Grating coupler and preparation method and application thereof
By employing a non-periodic apodized gratings and a grating coupler with a double taper structure, the problem of low grating coupling efficiency is solved, achieving efficient fiber-to-chip optical signal transmission and reducing production costs, making it suitable for diverse photonic chip designs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 广州光电存算芯片融合创新中心
- Filing Date
- 2024-12-25
- Publication Date
- 2026-06-09
AI Technical Summary
Existing grating coupling technology suffers from low coupling efficiency, making it difficult to achieve efficient fiber-to-chip optical signal transmission.
A grating coupler employing an aperiodic apodized grating structure and a double-tapered structure is used. By combining the large refractive index difference between amorphous silicon and silicon dioxide through vertical coupling, the etching depth and duty cycle of the grating are optimized to meet the Bragg diffraction conditions and improve coupling efficiency.
It significantly improves the optical signal coupling efficiency from fiber to chip, reduces production costs, and is compatible with CMOS processes, making it suitable for diverse photonic chip designs.
Smart Images
Figure CN119596454B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of integrated photonics, and more specifically, to a grating coupler, its fabrication method, and its application. Background Technology
[0002] In the context of rapid information technology development, optical communication and optical interconnect technologies have advanced rapidly in terms of transmission distance and capacity. The accompanying surge in global data volume has posed new challenges to data transmission and processing technologies. There is an urgent need for more efficient transmission and processing methods to meet the demands of this massive data growth. Traditional multiplexing dimensions such as amplitude, wavelength, and polarization are gradually approaching their performance limits. New multiplexing technologies based on multi-core, multimode optical fibers, such as space division and mode division, have become new means to improve system transmission capacity. However, these technologies introduce more complex problems such as distortion and crosstalk during transmission, placing higher performance demands on signal processing units. Electronic devices face significant challenges in processing massive amounts of data, mainly due to two core issues: first, the failure of Moore's Law has led to bottlenecks in the performance growth and energy efficiency improvement of electronic processors; second, although the clock frequencies of electronic processors have reached the GHz level, even through parallel computing or architectural optimization, it is impossible to fundamentally bridge the huge gap between processor operating speed and data flow speed.
[0003] Against this backdrop, integrated photonics technology offers a solution for high-speed data processing and transmission. Utilizing photons as information carriers, integrated photonics technology constructs optical systems to perform complex information processing or data computation. It boasts advantages such as high processing speed, low energy efficiency, strong anti-interference capabilities, compact structure, stability, and low cost, providing a new solution for overcoming current bottlenecks in information and data processing.
[0004] On the road to commercialization and maturity of photonic chip technology, a series of technical challenges need to be overcome. Among them, achieving efficient optical coupling between the chip and optical fiber is particularly critical. Currently, grating coupling technology has become the mainstream solution due to its design flexibility. Grating couplers can achieve optical signal coupling from optical fiber to chip, as well as reverse coupling, but they also face technical challenges such as coupling efficiency. Therefore, it is necessary to improve coupling efficiency. Summary of the Invention
[0005] In view of the problem of low coupling efficiency of existing coupling devices, the present invention provides a grating coupler, its fabrication method and application, to improve coupling performance.
[0006] In a first aspect, the present invention provides a grating coupler comprising, from bottom to top, a substrate layer, a silicon oxide lower cladding layer, a silicon nitride waveguide layer, a silicon oxide buffer layer, an amorphous silicon layer, and a silicon oxide upper cladding layer;
[0007] The amorphous silicon layer comprises, from bottom to top, an amorphous silicon waveguide and an amorphous silicon grating;
[0008] Both the amorphous silicon waveguide and the silicon nitride waveguide layer include a first straight waveguide, a linearly tapered waveguide, and a second straight waveguide connected in sequence. The silicon nitride waveguide layer and the amorphous silicon waveguide form a double taper structure.
[0009] The amorphous silicon grating is located on the second straight waveguide of the amorphous silicon waveguide.
[0010] The silicon nitride waveguide layer and the amorphous silicon waveguide form a double tapered structure. This structure uses a vertical coupling method to couple the mode of the silicon nitride waveguide into the amorphous silicon waveguide, and utilizes the large refractive index difference between amorphous silicon and silicon dioxide to achieve higher grating diffraction efficiency, thereby improving the coupling efficiency.
