Boundary mode conical concentrator based on two-dimensional nodal line photonic crystal

Abstract

The invention relates to a boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal. The boundary mode conical concentrator comprises a photonic crystal conical concentration area, a waveguide channel, an electromagnetic wave input port and an electromagnetic wave output port. The conical concentrator is composed of photonic crystals with different rotation degrees. The width of the photonic crystal structure is modulated to be gradually narrowed, so that a transmission channel of the concentrator is tapered, and the effect of concentrating electromagnetic waves is achieved. According to the boundary mode conical concentrator designed on the basis of the two-dimensional nodal line photonic crystal, the posture of the conical concentration area and the interface state in the waveguide channel are coupled and better matched with each other. According to the invention, the size of some waveguide modes can be modulated, so that one or more photonic devices with different sizes can be efficiently connected.

Description

Technical Field

[0001] The invention relates to the field of photonics and integrated devices, and in particular to a boundary mode cone concentrator based on a two-dimensional node line photonic crystal. Background Art

[0002] The 21st century is known as the information age. Optics has significant advantages in many application fields of information technology, including high density, digitization and high speed of processing of information. With the advancement of the times and the change of technology, higher requirements are placed on information processing and transmission devices. Mode mismatch is one of the common problems in the field of optics. This mode coupling is often used in optical systems to improve the coupling efficiency between large light sources and certain small samples. It is a key component of hybrid photonic integrated systems. Traditional photonic devices have certain difficulties in mode coupling due to size differences, and are subject to the limitations of electromagnetic wave transmission channels. A large number of reflections often occur during coupling, which reduces transmission efficiency. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention provides a boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal, which can reduce the limitation of the electromagnetic wave transmission channel and effectively improve the transmission efficiency.

[0004] In order to achieve the above-mentioned object, the present invention provides a boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal, comprising a photonic crystal conical concentration region and a waveguide channel, wherein the photonic crystal conical concentration region and the waveguide channel are connected from left to right through photonic crystal structures I, II, III, IV and photonic crystal structure V to form a conical concentrator; the photonic crystal structure of the photonic crystal conical concentration region and the waveguide channel is composed of A1, A2, A3, A4, A5, B1, B2, B3, B4, B5 and O arranged in an overlapping manner; the photonic crystal is composed of a shell structure arranged in a hexagonal lattice , the lattice constant a of the hexagonal lattice is 25mm; there is a shell structure in the primitive cell o of the photonic crystal, and the shell structure is divided into three equal parts by digging out three rectangular areas, wherein the width w of the rectangle is adjustable, the dielectric column in the shell structure is composed of alumina dielectric material, with a relative dielectric constant of 9.5, the background material is air, with a relative dielectric constant of 1, the inner radius of the dielectric column is R1 = 7.5mm, the outer radius is R2 = 10.5mm, and the height is d = 10mm. The various parameters of the photonic crystal can be freely adjusted according to the actual working frequency of the concentrator;

[0005] Move the dielectric column s at the bottom of the photonic crystal unit cell o to the right by the distances of dc1=0.08a, dc2=0.1a, dc3=0.12a, dc4=0.14a, and dc5=0.16a respectively, and rotate 120° counterclockwise and 120° clockwise based on the moved s and the center of the unit cell as the origin to obtain photonic crystals a1, a2, a3, a4, and a5 respectively; set the rightward movement of s as the positive direction;

[0006] The dielectric column s at the bottom of the photonic crystal unit cell o is moved to the left by the distances of dc1=0.08a, dc2=0.1a, dc3=0.12a, dc4=0.14a, and dc5=0.16a, respectively. Based on the moved s, the unit cell center is rotated 120° counterclockwise and 120° clockwise, respectively, to obtain photonic crystals b1, b2, b3, b4, and b5, respectively; the leftward movement of s is set as the negative direction;

[0007] The waveguide channel is formed by region V.

