Microwave I/Q down-converters are frequently used in image-reject super heterodyne receivers, zero intermediate frequency (zero-IF) receivers, and phase/frequency discriminators. However, due to the electronic bottleneck, conventional microwave I/Q mixers face a serious bandwidth limitation, I/Q imbalance, and even-order distortion. In this paper, photonic microwave fundamental and sub-harmonic I/Q down-converters are presented using a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM). Thanks to all-optical manipulation, the proposed system features an ultra-wide operating band (7–40 GHz in the fundamental I/Q down-converter, and 10–40 GHz in the sub-harmonic I/Q down-converter) and an excellent I/Q balance (maximum 0.7 dB power imbalance and 1 degree phase imbalance). The conversion gain, noise figure (NF), even-order distortion, and spurious free dynamic range (SFDR) are also improved by LO power optimization and balanced detection. Using the proposed system, a high image rejection ratio is demonstrated for a super heterodyne receiver, and good EVMs over a wide RF power range is demonstrated for a zero-IF receiver. The proposed broadband photonic microwave fundamental and sub-harmonic I/Q down-converters may find potential applications in multi-band satellite, ultra-wideband radar and frequency-agile electronic warfare systems.

Microwave I/Q up-converter is widely used in modern electronic systems to achieve single-sideband (SSB) up-conversion and vector modulation. However, due to the frequency-dependent mixer and quadrature coupler, conventional electronic I/Q up-converters suffer limited operating bandwidth. In this paper, a photonic microwave I/Q up-converter is proposed using a polarization-division multiplexing modulator. The I/Q up-conversion channels are built in all-optical methods without any frequency-dependent devices, so a wide operating bandwidth is obtained. Balanced detection is also realized to reduce the noise figure. In the experiment, SSB signals with wide operating bandwidth (14-40 GHz), high sideband and carrier suppression (>20 dB), and large spurious-free dynamic range (110.4 Hz ^2/3 ) are generated. 16 and 64 quadrature amplitude modulation vector signals with data rates of 400 and 600 Mb/s at 40-GHz carrier frequency are also demonstrated. Furthermore, subharmonic I/Q up-conversion with similar performance is also realized using the same structure, which can well reduce the frequency requirement of the local oscillator signal and the drive circuits.

We propose and experimentally demonstrate an ultraefficient broadband photonic channelizer. By polarization-division multiplexing the received signal and using dual-output Hartley image-reject receiving topology, 4N channels can be generated with only (N + 1)-line signal optical frequency comb (OFC) and N-line local oscillator (LO) OFC, and the frequency interval of the OFC is reduced to half of the typical value. With the use of the integrated dual-polarization coherent detection receiver (DP-CDR), the required quadrature optical hybrid (QOH) and the balanced photodetectors (BPDs) are reduced to half. The system size is reduced and stability is improved. Besides, assisted with a digital signal processor (DSP) algorithm, the IQ imbalance can be compensated, and approximately, ideal image rejection can be realized. A proof-of-concept experiment is carried out. A 2-14-GHz wideband signal is successfully divided into 12 channels with 1-GHz bandwidth by applying four-line signal OFC and three-line LO OFC. The image rejection ratio (IRR), channel isolation (CI), and spurious-free dynamic range (SFDR) are also measured and discussed.

Microwave photonic channelized receiver can break through the electronic bottleneck, improve the throughput of satellite payload, and is expected to be widely used in broadband satellite communications. To solve the self-interference problem in the full-duplex satellite relay system, a microwave photonic channelized receiver with a self-interference cancellation (SIC) function is proposed in this paper. The equal interval division of broadband radio frequency (RF) signals is realized through polarization multiplexing technology and optical frequency shifting technology. In addition, by constructing a reference interference signal and matching the delay and amplitude in the optical domain, the self-interference signal is eliminated to avoid the receiver blockage caused by interference leakage. Theoretical derivation and experiment research are carried out, and a wideband signal with 3-GHz bandwidth is down-converted to six sub-channels with a frequency range of 0.5 GHz–1 GHz. Under the single-tone test, the isolation between sub-channels exceeds 31 dB, and the SIC depth exceeds 40 dB. When the sub-channels carry the 16quadrature amplitude modulation (QAM) signals with the bandwidth of 50 MHz, the SIC depth over 26 dB is achieved, and the error vector magnitude (EVM) is 7.6%. Under the two-tone test, the SFDR of the sub-channel is 93.5 dB.Hz ^2/3 .

For the fronthaul between the baseband unit and the remote radio unit (RRU), radio over fiber (RoF) is promising to replace the Common Public Radio Interface in beyond fifth-generation and the sixth-generation wireless communication systems. The weight, size, and power consumption of the RRU can be greatly reduced, along with easy support for the millimeter-wave band. In this paper, a dual-band RoF link is proposed, where flexible switching between high-frequency (28 GHz) and low-frequency (3.5 GHz) RF channels is realized through polarization control. Single-sideband modulation is performed on 28 GHz signals to avoid periodic power fading during long-distance fiber transmission. By adjusting the DC bias, the third-order intermodulation distortion component in the 3.5 GHz signal is suppressed, and the spur-free dynamic range (SFDR) is improved. Experimental results show a channel isolation of above 43 dB. The link gain of the 28 GHz signal channel is flat, and the SFDR of the 3.5 GHz signal channel can reach 118.6 d B ⋅ H z 4 / 5 . In the case of RF vector signal transmission, the adjacent channel power ratio of the 3.5 GHz signal channel is optimally up to 48 dB, and the error vector magnitude is 2.9%.

In this paper, a novel photonic-assisted Doppler frequency shift (DFS) measurement scheme based on an integrated dual-polarization Mach–Zehnder modulator is presented. In the proposed scheme, the DFS to be identified is transformed into a low-frequency electrical signal through an optical frequency-conversion link. The value of the DFS can be acquired by analyzing the spectrum of the low-frequency electrical signal. Meanwhile, the orientation of the DFS can be easily determined utilizing a 90° hybrid coupler. If the receiver is moving toward the transmitter, only the positive port has an output signal, while only the negative port has an output signal if the receiver is moving away from the transmitter. The scheme can simultaneously obtain the value and the orientation of the DFS. In addition, to investigate the frequency tunability of the proposed scheme, the DFS, which varies from $-100$ to 100 KHz at a step of 10 KHz for different microwave signals at frequencies of 10, 15, and 18 GHz, is demonstrated experimentally, and the errors are within $\pm 5\times {10}^{-6}\mathrm{Hz}$.