between the waveguides and the spacing between the waveguides under the condition of different bending amplitudes A;
  • Figure 24 is a graph showing the variation of coupling degree with the spacing of the waveguides
  • FIG. 25 is a graph showing the variation of isolation with the spacing of the waveguides.
  • FIG. 26 is a graph showing the change of directivity with the spacing of the waveguides
  • Fig. 27 is a graph showing the propagation of the optical field in the waveguide under different waveguide spacings of the curved waveguide;
  • FIG. 28 is a graph showing the propagation of the optical field in the waveguide under different waveguide spacings of the curved waveguide.
  • 1 is a cascade structure of straight waveguide and curved waveguide (including multiple cascades); 2 is a curved waveguide array with zero coupling; 3 is two curved waveguides.
  • the purpose of the present invention is to provide a high-density integrated optical waveguide, which adopts the positive and negative coupling cascades brought by straight waveguides and curved waveguides to realize broadband low-crosstalk optical waveguide transmission;
  • Figure 2 is a schematic diagram of a zero-coupling curved waveguide array for broadband low-crosstalk optical waveguide transmission; the negative coupling brought by the curved waveguide is used for the stability of structure and wavelength to achieve robustness
  • broadband optical waveguide directional coupling as shown in FIG. 3 is a schematic diagram of a negatively coupled curved waveguide for realizing broadband robust optical waveguide directional coupling.
  • a high-density integrated optical waveguide the optical waveguide is arranged on a waveguide substrate, comprising: a plurality of curved waveguides; a rectangular coordinate system is established with the bending direction of the curved waveguide as the y-axis and the propagation direction of the light as the x-axis ; and based on the Cartesian coordinate system, the curved waveguide is periodically bent in the bending direction along the propagation direction; a plurality of curved waveguides are arranged in parallel along the y-axis direction, and the curved waveguide is parallel to the direction of the y-axis.
  • the y-axis directions are perpendicular to each other to form a curved waveguide array; the optical waveguide signal transmission function or the optical waveguide directional coupling function of the optical waveguide is realized by adjusting the coupling coefficient between the curved waveguides.
  • the curved waveguide is periodically curved along the propagation direction y in the x direction, for example, the curved shape is a trigonometric function: where A is the bending amplitude, P is the bending period, is the initial phase of bending, representing the initial state of the curved waveguide, as shown in Figure 6, showing the initial phase of the curved waveguide and the first phase Schematic diagram of the connection with the straight waveguide in both cases.
  • N is the total number of waveguides in the waveguide array, indicating the number of signal paths to be transmitted; M is the number of cascades, and M can be an integer greater than 1.
  • the coupling coefficient is adjusted according to the bending amplitude of the bending waveguide, the bending period, the incident wavelength of the incident light, the refractive index of the waveguide substrate, and the period interval of the bending waveguide.
  • the optical waveguide further includes: a first straight waveguide array and a second straight waveguide array;
  • the first straight waveguide array includes a plurality of first straight waveguides arranged in parallel along the y-axis a waveguide;
  • the second straight waveguide array includes a plurality of second straight waveguides arranged in parallel along the y-axis;
  • the coupling coefficient between the first straight waveguides is equal to the coupling coefficient between the second straight waveguides,
  • the coupling coefficient between the first straight waveguides and the coupling coefficient between the second straight waveguides are both greater than 0;
  • the output end of the first straight waveguide array is docked with the input end of the curved waveguide array, so
  • the output end of the curved waveguide array is butted with the input end of the second straight waveguide array, and the first straight waveguide array, the curved waveguide array and the second straight waveguide array form a three-stage cascade structure; the The incident light enters the three-stage cascade structure from the input end of
  • the optical waveguide includes a plurality of the three-stage cascade structures; and the plurality of the three-stage cascade structures are arranged in parallel in the x-axis direction.
  • N straight waveguides are arranged in parallel along the y direction to form a straight waveguide array structure, as shown in Figure 4, and then the straight waveguides in the straight waveguide array are arranged
  • the waveguide is bent to form a curved waveguide array structure, and then the two straight waveguide arrays and one curved waveguide array are butted along the x-direction to form a three-level cascade structure as shown in FIG. 5 .
  • Other multi-level cascade structures can be completed by connecting multiple straight waveguide arrays and curved waveguide arrays.
  • Each waveguide in the waveguide array is a channel for transmitting optical signals.
  • the optical signal entering from a certain waveguide can be output from the waveguide at the output end, while the waveguide without optical signal input is at the output end. There will be no optical signal output.
  • the signals will interact with each other.
  • a waveguide without signal input will also have a signal at the output, which is a crosstalk signal, and the smaller the waveguide array spacing, the more serious this crosstalk phenomenon will be, especially in the case of high-density integration (d ⁇ ⁇ / 2).
  • the crosstalk phenomenon generated in the straight waveguide structure can be eliminated.
  • this effect is broadband, low crosstalk or no crosstalk transmission under high-density integration can be realized in the broadband wavelength range. .
  • ci can be written as a function ci ( ⁇ ,x) of wavelength ⁇ and propagation distance x.
  • the coupling coefficient between dielectric straight waveguides is positive, and the magnitude of the coupling varies with wavelength. Therefore, to satisfy equation (2), one way is that there are both positive coupling and negative coupling in the cascade structure; the other way is that all coupling coefficients are equal to zero. In addition, if the transmission function of broadband is to be realized, then (2) must still be satisfied or approximately satisfied in a certain band.
  • the curved waveguide is analytically modeled as follows:
  • a curved waveguide is periodically bent in the y direction along the propagation direction x, for example, a bend in the shape of a trigonometric function:
  • A is the bending amplitude
  • P is the bending period
  • the coupling between the waveguides can be effectively reduced, and even zero or negative values can be taken.
  • the positive-coupling straight waveguides and the negatively-coupling curved waveguides are cascaded together to form a cascade structure. In straight waveguides, it diverges due to coupling, and in curved waveguides, it converges due to negative coupling, thereby realizing the transmission function. Alternatively, the transmission function can also be achieved with zero coupling.
  • Equation (2) can be satisfied in a certain band.
  • broadband optical waveguide transmission function can be realized. .
  • the incident light is transmitted in the curved waveguide array, so as to realize the optical waveguide signal transmission function of broadband and low crosstalk.
