An electro-optic modulator chip based on a two-dimensional topological photonic crystal

Abstract

This invention provides an electro-optic modulator chip based on a two-dimensional topological photonic crystal, comprising a waveguide layer, a two-dimensional topological photonic crystal module, and two electrodes. The two-dimensional topological photonic crystal module is directly connected to the waveguide layer. A first photonic crystal module and a second photonic crystal module are arranged adjacently to form a first physical boundary, which is a topological waveguide for optical transmission. A third photonic crystal module is located within the second photonic crystal module and close to the first photonic crystal module. A second physical boundary between the third photonic crystal module and the first photonic crystal module constitutes a resonant cavity. The first and second electrodes extend inward and outward along the second physical boundary. A high quality factor can be obtained through the topological photonic crystal resonant cavity, enabling high-performance electro-optic modulation. Furthermore, the topological photonic crystal resonant cavity inherits the advantages of ordinary photonic crystal modulators, has a small chip size, and can be further connected to more topological waveguides to meet future high integration requirements.

Description

Technical Field

[0001] This invention relates to the field of electro-optic modulators, and particularly to an electro-optic modulator chip based on a two-dimensional topological photonic crystal. Background Technology

[0002] Electro-optic modulators are core components of optical communication systems. They control the amplitude or phase characteristics of output light by varying the applied electric field at specific points in the light transmission path. Current electro-optic modulators face challenges such as large size and power consumption, low integration density, high manufacturing costs, and limited scalability, which will restrict their application to meet the ever-increasing data transmission demands of the future. Compared to traditional Mach-Zehnder interferometer modulators based on waveguide structures, designs using photonic crystals can significantly shorten the length of the modulation region by introducing a slow-light effect. This not only makes the device structure more compact but also ensures lower propagation loss.

[0003] As a novel artificial structural material proposed in the last thirty years, photonic crystals are characterized by their small size and low optical loss, making them suitable for fabricating miniature integrated optical devices. However, the manufacturing process of traditional photonic crystals inevitably introduces errors, leading to structural defects. This causes strong backscattering during light transmission, increasing the power loss of the device. In recent years, researchers have discovered that light propagating at the physical boundaries of photonic crystals with different topological numbers is topologically protected. That is, the optical transmission performance of the topological waveguides formed by these physical boundaries is immune to impurities or defects. This gives them a high tolerance for fabrication errors, making them a significant advantage in future practical applications.

[0004] In addition, the resonant cavity structure in photonic crystals can significantly affect the optical transmission characteristics through the resonance effect, which allows them to achieve high modulation efficiency with an extremely compact structure. Furthermore, topological photonic crystals also hold promise for flexible design of high-performance resonant cavity structures. Therefore, it is essential to design a modulator based on a topological photonic crystal resonant cavity to meet the requirements of smaller size, higher modulation efficiency, and higher functional stability. Summary of the Invention

[0005] The purpose of this invention is to provide an electro-optic modulator chip based on a two-dimensional topological photonic crystal.

[0006] To achieve the objective of this invention, an electro-optic modulator chip based on a two-dimensional topological photonic crystal is provided, comprising a waveguide layer, a two-dimensional topological photonic crystal module, a first electrode, and a second electrode. The two-dimensional topological photonic crystal module is directly connected to the waveguide layer. The two-dimensional topological photonic crystal module includes a first photonic crystal module, a second photonic crystal module, and a third photonic crystal module. The topological number of the first photonic crystal module is different from that of the second photonic crystal module, but the topological number of the first photonic crystal module is the same as that of the third photonic crystal module. The first photonic crystal module and the second photonic crystal module are arranged adjacent to each other and form a first physical boundary, which is a topological waveguide for optical transmission. The third photonic crystal module is located within the second photonic crystal module and close to the first photonic crystal module. The second physical boundary between the third photonic crystal module and the first photonic crystal module constitutes a resonant cavity. The first electrode is located within the third photonic crystal module and extends along the second physical boundary, and the second electrode is located within the second photonic crystal module and extends along the second physical boundary.

