CN111679363A - Silicon waveguide end-face coupling structure and fabrication method thereof - Google Patents

Abstract

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 includes a substrate silicon, an oxide layer, a silicon waveguide and a silicon nitride layer stacked in sequence from bottom to top. The end of the silicon nitride layer is configured as a ridge structure to form a ridge silicon nitride waveguide. The ridge nitride Silicon waveguides are used for coupling with common single-mode fiber endfaces. The method includes: preparing a silicon waveguide by using a thin-film silicon layer in a silicon-on-insulator substrate located on an oxide layer on the upper surface of the substrate silicon; preparing a tapered structure with a gradually narrowed width at one end of the silicon waveguide coupled with the optical fiber to form a silicon waveguide Waveguide tip-taper structure; depositing a silicon nitride layer over the silicon waveguide and the oxide layer; preparing a ridge-shaped structure by performing shallow etching on the silicon nitride layer to form a ridge-shaped silicon nitride waveguide. The transformation mode field of the ridge-shaped silicon nitride waveguide of the present invention can be matched with the common single-mode optical fiber, and is suitable for the low-loss coupling between the silicon waveguide and the common single-mode optical fiber in the packaging process of the silicon photonic chip.

Description

Silicon waveguide end-face coupling structure and fabrication method thereof

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 technique

Silicon photonics 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. Such a silicon photonic chip is generally prepared on a silicon on insulator (SOI) substrate, and a silicon material is used as the core region of the waveguide, and the cross-sectional size of the core region is in the order of 100 nanometers. The waveguide cladding material is generally silicon dioxide. Due to the high refractive index contrast between crystalline silicon and silicon dioxide, the mode field area of this silicon waveguide is generally less than 1 square micrometer, so it can support high-density photonic integration in high-performance and low-cost optical communication components and photonics Integrated devices have broad application prospects.

In practical applications of silicon photonic chips, silicon waveguides need to achieve low-loss optical coupling with single-mode fibers. However, the mode field area of ordinary single-mode fiber is about 80 square microns, and the very small mode field area of silicon waveguide makes it very difficult to directly couple with ordinary single-mode fiber. Theoretical calculations and experiments show that direct coupling between silicon waveguides and ordinary single-mode fibers will introduce more than 10 dB of coupling loss due to mode field mismatch. This greatly limits the practical application of silicon photonic chips.

Therefore, achieving high-efficiency coupling between silicon waveguides and ordinary single-mode fibers is a key issue for the practical application of silicon photonics integration technology. At present, the coupling between silicon waveguide and ordinary single-mode fiber mainly adopts two technical routes. The first is to prepare an upward diffraction grating on a silicon waveguide to realize the vertical coupling between the silicon waveguide and ordinary single-mode fiber. By adjusting the size of the silicon waveguide and the design of the grating, the effective area of the upward diffracted light field can be made the same as that of ordinary single-mode optical fibers. The mode field of the mode fiber is matched, thereby improving the coupling efficiency. However, the working bandwidth of this vertical coupling technology route is limited by the diffraction bandwidth of the grating, and the coupling efficiency is greatly limited due to the existence of scattering to other directions, and it is polarization dependent. In addition, the fabrication process of the grating is also complicated. The second technical route is to use end-face coupling, which has a wider coupling bandwidth and is polarization independent, and has wider adaptability. However, due to the large mismatch between the mode fields of the silicon waveguide and the fiber, it is necessary to design a mode field conversion structure on one side of the silicon waveguide, so that the output mode field of the waveguide matches the fiber, thereby reducing the coupling loss. One end of the silicon waveguide is usually designed into a tapered structure to improve the mode field mismatch between the fiber and the waveguide. In the tapered structure, as the size of the silicon waveguide gradually becomes smaller, the mode field of the silicon waveguide gradually becomes larger, which can play the role of mode field transformation. However, due to the limitation of microfabrication, the size of the silicon waveguide is difficult to be very small, which makes the mode field conversion capability of the simple tapered structure limited. A mode field conversion structure in which a large-sized silicon nitride waveguide or a polymer waveguide is wrapped around the tapered structure is further developed. However, in order to avoid the multi-mode transmission of silicon nitride waveguides or polymer waveguides, the size of this structure cannot be increased. In addition, the limitation on the etching depth of the silicon nitride etching process also restricts the mode field size supported by the mode field conversion structure. Therefore, the mode field conversion structure based on the tapered structure will still introduce a large loss when it is used for the coupling of the silicon waveguide and the ordinary single-mode fiber. Therefore, it is necessary to develop an end-face coupling structure with a simple preparation process and a mode field transformation size that matches that of common single-mode fibers for low-loss coupling between silicon waveguides and common single-mode fibers.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

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

(2) Technical solutions

In order to solve the above technical problems, an embodiment of the present invention provides a silicon waveguide end-face coupling structure, including: a substrate silicon, an oxide layer, a silicon waveguide and a silicon nitride layer stacked in sequence from bottom to top, and the silicon nitride layer has The ends are configured as ridges to form ridged silicon nitride waveguides for coupling with common single mode fiber endfaces.

