阅读说明：本技术 一种光波导模式转换器的制造方法及模式转换器 (Method for manufacturing optical waveguide mode converter and mode converter ) 是由 林天营 孙旭 汪军平 陈晓刚 胡朝阳 于 2021-03-15 设计创作，主要内容包括：本发明公开了一种光波导模式转换器的制造方法,选用一体化的波导体,波导体具有第一段、第二段以及第三段,根据要转换的高阶模阶数及模场对称性确定第一段和第三段的结构及相对位置,采用优化方法确定第二段的结构,第二段具有沿传播方向平滑缓变的特性,且第二段具有平滑的边缘。本发明还公开了一种模式转换器,采用上述光波导模式转换器的制造方法制成。所述光波导模式转换器的制造方法制造的模式转换器尺寸小、插入损耗低、转换利率高、带宽高,且所述光波导模式转换器的制造方法加工容忍度较好。(The invention discloses a manufacturing method of an optical waveguide mode converter, which selects an integrated waveguide body, wherein the waveguide body is provided with a first section, a second section and a third section, the structures and the relative positions of the first section and the third section are determined according to the higher-order mode order to be converted and the mode field symmetry, the structure of the second section is determined by adopting an optimization method, the second section has the characteristic of smooth and gradual change along the propagation direction, and the second section has a smooth edge. The invention also discloses a mode converter, which is manufactured by adopting the manufacturing method of the optical waveguide mode converter. The mode converter manufactured by the manufacturing method of the optical waveguide mode converter has the advantages of small size, low insertion loss, high conversion interest rate and high bandwidth, and the manufacturing method of the optical waveguide mode converter has better processing tolerance.)

1. A method of fabricating an optical waveguide mode converter, comprising the steps of:

(A) designing an integrated waveguide body, wherein the waveguide body is provided with a first section, a second section and a third section;

(B) determining the structures and relative positions of the first section and the third section according to the high-order mode order to be converted and the mode field symmetry;

(C1) equally dividing the second section into n-1 sections along the propagation direction, wherein 2n equally dividing points are formed at the edge of the second section;

(C2) optimizing the position of the uniform division point and the length of the second section along the propagation direction by adopting an optimization algorithm; wherein, the optimization algorithm is one of a heuristic optimization algorithm or a function approximation/approximation algorithm;

(C3) expanding the rest parts except 2n equipartition points on the edge of the second section in an interpolation mode with curve characteristics to enable the second section to have a smooth edge, determining the structure of the second section and finishing the structural design of the waveguide body;

(D) taking the substrate, and disposing the waveguide designed in the step (C3) on the substrate to form the mode converter.

2. The method of manufacturing an optical waveguide mode converter according to claim 1, wherein the division points optimized in the step (C2) are 2n-4 division points in the middle of the second segment.

3. The method of manufacturing an optical waveguide mode converter according to claim 1, wherein in the step (C2), an optimization algorithm is used to construct a mapping relationship between the position and the waveguide length of each division point and the mode conversion rate, and a parameter with the maximum conversion efficiency is determined, thereby determining the position and the waveguide length of each division point.

4. The method of manufacturing an optical waveguide mode converter according to claim 1, wherein the step (B) specifically includes the steps of:

(B1) determining widths of the first section and the third section according to waveguide widths supporting a fundamental mode and supporting a higher-order mode to be converted;

(B2) the relative positions of the first and third segments are determined based on the symmetry of the mode field distribution of the fundamental mode and the higher order modes to be converted.

5. The method of manufacturing an optical waveguide mode converter according to claim 1, wherein in the step (a), when the fundamental mode light is incident through the first section, the second section converts the fundamental mode light input from the first section into a higher-order mode light wave and outputs the higher-order mode light wave through the third section; when the high-order mode light enters from the third section, the second section converts the high-order mode light into the fundamental mode light and outputs the fundamental mode light through the first section.

6. The method of manufacturing an optical waveguide mode converter according to claim 1, wherein the first and third sections in step (a) are strip waveguides and the second section is a transition waveguide having smooth curve features at its edges.

7. A mode converter produced by the method for producing an optical waveguide mode converter according to any one of claims 1 to 6.

Technical Field

The present invention relates to the field of optical communication technology, and more particularly, to a method for manufacturing an optical waveguide mode converter and a mode converter.

