Design method of broadband anti-dispersion photon integrated coupling device

Abstract

The invention belongs to the technical field of integrated photoelectronics, and particularly relates to a broadband dispersion-resistant photonic integrated coupling device design method, which comprises the following steps: S1, based on a photonic integrated coupling device, the structure of the photonic integrated coupling device is established on a silicon substrate, and the photonic integrated coupling device comprises an input waveguide, an output waveguide and a transition region for connecting the input waveguide and the output waveguide; s2, the contour of the side wall of the transition area adopts a specially optimized nonlinear curve shape; s3, the curve contour is designed through a numerical optimization algorithm; and S4, the geometrical shape can guide the smooth and adiabatic evolution of the light mode, so that the device performance has high robustness to the refractive index change of the core layer material and the cladding layer material. The design method and the structural idea provided by the invention can be applied to various photonic integrated devices, and a new way is provided for developing various high-performance broadband photonic chips.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of integrated optoelectronic technology, and particularly relates to a design method of a broadband anti-dispersion photonic integrated coupling device. BACKGROUND

[0002] With the wide application of photonic integrated circuits (PIC) in the fields of optical communication, sensing and computing, the performance requirements of individual components are also increasingly high. Optical couplers or mode converters are basic building blocks in photonic integrated circuits, and their function is to realize efficient transmission of optical signals between different waveguides or devices.

[0003] At present, one of the mainstream material platforms for photonic devices is silicon-on-insulator (SOI), which uses silicon (Si) as the waveguide core layer and silicon dioxide (SiO2) as the cladding layer. However, the coupling device design in the prior art is usually optimized for a certain specific center wavelength. When the working wavelength range is wide (for example, from 1 μm to 4 μm in the mid-infrared band), a serious problem will appear: material dispersion.

[0004] Specifically, the refractive index (n) of the material (such as Si and SiO2) constituting the device will change significantly with the change of wavelength (λ). For example, in the wavelength range of 1 μm to 4 μm, the refractive index of silicon will decrease by about 3%, and the refractive index of silicon dioxide will decrease by about 4%. This change in refractive index will destroy the phase matching and mode matching conditions of the device at the design center wavelength, resulting in a sharp decline in the transmission efficiency of the device at other wavebands deviating from the center wavelength, thereby severely limiting the effective working bandwidth of the device.

[0005] Therefore, there is an urgent need for a coupling structure design method that is robust to changes in wavelength and suitable for broadband mid-infrared optical communication and sensing. SUMMARY

[0006] The present application aims to solve the fundamental problem of limited working bandwidth of silicon-based photonic integrated devices due to material dispersion effect. By proposing a novel anti-dispersion design method based on geometric structure optimization, the present application is committed to providing a photonic device that can maintain stable and efficient performance in a super wide spectral range, in order to meet the urgent needs of the next generation of optical communication, optical sensing and other frontier fields for broadband operation.

[0007] To achieve the above application purposes, the technical solutions adopted by the present application are as follows:

[0008] A broadband anti-dispersion photonic integrated coupling device design method, comprising the following steps:

[0009] S1, based on a photonic integrated coupling device, the structure of which is established on a silicon substrate and includes an input waveguide, an output waveguide, and a transition region connecting the two;

[0010] S2, the side wall profile of the transition region adopts a specially optimized non-linear curvilinear connection shape;

[0011] S3, the curvilinear profile is designed by a numerical optimization algorithm (for example, a genetic algorithm, a companion method topology optimization, etc.);

[0012] S4, the geometric shape can guide the smooth and adiabatic evolution of the light mode, so that the device performance is highly robust to the refractive index variation of the core layer material (Si) and the cladding layer material (SiO2).

[0013] Further, as a preferred technical solution of the application, the transition region is composed of two geometrically anti-symmetric curvilinear waveguides, which ensure mode matching and low loss characteristics during transmission of the optical signal.

[0014] Further, as a preferred technical solution of the application, the curvature variation of the curvilinear waveguide satisfies a piecewise continuous derivable function, such as a Clothoid curve or a cubic spline curve, to ensure adiabatic transmission of the optical field.

[0015] Further, as a preferred technical solution of the application, the width of the curvilinear waveguide gradually changes along the transmission direction according to a non-linear function (such as a high-order polynomial), to optimize the mode matching efficiency and suppress high-order mode scattering.

[0016] Further, as a preferred technical solution of the application, a taper matching structure is provided at the connection between the transition region and the input / output straight waveguide, to further reduce mode mismatch and reflection loss.

