Phase gradient metasurface type on-chip integrated optical switch based on phase change material

Abstract

The invention discloses a phase gradient metasurface type on-chip integrated optical switch based on a phase change material, and aims to solve the problems that an existing on-chip integrated optical modulator is large in size, low in integration level, single in function, free of memory characteristics and the like. According to the phase gradient metasurface type on-chip integrated optical switch based on the phase change material, a Si single-mode optical waveguide is arranged on a SiO2 substrate, a patterned micro-nano structure unit made of a GST material is deposited on the upper surface of the Si single-mode optical waveguide, a GST structure array is formed, the GST structure array is composed of a plurality of micro-nano structure units arranged at equal intervals, and the micro-nano structure units are arranged on the upper surface of the Si single-mode optical waveguide. And the plurality of micro-nano structure units are of a one-dimensional array structure. According to the optical switch, heterogeneous integration is carried out on the phase change material and an existing photon chip platform, efficient modulation of optical signals is achieved based on waveguide boundary perturbation by controlling phase change of the GST structure array, and meanwhile the optical switch has the remarkable advantages of being compatible with high performance and high integration level.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronic devices, and in particular relates to a phase gradient metasurface type on-chip integrated optical switch based on phase change material. Background Art

[0002] Photonic integration technology and photonic chips refer to integrated photonic systems that use photons as information carriers and have information processing functions such as storage and logical operations. They are one of the core technologies that support the development of future information fields such as communications and computing in the "post-Moore era". Optical modulators are key components of photonic chips. They modulate the multi-dimensional properties of transmitted light, such as phase, intensity, polarization, and mode, and then realize functions such as photoelectric signal conversion, optical switching, and mode conversion, completing the transmission and modulation of light wave signals and information carried.

[0003] In terms of device materials, common modulator materials include silicon, lithium niobate, graphene, black phosphorus, electro-optic polymers, phase change materials, etc. Lithium niobate modulators can achieve excellent extinction ratios, but the device size is too large, the integration is poor, the production cost is high, and the cycle is long. Silicon-based modulators also have large device sizes, which makes it difficult to meet the needs of high-density integration, and the extinction ratio is low, the driving voltage is large, and the energy consumption is high. Graphene and electro-optic polymer materials are limited by the stability of the materials themselves and are not suitable for large-scale production. Although existing phase change material modulators have advantages such as all-optical operation and storage characteristics, most devices are still based on traditional device structures, resulting in large device sizes. In terms of device structure, the mainstream optical modulator structure is mainly based on Mach-Zehnder interferometers (MZI) and microring resonators (MRR). MRR modulators use microring resonators for optical path selection and interference, and have fast response speeds, but have the disadvantages of wavelength selection characteristics, small bandwidth, and large crosstalk. MZI modulators have fast switching speeds, larger bandwidths, and high extinction ratios, but the device size is large.

[0004] Overall, the development history of on-chip integrated optical modulators has been continuously developing towards high bandwidth, small size, low power consumption and high integration from the early germanium silicon modulators to the current silicon photonics and lithium niobate modulators. However, up to now, various modulators still have shortcomings such as large device size, low integration, single function and no memory characteristics: ① Limited by the performance limitations of the material's own weak electro-optic coefficient and slow carrier transport rate, the size of mainstream silicon and thin-film lithium niobate-based modulators is in the order of millimeters or hundreds of microns, and the working bandwidth is limited; ② The device function is single and the functional flexibility is poor. Once the design is completed, the device function is solidified, and it is impossible to achieve multi-functional tuning and multi-working state switching; ③ The device does not have memory characteristics. The working state of the device is automatically reset in the passive state. It does not have storage capacity and cannot achieve storage and computing integration. The shortcomings of the modulation device make the existing technology unable to meet the development needs of high integration and future ultra-large-scale photonic chips. While achieving high performance, greatly compressing the size of the modulator, improving the flexibility of the device, and reducing the energy consumption of the device have become key challenges in photonic chip research.

