Reconfigurable microwave photonic band-pass filter chip and working method thereof

Abstract

The invention discloses a reconfigurable microwave photon band-pass filter chip and a working method thereof, and belongs to the field of optical communication and microwave photon signal processing. The chip adopts an on-chip optical frequency comb technology to generate multiple optical carriers with high stability and high coherence, so that the problem of unstable laser wavelength interval and phase in a traditional multi-laser array scheme is solved; comb teeth in an optical frequency comb are flexibly screened to serve as multiple optical carriers through an on-chip bandwidth tunable optical band-pass filter so as to adapt to different application requirements; and in combination with the design of the cascaded micro-ring, the out-of-band rejection ratio and the shape factor of the filter are remarkably improved, and the dynamic adjustability of the center frequency and the bandwidth is realized. The chip has high performance, reconfigurability and high stability, is suitable for the fields of high-speed communication, radar signal processing, spectral analysis and the like, and provides an efficient integrated solution for microwave photon signal processing.

Description

Technical Field

[0001] The present invention belongs to the fields of optical communication and integrated microwave photonic signal processing, and particularly relates to a chip design and working method of a reconfigurable microwave photonic bandpass filter using an on-chip optical frequency comb and a cascaded tunable microring structure. Background Art

[0002] In optical communication and microwave photonic signal processing, microwave photonic bandpass filters play a crucial role in aspects such as target signal extraction and spurious signal suppression of radio frequency signals, and are widely used in fields such as high-speed communication, radar systems, wireless transmission, and spectrum analysis. They are one of the core research directions in this technical field.

[0003] Current research shows that microwave photonic bandpass filtering based on a single optical carrier, electro-optic phase modulation, and a single tunable microring has become an important implementation scheme. By adjusting the phase and coupling coefficient of the microring, flexible control of the center frequency and bandwidth of the filter can be achieved. However, due to the residual phase problem of the microring resonator at the edge of the resonance region, the microwave photonic bandpass filter implemented by this scheme has significant performance bottlenecks in aspects such as insufficient out-of-band rejection ratio (OBRR), limited shape factor, and limited signal processing bandwidth. To solve these problems, a scheme using two independent lasers to generate two optical carriers has been proposed. However, due to the difficulty in achieving long-term stable synchronization of the wavelengths and phases between independent lasers, their relative instability will pose significant challenges to the working performance of the microwave photonic filter, and may even cause significant fluctuations in the filter performance. In addition, the bandwidth limitation of a single microring is also a major obstacle restricting the bandwidth reconfiguration performance of the microwave photonic filter. Therefore, it is of great significance to develop an integrated reconfigurable microwave photonic filter chip that takes into account out-of-band rejection ratio, shape factor, bandwidth, and stability at the same time. Summary of the Invention

[0004] Aiming at the deficiencies in the reconfiguration performance and stability of existing integrated microwave photonic bandpass filters, such as insufficient out-of-band rejection ratio (OBRR), limited shape factor, limited bandwidth reconfiguration range, and instability of the phases and wavelengths of multiple optical carriers in the multi-laser light source scheme, the present invention proposes a reconfigurable microwave photonic bandpass filter chip based on an on-chip optical frequency comb and a cascaded tunable microring. This chip uses an on-chip optical frequency comb as a stable multi-optical carrier source, and combines a tunable optical bandpass filter, a phase modulator, a cascaded tunable microring resonator, and a photodetector to achieve high-performance reconfigurable microwave photonic bandpass filtering function. The present invention has the characteristics of high flexibility, stable performance, and strong adaptability, and can meet the microwave signal processing requirements under various application scenarios.

[0005] The specific solution is as follows:

[0006] A reconfigurable microwave photonic bandpass filter chip, comprising an on-chip optical frequency comb generation module, a tunable optical bandpass filter module, a phase modulator module, a cascaded tunable microring resonator module, and a photodetector module connected in sequence; wherein,

[0007] The on-chip optical frequency comb generation module is used to generate multi-optical carriers with equal frequency intervals and high stability and high coherence;

[0008] The tunable optical bandpass filter module is used to select several optical frequency comb teeth from the on-chip optical frequency comb as multi-optical carrier signals;

[0009] The phase modulator module is used to load microwave signals onto multiple optical carriers selected by the tunable optical bandpass filter to generate multiple optical carrier microwave signals;

[0010] The cascaded tunable microring resonator module is used to perform frequency-domain filtering on multiple optical carrier microwave signals;

[0011] The photodetector module is used to down-convert multiple optical carrier microwave signals to the microwave domain and extract target microwave signals.

