阅读说明：本技术 硅波导端面耦合结构及其制作方法 (Silicon waveguide end face coupling structure and manufacturing method thereof ) 是由 张巍 顿鹏翔 黄翊东 冯雪 刘仿 崔开宇 于 2020-06-01 设计创作，主要内容包括：本发明涉及光子集成器件技术领域,公开了硅波导端面耦合结构及其制作方法。该结构包括由下至上依次叠放的衬底硅、氧化层、硅波导和氮化硅层,氮化硅层的端部构造为脊形结构以形成脊形氮化硅波导,脊形氮化硅波导用于与普通单模光纤端面耦合。该方法包括：利用绝缘体上硅衬底中位于衬底硅上表面氧化层之上的薄膜硅层制备硅波导；在硅波导与光纤耦合的一端制备成宽度逐渐收窄的尖锥结构以形成硅波导尖锥结构；在硅波导与氧化层上方沉积一层氮化硅层；通过对氮化硅层进行浅刻蚀制备出脊形结构以形成脊形氮化硅波导。本发明的脊形氮化硅波导变换模场可以与普通单模光纤匹配,适合硅光子芯片封装过程中硅波导与普通单模光纤的低损耗耦合。(The invention relates to the technical field of photonic integrated devices, and discloses a silicon waveguide end face coupling structure and a manufacturing method thereof. The structure comprises a substrate silicon, an oxide layer, a silicon waveguide and a silicon nitride layer which are sequentially stacked from bottom to top, wherein the end part of the silicon nitride layer is constructed into a ridge structure to form a ridge silicon nitride waveguide, and the ridge silicon nitride waveguide is used for being coupled with the end face of a common single-mode optical fiber. The method comprises the following steps: preparing a silicon waveguide by utilizing a thin film silicon layer positioned on an oxide layer on the upper surface of the substrate silicon in the silicon-on-insulator substrate; preparing a tapered structure with gradually narrowed width at one end of the silicon waveguide coupled with the optical fiber to form a silicon waveguide tapered structure; depositing a silicon nitride layer over the silicon waveguide and the oxide layer; a ridge structure is prepared by shallow etching of the silicon nitride layer to form a ridge silicon nitride waveguide. The ridge silicon nitride waveguide conversion mode field can be matched with a common single-mode fiber, and is suitable for low-loss coupling of the silicon waveguide and the common single-mode fiber in the silicon photonic chip packaging process.)

1. A silicon waveguide end-face coupling structure, comprising: the optical fiber comprises a substrate silicon, an oxide layer, a silicon waveguide and a silicon nitride layer which are sequentially stacked from bottom to top, wherein the end part of the silicon nitride layer is constructed into a ridge structure to form a ridge silicon nitride waveguide, and the ridge silicon nitride waveguide is used for end face coupling with a common single-mode optical fiber.

2. The silicon waveguide end-coupling structure of claim 1, further comprising a silicon dioxide protective layer, wherein the silicon dioxide protective layer is located between the oxide layer and the silicon nitride layer, and the silicon dioxide protective layer covers an upper surface of the silicon waveguide.

3. The silicon waveguide end-face coupling structure of claim 1, wherein the end of the silicon waveguide is configured to be tapered to form a silicon waveguide tapered structure, the tip of the silicon waveguide tapered structure facing the common single-mode optical fiber.

4. The silicon waveguide end-face coupling structure of claim 1, wherein the silicon waveguide has a height in the range of 200 nm to 340 nm and a width in the range of 350 nm to 500 nm.

5. The silicon waveguide end-face coupling structure of claim 3, wherein the length of the silicon waveguide tapered structure ranges from 100 microns to 300 microns, and the width of the tip is less than 150 nanometers.

6. The silicon waveguide end-coupling structure of claim 2, wherein the thickness of the silicon dioxide protective layer ranges from 120 nm to 400 nm.

7. The silicon waveguide end-coupling structure of claim 1, wherein the thickness of the silicon nitride layer ranges from 5 microns to 9 microns.

8. The silicon waveguide end-coupling structure of claim 1, wherein the width of the ridge silicon nitride waveguide ranges from 3 microns to 9 microns, and the depth of both sides of the ridge silicon nitride waveguide ranges from 0.5 microns to 3 microns.

