CN114839719A - A unidirectional large-area T-type waveguide beam splitter based on topological gyromagnetic photonic crystals - Google Patents

Abstract

The invention provides a topological gyromagnetic photonic crystal-based unidirectional large-area T-shaped waveguide beam splitter, which comprises a light source, a positive magnetic field area, a negative magnetic field area and a non-magnetic field area, wherein the non-magnetic field area is a cross-shaped area, the positive magnetic field area is positioned at the left lower part and the right upper part of the non-magnetic field area, the negative magnetic field area is positioned at the left upper part and the right lower part of the non-magnetic field area, and the light source is positioned at the left side of the non-magnetic field area. The invention successfully designs the micro-nano waveguide beam splitter with one direction, large area, high efficiency and large bandwidth, and realizes high-efficiency conversion in an integrated optical path. Compared with the existing micro-nano optical waveguide device realized based on the topological photonic crystal, the micro-nano optical waveguide device is not influenced by the width of a topological interface, has the advantages of large area, large capacity, coordination and other information transmission, and can meet the requirement of a continuously highly integrated photonic chip.

Description

A unidirectional large-area T-type waveguide beam splitter based on topological gyromagnetic photonic crystal

technical field

The invention relates to the fields of topological photonics, quantum communication and integrated photonic optical circuits, in particular to a design of a unidirectional large-area T-type waveguide beam splitter based on a topological gyromagnetic photonic crystal.

Background technique

Waveguide photonic devices based on topological gyromagnetic photonic crystals have immeasurable application prospects in the fields of topological photonics, quantum communication 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 communication. The integrated photonic optical circuit is constantly developing in the direction of large capacity, high efficiency and miniaturization. Therefore, low-cost, high-efficiency, and multi-functional micro-optical devices are continuously researched and developed.

In 1988, Professor Haldane of the University of California in the United States first proposed the existence of a strange quantum Hall state in the momentum space of non-Landau levels (Model for a Quantum Hall Eff'ect without Landau Levels: Condensed-Matter Realization of the" Parity Anomaly").

In 2008, Zheng Wang's group at MIT designed a unidirectional boundary waveguide transmission mode (Reflection-Free One-Way Edge Modes in a Gyromagnetic PhotonicCrystal) based on gyromagnetic materials, and in 2009 the first experimental observation of the Observation of unidirectional backscattering-immune topological electromagnetic states. Since then, waveguide optical devices based on magneto-optical photonic crystals have been continuously developed.

In 2011, Pu Yin and others from Nanjing University in China first observed the self-conducting unidirectional transmission characteristics of honeycomb magneto-optical photonic crystals (Experimental Realization of Self-Guiding Unidirectional Electromagnetic Edge States) in the laboratory. In 2021, Wang Mudi of Wuhan University in China constructed and observed a unidirectional large-area waveguide state (Topological One-Way Large-AreaWaveguide States in Magnetic Photonic Crystals) based on topological magneto-optical photonic crystals in the laboratory. This unidirectional large-area waveguide state not only has outstanding propagation characteristics such as robustness, defect immunity, and anti-backscattering, but also is not affected by the width of the topological interface, enabling large-area waveguide transmission.

In recent years, various micro-nano waveguide photonic devices have been developed, such as optical isolators, optical couplers, waveguide beam splitters, and optical memories. In particular, the development of waveguide beamsplitters based on traditional methods is greatly limited in terms of transmission capacity and interface width, making it difficult to meet the ever-increasing communication demands.

SUMMARY OF THE INVENTION

Aiming at the technical problems of small transmission capacity and narrow transmission width of traditional waveguide beam splitters, the present invention proposes a unidirectional large-area T-type waveguide beam splitter based on topological gyromagnetic photonic crystals, which realizes large-area, large-capacity, and large-bandwidth beam splitters. Waveguide transmission and beam splitting for efficient switching in integrated optical circuits. Compared with the existing micro-nano optical waveguide devices based on topological photonic crystals, it is not affected by the width of the topological interface and can be coordinated, which can meet the requirements of continuously highly integrated photonic chips.