[0012] Furthermore, the optical frequency comb generation module is an on-chip integrated optical frequency comb, which can generate a set of optical frequency comb teeth with equal frequency intervals and support dynamic tuning of the frequency interval. The tunable optical bandpass filter module can select and output several adjacent optical frequency comb teeth as multi-optical carriers.

[0013] The present invention uses an on-chip integrated optical frequency comb to generate a set of multi-optical carriers with equal frequency intervals and high stability, avoiding the problems of wavelength interval and phase instability in the traditional multi-laser array scheme. By selecting the optical comb teeth output by the optical frequency comb through the tunable optical bandpass filter module, an appropriate number of optical comb teeth are retained as multiple optical carriers for microwave signal processing according to requirements. This scheme with selectable multi-optical carrier numbers not only significantly improves the bandwidth of the microwave photonic filter, but also can effectively improve the out-of-band rejection ratio and overall performance of the microwave photonic filter by compensating for the residual phase of the microring.

[0014] Furthermore, the cascaded tunable microring resonator module includes two or more tunable microring resonators. The free spectral range (FSR) of the tunable microring resonator is designed according to the requirements of the filtering bandwidth. The resonant frequency and extinction ratio can be tuned, and high out-of-band rejection ratio and wide-bandwidth filtering characteristics can be achieved at the resonant frequency. The resonant frequency and coupling coefficient of the tunable microring resonator are dynamically adjusted through thermo-optic tuning or electro-optic tuning, so as to support the center frequency tuning and bandwidth reconfiguration functions of the microwave photonic bandpass filter. The photodetector module down-converts multiple optical carrier microwave signals to the microwave domain through the beat frequency effect and outputs the target radio frequency signal.

[0015] In the microwave signal processing section, an on-chip phase modulator is used to load microwave signals onto multiple optical carriers to generate multiple optical carrier microwave signals, where each optical carrier microwave signal includes an optical carrier, positive and negative first-order sidebands, and higher-order sidebands. Subsequently, the optical carrier microwave signals are subjected to frequency-domain filtering through a cascaded tunable microring resonator. Then, through the beat frequency effect of the photodetector, the optical domain signal is converted into a microwave domain signal. By tuning the phase and coupling coefficient of the cascaded tunable microring, a reconfigurable microwave photonic bandpass filtering function with adjustable filtering frequency, reconfigurable bandwidth, and high out-of-band rejection ratio is finally achieved.

[0016] Furthermore, the on-chip optical frequency comb generation module, tunable optical bandpass filter module, phase modulator module, cascaded tunable microring resonator module, and photodetector module are all integrated on the same on-chip chip, featuring high integration and low power consumption. This chip supports flexible configuration of the number of multi-optical carriers and the number of cascaded tunable microring resonators to adapt to the performance requirements in different scenarios and achieve a balance between performance and complexity.

[0017] The design of the present invention has flexible reconfigurability, allowing the selection of the number of optical carriers and the number of cascaded microrings according to actual needs to achieve a balance between performance and system complexity. In application scenarios with low complexity requirements, fewer optical carriers and tunable microrings can be selected; while in high-performance scenarios, the number of optical carriers and cascaded tunable microrings can be increased to further improve the bandwidth, shape factor, and out-of-band rejection ratio. This flexible configuration ability makes the present invention more adaptable to a variety of complex scenarios.

[0018] In summary, the reconfigurable microwave photonic bandpass filter chip of the present invention has the following significant advantages: tunable frequency, high out-of-band rejection ratio, excellent shape factor, wide bandwidth reconfiguration range, and on-chip integrated design with high stability and low complexity. This technology is applicable to fields such as high-speed optical communication, radar signal processing, wireless transmission, and spectral analysis, providing an efficient, flexible, and stable solution for microwave photonic signal processing. Description of the Drawings

[0019] Figure 1 Schematic diagram of the structure of a reconfigurable microwave photonic bandpass filter chip based on on-chip optical frequency comb and cascaded tunable microrings provided by the present invention. Figure 1 (a) Labels the main modules, including a tunable optical frequency comb, an optical bandpass filter, a phase modulator, a cascaded tunable microring resonator, and a photodetector; Figure 1 (b) Shows the schematic diagram of the structure of a typical optical bandpass filter (spectral interleaver); Figure 1 (c) Is the specific schematic diagram of the cascaded tunable microring resonator, labeling the input and output ends of the microring.