[0007] As can be seen from the above scheme, the first physical boundary formed between two photonic crystal modules with different topological numbers constitutes a topological waveguide for optical transmission. The third photonic crystal module is located inside the second photonic crystal module and close to the first photonic crystal module. Then, the second physical boundary is used to form a resonant cavity. The first electrode and the second electrode are located at the inner and outer edges of the second physical boundary, respectively. When optical transmission occurs in the topological waveguide, the electric field distribution of the resonant cavity is changed by energizing the electrodes. A high quality factor can be obtained through the topological photonic crystal resonant cavity, which can realize high-performance electro-optic modulation. Furthermore, the topological photonic crystal resonant cavity inherits the advantages of ordinary photonic crystal modulators. The chip structure size is small, and it can be further connected with more topological waveguides to meet the requirements of future high integration.

[0008] A further proposed approach is to have the valley number of the first photonic crystal module and the valley number of the second photonic crystal module having opposite signs, while the valley number of the first photonic crystal module and the valley number of the third photonic crystal module having the same sign.

[0009] A further proposed approach is that the first, second, and third photonic crystal modules are all constructed from two-dimensional orthorhombic crystals.

[0010] As can be seen from the above, given that the topological photonic crystal resonator is topologically protected, light can propagate unidirectionally along the topological waveguide formed at the boundary between the two two-dimensional photonic crystals through physical boundaries with different topological numbers or opposite valley-Chern numbers, thus avoiding power loss caused by back reflection in ordinary structured light. Furthermore, this design has high tolerance for structural disorder and fabrication defects, ensuring the stability of the device operation and reducing the requirements for fabrication technology.

[0011] A further proposed approach is to have at least five structural units on each side of the center of the resonant cavity in the third photonic crystal module, with the lower edge of the second physical boundary being at least three to nine structural units away from the first physical boundary.

[0012] As can be seen above, when light interacts with the topological waveguide at the lower edge of the resonant cavity, the light is coupled into the cavity.

[0013] A further proposed approach is to have the third photonic crystal module in the shape of a triangle, rhombus, or hexagon.

[0014] As can be seen from the above, light can be transmitted along the boundary of the third photonic crystal module and realize the function of the resonant cavity regardless of the different shapes of the arrangement.

[0015] A further proposed solution is that the third photonic crystal module is triangular in shape, with the first physical boundary arranged along a straight line and the lower edge of the second physical boundary parallel to the first physical boundary.

[0016] A further proposed solution is that both the first and second electrodes are arranged in a V-shape, with the V-shaped openings of the first and second electrodes both facing the first physical boundary.

[0017] As can be seen from the above, the modulation electrode adjusts the transmission characteristics of the topological waveguide and realizes the modulation function based on thermal effects, electro-optic effects or changes in carrier concentration.

[0018] A further approach is to include an input waveguide and an output waveguide in the electro-optic modulator chip, with the input waveguide and output waveguide respectively connected to the two ends of the first physical boundary.

[0019] A further approach is to use single-mode TE polarization for both the input and output waveguides.

[0020] A further proposed solution is to have a first line defect at the connection between the input waveguide and the first physical boundary, and a second line defect at the connection between the output waveguide and the first physical boundary.

[0021] As can be seen from the above, by connecting the input waveguide and the output waveguide to the two ends of the first physical boundary respectively, and introducing line defects respectively, not only can light be efficiently introduced and transmitted, but the insertion loss of the device can also be reduced by utilizing the line defects. Attached Figure Description

[0022] Figure 1 This is a planar schematic diagram of an embodiment of the electro-optic modulator chip of the present invention.

[0023] Figure 2 The structural parameters and band structure of PhC1 and PhC2 when silicon material is selected in the embodiment of the electro-optic modulator chip of the present invention.

[0024] Figure 3This describes the optical transmission characteristics of the topological waveguide formed by PhC1 and PhC2 in the embodiment of the electro-optic modulator chip of the present invention.

[0025] Figure 4 This is a schematic diagram of the position of the input and output waveguides and line defects in an embodiment of the electro-optic modulator chip of the present invention.

