CN115576053A - Blazed sub-wavelength grating coupler - Google Patents

Blazed sub-wavelength grating coupler Download PDF

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Publication number
CN115576053A
CN115576053A CN202211225703.5A CN202211225703A CN115576053A CN 115576053 A CN115576053 A CN 115576053A CN 202211225703 A CN202211225703 A CN 202211225703A CN 115576053 A CN115576053 A CN 115576053A
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blazed
sub
grating
grating coupler
wavelength
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程振洲
郭荣翔
刘铁根
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Tianjin University
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Tianjin University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/124—Geodesic lenses or integrated gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/12147—Coupler

Abstract

The invention discloses a blazed sub-wavelength grating coupler which is arranged on an optical waveguide layer and comprises a plurality of grating periods, wherein each grating period consists of a sub-wavelength grating structure area and a planar waveguide area; a plurality of blazed grating holes are arranged in the sub-wavelength grating structure area at equal intervals, the blazed grating holes are through holes which are used for communicating the top and the bottom of the optical waveguide layer, and a stepped structure is arranged in each blazed grating hole from the top to the bottom; the optical waveguide layer is provided with a coupling waveguide region. The invention can improve the directivity of the grating coupler. The grating coupler can be coupled with grating structures such as apodization and focusing, the optical field coupling efficiency of the grating coupler is further improved, reflection is reduced, the size of a device is reduced, and a new way is opened up for realizing a waveguide optical field coupling packaging technology with high performance and low cost.

