Measuring orbital angular momentum of vortex beams in optomechanics

TL;DR

This paper proposes a novel optomechanical method to measure the magnitude and sign of orbital angular momentum in vortex beams by analyzing spectral shifts in a double Laguerre-Gaussian cavity system, enabling sign distinction.

Contribution

It introduces a new scheme using asymmetric optomechanically induced transparency to distinguish the sign of OAM, improving measurement capabilities for high-order vortex beams.

Findings

Spectral shifts correlate with OAM magnitude and sign.

The method distinguishes OAM sign in high-order vortex beams.

Enhanced measurement accuracy for vortex beams with topological charge ±45.

Abstract

Measuring the orbital angular momentum (OAM) of vortex beams, including the magnitude and the sign, has great application prospects due to its theoretically unbounded and orthogonal modes. Here, the sign-distinguishable OAM measurement in optomechanics is proposed, which is achieved by monitoring the shift of the transmission spectrum of the probe field in a double Laguerre-Gaussian (LG) rotational-cavity system. Compared with the traditional single LG rotational cavity, an asymmetric optomechanically induced transparency window can occur in our system. Meanwhile, the position of the resonance valley has a strong correlation with the magnitude and sign of OAM. This originally comes from the fact that the effective detuning of the cavity mode from the driving field can vary with the magnitude and sign of OAM, which causes the spectral shift to be directional for different signs of OAM. Our scheme solves the shortcoming of the inability to distinguish the sign of OAM in optomechanics, and works well for high-order vortex beams with topological charge value $\pm 45$, which is a significant improvement for measuring OAM based on the cavity optomechanical system.