Filter device with high quality factor

Abstract

The invention relates to the technical field of photonic integrated chips, in particular to a high-quality-factor filtering device. Comprising a micro-ring resonator used for realizing periodic filtering to ensure a large quality factor, and a Mach-Zehnder interferometer used for filtering redundant wavelengths; and the Mach-Zehnder interferometer is connected in series to one side of the micro-ring of the micro-ring resonator, and is positioned on the front half micro-ring through which the input light is coupled into the micro-ring for transmission. The micro-ring resonator and the Mach-Zehnder interferometer are combined, the Mach-Zehnder interferometer can filter specific wavelengths, unnecessary parts in the wavelengths transmitted by the micro-ring resonator are filtered out, and the FSR of the micro-ring resonator is improved. The Mach-Zehnder interferometer is added into the micro-ring, so that the quality factor of the micro-ring resonator can be improved, and the line width of the filter can be further reduced; according to the invention, a large quality factor and a large FSR can be realized at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of photonic integrated chips, and more particularly to a high-quality factor filter device. Background Art

[0002] Optical filters enable wavelength selection and single-wavelength laser output to meet the needs of diverse applications. They are primarily used in optical communications, optical sensing, biomedical engineering, and other fields. Filter designs should meet requirements for high quality factor (QF) and high free spectral range (FFR) to achieve optimal wavelength selectivity. A high QF filter can more accurately select the desired wavelength, while a high FFR allows for a wider operating range.

[0003] As a filter, a microring resonator can output a filtered wavelength at the drop port. This is because the filtered wavelength, after passing through the microring, is in phase with the light entering the microring, allowing resonance within the microring. Wavelengths that do not meet the resonance condition are output from the through port. Furthermore, when two microrings are connected in series, the vernier effect can be exploited to tune the output wavelength. As a filtering device, a microring resonator must possess both a high free spectral range and a high quality factor. High quality factors can be achieved by increasing the microring radius. However, a large microring radius reduces the free spectral range (FSR), making single-wavelength filtering impossible and reducing the filter's operating wavelength range. Microring resonators experience losses as light oscillates within the microring due to bending and sidewall losses. As the microring radius increases, the transmittance of the microring resonator decreases, which in turn degrades filter performance. When a microring resonator is used as a filtering device, a sufficiently large FSR is required to ensure a larger operating range. However, increasing the FSR requires reducing the microring radius, which not only leads to a decrease in the quality factor but also increases the bending loss of the microring. Therefore, it is impossible to meet both design requirements at the same time. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiency of the prior art micro-ring structure that cannot simultaneously meet the requirements of a large quality factor and a large FSR, and to provide a high-quality factor filter device that can simultaneously achieve a large quality factor and a large FSR.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: Provided is a high-quality factor filtering device, comprising a microring resonator for achieving periodic filtering to ensure a high quality factor, and a Mach-Zehnder interferometer for filtering excess wavelengths; the Mach-Zehnder interferometer is connected in series on one side of a microring of the microring resonator and is located in the front half of the microring through which input light is coupled into and transmitted.

[0006] The present invention provides a high-quality filter device. A Mach-Zehnder interferometer is located in the microring portion of a microring resonator and arranged in series within the microring. By combining the microring resonator and the Mach-Zehnder interferometer, the Mach-Zehnder interferometer can filter specific wavelengths, removing unwanted portions of wavelengths transmitted by the microring resonator and improving the FSR of the microring resonator. Adding the Mach-Zehnder interferometer to the microring can also improve the quality factor of the microring resonator, further reducing the linewidth of the filter. The present invention can simultaneously achieve a high quality factor and a high FSR.

[0007] Furthermore, at least two Mach-Zehnder interferometers are provided: a first Mach-Zehnder interferometer and a second Mach-Zehnder interferometer, and the two Mach-Zehnder interferometers are connected in series on the same side of the microring in the microring resonator. Multiple Mach-Zehnder interferometers can be connected in series within the microring, and a greater number of these interferometers increase the extinction ratio.

[0008] Furthermore, the microring resonator includes an input straight waveguide, a first U-shaped waveguide, a second U-shaped waveguide and an output straight waveguide; the input straight waveguide is coupled to the first U-shaped waveguide, one end of the first U-shaped waveguide is connected to one end of the Mach-Zehnder interferometer, and the other end of the Mach-Zehnder interferometer is connected to one end of the second U-shaped waveguide; the other end of the first U-shaped waveguide is connected to the other end of the second U-shaped waveguide through a second straight waveguide; and the second U-shaped waveguide is coupled to the output straight waveguide.

