A rhombus-shaped hybrid one-dimensional photonic crystal nanobeam microcavity structure

Abstract

The present invention discloses a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, comprising: a waveguide, a rhombus air hole and a circular air hole; the rhombus air holes and the circular air holes are respectively arranged periodically on a waveguide with a rectangular cross section, and the circular air holes are symmetrically arranged on both sides of the rhombus air hole, forming a microcavity structure with line defects on the waveguide, wherein the line defects include: a tapered gradient area and a mirror area, the tapered gradient area includes: a rhombus air hole with a gradient radius, and the mirror area includes: a circular air hole with a constant radius, and the rhombus air holes in the tapered gradient area are symmetrically arranged along the center line of the waveguide. The present invention proposes a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, which has a small size, stable performance, and higher Q values and lower mode volumes V .

Description

Technical Field

[0001] The invention discloses a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, and relates to the technical field of optical devices. Background Art

[0002] Photonic crystals are artificially made, extremely small, periodic microstructures composed of media with different refractive indices. Depending on the dimensions of the periodic arrangement of their dielectric constants, photonic crystals can be divided into three types: one-dimensional photonic crystals, two-dimensional photonic crystals, and three-dimensional photonic crystals.

[0003] A one-dimensional photonic crystal is the simplest type of photonic crystal. It is made of overlapping layers of materials with different dielectric constants. In the direction perpendicular to the plane of the dielectric layer, the dielectric function is a periodic function of spatial position, while in the other two directions parallel to the dielectric layer, the dielectric function does not vary with spatial position. In this structure, its defect states can localize the energy of light.

[0004] A photonic crystal nanobeam cavity is a typical photonic crystal microcavity. It disrupts the periodicity of the original structure by artificially introducing defects into a one-dimensional photonic crystal. This allows light of a specific frequency (often called the resonant frequency) that would otherwise be unable to propagate in the bandgap to pass through the photonic crystal, thus forming a so-called resonant cavity structure. The quality factor (Q) and mode volume (V) are two important indicators of photonic crystal performance.

[0005] However, it is difficult for existing technologies to simultaneously meet the requirements of high quality factor Q and low mode volume V. For example, the slit-type one-dimensional photonic crystal nanobeam microcavity proposed by Judson D. Ryckman and S.M. Weiss [3] has a very small mode volume, but the quality factor Q is low, only 10 4 Level. Yiyang Gong and Jelena [4] The mode volume of the one-dimensional photonic crystal nanobeam microcavity with a rectangular dielectric hole is large, which is 2.0 (λ / n) 3 , the Q value is only 16000. Summary of the Invention

[0006] In view of the defects in the above-mentioned background technology, the present invention provides a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure with delicate structure and stable performance.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, comprising: a waveguide, a rhombus air hole and a circular air hole; the rhombus air holes and the circular air holes are respectively arranged periodically on a waveguide with a rectangular cross-section, and the circular air holes are symmetrically arranged on both sides of the rhombus air hole, forming a microcavity structure with a line defect on the waveguide.

[0008] Furthermore, the line defects include: a tapered gradient zone and a mirror zone, the tapered gradient zone includes: a diamond-shaped air hole with a gradient radius, and the mirror zone includes: a circular air hole with a constant radius. The diamond air holes in the tapered gradient zone are symmetrically arranged along the center line of the waveguide. The diamond air holes have better sealing properties, making the light energy more concentrated, and the light field is highly concentrated in the middle position of the waveguide; a section of circular air holes installed at both ends of the waveguide serves as a distributed Bragg reflector (DBR), and the DBR is a highly reflective film composed of alternating high and low refractive index materials, which can reflect light energy; adding DBRs at both ends of the waveguide helps to reduce waveguide coupling consumption and form reflections, so that more light energy is stored in the waveguide, thereby improving the quality factor.

