Micro-ring resonator and preparation method thereof

Abstract

The invention belongs to the technical field of integrated optical devices, and particularly relates to a micro-ring resonator and a preparation method thereof. A substrate; the annular waveguide is arranged at the center of the substrate; the U-shaped waveguide is arranged on the substrate, the U-shaped waveguide is formed by connecting two sections of straight waveguides and a semi-arc waveguide end to end, the annular waveguide is located between the two sections of straight waveguides to form coupling, and an etching hole is formed in the center of the semi-arc waveguide; the input waveguide is arranged on the substrate, and the input waveguide is connected with one straight waveguide section; and the output waveguide is arranged on the substrate, and the output waveguide is connected with the other straight waveguide section. According to the invention, the etching holes are introduced into the U-shaped waveguide to provide controllable loss, so that the coupling interference between a discrete state mode and a continuous state mode is realized, and asymmetric Fano resonance is generated. By adjusting the length of the waveguide and the size of the etching hole, high extinction ratio, large slope or uniform resonance can be realized under the target wavelength. The device is simple in structure, easy to manufacture, compatible with a silicon optical process and suitable for a high-performance photon integration system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of integrated optics, and particularly relates to a micro-ring resonator and a preparation method thereof. BACKGROUND

[0002] Micro-ring resonators are widely used in integrated photonic devices such as optical filters, modulators, sensors, etc. due to their compact structure, easy integration, high quality factor, etc. The traditional micro-ring resonator usually presents a symmetrical Lorentz-type resonance spectrum line, and its edge slope is limited, which restricts its performance in applications requiring high sensitivity or high-speed modulation.

[0003] Fano resonance has a non-symmetrical and steep resonance line type, and can realize high extinction ratio and high slope spectral response, and has attracted widespread attention in recent years. The existing technology for realizing Fano resonance includes micro-ring and Mach-Zehnder interferometer combination, multi-micro-ring coupling, nested micro-ring, or integration with photonic crystal structure, etc. However, these schemes have complex structure, large size, high process requirement, and are not conducive to large-scale integration. SUMMARY

[0004] The purpose of the present application is to provide a micro-ring resonator and a preparation method thereof, which is based on the coupling of a micro-ring resonator and a U-shaped waveguide, introduces an etching hole in the U-shaped waveguide to provide controllable loss, realizes the coupling interference of discrete state and continuous state modes, produces asymmetric Fano resonance, and has a compact micro-ring resonator with high extinction ratio and high slope spectral response. The device structure is simple, easy to manufacture, and can flexibly regulate the Fano resonance characteristics, is compatible with silicon optical process, and is suitable for high-performance photonic integrated systems.

[0005] The present application solves the above technical problems through the following technical solutions.

[0006] The first purpose of the present application is to provide a micro-ring resonator, which comprises: a substrate having a ring-shaped waveguide, a U-shaped waveguide, an input waveguide and an output waveguide arranged thereon.

[0007] a ring-shaped waveguide arranged at the center of the substrate, with a radius of R mr .

[0008] a U-shaped waveguide arranged on the substrate, the U-shaped waveguide being connected by two straight waveguides L u and a semicircular waveguide R u arranged in series, the ring-shaped waveguide being located between the two straight waveguides to form a coupling, the ring-shaped waveguide and the U-shaped waveguide being located in the same plane, and the center of the semicircular waveguide being provided with an etching hole for regulating the amplitude attenuation coefficient of the continuous state mode A uThe tuning of the transmission spectrum is realized by adjusting the length of the U-shaped waveguide and the radius of the etching hole.

[0009] An input waveguide is arranged on the substrate, and the input waveguide is connected with one straight waveguide section and is used for transmitting an incoming optical signal.

[0010] An output waveguide is arranged on the substrate, and the output waveguide is connected with another straight waveguide section and is used for transmitting an outgoing optical signal.

[0011] In the application, the micro-ring resonator is composed of a ring waveguide and a U-shaped waveguide, wherein the ring waveguide and the U-shaped waveguide are coupled between two straight waveguide sections, the ring waveguide and the U-shaped waveguide are located in the same plane, controllable loss is provided by introducing an etching hole in the U-shaped waveguide, coupling interference between discrete states and continuous states is realized, and asymmetric Fano resonance is generated. By adjusting the waveguide length and the etching hole size, high extinction ratio, large slope or uniform resonance at the target wavelength can be realized. The device has simple structure, is easy to manufacture, is compatible with silicon optical technology, and is suitable for high-performance photonic integrated systems.

