Micro-ring resonator and method for manufacturing the same

Abstract

This invention belongs to the field of integrated optical device technology, specifically relating to a microring resonator and its fabrication method. The device comprises: a substrate; a ring waveguide disposed at the center of the substrate; a U-shaped waveguide disposed on the substrate, wherein the U-shaped waveguide is formed by two straight waveguide segments and a semi-circular arc waveguide connected end-to-end, with the ring waveguide positioned between the two straight waveguide segments to form coupling; and an etched aperture located at the center of the semi-circular arc waveguide; an input waveguide disposed on the substrate and connected to one straight waveguide segment; and an output waveguide disposed on the substrate and connected to another straight waveguide segment. This invention provides controllable loss by introducing an etched aperture in the U-shaped waveguide, achieving coupling interference between discrete and continuous modes to generate asymmetric Fano resonance. By adjusting the waveguide length and the aperture size, high extinction ratio, large slope, or uniform resonance can be achieved at the target wavelength. This device has a simple structure, is easy to manufacture, is compatible with silicon photonics processes, and is suitable for high-performance photonic integrated systems.

Description

Technical Field

[0001] This invention belongs to the field of integrated optical device technology, specifically relating to a microring resonator and its fabrication method. Background Technology

[0002] Microring resonators are widely used in integrated photonic devices such as optical filters, modulators, and sensors due to their compact structure, ease of integration, and high quality factor. Traditional microring resonators typically exhibit symmetrical Lorentz-type resonance lines with finite edge slopes, limiting their performance in applications requiring high sensitivity or high-speed modulation.

[0003] Fano resonances, characterized by their asymmetric and steep resonant line shape, have attracted significant attention in recent years due to their ability to achieve high extinction ratios and high-slope spectral responses. Existing techniques for realizing Fano resonances include combining microrings with Mach-Zehnder interferometers, multi-microring coupling, nested microrings, or integration with photonic crystal structures. However, these methods are structurally complex, large in size, and require sophisticated fabrication processes, hindering large-scale integration. Summary of the Invention

[0004] The purpose of this invention is to provide a microring resonator and its fabrication method. Based on the coupling of the microring resonator with a U-shaped waveguide, controllable loss is provided by introducing etched holes in the U-shaped waveguide to achieve coupling interference between discrete and continuous modes, generating asymmetric Fano resonance. This results in a compact microring resonator with high extinction ratio and high slope spectral response. The device has a simple structure, is easy to manufacture, and can flexibly control the Fano resonance characteristics. It is compatible with silicon photonics processes and is suitable for high-performance photonic integrated systems.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] The first object of the present invention is to provide a microring resonator comprising:

[0007] A substrate on which a ring waveguide, a U-shaped waveguide, an input waveguide, and an output waveguide are disposed.

[0008] A ring waveguide, located at the center of the substrate, has a radius of [missing information]. R mr .

[0009] A U-shaped waveguide is disposed on a substrate, wherein the U-shaped waveguide consists of two straight waveguide segments. L u and semi-circular waveguide R u The two straight waveguides are connected end to end, forming a coupling. The ring waveguide and the U-shaped waveguide are located in the same plane. The semi-circular waveguide has an etched hole at its center to adjust the amplitude attenuation coefficient of the continuous mode. Au The transmission spectrum is tuned by adjusting the length of the U-shaped waveguide and the radius of the etched aperture.

[0010] An input waveguide, which is disposed on the substrate, is connected to a straight waveguide segment for transmitting optical signals.

[0011] An output waveguide, which is disposed on the substrate, is connected to another straight waveguide segment and is used to transmit optical signals.

[0012] In this invention, the microring resonator is constructed using a ring waveguide and a U-shaped waveguide. Two straight waveguide segments within the ring and U-shaped waveguides are coupled together. The ring and U-shaped waveguides are located in the same plane. Controllable loss is provided by introducing etched holes in the U-shaped waveguide, enabling coupling interference between discrete and continuous modes to generate asymmetric Fano resonance. By adjusting the waveguide length and the size of the etched holes, high extinction ratio, large slope, or uniform resonance can be achieved at the target wavelength. This device has a simple structure, is easy to manufacture, is compatible with silicon photonics processes, and is suitable for high-performance photonic integrated systems.

