A four-port vertical grating coupler based on aperiodic structure
By introducing a Bragg mirror layer and an aperiodic grating layer structure into silicon-based photonic integrated circuits, the problems of low coupling efficiency and substrate light leakage are solved, achieving efficient light energy routing and uniform light splitting effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EAST CHINA JIAOTONG UNIVERSITY
- Filing Date
- 2026-06-01
- Publication Date
- 2026-06-30
AI Technical Summary
Existing two-dimensional grating couplers in silicon-based photonic integrated circuits suffer from problems such as low coupling efficiency, severe substrate light leakage, and high reflectivity. In particular, traditional circular ring gratings cannot efficiently match vertically incident beams and suffer from severe substrate light leakage.
A four-port vertical grating coupler with an aperiodic structure is designed by introducing an aperiodic alternating positive and negative duty cycle distribution of a Bragg mirror layer at the bottom and a single-layer grating layer at the top, combined with the alternating arrangement of silicon dielectric blocks and low-refractive-index filling regions, to achieve efficient orthogonal routing of light energy.
It significantly improved the coupling efficiency to 70.4%, reduced the reflectivity to no more than 30%, and achieved uniform beam splitting effect at four ports.
Smart Images
Figure CN122307824A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of silicon-based photonics and photonic integrated circuits, and particularly to a four-port vertical grating coupler based on an aperiodic structure. Background Technology
[0002] In silicon-based photonic integrated circuits, grating couplers are the core devices for achieving efficient coupling between external optical fibers and nanoscale optical waveguides on the chip. While existing two-dimensional grating couplers (such as standard concentric ring gratings) can achieve perpendicular light incidence and distribute the beam within the chip plane, they typically suffer from the following significant drawbacks:
[0003] First, the coupling efficiency is low. Due to the isotropic nature of the structure, traditional circular ring gratings cannot perfectly match the optical field mode of a vertically incident Gaussian beam, resulting in most of the light energy being scattered to the upper cladding or reflected back into the fiber. The overall coupling efficiency of conventional designs is usually difficult to exceed 50%.
[0004] Secondly, there is severe light leakage from the substrate. When grating etching is performed in a conventional silicon-on-insulator (SOI) structure, the light beam penetrates the buried oxide layer (BOX layer) as it radiates downwards, causing a large amount of light energy to leak into the silicon substrate and resulting in severe insertion loss.
[0005] Therefore, how to break the limitations of the continuous structure of conventional concentric rings and design a grating coupler that can significantly suppress substrate light leakage, reduce vertical reflectivity, and achieve efficient and uniform light splitting to four orthogonal ports is a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0006] To overcome the shortcomings of existing two-dimensional grating couplers, such as low coupling efficiency, severe substrate light leakage, and high reflectivity, this invention provides a four-port vertical grating coupler based on an aperiodic structure. By introducing a Bragg mirror layer at the bottom and combining it with the aperiodic positive and negative alternating duty cycle distribution of the top single-layer grating layer, efficient orthogonal routing of light energy is achieved.
[0007] The technical solution adopted by the present invention to solve its technical problem is: a four-port vertical grating coupler based on an aperiodic structure, which includes, from bottom to top: a silicon substrate, a Bragg mirror layer, a silicon dioxide lower cladding layer, a silicon plate layer and a single-layer grating layer.
[0008] The Bragg reflector layer consists of five pairs of alternating silicon and silicon dioxide layers, wherein the thickness of a single silicon layer is 112 nm and the thickness of a single silicon dioxide layer is 269 nm; the thickness of the silicon dioxide underlayer is 1985 nm; the thickness of the silicon plate layer is 155 nm; and the single-layer grating layer is formed by etching the silicon layer to a depth of 65 nm.
[0009] The single-layer grating layer has about axis, axis, diagonal and A two-dimensional geometric pattern that is perfectly symmetrical along the diagonal; the single-layer grating layer is composed of discrete silicon dielectric blocks and low-refractive-index filling regions arranged alternately, and its minimum feature size in the plane is defined as 147nm;
[0010] The local duty cycle along the principal axis of the single-layer grating is defined as follows: The local duty cycle in the diagonal direction is And duty cycle difference ;
[0011] The single-layer grating layer includes a central region and a peripheral region surrounding the central region; within the central region, i.e., radial distance... Within the range, the duty cycle difference Approaching -1.0, the high-refractive-index silicon dielectric exhibits a cross-shaped distribution extending along the diagonal direction;
[0012] The duty cycle difference within the outer region It exhibits an alternating distribution of positive and negative values along the radial direction; among which, at a radial distance for as well as Within the specified range, the medium distribution density along the main axis is higher than that along the diagonal direction; in the radial distance... for Within the specified range, the medium distribution density along the diagonal direction is higher than that along the principal axis.
