# An Ultra-Wideband Microwave Photonic Channelized Receiver with Zero-IF Architecture
## 3 Results and Discussion  
### Generation of Polarization Multiplexed Signals  
The proposed system was simulated by VPItransmissionMaker software. The half-wave voltage of MZM was 3.5 V. The extinction ratio was 30 dB and the insertion loss was 6 dB. A continuous wave light was launched into DPMZM1 and DPMZM2 in parallel, with a frequency of 193.1 THz, an average power of 20 dBm, a linewidth of 10 kHz, and a maximum relative intensity noise (RIN) of \(-\)170 dB/Hz. DPMZM1 output five flat line combs with a frequency spacing of 0.6 GHz. The frequencies of the optical comb were \(-\)1.2 GHz, \(-\)0.6 GHz, 0 GHz, 0.6 GHz, and 1.2 GHz, respectively, relative to 193.1 THz. Figure 2 shows five flat comb lines with nearly the same amplitude. The unwanted mode suppression ratio (UMSR) was 23.3 dB.  
As is shown in Figure 3, DPMZM2 output carrier-suppressed positive and negative second-order optical sidebands, and the frequencies of positive and negative second-order sidebands were \(-\)20 GHz and 20 GHz, respectively, relative to 193.1 THz. The UMSR was 35.6 dB.  
The polarization multiplexed signal output from the DP-QPSK modulator was sent to the OBPF, and the optical frequency comb and the positive second-order optical sideband were filtered out. The  
Figure 3: The spectrum modulated by DPMZM2.  
Figure 2: The spectrum modulated by DPMZM1.  
optical frequency comb from the DPMZM1 was combed in the \(TE\) mode, and the positive and negative second-order optical sidebands from the DPMZM2 were in the \(TM\) mode. The output port of the OBPF was connected to a single polarization MZM. The five-symbol rate was 500 MSym/s and the modulation format was 16 quadrature amplitude modulation (16 QAM). The vector signals with center frequencies of 18.8 GHz, 19.4 GHz, 20 GHz, 20.6 GHz, and 21.2 GHz formed a wideband RF signal. The wideband RF signal was modulated in a single polarization MZM only in the \(TM\) mode (positive second-order optical sideband) and not modulated in the \(TE\) mode (optical frequency comb). The DC bias of the single-polarized MZM was set to MITP to achieve double-band modulation with carrier suppression. As shown in Figure 4, since the center frequency of the broadband RF signal is equal to twice the \(LO_{2}\) frequency, the center frequency of the lower sideband of the modulated broadband RF signal coincides with the center frequency of the optical frequency comb.  
The output of the single-polarized MZM was divided into five channels by an optical splitter, each passing through a narrow-band OBPF with different center frequencies. The center frequencies of the five channel filters were 193.0988 THz, 193.0994 THz, 193.1 THz, 193.1006 THz, and 193.110 THz, respectively. The polarization multiplexed light output from each narrowband OBPF included an optical carrier (one of the five comb lines) and a sub-channel RF signal, as shown in Figure 5, realizing the band division of the 3 GHz wideband signal. The frequency of the optical carrier was equal to the center frequency of the RF sub-channel, and the bandwidth of the five channels was 600 MHz.  
Figure 4: The spectrum modulated by the wideband RF signals.  
Figure 5: Five subchannels with a bandwidth of 600 HMz.