Heterogeneous integrated edge coupling structure based on evanescent coupling

Abstract

The invention discloses a heterogeneous integrated edge coupling structure based on evanescent coupling, which comprises a passive waveguide (002) and an ion exchange waveguide (003), and is characterized in that the ion exchange waveguide (003) is positioned in the center of a glass cladding (004), the cross section of the ion exchange waveguide (003) is semicircular, the upper surface of the ion exchange waveguide (003) is a plane, and the lower surface of the ion exchange waveguide (003) is an arc surface; the passive waveguide position (002) is located on the upper surface of the glass cladding (004), the passive waveguide position (002) is close to one side of the plane of the ion exchange waveguide (003), the front end of the passive waveguide position (002) is of a conical structure (006), and the passive waveguide (002) is coated with the silicon dioxide cladding (001). Aiming at the problems of difficulty in manufacturing and assembling, bandwidth limitation, high coupling loss and the like of an edge coupler, effective refractive index matching is realized by performing multi-section on a traditional linear inverted cone silicon waveguide, so that an optical mode in an ion exchange glass waveguide is smoothly transited to an optical mode in a passive multi-section cone silicon waveguide.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic integration, and particularly to a waveguide coupling structure based on evanescent coupling. Background Art

[0002] Integrated optoelectronics is a discipline that studies how to integrate photonic devices at the micro-nano scale. Its development is of great significance for improving the integration degree of optoelectronic devices, reducing size and power consumption. Among them, an edge coupler is an important optical device, and its function is to perform mode spot conversion to reduce the coupling performance loss introduced by mode spot mismatch. Therefore, the edge coupler can be used to achieve efficient coupling of optical signals between optical fibers and chips or different chips, making it one of the key components in silicon-based integrated photonic chip circuits and widely used in fields such as optical fiber communication, data centers, and photonic chip systems.

[0003] However, for the polymer material platform, it has relatively high propagation loss and serious dispersion near the 1550 nm band. At the same time, the relatively large coefficient of thermal expansion also makes it an important factor for an efficient optical interconnection platform. The advantages of low transmission loss and low dispersion presented by the graded-index glass waveguide in the communication window make it have the potential to become a future single-mode optical printed circuit board. In order to fully exert its potential, when combined with silicon photonic integrated devices, an efficient optical coupling scheme is required, including various schemes such as integrated lenses and diffraction gratings. These schemes have problems such as difficult manufacturing and assembly, bandwidth limitation, and high coupling loss. Summary of the Invention

[0004] In view of the problems of difficult manufacturing and assembly, bandwidth limitation, and high coupling loss existing in the edge coupler, the present invention proposes a structure for coupling an ion-exchanged glass waveguide and a passive silicon waveguide. By multi-segmenting the traditional linear tapered silicon waveguide to achieve effective refractive index matching, the optical mode in the ion-exchanged glass waveguide can be smoothly transitioned to the optical mode in the passive multi-segment tapered silicon waveguide. By optimizing the taper structure and the coupling region length, the coupling loss between the two is minimized as much as possible; at the same time, the minimum processing width of the taper tip is enlarged, so that the processing tolerance of the taper tip can be enlarged to the micron level.

[0005] The technical solution of the present invention:

[0006] A heterogeneous integrated edge coupling structure based on evanescent coupling, comprising a passive waveguide 002 and an ion-exchange waveguide 003. The ion-exchange waveguide 003 is located in the center of the glass cladding 004. The cross-section of the ion-exchange waveguide 003 is semi-circular, with a planar upper surface and a circular-arc lower surface. The passive waveguide 002 is located on the upper surface of the glass cladding 004, close to the planar side of the ion-exchange waveguide 003. The front end of the passive waveguide 002 is a tapered structure 006, and the passive waveguide 002 is coated with a silica cladding 001.

[0007] The tapered structure 006 at the front end of the passive waveguide 002 appears as a multi-segment taper when viewed from above.