A silicon dioxide protective layer is also included, the silicon dioxide protective layer is located between the oxide layer and the silicon nitride layer, and the silicon dioxide protective layer covers the upper surface of the silicon waveguide.

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

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

Wherein, the length of the silicon waveguide tip cone structure ranges from 100 microns to 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 microns to 9 microns.

Wherein, the width of the ridge-shaped silicon nitride waveguide ranges from 3 microns to 9 microns, and the depths on both sides of the ridge-shaped silicon nitride waveguide ranges from 0.5 microns to 3 microns.

The embodiment of the present invention also discloses a method for fabricating a silicon waveguide end-face coupling structure, and the method for fabricating the silicon waveguide end-face coupling structure is used to fabricate the silicon waveguide end-face coupling structure according to the embodiment of the present invention, and the silicon waveguide end-face coupling structure The production methods include:

S1, using the thin-film silicon layer in the silicon-on-insulator substrate located on the oxide layer on the upper surface of the silicon substrate to prepare a silicon waveguide;

S2, preparing a tapered structure with a gradually narrowed width at the coupling end of the silicon waveguide and the optical fiber to form a tapered silicon waveguide structure;

S3, depositing a silicon dioxide protective layer over the silicon waveguide and the oxide layer;

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

S5. A ridge-shaped structure is prepared by performing shallow etching on the silicon nitride layer to form a ridge-shaped silicon nitride waveguide.

(3) Beneficial effects

The embodiment of the present invention provides a silicon waveguide end-face coupling structure and a manufacturing method thereof. A ridge-shaped silicon nitride waveguide is formed on a silicon nitride layer through a shallow etching process, so as to realize mode field transformation, and the mode field is matched with a common single-mode optical fiber. It solves the problem of multi-mode transmission in the traditional large-size rectangular silicon nitride waveguide and the process difficulty that requires deep etching of the silicon nitride layer. The preparation process of the embodiment of the present invention is simple, the transformed mode field can be matched with the common single-mode fiber, and is especially suitable for the low-loss coupling between the silicon waveguide and the common single-mode fiber during the packaging process of the silicon photonic chip.

Description of drawings

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

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

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

Reference number:

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

Detailed ways

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

In the description of the present invention, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

As shown in FIG. 1 to FIG. 3 , an embodiment of the present invention discloses a silicon waveguide end face coupling structure, including: a substrate silicon 1 , an oxide layer 2 , a silicon waveguide 6 and a silicon nitride layer 7 stacked in sequence from bottom to top , the end of the silicon nitride layer 7 is configured as a ridge structure to form a ridge-shaped silicon nitride waveguide 5, and the ridge-shaped silicon nitride waveguide 5 is used for coupling 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, and the ridge structure extends all the way to the end face of the chip, so that the effective mode field area for single-mode transmission is comparable to that of ordinary single-mode transmission. Mode fiber matching waveguide, ridge silicon nitride waveguide 5 and ordinary single-mode fiber through mode field matching to achieve high-efficiency end-face coupling, so that the silicon waveguide end-face coupling structure realizes the connection between silicon waveguide 6 and ordinary single-mode fiber. High efficiency coupling.

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

The embodiment of the present invention provides a silicon waveguide end-face coupling structure and a manufacturing method thereof. A ridge-shaped silicon nitride waveguide 5 is formed on the silicon nitride layer 7 through a shallow etching process, so as to realize the mode field transformation, and the mode field is the same as that of a common single mode. The fiber-matched single-mode transmission solves the problem of multi-mode transmission in the traditional large-size rectangular silicon nitride waveguide and the technological difficulty that requires deep etching of the silicon nitride layer 7 . The preparation process of the embodiment of the present invention is simple, the transformed mode field can be matched with the common single-mode fiber, and is especially suitable for the low-loss coupling between the silicon waveguide and the common single-mode fiber in the silicon photonic chip package.

The silicon waveguide end-face coupling structure of this 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 tip structure 4 in the following embodiments. Specifically, in this embodiment, the silicon waveguide 6 and the silicon waveguide taper structure 4 are arranged between the silicon dioxide protective layer 3 and the oxide layer 2 , and the function of the silicon dioxide protective layer 3 is to reduce the effect of the silicon nitride layer 7 on the silicon dioxide. The influence of the transmission characteristics of the waveguide 6 avoids the requirement of removing the silicon nitride layer 7 above the silicon waveguide 6 in the traditional solution using the rectangular silicon nitride waveguide, and can greatly reduce the requirement for the deposition process of the silicon nitride layer 7 .

