CN-121995573-A - Low-loss edge coupling structure based on combination of trident waveguide and sub-wavelength grating

CN121995573ACN 121995573 ACN121995573 ACN 121995573ACN-121995573-A

Abstract

The invention discloses a low-loss edge coupling structure based on a trident waveguide and a sub-wavelength grating, which belongs to the field of photoelectron integration, wherein the trident waveguide consists of a middle waveguide in the middle and side waveguides on two sides, a section of sub-wavelength grating is arranged on the outer side of each side waveguide, the central axes of the sub-wavelength grating and the side waveguides are inclined to the center by a certain angle, and the two side waveguides and the two sub-wavelength gratings are symmetrically arranged on two sides of the middle waveguide. The structure can be used for effectively converting an external large-mode-spot optical field into a single-mode-field supported by a waveguide in an adiabatic manner by combining a unique trident layout with a sub-wavelength grating, so that high coupling efficiency, large alignment tolerance and good process compatibility are realized.

Inventors

YE NAN
SONG YIFEI
WU JUNYAN
LI WENYU
ZHU ZHENGLONG
HU YULIN

Assignees

上海大学

Dates

Publication Date: 20260508
Application Date: 20260126

Claims (10)

1. A low-loss edge coupling structure based on the combination of a trident waveguide and a sub-wavelength grating is characterized in that the outer side of each side waveguide is respectively provided with a section of sub-wavelength grating, the central axes of the sub-wavelength grating and the side waveguides are inclined to the center by a certain angle, and the two side waveguides and the two sub-wavelength gratings are symmetrically arranged on the two sides of the middle waveguide.
2. The low-loss edge coupling structure based on the combination of the trident waveguide and the sub-wavelength grating according to claim 1, wherein the middle waveguide consists of a first straight waveguide section, a transition section and a second straight waveguide section, the width of the side waveguide is gradually increased and then gradually decreased, and the width of the sub-wavelength grating is gradually decreased.
3. The low-loss edge coupling structure based on the combination of the trifurcate-based waveguide and the sub-wavelength grating according to claim 2, wherein the width of the first straight waveguide section is d1, the graded section is divided into two sections, the width d1 of the first graded section is increased to d2 at a smaller change rate k1, the width d2 of the second graded section is increased to d3 at a larger change rate k2, and the width of the second straight waveguide section is d3.
4. The low-loss edge-coupled structure based on a combination of a trifurcated and sub-wavelength grating as recited in claim 3, wherein the width of the edge waveguide increases gradually from d1 to d4 at a rate of change k and then decreases gradually from d4 to d1 at a rate of change-k.
5. The low-loss edge coupling structure based on a combination of a trifurcate-based waveguide and a sub-wavelength grating as claimed in claim 3, wherein the sub-wavelength grating has an initial width greater than d1 and an end width less than d1.
6. The low-loss edge coupling structure based on the combination of the trifurcate-based waveguide and the sub-wavelength grating according to claim 4, wherein the length of the first straight waveguide section is L1, the length of the first graded section is L2, the length of the second graded section is L3, the projection length of the edge waveguide on the central axis is L4, the projection length of the sub-wavelength grating on the central axis is L5, (L1+L2+L3) > L4> L5.
7. The low-loss edge coupling structure based on the combination of a trigeminal waveguide and a sub-wavelength grating according to claim 3, wherein the minimum spacing between the sub-wavelength grating and the side waveguide is greater than 110nm, and the minimum spacing between the side waveguide and the middle waveguide is greater than 110nm.
8. The low-loss edge coupling structure based on the combination of the trident waveguide and the sub-wavelength grating according to claim 3, wherein the sub-wavelength grating, the side waveguide and the middle waveguide have the same height.
9. The low-loss edge coupling structure based on the combination of a trifurcate-based waveguide and a sub-wavelength grating according to any one of claims 1-8, wherein the middle waveguide, the two side waveguides and the two sub-wavelength gratings are all located on the upper surface of the buried oxide layer and are encapsulated by the cladding.
10. The low-loss edge coupling structure based on the combination of the trident waveguide and the sub-wavelength grating according to claim 9, wherein the cladding is made of silicon dioxide, and the middle waveguide, the two side waveguides and the two sub-wavelength gratings are passive silicon waveguides.

