Single-cavity high-extinction-ratio micro-ring filter based on multimode multiplexing and asymmetric coupling

Abstract

The invention relates to the technical field of integrated photoelectronics, in particular to a single-cavity high-extinction-ratio micro-ring filter based on multimode multiplexing and asymmetric coupling, which comprises a bus waveguide, a multimode micro-ring resonant cavity, a discrete micro-ring resonant coupling area, an optical path loopback and mode conversion module and a thermal tuning electrode, the bus waveguide and the multi-mode micro-ring resonant cavity support TE0, TE1 and TE2 multi-mode transmission, the discrete micro-ring resonant coupling areas are distributed along the circumference of the micro-ring and are adaptive to different-mode coupling, and the optical path loopback and the mode conversion module realize mode conversion and optical signal turning back through an asymmetric directional coupler. The thermal tuning electrode enables multi-mode harmonic peaks to coincide at the working wavelength through the multi-mode vernier caliper effect. Through the design of single-cavity multi-mode cyclic filtering and asymmetric coupling mode conversion, in combination with multi-mode harmonic peak superposition and single thermal tuning control, the beneficial effects of ultrahigh extinction ratio, compact structure, simple and convenient control and multi-mode crosstalk suppression are achieved.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronics technology, and in particular to a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling. Background Technology

[0002] In silicon-based photonic integrated circuits, microring resonators are core devices for filtering, modulation, and wavelength division multiplexing, and are widely used in many important fields such as optical communication and optical sensing. However, existing microring devices face many intractable technical problems in practical applications: First, the limited extinction ratio (ER) is a core drawback of traditional single-mode microring devices. The filtering performance of traditional single-mode microrings relies on a strict critical coupling condition, meaning the coupling coefficient must equal the loss coefficient. However, in actual nanofabrication processes, process errors are unavoidable, making it difficult to precisely meet the critical coupling condition. This results in a typically low extinction ratio for traditional single-mode microrings, usually only around 20 dB. With the development of optical communication technology, higher-order modulation formats (such as PAM4) place higher demands on the signal-to-noise ratio, and the low extinction ratio of traditional microring devices can no longer meet practical application requirements.

[0003] Secondly, existing technologies for improving the extinction ratio have significant drawbacks. To enhance the extinction ratio, current technologies often employ a CROW structure with multiple microrings connected in series. This structure not only significantly increases the chip's footprint, hindering high-density device integration, but also requires multiple independent thermally tuned electrodes for complex alignment control of each microring due to their extreme temperature sensitivity. This not only increases the device's control complexity but also leads to a substantial increase in power consumption.

[0004] Finally, multimode crosstalk restricts the application of multimode waveguides. When attempting to increase bandwidth density using multimode waveguides, severe intermode crosstalk often occurs between different modes. This crosstalk directly leads to a deterioration in signal quality, affecting the filtering effect and transmission stability of the device.

[0005] Therefore, the industry urgently needs a micro-ring device structure that is compact, easy to control, and can stably achieve an ultra-high extinction ratio to solve the aforementioned technical problems in the existing technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of the prior art and provide a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling. This solves the core technical problems of traditional single-mode microring filters having low extinction ratios that make it difficult to meet high-order modulation requirements, as well as complex multi-microring series structures that are cumbersome to control and have high power consumption.

[0007] The above objectives are achieved through the following technical solutions: A single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling includes: The bus waveguide supports multiple transmission modes including TE0, TE1, and TE2, and is equipped with a tapered transition region and a U-shaped loop waveguide. A multimode microring resonant cavity, which is adapted to the bus waveguide, supports multiple modes of transmission such as TE0, TE1, and TE2, and provides a resonant filtering channel for optical signals; The discrete microring resonant coupling regions are distributed along the perimeter of the multimode microring resonant cavity, including at least three independent resonant coupling regions, each adapted to different modes of coupling. The optical path loopback and mode conversion module is located at both ends of the bus waveguide and at the U-shaped loopback waveguide. It includes multiple asymmetric directional couplers. The asymmetric directional couplers adjust the width of the two bus waveguides to meet the phase matching condition and realize the mode conversion of the transmitted light. The U-shaped loopback waveguide is used to fold the mode-converted optical signal back to the bus waveguide. A thermally tuned electrode is provided corresponding to the multimode microring resonator and is used to adjust the parameters of the multimode microring resonator so that the resonance peaks of different modes coincide at the working wavelength.

