阅读说明：本技术 基于tm0模式光的马赫曾德尔干涉仪及制备方法 (Mach-Zehnder interferometer based on TM0 mode light and preparation method ) 是由 赵瑛璇 黄海阳 仇超 甘甫烷 盛振 于 2021-01-06 设计创作，主要内容包括：本发明提供一种基于TM0模式光的马赫曾德尔干涉仪及其制备方法,结构包括：输入波导、第一模式转换器、连接臂、第二模式转换器及输出波导,其中,第二模式转化器与第一模式转换器的结构相同,具有双层锥形结构。本发明实现无论输入端输入TM0模式的入射光还是TE1模式的输入光,连接臂包括直波导段,其输出端均可以输出TM0模式和TE1模式的出射光；可以有效解决现有技术存在的马赫曾德尔干涉仪对温度较为敏感、结构复杂、尺寸大等问题：可以实现与CMOS工艺兼容,便于批量化生产。(The invention provides a Mach-Zehnder interferometer based on TM0 mode light and a preparation method thereof, and the structure comprises: the waveguide comprises an input waveguide, a first mode converter, a connecting arm, a second mode converter and an output waveguide, wherein the second mode converter has the same structure as the first mode converter and has a double-layer conical structure. The invention realizes that no matter the input end inputs incident light in a TM0 mode or input light in a TE1 mode, the connecting arm comprises a straight waveguide section, and the output end of the connecting arm can output emergent light in a TM0 mode and a TE1 mode; the problems that the Mach-Zehnder interferometer in the prior art is sensitive to temperature, complex in structure, large in size and the like can be effectively solved: can realize the compatibility with the CMOS process and is convenient for batch production.)

1. A mach-zehnder interferometer based on TM0 mode light, the mach-zehnder interferometer comprising:

an input waveguide;

a first mode converter connected to the input waveguide, the first mode converter having a double-layer tapered structure;

the second mode converter is positioned on one side of the first mode converter, a distance is reserved between the second mode converter and the first mode converter, and the second mode converter and the first mode converter are identical in structure and are symmetrically arranged;

a link arm positioned between the first mode converter and the second mode converter, one end of the link arm being connected to the first mode converter and the other end of the link arm being connected to the second mode converter, the link arm including a straight waveguide segment;

an output waveguide connected to the second mode converter to output mixed mode output light comprising TM0 mode light.

2. A mach-zehnder interferometer based on TM0 mode light according to claim 1, characterized in that the first mode converter comprises: the first symmetrical transmission section, the second symmetrical transmission section and the third symmetrical transmission section are connected in sequence, wherein the first symmetrical transmission section is connected with the input waveguide, and the third symmetrical transmission section is connected with the connecting arm; the second mode converter includes: the fourth symmetrical transmission section, the fifth symmetrical transmission section and the sixth symmetrical transmission section are connected in sequence, wherein the fourth symmetrical transmission section is connected with the connecting arm, and the sixth symmetrical transmission section is connected with the output waveguide.

3. A mach-zehnder interferometer based on TM0 mode light according to claim 2, wherein the first symmetric transmission segment includes a first upper waveguide segment and a first lower waveguide segment positioned therebelow and symmetric thereabout; the second symmetric transmission segment includes a second upper waveguide segment and a second lower waveguide segment located therebelow and symmetric thereabout; the fifth symmetric transmission segment includes a fifth upper waveguide segment and a fifth lower waveguide segment below and symmetric about the fifth upper waveguide segment; the sixth symmetric transmission segment includes a sixth upper waveguide segment and a sixth lower waveguide segment below and symmetric with respect thereto to form the double-layered tapered structure.

4. A TM0 mode light based mach-zehnder interferometer according to claim 3, wherein a sum of thicknesses of the first lower waveguide segment and the first upper waveguide segment, a sum of thicknesses of the second lower waveguide segment and the second upper waveguide segment, and a thickness of the third symmetric transmission segment are equal; the thickness of the fourth symmetrical transmission section, the sum of the thicknesses of the fifth lower waveguide section and the fifth upper waveguide section, and the sum of the thicknesses of the sixth lower waveguide section and the sixth upper waveguide section are equal.

5. A mach-zehnder interferometer based on TM0 mode light according to claim 4, wherein the first upper waveguide segment and the first lower waveguide segment are equal in thickness, and the input waveguide has a thickness 2 times the thickness of the first upper waveguide; the second upper waveguide segment and the second lower waveguide segment are equal in thickness; the fifth upper waveguide segment and the fifth lower waveguide segment are equal in thickness; the sixth upper waveguide segment and the sixth lower waveguide segment have equal thicknesses.

