Ultra-small size ultra-large free spectral range filter based on nanobeam cavity

Abstract

This invention discloses an ultra-small size, ultra-large free spectral range filter based on a nanobeam resonator. The structure includes a side-coupled waveguide consisting of an incident waveguide, a coupled waveguide, and an outgoing waveguide connected sequentially, and a left Bragg mirror aperture array, a tapered aperture array, a reverse tapered aperture array, and a right Bragg mirror aperture array located on the nanobeam waveguide. The periods of the left and right Bragg mirror aperture arrays are different, and the Bragg overlap band formed by them satisfies certain conditions with the free spectral range of the nanobeam resonator. This invention combines a waveguide coupler with an asymmetric nanobeam resonator. By adjusting the Bragg overlap band formed by the left and right Bragg mirrors to be smaller than the free spectral range of the nanobeam resonator, full-spectrum single-mode excitation can be achieved, thereby realizing single-channel signal filtering.

Description

Technical Field

[0001] This invention relates to the field of optical filters, specifically to an ultra-small size ultra-large free spectral range filter based on a nanobeam resonator. Background Technology

[0002] Wavelength division multiplexing (WDM) technology refers to the use of multiple wavelengths of light in a shared channel to increase optical communication capacity. It has been considered a classic technology for both long-distance and short-distance optical communication for decades. It provides an optimal solution for ultra-high-capacity data transmission and is adopted not only by operators and service providers but also by enterprises, organizations, and data centers. Optical filters have played a significant role in the development of WDM technology, activating various information processing fields. For example, integrating multiple optical filters on a single optical link allows for the individual modulation or processing of different wavelength channels. This multi-wavelength modulation can significantly improve optical communication capacity or increase the speed and energy efficiency of optical parallel computing. Furthermore, WDM technology may lead to many new multi-site and multi-parameter optical sensing applications. By arranging sensing units operating at different wavelengths according to specific rules, spatial distribution information of various physical quantities such as temperature, concentration, strain, and even ultrasound can be retrieved, achieving quasi-distributed sensing.

[0003] A key challenge is achieving a compact optical filter with an ultra-wide free spectral range. A larger free spectral range means supporting more independent wavelength channels without interference between them. Using a filter with a large free spectral range can effectively increase the number of independent sensors on a single sensing link, enabling simultaneous sensing of more sites and multiple parameters. Extensive research has already been conducted on this topic. Traditional approaches, including Bragg grating waveguides, Bragg grating-assisted reverse couplers, and cascaded microring resonators with vernier effects, suffer from unsatisfactory performance in terms of bandwidth, device size, and manufacturing tolerance. Side-coupled Bragg grating-assisted FP cavities can reduce the free spectral range of the Bragg emitter mirror to less than that of the FP cavity by compressing its stopband. However, this approach, which compresses the stopband of the Bragg emitter mirror by reducing the grating intensity, requires more periods to achieve high reflectivity, resulting in a filter length typically >100 μm. An ideal integrated filter should fully utilize the bandwidth advantage of the optics, featuring small size, a large free spectral range, high suppression ratio, and large manufacturing tolerance to avoid precise wavelength alignment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes an ultra-small size ultra-large free spectral range filter based on a nanobeam resonant cavity. This filter structure can not only achieve single-channel signal filtering over a wide spectral range, but also has a size much smaller than existing infinite free spectral range filters.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An ultra-small size, ultra-large free spectral range filter based on a nanobeam resonator is proposed. The filter structure is asymmetrical, comprising an incident waveguide, an outgoing waveguide, a coupling waveguide, a nanobeam waveguide, a left Bragg mirror aperture array, a right Bragg mirror aperture array, a tapered gradient aperture array, and a reverse tapered gradient aperture array, wherein:

[0007] The incident waveguide, coupling waveguide, and output waveguide are connected in sequence.

