A full-band direct-conversion receiver using a microwave photonic in-phase and quadrature (I/Q) mixer is proposed and experimentally evaluated in terms of radio frequency (RF) range, port isolation, phase imbalance, conversion gain, noise figure, spurious-free dynamic range, and error vector magnitude. The proposed microwave photonic I/Q mixer shows significant advantages in local oscillator leakage and I/Q phase imbalance over entire RF bands, which are recognized as major drawbacks of conventional direct-conversion receivers.

In this Letter, we experimentally demonstrate a full-duplex transmission system of IEEE 802.11ac-compliant multiple-input multiple-output (MIMO) signals over a 2-km 7-core fiber for in-building wireless local-area network (WLAN) distributed antenna systems. For full-duplex 3×3 MIMO demonstration, the crosstalk impacts of both fiber-transmission-only and optic-wireless transmission situation are evaluated. The results indicate that the impact of crosstalk on radio-over-fiber (ROF) link performance is not significant and the quality of the cascaded multi-core fiber and wireless channel is mainly determined by the wireless part. To further improve the system capacity, polarization multiplexing (PolMux) technology is employed to achieve a full-duplex 6×6 MIMO over a single 7-core fiber. Although employing the PolMux method will slightly decrease the EVM and condition number performance as opposed to a non-PolMux MCF system, it is still a competitive solution in large optical connection demand scenarios that require a low cost.

We propose a high-Q photonic-electronic hybrid cavity for single-longitudinal-mode narrow-linewidth oscillation, where part of the cavity is in the radio frequency (RF) domain by a pair of frequency conversions. In the RF part, we can easily achieve MHz filtering and a large delay by inserting an electronic filter. In mathematics, we prove that the frequency conversion pair and electronic filter in between can be equivalent to a high-Q optical filter cascaded low-noise optical amplifier as a whole. Finally, the 20-dB bandwidth of oscillation is 1/20 of that of an optical local oscillator, and the maximum phase noise suppression can reach 65 dB.

A novel compact optoelectronic oscillator (OEO) employing a Fabry–Perot (FP) resonant electro-optic (EO) modulator is proposed and experimentally demonstrated. The resonant modulator is used as the optical storage element as well as the mode selection element, which can greatly reduce the system complexity and make the system more portable. Moreover, the optical resonance and electrical transmission response for the FP resonant EO modulator are theoretically and experimentally studied. The proposed OEO oscillates at 10 and 20 GHz in the proof-of-concept experiment, and the corresponding single-sideband phase noise can reach below 118 and 108 dBc/Hz at 1 MHz offset frequency, respectively.

Microwave photonics (MWPs) uses the strength of photonic techniques to generate, process, control, and distribute microwave signals, combining the advantages of microwaves and photonics. As one of the main topics of MWP, radio-over-fiber (RoF) links can provide features that are very difficult or even impossible to achieve with traditional technologies. Meanwhile, a considerable number of signal-processing subsystems have been carried out in the field of MWP as they are instrumental for the implementation of many functionalities. However, there are still several challenges in strengthening the performance of the technology to support systems and applications with more complex structures, multiple functionality, larger bandwidth, and larger processing capability. In this paper, we identify some of the notable challenges in MWP and review our recent work. Applications and future direction of research are also discussed.