A programmable microwave photonic filter system based on graphene and micro-ring resonator array and implementation method thereof

Abstract

This invention provides a programmable microwave photonic filter system and its implementation method based on graphene and a microring resonator array, belonging to the field of tuning and filtering technology in microwave photonics. It includes an optical carrier generation subsystem, a radio frequency (RF) and optical modulation subsystem, a photonic filtering subsystem, and a photodetector subsystem. The optical carrier generation subsystem is connected to the RF and optical modulation subsystem, and the RF signal is input to the RF and optical modulation subsystem. The RF and optical modulation subsystem is connected to the photonic filtering subsystem, and the photonic filtering subsystem is connected to the photodetector subsystem. The photonic filtering subsystem employs a graphene two-dimensional microring resonator array structure for programmable filtering of modulated optical signals in the optical domain. Tuning is achieved through the sub-picosecond carrier electrical control effect of graphene, with a theoretical switching speed on the GHz scale.

Description

Technical Field

[0001] This invention relates to the field of tuning and filtering technology in microwave photonics, and in particular to a programmable microwave photonic filter system based on graphene and a microring resonator array and its implementation method. Background Technology

[0002] Microwave photonic filters, as the core signal processing unit in microwave photonic links, can directly perform filtering operations on radio frequency signals in the optical domain, overcoming the limitations of traditional electronic filters in terms of operating bandwidth, tunability, and electromagnetic interference resistance. In recent years, academia and industry have proposed numerous microwave filter implementation schemes based on photonic technology, whose technical approaches mainly cover the following four categories: (1) Microwave photonic filters based on dispersive fiber. This type of scheme utilizes the dispersion effect of single-mode fiber or dispersion-compensating fiber to convert the wavelength information of the modulated optical signal into phase / delay information in the microwave domain, and achieves finite impulse response (FIR) filtering through the combination of multi-wavelength light sources and dispersive media. For example, Hamidi et al. used a programmable spectral shaper in conjunction with dispersive fiber to realize a reconfigurable bandpass filter. However, the core drawback of the dispersive fiber scheme is that the periodic power fading caused by dispersion severely restricts the free spectrum range (FSR) and operating bandwidth of the filter; the extreme sensitivity of the fiber link to temperature changes leads to significant drift in the filtering characteristics; in addition, the fiber loop that is several kilometers long makes it difficult to miniaturize the system.

[0003] (2) Microwave photonic filters based on semiconductor optical amplifiers (SOA). SOA is mainly used in MPF ​​to realize negative tap coefficients, in order to overcome the physical limitation that all-optical positive taps can only achieve low-pass filtering. The principle is to use the nonlinear effect of cross-gain modulation (XGM) or cross-phase modulation (XPM) of SOA to invert the intensity information of one optical signal to another wavelength, thereby realizing π phase reversal. However, the structure of SOA-based schemes is complex (requiring additional lasers and splitters), the conversion bandwidth is limited by the carrier recovery time of SOA (usually on the order of hundreds of picoseconds), and the SOA gain is highly sensitive to the polarization state of the input light, resulting in poor system stability in non-laboratory environments.

[0004] (3) Microwave photonic filters based on Mach-Zehnder interferometer (MZI) structures. MZIs can be used as spectral dividers or tunable couplers, achieving comb filtering or optical power distribution functions by thermo-optical modulation of the interferometer arm length difference. Multi-stage cascaded MZIs combined with microring resonators have been used to realize programmable finite impulse response filtering. However, the MZI scheme has obvious limitations: the polarization states of the two arms need to be precisely matched (fringe visibility is significantly affected by polarization state drift), each MZI stage needs to be equipped with a thermo-optical phase shifter hundreds of micrometers long, the chip area increases sharply after multi-stage cascading, and the speed and energy consumption of thermo-optical tuning are not ideal.

[0005] (4) Integrated microwave photonic filters based on microring resonators (MRRs). In recent years, silicon-based microring resonators based on silicon-on-insulator (SOI) platforms have been widely studied for the realization of integrated microwave photonic filters. Microring resonators can be regarded as optical infinite impulse response (IIR) filters, and a filter response with a flat passband can be synthesized by cascading / coupling multiple microrings.

