Novel fabrication process of planar waveguides in rare-earth doped fluoroindate glasses

Article abstract of DOI:10.1063/1.114725

A method to fabricate planar waveguides in rare-earth doped fluoroindate glasses has been developed. This method of preparing waveguides in this kind of glass opens new prospects in fluoroindate glass research and development. The potential of these waveguides for devices operating in the communications wavelengths is anticipated to be very promising since the rare-earth doped fluoroindate glass exhibits small nonradiative relaxation rates for the rare-earth ions.

Full text of DOI:10.1063/1.114725

Novel fabrication process of planar waveguides in rareearth doped fluoroindate
glasses
R. P. de Melo Jr., B. J. P. da Silva, E. L. FalcãoFilho, E. F. da Silva Jr., D. V. Petrov, Cid B. de Araújo, Y.
Messaddeq, and M. A. Aegerter
Citation: Applied Physics Letters 67, 886 (1995); doi: 10.1063/1.114725
View online: http://dx.doi.org/10.1063/1.114725
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/67/7?ver=pdfcov
Published by the AIP Publishing
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Novel fabrication process of planar waveguides in rare-earth doped
fluoroindate glasses
˜
R. P. de Melo, Jr., B. J. P. da Silva, E. L. Falcao-Filho, E. F. da Silva, Jr., D. V. Petrov,
´
and Cid B. de Araujo
´
Departamento de Fısica, Universidade Federal de Pernambuco, 50670-901 Recife, PE, Brazil
Y. Messaddeq
´
˜
Departamento de Quımica, Universidade do Estado de Sao Paulo, 14800-900 Araraquara, SP, Brazil
M. A. Aegerter
´
´
˜
˜
˜
Instituto de Fısica e Quımica de Sao Carlos, Universidade de Sao Paulo, 13560-970 Sao Carlos, SP, Brazil
͑Received 4 January 1995; accepted for publication 16 June 1995͒
We report the successful fabrication of planar waveguides in rare-earth doped fluoroindate glass
substrates. A new procedure for waveguide fabrication using a thermally evaporated AgF
nonmetallic film was developed. The refractive index changes of more than 0.03, associated to low
propagation losses achieved, open new perspectives and show the potentiality of using this glass
family toward further developments in fabrication and design of integrated optical devices for
optical communication wavelengths. © 1995 American Institute of Physics.
Fluoroindate glasses are now emerging as a promising
group of halide glasses for optical amplifiers and fiber
lasers.1–8 In the midinfrared range ͑up to 8 ␮m͒, these
glasses present higher transparency compared to the fluo-
rozirconate glasses, they are more stable against atmospheric
moisture and their band gap is in the UV region, around 200
nm. The fluoroindate glasses have been successfully doped
with rare-earth ions and the spectroscopical studies4–7 indi-
cate small nonradiative relaxation rates of the dopant ions
levels which is due to their smaller phonon energies in com-
parison with other glasses. Also, frequency upconversion
processes have been demonstrated to be very efficient in this
material.8 Clearly, because of their spectroscopic properties,
the rare-earth doped fluoroindate glasses exhibit adequate
characteristics to be used for compact devices based on op-
tical waveguides. However, the feasibility of such guiding
structures in this material has not been demonstrated up to
the present. In this letter, we report a demonstration of the
successful fabrication of optical waveguides in rare-earth
doped fluoroindate glasses.
mond paste and washed with DI water and a special deter-
gent because common organic solvents such as alcohol and
acetone damage the substrate surfaces. Single and multimode
planar waveguides were made by modifying the refractive
index near the surface of the glass through diffusion of an
AgF nonmetallic film. An AgF film ͑thickness: у70 Å͒ was
produced by resistive thermal evaporation onto the samples
and the film diffusion was achieved at 300 °C during differ-
ent time intervals ranging from 1 to 8 h. It is important to
note that conventional methods were unsuccessful to obtain
waveguides in the fluoroindate glasses.9
The number of waveguide modes and their effective re-
fractive indices were measured using the prism-coupling
method.10 Figure 1 shows the refractive index profile for
three waveguides where the points represent the experimen-
tal values of the mode’s effective refractive indices. The re-
fractive index profiles were inferred using the method de-
scribed in Ref. 11 which is based on the inversion of the
WKB formula. This method does not require any initial as-
sumption for the profile function and uses only the experi-
mental values of the effective refractive indices. The corre-
The substrates used in the present work have the follow-