  • N bending waveguides In order to realize the transmission of multi-channel signals, it is first considered to arrange N bending waveguides in parallel along the y direction to form a single bending waveguide array.
  • the coupling coefficient in this array is zero, and can be approximately equal to zero in a certain band range. Light entering the waveguide array with zero coupling coefficient will not be coupled into adjacent waveguides, so a single curved waveguide array structure can also realize the function of low crosstalk transmission in a wide band.
  • the curved coupling array specifically includes two of the curved waveguides;
  • the waveguides are arranged in parallel along the y-axis direction to realize the directional coupling function of the optical waveguides in a wide band.
  • This structure is formed by arranging two curved waveguides in parallel along the y direction. By bending the waveguides, a broadband coupling effect between the waveguides can be achieved, that is, the optical signal entering from a certain waveguide can be in the broadband wavelength range. It is stably coupled to the adjacent waveguide to realize the broadband directional coupling function.
  • the coupling between the waveguides can be effectively reduced.
  • two curved waveguide structures are formed by arranging the two curved waveguides together in parallel along the y-direction.
  • the coupling effect of light between two curved waveguides can realize the directional coupling function of the waveguide, and maintain the directional coupling function in a very long wavelength band and a large change in the waveguide spacing.
  • ⁇ and ⁇ gap are the changes in wavelength and waveguide spacing, respectively.
  • the coupling in equations (4) and (5) takes a negative number. That is, stable negative coupling properties can be maintained in a large wavelength band or a large structural parameter variation range. At this time, a broadband optical waveguide directional coupling function with structural robustness can be realized.
  • the stable zero-coupling property can be maintained in a large waveband or a large range of structural parameters. At this time, a broadband optical waveguide transmission function with structural robustness can be realized.
  • bending the waveguide can realize the flexible regulation of the coupling effect between the waveguides.
  • the above-mentioned different functions such as broadband low crosstalk transmission and broadband directional coupling can be realized.
  • a curved waveguide is designed for a silicon waveguide on an alumina substrate in the near-infrared wavelength band in an air environment, and the invention is also applicable to other wavelength bands and material systems.
  • the optical waveguide transmission technology is based on two schemes: (1) Cascade structure of straight waveguides and curved waveguides (including multiple cascades), where a straight waveguide array is used to connect the curved waveguide array to the straight waveguide array Take the three-level cascade structure as an example; (2) a single curved waveguide array structure.
  • the optical waveguide directional coupling technology is based on (3) two curved waveguides.
  • COMSOL Multiphysics is used to simulate and test the device performance.
  • Figures 7-11 show the simulation results of cascading straight waveguides and curved waveguides to achieve broadband low crosstalk transmission.
  • the fundamental mode TE mode supported by the waveguide is used.
  • Figure 9 shows the propagation of the light field in the waveguide with different wavelengths of 100 ⁇ m and 200 ⁇ m. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band.
  • Figure 11 shows the propagation of the light field in the waveguide of this structure for 100 ⁇ m under different wavelengths. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band.
  • Figure 14 shows the propagation of the light field in the waveguide of this structure under different wavelengths.
  • Figure 16 shows the propagation of the light field in the waveguide of this structure for 100 ⁇ m under different wavelengths. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band.
  • Figures 17 to 22 show the simulation results of the bending waveguide to achieve broadband coupling.
  • the length is fixed, the energy distribution of the output port will also change.
  • the curved waveguide that is, A>0, it is found that the coupling coefficient between the two waveguides gradually becomes negative, and the coupling gradually slows down with the change of wavelength.
  • the length of the device was chosen to be 15.6 ⁇ m for the straight waveguide and 34.8 ⁇ m for the curved waveguide. It can be seen that, compared with the traditional straight waveguide coupler, the curved waveguide coupler has a lower coupling degree and a large bandwidth, and the bandwidth reaches nearly 200nm at a coupling degree of 1dB.
  • the curved waveguide coupler is superior to the traditional straight waveguide directional coupler in terms of isolation and directivity.
  • Figure 21 and Figure 22 intuitively show the propagation of the optical field in the straight waveguide coupler and the curved waveguide coupler. It can be seen that the optical field can be well coupled to another waveguide in the 1350-1550 nm band. In contrast, the performance of conventional straight-waveguide couplers varies dramatically with wavelength.
  • Figures 23-28 show the simulation results of structurally robust coupling achieved by curved waveguides.
  • the length is fixed, the energy distribution of the output port will also change.
  • A>0 it is found that the coupling coefficient between the two waveguides gradually becomes negative, and the coupling gradually slows down with the change of the spacing.
  • the length of the device was chosen to be 23 ⁇ m for the straight waveguide and 34.5 ⁇ m for the curved waveguide. It can be seen that compared with the traditional straight waveguide coupler, the curved waveguide coupler has a lower coupling degree, and the coupling degree can still be maintained less than 1dB under the change of the waveguide spacing near 200nm.
  • the curved waveguide coupler is superior to the traditional straight waveguide coupler in terms of isolation and directivity.
  • Figures 27 and 28 intuitively show the propagation of the optical field in the straight waveguide coupler and the curved waveguide coupler. It can be seen that even if the gap varies in a wide range from 200nm to 400nm, the optical field can still be well coupled to another root waveguide, while the performance of traditional straight-waveguide couplers varies drastically with the spacing of the waveguides.
  • the on-chip optical waveguide transmission and coupling based on curved waveguides can be expressed as:
  • the optical signal input from a certain waveguide port can realize the signal transmission function of wide band and low crosstalk through the cascade structure of positive coupling straight waveguide and negative coupling curved waveguide.
  • the negative coupling realized by the curved waveguide can realize the directional coupling function of the optical waveguide in a wide band.
  • the present invention adopts the positive and negative coupling cascading brought by straight waveguide and curved waveguide cascade to realize broadband low crosstalk optical waveguide transmission; adopts the zero coupling brought by the curved waveguide to the stability of wavelength to realize broadband low crosstalk optical waveguide transmission ; Adopting the stability of structure and wavelength due to the negative coupling brought by the curved waveguide to achieve robust and broadband optical waveguide directional coupling.
  • the present invention is fully compatible with the current manufacturing process, does not bring additional processing difficulties, is easy to mass-produce, and does not require high precision.

