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. 2016 Sep 6:6:31921.
doi: 10.1038/srep31921.

Millimetre Wave with Rotational Orbital Angular Momentum

Chao Zhang  1 , Lu Ma  1
Affiliations

Millimetre Wave with Rotational Orbital Angular Momentum

Chao Zhang et al. Sci Rep. .

Abstract

Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission.

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Figures

Figure 1
Figure 1. Transmission structure with a rotational OAM wave.
(a) Spiral phase plates with OAM l = −1. (b) Spiral phase plates with OAM mode l = +1. (c) Spiral phase plates with OAM mode l = +2. (d) The prototype of the transmitting antenna to generate the rotational OAM wave. (e) Schematic of the transmission with the rotational OAM wave.
Figure 2
Figure 2. Phase measurements of the rotational OAM waves.
(a) Schematic illustration of the phase measurements experiment. (b) Picture of the experiment scenario. (c) The received phases of the rotational OAM wave with different OAM modes. (d) Illustration of the received orthogonal signals generated by the rotational OAM waves.
Figure 3
Figure 3. Frequency measurements of the rotational OAM waves.
(a) Schematic illustration of the frequency measurements experiment. (b) Step plates used in the experiments. (c) Phase profiles detected for two types of plates with different OAM modes. (d) The received frequency shifts of the rotational OAM wave with different OAM modes.
Figure 4
Figure 4. Polarization measurements of the rotational OAM waves.
(a) Schematic illustration of the experiment. (b) Polarization measurements at different received polarization directions.
Figure 5
Figure 5. Measurements with a lens to focus the beam energy.
(a) Schematic illustration of the focusing system. (b) The measured energy and phase without a lens. (c) The measured energy and phase with a lens.
See this image and copyright information in PMC

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