A kind of micro-ring resonator with gradually changing cross-sectional width of micro-ring resonator

Abstract

The application belongs to the field of optical communication, optical interconnection and optical sensing, and particularly relates to a micro-ring resonator with gradually changed cross-section width of micro-ring resonant cavity, which comprises a micro-ring resonant cavity and a coupling waveguide; the cross-section width of the micro-ring resonant cavity satisfies: uniformly widening along the counterclockwise direction of the micro-ring from the center of the coupling area, reaching the maximum at the symmetrical position of the center of the coupling area relative to the center of the micro-ring, and uniformly narrowing along the counterclockwise direction of the micro-ring from the maximum, so as to limit the fundamental mode light field in the waveguide as much as possible, reduce the interaction between the light field and the side wall, and reduce the scattering loss caused by the roughness of the side wall, wherein the gradual change rates of the uniform widening and the uniform narrowing are the same and satisfy: the half angle of the width gradually changed waveguide is not greater than the mode diffusion half angle, so as to avoid the excitation of high-order modes of the input light in the micro-ring and realize the adiabatic transmission of the fundamental mode. Therefore, the scheme can reduce the transmission loss of the micro-ring resonant cavity and effectively improve the Q value of the micro-ring resonator.

Description

Technical Field

[0001] This invention belongs to the fields of optical communication, optical interconnection and optical sensing, and more specifically, relates to a microring resonator with a gradually varying cross-sectional width of a microring resonator. Background Technology

[0002] Microring resonators, consisting of a ring waveguide and adjacent coupled waveguides, are widely used in filtering, sensing, and modulation. The Q-factor, representing the ratio of stored energy to dissipated energy per unit time, is a key indicator of resonant cavity performance. High-Q microring resonators are crucial components in the fabrication of filters, ring oscillators, optical buffers, and sensors. Factors affecting the Q-factor of microring resonators include: the coupling efficiency between the microring resonator and the input / output waveguides; scattering loss due to roughness of the waveguide sidewalls in the coupling region; mode mismatch loss in the coupling region; absorption loss and bending loss of the ring waveguide; and scattering loss due to sidewall roughness. Among these, due to inherent limitations in exposure and etching processes, it is difficult to fabricate ideally smooth and flat sidewalls; therefore, scattering loss caused by the rough sidewalls of the microring and the coupled waveguide is a key factor limiting the Q-factor.

[0003] Currently, besides improving the fabrication process to reduce sidewall roughness, another effective method is to increase the waveguide width to confine the optical field within the waveguide as much as possible, reducing the interaction between the optical field and the sidewalls and improving the intrinsic Q value of the microring. However, widening the single-mode waveguide will enable multimode transmission, and the input light will excite higher-order modes within the coupled waveguide and microring, increasing the transmission loss within the microring resonant cavity and thus reducing the Q value of the microring. Summary of the Invention

[0004] To address the shortcomings of existing technologies and the need for improvement, this invention provides a microring resonator with a gradually varying cross-sectional width of the microring resonator, aiming to reduce the transmission loss of the microring resonator and thereby improve the Q value of the microring resonator.

[0005] To achieve the above objectives, according to one aspect of the present invention, a microring resonator with a gradually varying cross-sectional width of the microring resonator is provided, comprising: a microring resonator and a coupling waveguide;

[0006] The cross-sectional width of the microring resonator satisfies the following: it widens uniformly from the center of the coupling region along the counterclockwise direction of the microring, reaches its maximum at a position symmetrical to the center of the coupling region relative to the center of the microring, and then narrows uniformly from this maximum point along the counterclockwise direction of the microring. The rate of uniform widening and uniform narrowing is the same, and both satisfy the following: the half-angle of the width-gradient waveguide is not greater than the mode diffusion half-angle, so that the microring resonator can thermally transition between the single-mode waveguide and the multimode waveguide.

[0007] Furthermore, the outer wall radius R0 of the micro-ring resonant cavity is fixed, and the inner wall radius is: Rin =R0-K·α-W min ;

[0008] in, The linear rate of change of the cross-sectional width of the microring resonator is represented by α, where α represents the angle between the radius at the coupling point and the radius at the current position, and W represents the linear rate of change of the cross-sectional width of the microring resonator. min and W max These represent the minimum and maximum cross-sectional widths of the microring resonator, respectively.

[0009] Furthermore, the coupling waveguide includes an input straight waveguide and an output straight waveguide connected together. The micro-ring resonator and the coupling waveguide form a point coupling at the connection between the input straight waveguide and the output straight waveguide, and both the input straight waveguide and the output straight waveguide are single-mode waveguides.

