A photonic crystal polarization beam splitting device based on complementary defect modes

Abstract

The present invention proposes a photonic crystal polarization splitting device based on complementary defect modes. This device is based on a triangular lattice air ring photonic crystal with germanium as the background material and tellurium as the core material. By removing part of the air ring, an input waveguide, a symmetrical V-shaped branch waveguide, and two output waveguides are formed. A row of regulated tellurium dielectric columns and a row of regulated air holes are introduced into the upper and lower branches of the V-shaped branch waveguide, respectively, and a regulated air ring is provided at the intersection of the waveguides. By regulating the tellurium dielectric column structure of the upper branch, the TE mode is placed in the bandgap while the TM mode is conducted; by regulating the air hole structure of the lower branch, the TM mode is placed in the bandgap while the TE mode is conducted, thereby achieving polarization splitting. The present invention also optimizes the regulated air ring structure at the intersection, further improving performance. The device has the advantages of wide bandwidth, high extinction ratio, low loss, and small size. The waveguide design maintains the direction of beam propagation, making it suitable for miniaturized polarization-sensitive photonic devices.

Description

Technical Field

[0001] The present invention relates to the field of photonic integrated circuits, and in particular to a photonic crystal polarization beam splitting device based on complementary defect modes. Background Art

[0002] Polarization beam splitters are widely used in optical communications and photonic integrated systems to guide orthogonal polarized light to different propagation paths. Existing polarization beam splitters mainly include Mach-Zehnder interference type, directional coupling type, subwavelength grating type and photonic crystal type structures. Among them, the first three types of devices generally have problems such as complex preparation and large size, which make it difficult to meet the miniaturization and high integration requirements of chip-level devices. In recent years, polarization beam splitters based on photonic crystal structures have attracted widespread attention due to their compact structure and strong directionality. However, most existing photonic crystal polarization beam splitters can only achieve a high extinction ratio within a specific wavelength range, and have problems such as large output beam divergence and unstable direction, making it difficult to meet the dual performance requirements of high-density integrated systems for bandwidth and directionality. Summary of the Invention

[0003] The present invention proposes a photonic crystal polarization beam splitting device based on complementary defect modes to solve the problems raised in the above background technology. The present invention provides the following technical solutions:

[0004] A photonic crystal polarization beam splitter based on complementary defect modes is proposed. In a triangular lattice air ring photonic crystal with a germanium background and a tellurium core, an input waveguide, a symmetrical V-shaped branch waveguide, and two output waveguides are sequentially formed by removing part of the air ring. A controllable tellurium dielectric column and a controllable air hole are introduced into the upper and lower branches of the V-shaped branch waveguide, respectively. Controllable air rings are introduced at the intersections of the input waveguide and the V-shaped branch waveguide, and at the intersections of the V-shaped branch waveguide and the two output waveguides.

[0005] Preferably, the inner core material of the air rings on both sides of the upper branch of the V-shaped branch waveguide and the output waveguide connected thereto is replaced with germanium.

[0006] Preferably, the radii of the control tellurium dielectric columns introduced into the upper branch of the V-shaped branch waveguide are different.

[0007] Preferably, the radius of the control tellurium air hole introduced in the lower branch of the V-shaped branch waveguide is different.

[0008] Preferably, the inner and outer radii of the control air ring introduced at the intersection of the input waveguide and the V-shaped branch waveguide are different.

[0009] Preferably, the inner and outer radii of the control air ring introduced at the intersection of the V-shaped branch waveguide and the two output waveguides are different.

[0010] A photonic crystal polarization beam splitting method comprises the following steps: disposing a row of high-refractive-index dielectric pillars in the upper branch of a V-shaped branch waveguide so that the TE mode and the TM mode fall into the forbidden band and the defect mode, respectively, within the same operating frequency range; and disposing a row of air holes in the lower branch of the V-shaped branch waveguide so that the TE mode and the TM mode fall into the defect mode and the forbidden band, respectively, within the same operating frequency range; introducing a controllable air ring at the junction of the V-shaped branch waveguide and the input and output waveguides; and achieving optimal beam splitting performance by optimizing the inner and outer radius parameters of the controllable air ring, the radius parameters of the dielectric pillars, and the radius parameters of the air holes.