[0006] Existing filters suffer from the following problems: (i) Limited filtering modes. Existing integrated microwave photonic filters can only operate in a fixed filtering mode (usually bandpass filtering) after physical design. When communication / radar systems need to switch between low-pass, bandpass, or high-pass filtering functions in different operating frequency bands, multiple independent filters must be configured and routed through optical switches, leading to a sharp increase in system complexity, power consumption, and cost. Although the finite impulse response scheme based on MZI cascades can achieve a certain degree of programmability, its precise control of the weight coefficients of each tap depends on a large-scale thermo-optical phase shifter array. Each phase shifter consumes several milliwatts to tens of milliwatts of static power, and the overall chip power consumption increases linearly with the number of taps. Fixed filtering modes and inflexible switching. Existing microwave photonic filters can usually only achieve a single filtering mode (such as bandpass only or low-pass only). When the application scenario requires different types of filtering responses, the filter hardware must be replaced or the optical path system must be rebuilt. It is impossible to achieve real-time switching between low-pass, bandpass, and high-pass modes on the same device through external electrical control signals.

[0007] (II) Slow Tuning Speed. Currently, the most mature SOI-based microring filters all employ thermo-optical effect tuning schemes. The physical essence of the thermo-optical effect is that current passing through a metal thermoelectrode above the waveguide causes a change in the refractive index of the silicon material. Its tuning response time is determined by the heat conduction equation, and the speed cannot meet the real-time reconfiguration requirements of the following application scenarios: slow tuning speed and limited tuning range. The tuning speed of traditional thermo-optical effect-based microring filters is limited by the thermal relaxation time (typically on the order of microseconds), and temperature crosstalk effects limit the accuracy of independent tuning in large-scale arrays. Although schemes based on dispersive fiber or fiber gratings can achieve wide-band filtering, their tuning relies on mechanical stretching or temperature control, resulting in a slow response speed (on the order of milliseconds), which cannot meet the requirements of rapidly reconfigurable microwave photonic systems.

[0008] (III) The challenge of simultaneously achieving passband flatness and sideband suppression. The Lorentz-type transmission spectrum of a single microring resonator exhibits a high roll-off rate, but its passband is extremely uneven. Achieving a flat passband requires a multi-stage cascaded / coupled microring design. However, in thermo-optical tuning schemes, each microring requires an independent microheater for precise wavelength alignment control. As the number of cascades increases, thermal crosstalk causes a sharp deterioration in the independent tuning accuracy of each ring, resulting in a passband ripple in the actual chip significantly higher than the design value. Furthermore, the uneven frequency response of the device introduces group delay fluctuations, causing severe signal distortion in broadband microwave signal processing. The problem of insufficient passband flatness and sideband suppression capability arises. In applications such as microwave photonic signal processing, optoelectronic oscillators, and pre-modulation filters, the passband flatness of the filter directly affects the linearity and distortion characteristics of the signal; the sideband suppression ratio determines the filter's ability to filter out out-of-band noise and interference signals. Existing integrated filter solutions struggle to simultaneously achieve a wide, flat passband (passband ripple below 0.5 dB), high sideband rejection (above 30 dB), and excellent rectangular coefficient (close to 1.0), resulting in a significant performance trade-off among these three factors.

[0009] (iv) The contradiction between system size and integration is prominent. Traditional solutions based on discrete fiber optic devices (dispersive fiber, FBG, SOA) inherently lack miniaturization potential. Even in integrated solutions based on the SOI platform, the presence of numerous thermo-optical phase shifters causes a sharp increase in chip power consumption, severely limiting the practical application of large-scale arrays. In addition, existing integrated solutions still rely on passive filtering as the core, and tuning requires independent external voltage / current sources to control each unit individually, resulting in complex control circuits. The problem of large system size and low integration is also a concern. Microwave photonic filters built based on discrete fiber optic devices (dispersive fiber, fiber Bragg grating, MZI interferometer, semiconductor optical amplifier) ​​are bulky, consume high power, and have poor resistance to environmental disturbances, making it difficult to meet the development requirements of miniaturization and chip-based devices for space-constrained platforms such as airborne, spaceborne, and missile-borne applications. Summary of the Invention

