Non-Reciprocal Brillouin Scattering Induced Transparency (1408.1739v2)

Abstract: Electromagnetically induced transparency (EIT) provides a powerful mechanism for controlling light propagation in a dielectric medium, and for producing slow and fast light. EIT traditionally arises from destructive interference induced by a nonradiative coherence in an atomic system. Stimulated Brillouin scattering (SBS) of light from propagating hypersonic acoustic waves has also been used successfully for the generation of slow and fast light. However, EIT-type processes based on SBS were considered infeasible because of the short coherence lifetime of hypersonic phonons. Here, we report a new Brillouin scattering induced transparency (BSIT) phenomenon generated by acousto-optic interaction of light with long-lived propagating phonons. We demonstrate that BSIT is uniquely non-reciprocal due to the propagating acoustic phonon wave and accompanying momentum conservation requirement. Using a silica microresonator having naturally occurring forward-SBS phase-matched modal configuration, we show that BSIT enables compact and ultralow-power slow-light generation with delay-bandwidth product comparable to state-of-the-art SBS systems.

• The paper introduces BSIT, achieving non-reciprocal slow light via forward stimulated Brillouin scattering in silica microresonators.
• It employs a three-mode system with two optical and one long-lived acoustic mode to meet energy and momentum conservation for optical delay effects.
• Experimental results show a 110 µs transparency bandwidth under 1 mW control power, highlighting potential for compact integrated photonic devices.

Analysis of Non-Reciprocal Brillouin Scattering Induced Transparency

The paper discusses a novel phenomenon termed Brillouin scattering induced transparency (BSIT), a process that leverages the unique properties of stimulated Brillouin scattering (SBS) for creating non-reciprocal slow light effects. Utilizing a silica microresonator with naturally occurring forward-SBS phase-matched modal configurations, the authors explore the interaction between light and phonons, demonstrating that BSIT provides compact and ultralow-power generation of slow light with a delay-bandwidth product comparable to advanced SBS systems.

Stimulated Brillouin scattering, a nonlinear interaction where light fields are influenced by a traveling acoustic wave, is widely used across optical applications, including signal amplification, phase conjugation, and material characterization. Unlike electromagnetically induced transparency (EIT) in atomic systems, implementing transparency through SBS has historically been challenging due to the short life of multi-GHz phonons. However, BSIT arises within forward-SBS systems where phonon lifetimes exceed those of photons, allowing optical field coupling through long-lived phonon modes.

In this work, the mechanism of BSIT is explored in a three-mode system involving two optical and one acoustic mode. These modes meet both energy and momentum conservation requirements—critical for the unique phase matching featured in BSIT. The non-reciprocity of this process lays the groundwork for potential applications in integrated photonic devices, including optical isolators and circulators, negating the need for magnetic materials which are typically used for such purposes.

Results from the experiments show significant slow light and fast light responses achieved with minimal input power, demonstrating a transparency bandwidth of 110 µs under 1 mW of control laser power. Notably, the reported delay-bandwidth product, although not exceeding the state of the art of linear SBS systems, provides a substantial improvement in terms of power and device footprint. This indicates significant practical advantages for on-chip applications where size and power are critical constraints.

The implications of this research are profound, as the compact configuration and low power requirements open doors for efficient photonic technologies, fundamentally altering current practices in optical communications and signal processing. Furthermore, BSIT introduces new pathways for exploring non-linearities in photonic systems due to the versatility of electrostrictive effects across different media, potentially enacting innovative applications in nanophotonics.

Future developments of BSIT may focus on optimizing device configurations for enhanced performance, particularly in non-linear photonic circuits, considering both the theoretical and practical advancements in microresonator design. Additionally, exploration into alternative materials with higher electrostrictive coefficients might yield even greater efficiencies, further minimizing energy demands. The concept of momentum conservation in transparency mechanisms holds potential to drive further innovation beyond current Brillouin systems, fostering broader adoption in integrated photonics and reinforcing the foundational framework established by this research.