In order to achieve the above purpose, the technical scheme of the present invention is realized as follows: a unidirectional large-area T-type waveguide beam splitter based on a topological gyromagnetic photonic crystal, which is characterized in that: it includes a light source, a positive magnetic field region, and a negative magnetic field. Area and non-magnetic field area, the non-magnetic field area is a cross-shaped area, the positive magnetic field area is symmetric about the center of the non-magnetic field area, the positive magnetic field area is located in the lower left part and the upper right part of the non-magnetic field area, and it is centrally symmetric about the non-magnetic field area, and the negative magnetic field area The light source is located in the upper left part and the lower right part of the non-magnetic field area, and the light source is located in the non-magnetic field area.

a为数值为500nm的拓扑三角晶格常数。The light source is a linearly polarized source, with the lower left corner of the beam splitter as the origin, and the coordinates of the light source are (3.5a, 12H), where,

a is the topological triangular lattice constant with a value of 500 nm.

The interface between the positive magnetic field region and the non-magnetic field region is the magnetic field gyromagnetic photonic crystal interface I, and the interface between the negative magnetic field region and the non-magnetic field region is the magnetic field gyromagnetic photonic crystal interface II; the positive magnetic field region, the negative magnetic field region and the The magnetic field-free regions are all composed of YIG dielectric cylinders with a radius of 0.125a, a height of a, and the refractive index of air at room temperature is 1.

+z方向表示垂直纸面向里。The forward magnetic field region includes a plurality of YIG dielectric columns I with a bias magnetic field added along the +z direction. The relative permittivity and relative permeability of the YIG dielectric columns with the bias magnetic field added along the +z direction are 13.8.

The +z direction means vertical to the inside of the paper.

-z方向表示垂直纸面向外。The negative magnetic field region includes a plurality of YIG dielectric columns with a bias magnetic field added along the -z direction. The relative permittivity of the YIG dielectric column II with a bias magnetic field added along the -z direction is 13.8 and the relative permeability is 13.8.

The -z direction means perpendicular to the paper side out.

The magnetic field-free region includes a plurality of YIG dielectric pillars III without an added magnetic field; the relative permittivity of the YIG dielectric pillars without an added magnetic field is 13.8, and the relative magnetic permeability is μ ₀ .

When no magnetic field is added, the YIG dielectric cylinder can be regarded as an ordinary photonic crystal. In the energy band structure of the photonic crystal, the second photonic energy band and the third energy band degenerate, and the K point in the vector space of the first Brillouin zone Dirac point appears at ; when a bias magnetic field is added along the -z/+z direction, the YIG dielectric cylinder is regarded as a magneto-optical photonic crystal; if an external bias magnetic field is applied, the time reversal of the magneto-optical photonic crystal The symmetry is broken, and the Dirac point originally at the K point in the first Brillouin zone wave vector space is opened, and the separation occurs in the middle of the second photon energy band and the third energy band, forming a non-zero Chern number photon band gap to form a unidirectional large-area T-type beamsplitter waveguide based on topological gyromagnetic photonic crystals.

The present invention is a unidirectional large-area T-type waveguide beam splitter based on a topological gyromagnetic photonic crystal, and is based on using a gyromagnetic material yttrium iron garnet (YIG) cylindrical rod to form a topological magneto-optical photonic crystal. The magneto-optical photonic crystal domain sandwiching the directional magnetic field does not add a magnetic field to the gyromagnetic photonic crystal domain. Based on the magneto-optical effect, the time-reversal symmetry of the magneto-optical photonic crystal system is broken, and in the non-zero Chern number band gap, electromagnetic waves exhibit non-reciprocal transmission characteristics. In the present invention, unidirectional large-area waveguide transmission and beam splitting occur in the domain without the added gyromagnetic photonic crystal. The present invention successfully designs a unidirectional, large-area, high-efficiency, and large-bandwidth micro-nano waveguide beam splitter. Multifunctional conversion in the integrated optical path.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram of the overall structure of an embodiment of the present invention.

