A microring resonator

Abstract

The application discloses a thickness-based refractive index gradient micro-ring resonator, comprising: a ring optical waveguide located on a substrate; an input optical waveguide configured to couple light into the ring optical waveguide; the ring optical waveguide has a feature that the thickness decreases along the radial direction, so that the refractive index decreases linearly with the micro-ring radius from small to large, under the premise of realizing a wide free spectral range and low bending loss, the resonator has a higher quality factor, the structure is simple, the resonator can be obtained through a mature photolithography technology, and is suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and more specifically to a microring resonator. Background Technology

[0002] Microring resonators, as highly integrated and sensitive optical devices, have broad application prospects in fields such as optical communication, biosensing, and quantum information processing. A microring resonator consists of a microring-structured optical waveguide; that is, a section of the optical waveguide forms a ring structure. When an optical signal propagates in the ring waveguide, it undergoes multiple reflections and interferences, thus creating a resonance phenomenon. The microring is typically a circular waveguide ring, but in principle, it can be of any geometry. The microring is optically coupled to one or two transmission waveguides. When the microring is coupled to a single waveguide, it provides the ability to remove a set of wavelengths from the transmission waveguide, thus serving as a notch filter. When the microring is coupled to two transmission waveguides, the transmission waveguides couple light to or from the microring.

[0003] In a single microring resonator, for a given radius R, there exists a series of wavelengths (corresponding to different resonance orders) that satisfy the resonance condition. The wavelength difference between two adjacent resonant wavelengths is called the free spectral range (FSR). In wavelength division multiplexing (WDM) systems, the FSR should be as large as possible to avoid affecting other channels when downloading to one channel. However, the FSR is inversely proportional to the radius R. If the FSR is very large, R will be too small, resulting in significant losses in the microring and thus reducing the quality factor of the microring resonator.

[0004] Controlling the effective refractive index of a microring radially is an effective means of improving the quality factor. For example, a photonic crystal composed of dielectric pillars with gradually decreasing radial dimensions from the inside to the outside of a microring resonator is used, causing the effective refractive index of the microring resonator to gradually decrease as the microring radius increases. However, in the field of optical device manufacturing, including the fabrication of microring resonators, process stability and production cost are crucial factors. Among these, device structure design is a key link affecting process stability and cost control. Precise control of the dielectric pillars in existing schemes can easily lead to more defects and variations during manufacturing, which not only increases the time and cost of debugging and calibration but also reduces yield and increases scrap rate. Furthermore, complex or suboptimal designs may require the use of higher-precision manufacturing equipment and technologies, which undoubtedly increases production costs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a microring resonator with a simple structure. This resonator achieves a wide free spectral range while exhibiting smoother optical path curvature and lower losses; moreover, its simple structure can be obtained using mature photolithography techniques, making it suitable for industrial applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a microring resonator, comprising at least: a ring optical waveguide located on a substrate; an input optical waveguide configured to couple light into the ring optical waveguide; the thickness of the ring waveguide gradually decreases radially from the inside to the outside.

[0007] Furthermore, the thickness d gradually decreases radially from the inside to the outside. r satisfy:

[0008]

[0009] -

[0010]

[0011] Where r1≤r≤r2, n eff Let be the effective refractive index of the ring waveguide at a distance r from the center, m be the resonant order, and λ be the resonant wavelength. For transmission optical mode, k0 is the light wavenumber, k x Let n be the vertical light wave vector, n1 be the intrinsic refractive index of the ring, and n2 be the refractive index of the medium in the upper and lower edge regions of the micro-ring. denoted as the attenuation constant of the medium in the upper and lower edge regions of the microring.

[0012] In some embodiments of the present invention, the ring waveguide material is selected from any one of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0013] In some embodiments of the present invention, an output optical waveguide coupled to the ring optical waveguide is also included.

[0014] In some embodiments of the present invention, the input optical waveguide and the output optical waveguide are any one or more of strip waveguides, ridge waveguides, or multilayer waveguides.

