Grating coupler and design method thereof

Abstract

The invention provides a grating coupler and a design method thereof, relates to the technical field of optics, and aims to realize dynamic regulation and control of the grating coupler. The grating coupler comprises a substrate, a waveguide layer and a phase change material metasurface layer. The waveguide layer is disposed on the substrate. The phase change material metasurface layer is arranged on the side, away from the substrate, of the waveguide layer. Wherein the phase-change material metasurface layer comprises a plurality of protruding structures, so that filtering coupling and switching of the grating coupler on a target working wavelength are achieved.

Description

Technical Field

[0001] This application relates to the field of optical technology, and in particular to a grating coupler and its design method. Background Technology

[0002] In modern optical communication and optical information processing systems, grating couplers serve as key coupling elements between chips and external spatial light, and their coupling performance plays a decisive role in the efficiency and stability of the entire system.

[0003] However, existing grating couplers are insufficient to meet the requirements of dynamic control. Summary of the Invention

[0004] This application proposes a grating coupler and its design method, aiming to achieve dynamic control of the grating coupler.

[0005] To achieve the above objectives, embodiments of this application provide the following technical solutions: On one hand, a grating coupler is provided, comprising a substrate, a waveguide layer, and a phase change material metasurface layer. The waveguide layer is disposed on the substrate. The phase change material metasurface layer is disposed on the side of the waveguide layer away from the substrate. The phase change material metasurface layer includes multiple protrusion structures to achieve filtering coupling and switching of the grating coupler for a target operating wavelength.

[0006] In the above embodiments of this application, the grating coupler includes a substrate, a waveguide layer, and a phase change material metasurface layer. The waveguide layer and the phase change material metasurface layer are sequentially stacked on the substrate. The phase change material metasurface layer includes multiple protrusion structures to achieve filtering coupling and switching of the grating coupler for the target operating wavelength.

[0007] It is understandable that the multiple protrusions are phase change materials, capable of reversibly changing their crystalline state. This means the protrusions exhibit rapid phase transition characteristics, enabling reversible switching between crystalline and amorphous states. This allows the grating coupler to filter, couple, and switch at the target operating wavelength. Furthermore, by changing the crystalline state of the multiple protrusions, the grating coupler can flexibly select different specific wavelengths for switching and filtering, thus achieving dynamic control of the grating coupler.

[0008] In some embodiments, when the protrusion structure is crystalline, it has a first refractive index. When the protrusion structure is amorphous, it has a second refractive index. The difference between the first and second refractive indices is greater than 1, and the difference between the first and second extinction coefficients is greater than 1.

[0009] In some embodiments, the multiple protrusion structures are of the same size.

[0010] In some embodiments, the length of the protrusion structure ranges from 150 nm to 900 nm along a first direction parallel to the substrate. The width of the protrusion structure ranges from 150 nm to 900 nm along a second direction parallel to the substrate, and the second direction intersects the first direction.

[0011] In some embodiments, a plurality of protrusion structures are arranged periodically along a first direction parallel to the substrate and along a second direction parallel to the substrate, or a plurality of protrusion structures are arranged quasi-periodically. The second direction intersects the first direction.

[0012] In some embodiments, along a first direction, the phases of multiple protrusions are the same. Along a second direction, the phases of at least two protrusions are different.

[0013] In some embodiments, the shape of the protrusion structure includes an axisymmetric shape, and the shape of the orthographic projection of the protrusion structure onto the substrate includes a rectangle, a circle, an ellipse, a V-shape, or an H-shape.

[0014] In some embodiments, the phase change material includes Ge2Sb2Te5, Sb2Se3, Sb2Te3, or VO2.

[0015] In some embodiments, the grating coupler further includes a passivation layer disposed on the side of the phase change material metasurface layer away from the substrate.

[0016] On the other hand, a design method for a grating coupler is also provided, which is used to design the grating coupler as described in the above embodiments. The above design method includes: Provides target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limits; A metasurface unit structure is set up, and numerical simulation is performed on the metasurface unit structure to obtain its geometric parameters; the metasurface unit structure includes a substrate and a protrusion structure. Based on the target operating wavelength, target diffraction efficiency, target switching speed and target power consumption limit, the target phase value of multiple protrusion structures is calculated, and the target size of the protrusion structure is calculated through reverse design based on the target phase value; Multiple protrusions are arranged periodically or quasi-periodically according to the target phase value and target size.

[0017] In the above embodiments of this application, the design method of the grating coupler includes providing a target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limit, and performing numerical simulation on the metasurface unit structure to obtain the geometric parameters of the metasurface unit structure. Through reverse design, the target size of the protrusion structure is calculated based on the target phase value, and multiple protrusion structures are arranged periodically or quasi-periodically under the target size and target phase value to obtain the design of a reconfigurable grating coupler with grating function switching capability.

[0018] Understandably, multiple protrusion structures can reversibly change their crystalline state, meaning they possess rapid phase transition characteristics, enabling reversible switching between crystalline and amorphous states. This allows the grating coupler to filter, couple, and switch at the target operating wavelength. Furthermore, by altering the crystalline state of the multiple protrusion structures, the grating coupler can flexibly select different specific wavelengths for switching and filtering, thus achieving dynamic control of the grating coupler.

[0019] In some embodiments, after arranging multiple protrusion structures, the above-described fabrication method further includes: irradiating the protrusion structures with a pulsed laser beam to change the crystal state of the multiple protrusion structures, thereby controlling the filtering coupling and switching of the grating coupler to the target operating wavelength. Irradiating the protrusion structures with a pulsed laser beam includes: irradiating the protrusion structures with a first laser beam to make the protrusion structures crystalline and to turn on the coupling of the grating coupler; or irradiating the protrusion structures with a second laser beam to make the protrusion structures amorphous and to turn off the coupling of the grating coupler. The power of the first laser is less than the power of the second laser, and the pulse width of the first laser is less than the pulse width of the second laser.

