A nonlinear ring resonator and a multiwavelength converter

Abstract

The application belongs to the field of nonlinear integrated optics, optical interconnection and optical communication, and particularly relates to a nonlinear ring resonator and a multi-wavelength converter, which comprises a ring resonant cavity, a first coupling waveguide, a second coupling waveguide, a third coupling waveguide and a fourth coupling waveguide; the geometric size of the ring resonant cavity satisfies the phase matching condition of multi-wavelength conversion and is a multimode optical waveguide; the first coupling waveguide is close to the ring resonant cavity, and the waveguide cross-sectional size is the same, thereby forming a symmetric directional coupler; the second coupling waveguide, the third coupling waveguide and the fourth coupling waveguide are close to the ring resonant cavity, respectively, thereby forming a coupler for inputting / outputting light of different wavelengths, the cross-sectional size of which is different from that of the ring resonant cavity waveguide, thereby forming three asymmetric directional couplers for outputting light of different wavelengths. In order to avoid crosstalk between the interacting wavelengths in the ring resonant cavity, the four couplers only satisfy the coupling condition of the corresponding wavelength and do not couple with the other three wavelengths. Therefore, the application can simultaneously generate and output three different wavelengths of light under the condition of inputting only one pump light wavelength, and each wavelength is output through an independent channel without the need of an additional filter device.

Description

Technical Field

[0001] This invention relates to the field of optical microcavities, and in particular to a nonlinear ring resonator and a multi-wavelength converter. Background Technology

[0002] Microring resonators, by confining the light field to a limited area, significantly extend the interaction time between light and matter, showing broad application prospects in many fields such as sensing and nonlinear optics. In the field of nonlinear optics, the interaction of multi-wavelength light is key to achieving efficient wavelength conversion. When two or more different wavelengths of light can resonate simultaneously in a microring resonator, the nonlinear wavelength conversion efficiency can be significantly enhanced, which is crucial for applications such as optical communication and optical signal processing.

[0003] Some nonlinear optical materials exhibit both second-order and third-order nonlinearities (e.g., lithium niobate, aluminum nitride, etc.). Under the enhancement of a microcavity, they simultaneously excite various nonlinear interactions, such as second harmonic generation, sum / difference frequency generation, third harmonic generation, optical parametric oscillations, and cascaded nonlinear interactions. Traditional transmission-type nonlinear ring cavities consist of a main waveguide and a micro-ring resonator. A single coupler output design can avoid crosstalk between multiple wavelengths, affecting the quality factor (Q value) of different wavelengths within the cavity, but it cannot simultaneously output multiple wavelengths. A multi-coupler design can simultaneously couple new wavelengths generated within the cavity, but different couplers are prone to crosstalk with different wavelengths, affecting the nonlinear conversion efficiency.

[0004] Optimizing the ring resonator structure to achieve a compact optical device capable of generating, resonating, and outputting multiple wavelengths has become an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a nonlinear ring resonator that solves the problem of simultaneous output of light of different wavelengths through different couplers when multiple nonlinear interactions occur simultaneously, avoiding crosstalk between couplers, and achieving simultaneous output of multiple wavelengths without the need for additional filters.

[0006] To achieve the above objectives, the present invention provides the following technical solutions;

[0007] In a first aspect, the present invention provides a nonlinear ring resonator, comprising a ring resonant cavity, a first coupled waveguide, a second coupled waveguide, a third coupled waveguide, and a fourth coupled waveguide;

[0008] The ring resonant cavity, as the core component, has been meticulously designed in terms of geometry to meet the phase-matching conditions for multi-wavelength conversion and employs a multimode optical waveguide structure. This design enables the ring resonant cavity to support the transmission of multiple modes of optical waves, providing a basis for the interaction of light of different wavelengths.

[0009] Under phase-matching conditions that satisfy multi-wavelength conversion, it can effectively promote the occurrence of various nonlinear wavelength conversion processes, such as second harmonic generation, third harmonic generation, and sum-frequency generation. Simultaneously, the multimode waveguide structure allows different modes of light to coexist within the cavity, further increasing the possibility of nonlinear interactions and improving the efficiency of multi-wavelength conversion.