[0008] Furthermore, the width of the bus waveguide is 1.2 μm, the input waveguide width of the asymmetric directional coupler is 200 nm-600 nm, and the output waveguide width is 1.28 μm.

[0009] Furthermore, the mode switching coupling gaps of the asymmetric directional coupler are Gap1 and Gap2, ranging from 20nm to 200nm, and are independently optimized.

[0010] Furthermore, the asymmetric directional coupler can be of the directional coupling type, the adiabatic cone type, or the multimode interference (MMI) type.

[0011] Furthermore, the multimode microring resonator is made of SOI (silicon-on-insulator), with a radius ranging from 30μm to 60μm and a width of 1.2μm.

[0012] Furthermore, the resonant coupling gaps of the discrete micro-ring resonant coupling regions are Gap3, Gap4, and Gap5, ranging from 90nm to 300nm, and are independently optimized.

[0013] Furthermore, the coupling structure of the discrete micro-ring resonant coupling region is either straight waveguide coupling or kink waveguide coupling (Pulley coupling).

[0014] Furthermore, the transmission modes of the optical signal include dual-mode (TE0-TE1), tri-mode (TE0-TE1-TE2), or multi-mode combinations of four or more modes, and the number of resonant coupling regions is adapted to the number of transmission modes.

[0015] Furthermore, the transmission polarization state of the optical signal is TE mode or TM mode.

[0016] Furthermore, the operating wavelength is 1550 nm, and the free spectral range (FSR) of the multimode microring resonator varies slightly depending on the mode.

[0017] This invention provides a single-cavity high extinction ratio micro-ring filter based on multimode multiplexing and asymmetric coupling. Through single-cavity multimode cyclic filtering and asymmetric coupling mode conversion design, combined with multimode resonant peak superposition and single thermal tuning control, it achieves the beneficial effects of ultra-high extinction ratio, compact structure, simple control, and suppression of multimode crosstalk. Compared with existing technologies, the specific advantages are as follows: 1. Ultra-high extinction ratio: Through the superposition effect of multi-mode resonant peaks and the multi-mode vernier caliper effect, this invention achieves an extinction ratio of over 85dB, which is significantly better than traditional single-mode micro-ring devices. It can fully meet the signal-to-noise ratio requirements of high-order modulation formats and greatly improve the quality of filtered signals.

[0018] 2. Compact structure: It uses only one multimode microring resonator. Compared with the traditional CROW structure of three microrings in series, the chip occupies only the size of a single ring, which significantly reduces the space occupied by the device. This is conducive to the high-density integration of silicon-based photonic integrated circuits and provides strong support for the realization of large-scale photonic integrated systems.

[0019] 3. Simple control: Only one thermally tuned electrode is needed to achieve precise alignment of the resonant peaks of all modes through the multimode vernier caliper effect, avoiding the complex alignment control of multiple sets of thermally tuned electrodes in multi-ring cascaded structures, and greatly reducing the control complexity and power consumption of the device.

[0020] 4. High robustness: The ultra-high extinction ratio is achieved through multi-mode superposition effect, making it insensitive to errors in single-coupling nanofabrication processes. Even with certain process deviations (such as coupling gap deviations), the filtering performance of the device can be guaranteed through the cascade effect of multi-mode superposition, effectively ensuring the production yield of the device.

[0021] 5. Suppressing multimode crosstalk: Through the collaborative design of discrete micro-ring resonant coupling regions (independently adapting to different modes) and asymmetric directional couplers (precisely satisfying phase matching), the intermode crosstalk problem in the multimode transmission process is effectively solved, ensuring the independent transmission and stable resonance of each mode optical signal and guaranteeing the integrity of the filtered signal.

[0022] As an optimization of this solution, based on its core design principles, the following alternative solutions can be used to expand the application scope, all of which can achieve similar technical effects: 1. Polarization state adaptation: Although the embodiment of this solution is illustrated using the TE mode as an example, the structure is equally applicable to the TM mode. By simply adjusting the bus waveguide width and coupling gap of the mode converter according to the transmission characteristics and phase matching requirements of the TM mode, the phase matching conditions corresponding to the TM mode can be met, thereby realizing mode conversion and cyclic filtering of different orders of the TM mode (TM0, TM1, TM2, etc.), expanding the application scenarios of the device.

