D-type polymer microring resonator structure with fiber integrated and processing method

Abstract

The application discloses a D-shaped fiber integrated polymer double-ring microcavity Fano resonance structure and a processing method, and belongs to the field of all-fiber integrated optical devices. Two polymer WGM resonance cavities are respectively side-coupled to the two sides of a polymer micro-nano waveguide in a D-shaped single-mode optical fiber which is polished on the side, the two WGM resonance cavities are coupled as low-Q and high-Q microcavities respectively, controllable Fano resonance is generated, and the Q value of the D-shaped fiber integrated polymer double-ring microcavity Fano resonance structure is improved; the D-shaped fiber is prepared by using femtosecond laser ablation, the side wall is inclined, and the polymer WGM resonance cavity and the tapered waveguide are printed by using a femtosecond laser-induced two-photon polymerization technology (TPP). The flat area in the D-shaped fiber is used for accommodating the substrates of different kinds of optical elements, and the two ports of the D-shaped fiber are used for coupling the light in and out, so that the expandability of fiber direct integration equipment processing is significantly enhanced. The application has the advantages of high robustness, high expandability, high coupling efficiency, high compactness and high Q value.

Description

Technical Field

[0001] This invention belongs to the field of all-fiber integrated optical devices, and particularly relates to a D-type fiber integrated polymer double-ring microcavity Fano resonator structure and its fabrication method. Background Technology

[0002] Whispering-gallery (WGM) resonators are widely used in optical frequency combs, optical sensors, nonlinear optics, and optical modulators due to their high Q-value, small mode volume, strong optical field localization, and high sensitivity to the surrounding environment. WGM resonators forming Fano resonators can introduce novel phenomena and show promising applications in physics, chemistry, and biology. In recent years, on-chip integrated Fano resonator structures have been extensively studied due to their ease of integration, planar geometry, and high transmission efficiency. However, these devices typically require external input and output ports, increasing the complexity of Fano resonator integration.

[0003] The papers “Dynamic Fano Resonance in Thin Fiber Taper Coupled Cylindrical Microcavity” and “Fano resonance in a multimode tapered fiber coupled with a microspherical cavity” both propose WGM Fano resonance coupled with micro / nano fiber. The paper “Optical tentacle of suspended polymer micro-rings on a multicore fiber facet for vapor sensing” provides two-photon polymerization technology to fabricate micro / nano fiber integrated micro-ring structures. However, the size of micro / nano fibers makes tapered fibers relatively fragile, and micro / nano fibers are easily affected by the external environment. Adding optical components requires additional substrates, which increases the complexity of the structure. Alternatively, directly fabricating the structure onto the micro / nano fiber results in poor design flexibility and makes the structure even more fragile. The paper "In-fiber Mach–Zehnder interferometer and sphere whispering gallery moderesonator coupling structure" uses the core of a shallowly polished D-type fiber as a waveguide to couple a microcavity, and the sidewalls as a Mach-Zehnder interferometer to design an integrated Fano resonator structure. The paper "Integrated in-fiber coupler for awhispering-gallery mode microsphere resonator" places a sphere inside a single-mode fiber and uses different modes excited by a WGM resonator to generate Fano resonances, but the generation of these Fano resonances is difficult to control. Both designs use femtosecond laser ablation, resulting in rough surface textures, limited coupling efficiency and microcavity Q-value, and low scalability.

[0004] The above research shows that achieving direct integration of Fano resonances with optical fibers through simple coupling methods remains a challenging task. Summary of the Invention