[0010] The first coupling waveguide and the ring resonator are close to each other, and their waveguide cross-sectional dimensions are the same, together forming a symmetrical directional coupler 1. This symmetrical structural design gives the first coupling waveguide a unique advantage when optically coupling with the ring resonator. On the one hand, the geometric widths of the first coupling waveguide and the ring resonator satisfy the specific refractive index matching condition for coupling the input pump light wavelength λ1, ensuring that the pump light can be efficiently coupled into the ring resonator. On the other hand, the coupling length and coupling spacing between the first coupling waveguide and the ring resonator can be flexibly adjusted. When the coupling length is longer, the coupling coefficient λ1 can be increased, allowing more pump light to enter the ring resonator and participate in nonlinear interactions; while a larger coupling spacing can avoid coupling of other wavelengths of light, effectively reducing unnecessary interference and ensuring the accuracy and stability of pump light coupling.

[0011] The second, third, and fourth coupling waveguides are close to the ring resonant cavity, forming couplers for different wavelengths of light input / output. The cross-sectional dimensions of these three coupling waveguides are different from those of the ring resonant cavity waveguides, and each forms an asymmetric directional coupler 2, 3, and 4 for different wavelength outputs.

[0012] In the asymmetric directional coupler 2, the higher-order modes of λ2 inside the ring and the basic mode of the second coupled waveguide satisfy a specific refractive index matching condition, while light of other wavelengths does not satisfy this coupling condition, so no coupling occurs, thereby realizing the independent output of λ2 light.

[0013] In the asymmetric directional coupler 3, the higher-order modes of λ3 inside the ring and the basic mode of the third coupled waveguide satisfy a specific refractive index matching condition, ensuring the independent output of the λ3 light;

[0014] In the asymmetric directional coupler 4, the higher-order modes of λ4 within the ring and the fundamental mode of the fourth coupled waveguide satisfy a specific refractive index matching condition, enabling independent output of the λ4 light. In this way, the four couplers satisfy the coupling condition only for their corresponding wavelengths, without coupling to the other three wavelengths, effectively avoiding crosstalk between interacting wavelengths in the ring resonant cavity.

[0015] The ring resonator, first coupling waveguide, second coupling waveguide, third coupling waveguide, and fourth coupling waveguide can be any of the following forms: rectangular waveguide, ridge waveguide, loaded strip waveguide, or metal-diffused waveguide. These different waveguide forms have their own characteristics and advantages. For example, rectangular waveguides are simple in structure and easy to manufacture; ridge waveguides can better confine the optical field and improve the efficiency of light-matter interaction; loaded strip waveguides can achieve superior performance in specific applications; and metal-diffused waveguides possess unique optical properties in certain aspects.

[0016] Choosing different types of waveguides can be optimized based on specific application requirements and manufacturing processes to meet different performance requirements.

[0017] The first, second, third, and fourth coupling waveguides are made of any one of the following materials: thin-film lithium niobate, lithium tantalate, aluminum nitride, and silicon carbide. These materials all possess excellent optical properties. For example, thin-film lithium niobate and lithium tantalate have high nonlinear optical coefficients, effectively enhancing the nonlinear wavelength conversion efficiency; aluminum nitride and silicon carbide, on the other hand, exhibit good thermal stability and mechanical properties, improving the stability and reliability of the device while ensuring optical performance. Selecting these materials allows for full utilization of their optical advantages, thereby improving the overall performance of the nonlinear ring resonator.

[0018] Secondly, the present invention provides a multi-wavelength converter. This multi-wavelength converter uses the aforementioned nonlinear ring resonator as its core component. By inputting a pump light wavelength, and utilizing the nonlinear interactions within the nonlinear ring resonator, three other different wavelengths of light can be simultaneously generated and output.

[0019] Light of different wavelengths is output through their own independent channels (i.e., corresponding coupled waveguides), eliminating the need for additional filtering devices. This greatly simplifies the system structure of multi-wavelength conversion, reduces costs, and improves the efficiency and stability of multi-wavelength conversion.

[0020] This multi-wavelength converter also includes a pump source and a coupler. The pump source provides energy for the entire multi-wavelength conversion process, and its output pump light is coupled into a nonlinear ring resonator through the coupler. The coupler uses optical fiber and can be coupled to the optical chip using either end-face coupling or vertical coupling.

[0021] End-face coupling is simple, direct, and easy to implement, and can guarantee optical transmission efficiency to a certain extent.

[0022] Vertical coupling can reduce light loss during the coupling process and improve the stability and reliability of the coupling.