[0023] 2. Coupling Structure Selection: The coupling structure of the discrete micro-ring resonator coupling region can employ not only straight waveguide coupling but also purley coupling. Purley coupling better adapts to the arc-shaped structure of the multimode micro-ring resonator, reducing optical signal transmission loss, and can be flexibly selected based on the actual device integration requirements and process conditions.

[0024] 3. Mode Converter Types: Mode converters can be implemented in various ways, including not only directional coupling but also adiabatic cone or multimode interference (MMI) types. Adiabatic cone mode converters offer advantages such as low loss and wide bandwidth, while MMI mode converters feature compact structure and high manufacturing tolerance. Both types can meet the phase matching requirements of mode conversion, and the appropriate type can be selected based on different application scenarios (such as low loss requirements or high integration requirements).

[0025] 4. Mode Number Expansion: The number of modes in this scheme is not limited to three modes (TE0-TE1-TE2), but can also be expanded to two modes (TE0-TE1) or four modes or more. When expanded to two modes, one resonant coupling region and one mode converter can be reduced, and the radius of the multimode microring resonator can be adjusted according to the FSR difference between the two modes. When expanded to four modes or more, a corresponding resonant coupling region and mode converter need to be added, and the perimeter of the multimode microring resonator and the parameters of the mode converter need to be optimized. Through the superposition of multimode resonance peaks, the extinction ratio can be further improved. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the overall planar structure of a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling as described in this invention. The diagram clearly shows the spatial distribution, connection relationship, and optical signal transmission path of each functional module of the device: the left side is the input port, the right side is the output port, and the middle is centered on the multimode microring resonant cavity, surrounded by a bus waveguide, three discrete resonant coupling regions, four mode converters, and a thermally tuned electrode. The arrows in the diagram indicate the transmission directions of the three modes TE0, TE1, and TE2, intuitively presenting the cyclic path of "input → TE0 resonance → TE0 → TE1 conversion → TE1 resonance → TE1 → TE0 conversion → TE0 → TE2 conversion → TE2 resonance → TE2 → TE0 conversion → output". The diagram also indicates the position of the thermal electrode (set in close contact with the microring resonant cavity), the layout of the U-shaped loop waveguide, and the distribution of the tapered transition region, fully demonstrating the structural design of the "single-cavity multimode cyclic filter".

[0027] Figure 2 This is a magnified view of the asymmetric coupling region in a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling as described in this invention. The figure magnifies and displays the asymmetric coupling structure of mode converter 1-1 (TE0→TE1 conversion) and mode converter 2-1 (TE0→TE2 conversion): it clearly shows the layout of the two bus waveguides (waveguide 1 and waveguide 2 correspond to mode converter 1-1; waveguide 3 and waveguide 4 correspond to mode converter 2-1), the specific positions of coupling lengths (LC1, LC2) and coupling gaps (gap1, gap21); at the same time, it marks the mode conversion process of the optical signal in the coupling region (TE0→TE1, TE0→TE2), intuitively demonstrating the structure and function of the asymmetric directional coupler, and providing a clear reference for understanding the implementation of mode conversion.

[0028] Figure 3 This is an effective refractive index matching diagram for a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling, as described in this invention. The diagram, with waveguide width on the x-axis and effective refractive index on the y-axis, shows the curves of the effective refractive index of the three modes (TE0, TE1, and TE2) as a function of waveguide width. It can be seen from the diagram that when the waveguide width is adjusted to a specific value (e.g., the effective refractive index of the TE1 mode at an input waveguide width of 400 nm, and the effective refractive index of the TE2 mode at 500 nm), it can be equal to the effective refractive index of the corresponding mode (TE0 mode) in the output waveguide (1.28 μm), thus satisfying the phase matching condition. This provides a direct theoretical basis for the design of waveguide width parameters in the mode converter and verifies the feasibility of mode conversion.