[0008] The left Bragg mirror aperture array, the tapered gradient aperture array, the reverse tapered gradient aperture array, and the right Bragg mirror aperture array are sequentially arranged on the nanobeam waveguide; the left Bragg mirror aperture array, the tapered gradient aperture array, the reverse tapered gradient aperture array, and the right Bragg mirror aperture array are all periodic structures, the periods of the left Bragg mirror aperture array and the right Bragg mirror aperture array are different, and the periods of the tapered gradient aperture array and the reverse tapered gradient aperture array are gradual.

[0009] The lowest point of the coupled waveguide is close to the connection point of the tapered gradient aperture array and the reverse tapered gradient aperture array and there is a gap between it and the connection point, forming a side-coupled waveguide structure.

[0010] The left Bragg mirror aperture array, the tapered gradient aperture array, the reverse tapered gradient aperture array, and the right Bragg mirror aperture array together constitute a nanobeam FP resonant cavity.

[0011] The overlap value of the Bragg bandgap bandwidths of the left and right Bragg mirror aperture arrays is Δλ. over The free spectral range (FSR) of the nanobeam FP resonant cavity FP Both must meet one of the following conditions:

[0012] Condition 1: Δλ over <2FSR FP Furthermore, the resonant wavelength of the nanobeam FP resonant cavity is close to the middle of the bandgap overlap of the left Bragg mirror aperture array and the right Bragg mirror aperture array;

[0013] Condition 2: Δλ over ≤FSR FP Furthermore, the resonant wavelength of the nanobeam FP resonant cavity is close to the edge of the overlapping band of the left and right Bragg mirror aperture arrays.

[0014] Furthermore, the period and duty cycle of the tapered gradient hole array and the reverse tapered gradient hole array both follow the variation law of the gradient function, which is selected from any one of the linear function, quadratic function, Gaussian function, and Lorentz function.

[0015] Furthermore, the number of the tapered gradient aperture array and the reverse tapered gradient aperture array needs to be adjusted according to the period of the left Bragg mirror aperture array and the right Bragg mirror aperture array, as well as the gradient function used, so as to minimize the scattering loss at the reflective cavity interface and improve the quality factor of the filter.

[0016] Furthermore, Δλ over With FSR FP The implementation method that satisfies either condition one or condition two is as follows:

[0017] First, ensure that the left and right Bragg mirror aperture arrays have the same period, then gradually increase the period of either the left or right Bragg mirror aperture array, so that the nanobeam FP cavity has only one resonant mode.

[0018] Furthermore, the nanobeam waveguide is a straight waveguide, and the coupling waveguide is a curved waveguide; or, the nanobeam waveguide is a curved waveguide, and the coupling waveguide is a straight waveguide.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The ultra-small size ultra-large free spectral range filter based on nanobeam resonator of the present invention achieves ultra-large free spectral range operation and sub-nanometer optical bandwidth by adjusting the bandgap bandwidth of nanobeam FP resonator through the use of asymmetric Bragg mirror aperture array. It can support more independent wavelength channels and the channels do not interfere with each other.

[0021] (2) By using a Bragg mirror aperture array, the reflectivity of the Bragg mirror is improved, thereby reducing the size of the filter.

[0022] (3) The ultra-small size ultra-large free spectral range filter based on nanobeam resonator of the present invention has great application value in the fields of optical communication and distributed sensing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a filter structure with an ultra-large free spectral range according to Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram illustrating the working principle of a filter with an ultra-wide free spectral range according to Embodiment 1 of the present invention.

[0025] Figure 3 This diagram illustrates the transmittance of the filter in Example 1 within the 1300-1650nm wavelength range. The left Bragg mirror array has a fixed period of 340nm, while the right Bragg mirror array has periods of 340nm, 360nm, 380nm, 400nm, 420nm, and 480nm, respectively. The solid gray line represents the left Bragg bandgap, and the dashed gray line represents the right Bragg bandgap.

