Fabrication of arsenic selenide optical fiber with low hydrogen impurities

Article abstract of DOI:10.1111/j.1151-2916.2002.tb00541.x

Arsenic selenide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of 0.1 wtpercent tellurium tetrachloride (TeCl₄) to the glass. During melting, the chlorine from TeCl₄ reacts with the hydrogen impurities to produce volatile products (e.g., HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to give very low H-Se impurity content. Consequently, the H-Se absorption band centered at 4.57 μm has been reduced from tens of dB/m to 0.2 dB/m.

Full text of DOI:10.1111/j.1151-2916.2002.tb00541.x

J. Am. Ceram. Soc., 85 [11] 2849–51 (2002)
journal
Fabrication of Arsenic Selenide Optical Fiber with
Low Hydrogen Impurities
†
†
†
‡
†
Vinh Q. Nguyen, Jas S. Sanghera, Pablo Pureza, Frederic H. Kung, and Ishwar D. Aggarwal
Optical Science Division, Code 5606, Naval Research Laboratory, Washington, D.C. 20375-5000
University of Maryland Research Foundation, Greenbelt, Maryland 20770
Arsenic selenide glass optical fibers typically possess extrinsic
absorption bands in the infrared wavelength region associated
with residual hydrogen and oxygen related impurities, despite
using purified precursors. We report a purification process
based on the addition of 0.1 wt% tellurium tetrachloride
II. Experimental Procedure
(
1) Purification of Elemental Precursor (As, Se, and Te)
Commercially available six 9’s purity arsenic (All Chemie),
selenium (Johnson Matthew, Inc.), and tellurium (Kamis, Inc.)
were purified by heating at 450°, 300°, and 475°C, respectively,
for 8 h to remove oxide impurities such as As O , As O , SeO,
(
TeCl ) to the glass. During melting, the chlorine from TeCl4
4
2
3
2 5
reacts with the hydrogen impurities to produce volatile prod-
ucts (e.g., HCl) that can be removed by subsequent dynamic
distillation. The processing conditions have been modified
accordingly to give very low H–Se impurity content. Conse-
quently, the H–Se absorption band centered at 4.57 ␮m has
been reduced from tens of dB/m to 0.2 dB/m.
SeO , SeO , Se O , TeO, and TeO . The arsenic, selenium, and
2
3
2
3
3
tellurium were further purified by sublimation/distillation under
dynamic vacuum at 500°, 500°, and 600°C, respectively, to
remove scattering centers such as carbon, heavy elements, quartz
particles, and other volatile species. High-purity tellurium tetra-
chloride (TeCl ) was made inside an inert atmosphere glove box
4
via chlorination of high-purity elemental tellurium at 240°C and
collecting the TeCl4 condensate. TeCl4 was chosen over other
I. Introduction
halides (i.e., selenium tetrachloride (SeCl
4
) or arsenic trichloride
(
AsCl )) because TeCl is in solid form at room temperature,
3
4
NFRARED-TRANSMITTING chalcogenide optical fibers are being
atmospheric pressure, and under vacuum, whereas both SeCl and
4
1
–7
I
used for many applications
in the infrared (1–13 ␮m) from
AsCl are liquids under the same conditions.
3
laser power delivery (CO at 5.4 ␮m and CO at 10.6 ␮m) as well
2
as in fiber optic chemical sensor systems using absorption,
evanescent, and diffuse reflectance spectroscopy for environmen-
(
2) Fabrication of the Arsenic Selenide Optical Fibers
The core and clad compositions for the arsenic selenide fibers
3
–6
tal and facility cleanup.
through the development and fabrication of stable low-loss arsenic
sulfide based fiber (As S Se ) and tellurium-containing fiber