[0011] In a preferred embodiment, the amorphous silicon grating is an aperiodic apodized grating structure with an etching depth of 100-200 nanometers. The duty cycle f of each unit of the grating varies linearly along the z-direction and satisfies formulas (1) and (2).
[0012] f = f0 - R·z (1)
[0013]
[0014] Where f0 is the duty cycle of the initial grating cell, in %;
[0015] R is the apodilation coefficient, which is dimensionless;
[0016] z is the length along the z-direction, in nm;
[0017] ∧ represents the grating period, measured in nm.
[0018] λ is the wavelength of light; the unit is nm.
[0019] n eff It is the effective refractive index of light in the amorphous silicon grating, and is dimensionless.
[0020] θ is the diffraction angle, in degrees.
[0021] By selecting an amorphous silicon grating as a non-periodic apodized grating structure, and controlling the grating etching depth to a specific value and ensuring that the period and duty cycle of each unit satisfy the above formula, each unit of the grating coupler conforms to the Bragg diffraction condition, thereby maximizing the coupling performance.
[0022] In a preferred embodiment, f0 = 0.95, θ = 8°, and R = 0.025.
[0023] In a preferred embodiment, the thickness of the silicon oxide cladding layer is 1.27 micrometers, the thickness of the silicon oxide buffer layer is 50 nanometers, and the thickness of the amorphous silicon layer is 260 nanometers. Selecting the thickness of the silicon oxide cladding layer within the above range ensures that the diffracted light wave and the reflected light wave achieve constructive interference, further improving diffraction efficiency.
[0024] In a preferred embodiment, the width of the amorphous silicon grating is 36 micrometers and the length of the amorphous silicon waveguide is 125 micrometers.
[0025] In a preferred embodiment, the linearly tapered waveguide of the amorphous silicon waveguide includes a first end face and a second end face opposite to each other, wherein the width of the second end face is greater than the width of the first end face.
[0026] In the amorphous silicon waveguide, the width of the first straight waveguide is the same as the width of the first end face and the first straight waveguide is connected to the first end face; the width of the second straight waveguide is the same as the width of the second end face and the second straight waveguide is connected to the second end face.
[0027] In a preferred embodiment, the width and height of the amorphous silicon waveguide are consistent with those of the amorphous silicon grating connection end face.
[0028] In a preferred embodiment, the amorphous silicon grating includes an unetched portion of the amorphous silicon grating and an unetched portion of the amorphous silicon grating, with adjacent unetched portions of the amorphous silicon grating and the unetched portions of the amorphous silicon grating forming an L-shape, and the heights of the unetched portions of the amorphous silicon grating and the unetched portions of the amorphous silicon grating are consistent.
[0029] In a preferred embodiment, the adapter coupling fiber of the grating coupler is a single-mode fiber, the input light source is in TE mode, and the operating band is C-band.
[0030] In a second aspect, the present invention provides a method for fabricating the grating coupler, characterized by comprising the following steps: depositing a silicon nitride thin film on a thermally oxidized silicon wafer, then fabricating a silicon nitride waveguide on the silicon nitride thin film to form a silicon nitride waveguide layer, then depositing a silicon oxide buffer layer on the silicon nitride waveguide layer, subsequently depositing an amorphous silicon layer on the silicon oxide buffer layer and fabricating an amorphous silicon waveguide and an amorphous silicon grating, and finally depositing an upper silicon oxide cladding layer; wherein the thermally oxidized silicon wafer comprises a substrate layer and a lower silicon oxide cladding layer.
[0031] Thirdly, the present invention provides an optical waveguide chip, including the grating coupler.
[0032] This invention can bring the following positive effects:
[0033] (1) The present invention can improve the optical signal coupling efficiency from optical fiber to chip.
[0034] (2) The present invention is compatible with CMOS process and can reduce production costs.
[0035] (3) The grating coupler structure of the present invention can be more flexibly integrated into different photonic chip designs to meet diverse application needs. Attached Figure Description
[0036] To fully grasp the present invention and its significant advantages, a detailed description will be provided below in conjunction with the accompanying drawings, wherein:
[0037] Figure 1 This is a longitudinal cross-sectional schematic diagram of a grating coupler according to an embodiment of the present invention;
[0038] Figure 2 This is a top view of an amorphous silicon layer in a grating coupler according to an embodiment of the present invention;
[0039] Figure 3 This is a schematic diagram of the longitudinal cross-section of a grating unit in a grating coupler according to an embodiment of the present invention;
[0040] Figure 4 This is a top view of a silicon nitride-amorphous silicon composite layer in a grating coupler according to an embodiment of the present invention;
[0041] Figure 5 This is a specific application scenario of a grating coupler and external optical fiber coupling according to an embodiment of the present invention;
[0042] Figure 6 This is a schematic diagram of the fabrication process of a grating coupler according to an embodiment of the present invention.