[0010] The purpose of this invention is to provide a programmable microwave photonic filter system based on graphene and microring resonator array and its implementation method, thereby solving the existing technical problems.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A programmable microwave photonic filter system based on graphene and a microring resonator array includes an optical carrier generation subsystem, a radio frequency and optical modulation subsystem, a photonic filtering subsystem, and a photodetector subsystem. The optical carrier generation subsystem is connected to the radio frequency and optical modulation subsystem, and the radio frequency signal is input into the radio frequency and optical modulation subsystem. The radio frequency and optical modulation subsystem is connected to the photonic filtering subsystem, and the photonic filtering subsystem is connected to the photodetector subsystem. The photonic filtering subsystem adopts a graphene two-dimensional microring resonator array structure to perform programmable filtering processing of the modulated optical signal in the optical domain.

[0012] Furthermore, the optical carrier generation subsystem uses a distributed feedback laser with a center operating wavelength in the C-band of optical communication as the optical carrier source. In the radio frequency and optical modulation subsystem, the microwave or radio frequency signal to be filtered is loaded onto the optical carrier in the C-band of optical communication through an electro-optic modulator, transferring the radio frequency information to the optical domain. The photoelectric detection subsystem is used to perform square-law detection on the filtered optical signal by a high-speed photoelectric detector to recover the filtered radio frequency signal. Furthermore, the microwave signal is linearly mapped onto the sideband of the optical carrier through the modulator. The modulated spectrum undergoes frequency-selective transmission in the graphene two-dimensional micro-ring resonator array structure. Different frequency components obtain different amplitude transmission coefficients. After being detected by the square law of the photodetector, the amplitude filtering response in the optical domain is mapped back to the microwave domain, thereby achieving equivalent filtering of the radio frequency signal. Furthermore, the graphene two-dimensional microring resonator array structure includes a waveguide structure and a graphene-silicon hybrid waveguide structure. The waveguide structure is implemented using a strip silicon waveguide on the SOI platform. The graphene-silicon hybrid waveguide structure is a stacked structure, consisting of a silicon waveguide layer, an alumina isolation layer, a graphene layer, a top electrode, and a bottom electrode from bottom to top. By applying a DC bias voltage Vg between the top electrode and the bottom electrode, a controllable change in carrier concentration can be induced in the graphene layer, thereby altering the chemical potential μc of graphene and its in-plane photoelectric properties.

[0013] Furthermore, the waveguide cross-sectional parameters of the waveguide structure are as follows: the silicon waveguide height is 220 nm, the silicon waveguide width is 500 nm, the cladding above the waveguide is silicon dioxide, and the buried oxide layer below the waveguide is 2 μm SiO2; The waveguide cross-sectional parameters were optimized to support single-mode TE transmission at a working wavelength of 1550 nm, and the cross-sectional dimensions are fully compatible with standard SOI processes.

[0014] Furthermore, the silicon waveguide layer is the core medium for optical signal transmission. The alumina isolation layer is prepared using atomic layer deposition technology and is used to form a potential barrier between the graphene layer and the silicon waveguide to prevent charge carriers in the graphene from being injected into the silicon waveguide under bias conditions, thereby avoiding parasitic light absorption and nonlinear effects. At the same time, as the gate dielectric layer, it together with the graphene layer constitutes the metal, insulator and graphene capacitor structure. The graphene layer is directly deposited on the Al2O3 layer, and its in-plane conductivity and dielectric constant can be controlled by the applied external gate voltage. The top electrode forms an ohmic contact with the top of the graphene layer through a platinum transition layer. The role of the platinum layer is to reduce the contact resistance and improve the chemical stability of the electrode. The bottom electrode forms an electrical contact with the top of the extended silicon layer.

[0015] Furthermore, the graphene two-dimensional microring resonator array adopts an M-row × N-column two-dimensional microring resonator array topology. The number of columns N is the number of microring columns arranged along the signal propagation direction, and the number of rows M is the number of microring rows arranged perpendicular to the propagation direction. Each microring is simultaneously evanescently coupled to the upper bus waveguide and the lower bus waveguide, with a coupling coefficient of κ. The microring radius is uniformly R, and the corresponding single-ring free spectral range is FSR. The spacing between adjacent microrings along the column direction is L2, and the bus waveguide lengths between adjacent rows along the row direction are L1 and L3, respectively.