[0010] Furthermore, the coupling waveguide includes an input straight waveguide, a curved waveguide, and an output straight waveguide connected in sequence. The micro-ring resonator and the coupling waveguide form a weak tapered gap coupling at the curved waveguide, and the input straight waveguide, the curved waveguide, and the output straight waveguide are all single-mode waveguides.

[0011] Furthermore, the curved waveguide includes a first curved waveguide, a third curved waveguide, and a second curved waveguide that are sequentially connected and symmetrically distributed relative to the center of the coupling region. The micro-ring resonator and the coupling waveguide form a weak conical gap coupling at the third curved waveguide.

[0012] Furthermore, the gradual rate is obtained through simulation with the goal of minimizing the bending radius and bending loss of the microring resonator.

[0013] Furthermore, both the microring resonator and the coupling waveguide are independently selected from any one of strip waveguides, ridge waveguides, and multilayer waveguides;

[0014] The materials of the microring resonator and the coupling waveguide are independently selected from any one of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0015] Furthermore, it also includes a heating element for heating the microring resonant cavity and changing the refractive index of the microring resonant cavity material.

[0016] The present invention also provides a bandpass filter, which is made using the microring resonator described above.

[0017] The present invention also provides a band-stop filter, which is made using the microring resonator described above.

[0018] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0019] (1) The microring resonator proposed in this invention has a cross-sectional width that satisfies the following: it widens uniformly from the center of the coupling region along the counterclockwise direction of the microring, reaches its maximum at a position symmetrical to the center of the coupling region relative to the center of the microring, and then narrows uniformly from this maximum point along the counterclockwise direction of the microring. In other words, the cross-sectional width of the microring resonator proposed in this invention gradually changes, reaching its narrowest point at the center of the coupling region, then linearly widening on both sides of the microring, and reaching its maximum at a position symmetrical to the center of the coupling region relative to the center of the microring. This allows the fundamental mode optical field to be confined within the waveguide as much as possible, reducing the interaction between the optical field and the sidewalls, thereby reducing the scattering loss caused by sidewall roughness. Simultaneously, since the rates of uniform widening and narrowing are the same and both satisfy the condition that the half-angle of the width-gradient waveguide is no greater than the mode diffusion half-angle, the microring resonator can achieve an adiabatic transition between single-mode and multi-mode waveguides, preventing the input light from exciting higher-order modes within the microring and achieving adiabatic transmission of the fundamental mode. Therefore, the overall solution of this invention can reduce the transmission loss of the microring resonator and effectively improve the Q value of the microring resonator.

[0020] (2) Based on the micro-ring resonator proposed in this invention, the coupling method can be further selected as point coupling or weak tapered gap coupling, which can further improve the Q value of the micro-ring resonator.

[0021] (3) The cross-sectional width of the micro-ring resonator proposed in this invention can be optimized by simulation and changed at the best linear rate to achieve the minimum bending radius, thereby minimizing bending loss, making the resonator more compact, and having a higher Q value compared with micro-ring resonators of the same size. Attached Figure Description

[0022] Figure 1 A schematic diagram of a microring resonator with a gradually varying cross-sectional width provided in an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of a microring resonator provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram illustrating the relationship between the microring sidewall scattering loss and the waveguide width, simulated using the neff-width model, provided in an embodiment of the present invention.

[0025] Figure 4 A comparison diagram of the resonance peaks of a microring resonator with a gradually varying cross-sectional width of a microring resonator provided in an embodiment of the present invention and a single waveguide width microring resonator with the same arc length.

[0026] Figure 5 This is a schematic diagram of another microring resonator provided in an embodiment of the present invention.

[0027] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0028] 1 is a micro-ring resonator, 2 is a coupling waveguide, 21 is an input straight waveguide, 22 is an output straight waveguide, 23 is a first curved waveguide, 24 is a second curved waveguide, and 25 is a third curved waveguide. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] A microring resonator with a gradually varying cross-sectional width includes a microring resonator and a coupling waveguide. Wherein, as... Figure 1 As shown, the cross-sectional width of the aforementioned microring resonator satisfies the following: it widens uniformly counterclockwise from the center of the coupling region, reaches its maximum at a position symmetrical to the center of the microring relative to the center of the coupling region, and then narrows uniformly counterclockwise from this maximum point. The rate of widening and narrowing are the same, and both satisfy the following: the half-angle θ of the width-gradient waveguide... t Not greater than the mode diffusion half-angle θ d This allows the microring resonant cavity to thermally transition between single-mode and multimode waveguides.

