CN115494587A - Realization method of curved multimode waveguide with cubic polynomial curve for MDM - Google Patents

Abstract

A method for realizing a curved multimode waveguide with a cubic polynomial curve for MDM, setting the overall shape of the waveguide to meet the curved shape of a cubic polynomial curve, the maximum curvature radius R _max of the curved part is not less than 10 μm and the minimum curvature radius R _min is not greater than 10 μm In order to avoid the obvious mode field mismatch at the junction of the curved waveguide and the straight waveguide and to make the curved waveguide meet the adiabatic gradient condition, it is then prepared by electron beam lithography system (EBL) and deep silicon etching. The curved waveguide of the invention occupies a small area and can realize insertion loss <0.11dB and intermode crosstalk value <-25dB.

Description

Realization method of curved multimode waveguide with cubic polynomial curve for MDM

technical field

The present invention relates to a technology in the field of silicon-based photonic devices, specifically a method for realizing a curved multimode waveguide with a cubic polynomial curve for MDM, the insertion loss of which can be less than 0.11dB, and the crosstalk between modes can be less than -25dB .

Background technique

Mode Division Multiplexing (MDM) carries multiple data channels through the orthogonal eigenmodes in multimode waveguides, and provides bandwidth density expansion for on-chip optical interconnects without increasing the number of waveguides and chip area. huge potential. MDM is a space-efficient method to increase interconnect bandwidth, but multimode curved waveguides will produce significant inter-mode crosstalk introduced by bending, and curved waveguides are important components to change the propagation direction of light to achieve compact and flexible on-chip signal paths .

Existing MDM technologies include reducing mode mismatch by gradually changing the height of the curved waveguide, and step-tapered mode converters for compact curved waveguides that support the two lowest-order modes, but these existing technologies often require special The manufacturing process, such as the support of grayscale lithography, is difficult to realize the bending of multimode waveguides with more than two high-order modes, and it is difficult to meet the industrial needs of the adiabatic slow change performance.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention proposes a method for realizing a curved multimode waveguide of a cubic polynomial curve for MDM. The curved waveguide occupies a small area and has very low insertion loss and intermode crosstalk.

The present invention is achieved through the following technical solutions:

The invention relates to a method for realizing the curved multimode waveguide of the cubic polynomial curve used in MDM. The overall shape of the waveguide is set to meet the curved shape of the cubic polynomial curve, and the maximum curvature radius R _max of the curved part is not less than 10 μm and the minimum curvature radius R _min No more than 10 μm, to avoid obvious mode field mismatch at the junction of the curved waveguide and the straight waveguide and to make the curved waveguide meet the adiabatic gradient condition, and then prepared by electron beam lithography system (EBL) and deep silicon etching .

其中：x和y的单位均为μm，C为三次抛物线参数，它越大缓和曲线越缓。The cubic polynomial curve is

Where: the units of x and y are both μm, C is a cubic parabola parameter, the larger it is, the gentler the relaxation curve.

The curved multimode waveguide includes: a 90° curved multimode waveguide with low loss and low crosstalk based on a cubic polynomial curve and a 180° curved multimode waveguide with low loss and low crosstalk based on a cubic polynomial curve, wherein: the 90° curved multimode waveguide is specifically It includes two 45° curved waveguides with the same structure based on cubic polynomial curves, which are realized by splicing; 180° curved multimode waveguides include: curved waveguides with the same structure based on cubic polynomial curves at the upper and lower ends and a curved waveguide in the middle Arc waveguide, the three are sequentially spliced to achieve.

The low loss refers to: when the simulated input signals are in different modes, the insertion loss of the signal output by the 90° curved multimode waveguide is <0.17dB, the crosstalk between the modes is <-30dB, and the insertion loss of the output signal of the 180° curved multimode waveguide Loss <0.17dB, crosstalk between modes <-25dB.

technical effect

The invention adopts a simple cubic polynomial curve to realize waveguide design, and solves the defects of complex design in the prior art as a whole.