[0043] [Explanation of Labels in the Attached Image]
[0044] 101-Substrate layer; 102-Silicon oxide lower cladding layer; 103-Silicon nitride waveguide layer; 104-Silicon oxide buffer layer; 105-Amorphous silicon layer; 1051-Amorphous silicon waveguide; 1052-Amorphous silicon grating; 1052a-Unetched portion of amorphous silicon grating; 1052b-Etched portion of amorphous silicon grating; 106-Silicon oxide upper cladding layer; 107-Fiber optic cable. Detailed Implementation
[0045] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.
[0046] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;
[0047] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.
[0048] The present invention will now be described in conjunction with the accompanying drawings and embodiments.
[0049] Example 1
[0050] This embodiment provides a grating coupler, the structure of which is as follows: Figures 1-4 As shown.
[0051] Depend on Figure 1 It can be seen that the grating coupler includes, from bottom to top, a substrate layer 101, a silicon oxide lower cladding layer 102, a silicon nitride waveguide layer 103, a silicon oxide buffer layer 104, an amorphous silicon layer 105, and a silicon oxide upper cladding layer 106; wherein, the amorphous silicon layer 105 includes, from bottom to top, an amorphous silicon waveguide 1051 and an amorphous silicon grating 1052, and the amorphous silicon grating 1052 is connected to the amorphous silicon waveguide 1051; the amorphous silicon waveguide 1051 and the amorphous silicon grating 1052 are disposed between the silicon oxide buffer layer 104 and the silicon oxide upper cladding layer 106, and the silicon nitride waveguide 103, the amorphous silicon waveguide 1051, and the amorphous silicon grating 1052 together constitute a silicon nitride-amorphous silicon composite layer.
[0052] Depend on Figure 2 and 4 It is known that both the amorphous silicon waveguide 1051 and the silicon nitride waveguide layer 103 include a first straight waveguide, a linearly graded waveguide, and a second straight waveguide. The linearly graded waveguide of the amorphous silicon waveguide 1051 includes opposing first and second end faces, with the width of the second end face being greater than the width of the first end face. In the amorphous silicon waveguide 1051, the width of the first straight waveguide is the same as the width of the first end face and is connected to the first end face; the width of the second straight waveguide is the same as the width of the second end face and is connected to the second end face. The amorphous silicon grating 1052 is located on the second straight waveguide of the amorphous silicon waveguide 1051. The amorphous silicon waveguide 1051 and the silicon nitride waveguide layer 103 together form a double-tapered structure. This structure uses vertical coupling to couple light from the silicon nitride waveguide layer 103 into the amorphous silicon waveguide 1051, and utilizes the large refractive index difference between amorphous silicon and silicon dioxide to achieve higher grating diffraction efficiency, thereby improving coupling efficiency. In addition, the amorphous silicon grating 1052 is an aperiodic apodized grating structure with an etching depth of 160 nanometers. The duty cycle f of each unit of the grating varies linearly along the z-direction and satisfies formulas (1) and (2).
[0053] f = f0 - R·z (1)
[0054]
[0055] Where f0 is the duty cycle of the initial grating cell, in %;
[0056] R is the apodilation coefficient, which is dimensionless;
[0057] z is the length along the z-direction, in nm;
[0058] ∧ represents the grating period, measured in nm.
[0059] λ is the wavelength of light, measured in nm.
[0060] n eff It is the effective refractive index of light in the amorphous silicon grating 1052, which is dimensionless;
[0061] θ is the diffraction angle in degrees. By adjusting the etching depth of the grating and the period and duty cycle of each unit to satisfy the above formulas (1) and (2), each unit of the grating coupler conforms to the Bragg diffraction condition, thereby maximizing the coupling efficiency. Where f0 = 0.95, θ = 8°, and R = 0.025.
[0062] The amorphous silicon grating 1052 has a width of 36 micrometers, and the amorphous silicon waveguide 1051 has a length of 125 micrometers. The width and height of the connection end face between the amorphous silicon waveguide 1051 and the amorphous silicon grating 1052 are the same.