6. A mach-zehnder interferometer based on TM0 mode light according to claim 3, wherein the first lower waveguide segment has a narrow end face and a wide end face, the first upper waveguide segment has a narrow end face and a wide end face, and the narrow end face of the first lower waveguide segment is equal in width to the narrow end face of the first upper waveguide segment, and the wide end face of the first lower waveguide segment is larger than each of two sides of the wide end face of the first upper waveguide segment by a predetermined distance; the second lower waveguide section is provided with a narrow end face and a wide end face, the second upper waveguide section is provided with a narrow end face and a wide end face, the width of the wide end face of the second lower waveguide section is equal to that of the wide end face of the first lower waveguide section, the width of the narrow end face of the second upper waveguide section is equal to that of the wide end face of the first upper waveguide section, and the width of the narrow end face of the second lower waveguide section is equal to that of the wide end face of the second upper waveguide section; the fifth lower waveguide section has a narrow end face and a wide end face, the fifth upper waveguide section has a narrow end face and a wide end face, and the width of the narrow end face of the fifth lower waveguide section is equal to the width of the wide end face of the fifth upper waveguide section; the sixth lower waveguide section is provided with a narrow end face and a wide end face, the sixth upper waveguide section is provided with a narrow end face and a wide end face, the narrow end face of the sixth lower waveguide section is equal to the narrow end face of the sixth upper waveguide section in width and is connected with the output waveguide, the width of the wide end face of the sixth lower waveguide section is equal to the width of the wide end face of the fifth lower waveguide section, and the wide end face of the sixth lower waveguide section is larger than the preset distance on two sides of the wide end face of the sixth upper waveguide section.

7. A mach-zehnder interferometer based on TM0 mode light according to claim 6, wherein a width of the input waveguide is 0.40 μm to 0.50 μm, a width of the narrow end face of the first upper waveguide is 0.40 μm to 0.50 μm, a width of the wide end face of the first upper waveguide section is 0.50 μm to 0.60 μm, the preset distance is 0.45 μm to 0.55 μm, a width of the wide end face of the second upper waveguide is 0.57 μm to 0.67 μm, and a width of the narrow end face of the third symmetric transmission section is 0.40 μm to 0.50 μm; the length of the first symmetrical transmission section is 28-29 μm, the length of the second symmetrical transmission section is 24-26 μm, and the length of the third symmetrical transmission section is 5-10 μm; the width of the straight waveguide section of the connecting arm is 0.40-0.50 μm, the width of the wide end face of the fifth upper waveguide is 0.57-0.67 μm, the width of the narrow end face of the fifth upper waveguide is 0.40-0.50 μm, the width of the wide end face of the sixth upper waveguide section is 0.50-0.60 μm, and the width of the narrow end face of the fourth symmetrical transmission section is 0.40-0.50 μm; the length of the sixth symmetrical transmission section is 28-29 μm, the length of the fifth symmetrical transmission section is 24-26 μm, and the length of the fourth symmetrical transmission section is 5-10 μm.

8. A mach-zehnder interferometer based on TM0 mode light according to claim 1, characterized in that the mach-zehnder interferometer comprises an SOI substrate comprising a bottom silicon layer, a buried oxide layer and a top silicon layer, the first mode converter, the connecting arm and the second mode converter being formed by etching the top silicon layer.

9. A mach-zehnder interferometer based on TM0 mode light according to claim 8, further comprising a protective layer on an upper surface of the buried oxide layer and completely covering the first mode converter, the connecting arm, and the second mode converter.

10. A mach-zehnder interferometer based on TM0 mode light according to claim 1, characterized in that the width of the straight waveguide section of the linking arm is 569 nm.

11. A mach-zehnder interferometer based on TM0 mode light according to any one of claims 1 to 10, characterized in that incident light of TM0 mode is input from the input waveguide section; in the first symmetric transmission segment, the effective refractive indexes of TM0 and TE1 are equal, and the TM0 mode is converted into the TE1 mode; in the second symmetric transmission segment, part of the TE1 mode light is converted back to TM0 mode light to obtain mixed mode light of TM0 and TE 1.

12. A method of fabricating a mach-zehnder interferometer based on TM0 mode light according to any of claims 1 to 11, comprising the steps of:

providing an SOI substrate, wherein the SOI substrate comprises a bottom silicon layer, a buried oxide layer and a top silicon layer;

and etching the top silicon layer to form the first mode converter, the connecting arm and the second mode converter.

Technical Field

The invention belongs to the technical field of optics, and particularly relates to a TM0 mode light-based Mach-Zehnder interferometer and a preparation method thereof.

Background

Mach Zehnder Interferometers (MZIs) are the fundamental optical devices widely used in modern optical fiber transmission systems. Because the silicon-based material has a large thermo-optic coefficient, the silicon-based Mach-Zehnder interferometer is generally sensitive to temperature, and in order to solve the problem, the conventional Mach-Zehnder interferometer generally adopts a double-connection-arm structure. However, the conventional method has problems such as a complicated structure and a large size, and particularly relates to a mach-zehnder interferometer based on TM0 mode light.

Therefore, how to effectively solve the problem that the mach-zehnder interferometer based on TM0 mode light in the prior art is sensitive to temperature is necessary.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a mach-zehnder interferometer for solving the problems of temperature sensitivity, complicated structure, large size, etc. of the mach-zehnder interferometer based on TM0 mode light in the prior art.

