Topological photonic crystal silicon-based electro-optical modulator
By adopting topological photonic crystal structure and carrier dispersion effect in silicon-based electro-optical modulators, the problems of large size and poor temperature stability of existing silicon-based electro-optical modulators are solved, and stable movement and intensity modulation of resonant peaks are achieved, with high mode purity and stability.
Patent Information
- Application Number
- CN202510561419.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-30
- Publication Date
- 2025-06-27
AI Technical Summary
The existing silicon-based electro-optical modulators have problems such as large overall size, poor temperature stability, and small free spectrum width between multiple resonant peaks that can easily cause drift.
Using a topological photonic crystal silicon-based electro-optical modulator, two mirror-symmetric topological photonic crystals are constructed on a ridge waveguide. Each crystal is composed of two different protozoa PhC_A and PhC_B periodically superimposed along the extension direction of the convex strip. The carrier dispersion effect is used to change the equivalent refractive index of the protozoa, and the movement and intensity modulation of the resonant peak are achieved.
The stability and robustness of the resonant peak are achieved, and the errors caused by temperature drift between different resonant peaks are avoided. It has the advantages of high mode purity, compact structure and good stability.
Smart Images
Figure CN120215149A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of silicon optical modulators, and more specifically, relates to a topological photonic crystal silicon-based electro-optic modulator. Background Art
[0002] With the development of silicon-based optoelectronics, silicon-based optical modulators have become an important optoelectronic interconnection and optical communication device, and are widely used in current high-speed optical modules. Silicon-based modulators can be realized on a variety of silicon-based materials, including silicon-on-insulator (SOI) materials, hybrid integration of silicon and III-V compounds, silicon-based thin-film lithium niobate hybrid materials, etc. Among them, the electro-optic modulator fabricated based on the plasma dispersion effect of silicon is fully compatible with the CMOS process and is suitable for large-scale mass production, so it has received extensive attention from the industry and academia. Existing silicon-based electro-optic modulators can be divided into two categories according to the optical structure: modulators based on Mach-Zehnder interferometers (MZIs) and modulators based on microring resonators (MRRs). Among them, the modulator based on MZI has the advantages of good temperature stability and wavelength independence, but also has the disadvantages of large phase-shift arm length and low modulation efficiency; while the modulator based on MRR has a smaller volume, but also has the disadvantages of poor temperature stability and small free spectral range (FSR) between multiple resonant peaks, which is prone to drift. In recent years, in order to overcome the problem of small FSR of the modulator based on MRR, some researchers have proposed electro-optic modulators using Bragg gratings to form FP cavities and based on one-dimensional photonic crystal nanobeams. Although its FSR is very large, there are also problems of low mode purity and easy coupling between different modes, resulting in distortion of the transmission spectrum.
[0003] Research in condensed matter physics shows that systems in topologically non-trivial states often have special quantum states at the boundaries or surfaces, namely topological boundary states. Such states are topologically protected and have strong robustness to impurities, defects inside the system, and small external perturbations. Two mirror-symmetric topological photonic crystals will form such boundary states at the junction. Macroscopically, it is manifested that the transmission spectrum of the photonic device will generate resonant peaks similar to those of MRR and FP cavities, and will only occur in the photonic bandgap, with the advantages of strong robustness and extremely large FSR, which is very suitable for solving the problem of drift between different resonant peaks of resonant modulators. Summary of the Invention
[0004] Aiming at the defects of the prior art, the purpose of the present invention is to provide a topological photonic crystal silicon-based electro-optic modulator, aiming to reduce the overall size of the silicon-based electro-optic modulator while avoiding bit errors caused by drift between different resonant peaks due to temperature changes.
[0005] To achieve the above object, the present invention provides a topological photonic crystal silicon-based electro-optic modulator, comprising: a substrate, a ridge waveguide, a cladding covering the ridge waveguide, and lumped electrodes, wherein the ridge waveguide includes a flat region and a rib region located in the middle of the flat region; the rib region includes two topologically photonic crystals that are mirror-symmetric to each other, and each topologically photonic crystal is composed of two different primitive cells PhC_A and PhC_B that are periodically and alternately stacked along the rib extension direction, one being an "ABABAB···" structure and the other being a "BABABA···" structure. Their energy bands are the same but are mirror-symmetric to each other, forming a topologically protected edge state at the symmetry plane, which is localized near the boundary of the two topologically photonic crystals, and its wave function rapidly decays away from the boundary, and macroscopically, there will be a resonance peak in the transmission spectrum of the photonic device. The ridge waveguide is symmetrically divided into two doped regions along the rib extension direction, and is doped with n-type and p-type respectively; the lumped electrodes are distributed on both sides of the rib region and are connected to the flat region of the ridge waveguide, respectively used to apply voltages to the two doped regions; during operation, when the voltage of the lumped voltage is changed and the effective refractive indices of the two primitive cells PhC_A and PhC_B are changed, the energy band of the topologically photonic crystal will shift, and then the resonance peak will shift to achieve intensity modulation.
