Technological innovation with millimeter waves (mm waves), signals having carrier frequencies between 30 and 300 GHz, has become an increasingly important research field. While it is challenging to generate and distribute these high frequency signals using all-electronic means, photonic techniques that transfer the signals to the optical domain for processing can alleviate several of the issues that plague electronic components. By realizing optical signal processing in a photonic integrated circuit (PIC), one can considerably improve the performance, footprint, cost, weight, and energy efficiency of photonics-based mm-wave technologies. In this article, we detail the applications that rely on mm-wave generation and review the requirements for photonics-based technologies to achieve this functionality. We give an overview of the different PIC platforms, with a particular focus on hybrid silicon photonics, and detail how the performance of two key components in the generation of mm waves, photodetectors and modulators, can be optimized in these platforms. Finally, we discuss the potential of hybrid silicon photonics for extending mm-wave generation towards the THz domain and provide an outlook on whether these mm-wave applications will be a new milestone in the evolution of hybrid silicon photonics.

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Two photonic integrated circuits (PICs) are coupled to form a hybridly integrated semiconductor ring laser in the telecom C band with an intrinsic linewidth of (158±21) Hz. This is, to the best of our knowledge, the first time an InP active–passive platform is used in conjunction with an integrated low-loss resonator to obtain a narrow-linewidth laser implemented using generic foundry platforms. The presented results pave the way for a hybrid integrated platform for microwave photonics (MWP), as the demonstrated device includes multiple active–passive components, and its narrow optical linewidth can potentially be translated to a narrow-linewidth microwave signal. Furthermore, as the laser is based on hybrid integration of two PICs from generic foundry platforms, there is a path to reproducible and low-cost devices.

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