[0026] Figure 4 This is a schematic diagram of the simulated electric field distribution at 1400nm, 1460nm, 1513.76nm, 1540nm, and 1600nm for the filter (with a 420nm periodic array of Bragg mirrors on the right) that implements single-longitudinal-mode excitation in Example 1. The white arrows indicate the direction of the injected light.

[0027] Figure 5 This is a schematic diagram of the filter structure with an ultra-large free spectral range, as shown in Comparative Example 1.

[0028] Figure 6 This is a schematic diagram of the filter structure with an ultra-large free spectral range, as shown in Comparative Example 2.

[0029] Figure 7 This is a schematic diagram of the filter structure with an ultra-large free spectral range in Example 2;

[0030] Figure 8 This is a schematic diagram of the filter structure with an ultra-large free spectral range in Example 3. Detailed Implementation

[0031] The present invention, an ultra-small size ultra-large free spectral range filter based on a nanobeam resonator, will be described in more detail below with reference to schematic diagrams, wherein the schematic diagrams illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving the advantageous effects of the invention. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0032] In the description of this invention, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0033] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0034] like Figure 1 As shown, the ultra-small size ultra-large free spectral range filter based on nanobeam resonator of the present invention includes an incident waveguide 101, an outgoing waveguide 102, a coupling waveguide 103, a nanobeam waveguide 104, a left Bragg mirror aperture array 105, a right Bragg mirror aperture array 106, a tapered gradient aperture array 107, and a reverse tapered gradient aperture array 108.

[0035] The incident waveguide 101, coupling waveguide 103, and exit waveguide 102 are connected in sequence. The left Bragg mirror aperture array 105, the tapered aperture array 107, the reverse tapered aperture array 108, and the right Bragg mirror aperture array 106 are connected in sequence and arranged on the nanobeam waveguide 104. Preferably, the four aperture arrays are coaxially arranged on the nanobeam waveguide 104, collectively forming a nanobeam FP resonant cavity. The lowest point of the coupling waveguide 103 is close to the connection point of the tapered aperture array 107 and the reverse tapered aperture array 108, with a gap between them, forming a side-coupled waveguide structure.

[0036] Furthermore, the incident waveguide 101, coupling waveguide 103, outgoing waveguide 102, and nanobeam waveguide 104 are all single-mode waveguides, and the left Bragg mirror aperture array 105, tapered gradient aperture array 107, reverse tapered gradient aperture array 108, and right Bragg mirror aperture array 106 are all periodic structures. The periods of the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106 are different, while the periods of the tapered gradient aperture array 107 and the reverse tapered gradient aperture array 108 are gradual.

[0037] Preferably, the period and duty cycle of the tapered gradient aperture array 107 and the reverse tapered gradient aperture array 108 both follow the variation law of a gradient function, which is selected from any one of a linear function, a quadratic function, a Gaussian function, and a Lorentz function. The number of arrays of the tapered gradient aperture array 107 and the reverse tapered gradient aperture array 108 needs to be adjusted according to the period of the left Bragg reflector aperture array 105 and the right Bragg reflector aperture array 106, respectively, and the gradient function used, so as to minimize the scattering loss at the reflector cavity interface and improve the quality factor of the filter.