[0006] Optionally, the two different primitive cells PhC_A and PhC_B are periodically repeating units with two different geometric structures, including but not limited to rectangular waveguides with a circular hole etched in the center, rectangular waveguides with a rectangular hole etched in the center, fishbone grating waveguides, etc.
[0007] Optionally, there are two consecutive PhC_A or PhC_B at the interface between the two topologically photonic crystals, and the optical properties of the modulator are independent of whether it is PhC_A or PhC_B at the interface.
[0008] Optionally, for the topological photonic crystal silicon-based electro-optic modulator, the material of the ridge waveguide is silicon, and the substrate material and the upper cladding are silicon oxide.
[0009] Optionally, for the topological photonic crystal silicon-based electro-optic modulator, the rib region of the ridge waveguide is divided into two doped regions, doped with n-type and p-type respectively, and the two doped regions are separated by a line parallel to the extension direction of the rib.
[0010] Optionally, for the topological photonic crystal silicon-based electro-optic modulator, the left and right flat regions of the ridge waveguide are doped with n-type and p-type respectively, the n-doped flat region is connected to the n-doped rib region, and the same applies to the p-doped region.
[0011] Optionally, for the topological photonic crystal silicon-based electro-optic modulator, the electrodes adopt lumped electrodes, form an ohmic contact with the doped region through metal vias, and are used to apply voltages. The electrode materials can be selected from metals such as aluminum and copper.
[0012] Furthermore, for the topological photonic crystal silicon-based electro-optic modulator, the wavelength range where the resonant peak of the transmission spectrum lies is the operating wavelength, and a resonant peak is formed only when topological phase transitions occur in the upper and lower sidebands of the energy band. The operating wavelength can be selected from the O band, S band, C band, L band, U band, 2-μm band, and the operating wavelength is determined by the designed unit cell size.
[0013] Furthermore, for the resonant peak of the transmission spectrum, its central wavelength is located at the center of the topological photonic crystal bandgap and is determined by the geometric parameters and refractive indices of the unit cells PhC_A and PhC_B. When the modulator voltage changes, the refractive indices of the unit cells PhC_A and PhC_B change, and the movement of the resonant peak of the transmission spectrum realizes intensity modulation.
[0014] Through the above technical solution conceived by the present invention, compared with the prior art, the present invention uses two different unit cells PhC_A and PhC_B to alternately repeat and construct two mirror-symmetric topological photonic crystals. The two topological photonic crystals have the same energy band, and there are topologically protected edge states at the junction. Different carriers are doped on both sides of the modulator ridge waveguide. When the voltage of the modulator electrode is changed, due to the carrier dispersion effect, the equivalent refractive indices of the two unit cells PhC_A and PhC_B change, and then the movement of the resonant peak realizes intensity modulation. The resonant peaks of this structure are located in different bandgaps, and the spacing between the central wavelengths exceeds 1000 nm. There will be no crosstalk caused by the drift of adjacent resonant peaks, and it has the advantages of high mode purity, compact structure, and good stability. Therefore, the present invention is of great significance for the design of high-speed and small-size modulators. Description of the Drawings
[0015] Figure 1 is a schematic diagram of the overall structure of a silicon-based optical modulator based on topological photonic crystals.
[0016] Figure 2 is a schematic diagram of several different implementation methods of the unit cells PhC_A and PhC_B for constructing topological photonic crystals. (a) and (b) respectively represent etching holes of different shapes in the convex strip area of the ridge silicon waveguide, and (c) represents a fishbone grating waveguide formed by staggered arrangement of waveguides with different widths.
[0017] Figure 3 is a schematic diagram of an embodiment of a silicon-based optical modulator based on topological photonic crystals.
[0018] Figure 4 is a schematic diagram of the energy band simulation method and simulation results of an embodiment of a silicon-based optical modulator based on topological photonic crystals. (a) is a schematic diagram of the simulation method, and (b) and (c) are simulation results.
[0019] Figure 5It is a three-dimensional structure schematic diagram of an embodiment of a silicon-based optical modulator based on topological photonic crystals and a simulation result diagram of optical field transmission. (a) is the three-dimensional structure schematic diagram, (b) is the optical field distribution of topological edge states, and (c) is the transmission spectrum, where obvious resonance peaks can be seen.
[0020] Figure 6 It is a cross-sectional schematic diagram of an embodiment of a silicon-based optical modulator based on topological photonic crystals.
