CN113900181A

CN113900181A - Waveguide edge integrated coupler and preparation method thereof

Info

Publication number: CN113900181A
Application number: CN202111105651.3A
Authority: CN
Inventors: 顾文华; 李雄飞; 疏静; 桂桑; 韩明玺; 王雷
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-09-22
Filing date: 2021-09-22
Publication date: 2022-01-07
Anticipated expiration: 2041-09-22
Also published as: CN113900181B

Abstract

The invention discloses a waveguide edge integrated coupler and a preparation method thereof. The coupler structure includes a PIC device platform, an SOI waveguide structure and a silicon microlens; the light is transmitted and exited through the SOI waveguide structure on the PIC device platform, and the silicon microlens converts the beam spot, changes the light trajectory and limits the angle of the light entering the fiber core , and then the light travels through space and then enters the single-mode fiber core. The preparation method of the coupler is divided into four steps. First, the SOI structure is designed and simulated to obtain the mode characteristics of the waveguide emission; second, the lens parameters are designed; then, the coupler and the single-mode fiber are co-simulated to obtain the theoretical coupling efficiency ; Finally, the coupling structure is fabricated according to the design, and the actual active test results are optimized to determine the final parameters and coupling scheme. Compared with the discrete coupling, the overall structure of the coupler can be integrated on the integrated optical circuit chip platform, the process is simple, and the packaging is convenient.

Description

Waveguide edge integrated coupler and preparation method thereof

Technical Field

The invention relates to the technical field of silicon photonic integration, in particular to a coupler and a preparation method thereof.

Background

The development of high-speed optical communication pushes the progress of silicon-based photonics, and communication devices seek higher speed, larger bandwidth capacity and higher integration level. Semiconductor photonic devices, especially silicon photonic devices, have a wide prospect, wherein the input and output of light in semiconductor devices are often completed by adopting a silicon waveguide structure, but external transmission often needs to be coupled into optical fibers for long-distance transmission, so that the realization of efficient coupling of silicon waveguides and single-mode optical fibers is a key problem to be solved for improving the integration level of devices/systems.

The common discrete lens is a lens made of silicon dioxide material, is difficult to integrate with a silicon waveguide, has a large size, is usually coupled in a far field, causes a large volume of an optical path system, is not beneficial to packaging, has high cost due to non-arrayed coupling, and is difficult to meet the benefit requirement of unit integration.

Disclosure of Invention

The invention aims to provide a waveguide edge integrated coupler for realizing effective coupling of a near-field optical path in a PIC device from a silicon waveguide to a single-mode optical fiber and a preparation method thereof, and aims to solve the problem of coupling loss caused by mismatch of the size of a mode spot and high refractive index difference of a waveguide/a fiber core by using a micro-size structure and in a near field, so as to realize effective coupling of the waveguide and the single-mode optical fiber.

The technical solution for realizing the purpose of the invention is as follows:

a waveguide edge integrated coupler comprising a PIC device platform, an SOI (silicon on insulator) waveguide structure, and a silicon microlens; the silicon micro lens and the SOI waveguide structure are integrated on a PIC device platform on the same substrate; the silicon micro lens is positioned at the edge of the light-emitting end face of the SOI waveguide structure; the SOI waveguide structure can be used as the light output end of silicon-based waveguides with various structures in a PIC device platform, namely the SOI waveguide structure can be used for light transmission and can also be used as the output end of the silicon-based waveguides. The specific coupling process of the coupler is as follows: optical signals are transmitted and emitted through the SOI waveguide on the PIC device platform, the silicon micro-lens carries out mode spot conversion on light beams to a certain degree, light ray tracks are changed, the angle of light rays entering the fiber core is limited, and then the light rays enter the fiber core after being transmitted in space.

Furthermore, the SOI structure comprises a substrate layer, a buried oxide layer, a ridge waveguide outer ridge layer and a ridge waveguide inner ridge layer; the substrate layer, the buried oxide layer, the ridge waveguide outer ridge layer and the ridge waveguide inner ridge layer are sequentially stacked from bottom to top; the substrate layer is made of Si and the buried oxide layer is made of SiO₂The waveguide outer ridge layer and the ridge waveguide inner ridge layer are made of Si; there may be a cladding layer of other materials over the waveguide outer ridge layer, ridge waveguide inner ridge layer.