[0012] Further, the length of the straight waveguide section is 10-20 microns. L u The phase difference between the micro-ring resonance and the compound resonance determines the resonance depth. Δφ

[0013] Further, the radius of the etching hole is 100-250 nm, which is used for controlling the line type and depth of the Fano resonance by adjusting the amplitude attenuation coefficient.

[0014] Further, the etching hole is an air hole.

[0015] Further, the cross-sectional size of the ring waveguide and the U-shaped waveguide is 500 nm*220 nm.

[0016] Further, the substrate is a silicon-on-insulator platform.

[0017] The second object of the application is to provide a preparation method of the micro-ring resonator, comprising the following steps: S1, determining the radius of the ring waveguide and the radius of the semicircular waveguide in the U-shaped waveguide according to the application scene R mr . R h

[0018] S2, simulating the relationship between the radius of the etching hole and the reflection coefficient and the transmission coefficient by using the three-dimensional finite difference time domain method, and obtaining the radius of the etching hole R h and the amplitude attenuation coefficient of the U-shaped waveguide A u ​​The relationship between the radius of the etched hole and the transmission rate when the resonance is not met is determined, and the transmission rate is less than 5dB, the resonance is obviously asymmetric to achieve the extinction ratio greater than 20dB, and the radius of the etched hole is selected R h .

[0019] S3, according to formula 1, the wavelength is changed while Δφ The value change is analyzed, the distribution of the extinction ratio is observed, the target resonance wavelength and the extinction ratio requirement are combined, and the phase difference Δφ ; Formula 1 is: .

[0020] In the formula, A u The amplitude attenuation coefficient of the U-shaped waveguide.

[0021] t The transmission coefficient of the straight waveguide and the ring waveguide.

[0022] e The natural logarithm.

[0023] φ mr The phase change after one circle of the ring waveguide.

[0024] i The imaginary unit.

[0025] A mr The amplitude attenuation coefficient after one circle of the ring waveguide.

[0026] k The coupling coefficient of the straight waveguide and the ring waveguide.

[0027] S4, the length of the straight waveguide section of the U-shaped waveguide is determined L u So that the light signal modulated by the micro-ring resonator has a high extinction ratio Fano resonance at the required operating wavelength.

[0028] S5, the spectrum response is verified by 3D-FDTD simulation.

[0029] Further, the length of the straight waveguide section of the U-shaped waveguide is L u The calculation formula is: .

[0030] In the formula, R mr The radius of the ring waveguide.

[0031] Ru R is a radius of the semi-circular waveguide.

[0032] n n is any positive integer.

[0033] n eff n is an effective refractive index of the waveguide.

[0034] λ n is a wavelength.

[0035] Compared with the prior art, the present application has the following beneficial effects: The micro-ring resonator provided by the present application has a simple and compact structure: only the micro-ring is coupled with the U-shaped waveguide, and the loss is introduced by combining the etching hole, without complex interference structure or external electrode, and is convenient for integration. By adjusting the size of the etching hole and the length of the waveguide, high extinction ratio can be realized, and the highest extinction ratio is up to -42dB, 533dB / nm large slope Fano resonance, or uniform Fano resonance with good consistency. Based on the standard SOI process, without additional doping or metal electrode, it is suitable for large-scale manufacturing. It can be used for high-sensitivity sensors, high-speed optical switches, dense wavelength division multiplexing filters and other photonic integrated systems. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Fig. 1 is a structural schematic diagram of the micro-ring resonator of the present application.

[0037] Figure 2 Fig. 4 is a schematic diagram of the etching hole on the U-shaped waveguide of the present application.

[0038] Figure 3 Fig. 6 is a transmission principle model diagram of the micro-ring resonator of the present application.

[0039] Figure 4 Fig. 9 is a diagram of the influence of different U-shaped waveguide amplitude attenuation coefficients in the micro-ring resonator of the present application on the resonance state. A u Fig. 10 is a diagram of the influence of the resonance state.