[0005] Multi-material hybrid heterogeneous integration is an important technical route to further break through the performance of photonic modulation devices. In order to make up for the shortcomings of modulators based on a single material, new materials are introduced on the existing photonic platform to build a multi-material hybrid heterogeneous integration platform with complementary advantages. By coupling new materials and new mechanisms, new high-performance integrated optical modulation devices can be realized. Phase change materials can undergo phase changes under the synergistic effect of multiple fields such as light / heat / electricity, accompanied by changes in the optical refractive index n and extinction coefficient k. The phase change process of phase change materials has the advantages of fast speed, reversible process, low energy consumption, high cycle stability, photoinduced phase change, and multi-level phase change. It has become an excellent candidate material for heterogeneous integrated photonic modulators and has great application potential in further breaking through the performance of photonic modulation devices. Summary of the invention

[0006] The present invention aims to solve the problems of existing on-chip integrated optical modulators such as large size, low integration, single function and no memory characteristics, and provide a phase gradient metasurface on-chip integrated optical switch based on phase change material.

[0007] The phase gradient metasurface on-chip integrated optical switch based on phase change material of the present invention comprises a SiO2 substrate, a Si single-mode optical waveguide and a GST (phase change material) structure array. The Si single-mode optical waveguide is arranged on the SiO2 substrate, and a micro-nano structure unit of a patterned GST material is deposited on the upper surface of the Si single-mode optical waveguide to form a GST structure array. The GST structure array is composed of a plurality of micro-nano structure units arranged at equal intervals, and the plurality of micro-nano structure units present a one-dimensional array structure. The center distance between two adjacent micro-nano structure units is dx, and the phase difference introduced by the two adjacent micro-nano structure units to the reflected light at the waveguide interface is dΦ, that is, the GST structure array forms a phase gradient metasurface array, and the phase gradient is dΦ / dx.

[0008] The present invention proposes a phase gradient metasurface-type on-chip integrated optical switch based on phase change material GST, which integrates high extinction ratio, high integration, storage, reconfiguration, multi-level regulation, and all-optical control, through multi-material heterogeneous integration. Phase change material is introduced on a silicon-based optical platform (silicon on insulating substrate, SOI) to achieve hybrid heterogeneous integration of phase change material and silicon waveguide, and the phase change material is designed as an array arrangement structure with a phase gradient. The coupling effect between the evanescent wave on the waveguide boundary and the phase gradient metasurface is used to achieve effective modulation of the waveguide light intensity.

[0009] The phase gradient metasurface on-chip integrated optical switch based on phase change material of the present invention has the following beneficial effects:

[0010] ① Heterogeneous integration of phase change materials with existing photonic chip platforms. By controlling the phase change of materials, efficient modulation of optical signals can be achieved based on waveguide boundary perturbations, with an extinction ratio of 27 dB. At the same time, the size of optical switch devices can be significantly compressed to less than 1.5 μm, which has the significant advantages of high performance and high integration.

[0011] ② Phase change materials have reversible phase change and multi-level phase change characteristics, which can give modulation devices reconfigurable and tunable characteristics, greatly improving the flexibility and freedom of device design. The same device can be used to achieve multi-level working state switching and multi-function switching;

[0012] ③ Phase change materials have memory properties, which can keep the device working in a passive state, and simultaneously have zero static power consumption and storage functions, achieving low power consumption and storage-computing integration;

[0013] ④The phase change speed of phase change materials is extremely fast, and the phase change time can reach ns or even ps, which significantly improves the response speed of the device and achieves fast reading and writing;

[0014] ⑤ Phase change materials have photoinduced phase change properties and have unique and significant advantages in achieving all-optical operations. They can truly realize “light in, copper out” and promote the development of all-optical interconnection and all-optical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of a phase gradient metasurface on-chip integrated optical switch based on phase change material of the present invention;

[0016] Figure 2 It is a cross-sectional schematic diagram of a phase gradient metasurface on-chip integrated optical switch based on phase change material of the present invention;

[0017] Figure 3 A schematic diagram of the arrangement rules of the GST structure array on the upper surface of the Si single-mode optical waveguide;

[0018] Figure 4 is a phase value curve diagram introduced by GST structural units of different sizes in the embodiment, wherein aGST represents amorphous state and cGST represents crystalline state;

[0019] Figure 5 1 is a graph showing the electric field amplitude of GST structural units of different sizes in the embodiment, wherein aGST represents an amorphous state and cGST represents a crystalline state;