[0005] To achieve the above requirements, the main objective of this invention is to provide a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure and its fabrication method. Two polymer WGM resonator cavities are respectively side-coupled to both sides of a polymer micro / nano waveguide in a side-polished D-type single-mode fiber. The two WGM resonator cavities serve as low-Q and high-Q microcavities, respectively, generating controllable Fano resonance and improving the Q-value of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure. The D-type fiber is fabricated using femtosecond laser ablation with tilted sidewalls. The polymer WGM resonator cavities and the tapered waveguide are printed using femtosecond laser-induced two-photon polymerization (TPP) technology. The flat region in the D-type fiber serves as a substrate to accommodate different types of optical components, and the two ports of the D-type fiber are used for coupling light in and out, significantly enhancing the scalability of fiber-to-optic direct integration equipment fabrication. This invention has the advantages of high robustness, high scalability, high coupling efficiency, high compactness, and high Q-value.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] This invention discloses a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure. Two polymer WGM resonator cavities are respectively side-coupled to both sides of a polymer micro / nano waveguide in a side-polished D-type single-mode fiber. The two WGM resonator cavities serve as low-Q and high-Q microcavity couplings, respectively. Controllable Fano resonance is generated by adjusting the size and position of the WGM resonator microrings. The sidewall tilt angle of the polished region of the D-type fiber and the graded region of the tapered polymer fiber are used to improve the coupling efficiency from the fiber core to the micro / nano waveguide. The flat region in the D-type fiber is used as a substrate to accommodate different types of optical components, and the two ports of the D-type fiber are used for coupling light in and out.

[0008] The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure disclosed in this invention is as follows:

[0009] Step 1: Femtosecond laser ablation is used to polish the side surfaces of single-mode fiber, fabricating a D-type single-mode fiber. The D-type single-mode fiber is polished to a depth of 71μm–73μm, fully exposing the fiber core while preserving a sufficiently flat polished surface area as a substrate. The sidewalls at both ends of the polished area are angled, facilitating fabrication while improving the coupling efficiency between the fiber core and the tapered waveguide.

[0010] Preferably, in step one, the polishing depth of the D-type single-mode fiber is 72.5 μm.

[0011] Step 2: Immerse the polished area in photoresist and dry it.

[0012] Step 3: Using femtosecond laser two-photon polymerization technology, a dual micro-ring resonator and a tapered waveguide coupled to the microcavity are printed in the polished area. The waveguide cross-section connecting the sidewalls of the polished area is 6μm~9μm×19μm~21μm, balancing mode matching between the waveguide and the fiber core and the number of higher-order excited modes in the waveguide, to improve the transmission efficiency of the waveguide and the fiber core. The tapered gradient region has a length of 10μm~20μm to reduce losses caused by mode mismatch. Before the gradient is completed, the waveguide is attached to the polished substrate, and the width of the waveguide cross-section perpendicular to the substrate remains unchanged to ensure the stability of the waveguide. After the gradient, the waveguide cross-section is 0.6μm~1μm×8μm~10μm. The micro / nano waveguide is suspended by the waveguide in the gradient region. Utilizing the strong optical field localization characteristics of the micro / nano fiber waveguide, the gradient waveguide is suitable for coupling with the micro-ring resonator. The two microring resonators have outer diameters of 40 μm and 10 μm, respectively, with their centers spaced 0 μm apart in the direction perpendicular to the waveguide. The spacing between the two microrings and the waveguide is 0.3 μm to 0.6 μm and 0 μm, respectively. Different spacings are selected to ensure adequate coupling with the waveguide, taking into account the coupling capabilities of different microrings. The cross-section of the microring resonators is 2 μm to 4 μm × 19 μm to 21 μm, minimizing the generation of higher-order modes while ensuring structural stability.

[0013] Preferably, the waveguide cross-section connecting the sidewalls of the polished region is 6μm × 20μm. The length of the tapered gradient region is 10μm. The cross-section of the waveguide after the gradient is 1μm × 10μm. The outer diameters of the two microring resonators are 40μm and 10μm, respectively, and the distance between their centers in the direction perpendicular to the waveguide is 0. The spacing between the two microrings and the waveguide is 0.5μm and 0μm, respectively. The cross-section of the microring resonator is 3μm × 20μm, which reduces the generation of higher-order modes while ensuring structural stability. The structural schematic diagram is shown below. Figure 1 .

