A blazed subwavelength grating coupler

Abstract

The present invention discloses a blazed sub-wavelength grating coupler disposed on an optical waveguide layer. The grating coupler includes a plurality of grating periods, and each grating period is composed of a sub-wavelength grating structure region and a planar waveguide region. A plurality of blazed grating holes are arranged at equal intervals within the sub-wavelength grating structure region. The blazed grating holes are all through holes that connect the top and bottom of the optical waveguide layer. A stepped structure is arranged from the top to the bottom within each blazed grating hole. A coupled waveguide region is provided on the optical waveguide layer. The present invention can improve the directivity of the grating coupler. The grating coupler can be coupled with grating structures such as apodization and focusing, further improving the optical field coupling efficiency of the grating coupler, reducing reflection, and reducing the device size, opening up a new way for realizing high-performance and low-cost waveguide optical field coupling packaging technology.

Description

Technical Field

[0001] The present invention belongs to the field of integrated optoelectronics, and particularly relates to a novel blazed sub-wavelength grating coupler. Background Art

[0002] Integrated optoelectronic technology has been widely studied in recent years and has broad application prospects in many important fields such as optical communication, optical sensing, optical computing, and optical metrology. The grating coupler can realize the optical field coupling between the optical fiber and the optical waveguide, and has the advantages of not requiring lens optical fibers and chip edge polishing processes, easy alignment method, flexible alignment position, and easy realization of automatic alignment. It is an important packaging technology. Since the grating coupler has a flexible structure design and strong scalability, the grating coupler can be designed according to different requirements. For example, by combining the grating coupler with the sub-wavelength structure to develop a sub-wavelength grating coupler, the coupling strength of the coupler can be adjusted by regulating the effective refractive index of the sub-wavelength structure, and a novel grating coupler with low reflection and wide bandwidth can be developed. In addition, the fabrication of the grating coupler can be compatible with multi-project wafer (MPW) to realize mass production and low-cost device preparation.

[0003] The coupling efficiency is one of the most important performance indicators of a grating coupler. To improve the coupling efficiency, it is crucial to enhance the directivity of the grating coupler. In recent years, researchers have achieved some results in the study of the directivity of grating couplers. In terms of papers, in 2012, Zhenzhou Cheng et al. from The Chinese University of Hong Kong reported a focused apodized subwavelength grating coupler (Applied Physics Letters 101, 101104). The directivity of this subwavelength grating coupler mainly depends on the thickness of the top silicon layer and the buried oxide layer, and is independent of the parameters of the grating structure. In 2014, Daniel Benedikovic et al. from the University of Žilina in the Slovak Republic improved the directivity of the grating coupler by adjusting the thickness of the buried oxide layer and the fiber incident angle (Laser&Photonics Reviews 8, L93). This subwavelength grating coupler can achieve efficient coupling of -2.16 dB in the 1550 nm band. Further, the above research group also reported a blazed grating coupler with cross grooves (Optics Letters 40, 18, 4190). By controlling the parameters of the blazed structure of the cross grooves, the directivity of the grating coupler can be significantly improved, but the characteristic parameters of this blazed structure are small and the manufacturing process requirements are high. In 2017, Tatsuhiko Watanabe et al. from the Swiss Federal Institute of Technology in Zurich developed a vertically coupled blazed grating coupler (Journal of Lightwave Technology 35, 21, 4663). This grating coupler relies on an L-shaped blazed structure to improve the directivity and can achieve vertical coupling, but this blazed structure also faces the problems of too small characteristic parameters and high manufacturing process requirements. In 2021, Rongxiang Guo et al. from Tianjin University reported a ultra-thin subwavelength grating coupler (OpticsLetters 47, 5, 1226). This grating coupler is fabricated based on the MPW process, has a large spectral bandwidth and low reflection. By reducing the thickness of the grating coupler, the directivity of the grating coupler can also be improved, but the improvement of the directivity is relatively limited. In terms of patents, in 2012, Haisheng Rong et al. from Intel Corporation in the United States invented a high-efficiency silicon-on-insulator (SOI) grating coupler, and obtained a Chinese invention patent authorization (ZL201280016341.7). In 2015, Liu Liu et al. from South China Normal University invented an inclined silicon-based grating coupler for vertical coupling, and obtained a Chinese invention patent authorization (ZL201520845532.5). In 2019, Jiahui Ye et al. from China University of Geosciences invented an M-type waveguide grating coupler with high coupling efficiency, which achieved high-efficiency optical field coupling near the 1580 nm wavelength, and obtained a Chinese invention patent authorization (ZL201911238254.6).In 2021, Luo Xiangyu et al. from Zhejiang University invented an efficient broadband grating coupler, which uses a reflection grating with an oxide buried layer to improve directivity and was granted a Chinese invention patent (ZL202110543354.0). In 2022, Yang Sihan et al. from Shanghai Jiao Tong University invented a binary blazed grating coupler, which can be used for efficient vertical coupling and was granted a Chinese invention patent (ZL202111242481.3).

