Experimental evidence of Bloch surface waves
on photonic crystals with thin-film LiNbO
3
as a
top layer
TATIANA KOVALEVICH,
1,
*DJAFFAR BELHARET,
1
LAURENT ROBERT,
1
MYUN-SIK KIM,
2
HANS PETER HERZIG,
2
THIERRY GROSJEAN,
1
AND MARIA-PILAR BERNAL
1
1
Département d’Optique P. M. Duffieux, Institut FEMTO-ST, UMR 6174 CNRS, Université Bourgogne Franche-Comté,
15B Avenue des Montboucons, 25030 Besançon Cedex, France
2
Optics & Photonics Technology Laboratory, Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de la Maladière 71b,
Neuchâtel CH-2000, Switzerland
*Corresponding author: tnkovalevich@gmail.com
Received 28 June 2017; revised 5 October 2017; accepted 5 October 2017; posted 5 October 2017 (Doc. ID 300515); published 2 November 2017
Strong nonlinear, electro-optical, and thermo-optical properties of lithium niobate (LN) have gained much
attention. However, the implementation of LiNbO
3
in real devices is not a trivial task due to difficulties in manu-
facturing and handling thin-film LN. In this study, we investigate an optical device where the Bloch surface wave
(BSW) propagates on the thin-film LN to unlock its properties. First, access to the LN film from air (or open
space) is important to exploit its properties. Second, for sustaining the BSW, one-dimensional photonic crystal
(1DPhC) is necessary to be fabricated under the thin-film LN. We consider two material platforms to realize such
a device: bulk LN and commercial thin-film LN. Clear reflectance dips observed in far-field measurements dem-
onstrate the propagation of BSWs on top of the LN surface of the designed 1DPhCs.
© 2017 Chinese Laser Press
OCIS codes: (240.0310) Thin films; (130.3730) Lithium niobate; (160.5298) Photonic crystals; (240.6690) Surface waves.
https://doi.org/10.1364/PRJ.5.000649
1. INTRODUCTION
Lithium niobate (LN) is a high refractive index birefringent
crystal with tunable optical properties. It is widely used for
integrated optics due to its excellent ferroelectrical, piezoelec-
trical, and thermoelectrical properties, its transparency over a
wide wavelength range (350–5200 nm), its nonlinear optical
polarizability, and its Pockels effect [1]. In order to improve
the performance of integrated optical devices, several research
groups have developed different structures, such as ridge wave-
guides, photonic crystal waveguides, and periodically poled
lithium niobate structures [2]. As a high refractive index material,
LN as a top layer is used for enhanced light confinement for
many devices [3] and thin-film LiNbO
3
(TFLN) should be
used to improve the confinement even more.
In this work, we propose two different novel architectures
that can generate Bloch surface waves (BSWs) at TFLN layers.
BSWs perform a strong field confinement at the interface
between a periodic dielectric multilayer and a surrounding
medium due to Bragg reflection and total internal reflection
on two sides of the interface, respectively [4]. Light coupling
can be easily achieved by a grating coupler [5] or by using the
Kretschmann configuration [6,7]. Both coupling methods are
simpler and more efficient in terms of coupling losses than the
fiber-to-fiber coupling technique that is employed to horizon-
tally excite a guided mode on TFLN [8].
Moreover, BSWs can be considered as an attractive alterna-
tive to surface plasmon polaritons due to the low loss features of
dielectric materials in comparison with metals [6,9]. Therefore,
these dielectric surface modes dramatically increase the light
propagation length [7]. They were initially proposed for vapor
sensing [10], biosensing [6], fluorescence studies [11], and for
integrated optics [9,12]. The development of BSW-based de-
vices has also profited a great deal from the development of
different deposition techniques, such as atomic layer deposition
[13,14] or plasma-enhanced chemical vapor deposition (PECVD)
[15]. These techniques have allowed us to achieve the necessary
precision in the manufacturing of subwavelength thickness layers
required for the fabrication of BSW devices. Various materials
constituting multilayer structures have been used in different
designs of one-dimensional photonic crystal (1DPhC), offering
a large panel of configurations for different applications at differ-
ent wavelengths. The BSW propagation can be controlled by
manipulating the refractive index inside the device [12].
In this work, we propose a 1DPhC with a TFLN as the top
layer of the multilayer structure. The bonding into the 1DPhC
structure brings anisotropy into the whole crystal, allowing the
Research Article
Vol. 5, No. 6 / December 2017 / Photonics Research 649
2327-9125/17/060649-05 Journal © 2017 Chinese Laser Press