Adjustable resonant filter and communication system
By utilizing the electro-optic effect in tunable filters with lithium niobate thin films, the refractive index can be directly adjusted to change the resonant wavelength, solving the problem of slow response speed in traditional filters and achieving rapid wavelength tuning.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-04-07
AI Technical Summary
Traditional tunable filters require physical processing time due to mechanical movement or electrothermal effects, resulting in slow response speeds.
A lithium niobate thin film is electrically connected to the electrode, and the refractive index is changed by generating an electro-optic effect through tuning voltage, thereby instantly adjusting the resonant wavelength of the optical resonant structure.
It achieves a fast response speed, avoids the physical process time of mechanical movement or electrothermal effects, and improves the response speed.
Smart Images
Figure CN121806327A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of communication, in particular to a tunable resonant filter and a communication system. BACKGROUND
[0002] The tunable filter is a core device in the fields of optical communication, spectrum analysis, laser radar, etc., and its wavelength tuning mechanism and filtering performance directly affect the flexibility and precision of the system.
[0003] Traditional tunable filter technologies, such as Fabry-Perot (F-P) cavity filters, usually rely on mechanical movement to change the physical cavity length or rely on electrothermal effect to change the material refractive index for wavelength tuning. However, mechanical tuning is limited by the inertia and friction of movement, and electrothermal tuning is limited by the heating and cooling process, both of which need to go through a physical process time that cannot be ignored, resulting in slow response speed. SUMMARY
[0004] The main purpose of the present application is to provide a tunable resonant filter and a communication system, aiming to solve the technical problem of slow response speed caused by the need for a certain physical process time due to mechanical movement or electrothermal effect in the prior art.
[0005] To achieve the above-mentioned purpose, the present application provides a tunable filter, which comprises: an optical resonant structure and at least one lithium niobate thin film; The lithium niobate thin film is arranged in the optical resonant structure; The lithium niobate thin film is electrically connected with an electrode; The lithium niobate thin film is used for receiving a tuning voltage applied by the electrode and changing the refractive index based on the electro-optic effect generated by the tuning voltage to adjust the resonant wavelength of the optical resonant structure.
[0006] In an embodiment, the number of lithium niobate thin films is multiple; Each of the lithium niobate thin films is etched with a grating; The projections of the gratings on the adjacent lithium niobate thin films in the same plane are perpendicular to each other.
[0007] In an embodiment, the optical resonant structure further comprises: a plurality of dielectric layers; Each of the lithium niobate thin films and each of the dielectric layers are alternately stacked; The lithium niobate thin film and the dielectric layer arranged above the lithium niobate thin film constitute a basic unit; At the resonant wavelength, the local optical field distributions of adjacent basic units overlap and produce constructive and destructive interference, forming Fano resonance in the transmission spectrum.
[0008] In an embodiment, the optical resonant structure further comprises: a plurality of spacer layers. The spacer layers are arranged between adjacent groups of resonant units. The group of resonant units comprises adjacent basic units.
[0009] In an embodiment, the spacing between adjacent groups of resonant units is consistent with the spacing between adjacent basic units.
[0010] In an embodiment, the full width at half maximum of the transmission peak of the transmission spectrum is less than or equal to 0.28 nanometers, and the shift amount of the transmission peak covers the C band.
[0011] In an embodiment, the dielectric layer is a glass material. The glass material is one of silica, borosilicate glass, and sapphire. The spacer layer is consistent with the material of the dielectric layer.
[0012] In an embodiment, the grating period of the etched lithium niobate thin film is in the range of 410 nm to 500 nm, so that the tunable range of the optical resonant structure covers at least one of the C band, the O band, and the L band.
[0013] In an embodiment, the tunable filter further comprises: a heating element. The heating element is arranged at the bottom of the optical resonant structure. The heating element is configured to adjust the resonant wavelength of the optical resonant structure by the thermo-optic effect when receiving an electrical signal.
[0014] In an embodiment, the optical resonant structure is integrated with a silicon-based optical waveguide. The silicon-based optical waveguide is configured to transmit and / or receive an optical signal to and / or from the optical resonant structure. The silicon-based optical waveguide is in a ridge structure or a strip structure.
[0015] In addition, to achieve the above-mentioned purpose, the present application further provides a communication system, which comprises the tunable resonant filter described above.