[0004] In summary, although subwavelength grating couplers have the advantages of simple manufacturing process and large manufacturing tolerance, their directivity is generally not high and can only be controlled by adjusting the thickness of the oxide buried layer or the top silicon layer of the wafer. On the other hand, although blazed gratings can improve directivity by controlling the structure, their structure is complex, the feature size is small, and it is difficult to fabricate devices using standard MPW processes. Developing new grating structures to achieve high-efficiency optical field coupling is of great significance for the research and development of high-quality, low-cost, and highly integrated opto-electronic integrated circuits (OEICs). Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of low directivity of traditional grating couplers. A blazed subwavelength grating coupler is proposed and fabricated.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A blazed subwavelength grating coupler is disposed on an optical waveguide layer. The grating coupler includes a plurality of grating periods, and each grating period is composed of a subwavelength grating structure region and a planar waveguide region;

[0008] A plurality of blazed grating holes are arranged at equal intervals within the subwavelength grating structure region. The blazed grating holes are all through holes connecting the top and bottom of the optical waveguide layer, and a stepped structure is provided from the top to the bottom within each blazed grating hole;

[0009] A coupled waveguide region is provided on the optical waveguide layer.

[0010] Further, the stepped structure is composed of steps with different heights, and there are two or more steps.

[0011] Further, the incident angle of the optical field of the blazed subwavelength grating coupler is perpendicular to the plane of the blazed subwavelength grating coupler or has an inclined angle with the plane of the blazed subwavelength grating coupler.

[0012] Further, the blazed subwavelength grating coupler is any one or a combination of more than one of a suspended grating, a non-suspended grating, a focusing grating, a non-focusing grating, a tapered grating, or a uniform grating.

[0013] Furthermore, the operating mode of the blazed sub-wavelength grating coupler is the transverse electric mode or the transverse magnetic mode.

[0014] Furthermore, the material of the blazed sub-wavelength grating coupler is composed of any one of silicon, germanium, silicon-germanium mixture, silicon nitride, silicon carbide, indium phosphide, gallium arsenide, and lithium niobate.

[0015] Furthermore, the operating wavelength of the blazed sub-wavelength grating coupler is in the visible light, infrared, or terahertz band.

[0016] Furthermore, the blazed sub-wavelength grating coupler is fabricated by one or a combination of laser direct writing, electron beam lithography combined with etching, photolithography combined with etching, and focused ion beam.

[0017] Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are as follows:

[0018] 1. The directivity of a blazed sub-wavelength grating coupler involved in the present invention is higher than that of a traditional grating coupler, especially in the short-wave mid-infrared band.

[0019] 2. The manufacturing process of a blazed sub-wavelength grating coupler involved in the present invention can be compatible with the MPW process. Without changing the standard manufacturing process, the disadvantage of low directivity of the grating coupler is improved.

[0020] 3. A blazed sub-wavelength grating coupler involved in the present invention has the advantages of high efficiency, low reflection, and small device size.

[0021] 4. A blazed sub-wavelength grating coupler involved in the present invention can be produced in large quantities at low cost, opening up a new way for the research and application of a new generation of photon integrated circuit packaging technology. Description of the Drawings

[0022] Figure 1 It is a three-dimensional schematic diagram of the blazed sub-wavelength grating coupler in Embodiment 1.

[0023] Figure 2 It is a cross-sectional schematic diagram of the blazed sub-wavelength grating coupler in Embodiment 1.

[0024] Figure 3 It is a top view schematic diagram of the blazed sub-wavelength grating coupler in Embodiment 1.

[0025] Figure 4 It is a theoretical simulation diagram of a silicon-based blazed sub-wavelength grating coupler developed based on the MPW process.

[0026] Figure 5SEM image of a silicon-based blazed subwavelength grating coupler developed based on the MPW process.