[0038] Specifically, during filter operation, laser light is injected into the incident waveguide 101 of the filter, and then coupled to the nanobeam FP resonant cavity via the coupling waveguide 103. Non-resonant wavelengths are coupled from the nanobeam FP resonant cavity to the output waveguide 102, while resonant wavelengths are coupled into and amplified within the nanobeam FP resonant cavity until the input power, external coupling power, and cavity loss power reach a dynamic equilibrium. The light appears confined by the cavity and cannot couple from the nanobeam FP resonant cavity to the output waveguide 102, thus achieving filtering of specific wavelengths of light. By introducing a tapered aperture array 107 and a reverse tapered aperture array 108 between the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106, the mode mismatch between the two arrays is reduced, thereby reducing intracavity loss, suppressing sideband jitter, and increasing the quality factor of the resonant cavity. Specifically, by controlling the gradient functions of the period and duty cycle of the tapered gradient aperture array 107 and the reverse tapered gradient aperture array 108, as well as the number of aperture arrays, the mode fields of the gradient regions on both sides are made as symmetrical as possible, thus minimizing scattering losses at the reflective cavity interface. By controlling the periods of the left Bragg reflector aperture array 105 and the right Bragg reflector aperture array 106, the overlap of the Bragg bandgap on both sides can be freely adjusted. For example... Figure 2 As shown, if the overlap band of the band gaps of the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106 is smaller than the free spectral range of the nanobeam FP resonant cavity, only one longitudinal mode can operate in this resonant cavity, thus realizing a filter with a single peak or single valley across the entire spectral range and an ultra-large free spectral range. Wherein, Δλ over The FSR represents the overlap value of the Bragg bandgap of the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106. FP For the free spectral range of the FP cavity, both must satisfy one of the following conditions:

[0039] Condition 1: Δλ over <2FSR FP Furthermore, the resonant wavelength of the nanobeam FP resonant cavity is close to the middle of the overlapping band of the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106.

[0040] Condition 2: Δλ over ≤fSR FP Furthermore, the resonant wavelength of the nanobeam FP resonant cavity is close to the edge of the overlapping band of the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106.

[0041] The following are embodiments of the filter structure of the present invention.

[0042] Example 1

[0043] An integrated filter with an ultra-wide free spectral range is fabricated based on a silicon-on-insulator platform at a 220nm insulator layer. The coupling waveguide 103 is a curved waveguide, the nanobeam waveguide 104 is a straight waveguide, and the holes on the left Bragg mirror aperture array 105 and the right Bragg mirror aperture array 106 are square holes. The tangent at the lowest point of the coupling waveguide 103 is parallel to and has a gap with the nanobeam waveguide 104, forming a side-coupled waveguide structure. The perpendicular line from the lowest point of the coupling waveguide 103 to the nanobeam waveguide 104 passes through the connection point of the tapered aperture array 107 and the reverse tapered aperture array 108.

[0044] The incident waveguide 101, exit waveguide 102, coupling waveguide 103, and nanobeam waveguide 104 have a width of 500 nm. The waveguides are fully etched, and the bending radius of coupling waveguide 103 is 10 μm. The period of the left Bragg mirror aperture array 105 is always fixed at 340 nm, with a period count of 15. The periods of the right Bragg mirror aperture array 106 are 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, and 480 nm, with a period count of 15. The period gradient of the tapered aperture array 107 and the reverse tapered aperture array 108 follows a parabolic function, with the smallest square aperture having a period of 240 nm. The gap between coupling waveguide 103 and nanobeam waveguide 104 is 230 nm. Therefore, the lengths of the six filters corresponding to the six right Bragg mirror aperture arrays 106 are all less than 23 μm. In Example 1, the aperture has a size of 250 nm in the y-direction and a size in the x-direction that is the product of the period and the duty cycle, with a minimum size of 170 nm.

[0045] In this embodiment, when the filter is in use, a swept-frequency continuous laser is injected into the incident waveguide 101 of the filter. The laser is coupled to the nanobeam FP resonant cavity through a side-coupled waveguide structure. The resonant wavelength oscillates continuously in the resonant cavity and cannot be coupled from the resonant cavity to the output waveguide 102, while the non-resonant wavelength is coupled from the FP resonant cavity to the output waveguide 102, thereby achieving the filtering out of the resonant wavelength laser.