[0063] Depend on Figure 3 As can be seen, the amorphous silicon grating 1052 includes an unetched portion 1052a and an unetched portion 1052b. Adjacent unetched portions 1052a and 1052b form an L-shape, thus making the grating structure unit L-shaped. The heights of the unetched portions 1052a and 1052b are the same. The specific number of grating structure units can be determined by the technician based on the requirements of the target device size and performance.
[0064] The silicon oxide cladding layer 106 has a thickness of 1.27 micrometers, the substrate layer 101 has a thickness of 2 micrometers, the silicon nitride waveguide layer 103 has a thickness of 850 nanometers, the silicon oxide buffer layer 104 has a thickness of 50 nanometers, and the amorphous silicon layer 105 has a thickness of 260 nanometers. By optimizing the thickness of the silicon oxide cladding layer 106 to the above values, constructive interference conditions are achieved between the diffracted and reflected light waves, further improving diffraction efficiency. The thickness of each layer can be adjusted according to actual application conditions to meet specific requirements.
[0065] according to Figure 5 The grating coupler of this embodiment, combined with a single-mode fiber 107 with an 8-degree bevel angle, can be used to achieve optical coupling between the chip and an external light source. When the input light source of the single-mode fiber 107 is in TE mode and the operating wavelength is C-band, the coupling loss is 3.87 dB and the 3-dB bandwidth is 18 nanometers.
[0066] The fabrication method of the grating coupler in this embodiment includes the following steps: depositing a silicon nitride thin film on a thermally heated silicon oxide wafer, then fabricating a silicon nitride waveguide on the silicon nitride thin film to form a silicon nitride waveguide layer 103, then depositing a silicon oxide buffer layer 104 on the silicon nitride waveguide layer 103, then depositing an amorphous silicon layer 105 on the silicon oxide buffer layer 104 and fabricating an amorphous silicon waveguide 1051 and an amorphous silicon grating 1052, and finally depositing an upper silicon oxide cladding layer 106; the thermally heated silicon oxide wafer includes a substrate layer 101 and a lower silicon oxide cladding layer 102.
[0067] Comparative Example 1
[0068] This comparative example provides a grating coupler that differs from Example 1 in that both the silicon nitride waveguide layer and the amorphous silicon waveguide are straight waveguides, and the silicon nitride waveguide layer and the amorphous silicon waveguide do not form a double taper structure. When this comparative example grating coupler is combined with a single-mode fiber 107 with an 8-degree bevel angle, and the input light source of the single-mode fiber 107 is in TE mode and the operating wavelength is C-band, the coupling loss is 6.9 dB, and the 3-dB bandwidth is 15 nanometers.
[0069] Comparative Example 2
[0070] This embodiment provides a grating coupler, which differs from Embodiment 1 in that the depth of the amorphous silicon grating etching position is 260 nanometers. When this grating coupler is combined with a single-mode fiber 107 with an 8-degree grinding angle, and the input light source of the single-mode fiber 107 is in TE mode and the operating wavelength is C-band, the coupling loss is 5.87 dB, and the 3-dB bandwidth is 18 nanometers.
[0071] Comparative Example 3
[0072] This embodiment provides a grating coupler, which differs from Embodiment 1 in that the grating duty cycle f is fixed at 0.52 instead of varying linearly along the z-direction, i.e., it does not satisfy formula (1). When the grating coupler of this embodiment is combined with a single-mode fiber 107 with a ground angle of 8 degrees, and the input light source of the single-mode fiber 107 is in TE mode and the operating band is C-band, the coupling loss is 5.89 dB and the 3-dB bandwidth is 16 nanometers.
[0073] Comparative Example 4
[0074] This embodiment provides a grating coupler, which differs from Embodiment 1 in that the grating period ∧ = 1268 nm, which does not satisfy formula (2). When the grating coupler of this embodiment is combined with a single-mode fiber 107 with a ground angle of 8 degrees, and the input light source of the single-mode fiber 107 is in TE mode and the working band is C band, the coupling loss is 6.32 dB and the 3-dB bandwidth is 18 nm.
