Biomedical Engineering Reference
In-Depth Information
11.3.2
Experimental Demonstration of OAM Generation
and Control
In this final section, we will discuss the recent demonstration
of broad OAM azimuthal spectra produced by light scattering in
plasmonic Vogelspirals.
It has long been established that electromagnetic fields carry
linear momentum and angular spin. However, the possibility for
optical fields to additionally carry OAM has only recently been
realized [77, 78].
In general, OAM arises through the azimuthal phase dependence
of the complex optical field. Optical OAM has recently found uses
in rotating optical traps [79], secure optical communication [80],
and increasing data transfer rates through OAM multiplexing for
fiber-based systems [81]. Moreover, recent advances in the science
and technology of OAM have provided the possibility to detect light
waves carrying simultaneously multiple OAM values [82]. However,
the controlled generation of optical waves that can simultaneously
carry large values of OAM still remains very challenging.
Currently, the generation of OAM is achieved by converting
GaussianlasermodestoLaguerre-Gaussian(LG)modeswithexplicit
azimuthal phase dependence. This can be accomplished using a
system of cylindrical lenses [83] or spatial light modulators (SLMs)
[84]. However, SLMs are expensive and their pixel size limits the
complexity of patterns that can be created. More recently, the
generation of OAM from planar plasmonic devices has also been
demonstrated [34, 85]. Unfortunately though, most of the current
generation methods are limited to creating OAM states with only a
few azimuthal values.
The controlled generation and manipulation of OAM states
with large values of azimuthal numbers has very recently been
demonstrated experimentally by Lawrence et al. [46] using various
types of Vogel arrays of metal nanoparticles. The OAM content of a
diffractedopticalwaveat633nmwasanalyzedusingphasestepped
interferometric measurements to recover the complex optical field
[47]. Fourier-Hankel modal decomposition of scattered radiation
was performed to demonstrate the generation of OAM sequences
from Vogel spirals.