[0009] Furthermore, the radius of the rhombus-shaped air holes in the tapered gradient zone increases from the middle to both sides, and the radius of the rhombus-shaped air holes changes in a parabolic shape, which significantly reduces radiation loss and thus greatly improves the quality factor Q of the one-dimensional photonic crystal.

[0010] Furthermore, the radius gradient function of the diamond-shaped air hole is:

[0011] R i =R c +(R e -R c )*(i-1) 2 / (M-1) 2

[0012] Where: i is the i-th diamond air hole arranged in sequence from the center line of the waveguide to both sides, i = [1, M]; M is the total number of diamond air holes on one side, 2M is the total number of diamond air holes, R c R is the radius of the diamond-shaped air hole closest to the center line. e R is the radius of the outermost diamond air hole on the center line, i is the radius of the i-th diamond air hole.

[0013] Furthermore, the lattice constant a of the tapered gradient region k It gradually increases from the middle to the edges on both sides, according to the arithmetic function a k The maximum lattice constant of the diamond-shaped air hole in the tapered gradient area is set to be equal to the lattice constant of the circular center air hole in the mirror area.

[0014] a k =283.5+23.25*k;

[0015] Among them: a krepresents the lattice constant between the kth diamond air hole and the k+1th diamond air hole arranged to one side from the center line of the waveguide, k represents the kth diamond air hole starting from the center line of the waveguide to one side, k == [1, M-1], and 2M is the total number of diamond air holes.

[0016] Furthermore, the maximum lattice constant a of the circular air hole max =λ0 / 2n eff ,

[0017] Height of the waveguide: 0.5a max ≤H≤1.2a max ,

[0018] Width of the waveguide: 1.1a max ≤W≤2.5a max ,

[0019] The length of the waveguide: 2((2M+N-1)a max +R e )≤L

[0020] The total number of the diamond-shaped air holes: 2≤2M≤20

[0021] The total number of circular air holes: 2≤N≤50

[0022] Where: n eff is the effective refractive index of the waveguide, and λ0 is the target resonant wavelength of the microcavity structure.

[0023] Furthermore, the waveguide is made of silicon material.

[0024] A design method for a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure further comprises:

[0025] Determine the device operating wavelength λ0;

[0026] Determine the lattice constant a of the circular air hole in the mirror area max ;

[0027] Determine the device height H;

[0028] Set the device width W;

[0029] Determine the radius R of the central diamond hole c ;

[0030] Determine the radius R of the outermost air diamond hole e ;

[0031] The radius of the remaining diamond holes that form the tapered gradient area;

[0032] The lattice constant a of the diamond-shaped hole in the tapered gradient regionk

[0033] According to the actual requirements for quality factor Q and transmittance, the appropriate number of diamond holes is selected as 2M;

[0034] Determine the radius R of the circular hole e ;

[0035] The actual requirements for quality factor Q and transmittance are used to select the appropriate number of circular mirror holes N;

[0036] The total length L of the one-dimensional photonic crystal nanobeam microcavity is determined according to the number and size of the designed holes.

[0037] Beneficial effects:

[0038] 1. The present invention proposes a structure in which diamond-shaped air holes serve as the gradient zone and circular holes serve as the mirror zone. This hybrid structure can bring better properties to photonic crystals: greater stability and lower optical loss. The diamond-shaped air hole structure is unique in that light energy is primarily concentrated at the tips of the diamonds. Compared to commonly used circular air holes, diamond-shaped air holes have better sealing properties, resulting in more concentrated light energy. As can be seen from the electric field diagram, the light field is highly concentrated in the middle, i.e., the diamond-shaped portion, resulting in a very small mode volume.

[0039] 2. The method for designing a photonic crystal microcavity of the present invention is simple and easy to implement; this application adopts a deterministic design method to design a high-Q one-dimensional photonic crystal waveguide microcavity. This method is mainly based on band calculation and mode matching theory. The design process of this method is direct and does not require parameter scanning calculation based on trial methods. Therefore, the computing resource requirements are relatively low, and our pre-set target resonant wavelength can be obtained.

