Dual polarization multi-mode interlayer waveguide coupler

Abstract

The application provides a dual-polarization multi-mode interlayer waveguide coupler, and belongs to the technical field of optoelectronic devices and integration, which comprises a lower waveguide layer, a cladding layer and an upper waveguide layer; wherein the lower waveguide layer and the upper waveguide layer are both composed of 1*2 multi-mode interferometer type waveguides; wherein the 1*2 multi-mode interferometer type waveguide is composed of an input waveguide, a tapered waveguide, a wide multi-mode interference waveguide and two output waveguides connected in sequence; wherein the widths of the two output waveguides are changed from wide to narrow, and the two output waveguides are composed of subwavelength grating structures; the upper waveguide layer is above the lower waveguide layer in the vertical direction and does not contact each other, and is separated from each other by the cladding layer. The interlayer waveguide coupler of the technical scheme can realize the interlayer coupling function of dual-polarization multi-mode, and has the advantages of small size, high coupling efficiency, large working bandwidth, large process tolerance and the like, and is expected to improve the transmission capacity of on-chip three-dimensional optical chip interconnection and switching.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optoelectronic devices and integration, and particularly relates to a dual-polarization multi-mode interlayer waveguide coupler. BACKGROUND

[0002] In recent years, on-chip integrated photonics technology has developed rapidly due to its advantages of low cost, low power consumption and high integration density. Simply relying on physical miniaturization cannot meet the needs of high integration density of photonics chips in two-dimensional planes, and three-dimensional photonics integration technology has emerged as the times require. As an important device for on-chip interconnection and input / output applications, interlayer couplers are an indispensable part of two-layer or even multi-layer structures of three-dimensional photonics chips, and have been widely studied and applied in optical phased arrays, micro-ring arrays, cascaded optical switches and other fields. At present, various three-dimensional taper couplers for fiber chip coupling and multi-layer coupling have been reported, and the research direction mainly focuses on single-mode coupling transmission to achieve smaller footprint, higher coupling efficiency and lower crosstalk. In order to further improve the density and transmission capacity of three-dimensional integrated optical chips, dual-polarization multi-mode interlayer couplers are also key components, but have not been studied. SUMMARY

[0003] In view of the above technical problems of the prior art, the application discloses a multi-dual-polarization multi-mode interlayer waveguide coupler, which aims to solve the problem that the existing interlayer waveguide coupler structure and technical scheme cannot realize dual-polarization multi-mode interlayer coupling transmission, and further improve the density and transmission capacity of three-dimensional integrated optical chips.

[0004] To this end, the technical scheme adopted by the application is as follows:

[0005] A dual-polarization multi-mode interlayer waveguide coupler, the interlayer waveguide coupler comprises a lower waveguide layer, a cladding layer and an upper waveguide layer; wherein the lower waveguide layer and the upper waveguide layer are composed of 1x2 multi-mode interferometer type waveguides.

[0006] Further improvement of the technical scheme of the application is that in the vertical direction, the upper waveguide layer is in the upper layer, the lower waveguide layer is in the lower layer, and they do not contact each other and are isolated from each other by the cladding layer; in the transverse propagation direction of the optical field, the upper waveguide layer and the lower waveguide layer structure have an overlapping coupling region.

[0007] Further improvement of the technical scheme of the application is that the 1x2 multi-mode interferometer type waveguide is composed of an input waveguide, a taper waveguide, a wide multi-mode interference waveguide and two output waveguides connected in sequence, the upper waveguide layer comprises an upper waveguide layer output waveguide, an upper waveguide layer wide multi-mode interference waveguide, an upper waveguide layer taper waveguide and an upper waveguide layer input waveguide connected in sequence, and the lower waveguide layer comprises a lower waveguide layer input waveguide, a lower waveguide layer taper waveguide, a lower waveguide layer wide multi-mode interference waveguide and a lower waveguide layer output waveguide connected in sequence.