[0020] In some embodiments, the absolute value of the difference between the wavelengths of the first laser beam and the second laser beam and the target working wavelength is greater than 100 nm.

[0021] In some embodiments, the target operating wavelength includes 850 nm, 1064 nm, 1310 nm, or 1550 nm. The wavelength of the first laser beam includes 638 nm, 710 nm, 800 nm, or 808 nm. The wavelength of the second laser beam includes 638 nm, 710 nm, 800 nm, or 808 nm. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in some embodiments of this application will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not actual dimensions of the products or actual processes of the methods involved in the embodiments of this application.

[0023] Figure 1 This is a schematic diagram of the structure of the grating coupler provided in the embodiments of this application; Figure 2 for Figure 1 A partial cross-sectional view of the grating coupler along section line AA'; Figure 3 This is a flowchart illustrating the design method of the grating coupler provided in the embodiments of this application; Figure 4 These are top views and three-dimensional views of the metasurface unit structure provided in the embodiments of this application; Figure 5 This is a schematic diagram illustrating the principle of the phase change material metasurface layer provided in the embodiments of this application; Figure 6 This is a schematic diagram showing the phase response of the phase change material metasurface layer provided in the embodiments of this application to x-ray and y-ray polarized light emitted from free space. Detailed Implementation

[0024] The technical solutions in some embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments provided in this application, all other embodiments obtained by those skilled in the art are within the scope of protection of this application.

[0025] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open and encompassing, that is, "including, but not limited to".

[0026] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this application, unless otherwise stated, "a plurality of" means two or more.

[0027] In describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be interpreted broadly; for example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. For example, in describing some embodiments, the term "connection" may be used to indicate that two or more components have direct physical or electrical contact with each other.

[0028] In addition, the use of “based on” implies openness and inclusivity, because processes, steps, calculations or other actions “based on” one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0029] This document describes exemplary embodiments with reference to cross-sectional views, which are intended as idealized exemplary drawings. In the drawings, the thickness of the layers and the area of ​​the regions are enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations caused, for example, by manufacturing processes. For example, etched areas shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the areas of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0030] In modern optical communication and optical information processing systems, grating couplers serve as crucial coupling elements between chips and external spatial light, and their coupling performance plays a decisive role in the efficiency and stability of the entire system. Grating couplers primarily rely on the principle of grating diffraction to convert fiber mode or free-space light mode into planar waveguide mode, enabling efficient and stable transmission of optical signals between different media. When the grating period satisfies the Bragg condition, light of a specific wavelength can be coupled into the waveguide, thereby completing effective optical signal transmission.

[0031] Traditional grating couplers typically have low coupling efficiency, generally around 10%, with a maximum of only about 30%. This is mainly due to the imperfect mode matching between the grating and the waveguide, preventing most optical energy from being effectively coupled into the waveguide. Most grating couplers have strict requirements on the polarization state of light, only efficiently coupling light with specific polarization directions, such as TE or TM modes. This limits their application in multi-polarization optical transmission systems and increases the complexity of system design. Furthermore, traditional grating couplers have narrow bandwidths, typically only a few nanometers to tens of nanometers. This makes them unsuitable for broadband optical communication and optical computing, limiting the system's transmission capacity and processing speed.

[0032] To improve coupling efficiency and performance, some grating couplers employ complex structures, such as blazed gratings and two-dimensional gratings, as well as specialized manufacturing processes, such as electron beam lithography and focused ion beam etching. While these approaches can improve performance to some extent, they inevitably increase manufacturing costs and process complexity, hindering large-scale production and integration. To overcome the shortcomings of traditional grating couplers and achieve a certain degree of wavelength selectivity and modulation capabilities, some traditional grating coupling structures have begun to explore complex structural designs and novel materials and structures, such as multilayer thin film stacks and complex grating patterns. However, this not only increases the difficulty and cost of manufacturing processes but may also lead to a decrease in device stability and reliability.

[0033] Some grating couplers based on other phase change materials suffer from slow switching speeds. For example, while some phase change material grating couplers have faster phase transition speeds than those based on traditional materials, they still cannot meet the demands for rapid modulation of optical signals in certain high-speed optical communication applications. Some phase change materials are prone to performance degradation during repeated phase transitions, such as a decrease in the refractive index change amplitude and an increase in the phase transition threshold current. This leads to a gradual decline in the performance of the grating coupler, affecting its long-term stability and reliability. Furthermore, the relatively small refractive index change amplitude of some existing phase change materials limits the wavelength selectivity and modulation depth of the grating coupler under different phase transition states. This may result in unsatisfactory filtering effects on optical signals, making it difficult to achieve high-contrast switching filtering functions.

[0034] Therefore, there is currently a lack of a dynamic reconfigurable grating coupler that is simple in structure, low in power consumption, high in speed, high in modulation depth, and easy to integrate.

[0035] To address at least one of the aforementioned problems, embodiments of this application provide a grating coupler. Figure 1 This is a schematic diagram of the structure of the grating coupler provided in the embodiments of this application; Figure 2 for Figure 1 A partial cross-sectional view of the grating coupler along section line AA'.

[0036] See Figure 1 and Figure 2 The grating coupler 10 includes a substrate 1, a waveguide layer 2, and a phase change material metasurface layer 3.

[0037] For example, the grating coupler 10 can be applied to optical time division multiplexing (OTDM) and optical code division multiplexing (OCDM) systems to achieve high-speed signal switching and filtering functions. For example, the grating coupler 10 can also be applied to wavelength division multiplexing (WDM) systems, where it can dynamically adjust the filtering wavelength according to actual communication needs, thereby optimizing network resource allocation.