[0020] Figure 6 This is a test diagram of the extinction ratio of the optical switch with different numbers of GST structural units in the embodiment;

[0021] Figure 7 The comparison diagram of the size and extinction ratio performance of the phase gradient metasurface on-chip integrated optical switch based on phase change material in the embodiment and the existing optical switch device, ★ represents the present embodiment, and the other numbers correspond to the references in Table 2;

[0022] Figure 8 1 is a waveguide cross-sectional dimension diagram of a phase gradient metasurface on-chip integrated optical switch based on phase change material in an embodiment. DETAILED DESCRIPTION

[0023] Specific implementation method one: In this implementation method, a phase gradient metasurface on-chip integrated optical switch based on phase change material includes a SiO2 substrate 1, a Si single-mode optical waveguide 2 and a GST (phase change material) structure array 3. The Si single-mode optical waveguide 2 is arranged on the SiO2 substrate 1, and a micro-nano structure unit of patterned GST material is deposited on the upper surface of the Si single-mode optical waveguide 2 to form a GST structure array 3. The GST structure array 3 is composed of a plurality of micro-nano structure units arranged at equal intervals. The plurality of micro-nano structure units present a one-dimensional array structure. The center distance between two adjacent micro-nano structure units is dx. The phase difference introduced by two adjacent micro-nano structure units to the reflected light at the waveguide interface is dΦ, that is, the GST structure array 3 forms a phase gradient metasurface array with a phase gradient of dΦ / dx.

[0024] The phase gradient metasurface on-chip integrated optical switch based on phase change material in this embodiment includes three parts, namely SiO2 substrate 1, Si single-mode optical waveguide 2 and GST structure array 3. Light is transmitted in the optical waveguide along the direction indicated by the arrow, and the light transmitted through the optical switch is intensity modulated, thereby realizing the optical switch function. The refractive index of Si waveguide is higher than that of SiO2 substrate and air, so light can satisfy the law of total reflection at the Si / SiO2 and Si / air interfaces, ensuring that light can be transmitted in the silicon waveguide, that is, there is a transmittable mode in the silicon waveguide. SiO2 has certain thickness requirements to prevent boundary evanescent light leakage, ensure that light can be completely confined in the silicon waveguide, and reduce light transmission loss. The cross-sectional dimensions of the silicon waveguide are designed to support single-mode waveguides that support the propagation of the fundamental mode TE0 mode, ensuring that the light maintains a high mode purity during the propagation of the optical waveguide and reducing transmission losses.

[0025] The design of Si single-mode optical waveguide and SiO2 substrate ensures the normal transmission of light in the silicon waveguide. The design of GST microstructure array is the key point of the present invention. By heterogeneously integrating a specially designed one-dimensional GST array on the upper surface of the silicon waveguide, utilizing the phase change characteristics of GST, as well as the changes in the optical refractive index n and extinction coefficient k before and after the phase change, an ultra-compact optical switch function with a high extinction ratio is realized. The phase change reversibility, non-volatility, multi-level phase change and photoinduced phase change characteristics of GST phase change materials are utilized to endow the optical switch with reconfigurable, storable, multi-level control and all-optical control characteristics.

[0026] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the thickness of the SiO2 substrate 1 is 2 to 4 μm.

[0027] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the width of the SiO2 substrate 1 is greater than the width of the Si single-mode optical waveguide 2.

[0028] Specific embodiment 4: This embodiment is different from specific embodiments 1 to 3 in that the GST structure array 3 is deposited on the upper surface of the Si single-mode optical waveguide 2 by using an atomic layer deposition process.

[0029] Specific implementation example five: This implementation example is different from specific implementation examples one to four in that the material of the micro-nano structure unit in the GST structure array 3 is Ge2Te2Sb5.

[0030] Specific embodiment 6: The difference between this embodiment and specific embodiments 1 to 5 is that the GST structure array 3 is composed of 8 to 15 micro-nano structure units arranged at equal intervals.

[0031] Specific embodiment 7: The difference between this embodiment and any one of specific embodiments 1 to 6 is that the micro-nano structure units in the GST structure array 3 are rectangular parallelepiped structures.

[0032] Specific implementation example eight: This implementation example is different from specific implementation example seven in that the width w and thickness t of each micro-nano structure unit in the GST structure array 3 are the same, but the length l of the micro-nano structure units is different.