[0008] Using this technical solution, when the light beam is coupled from the lower waveguide layer to the upper waveguide layer, the input fundamental mode is split into two fundamental modes with the same phase by the 1×2 multimode interferometer waveguide of the lower waveguide layer. These fundamental modes are then transmitted to the upper waveguide layer through interlayer coupling via the two output waveguides of the 1×2 multimode interferometer waveguide. The fundamental mode is then recovered by combining the beams through the 1×2 multimode interferometer waveguide. This enables interlayer coupling of multiple modes with dual polarization. Furthermore, the device proposed in this invention has advantages such as small size, high coupling efficiency, large operating bandwidth, and large process tolerance. It is an important and meaningful work in the development of on-chip three-dimensional integrated optical chip technology.

[0009] A further improvement of the technical solution of the present invention is that the two output waveguides of the 1×2 multimode interferometer waveguide of the upper waveguide layer and the two output waveguides of the 1×2 multimode interferometer waveguide of the lower waveguide layer overlap each other along the transverse propagation direction of the optical field, thereby satisfying the interlayer waveguide coupling condition.

[0010] A further improvement of the technical solution of the present invention is that the 1×2 multimode interferometer waveguide is a polarization-insensitive multimode 1×2 power beam splitter, and the dual polarization multiple modes can simultaneously achieve high-efficiency 1×2 power beam splitting.

[0011] A further improvement of the technical solution of the present invention is that: the two output waveguides of the 1×2 multimode interferometer waveguide of the upper waveguide layer and the two output waveguides of the 1×2 multimode interferometer waveguide of the lower waveguide layer are insulated conical waveguides with a width that gradually narrows, forming a subwavelength grating structure.

[0012] A further improvement of the technical solution of the present invention is that: the materials of the upper waveguide layer and the lower waveguide layer are selected from silicon, silicon nitride, III-V group materials or polymers, and the cladding material is silicon dioxide; the spacing between the upper waveguide layer and the lower waveguide layer is 0-500nm.

[0013] A further improvement of the technical solution of the present invention is that: the lower waveguide layer is a 1×2 multimode interferometer-type silicon waveguide, and the size L2×w2 of the lower waveguide layer wide multimode interferometer waveguide is 15×6.2μm. 2 The width w1 of the input waveguide in the lower waveguide layer is set to 2.5 μm, and the length L1 of the tapered waveguide in the lower waveguide layer is set to 15 μm. The output waveguide in the lower waveguide layer is an adiabatic tapered waveguide with a width ranging from 3 μm to 0.12 μm and a length of 65 μm. The upper waveguide layer is a 1×2 multimode interferometer-type silicon nitride waveguide, and the size L5×w6 of the wide multimode interferometer waveguide in the upper waveguide layer is 10×6.2 μm. 2 The width w5 of the input waveguide in the upper waveguide layer is set to 2.5μm, the length L4 of the tapered waveguide in the upper waveguide layer is set to 15μm, and the width of the output waveguide in the upper waveguide layer ranges from 3μm to 0.2μm, with a length of 65μm.

[0014] Further improvement of the technical scheme of the present application is that the lower waveguide layer is a 1x2 multimode interferometer type silicon waveguide, the period of the subwavelength grating structure of the lower waveguide layer output waveguide is designed as 100 nm, and the duty cycle a1 is designed as 20 nm; the upper waveguide layer is a 1x2 multimode interferometer type silicon nitride waveguide, the period of the subwavelength grating structure of the waveguide layer output waveguide is designed as 150 nm, and the duty cycle a2 is designed as 50 nm; the overlapping length L7 of the lower waveguide layer output waveguide and the waveguide layer output waveguide coupling region is 10 μm.

[0015] As a further improvement of the present application, similar to the process of coupling from the lower waveguide layer to the upper waveguide layer, the fundamental mode and the first-order mode can be separated and converted into the fundamental mode through the 1x2 multimode interferometer type waveguide of the upper waveguide layer, and then coupled into the lower waveguide, and then emitted and recovered through the 1x2 multimode interferometer type waveguide of the lower waveguide layer.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] Firstly, the interlayer waveguide coupler of the present application realizes the coupling of supporting TE0, TE1, TM0 and TM1 four modes at the same time by optimizing the geometric parameters of the two reverse multimode interferometer structures, thereby improving the density and transmission capacity of the three-dimensional integrated optical chip.