[0038] Waveguide layer 2 is disposed on substrate 1.

[0039] For example, the choice of substrate 1 depends on the target wavelength and the integration platform. Substrate 1 can be a silicon-on-insulator (SOI) wafer substrate, a quartz substrate, a glass substrate, a SiN-on-insulator substrate, or a III-V compound substrate. "SiN-on-insulator" refers to a silicon nitride layer on an insulating layer. "III-V compound" refers to a binary / ternary / quaternary semiconductor crystal composed of elements from Group IIIA (B, Al, Ga, In, Tl) and Group VA (N, P, As, Sb, Bi) in a 1:1 or similar ratio.

[0040] For example, see Figure 2 When the substrate 1 is an SOI substrate, the SOI substrate includes a first silicon layer 11, and a buried oxide layer (BOX) 12 and a second silicon layer sequentially stacked on the first silicon layer 11. The first silicon layer 11 and the buried oxide layer (BOX) 12 can serve as the substrate 1 of this application, and the second silicon layer can serve as the waveguide layer 2 of this application.

[0041] Among them, the buried oxide layer 12 has unique functions compared to the phase change material metasurface layer 3, such as electrical isolation, thermal isolation, etch stop and release layer, which is beneficial to improving the performance and stability of the grating coupler 10.

[0042] For example, the thickness of the second silicon layer (waveguide layer 2) can be 220 nm, the thickness of the buried oxide layer 12 can be 2 μm, and the thickness of the first silicon layer 11 can be 725 μm.

[0043] For example, see Figure 1 When the substrate 1 is a quartz substrate, glass substrate, SiN-on-insulator substrate or III-V compound substrate, an additional film layer may be required between the substrate 1 and the waveguide layer 2, such as a protective layer and a buffer layer. For example, the material of the protective layer may be silicon dioxide or silicon nitride, and the material of the buffer layer may be silicon dioxide.

[0044] The aforementioned protective layer can be used to protect the upper edge of the waveguide layer 2 and maintain its shape. Furthermore, the protective layer can also serve as an anti-reflective coating. For example, the thickness of the protective layer can range from 10 nm to 100 nm. The aforementioned buffer layer can be used to reduce thermal stress. For example, the thickness of the buffer layer can range from 0.5 μm to 1 μm.

[0045] For example, see [link to previous article] Figure 1A portion of the waveguide layer 2 can be patterned into a first waveguide 20 using standard photolithography (deep ultraviolet lithography or electron beam lithography) and reactive ion etching processes. The first waveguide 20 can be used to achieve single-mode transmission of the target wavelength. For example, the first waveguide 20 can be a strip waveguide, a planar waveguide, or a ridge waveguide. In the case of a ridge waveguide 20, the typical ridge width of the first waveguide 20 can be 500 nm, and the length of the first waveguide 2 can be 1 mm.

[0046] See also Figure 1 A phase change material metasurface layer 3 is disposed on the side of the waveguide layer 2 away from the substrate 1. The phase change material metasurface layer 3 includes multiple protrusion structures 30 to enable the grating coupler 10 to filter, couple, and switch the target operating wavelength.

[0047] In some embodiments, the phase change material includes Ge2Sb2Te5, Sb2Se3, Sb2Te3, or VO2.

[0048] Among them, sulfide-based phase change materials (Ge2Sb2Te5, Sb2Se3, Sb2Te3, etc.) and VO2 have advantages such as low amorphous loss, high refractive index contrast, good thermal stability, and cycle durability. For example, antimony selenide (Sb2Se3) material has good phase change stability and can maintain good optical performance and material properties after multiple phase change cycles, thereby improving the reliability and stability of the grating coupler 10 during long-term use and reducing the loss and maintenance cost of the grating coupler 10.

[0049] For example, the communication band of the target operating wavelength can be 1550nm. In this band, the multiple protrusion structures 30 of the phase change material can reversibly switch between crystalline and amorphous states under different laser irradiation, so as to realize the reconstruction control of the target operating wavelength by the grating coupler 10.

[0050] For example, when the multiple protrusions 30 are crystalline, the grating coupler 10 enables filtering coupling to the target operating wavelength, allowing light with wavelengths at the target operating wavelength to enter the grating coupler 10 and be modulated. When the multiple protrusions 30 are amorphous, the grating coupler 10 disables filtering coupling to the target operating wavelength, preventing light with wavelengths at the target operating wavelength from entering the grating coupler 10.

[0051] For example, the phase change material metasurface layer 3 located above the waveguide layer 2 can serve as a grating structure, with the waveguide layer 2 disposed within the grating plane. The function of the phase change material metasurface layer 3 is to deflect perpendicular incident light to the propagation direction of the first waveguide 20 in the waveguide layer 2, for example, deflecting light propagating along the Z direction to propagate along the X direction. Simultaneously, the phase change material metasurface layer 3 can also focus light at a specific location in the waveguide layer 2 to improve coupling efficiency.

[0052] According to the grating equation dsinθ=n eff λ-mλ, after the light is coupled into waveguide layer 2, it propagates along a specific direction (e.g., direction X). Wherein, "n eff "m" represents the effective refractive index of the waveguide, "λ" represents the diffraction order, and "λ" represents the wavelength of the light. By changing the phase state of the protrusion structure 30 in a specific region above the waveguide layer 2, an equivalent grating periodic modulation can be formed.

[0053] It is understandable that, through the optical modulation effect of the phase change material metasurface layer 3, the grating coupler 10 can achieve high-precision filtering within a specific wavelength window. The filtering bandwidth can be flexibly set through device design, and different preset filtering bandwidth characteristics can be selected by switching phase change states during operation.