[0046] Figure 3 The spectral transmission diagram of the filter in Example 1 is given. It can be seen from the figure that when the period on the right side is increased to 420nm, a deep dip can only be seen at 1513.76nm in the ultra-large wavelength range of 250nm, while the response is flat at the non-resonant wavelength. Figure 4 The electric field distribution of the entire structure of the corresponding filter is shown at operating wavelengths of 1400nm, 1460nm, 1513.76nm, 1540nm and 1600nm.

[0047] For a wavelength of 1400 nm, within the stopband of the left Bragg emitter but outside the stopband of the right Bragg emitter, the light coupled into the cavity is reflected by the left Bragg emitter but can propagate through the right Bragg emitter. Therefore, light injected from the incident waveguide 101 propagates to the right port of the nanobeam waveguide. Conversely, for a wavelength of 1600 nm, the light is propagated to the left port of the nanobeam waveguide because it is within the stopband of the right Bragg emitter but outside the left. At wavelengths of 1460 nm and 1540 nm, which are in the Bragg overlap band but not resonant, light is coupled into the cavity, reflected by the left and right Bragg mirrors, and finally propagates to the through port. Due to the short coupling length, the insertion loss at non-resonant wavelengths is negligible. For the resonant wavelength of 1513.76 nm, light couples into the cavity, enhancing the power within the cavity until a dynamic balance is achieved between the coupling power, external coupling power, and loss power. Therefore, the light is essentially trapped inside the cavity, with almost no power coupled to the through port.

[0048] To further demonstrate the small size of the filter with an ultra-wide free spectral range of the present invention, the embodiments disclosed by the inventors in patent CN2020112788641 are selected as comparative examples one and two.

[0049] Comparative Example 1

[0050] like Figure 5 As shown, an integrated filter with an ultra-wide free spectral range is fabricated based on a silicon-on-insulator platform with a 220 nm insulating layer. The incident waveguide 101, exit waveguide 102, coupling waveguide 103, and single-mode waveguide 108 are all 500 nm wide. The waveguides are ridge waveguides with an etching depth (waveguide height) of 150 nm, and the bending radius of the coupling waveguide 103 is 20 μm. The left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 are composed of periodically alternating wide and narrow waveguides, with a wide waveguide width of 500 nm and a narrow waveguide width of 300 nm, a period of 317 nm, a period number of 150, and a period of 317 nm. The tapered gradient waveguide grating 106 is composed of alternating wide and narrow waveguides. The wide waveguide has a width of 500 nm and remains constant, while the narrow waveguide has a width that linearly increases from 300 nm to 500 nm. The number of periods is 5, and the period is 317 nm. The reverse tapered gradient waveguide grating 107 is composed of alternating wide and narrow waveguides. The wide waveguide has a width of 500 nm and remains constant, while the narrow waveguide has a width that linearly increases from 500 nm to 300 nm. The number of periods is 5, and the period is 317 nm. The single-mode waveguide 108 has a length of zero, and the gap between the coupling waveguide 103 and the single-mode waveguide 108 is 250 nm.

[0051] The difference between Embodiment 1 and Comparative Example 1 lies in the use of a Bragg mirror aperture array 105, 106, 107, and 108 in Embodiment 1, which has higher reflectivity compared to the Bragg gratings 105, 106, 107, and 108 in Comparative Example 1. To achieve the same reflectivity, the total number of cycles required for the filter in Embodiment 1 is much smaller than the number of cycles in Comparative Example 1. In Embodiment 1, the device operating at 1513.76 nm has a period of 340 nm for the left Bragg mirror aperture array 105 and a period of 15. The right Bragg mirror aperture array 106 has a period of 420 nm and a period of 15. The duty cycle of the aperture array is 0.5 in both the x and y directions. The length of the entire filter is less than 20 μm. In Comparative Example 1, the device operating at 1521 nm has a left Bragg waveguide grating 104 and a right Bragg waveguide grating 105 composed of alternating wide and narrow waveguides, with a duty cycle of 0.5 in the x direction. The wide waveguide has a width of 500 nm, the narrow waveguide has a width of 300 nm, the number of periods is 150, and the period is 317 nm. The total length of the filter is greater than 98 μm.