[0029] Figure 4This figure shows a comparison of simulation results for a single-cavity high extinction ratio microring filter based on multimode multiplexing and asymmetric coupling, as described in this invention. The figure includes simulation comparison curves of the transmission spectrum of a single-mode filter and the transmission spectrum of a three-mode superimposed filter. The horizontal axis represents wavelength (nm), covering the range of 1555nm-1560nm (the region surrounding the operating wavelength), and the vertical axis represents transmission intensity (dB). It is evident from the figure that the extinction ratio of the single-mode filter transmission spectrum is approximately 20dB (the level of a traditional single-mode microring filter), while the extinction ratio of the three-mode superimposed filter transmission spectrum exceeds 85dB. The filter peaks are sharper, and the signal-to-noise ratio is significantly improved. This directly verifies the superiority of the "single-cavity multimode cyclic filtering" technology of this invention and proves the effectiveness of the multimode resonant peak superposition effect and the multimode vernier caliper effect. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, this solution provides a single-cavity high extinction ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling, mainly comprising the following five core parts, which work together to achieve the function of "single-cavity multi-mode cyclic filtering": The bus waveguide is a wide silicon-based waveguide, specifically designed with a width of 1.2μm, capable of stably supporting multiple modes such as TE0, TE1, and TE2. The bus waveguide comprises an input section, a middle section, an output section, and a U-shaped loop waveguide. Tapered transition regions (with lengths adapted to optical signal coupling requirements) are provided at the connections to the mode converter and input / output ports to achieve low-loss transition and transmission of optical signals. The bus waveguide is arranged parallel to the multimode microring resonator, with the spacing matching the coupling gap of each resonant coupling region, ensuring efficient coupling of optical signals between them.

[0032] The multimode micro-ring resonator is located at the geometric center of the device and has a circular ring structure with a width of 1.2 μm, consistent with the bus waveguide, ensuring multimode coupling matching with the bus waveguide. This resonator supports resonant transmission in multiple modes, including TE0, TE1, and TE2, and is the core region for multiple resonant filtering of optical signals. It is made of SOI (silicon-on-insulator), possessing excellent optical performance and integration compatibility, meeting the requirements of silicon-based photonic integration.

[0033] The discrete microring resonant coupling regions are uniformly distributed along the perimeter of the multimode microring resonant cavity, including at least three independent resonant coupling regions (resonant coupling region 1, resonant coupling region 2, and resonant coupling region 3), corresponding to the coupling of TE0, TE1, and TE2 modes, respectively. Each coupling region provides a coupling path for the optical signal from the bus waveguide to the multimode microring resonant cavity. By independently optimizing the coupling gap of each region, the coupling coefficient of each mode is ensured to match its own loss coefficient, achieving critical coupling while avoiding intermode crosstalk.

[0034] The optical path loopback and mode converter module is a key component for realizing "optical signal foldback + mode conversion". It is located at both ends of the bus waveguide and at the U-shaped loopback waveguide, and includes multiple asymmetric directional couplers (mode converter 1-1, mode converter 1-2, mode converter 2-1, mode converter 2-2) and the U-shaped loopback waveguide. Specifically: Asymmetric directional couplers employ asymmetric coupling structures, such as... Figure 2 As shown, each coupler contains two bus waveguides with different widths (such as Wbus1 and Wbus2 of mode converter 1-1, and Wbus3 and Wbus4 of mode converter 2-1). By precisely adjusting the widths of the two waveguides, the corresponding phase matching conditions are met, and efficient conversion of specific modes is achieved. U-shaped loop waveguides are used to fold the mode-converted optical signal back to the corresponding segment of the bus waveguide, providing a physical path for the cyclic resonance of the optical signal and ensuring that the optical signal can sequentially pass through multiple resonant coupling regions to enter the same micro-ring resonant cavity.

[0035] The thermally tunable electrode is configured correspondingly to the multimode microring resonator, forming a single-electrode structure. It is used to adjust the refractive index parameter of the multimode microring resonator via Joule heating. Since different modes have different group refractive indices, their free spectral ranges (FSRs) have slight differences. Through precise adjustment of the thermally tunable electrode, the resonance peaks of the three modes TE0, TE1, and TE2 can be precisely overlapped at the operating wavelength (e.g., 1550 nm) while being offset at other wavelengths, thereby improving the signal-to-noise ratio.

[0036] In this scheme, the transmission of optical signals strictly follows a cyclic process of "three resonances + two mode conversions + one output". The specific workflow is as follows: 1. First-stage resonance (TE0): The input light enters the bus waveguide from the input port in the fundamental mode (TE0). After passing through the tapered transition region at the input end of the bus waveguide, it is transmitted to the first resonant coupling region (resonant coupling region 1). This region is specifically designed for TE0 mode coupling, allowing the TE0 mode in the bus waveguide to be efficiently coupled into the multimode microring resonant cavity. The optical signal resonates in the TE0 mode within the microring resonant cavity, and the resonant optical signal is output from the through port of the microring to the mode converter 1-1.