[0054] In the above embodiments of this application, the grating coupler 10 includes a substrate 1, a waveguide layer 2, and a phase change material metasurface layer 3. The waveguide layer 2 and the phase change material metasurface layer 3 are sequentially stacked on the substrate 1. The phase change material metasurface layer 3 includes multiple protrusion structures 30 to realize the filtering coupling and switching of the grating coupler 10 for the target operating wavelength.

[0055] It is understandable that the multiple protrusion structures 30 are phase change materials, capable of reversibly changing their crystalline state. That is, the multiple protrusion structures 30 possess rapid phase change characteristics, enabling reversible switching between crystalline and amorphous states, thereby achieving filtering coupling and switching of the grating coupler 10 at the target operating wavelength. Furthermore, by changing the crystalline state of the multiple protrusion structures 30, the grating coupler 10 can flexibly select different specific wavelengths for switching filtering, thus achieving dynamic control of the grating coupler 10.

[0056] For example, a dynamically programmable optical coding function can be introduced into the grating coupler 10, such as encoding coupling on as "1" and coupling off as "0", thereby improving the application flexibility and adaptability of the grating coupler 10 in optical communication and other fields, and realizing efficient, low-power, and fast dynamic control of grating coupling characteristics.

[0057] In some embodiments, when the protrusion structure 30 is crystalline, it has a first refractive index n1 and a first extinction coefficient k1. When the protrusion structure 30 is amorphous, it has a second refractive index n2 and a second extinction coefficient k2. The difference between the first refractive index n1 and the second refractive index n2 is greater than 1, and the difference between the first extinction coefficient k1 and the second extinction coefficient k2 is greater than 1.

[0058] For example, the material of the protrusion structure 30 is antimony selenide. When the protrusion structure 30 is crystalline, the peak value of the first refractive index n1 of crystalline antimony selenide is approximately 5.0, and the peak value of the first extinction coefficient k1 is approximately 3.2. When the protrusion structure 30 is amorphous, the peak value of the second refractive index n2 of amorphous antimony selenide is approximately 3.8, and the peak value of the second extinction coefficient k2 is approximately 1.9. n1-n2=1.2>1, k1-k2=1.3>1.

[0059] Understandably, by utilizing the significant refractive index difference between the protrusion structure 30 in its crystalline and amorphous states, the grating coupler 10 can produce a high-contrast switching filtering effect for optical signals of specific wavelengths under different phase transition states. By optimizing the geometry, size, and arrangement of the multiple protrusion structures 30 in the phase change material metasurface layer 3, as well as the layout of the multiple protrusion structures 30 in the grating coupler 10, higher filtering efficiency and lower insertion loss can be achieved.

[0060] In some embodiments, see Figure 1 The protrusion structure 30 has a shape including an axisymmetric shape. The orthographic projection of the protrusion structure 30 onto the substrate 1 includes a rectangular, circular, elliptical, V-shaped, or H-shaped shape. This embodiment illustrates the case where the protrusion structure 30 is a cube and its orthographic projection onto the substrate 1 is rectangular. Exemplarily, the protrusion structure 30 can be a rectangular nanopillar, nanodisc, nanoblock, V-shaped, H-shaped, etc., and the geometry of the protrusion structure 30 can be set according to requirements.

[0061] In some embodiments, see Figure 1 The multiple protrusions 30 are identical in size. For example, the size of the protrusion 30 includes its shape, length, height, and width. By setting the multiple protrusions 30 to have the same size, it is easier to achieve unified control of the multiple protrusions 30, thereby improving the accuracy of dynamic control of the grating coupler 10.

[0062] In some embodiments, see Figure 1 Along a first direction X parallel to the substrate 1, the length of the protrusion structure 30 ranges from 150 nm to 900 nm. For example, the length of the protrusion structure 30 can be 150 nm, 300 nm, 525 nm, 700 nm, or 900 nm.

[0063] Along a second direction Y parallel to the substrate 1, the width of the protrusion structure 30 ranges from 150 nm to 900 nm. For example, the length of the protrusion structure 30 can be 150 nm, 300 nm, 525 nm, 700 nm, or 900 nm. The second direction Y intersects the first direction X. In the embodiments of this application, the second direction Y is perpendicular to the first direction X as an example.

[0064] It is understandable that by optimizing the specific geometry, size parameters, and positional arrangement of multiple protrusion structures in the grating coupler, the effective integration of the phase change material metasurface layer 3 and the grating coupler 10 is achieved, ensuring the precise control of specific wavelength optical signals by the grating coupler 10 during the antimony selenide phase transition process.

[0065] In some embodiments, see Figure 1 Multiple protrusion structures 30 are periodically arranged along a first direction X parallel to substrate 1 and a second direction Y parallel to substrate 1. The second direction Y intersects the first direction X. In the embodiments of this application, the second direction Y is perpendicular to the first direction X as an example.

[0066] It is understandable that the periodic arrangement of multiple protrusions 30 refers to the structure or pattern in which multiple protrusions 30 repeat in space according to a certain rule. That is, each protrusion 30 is arranged in an array according to the unit period to achieve efficient coupling of light.

[0067] For example, multiple protrusions 30 can also be arranged in a quasi-periodic manner. "Quasi-periodic arrangement" means that each protrusion 30 is largely repeated, but controllable deviations in spacing, size, or angle are allowed, which can achieve efficient coupling of light and break the directional limitations imposed by strict periodicity.

[0068] Among them, the period, duty cycle (or unit size) and height of the protrusion structure 30 have been strictly optimized so that when the optical signal is coupled from the optical fiber or other external light source into the grating area of ​​the protrusion structure 30, the optical signal can generate efficient coupling at a specific wavelength (i.e., the target working wavelength) and at the same time effectively suppress optical signals of other wavelengths (non-target working wavelengths), thus playing a filtering role.

