## 3 Experiment and Results  
An experiment based on the proposed dual-passband MPF configuration shown in Figure 1 was performed to verify the effectiveness of the approach. In the experiment, a TLS (NKT E15) was used as an ML with a CW optical power up to 16 dBm and then the CW light was sent to a DOMZM (EOSPACE). The DOMZM was set at quadrature bias point. A VNA (Keysight N5227B) was used to measure the frequency response of the MPF. The output power of the VNA was \(-10\) dBm, with a frequency range of 1 to 45 GHz. The microwave signals to be tested were applied to the DOMZM from port 1, complementary intensity modulation is obtained at the two DOMZM outputs. So that two modulated signals with equal intensities could be obtained at the output of the DOMZM. Then the signals were injected into the SLs through PCs and CIRs. The PC was used to adjust the polarization state of the optical signals between the ML and the SL so that the maximum injection efficiency could be achieved in the experiment. Finally, a BPD (U2T) was used to realize the optical-to-electrical conversion and eliminate the common-mode noise of the MPF link. An optical spectrum analyzer (OSA) was used to analyze the optical spectrum after injection before the optical signals' beating in the BPD. As can be seen from Equation (4), the center frequency of the two passbands could be controlled by changing the parameter \(N\) which can be tuned by adjusting the detuning frequency \(\Delta f\) and injected ratio \(R\), individually or together. The influence of the detuning frequency was first demonstrated. In the experiment, the output power of the ML was set as 11.76 dBm with a wavelength of 1548.928 nm. The free-running wavelength of the SL1 was tuned from 1548.936 to 1549.128 nm, which can be controlled by tuning the temperature controller of the DFB laser driver. The free-running wavelengths of SL1 and SL2 were different. The detuning frequency \(\Delta f_{1}\) between the ML and SL1 was tuned from 1 to 25 GHz. Meanwhile, the detuning frequency \(\Delta f_{2}\) between the ML and SL2 was fixed, and the free-running power of two different SLs was also fixed. As shown in Figure 3, when the detuning frequency \(\Delta f_{1}\) was changed from 1 to 25 GHz, the central response frequency of the first passband could be tuned from 20.71 to 30.83 GHz based on the influence of the wavelength-selective amplification and the period-one (P1) oscillation state [13] under the optically injected DFB lasers. At the same time, the out-of-band suppression ratio of the MPF can be obtained from the \(Z\)-axis in Figure 3. The out-of-band suppression ratio of the first passband was around 20.9 dB, and the central response frequency of the second passband was fixed at 33.98 GHz with the out-of-band suppression ratio around 21.3 dB. However, the 3-dB bandwidths of the two passbands in our MPF were about 0.85 and 0.95 GHz, which were limited by the locking amplification area bandwidth under optical injection and the linewidth of the DFB lasers. Then the optical wavelengths of the ML and SL1 were different fixed, and the output optical powers of all three lasers were also fixed. The free-running wavelengths of SL1 and SL2 were different. The detuning frequency \(\Delta f_{2}\) could be continuously tuned by changing the free-running wavelength of the SL2 from 1549.605 to 1549.725 nm, which can be controlled by tuning the temperature controller of the DFB laser driver when the wavelength of ML was fixed at 1549.520 nm with a simultaneous stable detuning frequency \(\Delta f_{1}\). Therefore, the central response frequency of the first passband could be fixed at 19.13 GHz with the out-of-band suppression ratio around 26.2 dB, and the center frequency of the second passband could be tuned from 24.75 to 32.41 GHz with the out-of-band suppression ratio around 28.8 dB, as shown in Figure 4. The 3-dB bandwidth of the first passband was about 0.5 GHz, and the 3-dB bandwidth of the second passband was about 0.6 GHz.