阅读说明：本技术 基于双三叉戟亚波长光栅结构的端面耦合器 (End face coupler based on double-trident sub-wavelength grating structure ) 是由 郭旭涵 何安 张永 苏翼凯 于 2020-06-04 设计创作，主要内容包括：一种基于双三叉戟亚波长光栅结构的端面耦合器,包括：位于衬底层且对称设置的三个锥形亚波长光栅、三个亚波长光栅波导、若干用于模式转换的锥形波导和直波导,其中：锥形亚波长光栅和对应的亚波长光栅波导相连,锥形波导位于亚波长光栅波导之间,用于光在芯片上传输的直波导及其对应的锥形波导位于端面耦合器的输出端,具有低损耗、大带宽的特点,除了易于制备且与CMOS工艺兼容的同时,还能够实现单模光纤和硅波导之间的高效耦合。(An end-face coupler based on a dual-tridentate sub-wavelength grating structure, comprising: three tapered sub-wavelength gratings, three sub-wavelength grating waveguides, a plurality of tapered waveguides and straight waveguides for mode conversion, which are located on the substrate layer and symmetrically arranged, wherein: the tapered sub-wavelength grating is connected with the corresponding sub-wavelength grating waveguide, the tapered waveguide is positioned between the sub-wavelength grating waveguides, the straight waveguide used for transmitting light on the chip and the corresponding tapered waveguide are positioned at the output end of the end face coupler, the tapered sub-wavelength grating has the characteristics of low loss and large bandwidth, and the tapered sub-wavelength grating is easy to prepare and compatible with a CMOS (complementary metal oxide semiconductor) process, and can realize high-efficiency coupling between a single-mode optical fiber and a silicon waveguide.)

1. An end-face coupler based on a dual-tridentate sub-wavelength grating structure, comprising: three tapered sub-wavelength gratings, three sub-wavelength grating waveguides, a plurality of tapered waveguides and straight waveguides for mode conversion, which are located on the substrate layer and symmetrically arranged, wherein: the tapered sub-wavelength grating is connected with the corresponding sub-wavelength grating waveguide, the tapered waveguide is positioned between the sub-wavelength grating waveguides, and the straight waveguide for transmitting light on the chip and the corresponding tapered waveguide are positioned at the output end of the end face coupler; light is guided into an SOI chip through single-mode fiber coupling and then transmitted along first to third tapered sub-wavelength grating waveguides, enters the first to third sub-wavelength grating waveguides, is further coupled to the first and second tapered waveguides from the sub-wavelength grating waveguides and then enters the third and fourth tapered waveguides, and finally is coupled to the fifth tapered waveguide and finally enters the straight waveguide and then is output in a TE0 mode.

2. The dual-tridentate sub-wavelength grating structure-based end-face coupler of claim 1, wherein the second tapered sub-wavelength grating, the second sub-wavelength grating waveguide and the straight waveguide in the end-face coupler are located on an axial line of the end-face coupler, and the first and second tapered sub-wavelength gratings, the first and second sub-wavelength grating waveguides and the first tapered waveguide form a tridentate structure; the second and third tapered sub-wavelength gratings, the second and third sub-wavelength grating waveguides and the second tapered waveguide also form a trident structure.

3. The dual-tridentate sub-wavelength grating structure-based end-face coupler of claim 1, wherein the tapered sub-wavelength grating is gradually varied in width, the width of the tapered sub-wavelength grating near the end face of the single-mode fiber is gradually varied from narrow to wide, and the width of the ith silicon square from the end face satisfies the following conditions:wherein: w1 isThe width at the tip of the tapered sub-wavelength grating, w2 the width at the end of the tapered sub-wavelength grating, L the length of the grating, and P the period.

4. The dual-tridentate sub-wavelength grating structure-based end-face coupler of claim 1, wherein the sub-wavelength grating waveguides are constant in width.

5. The dual-tridentate sub-wavelength grating structure-based end-face coupler of claim 1, wherein grooves for limiting optical field diffusion are formed on the outer sides of the first and third tapered sub-wavelength gratings of the end-face coupler.

6. A method of manufacturing an end-face coupler according to any of the preceding claims based on electron beam lithography, characterized in that the silicon structure is realized by one electron beam lithography and then covered with a silicon dioxide layer, and trench structures for limiting the optical field diffusion are etched on both sides of the coupler.