[0009] Furthermore, the first Mach-Zehnder interferometer includes a first multimode interference coupler, a first short arm waveguide, a first long arm waveguide, and a second multimode interference coupler, wherein the output end of the first multimode interference coupler is respectively connected to one end of the first short arm waveguide and the first long arm waveguide, and the other end of the first short arm waveguide and the first long arm waveguide are combined through the second multimode interference coupler; the second Mach-Zehnder interferometer includes a third multimode interference coupler, a second short arm waveguide, a second long arm waveguide, and a fourth multimode interference coupler, wherein the output end of the third multimode interference coupler is respectively connected to one end of the second short arm waveguide and the second long arm waveguide, and the other end of the second short arm waveguide and the second long arm waveguide are combined through the fourth multimode interference coupler; the first U-shaped waveguide is connected to the input end of the first multimode interference coupler, the output end of the second multimode interference coupler is connected to the input end of the third multimode interference coupler through a first straight waveguide, and the output end of the fourth multimode interference coupler is connected to the second U-shaped waveguide.

[0010] Furthermore, the total length L of the first straight waveguide, the second straight waveguide, the first U-shaped waveguide, the second U-shaped waveguide, the first short arm waveguide, and the second short arm waveguide must meet the following conditions: , neff is the effective refractive index of the microring.

[0011] Furthermore, the length difference between the first short arm waveguide and the first long arm waveguide must meet the following conditions: after the light of the required wavelength enters the first short arm waveguide and the first long arm waveguide from the first multimode interference coupler, the two beams of light output from the first multimode interference coupler pass through the first short arm waveguide and the first long arm waveguide respectively and reach the second multimode interference coupler with a phase difference of .

[0012] Furthermore, the length difference between the second short arm waveguide and the second long arm waveguide must meet the following conditions: after the light of the required wavelength enters the second short arm waveguide and the second long arm waveguide from the third multimode interference coupler, the two beams of light output from the third multimode interference coupler pass through the second short arm waveguide and the second long arm waveguide respectively and reach the fourth multimode interference coupler with a phase difference of .

[0013] Furthermore, a length difference L1 between the first short arm waveguide and the first long arm waveguide needs to satisfy the following conditions: The length difference L2 between the second short arm waveguide and the second long arm waveguide must meet the following conditions: .

[0014] Furthermore, light of a desired wavelength undergoes constructive interference in the Mach-Zehnder interferometer, periodically undergoing destructive interference and constructive interference as the wavelength changes, thereby increasing the FSR by filtering out the resonant wavelengths around the desired wavelength.

[0015] Furthermore, the first Mach-Zehnder interferometer for: ; The second Mach-Zehnder interferometer for: ; The final FSR is and The lowest common multiple of; where neff is the effective refractive index of the microring, L 1 is the length difference between the first short arm waveguide and the first long arm waveguide; L 2 is the length difference between the second short arm waveguide and the second long arm waveguide; , , is the wavelength; n is the group refractive index of the waveguide.

[0016] Furthermore, the spacing between the input straight waveguide and the first U-shaped waveguide is equal to the spacing between the output straight waveguide and the second U-shaped waveguide, which determines the coupling coefficient of the microring. The lower the coupling coefficient, the greater the extinction ratio of the filter. Light is coupled from the input straight waveguide into the first U-shaped waveguide and from the second U-shaped waveguide into the output straight waveguide.

[0017] Furthermore, the quality factor of the filter device increases with the increase of the total microring length L. Meanwhile, the longer the lengths of the first long arm waveguide and the second long arm waveguide are, the greater the quality factor is.

[0018] Furthermore, since the long-arm waveguide of the Mach-Zehnder interferometer is relatively long, the long-arm waveguide adopts a spiral waveguide to reduce the area of ​​the device, which can further improve the integration of the device.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. A high-quality filter device of the present invention achieves a higher FSR by connecting a Mach-Zehnder interferometer in series with the microring portion of a microring resonator. Light selected by the microring is further filtered by the series-connected Mach-Zehnder interferometer, thereby achieving a higher FSR. Furthermore, increasing the total length L of the microring within a certain range can improve the filter's quality factor while ensuring that the FSR does not decrease, thus resolving the problem of simultaneously increasing both the FSR and the quality factor.