[0016] Furthermore, the microring spacing L2 is optimized to eliminate parasitic coupling crosstalk between adjacent microrings along the same bus waveguide. When the row spacing L2 of adjacent microrings satisfies the condition: L2 = n·πR, n = 1, 2, 3, ..., the crosstalk effect between adjacent microrings on the same bus waveguide is eliminated due to precise phase-deterministic destructive interference.

[0017] Furthermore, a multi-mode programming filter switching mechanism is adopted. By controlling the external bias voltage, the chemical potential of graphene is set to different specific values, so that the same physical filter can work in three basic filter modes: low-pass, band-pass, and high-pass. By adjusting the DC bias voltage Vg applied between the two electrodes, the carrier concentration in the graphene layer can be changed, thereby changing the chemical potential.

[0018] A method for implementing a programmable microwave photonic filter system based on graphene and a microring resonator array, the method comprising the following steps: Step 1: Fabricate strip silicon waveguides and microring resonator arrays on SOI wafers using deep ultraviolet lithography and inductively coupled plasma dry etching processes; Step 2: Deposit Al2O3 isolation layers on top of the phase adjustment region of the silicon waveguide using atomic layer deposition; Step 3: The monolayer graphene film grown by chemical vapor deposition is transferred to the surface of the Al2O3 isolation layer by a wet transfer process, and the active region pattern of the graphene is defined by photolithography and oxygen plasma etching. Step 4: Prepare the platinum transition layer, top electrode, and bottom electrode using electron beam evaporation / sputtering and lift-off processes, respectively; Step 5: Using a DFB laser as the light source, the microwave signal to be filtered is modulated onto the optical carrier through a Mach-Zehnder modulator, and the modulated optical signal is coupled into the waveguide. Step 6: The optical signal is filtered in an M×N micro-ring array by applying different bias voltages V between the top and bottom electrodes. g, This enables switching between low-pass, band-pass, and high-pass filtering modes. Step 7: The filtered optical signal is converted into a photoelectric signal by a photodetector, and the filtered radio frequency signal is output. The present invention, by adopting the above-described technical solution, has the following beneficial effects: This invention achieves tuning by utilizing the sub-picosecond carrier electrical control effect of graphene, with a theoretical switching speed on the order of GHz. Compared to traditional thermo-optical tuning (microseconds) and fiber mechanical tuning (milliseconds), the reconstruction speed is improved by thousands of times, meeting the requirements of high-speed, real-time, reconfigurable microwave photonics systems. The two-dimensional micro-ring array combined with global electrical control tuning of graphene eliminates thermal crosstalk, achieving passband ripple below 0.5 dB. It offers high linearity in broadband signal transmission, low group delay fluctuation, and significantly reduced signal distortion. The out-of-band sideband rejection ratio is greater than 30 dB, effectively filtering out out-of-band noise and clutter interference. The bandpass mode rectangular coefficient is only 1.29, with steep filtering edges, and filtering performance approaching that of an ideal filter. The silicon waveguide is optimized for single-mode TE transmission, and the filtering and tuning characteristics are almost unaffected by input light polarization drift. Compared to SOA and MZI structures, no additional polarization compensation module is required, resulting in stronger stability in complex outdoor and airborne environments. Attached Figure Description

[0019] Figure 1 This is the overall system architecture diagram of the filter of this invention; Figure 2 This is a structural diagram of the metal-insulator-graphene (MIG) capacitor of the present invention; Figure 3 This is a topology diagram of the two-dimensional micro-ring resonator array of the filter of this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the present invention, and these aspects of the invention can be implemented even without these specific details.

[0021] like Figure 1-3As shown, a programmable microwave photonic filter system based on graphene and a microring resonator array is described. The overall system architecture of the filter is as follows. Figure 1 As shown, it consists of the following core subsystems: (1) Optical carrier generation subsystem: A distributed feedback (DFB) laser with a center working wavelength of 1550 nm (C-band of optical communication) is used as the optical carrier source.

[0022] (2) Radio frequency-optical modulation subsystem: The microwave / radio frequency signal to be filtered is loaded onto a 1550 nm optical carrier through an electro-optic modulator (which may be a Mach-Zehnder modulator or a phase modulator) to transfer the radio frequency information to the optical domain.