[0013] Furthermore, the length of the straight waveguide segment L u Phase difference between micro-ring resonance and composite resonance Df That's for you to decide.

[0014] Furthermore, the radius of the etched holes is 100nm to 250nm, which is used to control the linearity and depth of the Fano resonance by adjusting the amplitude attenuation coefficient.

[0015] Furthermore, the etched holes are air holes.

[0016] Furthermore, both the ring waveguide and the U-shaped waveguide have a cross-sectional dimension of 500nm × 220nm.

[0017] Furthermore, the substrate is a silicon-on-insulator platform.

[0018] A second objective of this invention is to provide a method for fabricating the aforementioned microring resonator, comprising the following steps:

[0019] S1. Determine the radius of the ring waveguide according to the application scenario. R mr and the radius of the semicircular waveguide in the U-shaped waveguide. R h .

[0020] S2. The relationship between the radius of the etched hole and the reflection and transmission coefficients is simulated using the three-dimensional finite-difference time-domain method to obtain the radius of the etched hole. R h With U-shaped waveguide amplitude attenuation coefficient A uThe relationship between the transmittance and extinction ratio is considered, and the etching aperture radius is selected when the transmittance is <5dB during non-resonance, and significant asymmetry occurs during resonance to achieve an extinction ratio >20dB. R h .

[0021] S3. According to Formula 1, while the wavelength changes, the... Df By analyzing the changes in the values, the distribution of the extinction ratio was observed. Based on the target resonant wavelength and the required extinction ratio, the phase difference was selected. Df ;

[0022] Formula 1 is:

[0023] .

[0024] In the formula, A u This is the amplitude attenuation coefficient of the U-shaped waveguide.

[0025] t For straight waveguides and ring waveguides, denoted as .

[0026] e It is the natural logarithm.

[0027] f mr This represents the phase change after passing through a ring waveguide.

[0028] i It is the imaginary unit.

[0029] A mr This is the amplitude attenuation coefficient after passing through a ring waveguide.

[0030] k denoted as the coupling coefficient between the straight waveguide and the ring waveguide.

[0031] S4. Determine the length of the straight waveguide segment in the U-shaped waveguide. L u This is to enable the optical signal modulated by the microring resonator to achieve a high extinction ratio Fano-type resonance at the desired operating wavelength.

[0032] S5. Verify the spectral response using 3D-FDTD simulation.

[0033] Furthermore, the length of the straight waveguide segment in the U-shaped waveguide L u The calculation formula is:

[0034] .

[0035] In the formula, R mr The radius of the ring waveguide is given.

[0036] R u The radius of the semicircular waveguide is given.

[0037] n It can be any positive integer.

[0038] n eff The effective refractive index of the waveguide.

[0039] l λ is the wavelength.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] The microring resonator provided by this invention has a simple and compact structure: it is coupled only through a microring and a U-shaped waveguide, with losses introduced by etching holes. It eliminates the need for complex interference structures or external electrodes, facilitating integration. By adjusting the etching hole size and waveguide length, high extinction ratios can be achieved, with some reaching -42dB and 533dB / nm high-slope Fano resonances, or uniform Fano resonances with good consistency. Based on standard SOI technology, no additional doping or metal electrodes are required, making it suitable for large-scale manufacturing. It can be used in photonic integrated systems such as high-sensitivity sensors, high-speed optical switches, and dense wavelength division multiplexing filters. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the microring resonator of the present invention.

[0043] Figure 2 This is a schematic diagram of the etched holes on the U-shaped waveguide of the present invention.

[0044] Figure 3 This is a schematic diagram of the transmission principle of the microring resonator of the present invention.

[0045] Figure 4 Different U-shaped waveguide amplitude attenuation coefficients in the microring resonator of this invention A u The diagram showing the effect on the resonance state.

[0046] Figure 5 This diagram illustrates the effect of the radius of the etched hole on the reflection coefficient and transmission coefficient in the microring resonator of this invention.

[0047] Figure 6 Different microring resonators in this invention Df The resulting extinction ratio distribution diagram.

[0048] Figure 7 This is a simulated spectral response diagram of a microring resonator using 3D-FDTD, as presented in this invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] The following specific examples will provide further explanation.