[0013] The beneficial effects of this invention are:
[0014] 1. High coupling efficiency: The device efficiently reflects light that would otherwise leak into the substrate back to the top through five pairs of Bragg mirrors (DBR) at the bottom, and combines the non-periodic topological distribution of the single-layer grating layer to match the Gaussian beam, so that the total coupling efficiency of the device can reach 70.4% at the 1550nm operating wavelength.
[0015] 2. Low reflectivity: The high-refractive-index silicon dielectric in the central region of the single-layer grating layer is distributed in a cross pattern, which effectively breaks the strong reflection effect of the central continuous structure, so that the reflectivity when perpendicular light is incident is significantly reduced to no more than 30%.
[0016] 3. Good uniformity of four ports: The device has strict four-axis symmetry. Combined with the positive and negative oscillation law of the duty cycle of the principal axis and the diagonal direction, the equivalent refractive index gradient is precisely controlled, and the uniform routing of the four orthogonal waveguide ports of the perpendicularly incident light is perfectly realized. Attached Figure Description
[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0018] Figure 1 A longitudinal cross-sectional view of the high-coupling-efficiency four-port vertical grating coupler provided in this embodiment;
[0019] Figure 2 This is a top view schematic diagram of the single-layer grating layer provided in this embodiment.
[0020] In the figure: 1. Silicon substrate, 2. Bragg mirror layer, 3. Lower cladding layer of silicon dioxide, 4. Silicon plate layer, 5. Single-layer grating layer, 51. High refractive index silicon dielectric block, 52. Low refractive index filling hole, 6. Upper cladding layer of silicon dioxide, A. Incident light. Detailed Implementation
[0021]
Example 1
[0022] The following is combined Figure 1 and Figure 2 The present invention will be described in detail below.
[0023] like Figure 1 As shown in the cross-sectional structural diagram, this embodiment discloses a four-port vertical grating coupler based on an aperiodic structure, with a working center wavelength designed to be 1550nm. The device comprises, from bottom to top: a silicon substrate 1, a Bragg mirror layer 2, a silicon dioxide lower cladding layer 3, a silicon plate layer 4, and a single-layer grating layer 5.
[0024] The specific vertical dimensions and material configuration are as follows: The Bragg mirror layer 2 (DBR) is directly disposed on the silicon substrate 1, consisting of five pairs of alternating silicon and silicon dioxide layers. The thickness of a single silicon layer is designed to be 112 nm, and the thickness of a single silicon dioxide layer is designed to be 269 nm, providing high reflectivity blocking for light leakage from the underlying substrate. Above the Bragg mirror layer 2 is a 1985 nm thick silicon dioxide lower cladding layer 3 (i.e., the BOX layer). Adjacent to the silicon dioxide lower cladding layer 3 is a 155 nm thick silicon plate layer 4. A single-layer grating layer 5 is disposed on the silicon plate layer 4, formed by etching the silicon layer to a depth of 65 nm. A silicon dioxide upper cladding layer 6 covers and fills the top of the single-layer grating layer 5 and its internal holes.
[0025] Combination Figure 2 The top view shown shows that the single-layer grating layer 5 has information about axis, axis, diagonal and A complex two-dimensional geometric pattern with perfect diagonal symmetry. The single-layer grating layer 5 is composed of discrete high-refractive-index silicon dielectric blocks 51 and low-refractive-index filled holes 52 arranged alternately. To meet the manufacturing limitations of deep ultraviolet (DUV) lithography, the minimum feature size in the plane of this single-layer grating layer 5 (such as the minimum side length of the dielectric block or the minimum width of the hole) is strictly defined as 147 nm.