Furthermore, the SOI waveguide structure adopts a single-mode transmission mode; the thickness d of the ridge waveguide outer ridge layer and the thickness h of the ridge waveguide inner ridge layer meet the single mode condition, namely d is gamma multiplied by h, and gamma is more than 0.5; the integral length of the SOI waveguide structure is larger than the stable single-mode length of the designed SOI structure; the stable single-mode length of the SOI structure refers to the length of the SOI waveguide structure when the optical mode in which light is transmitted through the SOI waveguide structure and finally transmitted and coupled is a stable single-mode or a fundamental mode.

Furthermore, the silicon micro-lens is positioned at the edge of the light-emitting end face of the SOI waveguide structure and is tightly attached to the SOI waveguide structure but not limited to the attachment integration mode, namely, the waveguide and the rear end face of the micro-lens can have a short interval D₁. The interval D₁Should approach to 0 μm to realize the close fit between the silicon microlens and the waveguide structure, if the silicon microlens is not close to the waveguide, the waveguide end face should be located near the objective focal length of the lens, and the beam waist diameter of the incident beam is w₀The distance between the waist position of the incident beam and the lens is d_in. The silicon microlens is aligned with the inner ridge layer of the ridge waveguide in the form of center alignment, and the surface is asphericThe material is Si.

Furthermore, the end face of the silicon micro lens and the end face of the single-mode optical fiber are subjected to anti-reflection treatment to reduce Fresnel reflection loss of a waveguide emergent light beam entering the fiber core through air, so that the loss is not more than 1%.

Further, the near-field coupling distance between the end face of the silicon micro lens and the end face of the single-mode optical fiber is not more than 100 mu m, and the coupling distance D₂Satisfies the following conditions: d is not less than 0₂≤|do_ut±Z_RDesign tolerance of |, where do_utIs the distance, Z, between the image space beam waist position and the lens_RRayleigh distance, Z, being image-wise Gaussian beam_R＝πw₀′²/4λ，w₀' is the size of the beam waist diameter of an image space, and lambda is the light wavelength;

furthermore, the coupling structure and the fiber core should keep the center of the (x, y) section aligned, and the Z-direction incidence has no included angle.

In order to achieve the purpose of the invention, the invention also provides a preparation method of the waveguide edge integrated coupler, which comprises the following steps:

designing and simulating an SOI waveguide structure adopting single-mode transmission, and obtaining the mode characteristic of waveguide emergent light according to the structural parameters of the SOI waveguide;

designing the structural parameters of the silicon micro lens according to the single-mode fiber parameters and the near-field coupling distance requirements, and obtaining Gaussian beam parameters of emergent light through theoretical calculation and numerical simulation;

performing joint simulation on the whole structure of the coupler and the single-mode optical fiber to obtain theoretical coupling efficiency;

fourthly, manufacturing a coupling structure according to the theoretical design parameters of the SOI waveguide structure and the silicon micro-lens structure obtained in the first step and the second step; and debugging and optimizing the design parameters through an actual active test result to obtain corresponding coupling efficiency and dislocation tolerance meeting actual coupling requirements, and preparing the waveguide edge integrated coupler of the specific PIC platform according to the optimized structural parameters of the SOI waveguide and the silicon micro-lens.

Further, the structural parameters of the SOI waveguide in the first step comprise the thickness and the material of each layer of the substrate layer, the buried oxide layer, the ridge waveguide outer ridge layer and the ridge waveguide inner ridge layer; the mode characteristics of waveguide emergent light include polarization, energy distribution and spot size.