9. A method for manufacturing a silicon waveguide end-face coupling structure, wherein the method for manufacturing a silicon waveguide end-face coupling structure is used for preparing a silicon waveguide end-face coupling structure according to any one of claims 1 to 8, and the method for manufacturing a silicon waveguide end-face coupling structure comprises:

s1, preparing a silicon waveguide by utilizing a thin film silicon layer on an oxide layer on the upper surface of the substrate silicon in the silicon-on-insulator substrate;

s2, preparing a tapered structure with gradually narrowed width at one end of the silicon waveguide coupled with the optical fiber to form a silicon waveguide tapered structure;

s3, depositing a silicon dioxide protective layer on the silicon waveguide and the oxide layer

S4, depositing a silicon nitride layer above the silicon dioxide protective layer;

and S5, preparing a ridge structure by carrying out shallow etching on the silicon nitride layer to form a ridge silicon nitride waveguide.

Technical Field

The invention relates to the technical field of photonic integrated devices, in particular to a silicon waveguide end face coupling structure and a manufacturing method thereof.

Background

Silicon photonic integration based on silicon waveguides has become a key technology for the development of high performance and low cost optical communication components and photonic integrated devices. The silicon photonic chip is generally prepared on a Silicon On Insulator (SOI) substrate, and a silicon material is used as a waveguide core region part, and the cross section size of the core region is hundreds of nanometers. Silica is typically used as the waveguide cladding material. Because the crystalline silicon and the silicon dioxide have higher refractive index contrast, the area of the silicon waveguide mode field is generally smaller than 1 square micron, so that the high-density photonic integration can be supported, and the silicon waveguide has wide application prospect in the aspects of high-performance and low-cost optical communication components and photonic integrated devices.

In practical applications of silicon photonic chips, a silicon waveguide needs to be optically coupled with a single-mode fiber with low loss. However, the mode field area of a common single mode fiber is about 80 μm square, and the very small mode field area of the silicon waveguide makes it very difficult to directly couple with the common single mode fiber. Theoretical calculations and experiments indicate that direct coupling of silicon waveguides with conventional single mode fibers introduces coupling losses in excess of 10dB due to mode field mismatch. This greatly limits the practical application of silicon photonics chips.

Therefore, realizing the high-efficiency coupling of the silicon waveguide and the common single-mode fiber is a key problem of the silicon photonic integration technology towards practical application. At present, two technical routes are mainly adopted for coupling silicon waveguide and common single-mode optical fiber. The first is to prepare an upward diffraction grating on a silicon waveguide to realize the vertical coupling between the silicon waveguide and a common single-mode fiber, and the effective area of an upward diffraction light field can be matched with the mode field of the common single-mode fiber by adjusting the size of the silicon waveguide and the design of the grating, so that the coupling efficiency is improved. However, the working bandwidth of this vertical coupling is limited by the diffraction bandwidth of the grating, and the coupling efficiency is greatly limited due to the scattering in other directions and has polarization dependence. In addition, the grating fabrication process is also complex. The second technical route is end-face coupling, which has wider coupling bandwidth, is independent of polarization and has wider adaptability. However, since the mismatch between the mode fields of the silicon waveguide and the optical fiber is large, a mode field transformation structure needs to be designed on one side of the silicon waveguide, so that the output mode field of the waveguide is matched with the optical fiber, and the coupling loss is reduced. One end of a silicon waveguide is usually designed to be tapered to improve the mode field mismatch between the fiber and the waveguide. In the taper structure, as the size of the silicon waveguide is gradually reduced, the mode field of the silicon waveguide is gradually increased, and the effect of mode field conversion can be achieved. However, due to the limitation of micro-fabrication, the silicon waveguide is difficult to be made very small in size, so that the mode field conversion capability of a pure tapered structure is limited. Further develops a mode field conversion structure of a large-size silicon nitride waveguide or a polymer waveguide wrapped outside the conical structure. However, this structure cannot be made large in size in order to avoid the silicon nitride waveguide or the polymer waveguide from forming multimode transmission. In addition, the limitation of the silicon nitride etching process in the etching depth also limits the mode field size supported by the mode field transformation structure. Therefore, the mode field conversion structure based on the tapered structure is still used for coupling the silicon waveguide and the common single-mode fiber, and large loss is still introduced. Therefore, there is a need to develop an end-face coupling structure with simple fabrication process and mode field transformation size matching with a common single-mode fiber for low-loss coupling between a silicon waveguide and the common single-mode fiber.