[0015] In some embodiments of the present invention, the materials of the input optical waveguide and the output optical waveguide are selected from one or more of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0016] In some embodiments of the present invention, the coupled waveguides are single-mode waveguides and / or multimode waveguides.

[0017] In some embodiments of the present invention, the coupling relationship between the ring optical waveguide and the input optical waveguide and the output optical waveguide is horizontal coupling or vertical coupling.

[0018] Based on the structural design of this invention, the microring resonator of this invention can be directly obtained from the waveguide material layer by etching.

[0019] The beneficial technical effects of the present invention are as follows:

[0020] The free spectral range of the microring resonator provided by this invention can be more than doubled while maintaining the same bending loss. Furthermore, due to its excellent structural design, its manufacturing process is simple, and the production yield can be controlled at over 95%. Attached Figure Description

[0021] Figure 1 This is a top view of a microring resonator provided in an embodiment of the present invention.

[0022] Figure 2 For the present invention Figure 1 The embodiment shown is a three-dimensional schematic diagram of a ring-shaped optical waveguide.

[0023] Figure 3 This is the present invention. Figure 1 The illustrated embodiment is shown in cross-sectional view along the A-A' direction.

[0024] Figure 4 This is a schematic diagram illustrating the principle of optical signal transmission and modulation using a micro-ring resonator in an embodiment of the present invention.

[0025] Figure 5 This is a schematic curve illustrating the change of refractive index with thickness according to the present invention;

[0026] Figure 6 This is an example of thickness reduction provided in the embodiments of the present invention;

[0027] Figure 7 This is a schematic diagram of a straight waveguide provided in an embodiment of the present invention. Detailed Implementation

[0028] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0029] In the microring structure, the thickness is relatively small relative to the diameter. Although the thickness change appears linear in the figure, there is actually a certain curvature so that the effective refractive index changes linearly and continuously.

[0030] As is common knowledge in the field, the ring-shaped optical waveguide is placed parallel to the substrate, and the thickness mentioned in this invention refers to the thickness value perpendicular to the substrate direction.

[0031] This invention provides an embodiment of a microring resonator, comprising:

[0032] A ring-shaped optical waveguide is located on the substrate;

[0033] An input optical waveguide is configured to couple light into the ring optical waveguide;

[0034] The thickness of the ring waveguide gradually decreases radially from the inside to the outside, causing the effective refractive index of the microring resonant cavity to gradually decrease as the radius of the microring increases.

[0035] Specifically, the inner diameter of the ring waveguide is r1, the outer diameter is r2, and its thickness d is located at a distance r from the center. r satisfy:

[0036]

[0037] ;

[0038] ;

[0039] - ;

[0040] - ;

[0041] Where r1≤r≤r2, n eff Let be the effective refractive index of the ring waveguide at a distance r from the center, which decreases linearly with increasing r. Let m be the resonant order, λ be the resonant wavelength, a be the transmitted optical mode, k0 be the wavenumber, and k... x Let n be the light wave vector in the vertical direction, n1 be the intrinsic refractive index of the ring, and n2 and n3 be the refractive indices of the media above and below the micro-ring, where n2 = n3. , These are the edge region attenuation constants, The effective refractive index can be obtained by simultaneously solving the five equations, and the relationship between thickness and refractive index can be obtained through simulation, such as... Figure 5 As shown (silicon), it can be seen that an effective refractive index that varies linearly and continuously can be obtained by setting the thickness.

[0042] The thickness of the ring waveguide in the microring resonator of this invention is gradually varying. That is, the thickness of the ring waveguide gradually decreases radially from the inside out. Since the effective refractive index of the waveguide is related to its thickness—the thicker the waveguide, the greater the refractive index—the gradual thickness means that the effective refractive index of the ring waveguide decreases as the microring radius increases. During light propagation in a gradually varying refractive index medium, it bends from the low refractive index direction to the high refractive index direction. Because the refractive index varies within the ring waveguide, light naturally bends due to the difference in refractive index during propagation, thereby reducing bending loss. This allows for further reduction of the microring radius without increasing loss, resulting in a wider free spectral range.