[0011] Compared with the existing technology, the beneficial effects achieved by the present invention are: the beam splitting method of the photonic crystal polarization beam splitting device based on complementary defect modes proposed in the present invention is novel, and while realizing broadband polarization beam splitting, the device size is significantly reduced, and it has the advantages of wide bandwidth, high extinction ratio, low additional loss, and small device size. The waveguide design maintains the propagation direction of the incident light and significantly reduces the output beam size, showing its application prospects in the design of compact and efficient polarization beam splitters. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0013] Figure 1 TE and TM band diagrams of a complete triangular lattice air ring two-dimensional photonic crystal;

[0014] Figure 2 The supercell band diagram of TE and TM of triangular lattice air ring photonic crystal line defect;

[0015] Figure 3 The supercell band diagram of the TE and TM modes of a triangular lattice air ring photonic crystal line defect with a tellurium dielectric column in the line defect;

[0016] Figure 4 The supercell band diagram of TE and TM modes of a triangular lattice air ring photonic crystal line defect with an air hole in the line defect;

[0017] Figure 5 The supercell band diagram of the TE and TM modes of a triangular lattice air ring photonic crystal line defect with a tellurium dielectric column in the line defect and the inner core of the air rings on both sides replaced by germanium dielectric columns;

[0018] Figure 6 The supercell band diagram of the TE and TM modes of a triangular lattice air ring photonic crystal line defect with an air hole in the line defect and the inner cores of the air rings on both sides replaced by germanium dielectric pillars;

[0019] Figure 7The supercell band diagram of TE and TM modes of a triangular lattice air ring photonic crystal line defect with a tellurium dielectric column with a radius of 0.3a in the line defect;

[0020] Figure 8 The supercell band diagram of TE and TM modes of a triangular lattice air ring photonic crystal line defect with an air hole of radius 0.15a in the line defect;

[0021] Figure 9 It is a structural schematic diagram of the present invention;

[0022] Figure 10 The time domain steady-state diagram and steady-state field intensity distribution diagram of the polarization beam splitter under TM polarized light with an operating wavelength of 1550nm. The black vertical axis on the left represents the non-output port, and the red vertical axis on the right represents the output port.

[0023] Figure 11 The time domain steady-state diagram and steady-state field intensity distribution diagram of the polarization beam splitter under TE polarized light with an operating wavelength of 1550nm. The black vertical axis on the left represents the output port, and the red vertical axis on the right represents the non-output port.

[0024] Figure 12 is the transmittance diagram of the polarization beam splitter under broadband TM polarized light;

[0025] Figure 13 This is the transmittance diagram of the polarization beam splitter under broadband TE polarized light;

[0026] Figure 14 The extinction ratio diagram of the polarization beam splitter under broadband TE and TM polarization light. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0028] In order to make the above-mentioned objects, features and effects of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Air ring photonic crystals have a wider full band gap than simple structure photonic crystals, which makes it possible to design polarization devices. Figure 1As shown, the air ring photonic crystal is composed of tellurium dielectric columns periodically embedded in a germanium background material to form a triangular lattice structure. Its full band gap range at normalized frequency is 0.346-0.381 (unit is a / λ, where a is the lattice constant of the photonic crystal and λ is the wavelength of light, omitted below).

[0030] By removing a row of air rings from a complete air ring photonic crystal structure, a waveguide structure with line defects can be formed. The supercell structure of this waveguide is then studied. Figure 2 As shown in the figure, within the standardized frequency range of 0.335-0.375, the waveguide supports a relatively wide TE / TM defect mode, that is, it can effectively confine and transmit TE and TM polarized light at the same time without scattering into the surrounding medium.

[0031] Analysis of the plane wave expansion method reveals that when constructing a scatterer photonic crystal structure with a significant refractive index contrast within the same background material, the photonic band gaps of the TE and TM modes exhibit distinct characteristics. By designing structural parameters such as high-refractive-index dielectric columns or air holes, the position and width of the TE and TM mode photonic band gaps can be precisely controlled, thereby regulating the complementary distribution of defect modes and achieving polarization beam splitting.

[0032] As mentioned above, the photonic band gap can be tuned by introducing tellurium dielectric columns or air holes into the waveguide. Figure 3 As shown in Figure 2, when a tellurium dielectric rod with a radius of r = 0.15a is added to the waveguide, a TE mode bandgap appears in the frequency range of 0.347-0.352, while no TM bandgap is observed in this frequency range, indicating that only TM polarized light can be transmitted in this range. On the contrary, Figure 4 As shown in the figure, when an air hole with a radius of r = 0.3a is introduced into the waveguide, a wider TM bandgap appears in the frequency range of 0.319–0.359, and there is no corresponding TE bandgap in this range, which means that only TE polarized light can be transmitted at this time.