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Abstract

一种高密度集成光波导，光波导设于波导衬底上，包括：多根弯曲波导；以弯曲波导的弯曲方向为y轴，以光的传播方向为x轴建立直角坐标系；基于直角坐标系，弯曲波导沿着传播方向在弯曲方向上周期性弯曲；多根弯曲波导沿着y轴方向平行排列，且弯曲波导与y轴方向相互垂直，形成弯曲波导阵列；通过调节弯曲波导之间的耦合系数实现光波导的光波导信号传输功能或者光波导定向耦合功能。这种光波导摆脱了高密度集成下对波导间距、波长等参数的敏感性和依赖性，因此具有结构鲁棒性和宽带特性。

Description

一种高密度集成光波导
本申请要求于2020年07月17日提交中国专利局、申请号为202010690095.X、发明名称为“一种高密度集成光波导”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
本发明涉及集成光子领域，特别是涉及一种高密度集成光波导。
背景技术
随着现代物联网、大数据等行业的兴起，人类社会对更高速度、更大宽带网络容量、更强保密性等信息处理需求急剧增长，电学芯片显然到了瓶颈阶段。同理于集成电路的发展思路，将两个以上分立光学元件集成在一小片衬底上(厘米级以下)，可形成实现某种功能的集成光学芯片系统，它由于具有高速，低功耗和高密度集成的优点而有望成为大容量，高速率信息系统的有希望的发展方向。
而绝缘体上硅(SOI)已经成为集成光子学中最广泛使用的平台之一，基于此，人们已经发展出了许多具有广泛应用的光子器件，例如波导，定向耦合器等。然而，高密度集成的芯片中，衍射极限的存在使得元件之间的串扰增强，从而限制了芯片集成度的进一步提升。另一方面，这些集成光子器件通常表现出对结构和波长的敏感性。因此，如何在高密度集成的芯片中，在宽波段内实现信号的无串扰传输以及宽带耦合，是当前芯片行业急需解决的问题。
关于低串扰传输，目前主要有两种手段，第一种是调控波导的宽度，增大模式的失配从而减小串扰，这种方法需要对波导的宽度进行设计；第二种是在波导之间插入若干个辅助小波导，通过减小波导模式宽度来减小串扰，由于辅助波导尺寸往往很小，对于大规模的加工来说也是一个挑战。关于宽带耦合，目前主流方案有两种，一种是引入马赫-曾德尔干涉仪的补偿过程，可以通过热效应，电光效应等来调节干涉仪的一个臂上的相位，以实现耦合距离的动态调制；然而，在大规模集成中，它非常耗电并且具有很大的技术难度，并且尺寸很大。另一种是采用绝热的设计，同样，这种方案的尺寸也很大。此外，还有其他几种方案，如利用表面等离激元的设计，这种方案可以减小器件的尺寸，但是会引入较大的金属损耗。也可以采用非对称波导的设计，这种方案的损耗不大，尺寸也很小，但是对于带宽的提升却有限。最近，有报道基于使用局部 激光退火工艺可以实现可擦除的定向耦合器，它确实为按需制造提供了解决方案，然而，它将不可避免地引入更多的损耗并使整个加工过程更加繁琐。基于以上需求背景和技术现状可以看出，在目前集成芯片停留在直波导为主的设计范式下，在高密度集成、低串扰、高效率、鲁棒性、宽带这些重要性能指标上，某些性能的满足必然会牺牲掉其他一些性能，导致目前以直波导为主的集成芯片无法摆脱在高密度集成下对波导间距、波长等参数的敏感性和依赖性。如何同时实现高密度集成、低串扰、高效率、鲁棒性、宽带的集成器件，是集成光学技术领域研究人员长久以来追求的目标。
发明内容
本发明的目的是提供一种高密度集成光波导，以解决目前以直波导为主的集成芯片无法摆脱在高密度集成下对波导间距、波长等参数的敏感性和依赖性的问题。
为实现上述目的，本发明提供了如下方案：
一种高密度集成光波导，所述光波导设于波导衬底上，包括：多根弯曲波导；
以所述弯曲波导的弯曲方向为y轴，以光的传播方向为x轴建立直角坐标系；且基于所述直角坐标系，所述弯曲波导沿着所述传播方向在所述弯曲方向上周期性弯曲；
多根弯曲波导沿着所述y轴方向平行排列，且所述弯曲波导与所述y轴方向相互垂直，形成弯曲波导阵列；通过调节所述弯曲波导之间的耦合系数实现所述光波导的光波导信号传输功能或者光波导定向耦合功能。
可选的，所述耦合系数根据所述弯曲波导的弯曲振幅、弯曲周期、入射光的入射波长、所述波导衬底的折射率以及所述弯曲波导的周期间隔进行调节。
可选的，所述耦合系数的表达式为：c＝c 0J 0(4π 2An 0d/Pλ)；
其中，c为所述弯曲波导之间的耦合系数；c 0为直波导之间的耦合系数，c 0>0，所述直波导为第一直波导或第二直波导；A为弯曲振幅；P为弯曲周期；d为波导排列的周期间隔，d＝w+gap，w为波导宽度，gap为波导之间的间距；λ为入射波长；n 0为衬底折射率。
可选的，令J 0(4π 2An 0d/Pλ)小于0，所述耦合系数小于0，所述光波导还包括：第一直波导阵列以及第二直波导阵列；
所述第一直波导阵列包括沿着所述y轴平行排列的多根第一直波导；所述第二直波导阵列包括沿着所述y轴平行排列的多根第二直波导；所述第一直波 导之间的耦合系数等于所述第二直波导之间的耦合系数，且所述第一直波导之间的耦合系数以及所述第二直波导之间的耦合系数均大于0；
所述第一直波导阵列的输出端与所述弯曲波导阵列的输入端对接，所述弯曲波导阵列的输出端与所述第二直波导阵列的输入端对接，所述第一直波导阵列、所述弯曲波导阵列以及所述第二直波导阵列形成三级级联结构；所述入射光由所述第一直波导阵列的输入端进入所述三级级联结构，所述入射光在所述第一直波导阵列中由于耦合而发散，所述弯曲波导阵列由于负耦合将发散的光重新汇聚到所述第二直波导阵列，由于所述三级级联结构内的正耦合强度与所述负耦合强度相匹配，实现宽波段低串扰的光波导信号传输功能。