Description

Blazed sub-wavelength grating coupler
Technical Field
The invention belongs to the field of integrated photoelectron, and particularly relates to a novel blazed sub-wavelength grating coupler.
Background
The integrated photoelectronic technology has been widely researched in recent years, and has wide application prospects in a plurality of important fields such as optical communication, optical sensing, optical calculation, optical metering and the like. The grating coupler can realize the optical field coupling between the optical fiber and the optical waveguide, has the advantages of no need of lens optical fiber and chip edge polishing process, easy alignment mode, flexible alignment position, easy realization of automatic alignment and the like, and is an important packaging technology. Because the grating coupler is flexible in structural design and strong in expansibility, the grating coupler can be designed according to different requirements. For example, a grating coupler is combined with a sub-wavelength structure, a sub-wavelength grating coupler is developed, coupling strength of the coupler is adjusted by adjusting effective refractive index of the sub-wavelength structure, and a novel grating coupler with low reflection and wide bandwidth is developed. In addition, the grating coupler can be manufactured to be compatible with Multi-Project Wafer (MPW), and large-scale and low-cost device preparation can be realized.
The coupling efficiency is one of the most important performance indexes of the grating coupler, and it is very critical to enhance the directivity of the grating coupler in order to improve the coupling efficiency. In recent years, researchers have achieved some results in the study of the directivity of grating couplers. In the literature, in 2012, jones et al, university of chinese in hong kong, reported a focused apodized sub-wavelength grating coupler (Applied Physics Letters 101, 101104) whose directivity depends mainly on the thicknesses of the top silicon layer and the buried oxide layer, regardless of the parameters of the grating structure. In 2014, daniel Benedicovic et al, the university of Nissner in the Splovage republic, improved the directivity of the grating coupler by adjusting the thickness of the buried oxide layer and the incident angle of the optical fiber (Laser & Photonics Reviews 8, L93), and the sub-wavelength grating coupler can realize the high-efficiency coupling of-2.16 dB in the 1550 nm band. Further, the above-mentioned problem group reports a blazed grating coupler (Optics Letters 40,18, 4190) having a cross groove, which can greatly improve the directivity of the grating coupler by controlling the parameters of the blazed structure of the cross groove, but the characteristic parameters of the blazed structure are small and the requirement for the manufacturing process is high. In 2017, a blazed grating coupler (Journal of Lightwave Technology 35,21, 4663) with vertical coupling was developed by Tatsuhiko Watanabe et al, the federal institute of science and Technology, zurich, switzerland, and the grating coupler relies on an L-shaped blazed structure to improve directivity, so that vertical coupling can be achieved, but the blazed structure also faces the problems of too small characteristic parameters and high requirements for manufacturing processes. In 2021, guo rong and al at the university of tianjin reported an ultra-thin sub-wavelength grating coupler (Optics Letters 47,5, 1226) which was fabricated based on MPW process, had a larger spectral bandwidth and low reflection, and could improve the directivity of the grating coupler by reducing the thickness of the grating coupler, but the improvement of the directivity was limited. In the patent aspect, honor haisheng et al of intel corporation, 2012 invented a high efficiency Silicon-on-Insulator (SOI) grating coupler, and issued chinese patent of invention (ZL 201280016341.7). In 2015, liuliu et al of the university of south China invented an inclined silicon-based grating coupler for vertical coupling, and the inventor granted Chinese patent (ZL 201520845532.5). In 2019, a high-coupling-efficiency M-type waveguide grating coupler is invented by Neilaikui et al of China geological university, high-efficiency light field coupling is realized near 1580 nanometer wavelength, and a Chinese invention patent (ZL 201911238254.6) is granted. In 2021, the cone at the university of Zhejiang invented a high-efficiency broadband grating coupler, which uses a reflection grating of an embedded oxide layer to improve the directivity, and issued Chinese patent (ZL 2021103354.0). In 2022, yangxincang et al, the Shanghai university of traffic, invented a binary blazed grating coupler, which could be used for efficient vertical coupling, and granted the Chinese patent (ZL 202111242481.3).
In summary, although the sub-wavelength grating coupler has the advantages of simple manufacturing process and large manufacturing tolerance, its directivity is not high, and can only be controlled by adjusting the thickness of the buried oxide layer or the top silicon layer of the wafer. On the other hand, although blazed gratings can improve directivity by controlling the structure, they have a complicated structure and a small feature size, and it is difficult to fabricate devices using a standard MPW process. The development of a new grating structure to achieve high-efficiency optical field coupling is significant for the development of high-quality, low-cost, and high-integration optoelectronic Integrated Circuits (OEICs).
Disclosure of Invention
The invention aims to overcome the problem of low directivity of the traditional grating coupler. A blazed sub-wavelength grating coupler is provided and fabricated.
The purpose of the invention is realized by the following technical scheme:
a blazed sub-wavelength grating coupler is arranged on an optical waveguide layer and comprises a plurality of grating periods, wherein each grating period consists of a sub-wavelength grating structure region and a planar waveguide region;
a plurality of blazed grating holes are arranged in the sub-wavelength grating structure area at equal intervals, the blazed grating holes are through holes communicating the top and the bottom of the optical waveguide layer, and a stepped structure is arranged in each blazed grating hole from the top to the bottom;
and a coupling waveguide region is arranged on the optical waveguide layer.
Furthermore, the ladder-shaped structure is composed of steps with different heights, and the number of the steps is more than two.
Furthermore, the incident angle of the optical field of the blazed sub-wavelength grating coupler is perpendicular to the plane of the blazed sub-wavelength grating coupler, or an inclined angle exists between the incident angle of the optical field and the plane of the blazed sub-wavelength grating coupler.
Further, the blazed sub-wavelength grating coupler is any one or a combination of a suspension grating, a non-suspension grating, a focusing grating, a non-focusing grating, an apodizing grating or a uniform grating.
Further, the working mode of the blazed sub-wavelength grating coupler is a transverse electric mode or a transverse magnetic mode.
Furthermore, the blazed sub-wavelength grating coupler is made of any one of silicon, germanium, a silicon-germanium mixture, silicon nitride, silicon carbide, indium phosphide, gallium arsenide and lithium niobate.
Further, the operating wavelength of the blazed sub-wavelength grating coupler is a visible light band, an infrared band or a terahertz band.
Furthermore, the blazed sub-wavelength grating coupler is manufactured by combining one or more modes of laser direct writing, electron beam exposure combined etching, photoetching combined etching and ion beam focusing.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. the directivity of the blazed sub-wavelength grating coupler is higher than that of the traditional grating coupler, and particularly in the infrared band in short wave.