[0040] 3. The lattice constant of the tapered transition region of the photonic crystal of the present invention is gradually changing. The lattice constant in the tapered transition region gradually increases from the center to the sides according to an arithmetic function. This design forms an optical potential well, concentrating a large amount of light energy, thereby significantly reducing the mode volume and increasing the quality factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a top view of the rhombus hybrid photonic crystal nanobeam microcavity structure;

[0042] Figure 2 This is the main view of the rhombus hybrid photonic crystal nanobeam microcavity structure;

[0043] Figure 3 This is the resonance distribution diagram of the rhombus hybrid photonic crystal nanobeam microcavity light field;

[0044] Figure 4 This is the resonance peak diagram of the rhombus hybrid photonic crystal nanobeam microcavity. DETAILED DESCRIPTION

[0045] The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are not intended to limit the scope of protection of the present invention.

[0046] like Figures 1 to 3 An embodiment shown is a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, comprising: a waveguide, a rhombus air hole and a circular air hole; the rhombus air holes and the circular air holes are periodically arranged on a waveguide with a rectangular cross-section, and the circular air holes are symmetrically arranged on both sides of the rhombus air hole to form a microcavity structure with a linear defect on the waveguide, and the waveguide is made of silicon material.

[0047] The line defects include: a tapered gradient zone and a mirror zone. The tapered gradient zone includes: diamond-shaped air holes with a gradient radius, and the mirror zone includes: circular air holes with a constant radius. The diamond-shaped air holes in the tapered gradient zone are symmetrically arranged along the center line of the waveguide. The diamond-shaped air holes have better sealing properties, making the light energy more concentrated, and the light field is highly concentrated in the middle position of the waveguide; a section of circular air holes installed at both ends of the waveguide serves as a distributed Bragg reflector (DBR). The DBR is a highly reflective film composed of alternating high and low refractive index materials that can reflect light energy; adding DBRs at both ends of the waveguide helps reduce waveguide coupling consumption and forms reflections, so that more light energy is stored in the waveguide, thereby improving the quality factor.

[0048] The radius of the rhombus-shaped air hole increases parabolically from the middle to both sides, which significantly reduces radiation loss and thus greatly improves the quality factor Q of the one-dimensional photonic crystal.

[0049] The radius gradient function of the diamond-shaped air hole is:

[0050] R i =R c +(R e -R c )*(i-1) 2 / (M-1) 2

[0051] Where: i is the i-th diamond air hole arranged in sequence from the center line of the waveguide to both sides, i = [1, M]; M is the total number of diamond air holes on one side, 2M is the total number of diamond air holes, R c R is the radius of the diamond-shaped air hole closest to the center line. e The radius of the outermost diamond-shaped air hole on the center line.

[0052] Lattice constant a of the tapered gradient region k The middle line gradually increases towards the edges on both sides, according to the arithmetic function ak set up,

[0053] a k =283.5+23.25*k;

[0054] Among them: a k represents the lattice constant between the kth diamond air hole and the k+1th diamond air hole arranged to one side from the center line of the waveguide, k represents the kth diamond air hole starting from the center line of the waveguide to one side, k == [1, M-1], and 2M is the total number of diamond air holes.

[0055] Furthermore, the maximum lattice constant a of the circular air hole max =λ0 / 2n eff ,

[0056] Height of the waveguide: 0.5a max ≤H≤1.2a max ,

[0057] Width of the waveguide: 1.1a max ≤W≤2.5a max ,

[0058] The length of the waveguide: 2((2M+N-1)a max +R e )≤L

[0059] The total number of the diamond-shaped air holes: 2≤2M≤20

[0060] The total number of circular air holes: 2≤N≤50

[0061] Where: n eff is the effective refractive index of the waveguide, and λ0 is the target resonant wavelength of the microcavity structure.