[0043] Therefore, the microring resonator provided by this invention can simultaneously possess a high quality factor and a wide free spectral range, enabling it to have a wider range of applications and excellent performance. The gradual thickness allows for a linear change in refractive index, which, compared to existing methods involving the addition of dielectric pillars, results in smoother optical path bending and lower losses. Furthermore, the thickness-designed device causes less structural damage, is easier to design and manufacture, and has a higher yield rate.

[0044] like Figure 1 As shown in Figure 2, in a specific example, the microring resonator includes at least two straight waveguides 10 and 30 serving as coupling waveguides, and at least one ring optical waveguide 20 with a gradually decreasing thickness coupled to the straight waveguides. The straight waveguides 10 and 30 include an incident end, an exit end, a loading end, and a download end for transmitting optical signals; the ring optical waveguide 20 is used to modulate the intensity of the optical signal at a corresponding wavelength, and its thickness gradually decreases radially from the inside to the outside. Figure 4 This is a schematic diagram illustrating the principle of optical signal transmission and modulation using a micro-ring resonator provided in an embodiment of the present invention. An optical signal with a wavelength corresponding to the gradually thickened ring waveguide 20 is input from the input end of the straight waveguide 10. After passing through the gradually thickened ring waveguide 20, the optical signal with the wavelength corresponding to the gradually thickened ring waveguide 20 is in a resonant state during transmission within the resonant cavity. The resonant optical signal is coupled to the straight waveguide 30, and the desired wavelength optical signal is obtained after being output through the straight waveguide 30.

[0045] like Figure 3 As shown in the embodiment, the thickness of the annular optical waveguide 20 is not uniform; its thickness decreases radially from the inside to the outside, and is the same as the thickness at the same distance from the center of the annular optical waveguide.

[0046] Since this invention is based on a gradual change in refractive index through a gradual change in the thickness of the microring, any structural form capable of achieving thickness variation is applicable to this invention. Figure 6 The symbols A, B, and C in the diagram provide three structural forms, where A is... Figure 3 In the illustrated embodiment, the single-sided tilting method involves the bottom surface of the annular waveguide being bonded to the substrate, while the top surface tilts downwards, resulting in a gradual decrease in thickness d. Option B represents a double-sided tilting mode, where both the bottom and top surfaces of the annular waveguide are tilted, achieving a gradual decrease in thickness d. Option C, with its curved surface, utilizes the curve design of both the bottom and top surfaces to achieve a gradual decrease in thickness d.

[0047] It should be noted that, for simplicity, the above embodiments only use the simplest two straight waveguides 10 and 30 and a ring waveguide 20 with a gradually varying thickness as examples. In other embodiments, multiple ring waveguides 20 can be configured as needed.

[0048] In addition, the gradually thickened annular optical waveguide 20 and the straight waveguides 10 and 30 are coupled to each other. This coupling relationship can be horizontal or vertical, and no specific limitation is made here.

[0049] In different embodiments of the present invention, the ring waveguide is any one of a strip waveguide, a ridge waveguide, or a multilayer waveguide, and the coupled wave is any one or more of a strip waveguide, a ridge waveguide, or a multilayer waveguide, and can be a single-mode waveguide and / or a multimode waveguide, without being specifically limited herein.

[0050] In different embodiments of the present invention, the material constituting the dielectric pillar includes any one of dielectric materials such as silicon oxide or air, the material of the ring optical waveguide is selected from any one of silicon on insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide, and the material of the coupling waveguide is selected from any one or more of silicon on insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide, without specific limitations.

[0051] As a preferred embodiment, silicon-on-insulator (SiI) can be used to fabricate the straight waveguide and the thickness-gradient ring waveguide shown in the above embodiments. SiI uses silicon as the core waveguide layer and silicon dioxide as the cladding. Since the refractive index difference between the two is approximately 2, light can be confined to the core waveguide layer for transmission. Furthermore, because SiI is compatible with existing CMOS platform processes, it is currently the most important silicon photonics platform.

