Novel on-chip hybrid filter having fir cascaded with IIR, and filtering method

Abstract

A novel on-chip hybrid filter having FIR cascaded with IIR, and a filtering method, which are used for solving the technical problem of the existing FIR filters requiring a higher order to achieve a high out-of-band rejection ratio. The hybrid filter comprises an FIR filtering module and an IIR filtering module, which are cascaded with each other, wherein the FIR filtering module uses a first MZI structure, the IIR filtering module uses a DR-MZI structure, an input end of the FIR filtering module is used for receiving an externally input optical signal, an output of the FIR filtering module is used as an input of the IIR filtering module, and an output of the IIR filtering module is used as an output of the whole hybrid filter, which is equivalent to performing secondary filtering on the signal. The IIR filtering module involves a low and smooth in-band loss and a high out-of-band loss, so that the out-of-band rejection ratio of the whole filter can be effectively improved, rapid roll-off is achieved, and signals outside a passband are well suppressed without affecting in-band signals. In addition, low-order filters can also achieve good filtering effects.

Description

A novel on-chip hybrid filter based on FIR and IIR cascade and filtering method Technical Field

[0001] The present invention relates to an on-chip tunable optical filter, and in particular to a novel on-chip hybrid filter of FIR and IIR cascade and a filtering method. Background Art

[0002] Optical communications are information transmission technologies that use light waves as a carrier. They encompass both wired optical communications, which use optical fiber as the transmission medium, and wireless optical communications, which can transmit optical signals in free space, such as the atmosphere and outer space. Currently, a new round of scientific and technological revolution and industrial transformation continues to deepen globally, increasing reliance on networks across various sectors. Optical communications systems, which serve as their core support, face significant challenges.

[0003] Optical filters, as frequency selectors, can filter out certain frequency components or frequency bands of an input signal, thereby altering the signal's spectral structure. Optical filters are widely used in optical communications and interconnect systems, suppressing out-of-band noise and improving system performance. The tunability of optical filters enhances system flexibility and adaptability, a crucial prerequisite for their application. Optical filter tunability can be broadly categorized into three types: center wavelength tunability, bandwidth tunability, and both center wavelength and bandwidth tunability. Tunability of both center wavelength and bandwidth is crucial for the development of future dynamic network technologies. Silicon-based optoelectronics is an optoelectronic integration technology compatible with established microelectronics. It combines the ultra-large-scale logic and ultra-high-precision manufacturing capabilities of CMOS technology with the ultra-high speed and ultra-low power consumption of photonics. This innovative technology addresses the conflict between technological advancement and cost. Consequently, on-chip optical filters based on silicon-based optoelectronics have become a current research hotspot.

[0004] Currently, a variety of optical tunable filters have been realized using cascaded or coupled microring resonators (MRRs), cascaded asymmetric Mach-Zehnder interferometers (MZIs), and structures composed of both MRRs and MZIs. On-chip finite impulse response (FIR) filters have attracted widespread attention due to their stability, simplicity, and linear response. However, since the unit impulse response of FIR filters is finite in length and there is generally no feedback loop in the structure, a higher order is required to achieve a high out-of-band rejection ratio.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to solve the technical problem that the existing FIR filter requires a higher order to achieve a high out-of-band suppression ratio, and to provide a novel on-chip hybrid filter of FIR and IIR cascade and a filtering method.

[0007] In order to achieve the above objectives, the technical solutions of the present invention are as follows:

[0008] A new type of on-chip hybrid filter that is a cascade of FIR and IIR, which is special in that it includes an FIR filter module and an IIR filter module;

[0009] The FIR filter module adopts a first MZI structure, which includes a first beam splitter located at the front end of the first MZI, an amplitude modulation module and a first phase modulation module located in sequence on the upper arm of the first MZI, a delay line, an amplitude modulation module and a first phase modulation module located in sequence on the lower arm of the first MZI, and a first beam combiner located at the rear end of the first MZI; the amplitude modulation module adopts a second MZI structure, and the upper arm of the second MZI is provided with a second phase modulation module, which is used to change the result of mutual interference after light passes through the upper arm and lower arm of the second MZI to achieve amplitude modulation;

