Micro-ring resonator

Abstract

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

Description

Technical Field

[0001] The invention relates to the field of communication technology, and in particular to a microring resonator. Background Art

[0002] As a highly integrated and highly sensitive optical device, microring resonators have broad application prospects and can be used in optical communications, biosensing, quantum information processing and other fields. The microring resonator includes an optical waveguide with a microring structure, that is, a section of optical waveguide forms a ring structure. When the optical signal propagates in the ring waveguide, multiple reflections and interferences will occur, thus forming a resonance phenomenon. The microring is a waveguide ring that is usually circular, but in principle can be of any geometric shape. The microring is optically coupled to one or two transmission waveguides. In the case where the microring is coupled to a single waveguide, it provides the ability to remove a set of wavelengths from the transmission waveguide, thereby acting as a notch filter. In the case where the microring is coupled to two transmission waveguides, the transmission waveguide couples light to or from the microring.

[0003] In a single microring resonator, for a given radius R, there is a series of wavelengths that meet the resonance conditions (corresponding to different resonance orders). Among these resonant wavelengths, the wavelength difference between two adjacent resonant wavelengths is called the free spectral range (FSR). In a wavelength division multiplexing system, in order to download a certain channel without affecting other channels, the free spectral range should be as large as possible. However, FSR is inversely proportional to the radius R. If the FSR is too large, R will be too small, which will cause a large loss in the microring, thereby reducing the quality factor of the microring resonator.

[0004] Controlling the effective refractive index of the microring in radial direction is an effective means to improve the quality factor. For example, a photonic crystal composed of dielectric columns whose radial dimensions gradually decrease from the inside to the outside is distributed inside the microring resonator, so that the effective refractive index of the microring resonator gradually decreases as the radius of the microring increases from small to large. However, in the field of optical device manufacturing, including the manufacture of microring resonators, process stability and production cost are crucial factors. Among them, device structure design is a key link affecting process stability and cost control. The fine control of dielectric columns in existing solutions can easily lead to more defects and variations in the manufacturing process, which not only increases the time and cost of debugging and calibration, but also reduces the yield and increases the scrap rate. In addition, complex or non-optimal designs may require the use of higher-precision manufacturing equipment and techniques, which will undoubtedly increase production costs. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a micro-ring resonator with a simple structure. The resonator has a smoother light path transmission bend and lower loss under the premise of achieving a wide free spectral range; and the device structure is simple and can be obtained through mature photolithography technology, which is suitable for industrial application.

[0006] In order to achieve the above-mentioned purpose, 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 from the inside to the outside. r satisfy: - Among them, r1≤r≤r2, n eff is the effective refractive index of the annular optical waveguide at a distance r from the center of the circle, m is the resonance order, λ is the resonance wavelength, is the transmission light mode, k 0 is the light wave number, k x is the vertical light wave vector, n 1 is the intrinsic refractive index of the ring, n 2 is the refractive index of the medium in the upper and lower regions of the microring, is the attenuation constant of the medium in the upper and lower edge zones of the microring.

[0008] In some embodiments of the present invention, the ring optical waveguide material is selected from any one of silicon on insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0009] In some embodiments of the present invention, an output optical waveguide is further included, coupled to the ring optical waveguide.

[0010] In some embodiments of the present invention, the input optical waveguide and the output optical waveguide are any one or more of a strip waveguide, a ridge waveguide or a multilayer waveguide.

[0011] In some embodiments of the present invention, the materials of the input optical waveguide and the output optical waveguide are selected from any one or more of silicon on insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0012] In certain embodiments of the present invention, the coupled waveguides are single mode waveguides and / or multimode waveguides.

[0013] 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.

[0014] Based on the structural design of the present invention, the microring resonator of the present invention can be directly obtained by etching the waveguide material layer.

[0015] The beneficial technical effects of the present invention are as follows: The free spectral range of the microring resonator provided by the present invention can be more than doubled under the condition of the same bending loss. In addition, due to the excellent structural design and simple process, the production yield can be controlled at more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a top view of a microring resonator provided by an embodiment of the present invention.

[0017] Figure 2 For the present invention Figure 1 A three-dimensional schematic diagram of a ring-shaped optical waveguide in the illustrated embodiment; Figure 3 The present invention Figure 1 The embodiment shown is a cross-sectional view along the AA' direction.

[0018] Figure 4 It is a schematic diagram of the principle of optical signal transmission and modulation by a microring resonator in an embodiment of the present invention.

[0019] Figure 5 is a schematic curve showing the change of refractive index with thickness in the present invention; Figure 6 is an example of thickness reduction provided by an embodiment of the present invention; Figure 7 It is a schematic diagram of the structure of a straight waveguide provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The embodiments disclosed in the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present disclosure.

