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Hole-assisted multicore optical fiber for next generation telecom transmission systems

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We present a multicore fiber dedicated for next generation transmission systems. To overcome the issue of multicore fibers' integration with existing transmission systems, the fiber is designed in such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation, bending loss, etc.) are in total accordance with the obligatory standards for telecommunication single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk and compatibility with standard single-core single-mode transmission links making the fiber ready for implementation in the near future.
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Hole-assisted multicore optical fiber for next generation telecom transmission systems
A. Ziolowicz, M. Szymanski, L. Szostkiewicz, T. Tenderenda, M. Napierala, M. Murawski, Z. Holdynski, L.
Ostrowski, P. Mergo, K. Poturaj, M. Makara, M. Slowikowski, K. Pawlik, T. Stanczyk, K. Stepien, K. Wysokinski,
M. Broczkowska, and T. Nasilowski
Citation: Applied Physics Letters 105, 081106 (2014); doi: 10.1063/1.4894178
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Hole-assisted multicore optical fiber for next generation telecom
transmission systems
A. Ziolowicz,
M. Szymanski,
L. Szostkiewicz,
T. Tenderenda,
M. Napierala,
M. Murawski,
Z. Holdynski,
L. Ostrowski,
P. Mergo,
K. Poturaj,
M. Makara,
M. Slowikowski,
K. Pawlik,
T. Stanczyk,
K. Stepien,
K. Wysokinski,
M. Broczkowska,
and T. Nasilowski
InPhoTech Sp. z o. o., 17 Slominskiego St 31, Warsaw 00-195, Poland
Institute of Applied Physics, Faculty of Advanced Technologies and Chemistry, Military University
of Technology, 2 Kaliskiego St, Warsaw 00-908, Poland
Polish Centre For Photonics And Fibre Optics, 312 Rogoznica, 36-060 Glogow Malopolski, Poland
Laboratory of Optical Fibre Technology, Faculty of Chemistry, Maria Curie-Sklodowska University,
3 Marii Curie-Skłodowskiej Sq, Lublin 20-031, Poland
(Received 31 May 2014; accepted 16 August 2014; published online 27 August 2014)
We present a multicore fiber dedicated for next generation transmission systems. To overcome the
issue of multicore fibers’ integration with existing transmission systems, the fiber is designed in
such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation,
bending loss, etc.) are in total accordance with the obligatory standards for telecommunication
single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations
and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk
and compatibility with standard single-core single-mode transmission links making the fiber ready
for implementation in the near future. V
C2014 AIP Publishing LLC.
Space-division multiplexing (SDM) is recognized as the
most efficient way to meet the challenge of an increasing
need for telecommunication network capacity,
as it allows
jumping over the barrier of existing systems based on single-
core single-mode fibers (SMF) with the recently reported
optical SDM link record capacity of 1 Pb/s.
In addition,
SDM allows reducing power consumption and system foot-
print compared to the transmission over multiple fibers
which is of high importance in applications such as, for
instance, satellite communication.
Two ways of SDM utili-
zation are possible. First, the idea of mode-division multi-
plexing (MDM)
in which each mode represents one
transmission channel and which can be realized by means of
a single core few-mode fiber (FMF)
or a multi-core fiber
(MCF) with coupled cores.
Second, the idea of uncoupled
propagation in multiple cores of an MCF.
The key feature
of such uncoupled propagation is the core isolation which
eliminates core-to-core crosstalk (XT), hence allows treating
each core as a separate transmission channel. Since the meth-
odology of addressing individual modes in an FMF is tech-
nologically complex
and the transmission characteristics
(e.g., attenuation, chromatic dispersion-CD, etc.) of each
mode vary, the use of MCFs with isolated single mode cores
seems to be more convenient and commercially applicable.
The goal of isolating the cores in an MCF can be realized in
various ways. The most intuitive and straightforward method
is simply increasing the core spacing which, however, entails
larger fiber diameters when more cores are involved. When
willing to increase the number of cores while remaining the
standard 125 lm fiber diameter, more sophisticated fiber
structures such as microstructured,
MCFs must be applied. An alternative (or
complementary) method of increasing the core isolation is
differentiating size and refractive index of particular cores.
Although this approach is generally correct, the integration
of such heterogeneous fibers with standard devices and opti-
cal fibers, currently used in optical fiber networks, is trouble-
some (as each core is characterized by different CD and the
mismatch between its size and doping level will introduce
additional loss when coupling with existing, SMF based, net-
work components). To overcome this integration issue, while
retaining high core density, we have designed and developed
a hole-assisted seven-core MCF, in which the transmission
parameters for each core (i.e., CD, attenuation, bending loss,
etc.) are in accordance with the obligatory standards for tele-
communication single core fibers (i.e., ITU-T G.652 and
G.657). Moreover, fiber diameter as well as diameter and re-
fractive index of each core (n
) are SMF compliant, which
enable an immediate employment of our fiber in the existing
telecommunication networks. In the next paragraphs, we
present a numerical analysis of the propagation conditions in
the proposed fiber followed by measurement results of CD,
XT, and bending loss. The experimental results are in ac-
cordance with the numerical data and prove the appropriate-
ness of our initial concept making our fiber the candidate of
choice for next generation telecommunication systems.
