Engineering the emission of laser arrays
to nullify the jamming from passive obstacles
CONSTANTINOS VALAGIANNOPOULOS* AND VASSILIOS KOVANIS
Department of Physics, School of Science and Technology, Nazarbayev University, 53 Qabanbay Batyr Ave, Astana KZ-010000, Kazakhstan
*Corresponding author: konstantinos.valagiannopoulos@nu.edu.kz
Received 30 October 2017; revised 26 April 2018; accepted 29 May 2018; posted 1 June 2018 (Doc. ID 312268); published 10 July 2018
Non-Hermitian characteristics accompany any photonic device incorporating spatial domains of gain and loss.
In this work, a one-dimensional beam-forming array playing the role of the active part is disturbed from the
scattering losses produced by an obstacle in its vicinity. It is found that the placement of the radiating elements
leading to perfect beam shaping is practically not affected by the presence of that jammer. A trial-and-error inverse
technique of identifying the features of the obstacle is presented based on the difference between the beam target
pattern and the actual one. Such a difference is an analytic function of the position, size, and texture of the object,
empowering the designer to find the feeding fields for the lasers giving a perfect beam forming. In this way, an
optimal beam-shaping equilibrium is re-established by effectively cloaking the object and nullifying its jamming
effect.
© 2018 Chinese Laser Press
OCIS codes: (140.3300) Laser beam shaping; (160.3918) Metamaterials; (230.3205) Invisibility cloaks.
https://doi.org/10.1364/PRJ.6.000A43
1. INTRODUCTION
Collective operation of laser waveguides in arrays and networks
is the backbone of several state-of-the-art applications and
recent advances in photonics and lightwave technologies.
One-dimensional laser phased arrays characterized by strong
nonlinearity and non-Hermiticity have been experimentally in-
vestigated in Ref. [1], where the effect of various symmetries on
multimode emission and edge-mode lasing has been identified
(free-space wavelength λ
0
≅ 1.59 μm). In two dimensions, net-
works of optical nanoantennas have been found able to support
functionalities beyond conventional focusing and steering use-
ful in three-dimensional holography and biomedical testing [2]
(λ
0
≅ 1.55 μm). Of course, the major application of such
structures remains efficient beam shaping, which can be elec-
tronically controlled based on hybrid prototypes of dielectric
waveguides and metallic nanoemitters [3](λ
0
≅ 1.57 μm)
and provides grating lobe-free steering for light detection
and ranging [4](λ
0
≅ 1.55 μm).
Regarding beam forming in similar THz applications, an
inverse problem for the excitations of an array of emitters
has been lately formulated [5]. Inspired by long established
level-set methods for computing moving fronts [6], new limits
for the radiation of emitters [7] and the recent inverse-design
paradigm shift in photonic design [8], the optimal arrangement
of the cavity lasers is considered. It has been reported [5] that
the distance between two consecutive radiating elements
should fall within an approximate value range, so that the
aggregate far-field response mimics perfectly a specific target
pattern. In particular, it is found that the waveguides should
not be placed too close to each other, or they will act as one
source unable to create a directive collective pattern.
Additionally, they cannot be very distant from each other
because each emitter should talk with the neighboring ones to
give a combined response instead of a sum of isolated and
uncorrelated radiation patterns.
Forward and inverse problems such as the aforementioned
ones have appeared for various bands of operational frequen-
cies. In radio engineering, e.g., clusters of radiators have been
traditionally used for optimal beam forming and, most impor-
tantly, adaptive techniques are employed to avoid the jamming
of the collective radiation pattern due to several causes.
Indicatively, signal processing methods that allow the system
to fully adapt to a complex spatio-temporal environment con-
taining jammers are presented in Ref. [9]. Furthermore, filter-
ing techniques that suppress the perturbation of the
information signal from interference sources by selecting the
suitable transmitting array [10] or alleviate the harming effects
of array imperfections [11] are also known and available.
Alternatives to these historical signal cancellation [12]
approaches are the modern cloaking techniques that allow an
object to interact minimally with the background field.
Similarly, the jamming effect of an obstacle can be mitigated
with use of passive dielectric coats [13,14] or periodic metallic
flanges that guide the incident field around it [15]. More easily,
an object that jams the signal from the source can vanish by
neutralizing its scattering field with active components
Research Article
Vol. 6, No. 8 / August 2018 / Photonics Research A43
2327-9125/18/080A43-08 Journal © 2018 Chinese Laser Press