To achieve the above and other related objects, the present invention provides a mach-zehnder interferometer based on TM0 mode light, the mach-zehnder interferometer including:

an input waveguide;

a first mode converter connected to the input waveguide, the first mode converter having a double-layer tapered structure;

the second mode converter is positioned on one side of the first mode converter, a distance is reserved between the second mode converter and the first mode converter, and the second mode converter and the first mode converter are identical in structure and are symmetrically arranged;

a link arm positioned between the first mode converter and the second mode converter, one end of the link arm being connected to the first mode converter and the other end of the link arm being connected to the second mode converter, the link arm including a straight waveguide segment;

an output waveguide connected to the second mode converter to output mixed mode output light comprising TM0 mode light.

Optionally, the first mode converter comprises: the first symmetrical transmission section, the second symmetrical transmission section and the third symmetrical transmission section are connected in sequence, wherein the first symmetrical transmission section is connected with the input waveguide, and the third symmetrical transmission section is connected with the connecting arm; the second mode converter includes: the fourth symmetrical transmission section, the fifth symmetrical transmission section and the sixth symmetrical transmission section are connected in sequence, wherein the fourth symmetrical transmission section is connected with the connecting arm, and the sixth symmetrical transmission section is connected with the output waveguide.

Optionally, the first symmetric transmission segment comprises a first upper waveguide segment and a first lower waveguide segment below and symmetric with respect to the first upper waveguide segment, and the second symmetric transmission segment comprises a second upper waveguide segment and a second lower waveguide segment below and symmetric with respect to the second upper waveguide segment; the fifth symmetric transmission segment includes a fifth upper waveguide segment and a fifth lower waveguide segment below and symmetric with respect to the fifth upper waveguide segment, and the sixth symmetric transmission segment includes a sixth upper waveguide segment and a sixth lower waveguide segment below and symmetric with respect to the sixth upper waveguide segment, so as to constitute the double-layer tapered structure.

Optionally, a sum of thicknesses of the first lower waveguide segment and the first upper waveguide segment, a sum of thicknesses of the second lower waveguide segment and the second upper waveguide segment, and a thickness of the third symmetric transmission segment are equal; the thickness of the fourth symmetrical transmission segment, the sum of the thicknesses of the fifth lower waveguide segment and the fifth upper waveguide segment, and the sum of the thicknesses of the sixth lower waveguide segment and the sixth upper waveguide segment are equal.

Optionally, the first upper waveguide segment and the first lower waveguide segment are equal in thickness, and the input waveguide has a thickness 2 times the thickness of the first upper waveguide; the second upper waveguide segment and the second lower waveguide segment are equal in thickness; the fifth upper waveguide segment and the fifth lower waveguide segment are equal in thickness; the sixth upper waveguide segment and the sixth lower waveguide segment have equal thicknesses.

Optionally, the first lower waveguide segment has a narrow end face and a wide end face, the first upper waveguide segment has a narrow end face and a wide end face, the narrow end face of the first lower waveguide segment is equal in width to the narrow end face of the first upper waveguide segment, and the wide end face of the first lower waveguide segment is greater than the respective preset distance on both sides of the wide end face of the first upper waveguide segment; the second lower waveguide section is provided with a narrow end face and a wide end face, the second upper waveguide section is provided with a narrow end face and a wide end face, the width of the wide end face of the second lower waveguide section is equal to that of the wide end face of the first lower waveguide section, the width of the narrow end face of the second upper waveguide section is equal to that of the wide end face of the first upper waveguide section, and the width of the narrow end face of the second lower waveguide section is equal to that of the wide end face of the second upper waveguide section; the fifth lower waveguide section has a narrow end face and a wide end face, the fifth upper waveguide section has a narrow end face and a wide end face, and the width of the narrow end face of the fifth lower waveguide section is equal to the width of the wide end face of the fifth upper waveguide section; the sixth lower waveguide section is provided with a narrow end face and a wide end face, the sixth upper waveguide section is provided with a narrow end face and a wide end face, the narrow end face of the sixth lower waveguide section is equal to the narrow end face of the sixth upper waveguide section in width and is connected with the output waveguide, the width of the wide end face of the sixth lower waveguide section is equal to the width of the wide end face of the fifth lower waveguide section, and the wide end face of the sixth lower waveguide section is larger than the preset distance on two sides of the wide end face of the sixth upper waveguide section.

Optionally, the width of the input waveguide is 0.40 μm to 0.50 μm, the width of the narrow end face of the first upper waveguide is 0.40 μm to 0.50 μm, the width of the wide end face of the first upper waveguide section is 0.50 μm to 0.60 μm, the preset distance is 0.45 μm to 0.55 μm, the width of the wide end face of the second upper waveguide is 0.57 μm to 0.67 μm, and the width of the narrow end face of the third symmetric transmission section is 0.40 μm to 0.50 μm; the length of the first symmetrical transmission section is 28-29 μm, the length of the second symmetrical transmission section is 24-26 μm, and the length of the third symmetrical transmission section is 5-10 μm; the width of the straight waveguide section of the connecting arm is 0.40-0.50 μm, the width of the wide end face of the fifth upper waveguide is 0.57-0.67 μm, the width of the narrow end face of the fifth upper waveguide is 0.40-0.50 μm, the width of the wide end face of the sixth upper waveguide section is 0.50-0.60 μm, and the width of the narrow end face of the fourth symmetrical transmission section is 0.40-0.50 μm; the length of the fifth symmetrical transmission section is 24-26 μm, and the length of the fourth symmetrical transmission section is 5-10 μm.

