Optical Parametric Amplification Performance
in AsSe
2
-based Hybrid Microstructured Optical Fibers
Hoang Tuan Tong
1
, Kenshiro Nagasaka
1
, Morio Matsumoto
2
, Hiroshige Tezuka
2
,
Takenobu Suzuki
1
and Yasutake Ohishi
1
1
Research Center for Advanced Photon Technology, Toyota Technological Institute,
2-12-1 Hisakata, Tempaku, Nagoya, 468-8511, Japan
2
Furukawa Denshi Co., Ltd., 2-3-2, Marunouchi, Chioda-Ku, Tokyo, 100-8370, Japan
Keywords: Optical Parametric Amplification, Microstructured Optical Fiber, Chromatic Dispersion Control.
Abstract: The performance of fiber-optical parametric amplification is studied by employing the AsSe
2
-based hybrid
microstructured optical fiber (HMOF). By adding a buffer layer around the core with appropriate diameter
and refractive index difference, the chromatic dispersion profile of chalcogenide HMOFs can be tailored to
have a near-zero and flattened anomalous dispersion regime in the mid-infrared window. A very broad gain
bandwidth can be achieved from 3.0 to 9.0 µm by pumping at 4.7 µm. The signal gain can be as high as 32
dB. In addition, the HMOF with buffer layer can suppress the chromatic dispersion variation caused by the
fiber structure fluctuation and maintain the signal gain spectrum.
1 INTRODUCTION
Fiber optical parametric amplification (FOPA) has
attracted much attention since it can provide high
signal gain and broad gain bandwidth in the
wavelength range where other types of amplifiers
such as Erbium-doped fiber amplifiers (EDFAs) and
fiber Raman amplifiers (RAs) can’t reach. Their
potential applications are not only for high-speed and
long-haul transmission systems, but also for ultrafast
all-optical signal processing, pulse regeneration,
optical time-devision demultiplexing, optical
sampling, quantum noise and correlation (M. E.
Marhic, 2008). By expanding the wavelength range
of FOPA gain bandwidth towards the mid-infrared
region which exceeds the transparency limit of fused-
silica fibers, more interesting applications in
spectroscopy, sensing, biology and metrology can be
realized. However, it is still a challenging task.
Recently, many non-silica glasses such as tellurite
glasses (Domachuk et al., 2008, Liao et al., 2009),
heavy metal fluoride glasses (Xia et al., 2009, Qin et
al., 2009) and chalcogenide glasses (Mouawad et al.,
2014, Petersen et al., 2014) have been demonstrated
as alternative candidates. Among them, chalcogenide
glasses have very broad transmission window up to
10 µm and very high nonlinearities in comparison
with silica. But, the use of chalcogenide fibers suffers
from the large normal dispersion in the infrared
window, which dramatically reduces the efficiency of
FOPA performance. The zero dispersion wavelengths
(ZDWs) of chalcogenide fibers are commonly located
far away from the operating wavelengths of
commercially available laser sources. It leads to the
difficulty in pumping those fibers in the anomalous
dispersion region.
In this work, we propose AsSe
2
–based hybrid
microstructured optical fibers (HMOFs) (Tong et al.,
2013) with controlled chromatic dispersion profiles.
By employing the brilliant properties of chalcogenide
glass, and the control of near-zero and flattened
chromatic dispersion profile of HMOFs, it is expected
to achieve a novel performance of FOPA in the mid-
infrared window.
2 CHROMATIC DISPERSION
AND PARAMETRIC GAIN
CALCULATION
A commercial full-vectorial mode solver (Lumerical-
Mode Solution software) based on the finite element
method and the perfectly matched layer boundary
condition was used to calculate the chromatic
Tong, H., Nagasaka, K., Matsumoto, M., Tezuka, H., Suzuki, T. and Ohishi, Y.
Optical Parametric Amplification Performance in AsSe2-based Hybrid Microstructured Optical Fibers.
DOI: 10.5220/0005992300590063
In Proceedings of the 13th International Joint Conference on e-Business and Telecommunications (ICETE 2016) - Volume 3: OPTICS, pages 59-63
ISBN: 978-989-758-196-0
Copyright
c
 2016 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
59

dispersion profiles of the proposed chalcogenide
fibers.
The core material is the AsSe
2
glass which is
made by Furukawa Denshi company. Its refractive
indices at 20 wavelengths from 0.4 to 4.0 µm were
measured by using the glass prism and the minimum
deviation method (Werner, 1968). The fiber cladding
material was designed in order that the refractive
index difference (Δn) between core and cladding
materials is equal to 0.3. The refractive index profiles
of both core and cladding materials were input into
the Mode Solution software as initial parameters.