[0062] The design method of the above embodiment is as follows:

[0063] (1) First, the resonant wavelength of the designed device is determined. All devices of the present invention operate near the resonant wavelength λ0 = 1382 nm (about 216 THz).

[0064] (2) Determine the lattice constant a of the mirror area max : First, use the Bragg reflection condition a max =λ0 / 2n eff The maximum lattice constant a can be calculated max ; where 2n eff It represents the effective refractive index of the stable mode in the waveguide at the working wavelength. Since we use silicon as the waveguide material, the refractive index is substituted into the above formula to obtain a max =423nm. Then the lattice constant of the air holes in the mirror area is amax The lattice constant between the outermost diamond-shaped air hole and the adjacent diamond-shaped air hole in the tapered gradient area is also set to a max .

[0065] (3) Determine the device height H: The quality factor Q changes with the device height H. After a systematic simulation of the height of the microcavity, the height H was tested at 0.5a. max ~1.2a max The quality factor Q of the microcavity under the range is finally selected to have an equilibrium value H = 393.3nm. At this time, the microcavity has a higher quality factor and a relatively high transmittance.

[0066] (4) Set the width W of the nanobeam cavity: The larger the W is, the larger the proportion of the area occupied by the high refractive index material (silicon) in each period, thus having a higher effective refractive index; the high refractive index can reduce radiation loss and improve the quality factor of the microcavity, but too wide a waveguide will introduce high-order modes; therefore, after a systematic analysis, the width W of 1.1a was examined. max ~2.5a max The quality factor Q of the lower microcavity finally selects an equilibrium value W = 930.6nm. At this time, the microcavity has good quality and single-mode characteristics.

[0067] (5) Determine the radius R of the central diamond hole c :According to the target resonant wavelength λ0 and the mirror area lattice constant a max Calculate the energy band of the microcavity. In order to make the resonant wavelength of the microcavity close to the light wave, we take the radius of the circular hole in the central area R c =92.3342nm, ensuring that the edge of its dielectric band is near the target wavelength.

[0068] (6) Determine the radius R of the outermost air diamond hole e : Keeping the width W unchanged, the energy band under the edge circular hole radius is calculated so that it is exactly in the middle of the photon band gap. At this time, the defect mode can be confined to the center area of the microcavity to the greatest extent by the photon band gap effect on both sides, and R is calculated. e =118.14nm.

[0069] (7) Then, we start to construct the radius of the diamond hole part: the radius of the diamond hole between the central diamond hole and the outermost air diamond hole is constructed in a quadratic gradient manner. The radius gradient function is:

[0070] R i =R c +(R e -R c )*(i-1) 2 / (M-1) 2

[0071] Where: i is the i-th diamond air hole arranged in sequence from the center line of the waveguide to both sides, i = [1, M]; 2M is the total number of the first air holes, R c is the radius of the first air hole closest to the center line, R e is the radius of the first air hole on the outermost side of the center line.

[0072] The radius of the diamond-shaped air hole increases from the center to both sides. This design has a larger quality factor Q and a smaller mode volume V.

[0073] (8) The lattice constant a between the outermost diamond air hole in the tapered gradient zone and the adjacent diamond air hole max As the largest lattice constant a in the tapered gradient region M Then, the lattice constant a of the tapered gradient region is calculated according to the arithmetic function a k =283.5+23.25*k, gradually decreasing from the edges to the middle. k represents the lattice constant between the kth diamond air hole and the k+1th diamond air hole arranged to one side from the center line of the waveguide, k represents the distance between the kth diamond air hole and the adjacent diamond air hole starting from the center line of the waveguide to one side, k = [1, M-1], 2M is the total number of diamond air holes.

[0074] (9) Determine the number of diamond holes: According to the actual requirements for the quality factor Q and transmittance, select the appropriate number of gradient diamond air holes 2M: Perform a systematic simulation with 2M ranging from 2 to 20, and it is found that when 2M=14, a larger Q value is obtained.