Disclosure of Invention

Technical problem to be solved

The embodiment of the invention aims to provide a silicon waveguide end face coupling structure and a manufacturing method thereof, and aims to solve the technical problems that the silicon waveguide mode field size is small and the coupling loss of a common single-mode optical fiber is large in the prior art.

(II) technical scheme

In order to solve the above technical problem, an embodiment of the present invention provides a silicon waveguide end-face coupling structure, including: the optical fiber comprises a substrate silicon, an oxide layer, a silicon waveguide and a silicon nitride layer which are sequentially stacked from bottom to top, wherein the end part of the silicon nitride layer is constructed into a ridge structure to form a ridge silicon nitride waveguide, and the ridge silicon nitride waveguide is used for end face coupling with a common single-mode optical fiber.

The silicon nitride waveguide structure further comprises a silicon dioxide protective layer, wherein the silicon dioxide protective layer is located between the oxidation layer and the silicon nitride layer, and covers the upper surface of the silicon waveguide.

Wherein the end of the silicon waveguide is configured to be tapered to form a silicon waveguide tapered structure, and the tip of the silicon waveguide tapered structure faces the common single-mode optical fiber.

Wherein the height of the silicon waveguide ranges from 200 nm to 340 nm, and the width ranges from 350 nm to 500 nm.

Wherein, the length value range of the silicon waveguide sharp cone structure is 100-300 microns, and the width of the tip is less than 150 nanometers.

Wherein the thickness of the silicon dioxide protective layer ranges from 120 nanometers to 400 nanometers.

Wherein the thickness of the silicon nitride layer ranges from 5 micrometers to 9 micrometers.

Wherein the width of the ridge silicon nitride waveguide ranges from 3 microns to 9 microns, and the depth of the two sides of the ridge silicon nitride waveguide ranges from 0.5 microns to 3 microns.

The embodiment of the invention also discloses a manufacturing method of the silicon waveguide end-face coupling structure, which is used for preparing the silicon waveguide end-face coupling structure in the embodiment of the invention and comprises the following steps:

s1, preparing a silicon waveguide by utilizing a thin film silicon layer on an oxide layer on the upper surface of the substrate silicon in the silicon-on-insulator substrate;

s2, preparing a tapered structure with gradually narrowed width at one end of the silicon waveguide coupled with the optical fiber to form a silicon waveguide tapered structure;

s3, depositing a silicon dioxide protective layer above the silicon waveguide and the oxide layer;

s4, depositing a silicon nitride layer above the silicon dioxide protective layer;

and S5, preparing a ridge structure by carrying out shallow etching on the silicon nitride layer to form a ridge silicon nitride waveguide.

(III) advantageous effects

According to the silicon waveguide end face coupling structure and the manufacturing method thereof provided by the embodiment of the invention, the ridge-shaped silicon nitride waveguide is formed on the silicon nitride layer through a shallow etching process, so that mode field conversion is realized, single-mode transmission of a mode field matched with a common single-mode optical fiber is realized, and the problems of multi-mode transmission in a large-size rectangular silicon nitride waveguide and the process difficulty of deep etching of the silicon nitride layer in the traditional scheme are solved. The preparation process of the embodiment of the invention is simple, the transformation mode field can be matched with the common single-mode fiber, and the silicon photonic chip is particularly suitable for low-loss coupling of the silicon waveguide and the common single-mode fiber in the packaging process of the silicon photonic chip.

Drawings

FIG. 1 is a three-dimensional schematic diagram of a silicon waveguide end-face coupling structure according to an embodiment of the present invention;

FIG. 2 is a front view of a silicon waveguide end-coupling structure according to an embodiment of the present invention;

fig. 3 is a top view of a silicon waveguide end-coupling structure according to an embodiment of the invention.