2. The manufacturing process of the blazed sub-wavelength grating coupler can be compatible with an MPW (multi-wavelength beam forming) process, and overcomes the defect of low directivity of the grating coupler on the basis of not changing a standard manufacturing process.
3. The blazed sub-wavelength grating coupler has the advantages of high efficiency, low reflection, small device size and the like.
4. The blazed sub-wavelength grating coupler can be produced in a large scale and at low cost, and opens up a new way for the research, development and application of a new generation of photonic integrated circuit packaging technology.
Drawings
Fig. 1 is a three-dimensional schematic diagram of a blazed sub-wavelength grating coupler in embodiment 1.
Fig. 2 is a schematic cross-sectional view of a blazed subwavelength grating coupler in example 1.
Fig. 3 is a schematic top view of a blazed subwavelength grating coupler in example 1.
Fig. 4 is a theoretical simulation diagram of a silicon-based blazed sub-wavelength grating coupler developed based on the MPW process.
Fig. 5 is a scanning electron microscope image of a silicon-based blazed sub-wavelength grating coupler developed based on the MPW process.
Fig. 6 is a graph of experimental measurements of the silicon-based blazed sub-wavelength grating coupler of example 1.
Fig. 7 is a graph of experimental measurements of the silicon-based blazed sub-wavelength grating coupler of example 2.
Fig. 8 is a three-dimensional schematic diagram of a silicon-based blazed sub-wavelength grating coupler in an unfocused and uniform structure in example 3.
Fig. 9 is a theoretical simulation diagram of the silicon-based blazed sub-wavelength grating coupler adopting the non-focusing and uniform structure in the embodiment 3.
Fig. 10 is a theoretical simulation diagram of a germanium-based blazed sub-wavelength grating coupler in example 4.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Example 1
As shown in fig. 1, the present invention provides a blazed sub-wavelength grating coupler, which uses a blazed grating hole structure to increase the directivity of the coupler and an apodized structure to increase the overlap factor of the coupler, in order to increase the coupling efficiency of the grating coupler. The optical waveguide grating comprises a blazed grating hole 1, a sub-wavelength grating structure area 2, a planar waveguide area 3, a conical waveguide area 4 and a coupling waveguide area 5. The grating coupler comprises a plurality of grating periods, and each grating period consists of a sub-wavelength grating structure region 2 and a planar waveguide region 3. A plurality of blazed grating holes 1 are arranged in the sub-wavelength grating structure area 2 at equal intervals, the blazed grating holes 1 are through holes communicating the top and the bottom of the optical waveguide layer, and a stepped structure is arranged from the top to the bottom in each blazed grating hole 1; see fig. 2, in particular by etching depth d in the blazed grating holes 1 1 、d 2 And d 3 The pore of (a) was obtained.
First, the depth of etching in the flare gate hole 1 is d 1 、d 2 And d 3 All holes of (2) have a longitudinal period of Λ x Longitudinal duty cycles of f x1 ，f x2 ，f x3 (ii) a Secondly, the lateral period of the sub-wavelength grating structure region 2 is Λ y Transverse duty cycle of f y (ii) a By varying the duty cycle f x1 ，f x2 ，f x3 And selecting the appropriate Λ y And f y The directivity of the grating coupler can be optimized, in addition by choosing f with a high directivity y And f x1 ，f x2 ，f x3 The combination of (a) and (b) is apodized to optimize the overlap factor of the grating coupler.
In order to further explain the technology, the invention utilizes a Finite Difference Time Domain (FDTD) method to simulate the performance of the designed blazed sub-wavelength grating coupler, combines the MPW service to process the blazed sub-wavelength grating coupler, and performs experimental tests.
As shown in fig. 1, the grating coupler is fabricated on an SOI wafer with an optical waveguide layer thickness of 220 nm and a buried oxide layer thickness of 3 microns. As shown in FIGS. 2 and 3, the blazed grating holes 1 are formed to include an etching depth d 1 =220 nm, d 2 =150 nm and d 3 =70 nm pores. In addition, after optimization, the parameters are as follows: blazed grating holes 1 with longitudinal period Λ x And duty ratio f x1 ，f x2 ，f x3 As shown in table 1; sub-wavelength grating structure region 2 having a lateral period Λ y =600nm, lateral duty cycle as shown in table 1; as shown in fig. 4, a blazed sub-wavelength grating coupler designed according to two-dimensional FDTD simulation has a directivity of 83% and a maximum coupling efficiency of 71% (-1.52 dB). After the blazed sub-wavelength grating coupler with high coupling efficiency is processed by adopting MPW service, the hole-shaped structure is slightly deformed compared with the design, and a scanning electron microscope is shown in figure 5. Figure 6 shows experimental results for a blazed sub-wavelength grating coupler designed to have an efficiency of-4.53 dB at the center wavelength and a 3dB bandwidth of 107 nm. Meanwhile, the experimental result is consistent with the three-dimensional FDTD simulation result.
TABLE 1
Figure BDA0003879628500000041
Example 2
The structure of the optical grating coupler is the same as that of embodiment 1, and the optical grating coupler is fabricated on an SOI wafer with an optical waveguide layer thickness of 220 nm and a buried oxide layer thickness of 3 μm in this embodiment. The blazed grating hole 1 is formed to include an etching depth d 1 =220 nm, d 2 =150 nm and d 3 =70 nm pore. In addition, after optimization, the parameters are as follows: a blazed grating hole 1 whose longitudinal cycle duty ratio is shown in table 2; sub-wavelength grating structure region 2 having a lateral period Λ y =600nm, lateral duty cycle as shown in table 2; FIG. 7 shows experimental results of a blazed sub-wavelength grating coupler designed to have an efficiency of-4.61 dB and a 3dB bandwidth of 108 nm at the center wavelength。
TABLE 2
Figure BDA0003879628500000051
Example 3
As shown in fig. 8, this embodiment is a blazed sub-wavelength grating coupler that takes an unfocused and uniform structure. The grating coupler is manufactured on an SOI wafer with the optical waveguide layer thickness of 220 nanometers and the buried oxide layer thickness of 3 micrometers. In addition, the grating coupler is made with the same hole etching depth as in examples 1 and 2. After optimization, the parameters are as follows: blazed grating hole 1 with longitudinal period Λ x =1600nm, longitudinal duty cycle f x1 ，f x2 ，f x3 0.3,0.4,0.15; sub-wavelength grating structure region 2 with lateral period Λ y =600nm, transverse duty cycle f y =0.4; figure 9 shows the simulation results for the designed unfocused uniformly blazed sub-wavelength grating coupler with an efficiency of-4.9 dB at the center wavelength.
Example 4
This embodiment is a blazed sub-wavelength grating coupler based on the material germanium. The grating coupler is manufactured on a germanium-on-Insulator (GOI) wafer with the optical waveguide thickness of 220 nanometers and the buried oxide thickness of 3 micrometers. The blazed grating hole 1 is formed to include an etching depth d 1 =220 nm, d 2 =150 nm and d 3 =70 nm pores. In addition, after optimization, the parameters are as follows: blazed grating holes 1 with longitudinal period Λ x =1200nm, longitudinal duty cycle f x1 ，f x2 ，f x3 0.43,0.25,0.16; sub-wavelength grating structure region 2 with lateral period Λ y =400nm, transverse duty cycle f y =0.18; figure 10 shows the results of simulations of a blazed sub-wavelength grating coupler based on the material germanium, with an efficiency of-2.3 dB at the center wavelength.
Finally, the method of the above embodiments is only a preferred embodiment, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (8)

