Dyakonov Surface
Waves
Lluis Torner, David Artigas and Osamu Takayama
Surface waves are a special type of wave that is confined at a single
boundary between two di;erent media.
;ey are a topic of continuously renewed
interest and intense investigation due
to their unique properties and their
prospects for important applications.
By their very nature, surface waves are
unique tools for exploring the properties
of material interfaces. ;is includes not
only intrinsic properties but also extrinsic e;ects, thus making surface waves
ideal for sensing physical, chemical and
biological agents. Potential applications
range from subwavelength light microscopy and nanooptical tweezing, to
early diagnosis and minimally-invasive
therapy of diseases. However, guided
surface waves are rare, as they can be
supported by only a few types of materials and geometries.
M.I. Dyakonov predicted a unique
class of surface wave two decades ago. 1
Such surface waves exist under very
special conditions at the interface of
anisotropic crystals—either biaxial or
positive uniaxial. Under suitable material and geometrical conditions, hybrid
surface waves containing both ordinary
and extraordinary field components
can propagate within a narrow angular band relative to the crystalline
optical axis. ;e existence conditions
are not easy to meet in practice. ;us,
Dyakonov surface waves had never
been observed.
;e 20-year quest ended this year
when we observed Dyakonov surface
waves in an Otto-Kretchmann setting
set for an isotropic-anisotropic crystal
interface. 2 We used a specially designed
configuration based on a potassium
titanyl phosphate biaxial crystal and
a suitable index-matching liquid to
meet the conditions required for the
existence of the surface waves. 3, 4 We
(a)
(b)
(c) Leaky mode Leaky mode y z Dyakonov surface wave Dyakonov surface wave
Signature of Dyakonov surface wave
excitation. (a) Magni;ed view of the
modal spectrum obtained by a CCD
camera. (b) Integrated intensity along
the vertical axis. Large peak stands for
a leaky mode. The Dyakonov surface
waves appear as the weak secondary
peak. (c) Narrow angular band where
Dyakonov surface waves propagate
relative to crystallographic axis z.
confirmed surface wave excitation by
imaging the scattered mode spectrum
out of the Otto-Kretchmann prism on a
CCD camera and obtained the signature of surface wave excitation by using
a powerful polarization conversion
reflectance technique.
Technical challenges that we had to
overcome included light propagation inside the crystalline angular band, where
surface waves were allowed to exist under ideal conditions, and elucidation of
the extremely narrow peak corresponding to guided Dyakonov surface waves
among the set of broader peaks corresponding to leaky modes supported by
the actual Otto-Kretchmann multilayer
material structure.
;e significance and potential of
Dyakonov surface waves relies on their
most fascinating property: In contrast
to, for example, plasmon-polaritons,
they exist at the surface of fully transparent materials; therefore, they are
lossless. ;eir observation opens the
door for the exploration of lossless surface
wave propagation in a variety of suitable
settings, including nanoscale geometries
and metamaterial structures with form-anisotropy. 5
;is research was sponsored by Fundacio
Cellex Barcelona.
Lluis Torner ( lluis.torner@icfo.es), David Artigas
and Osamu Takayama are with ICFO-Institut de
Ciencies Fotoniques and Universitat Politecnica
de Catalunya, Mediterranean Technology Park,
Castelldefels (Barcelona), Spain.
References
1. M.I. Dyakonov. Sov. Phys. JE TP 67, 714 (1988).
2. O. Takayama et al. Phys. Rev. Lett. 102, 043903 (2009).
3. D.B. Walker et al. J. Opt. Soc. Am. A 15, 248 (1998).
4. O. Takayama et al. Electromagnetics 28, 126 (2008).
5. D. Artigas and L. Torner. Phys. Rev. Lett. 94, 013901
(2005).