Optionally, the mach-zehnder interferometer includes an SOI substrate including a bottom silicon layer, a buried oxide layer, and a top silicon layer, and the first mode converter, the connecting arm, and the second mode converter are formed by etching the top silicon layer.

Optionally, the mach-zehnder interferometer further includes a protective layer located on an upper surface of the buried oxide layer and completely covering the first mode converter, the connecting arm, and the second mode converter.

Optionally, the straight waveguide segment of the linking arm has a width of 569 nm.

Optionally, inputting incident light of TM0 mode from the input waveguide segment; in the first symmetric transmission segment, the effective refractive indexes of TM0 and TE1 are equal, and the TM0 mode is converted into the TE1 mode; in the second symmetric transmission segment, part of the TE1 mode light is converted back to TM0 mode light to obtain mixed mode light of TM0 and TE 1.

Further, the present invention provides a method for manufacturing a mach-zehnder interferometer based on TM0 mode light according to any one of the above aspects, including the steps of:

providing an SOI substrate, wherein the SOI substrate comprises a bottom silicon layer, a buried oxide layer and a top silicon layer;

and etching the top silicon layer to form the first mode converter, the connecting arm and the second mode converter.

As described above, the mach-zehnder interferometer based on TM0 mode light and the manufacturing method thereof of the present invention realize that no matter the input end inputs incident light in TM0 mode or input light in TE1 mode, the output end can output emergent light in TM0 mode and TE1 mode; the problems that the Mach-Zehnder interferometer in the prior art is sensitive to temperature, complex in structure, large in size and the like can be effectively solved: can realize the compatibility with the CMOS process and is convenient for batch production.

Drawings

FIGS. 1-2 show a schematic top view of a Mach-Zehnder interferometer according to the present invention; fig. 1 is a schematic view of the entire structure, and fig. 2 is a partially enlarged schematic view.

FIGS. 3-7 are schematic structural cross-sectional views obtained at various steps in the fabrication of a Mach-Zehnder interferometer according to the present invention.

FIG. 8 is a graph showing the width of a connecting arm in a Mach-Zehnder interferometer according to the present invention and the rate of change of the effective refractive index of different modes of incident light with respect to temperature.

FIG. 9 is a graph showing the wavelength of incident light and the input loss of a Mach-Zehnder interferometer according to the present invention at two different temperatures, 26.85 deg.C and 56.85 deg.C.

FIGS. 10-14 are schematic diagrams showing simulation results of overall performance of Mach-Zehnder interferometer devices provided in accordance with the present invention, wherein FIGS. 10-13 are graphs of input loss in different input-output modes; FIG. 14 is a schematic view of a simulated mode field of a device.

FIG. 15 is a schematic diagram showing an example of a Mach-Zehnder interferometer of the present invention having a ratio of TM0 to TE1 outputs of approximately 50: 50.

Description of the element reference numerals

11 input waveguide

12 first mode converter

121 first symmetric transmission segment

121a first upper waveguide segment

121b first lower waveguide segment

122 second symmetric transmission segment

122a second upper waveguide section

122b second lower waveguide section

123 third symmetrical transmission segment

13 connecting arm

14 second mode converter

15 output waveguide

201 bottom silicon layer

202 buried oxide layer

203 top silicon layer

204 etch mask layer

205 initial layer

206 upper waveguide segment layer

207 lower waveguide segment layer

208 protective layer

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

As in the detailed description of the embodiments of the present invention, the cross-sectional views illustrating the device structures are not partially enlarged in general scale for convenience of illustration, and the schematic views are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.

For convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. In addition, "between … …" as used herein includes both endpoints.

In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.

It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed freely, and the layout of the components may be more complicated.

As shown in fig. 1, the present invention provides a mach-zehnder interferometer based on TM0 mode light, the mach-zehnder interferometer including: an input waveguide 11, a first mode converter 12, a connecting arm 13, a second mode converter 14 and an output waveguide 15. Based on the design of the invention, the temperature insensitive Mach-Zehnder interferometer based on TM0 mode light can be obtained. The output end of the optical fiber can output emergent light of TM0 mode and TE1 mode no matter the input end inputs incident light of TM0 mode or input light of TE1 mode; two mode converters in the temperature insensitive Mach-Zehnder interferometer are connected through a connecting arm, and the temperature insensitive Mach-Zehnder interferometer is simple in structure and low in loss. Meanwhile, the interferometer can be compatible with a CMOS (complementary metal oxide semiconductor) process, and is convenient for batch production.

As shown in fig. 1 and 2, the input waveguide 11 may be a straight waveguide, having the same width throughout.

