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Chapter 5 203

Figure 5.1.6 Twisted beams: a) Hermite-Gaussian, b) Laguerre-Gaussian, c) Bessel

The Figure 5.1.6 demonstrates the phase and intensity distribution of three types of beams:
Hermite-Gaussian (HG), Laguerre-Gaussian (LG), and Bessel (B). Each set of beams consists
of 6 modes. All images are reprinted with Dr. C. Guzman’s permission from [28]. The first
column in each beam set reflects the phase variations while the second one gives the amplitude
intensity. All beams except the zeroed modes (first, third, fourth, and fifth in the top raw) carry
nonzero OAM. A more detailed discussion would be the subject of the different book. The
reader can find more information in [17, 28].

Twisted waves is widely used in modern applications such as microwave and
optical communications, quantum optics spectroscopy, and microscopy. In particular,
beams with (OAM) have been used as optical tweezers [29], in high-resolution
nanoscopy and optical measurements with increased angular resolution. Furthermore,
quantum information carried in the high-dimensional spatial structure of single and
entangled photons can be exploited in applications such as multi-dimensional quantum
teleportation and sensitive data encryption of the highest level to ensure confidentiality and
privacy.

All these new exciting research and development areas are waiting for your creative
contribution.

5.1.4 How Should Antenna Polarization Be Chosen?

As usual, in engineering practice, there is no unique and best answer but rather a range
of solutions. A detailed discussion of this topic is far beyond the scope of this course because
the selection of polarization is one of the most important system decision. So we will touch just
the tip of the “polarization” iceberg in quite general terms:

1. All antennas in the system should be properly aligned and share the same polarization to
get the maximum efficiency in any transmitting-receiving system. For example, the signal
emitted by RHCP antenna basically cannot be received by LHCP antenna and vice versa.
Practically we can lose up to 30 dB in signal strength without proper antenna alignments.
The same applies if we mix up with Vertical (VLP) and Horizontal (HLP) polarization.
Therefore, for optimal communication, antenna’s alignment must be V/V, H/H,
RHCP/RHCP and LHCP/LHCP.
2. Meanwhile, from the above discussion, it follows that a CP waves carry simultaneously
the energy of two orthogonal LP waves that can be transmitted and received as a whole
(i.e. classical CP ) or independently (i.e. each LP signal transports different data set at the