[0026] The core innovation of this invention lies in the specific spatial medium distribution pattern of the single-layer grating layer 5. The local duty cycle along the principal axis of the single-layer grating layer 5 is defined as... The local duty cycle in the diagonal direction is And duty cycle difference .
[0027] according to Figure 2 Layout analysis shows that the single-layer grating layer 5 includes a central region and a peripheral region surrounding the central region. Within the central region, i.e., the radial distance... Within the range, duty cycle difference =-1.0. This means that in this region, the high-refractive-index silicon dielectric blocks 51 are mainly concentrated in the diagonal direction, forming a cross-shaped (or star-shaped) distribution. This structure greatly alleviates the specular reflection of the perpendicularly incident light A at the very center.
[0028] Duty cycle difference within the aforementioned peripheral region It exhibits an aperiodic alternating distribution of positive and negative values along the radial direction outwards. Specifically, its characteristic structure is characterized by: a radial distance... for as well as Within the specified range, the medium distribution density along the principal axis is significantly higher than that along the diagonal direction. =0.95±0.05; while in the radial distance for Within the range, a reversal occurs, and the medium distribution density in the diagonal direction is higher than that in the principal axis direction.
[0029] Working principle and verification results: When the device is in operation, vertically incident light A with a wavelength of 1550nm illuminates the single-layer grating layer 5 from above. The incident light is modulated by the subwavelength structure with the specific duty cycle oscillation law described above, generating a strong azimuth phase gradient, which is uniformly guided to the four orthogonal planar waveguide directions. At the same time, the downward radiated energy is efficiently reflected by the five pairs of Bragg reflectors 2 at the bottom, and resonates with the top optical field. Through rigorous three-dimensional FDTD numerical simulation verification, the specific parameter combination structure disclosed in this invention successfully suppresses the vertical reflectivity of the device to 29.6% at a working wavelength of 1550nm, and the total coupling efficiency, i.e., the sum of the transmission rates of the four ports, is significantly improved to 70.8%.
Claims
1. A four-port vertical grating coupler based on an aperiodic structure, comprising a silicon substrate (1), a Bragg mirror layer (2) disposed on the silicon substrate (1), a silicon dioxide lower cladding layer (3) disposed on the Bragg mirror layer (2), and a silicon plate layer (4) disposed on the silicon dioxide lower cladding layer (3), characterized in that: A single-layer grating layer (5) formed by etching the silicon layer is disposed on the silicon plate layer (4), and the single-layer grating layer (5) has the following characteristics: axis, axis, diagonal and A two-dimensional geometric pattern with perfect diagonal symmetry. The single-layer grating layer (5) is composed of discrete high-refractive-index silicon dielectric blocks (51) and low-refractive-index filled holes (52) arranged alternately. The minimum feature size in the plane of the single-layer grating layer (5) is defined as 147 nm. The local duty cycle of the single-layer grating layer (5) in the principal axis direction is defined as... The local duty cycle in the diagonal direction is And duty cycle difference The single-layer grating layer (5) includes a central region and a peripheral region surrounding the central region, with a radial distance of Within the central region, the duty cycle difference The duty cycle difference is equal to -1.0 and the high refractive index silicon dielectric blocks (51) are distributed in a cross pattern extending diagonally, in the outer region. The distribution exhibits alternating positive and negative values along the radial direction, with the radial distance being... for as well as Within the specified interval, the medium distribution density along the main axis is higher than that along the diagonal direction, and the radial distance is... for Within the interval, the medium distribution density in the diagonal direction is higher than that in the principal axis direction.
2. The four-port vertical grating coupler based on an aperiodic structure according to claim 1, characterized in that: The Bragg reflector layer (2) consists of 5 pairs of alternating silicon and silicon dioxide layers, wherein the thickness of a single silicon layer is 112 nm and the thickness of a single silicon dioxide layer is 269 nm.
3. The four-port vertical grating coupler based on an aperiodic structure according to claim 1 or 2, characterized in that: The thickness of the silicon dioxide undercoat (3) is 1985 nm, the thickness of the silicon plate layer (4) is 155 nm, and the etching depth of the single-layer grating layer (5) is 65 nm.
4. The four-port vertical grating coupler based on an aperiodic structure according to claim 3, characterized in that: The low-refractive-index filling hole (52) above the single-layer grating layer (5) and the upper surface are covered with a silicon dioxide cladding layer (6).