[0023] (3) Core photonic filtering subsystem: The graphene two-dimensional micro-ring resonator array (M=3 rows × N=10 columns) proposed in this invention completes the programmable filtering processing of the modulated optical signal in the optical domain.

[0024] (4) Photoelectric detection subsystem: The filtered optical signal is detected by a high-speed photoelectric detector using square law to recover the filtered radio frequency signal.

[0025] The basic physical mechanism of optical domain filtering can be simply described as follows: the microwave signal is linearly mapped onto the sideband of the optical carrier through the modulator, and the modulated spectrum undergoes frequency-selective transmission in the two-dimensional micro-ring resonator array. Different frequency components obtain different amplitude transmission coefficients. After being detected by the square law of the photodetector, the amplitude filtering response of the optical domain is faithfully mapped back to the microwave domain, thereby realizing the equivalent filtering of the radio frequency signal.

[0026] Design of a two-dimensional micro-ring resonator array structure for filters 2.1 Waveguide Structure In an embodiment of the present invention, the filter body is implemented using a strip silicon waveguide on an SOI (Silicon-on-Insulator) platform. The basic waveguide cross-sectional parameters are as follows: silicon waveguide height: 220 nm; silicon waveguide width: 500 nm; upper cladding of the waveguide: silicon dioxide (SiO2); lower buried oxide layer of the waveguide: 2 μm SiO2.

[0027] The aforementioned waveguide cross-sectional parameters were optimized to support single-mode TE (transverse electric) transmission at a working wavelength of 1550 nm, and its cross-sectional dimensions are fully compatible with standard SOI processes.

[0028] 2.2 Graphene-Silicon Hybrid Waveguide Structure In the phase tuning region of the silicon waveguide, this invention introduces a graphene layer to achieve electrically controlled tuning capability. The stacked structure of this graphene-silicon hybrid waveguide, from bottom to top, is as follows: Figure 2 As shown: Silicon waveguide layer (220 nm Si, 500 nm wide): the core medium for optical signal transmission Aluminum oxide (Al2O3) insulating layer (10 nm thick): Precisely prepared using atomic layer deposition (ALD) process. Its functions are: (a) to form a potential barrier between the graphene layer and the silicon waveguide, preventing charge carriers (electrons / holes) in the graphene from being injected into the silicon waveguide under bias conditions, thereby avoiding parasitic light absorption and nonlinear effects; (b) to serve as a gate dielectric layer, forming a metal-insulator-graphene (MIG) capacitor structure together with the graphene layer. Graphene layer (monolayer, approximately 0.34 nm thick): Deposited directly on top of the Al2O3 layer, its in-plane conductivity and dielectric constant can be modulated by an applied external gate voltage. Top electrode: An ohmic contact is formed between the top of the graphene layer and the platinum (Pt) transition layer. The platinum layer serves to reduce contact resistance and improve the chemical stability of the electrode. Bottom electrode: forms an electrical contact with the top of the extended silicon layer. By applying a DC bias voltage Vg between the top and bottom electrodes, a controllable change in carrier concentration can be induced in the graphene layer, thereby altering the chemical potential μc and in-plane photoelectric properties of the graphene.

[0029] Micro-ring resonator array structure topology The core of the filter uses a two-dimensional micro-ring resonator array with M rows × N columns, such as Figure 3 As shown, where: column number N: the number of micro-rings arranged along the signal propagation direction (bus waveguide direction); row number M: the number of micro-rings arranged perpendicular to the propagation direction. Each micro-ring is coupled to the bus waveguide in the following way: Each microring is simultaneously evanescently coupled to both the upper and lower bus waveguides with a coupling coefficient of κ. The microring radius is uniformly set to R, which is approximately 103.15 μm, corresponding to a single-ring free spectral range (FSR) of approximately 193.41 GHz. The spacing between adjacent microrings along the column direction is L2. The bus waveguide lengths between adjacent rows along the row direction are L1 (input segment) and L3 (output segment), respectively. In the preferred embodiment, the dimension parameters are determined to be M=3 and N=10 through FDTD simulation optimization. These parameters can achieve the best balance between device size and filtering performance.