[0008] In addition, the boundary mode conical concentrator based on the two-dimensional nodal line photonic crystal proposed in the above embodiment of the present invention may also have the following additional technical features:

[0009] As a further improvement of the present invention, the photonic crystal structure A1 is composed of photonic crystal primitive cells a1, wherein the x direction contains 8 primitive cells and the y direction contains 3 primitive cells;

[0010] The photonic crystal structure A2 is composed of the photonic crystal a2, which includes 3 primitive cells in the x direction and 4 primitive cells in the y direction;

[0011] The photonic crystal structure A3 is composed of a photonic crystal a3, which includes 4 primitive cells in the x direction and 5 primitive cells in the y direction;

[0012] The photonic crystal structure A4 is composed of the photonic crystal a4, which includes 3 primitive cells in the x direction and 6 primitive cells in the y direction;

[0013] The photonic crystal structure A5 is composed of the photonic crystal a5, which includes 9 primitive cells in the x direction and 7 primitive cells in the y direction;

[0014] The photonic crystal structure B1 is composed of photonic crystal primitive cells b1, which include 8 primitive cells in the x direction and 3 primitive cells in the y direction;

[0015] The photonic crystal structure B2 is composed of the photonic crystal b2, which contains 3 primitive cells in the x direction and 4 primitive cells in the y direction;

[0016] The photonic crystal structure B3 is composed of the photonic crystal b3, which contains 4 primitive cells in the x direction and 5 primitive cells in the y direction;

[0017] The photonic crystal structure B4 is composed of the photonic crystal b4, which contains 3 primitive cells in the x direction and 6 primitive cells in the y direction;

[0018] The photonic crystal structure B5 is composed of the photonic crystal b5, which contains 9 primitive cells in the x direction and 7 primitive cells in the y direction;

[0019] The photonic crystal structures O1, O2, O3, O4, and O5 are composed of a photonic crystal primitive cell o, which respectively includes 8, 3, 4, 3, and 9 primitive cells in the x direction; and 9, 7, 5, 3, and 1 primitive cells in the y direction.

[0020] As a further improvement of the present invention, the concentrator is composed of five regions, and the upper, middle and lower parts of region I are arranged in the order of photonic crystal structures A1, O and B1;

[0021] Region II of the concentrator is composed of photonic crystal structures A2, O and B2 in order; region III of the concentrator is composed of photonic crystal structures A3, O and B3 in order; region IV of the concentrator is composed of photonic crystal structures A4, O and B4 in order; region V of the concentrator is composed of photonic crystal structures A5, O and B5 in order.

[0022] As a further improvement of the present invention, an excitation source P1 and an exit port P2 are respectively provided on both sides of the conical concentrator;

[0023] The excitation source P1 is located at the far left of the conical concentrator; the output port P2 is located at the far right of the photonic crystal concentrator.

[0024] As a further improvement of the present invention, the concentrating area of ​​the boundary mode cone concentrator is composed of area I, area II, area III, and area IV which are linked in sequence from left to right.

[0025] The present invention has the following beneficial effects:

[0026] In view of the problems of mode mismatch and low coupling efficiency caused by size differences in traditional photonic devices, the present invention designs a boundary mode conical concentrator by utilizing the transmission properties of the boundary state mode. The structure designed by the present invention can be used for coupling between photonic devices of different mode sizes by modulating the width of the conical concentration area of ​​the photonic crystal, thereby reducing transmission loss and improving coupling efficiency. The conical concentrator in the present invention has excellent characteristics such as low environmental requirements, high compatibility, low loss, and high degree of control freedom. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall structure of an implementation case of the present invention;

[0028] Figure 2 The photonic crystal primitive cell of the present invention and the energy band diagram after the primitive cell is rotated;

[0029] Figure 3a is the projected energy band diagram of the photonic crystal structure I in the present invention;

[0030] Figure 3b is the projected energy band diagram of the photonic crystal structure III in the present invention;

[0031] Figure 3c is the projected energy band diagram of the photonic crystal structure V in the present invention;

[0032] Figure 4a This is the electric field distribution diagram after being excited by an excitation source on the left side of the conical concentrator in the present invention;

[0033] Figure 4b For the present invention Figure 4a The normalized electric field intensity distribution diagram after integrating the electric field along the y direction at the positions of the four yellow dotted lines shown. DETAILED DESCRIPTION

[0034] A boundary mode tapered concentrator based on a two-dimensional nodal line photonic crystal of the present invention is described below in conjunction with the accompanying drawings.

