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ORIGINAL PAPER: SOL-GEL AND HYBRID MATERIALS FOR OPTICAL, PHOTONIC AND OPTOELECTRONIC APPLICATIONS
Sol–gel-derived planar waveguides of Er
3+
:Yb
3
Al
5
O
12
prepared
by a polyvinylpyrrolidone-based method
T. Hla
´sek
1
•V. Pola
´k
1
•K. Rubes
ˇova
´
1
•V. Jakes
ˇ
1
•P. Nekvindova
´
1
•
O. Jankovsky
´
1
•D. Mikola
´s
ˇova
´
1
•J. Oswald
2
Received: 16 February 2016 / Accepted: 30 May 2016 / Published online: 4 June 2016
Springer Science+Business Media New York 2016
Abstract Erbium (Er
3?
)-doped ytterbium garnet [(Er
x
Yb
1-x
)
3
Al
5
O
12
;x=0.005, 0.02 and 0.1, YbAG] planar waveguides
have been prepared by an aqueous sol–gel method using
polyvinylpyrrolidone as a gelling agent. The thermal behavior
of gel was studied by thermogravimetry and differential ther-
mal analysis. The phase composition of the films was deter-
minedusingX-raydiffraction.Surface analysis was carried out
by atomic force microscopy. A pure infrared emission of Er
3?
ions was observed in all prepared films. Light propagation was
studied by m-line spectroscopy using several wavelengths
(633, 964, 1311 and 1552 nm). The minimum coating cycles to
observe one propagated mode at 1552 nm were determined to
be 7. The sol–gel-derived Er:Yb
3
Al
5
O
12
seems to be a
promising material for light amplifiers in the IR region.
Graphical Abstract
Keywords Sol–gel Polyvinylpyrrolidone Planar
waveguide Ytterbium-aluminum garnet Erbium
1 Introduction
Nowadays, Er
3?
ion and its infrared emission are used
worldwide for optical signal transmission through silica
fibers. Even though the loss is low at 1530 nm, the signal
needs to be amplified every 70–100 km and in devices such
as splitters [1]. The amplification can be achieved in planar
waveguide structures doped with erbium. Garnets are
promising host materials for many optical applications
such as solid-state lasers [2], sensors [3] and also optical
signal amplifiers [4]. The garnets with a general formula
A
3
B
5
O
12
(where A is Y or a rare earth ion and B is a
trivalent metal such as Al, Fe or Ga) are non-toxic, ther-
mally and chemically stable, and their properties, such as
refractive index and unit cell parameter, can be adjusted by
changing the composition [5].
Besides the material parameters adjustment, the variable
composition of garnets can be used to overcome the
problem of a low absorption cross section of erbium ions.
This drawback is commonly solved by co-doping with
sensitizer ions. Ytterbium is a well-known sensitizer for
erbium with a pumping wavelength of 980 nm. This co-
doping was successfully used in materials such as LiNbO
3
[6,7], NaYF
4
[8], KY(WO
4
)
2
[9] or YAG [10,11]. The
energy transfer from ytterbium (
2
F
7/2
) to erbium (
4
I
11/2
)is
highly effective when ytterbium is used as a part of the host
matrix and not just as a co-dopant (e.g., YbAG) [12].
To produce the planar waveguide, it is necessary to use a
thin film preparation technique that leads to a homoge-
neous film with a low surface roughness. Commonly the
techniques like liquid-phase epitaxy [13], chemical vapor
&T. Hla
´sek
hlasekt@vscht.cz
1
Department of Inorganic Chemistry, University of Chemistry
and Technology Prague, Technicka
´5, 166 28 Prague 6,
Czech Republic
2
Institute of Physics v.v.i., Academy of Sciences of the Czech
Republic, Cukrovarnicka
´10, 162 00 Prague 6, Czech
Republic
123
J Sol-Gel Sci Technol (2016) 80:531–537
DOI 10.1007/s10971-016-4098-9
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