[0021] Figure 7 It is an electrical simulation schematic diagram of an embodiment of a silicon-based optical modulator based on topological photonic crystals. (a) is the carrier distribution diagram, (b) is the curve of refractive index changing with voltage for different doping widths, and (c) is the curve of modulation efficiency for different doping widths. Specific implementation manners
[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0023] The present invention discloses a topological photonic crystal silicon-based electro-optic modulator, which includes: a silicon substrate, a ridge waveguide, a topological photonic crystal waveguide structure, and a lumped electrode connected to the flat region of the ridge waveguide. The silicon substrate is located at the bottom of the entire device; the ridge waveguide includes a flat region and a rib region located in the middle of the flat region; the topological photonic crystal structure is located in the rib region and includes two topologically photonic crystals that are mirror-symmetric to each other. Each topological photonic crystal is composed of two different primitive cells PhC_A and PhC_B that are periodically and alternately stacked along the rib extension direction. The three-dimensional structure schematic diagram of the device is as Figure 1 shown. The two topologically photonic crystals that are mirror-symmetric to each other are distributed in the structures of "ABABAB···" and "BABABA···", and their energy bands are the same. Topologically protected edge states will be generated at the interface. When the refractive index of the material is changed, the equivalent refractive indices of the two primitive cells also change accordingly, and the energy bands of the topological photonic crystals will shift, thereby shifting the resonance peaks to achieve intensity modulation.
[0024] The two primitive cells PhC_A and PhC_B of the topological photonic crystal can be constructed in various ways, such as Figure 2As shown, different structures will result in different effective refractive indices for the unit cells PhC_A and PhC_B. The periodically arranged unit cells with different effective refractive indices form a topological photonic crystal. Since the topological photonic crystals formed by two different arrangement methods have non-trivial topological states in the band gap, they are called topological photonic crystals, and when specific conditions are met, there will be topologically protected edge states in the band gap.
[0025] Specifically, in this embodiment, the refractive index of the unit cell is regulated by etching rectangular holes with different widths on the ridge waveguide. The holes with different widths etched on the ridge waveguide form the unit cells PhC_A and PhC_B, and the alternating arrangement of PhC_A and PhC_B forms a topological photonic crystal. Two mirror-symmetric topological photonic crystals form the optical resonance structure of the silicon-based optical modulator, as specifically shown in Figure 3 As shown, where the waveguide width W = 580 nm, the period is Λ, the hole length of PhC_A is d1, the hole width is w1, and the duty cycle ρ A = 2w1 / Λ; the hole length of PhC_B is d2, the hole width is w2, and the duty cycle ρ B = 2w2 / Λ.
[0026] Specifically, the method for calculating the energy bands of the topological photonic crystal is as shown in (a) of Figure 4 The unit cells PhC_A and PhC_B can both be divided into region 1 with holes in the middle and region 2 without holes. The fundamental mode effective refractive indices of the two regions are calculated respectively. The effective refractive indices of the two regions of the unit cell PhC_A are denoted as n effA1 and n effA2 , and the effective refractive indices of the two regions of the unit cell PhC_B are denoted as n effB1 and n effB2 , and then the formula
[0027] n effA = ρ A n effA1 +(1 - ρ A )n effA2
[0028] n effB = ρ B n effB1 +(1 - ρ B )n effB2
[0029] is used to calculate the effective refractive index of the entire unit cell. The n effA and n effB obtained by the above method are used to calculate the energy bands of the two topological photonic crystals as shown in (b) and (c) of Figure 4 . To study whether there are topologically protected edge states in the band gap, the Zak phase of the topological system must be calculated. The Zak phase is an important indicator of the topological properties of the system, and its calculation method is as follows:
[0030]
[0031] where \(k\) is the Bloch wave vector, and \(\mu\) jk (x) is the \(j\)-th energy band and the periodic Bloch wave function with wave vector \(k\), which can be specifically calculated by the transfer matrix. For a system with space inversion symmetry, the Zak phase can be quantized to 0 or \(\pi\). When the Zak phase is 0, it is called a topologically trivial state, meaning that the energy band structure of the system is topologically simple and conventional; when the Zak phase is \(\pi\), it is called a topologically non-trivial state, indicating that the system has unique topological properties and there are topologically protected physical phenomena. During the process of increasing from the lowest energy band to higher energy bands in sequence, the Zak phase alternates between 0 and \(\pi\). By calculating the energy bands and Zak phases of the two topological photonic crystals respectively, it can be seen that the energy bands of the two topological photonic crystals are the same, but the Zak phases are exactly opposite. The comparison diagrams are as shown in Figure 4 (b) and (c) in
[0032] Based on the Zak phase, it can be judged whether there are topologically protected edge states in the band gap. For the \(n\)-th band gap, according to the formula
[0033]
[0034] calculate \(\zeta\) n . Similar to the Zak phase, \(\zeta\) n is also a topological invariant, which is used to describe the topological characteristics related to the \(n\)-th band gap, and can also predict whether there are topologically protected edge states in this band gap. When the signs of \(\zeta\) n of the left and right topological photonic crystals are opposite, topologically protected edge states will be generated. It is analyzed that when \(j = 1, 3\), that is, the first and third band gaps, topologically protected edge states will be generated, and when \(j = 2, 4\), that is, the second and fourth band gaps, topologically protected edge states will not be generated.