[0030] Crosstalk suppression design This invention specifically optimizes the microring spacing L2 to eliminate parasitic coupling crosstalk between adjacent microrings along the same bus waveguide. When the row spacing L2 of adjacent microrings satisfies the condition: L2 = n·πR (n = 1, 2, 3, ...), the crosstalk effect between adjacent microrings on the same bus waveguide is eliminated due to precise phase-deterministic destructive interference. This crosstalk suppression condition is one of the core design principles of this invention.

[0031] The system adopts a multi-mode programming filter switching mechanism. By controlling the external bias voltage, the chemical potential of graphene is set to different specific values, so that the same physical filter can work in three basic filtering modes: low-pass, band-pass, and high-pass.

[0032] In actual device operation, the carrier concentration in the graphene layer can be changed by adjusting the DC bias voltage Vg applied between the two electrodes, thereby altering the chemical potential. In the simulation of this invention, five characteristic operating points were selected: μc = 0 eV, 0.25 eV, 0.3 eV, 0.34 eV, and 0.39 eV. Using the 1550 nm pump laser resonant peak at the initial μc = 0 eV as a reference, the corresponding filter center frequency offsets are as follows: Bandpass mode: When the graphene chemical potential is set at a certain intermediate value (e.g., μc in the range of 0.25~0.35 eV), the transmission spectrum of the filter exhibits bandpass response characteristics in the target frequency band—a flat high transmission window appears near a certain center frequency f0, and frequency components below and above this window are effectively suppressed. The typical bandpass response parameters obtained from simulations in this invention are: passband width (3-dB bandwidth): 3.7401 GHz, sideband rejection ratio: >30 dB. Rectangular coefficient (20 dB bandwidth / 3 dB bandwidth): 1.29.

[0033] This bandpass mode is suitable for applications such as channel selection filtering in wireless communication receivers and extraction of specific frequency band signals in radar systems.

[0034] Low-pass mode: By adjusting the bias voltage to achieve a specific chemical potential value, the high-frequency cutoff edge of the filter's transmission spectrum corresponds to the desired cutoff frequency fcl. Below fcl, the signal passes through with low loss; frequency components above fcl are attenuated and suppressed. The typical low-pass response cutoff frequency obtained through simulation in this invention is approximately 1.87 GHz, with sideband suppression better than 30 dB. This low-pass mode is suitable for anti-aliasing filtering, baseband signal processing, and other scenarios.

[0035] High-pass mode: Similarly, at another chemical potential setting, the filter's transmission spectrum exhibits a high-pass response—frequency components above a certain cutoff frequency fch pass through with low loss, while frequency components below fch are significantly suppressed. The typical high-pass response cutoff frequency obtained from simulations in this invention is approximately 9.90 GHz, with sideband suppression better than 30 dB. This high-pass mode is suitable for applications such as eliminating DC drift and low-frequency flicker noise, and high-frequency carrier extraction.

[0036] The physical mechanism of mode switching, and the physical implementation of the three filtering modes, relies on the following combined effects: changes in the effective refractive index of the hybrid waveguide caused by graphene chemical potential variations → synchronous shift of the resonant wavelengths of all microrings → overall translation of the joint transmission function of the microring array on the microwave frequency axis. The modulated double-sidebands experience different transmittances at different frequency positions in the joint transmission spectrum of the microring array → after square-law detection by a photodetector, the microwave domain filtering function exhibits different shapes (low-pass / band-pass / high-pass) depending on the position of the optical carrier relative to the joint transmission spectrum. By rationally optimizing the coupling coefficient distribution of the microring array, the joint transmission spectrum has a sufficiently steep edge transition band and a sufficiently flat passband in the wavelength domain, ensuring that the microwave domain filtering function possesses a high-quality shape. Since mode switching only requires changing the bias voltage on the graphene layer (an electronic effect), the switching speed is extremely fast. It is mainly dominated by the sub-picosecond in-band scattering process of carrier dynamics in graphene, and theoretically, it can achieve modulation / switching speeds on the order of GHz, far exceeding the microsecond response of traditional thermo-optical tuning.