[0020] 2. A high-quality filter device of the present invention achieves wavelength selection by serially connecting a Mach-Zehnder interferometer to the microring portion of a microring resonator. This achieves a higher extinction ratio than a direct external serial connection and further improves the device's filter quality factor. Based on the principle and structure of the Mach-Zehnder interferometer, a spiral waveguide can be used for the long-arm waveguide, achieving a higher FSR in a smaller device area and exhibiting improved integration.

[0021] In summary, the present invention is designed as a filter device to achieve narrow-bandwidth wavelength selection. The device has advantages such as high integration, high filter quality factor, and a large FSR of the wavelength-selective spectrum, which facilitates the device to operate over a wider wavelength range. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of a high quality factor filter device; Figure 2 This is a schematic diagram of the structure of the first Mach-Zehnder interferometer; Figure 3 This is a schematic diagram of the structure of the second Mach-Zehnder interferometer; Figure 4 This is a transmission spectrum diagram of the filter device in Example 1.

[0023] In the accompanying drawings: 11. Input straight waveguide; 12. First U-shaped waveguide; 13. Second U-shaped waveguide; 14. Output straight waveguide; 15. Input port; 16. Drop port; 2. First Mach-Zehnder interferometer; 21. First multimode interference coupler; 22. First short-arm waveguide; 23. First long-arm waveguide; 24. Second multimode interference coupler; 3. Second Mach-Zehnder interferometer; 31. Third multimode interference coupler; 32. Second short-arm waveguide; 33. Second long-arm waveguide; 34. Fourth multimode interference coupler; 4. First straight waveguide; 5. Second straight waveguide. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced in size, and do not represent the actual dimensions of the products. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0025] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "up", "down", "left", "right", etc. indicate directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0026] Example 1 This embodiment is the first embodiment of a high quality factor filter device. Figure 1 As shown, the system includes a microring resonator for periodic filtering to ensure a high quality factor, and two Mach-Zehnder interferometers for filtering unwanted wavelengths. The two Mach-Zehnder interferometers are connected in series on one side of the microring of the microring resonator, located in the first half of the microring where the input light is coupled into and transmitted. Light entering through the input straight waveguide 11 resonates and is filtered in the microring, and finally outputs the desired wavelength through the output straight waveguide 14, achieving wavelength selection.

[0027] In this embodiment, if Figures 1 to 3As shown, the microring resonator includes an input straight waveguide 11, a first U-shaped waveguide 12, a second U-shaped waveguide 13 and an output straight waveguide 14; the input straight waveguide 11 is coupled to the first U-shaped waveguide 12, one end of the first U-shaped waveguide 12 is connected to one end of the Mach-Zehnder interferometer, and the other end of the Mach-Zehnder interferometer is connected to one end of the second U-shaped waveguide 13; the other end of the first U-shaped waveguide 12 is connected to the other end of the second U-shaped waveguide 13 through the second straight waveguide 5; the second U-shaped waveguide 13 is coupled to the output straight waveguide 14. The first Mach-Zehnder interferometer 2 includes a first multimode interference coupler 21, a first short arm waveguide 22, a first long arm waveguide 23 and a second multimode interference coupler 24. The output end of the first multimode interference coupler 21 is connected to one end of the first short arm waveguide 22 and one end of the first long arm waveguide 23 respectively. The other ends of the first short arm waveguide 22 and the first long arm waveguide 23 are combined by the second multimode interference coupler 24. The second Mach-Zehnder interferometer 3 includes a third multimode interference coupler 31, a second short arm waveguide 32, a second long arm waveguide 33 and a fourth multimode interference coupler. The output end of the third multimode interference coupler 31 is connected to one end of the second short arm waveguide 32 and the second long arm waveguide 33 respectively, and the other ends of the second short arm waveguide 32 and the second long arm waveguide 33 are combined through the fourth multimode interference coupler 34; the first U-shaped waveguide 12 is connected to the input end of the first multimode interference coupler 21, the output end of the second multimode interference coupler 24 is connected to the input end of the third multimode interference coupler 31 through the first straight waveguide 4, and the output end of the fourth multimode interference coupler 34 is connected to the second U-shaped waveguide 13.