[0026] Figure 5 This is a schematic diagram of the topology-protected resonant cavity structure and the electric field distribution in the resonant state in an embodiment of the electro-optic modulator chip of the present invention.

[0027] Figure 6 This is a comparative optical performance diagram of the electro-optic modulator chip embodiment of the present invention with and without electrodes.

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0029] Reference Figure 1 The electro-optic modulator chip includes a substrate, a chip insulating layer, a waveguide layer, a two-dimensional topological photonic crystal module, a first electrode 11, a second electrode 12, an input waveguide 13, and an output waveguide 14. The chip insulating layer is disposed on the substrate, and the waveguide layer is disposed on the chip insulating layer. The two-dimensional topological photonic crystal module is connected to the waveguide layer. The two-dimensional topological photonic crystal module includes a first photonic crystal module, a second photonic crystal module, and a third photonic crystal module. The topological number of the first photonic crystal module is different from that of the second photonic crystal module, and the topological number of the first photonic crystal module is the same as that of the third photonic crystal module. The first photonic crystal module and the second photonic crystal module are arranged adjacent to each other and form a first physical boundary 21. The first physical boundary 21 is a topological waveguide used for optical transmission. The third photonic crystal module is located inside the second photonic crystal module and close to the first photonic crystal module. The second physical boundary 22 between the third photonic crystal module and the first photonic crystal module constitutes a resonant cavity.

[0030] The third photonic crystal module is triangular in shape, with the first physical boundary 21 arranged along a straight line and the lower edge of the second physical boundary 22 parallel to the first physical boundary 21. The first electrode 11 is located within the third photonic crystal module and extends along the second physical boundary 22, and the second electrode 12 is located within the second photonic crystal module and extends along the second physical boundary 22. Both the first electrode 11 and the second electrode 12 are arranged in a V-shape, with the V-shaped opening of the first electrode 11 and the V-shaped opening of the second electrode 12 both facing the first physical boundary 21.

[0031] The valley number of the first photonic crystal module and the valley number of the second photonic crystal module have opposite signs. The valley number of the first photonic crystal module and the valley number of the third photonic crystal module have the same sign. The first, second and third photonic crystal modules are all constructed of two-dimensional orthorhombic crystals. Taking the first and third photonic crystal modules as having the same structural unit as an example, the first and third photonic crystal modules are both labeled PhC1, and the second photonic crystal module is labeled PhC2.

[0032] Reference Figure 2 , Figure 2 A schematic diagram of the structural unit is shown in Figure A. The structural unit has a two-dimensional orthorhombic crystal structure, and the air pillars in the unit cell are all located at the center of the corresponding equilateral triangles. The single-mode waveguide width is 250 nm. The corresponding structural design can be realized by electron beam lithography and plasma dry etching. Although PhC1 and PhC2 have the same energy band, according to current theoretical explanations, the transition from PhC1 to PhC2 will undergo a band reversal, such as... Figure 2 When the relative sizes of the two cylinders in C are adjusted, the band structure Δr undergoes inversion, resulting in different valley Chern numbers. Various topological waveguides can be obtained by arranging the two structural units in different ways on both sides, with corresponding optical transmission performance such as… Figure 2 As shown. This topological waveguide possesses the optical transmission performance of a conventional waveguide, and due to topological protection, it has a greater tolerance for processing errors and defects in photonic crystals. That is, as long as the corresponding band structure and topology number are met, errors in localized regions will not affect the optical transmission performance. Furthermore, since the corresponding topological waveguide can only transmit light along a specific direction, this means that according to… Figure 1 The arrangement shown allows for the placement of the two structural units in different regions, thus realizing both a topological waveguide and a photonic crystal resonator. Light propagates along the boundaries of the two photonic crystal modules after passing through the input waveguide. When a suitable distance is chosen between the lower boundaries of the topological waveguide and the resonator, the optical field can be coupled into the interior of the photonic crystal resonator.

