CN115826136B - Dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal - Google Patents

Abstract

The present invention proposes a dual-bandwidth valley Hall polarization twisted waveguide based on a triangular lattice valley photonic crystal to solve the technical problems of large reflection loss, narrow working bandwidth and single working bandwidth in traditional waveguide transmission. The present invention includes a triangular lattice valley photonic crystal with a valley Chern number of 1 and a triangular lattice valley photonic crystal with a valley Chern number of 1. The area formed by the triangular lattice valley photonic crystal with a valley Chern number of 1 is the first area, and the area formed by the triangular lattice valley photonic crystal with a valley Chern number of 1 is the second area. The connection between the first area and the second area constitutes a sawtooth interface, and a light source is provided on the sawtooth interface. The present invention can realize large-bandwidth, large-capacity and high-efficiency waveguide transmission, is simpler to construct, has low R&D cost, and has dual-channel bandwidth, can be used to realize multi-band, integrated and controllable micro-nano waveguide device design, can meet the requirements of increasingly highly integrated photonic chips and the communication needs of wavelength division multiplexing and frequency conversion.

Description

Dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal

Technical Field

The invention relates to the technical field of topological photonics, quantum communication, integrated photonic devices and integrated optical circuit design, and in particular to a dual-bandwidth valley Hall polarization twisted state waveguide based on a triangular lattice valley photonic crystal.

Background technique

Photonic devices based on all-dielectric topological valley photonic crystal waveguides have important application prospects in the fields of topological photonics, quantum communications, and integrated photonic optical circuits. At present, with the advent of the 6G era, the requirements for optoelectronic communication systems are getting higher and higher, especially all-optical network communications. Integrated photonic optical circuits are constantly developing in the direction of large capacity, high efficiency, and miniaturization. Therefore, low-cost, high-efficiency, and multifunctional miniature optical devices are constantly being researched and developed.

In 2016, Professors Tzuhsuan Ma and Gennady Shvets of The University of Texas at Austin proposed to construct a valley Hall state (All-Si valley-Hall photonic topological insulator) using topological valley photonic crystals of all-silicon graphene lattices. The valley Hall state is achieved under the excitation of electromagnetic wave TE mode (Transverse Electric modes).

In 2017, Professor Dong Jianwen of Sun Yat-sen University in China proposed to construct a valley Hall polarization twist state (Valley-contrasting physics in all-dielectric photonic crystals: Orbitalangular momentum and topological propagation) using an all-silicon rod-like graphene lattice topological valley photonic crystal under the excitation of the electromagnetic field TM mode (Transverse Magnetic modes). This valley Hall polarization twist state is generated at the interface of two valley photonic crystals with broken spatial symmetry, and this twisted state waveguide is determined by the polarization direction of the chiral source. In 2019, Professor Dong Jianwen experimentally constructed this valley photonic crystal structure using a silicon substrate, and observed this special valley Hall polarization twist state at the boundary of valley photonic crystals with different valley Chern numbers (Asilicon-on insulator slab for topological valley transport).

In 2019, Professor Yihao Yang of Zhejiang University proposed to construct a dual-bandwidth valley Hall polarization twist waveguide using all-dielectric (relative dielectric constant 3.2) graphene-like topological valley photonic crystals. The existence of this waveguide was experimentally observed and confirmed, and the related work was published in the top international journal Advance Optical Material (Valley-Hall Photonic Topological Insulators with Dual-Band Kink States). In 2020, Professor Yihao Yang experimentally constructed an all-silicon valley photonic crystal chip, which was the first time in the world to realize and observe the efficient communication of this valley Hall twist waveguide in the terahertz band. The work was published in the world's top journal Nature Photonics (Terahertztopological photonics for on-chip communication).

This valley Hall polarization twisted state waveguide not only has outstanding propagation characteristics such as robustness, defect immunity, and anti-backscattering, but also its working bandwidth is determined by the degree of breaking of the spatial symmetry of the topological valley photonic crystal. The valley photon state has a binary degree of freedom to regulate the light field, so this valley Hall state is regarded as the best information carrier in the field of integrated photonic communications.

In recent years, valley Hall states have been used as a new type of information carrier in various micro-nano waveguide photonic devices, such as waveguide beam splitters, waveguide delays, wavelength division multiplexing and multi-channel communications, and quantum entanglement communications of valley Hall states.