[0033] To broaden Figure 3 and 4 To improve the TE or TM mode band gap in the structure shown, the core material of the air ring structure on both sides of the waveguide is replaced with the background material germanium. Figure 5 As shown in Figure 2, the TE mode band gap is widened to 0.348–0.359, while the TM mode band gap remains unchanged, indicating that its polarization splitting characteristics are enhanced and have better broadband polarization splitting performance. Figure 6 In the structure shown, the upper limit of the TM mode band gap is from Figure 4 0.359 in the red shift to 0.345, away from Figure 2 The defect mode frequency range shown is not conducive to achieving broadband polarization beam splitting.

[0034] Further study the effect of dielectric pillar and air hole size on photonic band gap, e.g. Figure 7 As shown, in Figure 5 Increasing the radius of the dielectric column to 0.3a based on the structure shown above will cause a blue shift in the TE mode band gap. Figure 8 As shown, in Figure 4 Reducing the radius of the air hole in the waveguide to 0.15 Å based on the structure shown above results in a redshift of the TM mode bandgap. Therefore, by adjusting the radius of the dielectric pillar or air hole, the positions of the TE and TM mode bandgaps can be effectively controlled.

[0035] The structure of the photonic crystal broadband polarization beam splitter proposed by the present invention is as follows: Figure 9 As shown, 11 x 17 air ring photonic crystals are periodically arranged in a triangular lattice within a germanium background material. The core dielectric pillars are made of tellurium. The refractive indices of the background germanium material and the core dielectric pillars are n1 = 4 and n2 = 6.2, respectively. The outer radius R and inner radius r of the air ring photonic crystal are 0.45 Å and 0.15 Å, respectively.

[0036] According to the above research, Figure 2 、 Figure 4 and Figure 5 The waveguide structures in the figure serve as initial references for the design of the transmission waveguide W1 and the two branches of the V-shaped waveguide. In the complete photonic crystal structure, four air rings are removed along the x-axis to form the input waveguide W1. At the right end of W1, the four air rings arranged 60° counterclockwise are replaced with tellurium dielectric rods, while the four air rings arranged 60° clockwise are replaced with air holes, forming a V-shaped structure. At each end of the V-shaped waveguide, six air rings are removed parallel to the input waveguide to form output waveguides W2 and W3, with their corresponding output ports being Port 1 and Port 2. Furthermore, replacing the tellurium dielectric rods in the upper branch of the V-shaped waveguide and on both sides of W2 with germanium dielectric rods widens the TE mode bandgap and achieves better polarization beam splitting performance.

[0037] In order to reduce the back reflection loss of the signal light in the device, five adjustable air ring structures are introduced at the connection between the V-shaped waveguide and W1, W2, and W3, and their outer and inner radii are recorded as R1~R5 and r1~r5 respectively. In order to further improve the polarization beam splitting performance, the radius of the tellurium dielectric column and air hole in the V-shaped waveguide is also listed as an optimization parameter, and its radius is set to r6~r 13 .

[0038] The incident light enters the input waveguide W1 and is transmitted to the V-shaped waveguide in the positive direction along the x-axis. Under the action of the defect mode and the photonic bandgap, the TM polarized light is prohibited from propagating downward and can only enter the output waveguide W2 upward and finally output from port Port1. On the contrary, the TE polarized light is prohibited from propagating upward and can only enter the output waveguide W3 downward and finally output from port Port2, thus realizing the polarization splitting function.

[0039] Using the optimization algorithm, the structural parameters of the above-mentioned beam splitter can be optimized in reverse, that is, the inner and outer radii of the air ring, the radii of the tellurium medium column and the air hole can be adjusted.

[0040] Based on the downhill simplex algorithm and the particle swarm algorithm, this embodiment proposes a set of reverse design structural parameters, specifically: R1=0.249μm, R2=0.249μm, R3=0.2395μm, R4=0.242μm, R5=0.243μm, r1=0.077μm, r2=0.0935μm, r3=0.08μm, r4=0.073μm, r5=0.0885μm, r6=0.12μm, r7=0.144μm, r8=0.1465μm, r9=0.1595μm, r 10 =0.0935μm, r 11 =0.014μm, r 12 =0.0605μm, r 13 =0.0235 μm. It should be noted that this set of parameters is designed for the subsequent evaluation of the polarization beam splitter performance and is only one of the preferred cases of the present invention.