[0035] like Figure 1 As shown, in a specific embodiment of the present invention, a photonic crystal boundary mode tapered concentrator is provided, comprising a photonic crystal tapered concentrating region and a waveguide channel;

[0036] The photonic crystal boundary mode conical concentrator comprises an excitation source P1 and an exit port P2;

[0037] The photonic crystal boundary mode cone concentrator also includes a photonic crystal structure I, a photonic crystal structure II, a photonic crystal structure III, a photonic crystal structure IV and a photonic crystal structure V;

[0038] The photonic crystal structures I, II, III, IV, and V are sequentially connected to form a photonic crystal conical concentration region and a waveguide channel;

[0039] The photonic crystal region I has eight primitive cells in the x direction in the rectangular coordinate system; the photonic crystal region II has three primitive cells in the x direction; the photonic crystal region III has four primitive cells in the x direction; the photonic crystal region IV has three primitive cells in the x direction; the photonic crystal region V has nine primitive cells in the x direction; and the photonic crystal regions I, II, III, IV, and V have fifteen primitive cells in the y direction.

[0040] The upper, middle and lower parts of the photonic crystal region I are arranged in the order of photonic crystal structures A1, O and B1; the region II is arranged in the order of photonic crystal structures A2, O and B2; the region III is arranged in the order of photonic crystal structures A3, O and B3; the region IV is arranged in the order of photonic crystal structures A4, O and B4; the region V is arranged in the order of photonic crystal structures A5, O and B5;

[0041] The photonic crystal primitive cells a1, a2, a3, a4, a5 and b1, b2, b3, b4, b5 are deformed from the photonic crystal primitive cell o; the photonic crystal primitive cell o is composed of a shell structure arranged in a hexagonal lattice, and the lattice constant a of the hexagonal lattice is 25 mm;

[0042] The inner radius of the shell structure medium column is R1=7.5mm, the outer radius is R2=10.5mm, and the height is d=10mm;

[0043] The dielectric column s at the bottom of the photonic crystal unit cell o is moved forward by a distance of dc=0.08a, 0.1a, 0.12a, 0.14a, and 0.16a, and the unit cell center is used as the origin, and the unit cell is rotated 120° in the counterclockwise direction and 120° in the clockwise direction, respectively, to obtain photonic crystal unit cells a1, a2, a3, a4, and a5, respectively;

[0044] The dielectric column s at the bottom of the photonic crystal unit cell o is negatively moved by distances of dc = 0.08a, 0.1a, 0.12a, 0.14a, and 0.16a, and based on s, the unit cell center is rotated 120° counterclockwise and 120° clockwise respectively to obtain photonic crystal units b1, b2, b3, b4, and b5;

[0045] The excitation source is a Gaussian beam source, with the center of the leftmost shell structure medium column as the coordinate origin, and the coordinates of the excitation source are The excitation source is located on the left side of structure O1.

[0048] Figure 1The overall structure diagram of the implementation case of the present invention. o is a photonic crystal unit cell when the shell structure dielectric column does not rotate, the inner radius of the shell structure dielectric column is R1 = 7.5mm, the outer radius is R2 = 10.5mm, and the lattice constant is a = 25mm; the dielectric column s at the bottom of the photonic crystal unit cell o is positively moved by a distance of dc = 0.08a, and the center of the unit cell is used as the origin to rotate 120° counterclockwise and 120° clockwise respectively, to obtain the photonic crystal unit cell structure a1; the dielectric column at the bottom of the photonic crystal unit cell o is negatively moved by a distance of dc = 0.08a, and the center of the unit cell is used as the origin to rotate 120° counterclockwise and 120° clockwise respectively, to obtain the photonic crystal unit cell structure b1. ; The upper, middle and lower parts of the concentrator region I are arranged in the order of photonic crystal structures A1, O and B1; the upper, middle and lower parts of the concentrator region II are arranged in the order of photonic crystal structures A2, O and B2; the upper, middle and lower parts of the concentrator region III are arranged in the order of photonic crystal structures A3, O and B3; the upper, middle and lower parts of the concentrator region IV are arranged in the order of photonic crystal structures A4, O and B4; the upper, middle and lower parts of the concentrator region V are arranged in the order of photonic crystal structures A5, O and B5; P1 represents the electromagnetic wave input port of the boundary mode cone concentrator, and P2 represents the electromagnetic wave output port of the boundary mode cone concentrator.