[0018] Secondly, the interlayer waveguide coupler of the present application has the advantages of small size, high coupling efficiency, large working bandwidth, large process tolerance, etc. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Fig. 1 is a three-dimensional structure schematic diagram of the interlayer waveguide coupler of the present application;

[0020] Figure 2 Fig. 2 is a cross-sectional structure schematic diagram of the interlayer waveguide coupler of the present application;

[0021] Figure 3 Fig. 3 is a planar structure schematic diagram of the interlayer waveguide coupler of the present application;

[0022] Figure 4 Fig. 4 is a simulated light field distribution diagram of the TE0 mode in different direction cross sections of the present application;

[0023] Figure 5 Fig. 5 is a simulated light field distribution diagram of the TE1 mode in different direction cross sections of the present application;

[0024] Figure 6Figure 2 shows the simulated light field distribution of the TM0 mode of the present application in different direction cross-sections;

[0025] Figure 7 Figure 3 shows the simulated light field distribution of the TM1 mode of the present application in different direction cross-sections;

[0026] Figure 8 Figure 4 shows the simulated coupling transmission spectrum of the dual-polarization multi-mode of the present application in the 1450-1650 nm wavelength band.

[0027] Wherein: 1, lower waveguide layer, 2, cladding layer, 3, upper waveguide layer, 4, lower waveguide layer input waveguide, 5, lower waveguide layer tapered waveguide, 6, lower waveguide layer wide multimode interference waveguide, 7, lower waveguide layer output waveguide, 8, upper waveguide layer output waveguide, 9, upper waveguide layer wide multimode interference waveguide, 10, upper waveguide layer tapered waveguide, 11, upper waveguide layer input waveguide. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present application are further described in detail below.

[0029] As shown in Figure 1 and Figure 2 , a dual-polarization multi-mode interlayer waveguide coupler comprises: a lower waveguide layer 1, a cladding layer 2, and an upper waveguide layer 3; both the lower waveguide layer and the upper waveguide layer are composed of 1x2 multimode interferometer type waveguides; in the vertical direction (z-axis), the upper waveguide layer 3 is on the upper layer, the lower waveguide layer 1 is on the lower layer, and they are not in contact with each other, and are separated from each other by the cladding layer 2; along the transverse propagation direction of the light field (x-axis), the upper waveguide layer 3 and the lower waveguide layer 1 have an overlapping coupling region in structure.

[0030] The material of the lower waveguide layer 1 is set to silicon, the material of the cladding layer 2 is set to silicon dioxide, and the material of the upper waveguide layer 3 is set to silicon nitride.

[0031] As shown in Figure 3 , the 1x2 multimode interferometer type waveguide is composed of an input waveguide, a tapered waveguide, a wide multimode interference waveguide, and two output waveguides connected in sequence, the upper waveguide layer is a 1x2 multimode interferometer type silicon nitride waveguide, including the upper waveguide layer output waveguide 8, the upper waveguide layer wide multimode interference waveguide 9, the upper waveguide layer tapered waveguide 10, and the upper waveguide layer input waveguide 11 connected in sequence, and the lower waveguide layer 1 is a 1x2 multimode interferometer type silicon waveguide, including the lower waveguide layer input waveguide 4, the lower waveguide layer tapered waveguide 5, the lower waveguide layer wide multimode interference waveguide 6, and the lower waveguide layer output waveguide 7 connected in sequence.

[0032] The 1x2 multimode interferometer type waveguide is designed as a polarization-insensitive multimode 1x2 power splitter, ensuring that the dual-polarization multiple modes (TE0, TE1, TM0, TM1) can simultaneously achieve high-efficiency 1x2 power splitting. For the 1x2 multimode interferometer type silicon waveguide, the size L2xw2 of the wide multimode interference waveguide is 15x6.2μm 2 The width w1 of the lower waveguide layer input waveguide 4 is set to 2.5μm to support the fundamental mode and the first-order mode, and the length L1 of the lower waveguide layer tapered waveguide is set to 15μm to expand the mode field diameter. The lower waveguide layer output waveguide 7 is an adiabatic taper with a width from 3μm to 0.12μm and a length of 65μm. Similarly to the parameter settings of the silicon waveguide, the main parameters of the 1x2 multimode interferometer type silicon nitride waveguide are designed as follows: the size L5xw6 of the upper waveguide layer wide multimode interference waveguide 9 is 10x6.2μm 2 The width w5 of the upper waveguide layer input waveguide 11 is set to 2.5μm, the length L4 of the upper waveguide layer tapered waveguide 10 is set to 15μm, and the width of the upper waveguide layer output waveguide 8 is from 3μm to 0.2μm, and the length is 65μm.