Further, the parameters of the single-mode fiber in the second step include mode field diameter MFD, numerical aperture NA, and refractive index distribution n-profile; the near-field coupling distance is not more than 100 μm, and the coupling distance D₂Satisfies the following conditions: d is not less than 0₂≤|do_ut±Z_RDesign tolerance of |, where do_utIs the distance, Z, between the image space beam waist position and the lens_RRayleigh distance, Z, being image-wise Gaussian beam_R＝πw₀′²/4λ，w₀' is the size of the beam waist diameter of an image space, and lambda is the light wavelength; the structural parameters of the silicon micro lens comprise front curvature R, thickness and surface shape size; the Gaussian beam parameters of the emergent light comprise the size of a waist spot, the shape of a light spot, the spatial position, the Rayleigh distance, the divergence angle and the energy distribution.

Further, the simulation method in the third step is a beam propagation method BPM or a time domain finite difference method FDTD.

Compared with the prior art, the invention has the advantages that:

1) the problem of coupling loss caused by mode spot matching and high refractive index difference of the waveguide/single-mode fiber is solved in a near field by using a small-size structure, and far-field energy loss is avoided; 2) the edge integration mode improves the unit integration level, reduces the packaging difficulty and can reduce the volume of the silicon photonic device; 3) compared with a discrete coupling mode, the non-arrayed coupling mode has obvious cost advantage.

To better explain the functional characteristics and structural parameters of the devices according to the claims and the summary of the invention, the following description is given with reference to the accompanying drawings and the detailed description.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:

FIG. 1 is a schematic diagram of a waveguide edge integrated coupler structure;

FIG. 2 is a schematic diagram of an SOI waveguide structure;

FIG. 3 is a graph showing the relationship between front and rear waist spots of a silicon microlens;

FIG. 4 is a schematic diagram of a light field coupling process;

FIG. 5 is a graph of coupling distance versus coupling efficiency;

FIG. 6 is a contour plot of end face misalignment versus coupling efficiency;

the reference signs are: 1. PIC device platform, 2, SOI waveguide structure, 3, silicon micro lens, 4, single mode fiber, 2_aThe substrate layer, 2b, the buried oxide layer, 2c, the ridge waveguide outer ridge layer and 2d the ridge waveguide inner ridge layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples

As shown in fig. 1 to 6, the present invention provides a waveguide edge integrated coupler and a manufacturing method thereof, which are used for realizing effective coupling of a near-field optical path from a silicon waveguide to a single-mode optical fiber in a PIC device platform.

In this embodiment, an edge integrated coupling structure is designed, in which an SOI waveguide structure with a ridge layer size of 3 μm × 3 μm in ridge waveguide and a single-mode fiber with a core diameter of 8.6 μm are coupled at a near-field distance of 100 μm under 1550nm wavelength light, and the specific contents are as follows:

as shown in fig. 1, the waveguide edge integrated coupler includes a PIC device platform, an SOI waveguide structure, a silicon microlens, and a single-mode fiber; the silicon micro lens and the SOI waveguide structure are integrated on the same substrate, and the silicon micro lens is positioned at the edge of the light-emitting surface of the SOI waveguide structure.

As shown in FIG. 2, the SOI waveguide structure comprises a substrate layer, a buried oxide layer and a ridgeThe ridge layer outside the waveguide, ridge layer in the ridge waveguide, wherein ridge waveguide outer ridge layer thickness is d, ridge waveguide inner ridge layer thickness is h, ridge waveguide inner ridge layer width is w, ridge waveguide outer ridge layer thickness d, ridge waveguide inner ridge layer thickness h satisfy the single mode condition, namely d is gamma x h, gamma>0.5. According to stable single-mode conditions, an SOI waveguide structure is designed, and the specific parameters are as follows: ridge layer width and thickness within ridge waveguide: w-h-3 μm, ridge waveguide outer ridge layer thickness: d is 1.8 μm, the buried oxide layer is 1.2 μm thick, and the substrate layer is 2 μm thick. The substrate layer is made of Si and the buried oxide layer is made of SiO₂The ridge waveguide layer is made of Si; above the ridge waveguide layer is air.