[0016] The one or more technical solutions provided by the present application have at least the following technical effects: The application discloses a tunable resonant filter and a communication system, and relates to the technical field of communication. BRIEF DESCRIPTION OF DRAWINGS
[0017] The drawings incorporated in the specification illustrate one or more embodiments of the present application and, together with the specification, serve to explain the principles of the present application.
[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings required to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.
[0019] Figure 1 FIG. 1 is a structural schematic diagram of a first embodiment of the tunable filter of the present application; Figure 2 FIG. 2 is a structural schematic diagram of a second embodiment of the tunable filter of the present application; Figure 3 FIG. 3 is a top view of the lithium niobate thin film in the second embodiment of the present application; Figure 4 FIG. 4 is a structural schematic diagram of a third embodiment of the tunable filter of the present application.
[0020] The object, functional features and advantages of the present application will be further explained with reference to the embodiments and the drawings. DETAILED DESCRIPTION
[0021] It should be understood that the specific embodiments described herein are merely intended to explain the technical solutions of the present application, and are not used to limit the present application.
[0022] In order to better understand the technical solutions of the present application, the drawings and specific embodiments will be described in detail below.
[0023] The main solution of the embodiments of the present application is that the tunable filter comprises an optical resonant structure and at least one layer of lithium niobate thin film; the lithium niobate thin film is arranged in the optical resonant structure; and the lithium niobate thin film is electrically connected with an electrode.
[0024] Due to the traditional tunable filter technology, mechanical tuning is limited by the inertia and friction of movement, and electro-thermal tuning is limited by the necessary heating and cooling processes, both of which need to go through a non-negligible physical process time, resulting in slow response speed.
[0025] The present application provides a solution that receives a tuning voltage applied by an electrode through a lithium niobate thin film and changes the refractive index based on the electro-optic effect generated by the tuning voltage to adjust the resonant wavelength of the optical resonant structure. Since the present application directly utilizes the electro-optic effect of the lithium niobate thin film, the refractive index can be changed instantaneously by applying an electric field, thereby realizing the tuning of the resonant wavelength, thus avoiding the physical process time required by mechanical movement or electro-thermal effect, and effectively improving the response speed.
[0026] Based on this, the present application provides a tunable filter, referring to Figure 1 , Figure 1 Figure 1 is a structural schematic diagram of a first embodiment of the tunable filter of the present application.
[0027] In this embodiment, the tunable filter comprises an optical resonant structure 10 and at least one layer of lithium niobate thin film 20.
[0028] The lithium niobate thin film is arranged in the optical resonant structure 10, and the lithium niobate thin film 20 is electrically connected to the electrode.
[0029] Among them, Figure 1 Figure 1 shows the front view of the tunable filter in the xz plane.
[0030] It should be noted that the optical resonant structure 10 can be a physical structure that allows specific color light to produce strong resonance and pass efficiently, while other colors of light are suppressed.
[0031] It can be understood that the lithium niobate thin film 20 can be prepared using lithium niobate crystal material with extremely high electro-optic coefficient, as a key component of the optical resonant structure 10.
[0032] The lithium niobate thin film 20 is used to receive a tuning voltage applied by the electrode, and changes the refractive index based on the electro-optic effect generated by the tuning voltage to adjust the resonant wavelength of the optical resonant structure 10.
[0033] In a specific implementation, the lithium niobate thin film 20 is electrically connected with the electrode. When receiving a tuning voltage (direct current or low-frequency alternating voltage) applied by the electrode, the tuning voltage generates a tuning electric field on both sides of the lithium niobate thin film 20. The tuning electric field triggers a linear electro-optic effect of the lithium niobate thin film 20, causing a slight relative displacement of positive and negative charge centers inside the lithium niobate thin film 20, resulting in a transient polarization of the electron cloud distribution of the lithium niobate thin film 20, thereby changing the refractive index of the lithium niobate thin film 20 to light of different polarization directions. The effective optical path of the optical resonant structure 10 is equal to the product of the physical length and the effective refractive index. The change of the refractive index of the lithium niobate thin film 20 will change the effective optical path of the optical resonant structure 10. In order to re-satisfy the resonance condition at the new optical path, the optical resonant structure 10 will select a different resonance wavelength to re-satisfy the resonance condition. Therefore, by changing the resonance voltage and then controlling the process of the optical resonant structure 10, the resonance wavelength can be forced to move, and the adjustment of the resonance wavelength of the optical resonant structure 10 is realized.