[0035] Specifically, in order to further verify the results of the theoretical analysis and optimize the geometric parameters to obtain better performance, a geometric model as shown in Figure 5 was established and simulation calculations were carried out using the finite-difference time-domain algorithm. By continuously optimizing, the best geometric parameters were obtained. It can be seen that the optical field distribution is as shown in Figure 5 (b) in Figure 5 (c) in
[0036] For a silicon-based electro-optic modulator, since there is no electro-optic effect in silicon crystals, the change in the refractive index of its material can only be achieved through the thermo-optic effect and the plasma dispersion effect. The response time of the thermo-optic effect is relatively long and cannot be used for high-speed modulation. Therefore, the refractive index can only be regulated by injecting carriers. The cross-sectional structure of the topological photonic crystal silicon-based electro-optic modulator is as shown in Figure 6 and includes two regions of n-doping and p-doping.
[0037] Specifically, in order to further verify the carrier distribution and refractive index change after applying voltage, the present invention conducted an electrical simulation of the modulator. When the width of the p-region is 270 nm, the calculated carrier distribution is as shown in Figure 7 (a) in, and it can be seen that the change in carrier concentration under different voltages is obvious. Based on this, the equivalent refractive index under different voltages was further calculated, and the results are as shown in Figure 7 (b) in.
[0038] Specifically, the present invention calculated the change of the equivalent refractive index with voltage under different widths of the p-region, obtained the functional relationship between the two through polynomial fitting, and the coefficient of the first-order term can be used to represent the modulation efficiency. A schematic diagram of the modulation efficiency changing with voltage was drawn. Preferably, the width of the p-region can be selected between 250 nm and 270 nm.
[0039] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A topological photonic crystal silicon-based electro-optic modulator, characterized in that: From bottom to top, it includes: a substrate, a ridge waveguide, a cladding and a lumped electrode, the ridge waveguide includes a flat plate area and a convex strip area located in the middle of the flat plate area; the convex strip area includes two topological photonic crystals that are mirror-symmetrical to each other, and the two topological photonic crystals are composed of two different primitive cells PhC_A and PhC_B that are periodically and alternately superimposed along the extension direction of the convex strips. The two topological photonic crystals form a topologically protected boundary state on the symmetry plane, and the transmission spectrum forms a resonance peak; the ridge waveguide is symmetrically divided into two doped areas with respect to the extension direction of the convex strips, and n-doped and p-doped are performed respectively; the lumped electrodes are distributed on both sides of the convex strip area, connected to the flat plate area of the ridge waveguide, and are used to apply voltage to the two doped areas respectively; when working, when the voltage of the lumped voltage is changed, the resonance peak moves to achieve intensity modulation.
2. The topological photonic crystal silicon-based electro-optic modulator according to claim 1, characterized in that: The primitive cells PhC_A and PhC_B are two periodic repeating units with different geometric structures, and the geometric structures are a rectangular waveguide with a circular hole etched in the center, a rectangular waveguide with a rectangular hole etched in the center, or a fishbone grating waveguide.
3. The topological photonic crystal silicon-based electro-optic modulator according to claim 1, characterized in that: There are two continuous PhC_A or PhC_B at the interface of two topological photonic crystals, and the optical properties of the modulator are independent of whether it is PhC_A or PhC_B at the interface.
4. The topological photonic crystal silicon-based electro-optic modulator according to claim 1, characterized in that: The material of the ridge waveguide is silicon, and the materials of the substrate and the cladding are silicon oxide.
5. The topological photonic crystal silicon-based electro-optic modulator according to claim 4, characterized in that: The concentrations of the n-doped convex stripe region and the slab region are different, and the concentrations of the p-doped convex stripe region and the slab region are different.
6. The topological photonic crystal silicon-based electro-optic modulator according to claim 1, characterized in that: The material of the lumped electrode is aluminum or copper.
7. The topological photonic crystal silicon-based electro-optic modulator according to claim 1, characterized in that: The operating wavelength of the modulator is O-band, S-band, C-band, L-band, U-band or 2 micron band.