[0010] The first beam splitter is used to receive an external input optical signal and split it equally into two beams to form a first upper optical path and a first lower optical path; the first MZI upper arm is located on the first upper optical path, and the first MZI lower arm is located on the first lower optical path, and is used to respectively achieve amplitude modulation and phase modulation of the optical signals on the first upper optical path and the first lower optical path by adjusting the power applied to each amplitude modulation module and the first phase modulation module; the first beam combiner is used to combine the modulated optical signals of the first MZI upper arm and the lower arm, and use them as the output of the FIR filter module;

[0011] The IIR filter module adopts a DR-MZI structure, which includes a second beam splitter located at the front end of the DR-MZI, microring resonators respectively coupled to the upper and lower arms of the DR-MZI, two third phase modulation modules respectively arranged on the two microring resonators and symmetrically positioned, and a second beam combiner located at the rear end of the DR-MZI; the third phase modulation module is located on the side of the corresponding microring resonator away from the DR-MZI structure;

[0012] The input end of the second beam splitter is connected to the output end of the first beam combiner, and is used to receive the optical signal output by the FIR filter module and divide it into two beams, forming a second upper optical path and a second lower optical path; the DR-MZI upper arm is located on the second upper optical path, and the DR-MZI lower arm is located on the second lower optical path. By adjusting the power of the third phase modulation module on the corresponding microring resonator, the DR-MZI upper arm and the lower arm are controlled to produce a phase difference to achieve modulation of the optical signal; the second beam combiner is used to combine the optical signals modulated by the DR-MZI upper arm and the lower arm, and use them as the output of the entire filter.

[0013] Furthermore, the first phase modulation module, the second phase modulation module and the third phase modulation module are all micro heaters.

[0014] Furthermore, the first beam splitter, the first beam combiner, the second beam splitter and the second beam combiner all adopt multimode interferometers; and the delay line adopts a spiral line generated by an Archimedean spiral constructor.

[0015] Furthermore, the materials of the first beam splitter, the first beam combiner, the amplitude modulation module, the delay line, the second beam splitter, the second beam combiner and the microring resonator are all silicon, silicon oxide, silicon nitride, III-V materials or lithium niobate materials.

[0016] The present invention also provides another novel on-chip hybrid filter of FIR and IIR cascade, which is special in that:

[0017] Including FIR filter unit and IIR filter unit;

[0018] The FIR filter unit includes a third beam splitter, M parallel FIR filter modules and a third beam combiner, where M is an integer greater than or equal to 2;

[0019] The FIR filter module adopts a first MZI structure, which includes a first beam splitter located at the front end of the first MZI, an amplitude modulation module and a first phase modulation module located in sequence on the upper arm of the first MZI, a delay line, an amplitude modulation module and a first phase modulation module located in sequence on the lower arm of the first MZI, and a first beam combiner located at the rear end of the first MZI; the amplitude modulation module adopts a second MZI structure, and the upper arm of the second MZI is provided with a second phase modulation module, which is used to change the result of mutual interference after light passes through the upper arm and lower arm of the second MZI to achieve amplitude modulation;

[0020] A delay line is provided on the first MZI lower arm in the first FIR filter module, the first MZI upper arm in the second to M-th FIR filter modules, and the first MZI lower arm. The duration of the delay line doubles in sequence from the first MZI lower arm in the first FIR filter module to the first MZI lower arm in the M-th FIR filter module.

[0021] The first beam splitter is used to split the received optical signal into two beams, forming a first upper optical path and a first lower optical path; the first MZI upper arm is located on the first upper optical path, and the first MZI lower arm is located on the first lower optical path, and is used to respectively achieve amplitude modulation and phase modulation of the optical signals on the first upper optical path and the first lower optical path by adjusting the power applied to each amplitude modulation module and the first phase modulation module; the first beam combiner is used to combine the modulated optical signals of the first MZI upper arm and the lower arm, and use them as the output of the FIR filter module;

[0022] The IIR filter unit includes N serially connected IIR filter modules, where N is an integer greater than or equal to 2;