[0033] The two output waveguides 8 of the 1x2 multimode interferometer type waveguide of the upper waveguide layer 3 and the two output waveguides 7 of the 1x2 multimode interferometer type waveguide of the lower waveguide layer 1 are adiabatic taper waveguides with a width that changes from wide to narrow, and are subwavelength grating structures that can shorten the coupling length, accelerate the light field coupling, and improve the coupling efficiency. The period Λ1 of the subwavelength grating structure of the silicon output waveguide is designed to be 100nm, and the duty cycle a1 is designed to be 20nm; the period Λ2 of the subwavelength grating structure of the silicon nitride output waveguide is designed to be 150nm, and the duty cycle a2 is designed to be 50nm; and the overlap length L7 of the coupling region of the silicon output waveguide and the silicon nitride output waveguide is 10μm.

[0034] As shown in FIG. 1, the 1x2 multimode interferometer type waveguide is designed as a polarization-insensitive multimode 1x2 power splitter, ensuring that the dual-polarization multiple modes (TE0, TE1, TM0, TM1) can simultaneously achieve high-efficiency 1x2 power splitting. Figures 4-7 The simulated light field distribution diagrams of the TE0, TE1, TM0, and TM1 modes in different direction sections are shown in FIG. 2, and the numerical calculation of the light field distribution is performed by using the three-dimensional finite difference time domain (3D FDTD) method.

[0035] As shown in FIG. 3, the 1x2 multimode interferometer type waveguide is designed as a polarization-insensitive multimode 1x2 power splitter, ensuring that the dual-polarization multiple modes (TE0, TE1, TM0, TM1) can simultaneously achieve high-efficiency 1x2 power splitting. Figure 4 Taking the TE0 fundamental mode as an example, at a wavelength of 1550nm, the TE0 input light waveguide is divided into two TE0 modes with the same phase (TE0-TE0), then transmitted to the silicon nitride waveguide through the designed interlayer coupler, and finally, the two TE0 modes with the same phase are combined in the silicon nitride waveguide to form a TE0 mode (TE0-TE0).

[0036] As shown in FIG. 4, the 1x2 multimode interferometer type waveguide is designed as a polarization-insensitive multimode 1x2 power splitter, ensuring that the dual-polarization multiple modes (TE0, TE1, TM0, TM1) can simultaneously achieve high-efficiency 1x2 power splitting. Figure 5Taking the TE1 first-order mode as an example, the TE1 input optical waveguide is divided into two TE0 modes with a phase difference of π (TE1-TE0), then transmitted to the silicon nitride waveguide through the designed interlayer waveguide coupler, and finally, the two TE0 modes with a phase difference of π are combined in the silicon nitride waveguide to form a TE1 mode (TE0-TE1). The working mechanism of the device for TM polarization is the same as that for TE polarization.

[0037] Figure 8 For the simulated transmission spectrum, it can be observed that the transmission loss of the TE0 and TE1 modes is less than 0.73 dB, and the transmission loss of the TM0 and TM1 modes is less than 0.36 dB in the range of 1450 nm to 1650 nm, indicating that the present application has a low transmission loss in a waveband of 200 nm. It can be seen that the double-polarization multi-mode interlayer waveguide coupler of the present application can simultaneously support the interlayer coupling of four modes (TE0, TE1, TM0, TM1), and has the characteristics of supporting multi-mode, high coupling efficiency, small size and low transmission loss.