[0021] In the micro-ring structure, the ratio of thickness to diameter is small. In the figure, although the change in thickness appears linear, there is actually a certain curvature, so that the effective refractive index changes linearly and continuously.

[0022] As is common knowledge in the art, the annular optical waveguide is placed parallel to the substrate, and the thickness described in the present invention refers to the thickness value perpendicular to the substrate.

[0023] The embodiment of the present invention shows a microring resonator, comprising: a ring optical waveguide, located on the substrate; an input optical waveguide 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, so that the effective refractive index of the micro-ring resonant cavity gradually decreases as the radius of the micro-ring increases from small to large.

[0024] Specifically, the inner diameter of the annular waveguide is r1, the outer diameter is r2, and the thickness d at a distance r from the center of the circle is r satisfy: ; ; - ; - ; Among them, r1≤r≤r2, n eff is the effective refractive index of the annular optical waveguide at a distance r from the center of the circle, which decreases linearly with the increase of r. m is the resonance order, λ is the resonance wavelength, a is the transmission light mode, k 0 is the light wave number, k x is the vertical light wave vector, n 1 is the intrinsic refractive index of the ring, n 2 、n 3 is the refractive index of the media above and below the microring, n 2 =n 3 , , are the edge attenuation constants, The effective refractive index can be obtained by combining 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 a linearly continuous change in effective refractive index can be obtained by setting the thickness.

[0025] The thickness of the annular optical waveguide of the microring resonator of the present invention is gradual. That is, the thickness of the annular optical waveguide gradually decreases radially from the inside to the outside. Since the effective refractive index of the waveguide is related to its thickness, the thicker the thickness, the greater the refractive index. The gradual thickness makes the effective refractive index of the annular optical waveguide decrease from small to large along with the radius of the microring. During the transmission of light in the gradient refractive index medium, it will bend from the low refractive index to the high refractive index direction. Since the refractive index in the annular optical waveguide is changing, the light will naturally bend due to the difference in refractive index when it is transmitted in the annular optical waveguide, thereby reducing bending loss. In this way, the radius of the microring can be further reduced without increasing the loss to obtain a larger free spectral range.

[0026] It can be seen that the microring resonator provided by the present invention can have both high quality factor and wide free spectral range, so that the microring resonator has a larger application range and good working performance. The refractive index changes linearly through the gradual thickness. Compared with the existing form of adding dielectric columns, the linearity of the refractive index makes the light path transmission bend smoother and the loss lower; the device designed by thickness is less destructive to the structure, easier to design and manufacture, and has a higher yield rate.

[0027] like Figure 1 As shown in Figures 1 and 2, in a specific example, the microring resonator includes at least two straight waveguides 10 and 30 as coupled waveguides, and at least one annular optical waveguide 20 with a gradually changing thickness that is mutually coupled with the straight waveguides. The straight waveguides 10 and 30 include an incident end, an output end, a loading end, and a downloading end, and are used to transmit optical signals; the annular optical waveguide 20 is used to modulate the intensity of the optical signal of the corresponding wavelength, and its thickness gradually decreases radially from the inside to the outside. Figure 4 Schematic diagram of the principle of transmission and modulation of optical signals by the microring resonator provided in an embodiment of the present invention. An optical signal of a wavelength corresponding to the thickness gradient annular optical waveguide 20 is input from the input end of the straight waveguide 10. After passing through the thickness gradient annular optical waveguide 20, the optical signal of a wavelength corresponding to the thickness gradient annular optical waveguide 20 is in a resonant state during the transmission process in the resonant cavity. The optical signal in the resonant state is coupled with the straight waveguide 30, and after being output through the straight waveguide 30, an optical signal of a desired wavelength can be obtained.

[0028] like Figure 3 As shown, in the illustrated embodiment, the thickness of the annular optical waveguide 20 is not uniform, and its thickness decreases radially from the inside to the outside, and the thickness is the same at the same distance from the center of the annular optical waveguide.

[0029] Since the present invention is based on the gradual change of refractive index of the micro-ring thickness, any structural form that can achieve thickness change is applicable to the present invention. Figure 6 A, B, and C in the figure give three structural forms, A is Figure 3 In the embodiment shown, the bottom surface of the annular optical waveguide is in contact with the substrate, and the top surface is tilted downward, so that the thickness d is gradually reduced. B is a double-sided tilt mode, and both the bottom and top surfaces of the annular optical waveguide are tilted to achieve a gradual reduction in thickness d. The curved surface of C is designed with curves on the bottom and top surfaces, so that the thickness d is gradually reduced.