[0023] The IIR filter module adopts a DR-MZI structure, which includes a second beam splitter located at the front end of the DR-MZI, microring resonators respectively coupled to the upper and lower arms of the DR-MZI, two third phase modulation modules respectively arranged on the two microring resonators and symmetrically positioned, and a second beam combiner located at the rear end of the DR-MZI; the third phase modulation module is located on the side of the corresponding microring resonator away from the DR-MZI structure;

[0024] The second beam splitter is used to divide the received optical signal into two beams, forming a second upper optical path and a second lower optical path; the DR-MZI upper arm is located on the second upper optical path, and the DR-MZI lower arm is located on the second lower optical path, and is used to respectively realize amplitude modulation and phase modulation of the optical signals on the second upper optical path and the second lower optical path through the corresponding microring resonator and the third phase modulation module; the second beam combiner is used to combine the modulated optical signals of the DR-MZI upper arm and the lower arm, and use them as the output of the IIR filter module.

[0025] The M output ends of the third beam splitter are respectively connected to the input ends of the M first beam splitters, so as to evenly divide the received external input optical signal into M beams and then send them into each first beam splitter; the M input ends of the third beam combiner are respectively connected to the output ends of the M first beam combiners, so as to combine the optical signals output by the M FIR filter modules; the input end of the second beam splitter in the first IIR filter module is connected to the output end of the third beam combiner, and the optical signal output by the second beam combiner in the Nth IIR filter module serves as the output of the entire filter.

[0026] Furthermore, the first phase modulation module, the second phase modulation module and the third phase modulation module are all micro heaters.

[0027] Furthermore, the first beam splitter, the first beam combiner, the second beam splitter, the second beam combiner, the third beam splitter and the third beam combiner all adopt multimode interferometers; and the delay line is a spiral line generated by an Archimedean spiral constructor.

[0028] Furthermore, the materials of the first beam splitter, the first beam combiner, the amplitude modulation module, the delay line, the second beam splitter, the second beam combiner, the microring resonator, the third beam splitter and the third beam combiner are all silicon or silicon oxide or silicon nitride or III-V material or lithium niobate material.

[0029] Based on the novel on-chip hybrid filter of the FIR and IIR cascade, the present invention further provides a filtering method, which is special in that it includes the following steps:

[0030] 1] Adjusting the power applied to each first phase modulation module and each second phase modulation module to change the amplitude and phase of the optical signal on the first uplink optical path and the first downlink optical path to achieve a desired spectral shape;

[0031] 2] Adjust the power applied to the third phase modulation module so that the IIR filter module operates in the bar state and the center wavelength of the passband is aligned with the center wavelength of the FIR filter module.

[0032] The beneficial effects of the present invention compared to the prior art are as follows:

[0033] 1. The novel on-chip hybrid filter of FIR and IIR cascade provided by the present invention adopts the structure of cascade of FIR filter and IIR filter, which is equivalent to performing secondary filtering on the signal, and can effectively improve the out-of-band suppression ratio of the entire filter and achieve rapid roll-off. Without affecting the in-band signal, it can well suppress the signal outside the passband, and low-order filters can also achieve good filtering effect.

[0034] 2. The present invention provides a novel on-chip hybrid filter of FIR and IIR cascade, in which a first phase modulation module and a second phase modulation module are provided on the FIR modulation module, and a third phase modulation module is provided on the IIR modulation module. By adjusting the power applied to the first phase modulation module, the second phase modulation module and the third phase modulation module, and then controlling the phase change, the passband shape and the center wavelength can be flexibly tunable in changing, thereby improving the flexibility and adaptability of the system.

[0035] 3. The novel on-chip hybrid filter of FIR and IIR cascade provided by the present invention has significant advantages such as compact structure, low power consumption and low cost compared with existing filters based on optical fiber technology, spatial optical technology and liquid crystal modulation.

[0036] 4. The novel on-chip hybrid filter of FIR and IIR cascade provided by the present invention has a device manufacturing process that is highly compatible with the traditional VLSI complementary metal oxide semiconductor process and does not require special processes, which is conducive to large-scale manufacturing of the device and cost reduction.