[0033] Specific embodiment 9: This embodiment is different from specific embodiment 8 in that the length l of the micro-nano structure unit gradually increases along the transmission direction of the waveguide optical signal in the Si single-mode optical waveguide 2.

[0034] Specific embodiment ten: This embodiment is different from specific embodiment nine in that the size of the phase gradient metasurface on-chip integrated optical switch based on phase change material is 1200nm to 1500nm.

[0035] Embodiment: In this embodiment, a phase gradient metasurface on-chip integrated optical switch based on phase change material includes a SiO2 substrate 1, a Si single-mode optical waveguide 2 and a GST structure array 3. The Si single-mode optical waveguide 2 is arranged on the SiO2 substrate 1, and micro-nano structure units of patterned GST material are atomically deposited on the upper surface of the Si single-mode optical waveguide 2 to form a GST structure array 3. The GST structure array 3 is composed of eight micro-nano structure units arranged at equal intervals. The eight micro-nano structure units are in a one-dimensional array structure. The center distance between two adjacent micro-nano structure units is dx. The phase difference introduced to the reflected light by two adjacent micro-nano structure units at the waveguide interface is dΦ, that is, the GST structure array 3 forms a phase gradient metasurface array with a phase gradient of dΦ / dx.

[0036] The GST material described in this embodiment is Ge2Te2Sb5.

[0037] like Figure 8 As shown, the thickness t1 of the silicon dioxide substrate in this embodiment is 3 μm, and the width w1 is greater than the silicon waveguide width w0. The silicon waveguide width w0 is 500 nm, and the height t0 is 220 nm. The width w and thickness t of the GST structural unit are 80 nm and 50 nm respectively, the number N is 8, and the length of each micro-nano structural unit is 339 nm, 353 nm, 368 nm, 385 nm, 404 nm, 426 nm, 451 nm, and 481 nm respectively. The phase difference between two adjacent structural units is 2°, and the distance dx between the micro-nano structural units is 120 nm.

[0038] The design and arrangement rules of the GST microstructure array in this embodiment are as follows Figure 3 As shown. A GST structure array consists of 8 GST structure units (micro-nano structure units), numbered 3-1 to 3-8, and each GST structure unit has a different size. Figure 3As shown, the GST structural unit is a cuboid with characteristic dimensions of width w, thickness t, and length l. The dimensions of w and t of different structural units remain the same, but the length l varies. For the eight micro-nano structural units, their lengths are marked as l i (i=1,2,3…8) There are eight different values. When GST is in a crystalline state, the existence of the structural unit will introduce a phase mutation to the waveguide light. When the size of the structural unit changes, the introduced phase value changes. The phase introduced by each structural unit is recorded as Φ i (i=1,2,3…8). By designing each unit phase Φ i , so that the phase difference dΦ introduced by two adjacent structural units is constant. The GST structural units are arranged into a one-dimensional array, and the center distance between each structural unit is a constant dx. At this time, the one-dimensional array forms a phase gradient metasurface array with a phase gradient of dΦ / dx. This phase gradient metasurface will interact strongly with the waveguide light and put the optical switch in a closed state, preventing the light signal from passing through. When GST is in an amorphous state, the phase introduced by the GST array no longer has the phase gradient of the initial design, and the degree of interaction with the waveguide light signal is greatly weakened. At this time, the optical switch is in an open state.

[0039] The transition between the crystalline state and the amorphous state of the GST material of this embodiment can be achieved by applying pulsed lasers with different pulse widths. When the pulse width of the applied pulsed light is 40-50 μs, the GST can be switched from the amorphous state to the crystalline state, and when the pulse width of the laser is 50-100 ns, the GST can be switched from the crystalline state to the amorphous state.

[0040] According to the generalized Snell theorem, for reflected light, we can get

[0041]

[0042] Where n i : refractive index of incident medium; k i : wave vector of incident light in the incident medium; θ i : angle of incidence; θ r : reflection angle; λ0: vacuum wavelength; k x (r) : component of the reflected light wave vector in the x direction; k x (i) : The component of the incident light wave vector in the x direction.