[0052] Based on this, another embodiment of the present invention also shows a method for fabricating a microring resonator, used to fabricate the above-mentioned thickness-gradient refractive index-gradient microring resonator, the method comprising:

[0053] Simulations were performed with the goal of minimizing bending loss to determine the width and radius of the ring waveguide, the width of the coupled waveguide, and the coupling distance between the coupled waveguide and the ring waveguide. The thickness and rate of change of the microring resonator were calculated based on the aforementioned formulas.

[0054] A waveguide material layer is formed on the substrate;

[0055] Spin-coating photoresist onto the waveguide material layer;

[0056] Grayscale lithography is used to expose the photoresist, transferring the simulated device pattern onto the photoresist.

[0057] Etching is performed to obtain a ring-shaped optical waveguide and waveguide structure;

[0058] By using a dielectric material for overlay filling, a microring resonator based on a thickness gradient refractive index is fabricated.

[0059] like Figure 7 As shown in the illustration, in a specific example, the fabricated basic microring structure and coupled waveguide include:

[0060] Substrate 101;

[0061] The lower cladding layer 102 is located on the surface of the substrate 101;

[0062] The first waveguide layer 103 is located on the surface of the lower cladding layer 102 on the side away from the substrate 101;

[0063] The upper cladding 104 encloses the first waveguide layer 103, and the surface on the side away from the first waveguide layer 103 is planar.

[0064] For example, substrate 101 can be made of silicon, lower cladding layer 102 can be made of silicon dioxide, first waveguide layer 103 can be made of silicon, and upper cladding layer 104 can be made of silicon dioxide. This structure has the following advantages:

[0065] (1) The silicon core waveguide layer is nearly transparent to the most commonly used 1550nm wavelength optical signal, thus achieving very low transmission loss.

[0066] (2) The refractive index of silicon is about 3.42 and the refractive index of silicon dioxide is about 1.45. The difference between the two refractive indices is large, so it can effectively limit the propagation of optical signals in the core silicon waveguide.

[0067] (3) Silicon on Insulator is fully compatible with current CMOS manufacturing technology, which provides great support for the future production of silicon photonic devices.

[0068] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.

[0069] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A microring resonator, characterized in that, At least including: A ring-shaped optical waveguide is located on the substrate; An input optical waveguide is configured to couple light into the ring optical waveguide; The thickness of the annular optical waveguide gradually decreases radially from the inside to the outside. The annular optical waveguide has an inner diameter of r1 and an outer diameter of r2, and its thickness d is located at a distance r from the center of the circle. r satisfy: ； Where r1≤r≤r2, n eff Let be the effective refractive index of the ring waveguide at a distance r from the center, m be the resonant order, and λ be the resonant wavelength. For transmission optical mode, k0 is the light wavenumber, k x Let n be the vertical light wave vector, n1 be the intrinsic refractive index of the ring, and n2 be the refractive index of the medium in the upper and lower edge regions of the micro-ring. denoted as the attenuation constant of the medium in the upper and lower edge regions of the microring.

2. The microring resonator according to claim 1, characterized in that, The ring waveguide material is selected from any one of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

3. The microring resonator according to claim 1, characterized in that, It also includes an output optical waveguide, which is coupled to the ring optical waveguide.

4. The microring resonator according to claim 3, characterized in that, The input optical waveguide and output optical waveguide are any one or more of the following: strip waveguide, ridge waveguide, or multilayer waveguide.

5. The microring resonator according to claim 3, characterized in that, The materials of the input and output optical waveguides are selected from one or more of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

6. The microring resonator according to claim 1, characterized in that, The coupled waveguides are single-mode waveguides and / or multimode waveguides.

7. The microring resonator according to claim 1, characterized in that, The coupling relationship between the ring optical waveguide and the input optical waveguide and the output optical waveguide is either horizontal or vertical.

8. The microring resonator according to claim 1, characterized in that, It is obtained by etching a waveguide material layer.

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