As shown in fig. 3, the Z axis represents the light propagation direction, the image-side waist spot position relationship is calculated by Finite Difference Time Domain (FDTD), and the silicon microlens designed in this embodiment is closely attached to the waveguide, i.e., D ₁0 μm, at which the incident beam waist diameter w₀The size of the emergent light mode spot is similar to that of the SOI waveguide, about 3.5 mu m, and the distance d between the incident beam waist position and the lens _in0 μm. In this embodiment, the ridge waveguide mode spot/core mode field size (MFD) is about 3.5 μm/9.89 μm, and the structure of the silicon microlens 3 is designed according to the mode spot matching requirement, and the specific parameters are as follows: the front curvature R is 25 μm, the thickness is 30 μm, the profile size is 10 μm × 10 μm, and the material is Si. The effective focal length of the lens image space is about 13 μm, and the diameter w of the beam waist of the lens image space is calculated after the beam exits from the lens₀' about 10.6 μm, matching the mode field diameter MFD of a single-mode fiber, Rayleigh distance Z_RAbout 40 μm, the distance do between the image beam waist and the lens_utAbout 18 μm, the theoretical design tolerance of the coupling distance D2 is satisfied: d is not less than 0₂Less than or equal to 58 mu m, and the coupling efficiency can reach more than 80 percent in the range.

As shown in fig. 4, the light beam is emitted from the ridge waveguide, passes through the microlens to change the propagation path of the light beam, undergoes a certain degree of mode spot conversion, and enters the core of the single-mode optical fiber after being spatially propagated. The optical field profile in the Z-direction from the ridge waveguide into the core of the single mode fiber is calculated using a beam propagation algorithm (BPM). The specific process is as follows: performing combined simulation on the SOI structure, the silicon micro lens and the single-mode fiber, wherein the light beam is transmitted along the Z direction; the ridge waveguide/core mode field size is about 3.5 μm/9.89 μm; the ridge waveguide/core index profile at 1550nm wavelength was 3.45/1.4682. Meanwhile, the micro lens and the end face of the optical fiber are subjected to anti-reflection treatment, and the reflection loss is controlled within 1%.

As shown in fig. 5, a coupling distance D is obtained₂From the relationship between the coupling efficiency and the coupling efficiency, it can be seen that in this embodiment, the 1dB coupling range is 0 μm to 60 μm, and the coupling efficiency can reach more than 90% in 40 μm, and 68% in 100 μm of the near field can be ensured.

As shown in fig. 6, a contour diagram of the relationship between the end face dislocation and the coupling efficiency is obtained by setting dislocation parameters of the sections of the single-mode fiber and the SOI waveguide and simulating the dislocation loss tolerance in the case of the parallel end faces in consideration of the coupling loss caused by the end face dislocation in the actual coupling. It can be seen that in the (x, y) cross section, the coupling efficiency is more sensitive to the shift in the y direction, and more than 80% can be obtained when the lateral shift δ x and the longitudinal shift δ y are both less than 1.5 μm.

Finally, the coupling device can be manufactured according to the design structure of the embodiment, the design parameters are debugged and optimized through actual active test results to obtain corresponding coupling efficiency and dislocation tolerance meeting actual coupling requirements, and the waveguide edge integrated coupler of the specific PIC platform is prepared according to the optimized structure parameters of the SOI waveguide and the silicon micro-lens.

Claims

1. A waveguide edge integrated coupler, characterized in that the coupler comprises a PIC device platform (1), a SOI waveguide structure (2) and a silicon microlens (3); the silicon micro lens (3) and the SOI waveguide structure (2) are integrated on a PIC device platform (1) by the same substrate; the silicon micro lens (3) is positioned at the edge of the light-emitting end face of the SOI waveguide structure (2); the light rays are emitted from the PIC device platform (1) through the SOI waveguide structure (2), the silicon micro lens (3) performs mode spot conversion on the light beams, the light ray track is changed, the angle of the light rays entering the fiber core is limited, and then the light rays enter the fiber core of the single mode fiber (4) after being transmitted in space.