[0037] 2. First Mode Conversion: The TE0 mode optical signal output from the through port is shaped through a tapered transition zone before entering mode converter 1-1 (asymmetric directional coupler). For example... Figure 2 As shown, mode converter 1-1 adjusts the width W of the two bus waveguides. bus1 and W bus2 To satisfy the phase matching condition: n eff(Bus1,TE1) =n eff(Bus2,TE0) This allows for the efficient conversion of TE0 mode to TE1 mode.

[0038] 3. Second-stage resonance (TE1): The converted TE1 mode optical signal is folded back to the middle section of the bus waveguide through a U-shaped loop waveguide, and then transmitted to the second resonant coupling region (resonant coupling region 2). This region is adapted for TE1 mode coupling, and the optical signal is coupled again into the multimode micro-ring resonator in TE1 mode. After completing the second resonance within the ring, it is output from the through port. The output TE1 mode optical signal is converted to TE0 mode by mode converter 1-2, which has the same structure as mode converter 1-1, in preparation for the subsequent second mode conversion.

[0039] 4. Second Mode Conversion: The TE0 mode optical signal output from the previous stage is redirected through a U-shaped loop waveguide and, after passing through a tapered transition region, enters the new mode converter 2-1 (asymmetric directional coupler). For example... Figure 2 As shown, the mode converter 2-1 adjusts the width W of the two bus waveguides. bus3 and W bus4 The phase matching condition is satisfied: n eff(Bus4,TE2) =n eff(Bus3,TE0) This converts TE0 mode to TE2 mode.

[0040] 5. Third-stage resonance (TE2): The optical signal converted to TE2 mode is transmitted to the third resonant coupling region (resonant coupling region 3). This region is adapted for TE2 mode coupling, and the optical signal is coupled again into the multimode microring resonant cavity in TE2 mode, completing the third resonance. The resonant TE2 mode optical signal is output from the microring through port and converted to TE0 mode by mode converter 2-2, which has the same structure as mode converter 2-1, for subsequent output.

[0041] 6. Output: The final optical signal, converted to TE0 mode, passes through the tapered transition zone of the bus waveguide output section and is output from the output port. This optical signal undergoes three resonant superpositions of TE0, TE1, and TE2 modes to obtain a three-mode superimposed filtered transmission spectrum, achieving an ultra-high extinction ratio filtering effect.

[0042] The core parameters in this solution are designed as follows to ensure that all components work together to achieve the expected functions: 1. Waveguide material: Both the bus waveguide and the multimode microring resonator are made of SOI (silicon on insulator), and the thickness of the top silicon layer and the buried oxide layer are adapted to the requirements of silicon-based photonic integration process.

[0043] 2. Multimode microring resonator radius: The radius is set between 30μm and 60μm, which can be flexibly selected according to the actual filtering bandwidth and integration density requirements to ensure the stability of the resonant mode and the filtering performance.

[0044] 3. Asymmetric coupling waveguide width for mode converter: Input waveguide width: designed to be 200nm-600nm, which can be precisely adjusted according to mode conversion requirements (such as TE0→TE1, TE0→TE2); Output waveguide width: To match the same-mode resonant coupling of the multimode microring resonator, it is uniformly designed to be 1.28μm.

[0045] 4. Coupling gap optimization: Mode switching coupling gap: For different mode switching (TE0→TE1, TE0→TE2), the gap is set to Gap1 and Gap2 respectively, ranging from 20nm to 200nm. The phase matching condition is met by independent optimization, while improving the mode switching efficiency. Micro-ring resonant coupling gap: For coupling of different modes (TE0, TE1, TE2), the gaps are set to Gap3, Gap4, and Gap5 respectively, ranging from 90nm to 300nm. Independent optimization is performed to ensure critical coupling of each mode.

[0046] Explanation of the physical mechanism of this scheme: 1. Extinction Ratio Superposition Mechanism: One of the core physical mechanisms of this invention is the superposition effect of extinction ratios. After the optical signal passes through three resonances in TE0, TE1, and TE2 modes, the total transmittance satisfies the formula: T total ≈T TE0 ×T TE1 ×T TE2 (in T TE0 , TTE1 , T TE2 (These are the transmittances for TE0, TE1, and TE2 modes, respectively).

[0047] On the decibel scale, the total extinction ratio satisfies the formula: ER total ≈ER 1 + ER 2 + ER 3 (in ER 1 , ER 2 , ER 3 (These are the extinction ratios for TE0, TE1, and TE2 modes, respectively).