[0027] Figure 6 Experimental measurement diagram of the silicon-based blazed subwavelength grating coupler in Example 1.

[0028] Figure 7 Experimental measurement diagram of the silicon-based blazed subwavelength grating coupler in Example 2.

[0029] Figure 8 3D schematic diagram of a silicon-based blazed subwavelength grating coupler with a non-focusing and uniform structure in Example 3.

[0030] Figure 9 Theoretical simulation diagram of a silicon-based blazed subwavelength grating coupler with a non-focusing and uniform structure in Example 3.

[0031] Figure 10 Theoretical simulation diagram of a germanium-based blazed subwavelength grating coupler in Example 4. Detailed implementation manners

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Example 1

[0034] As Figure 1 shown, the present invention provides a blazed subwavelength grating coupler. In order to improve the coupling efficiency of the grating coupler, the grating coupler uses a blazed grating hole structure to improve the directivity of the coupler and a apodization structure to improve the overlap factor of the coupler. It includes blazed grating holes 1, a subwavelength grating structure region 2, a planar waveguide region 3, a tapered waveguide region 4, and a coupled waveguide region 5. The grating coupler includes a plurality of grating periods, and each grating period is composed of a subwavelength grating structure region 2 and a planar waveguide region 3. A plurality of blazed grating holes 1 are arranged equidistantly in the subwavelength grating structure region 2. The blazed grating holes 1 are all through holes connecting the top and bottom of the optical waveguide layer. A stepped structure is arranged from the top to the bottom in each blazed grating hole 1; see Figure 2 , specifically, holes with etching depths of d1, d2, and d3 are obtained in the blazed grating holes 1.

[0035] First, the holes with etching depths of d1, d2, and d3 in the blazed grating holes 1 have a longitudinal period of Λ x , and the longitudinal duty cycles are f x1 , f x2 , f x3 respectively; second, the transverse period of the subwavelength grating structure region 2 is Λ y, the horizontal duty cycle is f y ; By changing the duty cycle f x1 , f x2 , f x3 And by selecting a suitable Λ y And f y The directivity of the grating coupler can be optimized. Additionally, by selecting f with high directivity y And f x1 , f x2 , f x3 The apodization of the combination can optimize the overlap factor of the grating coupler.

[0036] To further illustrate the proposed technology, the present invention uses the finite difference time domain (FDTD) method to simulate and design the performance of a blazed subwavelength grating coupler, processes a blazed subwavelength grating coupler using MPW service, and conducts experimental tests.

[0037] As Figure 1 shown, the grating coupler is fabricated on an SOI wafer with a waveguide layer thickness of 220 nm and a buried oxide layer thickness of 3 μm. As Figure 2 And Figure 3 shown, the blazed grating hole 1 is a hole including an etching depth d1 = 220 nm, d2 = 150 nm, and d3 = 70 nm. In addition, after optimization, each parameter is: for the blazed grating hole 1, its longitudinal period Λ x And the duty cycle f x1 , f x2 , f x3 As shown in Table 1; for the subwavelength grating structure region 2, its transverse period Λ y = 600 nm, and the horizontal duty cycle is as shown in Table 1; as Figure 4 shown, the designed blazed subwavelength grating coupler has a directivity of 83% and a maximum coupling efficiency of 71% (-1.52 dB) according to two-dimensional FDTD simulation. After processing a blazed subwavelength grating coupler with high coupling efficiency using MPW service, the hole structure has a slight deformation compared with the design, and its scanning electron microscope is as Figure 5 shown. Figure 6 Shows the experimental results of the designed blazed subwavelength grating coupler, which has an efficiency of -4.53 dB at the center wavelength and a 3 dB bandwidth of 107 nm. At the same time, the experimental results are in agreement with the three-dimensional FDTD simulation results.

[0038] Table 1

[0039]

[0040] Example 2

[0041] The structure is the same as that in Embodiment 1. In this embodiment, the grating coupler is fabricated on an SOI wafer with a thickness of 220 nm for the optical waveguide layer and a thickness of 3 μm for the buried oxide layer. The blazed grating hole 1 is a hole including etching depths d1 = 220 nm, d2 = 150 nm, and d3 = 70 nm. In addition, after optimization, each parameter is as follows: for the blazed grating hole 1, its longitudinal period duty ratio is shown in Table 2; for the sub-wavelength grating structure region 2, its transverse period Λ y = 600 nm, and its transverse duty ratio is shown in Table 2; Figure 7 The experimental results of the designed blazed sub-wavelength grating coupler are shown. Its efficiency at the central wavelength is -4.61 dB and the 3-dB bandwidth is 108 nm.

