Pis’ma v ZhETF, vol. 114, iss. 12, pp. 787 - 788
© 2021 December 25
Topological photonics
(Mini-review)
A. S. Ustinov+, A. S. Shorokhov+, D. A. Smirnova∗×1)
+Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia
∗Institute of Applied Physics, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia
×Research School of Physics, Australian National University, Canberra ACT 2601, Australia
Submitted 4 November 2021
Resubmitted 4 November 2021
Accepted 5 November 2021
DOI: 10.31857/S1234567821240010
Topological photonics has recently emerged as a
preferential in optics because magneto-optical response
novel approach to robust waveguiding and routing of
is weak at optical frequencies. TR-invariant topologi-
light [1, 2]. It exploits engineered photonic structures
cal phases were realised in lattices of coupled silicon
with the properties analogous to electronic topologi-
ring resonators [6] (Figs. 1d, e), waveguide arrays [7]
cal insulators (TIs) [3], which are insulating in their
(Figs. 1f, g), and bianisotropic metamaterials [8]. Moti-
bulk but exhibit conducting states at the surfaces. Un-
vated by optical on-chip applications, the most recent
usual manifestations inherent to topologically nontrivial
realisations of topological phases in photonics have ad-
states, including the ability of edge modes to overcome
vanced to the nanoscale. For example, spin-polarized
structural imperfections without back reflection, drive
nanophotonic topological edge states were imaged via
general interest in topological effects within photonics
third-harmonic generation (Figs. 1h, i) in topological ar-
and optical communications.
rays of silicon nanopillars [9]. The high-quality-factor
Intriguing properties of TIs are rooted in the
topological modes, including strongly confined corner
wavevector-space topology and the existence of abstract
states, can also be employed for nanolasing with im-
“holes” in the modes of the media in momentum space,
proved stability and nontrivial radiation characteris-
similar to how a sphere is topologically distinct from
tics [10, 11].
a torus. Whenever a system can be characterised by a
Topological photonics is likely to continue to be a
topological invariant with nonzero value, one can expect
highly active and flourishing area of research for the
physical features that remain insensitive to a range of
next decade. It proves itself not only useful for classical
perturbations, giving rise to resilience in operation and
light control but also promising for a variety of quantum
disorder resistance.
optical applications [12]. Links are being established be-
Figure 1 shows the actual representative demon-
tween topological photonics and other frontier topics, in-
strations of two-dimensional topological photonic sys-
cluding bound states in the continuum [13], structured
tems in their historical sequence. Following a theoret-
light, transformation optics, and leaky mode theory [14].
ical proposal by Raghu and Haldane [4], Wang et al.
We anticipate harnessing topological photonic phases in
were first to implement the photonic counterpart of
nonlinear and quantum optics [2] will drive the cutting-
the quantum Hall effect, the seminal example of the
edge developments in quantum computing and on-chip
topologically nontrivial phase, at microwave frequen-
neuromorphic signal processing with ultrafast operation
cies [5]. In their experiment, time-reversal (TR) sym-
speed and low energy consumption.
metry was broken by the magnetic field applied in a
This work was supported by the Russian Science
square-lattice photonic crystal of gyromagnetic ferrite
Foundation (Grant # 20-72-00148).
rods (Figs.1a,b). The resultant band structure hosts a
D. A. Smirnova thanks Y. S. Kivshar for the useful
gapless chiral edge state that propagates around defects
advice.
with back scattering significantly suppressed within the
band gap frequency range shaded yellow in Fig. 1c. How-
This is an excerpt of the article “Topological photon-
ever, the path with preserved TR symmetry appears
ics”. Full text of the paper is published in JETP Letters
journal. DOI: 10.1134/S0021364021240012
1)e-mail: daria.smirnova@anu.edu.au
Письма в ЖЭТФ том 114 вып. 11 - 12
2021
787
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