Summary of the invention

In view of the technical problems of large reflection loss and narrow working bandwidth in traditional waveguide transmission, the present invention proposes a dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystals, which can realize large bandwidth, large capacity and high-efficiency waveguide transmission. Compared with the micro-nano optical waveguide devices realized by existing graphene-like topological valley photonic crystals, it is simpler to construct, has low R&D cost, and has dual-channel bandwidth, which can meet the requirements of increasingly highly integrated photonic chips and the communication needs of wavelength division multiplexing and frequency conversion.

In order to achieve the above-mentioned purpose, the technical solution of the present invention is implemented as follows: a dual-bandwidth valley Hall polarization twisted waveguide based on a triangular lattice valley photonic crystal, comprising a triangular lattice valley photonic crystal with a valley Chern number of 1 and a triangular lattice valley photonic crystal with a valley Chern number of -1, the area formed by the triangular lattice valley photonic crystal with a valley Chern number of 1 is the first area, the area formed by the triangular lattice valley photonic crystal with a valley Chern number of -1 is the second area, the connection between the first area and the second area constitutes a sawtooth interface, and a light source is placed on the sawtooth interface.

Preferably, the light source is a chiral polarization source, and the chiral polarization source is placed on the sawtooth interface.

Preferably, the chiral polarization source comprises four antennas perpendicular to the z-axis, linear polarization sources are added to the antennas, and the phases of adjacent linear polarization sources increase or decrease by π/2.

Preferably, the four antennas are arranged in a square, and the side length of the square is 0.2a, where a is the lattice constant of the lattice unit.

Preferably, the dielectric column of the triangular lattice valley photonic crystal with a valley-Chen number of 1 and the triangular lattice valley photonic crystal with a valley-Chen number of -1 is a fully dielectric cylindrical silicon rod, and the diameter of the cylindrical silicon rod is The backgrounds of the triangular lattice valley photonic crystal with a dielectric constant of 11.7 and a valley-Chern number of 1 and the triangular lattice valley photonic crystal with a valley-Chern number of -1 are both air; wherein a is the lattice constant of the lattice unit.

Preferably, the waveguide state is generated at the interface of valley photonic crystals with different valley numbers, and the zigzag interface is a zigzag shape in the graphene lattice arrangement.

Preferably, the length of the side of the regular hexagon in the honeycomb lattice unit cell structure of the triangular lattice valley photonic crystal with a valley-Chen number of 1 and the triangular lattice valley photonic crystal with a valley-Chen number of -1 is L.

Preferably, the honeycomb lattice unit cell structure I of the triangular lattice valley photonic crystal with a valley-Chern number of 1 is rotated 60° to completely overlap with the honeycomb lattice unit cell structure II of the triangular lattice valley photonic crystal with a valley-Chern number of -1; the honeycomb lattice unit cell structure I and the honeycomb lattice unit cell structure II both satisfy the C _3v spatial rotational symmetry.

Compared with the prior art, the invention has the following beneficial effects: a triangular lattice valley photonic crystal is constructed based on an all-dielectric cylindrical silicon rod, and the C _3v spatial rotational symmetry of the triangular crystal valley photonic crystal is broken, forming two triangular lattice valley photonic crystals with different valley Chern numbers; a sawtooth interface is formed in adjacent regions of valley photonic crystals with different valley Chern numbers, and is generated on the sawtooth boundary under the excitation of a chiral polarization source. The invention successfully designs a dual-bandwidth, large-bandwidth, robust dual-bandwidth valley Hall polarization twisted waveguide, which can be used to realize multi-band, integrated, and controllable micro-nano waveguide device design, and is used to realize wavelength division multiplexing and multi-channel communication in integrated optical circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the overall structure of the present invention.

FIG. 2 is an energy band distribution diagram of the lattice unit cell in the entire first Brillouin zone of the present invention, and the small figure on the right represents the electric field phase distribution.

FIG3 (a) is a schematic diagram of a part of the structure of the present invention, and the dotted rectangle represents the structural supercell; (b) is the projected band diagram along the Kx direction of the present invention, and the right side represents the electric field eigenmode and Poynting vector distribution corresponding to the valley K point.

Figure 4 is a schematic diagram of the structure of the dual-bandwidth valley Hall polarization twisted waveguide of the present invention and the corresponding electric field intensity distribution diagram, wherein (a) is a schematic diagram of the structure of a linear sawtooth interface, (d) is the electric field energy distribution of (a) at a frequency of 0.28995THz, and (h) is the electric field energy distribution of (a) at a frequency of 0.54185THz; (b) is a schematic diagram of the structure for verifying robustness, (e) is the electric field energy distribution of (b) at a frequency of 0.28995THz, (i) is the electric field energy distribution of (b) at a frequency of 0.54185THz; (c) is a schematic diagram of the structure for verifying immune deficiency, (f) is the electric field energy distribution of (c) at a frequency of 0.28995THz, and (j) is the electric field energy distribution of (c) at a frequency of 0.54185THz.

