Controllable terahertz wave 1*4 beam splitter based on photonic crystal

Abstract

The invention relates to the field of terahertz devices, in particular to an adjustable terahertz wave 1 * 4 beam splitter based on photonic crystals. The photonic crystal is characterized by being composed of a two-dimensional photonic crystal of a triangular lattice circular silicon dielectric cylinder structure; a main waveguide is formed in a complete triangular lattice by removing a plurality of dielectric cylinders, the left end of the main waveguide is a light source input end, and parts of the dielectric cylinders are removed from the upper side and the lower side of the main waveguide to form four bent waveguides which are respectively four output channels; a micro-cavity is arranged between the main waveguide and the bent waveguide, and point defect dielectric cylinders are introduced into intersections of the bent waveguide and the micro-cavity. The terahertz wave beam splitter solves the problems that an existing terahertz wave beam splitter is fixed in splitting ratio, small in adjustable range and difficult to meet actual requirements, and has good application prospects in the fields of photon integrated circuits and terahertz wave communication in the future.

Description

Technical Field

[0001] The present invention relates to the field of terahertz devices, and in particular to an adjustable terahertz wave 1×4 beam splitter based on photonic crystals. Background Art

[0002] Terahertz (THz) waves refer to electromagnetic waves with a frequency of 0.1 to 10 THz (wavelength of 30 to 3000 μm), and the frequency band is between microwaves and infrared waves. Due to its special position and the characteristics of strong penetration, high transmission rate, strong directionality and high safety, terahertz waves have considerable scientific research value and broad application prospects in the fields of object imaging, radar communication, security inspection, biomedicine, environmental monitoring, materials science, and national defense and military. The development of terahertz communication systems requires low-loss THz waveguide structures to achieve efficient transmission of THz waves, and also requires key functional devices such as high-speed switches, modulators, beam splitters and couplers. Terahertz wave beam splitters are key power distribution passive devices that affect the output power of solid-state sources. Since photonic crystals have the advantages of strong light confinement, low polarization sensitivity, and easy integration, they can be widely used in the design of high-efficiency, low-loss, and highly integrated beam splitters.

[0003] In recent years, domestic and foreign scholars have conducted a lot of research and exploration on terahertz wave beam splitters based on photonic crystals, including realizing equal-splitting beam splitters using photonic crystal waveguides alone, realizing ultra-compact equal-splitting beam splitters using the coupling effect of photonic crystal waveguides and resonant cavities, realizing beam splitters with adjustable splitting ratios by changing the refractive index of magneto-photonic crystals by applying an external magnetic field, and realizing beam splitter routing and splitting by optically controlling the refractive index of point defects in nonlinear resonant cavities. Existing photonic crystal terahertz wave beam splitters are large in size and cannot meet the needs of the development of high-density photonic integrated circuits. Summary of the invention

[0004] The present invention provides an adjustable terahertz wave 1×4 beam splitter based on photonic crystal, which solves the problem that the existing terahertz wave beam splitter has a fixed splitting ratio and a small adjustable range and is difficult to meet actual needs.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A controllable terahertz wave 1×4 beam splitter based on photonic crystal is characterized in that it is composed of a two-dimensional photonic crystal with a triangular lattice circular silicon dielectric column structure; a main waveguide is formed in the complete triangular lattice by removing several dielectric columns, the left end of the main waveguide is the light source input end, and some dielectric columns are removed on the upper and lower sides of the main waveguide to form four curved waveguides, which are four output channels respectively; there is a microcavity between the main waveguide and the curved waveguide, and point defect dielectric columns are introduced at the intersection of the curved waveguide and the microcavity.

[0007] In the above scheme, the microcavity is composed of 7 dielectric columns of a two-dimensional triangular lattice photonic crystal, wherein 6 outer ring dielectric columns form a hexagon and 1 central dielectric column is at the center of the hexagon.

[0008] In the above scheme, the radius of the dielectric column in the outer ring of the microcavity is different from the radius of the dielectric column in the center.

[0009] In the above scheme, the refractive index of the microcavity dielectric column is the same as the refractive index of the dielectric column in the photonic crystal.

