Photonic Signal Processing Using Nonlocal Brillouin Interactions

Date of Award

Spring 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Applied Physics

First Advisor

Rakich, Peter


In this dissertation, we explore the possibilities offered by the unique properties of Brillouin scattering to implement signal-processing operations in photonic devices. Brillouin scattering |the coupling of light and sound waves| enables access to long-lived acoustic modes directly from the optical domain and results in processes very different compared with other optical systems. Furthermore, when utilized to process microwave signals, Brillouin-active photonic systems are compelling for their ability to bridge the vastly different frequency scales of microwave and optical signals.We analyze the dynamics of forward Brillouin scattering, showing how they can give rise to a nonlocal effect, in stark contrast with other optical nonlinear interactions. We describe how these unusual properties can be exploited to engineer new types of devices, where highly delocalized acoustic modes mediate scattering processes between spatially separated light waves. Examining the potential of utilizing this scheme to perform filtering operations, we identify a path towards low-noise and low-distortion performance for these Brillouin-based technologies. Furthermore, we show how these photonic-phononic devices can be implemented in a standard silicon platform. Using these devices, we present tunable narrowband microwave-photonic filters, performing both bandpass and notch filtering operations demonstrating sharp frequency roll-off and excellent out-of-band rejection previously unattainable in silicon photonics. Looking forward, we explore the potential of utilizing multiple optical spatial modes in such devices, showing their unique properties, and study new waveguide designs that could enable silicon Brillouin-active devices to handle higher optical power. In addition to bringing greatly enhanced functionality to silicon photonics, we demonstrate the reliability and robustness of the devices, key features for high-impact optomechanical applications. The photonic circuits demonstrated here could be another step towards integrated signal processing systems.

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