In addition, the interferometer of the present invention includes a first modal converter 12 and a second modal converter 14. In one example, both are identical double-layer tapered structures, symmetrically arranged about the central connecting arm 13 in the structure of the interferometer. The double-layer conical structure is characterized in that the converter structure comprises an upper material layer and a lower material layer, the two material layers have different parts, the two material layers continue to be transmitted to the connecting arm after receiving signals from the input waveguide, and the signals are output from the output waveguide through the converter symmetrically arranged in the same structure.

In one example, the first mode converter 12 specifically includes: the first symmetric transmission section 121, the second symmetric transmission section 122 and the third symmetric transmission section 123 are connected in sequence, one end (the first symmetric transmission section 121) of the first mode converter 12 is connected with the input waveguide 11, and the other end (the third symmetric transmission section 123) is connected with the connecting arm 13, as shown in fig. 2.

In addition, in an example, the second mode converter 14 specifically includes: a fourth symmetric transmission section, a fifth symmetric transmission section and a sixth symmetric transmission section, which are connected in sequence, one end (the sixth symmetric transmission section) of the second mode converter 14 is connected with the output waveguide 15, and the other end (the fourth symmetric transmission section) is connected with the connecting arm 13, as shown in the structure of fig. 1.

It should be noted that, the first mode converter 12 and the second mode converter 14 have the same structure and are symmetrically disposed, which means that the first symmetric transmission section of the first mode converter and the sixth symmetric transmission section of the second mode converter have the same structure and are symmetrically disposed, and the size of the first symmetric transmission section and the sixth symmetric transmission section of the second mode converter are the same. It is understood that the second mode converter is equivalent to a first mode converter which is rotated by 180 ° and then connected to the rear of the connecting arm 13.

As shown in fig. 2 and 6, by way of example, the first symmetric transmission segment 121 includes a first upper waveguide segment 121a and a first lower waveguide segment 121b located therebelow and symmetric thereto, and the second symmetric transmission segment 122 includes a second upper waveguide segment 122a and a second lower waveguide segment 122b located therebelow and symmetric thereto. It should be noted that, here, the symmetry is that the structural size of the lower waveguide is symmetrical with respect to both sides of the upper waveguide, the size of the first upper waveguide segment 121a changes symmetrically, for example, in an isosceles trapezoid structure, and further, the portion of the first lower waveguide segment 121b beyond the first upper waveguide segment 121a is distributed symmetrically on the upper and lower sides (actually, the left and right sides in the extending direction of the first upper waveguide segment) shown in the figure.

Similarly, referring to the second symmetric transmission section 122, the fifth symmetric transmission section includes a fifth upper waveguide section and a fifth lower waveguide section located therebelow and symmetric about thereto; referring to the first symmetric transmission segment 121, the sixth symmetric transmission segment includes a sixth upper waveguide segment and a sixth lower waveguide segment located therebelow and symmetric thereabout.

Based on the above design, the first mode converter and the second mode converter obtained by the present invention actually include an upper layer structure and a lower layer structure, which form a double-layer tapered structure, so as to be beneficial to adapt to the TM0 mode light, and are corresponding designs for the TM0 mode light, and since the effective refractive indexes of the TE0 mode and the TM0 mode are very different, different structures must be designed to complete transmission of different modes. In the double-sided taper mode, the symmetry of the cross section of the structure is broken, so that the effective refractive indexes of the TM0 mode and the TE1 mode are designed to be the same in the double-layer taper structure, and the conversion between the TM0 mode and the TE1 mode is realized based on the design.

As an example, the upper and lower waveguide segments of each symmetrical transmission segment of the present invention are formed based on the same material layer etching. Such that the sum of the thicknesses of the first lower waveguide segment 121b and the first upper waveguide segment 121a is the thickness of the layer of material; the sum of the thicknesses of the second lower waveguide segment 122b and the second upper waveguide segment 122a is the thickness of the layer of material; the thickness of the third symmetrical transmission segment 123 is the thickness of the layer of material, so that the upper surfaces of the three are flush. Likewise, it will be appreciated that the thickness of the fourth symmetric transport segment, the sum of the thicknesses of the fifth lower waveguide segment and the fifth upper waveguide segment, and the sum of the thicknesses of the sixth lower waveguide segment and the sixth upper waveguide segment are equal.

In one example, the thickness of the first upper waveguide segment is equal to that of the first lower waveguide segment, and in addition, the thickness of the input waveguide is 2 times that of the first upper waveguide segment, and the input waveguide 11 is also formed on the basis of the same material layer etching; similarly, it will be appreciated that the second upper waveguide segment and the second lower waveguide segment are of equal thickness; the fifth upper waveguide segment and the fifth lower waveguide segment are equal in thickness; the sixth upper waveguide segment and the sixth lower waveguide segment have equal thicknesses. The output waveguide 15 may be formed by etching the same material layer, and may have the same thickness as the input waveguide 11.