[0031] The microring resonator proposed in this embodiment has a cross-sectional width that satisfies the following: it widens uniformly counterclockwise from the center of the coupling region, reaches its maximum at a position symmetrical to the center of the microring relative to the center of the coupling region, and then narrows uniformly counterclockwise from this maximum point. In other words, the cross-sectional width of the microring resonator proposed in this embodiment gradually changes, being narrowest at the center of the coupling region, linearly widening on both sides of the microring, and reaching its maximum at a position symmetrical to the center of the microring relative to the center of the coupling region. This effectively confines the fundamental mode optical field within the waveguide as much as possible, reducing the interaction between the optical field and the sidewalls, thereby reducing scattering loss caused by sidewall roughness. Simultaneously, since the rates of uniform widening and narrowing are the same and both satisfy the condition that the half-angle of the width-gradient waveguide is no greater than the mode diffusion half-angle, the microring resonator can achieve an adiabatic transition between the single-mode and multi-mode waveguides, preventing the input light from exciting higher-order modes within the microring and achieving adiabatic transmission of the fundamental mode. Therefore, the overall solution of this embodiment can reduce the transmission loss of the microring resonator and effectively improve the Q value of the microring resonator.

[0032] Preferably, the outer wall radius R0 of the microring resonator is fixed, and the inner wall radius is: R in =R0-K·α-W min ;in, The linear rate of change of the cross-sectional width of the microring resonator is represented by α, where α represents the angle between the radius at the coupling point and the radius at the current position, and W represents the linear rate of change of the cross-sectional width of the microring resonator. min and W max These represent the minimum and maximum cross-sectional widths of the microring resonator, respectively.

[0033] Preferred, such as Figure 2 As shown, the coupled waveguide 2 includes a connected input straight waveguide 21 and an output straight waveguide 22. The microring resonator 1 and the coupled waveguide 2 form a point coupling at the connection between the input straight waveguide 21 and the output straight waveguide 22, and both the input straight waveguide and the output straight waveguide are single-mode waveguides. The cross-sectional widths of the input straight waveguide 21 and the output straight waveguide 22 can be the same.

[0034] The cross-sectional width of the micro-ring resonator increases uniformly in the counterclockwise direction in the coupling region, reaches its maximum width at a position symmetrical to the center of the coupling region, and then continues to decrease uniformly in the counterclockwise direction. The two waveguide segments have the same rate of change.

[0035] Incident light enters the input straight waveguide. Light that satisfies the resonant frequency is directly coupled into the microring resonator in the coupling region, while light that does not satisfy the resonant frequency is output through the output straight waveguide. Since both the input and output straight waveguides are single-mode waveguides, the optical field coupled to the microring resonator only contains the fundamental mode. Furthermore, since the microring resonator does not excite higher-order modes for the fundamental mode, and there are no higher-order modes coupled into the microring resonator and the resulting losses, point coupling is preferred. Combining the microring resonator with this coupling waveguide can further improve the Q value of the entire microring resonator.

[0036] As mentioned earlier, with the increase of the microring cross-sectional width, most of the fundamental mode optical field is confined inside the waveguide, the interaction between the optical field and the sidewalls weakens, and the scattering loss caused by the sidewall roughness is reduced. Under the microring resonator structure proposed in this preferred embodiment, as... Figure 3 As shown, the waveguide width of the microring resonator is obtained by simulation using the neff-width (nw) model.

[0037] Furthermore, a reasonable waveguide width gradient rate can be derived through simulation, ensuring that the fundamental mode propagates within the waveguide such that the half-angle of the gradient-width waveguide is no greater than the mode diffusion half-angle, guaranteeing adiabatic mode propagation within the microring. Based on this, the optimal linear rate of change can be further simulated, achieving the minimum bending radius and minimizing bending loss. This results in a more compact resonator and a higher Q-value compared to microring resonators of the same size. Under the microring resonator structure proposed in this preferred scheme, as... Figure 4 As shown, for a microring with a single waveguide width of R = 100 μm and W = 0.5 μm, assuming a waveguide loss of 1.0 dB / cm and an autocoupling coefficient of 0.992, the simulated spectral response curve is as follows.Figure 4 As shown by the dashed line, the fundamental mode transmission curve corresponding to this coupling coefficient has a 3dB bandwidth of 475MHz and an extinction ratio of 15dB. For a micro-ring waveguide with a waveguide width gradually changing from W = 0.5μm to W = 2μm at the same radius, the loss is set to 0.2dB / cm, and the self-coupling coefficient t is set to 0.998. Figure 4 As shown by the solid line, the fundamental mode transmission curve corresponding to this coupling coefficient has a 3dB bandwidth of 96MHz and an extinction ratio of 15dB. It can be seen that the micro-ring resonator based on gradually varying waveguide width can achieve a higher Q value while maintaining small size and low loss; compared to traditional micro-rings, the Q value can be increased by five times. Therefore, compared to existing technologies, this embodiment, with the same waveguide loss, features a smaller size and more compact structure based on the gradually varying width micro-ring.