Technical Field

The invention relates to the technology in the field of optical fiber communication and integrated optics, in particular to an end face coupler based on a double-tridentate sub-wavelength grating structure.

Background

The coupling of existing single mode optical fibers to silicon waveguides is typically via grating coupling or end-coupling. The grating coupling is to place the single mode fiber at an angle close to 90 degrees with the grating structure on the SOI chip, and to couple the light in the fiber into the silicon waveguide by the diffraction action of the grating. The end face coupling is to butt joint the optical fiber and the end face of the chip, and the coincidence degree of the mode field distribution on the chip and the mode field distribution of the optical fiber is increased through the end face coupling structure on the SOI, so that light is transmitted between the single-mode optical fiber and the SOI chip.

However, the grating coupler has high coupling loss, narrow bandwidth and is sensitive to the polarization of light; the end-face coupler is complex in preparation process, needs parts which are difficult to manufacture such as a multilayer waveguide structure, a suspension structure, a trunk-shaped bending structure and the like, and the coupler needs to be added with materials such as silicon nitride and polymers, and is incompatible with a CMOS (complementary metal oxide semiconductor) process, so that difficulty is brought to large-scale production.

Disclosure of Invention

The invention provides an end face coupler based on a double-tridentate sub-wavelength grating structure aiming at the problems of high loss, difficult preparation, wavelength dependence and the like of the existing coupling device, belongs to an end face coupler based on a Complementary Metal Oxide Semiconductor (CMOS) process, and is low in loss and large in bandwidth, and can realize efficient coupling between a single-mode optical fiber and a silicon waveguide while being easy to prepare and compatible with the CMOS process.

The invention is realized by the following technical scheme:

the invention relates to an end face coupler based on a double-tridentate sub-wavelength grating structure, which comprises: three tapered sub-wavelength gratings, three sub-wavelength grating waveguides, a plurality of tapered waveguides and straight waveguides for mode conversion, which are located on the substrate layer and symmetrically arranged, wherein: the tapered sub-wavelength grating is connected with the corresponding sub-wavelength grating waveguide, the tapered waveguide is positioned between the sub-wavelength grating waveguides, and the straight waveguide for transmitting light on the chip and the corresponding tapered waveguide are positioned at the output end of the end face coupler.

The second conical sub-wavelength grating, the second sub-wavelength grating waveguide and the straight waveguide in the end face coupler are positioned on the central axis of the end face coupler, and the first and second conical sub-wavelength gratings, the first and second sub-wavelength grating waveguides and the first conical waveguide form a tridentate structure; the second and third tapered sub-wavelength gratings, the second and third sub-wavelength grating waveguides and the second tapered waveguide also form a trident structure.

The tapered sub-wavelength grating is gradually changed in width, the width of the tapered sub-wavelength grating close to the end face of the single-mode fiber is widened from narrow to wide, and the width of the ith silicon square from the end face meets the following requirements:wherein: w1 is the width at the tip of the tapered sub-wavelength grating, w2 is the width at the tip of the tapered sub-wavelength grating, L is the length of the grating, and P is the period. The optical field size at the end face is enlarged, the overlapping rate of the optical field size and the optical field in the single-mode optical fiber can reach 97.2%, the effective refractive index can be matched, and efficient coupling between the optical fiber and the chip can be further realized.

The sub-wavelength grating waveguide has a constant width.

And grooves for limiting the light field diffusion are arranged on the outer sides of the first and third tapered sub-wavelength gratings of the end face coupler.

The invention relates to a preparation method of an end face coupler based on a double-tridentate sub-wavelength grating structure, which only needs one-time electron beam lithography, after a silicon structure is made, a silicon dioxide layer is covered, and then groove structures are etched on two sides of the coupler for limiting light field diffusion so that light is concentrated near the coupler; the coupler is manufactured on a conventional SOI wafer, and all silicon structures can be processed by only one process.

Technical effects

The invention integrally solves the problems that the preparation process of the silicon-based end face coupler in the prior art is complex, the mass production is difficult, the coupling loss of light from the optical fiber to the silicon chip is large, the coupling bandwidth of light from the optical fiber to the silicon chip is narrow, and the coupling of light from the optical fiber to the silicon chip has wavelength sensitivity; the invention realizes the end face coupler between the single mode fiber and the nanowire silicon optical waveguide based on the double-tridentate sub-wavelength grating structure, the preparation process is completely compatible with the CMOS process, the preparation flow is simple, the large-scale production can be realized, the coupling loss is low, the bandwidth is large, and the wavelength is not sensitive.