[0010] In the above scheme, the radii of the point defect dielectric columns on both sides are different.

[0011] In the above scheme, the refractive index of the point defect dielectric column is the same as the refractive index of the dielectric column in the photonic crystal.

[0012] Compared with the prior art, the present invention has the following characteristics:

[0013] 1. The present invention only performs deletion and size design on the basis of the two-dimensional photonic crystal of the triangular lattice circular silicon dielectric column structure, and does not increase the dielectric column. Moreover, the structural parameters of most dielectric columns are the same, which is convenient in actual production;

[0014] 2. The present invention has the characteristics of simple structure, small size, high transmittance and fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structure of the terahertz wave beam splitter of the present invention.

[0016] Figure 2 This is the energy band diagram of the complete photonic crystal structure.

[0017] Figure 3 This is the steady-state field strength distribution diagram corresponding to Example 1.

[0018] Figure 4 is the time domain steady-state response corresponding to example 1.

[0019] Figure 5 This is the steady-state field strength distribution diagram corresponding to Example 2.

[0020] Figure 6 This is the time domain steady-state response corresponding to Example 2.

[0021] Figure 7 This is the steady-state field strength distribution diagram corresponding to Example 3.

[0022] Figure 8 This is the time domain steady-state response corresponding to Example 3. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific examples.

[0024] like Figure 1 As shown, a controllable terahertz wave 1×4 beam splitter based on photonic crystal is characterized in that it is composed of a two-dimensional photonic crystal with a triangular lattice circular silicon dielectric column structure. By removing several dielectric columns, a main waveguide (1), four curved waveguides (2, 3, 4, 5) and a microcavity (6) are formed in the complete triangular lattice. In a preferred embodiment of the present invention, the overall structure of the two-dimensional triangular lattice photonic crystal is 25×25 dielectric columns. The background material of the two-dimensional triangular lattice photonic crystal is air. Port A in the figure is the input port, and ports B, C, D, and E are output ports.

[0025] The microcavity is composed of 7 dielectric columns, of which 6 outer ring dielectric columns form a hexagon and 1 central dielectric column, i.e., the inner ring dielectric column, is located at the center of the hexagon. The 7 dielectric columns of the microcavity, i.e., the 6 outer ring dielectric columns and the 1 central dielectric column, have the same refractive index but different radii.

[0026] Point defect dielectric columns are introduced at the intersection of the curved waveguide and the microcavity, specifically including right point defect dielectric columns (7, 8) and left point defect dielectric columns (9, 10). The right point defect dielectric columns (7, 8) have the same radius R3, and the left point defect dielectric columns (9, 10) have the same radius R4. The point defect dielectric columns are used to control light from the input waveguide (1) to the output waveguide (2, 3, 4, 5). By changing the parameters of the point defect dielectric columns, multi-channel arbitrary splitting ratio output is achieved.

[0027] In a preferred embodiment of the present invention, the lattice constant a is 38 μm, and the refractive index n is 3.46. The radius of the outer ring dielectric column of the microcavity is R1=0.16a, and the radius of the central dielectric column is R2=0.04a.

[0028] In a complete two-dimensional square lattice silicon photonic crystal, the energy band diagram is as follows Figure 2 As shown in the figure, there is a wide TE mode bandgap in its energy band diagram, and the position of the bandgap is determined by the value of the lattice constant. By introducing defect modes in the bandgap, the operating wavelength of the beam splitter can be designed.

[0029] In the preferred embodiment of the present invention, total transmittance and additional loss are the main performance indicators of the photonic crystal terahertz wave beam splitter. The total transmittance is the sum of the transmittances of all output ports of the beam splitter. The additional loss (EL) is the loss of the sum of the optical power of all output ports of the beam splitter relative to the total input optical power, and its expression is:

[0030]

[0031] In a preferred embodiment of the present invention, a finite-difference time-domain (FDTD) method is used to study and analyze the transmission characteristics of a terahertz wave 1×4 beam splitter when the operating wavelength is 95.1 μm, that is, the frequency is 3.15 THz.

