Low-loss and high-alignment-tolerance end-face couplers for hybrid integration
By using a double-layer silicon nitride structure and a fork-shaped end-face coupler, the problem of mode field mismatch between III-V group lasers and silicon nitride chips is solved, achieving low-loss, high-efficiency coupling and large alignment tolerance, which is suitable for mass production in CMOS processes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI JIAOTONG UNIV
- Filing Date
- 2024-11-25
- Publication Date
- 2026-05-26
AI Technical Summary
In existing hybrid integration technologies, the mismatch in mode field size between III-V lasers and silicon nitride chips leads to significant coupling losses, and the manufacturing process is difficult, with small alignment tolerances, making mass production challenging.
The end-face coupler employs a double-layer silicon nitride structure and a fork-shaped structure, including tapered waveguides, inverted tapered structures, and narrow straight waveguides, to improve mode field overlap and alignment tolerance, and achieves efficient coupling through evanescent wave coupling.
It achieves low-loss coupling efficiency, increases alignment tolerance, simplifies the manufacturing process, is suitable for CMOS technology, and is easy to mass-produce.
Smart Images
Figure CN122085448A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a technology in the field of end-face coupling, specifically an end-face coupler for hybrid integration, achieving a coupling loss of 0.5 dB at a wavelength of 1.31 μm. Increasing the distance between the laser and the coupler from 0 μm to 10 μm only increases the coupling loss by 2 dB. Background Technology
[0002] Hybrid integration technology refers to the process where III-V active devices and silicon nitride passive devices are optimized and fabricated separately on their respective wafers, tested independently, and the best-performing devices are selected before being integrated together via end-face coupling. In existing hybrid integration schemes, the lack of efficient end-face couplers results in a significant mismatch in mode field dimensions between the III-V laser and the silicon nitride chip, leading to substantial coupling losses (typically greater than 3dB). This reduces device performance and increases the overall system power consumption, hindering its widespread application. Summary of the Invention
[0003] This invention addresses the shortcomings of existing technologies, such as high coupling loss, complex structure, difficult processing, difficulty in mass production, and large alignment tolerance. It proposes a low-loss and high-alignment-tolerance end-face coupler for hybrid integration, which uses a double-layer silicon nitride structure and a fork-shaped structure to improve the mode field overlap rate, increase coupling efficiency, and increase the longitudinal alignment tolerance between the III-V laser and the coupler.
[0004] This invention is achieved through the following technical solution:
[0005] The present invention relates to a low-loss and high-alignment-tolerance end-face coupler for hybrid integration, comprising: a tapered waveguide disposed on a buried oxide layer for evanescent wave coupling into a straight waveguide, a pair of narrow straight waveguides disposed in a silicon oxide cladding, and a pair of inverted tapered structures and straight waveguides located between the buried oxide layer and the silicon oxide cladding.
[0006] The pair of inverted cone structures include: a left-arm inverted cone structure and a right-arm inverted cone structure symmetrically arranged on both sides of the straight waveguide. The three together form a fork-shaped structure to improve the mode field overlap rate, increase the coupling efficiency, and at the same time increase the lateral alignment tolerance between the III-V group laser and the coupler.
[0007] The pair of narrow straight waveguides includes a left-arm narrow straight waveguide and a right-arm narrow straight waveguide symmetrically arranged on the outside of a pair of inverted conical structures, which together form a double-layer silicon nitride structure to improve the mode field overlap rate, increase the coupling efficiency, and increase the longitudinal alignment tolerance between the III-V group laser and the coupler.
[0008] The front end of the straight waveguide and the end of the inverted cone structure are respectively provided with tapered waveguides. The tapered waveguides are located on the buried oxide layer. The input optical signal is coupled into the straight waveguide through the tapered evanescent wave coupling structure, thereby improving the coupling efficiency. Technical effect
[0009] This invention uses a coupler with a double-layer coupling structure to achieve a greater overlap between the optical mode field generated by the III-V laser and the optical mode field at the end face of the silicon nitride chip, resulting in higher coupling efficiency. At the same time, the coupler of this invention is easy to process, can achieve coupling without grooving, suspension or polymer assistance, and has a large alignment tolerance, and is fully compatible with CMOS technology. Attached Figure Description
[0010] Figure 1 This is a schematic diagram of the structure of the present invention;
[0011] Figure 2 for Figure 1 Sectional view;
[0012] Figure 3 This is a schematic diagram of the first layer structure of a double-layer silicon nitride coupler.