[0034] It should be understood that the above electro-optic tuning control object is an electron. When the voltage is applied, the electric field is established, and the formed electric field can transiently and slightly distort the electron cloud distribution in the lithium niobate thin film 20 (i.e., electron polarization), directly leading to the change of the refractive index of the crystal. The whole tuning process is completed in nanoseconds without mechanical inertia and thermal inertia, and the response speed is fast.
[0035] The tunable filter provided in the embodiment includes an optical resonant structure and at least one lithium niobate thin film. The lithium niobate thin film of the application is arranged in the optical resonant structure; the lithium niobate thin film is electrically connected with the electrode; the application receives a tuning voltage applied by the electrode through the lithium niobate thin film, and changes the refractive index based on the electro-optic effect generated by the tuning voltage, to adjust the resonance wavelength of the optical resonant structure. Since the application directly utilizes the electro-optic effect of the lithium niobate thin film, the refractive index of the lithium niobate thin film can be changed instantaneously by applying an electric field, so as to realize the tuning of the resonance wavelength, thereby avoiding the physical process time required by mechanical movement or electro-thermal effect, and effectively improving the response speed.
[0036] Based on the first embodiment of the application, the second embodiment of the application is proposed. In the second embodiment of the application, the same or similar contents as the above first embodiment can be referred to the above introduction, and will not be described in detail hereinafter. On this basis, please refer to Figure 2 , Figure 2 FIG. 2 is a structural schematic diagram of the tunable filter of the second embodiment of the application.
[0037] In the embodiment, the number of the lithium niobate thin films 20 is multiple.
[0038] Each of the lithium niobate thin films 20 is etched with a grating 30, and the projections of the gratings 30 on the adjacent lithium niobate thin films 20 in the same plane are perpendicular to each other.
[0039] wherein, Figure 2 A front view of the tunable filter in the xz plane is shown.
[0040] It should be noted that the lithium niobate thin film 20 is an anisotropic crystal, and its response (refractive index) to light of different polarization directions is different. If the filter is sensitive to polarization, when a beam of light with randomly changing polarization passes through, the polarization state of the light is random and constantly changing, which will cause the performance of the tunable filter to be unstable and the signal to fluctuate.
[0041] To solve the above problems, the lithium niobate thin film 20 is provided in multiple layers, and each layer of lithium niobate thin film 20 is parallel to each other. A series of equidistant and extremely fine grooves are engraved on the surface of each layer of lithium niobate thin film 20 to form a grating 30. In any adjacent lithium niobate thin film 20, the projection of the grating 30 on the upper layer of lithium niobate thin film 20 and the grating 30 on the lower layer of lithium niobate thin film 20 in the same plane are perpendicular to each other.
[0042] Transverse gratings 31 can be etched on the odd-numbered layers of lithium niobate thin film 20, longitudinal gratings 32 can be etched on the even-numbered layers of lithium niobate thin film 20, or transverse gratings 31 can be etched on the even-numbered layers of lithium niobate thin film 20, and longitudinal gratings 32 can be etched on the odd-numbered layers of lithium niobate thin film 20, which is not limited in the present embodiment.
[0043] Referring to Figure 3 , Figure 3 A top view of the lithium niobate thin film in the second embodiment of the present application is shown. As shown in Figure 3 In the xy plane, the extension direction of the transverse grating 31 on the lithium niobate thin film 20 is the x-axis, and the extension direction of the longitudinal grating 32 on the lithium niobate thin film 20 is the y-axis.
[0044] For x-direction polarized light, it will be strongly modulated by the longitudinal grating 32 when passing through the y-direction longitudinal grating 32, and the equivalent refractive index changes greatly, and it will be weakly modulated by the transverse grating 31 when passing through the x-direction transverse grating 31, and mainly experiences the refractive index of the lithium niobate thin film 20 itself. For y-direction polarized light, it will be strongly modulated by the transverse grating 31 when passing through the x-direction transverse grating 31, and the equivalent refractive index changes greatly, and it will be weakly modulated by the longitudinal grating 32 when passing through the y-direction longitudinal grating 32, and mainly experiences the refractive index of the lithium niobate thin film 20 itself. By accurately designing the parameters (period, etching depth, etc.) of the grating 30, the average equivalent refractive index experienced by the x-polarized light and the y-polarized light after passing through the entire multi-layer structure can be made to be exactly the same, ensuring that the optical resonant structure 10 can work with exactly the same performance (such as center wavelength, bandwidth) regardless of the polarization direction of the incident light, thereby realizing polarization-independent characteristics, improving the performance stability of the tunable filter, and avoiding signal fluctuation.