1. A blazed sub-wavelength grating coupler is characterized by being arranged on an optical waveguide layer, and the grating coupler comprises a plurality of grating periods, wherein each grating period consists of a sub-wavelength grating structure region and a planar waveguide region;
a plurality of blazed grating holes are arranged in the sub-wavelength grating structure area at equal intervals, the blazed grating holes are through holes communicating the top and the bottom of the optical waveguide layer, and a stepped structure is arranged in each blazed grating hole from the top to the bottom;
and a coupling waveguide region is arranged on the optical waveguide layer.
2. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the stepped structure is formed by two or more steps having different heights.
3. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the angle of incidence of the optical field of the blazed sub-wavelength grating coupler is perpendicular to the plane of the blazed sub-wavelength grating coupler or has an oblique angle with the plane of the blazed sub-wavelength grating coupler.
4. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the blazed sub-wavelength grating coupler is any one or more of a suspended grating, an unsettled grating, a focused grating, an unfocused grating, an apodized grating, or a uniform grating in combination.
5. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the operating mode of the blazed sub-wavelength grating coupler is a transverse electric mode or a transverse magnetic mode.
6. A blazed subwavelength grating coupler as claimed in claim 1, wherein the material of the blazed subwavelength grating coupler is composed of any one of silicon, germanium, a silicon-germanium mixture, silicon nitride, silicon carbide, indium phosphide, gallium arsenide, and lithium niobate.
7. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the operating wavelength of the blazed sub-wavelength grating coupler is in the visible, infrared or terahertz band.
8. A blazed sub-wavelength grating coupler as claimed in claim 1, wherein the blazed sub-wavelength grating coupler is fabricated by combining one or more of laser direct writing, electron beam exposure combined etching, lithography combined etching, and focused ion beam.
CN202211225703.5A 2022-10-09 2022-10-09 Blazed sub-wavelength grating coupler Pending CN115576053A (en)

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