Strong Optomechanical Interactions with Long-lived Fundamental Acoustic Waves

TL;DR

This paper demonstrates a new approach to optomechanical interactions that decouples interaction strength from phonon lifetime, enabling high coupling and long-lived acoustic waves for advanced photonic applications.

Contribution

It introduces a novel paradigm where phonon lifetime and optomechanical coupling are independently optimized, supported by experimental observations and a comprehensive theoretical model.

Findings

Achieved >2 μs phonon lifetimes in a tapered fiber.

Observed strong optomechanical coupling >400 W^{-1} m^{-1}.

Demonstrated phonon self-interference effects.

Abstract

Traveling-wave optomechanical interactions, known as Brillouin interactions, have now been established as a powerful and versatile resource for photonic sources, sensors, and radio-frequency processors. However, established Brillouin-based interactions with sufficient interaction strengths involve short phonon lifetimes, which critically limit their performance for applications including radio-frequency filtering and optomechanical storage devices. Here, we investigate a new paradigm of optomechanical interactions with fundamental acoustic modes, where interaction strength is decoupled from phonon lifetimes, enabling the uniquely desirable combination of high optomechanical coupling, long phonon lifetimes, tunable phonon frequencies, and single-sideband amplification. Using sensitive four-wave mixing spectroscopy controlling for noise and spatial mode coupling, optomechanical interactions with long > 2 $\mu s$ phonon lifetimes and strong > 400 $W^{-1} m^{-1}$ coupling are observed in a tapered fiber. In addition, we demonstrate novel phonon self-interference effects resulting from the unique combination of an axially varying device geometry with long phonon lifetimes. A generalized theoretical model, in excellent agreement with experiments, is developed with broad applicability to inhomogeneous optomechanical systems.