[0040] Figure 5 Fig. 12 is a diagram of the influence of the radius of the etching hole in the micro-ring resonator of the present application on the reflection coefficient and the transmission coefficient.

[0041] Figure 6 Fig. 14 is a diagram of the extinction ratio distribution caused by different Δφ Fig. 15 is a diagram of the influence of the length of the etching hole in the micro-ring resonator of the present application on the resonance state.

[0042] Figure 7 Fig. 18 is a simulated spectrum response diagram of the micro-ring resonator of the present application by using 3D-FDTD. DETAILED DESCRIPTION

[0043] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0044] The following is further illustrated by specific embodiments.

[0045] Embodiment 1 A microring resonator, as shown in Figures 1 to 3 , comprises: a substrate 1, on which a ring waveguide 2, a U-shaped waveguide 3, an input waveguide 5 and an output waveguide 6 are arranged; The ring waveguide 2, the U-shaped waveguide 3, the input waveguide 5 and the output waveguide 6 are all grown on the substrate 1 and located in the same plane; the substrate 1 is a silicon-on-insulator platform. The material medium of the ring waveguide 2, the U-shaped waveguide 3, the input waveguide 5 and the output waveguide 6 is silicon. The ring waveguide 2 is arranged at the center of the substrate 1, and the radius thereof is R mr , the radius R mr is determined according to the application scenario.

[0046] The U-shaped waveguide 3 is arranged on the substrate 1, and the U-shaped waveguide 3 is connected in a head-to-tail manner by two straight waveguides and a semicircular waveguide 8, and the ring waveguide 2 is located between the two straight waveguides to form a coupling, as shown in Figure 3 The two straight waveguides are a first straight waveguide 7 with a length of L u and a second straight waveguide 9 with a length of L u The ring waveguide 2 and the U-shaped waveguide 3 are located in the same plane, and the center of the semicircular waveguide 8 is provided with an etching hole 4 for adjusting 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 etching hole 4; the input waveguide 5 is arranged on the substrate 1, and the input waveguide 5 is connected with one straight waveguide for transmitting an optical signal; the output waveguide 6 is arranged on the substrate, and the output waveguide 6 is connected with another straight waveguide section for transmitting an optical signal.

[0047] As shown in Figure 1As shown, the input waveguide 5 extends rightward in parallel to the x-axis, and the right end is connected to the first straight waveguide 7; the first straight waveguide 7 and the right end of the second straight waveguide 9 are connected to the semicircular waveguide 8; the output waveguide 6 extends leftward in parallel to the x-axis, and the right end is connected to the second straight waveguide 9; the etching hole 4 is located at the center of the semicircular waveguide 8; the ring waveguide 2 is located in the middle of the two straight waveguides composed of the input waveguide 5, the first straight waveguide 7, the output waveguide 6 and the second straight waveguide 9, and the distance from the ring waveguide 2 to the two straight waveguides is equal, and the horizontal coordinate of the center of the ring waveguide 2 is the same as the connection position of the input waveguide 5 and the first straight waveguide 7.

[0048] As shown in Figure 2 and Figure 3 , the radius of the etching hole 4 is R h , and the length of the first straight waveguide 7 and the second straight waveguide 9 is L u The optical signal enters the micro-ring resonator from the input waveguide 5 and is transmitted to the coupling area at the joint of the input waveguide 5 and the first straight waveguide 7, a part of the light enters the ring waveguide 2 to form a micro-ring resonance, and a part of the light enters the U-shaped waveguide 3 and attenuates after passing through the etching hole 4. The two parts of light interfere at the coupling area at the joint of the second straight waveguide 9 and the output waveguide 6, and the modulated optical signal is finally output by the output waveguide 6, forming three transmission regions and two coupling regions.

[0049] The preparation method of the micro-ring resonator comprises the following steps: S1, determining the radius of the ring waveguide according to the application scenario R mr ; the radius of the semicircular waveguide in the U-shaped waveguide R h .

[0050] S2, simulating the relationship between the radius of the etching hole and the reflection coefficient and the transmission coefficient by using the three-dimensional finite difference time domain method, obtaining the curve of the intensity change of the light after passing through the etching hole with the change of the radius of the etching hole R h , and obtaining the relationship between the radius of the etching hole R h and the amplitude attenuation coefficient of the U-shaped waveguide A u , and selecting the radius of the etching hole under the condition that the non-resonance has a higher transmittance <5dB and the resonance has an obvious asymmetry to achieve a higher extinction ratio >20dB. R h .