[0037] 5. The filtering method of the novel on-chip hybrid filter based on the above-mentioned FIR and IIR cascade has simple adjustment and good filtering effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a schematic structural diagram of a novel on-chip hybrid filter of FIR and IIR cascades according to a first embodiment of the present invention;

[0039] FIG2 is a schematic diagram of the structure of an FIR filter module in Embodiment 1 of the present invention;

[0040] FIG3 is a schematic diagram of the structure of an IIR filter module in Embodiment 1 of the present invention;

[0041] FIG4 is a schematic diagram of the spectrum of the I1-O2 port of the IIR filter module in the cross state in Example 1 of the present invention;

[0042] FIG5 is a schematic diagram of the spectrum of the I1-O2 port of the IIR filter module in the bar state in Example 1 of the present invention;

[0043] FIG6 is a schematic diagram of the spectrum of the I1-O1 port of the IIR filter module in the bar state in Example 1 of the present invention;

[0044] FIG7 is a schematic diagram of the out-of-band suppression effect of the first embodiment of the present invention;

[0045] FIG8 is a schematic structural diagram of a second embodiment of a novel on-chip hybrid filter of FIR and IIR cascade connection according to the present invention.

[0046] The specific reference numerals are as follows:

[0047] 1-first beam splitter; 2-first beam combiner; 3-amplitude modulation module; 4-first phase modulation module; 5-delay line; 6-second phase modulation module; 7-second beam splitter; 8-second beam combiner; 9-microring resonator; 10-third phase modulation module; 11-third beam splitter; 12-third beam combiner. DETAILED DESCRIPTION

[0048] Example 1

[0049] A novel on-chip hybrid filter of FIR and IIR cascades, in this embodiment, is a novel hybrid filter of 2nd-order FIR and 2nd-order IIR cascades, as shown in FIG1 , including an FIR filter module and an IIR filter module.

[0050] As shown in Figure 2, the FIR filter module adopts a first MZI (Mach-Zehnder Interferometer) structure, which includes a first beam splitter 1 located at the front end of the first MZI, an amplitude modulation module 3 and a first phase modulation module 4 located in sequence on the upper arm of the first MZI, a delay line 5 located in sequence on the lower arm of the first MZI, the amplitude modulation module 3 and the first phase modulation module 4, and a first beam combiner 2 located at the rear end of the first MZI. Among them, the amplitude modulation module 3 adopts a second MZI structure, and the upper arm of the second MZI is provided with a second phase modulation module 6. It is used to form an asymmetric MZI structure through the second phase modulation module 6, change the result of mutual interference after light passes through the upper and lower arms of the second MZI, and achieve amplitude modulation. The delay line 5 is used to generate a time delay τ between two adjacent optical paths. In this embodiment, the delay line 5 adopts a spiral generated by an Archimedean spiral constructor. Other embodiments of the present invention may also adopt delay lines of other structures.

[0051] The first beam splitter 1 is used to receive an external input optical signal and divide it into two beams, forming a first upper optical path and a first lower optical path; the first MZI upper arm is located on the first upper optical path, and the first MZI lower arm is located on the first lower optical path, and is used to achieve amplitude modulation and phase modulation of the optical signals on the first upper optical path and the first lower optical path respectively by adjusting the power applied to each amplitude modulation module 3 and the first phase modulation module 4; the first combiner 2 is used to combine the modulated optical signals of the first MZI upper arm and lower arm, and use them as the output of the FIR filter module.

[0052] The implementation principle of the FIR filter module is as follows: by modifying the weights of the amplitude and phase of the two optical paths in the FIR filter module, that is, adjusting the power applied to the amplitude modulation module 3 and the first phase modulation module 4, the output spectrum can be reshaped and the central wavelength and bandwidth can be tuned.

[0053] As shown in Figure 3, the IIR filter module adopts a DR-MZI (dual microring assisted Mach-Zehnder interferometer) structure, which includes a second beam splitter 7 at the front end of the DR-MZI, a microring resonator 9 coupled to the upper and lower arms of the DR-MZI, two third phase modulation modules 10 symmetrically arranged on the two microring resonators 9, and a second beam combiner 8 at the rear end of the DR-MZI. The third phase modulation module 10 is located on the side of the corresponding microring resonator 9 away from the DR-MZI structure. The IIR filter module ensures that the microring resonator 9 operates in an overcoupled state by setting parameters such as the radius of the microring resonator 9 and the gap between the microring resonator 9 and the upper and lower arms of the DR-MZI, thereby achieving strong coupling. At the same time, because the third phase modulation module 10 is integrated on the microring resonator 9, low-loss thermo-optical phase tuning can be achieved.