[0037] A method for implementing a graphene programmable microwave photonic filter based on a microring resonator array with M=3 rows and N=10 columns includes the following steps: Step 1: On an SOI wafer (220 nm top silicon / 2 μm buried oxide / Si substrate), a strip silicon waveguide and micro-ring resonator array (R = 103.15 μm, waveguide width 500 nm, height 220 nm) are fabricated by deep ultraviolet lithography (193 nm) and inductively coupled plasma (ICP) dry etching process.

[0038] Step 2: Deposit 10 nm Al2O3 isolation layers on top of the phase adjustment region of the silicon waveguide by atomic layer deposition (ALD).

[0039] Step 3: The monolayer graphene film grown by chemical vapor deposition (CVD) is transferred to the surface of the Al2O3 isolation layer using a wet transfer process, and the active region pattern of the graphene is defined by photolithography and oxygen plasma etching.

[0040] Step 4: Prepare the platinum transition layer, top electrode (in contact with graphene), and bottom electrode (in contact with the silicon waveguide extension region) by electron beam evaporation / sputtering and lift-off processes, respectively.

[0041] Step 5: Using a 1550 nm DFB laser as the light source, the microwave signal to be filtered is modulated onto the optical carrier through a Mach-Zehnder modulator, and the modulated optical signal is coupled into the waveguide.

[0042] Step Six: The optical signal is filtered in an M×N micro-ring array. By applying different bias voltages Vg (corresponding to different chemical potentials μc) between the top and bottom electrodes, the filtering mode is switched between low-pass, band-pass, and high-pass.

[0043] Step 7: The filtered optical signal is converted into a photoelectric signal by a photodetector, and the filtered radio frequency signal is output.

[0044] Matters not covered in this invention are common knowledge.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A programmable microwave photonic filter system based on graphene and a microring resonator array, characterized in that: It includes an optical carrier generation subsystem, an radio frequency and optical modulation subsystem, a photonic filtering subsystem, and a photodetector subsystem. The optical carrier generation subsystem is connected to the radio frequency and optical modulation subsystem. Radio frequency signals are input into the radio frequency and optical modulation subsystem. The radio frequency and optical modulation subsystem is connected to the photonic filtering subsystem. The photonic filtering subsystem is connected to the photodetector subsystem. The photonic filtering subsystem adopts a graphene two-dimensional micro-ring resonator array structure to perform programmable filtering processing of modulated optical signals in the optical domain.

2. The programmable microwave photonic filter system based on graphene and microring resonator array according to claim 1, characterized in that: The optical carrier generation subsystem uses a distributed feedback laser with a center operating wavelength in the C-band of optical communication as the optical carrier source. In the radio frequency and optical modulation subsystem, the microwave or radio frequency signal to be filtered is loaded onto the optical carrier in the C-band of optical communication through an electro-optic modulator, and the radio frequency information is transferred to the optical domain. The photoelectric detection subsystem is used to perform square-law detection on the filtered optical signal by a high-speed photoelectric detector to recover the filtered radio frequency signal.

3. The programmable microwave photonic filter system based on graphene and microring resonator array according to claim 2, characterized in that: The microwave signal is linearly mapped onto the sideband of the optical carrier through a modulator. The modulated spectrum undergoes frequency-selective transmission in the graphene two-dimensional microring resonator array structure. Different frequency components obtain different amplitude transmission coefficients. After being detected by the square law of the photodetector, the amplitude filtering response in the optical domain is mapped back to the microwave domain, thereby achieving equivalent filtering of the radio frequency signal.

4. The programmable microwave photonic filter system based on graphene and microring resonator array according to claim 1, characterized in that: The graphene two-dimensional microring resonator array structure includes a waveguide structure and a graphene-silicon hybrid waveguide structure. The waveguide structure is implemented using a strip silicon waveguide on the SOI platform. The graphene-silicon hybrid waveguide structure is a stacked structure, consisting of a silicon waveguide layer, an alumina isolation layer, a graphene layer, a top electrode, and a bottom electrode from bottom to top. By applying a DC bias voltage Vg between the top electrode and the bottom electrode, a controllable change in carrier concentration can be induced in the graphene layer, thereby altering the chemical potential μc of graphene and its in-plane photoelectric properties.