[0052] Comparative Example 2

[0053] like Figure 6 As shown, the filter parameters in Comparative Example 2 are the same as those in Comparative Example 1. The difference lies in the fact that the alternating wide and narrow waveguide schemes of the left Bragg waveguide grating 104, right Bragg waveguide grating 105, tapered gradient waveguide grating 106, and reverse tapered gradient waveguide grating 107 are changed to a scheme of etching small holes within the waveguides. The left Bragg waveguide grating 104 and right Bragg waveguide grating 105 are both formed by periodically alternating ordinary single-mode waveguides and perforated single-mode waveguides; the tapered gradient waveguide grating 106 is formed by periodically alternating single-mode waveguides and perforated single-mode waveguides, with the single-mode waveguide width remaining constant and the radius of the circular holes gradually decreasing; the reverse tapered gradient waveguide grating 107 is formed by periodically alternating single-mode waveguides and perforated single-mode waveguides, with the single-mode waveguide width remaining constant and the radius of the circular holes gradually increasing.

[0054] The difference between Example 1 and Comparative Example 2 lies in the aperture size of the Bragg reflector array 105, 106, 107, and 108 used in Example 1. To achieve an infinitely free spectral range at the same wavelength, Example 1 uses a larger aperture array 105, 106, 107, and 108, while the aperture size in Comparative Example 2 needs to be as small as possible, significantly increasing the requirements for manufacturing precision. Furthermore, Example 1 exhibits higher reflectivity than the aperture array 105, 106, 107, and 108 in Comparative Example 2. To achieve the same reflectivity, the number of cycles required in Example 1 is much smaller than that in Comparative Example 2, and the length of the filter fabricated in Example 1 is much shorter than that in Comparative Example 2.

[0055] Example 2

[0056] The difference between Embodiment 2 and Embodiment 1 is that the incident waveguide 101, the exit waveguide 102, and the coupling waveguide 103 in Embodiment 1 are all replaced with straight waveguides. For example... Figure 7 As shown, the nanobeam waveguide 104 is a bent nanobeam waveguide. The radius (R) of the bent waveguide can be reduced to below 4.5 μm, which greatly reduces the footprint compared to Example 1, laying the foundation for the design of more compact large-scale cascaded devices in the future.

[0057] Example 3

[0058] The difference between Embodiment 3 and Embodiment 1 is that the periods of the left Bragg reflector aperture array 105, the right Bragg reflector aperture array 106, the tapered aperture array 107, and the reverse tapered aperture array 108 in Embodiment 1 remain unchanged. However, the widths of the tapered aperture array 107 and the reverse tapered aperture array 108 follow a quadratic function, such as... Figure 8 As shown.

[0059] In the three embodiments described above, the small holes in the left Bragg reflector array 105, the right Bragg reflector array 106, the tapered aperture array 107, and the reverse tapered aperture array 108 can be rectangular, square, circular, or elliptical. Furthermore, those skilled in the art can make several improvements and modifications without departing from the principles of this invention, employing other integrated optical platforms, such as silicon-on-insulator platforms, inorganic chalcogenide glass platforms, titanium oxide platforms, silicon nitride platforms, lithium niobate-on-insulator platforms, and indium phosphide (INP) platforms; and using different optical operating bands, such as ultraviolet, visible, near-infrared, mid-infrared, and far-infrared bands.

[0060] In summary, in this embodiment, the proposed ultra-large free spectral range filter structure combines a waveguide coupler with a nanobeam FP resonator. By adjusting the Bragg overlap band formed by the left and right Bragg mirrors to make it smaller than the free spectral range of the nanobeam resonator, single longitudinal mode excitation can be achieved, thereby realizing a filter with an ultra-large free spectral range of a single peak or a single valley across the entire spectrum.