These applications are made possible
were As Se and As Se , respectively. High-quality quartz
3
9
61
37 63
distillation ampules were cleaned by etching with 50/50 mol% of
HF/deionized water and then rinsed with deionized water. The
ampules were dried in a vacuum oven at 115°C for 8 h and then
baked out under vacuum at elevated temperature (ϳ900°C) using
an oxygen–methane flame. For comparison purposes, glass sam-
ples were made with and without the addition of TeCl4 using
purified chemicals. We describe the technique associated with the
glass samples without TeCl as a two-step process. For the glass
samples made without the addition of TeCl , ϳ100 g batches of
chemicals and 10 ppm of elemental Al were batched in ampules
4
0
(60Ϫx)
x
8
–10
(Ge As Se Te ) with minimum loss of 0.1 dB/m.
30 10 30 30
Although purification has resulted in low fiber scattering losses,
impurities related to hydrogen, carbon, and oxygen still leave
discrete absorption bands in the infrared (H–Se at 4.57 ␮m, CO at
2
9
4
.3 ␮m, and O–H at 2.92 ␮m). The majority of the impurity bands
are associated with hydrogen-containing species. To minimize
these impurities in the glass melt, it is necessary to getter the
hydrogen using a reactive chlorine atmosphere.
4
4
1
0–12
This will
create volatile species containing hydrogen, which allows for
subsequent elimination through dynamic distillation of the glass.
In our previous work, in the arsenic sulfide glass we have
successfully developed a glass purification/fabrication process to
reduce the H–S absorption at 4.03 ␮m from 50 dB/m to 1.5 dB/m
inside a controlled atmosphere glove box under nitrogen (Ͻ1 ppm
Ϫ5
H O, O ). The ampules were evacuated at 2 ϫ 10 torr, sealed
2
2
1
2
with an oxygen–methane torch, and placed in a two-zone furnace
for melting. The batch was melted above 700°C, distilled, and then
remelted for homogeneity in a rocking furnace. The presence of
aluminum in the glass melt getters the oxygen impurities during
melting before distillation. The glasses were remelted in a rocking
furnace and subsequently quenched from 400°C by immersion of
the ampules in water for about 2 s, followed by annealing at
using tellurium tetrachloride (TeCl ) as a getter for hydrogen
4
impurity. This paper describes the results of the effect of TeCl on
4
arsenic selenide glass, which typically possesses intense impurity
absorption bands associated with H–Se centered around 4.57 ␮m.
The arsenic selenide fibers are of great interest because of many
potential applications in the mid-IR.
1
80°C.
For the glass samples prepared with the additions of TeCl we
4
describe this technique as a four-step process. In this four-step
process, the first two steps are exactly the same as that of the above
two-step process. The third step involves the addition of 0.1 wt%
of TeCl to the glass cullet. The samples were heated at 750°C for
4
J. Ballato—contributing editor
2
4 h to allow melting and reaction to occur between the TeCl and
4
hydrogen impurities. Next, the ampules containing the melts were
rapidly quenched in water from 650°C to preserve the integrity of
the byproducts of the reaction with TeCl . In step three, the glass
4
Manuscript No. 186937. Received May 31, 2002; approved August 2, 2002.
†
‡
cullet containing TeCl was subsequently distilled under dynamic
Optical Science Division, Naval Research Laboratory.
University of Maryland Research Foundation.
4
vacuum at 550°C for 15 h to leave behind particulate matter
2
849

