No abstract

A quantitative analysis of optical fields is essential, particularly when the light is structured in some desired manner, or when there is perhaps an undesired structure that must be corrected for. A ubiquitous procedure in the optical community is that of optical mode projections—a modal analysis of light—for the unveiling of amplitude and phase information of a light field. When correctly performed, all the salient features of the field can be deduced with high fidelity, including its orbital angular momentum, vectorial properties, wavefront, and Poynting vector. Here, we present a practical tutorial on how to perform an efficient and effective optical modal decomposition, with emphasis on holographic approaches using spatial light modulators, highlighting the care required at each step of the process.

Secret sharing allows three or more parties to share secret information which can only be decrypted through collaboration. It complements quantum key distribution as a valuable resource for securely distributing information. Here we take advantage of hybrid spin and orbital angular momentum states to access a high dimensional encoding space, demonstrating a protocol that is easily scalable in both dimension and participants. To illustrate the versatility of our approach, we first demonstrate the protocol in two dimensions, extending the number of participants to ten, and then demonstrate the protocol in three dimensions with three participants, the highest realisation of participants and dimensions thus far. We reconstruct secrets depicted as images with a fidelity of up to 0.979. Moreover, our scheme exploits the use of conventional linear optics to emulate the quantum gates needed for transitions between basis modes on a high dimensional Hilbert space with the potential of up to 1.225 bits of encoding capacity per transmitted photon. Our work offers a practical approach for sharing information across multiple parties, a crucial element of any quantum network.

Quantum secret sharing is the art of securely sharing information between more than two people in such a way that its reconstruction requires the collaboration of a certain number of parties. Here, by taking advantage of the high‐dimensional Hilbert space for orbital angular momentum and using Perfect Vortex beams as their carriers, a proof‐of‐principle implementation of a high‐dimensional quantum secret sharing scheme is presented. This scheme is experimentally implemented with a fidelity of 93.4%, for 10 participants in d=11 dimensions—the highest number of participants and dimensions to date. The implementation can easily be scaled to higher dimensions and any number of participants, opening the way for securely distributing information across a network of nodes.

Perfect (optical) vortex (PV) beams are fields which are mooted to be independent of the orbital angular momentum (OAM) they carry. To date, the best experimental approximation of these modes is obtained from passing Bessel-Gaussian beams through a Fourier lens. However, the OAMdependent width of these quasi-PVs is not precisely known and is often understated. We address this here by deriving and experimentally confirming an explicit analytic expression for the second moment width of quasi-PVs. We show that the width scales in proportion to √ in the best case, the same as most "regular" vortex modes albeit with a much smaller proportionality constant. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping, tweezing and communications.

No abstract

Perfect (optical) vortices (PVs) have the mooted ability to encode orbital angular momentum (OAM) onto the field within a well-defined annular ring. Although this makes the near-field radial profile independent of OAM, the far-field radial profile nevertheless scales with OAM, forming a Bessel structure. A consequence of this is that quantitative measurement of PVs by modal decomposition has been thought to be unviable. Here, we show that the OAM content of a PV can be measured quantitatively, including superpositions of OAM within one perfect vortex. We outline the theory and confirm it by experiment with holograms written to spatial light modulators, highlighting the care required for accurate decomposition of the OAM content. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping and tweezing, and optical communication.

Spatial light modulators (SLMs) are popular tools for generating structured light fields and have fostered numerous applications in optics and photonics. Here, we explore the limits of what fields these devices are capable of generating and detecting in the context of so-called vortex beams carrying orbital angular momentum (OAM). Our main contributions are to quantify (theoretically and experimentally) how the pixelation of the SLM screen affects the quality of the generated vortex mode and to offer useful heuristics on how to optimise the performance of the displayed digital hologram. In so doing, we successfully generate and detect a very high order optical vortex mode with topological charge ℓ = 600 , the highest achieved to date using SLMs. Since the OAM degree of freedom is frequently touted as offering a potentially unbounded state space, we hope that this work will inspire researchers to make more use of higher-order vortex modes.