[0038] Preferably, the aforementioned coupled waveguide includes an input straight waveguide, a bent waveguide, and an output straight waveguide connected in sequence. The micro-ring resonator and the coupled waveguide form a weak tapered gap coupling at the distorted waveguide, and the input straight waveguide, the bent waveguide, and the output straight waveguide are all single-mode waveguides.

[0039] During the propagation and evolution of the optical field within the coupling region between the microring waveguide and adjacent waveguides, changes in the coupling gap can lead to optical field mode mismatch, exciting higher-order modes and radiation modes within the waveguide. This results in increased losses and decreased Q-values ​​within the microring resonator. To avoid this problem, this preferred solution proposes using a weakly tapered gap coupling. Since the weakly tapered gap coupling satisfies the refractive index matching between a specific mode in the curved waveguide and the specific mode in the microring resonator (i.e., the curvature of the curved waveguide and the microring resonator satisfies the refractive index matching of the fundamental mode), the excitation efficiency of this mode is higher, and adiabatic mode propagation is more easily achieved.

[0040] Incident light enters from the input straight waveguide. Light that satisfies the resonant frequency enters the microring resonator via weak tapered gap coupling at the curved waveguide. Light that does not satisfy the resonant frequency exits via the output straight waveguide. Since the input straight waveguide, curved waveguide, and output straight waveguide are all single-mode waveguides, only the fundamental mode is coupled into the microring resonator, and no higher-order modes exist. Furthermore, since the microring resonator does not excite higher-order modes for the fundamental mode, and there are no higher-order modes coupled into the microring resonator and the resulting losses, the weak tapered gap coupling is preferred. Combining the microring resonator with this coupling waveguide can further improve the Q value of the entire microring resonator.

[0041] Preferably, the aforementioned curved waveguide includes a first curved waveguide, a third curved waveguide, and a second curved waveguide that are sequentially connected and symmetrically distributed relative to the center of the coupling region, and the micro-ring resonator and the coupling waveguide form a weak conical gap coupling at the third curved waveguide.

[0042] Specifically, in this preferred solution, such as Figure 5 As shown, the coupling waveguide 2 includes a symmetrically distributed input straight waveguide 21, an output straight waveguide 22, a first curved waveguide 23, a second curved waveguide 24, and a third curved waveguide 25; the first curved waveguide, the third curved waveguide, and the second curved waveguide are connected end-to-end to form a bus waveguide; the bus waveguide is located between the input and output straight waveguides; the first curved waveguide, the second curved waveguide, the third curved waveguide, the input straight waveguide, and the output straight waveguide are all single-mode waveguides.

[0043] Incident light enters from the input straight waveguide 21, passes through the first curved waveguide 23 and enters the third curved waveguide 25. Light that meets the resonant frequency enters the micro-ring resonant cavity at the third curved waveguide 25 in a weakly tapered gap coupling manner, while light that does not meet the resonant frequency is output through the second curved waveguide 24 and the output straight waveguide 22 in sequence.

[0044] The width of the third curved waveguide and the width of the microring resonator satisfy the mode matching condition in the coupling region, that is, the product of the effective refractive index of the fundamental mode of the third curved waveguide and its radius is equal to the product of the effective refractive index of the fundamental mode of the microring waveguide and its radius. The effective refractive index of the fundamental mode can be adjusted by changing the radius.

[0045] The lengths of the input straight waveguide, output straight waveguide, first curved waveguide, and second curved waveguide can be arbitrarily set while ensuring adiabatic transmission. However, the gaps between them and the microring resonator should be large enough to avoid coupling with the microring. The length of the third curved waveguide is variable, thus the coupling coefficient can be controlled by controlling the coupling length.