[0023] Choosing the appropriate coupling method can be optimized based on the actual application scenario and system requirements to ensure that the pump light can enter the nonlinear ring resonator efficiently and stably, thus promoting the smooth progress of the multi-wavelength conversion process. Attached Figure Description

[0024] Figure 1 A schematic diagram of the nonlinear ring resonator and multi-wavelength converter of the present invention is shown. In the diagram, the ring resonator is located at the center, surrounded by a first coupling waveguide, a second coupling waveguide, a third coupling waveguide, and a fourth coupling waveguide. The first coupling waveguide and the ring resonator form a symmetrical directional coupler 1, used for input pump light wavelength λ1. The second, third, and fourth coupling waveguides, together with the ring resonator, form asymmetrical directional couplers 2, 3, and 4, respectively, used for outputting light of different wavelengths, namely λ2 output, λ3 output, and λ4 output. Detailed Implementation

[0025] In the actual fabrication of nonlinear ring resonators, the geometric dimensions of the ring resonator are first precisely designed based on the required nonlinear wavelength conversion process (such as second harmonic generation, third harmonic generation, sum frequency generation, etc.) and the corresponding energy and momentum conservation conditions.

[0026] For example, for the generation of second harmonics, based on the energy conservation condition ν2=2ν1 and the momentum conservation condition βλ2=2βλ1, and combined with the optical properties of the selected material, the cross-sectional dimensions, radius and other parameters of the ring resonant cavity are calculated and determined to ensure that it can support the multimode optical waveguide structure and meet the phase matching conditions for multi-wavelength conversion.

[0027] When fabricating the first coupling waveguide, its cross-sectional dimensions are made identical to those of the ring resonant cavity to form a symmetrical directional coupler 1. During fabrication, the geometric widths of the first coupling waveguide and the ring resonant cavity are strictly controlled to ensure that they meet the specific refractive index matching conditions for coupling the input pump light wavelength λ1.

[0028] Based on actual needs, the coupling length and coupling spacing between the first coupling waveguide and the ring resonant cavity are precisely controlled through micro-nano fabrication processes such as photolithography and etching. If it is necessary to increase the coupling coefficient λ1, the coupling length can be appropriately increased; if it is necessary to avoid coupling interference from other wavelengths of light, the coupling spacing can be increased.

[0029] When fabricating the second, third, and fourth coupling waveguides, their waveguide widths are made smaller than the waveguide width of the ring resonant cavity, thus forming asymmetric directional couplers 2, 3, and 4, respectively.

[0030] For each asymmetric directional coupler, based on the required output wavelengths (λ2, λ3, λ4), the parameters that satisfy specific refractive index matching conditions between the higher-order modes of the corresponding wavelengths within the ring and the basic modes of the coupled waveguide are determined through theoretical calculations and simulation analysis, and these parameters are strictly controlled during the fabrication process.

[0031] For asymmetric directional coupler 2, ensure that the higher-order modes of λ2 within the loop satisfy a specific refractive index matching condition with the fundamental mode of the second coupled waveguide, so that light of other wavelengths does not satisfy the coupling condition, thereby achieving independent output of λ2 light. Similarly, when fabricating asymmetric directional couplers 3 and 4, ensure independent output of λ3 and λ4 light, respectively.

[0032] When choosing a waveguide type, the appropriate type should be selected based on the specific application scenario and performance requirements. If structural simplicity and ease of manufacturing are important, a rectangular waveguide can be chosen; if better confinement of the light field and improvement of the light-matter interaction efficiency are required, a ridge waveguide can be selected; if there are special performance requirements in a specific application, such as when the unique optical properties of a loaded strip waveguide or a metal diffused waveguide can meet the requirements, the corresponding waveguide type can also be selected.

[0033] When selecting waveguide materials, suitable materials are chosen from thin-film lithium niobate, lithium tantalate, aluminum nitride, and silicon carbide, based on the required optical performance and device stability requirements. If a higher nonlinear optical coefficient is desired to enhance the nonlinear wavelength conversion efficiency, thin-film lithium niobate or lithium tantalate can be selected; if thermal stability and mechanical properties are more important to improve the stability and reliability of the device, aluminum nitride or silicon carbide can be used.

[0034] In fabricating a multi-wavelength converter, the fabricated nonlinear ring resonator is assembled with a pump light source and a coupler. A suitable pump light source is selected based on actual requirements, and its output pump light wavelength should match the designed pump light wavelength λ1 in the nonlinear ring resonator to provide sufficient energy for the multi-wavelength conversion process.

[0035] For couplers, the choice between end-face coupling and vertical coupling between the optical fiber and the optical chip depends on factors such as system design requirements and installation space. If simplicity and ease of implementation are paramount in the coupling method, end-face coupling can be chosen; if optical loss and stability during coupling are of greater concern, vertical coupling can be used.

