Utilizing multiplexing of structured THz beams carrying orbital-angular-momentum for high-capacity communications

Abstract

Structured electromagnetic (EM) waves have been explored in various frequency regimes to enhance the capacity of communication systems by multiplexing multiple co-propagating beams with mutually orthogonal spatial modal structures (i.e., mode-division multiplexing). Such structured EM waves include beams carrying orbital angular momentum (OAM). An area of increased recent interest is the use of terahertz (THz) beams for free-space communications, which tends to have: (a) larger bandwidth and lower beam divergence than millimeter-waves, and (b) lower interaction with matter conditions than optical waves. Here, we explore the multiplexing of THz OAM beams for high-capacity communications. Specifically, we experimentally demonstrate communication systems with two multiplexed THz OAM beams at a carrier frequency of 0.3 THz. We achieve a 60-Gbit/s quadrature-phase-shift-keying (QPSK) and a 24-Gbit/s 16 quadrature amplitude modulation (16-QAM) data transmission with bit-error rates below 3.8 × 10−3. In addition, to show the compatibility of different multiplexing approaches (e.g., polarization-, frequency-, and mode-division multiplexing), we demonstrate an 80-Gbit/s QPSK THz communication link by multiplexing 8 data channels at 2 polarizations, 2 frequencies, and 2 OAM modes.

Mobile near-field terahertz communications for 6G and 7G networks: Research challenges

“…An interesting opportunity is to utilize orbital angular momentum (OAM) for orthogonal mode division multiplexing (MDM) (Yan et al, 2014;Ren et al, 2017;Zhou et al, 2022), ideal for line-of-sight scenarios. MDM provides the same increase in capacity as perfect, uncorrelated MIMO for the same array size (Oldoni et al, 2015), with significantly reduced signal processing components (Zhang et al, 2016).…”

Wireless communications sensing and security above 100 GHz

“…Further, all these beams can also be engineered to carry orbital angular momentum (OAM). Different OAM mode orders are orthogonal, enabling the multiplexing of streams at the same frequency, at the same time, and in the same direction 39 . As discussed in the literature 40 , OAM multiplexing can be seen as a particular case of multiple input multiple output (MIMO) communications, but one in which channels are orthogonal from the start (and not because of how multi-path propagation affects them).…”

“…Beam steering devices must also consider the new wavefronts described in Section 3. For example, in typical demonstrations of beams such as OAM 39 , the transmitter, and receiver are manually aligned and are typically placed broadside. To employ such wavefronts in a mobile network will require adaptation not only for location, but also for the relative orientations of the transmitter and receiver when they are not ideally oriented.…”

Holographic THz Beam Generation by Nonlinear Plasmonic Metasurface Emitters

“…12−14 In addition, electromagnetic waves carrying structured orbital angular momentum may promote the advancement of fast and secure optical communication systems. 15,16 To effectively control and shape the THz emission, both passive and active configurations have been comprehensively studied over the years. Passive components such as diffractive optical elements provide various degrees of freedom on the post-generation shaping of the emitted wavefront.…”

“…In this regard, the adoption of structured light has fundamentally shaped recent progress in science and technology. For example, in the THz regime, structured illumination facilitates the emission of spatially tailored and nondiffracting beams, allowing for high resolution imaging, microscopy, and metrology schemes. – In addition, electromagnetic waves carrying structured orbital angular momentum may promote the advancement of fast and secure optical communication systems. , To effectively control and shape the THz emission, both passive and active configurations have been comprehensively studied over the years. Passive components such as diffractive optical elements provide various degrees of freedom on the post-generation shaping of the emitted wavefront. , However, inherent material losses result in limitations to the operational bandwidth and difficulties in the integration to on-chip designs, introducing engineering constraints to the design of THz systems.…”