[0008] The tapered structure 006 is divided into three tapered segments with slopes k1, k2, and k3 respectively, where k1 > k3 > k2.

[0009] The tip width of the tapered structure 006 is greater than 130 nm.

[0010] The width of the silica cladding 001 is less than the width of the ion-exchange waveguide 003.

[0011] The refractive index of the ion-exchange waveguide 003 gradually decreases from top to bottom through ion exchange.

[0012] Compared with the prior art, the advantages of the present invention are as follows:

[0013] 1. Through the tapered coupling structure proposed by the present invention, extremely low-loss transmission of light between the ion-exchange glass waveguide and the passive multi-segment tapered silicon waveguide can be achieved, effectively reducing the coupling loss between the two.

[0014] 2. When the tip width of the passive multi-segment tapered silicon waveguide in the present invention is 130 nm, the coupling loss is still very low. Therefore, the process tolerance of the passive silicon waveguide for evanescent coupling with the glass waveguide can be increased through the structure proposed by the present invention, effectively reducing the processing cost and processing difficulty.

[0015] 3. The multi-segment tapered structure is composed of multiple single tapers. Since the range of tip widths for effective refractive index matching is limited, achieving high-efficiency coupling and stable single-mode transmission only through a single taper will result in an overly long length of the coupler structure, posing a certain challenge to subsequent process preparation. However, through the multi-segment tapered structure, while ensuring the coupling length in the region of effective refractive index matching, the distance for other optical transmissions can be shortened, thereby shortening the overall length of the coupling structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a cross-sectional view of the novel multi-segment tapered coupling structure.

[0017] Figure 2It is a top view of the coupling structure.

[0018] Figure 3 It is the propagation path of light in the evanescent coupling system.

[0019] In the figure: 001 - silica cladding; 002 - passive multi - segment tapered silicon waveguide; 003 - ion - exchanged glass waveguide; 004 - glass cladding; 005 - optical input end of the glass waveguide; 006 - multi - segment tapered waveguide; 007 - straight waveguide section. Detailed implementation manner

[0020] Referring to the appendix Figure 1 、 Figure 2 The novel coupling structure provided by the present invention consists of two parts: an ion - exchanged glass waveguide part and a passive multi - segment tapered silicon waveguide. The structure of the passive part includes a silica cladding 001 and a passive silicon waveguide 002. The silica cladding 001 covers the upper surface and the left and right side surfaces of the passive silicon waveguide 002. The front end of the passive waveguide 002 is a tapered structure 006; the ion - exchanged glass waveguide part includes an ion - exchanged waveguide 003 and a glass cladding 004; the ion - exchanged waveguide 003 is located in the center of the glass cladding 004. The cross - section of the ion - exchanged waveguide 003 is semi - circular, with a flat upper surface and a circular - arc lower surface. Place the silica cladding 001 and the passive silicon waveguide 002 on the upper surface of the glass cladding 004, and the passive waveguide 002 is close to the flat side of the ion - exchanged waveguide 003. The refractive index distribution of the ion - exchanged waveguide 003 has a certain pattern through ion - exchange, as shown in Table 1 specifically. The gradually changing refractive index is used to limit the input light to only propagate in this area.

[0021] Table 1: Refractive index distribution of ion - exchanged glass waveguide

[0022] Depth μm Refractive index 0 1.5353 0.5 1.533561329 1 1.531832394 1.5 1.530122767 2 1.5284417 2.5 1.526797971 3 1.525199751 3.5 1.523654482 4 1.522168775 4.5 1.520748333 5 1.519397895 5.5 1.518121199 6 1.516920976 6.5 1.515798966 7 1.514755944 7.5 1.513791779 8 1.5129055 8.5 1.512095377 9 1.511359013

[0023] According to the process requirements provided by the foundry, the silicon waveguides involved in the present invention are all strip - type waveguides, and the lithography method uses 220nm deep etching, that is, the total height of the passive silicon waveguide 002 is 220nm, and the etching area is 220nm. The passive silicon waveguide includes a multi - segment tapered structure 006 and a straight waveguide 007; the tapered structure 006 is divided into three tapered segments with slopes k1, k2, and k3 respectively, and k1 > k3 > k2.