[0038] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A dual-polarization multi-mode interlayer waveguide coupler, characterized by: The interlayer waveguide coupler comprises a lower waveguide layer (1), a cladding layer (2) and an upper waveguide layer (3); wherein the lower waveguide layer (1) and the upper waveguide layer (3) are composed of 1x2 multimode interferometer type waveguides; in the vertical direction, the upper waveguide layer (3) is on the upper layer, the lower waveguide layer (1) is on the lower layer, and they are not in contact with each other and are separated from each other by the cladding layer (2); along the transverse propagation direction of the optical field, the upper waveguide layer (3) and the lower waveguide layer (1) have an overlapping coupling region in structure; the 1x2 multimode interferometer type waveguide is composed of an input waveguide, a tapered waveguide, a wide multimode interference waveguide and two output waveguides connected in sequence, the upper waveguide layer (3) comprises upper waveguide layer output waveguides (8), upper waveguide layer wide multimode interference waveguides (9), upper waveguide layer tapered waveguides (10) and upper waveguide layer input waveguides (11) connected in sequence, and the lower waveguide layer (1) comprises lower waveguide layer input waveguides (4), lower waveguide layer tapered waveguides (5), lower waveguide layer wide multimode interference waveguides (6) and lower waveguide layer output waveguides (7) connected in sequence; the two upper waveguide layer output waveguides (8) of the 1x2 multimode interferometer type waveguide of the upper waveguide layer (3) and the two lower waveguide layer output waveguides (7) of the 1x2 multimode interferometer type waveguide of the lower waveguide layer (1) overlap each other along the transverse propagation direction of the optical field, and satisfy the interlayer waveguide coupling condition; the 1x2 multimode interferometer type waveguide is a polarization-insensitive multimode 1x2 power splitter, and dual-polarization multiple modes can simultaneously achieve high-efficiency 1x2 power splitting; the two upper waveguide layer output waveguides (8) of the 1x2 multimode interferometer type waveguide of the upper waveguide layer (3) and the two lower waveguide layer output waveguides (7) of the 1x2 multimode interferometer type waveguide of the lower waveguide layer (1) are insulating tapered waveguides with a width changing from wide to narrow, and are subwavelength grating structures.

2. The dual-polarization multi-mode interlayer waveguide coupler according to claim 1, wherein: The materials of the upper waveguide layer (3) and the lower waveguide layer (1) are selected from one of silicon, silicon nitride, III-V group materials or polymers, and the material of the cladding layer (2) is silica; the spacing size of the upper waveguide layer (3) and the lower waveguide layer (1) is 0-500nm.

3. The dual-polarization multi-mode interlayer waveguide coupler according to claim 2, wherein: The lower waveguide layer (1) is a 1x2 multimode interferometer type silicon waveguide, the size L2xw2 of the lower waveguide layer wide multimode interference waveguide (6) is 15x6.2 μm 2 , the width w1 of the lower waveguide layer input waveguide (4) is set to 2.5 μm, the length L1 of the lower waveguide layer tapered waveguide (5) is set to 15 μm, the lower waveguide layer output waveguide (7) is an adiabatic taper, the width is from 3 μm to 0.12 μm, and the length is 65 μm, the upper waveguide layer (3) is a 1x2 multimode interferometer type silicon nitride waveguide, the size L5xw6 of the upper waveguide layer wide multimode interference waveguide (9) is 10x6.2 μm 2 , the width w5 of the upper waveguide layer input waveguide (11) is set to 2.5 μm, the length L4 of the upper waveguide layer tapered waveguide (10) is set to 15 μm, the width of the upper waveguide layer output waveguide (8) is from 3 μm to 0.2 μm, and the length is 65 μm.

4. The dual-polarization multi-mode interlayer waveguide coupler according to claim 3, wherein: The lower waveguide layer (1) is a 1x2 multimode interferometer type silicon waveguide, the period Λ1 of the subwavelength grating structure of the lower waveguide layer output waveguide (7) is designed as 100nm, and the duty cycle a1 is designed as 20nm; the upper waveguide layer (3) is a 1x2 multimode interferometer type silicon nitride waveguide, the period Λ2 of the subwavelength grating structure of the upper waveguide layer output waveguide (8) is designed as 150nm, and the duty cycle a2 is designed as 50nm; the overlapping length L7 of the coupling region of the lower waveguide layer output waveguide (7) and the upper waveguide layer output waveguide (8) is 10μm.

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