Drawings

FIG. 1 is a schematic three-dimensional structure of an end-face coupler of the present invention;

in the figure: the single-mode fiber comprises a single-mode fiber 1, a silicon substrate layer 2, a silicon dioxide buried layer 3, a silicon dioxide covering layer 4, tapered sub-wavelength grating structures 7, 8 and 9, sub-wavelength grating waveguides 10, 11 and 12, tapered waveguides 13, 14, 15, 16 and 17 and a straight waveguide 18;

FIG. 2 is a schematic top view of the end-face coupler of the present invention;

FIG. 3 is a schematic lateral side view of an end-face coupler of the present invention;

FIG. 4 is a diagram of the optical field propagation of the end-face coupler of the present invention;

fig. 5 is a diagram of the coupling loss spectrum of the end coupler of the present invention.

Detailed Description

As shown in fig. 1-3, the present embodiment relates to an end-face coupler based on a dual-tridentate sub-wavelength grating structure, which is fabricated on an SOI wafer.

The SOI wafer sequentially comprises from bottom to top: a silicon substrate layer 2, a buried silicon dioxide layer 3 and a silicon dioxide covering layer 4.

The buried silicon dioxide layer 3 in this example is 3 μm thick, the silicon layer used to fabricate the coupler is 220nm thick, the blanket silicon dioxide layer 4 is 3.5 μm thick, the trench depth is 6.5 μm and the trench width is 1 μm.

The end face coupler includes: three tapered sub-wavelength grating structures 7, 8, 9 with gradually changed widths, three sub-wavelength grating waveguides 10, 11, 12 with equal widths respectively located at the respective ends thereof, four tapered waveguides 13, 14, 15, 16 for mode conversion symmetrically arranged between the sub-wavelength grating waveguides and one tapered waveguide 17 and a straight waveguide 18 for light transmission on the chip arranged at the end of the second sub-wavelength grating waveguide 11 at the center, and trenches 5, 6 located at both sides of the coupler for limiting the optical field diffusion, wherein: the first and second tapered sub-wavelength gratings 7 and 8, the first and second sub-wavelength grating waveguides 10 and 11 and the first tapered waveguide 13 form a trident structure; the second and third tapered sub-wavelength gratings 8, 9, the second and third sub-wavelength grating waveguides 11, 12 and the second tapered waveguide 14 also form a trident structure.

The lengths of the first to third tapered sub-wavelength gratings 7, 8 and 9 in the embodiment are 30 to 40 μm, the period is 300nm, and the duty ratio is 0.4 to 0.6; the lengths of the first and second tapered waveguides 13, 14 are 10 to 20 μm, and the lengths of the fifth to seventh tapered waveguides 15, 16, 17 are 30 to 40 μm.

In the coupling method of the end-face coupler, light is coupled from a single-mode fiber into an SOI chip, then transmitted along first to third tapered sub-wavelength grating waveguides 7, 8 and 9, and enters first to third sub-wavelength grating waveguides 10, 11 and 12; as the widths of the first and second tapered waveguides 13 and 14 are gradually increased, the effective refractive index is increased, and light enters the third and fourth tapered waveguides 15 and 16 after being coupled to the first and second tapered waveguides 13 and 14 from the sub-wavelength grating waveguide; since the widths of the third and fourth tapered waveguides 15 and 16 become gradually smaller, the effective refractive index decreases, and meanwhile, the width of the fifth tapered waveguide 17 becomes gradually larger, the effective refractive index increases, and light is coupled into the fifth tapered waveguide 17 and finally enters the straight waveguide 18 and then is output in the TE0 mode, as shown in fig. 4.

As shown in fig. 5, which is a graph of the coupling loss of light from a single mode fiber 1 having a diameter of 10 μm to a straight waveguide 18, the coupling loss is less than 0.9dB in the wavelength range of 1.5 μm to 1.62 μm, the coupling bandwidth is 120nm, and the coupler is not sensitive to wavelength. At a wavelength of 1.55 μm, the loss is 0.62 dB.

The device further reduces the effective refractive index of the end face of the silicon chip by adopting a grating structure, so that the effective refractive index of the end face of the silicon chip is more matched with that of the optical fiber, the coupling efficiency is increased, the effective refractive index is regulated and controlled by the duty ratio of the grating, and the regulation and control dimension is increased.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.