[0051] S3, according to formula 1, analyzing the value change of Δφ while the wavelength changes, observing the distribution of the extinction ratio, and selecting the phase difference Δφ combined with the target resonant wavelength and the extinction ratio requirement.

[0052] Equation 1 is: .

[0053] wherein, A u is the amplitude attenuation coefficient of the U-shaped waveguide.

[0054] t is the transmission coefficient of the straight waveguide and the ring waveguide.

[0055] e is the natural logarithm.

[0056] φ mr is the phase change after one round of the ring waveguide.

[0057] i is the imaginary unit.

[0058] A mr is the amplitude attenuation coefficient after one round of the ring waveguide.

[0059] k is the coupling coefficient of the straight waveguide and the ring waveguide.

[0060] S4, determining the length of the straight waveguide section of the U-shaped waveguide L u so that the light signal modulated by the device occurs Fano-type resonance with high extinction ratio at the required operating wavelength.

[0061] The advantages of the compact micro-ring resonator of the present application are described below by specific means. The material parameters of the present example are as follows: the ring waveguide, the output waveguide, the input waveguide and the U-shaped waveguide are Si, the medium strip is 500 nm wide and 220 nm high; the refractive index n Si = 3.476; the substrate is SiO2, the refractive index n SiO2 = 1.444; the operating wavelength is λ = 1.55 μm, the channel spacing is 8 nm; the etched hole is an air hole.

[0062] First, the radius of the ring waveguide R mr = 10 μm can be determined by the properties of the micro-ring resonator; the coupling distance between the straight waveguide and the MRR is 0.1 μm, so the coupling coefficient k is about 0.13. The radius of the U-shaped waveguide 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.

[0063] Assume the phase change of light during one revolution in a ring waveguide is as follows: φ mr Phase changes in a U-shaped waveguide φ u Having phase difference Δφ ,So The output optical signal can then be expressed as . Figure 6 This invention demonstrates how the wavelength changes while simultaneously affecting... Δφ 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. ΔφThe 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. Δφ 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 Δφ Combined with wavelength, the phase difference at this time Δφ =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:

[0064] .

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 micro-ring resonator, characterized by, 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. 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 and is used to transmit optical signals.

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

3. The micro-ring resonator of claim 1, wherein, The etched holes have a radius of 100nm to 250nm and are used to control the linearity and depth of the Fano resonance by adjusting the amplitude attenuation coefficient.

4. The micro-ring resonator of claim 1, wherein, The etched holes are air holes.

5. The micro-ring resonator of claim 1, wherein, Both the ring waveguide and the U-shaped waveguide have a cross-sectional dimension of 500nm × 220nm.

6. The micro-ring resonator of claim 1, wherein, The substrate is a silicon-on-insulator platform.

7. A method of fabricating a microring resonator as claimed in any one of claims 1 to 6, characterized in that, Includes the following steps: Determining annular waveguide radius according to application scenario R mr And radius of semi-circular waveguide in U-shaped waveguide R h ; The relationship between the radius of the etching hole and the reflection coefficient and the transmission coefficient is simulated by using a three-dimensional time domain finite difference method to obtain the radius of the etching hole R h The relationship between the radius of the etching hole and the amplitude attenuation coefficient of the U-shaped waveguide A u The radius of the etching hole is selected under the condition that the transmission is less than 5dB when non-resonance is met and the extinction ratio is greater than 20dB when obvious asymmetry of resonance appears R h ​ According to formula 1, the phase difference Δφ The value change is analyzed, the distribution of the extinction ratio is observed, and the phase difference Δφ ; Formula 1 is: ； wherein A u is the amplitude attenuation coefficient of the U-shaped waveguide; t is the transmission coefficient of the straight waveguide and the ring waveguide; e is the natural logarithm; φ mr is the phase change after one round of the ring waveguide; i is the imaginary unit; A mr is the amplitude attenuation coefficient of the ring waveguide after one round; k is the coupling coefficient of 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.

8. The method for fabricating a microring resonator according to claim 7, 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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