5. A programmable microwave photonic filter system based on graphene and a microring resonator array according to claim 4, characterized in that: The waveguide cross-sectional parameters of the waveguide structure are as follows: the silicon waveguide height is 220 nm, the silicon waveguide width is 500 nm, the cladding above the waveguide is silicon dioxide, and the buried oxide layer below the waveguide is 2 μm SiO2; The waveguide cross-sectional parameters were optimized to support single-mode TE transmission at a working wavelength of 1550 nm, and the cross-sectional dimensions are fully compatible with standard SOI processes.

6. A programmable microwave photonic filter system based on graphene and a microring resonator array according to claim 5, characterized in that: The silicon waveguide layer is the core medium for optical signal transmission. The alumina isolation layer is prepared using atomic layer deposition and is used to form a barrier between the graphene layer and the silicon waveguide to prevent charge carriers in the graphene from being injected into the silicon waveguide under bias conditions, thereby avoiding parasitic light absorption and nonlinear effects. At the same time, it serves as the gate dielectric layer and together with the graphene layer, it constitutes the metal, insulator, and graphene capacitor structure. The graphene layer is directly deposited on the Al2O3 layer, and its in-plane conductivity and dielectric constant can be controlled by the applied external gate voltage. The top electrode forms an ohmic contact with the top of the graphene layer through a platinum transition layer. The role of the platinum layer is to reduce the contact resistance and improve the chemical stability of the electrode. The bottom electrode forms an electrical contact with the top of the extended silicon layer.

7. A programmable microwave photonic filter system based on graphene and a microring resonator array according to claim 1, characterized in that: The topology of the graphene two-dimensional microring resonator array adopts an M-row × N-column two-dimensional microring resonator array. The number of columns N is the number of microring columns arranged along the signal propagation direction, and the number of rows M is the number of microring rows arranged perpendicular to the propagation direction. Each microring is simultaneously evanescently coupled to the upper bus waveguide and the lower bus waveguide, with a coupling coefficient of κ. The microring radius is uniformly R, and the corresponding single-ring free spectral range is FSR. The spacing between adjacent microrings along the column direction is L2, and the bus waveguide lengths between adjacent rows along the row direction are L1 and L3, respectively.

8. A programmable microwave photonic filter system based on graphene and a microring resonator array according to claim 7, characterized in that: The spacing L2 between microrings is optimized to eliminate parasitic coupling crosstalk between adjacent microrings along the same bus waveguide. When the spacing L2 between adjacent microrings satisfies the condition: L2 = n·πR, n = 1, 2, 3, ..., the crosstalk effect between adjacent microrings on the same bus waveguide is eliminated due to precise phase-deterministic destructive interference.

9. A programmable microwave photonic filter system based on graphene and a microring resonator array according to claim 1, characterized in that: A multi-mode programming filter switching mechanism is adopted. By controlling the external bias voltage, the chemical potential of graphene is set to different specific values, so that the same physical filter can work in three basic filter modes: low-pass, band-pass, and high-pass. By adjusting the DC bias voltage Vg applied between the two electrodes, the carrier concentration in the graphene layer can be changed, thereby changing the chemical potential.

10. A method for implementing a programmable microwave photonic filter system based on graphene and a microring resonator array, characterized in that, The method includes the following steps: Step 1: Fabricate strip silicon waveguides and microring resonator arrays on SOI wafers using deep ultraviolet lithography and inductively coupled plasma dry etching processes; Step 2: Deposit Al2O3 isolation layers on top of the phase adjustment region of the silicon waveguide using atomic layer deposition; Step 3: The monolayer graphene film grown by chemical vapor deposition is transferred to the surface of the Al2O3 isolation layer by a wet transfer process, and the active region pattern of the graphene is defined by photolithography and oxygen plasma etching. Step 4: Prepare the platinum transition layer, top electrode, and bottom electrode using electron beam evaporation / sputtering and lift-off processes, respectively; Step 5: Using a DFB laser as the light source, the microwave signal to be filtered is modulated onto the optical carrier through a Mach-Zehnder modulator, and the modulated optical signal is coupled into the waveguide. Step 6: The optical signal is filtered in an M×N micro-ring array by applying different bias voltages V between the top and bottom electrodes. g, This enables switching between low-pass, band-pass, and high-pass filtering modes. Step 7: The filtered optical signal is converted into a photoelectric signal by a photodetector, and the filtered radio frequency signal is output.

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