[0020] Figure 2 For the modulation signal spectrum distribution diagrams of two optical carriers (ω c1 and ω c2 ) generated by the on-chip optical frequency comb after passing through the phase modulator, showing the frequency distribution of the positive and negative first-order sidebands (frequencies ω c1 ±ω RF and ω c2 ±ω RF ).

[0021] Figure 3 Is the schematic diagram of the resonance frequency distribution of the microring resonator, showing the relative frequency relationship between the optical carrier and its sidebands and the resonance peaks of the cascaded microrings.

[0022] Figure 4 Is the effect diagram of the bandpass filtering down-converted back to the microwave domain through the photodetector.

[0023] Figure 5 Is the performance comparison diagram of different microwave photonic bandpass filter schemes at 15 GHz. Among them, the -3dB bandwidth of the "single optical carrier and one microring" scheme is 259 MHz, and the shape factor is 3.03. While for a special case of this patent: the -3dB bandwidth of the "two optical carriers and two cascaded microrings" scheme is significantly increased to 619 MHz, and the shape factor is reduced to 1.58, showing a wider bandwidth and a steeper edge transition characteristic. The scheme of this patent has significantly better performance than the traditional scheme under the same conditions, proving its superiority in terms of filtering performance, frequency selectivity, bandwidth, etc., and can better meet the actual application requirements.

[0024] List of reference numerals:

[0025] 1 - Tunable optical frequency comb, 2 - Optical bandpass filter, 3 - Phase modulator, 4 - Cascaded tunable microring resonator, 5 - First microring phase shifter, 6 - First microring power coupler, 7 - Second microring phase shifter, 8 - Second microring power coupler, 9 - Photodetector. Detailed implementation manner

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0027] Figure 1 FIG. is a schematic structural diagram of a reconfigurable microwave photonic bandpass filter chip based on an on-chip optical frequency comb and a cascaded tunable microring provided by the present invention. This figure includes the following parts: Figure 1 (a): Overall chip architecture diagram; Figure 1 (b): Schematic structural diagram of a typical tunable optical bandpass filter module (spectral interleaver); Figure 1 (c): Schematic microring structure diagram.

[0028] The component modules of the chip include a tunable optical frequency comb (1), an optical bandpass filter (2), a phase modulator (3), a cascaded tunable microring resonator (4), and a photodetector (9). The connection relationships of each module are as follows: The output end of the on-chip optical frequency comb generation module (1) is connected to the input end of the tunable optical bandpass filter module (2); the output end of the tunable optical bandpass filter module (2) is connected to the input end of the phase modulator module (3); the output end of the phase modulator module (3) is connected to the input end of the cascaded tunable microring resonator module (4); the output end of the cascaded tunable microring resonator module (4) is connected to the input end of the photodetector module (9).

[0029] The cascaded tunable microring resonator module (4) includes several tunable microrings, and the input and output ends of the microrings are connected in series. In this embodiment, taking two comb teeth generated by the on-chip optical frequency comb and two cascaded microrings as an example, the working method of the reconfigurable microwave photonic bandpass filter chip is introduced, and the specific steps are as follows:

[0030] Step 1: Optical frequency comb generation and screening

[0031] The on-chip optical frequency comb generation module (1) generates a group of frequency comb teeth with equal frequency intervals and coherence. Two comb teeth in the optical frequency comb are selected through the tunable optical bandpass filter module (2) as the two optical carriers in the microwave signal processing region. The frequencies of the two selected optical carriers are ω c1 and ω c2 ;

[0032] Step 2: Phase modulation and modulation signal generation

[0033] After the two optical carriers are modulated by the microwave signal with a frequency of ω RF through the phase modulator module (3), positive and negative first-order sidebands based on the two optical carriers are respectively generated (as shown in Figure 2 ). Under small-signal modulation, the optical signal of the double optical carriers after passing through the phase modulator can be expressed as:

[0034]

[0035] where E C1 , E C2 , ω C1 , ω C2 , and are the amplitudes, angular frequencies, and initial phases of two optical carriers, respectively; J 0 (m) and J 1 (m) are the Bessel functions of the first kind of order 0 and 1, respectively, m is the modulation depth; j represents the imaginary unit, t represents the time variable, and e is the base of the natural logarithm. It can be seen from Equation (1) that the amplitudes of the positive and negative first-order sidebands after passing through the phase modulator are the same, but the phases differ by π.