[0014] Step 4: Immerse the optical fiber in alcohol to remove the uncured photoresist and obtain the processed D-type optical fiber integrated polymer double-ring microcavity Fano resonant structure.

[0015] Furthermore, the intrinsic mode expansion method is used to optimize the sidewall tilt angle of the polished region of the D-type fiber and the length of the tapered waveguide gradient region, thereby improving the coupling efficiency from the fiber core to the micro / nano waveguide.

[0016] The coupling efficiency mainly depends on the overlap integral formula of the waveguide cross-section optical field distribution of each cell in the simulation. The overlap integral formula is as follows:

[0017]

[0018] in and These are the electric and magnetic field distributions of the m-th mode in cell 1 and the n-th mode in cell 2, respectively, in two adjacent cells. This is the simulation region along the waveguide cross-section. The final transmission transmittance is optimized through continuous iteration.

[0019] Furthermore, the optimization method for coupling between the micro-ring resonator and the tapered waveguide is as follows: the distance between the micro / nano waveguide and the micro-ring resonator determines their coupling efficiency, and the length of the micro / nano waveguide determines the fabrication stability and robustness of the coupling structure.

[0020] The distance between the micro / nano waveguide and the micro-ring resonator depends on the following formula:

[0021]

[0022] Where Q0 is the intrinsic quality factor of the microcavity, Q ex It is the quality factor generated after the introduction of the waveguide, and the total quality factor Q of the structure after coupling the microcavity and the waveguide. tot The relationship is:

[0023]

[0024] The intrinsic quality factor Q0 of the microring resonator was calculated using the variational finite-difference time method (varFDTD), and the overall quality factor Q of the structure after coupling the microcavity and waveguide at different spacings was also calculated. tot When Q0 = 2Q tot The highest coupling efficiency is achieved at this point, and the distance between the microcavity and the waveguide at this point is the optimal distance D1.

[0025] Furthermore, the method for determining the shortest length of a micro / nano waveguide is as follows:

[0026] Micro- and nano-waveguide structures are fragile; excessively long micro- and nano-waveguides are prone to deformation during fabrication and breakage after fabrication. Therefore, when coupling with microcavities, the shortest possible micro- and nano-waveguide length should be selected. The distance between the waveguide's gradient region and the micro-ring should be sufficiently large to prevent coupling between the gradient region and the micro-ring. The electric field distribution of the waveguide mode outside the waveguide is calculated using the finite difference method (FDE) of intrinsic modes. Based on the electric field distribution, a suitable minimum length L of the micro- and nano-waveguide is determined. According to geometric relationships, when the outer radius of the micro-ring is R and the width of the micro- and nano-waveguide cross-section is W, the minimum length L of the micro- and nano-waveguide is calculated as follows:

[0027] when hour

[0028]

[0029] when hour

[0030]

[0031] Where D1 is the distance from the micro-ring resonator to the micro / nano waveguide, W1 is the cross-sectional width of the wide waveguide, and L1 is the length of the tapered gradient region of the waveguide.

[0032] Beneficial effects:

[0033] 1. This invention discloses a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure and its fabrication method. Two polymer WGM resonator cavities are respectively side-coupled to both sides of a polymer micro / nano waveguide in a side-polished D-type single-mode fiber. The two WGM resonator cavities serve as low-Q and high-Q microcavities, respectively, to generate controllable Fano resonance, thereby improving the Q value of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure to 2.85 × 10⁻⁶. 4 .

[0034] 2. This invention discloses a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure and its fabrication method. The two WGM resonators are used as low-Q and high-Q microcavities for coupling, respectively. Controllable Fano resonance is generated by adjusting the size and position of the microrings in the WGM resonators. With the help of waveguides, the size and position of the two microrings have a good degree of freedom, which significantly improves the design flexibility of fiber-integrated coupled microring resonators.

