Microwave photonics is a rapidly-growing interdisciplinary field linking microwave and optical technologies. This paper intends to trace the evolution of microwave photonics over the last three decades emphasizing some major research areas and application fields. Currently, microwave photonics is a vivid research area with several practical applications. In this paper, we attempt to project potential future trends as well.Index Terms-Analog fiber-optic link, microwave photonics, optical control, optical generation of microwave signals, optical signal processing, phased-array antennas, radio-over-fiber (RoF) links.

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A new integrated W-band frequency source MMIC is presented which consists of a 94-GHz voltage-controlled oscillator (VCO) with large tuning range and a phase comparator, forming a subharmonic injection-locked phase-locked loop (ILPLL). The ILPLL combines conventional injection-locking with an additional phase control loop to improve the locking range of the oscillator significantly. The 4th subharmonic frequency is used as the reference signal. The locking range was increased from 80 MHz without ILPLL to 4.5 GHz with ILPLL by closing the loop with an external dc amplifier. A phase noise of -83 dBc/Hz at 100-KHz offset was achieved. Pseudomorphic GaAs HEMT's and a coplanar circuit topology were used to allow integration into complex single-chip subsystems and flip-chip packaging