Wherein, the end of the silicon waveguide 6 is configured as a sharp taper to form the silicon waveguide taper structure 4, and the tip of the silicon waveguide taper structure 4 faces the common single-mode optical fiber, that is, the end of the silicon waveguide 6 coupled with the optical fiber is prepared to have a gradually width. The sharp-cone structure with limited length is narrowed, and the high-efficiency optical adiabatic conversion coupling is realized between the silicon waveguide 6 and the ridge-shaped silicon nitride waveguide 5 through the sharp-cone structure. Specifically, the ridge-shaped silicon nitride waveguide 5 is located above the silicon waveguide taper structure 4, and the ridge-shaped silicon nitride waveguide 5 further extends to the chip end face.

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

Wherein, the length of the silicon waveguide tip cone structure 4 ranges from 100 micrometers to 300 micrometers, and the width of the tip is less than 150 nanometers. Specifically, one end of the silicon waveguide taper structure 4 is connected to the silicon waveguide 6 and has the same width as the silicon waveguide 6 , and the width of the silicon waveguide taper structure 4 gradually narrows as it is coupled to the fiber.

The thickness of the silicon dioxide protective layer 3 ranges from 120 nanometers to 400 nanometers.

The thickness of the silicon nitride layer 7 ranges from 5 microns to 9 microns.

The width of the ridge-shaped silicon nitride waveguide 5 ranges from 3 μm to 9 μm, and the depth of the two sides of the ridge-shaped silicon nitride waveguide 5 ranges from 0.5 μm to 3 μm.

The dimensions of the silicon waveguide 6 , the silicon waveguide taper structure 4 , the silicon dioxide protective layer 3 , the silicon nitride layer 7 and the ridge-shaped silicon nitride waveguide 5 can be set according to the actual situation, and the present invention is not limited thereto. .

The present invention provides a type of silicon waveguide end-face coupling structure. In this embodiment, the silicon photonic chip is prepared by using a silicon-on-insulator (SOI) substrate with a thin-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 tip cone structure 4 has a height of 220 nm and a length of 200 microns, and the tip width of the tip cone structure is 120 nm. The silicon dioxide protective layer 3 has a thickness of 200 nanometers. The silicon nitride layer 7 has a thickness of 7 microns, and the ridge-shaped silicon nitride waveguide 5 has a ridge width of 7 microns and a ridge depth of 2 microns. Based on the silicon waveguide end-face coupling structure in this embodiment, theoretical calculations show that the light wave propagating in the silicon waveguide 6 can be coupled into the ridge-shaped silicon nitride waveguide 5 through a high-efficiency adiabatic transformation through the tapered structure; The optical field in the silicon waveguide 5 exists in the form of a fundamental mode, and the mode field area is about 42.58 square microns, which roughly matches the mode field area of an ordinary single-mode fiber. It can be calculated by the overlap integral of the mode field of the ridged silicon nitride waveguide 5 and the mode field of the ordinary single-mode fiber. The coupling loss between the silicon waveguide 6 and the ordinary single-mode fiber realized by this structure is only 1.97dB.

The embodiment of the present invention further discloses a method for fabricating a silicon waveguide end-face coupling structure. The fabrication method for the silicon waveguide end-face coupling structure is used to fabricate the silicon waveguide end-face coupling structure of the above-mentioned embodiment, and the fabrication method for the silicon waveguide end-face coupling structure includes:

S1, a silicon waveguide 6 is prepared by using the thin-film silicon layer located on the oxide layer 2 on the upper surface of the silicon-on-insulator (SOI) substrate in the silicon-on-insulator (SOI) substrate;

S2, preparing a tapered structure with a gradually narrowed width at one end where the silicon waveguide 6 is coupled with the optical fiber to form the silicon waveguide tapered structure 4;

S3, depositing a silicon dioxide protective layer 3 over the silicon waveguide 6 and the oxide layer 2;

S4, depositing a layer of silicon nitride layer 7 above the silicon dioxide protective layer 3;

S5 , a ridge structure is prepared by performing shallow etching on the silicon nitride layer 7 to form a ridge silicon nitride waveguide 5 .

The manufacturing method of this embodiment is as follows: a silicon waveguide 6 is prepared by using a thin-film silicon layer on a silicon-on-insulator (SOI) substrate, and one end of the silicon waveguide 6 coupled with the optical fiber is prepared into a silicon waveguide tapered structure 4 with a gradually narrowed width and a limited length, 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 . A ridge-shaped silicon nitride waveguide 5 is prepared by shallow etching the silicon nitride layer 7 above the silicon waveguide taper structure 4 . The ridge-shaped silicon nitride waveguide 5 realizes end-face coupling with a common single-mode fiber.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (9)

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.

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