[0042] Table 2

[0043]

[0044] Embodiment 3

[0045] As Figure 8 shown, this embodiment is a blazed sub-wavelength grating coupler with a non-focusing and uniform structure. The grating coupler is fabricated on an SOI wafer with a thickness of 220 nm for the optical waveguide layer and a thickness of 3 μm for the buried oxide layer. In addition, the etching depth of the holes fabricated for the grating coupler is the same as that in Embodiment 1 and Embodiment 2. After optimization, each parameter is as follows: for the blazed grating hole 1, its longitudinal period Λ x = 1600 nm, and its longitudinal duty ratios f x1 , f x2 , f x3 are 0.3, 0.4, and 0.15 respectively; for the sub-wavelength grating structure region 2, its transverse period Λ y = 600 nm, and its transverse duty ratio f y = 0.4; Figure 9 The simulation results of the designed non-focusing uniform blazed sub-wavelength grating coupler are shown. Its efficiency at the central wavelength is -4.9 dB.

[0046] Embodiment 4

[0047] This embodiment is a blazed sub-wavelength grating coupler based on the material germanium. The grating coupler is fabricated on an insulator-germanium (GOI) wafer with a thickness of 220 nm for the optical waveguide and a thickness of 3 μm for the buried oxide layer. The blazed grating hole 1 is a hole including etching depths d1 = 220 nm, d2 = 150 nm, and d3 = 70 nm. In addition, after optimization, each parameter is as follows: for the blazed grating hole 1, its longitudinal period Λ x = 1200 nm, and its longitudinal duty ratios f x1 , f x2 , f x3They are 0.43, 0.25, and 0.16 respectively; the sub-wavelength grating structure region 2 has a transverse period Λ y = 400 nm, and a transverse duty cycle f y = 0.18; Figure 10 The simulation results of the blazed sub-wavelength grating coupler based on the material germanium are shown, and its efficiency at the central wavelength is -2.3 dB.

[0048] Finally, the methods of the above embodiments are only preferred implementation schemes and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0049] The present invention is not limited to the embodiments described above. The description of the specific embodiments above is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the spirit of the present invention and the scope protected by the claims, those of ordinary skill in the art can also make many specific transformations in various forms under the inspiration of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A blazed subwavelength grating coupler, characterized in that: It is disposed on the optical waveguide layer, and the grating coupler includes a plurality of grating periods, and each grating period is composed of a sub-wavelength grating structure region and a planar waveguide region; A plurality of blazed grating holes are arranged at equal intervals in the sub-wavelength grating structure region. The blazed grating holes are all through holes connecting the top and bottom of the optical waveguide layer, and a stepped structure is arranged from the top to the bottom in each blazed grating hole; A coupled waveguide region is provided on the optical waveguide layer; The stepped structure is composed of steps with different heights, and there are more than two steps; The light field incident angle of the blazed sub-wavelength grating coupler is perpendicular to the plane of the blazed sub-wavelength grating coupler, or has an inclined angle with the plane of the blazed sub-wavelength grating coupler.

2. The blazed sub-wavelength grating coupler according to claim 1, wherein The blazed sub-wavelength grating coupler is any one or a combination of a suspended grating, a non-suspended grating, a focusing grating, a non-focusing grating, a apodized grating or a uniform grating.

3. The blazed sub-wavelength grating coupler according to claim 1, wherein The working mode of the blazed sub-wavelength grating coupler is the transverse electric mode or the transverse magnetic mode.

4. The blazed sub-wavelength grating coupler according to claim 1, wherein The material of the blazed sub-wavelength grating coupler is composed of any one of silicon, germanium, silicon-germanium mixture, silicon nitride, silicon carbide, indium phosphide, gallium arsenide, lithium niobate.

5. The blazed sub-wavelength grating coupler according to claim 1, wherein The working wavelength of the blazed sub-wavelength grating coupler is in the visible light, infrared or terahertz band.

6. The blazed subwavelength grating coupler according to claim 1, wherein The blazed sub-wavelength grating coupler is fabricated by one or a combination of laser direct writing, electron beam lithography combined with etching, photolithography combined with etching, focused ion beam.

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