可选的，所述光波导包括多个所述三级级联结构；多个所述三级级联结构在x轴方向上平行排列。
可选的，令J 0(4π 2An 0d/Pλ)等于0，所述耦合系数等于0，入射光在所述弯曲波导阵列中传输，实现宽波段低串扰的光波导信号传输功能。
可选的，令J 0(4π 2An 0d/Pλ)小于0，所述耦合系数小于0，所述弯曲耦合阵列具体包括两根所述弯曲波导；两根所述弯曲波导沿y轴方向平行排列，实现宽波段的光波导定向耦合功能。
可选的，所述弯曲波导的周期性弯曲表达式为：
Figure PCTCN2021105519-appb-000001
其中，y(x)为所述弯曲波导的周期性弯曲函数；A为弯曲振幅；P为弯曲周期；
Figure PCTCN2021105519-appb-000002
为弯曲初相。
根据本发明提供的具体实施例，本发明公开了以下技术效果：本发明提供了一种高密度集成光波导，在波导衬底上设置多根弯曲波导，形成弯曲波导阵列，通过调节所述弯曲波导之间的耦合系数实现所述光波导的光波导信号传输功能或者光波导定向耦合功能。
本发明利用弯曲波导对于耦合的调控，实现了高密度集成下的宽带的低串扰传输和鲁棒性耦合，对结构偏差和波长变化表现出相当好的鲁棒性，提高了加工容错度，从而节约加工成本。
同时，本发明所提供的光波导在加工完成后不需要进一步进行调整和修正，从而避免了额外的能量消耗与损耗；与当前制造工艺完全兼容，不会带来额外的加工困难，易于大规模生产，对生产精度要求低。
说明书附图
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是 本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为实现宽带低串扰光波导传输的级联正耦合直波导阵列和负耦合弯曲波导阵列的示意图；
图2为实现宽带低串扰光波导传输的零耦合弯曲波导阵列的示意图；
图3为实现宽带鲁棒性光波导定向耦合的负耦合弯曲波导示意图；
图4为N根波导的直波导阵列和N根波导的弯曲波导阵列的示意图；
图5为将两个直波导阵列和一个弯曲波导阵列级联在一起形成的三级级联结构示意图；
图6为弯曲波导的初相
Figure PCTCN2021105519-appb-000003
和初相
Figure PCTCN2021105519-appb-000004
两种情况下与直波导连接的示意图；
图7为级联结构在不同弯曲幅度A＝0，A＝0.74μm的情况下，波导之间的耦合系数c随波长的变化关系图；
图8为级联结构中N＝2的情况下传输端口和串扰端口的传输效率随波长的变化关系图；
图9为级联结构中相应的不同波长下波导内光场的传播100μm和200μm的情况示意图；
图10为级联结构中N＝7的情况下，传输端口和串扰端口的传输效率随波长的变化关系图；
图11为级联结构中不同波长下相应的光场的传播100μm的情况示意图；
图12为零耦合弯曲波导在弯曲幅度A＝0.51μm的情况下，波导之间的耦合系数c随波长的变化关系图；
图13为零耦合弯曲波导N＝2的情况下，传输端口和串扰端口的传输效率随波长的变化关系图；
图14为零耦合弯曲波导相应的不同波长下波导内光场的传播100μm的情况示意图；
图15为零耦合弯曲波导N＝7的情况下，传输端口和串扰端口的传输效率随波长的变化关系图；
图16为零耦合弯曲波导不同波长下相应的光场的传播100μm的情况示意图；
图17为在不同弯曲幅度A的情况下，波导之间的耦合系数c随波长的变化关系图；
图18为耦合度随波长的变化关系图；
图19为隔离度随波长的变化关系图；
图20为方向性随波长的变化关系图；
图21为直波导不同波长下波导内光场的传播情况示意图；
图22为弯曲波导不同波长下波导内光场的传播情况示意图；
图23为在不同弯曲幅度A的情况下，波导之间的耦合系数c随波导间距的变化关系图；
图24为耦合度随波导间距的变化关系图；
图25为隔离度随波导间距的变化关系图；
图26为方向性随波导间距的变化关系图；
图27为弯曲波导不同波导间距下波导内光场的传播情况图；
图28为弯曲波导不同波导间距下波导内光场的传播情况图。
符号解释：1为直波导与弯曲波导的级联结构(含多次级联)；2为零耦合的弯曲波导阵列；3为两根弯曲波导。
具体实施方式
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，都属于本发明保护的范围。
本发明的目的是提供一种高密度集成光波导，采用直波导弯曲波导级联带来的正负耦合级联实现宽带低串扰光波导传输；采用弯曲波导带来的零耦合对于波长的稳定性来实现宽带的低串扰光波导传输，如图2为实现宽带低串扰光波导传输的零耦合弯曲波导阵列的示意图；采用弯曲波导带来的负耦合对于结构和波长的稳定性来实现鲁棒性且宽带的光波导定向耦合，如图3为实现宽带鲁棒性光波导定向耦合的负耦合弯曲波导示意图。
为使本发明的上述目的、特征和优点能够更加明显易懂，下面结合附图和具体实施方式对本发明作进一步详细的说明。
一种高密度集成光波导，所述光波导设于波导衬底上，包括：多根弯曲波导；以所述弯曲波导的弯曲方向为y轴，以光的传播方向为x轴建立直角坐标系；且基于所述直角坐标系，所述弯曲波导沿着所述传播方向在所述弯曲方向上周期性弯曲；多根弯曲波导沿着所述y轴方向平行排列，且所述弯曲波导与所述y轴方向相互垂直，形成弯曲波导阵列；通过调节所述弯曲波导之间的耦合系数实现所述光波导的光波导信号传输功能或者光波导定向耦合功能。
所述弯曲波导，是沿着传播方向y在x方向上进行周期性的弯曲，比如，形为三角函数的弯曲：
Figure PCTCN2021105519-appb-000005
其中，A为弯曲的振幅，P为弯曲的周期，
Figure PCTCN2021105519-appb-000006