The calculation of parametric gain in this work
has based on the theory of the degenerate four-wave
mixing process whose phase-matching condition is
given by (G. P. Agrawal, 2007)
2 P κβγ =Δ +
(1)
where P is the pump power,
γ is the nonlinear
coefficient and the linear phase-mismatch Δ
β is
expressed by (G. P. Agrawal, 2007)
2
is p
ββ β β Δ= + −
() () 2 ( )
eff i i eff s s eff p p
nn n
cc c
ωω ωω ω ω
=+ −
(2)
The effective refractive indices at the frequencies of
the pump
ω
p
, signal ω
s
and idler ω
i
are n
eff
( ω
i
), n
eff
( ω
s
)
and n
eff
( ω
p
), respectively.
Commonly, the linear phase-mismatch Δ
β is
calculated by using the second and fourth terms of the
Taylor series expansion. But in this work, Δ
β is fully
calculated by using the frequency dependent effective
refractive index n
eff
( ω
i
) obtained from Mode solution
software. For this reason, the contributions of higher
order dispersion parameters (
β
6
, β
8
…) are taken into
account to improve the accuracy of the phase
matching condition and FOPA gain.
The optical signal gain (G
s
) is given by (Hansryd
et al., 2002)
)(sinh)(1
)0(
)(
22
gL
g
P
P
LP
G
s
s
s
γ
+==
(3)
where L is the fiber length, P
s
(0) and P
s
(L) are the
signal power at the input and output of the fiber. The
parametric gain coefficient g is given by (Hansryd et
al., 2002).
22 2 2
()() ()( )
22
gP PP
κ
β
γγγ
Δ
=−=−+
(4)
3 RESULTS AND DISCUSSIONS
The conventional step index was first designed and its
structure is shown in Fig. 1a. The diameter of the
AsSe
2
core was 2.0 µm. The chromatic dispersion
profile of the fundamental mode was calculated
within the wavelength range from 2.0 to 11.0 µm and
is shown in Fig. 1b. As can be seen, only normal
dispersion region was obtained from 2.0 to 8.1 µm.
At the wavelengths larger than 8.1 µm, the modal
confinement was so weak that no mode could be
found in the core.
1a)
1b)
Figure 1: a) Fiber structure of an AsSe
2
step-index fiber and
b) its calculated chromatic dispersion profile of the
fundamental mode.
In order to enhance the modal confinement in the
core, a ring of six air holes with hexagonal structure
was designed in the cladding region. The diameter of
the AsSe
2
core was still 2.0 µm. The diameter of each
air hole was 4.0 µm and the pitch which is the
distance between two adjacent air holes was 7.0 µm.
This fiber structure is shown in Fig. 2a and is named
as a hybrid microstructured optical fiber. The
chromatic dispersion profile of the fundamental mode
was calculated and is shown in Fig. 2b. In comparison
with the conventional AsSe
2
step index fiber, the
AsSe
2
HMOF could support the fundamental mode at
wavelengths longer than 8.1 µm. The zero-dispersion
wavelength was found at 10.1 µm. The anomalous
dispersion regime was realized at wavelengths over
10.1 µm.
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-200
-100
0
100
200
300
Step-index fiber
Dispersion (ps/km-nm)
Wavelen
g
th
(
μ
m
)
OPTICS 2016 - International Conference on Optical Communication Systems
60

2a)
2b)
2c)
2d)
Figure 2: a) Fiber structure of an AsSe
2
HMOF, b) its
calculated chromatic dispersion profile of the fundamental
mode, c) signal gain map obtained by pumping the AsSe
2
HMOF at different pump wavelength from 3.0 to11.0 µm
and d) calculated signal gain spectrum obtained by pumping
at 4.7 µm.
The calculation of FOPA signal gain was carried
out by using the chromatic dispersion profile of the
AsSe
2
HMOF in Fig. 2b. The fiber length was 3 cm.
The pump power was 3 W and the nonlinear
coefficient was supposed to be 4.9 x10
4
W
-1
km
-1
(Cheng et al., 2014). The FOPA performance was
investigated when the pump and signal wavelengths
varied from 3.0 to 11.0 µm. Figure 2c shows the
signal gain map in which the colour scale expresses
the intensity of the signal gain. At different pump
wavelength, the gain bandwidth can be estimated
from the horizontal dimension of the signal gain map.
Figure 2c depicts that FOPA gain bandwidth is very
narrow when the pump wavelength is from 3.0 to
about 9.0 µm. For instance, the FOPA signal gain and
bandwidth is calculated and shown in Fig. 2d when
the pump wavelength is at 4.7 µm. But, the gain
bandwidth increases when the pump wavelength
becomes closer to the ZDW (10.1 µm) as shown in
Fig. 2c. When the pump wavelength locates in the
anomalous dispersion regime, both of signal gain and
bandwidth improve greatly. This feature implies that
the anomalous dispersion regime should be realized
at shorter wavelengths because it is not easy to pump
the fiber at wavelengths over 10 µm by several
commercially available laser sources at this time.