[0069] In some embodiments, along the first direction X, the multiple protrusion structures 30 have the same phase. Along the second direction Y, at least two protrusion structures 30 have different phases. By setting protrusion structures 30 with different phases and protrusion structures 30 with the same phase on the plane XY, the phase coverage of the protrusion structures 30 can be improved, thereby improving the coupling efficiency of the grating coupler 10 for light of the target operating wavelength.

[0070] It is understandable that, along the first direction X, multiple protrusions 30 rotate in the same direction, while along the second direction Y, at least two protrusions 30 rotate in different directions. The phase distribution (Φ(x, y)) of the protrusions 30 can be calculated.

[0071] In some embodiments, the grating coupler 10 further includes a passivation layer 4 disposed on the side of the phase change material metasurface layer 3 away from the substrate 1. The passivation layer 4 can protect the grating coupler 10 from oxidation or moisture erosion, thereby improving the long-term stability and reliability of the grating coupler 10.

[0072] For example, the passivation layer 4 covers the sides of the plurality of protrusion structures 30 and the surface of the waveguide layer 2 away from the substrate 1. The material of the passivation layer 4 can be aluminum oxide (Al2O3) or silicon dioxide (SiO2). The thickness of the passivation layer 4 can be 50 nm.

[0073] On the other hand, a design method for a grating coupler is also provided, which is used to design the grating coupler 10 as described in the above embodiments. Figure 3 This is a flowchart illustrating the design method of the grating coupler provided in an embodiment of this application.

[0074] See Figure 3 The above design method includes the following steps S1 to S4: Step S1: Provide the target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limit.

[0075] Understandably, the reconfigurable function of the grating coupler 10 is first defined. Based on the target reconfigurable function, target parameters such as the target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limit of the grating coupler 10 are determined. For example, the reconfigurable function includes switchable diffraction angle (beam deflection direction), adjustable diffraction efficiency, adjustable operating wavelength, dynamic control of polarization state conversion, and focus / defocus function switching.

[0076] Figure 4 These are top views and three-dimensional views of the metasurface unit structure provided in the embodiments of this application. Figure 4 (1) is a top view of the metasurface unit structure 5. Figure 4 (1) The geometry of the protrusion structure 30 is shown. Figure 4 (2) is a three-dimensional diagram of metasurface unit structure 5. Figure 4 (2) The height of the protrusion structure 30 and its contact relationship with the substrate 1 are shown.

[0077] Step S2: See Figure 4A metasurface unit structure 5 is configured and numerical simulations are performed on the metasurface unit structure 5 to obtain its geometric parameters. The metasurface unit structure 5 includes a substrate 1 and a protrusion structure 30.

[0078] For example, see Figure 4 The FDTD Solutions electromagnetic simulation software can be used to numerically simulate the metasurface unit structure 5 at the target operating wavelength, scanning its key geometric parameters and material state, and calculating the amplitude and phase of its transmission or reflection of specific polarized light at the target operating wavelength. For example, the target operating wavelength can be 1550 nm, and can also be extended to the optical communication band and visible light. The key geometric parameters include the dimensions Px of the protrusion structure 30 in the X direction, the dimensions Py in the Y direction, the height H, and the rotation angle Rotation. The material state of the protrusion structure 30 can be amorphous or crystalline.

[0079] For example, the metasurface unit structure 5 can be a rectangular nanopole, or an H-shaped antenna, V-shaped antenna, etc., to achieve a specific polarization or phase response. The geometric parameters (width, length, and height) of the rectangular nanopole are optimized for the target operating wavelength (e.g., 1550 nm). When the metasurface unit structure 5 is in a crystalline state, it can introduce a specific phase delay (Φcry) to the incident light. When the metasurface unit structure 5 is in an amorphous state, it introduces a significantly different phase delay (Φam), or a lower phase modulation efficiency, or a higher absorption loss.

[0080] By performing parameter scanning on the width, length, and height of rectangular nanopillars, ΔΦ = Φcry - Φam can be made close to 180° (or π radians) in the critical region. This is the basis for achieving efficient binary phase modulation (such as focusing and deflection). For example, the length of the rectangular nanopillars can range from 150 nm to 350 nm, the width from 80 nm to 150 nm, and the height from 50 nm to 1500 nm.

[0081] Furthermore, through the aforementioned step S2, the metasurface unit structure 5 can achieve a phase coverage range close to 2π and exhibit high transmission or reflection efficiency, regardless of whether the protrusion structure 30 is in an amorphous or crystalline state. Moreover, by optimizing the protrusion structure 30, the phase difference (ΔΦ) caused by the phase transition can be made sufficiently large at the target position (typically close to π or a multiple of π to achieve a significant switching).

[0082] Step S3: Calculate the target phase value of multiple protrusion structures based on the target operating wavelength, target diffraction efficiency, target switching speed and target power consumption limit, and calculate the target size of the protrusion structure through reverse design based on the target phase value.

[0083] For example, the required discrete phase distribution Φ(x, y) on the metasurface plane (phase change material metasurface layer 3) can be calculated based on the target grating function. The target phase value of the protrusion structure at each spatial location is determined based on the phase delay required by the target grating function. Furthermore, by combining the phase-size mapping relationship and transmittance characteristics obtained from simulation, the geometry of each protrusion structure is designed and optimized in reverse.

[0084] Step S4: Arrange multiple protrusion structures periodically or quasi-periodically according to the target phase value and target size to form a phase change material metasurface layer 3.

[0085] Understandably, the optimized metasurface unit structure 5 from step 2 is arranged into a periodic or quasi-periodic array according to the phase distribution Φ(x, y) calculated in step S3. Under the target state of the antimony selenide material, the geometric parameters of the protrusion structure 30 are selected based on the required phase values ​​at different locations. Finally, by controllably changing the crystallization state (amorphous or crystalline) of the antimony selenide material, dynamic modulation of the overall phase distribution of the phase change material metasurface layer 3 is achieved, thereby completing the design of the reconfigurable grating coupler 10 with grating function switching capability.