Background

With the rapid development of information technology, the demand of the global optical communication market for bandwidth is more and more urgent. At present, the bandwidth is promoted mainly by the following three schemes: 1. improving the single-channel transmission rate; 2. the transmission channel is promoted; 3. wavelength Division Multiplexing (WDM) or Mode Division Multiplexing (MDM) techniques. For the above schemes 1 and 2, the increase of the rate and the increase of the transmission channel inevitably bring about the increase of the cost and the increase of the technical complexity, and do not meet the market demand. In the scheme 3, the mode division multiplexing technology is a technology for simultaneously transmitting multiple modes by using a single few-mode optical fiber, and compared with the wavelength division multiplexing technology, the mode division multiplexing technology has the advantages that laser light sources with different wavelengths are not needed, so that a complex wavelength stabilizing system is not needed, and the cost and the power consumption of the whole system can be effectively reduced.

In the analog-to-digital multiplexing system, a mode converter is a key device for realizing conversion between different modes, and the prior art routes for realizing the mode converter can be mainly divided into three categories: the phase matching, coherent scattering and beam shaping are carried out, and the specific structure comprises asymmetric Bragg light, a conical directional coupler, an asymmetric Y junction, a Mach-Zehnder interferometer and the like. The mode conversion device designed by adopting the structure is large in size generally, and is not beneficial to large-scale integration of silicon-based photons. The principle of the asymmetric bragg grating is to compensate the propagation constant difference between two modes by using a grating structure, so that the two modes are phase-matched. However, the grating structure requires a long propagation length under weak coupling, the size of the mode converter cannot be controlled, the energy between the waveguides cannot be completely transferred under strong coupling, and the conversion efficiency of the mode converter cannot be improved well. Directional coupler based devices are quite sensitive to machining errors in the waveguide gap. The device based on the Mach-Zehnder interferometer and the multi-channel branch waveguide has higher requirements on photoetching and etching precision.

In view of the above, there is a need in the art for a method of manufacturing a small-sized, low insertion loss, high conversion rate, high bandwidth mode converter while ensuring that the method is process tolerant.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a method for manufacturing an optical waveguide mode converter, wherein an integrated waveguide is selected, the waveguide has a first segment, a second segment and a third segment, the structures and relative positions of the first segment and the third segment are determined according to the higher-order mode number and mode field symmetry to be converted, the structure of the second segment is determined by an optimization method, the second segment has a characteristic of smooth and gradual change along a propagation direction, and the second segment has a smooth edge.

It is another object of the present invention to provide a mode converter fabricated by the above method of fabricating an optical waveguide mode converter.

In order to achieve the above object, the present invention provides a method of manufacturing an optical waveguide mode converter, comprising the steps of:

(A) designing an integrated waveguide body, wherein the waveguide body is provided with a first section, a second section and a third section;

(B) determining the structures and relative positions of the first section and the third section according to the high-order mode order to be converted and the mode field symmetry;

(C1) equally dividing the second section into n-1 sections along the propagation direction, wherein 2n equally dividing points are formed at the edge of the second section;

(C2) optimizing the position of the uniform division point and the length of the second section along the propagation direction by adopting an optimization algorithm; wherein, the optimization algorithm is one of a heuristic optimization algorithm or a function approximation/approximation algorithm;

(C3) expanding the rest parts except 2n equipartition points on the edge of the second section in an interpolation mode with curve characteristics to enable the second section to have a smooth edge, determining the structure of the second section and finishing the structural design of the waveguide body;

(D) taking the substrate, and disposing the waveguide designed in the step (C3) on the substrate to form the mode converter.

Preferably, the optimized bisection points in step (C2) are 2n-4 bisection points in the middle of the second segment.

Preferably, in the step (C2), an optimization algorithm is adopted to construct a mapping relationship between the position and the waveguide length of each division point and the mode conversion rate, and a parameter with the maximum conversion efficiency is determined, so as to determine the position and the waveguide length of each division point.

Preferably, the step (B) specifically includes the steps of:

(B1) determining widths of the first section and the third section according to waveguide widths supporting a fundamental mode and supporting a higher-order mode to be converted;

(B2) the relative positions of the first and third segments are determined based on the symmetry of the mode field distribution of the fundamental mode and the higher order modes to be converted.