[0035] 3. The present invention discloses a D-type fiber integrated polymer dual-ring microcavity Fano resonator structure and its fabrication method. The flat region in the D-type fiber is used as a substrate to accommodate different types of optical elements. The polished region of the D-type fiber is used as the substrate of the optical structure, which significantly enhances the scalability of the fiber direct integration equipment.

[0036] 4. The present invention discloses a D-type fiber integrated polymer double-ring microcavity Fano resonator structure and its fabrication method, wherein a tapered gradient region is added to the waveguide, which significantly improves the coupling efficiency between the fiber core and the tapered waveguide.

[0037] 5. The present invention discloses a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure and its fabrication method. The micro / nano waveguide is supported by a gradient region waveguide to achieve suspension. After the gradient, the waveguide is suspended, which can reduce mode crosstalk.

[0038] 6. The present invention discloses a D-type fiber integrated polymer double-ring microcavity Fano resonator structure and its processing method. The D-type fiber is prepared by femtosecond laser ablation. The sidewall of the D-type fiber is inclined, which makes it easier to process by laser. The polymer WGM resonator and the tapered waveguide are printed by femtosecond laser-induced two-photon polymerization (TPP) technology, which has the advantage of being easy to implement. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure.

[0040] Figure 2This is a geometric diagram showing the relationship between the microring resonator and the tapered waveguide. Where R is the outer radius of the microring, W is the width of the micro / nano waveguide cross-section, L is the length of the micro / nano waveguide, D1 is the distance from the microring resonator to the micro / nano waveguide, D2 is the spacing between the microring and the tapered waveguide, W1 is the cross-sectional width of the wide waveguide, L1 is the length of the tapered transition region of the waveguide, and W2 = (W1 - W) / 2.

[0041] Figure 3 These are the transmission spectra of a 40μm diameter microring resonator with cross-sectional widths of 1, 2, 3, 4, 5, and 6μm.

[0042] Figure 4 (a) is a diagram showing the electric field distribution across the cross section of a micro / nano waveguide.

[0043] Figure 4 (b) is the electric field distribution diagram of the wide waveguide cross section.

[0044] Figure 5 This is a femtosecond laser processing trajectory diagram of a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure.

[0045] Figure 6 This is a confocal microscopy image of a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure.

[0046] Figure 7 This is a simulated transmission transmission spectrum of a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure and an enlarged image of the resonant transmission near a wavelength of 1568 nm. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] Example 1:

[0049] like Figure 1As shown in this embodiment, a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure is disclosed. Two polymer WGM resonator cavities are respectively side-coupled to both sides of the polymer micro / nano waveguide in a side-polished D-type single-mode fiber. The two WGM resonator cavities serve as low-Q and high-Q microcavity couplings, respectively. Controllable Fano resonance is generated by adjusting the size and position of the WGM resonator microrings. The sidewall tilt angle of the polished region of the D-type fiber and the graded region of the tapered polymer fiber are used to improve the coupling efficiency from the fiber core to the micro / nano waveguide. The flat region in the D-type fiber is used as a substrate to accommodate different types of optical components, and the two ports of the D-type fiber are used for coupling light in and out. The outer diameters of the two microring resonator cavities are 40 μm and 10 μm, respectively, and the cross-sections are both 3 μm × 20 μm. The distance between the centers of the two microrings in the direction perpendicular to the waveguide is 0, and the spacing between the two microrings and the waveguide is 0.5 μm and 0 μm, respectively.

[0050] Taking advantage of the inherent substrate of D-type optical fiber, a double-ring microcavity Fano resonator structure directly integrated with optical fiber is realized by using a method of coupling microcavities with different Q values ​​to micro / nano waveguides.

[0051] The D-shaped fiber has inclined sidewalls, making it easier to process with lasers. EME calculations were used to optimize the parameters of the tapered waveguide structure in the D-shaped fiber. The polishing depth was 72.5 μm, and the wide waveguide cross-section connecting the polished sidewalls was 6 μm × 20 μm to improve coupling efficiency with the fiber core. The tapered gradient region was 10 μm long to reduce losses caused by mode mismatch. Before the gradient was completed, the waveguide was attached to the polished substrate, and the waveguide cross-section width perpendicular to the substrate remained unchanged to ensure waveguide stability. After the gradient, the waveguide cross-section was 1 μm × 10 μm, suitable for 50x objective-focused femtosecond laser-guided two-photon polymerization processing. The gradient-suspended waveguide exhibited the strong optical field localization characteristics of micro / nano waveguides.