[0028] The input straight waveguide 11 is coupled to the first U-shaped waveguide 12, and input light is input from the input port 15. The first U-shaped waveguide 12 is connected to the first multimode interference coupler 21. The output end of the first multimode interference coupler 21 is respectively connected to the first short arm waveguide 22 and the first long arm waveguide 23. The first short arm waveguide 22 and the first long arm waveguide 23 are respectively connected to the second multimode interference coupler 24 for beam combination, forming a first Mach-Zehnder interferometer. The other end of the first U-shaped waveguide 12 is connected to the second U-shaped waveguide 13 via the second straight waveguide 5. The output end of the fourth multimode interference coupler 34 is connected to the other end of the second U-shaped waveguide 13. The output end of the third multimode interference coupler 31 is respectively connected to the second short arm waveguide 32 and the second long arm waveguide 33. The second short arm waveguide 32 and the second long arm waveguide 33 are connected and beam combined via the fourth multimode interference coupler 34, forming a second Mach-Zehnder interferometer. The two Mach-Zehnder interferometers are connected in series via a first straight waveguide 4. The second Mach-Zehnder interferometer 3 is connected to a second U-shaped waveguide 13, which is coupled to an output straight waveguide 14. The transmitted light is output from a drop port 16. Both Mach-Zehnder interferometers are connected in series on the same side of the microring, located in the first half of the microring where the input light is coupled into and transmitted through.

[0029] The principle of the first-layer filtering of the microring resonator is that when light is input from the input port 15 of the device and passes through the first U-shaped waveguide 12, it is coupled into the first U-shaped waveguide 12. When the light circles around the microring and returns to the coupling area of ​​the first U-shaped waveguide 12, it is exactly in phase with the light coupled into the input straight waveguide 11, meeting the resonance condition and enhancement. Finally, the light is coupled from the second U-shaped waveguide 13 to the output straight waveguide 14, and the output light wavelength is the wavelength that meets the resonance condition.

[0030] In this embodiment, the total length L of the first straight waveguide 4, the second straight waveguide 5, the first U-shaped waveguide 12, the second U-shaped waveguide 13, the first short arm waveguide 22, and the second short arm waveguide 32 must meet the following conditions: , neff is the effective refractive index of the microring. At this time, the required wavelength λ satisfies the resonance condition and is output from the Drop port. After the light is input from the Input port 15, the phase change after passing through the microring with a total length of L is The longer the total length, the larger the quality factor of the filter.

[0031] In the first Mach-Zehnder interferometer 2, the length difference L1 between the first short arm waveguide 22 and the first long arm waveguide 23 must satisfy the following condition: After the light of the required wavelength enters the first short arm waveguide 22 and the first long arm waveguide 23 from the first multimode interference coupler 21, the two beams of light output from the first multimode interference coupler 21 pass through the first short arm waveguide 22 and the first long arm waveguide 23 respectively and reach the second multimode interference coupler 24 with a phase difference of The light of the desired wavelength undergoes constructive interference in the first Mach-Zehnder interferometer 2, and periodically undergoes destructive interference and constructive interference as the wavelength changes, thereby increasing the FSR by filtering out the resonant wavelengths around the desired wavelength. for: , is the group refractive index of the waveguide, Indicates wavelength.

[0032] In the second Mach-Zehnder interferometer 3, the length difference L2 between the second short arm waveguide 32 and the second long arm waveguide 33 must satisfy the following conditions: After the light of the required wavelength enters the second short arm waveguide 32 and the second long arm waveguide 33 from the third multimode interference coupler 31, the two beams of light output from the third multimode interference coupler 31 pass through the second short arm waveguide 32 and the second long arm waveguide 33 respectively and reach the fourth multimode interference coupler 34 with a phase difference of The light of the desired wavelength undergoes constructive interference in the second Mach-Zehnder interferometer 3, and periodically undergoes destructive interference and constructive interference as the wavelength changes, thereby increasing the FSR by filtering out the resonant wavelengths around the desired wavelength. for: .

[0033] After two Mach-Zehnder interferometers are connected in series, a larger FSR can be obtained due to the different FSRs of the filtered spectra. The final FSR is and The length difference between the first short arm waveguide 22 and the first long arm waveguide 23 and the length difference between the second short arm waveguide 32 and the second long arm waveguide 33 determine the FSR of the final narrowband filter.