[0075] Comparative Example 5
[0076] This embodiment provides a grating coupler, which differs from Embodiment 1 in that the cladding thickness on the silicon oxide layer is 3 micrometers. When this grating coupler is combined with a single-mode fiber 107 with an 8-degree bevel angle, and the input light source of the single-mode fiber 107 is in TE mode and the operating wavelength is C-band, the coupling loss is 5.43 dB, and the 3-dB bandwidth is 18 nanometers.
[0077] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.
[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A grating coupler, characterized in that, From bottom to top, it includes a substrate layer (101), a silicon oxide lower cladding layer (102), a silicon nitride waveguide layer (103), a silicon oxide buffer layer (104), an amorphous silicon layer (105), and a silicon oxide upper cladding layer (106). The amorphous silicon layer (105) includes, from bottom to top, an amorphous silicon waveguide (1051) and an amorphous silicon grating (1052). The amorphous silicon waveguide (1051) and the silicon nitride waveguide layer (103) each contain a first straight waveguide, a linearly tapered waveguide and a second straight waveguide connected in sequence. The silicon nitride waveguide layer (103) and the amorphous silicon waveguide (1051) form a double tapered structure. The amorphous silicon grating (1052) is located on the second straight waveguide of the amorphous silicon waveguide (1051); The amorphous silicon grating (1052) is a non-periodic apodized grating structure with an etching depth of 100-200 nanometers; the duty cycle of each unit of the grating is... f It varies linearly along the z-direction and satisfies formulas (1) and (2). in, It is the duty cycle of the initial unit of the grating, which is dimensionless; R It is the apodilation coefficient, which is dimensionless; It is the normalized position of the amorphous silicon grating (1052) along the lead-out direction, and is dimensionless; It is the grating period, in nm; λ is the wavelength of light; the unit is nm. It is the effective refractive index of light in the amorphous silicon grating (1052), which is dimensionless; It is the diffraction angle, in degrees (°). The z-direction is the lead-out direction of the amorphous silicon grating (1052).
2. The grating coupler according to claim 1, characterized in that, The =0.95, the The R =0.
025.
3. The grating coupler according to claim 1, characterized in that, The silicon oxide cladding layer (106) has a thickness of 1.27 micrometers, the silicon oxide buffer layer (104) has a thickness of 50 nanometers, and the amorphous silicon layer (105) has a thickness of 260 nanometers.
4. The grating coupler according to claim 1, characterized in that, The amorphous silicon grating (1052) has a width of 36 micrometers, and the amorphous silicon waveguide (1051) has a length of 125 micrometers.
5. The grating coupler according to claim 1, characterized in that, The linearly tapered waveguide of the amorphous silicon waveguide (1051) includes a first end face and a second end face opposite to each other, wherein the width of the second end face is greater than the width of the first end face. In the amorphous silicon waveguide (1051), the width of the first straight waveguide is the same as the width of the first end face and the first straight waveguide is connected to the first end face; the width of the second straight waveguide is the same as the width of the second end face and the second straight waveguide is connected to the second end face. The width and height of the connection end face between the amorphous silicon waveguide (1051) and the amorphous silicon grating (1052) are the same.
6. The grating coupler according to claim 1, characterized in that, The amorphous silicon grating (1052) is composed of alternating etched portions (1052b) and unetched portions (1052a). In the cross-section along the extension direction of the grating, adjacent etched portions (1052b) and unetched portions (1052a) form an L-shaped stepped structure. The height of each unetched portion (1052a) is consistent, and the depth of each etched portion (1052b) is consistent.
7. The grating coupler according to claim 1, characterized in that, The adapter coupling fiber of the grating coupler is a single-mode fiber, the input light source is in TE mode, and the operating band is C-band.
8. The method for fabricating a grating coupler according to any one of claims 1 to 7, characterized in that, Includes the following steps: A silicon nitride thin film is deposited on a thermally oxidized silicon wafer, and a silicon nitride waveguide is then fabricated on the silicon nitride thin film to form a silicon nitride waveguide layer (103). A silicon oxide buffer layer (104) is then deposited on the silicon nitride waveguide layer (103). Subsequently, an amorphous silicon layer (105) is deposited on the silicon oxide buffer layer (104) and an amorphous silicon waveguide (1051) and an amorphous silicon grating (1052) are fabricated. Finally, an upper silicon oxide cladding layer (106) is deposited. The thermally oxidized silicon wafer includes a substrate layer (101) and a lower silicon oxide cladding layer (102).
9. An optical waveguide chip, characterized in that, Includes the grating coupler as described in any one of claims 1 to 7.