[0075] (10) Determine the radius of the circular hole: Since the radius of the air holes in the mirror area is consistent, it can form a distributed Bragg reflector, which can increase the Q value. Therefore, the radius of the circular air holes in the mirror is R e .

[0076] (11) According to the actual requirements for quality factor Q and transmittance, the appropriate number of circular mirror holes N is selected: a systematic simulation is performed with N ranging from 2 to 50, and a larger Q value is obtained when N = 34.

[0077] (12) Finally, according to the number and size of the designed holes, the length of the microcavity is required to accommodate all the air holes, so the waveguide length L ≥ 2((2M+N-1)a max +R e ), and finally determined the total length of the one-dimensional photonic crystal nanobeam microcavity L = 20000nm.

[0078] like Figure 4As shown in the figure, after simulation calculation, the quality factor Q is as high as 135553, and the mode volume V is 0.139 (λ / n) 3 One-dimensional photonic crystal nanobeam microcavity; the electric field energy of this structure is mainly concentrated in the center of the cavity, and gradually decreases from the center to both sides; it contains two resonance peaks, respectively 205THZ and 216THZ.

[0079] The present invention proposes a rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure with small size, stable performance, higher Q value and lower mode volume V. 5 The quality factor Q of the level is as low as 10 -1 The smallest mode volume V.

[0080] 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 technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure, characterized in that: include: Waveguide, diamond-shaped air holes and circular air holes; the diamond-shaped air holes and circular air holes are periodically arranged on the waveguide with a rectangular cross section, and the circular air holes are symmetrically arranged on both sides of the diamond-shaped air holes, forming a microcavity structure with a line defect on the waveguide. The line defect includes: a tapered gradient area and a mirror area, and the tapered gradient area includes: The diamond-shaped air holes with a gradual radius, the mirror area includes: circular air holes with a constant radius, and the diamond-shaped air holes in the tapered gradual area are symmetrically arranged along the center line of the waveguide. The radius of the diamond-shaped air holes in the tapered gradient zone increases from the middle to both sides, and the radius of the diamond-shaped air holes changes in a parabolic shape. The radius gradient function of the diamond-shaped air hole is: R i =R c +(R e -R c )*(i-1) 2 / (M-1) 2 , Where: i is the i-th diamond air hole arranged in sequence from the center line of the waveguide to both sides, i = [1, M]; M is the total number of diamond air holes on one side, R c R is the radius of the diamond-shaped air hole closest to the center line. e R is the radius of the outermost diamond air hole on the center line, i is the radius of the i-th diamond air hole; Lattice constant a of the rhombus air hole in the tapered transition zone k It gradually increases from the middle to the edges on both sides, according to the arithmetic function a k The maximum lattice constant of the diamond-shaped air holes in the tapered gradient area is set to be equal to the lattice constant of the circular center air holes in the mirror area; a k =283.5+23.25*k; Among them: a k represents the lattice constant between the kth diamond air hole and the k+1th diamond air hole arranged to one side from the center line of the waveguide, k represents the kth diamond air hole starting from the center line of the waveguide to one side, k == [1, M-1], and 2M is the total number of diamond air holes.

2. The rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure according to claim 1, characterized in that: The maximum lattice constant a of a circular air hole max =λ0 / 2n eff , Height of the waveguide: 0.5a max ≤H≤1.2a max , Width of the waveguide: 1.1a max ≤W≤2.5a max , The length of the waveguide: 2((2M+N-1)a max +r e )≤L, The total number of the diamond-shaped air holes: 2≤2M≤20, The total number of the circular air holes: 2≤N≤50, Where: n eff is the effective refractive index of the waveguide, and λ0 is the target resonant wavelength of the microcavity structure.

3. The rhombus hybrid one-dimensional photonic crystal nanobeam microcavity structure according to claim 1, characterized in that: The waveguide is made of silicon material.

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