Figure 5 is the simulation result of the present invention, wherein (a) is the normalized electric field energy distribution diagram of the transmission cross section along the y-axis direction of the present invention; (b) is the transmission spectrum diagram in the low energy band gap; and (c) is the transmission spectrum diagram in the high energy band gap.

In the figure, 1 is a triangular lattice valley photonic crystal with a valley-Chen number of 1, 2 is a triangular lattice valley photonic crystal with a valley-Chen number of -1, 3 is the first region constructed by the triangular lattice valley photonic crystal with a valley-Chen number of 1, 4 is the second region constructed by the triangular lattice valley photonic crystal with a valley-Chen number of -1, 5 is a zigzag interface, 6 is the side length of the regular hexagon in the honeycomb lattice, 7 is the lattice constant of the lattice unit, 8 is the lattice unit cell I, 9 is the lattice unit cell II, 11 is the honeycomb lattice unit cell structure I, 12 is the honeycomb lattice unit cell structure II, 13 is a light source, 14 is an antenna, 15 is an amplifying structure of the light source, 16 and 17 are two-dimensional cross-sections, and 18 is a structural supercell.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

As shown in FIG1 , a dual-bandwidth valley Hall polarization twisted state waveguide based on a triangular lattice valley photonic crystal includes a triangular lattice valley photonic crystal 1 with a valley Chern number of 1 and a triangular lattice valley photonic crystal 2 with a valley Chern number of −1. The region formed by the triangular lattice valley photonic crystal 1 with a valley Chern number of 1 is a first region 3, and the region formed by the triangular lattice valley photonic crystal 2 with a valley Chern number of −1 is a second region 4. The connection between the first region 3 and the second region 4 forms a sawtooth interface 5, and a light source 13 is provided on the sawtooth interface 5. The two triangular lattice valley photonic crystal regions with different valley Chern numbers are correspondingly formed by the two triangular valley photonic crystals with different valley Chern numbers, that is, there is only one triangular lattice valley photonic crystal with a valley Chern number in one region. The sawtooth interface is formed by the two triangular lattice valley photonic crystal regions with different valley Chern numbers. The waveguide state is generated at the interface of the valley photonic crystals with different valley Chern numbers, and the sawtooth interface 5 is a sawtooth shape in the graphene lattice arrangement, which originates from the inherent arrangement mode in the graphene lattice arrangement. The valley effect of the structural design of the present invention is relatively weak, and not only can dual bandwidths appear, but each bandwidth is also very large.

The triangular lattice valley photonic crystal 1 with a valley Chern number of 1 is called Type-A, and the triangular lattice valley photonic crystal 2 with a valley Chern number of -1 is called Type-B. The valley Chern number is obtained by integrating the Berry phase of its energy band in the entire Brillouin zone. The triangular lattice valley photonic crystal is evolved from a honeycomb lattice valley photonic crystal. The length of the side 6 of the regular hexagon in the honeycomb lattice of the triangular lattice valley photonic crystal 1 with a valley Chern number of 1 and the triangular lattice valley photonic crystal 2 with a valley Chern number of -1 is L. The lattice constant 7 of the lattice unit is a, which is 246um. The purpose is to obtain the low-frequency terahertz band frequency, which can be fully confirmed in the experiment.

The dielectric columns of the triangular lattice valley photonic crystal 1 with a valley Chern number of 1 and the triangular lattice valley photonic crystal 2 with a valley Chern number of -1 are all-dielectric cylindrical silicon rods, and the diameter of the cylindrical silicon rods is The background of the triangular lattice valley photonic crystal 1 with a dielectric constant of 11.7 and a valley number of 1 and the triangular lattice valley photonic crystal 2 with a valley number of -1 are both air; where a is the lattice constant of the lattice unit. The dielectric column of the lattice unit cell I8 (VPC-A) of the triangular lattice valley photonic crystal 1 with a valley number of 1 is composed of single crystal silicon of all dielectric materials, with a relative dielectric constant of 11.7, and the background is air by default, and the diameter of the cylindrical silicon rod is d _A = L. The dielectric column of the lattice unit cell II9 (VPC-B) of the triangular lattice valley photonic crystal 2 with a valley number of -1 is composed of single crystal silicon of all dielectric materials, with a dielectric constant of 11.7, and the diameter of the cylindrical silicon rod is d _B = L.