Preferably, in the step (a), when the fundamental mode light enters through the first section, the second section converts the fundamental mode light input from the first section into a higher-order mode light wave, and outputs the higher-order mode light wave through the third section; when the high-order mode light enters from the third section, the second section converts the high-order mode light into the fundamental mode light and outputs the fundamental mode light through the first section.

Preferably, the first segment and the third segment in step (a) are strip waveguides, and the second segment is a transition waveguide with smooth curve characteristics at the edge.

The invention provides a mode converter, which is manufactured by adopting the manufacturing method of the optical waveguide mode converter.

Compared with the prior art, the optical waveguide mode converter disclosed by the invention has the advantages that: the mode converter manufactured by the manufacturing method of the optical waveguide mode converter is small in size, low in insertion loss, high in conversion interest rate and high in bandwidth, and the manufacturing method of the optical waveguide mode converter can maintain high mode conversion rate and is good in processing tolerance under the condition of a large processing error range.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a flow chart showing a method of manufacturing an optical waveguide mode converter according to the present invention.

Fig. 2 is a schematic structural diagram of a mode converter according to the present invention.

Fig. 3 shows a top view of a waveguide of a mode converter of the present invention.

Fig. 4 shows a top view of a waveguide of an embodiment of the mode converter of the invention.

Fig. 5 is a graph showing the relationship between the wavelength and the conversion efficiency of the time-based mode converted into the second-order mode and the second-order mode converted into the base mode according to an embodiment of the mode converter of the present invention.

Fig. 6 is a graph showing the relationship between the average conversion rate in the 1.5-1.6-micron wavelength band and the waveguide width processing error according to an embodiment of the mode converter of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a method for manufacturing an optical waveguide mode converter according to the present invention includes the steps of:

(A) designing an integrated waveguide body, wherein the waveguide body is provided with a first section serving as an input waveguide, a second section serving as a transition waveguide and a third section serving as an output waveguide;

(B) determining the structures and relative positions of the first section and the third section according to the high-order mode order to be converted and the mode field symmetry;

(C) determining the structure of a second section by adopting an optimization method, wherein the second section has a smooth edge, and the structural design of the waveguide is completed;

(D) and (C) taking a substrate, and arranging the waveguide designed in the step (C) on the substrate to manufacture the mode converter.

In the step (A), the integrated waveguide body is designed, so that the manufactured mode converter can be ensured to be small in size and more suitable for small-size and large-scale optical path integration.

In the step (A), the first section is used for transmitting input light waves, the second section is used for converting the fundamental mode light input by the first section into specific high-order mode light waves, and the third section is used for transmitting output light waves. It is to be noted that the mode converter manufactured by the method of manufacturing a waveguide mode converter is a reciprocal device, and therefore, if a specific high-order mode light is incident from the third section, the specific high-order mode light can be efficiently converted into a fundamental mode light through the second section and output through the first section.

The substrate in the step (D) can be made of silicon dioxide and the like, and the waveguide can be made of silicon, silicon nitride, silicon dioxide and the like.

Wherein, the step (B) comprises the following steps:

(B1) determining widths of the first section and the third section according to waveguide widths supporting a fundamental mode and supporting a higher-order mode to be converted;

(B2) the relative positions of the first and third segments are determined based on the symmetry of the mode field distribution of the fundamental mode and the higher order modes to be converted.

Wherein the first segment in step (a) is a single-mode or multi-mode waveguide, typically a single-mode waveguide, and the width of the first segment is limited by the width of the waveguide supporting fundamental mode light. The third segment is a multimode waveguide, the width of the third segment is limited by the width of the waveguide supporting the higher-order mode light to be converted, and its relative position to the first segment can be determined by the mode field symmetry of the mode to be converted. Since the mode field distribution of the fundamental mode light is even symmetric, the first and third sections are preferably centrally aligned when the optical mode field of the higher order modes is also even symmetric, in which way the optimized optical waveguide structure is relatively small in size.

Wherein, the step (C) comprises the following steps:

(C1) equally dividing the second section into n-1 sections along the propagation direction, wherein 2n equally dividing points are formed at the edge of the second section;

(C2) optimizing the position of the uniform division point and the length of the second section along the propagation direction by adopting an optimization algorithm;

(C3) and expanding the rest parts except 2n uniform points on the edge of the second section in an interpolation mode with curve characteristics to ensure that the second section has a smooth edge, determining the structure of the second section and finishing the structural design of the waveguide.