[0049] Figure 2 The energy band diagrams representing the photonic crystal unit cell o and the photonic crystal unit cell a1. When the shell structure dielectric column is not rotated, the two energy bands of the photonic crystal o are degenerate. When the shell structure dielectric column is moved and rotated, the degenerate Dirac point of the photonic crystal a1 will be opened and a band gap will be formed.

[0050] Figure 3a is the projected energy band of the photonic crystal structure I, the abscissa represents the wave vector kx, and the ordinate represents the frequency. From the dispersion diagram, we can see that the electromagnetic wave propagates in the structure I in a bulk state. Figure 3b It is the projected energy band of the photonic crystal structure III. At this time, the electromagnetic wave still propagates in the structure III in a bulk state. Figure 3c The projected energy band of the photonic crystal structure V shows two interface state dispersions at the common band gap. The electric field of the interface state has good localization.

[0051] Figure 4aThe electric field distribution diagram of the boundary mode conical concentrator of the present invention at a frequency of 8.877 GHz. When the electromagnetic wave is incident on the designed photonic crystal structure from the P1 port, it propagates in the bulk state in the photonic crystal structures Ⅰ, Ⅱ, Ⅲ, and Ⅳ, and propagates in the interface state in the photonic crystal structure V. The propagation range of the electromagnetic wave remains basically unchanged in region Ⅰ. After the electromagnetic wave enters regions Ⅱ, Ⅲ, and Ⅳ, the propagation area gradually narrows, and then gradually couples to the photonic crystal region V. Photonic crystal structure Ⅰ, photonic crystal structure Ⅲ, and photonic crystal structure Ⅴ have 8, 4, and 9 primitive cells in the x direction, respectively, and 15 primitive cells in the y direction. Figure 4b The normalized electric field intensity distribution diagram after integrating the electric field along the y direction at the positions of the four yellow dotted lines. The horizontal axis represents the distance from the origin of the coordinate in the y-axis direction, and the vertical axis represents the normalized electric field intensity. As the conical structure of the photonic crystal gradually narrows, the distribution width of the electric field gradually decreases. At the same time, the intensity of the electric field reaches its maximum at the waveguide channel. This shows that the designed conical concentrator has a good concentration effect on electromagnetic waves.

[0052] The theoretical basis of the present invention is:

[0053] 1. When the dielectric column of the photonic crystal shell structure does not rotate, that is, when the position of the dielectric column s at the bottom of the lattice does not move, the primitive cell structure satisfies C 3V Symmetry, at this time, there are nodal rings in the energy band structure of the photonic crystal. When the dielectric column s at the bottom of the photonic crystal o unit cell is moved forward by a distance of dc = 0.08a, and the mirror symmetry of the photonic crystal unit cell is broken when the center of the unit cell is rotated 120° counterclockwise and 120° clockwise based on s and the origin, an effective interaction mass m proportional to the degree of rotation is introduced into the effective Hamiltonian, resulting in the opening of the degenerate nodal ring energy band.

[0054] 2. Photonic Crystal A 1-5 and B 1-5 With opposite effective interaction masses, two flat interface state dispersions will appear in the common band gap of the two, that is, a local electric field will appear at the interface between the two. 1-5 and B 1-5 In the middle, two interface state dispersions will overlap. Based on the regulation of the boundary state distribution area, the present invention designs a photonic crystal cone concentrator.

[0055] The present invention provides a boundary mode cone concentrator. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal, characterized in that: The invention comprises a photonic crystal conical concentration region and a waveguide channel, wherein the photonic crystal conical concentration region and the waveguide channel are connected from left to right through photonic crystal structures Ⅰ, Ⅱ, Ⅲ, Ⅳ and photonic crystal structure Ⅴ to form a conical concentrator; the photonic crystal structure of the photonic crystal conical concentration region and the waveguide channel is composed of A1, A2, A3, A4, A5, B1, B2, B3, B4, B5 and O arranged in an overlapping manner; the photonic crystal is composed of a shell structure arranged in a hexagonal lattice, and the lattice constant a of the hexagonal lattice is 25 mm; There is a shell structure in the primitive cell o of the photonic crystal. The shell structure is divided into three equal parts by digging out three rectangular areas, where the width w of the rectangle is adjustable. The dielectric column in the shell structure is made of alumina dielectric material with a relative dielectric constant of 9.