[0041] In order to evaluate the performance of the designed polarization beam splitter, a simulation study is first conducted at a wavelength of 1550nm. Figure 10 and 11 As shown in the figure, the time domain steady-state response and field intensity distribution under the action of TE and TM polarized light are shown. For TE polarized light, as Figure 10 As shown, the transmittance of the output port is 96.2%, and that of the non-output port is 0.917%. For TM polarized light, as shown Figure 11 As shown in the figure, the transmittance of the output port is 82.8%, while that of the non-output port is only 0.096%. The TE and TM mode extinction ratios of the device at a wavelength of 1550nm are 29.9dB and 19.5dB, respectively, indicating that the structure has excellent polarization beam splitting performance in this band.

[0042] The beam splitting performance of the polarization beam splitter in a wide band is as follows Figure 12 and 13 As shown. Figure 12As shown in Figure 2, for TE polarized light, the output port transmittance exceeds 88% in the 1530–1560 nm band and reaches 100% near the 1540 nm wavelength. The average transmittance is 94%, and the transmittance of the non-output port remains below 1%. Figure 13 As shown, for TM polarized light, the transmittance at the output port exceeds 76% within the wavelength range of 1540–1560nm, reaching a maximum of 83% at 1552nm, with an average transmittance of 80%. The transmittance at the non-output port is consistently below 1%, reaching a minimum of 0.05%. These results demonstrate that the photonic crystal polarization beam splitter has excellent transmission efficiency and non-target mode suppression capabilities within the 1540–1560nm range, demonstrating robust broadband polarization beamsplitting performance.

[0043] The extinction ratio performance of the polarization beam splitter in the wavelength range of 1540–1560 nm is as follows: Figure 14 As shown in Figure 2, for TE polarized light, the extinction ratio consistently remains above 24.2dB, reaching a maximum of 31.8dB at 1554nm. For TM polarized light, the extinction ratio also remains above 12.8dB, reaching a maximum of 20.3dB at 1552nm. These results further verify that this structure has superior beam-splitting properties for TE-mode polarized light within the operating band.

[0044] The photonic crystal polarization beam splitting device proposed in the present invention achieves broadband polarization beam splitting while significantly reducing its size to 58.8μm².

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A photonic crystal polarization beam splitting device based on complementary defect modes, characterized in that: In a triangular lattice air ring photonic crystal with a germanium background and a tellurium core, an input waveguide, a symmetrical V-shaped branch waveguide, and two output waveguides are formed in sequence by removing part of the air ring; a controllable tellurium dielectric column and a controllable air hole are introduced into the upper and lower branches of the V-shaped branch waveguide, respectively; and a controllable air ring is introduced at the junction of the input waveguide and the V-shaped branch waveguide, as well as at the junction of the V-shaped branch waveguide and the two output waveguides.

2. The photonic crystal polarization beam splitting device based on complementary defect modes according to claim 1, characterized in that: The inner core material of the air rings on both sides of the upper branch of the V-shaped branch waveguide and the output waveguide connected thereto is replaced with germanium.

3. The photonic crystal polarization beam splitting device based on complementary defect modes according to claim 2, characterized in that: The radius of the controllable tellurium dielectric column introduced in the upper branch of the V-shaped branch waveguide is different.

4. The photonic crystal polarization beam splitting device based on complementary defect modes according to claim 2, characterized in that: The radius of the controllable tellurium air hole introduced in the lower branch of the V-shaped branch waveguide is different.

5. The photonic crystal polarization beam splitting device based on complementary defect modes according to claim 2, characterized in that: The inner and outer radii of the control air ring introduced at the intersection of the input waveguide and the V-shaped branch waveguide are different.

6. The photonic crystal polarization beam splitting device based on complementary defect modes according to claim 2, characterized in that: The inner and outer radii of the control air ring introduced at the intersection of the V-shaped branch waveguide and the two output waveguides are different.

7. A photonic crystal polarization beam splitting method, used in a photonic crystal polarization beam splitting device based on complementary defect modes according to any one of claims 1 to 6, characterized in that: A row of high-refractive-index dielectric columns is set in the upper branch of the V-shaped branch waveguide, so that the TE mode and TM mode fall into the forbidden band and defect mode respectively within the same operating frequency range. A row of air holes is set in the lower branch of the V-shaped branch waveguide, so that the TE mode and TM mode fall into the defect mode and forbidden band respectively within the same operating frequency range. A control air ring is introduced at the junction of the V-shaped branch waveguide and the input and output waveguides. The optimal beam splitting performance is achieved by optimizing the inner and outer radius parameters of the control air ring, the radius parameters of the dielectric columns, and the radius parameters of the air holes.

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