It is to be noted that the optimization algorithm in the step (C2) is one of heuristic optimization algorithms such as genetic algorithm, particle swarm optimization, ant colony optimization, simulated annealing algorithm, etc., and the optimization algorithm may also be one of function approximation/approximation algorithms such as linear programming, regression analysis, gradient descent, etc.

It should be noted that the averaging points optimized in step (C2) are 2n-4 averaging points in the middle of the second segment, because the 4 averaging points at the two ends of the second segment along the propagation direction are respectively butted with the first segment and the third segment, and the position is determined without optimization.

Specifically, in the step (C2), an optimization algorithm is adopted to construct a mapping relation between the position and waveguide length of each division point and the mode conversion rate, and a parameter with the maximum conversion efficiency is determined, so as to determine the position and waveguide length of each division point.

The interpolation method with the curve characteristic in the step (C3) includes polynomial interpolation, quadratic spline interpolation, cubic spline interpolation, lagrange polynomial interpolation, and the like. It should be noted that the interpolation method cannot be selected from a linear interpolation, which is a one-time spline interpolation, because the interpolation method cannot obtain a smooth curve edge. The second section as a transition waveguide has the characteristic of smooth gradual change through an interpolation mode with curve characteristics, and the mode converter with low insertion loss, high conversion rate, high bandwidth and good processing tolerance can be obtained through the design method.

Referring to fig. 2, the mode converter manufactured by the method of manufacturing an optical waveguide mode converter includes a substrate 10 and a waveguide 20, the waveguide 20 having a first section 21 as an input waveguide, a second section 22 as a transition waveguide, and a third section 23 as an output waveguide, wherein the first section 21 and the third section 23 are both strip waveguides, and the second section 22 is designed and manufactured by the method of manufacturing an optical waveguide mode converter.

Referring to fig. 3, the second segment 22 is equally divided into n-1 segments along the propagation direction, the edge of the second segment 22 has n groups (2 n) of averaging points (Xa 1 and Xb1, Xa2 and Xb2.. Xn1 and Xn 2), the structure of the second segment 22 can be determined by optimizing the positions and the widths of the n groups of averaging points, since the two groups of averaging points of Xa1 and Xb1 and Xn1 and Xn2 are respectively located at the ends of the first segment 21 and the third segment 23, the two groups of averaging points do not need to be optimized, the positions of the remaining 2n-4 averaging points need to be optimized actually, and the length of the second segment 22 and the positions of all the averaging points are determined after the optimization is performed by adopting a symmetric optimization method and the like. And then, the rest parts except 2n uniform points on the edge of the second section are expanded in an interpolation mode with curve characteristics, so that the second section has a smooth edge.

Referring to fig. 4, a mode converter according to an embodiment of the present invention is described in detail, in which a waveguide of the mode converter is made of silicon material and has a thickness of 0.22 μm. The substrate material was silicon dioxide and the substrate thickness was 3 microns. The width W0=0.5 μm of the first section 21 of the waveguide and the width W1=1.2 μm of the third section 23 of the waveguide. The high-order mode to be converted is a second-order mode, i.e., the second section 22 needs to implement a mode conversion function of converting the base mode into the second-order mode or converting the second-order mode into the base mode. Since the second order mode field is even symmetrically distributed, the relative positions of the third section 23 and the first section 21 are set to be centered alignment. Thereafter, the second segment 22 is divided equally into 10 segments, and the number of division points to be determined is 18. Since the mode field distribution of the higher-order mode is even symmetric, the third section 23 and the first section 21 are aligned in the center, the second section 22 selects a symmetric optimization mode, the parameters to be optimized are the length L of the second section graded waveguide in fig. 4 and the 10 width parameters p1 to p9, and the optimized structural parameters are shown in table 1. The width of each location in second segment 22 is then determined by means of cubic spline interpolation.

Fig. 5 shows the conversion efficiency of the embodiment of the mode converter in the 1.5 micron to 1.6 micron wavelength band. As can be seen from fig. 5, the performance of the device is very superior whether the fundamental mode is converted into the second order mode or the second order mode is converted into the fundamental mode. Fig. 6 shows the relationship between the average conversion rate of the mode converter in the 1.5-1.6-micron band and the waveguide width processing error, and it can be seen that the conversion rate of the mode converter can be maintained at a relatively high level under a large processing error range.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.