Description of drawings

Figure 1 is a structural diagram of a 90° curved multimode waveguide;

Figure 2 is a structural diagram of a 180° curved multimode waveguide;

Fig. 3 is a schematic diagram of curve curvature variation;

Fig. 4 and Fig. 5 are embodiment effect schematic diagrams;

In Fig. 4: (a) When the input signal mode is TE ₀ , the insertion loss and intermode crosstalk of the 90° bend multimode waveguide; (b) when the input signal mode is TE ₁ , the insertion loss of the 90° bend multimode waveguide and inter-mode crosstalk values; (c) when the input signal mode is TE ₂ , the insertion loss and inter-mode crosstalk values of the 90°bent multimode waveguide;

In Figure 5: (a) is when the input signal mode is TE ₀ , the 180° bending multimode waveguide insertion loss and intermode crosstalk values; (b) when the input signal mode is TE ₁ , the 180° bending multimode waveguide insertion loss Loss and intermode crosstalk values; (c) When the input signal mode is TE ₂ , the insertion loss and intermode crosstalk values of 180°bent multimode waveguide.

detailed description

As shown in Figure 1, this embodiment relates to a structural diagram of a 90° curved multimode waveguide constructed based on a cubic polynomial function, the 90° curved waveguide is symmetrically constructed by two 45° curved waveguides with identical structures, where : The 45° curved waveguide is constructed with a cubic polynomial curve, and the curve parameter C is set to 374.26. The width of the waveguide is set to 1.6 μm, the height of the waveguide is set to 220 nm, the waveguide is a silicon waveguide, and is coated with silicon dioxide. R _eff =36.5 μm, the device is very compact.

As shown in FIG. 2 , it is a structural diagram of a 180° curved multimode waveguide constructed based on a cubic polynomial function in this embodiment. The waveguide includes: two sections of cubic polynomial curved curved waveguides with the same structure and a circular arc waveguide, Wherein: the C of the cubic polynomial curve is still set to 374.26, the waveguide width is set to 1.6 μm, the waveguide height is set to 220nm, and the silicon dioxide is coated.

As shown in Figure 1 and Figure 2, a Cartesian coordinate system is established for the 90° curved multimode waveguide and the 180° curved multimode waveguide to specifically characterize the geometric parameters of the device. The origin is located at the bottom left end of the structure, and the horizontal direction is represented by the coordinate x , and the longitudinal direction is represented by the coordinate y.

得到该曲线的曲率半径特性函数。其中：y’表示y对x的一次导数，y”表示y对x的二次导数。For the cubic polynomial curve, use the formula for calculating the radius of curvature:

The radius of curvature characteristic function of the curve is obtained. Among them: y' represents the first derivative of y to x, and y" represents the second derivative of y to x.

As shown in FIG. 3 , the radius of curvature of the cubic polynomial curve has a minimum value. This embodiment calculates that when x=18.2960pm, the minimum radius of curvature R _min =26.8897 μm is obtained, and x is intercepted to belong to [0, 18.2960] as the lower half of the curved waveguide, and then the curved waveguide is constructed with R _min as the waveguide In the middle section, a curved waveguide exactly the same as the lower section is connected as the upper section. The size of the waveguide along the x-axis direction is 35 μm, and the size along the y-axis is 55 μm, which occupies a small area.

设为1.445。The 90° curved multimode waveguide and the 180° curved multimode waveguide are respectively simulated using LumericalFDTD simulation software, the wavelength range of the light source is set to 1.5 μm to 1.6 μm, and the shape parameters such as curve parameter C and waveguide width are set as above As stated, the refractive index n _Si of silicon is set to 3.455, and the refractive index of silicon dioxide

Set to 1.445.

The simulation can obtain the specific situation of light transmission in the waveguide, including key parameters such as insertion loss and crosstalk between modes.

As shown in Figure 4(a), when the input signal mode is TE ₀ , the insertion loss of the 90° curved multimode waveguide is <0.11dB and the crosstalk between modes is <-32dB.