[0052] To achieve Fano resonance, the outer diameters of the two microrings are 10 μm and 40 μm, respectively, to enable coupling between the high-Q and low-Q microcavities. The generation of higher-order modes in the 40 μm outer diameter microring under different cross-sectional widths is analyzed using varFDTD calculations. Figure 3 The transmission spectra are shown for cross-sectional widths of 1, 2, 3, 4, 5, and 6 μm. Considering the structural strength, it is shown that a cross-sectional width in the range of 2 μm to 4 μm can reduce the generation of higher-order modes while maintaining high structural robustness, with a width of 3 μm being the preferred option.

[0053] The spacing between the microring and the micro / nano waveguide was calculated and analyzed using varFDTD. The cross-sectional width of the microring was set to 3 μm. Since the 10 μm outer diameter microring is a low-Q microcavity, its spacing with the waveguide was set to 0 μm. The inherent quality factor Q0 of the 40 μm outer diameter microring and the total quality factor Q of the structure coupled with different spacings between the microcavity and the waveguide were calculated. totThe optimal coupling distance was found to be approximately 0.5 μm. The two WGM resonant cavities were used as low-Q and high-Q microcavities for coupling, respectively, to generate a controllable Fano resonance with a Q value reaching 2.85 × 10⁻⁶. 4 .

[0054] Calculate the shortest length of micro / nano waveguides using FDE. Figure 4 As shown in the electric field distribution, the smaller the waveguide width, the larger the spatial distribution of the optical field outside the waveguide. The electric field strength is already less than 10 when the optical field is 4 μm away from the edge of the micro / nano waveguide section. -12 Its coupling strength to the microcavity is negligible, therefore D2 = 4μm. The shortest length of the micro / nano waveguide is calculated to be 25.0 μm.

[0055] Example 2:

[0056] The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure disclosed in this embodiment is as follows: a tapered polymer waveguide is side-coupled to the D-type single-mode fiber dual-microring resonator cavity.

[0057] Sample preparation: Use double-sided tape to attach the cut silicon wafer to the glass slide to improve the quality of reflective imaging during femtosecond laser processing. Secure the optical fiber to the silicon wafer using high-temperature resistant tape.

[0058] Femtosecond laser ablation fabrication of tilted D-type single-mode fiber: A femtosecond laser, after frequency doubling by an OPA crystal, generates a 515nm Gaussian beam. An electrically driven attenuator and an electronic shutter adjust the energy and control the laser's on / off state, respectively. A 20X objective lens is used for focusing. The sample is placed on a moving stage, with the focal plane positioned on the upper surface of the fiber cylinder. The laser is vertically scanned perpendicular to the single-mode fiber's extension direction, with a laser power of 8mW, a scanning speed of 1mm / s, and a spacing of 1μm between adjacent tracks. After each layer is scanned, the focal plane is moved downwards by 2μm perpendicular to the fiber core, for a total of 35 layers scanned. The processed sample is cleaned with deionized water in an ultrasonic cleaner for 5 minutes, then removed and air-dried.