[0013] Figure 4 This is a schematic diagram of the second layer structure of a double-layer silicon nitride coupler.
[0014] In the figure: 1 III-V laser, 2 silicon substrate, 3 buried oxide layer, 4 left arm inverted cone structure, 5 right arm inverted cone structure, 6-8 tapered waveguides for evanescent wave coupling into straight waveguides, 9 straight waveguide, 10 silicon oxide cladding, 11 left arm narrow straight waveguide, 12 right arm narrow straight waveguide;
[0015] Figure 5 This is a schematic diagram showing the simulation results of the coupler performance;
[0016] In the figure: (a) is the O-band coupling loss, (b) is the spacing alignment tolerance, (c) is the lateral alignment tolerance, and (d) is the longitudinal alignment tolerance. Detailed Implementation
[0017] like Figures 1-4 As shown, this embodiment relates to a low-loss and high-alignment-tolerance end-face coupler for hybrid integration, including: tapered waveguides 6-8 disposed in the buried oxide layer 3 for evanescent wave coupling into a straight waveguide, a pair of narrow straight waveguides 11 and 12 disposed in the silicon oxide cladding layer 10, and a pair of inverted cone structures 4 and 5 and a straight waveguide 9 located between the buried oxide layer 3 and the silicon oxide cladding layer 10.
[0018] The buried oxide layer 3 has a thickness of 3 μm, and a substrate silicon 2 is disposed beneath it.
[0019] like Figure 2 and Figure 3 As shown, the pair of inverted cone structures include a left-arm inverted cone structure 4 and a right-arm inverted cone structure 5, which are symmetrically arranged on both sides of the straight waveguide 9, and their thickness is 300nm.
[0020] like Figure 2 and Figure 3 As shown, the front end of the straight waveguide 9 and the ends of the inverted conical structures 4 and 5 are respectively provided with conical waveguides 6, 7 and 8, which are located on the buried oxide layer 3.
[0021] like Figure 2 and Figure 4 As shown, the pair of narrow straight waveguides includes a left-arm narrow straight waveguide 11 and a right-arm narrow straight waveguide 12, which are symmetrically arranged on the outside of a pair of inverted conical structures, and have a thickness of 300 nm.
[0022] This embodiment relates to the fabrication method of the above-mentioned coupler: First, a first silicon nitride structure is obtained on a SiNOI chip by ultraviolet lithography and etching processes. Then, a silicon oxide intermediate layer is deposited by plasma-enhanced chemical vapor deposition (PECVD). Next, a second silicon nitride layer is deposited by low-pressure chemical vapor deposition (LPCVD). Then, a second silicon nitride structure is obtained by ultraviolet lithography and etching processes. Then, a silicon oxide capping layer is deposited by PECVD. Finally, the chip is sliced.
[0023] like Figure 1 As shown, this embodiment relates to a signal processing method for the aforementioned coupler. By placing a III-V group laser at the middle position opposite the coupler, when the laser enters the coupler, it is transmitted along the left arm inverted cone structure 4, the right arm inverted cone structure 5, the left arm narrow straight waveguide 11, and the right arm narrow straight waveguide 12. During the transmission process, the light in the left arm narrow straight waveguide 11 and the right arm narrow straight waveguide 12 will enter the left arm inverted cone structure 4 and the right arm inverted cone structure 5 through evanescent wave coupling, and then be coupled into the straight waveguide 9 through the conical evanescent wave coupling structures 6 to 8, thereby realizing the function of efficient coupling between the III-V group laser and the silicon nitride chip.
[0024] like Figure 5 The figure shows the simulation results of the coupler's performance. Figure 5 (a) is the coupling loss between the coupler and the III-V laser in the O band (1260nm~1360nm). The coupling loss is less than 0.65dB throughout the O band, and only 0.5dB at 1310nm. Figure 5 (b) is the pitch alignment tolerance between the coupler and the III-V laser. As the pitch increases from 0 μm to 10 μm, the coupling loss only increases by 2 dB. Figure 5(c) represents the lateral alignment tolerance between the coupler and the III-V laser. The relative lateral position deviation between the two is ±3.25 μm, which increases the coupling loss by 3 dB. Figure 5 (c) represents the longitudinal alignment tolerance between the coupler and the III-V laser. The longitudinal relative position deviation between the two is ±2.35 μm, which increases the coupling loss by 3 dB.