为弯曲的初相，代表弯曲波导的初始状态，如图6所示，展示了弯曲波导的初相
Figure PCTCN2021105519-appb-000007
和初相
Figure PCTCN2021105519-appb-000008
两种情况下与直波导连接的示意图。N为波导阵列的波导总数，表示需要传输的信号路数；M为级联个数，M可以取大于1的整数，若为三级级联结构，则M＝3；d为波导排列的周期间隔；w为波导宽度，gap为波导之间的间距，满足d＝w+gap；λ为入射波长，n是波导折射率，n 0是衬底折射率，c是弯曲波导之间的耦合系数，c与A、n 0、d、P和λ等参数有关。
所述耦合系数根据所述弯曲波导的弯曲振幅、弯曲周期、入射光的入射波长、所述波导衬底的折射率以及所述弯曲波导的周期间隔进行调节。
所述耦合系数的表达式为：c＝c 0J 0(4π 2An 0d/Pλ)；其中，c为所述弯曲波导之间的耦合系数；c 0为直波导之间的耦合系数，c 0>0，所述直波导为第一直波导或第二直波导；A为弯曲振幅；P为弯曲周期；d为波导排列的周期间隔，d＝w+gap，w为波导宽度，gap为波导之间的间距；λ为入射波长；n 0为衬底折射率。
作为一种可选的实施方式，所述光波导还包括：第一直波导阵列以及第二直波导阵列；所述第一直波导阵列包括沿着所述y轴平行排列的多根第一直波导；所述第二直波导阵列包括沿着所述y轴平行排列的多根第二直波导；所述第一直波导之间的耦合系数等于所述第二直波导之间的耦合系数，且所述第一直波导之间的耦合系数以及所述第二直波导之间的耦合系数均大于0；所述第一直波导阵列的输出端与所述弯曲波导阵列的输入端对接，所述弯曲波导阵列的输出端与所述第二直波导阵列的输入端对接，所述第一直波导阵列、所述弯曲波导阵列以及所述第二直波导阵列形成三级级联结构；所述入射光由所述第一直波导阵列的输入端进入所述三级级联结构，所述入射光在所述第一直波导阵列中由于耦合而发散，所述弯曲波导阵列由于负耦合将发散的光重新汇聚到所述第二直波导阵列，由于所述三级级联结构内的正耦合强度与所述负耦合强度相匹配，实现宽波段低串扰的光波导信号传输功能。
所述光波导包括多个所述三级级联结构；多个所述三级级联结构在x轴方向上平行排列。
下面以三级结构为例对该结构的形成方式进行详细说明：首先将N根直波导沿y方向平行排列在一起形成直波导阵列结构，如图4所示，再将直波导 阵列中的直波导进行弯曲，形成弯曲波导阵列结构，接着将所述的两个直波导阵列和一个弯曲波导阵列沿x方向进行对接，则可形成如图5所示的三级级联结构。其他多级级联结构可通过多个直波导阵列和弯曲波导阵列对接完成。波导阵列中每一根波导都是一个传输光信号的通道，在理想情况下，从某一根波导进入的光信号都能够在输出端从该波导输出，而没有光信号输入的波导在输出端都不会有光信号输出。但是由于波导之间存在倏逝波耦合效应，信号会出现相互影响。有时候没有信号输入的波导在输出端也会出现信号，这就是串扰信号，且波导阵列间隔越小，这种串扰现象就会越严重，尤其是在高密度集成的情况下(d～λ/2)。这里通过弯曲波导的引入，可以将直波导结构中产生的串扰现象进行消除，同时由于这种效应是宽带的，则可在宽带的波长范围内实现高密度集成情况下的低串扰或无串扰传输。
通过将波导弯曲，可以有效地减小波导之间的耦合，若波导体系满足弱导弱耦的条件，那么弯曲波导之间的耦合系数c与其他参数之间的关系可以近似写为：c＝c 0J 0(4π 2An 0d/Pλ)，其中c 0是直波导之间的耦合系数，一般来说c 0>0；J 0是第一类的最低阶贝塞尔函数。因此当A、P、d、λ、n 0取合适参数时，可以使得函数J 0(4π 2An 0d/Pλ)<0，因此波导之间的耦合系数c可以取负值。值得注意的是，在高密度集成的条件下，弱导若耦的条件不会满足，所以弯曲波导之间的耦合系数不会严格满足该式c＝c 0J 0(4π 2An 0d/Pλ)，而是呈现更复杂的形式。但是由于弯曲波导带来的负耦合的效应依然存在，并且可以通过仿真的手段，得到高密度集成条件下弯曲波导之间的耦合系数随其中一些参数的关系图，如图7所示。
为了实现多路信号的传输，首先考虑将N个直波导沿y方向平行排列在一起形成直波导阵列，波导的宽度为w，波导的间隔为gap，则该波导阵列的周期为d＝w+gap，如图1所示，直波导之间的耦合系数c 0大于零。再考虑一个波导阵列，这个波导阵列和刚刚所述的直波导阵列参数完全一致，只是将每个波导都进行弯曲，则可得到一个弯曲波导阵列，这个阵列中的耦合系数为负数。然后将若干个所述的弯曲波导阵列和直波导阵列在传播方向上(x方向)将波导对接在一起形成多级级联结构，如图1所示。光在直波导中由于耦合而发散，而在弯曲波导中由于负耦合而汇聚，因此光在特定的传播距离处会重新汇聚到入射端口所在波导，完成信号传输功能。同时由于正负耦合的强度在很长的波长范围内保持匹配，因此可以实现宽波段的低串扰传输功能。
考虑一般情况，即M个波导阵列在传播方向x上进行M级级联，第i个 波导阵列的长度和耦合系数分别为L i，c i。一般地，c i可写成波长λ和传播距离x的函数c i(λ,x)。器件总长度为L＝L 1+L 2+…+L i+…，以x＝0作为输入端，则x＝L为输出端，在输入端的N个波导可任意输入N路不同的信号。
如果满足：
Figure PCTCN2021105519-appb-000009
那么光在输出端x＝L处会完美地得到这N路信号，完美指的是输出端x＝L处的信号与输入端x＝0处的信号强度和相位分布完全一致，从而完成信号传输功能。为方便起见，令耦合系数不随传播x而变化，上式可简化为
c 1(λ)L 1+c 2(λ)L 2+…+c i(λ)L i+…＝0，        (2)