[0054] The input end of the second beam splitter 7 is connected to the output end of the first combiner 2, and is used to receive the optical signal output by the FIR filter module and divide it into two beams, forming a second upper optical path and a second lower optical path; the DR-MZI upper arm is located on the second upper optical path, and the DR-MZI lower arm is located on the second lower optical path. By adjusting the power of the third phase modulation module 10 on the corresponding microring resonator 9, a phase difference is generated between the DR-MZI upper arm and the lower arm to achieve modulation of the optical signal; the second combiner 8 is used to combine the optical signals modulated by the DR-MZI upper arm and the lower arm, and use them as the output of the entire filter.

[0055] The IIR filter module operates as follows: When the resonant wavelengths of the two microring resonators 9 are identical, as shown in Figure 4, light energy is transmitted from input port I1 to output port O2 with maximum transmittance, and the IIR filter module is in the crossover state. At this point, the output spectra of both the crossover port (I1-O2) and the bar port (I1-O1) are nearly flat, with the difference being that the bar port (I1-O1) exhibits loss, while the crossover port (I1-O2) exhibits almost no loss. By increasing the phase difference Δφ between the upper and lower IIR arms in a push-pull manner, the resonant wavelengths of the two MRRs are shifted in opposite directions. When the phase difference between the two arms reaches π at the resonant wavelength, the IIR filter module enters the barover state. At this point, as shown in Figure 5, the spectrum of the crossover port (I1-O2) exhibits a deep notch near the resonant wavelength, while the spectrum of the bar port (I1-O1) exhibits a peak, as shown in Figure 6.

[0056] In the present invention, the first beam splitter 1, the first beam combiner 2, the amplitude modulation module 3, the delay line 5, the second beam splitter 7, the second beam combiner 8, and the microring resonator 9 are all waveguides, and their materials can be selected from silicon, silicon oxide, silicon nitride, III-V materials, or lithium niobate materials. In this embodiment, silicon is used. Because the refractive index of silicon changes with temperature, and the first phase modulation module 4, the second phase modulation module 6, and the third phase modulation module 10 are all microheaters, the microheaters can achieve phase modulation through the thermo-optical effect of the silicon material. In other embodiments of the present invention, the first phase modulation module 4, the second phase modulation module 6, and the third phase modulation module 10 can also be PIN junctions, which can achieve phase modulation through the electro-optical effect of the above materials.

[0057] Preferably, due to the characteristics of multimode interferometer (MMI) being small in size, large in optical bandwidth, large in manufacturing tolerance and polarization-independent, in this embodiment, the first beam splitter 1, the first beam combiner 2, the second beam splitter 7 and the second beam combiner 8 all adopt multimode interferometers. In other embodiments of the present invention, the first beam splitter 1, the first beam combiner 2, the second beam splitter 7 and the second beam combiner 8 may also adopt other types of beam splitters and combiners such as Y-branch couplers and directional couplers. The first beam splitter 1 and the second beam splitter 7 are both 3dB splitters, which are used to divide the input optical signal into two paths. The ports of the first beam splitter 1 and the first beam combiner 2 are 1X2 ports, and the ports of the second beam splitter 7 and the second beam combiner 8 are 2X2 ports; the two input ports of the second beam splitter 7 are respectively denoted as I1 and I2, and the two output ports of the second beam combiner 8 are respectively denoted as O1 and O2, that is, the input ports of each IIR filter module are I1 and I2, and the output ports are O1 and O2. The input port I1 of the IIR filter module is used to connect to the output of the FIR filter module, and the output port O2 serves as the output port of the entire new hybrid filter, for outputting the final filtered signal.