2
850
Communications of the American Ceramic Society
Vol. 85, No. 11
impurities and eliminate any gaseous byproducts from the reaction
Table I. Estimated Concentration of H–Se Impurity
†
with TeCl . Finally, in step four, the distillate was remelted at
at 4.57 ␮m in the Selenide Optical Fiber
4
7
50°C for 24 h followed by quenching from 400°C by immersion
Absorption loss
(dB/m)
Impurity concentration
(ppm)
of the ampules in water for about 2 s and then annealed at 180°C.
The arsenic selenide glass cullet with a nominal core (As Se )
4
TeCl addition
3
9
61
and clad (As Se ) compositions was drawn into optical fiber
No
10
9.07
0.18
3
7
63
using a controlled double-crucible process. Over 250 m of fibers
was drawn under inert atmosphere at a rate of ϳ5.0 m/min. The
resulting fiber had an outer diameter of 200 ␮m and core size of
Yes
0.2
†
Extinction coefficient: H–Se ϭ 1.103 dB/(m/ppm) at 4.57 ␮m. After
Refs. 15 and 16.
1
50 ␮m.
(
3) Fiber Characterization
The fiber optical attenuation at room temperature was charac-
is incorporated into the glass network while the chlorine is being
removed as byproducts through dynamic vacuum. However, the
magnitude of the shift in both edges appears high considering only
terized using a FTIR spectrometer (Analect Diamond 20) and
standard cutback technique. The light source was a broadband
NiCr wire and the detector was a liquid-nitrogen-cooled MCT
1
3
0.1 wt% of TeCl was added. Further work is needed to elucidate
4
the reason for this. The intensity of the H–Se peak at 4.57 ␮m
decreases from 10 dB/m in Fig. 1(a) to 0.2 dB/m in Fig. 1(b). The
higher temperature 650°C quench appears to be the most effective
and lowers the H–Se intensity at 4.57 ␮m to 0.2 dB/m. Table I lists
the H–Se impurity absorption band intensity and estimated con-
centrations. The H–Se concentration has been reduced from ϳ9 to
less than 0.2 ppm.
(HgCdTe) detector. The fiber attenuation (dB/m) was determined
from the following relationship:
Attenuation ͑dB/m͒ ϭ ͓10 log ͑P /P͔͒/͑L Ϫ L ͒
(1)
0
0
where P and P are the measured powers at a given wavelength for
the cutback length and the long length, respectively, and L and L0
are the lengths of the fiber and the cutback section, respectively.
0
12
As in our previous work in this study we also propose that at
high temperature TeCl reacts with the H–Se species according to
4
the following reaction:
III. Results and Discussion
TeCl ϩ 4H–Se
3 4HCl͑gas͒1 ϩ Te͑glass͒ ϩ 4Se͑glass͒ (2)
͑glass͒
4
Figure 1 shows the attenuation spectra for the fibers fabricated
The HCl formed is a gaseous product and is conveniently elimi-
nated from the glass during dynamic distillation. The Te and Se
become a part of the glass structure. We suggest that Te (also a
chalcogen element with the same outer valence electron) is
incorporated into the As–Se glass structure, along with the Se. The
excess of Cl could also be incorporated into the glass structure as
from glasses made without and with the addition of TeCl using
4
the two-step or four-step process, respectively. Attenuation was
measured by a standard cutback technique over a 5 m length.
Figure 1(a) shows the attenuation for fiber fabricated from glasses
made without the addition of TeCl . The minimum loss is 0.64
4
dB/m at 6.6 ␮m. At 4.57 ␮m, the attenuation due to the H–Se
stretching vibration is approximately 10 dB/m. The three minor
bands at 4.15, 3.55, and 2.32 ␮m are attributed to the combination
17
a network modifier.
Considering that 0.1 wt% (0.14 mol%) of TeCl was added,
4
ideally all of the H–Se impurity should be removed since a large
excess of chlorine was present in the glass melt. From Table I,
there is only about 9 ppm of H–Se present for the fiber (Fig. (1a))
without TeCl addition. After the four-step purification with TeCl
1
4
and first overtone of the H–Se stretching vibration at 4.57 ␮m.
The fiber exhibits less than 1 dB/m loss in the region between 2
and 8 ␮m.
Figure 1(b) shows the optical attenuation of the fibers made
4
4
the H–Se concentration at 4.57 ␮m has been significantly reduced
to 0.18 ppm (Fig. 1(b)), but not all of the H–Se has been removed.
from glass prepared with the addition of TeCl using the four-step
4
process. The minimum loss is 0.49 dB/m at 7.42 ␮m. The two
small peaks at 4.3 and 4.57 ␮m are due to the stretching vibration
Melting for longer periods of time or using higher TeCl concen-
4
trations may help to completely eliminate the H–Se absorption
band.
of CO and H–Se, respectively. The electronic and multiphonon
2
edges are shifted to longer wavelengths. This may be attributed to
Te, which is a heavier atom compared with As and Se atoms and
IV. Conclusions
We have developed a four-step purification process to reduce
the hydrogen-related impurities in the selenide fiber. This is
facilitated by the removal of oxide in the first two steps and with
the addition of TeCl in the third step. This leads to the formation
4
of HCl, a gaseous byproduct that can be removed by distillation.
We have utilized this four-step purification process to obtain low
loss and high-quality selenide optical fiber containing low
hydrogen-related impurities (Ͻ0.2 ppm H–Se) and consequently a
low H–Se absorption loss of 0.2 dB/m at 4.57 ␮m.
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Ⅺ