[0086] In the above embodiments of this application, the design method of the grating coupler 10 includes providing a target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limit, and performing numerical simulation on the metasurface unit structure 5 to obtain the geometric parameters of the metasurface unit structure 5. Through reverse design, the target size of the protrusion structure 30 is calculated based on the target phase value, and multiple protrusion structures 30 are arranged periodically or quasi-periodically under the target size and target phase value to obtain the design of a reconfigurable grating coupler 10 with grating function switching capability.

[0087] It is understandable that the multiple protrusion structures 30 can reversibly change their crystalline state, meaning that the multiple protrusion structures 30 have rapid phase transition characteristics and can reversibly switch between crystalline and amorphous states, thereby realizing the filtering coupling and switching of the grating coupler 10 for the target operating wavelength. Furthermore, by changing the crystalline state of the multiple protrusion structures 30, the grating coupler 10 can flexibly select different specific wavelengths for switching filtering, thereby achieving dynamic control of the grating coupler 10.

[0088] For example, the phase change material metasurface layer 3 consists of periodically arranged subwavelength structures, each of which can modulate the phase of the incident light. When perpendicularly incident light passes through the metasurface, surface waves or leakage waves are generated due to the presence of a phase gradient. Assuming the metasurface is located in the z=0 plane, the incident light is a perpendicularly incident plane wave, and the electric field is:

[0089] Where k = 2π / λ is the wave number and P is the polarization direction.

[0090] Each protrusion 30 on the metasurface introduces a local phase delay Φ(x,y) at position (x,y). Assuming the phase change material metasurface layer 3 has 100% transmittance and pure phase modulation (i.e., amplitude is 1, only the phase changes), the complex amplitude of the metasurface layer's emitted field can be expressed as:

[0091] To achieve beam coupling to the waveguide, a linear phase gradient needs to be designed on the metasurface layer. Assume a linear phase gradient along the x-direction:

[0092] Where Λ is the equivalent period (phase gradient period) of the metasurface.

[0093] According to Fourier optics, the outgoing field can be decomposed into plane waves of different spatial frequencies, at z=0. + In a plane, the electric field can be written as:

[0094] Its spatial frequency is k x =2π / Λ, meaning there is an additional wave vector component along the x-direction. Where k0 = 2π / λ is the free-space wave number. When k x At k0, the transmitted light field decays exponentially along the z-direction.

[0095] This is a surface wave (or evanescent wave). This wave is confined to the vicinity of the metasurface and propagates in the x-direction.

[0096] A waveguide exists at a distance *d* below the metasurface (the waveguide layer is located at *z=d*). The electric field of the surface wave generated by the metasurface at the waveguide location is:

[0097]

[0098] There exist specific guided modes in the waveguide, and their field distribution is as follows:

[0099] Where β is the propagation constant (effective wave vector). To achieve effective coupling, the phase matching condition must be satisfied: k x =β That is, the wave vector of the surface wave generated by the metasurface in the x-direction must be equal to the propagation constant of the waveguide mode. In addition, the coupling efficiency depends on the overlap integral of the evanescent wave field at the waveguide location and the waveguide mode field.

[0100] After a vertically incident beam passes through a metasurface, its propagation direction needs to be deflected and focused to enter the underlying waveguide via evanescent wave coupling. This requires the metasurface to simultaneously perform three functions: deflection: changing the beam's propagation direction so that it is incident on the waveguide surface at a specific angle; focusing: focusing the beam near the waveguide surface to form a locally enhanced evanescent field; and phase matching: satisfying the phase matching condition (i.e., wave vector matching) of the waveguide mode.

[0101] Therefore, the corresponding target distribution should include the following three parts: (1) Linear phase term: to achieve beam deflection so that the beam is incident on the waveguide surface at a specific angle (this angle is to satisfy the phase matching condition). (2) Second phase term: to achieve focusing, so that the beam forms a small spot near the waveguide surface (to improve coupling efficiency). (3) Grating periodic phase term: In order to meet the phase matching condition of evanescent wave coupling, periodic modulation needs to be introduced.

[0102] Target phase distribution formula:

[0103] The first term is the wave vector matching term, which provides the grating periodicity and satisfies the phase matching condition ∆k. x =β, establishing a period in the waveguide direction (Y direction).

[0104]

[0105] The second term is the field distribution matching term, which mainly optimizes the evanescent field distribution and suppresses sidelobes. Lcoup is the coupling length, typically 10 periods.

[0106]

[0107] The third term is the focusing term, which mainly aims to form a diffraction-limited spot at the waveguide coupling point, thereby improving coupling efficiency. Here, f is the focal length, which needs to be determined based on the distance from the metasurface to the waveguide surface and the desired focusing position. It should be taken as the distance from the metasurface to the coupling point on the waveguide surface (optical path along the beam propagation direction). If the waveguide surface is parallel to the metasurface, and we want the focusing point to be located at the center of the waveguide surface directly below the metasurface, then for the deflection case, the focal length f should be greater than the perpendicular distance from the metasurface to the waveguide (because of oblique incidence).

[0108]

[0109] For the geometric phase modulation unit, the relationship between the rotation angle θ(x, y) of each matrix nanopillar and the target phase is as follows:

[0110] Where σ=±1 corresponds to left-hand and right-hand circularly polarized light, respectively.

[0111] Through numerical simulation and optimization algorithms, the optimal combination of grating parameters is determined, so that when the metasurface layer 3 of the phase change material is in different phase change states, the grating coupler 10 can produce high-efficiency coupling and filtering effects for optical signals of specific wavelengths.

[0112] Figure 5 This is a schematic diagram illustrating the principle of the phase change material metasurface layer provided in the embodiments of this application.