[0048] Through this superposition effect, even if the extinction ratio of a single mode is limited (such as 20dB for a traditional single-mode microring), the superposition of the three modes can achieve an ultra-high total extinction ratio of over 85dB.

[0049] 2. Vernier Effect (multimodal vernier caliper effect): such as Figure 3 and Figure 4 As shown, the three modes TE0, TE1, and TE2 have different group refractive indices, resulting in slight differences in their free spectral range (FSR). By finely adjusting the geometric parameters of the bus waveguide (such as its width) and the perimeter of the multimode microring resonator, a specific coincidence point can be designed at the operating wavelength (such as 1550 nm). This allows the resonance peaks of the three modes to precisely coincide at the operating wavelength while being offset from each other at other wavelengths, thereby effectively improving the signal-to-noise ratio of the filtered signal and further enhancing the filtering effect.

[0050] Figure 3 The effective refractive index matching diagram provides a theoretical basis for adjusting the waveguide width of the mode converter, ensuring that the phase matching condition is met; Figure 4 The simulation results comparison chart intuitively verifies this effect, showing that the extinction ratio of the three-mode superimposed filter transmission spectrum is significantly better than that of the single-mode filter transmission spectrum.

[0051] The above description is merely illustrative of the embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling, characterized in that, The application relates to a multi-mode micro-ring resonator, which comprises the following parts: a bus waveguide supporting TE0, TE1 and TE2 mode transmission and provided with a tapered transition area and a U-shaped loop waveguide; a multi-mode micro-ring resonant cavity matched with the bus waveguide, supporting TE0, TE1 and TE2 mode transmission and providing a resonant filter channel for an optical signal; a separate micro-ring resonant coupling area distributed along the circumference of the multi-mode micro-ring resonant cavity and comprising at least three independent resonant coupling areas matched with different modes respectively; an optical path loop and mode conversion module located at both ends of the bus waveguide and the U-shaped loop waveguide and comprising a plurality of asymmetric directional couplers, the asymmetric directional couplers satisfying a phase matching condition by adjusting the width of the two bus waveguides to realize mode conversion of the transmitted light, and the U-shaped loop waveguide being used for folding the mode-converted optical signal back to the bus waveguide; a thermal tuning electrode arranged correspondingly to the multi-mode micro-ring resonant cavity and used for adjusting the parameters of the multi-mode micro-ring resonant cavity so that the resonant peaks of different modes coincide at a working wavelength.

2. The single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling according to claim 1, characterized in that, The width of the bus waveguide is 1.2 mu m, the input waveguide width of the asymmetric directional coupler is 200 nm-600 nm, and the output waveguide width is 1.28 mu m.

3. The single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling according to claim 2, characterized in that, The mode conversion coupling gap of the asymmetric directional coupler is Gap1 and Gap2, and ranges between 20 nm and 200 nm and is independently optimized.

4. The single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling according to claim 3, characterized in that, The type of the asymmetric directional coupler is a directional coupling type, an adiabatic taper type or a multi-mode interference type.

5. The single-cavity high-extinction-ratio microring filter based on multi-mode multiplexing and asymmetric coupling of claim 1, wherein, The material of the multi-mode micro-ring resonant cavity is SOI, the radius ranges between 30 mu m and 60 mu m, and the width is 1.2 mu m.

6. The single-cavity high-extinction-ratio microring filter based on multi-mode multiplexing and asymmetric coupling according to claim 1, characterized in that, The resonant coupling gap of the separate micro-ring resonant coupling area is Gap3, Gap4 and Gap5, and ranges between 90 nm and 300 nm and is independently optimized.

7. The single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling according to claim 6, characterized in that, The coupling structure of the separate micro-ring resonant coupling area is a straight waveguide coupling or a curved waveguide coupling.

8. The single-cavity high-extinction-ratio microring filter based on multi-mode multiplexing and asymmetric coupling of claim 1, wherein, The transmission mode of the optical signal comprises a combination of double mode, triple mode or four mode and more modes, the number of the resonant coupling areas is matched with the number of the transmission modes.

9. The single-cavity high-extinction-ratio micro-ring filter based on multi-mode multiplexing and asymmetric coupling according to claim 8, characterized in that, The transmission polarization state of the optical signal is a TE mode or a TM mode.

10. The single-cavity high-extinction-ratio microring filter based on multimode multiplexing and asymmetric coupling of claim 1, wherein, The working wavelength is 1550 nm, and the free spectral range of the multi-mode micro-ring resonant cavity slightly differs with different modes.

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