In a specific example, the thickness of the input waveguide is 200 nm and 240nm, which can be both end values or any value in the middle. As in this example 220 nm. Optionally, the thickness of the first upper waveguide segment 121a is 100-120nm, which is selected to be 110nm in this example, and is half of the thickness of the input waveguide, and meanwhile, the thickness of the corresponding first lower waveguide segment 121 may be 110 nm. Based on this, it is understood that the upper waveguide segment of each symmetric transmission segment may have the same chosen design for thickness as the first upper waveguide segment, and the lower waveguide segment of each symmetric transmission segment may have the same chosen design for thickness as the first lower waveguide segment. In addition, the third symmetrical transmission section and the fourth symmetrical transmission section are of a single-layer structure, and the thickness of the third symmetrical transmission section and the thickness of the fourth symmetrical transmission section are the same as that of the input waveguide.

As shown in fig. 2, by way of example, the first lower waveguide segment 121b has a narrow end face and a wide end face, the first upper waveguide segment 121a has a narrow end face and a wide end face, and the narrow end face of the first lower waveguide segment 121b is equal in width to the narrow end face of the first upper waveguide segment 121a, both W0; the wide end surface of the first lower waveguide section is larger than the preset distance Ws of the two sides of the wide end surface of the first upper waveguide section. In one example, the width of the input waveguide 11 is also W0.

The second lower waveguide segment 122b has a narrow end face and a wide end face, the second upper waveguide segment 122a has a narrow end face and a wide end face, the width of the wide end face of the second lower waveguide segment 122b is equal to the width of the wide end face of the first lower waveguide segment 121b, the width of the narrow end face of the second upper waveguide segment 122a is equal to the width of the wide end face of the first upper waveguide segment 121a, W1 is the same, and the width of the narrow end face of the second lower waveguide segment 122b is equal to the width of the wide end face of the second upper waveguide segment 122a, W2 is the same.

The third symmetric transmission section 123 has a narrow end face and a wide end face, and the wide end face of the third symmetric transmission section is equal to the wide end face width W2 of the second upper waveguide section 122 a. In addition, in one example, the connecting arm 13 is formed of only straight waveguide segments, including a multimode waveguide having a width equal to the width W3 of the narrow end face of the third symmetric transmission segment 123.

Similarly, it is understood that the fifth symmetric transmission segment has the same design as the second symmetric transmission segment, the sixth symmetric transmission segment has the same design as the first symmetric transmission segment, and the fourth symmetric transmission segment has the same design as the third symmetric transmission segment. The fifth lower waveguide section has a narrow end face and a wide end face, the fifth upper waveguide section has a narrow end face and a wide end face, and the width of the narrow end face of the fifth lower waveguide section is equal to the width of the wide end face of the fifth upper waveguide section; the sixth lower waveguide section is provided with a narrow end face and a wide end face, the sixth upper waveguide section is provided with a narrow end face and a wide end face, the narrow end face of the sixth lower waveguide section is equal to the narrow end face of the sixth upper waveguide section in width and is connected with the output waveguide, the width of the wide end face of the sixth lower waveguide section is equal to the width of the wide end face of the fifth lower waveguide section, and the wide end face of the sixth lower waveguide section is larger than the preset distance on two sides of the wide end face of the sixth upper waveguide section.

Illustratively, the width W0 of the input waveguide is 0.40 μm to 0.50 μm, the width W0 of the narrow end face of the first upper waveguide is 0.40 μm to 0.50 μm, the width W1 of the wide end face of the first upper waveguide section is 0.50 μm to 0.60 μm, the preset distance Ws is 0.45 μm to 0.55 μm, the width W2 of the wide end face of the second upper waveguide is 0.57 μm to 0.67 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.40 μm to 0.50 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28 μm to 29 μm, the length Ltp2 of the second symmetric transmission segment 122 is 24 μm to 26 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 5 μm to 10 μm. In addition, the width W3 of the straight waveguide segment of the connecting arm 13 is 0.40 μm to 0.50 μm. Similarly, the width of the wide end face of the fifth upper waveguide is 0.57 μm to 0.67 μm, the width of the narrow end face of the fifth upper waveguide is 0.50 μm to 0.60 μm, the width of the wide end face of the sixth upper waveguide section is 0.50 μm to 0.60 μm, the width of the narrow end face of the sixth upper waveguide section is 0.40 μm to 0.50 μm, and the width of the narrow end face of the fourth symmetrical transmission section is 0.40 μm to 0.50 μm. In addition, the length of the sixth symmetrical transmission section is 28-29 μm, the length of the fifth symmetrical transmission section is 24-26 μm, and the length of the fourth symmetrical transmission section is 5-10 μm.