FIG. 2 is an energy band diagram of the unidirectional large-area T-type waveguide beam splitter in the present invention.

Figure 3(a) is a diagram of the electric field distribution of the unidirectional large-area T-type waveguide beam splitter in the present invention.

Figure 3(b) is the Poynting vector of the unidirectional large area T-type waveguide beam splitter in the present invention.

FIG. 4 is the normalized energy distribution propagating along the Y-direction at different positions in the unidirectional large-area T-type waveguide beam splitter in the embodiment of the present invention.

FIG. 5 is a spectral diagram of forward and reverse transmission loss of a unidirectional large-area T-shaped waveguide beam splitter with a transmission distance of 20a in the embodiment of the present invention.

In the figure, 1 is the light source, 2 is a YIG dielectric column with a bias magnetic field added along the +z direction, 3 is a YIG dielectric column with a bias magnetic field added along the -z direction, 4 is a YIG dielectric column with no added magnetic field, 5 is the magnetic field gyromagnetic photonic crystal interface I, 6 is the magnetic field gyromagnetic photonic crystal interface II, 7 is the negative magnetic field region, 8 is the non-magnetic field region, 9 is the positive magnetic field region, and 10 is the two-dimensional tangent at X=7, 11 is the two-dimensional tangent at X=17, 12 is the two-dimensional tangent at X=27, 13 is the supercell structure used to calculate the photon energy band dispersion curve, 14 is the topological triangular lattice structure, and 15 is the lattice constant a , 16 is the lattice unit, 17 is the first Brillouin zone structure distribution of the triangular lattice, and A, B, C, and D represent the waveguide transmission ports.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

+z方向表示垂直纸面向里。负向磁场区域7由沿着-z方向添加偏置磁场的YIG介质柱3组成，沿着-z方向添加偏置磁场的YIG介质柱3相对介电常数为13.8，相对磁导率为

-z方向表示垂直纸面向外。无磁场区域8由无添加磁场的YIG介质柱4组成，无添加磁场的YIG介质柱4的相对介电常数为13.8，相对磁导率为μ₀。正向磁场区域9、负向磁场区域7与无磁场区域8均由YIG介质圆柱组成、其半径为0.125a，高度为a，拓扑三角晶格常数a＝500mn，常温下空气折射率为1，结构参数

As shown in Fig. 1, a unidirectional large-area T-type waveguide beam splitter based on topological gyromagnetic photonic crystal includes a light source 1, a positive magnetic field region 9, a negative magnetic field region 7 and a non-magnetic field region 8, and the non-magnetic field region 8 is a cross-shaped area, the positive magnetic field area 9 is located in the lower left part and the upper right part of the non-magnetic field area 8, the negative magnetic field area 7 is located in the upper left part and the lower right part of the non-magnetic field area 8, and the light source 1 is located on the left side of the non-magnetic field area 8. Among them, the light source 1 is a linear light source, with the lower left corner of the beam splitter as the origin, and the coordinates of the light source 1 are (3.5a, 12H). Negative magnetic field region 7 is the region constructed by a single dielectric column of gyromagnetic photonic crystal with a bias magnetic field added along the -z direction, denoted by H-, and the non-magnetic field region 8 is a single dielectric column of gyromagnetic photonic crystal without a magnetic field added The constructed region is represented by H=0, and the forward magnetic field region 9 is the region constructed by a single dielectric column of gyromagnetic photonic crystal with a bias magnetic field added along the +z direction, represented by H+. The forward magnetic field region 9 consists of a YIG dielectric column 2 with a bias magnetic field added along the +z direction. The relative permittivity of the YIG dielectric column 2 with a bias magnetic field added along the +z direction is 13.8, and the relative permeability is