Description

Low-loss edge coupling structure based on combination of trident waveguide and sub-wavelength grating Technical Field The invention belongs to the field of photoelectron integration, and particularly relates to an edge coupler structure for realizing low-loss coupling of a single-mode SOI waveguide and a large-mode-spot-scale edge-emitting laser by utilizing a three-fork structure. Background Due to the advantages of broadband optical signals, low delay, low power consumption and low crosstalk, on-chip silicon photonic interconnects based on silicon-based photonic chips are an advantageous candidate for breaking through the bandwidth bottleneck of large-scale integrated circuits. However, because of the large mode mismatch between the outgoing light spot of the edge-emitting semiconductor laser (edge-emitting semiconductor optical amplifier/modulator, and edge-incident photodetector) and the light spot transmitted between the on-chip integrated silicon-based waveguide, achieving high performance coupling with the chip is critical. The mode-spot-transformer based edge coupling scheme allows for efficient edge-emitting semiconductor laser-chip coupling with a larger operating bandwidth compared to vertical coupling schemes that have a small operating bandwidth and are extremely polarization sensitive. The most common approach for coupling a side-emitting semiconductor laser (side-emitting semiconductor optical amplifier/modulator, side-incident photodetector) to a silicon optical chip is to use a linear back taper as an edge coupler. But the coupling efficiency of the edge coupler is closely related to the cone tip width. Because of the large aspect ratio of the back taper, it is difficult to realize an edge coupling scheme with strong single mode characteristics by using a 2-3 μm thick silicon waveguide. Therefore, a series of dual port edge couplers such as Y-couplers, directional couplers, MMI couplers, and the like, which require connection to bus waveguides, have been designed in the past. These schemes not only add complexity to the device itself and tolerances in process fabrication, but also introduce additional polarization and wavelength effects on the structure. Other approaches, such as cantilever couplers and sub-wavelength back taper coupler structures, require more complex fabrication processes, materials and precision requirements for standard CMOS processes. Meanwhile, there is a general need in the industry for a side-emitting semiconductor laser (side-emitting semiconductor optical amplifier/modulator, and side-incident photodetector) having a large exit spot to facilitate spatial optical coupling with the outside. However, edge-emitting semiconductor lasers (edge-emitting semiconductor optical amplifiers/modulators, and edge-incident photodetectors) typically possess large spot sizes and asymmetric characteristics. Thus, it requires special structures to achieve low loss coupling when SOI platforms are integrated on-chip. The edge coupler structure losses of the current mainstream are generally higher than 3dB. Existing on-chip edge couplers are more based on silicon nitride platforms. Silicon nitride processing is more difficult than SOI platforms and cannot be integrated with active materials (e.g., ge, etc.). Meanwhile, the edge coupler of the SOI platform mostly uses a single cone structure. The single cone structure is often suitable for coupling with optical fibers, and when it is coupled with the light spot of an edge-emitting semiconductor laser (edge-emitting semiconductor optical amplifier/modulator, and edge-incident photoelectric detector) with asymmetric characteristics, it is difficult to further optimize the light spot according to the large-size light spot due to the symmetric light spot characteristics of the structure itself. Based on the above factors, the edge coupler structure utilizing the combination of the trident and the sub-wavelength grating waveguide is provided, and the edge coupler structure has the advantages of high coupling performance, large working bandwidth, insensitivity to polarization and large process tolerance on the basis of being compatible with the traditional thin film waveguide silicon light preparation process. Disclosure of Invention The invention aims to provide a low-loss edge coupling structure based on the combination of a trident waveguide and a sub-wavelength grating. The structure can be used for effectively converting an external large-mode-spot optical field into a single-mode-field supported by a waveguide in an adiabatic manner by combining a unique trident layout with a sub-wavelength grating, so that high coupling efficiency, large alignment tolerance and good process compatibility are realized. The technical scheme of the invention is as follows: The low-loss edge coupling structure based on the combination of the trident waveguide and the sub-wavelength grating comprises a middle waveguide in the middle and side waveguides on t