2. A waveguide edge integrated coupler according to claim 1, wherein said waveguide edge integrated coupler is configured to be coupled to a waveguideThe SOI structure (2) comprises a substrate layer (2a), a buried oxide layer (2b), a ridge waveguide outer ridge layer (2c) and a ridge waveguide inner ridge layer (2 d); the substrate layer (2a), the buried oxide layer (2b), the ridge waveguide outer ridge layer (2c) and the ridge waveguide inner ridge layer (2d) are stacked in sequence from bottom to top; the substrate layer (2a) is made of Si, and the buried oxide layer (2b) is made of SiO₂The ridge waveguide outer ridge layer (2c) and the ridge waveguide inner ridge layer (2d) are made of Si; and a cladding layer made of other materials can exist on the ridge waveguide outer ridge layer (2c) and the ridge waveguide inner ridge layer (2 d).

3. A waveguide edge integrated coupler according to claim 2, characterized in that said SOI waveguide structure (2) employs single mode transmission; the thickness d of the ridge waveguide outer ridge layer (2c) and the thickness h of the ridge waveguide inner ridge layer (2d) meet a single mode condition, namely d is gamma multiplied by h, and gamma is more than 0.5; the overall length of the SOI waveguide structure (2) is larger than the stable single-mode length of the SOI waveguide; the stable single-mode length of the SOI waveguide refers to the length of the SOI waveguide structure (2) when the optical mode which is finally transmitted and coupled is a stable single-mode or a fundamental mode after light is transmitted through the SOI waveguide structure (2).

4. A waveguide edge integrated coupler according to claim 2, characterized in that the spacing between the silicon microlens (3) and the light-exit end face of the SOI waveguide structure (2) is D₁，D₁The focal length of the silicon micro lens (3) is not less than 0 mu m; the silicon micro lens (3) is aligned with the ridge layer (2d) in the ridge waveguide in a center alignment mode, the surface of the silicon micro lens (3) is aspheric, and the material is Si.

5. The waveguide edge integrated coupler according to claim 1, wherein the end face of the silicon microlens (3) and the end face of the single-mode fiber (4) are both anti-reflection treated to reduce the fresnel reflection loss of the waveguide emergent light beam through the air incident core, so that the loss is not more than 1%.

6. A waveguide edge integration according to claim 1Coupler, characterized in that the near-field coupling distance between the end face of the silicon microlens (3) and the end face of the single-mode optical fiber (4) does not exceed 100 [ mu ] m, and the coupling distance D₂Satisfies the following conditions: d is not less than 0₂≤|d_out±Z_RDesign tolerance of |, where d_outIs the distance between the image-side waist spot position and the lens, Z_RRayleigh distance, Z, being image-wise Gaussian beam_R＝πw₀′²/4λ，w₀' is the size of the beam waist diameter at the image side, and λ is the wavelength of light.

7. A method for preparing a waveguide edge integrated coupler is characterized by comprising the following steps:

8. The method according to claim 7, wherein the structural parameters of the SOI waveguide in the first step include the thickness and the material used for the substrate layer, the buried oxide layer, the ridge waveguide outer ridge layer and the ridge waveguide inner ridge layer; the mode characteristics of waveguide emergent light include polarization, energy distribution and spot size.

9. The method according to claim 7, wherein the parameters of the single-mode fiber in the second step include mode field diameter MFD, numerical aperture NA, refractive index profile n; the near-field coupling distance is not more than 100 μm, and the coupling distance D₂Satisfies the following conditions: d is not less than 0₂≤|d_out±Z_RDesign tolerance of |, where d_outIs the distance, Z, between the image space beam waist position and the lens_RRayleigh distance, Z, being image-wise Gaussian beam_R＝πw₀′²/4λ，w₀' is the size of the beam waist diameter of an image space, and lambda is the light wavelength; the structural parameters of the silicon micro lens comprise front curvature R, thickness and surface shape size; the Gaussian beam parameters of the emergent light comprise the size of a waist spot, the shape of a light spot, the spatial position, the Rayleigh distance, the divergence angle and the energy distribution.

10. The method of claim 7, wherein the simulation method in step three is Beam Propagation (BPM) or Finite Difference Time Domain (FDTD).