[0058] Since on-chip infinite impulse response (IIR) filters are highly efficient and have a simple optical structure, they can be made very compact. Under the same out-of-band suppression ratio, the number of stages required can be less than that of FIR filters. Therefore, the novel on-chip hybrid filter of FIR and IIR cascade provided by the present invention adopts a cascade structure of FIR filters and IIR filters, which is equivalent to performing secondary filtering on the signal. The IIR filter module has low and flat in-band loss and high out-of-band loss, which can effectively improve the out-of-band suppression ratio of the entire filter and achieve rapid roll-off. As shown in FIG7 , without affecting the in-band signal, the degree of suppression of signals outside the passband is very good, and at the same time, low-order filters can also achieve good filtering effects.

[0059] Based on the novel on-chip hybrid filter of the FIR and IIR cascade, the present invention further provides a filtering method, which specifically includes the following steps:

[0060] 1] Adjusting the power applied to each first phase modulation module 4 and each second phase modulation module 6 in the FIR filter module, that is, adjusting the power applied to each micro heater in the FIR filter module, so as to change the amplitude and phase of the input optical signal to achieve the desired spectral shape;

[0061] 2] Adjust the power applied to each third phase modulation module 10 in the IIR filter module, that is, adjust the power applied to each micro heater in the IIR filter module, so that the IIR filter module operates in the bar state and the center wavelength of the passband is aligned with the center wavelength of the FIR filter module.

[0062] Example 2

[0063] By increasing the number of the FIR filter modules and the IIR filter modules, the present invention can obtain a more complex filter transfer function, thereby improving the performance of the filter.

[0064] The novel on-chip hybrid filter of FIR and IIR cascade provided in this embodiment is a novel hybrid filter of 4th-order FIR and 4th-order IIR cascade, as shown in FIG8 , including an FIR filter unit and an IIR filter unit.

[0065] The FIR filter unit includes a third beam splitter 11, two parallel FIR filter modules, and a third beam combiner 12. The first FIR filter module in this embodiment has the same structure as the FIR filter module in the first embodiment, except that a delay line 5 is provided on both the first MZI upper arm and the first MZI lower arm in the second FIR filter module in this embodiment, and the time extension of the delay line 5 is doubled from the first MZI lower arm in the first FIR filter module to the first MZI lower arm in the second FIR filter module, that is, the time extension of the delay line 5 on the first MZI upper arm in the second FIR filter module is twice as long as the delay line 5 on the first MZI lower arm in the first FIR filter module, and the time extension of the delay line 5 on the first MZI lower arm in the second FIR filter module is three times as long as the delay line 5 on the first MZI lower arm in the first FIR filter module, so as to ensure that the delay difference between two adjacent optical paths from top to bottom is constant at τ.

[0066] The IIR filter unit includes two IIR filter modules connected in series. The IIR filter module in this embodiment has the same structure as the IIR filter module in the first embodiment.

[0067] In this embodiment, both the third beam splitter 11 and the third beam combiner 12 utilize a multimode interferometer (MMI), each having a 1x2 port, i.e., a 3dB splitter, for splitting an input optical signal into two paths or combining two optical signals into one path. Specifically, in this embodiment, the third beam splitter 11 is configured to receive an external input optical signal and split the optical signal into two beams. The first beam splitters 1 in the two FIR filter modules are located in the optical paths of the two beams, respectively, for inputting the received optical signals into the upper and lower FIR filter modules, respectively. The third beam combiner 12 is configured to combine the optical signals output by the two FIR filter modules. The second beam splitter 7 in the first IIR filter module is located on the optical path of the third beam combiner 12. Its input port, I1, is connected to the output of the third beam combiner 12, and is used to input the optical signal output by the third beam combiner 12 into the first IIR filter module. The output port O2 of the second beam combiner 8 in the first IIR filter module is connected to the input port I1 of the second beam splitter 7 in the second IIR filter module. The output port O2 of the second beam combiner 8 in the second IIR filter module serves as the output port of the entire new hybrid filter, and is used to output the final filtered signal. This achieves the expansion of the order of the new hybrid filter of the FIR and IIR cascade.

[0068] The novel hybrid filter structure of the FIR and IIR cascade in the present invention is not limited to the above-mentioned second-order FIR cascade second-order IIR and fourth-order FIR cascade fourth-order IIR forms. Theoretically, it can be (2MFIR)×(2NIIR), where M and N are both positive integers. In practical applications, the appropriate order can be selected based on requirements such as performance and chip size. The corresponding filtering method is the same as the filtering method in Example 1.