一般来说，介质直波导之间的耦合系数是正值，并且耦合大小会随波长的变化而变化。因此，要满足(2)式，一种方式是级联结构中同时存在正耦合与负耦合；另一种方式是所有的耦合系数均等于零。此外，如果要实现宽波段的传输功能，那么(2)式必须在一定波段内依然得到满足或近似满足。
为了得到零耦合和负耦合，对弯曲波导进行分析建模，如下：
弯曲波导是沿着传播方向x在y方向上进行周期性地弯曲，比如，形为三角函数的弯曲：
Figure PCTCN2021105519-appb-000010
其中，A为弯曲的振幅，P为弯曲的周期，
Figure PCTCN2021105519-appb-000011
为弯曲的初相。
Figure PCTCN2021105519-appb-000012
的取值对于结果的影响很小，令
Figure PCTCN2021105519-appb-000013
等于π(或0)，如图6所示。因为此时弯曲的斜率为零，这样光可以无损耗得进入弯曲波导体系。
通过将波导弯曲，可以有效地减小波导之间的耦合，甚至可以取零值、负值，此时将正耦合的直波导与负耦合的弯曲波导级联在一起形成级联结构，光在直波导中由于耦合而发散，而在弯曲波导中由于负耦合而汇聚，从而实现传输功能。或者利用零耦合，也可实现传输功能。
当A、P、d、λ、n 0取合适参数时，(2)式可以在一定波段内得到满足，对于正负耦合级联的方案或零耦合方案，都可实现宽带的光波导传输功能。
作为一种可选的实施方式，入射光在所述弯曲波导阵列中传输，实现宽波段低串扰的光波导信号传输功能。
将N根弯曲波导沿y方向平行排列在一起，通过将波导弯曲，可以消除波导之间的耦合效应，从某根波导进入的光信号不会耦合到相邻波导，从而消除串扰，实现低串扰传输。同时这种效应是宽带的，则可在宽带的波长范围内实现低串扰传输功能。
通过将波导弯曲，可以有效地减小波导之间的耦合，若波导体系满足弱导弱耦的条件，那么弯曲波导之间的耦合系数c与其他参数之间的关系可以近似写为：c＝c 0J 0(4π 2An 0d/Pλ)，其中c 0是直波导之间的耦合系数；J 0是第一类的最低阶贝塞尔函数。因此当A、P、d、λ、n 0取合适参数时，可以使得函数J 0(4π 2An 0d/Pλ)＝0，因此波导之间的耦合系数c可以取零。值得注意的是，在高密度集成的条件下，弱导若耦的条件不会满足，所以弯曲波导之间的耦合系数不会严格满足该式子c＝c 0J 0(4π 2An 0d/Pλ)，而是呈现更复杂的形式。但是由于弯曲波导带来的零耦合的效应依然存在，并且可以通过仿真的手段，得到高密度集成条件下弯曲波导之间的耦合系数随其中一些参数的关系图，如图12所示。
为了实现多路信号的传输，首先考虑将N个弯曲波导沿y方向平行排列在一起形成单一的弯曲波导阵列，在这个阵列中的耦合系数为零，并且在一定波段范围内均可以近似等于零。光进入这种耦合系数为零的波导阵列不会耦合到相邻的波导中去，因此也可以通过单一的弯曲波导阵列结构实现宽波段的低串扰传输功能。
作为一种可选的实施方式，令J 0(4π 2An 0d/Pλ)小于0，所述耦合系数小于0，所述弯曲耦合阵列具体包括两根所述弯曲波导；两根所述弯曲波导沿y轴方向平行排列，实现宽波段的光波导定向耦合功能。
这种结构是通过将两根弯曲波导沿y方向平行排列在一起形成的，通过将波导弯曲，可以实现波导之间的宽带耦合效应，即从某根波导进入的光信号能够在宽带的波长范围内稳定地耦合到相邻波导，实现宽带定向耦合功能。
通过将波导弯曲，可以有效地减小波导之间的耦合，若波导体系满足弱导弱耦的条件，那么弯曲波导之间的耦合系数c与其他参数之间的关系可以近似写为：c＝c 0J 0(4π 2An 0d/Pλ)，其中c 0是直波导之间的耦合系数；J 0是第一类的最 低阶贝塞尔函数。因此当A、P、d、λ、n 0取合适参数时，可以使得函数J 0(4π 2An 0d/Pλ)<0，因此波导之间的耦合系数c可以取负数。值得注意的是，在高密度集成的条件下，弱导若耦的条件不会满足，所以弯曲波导之间的耦合系数不会严格满足该式子c＝c 0J 0(4π 2An 0d/Pλ)，而是呈现更复杂的形式。但是由于弯曲波导带来的零耦合的效应依然存在，并且可以通过仿真的手段，得到高密度集成条件下弯曲波导之间的耦合系数随其中一些参数的关系图，如图17所示。不同于直波导之间的正耦合对波长和结构参数的敏感性，这种负耦合可以在很长的波长范围内、很大的波导间距变化范围内保持很小的变化。因此，通过将两根弯曲波导沿y方向平行排列在一起形成两根弯曲波导结构。光在两根弯曲波导之间的耦合效应可以实现波导定向耦合功能，并且在很长的波段内、以及很大的波导间距变化内保持定向耦合功能。
通过将波导弯曲实现负耦合后，发现当A、P、d、λ、n 0取合适参数时，波导之间的耦合在很长的波长范围内、很大的波导间距变化范围内保持很小的变化，即
c(λ+Δλ)≈c(λ)，                       (4)
c(gap+Δgap)≈c(gap)，                    (5)
其中，Δλ，Δgap分别为波长和波导间距的变化。
一般在高密度集成的条件下，(4)式、(5)式中的耦合取负数。即可以在很大的波段内或很大的结构参数变化范围内都能够保持稳定的负耦合的性质。此时，可以实现宽波段的以及具有结构鲁棒性的光波导定向耦合功能。
值得注意的是，之前是通过(2)式得到零耦合实现光传输的方案。但其实，零耦合方案也可认为是(4)式、(5)式的一个特例，即当A、P、d、λ、n 0取合适参数时可以使得
c(λ+Δλ)≈c(λ)＝0，                     (6)
c(gap+Δgap)≈c(gap)＝0，                  (7)
在很大的波段内或很大的结构参数变化范围内都能够保持稳定的零耦合的性质。此时，可以实现宽波段的以及具有结构鲁棒性的光波导传输功能。