[0034] In this embodiment, the structure of the Mach-Zehnder interferometer consists of two 1×2 multimode interference couplers, a long-arm waveguide, and a short-arm waveguide. According to the principle of self-imaging, since the various high-order modes excited by light in the wide waveguide interfere with each other during transmission, images of the light source will periodically appear in the transmission direction of the light. Based on this principle, the use of a multimode interference coupler can achieve uniform in-phase splitting, evenly dividing the light input to the Mach-Zehnder interferometer into the long-arm waveguide and the short-arm waveguide. The optical path difference between the two arms determines the wavelength that can be combined and output by the multimode interference coupler after constructive interference.

[0035] For example, if the wavelength required to be transmitted is 2000nm, for a waveguide with a thickness of 300nm and a width of 2200nm, its effective refractive index is 1.5619 and its group refractive index is 1.8876. Based on these parameters, the total length of the microring can be calculated to be 832.32μm. and , then the difference in length between the two arms of the first Mach-Zehnder interferometer is 256.098 μm, the difference in length between the two arms of the second Mach-Zehnder interferometer is 192.074 μm, and the common multiple of the FSR of the two Mach-Zehnder interferometers is , that is, the FSR of the filter of this embodiment is about 33.1nm. Figure 4 shown.

[0036] The present embodiment provides a high-quality filter device that achieves a multiple filtering effect by integrating a series-connected Mach-Zehnder interferometer in the microring portion of a microring resonator. The total length of the short-arm waveguide of the microring and the Mach-Zehnder interferometer should meet the resonance condition of the required wavelength in the microring resonator, and the required light wavelength is output by the Drop port. Since the optical path difference between the two arms of the Mach-Zehnder interferometer determines the wavelength of constructive interference and the FSR between the wavelengths, when the length difference between the long arms and the short arms of multiple Mach-Zehnder interferometers meets a certain multiple condition, the FSR after series connection is the lowest common multiple of the FSR of the Mach-Zehnder interferometers before series connection. Since the FSR of the present embodiment is determined by the parameters of the two series-connected Mach-Zehnder interferometers, increasing the quality factor of the filter by increasing the length of the microring within a certain range will not reduce the FSR, and a narrow linewidth wavelength output can be achieved.

[0037] Example 2 This embodiment is the second embodiment of a high-quality factor filter device. This embodiment is similar to the first embodiment, except that, in this embodiment, since the long-arm waveguide of the Mach-Zehnder interferometer is relatively long, a spiral waveguide is used to reduce the device area, thereby further improving the device integration.

[0038] Example 3 This embodiment is the third embodiment of a high-quality factor filter device. This embodiment is similar to the first embodiment, except that, in this embodiment, three Mach-Zehnder interferometers are connected in series in the microring to further improve the extinction ratio of the filter and simultaneously improve the quality factor of the device.

[0039] In this embodiment, two of the Mach-Zehnder interferometers are the same as those in Example 1. The length of the short arm waveguide of the added Mach-Zehnder interferometer is 10 μm, and the length of the first U-shaped waveguide is reduced by 10 μm to ensure that the total length of the microring remains unchanged. The length of the long arm waveguide is 138.049 μm. Since the common multiple of the FSRs of the three Mach-Zehnder interferometers is the same as that in Example 1, the FSR of the device is the same as that in Example 1, which is approximately 33.1 nm, while the quality factor and extinction ratio are further improved.

[0040] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0041] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A high quality factor filter device, characterized in that The invention comprises a microring resonator for realizing periodic filtering to ensure a large quality factor, and a Mach-Zehnder interferometer for filtering unnecessary wavelengths; the Mach-Zehnder interferometer is connected in series on one side of the microring of the microring resonator and is located in the front half of the microring through which the input light is coupled into the microring for transmission.

2. The high quality factor filter device according to claim 1, characterized in that At least two Mach-Zehnder interferometers are provided: a first Mach-Zehnder interferometer (2) and a second Mach-Zehnder interferometer (3), and the two Mach-Zehnder interferometers are connected in series on the same side of the microring in the microring resonator.