The +z direction means vertical to the inside of the paper. The negative magnetic field region 7 consists of a YIG dielectric column 3 with a bias magnetic field added along the -z direction. The relative permittivity of the YIG dielectric column 3 with a bias magnetic field added along the -z direction is 13.8, and the relative permeability is

The -z direction means perpendicular to the paper side out. The magnetic field-free region 8 is composed of a YIG dielectric column 4 without an added magnetic field. The relative permittivity of the YIG dielectric column 4 without an added magnetic field is 13.8, and the relative magnetic permeability is μ ₀ . The positive magnetic field area 9, the negative magnetic field area 7 and the non-magnetic field area 8 are all composed of YIG dielectric cylinders with a radius of 0.125a, a height of a, a topological triangular lattice constant a=500mn, and the refractive index of air at room temperature is 1, Structural parameters

When no magnetic field is added, the second photonic energy band and the third energy band in the photonic crystal band structure degenerate, and a Dirac point appears at the K point in the wave vector space in the first Brillouin zone; YIG dielectric cylinder When a bias magnetic field is added along the -z/+z direction, the YIG dielectric cylinder is regarded as a magneto-optical photonic crystal; if the bias magnetic field is applied, the time-reversal symmetry of the magneto-optical photonic crystal is broken, and the original The Dirac point of the K point in the wave vector space of the first Brillouin zone is opened, and the separation occurs in the middle of the second photon energy band and the third energy band, forming a photonic band gap with a non-zero Chern number. In this non-zero Chern number forbidden band, unidirectional transmission of electromagnetic waves occurs. The unidirectional large-area T-type waveguide beam splitting designed by the present invention is generated in such a photonic band gap of non-zero Chern number.

As shown in Fig. 2, the energy band diagram in one lattice period in the direction of the projected wave vector Kx of the unidirectional large-area T-type waveguide beam splitter is obtained by calculating the structural supercell 13 (a×24H). The area indicates that the working bandwidth of the waveguide beam splitter proposed by the present invention is 0.6073c/a-0.6653c/a, where c represents the speed of light in vacuum, and the curve in the figure represents the photon energy band dispersion curve.

As shown in Fig. 3, the electric field energy distribution and the corresponding Poynting vector of the topological gyromagnetic photonic crystal unidirectional large-area T-type waveguide beam splitter can be obtained by arbitrarily taking the frequencies on the two curves in the shaded area of Fig. 2 , where the excitation frequency of the corresponding light source is 0.62805c/a. As can be seen from FIG. 3 , the waveguide beam splitter proposed by the present invention realizes the unidirectional large-area T-type waveguide beam splitting function.

As shown in Figure 4, in order to quantitatively study the transmission characteristics of the unidirectional large-area T-type waveguide beam splitter, the two-dimensional tangent 10 at X=7, the two-dimensional tangent 11 at X=17 and the two-dimensional tangent at X=27 are used. The two-dimensional tangents measure and calculate the distribution of normalized energy propagating along the Y-axis along the X-axis, respectively. Figure 4 shows that when the waveguide of the port A channel of the waveguide beam splitter is transmitted in the forward direction, the waveguide of the port B channel is cut off, and the port C channel and the port D channel respectively obtain 50% of the total energy. This shows that the design of the present invention achieves outstanding characteristics such as the splitting function of the waveguide divided into two, one-way transmission, large area, and high efficiency.