[0113] For example, see Figure 5 Incident light at the target operating wavelength enters perpendicularly into the grating coupling region composed of a phase change material metasurface layer 3. After phase modulation, it generates an evanescent wave, which diffracts to the lower waveguide layer, exciting the waveguide mode. By switching the phase state of antimony selenide, reconstruction control is performed, thereby enabling and disabling the light coupling.

[0114] In some embodiments, after arranging the plurality of protrusion structures 30, the above-described preparation method further includes irradiating the protrusion structures 30 with a pulsed laser beam to change the crystal state of the plurality of protrusion structures 30, so as to control the filtering coupling and switching of the grating coupler 10 to the target working wavelength.

[0115] For example, an externally focused pulsed laser beam can be used as the excitation source. This laser beam is not the coupling light, but rather the pump light used to induce a phase change in the phase change material. Since the phase change material has strong absorption in the near-infrared region, the preferred wavelength of the laser beam is located in the band where the phase change material has a high absorption coefficient, which can improve the photothermal conversion efficiency of the grating coupler 10.

[0116] For example, an electro-optic modulator (EOM) can be connected after the laser source described above. The electro-optic modulator can be used to precisely control the on or off of the pump light pulse, the pulse width, and the pulse repetition frequency. Furthermore, the electro-optic modulator can also collimate and expand the pulsed laser to obtain a uniform beam suitable for subsequent focusing, and use a high numerical aperture objective lens to highly focus the beam onto the grating region on the surface of the grating coupler 10.

[0117] For example, when the phase transition material is Sb₂Se₃, a pulsed laser beam can be used as an external excitation source to trigger the phase transition process of Sb₂Se₃. For instance, the power range of the pulsed laser beam can be 10mW to 200mW, the pulse width range can be 500ns to 50ms, and the pulse frequency range can be 20Hz to 2MHz.

[0118] The process of irradiating the protruding structure 30 with a pulsed laser beam includes: The protruding structure 30 is irradiated with a first laser beam, causing it to become crystalline and enabling the grating coupler 10 to couple. Alternatively, the protruding structure 30 is irradiated with a second laser beam, causing it to become amorphous and enabling the grating coupler 10 to couple. The power of the first laser is less than that of the second laser, and the pulse width of the first laser is less than that of the second laser.

[0119] It is understandable that by controlling the energy density, pulse width, and frequency of the laser beam, stable switching between crystalline and amorphous states of the phase change material metasurface unit structure 5 can be achieved. By precisely controlling the pulse parameters of the laser beam, reversible phase transitions of the phase change material metasurface unit structure 5 can be realized, and its performance stability can be ensured after multiple phase transition cycles.

[0120] For example, taking Sb2Se3 as a phase change material, during the process of irradiating Sb2Se3 with a first laser beam to crystallize it, a laser pulse with a lower power and a shorter pulse width is applied to gradually heat the Sb2Se3 material to above the crystallization temperature and hold it for a certain period of time, and then slowly cool it to form a stable crystalline phase.

[0121] For example, in the process of irradiating Sb2Se3 with a second laser beam to make it amorphous, a laser pulse with high power and long pulse width is applied to rapidly heat the Sb2Se3 material above its melting point and then rapidly cool it to form an amorphous phase.

[0122] In some embodiments, the absolute value of the difference between the wavelengths of the first laser beam and the second laser beam and the target working wavelength is greater than 100 nm.

[0123] Understandably, both the first and second laser beams are pump wavelengths. The pump wavelength must be significantly different from the target operating wavelength of the grating coupling so that the pump light can be separated from the signal light by using a dichroic mirror, bandpass filter, or longpass filter to avoid interference between the two.

[0124] In some embodiments, the target operating wavelength includes 850 nm, 1064 nm, 1310 nm, or 1550 nm. The wavelength of the first laser beam includes 638 nm, 710 nm, 800 nm, or 808 nm. The wavelength of the second laser beam includes 638 nm, 710 nm, 800 nm, or 808 nm. It is understood that the target operating wavelength is a general-purpose on-chip wavelength, and the wavelengths of the first and second laser beams are wavelengths related to the phase change material.

[0125] For example, both the first laser beam and the second laser beam are pump wavelengths. When the target operating wavelength is 1550nm, the wavelengths of both the first laser beam and the second laser beam can be 638nm, thereby avoiding interference between the pump light and the signal light.

[0126] Figure 6 This is a schematic diagram illustrating the phase response of the phase change material metasurface layer provided in this application to x-ray and y-ray polarized light emitted from free space. Taking Sb₂Se₃ as an example, the free space light wavelength is 1550 nm, and the length and width of the protrusion structure 30 are scanned within the range of 300 nm to 900 nm. Figure 6 (1) is a schematic diagram of the response of free-space X-ray polarized light. Figure 6 (2) is a schematic diagram of the response of free space light emitted by y-line polarization. Figure 6 (1) and Figure 6 (2) The contrast parameter on the right represents the color of light rays with a phase angle between -π and π.

[0127] For example, by Figure 6 It is known that the protrusion structure 30, within a size range of 300nm to 900nm, can modulate light within an angle range of -π to π, thereby significantly improving the coupling efficiency of the optical signal. Compared with traditional grating couplers, the coupling efficiency of the grating coupler 10 provided in the embodiments of this application can be significantly improved within the same wavelength range. This helps to reduce optical signal loss in the system, improve overall energy utilization efficiency, and thus increase the transmission distance and data transmission rate of the optical communication system.

[0128] Furthermore, by using the electromagnetic simulation software FDTD solutions to simulate the grating coupler 10, it can be seen that the free space light located above the waveguide layer 2 is significantly confined to the transverse waveguide after being coupled by the phase change material metasurface layer 3, which significantly improves the coupling efficiency of the grating coupler 10.