[0051] Example 1

[0052] A microring resonator, such as Figure 1~Figure 3 As shown, it includes:

[0053] Substrate 1, on which a ring waveguide 2, a U-shaped waveguide 3, an input waveguide 5, and an output waveguide 6 are disposed;

[0054] Ring waveguide 2, U-shaped waveguide 3, input waveguide 5, and output waveguide 6 are all grown on substrate 1 and located in the same plane; substrate 1 is a silicon-on-insulator platform. The dielectric material of ring waveguide 2, U-shaped waveguide 3, input waveguide 5, and output waveguide 6 is silicon. Ring waveguide 2 is located at the center of substrate 1, and its radius is... R mr ,radius R mr Determined based on the application scenario.

[0055] A U-shaped waveguide 3 is disposed on a substrate 1. The U-shaped waveguide 3 consists of two straight waveguide segments and a semi-circular arc waveguide 8 connected end to end. A ring waveguide 2 is located between the two straight waveguide segments to form coupling. Figure 3 As shown, the two straight waveguides contain a length of L u The first straight waveguide 7 and containing a length of L u The second straight waveguide 9, the ring waveguide 2, and the U-shaped waveguide 3 are located in the same plane. The center of the semi-circular arc waveguide 8 is provided with an etched hole 4, which is used to adjust the amplitude attenuation coefficient of the continuous mode. The transmission spectrum is tuned by adjusting the length of the U-shaped waveguide 3 and the radius of the etched hole 4. The input waveguide 5 is set on the substrate 1 and is connected to a straight waveguide for transmitting optical signals. The output waveguide 6 is set on the substrate and is connected to another straight waveguide segment for transmitting optical signals.

[0056] like Figure 1As shown, the input waveguide 5 extends to the right parallel to the x-axis, and its right end is connected to the first straight waveguide 7; the right ends of the first straight waveguide 7 and the second straight waveguide 9 are connected to the semi-circular waveguide 8; the output waveguide 6 extends to the left parallel to the x-axis, and its right end is connected to the second straight waveguide 9; the etched hole 4 is located at the center of the semi-circular waveguide 8; the ring waveguide 2 is located between the two straight waveguides formed by the input waveguide 5, the first straight waveguide 7, the output waveguide 6, and the second straight waveguide 9, and is equidistant from the two straight waveguides, with the x-coordinate of the center position being the same as the connection position of the input waveguide 5 and the first straight waveguide 7.

[0057] like Figure 2 and Figure 3 As shown, the radius of etched hole 4 is R h The lengths of the first straight waveguide 7 and the second straight waveguide 9 are L u The optical signal enters the micro-ring resonator through the input waveguide 5 and is transmitted to the coupling region at the junction of the input waveguide 5 and the first straight waveguide 7. Part of the light enters the ring waveguide 2 to form a micro-ring resonance, while part of the light enters the U-shaped waveguide 3 and is attenuated after passing through the etched aperture 4. The two parts of the light interfere with each other at the coupling region at the junction of the second straight waveguide 9 and the output waveguide 6. Finally, the modulated optical signal is output through the output waveguide 6, forming three transmission regions and two coupling regions.

[0058] The method for fabricating a microring resonator includes the following steps:

[0059] S1. Determine the radius of the ring waveguide according to the application scenario. R mr The radius of the semicircular waveguide in a U-shaped waveguide R h .

[0060] S2. The relationship between the radius of the etched aperture and the reflection and transmission coefficients is simulated using the three-dimensional finite-difference time-domain method. The intensity change of light after passing through the etched aperture is simulated as a function of the aperture radius. R h The changing curve is used to obtain the radius of the etched hole. R h With U-shaped waveguide amplitude attenuation coefficient A u The relationship between the two factors, and the selection of the etching aperture radius, is based on the condition that the non-resonant state has a high transmittance (<5dB), while the resonance exhibits significant asymmetry to achieve a high extinction ratio (>20dB). R h .

[0061] S3. According to Formula 1, while the wavelength changes, the... Df By analyzing the changes in the values, the distribution of the extinction ratio was observed. Based on the target resonant wavelength and the required extinction ratio, the phase difference was selected. Df .

[0062] Formula 1 is:

[0063] .

[0064] In the formula, A u This is the amplitude attenuation coefficient of the U-shaped waveguide.

[0065] t For straight waveguides and ring waveguides, denoted as .

[0066] e It is the natural logarithm.

[0067] f mr This represents the phase change after passing through a ring waveguide.