[0059] Polymer waveguide on a D-type fiber surface fabricated by two-photon polymerization and micro-ring resonators on both sides:

[0060] SZ2080 photoresist was applied to the D-shaped fiber area polished by a femtosecond laser using a dropper, and a coverslip was placed on top. The area was then placed in a furnace at 95 degrees Celsius for one hour to remove moisture. The 1030nm Gaussian beam generated by the femtosecond laser was controlled by an electrically operated attenuator and an electronic shutter to regulate energy and control laser on / off. A 50X objective lens was used for focusing. The sample was placed on a moving stage with the polished D-shaped fiber surface positioned at the focal plane. The processing trajectory was designed using the optimized parameters from Example 1 as follows: Figure 5The structure was printed using this method. For ease of design, the micro / nano waveguide was designed with a length of 50 μm. The laser power was 4 mW, the scanning speed was 0.2 mm / s, and the spacing between adjacent tracks was 0.3 μm. After scanning, the sample was immersed in alcohol to completely remove any uncured photoresist, resulting in a D-type single-mode fiber tapered waveguide and a dual-microring resonant cavity side-coupled integrated structure sample, as shown below. Figure 6 The structural transmission simulation results are as follows: Figure 7 .

[0061] A Light Conversion pH2 femtosecond laser with a Gaussian intensity distribution, a wavelength of 1030 nm, and a repetition rate of 200 kHz was used. Both the 20X and 50X objectives were Olympus achromatic reflection imaging objectives.

[0062] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., 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 method for fabricating a D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure, characterized in that: Includes the following steps, Step 1: Use femtosecond laser ablation to polish the side of single-mode fiber to form D-type single-mode fiber; polish the D-type single-mode fiber to fully expose the fiber core and retain a sufficiently flat polished surface area as a substrate; the sidewalls at both ends of the polished area are processed with an inclination angle to facilitate processing and improve the coupling efficiency between the waveguide fiber core and the tapered waveguide. Step 2: Immerse the polished area in photoresist and dry it; Step 3: Using femtosecond laser two-photon polymerization technology, a dual micro-ring resonant cavity and a tapered waveguide coupled to the microcavity are printed in the polished area; The waveguide cross-section connecting the sidewalls of the polished region is 6μm~9μm×19μm~21μm, balancing mode matching between the waveguide and the fiber core coupling with the number of higher-order modes excited in the waveguide, thus improving the transmission efficiency of the fiber core and polymer waveguide. The tapered gradient region has a length of 10μm~20μm to reduce losses caused by mode mismatch. Before the gradient is completed, the waveguide is attached to the polished substrate, and the waveguide cross-sectional width perpendicular to the substrate remains unchanged to ensure the stability of the waveguide. After the gradient, the waveguide cross-section is 0.6μm~1μm×8μm~10μm. The micro / nano waveguide is formed by the gradient region. The waveguide provides support to achieve suspension. Utilizing the strong optical field localization characteristics of the graded waveguide, which is similar to micro / nano fiber waveguides, the graded waveguide is suitable for coupling with micro-ring resonators. The outer diameters of the two micro-ring resonators are 40 μm and 10 μm, respectively, and the distance between their centers in the direction perpendicular to the waveguide is 0. The spacing between the two micro-rings and the waveguide is 0.3 μm to 0.6 μm and 0 μm, respectively. Different spacings are selected according to the coupling capabilities of different micro-cavities to ensure an appropriate coupling effect with the waveguide. The cross-section of the micro-ring resonators is 2 μm to 4 μm × 19 μm to 21 μm, which reduces the generation of higher-order modes while ensuring structural stability. Step 4: Immerse the optical fiber in alcohol to remove the uncured photoresist and obtain the processed D-type optical fiber integrated polymer double-ring microcavity Fano resonant structure; The D-type fiber integrated polymer dual-ring microcavity Fano resonant structure has two polymer WGM resonant cavities that are respectively side-coupled to both sides of the polymer micro / nano waveguide in the side-polished D-type single-mode fiber. The two WGM resonant cavities are respectively used as low-Q and high-Q microcavities for coupling. Controllable Fano resonance is generated by adjusting the size and position of the WGM resonant cavity microrings. The sidewall tilt angle of the polished region of the D-type fiber and the gradient region of the tapered polymer fiber are used to improve the coupling efficiency from the fiber core to the micro / nano waveguide; the flat region in the D-type fiber is used to accommodate substrates for different types of optical elements, and the two ports of the D-type fiber are used for coupling light in and out.

2. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 1, characterized in that: The outer diameters of the two microring resonators are 40 μm and 10 μm, respectively, and the cross-sections are both 2 μm to 4 μm × 19 μm to 21 μm. The distance between the centers of the two microrings in the direction perpendicular to the waveguide is 0. The spacing between the two microrings and the waveguide is 0.3 μm to 0.6 μm and 0 μm, respectively.

3. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 1, characterized in that: In step one, the polishing depth of the D-type single-mode fiber is 71μm to 73μm.

4. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 1, characterized in that: The waveguide cross-section connecting the sidewalls of the polished region is 6μm~9μm×19μm~21μm; the length of the tapered gradient region is 10μm~20μm; the cross-section of the gradient waveguide is 0.6μm~1μm×8μm~10μm; the outer diameters of the two microring resonators are 40μm and 10μm, respectively, and the distance between their centers in the direction perpendicular to the waveguide is 0. The spacing between the two microrings and the waveguide is 0.3μm~0.6μm and 0μm, respectively; the cross-section of the microring resonator is 3μm×20μm, which reduces the generation of higher-order modes while ensuring structural stability.

5. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 1, characterized in that: The intrinsic mode expansion method is used to optimize the sidewall tilt angle of the polished region of D-type fiber and the length of the graded region of tapered fiber, thereby improving the coupling efficiency from the fiber core to the micro / nano waveguide. The coupling efficiency mainly depends on the overlap integral formula of the waveguide cross-section optical field distribution of each cell in the simulation. The overlap integral formula is as follows: in and These are the electric and magnetic field distributions of the m-th mode in cell 1 and the n-th mode in cell 2, respectively, in two adjacent cells. It is the simulation region along the waveguide cross-section; the final transmission transmittance is optimized through continuous iteration.

6. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 5, characterized in that: The optimization method for coupling between micro-ring resonators and tapered waveguides is as follows: the distance between the micro / nano waveguide and the micro-ring resonator determines their coupling efficiency, and the length of the micro / nano waveguide determines the fabrication stability and robustness of the coupling structure. The distance between the micro / nano waveguide and the micro-ring resonator depends on the following formula: Where Q0 is the intrinsic quality factor of the microcavity, Q ex It is the quality factor generated after the introduction of the waveguide, and the total quality factor Q of the structure after coupling the microcavity and the waveguide. tot The relationship is: The intrinsic quality factor Q0 of the microring resonator was calculated using the variational finite-difference time method (varFDTD), and the overall quality factor Q of the structure after coupling the microcavity and waveguide at different spacings was also calculated. tot When Q0 = 2Q tot The highest coupling efficiency is achieved at this point, and the distance between the microcavity and the waveguide at this point is the optimal distance D1.

7. The fabrication method of the D-type fiber-integrated polymer dual-ring microcavity Fano resonator structure as described in claim 6, characterized in that: The method for determining the shortest length of micro / nano waveguides is as follows: Micro- and nano-waveguide structures are fragile; excessively long micro- and nano-waveguides are prone to deformation during fabrication and breakage after fabrication. Therefore, when coupling with microcavities, the shortest possible micro- and nano-waveguide length should be selected. The distance between the waveguide gradient region and the micro-ring should be sufficiently large to prevent coupling between the gradient region and the micro-ring. The electric field distribution of the waveguide mode outside the waveguide is calculated using the intrinsic mode finite difference method (FDE). Based on the electric field distribution, a suitable spacing D2 between the micro-ring and the tapered waveguide is determined. According to geometric relationships, when the outer radius of the micro-ring is R and the width of the micro- and nano-waveguide cross-section is W, the formula for calculating the shortest length L of the micro- and nano-waveguide is as follows: when hour when hour Where D1 is the distance from the micro-ring resonator to the micro / nano waveguide, W1 is the cross-sectional width of the wide waveguide, L1 is the length of the tapered gradient region of the waveguide, and W2 = (W1 - W) / 2.

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