[0033] Specifically, the third photonic crystal module has at least five structural units on each side of the center of the resonant cavity, and the lower edge of the second physical boundary 22 is at least 3 to 9 structural units away from the first physical boundary 21. Figure 5 Therefore, when light interacts with the topological waveguide at the lower edge of the resonant cavity, the light is coupled into the resonant cavity.

[0034] Transmission spectra between input / output waveguides at different frequencies, such as Figure 3As shown, since light propagates unidirectionally and without loss within the topological photonic crystal, this design can theoretically realize a resonant cavity with an infinite quality factor. It is worth noting that the single-mode TE waveguide needs to be located at the boundary between the two structural units of the topological waveguide, and some line defects need to be introduced to enhance optical transmission performance. Specifically, the input waveguide 13 and the output waveguide 14 are respectively connected to the two ends of the first physical boundary 21, and the vertical deviation of the positions of the input and output waveguides at the PhC2 and PhC1 boundaries does not exceed one structural unit. The propagation mode of both the input waveguide 13 and the output waveguide 14 is single-mode TE polarization. A first line defect is provided at the connection between the input waveguide 13 and the first physical boundary 21, and a second line defect is provided at the connection between the output waveguide 14 and the first physical boundary 21, such as... Figure 4 As shown, taking the input waveguide as an example, the connection between the input waveguide and the first physical boundary introduces a line defect by removing part of the dielectric tube in the optical transmission direction. That is, there is no structure within the dashed box in the direction of the extended line of the input waveguide. Figure 4 The structure shown is to illustrate the structure before preparation, but it is actually empty.

[0035] Reference Figure 5 It is a schematic diagram of the topology-protected resonant cavity structure and the electric field distribution in the resonant state. After the light is coupled to the corresponding topology waveguide through the input waveguide, it is modulated in the resonant cavity and then output through the output waveguide. Figure 5 The top left figure shows PhC1 and PhC2 arranged in the three regions of the figure. The light will be coupled to the resonant cavity above along the topological waveguide connected to the single-mode TE waveguide, and then output through the right waveguide. The black line in the figure marks the physical boundary formed by PhC1 and PhC2, and the light will be transmitted along this boundary. Figure 5 The upper right figure shows the electric field distribution for light transmission that satisfies the resonance condition of the resonant cavity. The electric field strength is greatest in the boundary region of the resonant cavity, and the electrodes located on both sides of this region can be effectively controlled. Figure 5 The figure below shows the input / output optical spectrum, and the modulator can modulate at the corresponding resonance peak.

[0036] Further analysis of the field distribution at the resonant frequency reveals that the electric field energy is concentrated at the boundary of the resonant cavity composed of PhC1 and PhC2. Since thermal effects, electro-optic effects, and carrier concentration can all alter the effective refractive index of the corresponding region, the modulation electrode may change the transmission characteristics to achieve electro-optic modulation. Furthermore, the longest side of this structure is less than 10 micrometers, verifying the feasibility of realizing a small-sized resonant cavity through topological photonic crystal design.

[0037] To verify the feasibility of modulation and the effect of the electrodes on the photonic crystal resonator, refer to Figure 6 , Figure 6 A is equipped with electrodes for modulation. Figure 6B is a structure without electrodes, where the simulation results for the distance between the two electrodes is greater than 10 structural units are as follows: Figure 6 As shown in the waveform diagram, the presence of surface electrodes does not significantly affect the energy band and corresponding topological properties of the photonic crystal. The electrode layout described in this invention provides a topology-protected resonant cavity. Furthermore, when different modulation signals are applied to the modulation electrodes, the characteristics of the resonant cavity (the effective refractive index can change the transmission performance of the topological waveguide) will change, affecting the output signal and thus achieving a high-performance electro-optic modulator. All the above results demonstrate that the design of the topological photonic crystal in this invention can realize a small-size, topology-protected electro-optic modulator.