[0068] i It is the imaginary unit.

[0069] A mr This is the amplitude attenuation coefficient after passing through a ring waveguide.

[0070] k denoted as the coupling coefficient between the straight waveguide and the ring waveguide.

[0071] S4. Determine the length of the straight waveguide segment in the U-shaped waveguide. L u This allows the optical signal modulated by the device to achieve a high extinction ratio Fano-type resonance at the desired operating wavelength.

[0072] The advantages of the compact microring resonator of this invention are illustrated below through specific examples. The relevant material parameters for this example are as follows: the ring waveguide, output waveguide, input waveguide, and U-shaped waveguide dielectric strip are made of Si, with a width of 500 nm and a height of 220 nm; refractive index... n Si =3.476; the substrate is SiO2, and the refractive index is... n SiO2 =1.444; operating wavelength is l =1.55μm, channel spacing is 8nm; etched holes are air holes.

[0073] Firstly, the radius of the ring waveguide can be determined by the properties of the microring resonator. R mr =10μm; the coupling distance between the straight waveguide and the MRR is 0.1μm, at which point the coupling coefficient is... k Approximately 0.13. U-shaped waveguide radius. R h=10.6μm. The relationship between the radius of the etched hole and the reflection and transmission coefficients was simulated using the three-dimensional finite-difference time-domain method (3D-FDTD). Figure 5 This diagram illustrates the effect of the etched aperture radius on the reflection and transmission coefficients of this invention. The aperture radius is determined based on this. Figure 5 As shown, for the TE mode with a wavelength of 1550 nm, when the etched aperture radius increases from 0 to 250 nm, the transmittance coefficient... t h The amplitude attenuation coefficient decreases from 1 to 0.46. Since the waveguide's transmission loss is very low, it is negligible compared to the attenuation caused by the etched vias. Therefore, the amplitude attenuation coefficient of the entire U-waveguide is... A u It can be approximately equal to the transmission coefficient of the etched hole. t h . Figure 4 Different U-shaped waveguide amplitude attenuation coefficients of this invention A u The diagram showing the effect on the resonance state. When... A u When =1 or 0, the resonance is of the Lorentz type; when 0 < =1, the resonance is of the Lorentz type. A u When the value is less than 1, the resonance is of the Fano type. This is used to determine the amplitude attenuation coefficient. From... Figure 4 It can be seen that, in order to achieve a significant asymmetry in the resonance and thus a higher extinction ratio, the amplitude attenuation coefficient... A u The value of cannot be too close to 1, and at the same time, in order to have high transmittance during non-resonance, A u The value should not be too close to 0. To simultaneously satisfy the requirements of simple process and high performance, the etched hole radius is set to 180 nm, at which point the amplitude attenuation coefficient... A u The value is approximately 0.63.

[0074] Assume the phase change of light during one revolution in a ring waveguide is as follows: f mr Phase changes in a U-shaped waveguide f u Having phase difference Df ,So The output optical signal can then be expressed as . Figure 6 This invention demonstrates how the wavelength changes while simultaneously affecting... Df The distribution of extinction ratios was observed by analyzing the changes in the values. On the wavelength axis, the resonance still follows the previously derived distribution; however, its extinction ratio will vary depending on the phase difference. DfThe changes in wavelength result in a patchy distribution in the graph because the resonant wavelength range is very small. Each peak represents a resonant wavelength and phase difference. Df The combination of these values ​​represents the maximum depth at which resonance occurs at that wavelength. (Selection) Figure 6 Point P as the phase difference Df Combined with wavelength, the phase difference at this time Df =5.82rad, resonant wavelength is 1557.7nm, selected as the working wavelength, its maximum extinction ratio was observed to be -40.8dB, and the number of wavelengths was taken. n= 13. According to the formula:

[0075] .

[0076] The length of the straight waveguide was calculated. L u =10.347μm. Thus, the design of this embodiment of a compact microring resonator based on SOI with high extinction ratio and high slope spectral response is complete.

[0077] Figure 7 This is a simulated spectral response diagram of a microring resonator using 3D-FDTD, as described in this invention. Figure 7 As shown, its spectral response is compared with that obtained through theoretical calculation. Figure 7 The dashed line represents the theoretical result, and the solid line represents the experimental result. In the experimental results, the Fano resonance occurring at a wavelength of 1557.7 nm yielded an extinction ratio of approximately -42.1 dB and an average slope of 533 dB / nm for the falling edge, which is basically the same as the theoretically calculated result of -40.8 dB.