[0017] The design method of the broadband anti-dispersion photonic integrated coupling device according to the application has the following technical effects compared with the prior art by adopting the above technical solutions:

[0018] (1) Ultra-wide working bandwidth: the design of the application can effectively overcome the material dispersion effect. Simulation results show that in a wavelength range of 3 μm to 3.6 μm or even wider, the device can maintain a theoretical transmission efficiency close to 100%, which is much better than the traditional design.

[0019] (2) High transmission efficiency and stability: by comparing the simulation results using constant refractive index and actual refractive index varying with wavelength, the transmission efficiency of the device of the application is almost the same in both cases, which proves its high insensitivity to material dispersion, ensuring high efficiency and stable transmission in the entire working bandwidth.

[0020] (3) Potential tolerance to fabrication errors: The smooth transition geometry has better tolerance to fabrication errors caused by photoresist non-uniformity, sidewall roughness, etc. compared to traditional structures with sharp corners or abrupt cross-sections.

[0021] (4) Design scalability: The design method and structural concept proposed in this application can be applied to a variety of photonic integrated devices, providing a new approach for developing various high-performance broadband photonic chips. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a cross-sectional view of a photonic integrated coupling device in an embodiment of the application;

[0023] Figure 2 is a top view of a photonic integrated coupling device in an embodiment of the application;

[0024] In the figure, 1 - cladding layer; 2 - first silicon core structure; 3 - second silicon core structure; 4 - straight input waveguide; 5 - first waveguide; 6 - second waveguide; 7 - straight output waveguide. DETAILED DESCRIPTION

[0025] The application will be described in further detail below with reference to the drawings, which are provided to give those skilled in the art a further understanding of the application and enable them to carry out the application, but the following examples are only used to explain the application and do not limit the application.

[0026] The method of the application is based on a photonic integrated coupling device, which is built on a silicon substrate (such as SOI) and includes an input waveguide, an output waveguide, and a transition region connecting the two. The core of the device is that:

[0027] The sidewall profile of the transition region adopts a specially optimized non-linear curve shape. The curve profile is designed by a numerical optimization algorithm (for example, a genetic algorithm, a companion method topology optimization, etc.), and its geometric shape can guide the smooth and adiabatic evolution of the light mode, making the device performance highly robust to the refractive index changes of the core layer material (Si) and the cladding layer material (SiO2).

[0028] In a preferred embodiment, the technical features of the device can further include one or a combination of the following:

[0029] Structural design: The transition region is composed of two geometrically anti-symmetric curve waveguides, which ensure mode matching and low loss characteristics of the light signal during transmission.

[0030] Curved function: the curvature variation of the curved waveguide satisfies a piecewise continuous derivable function, such as Clothoid curve or cubic spline curve, to ensure adiabatic transport of the light field.

[0031] Width variation: the width of the curved waveguide varies along the transmission direction according to a nonlinear function (such as a high-order polynomial) to optimize the mode matching efficiency and suppress high-order mode scattering.

[0032] Matching structure: a tapered matching structure is provided at the connection between the transition region and the input / output straight waveguide to further reduce mode mismatch and reflection loss.

[0033] The device of the present application can be specifically implemented in the form of a mode converter, a curved waveguide, a coupler, etc. The core idea of the present application, i.e. using an optimized nonlinear geometric structure to achieve anti-dispersion, can also be applied to other devices with symmetric or asymmetric structures.

[0034] The present embodiment provides a broadband mode converter based on an SOI platform. The first and second silicon core mechanisms 2 and 3 are made of silicon (Si), and the cladding layer 1 is made of silicon dioxide (SiO2), as shown in Figure 1 .

[0035] The connection mode of the first and second silicon core mechanisms 2 and 3 is shown in Figure 2 . This structure mainly consists of three parts: a straight input waveguide 4, a straight output waveguide 7, and a nonlinear transition region connecting the two, which is composed of two geometrically antisymmetric curved first and second waveguides 5 and 6. In this embodiment, the specific design parameters of the transition region satisfy: the curvature variation of the first and second waveguides 5 and 6 follows a cubic spline curve function; the waveguide width varies along the transmission direction according to a high-order polynomial function; the total length of the transition region is controlled within 100 μm, achieving an insertion loss of less than 0.3 dB.