[0045] It should be understood that, according to the Pockels electro-optic effect of the lithium niobate thin film 20, the electric field loaded along the z-axis direction will cause the refractive index changes in the x, y and z directions, at this time the refractive indices in the three directions are:
[0046]
[0047]
[0048] wherein, , is the tuning voltage, is the thickness of the lithium niobate thin film, is the z-direction electric field intensity, , , is the refractive index of the light in the x, y, z three principal axis directions after the tuning voltage is applied, is the refractive index of the light with the polarization direction perpendicular to the optical axis (z-axis), is the refractive index of the light with the polarization direction parallel to the optical axis (z-axis), is the modulation ability of , is the modulation ability of .
[0049] It can be known from the above formula that the change amount Δ n of the refractive index is in linear relationship with the applied electric field , and since , the tuning ability for the z-direction polarized light (proportional to ) is much stronger than the tuning ability for the x, y direction polarized light (proportional to ). By applying the tuning voltage U , the electric field is generated, and based on the above formula, the refractive index n of the lithium niobate thin film 20 can be linearly changed, so as to change the effective optical path of the optical resonant cavity, and finally realize the continuous and rapid movement of the resonance wavelength λ.
[0050] Based on the first embodiment and the second embodiment of the present application, the third embodiment of the present application is proposed. In the third embodiment of the present application, the same or similar contents as the above first embodiment and the second embodiment can be referred to the above introduction, and will not be described in detail hereinafter. On this basis, please refer to Figure 4 , Figure 4 is a structural schematic diagram of the third embodiment of the tunable filter of the present application.
[0051] In the embodiment, the optical resonant structure 10 further comprises a plurality of dielectric layers 40.
[0052] Each of the lithium niobate thin films 20 and each of the dielectric layers 40 are alternately stacked.
[0053] The lithium niobate thin film 20 and the dielectric layer 40 arranged above the lithium niobate thin film 20 form a basic unit 50.
[0054] At the resonant wavelength, the local optical field distributions of adjacent basic units 50 overlap and produce constructive and destructive interferences, forming a Fano resonance in the transmission spectrum.
[0055] wherein, Figure 4 A front view of the tunable filter in the xz plane is shown.
[0056] It should be noted that the dielectric layer 40 can be a planar optical thin film that is transparent, insulating, and has a lower refractive index than lithium niobate. The dielectric layer 40 can be a glass material, specifically one of silica, borosilicate glass, and sapphire. The dielectric layer 40 is sandwiched between two lithium niobate thin films 20, and each lithium niobate thin film 20 and the dielectric layer 40 between the lithium niobate thin films 20 are alternately stacked.
[0057] It can be understood that the transmission spectrum characterizes the transfer function of the optical resonant structure 10 in the frequency domain (or wavelength domain), and completely describes the linear response of the optical resonant structure 10 to different frequency incident light. The transmission peak can correspond to the local maximum region of the optical resonant junction resonance mode. The transmission valley can correspond to the local minimum region of the optical resonant junction resonance mode.
[0058] In a specific implementation, any lithium niobate thin film 20 and the dielectric layer 40 arranged above the lithium niobate thin film 20 form a basic unit 50. Each basic unit 50 can form a structure of lithium niobate thin film 20-dielectric layer 40-lithium niobate thin film 20. By using the reflection of high and low refractive index materials at the interface, a structure is constructed for light to reflect back and forth in it. When the wavelength of light exactly meets the condition that the optical path difference of its round trip in the dielectric layer 40 is an integer multiple of the wavelength, all the reflected light will produce constructive interference, the light waves will superimpose on each other, the energy will be greatly enhanced and confined in the cavity, and cannot easily escape, thereby making the basic unit 50 form a micro resonator that can trap specific wavelength light inside and form a higher intensity local optical field.
[0059] The localized light will tunnel through the intermediate dielectric layer 40 and penetrate into the adjacent basic unit 50, so that the localized light field distribution of the adjacent basic unit 50 is overlapped. The light reaches the output end in two ways: path one: the light resonates in a basic unit 50, tunnels to the next unit, and continues to resonate and tunnel until it reaches the output end. Path two: the light does not experience such strong resonance, but passes through the entire structure quickly in a straight-through manner. At a very precise wavelength, the phases of the two paths are completely opposite, and they cancel each other out (i.e., destructive interference), resulting in a transmittance of zero (i.e., a transmission valley). At another very similar wavelength, the phases of the two paths are completely the same, and they reinforce each other (i.e., constructive interference), resulting in a sharp peak in transmittance (i.e., a transmission peak). The above asymmetric line shape from the steep valley to the sharp peak, which is generated by the interference between the resonance characteristics of one path and the non-resonance characteristics of the other path, is the Fano resonance that can enhance the transmission effect.