In addition, it should be noted that the size parameters need to have a one-to-one correspondence relationship within the above range, which is beneficial to the implementation of the mode conversion of the present invention. The following is illustrated with several examples: such as: in the first example, the width W0 of the input waveguide is 0.45 μm, the width W0 of the narrow end face of the first upper waveguide is 0.45 μm, the width W1 of the wide end face of the first upper waveguide section is 0.55 μm, the preset distance Ws is 0.5 μm, the width W2 of the wide end face of the second upper waveguide is 0.62 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.45 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28.5 μm, the length Ltp2 of the second symmetric transmission segment 122 is 24 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 5 μm. In a second example, the width W0 of the input waveguide is 0.41 μm, the width W0 of the narrow end face of the first upper waveguide is 0.41 μm, the width W1 of the wide end face of the first upper waveguide section is 0.51 μm, the preset distance Ws is 0.46 μm, the width W2 of the wide end face of the second upper waveguide is 0.58 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.41 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28.1 μm, the length Ltp2 of the second symmetric transmission segment 122 is 24.5 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 6 μm. In a third example, the width W0 of the input waveguide is 0.43 μm, the width W0 of the narrow end face of the first upper waveguide is 0.43 μm, the width W1 of the wide end face of the first upper waveguide section is 0.53 μm, the preset distance Ws is 0.48 μm, the width W2 of the wide end face of the second upper waveguide is 0.60 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.43 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28.3 μm, the length Ltp2 of the second symmetric transmission segment 122 is 25 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 7 μm. In a fourth example, the width W0 of the input waveguide is 0.47 μm, the width W0 of the narrow end face of the first upper waveguide is 0.47 μm, the width W1 of the wide end face of the first upper waveguide section is 0.57 μm, the preset distance Ws is 0.52 μm, the width W2 of the wide end face of the second upper waveguide is 0.64 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.47 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28.7 μm, the length Ltp2 of the second symmetric transmission segment 122 is 25.5 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 8 μm. In a fifth example, the width W0 of the input waveguide is 0.49 μm, the width W0 of the narrow end face of the first upper waveguide is 0.49 μm, the width W1 of the wide end face of the first upper waveguide section is 0.59 μm, the preset distance Ws is 0.54 μm, the width W2 of the wide end face of the second upper waveguide is 0.66 μm, and the width W3 of the narrow end face of the third symmetric transmission section is 0.47 μm. In addition, the length Ltp1 of the first symmetric transmission segment 121 is 28.9 μm, the length Ltp2 of the second symmetric transmission segment 122 is 26 μm, and the length Ltp3 of the third symmetric transmission segment 123 is 10 μm.

As an example, the mach-zehnder interferometer includes an SOI substrate including a bottom silicon layer 201, a buried oxide layer 202, and a top silicon layer, and the first mode converter 12, the connecting arm 13, and the second mode converter 14 are formed by etching the top silicon layer. The upper waveguide segment layer 206 and the lower waveguide segment layer 207, which are symmetrically transmitted, are formed by two etching processes, that is, each upper waveguide segment may be considered to form the upper waveguide segment layer 206, and each lower waveguide segment may be considered to form the lower waveguide segment layer 207, which may be specifically shown in fig. 3 to 6. The first mode converter, the connecting arm and the second mode converter in the temperature insensitive Mach-Zehnder interferometer based on the Y-branch symmetrical structure are prepared based on the SOI substrate, and because the thermo-optic coefficient of silicon in the SOI substrate is very large (can reach 1.86 multiplied by 10-4RIU/K, wherein RIU is a refractive index unit), the considerable wavelength drift (about 80pm/K) changing along with the temperature can be caused, and on the basis, the insensitivity to the temperature can be realized by setting parameters such as the width and the thickness of the connecting arm; meanwhile, the temperature insensitive Mach-Zehnder interferometer can be compatible with a CMOS process, and is convenient for batch production. The two mode converters in the Mach-Zehnder interferometer are connected through a connecting arm, so that the Mach-Zehnder interferometer is simple in structure and low in loss. In addition, in an alternative example, the input waveguide and the output waveguide are also prepared based on the top silicon layer.

As an example, as shown in fig. 7, the temperature insensitive mach-zehnder interferometer further includes a protection layer 208, where the protection layer 208 is located on the upper surface of the buried oxide layer 202 and completely covers the first mode converter, the connecting arm, and the second mode converter, so as to protect the first mode converter, the connecting arm, and the second mode converter. In one example, the protective layer 208 may include, but is not limited to, a silicon oxide layer.

As an example, the width of the connecting arm 13 can be set according to actual requirements, and preferably, the width of the connecting arm 13 is 569nm, wherein, to realize the temperature insensitive characteristic of the device, the width of the multimode waveguide needs to satisfy d in different modes_neffthe/dT coefficients are equal; FIG. 8 is a graph showing the variation rate of the effective refractive index with respect to temperature (d) for the width of the connecting arm and the variation rate with respect to temperature for different modes of incident light in the temperature insensitive Mach-Zehnder interferometer provided by the present invention, where two modes of incident light are selected to have the same effective refractive index with respect to temperature_neffThe width of the connecting arm 13 corresponding to the dT) is the width of the connecting arm 13 corresponding to the temperature insensitivity, and it can be seen that when the width of the multimode waveguide is 569nm, the TM is₀And TE₁The dneff/dT coefficients in the pattern are all 1.289 x 10^-4and/K, the device can realize the temperature insensitive characteristic.