[0036] Step 3: Use a cascaded tunable microring to achieve frequency-domain filtering of the modulation signal

[0037] The modulation signal is processed by frequency-domain filtering through a cascaded tunable microring. The first microring phase shifter (5), the first microring power coupler (6), the second microring phase shifter (7), and the second microring power coupler (8) are tuned to make the extinction ratio consistent and all in an over-coupled state. In a single microring, its spectral response exhibits a narrow-band Lorentzian notch characteristic. By precisely tuning the resonance frequencies of the two microrings so that their frequencies are close to each other, a notch response with a larger extinction ratio, wider bandwidth, and tunability can be achieved. To avoid signal interference and sideband overlap and provide a wider filtering bandwidth and tunability, two optical carriers (with frequencies ω c1 and ω c2 ) are set on the low-frequency side and high-frequency side of the two non-adjacent resonance frequencies of the cascaded microring. The frequency differences between the optical carriers and their nearest resonance peaks are denoted by Δω 1 and Δω 2 , and let Δω = Δω 1 - Δω 2 . The cascaded microring, as an optical notch filter, can change the frequency filtered in the optical carrier microwave signal by tuning its resonance frequency. This design lays the foundation for subsequent processing. The resonance frequency distribution and its relative relationship with the optical carrier and modulation sidebands are as shown in Figure 3 .

[0038] Step 4: Down-convert the modulation signal back to the microwave domain through a photodetector

[0039] The optical carrier microwave signal processed by the cascaded tunable microring contains multiple frequency components, mainly including the optical carriers (with frequencies ω c1 and ω c2 ) and their positive and negative first-order sidebands (with frequencies ω c1 ±ω RFand ω c2 ±ω RF )。After these frequency components pass through the photodetector module (9), the high-frequency optical signal is down-converted to the microwave domain by using the beat frequency effect, and the target signal is extracted. Assuming that the optical powers of the two optical carriers and the link losses are the same, the photocurrents obtained after the optical carriers 1 and 2 and their corresponding positive and negative sidebands pass through the photodetector for beating are as follows:

[0040]

[0041] where α is the link loss, η is the responsivity of the photodetector, P C is the power of the optical carrier; T(ω) is the amplitude attenuation factor of the cascaded tunable microring resonator module; and are the phases introduced by the cascaded microrings.

[0042] As can be seen from formula (2), in the non-resonant frequency band of the cascaded microring, due to the fixed phase difference π between the positive and negative sidebands, the beat frequency results cancel each other out, and only a DC component is generated (i 1,+1 (t) and i 1,-1 (t) have equal amplitudes and opposite phases, and i 2,+1 (t) and i 2,-1 (t) also have equal amplitudes and opposite phases); when the frequency of a certain sideband falls at the resonant frequency of the microring, the power of this sideband is significantly attenuated or even completely filtered out, and it cannot beat effectively with the optical carrier. For the other sideband that is not affected by the microring resonance, the power is retained and it can beat normally with the optical carrier, thus generating a radio frequency signal. This selective filtering destroys the power balance between the positive and negative sidebands and breaks the mutual cancellation of the beat frequency signals, enabling the effective recovery of the radio frequency signal in the resonant frequency band. During this process, the phase information is converted into the intensity information output by the photodetector through the frequency domain selectivity of the microring, thus realizing the band-pass filtering function at the resonant frequency of the cascaded microring. The center frequency of the implemented microwave photonic band-pass filter is related to Δω 1 and Δω 2 and can be written as:

[0043]

[0044] Changing the frequency of the optical carrier or the frequency of the cascaded microring resonance, that is, changing the attached Figure 3 shown Δω 1 and Δω 2 , the tuning of the center frequency ω center of the microwave photonic band-pass filter can be realized, and changing the transmission spectrum bandwidth of the cascaded tunable microring can realize the bandwidth tuning of the microwave photonic band-pass filter. The effect of microwave photonic band-pass filtering is as shown in the attached Figure 4As shown. The shape factor (SF) is one of the important indicators for measuring the performance of microwave photonic bandpass filters. The smaller its value, the steeper the transition band of the filter and the better the performance. In this specific embodiment, the shape factor is obtained through Figure 4 The -10 dB bandwidth (BW -10dB ) and -3 dB bandwidth (BW -3dB ) shown in are used to define it, that is:

[0045]

[0046] To verify the effectiveness of this patent, a transmission matrix model was established for the overall structure of the chip, and its performance was deeply analyzed. At the same time, the modulation and demodulation processes of microwave signals were simulated. In this specific implementation manner, a scheme of "two optical carriers and two cascaded microrings" was adopted and compared with the scheme of "a single optical carrier and a microring". In the simulation, the parameter settings of each scheme were exactly the same, and the results of microwave photonic bandpass filtering at 15 GHz were simulated. The results are as Figure 5 shown. It can be seen from Figure 5 that under the same conditions, the scheme proposed in this patent shows significant performance advantages. It not only increases the -3 dB bandwidth from 259 MHz to 619 MHz, but also reduces the shape factor from 3.03 to 1.58, reflecting better filtering performance and steeper edge transition characteristics. It should be noted that as the number of optical carriers and microrings increases, the overall complexity of the system and its control difficulty also increase accordingly. However, this patent proposes a flexible design method that can flexibly select the number of optical carriers and cascaded microrings according to actual needs to achieve a balance between performance and system complexity. This flexible configuration ability enables the present invention to better meet the actual application requirements in a variety of complex scenarios.

Claims

1. A reconfigurable microwave photonic bandpass filter chip, characterized in that: It includes an on-chip optical frequency comb generation module, a tunable optical bandpass filter module, a phase modulator module, a cascaded tunable microring resonator module and a photodetector module which are connected in sequence; wherein the on-chip optical frequency comb generation module is used to generate multiple optical carriers with equal frequency intervals and high stability and high coherence; the tunable optical bandpass filter module is used to select a number of optical frequency comb teeth from the on-chip optical frequency comb as multiple optical carrier signals; the phase modulator module is used to load microwave signals onto multiple optical carriers selected by the tunable optical bandpass filter to generate multiple optically-carried microwave signals; the cascaded tunable microring resonator module is used to perform frequency domain filtering on multiple optically-carried microwave signals; the photodetector module is used to down-convert multiple optically-carried microwave signals to the microwave domain and extract target microwave signals.

2. The reconfigurable microwave photonic bandpass filter chip according to claim 1, characterized in that: The on-chip optical frequency comb generation module is an on-chip integrated optical frequency comb, which can generate a group of optical frequency comb teeth with equal frequency intervals and support dynamic tuning of the frequency intervals.

3. The reconfigurable microwave photonic bandpass filter chip according to claim 1, characterized in that: The tunable optical bandpass filter module can screen and output a number of adjacent optical frequency comb teeth as multiple optical carriers.

4. The reconfigurable microwave photonic bandpass filter chip according to claim 1, characterized in that: The cascaded tunable microring resonator module includes two or more tunable microring resonators, the free spectrum range of the tunable microring resonator is designed according to the requirements of the filtering bandwidth, the resonant frequency and the extinction ratio can be tuned, and the filtering characteristics of high out-of-band suppression ratio and wide bandwidth can be achieved at the resonant frequency.

5. The reconfigurable microwave photonic bandpass filter chip according to claim 4, characterized in that: The resonant frequency and coupling coefficient of the tunable microring resonator are dynamically adjusted through thermo-optical tuning or electro-optical tuning, thereby supporting the center frequency tuning and bandwidth reconstruction functions of the microwave photonic bandpass filter.

6. The reconfigurable microwave photonic bandpass filter chip according to claim 1, characterized in that: The photoelectric detector module down-converts a plurality of light-carrying microwave signals into the microwave domain through the beat frequency effect, and outputs a target radio frequency signal.

7. The reconfigurable microwave photonic bandpass filter chip according to claim 1, characterized in that: The on-chip optical frequency comb generation module, the tunable optical bandpass filter module, the phase modulator module, the cascade tunable microring resonator module and the photodetector module are all integrated in the same on-chip chip.