[0043] When dΦ / dx≠0, the phase gradient metasurface can achieve the decoupling of the incident angle and the reflection angle. The phase gradient dΦ / dx introduced by the phase gradient metasurface formed by the GST array is equivalent to providing an additional additional wave vector k to the waveguide light at the optical waveguide interface. eff, the wave vector is parallel to the interface direction. At this time, in the horizontal direction parallel to the interface, the wave vector of the reflected light is equal to the sum of the wave vector of the incident light and the wave vector provided by the phase gradient dΦ / dx, breaking the continuity of the in-plane wave vector in the traditional law of refraction and reflection, thus strongly affecting the equivalent refractive index and propagation constant of the light in the waveguide, and causing the change of the light transmission mode of the waveguide, resulting in the inability of the initial mode of light to maintain normal transmission in the waveguide, and the closed state of the optical switch is achieved by blocking the transmission of light.

[0044] Figure 4 and Figure 5 The phase and amplitude changes of the reflected light introduced by GST structural units of different sizes are respectively: Figure 4 and Figure 5 Select the size of the GST structural unit corresponding to the required phase.

[0045] Figure 6 The optical switch performance with different numbers of GST structural units is shown in Table 1. The size, number and phase of the GST structural unit are shown in Table 1. The phase difference between the structural units is dΦ = 2°, and the distance dx = 200nm. When the number of structural units is 8, a 27dB extinction ratio can be achieved, and the device length L is only 1480nm.

[0046] L=dx*N+w

[0047] Where N is the number of structural units, dx is the distance between structures, and w is the width of the structural unit, such as Figure 3 shown.

[0048] Table 1 Number, size and phase of structural units

[0049]

[0050] Figure 7 The extinction ratio and device length of the optical switch of this embodiment are compared with the published results (Table 2). It can be seen that the present invention can achieve an excellent extinction ratio of the optical switch and compress the device size to 1480nm. Compared with the published results, the present invention can significantly reduce the device size and improve the integration of the device while maintaining the excellent extinction ratio performance.

[0051] Table 2

[0052]

[0053]

[0054] The references in Table 2 are as follows:

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[0075]

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[0077]

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[0078]

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[0080]

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[0081]

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Claims

1. A phase gradient metasurface on-chip integrated optical switch based on phase change material, characterized in that The phase gradient metasurface type on-chip integrated optical switch based on phase change material comprises a SiO2 substrate (1), a Si single-mode optical waveguide (2) and a GST structure array (3). The Si single-mode optical waveguide (2) is arranged on the SiO2 substrate (1). Micro-nano structure units of patterned GST materials are deposited on the upper surface of the Si single-mode optical waveguide (2) to form a GST structure array (3). The GST structure array (3) is composed of a plurality of micro-nano structure units arranged at equal intervals. The plurality of micro-nano structure units present a one-dimensional array structure. The center distance between two adjacent micro-nano structure units is dx. The phase difference introduced by the two adjacent micro-nano structure units to the reflected light at the waveguide interface is dΦ, that is, the GST structure array (3) forms a phase gradient metasurface array, and the phase gradient is dΦ / dx.

2. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The thickness of the SiO2 substrate (1) is 2 to 4 μm.

3. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The width of the SiO2 substrate (1) is greater than the width of the Si single-mode optical waveguide (2).

4. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The GST structure array (3) is deposited on the upper surface of the Si single-mode optical waveguide (2) by using an atomic layer deposition process.

5. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The material of the micro-nano structure unit in the GST structure array (3) is Ge2Te2Sb5.

6. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The GST structure array (3) is composed of 8 to 15 micro-nano structure units arranged at equal intervals.

7. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 1, characterized in that The micro-nano structural units in the GST structural array (3) are rectangular parallelepiped structures.

8. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 7, characterized in that The width w and thickness t of each micro-nano structure unit in the GST structure array (3) are the same, but the length l of the micro-nano structure units is different.

9. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 8, characterized in that Along the transmission direction of the waveguide optical signal in the Si single-mode optical waveguide (2), the length l of the micro-nano structure unit gradually increases.

10. The phase gradient metasurface on-chip integrated optical switch based on phase change material according to claim 9, characterized in that The size of the phase gradient metasurface on-chip integrated optical switch based on phase change material is 1200nm-1500nm.

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