The honeycomb lattice primitive cell structure I11 of the triangular lattice valley photonic crystal 1 with a valley-Chen number of 1 is rotated 60° and completely overlaps with the honeycomb lattice primitive cell structure II12 of the triangular lattice valley photonic crystal 2 with a valley-Chen number of -1; the honeycomb lattice primitive cell structure I11 and the honeycomb lattice primitive cell structure II12 both satisfy the C _3v spatial rotational symmetry. The dielectric columns in the lattice unit cell I8 of the triangular lattice valley photonic crystal 1 with a valley-Chen number of 1 and the lattice unit cell II9 of the triangular lattice valley photonic crystal 2 with a valley-Chen number of -1 are symmetric about the center.

Furthermore, the light source 13 is a chiral polarization source, and the chiral polarization source is arranged on the sawtooth interface 5. 15 represents the amplification structure of the chiral source 13, and the chiral polarization source includes 4 antennas 14 perpendicular to the z-axis, and a linear polarization source is added to the antenna 14, and the phases of adjacent linear polarization sources increase or decrease by π/2 to realize a chiral polarization light source. The 4 antennas 14 are arranged in a square, which is perfectly symmetrical. Such a chiral polarization source is a chiral circular polarization, and the side length of the square is 0.2a, where a is the lattice constant of the lattice unit.

16 represents a two-dimensional cross-section at x=10a, and 17 represents a two-dimensional cross-section at x=30a, which is used to measure the normalized electric field energy distribution of the waveguide along the y-axis. 18 represents a structural supercell, which is used to calculate the projected energy band of the designed structure in the Kx direction.

As shown in FIG2, by calculating the energy bands of the lattice unit cell I8 of the triangular lattice valley photonic crystal 1 with a valley Chern number of 1 in the first Brillouin zone, two bandwidths of 0.28THz-0.39THz and 0.52THz-0.66THz are obtained between valleys K and K'. At valley K', the valley K' point of the first energy band from top to bottom has a valley-locked polarization spin-up state, while the second and third energy bands merge into a weak valley-locked polarization spin-down state, and the fourth and fifth energy bands merge into a weak valley-locked polarization spin-up state. At valley K, all valley-locked polarization spin states are opposite. As shown in the phase distribution of the 12 lattice units on the right side of FIG2, which represents the phase distribution of the electric field, the rotational polarization of the valley state can be seen, where the arrow at each K point of each energy band indicates the spin-up and spin-down direction.

As shown in Figure 3, (a) in Figure 3 is a schematic diagram of a partial structure of the design, where the dotted rectangle represents the structural supercell 18, which is used to calculate the body band gap structure of the system structure projected in the Kx direction. (b) represents the body energy band projected in the Kx direction obtained by supercell calculation, the shadow represents the body mode energy band, and the two curves represent the dispersion curves of the boundary mode. M1 represents eigenmode 1, and M2 represents eigenmode 2. The two curves are the dispersion curves of the valley Hall polarization twisted waveguide of the triangular lattice valley photonic crystal, indicating that the invention of the present invention is dual-bandwidth. The shadow is the body mode, which cannot be transmitted by waveguide. The rectangle on the right represents the boundary eigenmode electric field distribution (Ez and |Ez|) at the valley K and the corresponding Poynting vector, where S _M1 and S _M2 represent the Poynting vector of eigenmode 1 and the Poynting vector of eigenmode 2, respectively. We know that the slope of the dispersion curve represents the group velocity The magnitude and direction of the two energy bands can be determined, so the propagation group velocities are in opposite directions. From the distribution of the Poynting vector of the eigenmode, it can also be seen that their energy flows are opposite.

As shown in Figure 4, (a) is a schematic diagram of the structure of the present design, the sawtooth interface 5 is a straight line, (d) and (h) represent the electric field energy distribution of the dual-bandwidth valley Hall polarization twist waveguide based on the structural design. It shows that the present invention can realize a dual-bandwidth valley Hall polarization twist waveguide. (b) is a schematic diagram of the robustness structure of the verification waveguide, the sawtooth interface 5 is an Ω-type shape with a large bend, (e) and (i) represent the electric field energy distribution of the dual-bandwidth valley Hall polarization twist waveguide in the Ω-type interface structure. It shows that the dual-bandwidth valley Hall polarization twist waveguide of the present invention has robustness, and robustness is stability, because the general waveguide will reflect when encountering a curved interface, while the waveguide here will not reflect when encountering a bend, and can stably transmit in one direction. (c) is a schematic diagram of the structure for verifying the immune defect of the waveguide, in which one of the circles is a disordered dielectric column, one is missing a dielectric column, and one has a metal rod. (f) and (j) are the electric field energy distribution of the dual-bandwidth valley Hall polarization twist waveguide in the interface structure containing defects. The five-pointed star represents the chiral polarization source, and the arrow represents the polarization direction. (c), (f) and (j) of Figure 4 illustrate that the dual-bandwidth valley Hall polarization twisted state waveguide of the present invention has the characteristic of resisting defect immunity, and even if the interface is destroyed, it can still transmit normally without being destroyed due to the existence of defects.

