Measuring orbital angular momentum of vortex beams in optomechanics
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Front. Phys. 16(3), 32503 (2021)
Research article Measuring orbital angular momentum of vortex beams in optomechanics Zhucheng Zhang1 , Jiancheng Pei1 , Yi-Ping Wang2 , Xiaoguang Wang1,3,† 1
Zhejiang Institute of Modern Physics, Department of Physics, Zhejiang University, Hangzhou 310027, China 2 College of Science, Northwest A&F University, Yangling 712100, China 3 Graduate School of China Academy of Engineering Physics, Beijing 100193, China Corresponding author. E-mail: † [email protected] Received August 18, 2020; accepted October 30, 2020
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 ±45, which is a significant improvement for measuring OAM based on the cavity optomechanical system. Keywords orbital angular momentum, optomechanically induced transparency, Laguerre–Gaussian rotational-cavity system, optomechanics
1 Introduction Vortex beams, such as Laguerre–Gaussian (LG) beam, possess an azimuthal phase structure eilψ , which can carry a well-defined orbital angular momentum (OAM) of l¯h per photon, with ψ and l being its azimuthal angle and topological charge value [1, 2]. This type of beams can be generated by diffracting a non-helical beam off a spiral phase plate [3, 4] or off a computer-generated hologram [5, 6]. Recently, the generation and detection of OAM-tunable vortex microlaser on the photonic chip were realized [7, 8]. Due to their quantized OAM and their dynamic characteristics, these helically phased beams are widely used in many fields, such as quantum information technologies [9], optical communications [10, 11], optical trapping [12], optical tweezers [13, 14], and so on. Thus, it is of great importance to measure OAM of vortex beams (or its topological charge value) accurately, including the magnitude and the sign. ∗ arXiv:
2005.08769. This article can also be found at http:// journal.hep.com.cn/fop/EN/10.1007/s11467-020-1030-0.
To measure OAM of vortex beams, in general, we can analyze the related interference patterns directly, for example, the interference pattern betw
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