Reference numerals:

1: a substrate silicon; 2: an oxide layer; 3: a silicon dioxide protective layer; 4: a silicon waveguide taper structure; 5: a ridge silicon nitride waveguide; 6: a silicon waveguide; 7: a silicon nitride layer.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

As shown in fig. 1 to fig. 3, an embodiment of the present invention discloses a silicon waveguide end-face coupling structure, including: the optical fiber comprises a substrate silicon 1, an oxide layer 2, a silicon waveguide 6 and a silicon nitride layer 7 which are sequentially stacked from bottom to top, wherein the end part of the silicon nitride layer 7 is constructed into a ridge structure to form a ridge silicon nitride waveguide 5, and the ridge silicon nitride waveguide 5 is used for being coupled with the end face of a common single-mode optical fiber.

Specifically, in the embodiment of the present invention, a shallow ridge structure is prepared at the end of the silicon nitride layer 7 by a shallow etching process, the ridge structure extends to the end face of the chip, so as to implement a waveguide in which the effective mode field area of single-mode transmission is matched with that of a common single-mode fiber, and the ridge silicon nitride waveguide 5 and the common single-mode fiber are efficiently coupled by mode field matching, so that the silicon waveguide end-face coupling structure implements efficient coupling between the silicon waveguide 6 and the common single-mode fiber.

In the present embodiment, the silicon waveguide 6 is prepared using a thin film silicon layer on a silicon-on-insulator (SOI) substrate.

According to the silicon waveguide end face coupling structure and the manufacturing method thereof provided by the embodiment of the invention, the ridge-shaped silicon nitride waveguide 5 is formed on the silicon nitride layer 7 through a shallow etching process, so that mode field conversion is realized, single-mode transmission of a mode field matched with a common single-mode optical fiber is realized, and the problems of multi-mode transmission in a large-size rectangular silicon nitride waveguide and the process difficulty of deep etching of the silicon nitride layer 7 in the traditional scheme are solved. The preparation process of the embodiment of the invention is simple, the transformation mode field can be matched with the common single-mode fiber, and the invention is particularly suitable for low-loss coupling of the silicon waveguide and the common single-mode fiber in silicon photonic chip packaging.

The silicon waveguide end-face coupling structure of the present embodiment further includes a silicon dioxide protective layer 3, the silicon dioxide protective layer 3 is located between the oxide layer 2 and the silicon nitride layer 7, and the silicon dioxide protective layer 3 covers the silicon waveguide 6 and the upper surface of the silicon waveguide tapered structure 4 in the following embodiments. Specifically, in the present embodiment, the silicon waveguide 6 and the silicon waveguide tapered structure 4 are disposed between the silicon dioxide protection layer 3 and the oxide layer 2, and the silicon dioxide protection layer 3 functions to reduce the influence of the silicon nitride layer 7 on the transmission characteristics of the silicon waveguide 6, thereby avoiding the requirement of removing the silicon nitride layer 7 above the silicon waveguide 6 in the conventional scheme using a rectangular silicon nitride waveguide, and greatly reducing the requirement on the deposition process of the silicon nitride layer 7.

The end part of the silicon waveguide 6 is constructed into a sharp cone to form a silicon waveguide sharp cone structure 4, the tip end of the silicon waveguide sharp cone structure 4 faces to a common single mode optical fiber, namely, the end of the silicon waveguide 6 coupled with the optical fiber is prepared into a sharp cone structure with the width gradually narrowed and the length limited, and the silicon waveguide 6 and the ridge silicon nitride waveguide 5 are coupled through the sharp cone structure to realize high-efficiency optical adiabatic conversion. Specifically, the ridge silicon nitride waveguide 5 is positioned above the silicon waveguide tapered structure 4, and the ridge silicon nitride waveguide 5 further extends to the end face of the chip.

Wherein, the height of the silicon waveguide 6 ranges from 200 nm to 340 nm, and the width ranges from 350 nm to 500 nm.

