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1. Electrically controlled phased array OAM radar

   https://doi.org/10.1117/12.2559388  

   Orfeo, Dan; Burns, Dylan; Huston, Dryver R.; Xia, Tian (May 2020, SPIE Defense + Commercial Sensing, Proc Vol 11408, Radar Sensor Technology XXIV)

   Raynal, Ann M.; Ranney, Kenneth I. (Ed.)

   Control of orbital angular momentum (OAM) offers the potential for increases in control, sensitivity, and security for high-performance microwave systems. OAM is characterized by an integer OAM mode where zero represents the case of a plane wave. Microwaves with a nonzero OAM mode propagate with a helical wavefront. Orthogonal OAM modes can be used to carry distinct information at the same frequency and polarization, increasing the data rate. The OAM waveform may also increase radar detection capability for certain shaped objects. OAM can be induced by broadcasting a plane wave through a spatial phase plate (SPP) dielectric which introduces an azimuthally dependent phase delay. However, SPPs are frequency-specific, which presents an obstacle for harnessing OAM in frequency-modulated communication systems and wide-bandwidth radar. In this study, we develop a circular phased array to synthesize the desired vortex-shaped wavefront. This approach offers a critical advantage: the phases of all antenna elements are easily programmable under different frequencies. As a result, transmission and reception of the OAM beam can be controlled with great flexibility, making it operable over a wide frequency spectrum, which leverages OAM radar functionality and performance. In this paper, we will investigate a wide-bandwidth radar with OAM mode-control and signal processing. 

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2. Study of OAM for Communication and Radar

   https://doi.org/10.1109/RadarConf2147009.2021.9455299  

   Orfeo, Daniel; Huston, Dryver; Xia, Tian (January 2021, 2021 IEEE Radar Conference (RadarConf21))

   Radio-frequency sensing and communication systems which use a waveform for more than one function offer the promise of improved spectral efficiency and streamlined hardware requirements. Control of orbital angular momentum (OAM) may be used to increase data-rates and improve radar sensitivity to certain chiral targets. This paper presents finite-difference time-domain simulations which model a gigahertz-frequency OAM radar capable of transmitting information via OAM-mode modulation. The unique chirality-detection capability of OAM radar is demonstrated, as well as simple information transmission. Simulation scope and radar specifications are designed with an eye toward developing a dual function ground penetrating radar (GPR) with OAM mode control. 

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3. Pair-OAM properties in scalar light beams

   https://doi.org/10.1364/OL.537195  

   Martinez, Sebastian; Pokharel, Sushil; Korotkova, Olga (October 2024, Optics Letters)

   We reveal the geometric structure existing on segregation of a pair of orbital angular momentum (OAM) states from the total random light beam and introduce new quantities, to the best of our knowledge, for its characterization. In particular, the degree and the ellipse of orbitalization are introduced in analogy with those in the polarization theory. Free-space propagation of these quantities is illustrated by numerical examples. The limiting case of a deterministic light beam is also separately discussed. 

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4. Toward OAM-selective frequency conversion in a three-mode fiber

   https://doi.org/10.1364/CLEO_SI.2021.SM1F.5  

   Shamsshooli, Afshin; Guo, Cheng; Parmigiani, Francesca; Li, Xiaoying; Vasilyev, Michael (May 2021, CLEO conference 2021)

   null (Ed.)

   We describe OAM-compatible mode-selective frequency conversion in a few-mode fiber and experimentally demonstrate downconversion of various superpositions of signal modes LP11a and LP11b to the same LP11b mode with conversion efficiency differences <0.8 dB. 

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5. A Low-Power OAM Metasurface for Rank-Deficient Wireless Environments

   https://doi.org/10.1109/GLOBECOM54140.2023.10436974  

   Cho, Kun Woo; Kasi, Srikar; Jamieson, Kyle (December 2023, IEEE Global Communications Conference)

   This paper presents Monolith, a high bitrate, low-power, metamaterials surface-based Orbital Angular Momentum (OAM) MIMO multiplexing design for rank deficient, free space wireless environments. Leveraging ambient signals as the source of power, Monolith backscatters these ambient signals by modulating them into several orthogonal beams, where each beam carries a unique OAM. We provide insights along the design aspects of a low-power and programmable metamaterials-based surface. Our results show that Monolith achieves an order of magnitude higher channel capacity than traditional spatial MIMO backscattering networks. 

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