Abstract
Orbital angular momentum (OAM) beams with topological charge l are commonly generated and detected by modulating an incoming field with an azimuthal phase profile of the form exp(ilϕ) by a variety of approaches. This results in unwanted radial modes and reduced power in the desired OAM mode. Here, we show how to enhance the modal purity in the creation and detection of classical OAM beams and in the quantum detection of OAM photons. Classically, we combine holographic and metasurface control to produce high purity OAM modes and show how to detect them with high efficiency, extending the demonstration to the quantum realm with spatial light modulators. We demonstrate ultra-high purity OAM modes in orders as high as l = 100 and a doubling of dimensionality in the quantum OAM spectrum from a spontaneous parametric downconversion source. Our work offers a simple route to increase the channel capacity in classical and quantum communication using OAM modes as a basis.
Highlights
It has been known for at least a century that photons could carry both a spin angular momentum and an orbital angular momentum (OAM), but the “creation” of the latter required rare quadrupole transitions in atoms to occur and so remained largely unstudied
In each case, the beam waist size is varied on the projection hologram for the detection of each radial mode ranging from p = 0 to p = 10
Our aim is to engineer the mode by the metasurface and holographic control to produce |c0|2 → 1, i.e., 100% of the power in the desired Orbital angular momentum (OAM) mode in order to emphasize the effect of amplitude control in the generation process
Summary
It has been known for at least a century that photons could carry both a spin angular momentum and an orbital angular momentum (OAM), but the “creation” of the latter required rare quadrupole transitions in atoms to occur and so remained largely unstudied. Just over 25 years ago, Allen and co-workers realized that OAM carrying beams could be created in the laboratory using conventional optics in a deterministic manner. They noticed that a phase vortex of the form exp(ilφ) would give each photon a “twist” in wavefront, resulting in OAM of lhper photon. The use of azimuthal phase elements for the creation of such vortex beams has become ubiquitous, implemented by dynamic phase approaches on spatial light modulators (SLMs), as well as by geometric phase approaches using liquid crystals or metasurfaces (MSs), and has been pioneered to harness the radial degree of freedom by merging these approaches in a single element.. The use of azimuthal phase elements for the creation of such vortex beams has become ubiquitous, implemented by dynamic phase approaches on spatial light modulators (SLMs), as well as by geometric phase approaches using liquid crystals or metasurfaces (MSs), and has been pioneered to harness the radial degree of freedom by merging these approaches in a single element. These phase-only vortex beams have found a myriad of applications, making them highly topical forms of structured light.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