[0032] Example 1:

[0033] When R3=10.2μm, R4=2.28μm, the steady-state field intensity distribution of a 1×4 beam splitter with a splitting ratio of 1:1:1:1 is as follows Figure 3 The time domain steady-state response is shown as Figure 4 As shown. Figure 3 It can be seen that when light is incident from input port A, it is first coupled into the microcavity, and after being enhanced by the microcavity, it is coupled into the four output waveguides respectively, and the energy is output evenly from output ports B, C, D, and E at the same time, realizing the beam splitting function. Figure 4 It can be seen that the transmittance of each output channel reaches 24.9%, the total transmittance is 99.6%, and the additional loss is 0.017dB.

[0034] Example 2:

[0035] When R3=9.384μm, R4=3.8μm, the steady-state field intensity distribution of a 1×4 beam splitter with a splitting ratio of 2:2:1:1 is as follows Figure 5 The time domain steady-state response is shown as Figure 6 As shown. Figure 5 It can be seen that when light is incident from input port A, it is coupled into the microcavity through the input waveguide, and then coupled into the four output waveguides by the microcavity, and then outputted symmetrically from the four output ports. Figure 6 The transmittance of the beam splitter output ports B and C is 33.11%, and the transmittance of the output ports D and E is 16.55%, achieving an energy output with a splitting ratio of 2:2:1:1, a total transmittance of 99.3%, and an additional loss of 0.031 dB.

[0036] Example 3:

[0037] When R3=0.76μm, R4=1.52μm, the steady-state field intensity distribution of a 1×4 beam splitter with a splitting ratio of 1:1:2:2 is as follows Figure 7 The time domain steady-state response is shown as Figure 8 As shown. Figure 7 It can be seen that when light is incident from input port A, the point defect dielectric column couples with the photonic crystal microcavity, and the energy splitting situation changes. Figure 8 The transmittance of the beam splitter output ports B and C is 14.65%, and the transmittance of the output ports D and E is 29.3%, achieving an energy output with a splitting ratio of 1:1:2:2, a total transmittance of 87.9%, and an additional loss of 0.56 dB.

[0038] In summary, the present invention can realize a controllable terahertz wave 1×4 beam splitter based on photonic crystal by introducing point defects and microcavities in photonic crystals and controlling the coupling between point defects and microcavities. The present invention has the characteristics of simple structure, excellent performance, easy integration, etc., and has good application prospects in the fields of high-density photon integration and terahertz wave communication in the future.

[0039] The above is only a preferred embodiment of the present invention and cannot be used to limit the scope of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention are still within the scope of the invention.

Claims

1. A controllable terahertz wave 1×4 beam splitter based on photonic crystal, characterized in that: It is composed of a two-dimensional photonic crystal with a triangular lattice circular silicon dielectric column structure; a main waveguide is formed in the complete triangular lattice by removing several dielectric columns, the left end of the main waveguide is the input end of the light source, and some dielectric columns are removed on the upper and lower sides of the main waveguide to form four curved waveguides, which are four output channels respectively; there is a microcavity between the main waveguide and the curved waveguide, and point defect dielectric columns are introduced at the intersection of the curved waveguide and the microcavity.

2. The controllable terahertz wave 1×4 beam splitter based on photonic crystal according to claim 1 is characterized in that: The microcavity is composed of seven dielectric columns of a two-dimensional triangular lattice photonic crystal, of which six outer ring dielectric columns form a hexagon and one central dielectric column is at the center of the hexagon.

3. The controllable terahertz wave 1×4 beam splitter based on photonic crystal according to claim 1 is characterized in that: The radius of the dielectric column in the outer ring of the microcavity is different from that of the dielectric column in the center.

4. The controllable terahertz wave 1×4 beam splitter based on photonic crystal according to claim 1 is characterized in that: The refractive index of the microcavity dielectric column is the same as that of the dielectric column in the photonic crystal.

5. The controllable terahertz wave 1×4 beam splitter based on photonic crystal according to claim 1 is characterized in that: The radii of the point defect dielectric columns on both sides are different.

6. The controllable terahertz wave 1×4 beam splitter based on photonic crystal according to claim 1 is characterized in that: The refractive index of the point defect dielectric column is the same as that of the dielectric column in the photonic crystal.

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