5. The background material is air with a relative dielectric constant of 1. The inner radius of the dielectric column is R1 = 7.5 mm, the outer radius is R2 = 10.5 mm, and the height is d = 10 mm. The various parameters of the photonic crystal can be freely adjusted according to the actual working frequency of the concentrator. Move the dielectric column s at the bottom of the photonic crystal unit cell o to the right by the distances of dc1=0.08a, dc2=0.1a, dc3=0.12a, dc4=0.14a, and dc5=0.16a respectively, and rotate 120° counterclockwise and 120° clockwise based on the moved s and the center of the unit cell as the origin to obtain photonic crystals a1, a2, a3, a4, and a5 respectively; set the rightward movement of s as the positive direction; The dielectric column s at the bottom of the photonic crystal unit cell o is moved to the left by the distances of dc1=0.08a, dc2=0.1a, dc3=0.12a, dc4=0.14a, and dc5=0.16a, respectively. Based on the moved s, the unit cell center is rotated 120° counterclockwise and 120° clockwise, respectively, to obtain photonic crystals b1, b2, b3, b4, and b5, respectively; the leftward movement of s is set as the negative direction; The waveguide channel is formed by region V.

2. A boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal according to claim 1, characterized in that: The photonic crystal structure A1 is composed of photonic crystal primitive cells a1, wherein the x direction contains 8 primitive cells and the y direction contains 3 primitive cells; The photonic crystal structure A2 is composed of the photonic crystal a2, which includes 3 primitive cells in the x direction and 4 primitive cells in the y direction; The photonic crystal structure A3 is composed of a photonic crystal a3, which includes 4 primitive cells in the x direction and 5 primitive cells in the y direction; The photonic crystal structure A4 is composed of the photonic crystal a4, which includes 3 primitive cells in the x direction and 6 primitive cells in the y direction; The photonic crystal structure A5 is composed of the photonic crystal a5, which includes 9 primitive cells in the x direction and 7 primitive cells in the y direction; The photonic crystal structure B1 is composed of photonic crystal primitive cells b1, which include 8 primitive cells in the x direction and 3 primitive cells in the y direction; The photonic crystal structure B2 is composed of the photonic crystal b2, which contains 3 primitive cells in the x direction and 4 primitive cells in the y direction; The photonic crystal structure B3 is composed of the photonic crystal b3, which contains 4 primitive cells in the x direction and 5 primitive cells in the y direction; The photonic crystal structure B4 is composed of the photonic crystal b4, which contains 3 primitive cells in the x direction and 6 primitive cells in the y direction; The photonic crystal structure B5 is composed of the photonic crystal b5, which contains 9 primitive cells in the x direction and 7 primitive cells in the y direction; The photonic crystal structures O1, O2, O3, O4, and O5 are composed of a photonic crystal primitive cell o, which respectively includes 8, 3, 4, 3, and 9 primitive cells in the x direction; and 9, 7, 5, 3, and 1 primitive cells in the y direction.

3. A boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal according to claim 2, characterized in that: The concentrator is composed of five regions, and the upper, middle and lower parts of region I are arranged in the order of photonic crystal structures A1, O and B1; Region II of the concentrator is composed of photonic crystal structures A2, O and B2 arranged in sequence; region III of the concentrator is composed of photonic crystal structures A3, O and B3 arranged in sequence; region IV of the concentrator is composed of photonic crystal structures A4, O and B4 arranged in sequence; Region V of the concentrator is composed of photonic crystal structures A5, O and B5 arranged in sequence.

4. A boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal according to claim 3, characterized in that: The excitation source P1 and the emission port P2 are respectively arranged on both sides of the conical concentrator; The excitation source P1 is located at the far left of the conical concentrator; the output port P2 is located at the far right of the photonic crystal concentrator.

5. A boundary mode conical concentrator based on a two-dimensional nodal line photonic crystal according to claim 4, characterized in that: The concentrating area of ​​the boundary mode cone concentrator is composed of area I, area II, area III and area IV which are linked in sequence from left to right.

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