Claims

1. A novel on-chip hybrid filter of FIR and IIR cascade, characterized by: Including FIR filter module and IIR filter module; The FIR filter module adopts a first MZI structure, comprising a first beam splitter (1) located at the front end of the first MZI, an amplitude modulation module (3) and a first phase modulation module (4) located in sequence at the upper arm of the first MZI, a delay line (5), an amplitude modulation module (3) and a first phase modulation module (4) located in sequence at the lower arm of the first MZI, and a first beam combiner (2) located at the rear end of the first MZI; the amplitude modulation module (3) adopts a second MZI structure, and the upper arm of the second MZI is provided with a second phase modulation module (6) for changing the result of mutual interference of light after passing through the upper arm and the lower arm of the second MZI, thereby realizing amplitude modulation; The first beam splitter (1) is used to receive an external input optical signal and divide it into two beams to form a first upper optical path and a first lower optical path; the first MZI upper arm is located on the first upper optical path, and the first MZI lower arm is located on the first lower optical path, and is used to respectively realize amplitude modulation and phase modulation of the optical signals on the first upper optical path and the first lower optical path by adjusting the power applied to each amplitude modulation module (3) and the first phase modulation module (4); the first beam combiner (2) is used to combine the modulated optical signals of the first MZI upper arm and the lower arm, and use them as the output of the FIR filter module; The IIR filter module adopts a DR-MZI structure, comprising a second beam splitter (7) located at the front end of the DR-MZI, microring resonators (9) respectively coupled and arranged on the upper arm and the lower arm of the DR-MZI, two third phase modulation modules (10) respectively arranged on the two microring resonators (9) and symmetrically positioned, and a second beam combiner (8) located at the rear end of the DR-MZI; the third phase modulation module (10) is located on a side of the corresponding microring resonator (9) away from the DR-MZI structure; The input end of the second beam splitter (7) is connected to the output end of the first beam combiner (2), and is used to receive the optical signal output by the FIR filter module and divide it into two beams, forming a second upper optical path and a second lower optical path; the DR-MZI upper arm is located on the second upper optical path, and the DR-MZI lower arm is located on the second lower optical path. The power of the third phase modulation module (10) on the corresponding microring resonator (9) is adjusted to control the DR-MZI upper arm and the lower arm to produce a phase difference, thereby realizing modulation of the optical signal; the second beam combiner (8) is used to combine the optical signals modulated by the DR-MZI upper arm and the lower arm, and use them as the output of the entire filter.

2. The novel on-chip hybrid filter of FIR and IIR cascade according to claim 1, characterized in that: The first phase modulation module (4), the second phase modulation module (6) and the third phase modulation module (10) are all micro-heaters.

3. The novel on-chip hybrid filter of FIR and IIR cascade connection according to claim 1 or 2, characterized in that: The first beam splitter (1), the first beam combiner (2), the second beam splitter (7) and the second beam combiner (8) all adopt multi-mode interferometers; The delay line (5) is a spiral line generated by an Archimedean spiral constructor.

4. The novel on-chip hybrid filter of FIR and IIR cascade according to claim 3, characterized in that: The materials of the first beam splitter (1), the first beam combiner (2), the amplitude modulation module (3), the delay line (5), the second beam splitter (7), the second beam combiner (8) and the microring resonator (9) are all silicon, silicon oxide, silicon nitride, III-V materials or lithium niobate materials.