As shown in Figure 4(b), when the input signal mode is TE ₁ , the insertion loss of the 90° curved multimode waveguide is <0.17dB and the crosstalk between modes is <-32dB.

As shown in Figure 4(c), when the input signal mode is TE ₂ , the insertion loss of the 90° curved multimode waveguide is <0.15dB and the crosstalk between modes is <-30dB.

As shown in Figure 5(a), when the input signal mode is TE ₀ , the insertion loss of the 180° curved multimode waveguide is <0.17dB and the crosstalk between modes is <-25dB.

As shown in Figure 5(b), when the input signal mode is TE ₁ , the insertion loss of the 180° curved multimode waveguide is <0.11dB and the crosstalk between modes is <-25dB.

As shown in Figure 5(c), when the input signal mode is TE ₂ , the insertion loss of the 180° curved multimode waveguide is <0.11dB and the crosstalk between modes is <-25dB.

Compared with the prior art, the device uses a cubic polynomial curve to construct the curved multimode waveguide, and compared with the previous construction using Bezier curves or Euler curves, the construction method is simpler. In addition, the device has very low insertion loss and intermode crosstalk over a broadband range of 100nm centered at 1550nm. Most importantly, it can be fabricated on an SOI platform with a CMOS-compatible process, and the proposed multimode waveguide bend can be applied in mode-division multiplexing technology as an important element to realize a compact and flexible on-chip signal path.

The above specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The scope of protection of the present invention is subject to the claims and is not limited by the above specific implementation. Each implementation within the scope is bound by the invention.

Claims (4)

1. A method for realizing the curved multimode waveguide of the cubic polynomial curve for MDM, characterized in that the overall shape of the waveguide is set to meet the curved shape of the cubic polynomial curve, the maximum radius of curvature R _max of the curved part is not less than 10 μm and the minimum curvature The radius R _min is not greater than 10 μm to avoid obvious mode field mismatch at the junction of the curved waveguide and the straight waveguide and to make the curved waveguide meet the adiabatic gradient condition, and then through the electron beam lithography system (EBL) and deep silicon etching prepared in a manner; The cubic polynomial curve is

Where: the units of x and y are both μm, and C is a cubic parabola parameter. 2. The method for realizing the curved multimode waveguide of the cubic polynomial curve for MDM according to claim 1, wherein the curved multimode waveguide comprises: a 90° bend with low loss and low crosstalk based on the cubic polynomial curve Multimode waveguide and low loss and low crosstalk 180° curved multimode waveguide based on cubic polynomial curve, among which: 90° curved multimode waveguide specifically includes two 45° curved waveguides with the same structure based on cubic polynomial curve, and the two are spliced together Realization; the 180° curved multimode waveguide includes: the curved waveguide based on the cubic polynomial curve with the same structure at the upper and lower ends and the arc waveguide in the middle, and the three are sequentially spliced to achieve. 3. The method for realizing the curved multimode waveguide of the cubic polynomial curve for MDM according to claim 1 or 2, characterized in that, the parameter C of the cubic parabola is 374.26. 4. the method for realizing the curved multimode waveguide used for the cubic polynomial curve of MDM according to claim 2 is characterized in that, the Cartesian coordinate system is established for 90 ° curved multimode waveguide and 180 ° curved multimode waveguide respectively, to Specifically characterize the geometric parameters of the device, where the origin is located at the lower left end of the structure, the horizontal coordinate is represented by x, and the vertical coordinate is represented by y; corresponding to the cubic polynomial curve, the calculation formula of the radius of curvature is used:

Obtain the curvature radius characteristic function of the curve, wherein: y' represents the first derivative of y to x, and y" represents the second derivative of y to x, and when x=18.2960 μm, the minimum curvature radius R _min =26.8897 μm is calculated , intercepting x belongs to [0,18.2960] as the lower half of the curved waveguide, then constructing the curved waveguide with R _min as the middle section of the waveguide, and then connecting a curved waveguide exactly the same as the lower half as the upper half, The dimension of the waveguide is 35 μm along the x-axis and 55 μm along the reverse direction of the y-axis, occupying a small area.

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