[0038] Of course, the above embodiments are only preferred embodiments of this invention. In practical applications, there are many variations. For example, the shape of the third photonic crystal module can be triangular, rhomboid, or hexagonal, and the first and second electrodes can be adjusted accordingly based on the specific shape. As long as they are arranged along the inner and outer sides of the edge, the modulation purpose of this invention can also be achieved. In addition, when the electrodes are modulated based on the thermal effect, they can be located on the photonic crystal structure, while when modulated based on the electro-optic effect, they can be located outside the boundary region with at least 8 structural units. The electrodes can be placed in the unstructured device layer or insulating layer in the chip. When modulated based on carrier concentration, PhC1 and PhC2 constituting the resonant cavity need to be located in different doped regions to form a PN junction to achieve modulation.

[0039] As can be seen from the above, the first physical boundary formed between two photonic crystal modules with different topological numbers constitutes a topological waveguide for optical transmission. The third photonic crystal module is located inside the second photonic crystal module and close to the first photonic crystal module. Then, the second physical boundary is used to form a resonant cavity. The first electrode and the second electrode are located at the inner and outer edges of the second physical boundary, respectively. When optical transmission occurs in the topological waveguide, the electric field distribution of the resonant cavity is changed by energizing the electrodes. A high quality factor can be obtained through the topological photonic crystal resonant cavity, which can realize high-performance electro-optic modulation. Furthermore, the topological photonic crystal resonant cavity inherits the advantages of ordinary photonic crystal modulators. The chip structure size is small, and it can be further connected with more topological waveguides to meet the requirements of future high integration.

Claims

1. An electro-optic modulator chip based on a two-dimensional topological photonic crystal, characterized in that, The device includes a waveguide layer, a two-dimensional topological photonic crystal module, a first electrode, and a second electrode. The two-dimensional topological photonic crystal module is directly connected to the waveguide layer. The two-dimensional topological photonic crystal module includes a first photonic crystal module, a second photonic crystal module, and a third photonic crystal module. The topological number of the first photonic crystal module is different from that of the second photonic crystal module, and the topological number of the first photonic crystal module is the same as that of the third photonic crystal module. The first photonic crystal module and the second photonic crystal module are arranged adjacent to each other and form a first physical boundary. The first physical boundary is a topological waveguide for optical transmission. The third photonic crystal module is located inside the second photonic crystal module and close to the first photonic crystal module. The second physical boundary between the third photonic crystal module and the first photonic crystal module constitutes a resonant cavity. The first electrode is located within the third photonic crystal module and extends along the second physical boundary, and the second electrode is located within the second photonic crystal module and extends along the second physical boundary; Both the first electrode and the second electrode are arranged in a V-shape, with the V-shaped openings of the first electrode and the second electrode both facing the first physical boundary.

2. The electro-optic modulator chip according to claim 1, characterized in that: The valley number of the first photonic crystal module and the valley number of the second photonic crystal module have opposite signs, while the valley number of the first photonic crystal module and the valley number of the third photonic crystal module have the same sign.

3. The electro-optic modulator chip according to claim 2, characterized in that: The first photonic crystal module, the second photonic crystal module, and the third photonic crystal module are all constructed of two-dimensional orthorhombic crystals.

4. The electro-optic modulator chip according to claim 1, characterized in that: The third photonic crystal module has at least 5 structural units on each side of the center of the resonant cavity, and the lower edge of the second physical boundary is at least 3 to 9 of the structural units away from the first physical boundary.

5. The electro-optic modulator chip according to claim 1, characterized in that: The third photonic crystal module is triangular, rhomboid, or hexagonal in shape.

6. The electro-optic modulator chip according to any one of claims 1 to 4, characterized in that: The third photonic crystal module is triangular in shape, with the first physical boundary arranged along a straight line and the lower edge of the second physical boundary parallel to the first physical boundary.

7. The electro-optic modulator chip according to any one of claims 1 to 5, characterized in that: The electro-optic modulator chip further includes an input waveguide and an output waveguide, which are respectively connected to the two ends of the first physical boundary.

8. The electro-optic modulator chip according to claim 7, characterized in that: Both the input waveguide and the output waveguide propagate in single-mode TE polarization.

9. The electro-optic modulator chip according to claim 7, characterized in that: A first line defect is provided at the connection between the input waveguide and the first physical boundary; A second line defect is provided at the connection between the output waveguide and the first physical boundary.

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