  Microwave photonics (MWP) studies the interaction between microwave and
optical waves for the generation, transmission and processing of microwave
signals (i.e., three key domains), taking advantages of broad bandwidth and low
loss offered by modern photonics. Integrated MWP using photonic integrated
circuits (PICs) can reach a compact, reliable and green implementation. Most
PICs, however, are recently developed to perform one or more functions
restricted inside a single domain. In this paper, as highly desired, a
multifunctional PIC is proposed to cover the three key domains. The PIC is
fabricated on InP platform by monolithically integrating four laser diodes and
two modulators. Using the multifunctional PIC, seven fundamental functions
across microwave signal generation, transmission and processing are
demonstrated experimentally. Outdoor field trials for electromagnetic
environment surveillance along an in-service high-speed railway are also
performed. The success to such a PIC marks a key step forward for practical and
massive MWP implementations.