As shown in Figure 5, the S-parameter method is used to calculate the forward and reverse transmission loss spectra of the transmission distance 20a of the waveguide beam splitter. The light gray shaded width is basically the same as the shaded area in Figure 2, both are 0.6073c/a-0.6653c/a, the light gray shade represents the working bandwidth of the unidirectional large-area T-type waveguide beam splitter, and the dark gray shaded area is the width For the optimal working bandwidth is 0.616c/a-0.6401c/a, the loss difference between forward and reverse transmission in this area is relatively large, and the loss reaches more than 40dB.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (7)

1. A unidirectional large-area T-shaped waveguide beam splitter based on topological gyromagnetic photonic crystals is characterized in that: the magnetic field-free light source comprises a light source (1), a positive magnetic field area (9), a negative magnetic field area (7) and a magnetic field-free area (8), wherein the magnetic field-free area (8) is a cross-shaped area, the positive magnetic field area (9) is centrosymmetric with respect to the magnetic field-free area (8), the positive magnetic field area (9) is positioned at the left lower part and the right upper part of the magnetic field-free area (8), the negative magnetic field area (7) is positioned at the left upper part and the right lower part of the magnetic field-free area (8), and the light source (1) is positioned in the magnetic field-free area (8).

2. The design of the topological gyromagnetic photonic crystal based unidirectional large area T-shaped waveguide beam splitter according to claim 1, wherein: the light source (1) is a linear polarization source, the left lower corner of the beam splitter is taken as an origin, the coordinates of the light source (1) are (3.5a, 12H), wherein,

a is the topological triangular lattice constant with a value of 500 nm.

3. The topological gyromagnetic photonic crystal based unidirectional large area T-type waveguide beam splitter of claim 2, wherein: the interface of the positive magnetic field area (9) and the non-magnetic field area (8) is a magnetic field gyromagnetic photonic crystal interface I (5), and the interface of the negative magnetic field area (7) and the non-magnetic field area (8) is a magnetic field gyromagnetic photonic crystal interface II (6);

the positive magnetic field area (9), the negative magnetic field area (7) and the magnetic field-free area (8) are all composed of YIG medium cylinders, the radius of the YIG medium cylinders is 0.125a, the height of the YIG medium cylinders is a, and the air refractive index at normal temperature is 1.

4. The topological gyromagnetic photonic crystal based unidirectional large area T-shaped waveguide beam splitter of claim 3, wherein: the positive magnetic field area (9) comprises a plurality of YIG medium columns (2) which add bias magnetic fields along the + z direction, the relative dielectric constant of the YIG medium columns (2) which add the bias magnetic fields along the + z direction is 13.8, and the relative permeability is

The + z direction indicates into the vertical plane of the paper.

5. The topological gyromagnetic photonic crystal based unidirectional large area T-shaped waveguide beam splitter of claim 4, wherein: the negative magnetic field area (7) comprises a plurality of YIG medium columns (3) which add a bias magnetic field along the-z direction, and the YIG medium columns (3) which add the bias magnetic field along the-z direction have the relative dielectric constant of 13.8 and the relative permeability of 13.8

The-z direction represents out of the plane of the paper.

6. The topological gyromagnetic photonic crystal-based unidirectional large area crystal of claim 6T-type waveguide beam splitter characterized by: the magnetic field-free area (8) comprises a plurality of YIG medium columns (4) without added magnetic fields; the YIG dielectric column (4) without the added magnetic field has a relative dielectric constant of 13.8 and a relative magnetic permeability of mu ₀ 。

7. The topological gyromagnetic photonic crystal based unidirectional large area T-type waveguide beam splitter according to any one of claims 5 to 7, wherein: when no magnetic field is added, the YIG medium cylinder can be regarded as a common photonic crystal, a second photonic band in the energy band structure of the photonic crystal is degenerated with a third photonic band, and a Dirac point appears at a K point in a vector space in a first Brillouin zone; when a bias magnetic field is added to the YIG medium cylinder along the-z/+ z direction, the YIG medium cylinder is regarded as a magneto-optical photonic crystal; if under the condition of applying a bias magnetic field, the time reversal symmetry of the magneto-optical photonic crystal is broken, the original Dirac point of the K point in the wave vector space of the first Brillouin region is opened, the second photonic band and the third photonic band are separated, a photonic band gap with a non-zero number is formed, and the unidirectional large-area T-shaped beam splitting waveguide based on the topological gyromagnetic photonic crystal is formed.

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