[0036] By properly assembling the various components, the multi-wavelength converter is fabricated. In actual use, the pump light emitted from the pump source is coupled into the nonlinear ring resonator through a coupler. Various nonlinear interactions occur within the ring resonator cavity, generating three other different wavelengths of light. These lights are output through the second, third, and fourth coupling waveguides, respectively, thus realizing the multi-wavelength conversion function.

[0037] 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 nonlinear ring resonator, characterized in that, include: The ring resonant cavity, the first coupled waveguide, the second coupled waveguide, the third coupled waveguide, and the fourth coupled waveguide.

2. The annular resonant cavity as described in claim 1, characterized in that... The cross-sectional dimensions satisfy the energy and momentum conservation conditions required for various nonlinear wavelength conversion processes, such as the generation of second harmonics, where the energy conservation condition requires ν2 = 2ν1 and the momentum conservation condition is β. λ2 =2*β λ1 The generation of the third harmonic requires the energy conservation condition ν3 = 3ν1, and the momentum conservation condition is β. λ3 =3*β λ1 The generation of sum frequencies requires the energy conservation condition ν1 + ν3 = ν4, and the momentum conservation condition is β. λ4 =β λ1 +β λ3 Among them, ν m β represents the frequency of the interaction wavelength in the ring resonant cavity. m This represents the propagation constant of the interaction wavelengths in the ring resonant cavity.

3. The ring resonator as described in claim 2, characterized in that, The energy conservation condition required for nonlinear wavelength conversion can be achieved by controlling the geometric dispersion and mode dispersion of the waveguide. That is, by selecting four spatial modes with different interacting wavelengths and the cross-sectional dimensions of the ring resonator, the three nonlinear wavelength conversion processes can simultaneously satisfy the energy conservation and momentum conservation conditions.

4. As claimed in claim 1, the first coupling waveguide and the ring resonant cavity are close to each other and have the same cross-sectional dimensions as the ring resonant cavity, thus forming a symmetrical directional coupler 1; The directional coupler 1 is characterized in that, The combined width of the first coupled waveguide and the ring resonator satisfies the specific refractive index matching condition for the input pump light wavelength λ1. The directional coupler 1 is characterized in that the coupling length and coupling spacing between the first coupling waveguide and the ring resonant cavity are adjustable, with different parameters corresponding to different coupling coefficients. A longer coupling length can increase the coupling coefficient λ1; a larger coupling spacing can prevent coupling of light of other wavelengths.

5. As claimed in claim 1, the second coupling waveguide and the ring resonant cavity are close to each other and the waveguide width of the second coupling waveguide is smaller than the waveguide width of the ring resonant cavity, thus forming an asymmetric directional coupler 2; The directional coupler 2 is characterized in that, The higher-order modes of λ2 within the ring satisfy specific refractive index matching conditions with the fundamental modes of the second coupled waveguide; light of other wavelengths does not satisfy the coupling conditions and does not couple.

6. As described in claim 1, the third coupling waveguide is close to the ring resonant cavity and its waveguide width is smaller than the waveguide width of the ring resonant cavity, thus forming an asymmetric directional coupler 3; The higher-order modes of λ3 within the directional coupler ring 3 and the basic mode of the third coupled waveguide satisfy a specific refractive index matching condition; light of other wavelengths does not satisfy the coupling condition and does not couple.

7. As described in claim 1, the fourth coupling waveguide and the ring resonant cavity are close to each other and the waveguide width of the fourth coupling waveguide is smaller than the waveguide width of the ring resonant cavity, thus forming an asymmetric directional coupler 4; The higher-order modes of λ4 within the directional coupler ring 4 and the basic mode of the fourth coupled waveguide satisfy a specific refractive index matching condition; light of other wavelengths does not satisfy the coupling condition and does not couple.

8. A nonlinear ring resonator as described in claim 1, characterized in that, The ring resonant cavity, the first coupling waveguide, the second coupling waveguide, the third coupling waveguide, and the fourth coupling waveguide can be any one of the following forms: rectangular waveguide, ridge waveguide, loaded strip waveguide, or metal diffused waveguide.

9. A nonlinear ring resonator as described in claim 1, characterized in that, The first coupling waveguide, the second coupling waveguide, the third coupling waveguide, and the fourth coupling waveguide are made of any one of the following materials: thin-film lithium niobate, lithium tantalate, aluminum nitride, and silicon carbide.

10. A multi-wavelength converter, characterized in that, The multi-wavelength converter employs a nonlinear ring resonator as described in any one of claims 1-9.

11. A multi-wavelength converter, characterized in that, include: Pump light source, nonlinear ring resonator, coupler; The coupler can be either end-face coupling or vertical coupling between the optical fiber and the optical chip.

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