[0046] The widths of the first, second, and third curved waveguides and the micro-ring resonator, as well as the gap width of the coupling region, are all rigorously designed to achieve mode matching conditions for the fundamental mode.

[0047] Preferably, both the microring resonator and the coupling waveguide are independently selected from any one of strip waveguides, ridge waveguides, and multilayer waveguides.

[0048] Preferably, the materials of the microring resonator and the coupling waveguide are independently selected from any one of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

[0049] Preferably, a heating electrode can also be introduced into the microring resonator. The heating electrode can be located above the edge of the microring resonator, that is, the heating electrode covers the surface of the microring. Heating is achieved by an electrical signal, which causes a change in the refractive index of the microdisk waveguide material, thereby achieving tuning of the resonant wavelength.

[0050] Example 2

[0051] A bandpass filter employs the microring resonator described in Embodiment 1 above. The related technical solutions are the same as in Embodiment 1 and will not be repeated here.

[0052] Example 3

[0053] A band-stop filter employs the micro-ring resonator described in Embodiment 1 above. The related technical solutions are the same as in Embodiment 1 and will not be repeated here.

[0054] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microring resonator with a gradually varying cross-sectional width, characterized in that, include: Micro-ring resonator and coupled waveguide; The cross-sectional width of the microring resonator satisfies the following: it widens uniformly from the center of the coupling region along the counterclockwise direction of the microring, reaches its maximum at a position symmetrical to the center of the coupling region relative to the center of the microring, and then narrows uniformly from this maximum point along the counterclockwise direction of the microring. The rate of uniform widening and uniform narrowing is the same, and both satisfy the following: the half-angle of the width-gradient waveguide is not greater than the mode diffusion half-angle. The rate of gradual change is obtained through simulation with the goal of minimizing the bending radius and bending loss of the microring resonator. This allows the microring resonator to achieve adiabatic transition between single-mode and multi-mode waveguides, preventing the input light from exciting higher-order modes within the microring and achieving adiabatic transmission of the fundamental mode. Wherein, the outer wall radius of the micro-ring resonant cavity The inner wall radius is fixed as follows: ;in, , representing the linear rate of change of the cross-sectional width of the microring resonator. This represents the angle between the radius at the coupling point and the radius of the current position. and These represent the minimum and maximum cross-sectional widths of the microring resonator, respectively. The coupling waveguide includes an input straight waveguide and an output straight waveguide connected together. The micro-ring resonator and the coupling waveguide form a point coupling at the connection between the input straight waveguide and the output straight waveguide. Both the input straight waveguide and the output straight waveguide are single-mode waveguides. Alternatively, the coupling waveguide may include an input straight waveguide, a curved waveguide, and an output straight waveguide connected in sequence, wherein the micro-ring resonator and the coupling waveguide form a weak tapered gap coupling at the curved waveguide, and the input straight waveguide, the curved waveguide, and the output straight waveguide are all single-mode waveguides; The curved waveguide includes a first curved waveguide, a third curved waveguide, and a second curved waveguide that are connected in sequence and symmetrically distributed relative to the center of the coupling region. The micro-ring resonator and the coupling waveguide form a weak conical gap coupling at the third curved waveguide. The curvature of the curved waveguide and the microring resonator satisfies the refractive index matching of the fundamental mode; the product of the effective refractive index of the fundamental mode and the radius of the third curved waveguide is equal to the product of the effective refractive index of the fundamental mode and the radius of the microring waveguide; The lengths of the input straight waveguide, output straight waveguide, first curved waveguide, and second curved waveguide, while satisfying the condition of thermal transmission, should have sufficiently large gaps with the microring resonant cavity to avoid coupling with the microring; the coupling coefficient is controlled by controlling the coupling length of the third curved waveguide. It also includes a heating element for heating the microring resonant cavity and changing the refractive index of the microring resonant cavity material. The heating electrode is located above the edge of the microring resonant cavity, that is, the heating electrode covers the surface of the microring.

2. The microring resonator according to claim 1, characterized in that, Both the microring resonant cavity and the coupling waveguide are independently selected from any one of strip waveguides, ridge waveguides, and multilayer waveguides. The materials of the microring resonator and the coupling waveguide are independently selected from any one of silicon-on-insulator, lithium niobate, silicon nitride, indium phosphide, and gallium arsenide.

3. A bandpass filter, characterized in that, It is made using a microring resonator as described in any one of claims 1-2.

4. A band-stop filter, characterized in that, It is made using a microring resonator as described in any one of claims 1-2.

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