[0036] To verify the anti-dispersion performance of the design of the present application, strict numerical simulation is carried out. Four key wavelength points in the mid-infrared band are selected: 3.00 μm, 3.50 μm, 3.60 μm and 4.00 μm. In the simulation, two cases are compared:

[0037] Case A (constant refractive index): assuming no dispersion of the material, the refractive index of Si nSi is constant at 3.455, and the refractive index of SiO2 nSiO2 is constant at 1.445. This is a simplified ideal model in traditional device design.

[0038] Case B (actual refractive index): considering the dispersion of the material, the actual measured refractive indices of Si and SiO2 at each wavelength are used, as shown in Table 1: Table 1 Refractive indices of silicon and silicon dioxide varying with wavelength

[0039] λ (μm) n (Si) [n(SiO2)] 3.0 3.436 1.430 3.5 3.432 1.406 3.6 3.431 1.402 4.0 3.429 1.384

[0040] The transmission efficiency (T) results obtained by simulation are summarized in Table 2:

[0041] Table 2 Comparison of transmission efficiency of actual refractive index and constant refractive index at different wavelengths

[0042]

[0043] Result analysis:

[0044] (1) From the above table data, it can be seen that at wavelengths of 3.00 μm, 3.50 μm, and 3.60 μm, the devices all show extremely high transmission efficiency, close to 1.

[0045] (2) Core verification: comparing the results of case A and case B, the difference in transmission efficiency is minimal. For example, at 3.50 μm, although the actual refractive indices of Si and SiO2 (3.432 and 1.406) have changed significantly compared to the constant values (3.455 and 1.445), the difference in transmission efficiency is only 0.998484-0.998452=0.000032. This difference is so small that it can be ignored. At 3.60 μm, the difference is only one ten-thousandth.

[0046] (3) The results strongly prove that the geometric structure design proposed in the present application itself functions to replace the traditional dispersion compensation mechanism, achieving structural anti-dispersion and having significant theoretical innovation.

[0047] (4) At 4.00 μm, due to material absorption and other physical mechanisms, the transmission efficiency decreases to zero, which is consistent with the physical laws of this wavelength band, but does not affect the effectiveness of the present application within the transparent window of 3.00 μm to 3.60 μm.

[0048] The present application acknowledges that high-precision curved profiles present challenges in manufacturing. However, the smooth transition design of the present application is less sensitive to sidewall roughness compared to traditional structures that include sharp bends and sharp corners. With the development of electron beam lithography (EBL) and advanced lithography processes, it has become possible to manufacture sub-micron curved structures with smooth edges, ensuring the feasibility of the present application.

[0049] The coupling structure and its design method proposed in the present application are suitable for multi-band signal connection, signal conversion, and photonic interconnection in silicon-based photonic integrated chips, and have wide application value in fields such as mid-infrared optical communication, environmental sensing, and biological detection. In addition, the structure is robust to refractive index fluctuations, which is beneficial to improving the stability and yield of the device under different manufacturing batches and different working environments.

[0050] The above-described specific embodiments further illustrate the objects, technical solutions and advantages of the present application. It should be understood that the above-described specific embodiments are merely for the purpose of illustrating the present application, and are not intended to limit the scope of the present application. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present application shall fall within the scope of the present application.

Claims

1. A method for designing a broadband dispersion-resistant photonic integrated coupling device, characterized in that: The following steps are involved: S1, based on a photonic integrated coupling device, its structure is built on a silicon substrate and includes an input waveguide, an output waveguide, and a transition region connecting the two; S2. The sidewall profile of the transition zone adopts a specially optimized nonlinear curve shape; S3, the curve profile is designed through a numerical optimization algorithm; S4. The geometry can guide the smooth and adiabatic evolution of the optical mode, making the device performance highly robust to changes in the refractive index of the core and cladding materials.

2. The method for designing a broadband dispersion-resistant photonic integrated coupling device according to claim 1, wherein: The transition region is composed of two geometrically antisymmetric curved waveguides, which ensures mode matching and low loss characteristics of the optical signal during transmission.

3. The method for designing a broadband dispersion-resistant photonic integrated coupling device according to claim 2, wherein: The curvature change of the curved waveguide satisfies a piecewise continuous differentiable function to ensure adiabatic transmission of the light field.

4. The method for designing a broadband dispersion-resistant photonic integrated coupling device according to claim 3, wherein: The width of the curved waveguide changes gradually along the transmission direction according to a nonlinear function to optimize mode matching efficiency and suppress high-order mode scattering.

5. The method for designing a broadband dispersion-resistant photonic integrated coupling device according to claim 4, characterized in that: A tapered matching structure is provided at the connection between the transition zone and the input / output straight waveguide to reduce mode mismatch and reflection loss.

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