[0060] Further, in the embodiment, the optical resonant structure 10 further comprises: a plurality of spacer layers 60.
[0061] The spacer layer 60 is arranged between adjacent resonant unit groups 70, and the resonant unit group 70 comprises adjacent basic units 50.
[0062] It should be noted that the above spacer layer 60 can be consistent with the material of the dielectric layer 40, but its thickness is greater than that of the dielectric layer.
[0063] In a specific implementation, any two adjacent basic units 50 can be regarded as a resonant unit group 70, and the spacer layer 60 can be configured to couple adjacent resonant unit groups 70, so that the localized light field of adjacent resonant unit groups 70 overlaps and interferes through the spacer layer 60, wherein the constructive interference forms a passband, and the destructive interference enhances the out-of-band suppression, thereby producing a narrow-band bandpass filtering effect in the overall transmission spectrum of the optical resonant structure 10.
[0064] It should be understood that each resonant unit group 70 itself can provide a bandpass filtering characteristic, and the adjacent resonant unit groups 70 coupled by the spacer layer 60 form a cascaded filtering structure. This cascaded structure makes the light signal pass through the two resonant unit groups 70 in turn, and the transmittance is the product of the transmittances of the resonant unit groups 70, thereby significantly suppressing the background transmission outside the passband while maintaining a narrow passband, and finally obtaining a narrow-band bandpass filtering characteristic with high out-of-band suppression ratio.
[0065] It should be noted that the thicknesses of the lithium niobate film 20 and the dielectric layer 40 in the basic unit 50 can be preliminarily designed according to a λ / 4 film system, where λ is a center wavelength allowed to pass, and then the thicknesses of the lithium niobate film 20 and the glass layer in the basic unit 50, the distance between two basic units 50, and the distance between two resonant unit groups 70 are optimized by using a finite-difference time-domain method to maximize the transmittance. Changes in the refractive index of the lithium niobate film 20 change the interference effect in the optical resonant structure 10, and further change the center wavelength allowed to pass.
[0066] Further, in the embodiment, the interval between adjacent resonant unit groups 70 is consistent with the interval between adjacent basic units 50; the half-height width of a transmission peak of a transmission spectrum is less than or equal to 0.28 nm, and the moving amount of the transmission peak covers the C band.
[0067] Exemplarily, taking the thicknesses of the lithium niobate film 20 and the dielectric layer 40 in the basic unit 50 as 250 nm and 180 nm respectively, the interval between the basic units 50 and the interval between the resonant unit groups 70 as 275 nm, the grating period as 900 nm, and the width of grating etching as 410 nm and the etching depth as 180 nm as examples, in this scenario, strong interference effect is formed in the cavity of the optical resonant structure 10, and high-Q (Q=5593.24 when the voltage is 0 V) filtering is achieved. This thickness design directly determines the narrowband characteristics of the filter (the half-height width FWHM of the transmission curve can reach 0.28 nm when the voltage is 0 V). At the same time, a wavelength moving range of 16 nm (1540.73-1556.84 nm, covering the main communication window of the C band) is obtained by applying an external voltage. And in the change of the external voltage, the quality factor is always greater than or equal to 5593.24, and the FWHM is always less than or equal to 0.28 nm. This combination of performance is superior to existing tunable filters, and can support a more dense wavelength division multiplexing system.
[0068] In the embodiment, the grating period of the etching of the lithium niobate film 20 is in the range of 410 nm-500 nm, so that the tunable range of the optical resonant structure 10 covers at least one of the C band, the O band and the L band.
[0069] In a specific implementation, by setting the grating period in the range of 410 nm-500 nm, the working center wavelength of the optical resonant structure 10 can be offset to cover at least one of the O band and the L band in addition to the C band.
[0070] In the embodiment, the tunable filter further comprises a heating element.
[0071] The heating element is arranged at the bottom of the optical resonant structure 10.
[0072] The heating element is configured to adjust the resonant wavelength of the optical resonant structure 10 by the thermo-optic effect when receiving an electrical signal.
