Nonreciprocity and magnetic-free isolation based on optomechanical interactions (1607.07180v1)

Abstract: Photonic nonreciprocal components, such as isolators and circulators, provide highly desirable functionalities for optical circuitry. This motivates the active investigation of mechanisms that break reciprocity, and pose alternatives to magneto-optic effects in on-chip systems. In this work, we use optomechanical interactions to strongly break reciprocity in a compact system. We derive minimal requirements to create nonreciprocity in a wide class of systems that couple two optical modes to a mechanical mode, highlighting the importance of optically biasing the modes at a controlled phase difference. We realize these principles in a silica microtoroid optomechanical resonator and use quantitative heterodyne spectroscopy to demonstrate up to 10 dB optical isolation at telecom wavelengths. We show that nonreciprocal transmission is preserved for nondegenerate modes, and demonstrate nonreciprocal parametric amplification. These results open a route to exploiting various nonreciprocal effects in optomechanical systems in different electromagnetic and mechanical frequency regimes, including optomechanical metamaterials with topologically non-trivial properties.

• The paper presents a theoretical framework leveraging optomechanical interactions to achieve nonreciprocal transmission without relying on magneto-optic effects.
• Experimental validation in a silica microtoroid resonator demonstrated up to 10 dB optical isolation at telecom wavelengths by controlling the phase difference between modes.
• The study establishes key design conditions for phase manipulation and asymmetric coupling, paving the way for advanced nonreciprocal devices in integrated photonics and quantum networks.

Nonreciprocity and Magnetic-Free Isolation Based on Optomechanical Interactions

The paper investigates a method to achieve nonreciprocity in photonic systems by leveraging optomechanical interactions without relying on traditional magneto-optic effects. Nonreciprocal components, such as isolators and circulators, are crucial for the development of optical circuits, where control over the direction of light propagation is essential. The push to find alternatives to magneto-optic effects is driven by the inherent limitations of existing materials, such as weak magneto-optic coefficients and associated losses, as well as the technological shift towards integrated on-chip systems.

Optomechanical Systems Framework

The authors propose a theoretical framework for nonreciprocity in systems coupling two optical modes to a single mechanical mode. This approach is predicated on manipulating the phase difference between optical modes. Key to this method is the ability to induce nonreciprocal transmission through optomechanical interactions, thus breaking Lorentz reciprocity which posits that wave transmission remains unchanged when source and observer are interchanged.

Experimental Realization

A silica microtoroid optomechanical resonator is employed to demonstrate the principles outlined. Through quantitative heterodyne spectroscopy, the paper achieves up to 10 dB of optical isolation at telecom wavelengths, showcasing the potential of optomechanical systems for robust nonreciprocal functionalities. This was achieved by tailoring the phase difference between the optical modes in the resonator, which inherently supports the required phase relationships for breaking reciprocity.

Results and Implications

Experimental results indicate that the nonreciprocal transmission is maintained even for nondegenerate optical modes. Furthermore, the paper demonstrates nonreciprocal parametric amplification, suggesting a mechanism wherein only co-propagating probe signals with the pump are amplified - a feature with potential applications in nonreciprocal RF filtering.

The results extend the understanding of nonreciprocal effects in optomechanical systems, potentially informing future research in optomechanical metamaterials with topologically non-trivial properties. These findings may influence the design of photonic systems where minimizing losses and bidirectional transmission is critical.

Theoretical Impact

The derived minimal conditions for achieving nonreciprocity accentuate the necessity of asymmetric coupling between optical modes and input-output channels, coupled with a precise $\pi/2$ phase difference in their drive. This theoretical model unifies various manifestations of optomechanical nonreciprocity, underscoring its applicability across different electromagnetic and mechanical frequency regimes.

Future Directions

The paper's findings pose intriguing questions about the broader applicability of optomechanical systems in complex signal processing tasks and potentially in topologically protected states. Advances building on this work could see the development of novel nonreciprocal devices or enhancement of existing technologies through integration with silicon photonics or the development of quantum networks where lossless nonreciprocal transmission is pivotal.