[0129] For example, the structure of the entire grating coupler 10 is based on standard silicon photonics manufacturing processes, including thin film deposition, photolithography and etching, which facilitates large-scale integration with other on-chip optical components such as waveguides and modulators. This is beneficial for building highly integrated optical communication and optical information processing chips, reducing system complexity and cost, and improving system reliability and stability.

[0130] For example, the following are the operating parameters and simulation results analysis of a grating coupler 10 provided in this application: The grating coupler 10 operates at the center wavelength of 1550 nm, the center wavelength of the C-band optical communication band. The substrate 1 is SOI (waveguide layer 2 is 220 nm thick, buried oxide layer 12 is 2 μm thick). The first waveguide 20 is a strip waveguide with a width of 500 nm and a height of 220 nm. The protrusion structure 30 is made of Sb₂Se₃ and is a rectangular nanopillar with a height of 300 nm, a length of 300 nm, and a width of 150 nm. The grating period Λ = λ / n eff =544nm, focal length f=5um, coupling length Lcoup=8Λ=4.4μm.

[0131] When free-space light with a wavelength of 1550nm irradiates the phase change material metasurface layer 3 at a specific angle θ=8°, multiple protrusion structures 30 act as scatterers and interact with the underlying waveguide layer 2.

[0132] The optimized phase change material metasurface layer 3 was simulated and verified using electromagnetic simulation software (such as Lumerical FDTD Solutions). The coupling efficiency of the grating coupler 10 was 45.6% when multiple protrusion structures 30 were distributed in a crystalline state, and 5.33% when the multiple protrusion structures were distributed in an amorphous state.

[0133] As can be seen from the above embodiments, the grating coupler 10 provided in this application effectively improves the coupling efficiency of light at the target working wavelength, and the coupling can be effectively turned on and off by changing the material crystal state of the phase change material metasurface layer 3.

[0134] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A grating coupler, characterized in that, include: Substrate; A waveguide layer is disposed on the substrate; A phase change material metasurface layer is disposed on the side of the waveguide layer away from the substrate; The phase change material metasurface layer includes multiple protrusion structures to enable the grating coupler to filter, couple, and switch the target operating wavelength.

2. The grating coupler according to claim 1, characterized in that, When the protrusion structure is crystalline, the protrusion structure has a first refractive index and a first extinction coefficient; when the protrusion structure is amorphous, the protrusion structure has a second refractive index and a second extinction coefficient. The difference between the first refractive index and the second refractive index is greater than 1; the difference between the first extinction coefficient and the second extinction coefficient is greater than 1.

3. The grating coupler according to claim 1, characterized in that, The multiple protrusion structures are of the same size.

4. The grating coupler according to claim 3, characterized in that, Along a first direction parallel to the substrate, the length of the protrusion structure ranges from 150 nm to 900 nm; along a second direction parallel to the substrate, the width of the protrusion structure ranges from 150 nm to 900 nm; the second direction intersects the first direction.

5. The grating coupler according to claim 3, characterized in that, The plurality of protrusions are arranged periodically along a first direction parallel to the substrate and along a second direction parallel to the substrate; or, the plurality of protrusions are arranged quasi-periodically, wherein the second direction intersects the first direction.

6. The grating coupler according to claim 5, characterized in that, Along the first direction, the phases of the plurality of protrusion structures are the same; Along the second direction, at least two of the protrusion structures are in different phases.

7. The grating coupler according to claim 1, characterized in that, The shape of the protrusion structure includes an axisymmetric shape; The shape of the orthographic projection of the protrusion structure onto the substrate includes rectangular, circular, elliptical, V-shaped, or H-shaped.

8. The grating coupler according to claim 1, characterized in that, The phase change material includes Ge2Sb2Te5, Sb2Se3, Sb2Te3, or VO2.

9. The grating coupler according to claim 3, characterized in that, The grating coupler also includes a passivation layer disposed on the side of the phase change material metasurface layer away from the substrate.

10. A design method for a grating coupler, characterized in that, Used for designing the grating coupler as described in claims 1-9; The design method includes: Provide the target operating wavelength, target diffraction efficiency, target switching speed, and target power consumption limits; A metasurface unit structure is configured, and numerical simulation is performed on the metasurface unit structure to obtain its geometric parameters; the metasurface unit structure includes the substrate and a protrusion structure. Based on the target operating wavelength, the target diffraction efficiency, the target switching speed, and the target power consumption limit, the target phase values ​​of multiple protrusion structures are calculated, and the target size of the protrusion structure is calculated through reverse design based on the target phase values. The multiple protrusion structures are arranged periodically or quasi-periodically according to the target phase value and the target size.

11. The design method according to claim 10, characterized in that, After arranging the plurality of the protrusion structures, the design method further includes: The protruding structure is irradiated with a pulsed laser beam to change the crystal state of the multiple protruding structures, thereby controlling the filtering coupling and switching of the grating coupler to the target operating wavelength; The process of irradiating the protruding structure with a pulsed laser beam includes: The protruding structure is irradiated with a first laser beam, causing the protruding structure to become crystalline and activating the coupling of the grating coupler. Alternatively, the protrusion structure can be irradiated with a second laser beam to make the protrusion structure amorphous and to shut down the coupling of the grating coupler; the power of the first laser is less than the power of the second laser, and the pulse width of the first laser is less than the pulse width of the second laser.

12. The design method according to claim 11, characterized in that, The absolute value of the difference between the wavelengths of the first laser beam and the second laser beam and the target working wavelength is greater than 100 nm.

13. The design method according to claim 11, characterized in that, The target operating wavelengths include 850nm, 1064nm, 1310nm, or 1550nm; The wavelength of the first laser beam includes 638nm, 710nm, 800nm ​​or 808nm; The wavelength of the second laser beam includes 638nm, 710nm, 800nm ​​or 808nm.

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