5. A novel on-chip hybrid filter of FIR and IIR cascade, characterized by: Including FIR filter unit and IIR filter unit; The FIR filter unit comprises a third beam splitter (11), M parallel-connected FIR filter modules and a third beam combiner (12), where M is an integer greater than or equal to 2; The FIR filter module adopts a first MZI structure, comprising a first beam splitter (1) located at the front end of the first MZI, an amplitude modulation module (3) and a first phase modulation module (4) located in sequence at the upper arm of the first MZI, a delay line (5), an amplitude modulation module (3) and a first phase modulation module (4) located in sequence at the lower arm of the first MZI, and a first beam combiner (2) located at the rear end of the first MZI; the amplitude modulation module (3) adopts a second MZI structure, and the upper arm of the second MZI is provided with a second phase modulation module (6) for changing the result of mutual interference of light after passing through the upper arm and the lower arm of the second MZI, thereby realizing amplitude modulation; A delay line (5) is provided on the first MZI lower arm in the first FIR filter module, the first MZI upper arm in the second to the Mth FIR filter modules, and the first MZI lower arm, and the time extension of the delay line (5) is doubled in sequence from the first MZI lower arm in the first FIR filter module to the first MZI lower arm in the Mth FIR filter module; The first beam splitter (1) is used to split the received optical signal into two beams to form a first upper optical path and a first lower optical path; the first MZI upper arm is located on the first upper optical path, and the first MZI lower arm is located on the first lower optical path, and is used to respectively realize amplitude modulation and phase modulation of the optical signals on the first upper optical path and the first lower optical path by adjusting the power applied to each amplitude modulation module (3) and the first phase modulation module (4); the first beam combiner (2) is used to combine the modulated optical signals of the first MZI upper arm and the lower arm, and use them as the output of the FIR filter module; The IIR filter unit includes N serially connected IIR filter modules, where N is an integer greater than or equal to 2; The IIR filter module adopts a DR-MZI structure, which includes a second beam splitter (7) located at the front end of the DR-MZI, a micro-ring resonator (9) respectively coupled to the upper arm and the lower arm of the DR-MZI, and Two third phase modulation modules (10) are symmetrically arranged on two microring resonators (9), and a second beam combiner (8) is located at the rear end of the DR-MZI; the third phase modulation module (10) is located on a side of the corresponding microring resonator (9) away from the DR-MZI structure; The second beam splitter (7) is used to equally split the received optical signal into two beams to form a second upper optical path and a second lower optical path; the DR-MZI upper arm is located on the second upper optical path, and the DR-MZI lower arm is located on the second lower optical path, and is used to respectively implement amplitude modulation and phase modulation on the optical signals on the second upper optical path and the second lower optical path through corresponding microring resonators (9) and third phase modulation modules (10); the second beam combiner (8) is used to combine the modulated optical signals of the DR-MZI upper arm and the lower arm, and use them as the output of the IIR filter module; The M output ends of the third beam splitter (11) are respectively connected to the input ends of the M first beam splitters (1), and are used to evenly split the received external input optical signal into M beams and then send them to each first beam splitter (1); the M input ends of the third beam combiner (12) are respectively connected to the output ends of the M first beam combiners (2), and are used to combine the optical signals output by the M FIR filter modules; The input end of the second beam splitter (7) in the first IIR filter module is connected to the output end of the third beam combiner (12), and the optical signal output by the second beam combiner (8) in the Nth IIR filter module serves as the output of the entire filter.

6. The novel on-chip hybrid filter of FIR and IIR cascade connection according to claim 5, characterized in that: The first phase modulation module (4), the second phase modulation module (6) and the third phase modulation module (10) are all micro-heaters.

7. The novel on-chip hybrid filter of FIR and IIR cascade connection according to claim 5 or 6, characterized in that: The first beam splitter (1), the first beam combiner (2), the second beam splitter (7), the second beam combiner (8), the third beam splitter (11) and the third beam combiner (12) all adopt multi-mode interferometers; The delay line (5) is a spiral line generated by an Archimedean spiral constructor.

8. The novel on-chip hybrid filter of FIR and IIR cascade connection according to claim 7, characterized in that: The materials of the first beam splitter (1), the first beam combiner (2), the amplitude modulation module (3), the delay line (5), the second beam splitter (7), the second beam combiner (8), the microring resonator (9), the third beam splitter (11) and the third beam combiner (12) are all silicon, silicon oxide, silicon nitride, III-V material or lithium niobate material.

9. A filtering method based on a novel on-chip hybrid filter of FIR and IIR cascade according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1] adjusting the power applied to each first phase modulation module (4) and each second phase modulation module (6), changing the amplitude and phase of the optical signal on the first upper optical path and the first lower optical path, and realizing the desired spectral shape; 2] Adjust the power applied to the third phase modulation module (10) so that the IIR filter module operates in a bar state and the central wavelength of the passband is aligned with the central wavelength of the FIR filter module.

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