[0073] It should be noted that the heating element can be an element that converts electrical energy into heat energy, such as a TiN thin-film resistor.
[0074] In a specific implementation, when an electrical signal is applied to the heating element integrated at the bottom of the optical resonant structure 10, the heating element generates heat by the Joule effect as a thin-film resistor; the heat establishes a stable temperature field in the optical resonant structure 10 by heat conduction, causing the lithium niobate thin film 20 and the dielectric layer 40 to change in refractive index due to the thermo-optic effect; the change in refractive index directly modulates the equivalent optical path of the optical resonant structure 10, thereby achieving precise and continuous drift of the resonant wavelength. This thermo-optic tuning mechanism, as an auxiliary tuning means with a large range and high linearity, cooperates with the fast and accurate electro-optic tuning to jointly expand the overall tuning range of the tunable filter and improve the wavelength control accuracy and long-term stability.
[0075] In this embodiment, the optical resonant structure 10 is integrated with a silicon-based optical waveguide.
[0076] The silicon-based optical waveguide is configured to transmit an optical signal to the optical resonant structure 10 and / or receive an optical signal from the optical resonant structure 10.
[0077] The silicon-based optical waveguide is in a ridge structure or a strip structure.
[0078] In a specific implementation, the optical resonant structure 10 can be integrated with a silicon-based optical waveguide in a ridge structure or a strip structure, so that the silicon-based optical waveguide can transmit an optical signal from a laser, a modulator or other functional units to the optical resonant structure 10 and / or receive an optical signal from the optical resonant structure 10 and transmit it to the next functional unit (such as a photodetector or another processing device). This realizes ultra-low-loss, stable and reliable on-chip transmission and routing of optical signals.
[0079] The application also provides a communication system, which includes the tunable resonant filter described above.
[0080] The above only describes some embodiments of the application, and does not limit the patent scope of the application. Any equivalent structural transformation made by using the content of the specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the application.
Claims
1. A tunable filter, characterized in that, The tunable filter includes: an optical resonant structure and at least one lithium niobate thin film; The lithium niobate thin film is disposed in the optical resonant structure; The lithium niobate film is electrically connected to the electrode; The lithium niobate film is used to receive the tuning voltage applied by the electrode and change the refractive index based on the electro-optic effect generated by the tuning voltage to adjust the resonant wavelength of the optical resonant structure.
2. The tunable filter as described in claim 1, characterized in that, The lithium niobate film is multilayered; Each of the lithium niobate films is etched with a grating; The projections of the gratings on adjacent lithium niobate films onto the same plane are perpendicular to each other.
3. The tunable filter as described in claim 2, characterized in that, The optical resonant structure further includes: a multilayer dielectric layer; The lithium niobate films and the dielectric layers are stacked alternately. The lithium niobate film and the dielectric layer disposed above the lithium niobate film constitute a basic unit; At the resonant wavelength, the local optical field distributions of adjacent basic units overlap and produce constructive and destructive interference, forming Fano resonance in the transmission spectrum.
4. The tunable resonant filter as described in claim 3, characterized in that, The optical resonant structure further includes: multiple spacer layers; The spacer layer is disposed between adjacent resonant unit groups; The resonant unit group comprises adjacent basic units.
5. The tunable resonant filter as described in claim 4, characterized in that, The spacing between adjacent resonant unit groups is consistent with the spacing between adjacent basic units.
6. The tunable resonant filter as described in claim 5, characterized in that, The full width at half maximum (FWHM) of the transmission peak in the transmission spectrum is less than or equal to 0.28 nm, and the shift of the transmission peak covers the C-band.
7. The tunable resonant filter as described in claim 3, characterized in that, The dielectric layer is made of glass. The glass material is one of silicon dioxide, borosilicate glass, and sapphire. The spacer layer is made of the same material as the dielectric layer.
8. The tunable resonant filter as described in claim 2, characterized in that, The grating period of the lithium niobate thin film etching is in the range of 410nm to 500nm, so that the tunable range of the optical resonant structure covers at least one of the C-band, O-band and L-band.
9. The tunable resonant filter according to any one of claims 1 to 7, characterized in that, The tunable filter further includes: a heating element; The heating element is located at the bottom of the optical resonant structure; The heating element is used to adjust the resonant wavelength of the optical resonant structure through the thermo-optical effect when an electrical signal is received.
10. A communication system, characterized in that, The communication system includes the tunable resonant filter according to any one of claims 1 to 9.