As shown in Figure 5, (a) represents the normalized electric field energy of the transmission cross section along the y-axis direction in different band gaps, (b) represents the transmission spectrum in the low energy band gap, and (c) represents the transmission spectrum in the high energy band gap. Figure (a) is the electric field distribution of the dual-bandwidth valley Hall polarization twist waveguide in the Y direction measured by two-dimensional cross-sections 16 and 17. Gap1 represents low bandwidth, gap2 represents high bandwidth, line1 represents two-dimensional cross-section 16, and line2 represents two-dimensional cross-section 17, and they are 20 lattice constants apart. It can be seen from line1 and line2 in gap1 that the valley Hall polarization twist waveguide has a certain waveguide width, and they basically overlap, indicating that our waveguide has a high unidirectional transmission efficiency; it can be seen from line1 and line2 in gap2 that the valley Hall polarization twist waveguide is similar to a pulse, has a very strong high energy density, and they still almost overlap, indicating that the waveguide of this application has a high unidirectional transmission efficiency. Figure (b) and Figure (c) respectively represent the transmission spectra in low bandwidth and high bandwidth, where the shaded part represents the working bandwidth width.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A dual-bandwidth valley Hall polarization twisted waveguide based on a triangular lattice valley photonic crystal, characterized in that it comprises a triangular lattice valley photonic crystal (1) with a valley Chern number of 1 and a triangular lattice valley photonic crystal (2) with a valley Chern number of -1, wherein the area formed by the triangular lattice valley photonic crystal (1) with a valley Chern number of 1 is a first area (3), and the area formed by the triangular lattice valley photonic crystal (2) with a valley Chern number of -1 is a second area (4), and the connection between the first area (3) and the second area (4) forms a sawtooth interface (5), and a light source (13) is placed on the sawtooth interface (5). 2. The dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal according to claim 1 is characterized in that the light source (13) is a chiral polarization source, and the chiral polarization source is placed on the sawtooth interface (5). 3. According to the dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystals according to claim 2, it is characterized in that the chiral polarization source includes 4 antennas (14) perpendicular to the z-axis, a linear polarization source is added to the antenna (14), and the phases of adjacent linear polarization sources increase or decrease by π/2. 4. The dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal according to claim 3 is characterized in that the four antennas (14) are arranged in a square, and the side length of the square is 0.2a, where a is the lattice constant of the lattice unit. 5. The dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal according to any one of claims 1 to 4, characterized in that the dielectric column of the triangular lattice valley photonic crystal (1) with valley Chern number 1 and the triangular lattice valley photonic crystal (2) with valley Chern number -1 is a fully dielectric cylindrical silicon rod, and the diameter of the cylindrical silicon rod is The backgrounds of the triangular lattice valley photonic crystal (1) with a dielectric constant of 11.7 and a valley-Chen number of 1 and the triangular lattice valley photonic crystal (2) with a valley-Chen number of -1 are both air; wherein a is the lattice constant of the lattice unit. 6. The dual-bandwidth valley Hall polarization twisted state waveguide based on triangular lattice valley photonic crystal according to claim 5 is characterized in that the waveguide state is generated at the interface of valley photonic crystals with different valley Chern numbers, and the sawtooth interface (5) is a sawtooth shape in the graphene lattice arrangement. 7. The dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal according to claim 6 is characterized in that the length of the side of the regular hexagon in the honeycomb lattice unit cell structure of the triangular lattice valley photonic crystal (1) with valley Chern number 1 and the triangular lattice valley photonic crystal (2) with valley Chern number -1 is L. 8. According to the dual-bandwidth valley Hall polarization twisted waveguide based on triangular lattice valley photonic crystal of claim 7, it is characterized in that the honeycomb lattice unit cell structure I (11) of the triangular lattice valley photonic crystal (1) with valley Chern number 1 is rotated 60° to completely overlap with the honeycomb lattice unit cell structure II (12) of the triangular lattice valley photonic crystal (2) with valley Chern number -1; the honeycomb lattice unit cell structure I (11) and the honeycomb lattice unit cell structure II (12) both satisfy the C _3v spatial rotational symmetry.