In addition, referring to fig. 9, in order to verify the temperature characteristics of the device, the transmission spectrum of the device at 20 ℃ and 50 ℃ is simulated, wherein the incident light is in a TM0 mode, and the output light is in a TM0 mode as an example, as can be seen from fig. 9, the simulation result is shown that the temperature sensitivity of the device with temperature change is only 15 pm/deg.c, and the device has a temperature insensitive characteristic. The temperature insensitive Mach-Zehnder interferometer of the present invention has substantially the same performance at different temperatures, and the performance of the temperature insensitive Mach-Zehnder interferometer of the present invention is not greatly affected by the temperature, that is, FIG. 9 further demonstrates that the temperature insensitive Mach-Zehnder interferometer of the present invention is not sensitive to temperature.

In addition, please refer to fig. 10 to fig. 13, wherein the light obtained in the device of the present invention is mixed mode, the output light is not mixed mode, and finally a single output light is obtained, wherein, as shown in the figure, the input and the output have four conditions in total: i.e. incident in the TM0 mode, and the output light is in the TM0 mode; incident in a TM0 mode, and outputting light in a TE1 mode; incident in a TE1 mode, and outputting light in a TM0 mode; incident in the TE1 mode, and outputting light in the TE1 mode; the mixed mode light is transmitted by 569nm wide waveguide (connecting arm) in the middle of the device, and the two ends of the device adopt symmetrical patterns to obtain single output light. The result of the graph shows that in order to verify the overall performance of the device for simulation, the temperature insensitive Mach-Zehnder interferometer of the invention can obtain mixed-mode emergent light of a TM0 mode and a TE1 mode no matter the input of incident light of the TM0 mode or incident light of the TE1 mode. The simulation result of the whole device is shown in the figure, the insertion loss of the device under each port is less than 0.3dB, and the extinction ratio is greater than 20 dB. In addition, fig. 14 shows a schematic view of the simulated mode field of the device.

It should be noted that, based on the design of the present invention, the device includes two identical double-layer tapered structures and one multimode waveguide. The output end of the temperature insensitive Mach-Zehnder interferometer can output emergent light in a TM0 mode and a TE1 mode no matter the input end inputs incident light in a TM0 mode or input light in a TE1 mode. The purpose of the double-layer conical structure is to obtain a mixed mode, and the working principle can be as follows: for example, when the TM0 mode is incident into the device, there is a mode-mixing region where the effective refractive indices of TM0 and TE1 are equal in the portion where the width of the waveguide changes from W0 to W1, and the symmetry of the structure in the vertical direction is partially broken by etching, at which time the TM0 mode is converted into the TE1 mode. In the variation range of the waveguide width W1-W2 of the structure, when the width of W2 is 0.62 μm, a part of TE1 mode is converted back to TM0 mode, so that a mixed mode of TM0 and TE1 can be obtained. The ratio of TM0 to TE1 after passing through the double-layer tapered mode coupler at this time is about 50:50, and the simulation results are shown in fig. 15. Inputting incident light of a TM0 mode from the input waveguide segment; in the first symmetric transmission segment, the effective refractive indexes of TM0 and TE1 are equal, and the TM0 mode is converted into the TE1 mode; in the second symmetric transmission segment, part of the TE1 mode light is converted back to TM0 mode light to obtain mixed mode light of TM0 and TE 1. Furthermore, a Mach-Zehnder interferometer is finally prepared from the device, the mixed-mode light has the effect of making the temperature of the device insensitive, the symmetrical structure is added on the right side of the device, the mixed-mode light can be converted into single-mode light again, and therefore an interference pattern is obtained.

In addition, referring to fig. 1 to 7, the present invention further provides a method for manufacturing a mach-zehnder interferometer based on TM0 mode light according to any one of the above schemes, wherein the structure, material composition and feature description of each material layer may refer to the description of the present invention in the interferometer structure, and will not be described herein again. In the preparation process, firstly, a mask is deposited, then, photoresist is coated in a spinning mode for photoetching, then, silicon etching is carried out, and finally, an upper cladding layer is deposited. The preparation method specifically comprises the following steps:

1) providing an SOI substrate, wherein the SOI substrate comprises a bottom silicon layer 201, a buried oxide layer 202 and a top silicon layer 203;

2) the top silicon layer 203 is etched on the basis of an etch mask layer 204 to form the first modal converter 12, the link arm 12 and the second modal converter 14. Wherein, two etching methods are adopted to form the upper waveguide segment layer 206 and the lower waveguide segment layer 207 which are symmetrically transmitted, for example, the first etching is performed to form the initial layer 205, and then the second etching is performed to form the upper waveguide segment layer 206 and the lower waveguide segment layer 207. That is, the individual upper waveguide segments may be considered to constitute an upper waveguide segment layer 206, and the individual lower waveguide segments may be considered to constitute a lower waveguide segment layer 207. In addition, a step of depositing a protective layer 208 may also be included.

In summary, the mach-zehnder interferometer based on TM0 mode light and the manufacturing method thereof of the present invention realize that the output end can output the emergent light of TM0 mode and TE1 mode no matter the input end inputs the incident light of TM0 mode or the input light of TE1 mode; the problems that the Mach-Zehnder interferometer in the prior art is sensitive to temperature, complex in structure, large in size and the like can be effectively solved: the method can be compatible with the CMOS process, is convenient for batch production, and can realize high-quality large-scale production on a silicon photonic process platform. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.