总之，将波导进行弯曲，可以实现对波导之间的耦合效应的灵活调控，通过对弯曲的参数控制，可以实现上述的宽带低串扰传输、宽带定向耦合等不同的功能。
为了更好的理解本发明，下面结合实施例进行进一步解释。
不失一般性，本实施例针对近红外波段，在空气的环境中，针对氧化铝衬底上的硅波导设计了弯曲波导，该发明同样适用于其他波段和材料体系。如图1所示，其中，光波导传输技术基于两种方案：(1)直波导与弯曲波导的级联结构(含多次级联)，这里以直波导阵列连接弯曲波导阵列连接直波导阵列的三级级联结构为例；(2)单一的弯曲波导阵列结构。光波导定向耦合技术，是基于(3)两根弯曲波导。波硅导的宽度w为400nm，弯曲调制的周期P＝10μm，本实施例采用COMSOL Multiphysics对器件性能进行仿真测试。
图7-图11为级联直波导和弯曲波导实现宽带低串扰传输的仿真结果。仿真过程中，采用波导所支持的基模TE模式入射。在d＝760nm的情况下模拟了不同弯曲幅度A和不同波长λ情况下的耦合情况。当A＝0时，弯曲波导退化为直波导。可以看到，在直波导的情况下，随着波长的增大，两根波导之间的耦合系数逐渐增大。当A从0逐渐增大到0.74μm时，即直波导变为弯曲波导，发现两根波导之间的耦合系数变为负值，并且此时的耦合系数的绝对值与直波导的耦合系数近似相等，并且这种相等性可以在很长的波段内保持，即c A＝0(λ)≈-c A＝0.74μm(λ)。由于直波导和弯曲波导宽度一致，均为w＝400nm，因此可以把两者级联起来。考虑直波导-弯曲波导-直波导的三级级联结构，在总长度为L的情况下，两段直波导长度选为L/4，中间弯曲波导的长度选为L/2，这样(2)式可以得到满足。图8计算了两根波导N＝2时不同长度L(L＝100μm,200μm)的情况下的传输和串扰随波长的变化。可以看到该器件(L＝100μm)在很长的波段范围内(>200nm)均能维持很高的传输效率(>-0.1dB)和很低的串扰(<-20dB)。若长度增加到200μm，虽然串扰有所增大，但其依然可以在很长的波段内(>200nm)保持较高的传输效率(>-0.19dB)。图9展示了不同波长情况下光场在该结构波导内的传播100μm 和200μm的情况，可以看到在很长的波段内光场都能够保持很高地传输效率和很低的串扰。图10和图11展示了利用阵列N＝7传输多路信号的模拟结果。以7根波导为例进行多通道的信号传输，比如“1011010”，其中“1”代表有信号传输，“0”代表无信号传输。图10计算了长度L＝100μm的情况下的不同通道传输效率和串扰随波长的变化。可以看到该器件在很长的波段范围内(1300～1450nm)均能维持很高的传输效率(-0.46～0.27dB)和很低的串扰(<-20.3dB)。图11展示了不同波长情况下光场在该结构波导内的传播100μm的情况，可以看到在很长的波段内光场都能够保持很高地传输效率和很低的串扰。
图12-图16为零耦合弯曲波导实现宽带低串扰传输的仿真结果。在d＝760nm的情况下发现当A＝0.51μm时，两根波导之间的耦合系数近似为零，并且可以在很长的波段内保持为零，即(6)式可以得到满足。图13计算了N＝2时传播100μm的情况下的传输和串扰随波长的变化。可以看到该器件在较长的波段范围内(～100nm)均能维持很高的传输效率(>-0.138dB)和较低的串扰(<-15dB)。图14展示了不同波长情况下光场在该结构波导内的传播的情况，可以看到在很长的波段内光场都能够保持很高地传输效率和很低的串扰。图15和图16展示了利用阵列N＝7传输多路信号的模拟结果。以7根波导为例进行多通道的信号传输，比如“1011010”，其中“1”代表有信号传输，“0”代表无信号传输。图15计算了长度L＝100μm的情况下的不同通道传输效率和串扰随波长的变化。可以看到该器件在很长的波段范围内(1300～1450nm)均能维持很高的传输效率(-0.85～0.63dB)和较低的串扰(<-9.8dB)。图16展示了不同波长情况下光场在该结构波导内的传播100μm的情况，可以看到在很长的波段内光场都能够保持很高地传输效率和较低的串扰。
图17-图22为弯曲波导实现宽带耦合的仿真结果。在gap＝200nm，即d＝600nm的情况下模拟了不同弯曲幅度A和不同波长λ情况下的耦合情况。在A＝0时，为传统的直波导耦合情形，可以看到，此时耦合大小随波长改变而发生变化，当固定长度后，输出端口的能量分配情况也会发生改变。当考虑弯曲 波导，即A>0时，发现两根波导之间的耦合系数逐渐变为负值，并且耦合随波长的变化逐渐放缓。特别地，当A＝0.9μm时，此时的耦合系数几乎不随波长变化而变化，即(4)式可以得到满足。图18-图20分别计算了直波导(A＝0)和弯曲波导(A＝0.9μm)两种情况下在不同波长时的耦合度、隔离度和方向性。对于直波导，器件的长度选为15.6μm，弯曲波导的长度为34.8μm。可以看到，相比于传统的直波导耦合器，弯曲波导耦合器具有更低的耦合度，并且具有很大的带宽，在1dB的耦合度下带宽达到了近200nm。此外，弯曲波导耦合器在隔离度、方向性指标上均优于传统的直波导定向耦合器。图21和图22直观的展示了光场在直波导耦合器和弯曲波导耦合器的传播情况，可以看到在1350-1550nm波段内光场能够很好的耦合到另一根波导。而传统直波导耦合器的性能随波长改变而发生剧烈变化。