8. A working method of a reconfigurable microwave photonic bandpass filter chip, characterized in that: Using the chip as described in any one of claims 1 to 7, the specific steps are as follows: Step 1: Frequency comb generation and screening The on-chip optical frequency comb generation module generates a set of equally spaced and coherent frequency comb teeth. The tunable optical bandpass filter module selects two comb teeth in the optical frequency comb as two optical carriers in the microwave signal processing area. The frequencies of the selected optical carrier 1 and optical carrier 2 are ω c1 and ω c2 ; Step 2: Phase modulation and modulation signal generation The two optical carriers are modulated by the phase modulator module at a frequency of ω RF After the microwave signal is transmitted, the positive and negative first-order sidebands based on the two optical carriers are generated respectively; under small signal modulation, the optical signal after the dual optical carriers pass through the phase modulator is expressed as: Where E C1 ,E C2 ,ω C1 ,ω C2 , and are the amplitude, angular frequency and initial phase of the two optical carriers respectively; J0(m) and J1(m) are the first-order 0th and 1st-order Bessel functions respectively, and m is the modulation depth; j represents the imaginary unit, t represents the time variable, and e is the base of the natural logarithm; the positive first-order and negative first-order sidebands after the phase modulator module have the same amplitude, but the phase difference is π; Step 3: Frequency domain filtering of modulated signals using cascaded tunable microrings The modulated signal is filtered in the frequency domain through a cascaded tunable microring resonator module; the key parameters of the two microrings are tuned, such as the free spectral range is completely consistent, and both are in an overcoupled state and have the same extinction ratio; in a single microring, its spectral response exhibits a narrow-bandwidth Lorentz-type notch characteristic; by precisely tuning the resonant frequencies of the two microrings, their frequencies are brought close to each other, achieving a notch response with a larger extinction ratio, wider bandwidth and tunability; in order to avoid signal interference and sideband overlap and provide a wider filtering bandwidth and tunability, two optical carriers are set on the low-frequency side and high-frequency side of two non-adjacent resonant frequencies of the cascaded microrings; the frequency difference between the optical carrier and its nearest resonant peak is represented by Δω1 and Δω2, and Δω=Δω1-Δω2; Step 4: Down-convert the modulated signal back to the microwave domain via a photodetector The optically-carried microwave signal processed by the cascaded tunable microring resonator module contains multiple frequency components, including the optical carrier and its positive and negative first-order sidebands; After these frequency components pass through the photodetector module, the beat frequency effect is used to down-convert the high-frequency optical signal to the microwave domain and extract the target signal. Assuming that the optical power and link loss of the two optical carriers are the same, the photocurrent obtained after the optical carrier 1 and optical carrier 2 and their corresponding positive and negative sidebands after passing through the micro-ring and the beat frequency of the photodetector is: Where α is the link loss, η is the responsivity of the photodetector, and P C is the power of the optical carrier; T(ω) is the amplitude attenuation factor of the cascaded tunable microring resonator module; and It is due to the phase introduced by the cascaded microrings; In the non-resonant frequency band of the cascaded micro-ring, since the positive and negative sidebands have a fixed phase difference π, the beat frequency results cancel each other and only the DC component is generated, i.e. 1,+1 (t) and i 1,-1 (t) equal amplitude and opposite phase, i 2,+1 (t) and i 2,-1 (t) also have equal amplitudes and opposite phases; when the frequency of a sideband falls at the resonant frequency of the microring, the power of the sideband is significantly attenuated or even completely filtered out, and it cannot effectively beat with the optical carrier; while the power of the other sideband that is not affected by the microring resonance is retained and beats with the optical carrier normally, thereby generating a radio frequency signal; in this process, the phase information is selectively converted into the intensity information of the photodetector output through the frequency domain of the microring, thereby realizing the bandpass filtering function at the resonant frequency of the cascaded microrings; the center frequency ω of the realized microwave photonic bandpass filter is center It is related to Δω1 and Δω2 and written as: By changing the frequency of the optical carrier or the frequency of the cascaded microring resonance, that is, changing Δω1 and Δω2, the center frequency ω of the microwave photonic bandpass filter is realized. center The bandwidth of the microwave photonic bandpass filter can be tuned by changing the transmission spectrum bandwidth of the cascaded tunable microring. The smaller the shape factor value, the steeper the transition band of the filter and the better the performance. The shape factor SF is defined by the ratio of -10dB bandwidth to -3dB bandwidth, that is: Where BW -10dB For -10dB bandwidth and BW -3dB is -3dB bandwidth.

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