Wherein, the length value range of the silicon waveguide taper structure 4 is 100 micrometers to 300 micrometers, and the width of the tip is less than 150 nanometers. Specifically, one end of the silicon waveguide tapered structure 4 is connected to the silicon waveguide 6, the width of the silicon waveguide tapered structure is the same as that of the silicon waveguide 6, and the width of the silicon waveguide tapered structure 4 gradually narrows as it is coupled to the optical fiber.

Wherein, the thickness range of the silicon dioxide protective layer 3 is 120 nm to 400 nm.

Wherein the thickness of the silicon nitride layer 7 ranges from 5 micrometers to 9 micrometers.

Wherein the width of the ridge silicon nitride waveguide 5 ranges from 3 microns to 9 microns, and the depth of the two sides of the ridge silicon nitride waveguide 5 ranges from 0.5 microns to 3 microns.

The dimensions of the silicon waveguide 6, the silicon waveguide tapered structure 4, the silicon dioxide protective layer 3, the silicon nitride layer 7 and the ridge silicon nitride waveguide 5 based on the above-described embodiment may be set according to actual circumstances, and the present invention is not limited thereto.

The invention provides a silicon waveguide end-face coupling structure of a size type, and a silicon photonic chip in the embodiment is prepared by adopting a silicon-on-insulator (SOI) substrate with a film silicon layer thickness of 220 nanometers. The silicon waveguide 6 has a height of 220 nm and a width of 460 nm. The silicon waveguide sharp taper structure 4 has a height of 220 nm and a length of 200 μm, and the tip width of the sharp taper structure is 120 nm. The silicon dioxide protective layer 3 is 200 nm thick. The thickness of the silicon nitride layer 7 is 7 microns, the width of the ridge-shaped silicon nitride waveguide 5 is 7 microns, and the depth of the ridge is 2 microns. Based on the silicon waveguide end-face coupling structure in this embodiment, theoretical calculation finds that: the light wave propagating in the silicon waveguide 6 can be coupled into the ridge silicon nitride waveguide 5 through the sharp taper structure by high-efficiency adiabatic transformation; the optical field in the ridge silicon nitride waveguide 5 exists in the form of a fundamental mode, and the mode field area is about 42.58 square microns, which is approximately matched with the mode field area of a common single mode optical fiber. The coupling loss between the silicon waveguide 6 and the common single-mode fiber realized by the structure is only 1.97dB, which can be calculated by the overlapping integral of the ridge silicon nitride waveguide 5 mode field and the common single-mode fiber mode field.

The embodiment of the invention also discloses a manufacturing method of the silicon waveguide end-face coupling structure, which is used for preparing the silicon waveguide end-face coupling structure of the embodiment, and the manufacturing method of the silicon waveguide end-face coupling structure comprises the following steps:

s1, preparing a silicon waveguide 6 by utilizing a thin film silicon layer which is positioned on an oxide layer 2 on the upper surface of a substrate silicon 1 in a silicon-on-insulator (SOI) substrate;

s2, preparing a tapered structure with gradually narrowed width at one end of the silicon waveguide 6 coupled with the optical fiber to form a silicon waveguide tapered structure 4;

s3, depositing a silicon dioxide protective layer 3 above the silicon waveguide 6 and the oxide layer 2;

s4, depositing a silicon nitride layer 7 above the silicon dioxide protective layer 3;

s5, a ridge structure is prepared by shallow etching the silicon nitride layer 7 to form a ridge silicon nitride waveguide 5.

The manufacturing method of the embodiment comprises the following steps: the silicon waveguide 6 is prepared by utilizing a thin film silicon layer on a silicon-on-insulator (SOI) substrate, the silicon waveguide 6 and one end coupled with an optical fiber are prepared into a silicon waveguide tapered structure 4 with the width gradually narrowed and the length limited, a silicon dioxide protective layer 3 is deposited on the silicon waveguide 6, and a thicker silicon nitride layer 7 is deposited on the silicon dioxide protective layer 3. And preparing the ridge-shaped silicon nitride waveguide 5 by performing shallow etching on the silicon nitride layer 7 above the silicon waveguide tapered structure 4. The ridge silicon nitride waveguide 5 is end-coupled with a common single-mode fiber.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.