[0024] The optical signal enters through the optical input end of the ion-exchange waveguide 003, and enters the upper passive waveguide 002 through evanescent coupling. Since the passive waveguide position 02 adopts a new multi-segment linear taper structure for transition, the effective refractive indices of the ion-exchange waveguide 003 and the passive waveguide 002 are matched. After the optical signal enters the passive waveguide 002 through evanescent coupling in the overlapping section of the ion-exchange waveguide 003 and the passive waveguide 002, adiabatic transmission is carried out inside the passive waveguide 002. Most of the optical signal is coupled into the passive waveguide 002 through evanescent coupling. According to the FDTD simulation results, the optical fields in both the ion-exchange waveguide 003 and the passive waveguide 002 are stably distributed, and when the length of the multi-segment tapered silicon waveguide 006 is greater than 500 μm, lossless transmission can be basically achieved. The numerical analysis results show that the coupling efficiency changes little when the taper tip width of the multi-segment tapered silicon waveguide 006 varies within 130 nm to 180 nm, which can greatly relax the process requirements for the processing of the multi-segment tapered silicon waveguide.

[0025] The working principle of the novel coupling structure of the present invention is as follows:

[0026] The 1550 nm optical signal output by the external laser source is input into the optical input end 005 of the ion-exchange glass waveguide through an end-face coupler or a grating coupler, and enters the multi-segment tapered silicon waveguide section 006 through evanescent coupling, and continues to be transmitted in the straight waveguide section 007. Since the width of the multi-segment taper section 006 gradually increases, during this process, the effective refractive indices of the lower ion-exchange glass waveguide 003 and the multi-segment tapered silicon waveguide 006 are matched, and part of the optical signal enters the multi-segment tapered silicon waveguide 006 from the ion-exchange glass waveguide 003 through evanescent coupling..

[0027] In the above specific embodiments, the purpose, technical solution and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit 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.

Claims

1. A heterogeneous integrated edge coupling structure based on evanescent coupling, comprising a passive waveguide (002) and an ion-exchange waveguide (003), characterized in that: The ion-exchange waveguide (003) is located at the center of the glass cladding (004). The cross-section of the ion-exchange waveguide (003) is semi-circular, with the upper surface being planar and the lower surface being an arc surface. The passive waveguide position (002) is located on the upper surface of the glass cladding (004). The passive waveguide position (002) is close to the planar side of the ion-exchange waveguide (003). The front end of the passive waveguide position (002) is a tapered structure (006), and the passive waveguide (002) is coated with a silica cladding (001).

2. The heterogeneous integrated edge coupling structure based on evanescent coupling according to claim 1, wherein: The tapered structure (006) at the front end of the passive waveguide (002) is multi-segmented tapered when viewed from the top-down direction.

3. The heterogeneous integrated edge coupling structure based on evanescent coupling according to claim 2, characterized in that: The tapered structure (006) is divided into three tapered segments with slopes k1, k2, and k3 respectively, where k1 > k3 > k2.

4. The evanescent-coupling-based heterogeneous integrated edge-coupling structure according to claim 3, wherein: The width of the tip of the tapered structure (006) is greater than 130 nm.

5. The heterogeneous integrated edge coupling structure based on evanescent coupling according to claim 1, wherein: The width of the silica cladding (001) is less than the width of the ion-exchange waveguide (003).

6. The heterogeneous integrated edge coupling structure based on evanescent coupling according to claim 1, characterized in that: The refractive index of the ion-exchange waveguide (003) gradually decreases from top to bottom through ion exchange.

7. The heterogeneous integrated edge coupling structure based on evanescent coupling according to claim 1, wherein: The length of the tapered structure (006) is greater than 500 μm.

Images