[0061] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A filter with an ultra-small size and ultra-large free spectral range based on a nanobeam resonator, characterized in that, The filter structure is asymmetrical, comprising an incident waveguide (101), an outgoing waveguide (102), a coupling waveguide (103), a nanobeam waveguide (104), a left Bragg mirror aperture array (105), a right Bragg mirror aperture array (106), a tapered aperture array (107), and a reverse tapered aperture array (108), wherein: The incident waveguide (101), the coupling waveguide (103), and the outgoing waveguide (102) are connected in sequence; The left Bragg mirror aperture array (105), the tapered gradient aperture array (107), the reverse tapered gradient aperture array (108), and the right Bragg mirror aperture array (106) are arranged sequentially on the nanobeam waveguide (104). The left Bragg mirror aperture array (105), the tapered gradient aperture array (107), the reverse tapered gradient aperture array (108), and the right Bragg mirror aperture array (106) are all periodic structures. The periods of the left Bragg mirror aperture array (105) and the right Bragg mirror aperture array (106) are different, while the periods of the tapered gradient aperture array (107) and the reverse tapered gradient aperture array (108) are gradual. The lowest point of the coupled waveguide (103) is close to the connection point of the tapered gradient aperture array (107) and the reverse tapered gradient aperture array (108) and there is a gap between them, forming a side-coupled waveguide structure. The left Bragg mirror aperture array (105), the tapered gradient aperture array (107), the reverse tapered gradient aperture array (108), and the right Bragg mirror aperture array (106) together constitute the nanobeam FP resonant cavity. The overlap value of the Bragg stop band bandwidths of the left Bragg mirror hole array (105) and the right Bragg mirror hole array (106) is Δλ over , the free spectral range FSR of the nano-beam F-P resonant cavity FP , both of which need to satisfy one of the following conditions: Condition one: Δλ over <2FSR FP , and the resonance wavelength of the nano-beam F-P resonant cavity is close to the middle of the forbidden band overlap zone of the left Bragg mirror hole array (105) and the right Bragg mirror hole array (106). Condition 2: Δλ over ≤FSR FP Furthermore, the resonant wavelength of the nanobeam FP resonant cavity is close to the edge of the bandgap overlap of the left Bragg mirror aperture array (105) and the right Bragg mirror aperture array (106).

2. The ultra-small size ultra-large free spectral range filter based on a nanobeam resonator according to claim 1, characterized in that, The period and duty cycle of the tapered tapered hole array (107) and the reverse tapered tapered hole array (108) both follow the variation law of the tapering function, which is selected from any one of the linear function, quadratic function, Gaussian function, and Lorentz function.

3. The ultra-small size ultra-large free spectral range filter based on a nanobeam resonator according to claim 1, characterized in that, The number of arrays of the tapered gradient aperture array (107) and the reverse tapered gradient aperture array (108) needs to be adjusted according to the period of the left Bragg mirror aperture array (105) and the right Bragg mirror aperture array (106) and the gradient function used, respectively, so as to minimize the scattering loss at the interface of the reflective cavity and improve the quality factor of the filter.

4. The ultra-small size ultra-large free spectral range filter based on a nanobeam resonator according to claim 1, characterized in that, Δλ over With FSR FP The implementation method that satisfies either condition one or condition two is as follows: First, ensure that the left Bragg reflector aperture array (105) and the right Bragg reflector aperture array (106) have the same period, and then gradually increase the period of either the left Bragg reflector aperture array (105) or the right Bragg reflector aperture array (106) so that the nanobeam FP cavity has only one resonant mode.

5. The ultra-small size ultra-large free spectral range filter based on a nanobeam resonator according to claim 1, characterized in that, The nanobeam waveguide (104) is a straight waveguide, and the coupling waveguide (103) is a curved waveguide; or, the nanobeam waveguide (104) is a curved waveguide, and the coupling waveguide (103) is a straight waveguide.

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