[0025] Compared with existing technologies, this invention exhibits low loss, with a coupling loss of only 0.5 dB at a wavelength of 1.31 μm. The process is simple, easy to fabricate, and mass-producible. The coupling is a simple two-layer silicon nitride structure, requiring no grooving, suspension, or polymer assistance, and is fully compatible with CMOS processes. The alignment tolerance between the laser and the coupler was investigated, and the coupler demonstrates excellent alignment tolerance performance; as the distance between the laser and the coupler increased from 0 μm to 10 μm, the coupling loss only increased by 2 dB.
[0026] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.
Claims
1. A low-loss and high-alignment-tolerance end-face coupler for hybrid integration, characterized in that, include: A tapered waveguide disposed in the buried oxide layer for evanescent wave coupling into a straight waveguide, a pair of narrow straight waveguides disposed in the silicon oxide cladding, and a pair of inverted tapered structures and straight waveguides located between the buried oxide layer and the silicon oxide cladding; The pair of inverted cone structures include: a left-arm inverted cone structure and a right-arm inverted cone structure symmetrically arranged on both sides of the straight waveguide; The pair of narrow straight waveguides includes a left-arm narrow straight waveguide and a right-arm narrow straight waveguide, which are symmetrically arranged on the outside of a pair of inverted conical structures.
2. The low-loss and high-alignment-tolerance end-face coupler for hybrid integration according to claim 1, characterized in that, The left and right inverted cone structures on both sides of the straight waveguide together form a fork-shaped structure to improve the mode field overlap rate, increase the coupling efficiency, and at the same time increase the lateral alignment tolerance between the III-V group laser and the coupler.
3. The low-loss and high-alignment-tolerance end-face coupler for hybrid integration according to claim 1, characterized in that, The left and right narrow straight waveguides on the outer side of the pair of inverted conical structures together form a double-layer silicon nitride structure to improve the mode field overlap rate, increase the coupling efficiency, and at the same time increase the longitudinal alignment tolerance between the III-V group laser and the coupler.
4. The low-loss and high-alignment-tolerance end-face coupler for hybrid integration according to claim 1, characterized in that, The front end of the straight waveguide and the end of the inverted cone structure are respectively provided with tapered waveguides. The tapered waveguides are located on the buried oxide layer. The input optical signal is coupled into the straight waveguide through the tapered evanescent wave coupling structure, thereby improving the coupling efficiency.
5. The low-loss and high-alignment-tolerance end-face coupler for hybrid integration according to any one of claims 1-4, characterized in that, The thickness of the buried oxide layer is 3 μm; the thickness of the pair of inverted conical structures is 300 nm; and the thickness of the pair of narrow straight waveguides is 300 nm.
6. A method for manufacturing the coupler according to any one of claims 1-5, characterized in that, First, a first silicon nitride structure is obtained on the SiNOI chip through ultraviolet lithography and etching processes. Then, a silicon oxide intermediate layer is deposited using plasma-enhanced chemical vapor deposition (PECVD). Next, a second silicon nitride layer is deposited using low-pressure chemical vapor deposition (LPCVD). Then, a second silicon nitride structure is obtained again using ultraviolet lithography and etching processes. Finally, a silicon oxide capping layer is deposited using PECVD. Finally, the chip is sliced.
7. A signal processing method based on any one of the couplers described in claims 1-5, characterized in that, By placing a III-V laser in the middle of the coupler, when the laser enters the coupler, it propagates along the inverted cone structure of the left arm and the inverted cone structure of the right arm, as well as the narrow straight waveguide of the left arm and the narrow straight waveguide of the right arm. During the propagation, the light in the narrow straight waveguide of the left arm and the narrow straight waveguide of the right arm will enter the inverted cone structure of the left arm and the inverted cone structure of the right arm through evanescent wave coupling, and then be coupled into the straight waveguide through the tapered evanescent wave coupling structure, thus realizing the function of efficient coupling between the III-V laser and the silicon nitride chip.