[0030] It should be noted that, for the sake of simplicity, the above embodiment is described by taking only the simplest two straight waveguides 10, 30 and one annular optical waveguide 20 with a gradually varying thickness as an example. In other embodiments, the annular optical waveguide 20 can be provided in plurality as required.

[0031] In addition, the ring optical waveguide 20 with gradually varying thickness and the straight waveguides 10 and 30 are coupled to each other, and the coupling relationship may be horizontal coupling or vertical coupling, which is not specifically limited here.

[0032] In different embodiments of the present invention, the annular optical waveguide is any one of a strip waveguide, a ridge waveguide or a multilayer waveguide, 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 multi-mode waveguide, which is not specifically limited herein.

[0033] In different embodiments of the present invention, the material constituting the dielectric column includes any one of dielectric materials such as silicon oxide or air, the material of the annular 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, and is not specifically limited here.

[0034] As a preferred embodiment, silicon on insulator can be used to make the straight waveguide and thickness gradient annular optical waveguide shown in the above embodiments. Silicon on insulator uses silicon as the core waveguide layer and silicon dioxide as the cladding. Since the refractive index difference between the two is about 2, light can be confined to the core waveguide layer for transmission. And because silicon on insulator is compatible with the existing CMOS platform process, it is currently the most important silicon photonic platform.

[0035] Based on this, another embodiment of the present invention also shows a method for preparing a microring resonator, which is used to make the above-mentioned refractive index gradient microring resonator based on thickness gradient, and the preparation method includes: The simulation is performed with the goal of minimizing the bending loss to determine the width and radius of the annular optical waveguide; the width of the coupling waveguide and the coupling distance between the coupling waveguide and the annular optical waveguide; the thickness of the microring resonator and its rate of change are calculated based on the above formula; forming a waveguide material layer on a substrate; spin coating a photoresist on the waveguide material layer; Expose the photoresist using grayscale lithography technology and transfer the simulated device pattern to the photoresist; Etching is performed to obtain a ring optical waveguide and a waveguide structure; The dielectric material is used for covering and filling to complete the production of the gradient refractive index microring resonator based on thickness gradient.

[0036] like Figure 7 As shown, in a specific example, the prepared basic micro-ring structure and coupled waveguide include: Substrate 101; The lower cladding layer 102 is located on the surface of the substrate 101; A first waveguide layer 103 is located on a surface of the lower cladding layer 102 away from the substrate 101; The upper cladding layer 104 wraps the first waveguide layer 103 , and a surface away from the first waveguide layer 103 is a plane.

[0037] For example, the substrate 101 may be made of silicon material, the lower cladding layer 102 may be made of silicon dioxide material, the first waveguide layer 103 may be made of silicon material, and the upper cladding layer 104 may be made of silicon dioxide material. Such a structure has the following advantages:

[0038] (1) The silicon core waveguide layer is nearly transparent to the most commonly used 1550nm wavelength optical signal, so very low transmission loss can be achieved.

[0039] (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.

[0040] (3) Silicon on insulator is fully compatible with current CMOS manufacturing technology, providing great support for the future production of silicon photonic devices.

[0041] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present application (including the claims) is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0042] The embodiments of the present 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 the present application should be included in the scope of protection of the present application.

Claims

1. A microring resonator, characterized in that: At least: a ring optical waveguide, located on the substrate; an input optical waveguide configured to couple light into the ring optical waveguide; The thickness of the annular waveguide gradually decreases radially from the inside to the outside.

2. The microring resonator according to claim 1, characterized in that: The inner diameter of the annular waveguide is r1, the outer diameter is r2, and the thickness d at a distance r from the center of the circle is r satisfy: ； - ； ； Among them, r1≤r≤r2, n eff is the effective refractive index of the annular optical waveguide at a distance r from the center of the circle, m is the resonance order, λ is the resonance wavelength, is the transmission light mode, k0 is the light wave number, k x is the vertical light wave vector, n1 is the intrinsic refractive index of the ring, n2 is the refractive index of the medium in the upper and lower edge regions of the micro-ring, is the attenuation constant of the medium in the upper and lower edge zones of the microring.

3. The microring resonator according to claim 1, characterized in that: The material of the annular optical waveguide is selected from any one of silicon on insulator, lithium niobate, silicon nitride, indium phosphide and gallium arsenide.

4. The microring resonator according to claim 1, characterized in that: The invention also comprises an output optical waveguide coupled with the ring optical waveguide.

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

6. The microring resonator according to claim 4, characterized in that: The materials of the input optical waveguide and the output optical waveguide are selected from any one or more of silicon on insulator, lithium niobate, silicon nitride, indium phosphide and gallium arsenide.

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

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

9. The microring resonator according to claim 1, characterized in that: Obtained by etching the waveguide material layer.

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