To obtain the anomalous dispersion regime in the
shorter wavelength range, a new fiber structure of
AsSe
2
HMOF was proposed. A new layer of material
which is called as the buffer layer was added around
the core. By changing the diameter of the buffer and
the Δn between the buffer and core materials, the
chromatic dispersion profile of the original HMOF
can be modified. In Fig. 3a, the buffer layer whose
diameter is 5.2 µm was added. The Δn between the
buffer and core is equal to 0.02.
The properties of chromatic dispersion, signal
gain map and signal gain spectrum for the AsSe
2
HMOF with the buffer layer are shown in Fig. 3. They
are totally different from those of the original AsSe
2
HMOF shown in Fig. 2. The anomalous dispersion
regime was obtained from 4.45 to 11.00 µm. It is very
close to zero and flattened. The ZDW was shifted
from 10.0 to 4.45 µm. The new FOPA performance
shown in Fig. 3c is consistent with the discussions for
Fig. 2c. When the pump wavelength is close to the
ZDW and locates in the anomalous dispersion
regime, a very broad gain bandwidth can be realized.
Figure 3d shows the signal gain spectrum when the
pump wavelength is 4.7 µm. The signal gain can be
as high as 32 dB. At 12 dB, a broad gain bandwidth
about 6500 nm was obtained. It is much broader than
the 1000-nm bandwidth near 2.94 µm simulated by
using a 20-cm-long chalcogenide step-index fiber
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-200
-100
0
100
200
300
Dispersion (ps/km-nm)
Wavelength ( μ m)
AsSe
2
HMOF
ZDW~10.1
μ m
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5
10
15
20
25
30
35
Wavelen
g
th
(
μ
m
)
Signal gain (dB)
Optical Parametric Amplification Performance in AsSe2-based Hybrid Microstructured Optical Fibers
61

with 20-W CW pump (Singh et al., 2012).
3a)
3b)
3c)
3d)
Figure 3: a) Fiber structure of an AsSe
2
HMOF with a buffer
layer, b) its calculated chromatic dispersion profile of the
fundamental mode, c) signal gain map obtained by pumping
the AsSe
2
HMOF with a buffer layer at different pump
wavelength from 3.0 to11.0 µm and d) calculated signal
gain spectrum obtained by pumping at 4.7 µm.
In addition, the effect of fiber structure variation
was investigated in this work. The whole structure of
the AsSe
2
HMOF with buffer layer was supposed to
fluctuate by ±1 %. However, the calculated chromatic
dispersion was almost invariant to the fluctuation of
fiber structure as shown in Fig. 4a. The shape of the
signal gain spectrum was maintained in the
wavelength range from 3.0 to 8.0 µm while the gain
bandwidth slightly changed as shown in Fig. 4b.
a)
b)
Figure 4: a) calculated chromatic dispersion profiles of the
fundamental mode of the AsSe
2
HMOF and a buffer layer
in Fig. 3a with ±1 % fiber structure fluctuation and b)
calculated signal gain spectra correspond to the chromatic
dispersion profiles in Fig. 4a, obtained by pumping at 4.7
µm.
4 CONCLUSIONS
Chalcogenide HMOFs with a buffer layer are
favourable for the performance of FOPA in the mid-
infrared window. The advantages of wide
transmission range, high nonlinearity, near-zero and
flattened anomalous dispersion control by using
chalcogenide HMOFs lead to a very broad FOPA
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-200
-100
0
100
200
300
Dispersion (ps/km-nm)
Wavelength ( μ m)
AsSe
2
HMOF with buffer layer
ZDW~4.45
μ m
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5
10
15
20
25
30
35
Wavelength ( μ m)
Signal gain (dB)
~6500 nm
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0
10
20
30
40
50
Structure fluctuation -1%
Structure fluctuation 0%
Structure fluctuation +1%
Dispersion (ps/km-nm)
Wavelength (μm)
ZDW~4.45
μm
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15
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35
Wavelength ( μ m)
Signal gain (dB)
Structure fluctuation -1%
Structure fluctuation 0%
Structure fluctuation +1%
~6500 nm
OPTICS 2016 - International Conference on Optical Communication Systems
62

gain bandwidth and high signal gain. Moreover, it is
very interesting that the chromatic dispersion can be
invariant to the fiber structure fluctuation and the
signal gain spectrum can be maintained.
ACKNOWLEDGEMENTS
This work is supported by MEXT, the Support
Program for Forming Strategic Research
Infrastructure (2011-2015)
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