图23-图28为弯曲波导实现结构鲁棒性耦合的仿真结果。在λ＝1550nm的情况下模拟了不同弯曲幅度A和不同波导间距gap情况下的耦合情况。在A＝0时，为传统的直波导耦合情形，可以看到，此时耦合大小随波导间距的改变而发生变化，当固定长度后，输出端口的能量分配情况也会发生改变。当考虑弯曲波导，即A>0时，发现两根波导之间的耦合系数逐渐变为负值，并且耦合随间距的变化逐渐放缓。特别地，当A＝0.9μm时，此时的耦合系数几乎不随间距变化而变化，即(5)式可以得到满足。图24-图26分别计算了直波导(A＝0)和弯曲波导(A＝0.9μm)两种情况下在不同波长时的耦合度、隔离度和方向性。对于直波导，器件的长度选为23μm，弯曲波导的长度为34.5μm。可以看到，相比于传统的直波导耦合器，弯曲波导耦合器具有更低的耦合度，近200nm的波导间距变化的情况下仍能维持小于1dB的耦合度。此外，弯曲波导耦合器在隔离度、方向性指标上均优于传统的直波导耦合器。图27和图28直观的展示了光场在直波导耦合器和弯曲波导耦合器的传播情况，可以看到即便gap在200nm～400nm大范围内变化，光场仍能够很好的耦合到另一根波导，而传统直波导耦合器的性能随波导间距改变而发生剧烈变化。
基于弯曲波导实现的片上光波导传输和耦合表现为：
1)从某一波导端口输入的光信号通过正耦合的直波导和负耦合的弯曲波导级联结构，可以实现宽波段的低串扰的信号传输功能。
2)从某一波导端口输入的光信号通过零耦合的弯曲波导，可以实现宽波段的低串扰的信号传输功能。
3)通过弯曲波导实现的负耦合，可以实现宽波段的光波导定向耦合功能。
综上，本发明采用直波导弯曲波导级联带来的正负耦合级联实现宽带低串扰光波导传输；采用弯曲波导带来的零耦合对于波长的稳定性来实现宽带的低串扰光波导传输；采用弯曲波导带来的负耦合对于结构和波长的稳定性来实现鲁棒性且宽带的光波导定向耦合。
本发明与当前制造工艺完全兼容，不会带来额外的加工困难，易于大规模生产，且精度要求不高。
本说明书中各个实施例采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似部分互相参见即可。
本文中应用了具体个例对本发明的原理及实施方式进行了阐述，以上实施例的说明只是用于帮助理解本发明的方法及其核心思想；同时，对于本领域的一般技术人员，依据本发明的思想，在具体实施方式及应用范围上均会有改变之处。综上所述，本说明书内容不应理解为对本发明的限制。

Claims (8)

  1. 一种高密度集成光波导，所述光波导设于波导衬底上，其特征在于，包括：多根弯曲波导；
    以所述弯曲波导的弯曲方向为y轴，以光的传播方向为x轴建立直角坐标系；且基于所述直角坐标系，所述弯曲波导沿着所述传播方向在所述弯曲方向上周期性弯曲；
    多根弯曲波导沿着所述y轴方向平行排列，且所述弯曲波导与所述y轴方向相互垂直，形成弯曲波导阵列；通过调节所述弯曲波导之间的耦合系数实现所述光波导的光波导信号传输功能或者光波导定向耦合功能。
  2. 根据权利要求1所述的一种高密度集成光波导，其特征在于，所述耦合系数根据所述弯曲波导的弯曲振幅、弯曲周期、入射光的入射波长、所述波导衬底的折射率以及所述弯曲波导的周期间隔进行调节。
  3. 根据权利要求2所述的一种高密度集成光波导，其特征在于，所述耦合系数的表达式为：c＝c 0J 0(4π 2An 0d/Pλ)；
    其中，c为所述弯曲波导之间的耦合系数；c 0为直波导之间的耦合系数，c 0>0，所述直波导为第一直波导或第二直波导；A为弯曲振幅；P为弯曲周期；d为波导排列的周期间隔，d＝w+gap，w为波导宽度，gap为波导之间的间距；λ为入射波长；n 0为衬底折射率。
  4. 根据权利要求3所述的一种高密度集成光波导，其特征在于，令J 0(4π 2An 0d/Pλ)小于0，所述耦合系数小于0，所述光波导还包括：第一直波导阵列以及第二直波导阵列；
    所述第一直波导阵列包括沿着所述y轴平行排列的多根第一直波导；所述第二直波导阵列包括沿着所述y轴平行排列的多根第二直波导；所述第一直波导之间的耦合系数等于所述第二直波导之间的耦合系数，且所述第一直波导之间的耦合系数以及所述第二直波导之间的耦合系数均大于0；
    所述第一直波导阵列的输出端与所述弯曲波导阵列的输入端对接，所述弯曲波导阵列的输出端与所述第二直波导阵列的输入端对接，所述第一直波导阵列、所述弯曲波导阵列以及所述第二直波导阵列形成三级级联结构；所述入射光由所述第一直波导阵列的输入端进入所述三级级联结构，所述入射光在所述第一直波导阵列中由于耦合而发散，所述弯曲波导阵列由于负耦合将发散的光 重新汇聚到所述第二直波导阵列，由于所述三级级联结构内的正耦合强度与所述负耦合强度相匹配，实现宽波段低串扰的光波导信号传输功能。
  5. 根据权利要求4所述的一种高密度集成光波导，其特征在于，所述光波导包括多个所述三级级联结构；多个所述三级级联结构沿x轴方向平行排列。
  6. 根据权利要求3所述的一种高密度集成光波导，其特征在于，令J 0(4π 2An 0d/Pλ)等于0，所述耦合系数等于0，入射光在所述弯曲波导阵列中传输，实现宽波段低串扰的光波导信号传输功能。
  7. 根据权利要求3所述的一种高密度集成光波导，其特征在于，令J 0(4π 2An 0d/Pλ)小于0，所述耦合系数小于0，所述弯曲耦合阵列具体包括两根所述弯曲波导；两根所述弯曲波导沿y轴方向平行排列，实现宽波段的光波导定向耦合功能。
  8. 根据权利要求1-7任一项所述的一种高密度集成光波导，其特征在于，所述弯曲波导的周期性弯曲表达式为：
    Figure PCTCN2021105519-appb-100001
    其中，y(x)为所述弯曲波导的周期性弯曲函数；A为弯曲振幅；P为弯曲周期；
    Figure PCTCN2021105519-appb-100002
    为弯曲初相。
PCT/CN2021/105519 2020-07-17 2021-07-09 一种高密度集成光波导 Ceased WO2022012434A1 (zh)

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