3. The high quality factor filter device according to claim 2, characterized in that: The microring resonator comprises an input straight waveguide (11), a first U-shaped waveguide (12), a second U-shaped waveguide (13) and an output straight waveguide (14); the input straight waveguide (11) is coupled to the first U-shaped waveguide (12), one end of the first U-shaped waveguide (12) is connected to one end of the Mach-Zehnder interferometer, and the other end of the Mach-Zehnder interferometer is connected to one end of the second U-shaped waveguide (13); the other end of the first U-shaped waveguide (12) is connected to the other end of the second U-shaped waveguide (13) through a second straight waveguide (5); and the second U-shaped waveguide (13) is coupled to the output straight waveguide (14).

4. The high quality factor filter device according to claim 3, characterized in that: The first Mach-Zehnder interferometer (2) comprises a first multimode interference coupler (21), a first short arm waveguide (22), a first long arm waveguide (23) and a second multimode interference coupler (24); the output end of the first multimode interference coupler (21) is connected to one end of the first short arm waveguide (22) and the first long arm waveguide (23), respectively; the other ends of the first short arm waveguide (22) and the first long arm waveguide (23) are combined through the second multimode interference coupler (24); the second Mach-Zehnder interferometer (3) comprises a third multimode interference coupler (31), a second short arm waveguide (32), a second long arm waveguide (33) and a fourth multimode interference coupler The output end of the third multimode interference coupler (31) is connected to one end of the second short arm waveguide (32) and the second long arm waveguide (33), respectively, and the other ends of the second short arm waveguide (32) and the second long arm waveguide (33) are combined through the fourth multimode interference coupler (34); the first U-shaped waveguide (12) is connected to the input end of the first multimode interference coupler (21), the output end of the second multimode interference coupler (24) is connected to the input end of the third multimode interference coupler (31) through the first straight waveguide (4), and the output end of the fourth multimode interference coupler (34) is connected to the second U-shaped waveguide (13).

5. The high quality factor filter device according to claim 4, characterized in that: The total length L of the first straight waveguide (4), the second straight waveguide (5), the first U-shaped waveguide (12), the second U-shaped waveguide (13), the first short arm waveguide (22), and the second short arm waveguide (32) must meet the following conditions: , neff is the effective refractive index of the microring.

6. The high quality factor filter device according to claim 5, characterized in that: The length difference between the first short arm waveguide (22) and the first long arm waveguide (23) must satisfy the following condition: after light of a desired wavelength enters the first short arm waveguide (22) and the first long arm waveguide (23) from the first multimode interference coupler (21), the phase difference of the two beams of light output from the first multimode interference coupler (21) after passing through the first short arm waveguide (22) and the first long arm waveguide (23) and reaching the second multimode interference coupler (24) is , = .

7. The high quality factor filter device according to claim 6, characterized in that: The length difference between the second short arm waveguide (32) and the second long arm waveguide (33) must satisfy the following condition: after light of a desired wavelength enters the second short arm waveguide (32) and the second long arm waveguide (33) from the third multimode interference coupler (31), the two beams of light output from the third multimode interference coupler (31) pass through the second short arm waveguide (32) and the second long arm waveguide (33) respectively, and then reach the fourth multimode interference coupler (34) with a phase difference of , = .

8. The high quality factor filter device according to claim 7, characterized in that: The length difference between the first short arm waveguide (22) and the first long arm waveguide (23) is L 1The following conditions must be met: The length difference between the second short arm waveguide (32) and the second long arm waveguide (33) is L 2The following conditions must be met: .

9. The high quality factor filter device according to any one of claims 4 to 8, characterized in that: Light of the desired wavelength undergoes constructive interference in the Mach-Zehnder interferometer, periodically undergoing destructive and constructive interference as the wavelength changes, thereby increasing the FSR by filtering out the resonant wavelengths around the desired wavelength.

10. The high quality factor filter device according to claim 9, characterized in that: The FSR of the first Mach-Zehnder interferometer (2) is: ; The FSR of the second Mach-Zehnder interferometer (3) is: ; The final FSR is and The lowest common multiple of; where neff is the effective refractive index of the microring, L 1 is the length difference between the first short arm waveguide (22) and the first long arm waveguide (23); L 2 is the length difference between the second short arm waveguide (32) and the second long arm waveguide (33); ; ; is the wavelength; n is the group refractive index of the waveguide.

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