[0078] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0079] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A microring resonator, characterized in that, include: Substrate; A ring waveguide is disposed at the center of the substrate; A U-shaped waveguide is disposed on a substrate. The U-shaped waveguide consists of two straight waveguides and a semi-circular arc waveguide connected end to end. A ring waveguide is located between the two straight waveguides to form a coupling. The ring waveguide and the U-shaped waveguide are located in the same plane. An etched hole is provided at the center of the semi-circular arc waveguide to adjust the amplitude attenuation coefficient of the continuous mode. The transmission spectrum is tuned by adjusting the length of the U-shaped waveguide and the radius of the etched hole. The radius of the etched holes is 100nm to 250nm, which is used to control the linearity and depth of the Fano resonance by adjusting the amplitude attenuation coefficient; An input waveguide, which is disposed on the substrate, is connected to a straight waveguide segment for transmitting optical signals; An output waveguide, which is disposed on the substrate, is connected to another straight waveguide segment for transmitting optical signals. Among them, the radius of the ring waveguide is determined according to the application scenario. R mr and the radius of the semicircular waveguide in the U-shaped waveguide. R h The relationship between the radius of the etched hole and the reflection and transmission coefficients was simulated using the three-dimensional finite-difference time-domain method to obtain the radius of the etched hole. R h With U-shaped waveguide amplitude attenuation coefficient A u The relationship between the transmittance and extinction ratio is considered, and the etching aperture radius is selected when the transmittance is <5dB during non-resonance, and significant asymmetry occurs during resonance to achieve an extinction ratio >20dB. R h ; Determine the length of the straight waveguide segment in a U-shaped waveguide L u This is to enable the optical signal modulated by the microring resonator to achieve a high extinction ratio Fano-type resonance at the desired operating wavelength.

2. The microring resonator according to claim 1, characterized in that, The length of the straight waveguide segment is determined by the phase difference between the micro-ring resonance and the composite resonance.

3. The microring resonator according to claim 1, characterized in that, The etched holes are air holes.

4. The microring resonator according to claim 1, characterized in that, Both the ring waveguide and the U-shaped waveguide have a cross-sectional dimension of 500nm × 220nm.

5. The microring resonator according to claim 1, characterized in that, The substrate is a silicon-on-insulator platform.

6. A method for fabricating a microring resonator according to any one of claims 1 to 5, characterized in that, Includes the following steps: Determine the radius of the ring waveguide based on the application scenario. R mr and the radius of the semicircular waveguide in the U-shaped waveguide. R h ; The relationship between the radius of the etched hole and the reflection and transmission coefficients was simulated using the three-dimensional finite-difference time-domain method, and the radius of the etched hole was obtained. R h With U-shaped waveguide amplitude attenuation coefficient A u The relationship between the transmittance and extinction ratio is considered, and the etching aperture radius is selected when the transmittance is <5dB during non-resonance, and significant asymmetry occurs during resonance to achieve an extinction ratio >20dB. R h ; According to Formula 1, while the wavelength changes, the... Δφ By analyzing the changes in the values, the distribution of the extinction ratio was observed. Based on the target resonant wavelength and the required extinction ratio, the phase difference was selected. Δφ ; Formula 1 is: ； In the formula, A u The amplitude attenuation coefficient of the U-shaped waveguide; t For straight waveguides and loop waveguides, represents the transmission coefficients. e It is the natural logarithm; φ mr This represents the phase change after passing through a loop waveguide; i The imaginary unit; A mr This is the amplitude attenuation coefficient after passing through a ring waveguide; k The coupling coefficient between the straight waveguide and the ring waveguide; Determine the length of the straight waveguide segment in a U-shaped waveguide L u This is to enable the optical signal modulated by the microring resonator to achieve a high extinction ratio Fano-type resonance at the desired operating wavelength.

7. The method for fabricating a microring resonator according to claim 6, characterized in that, U-shaped waveguide straight waveguide section length L u The calculation formula is: ； In the formula, R mr The radius of the ring waveguide; u The radius of the semi-circular waveguide; n It can be any positive integer; n eff The effective refractive index of the waveguide; λ λ is the wavelength.

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