ing compositions: ͑mole %͒ 37 InF3–20ZnF2–16BaF2–
20SrF2–2GdF3–2NaF–1GaF3–2TmF3 ͑sample A and C͒;
and ͑mole %͒ 38.95 InF3–30ZnF2–16BaF2–20SrF2–2GdF3
–2NaF–1GaF3–0.05PrF3 ͑sample B͒. The substrate prepara-
tion was done using the procedure of Refs. 5–8. InF3 was
obtained by fluoration of In2O3 at 400 °C with NH4F and HF
in a platinum crucible. Then, all the fluoride components
were mixed and heated in a dry box under argon atmosphere
at 700 °C for melting and 800 °C for finning. After this pro-
cess the melt was poured and cooled into a preheated brass
mold. The obtained glass substrates have good optical qual-
ity and are nonhygroscopic. Their refractive index, n1
ϭ1.503Ϯ0.005, at 632.8 nm was determined with a
refractometer.
Initial processing of the substrates for waveguide prepa-
ration involved cutting and polishing the glass to optical
quality. The samples were mechanically polished with dia-
FIG. 1. Refractive index profile of the fluoroindate glass planar waveguides.
The solid lines were obtained using the method introduced in Ref. 11.
886
Appl. Phys. Lett. 67 (7), 14 August 1995
0003-6951/95/67(7)/886/2/$6.00
© 1995 American Institute of Physics
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This method of preparing waveguides in this kind of glass
opens new prospects in fluoroindate glass research and de-
velopment. We anticipate the potential of these waveguides
for devices operating in the communications wavelengths to
be very promising since the rare-earth doped fluoroindate
glass exhibits small nonradiative relaxation rates for the rare-
earth ions. Extension of this research to develop channel
waveguides structures and its characterization is in progress.
This work was supported by the Brazilian Agencies Con-
TABLE I. Dependence of the waveguide parameters on t ͑the duration of
the AgF film diffusion process͒. ⌬n is the maximal refractive index change
calculated as the difference between the refractive index of the surface and
substrate.
Sample
t ͑h͒
Number of modes
⌬n
A
B
C
2
4
8
2
3
5
0.0302
0.0209
0.0125
´
´
selho Nacional de Desenvolvimento Cientıfico e Tecnologico
͑CNPq͒ and Financiadora de Estudos e Projetos ͑FINEP͒. We
also thank R. Srivastava for the collaboration and fruitful
discussions during the initial part of this work.
sponding results are represented by the solid lines in Fig. 1.
The dependence of the waveguide parameters on the du-
ration of the diffusion process is illustrated in Table I where
we indicate the number of modes obtained for each wave-
guide as well as the maximal refractive index change ⌬n.
To determine the diffusion coefficient D, we approxi-
mate the waveguide index profile by the function n(x)
ϭn1ϩ⌬nerfc(x/␦), xу0, where erfc is the complimen-
tary error function, ␦ϭͱ4Dt is the effective penetration
depth, and xϭ0 represents the air-glass interface such that
n(x)ϭ1 when xϽ0. The values obtained for the diffusion
coefficient were Dϭ1 ␮m2/h for samples A and B, and
Dϭ2 ␮m2/h for sample C. The larger value obtained for
the last sample is probably due to the long diffusion time
used.
The propagation losses of the waveguides prepared were
determined by a photometric method which measures the
scattered light from the side of the waveguide using a camera
coupled with a computer. The scattered light intensity is very
weak and the losses measured were dependent on the AgF
diffusion time and the film thickness. For the single mode
waveguides prepared with a 70 Å AgF film thickness and
diffusion time of 1.25 h, the measured propagation losses
were smaller than 2.4 dB/cm at 632.8 nm.
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ˆ
ceedings of the 16th International Congress on Glass ͑Sociedad Espanola
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8
´
´
L. E. E. de Araujo, A. S. L. Gomes, Cid B. de Araujo, Y. Messaddeq, A.
Florez, and M. A. Aegerter, Phys. Rev. B 50, 16219 ͑1994͒.
9 An excellent review of the ion-exchange methods to prepare glass
waveguides has been published by R. V. Ramaswamy and R. Srivastava, J.
Lightwave Technol. 6, 984 ͑1988͒. Based on this report we have tried
unsuccessfully to prepare waveguides using the following ion sources:
pure KNO3 ; KNO3–NaNO3; and AgNO3–NaNO3. The process of elec-
trodiffusion of silver films ͓S. I. Najafi, P. G. Suchoski, Jr., and R. V.
Ramaswamy, IEEE J. Quantum Electron. QE-22, 2213 ͑1986͔͒ has also
shown to be inadequate for use with the fluoroindate glasses.
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In summary, we have developed a method to fabricate
planar waveguides in rare-earth doped fluoroindate glasses.
Appl. Phys. Lett., Vol. 67, No. 7, 14 August 1995
de Melo, Jr. et al.
887
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