The proposed MCF structure is created by means of ba-
sic cells (Fig. 1(a))inwhichthe8.2lm diameter and
3.5 mol. % GeO
doped core is surrounded by twelve air-
holes. In such a basic cell, the refractive index contrast
between the core and cladding is the same as in an SMF.
The basic cells may be easily combined in a hexagonal grid
forming 7-core (Fig. 1(b)) or 19-core (Fig. 1(c)) fibers (with
other core counts possible).
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0003-6951/2014/105(8)/081106/4/$30.00 V
C2014 AIP Publishing LLC105, 081106-1
APPLIED PHYSICS LETTERS 105, 081106 (2014)
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The role of the air-holes in the basic cell is twofold. Their
main function is to isolate cores from each other, thus to elim-
inate XT and increase core density. The second role is to
reduce macrobend induced XT
and loss (due to suppression
of penetration of the optical field outside the basic cell) mak-
ing the fiber bend insensitive.
While the above mentioned
benefits of introducing air-holes into the MCF cladding are
clear and unquestionable, some downsides of such an
approach also need to be considered. First, the air-holes may
also modify the propagation characteristics such as CD and
mode field diameter (MFD), hence may decay the SMF-MCF
compatibility. Second, the air-holes not only isolate the cores
from each other but also create a second waveguide inside the
basic cell which may enable a low-loss propagation of clad-
ding modes (depicted as CL
, and CL
in Fig. 1(d)).
Third, a large air-filling factor (d
/K, where d
is the air-
hole diameter and Kis the lattice constant) has a detrimental
impact on the fiber cleaving process (as it affects the fracture
propagation in the structure
), which is essential when con-
sidering industrial applications of the MCF. Nevertheless, as
we present that by a proper fiber design, the negative conse-
quences of introducing air-holes in the fiber cladding can be
eliminated or significantly limited.
In doped core microstructured fibers, the light guidance
may be explained by two coexisting phenomena—first, by the
so called material guiding resulting from the difference in ma-
terial properties of core and cladding, and second, by the so
called geometrical guiding in which the cladding geometry
plays the major role and makes the fiber properties very wave-
length dependent. The strength of both of these guiding mech-
anisms may be altered by the size and distribution (e.g.,
distance from the core) of the air-holes, as well as by the core
size, shape, and doping level. The goal of our microstructured
basic cell design was, on one hand, to maintain strong material
guiding of the fundamental mode (in order to comply with the
mode distribution of an SMF) while, on the other hand, to
geometrically limit XT and macrobend loss. Furthermore,
eliminating the strongly geometrically guided cladding modes
, and CL
—Fig. 1(d)) was an additional concern.
With the initially set core GeO
doping level of
3.5 mol. % (as in an SMF), we proposed the basic cells’ lat-
tice constant value of K¼8.2 lm and carried out spectral nu-
merical simulations (with the use of Lumerical MODE
for confinement loss, dispersion, and MFD calcu-
lation, and COMSOL Multiphysics
for calculation of XT),
on how the fundamental modes’ propagation characteristics
depend on the air-hole diameter.
First, as one can see in Figs. 2(a) and 2(b), in the pro-
posed fiber design, the slope of the dispersion curve, as well
as the MFD, changes insignificantly with the changes of
, thus material guiding mechanism is clearly stronger
than geometrical guiding. Furthermore, the SMF-MCF fun-
damental mode overlap (Fig. 2(b)) remains at the level of
over 99.7% in a broad range of air-hole diameters (2.0 lm
<7.0 lm) ensuring negligible MCF-SMF coupling
loss, hence an etched SMF based fan-in/fan-out device may
be used for independent core addressing.
Since in the designed basic cell the air-holes do not influ-
ence the propagation characteristics of the core, the diameter
of air-holes was optimized to ensure the settlement between
strong isolation of cores (i.e., negligible XT level as in
Fig. 2(c)) and suppression of cladding modes depicted in
Fig. 1(d). The XT was calculated on a dual core structure
(formed by two neighboring basic cells) as the maximum
power ratio transmitted through the excited core (right basic
cell of Figs. 2(c) and 2(d)) and the neighboring core (left basic
cell of Figs. 2(c) and 2(d)) after the distance of the coupling
length defined as L ¼k/2Dn
,wherekis the wavelength and
is the difference of the effective refractive indices of the
symmetric and antisymmetric mode propagating in the dual
core structure. As one can see in Fig. 2(e), such a settlement
can be found for the air-hole diameter of approximately
5.6 lm at which the XT is at the level of approximately
28 dB at a coupling length of 770 m, and the cladding
modes’ confinement loss of over 30 dB/km ensures their high
suppression. Furthermore, such an air-hole diameter ensures
the fibers’ bend insensitivity with the calculated macrobend
loss at a negligible level of below 10
dB per turn over a
5 mm radius mandrel at 1550nm wavelength, which is in
compliance with the ITU-T G.657.B3 bend insensitive single-
mode optical fiber recommendation.
In order to experimentally prove our theoretical assump-
tions and numerical simulation results, we have fabricated a
7-core fiber according to our design (Fig. 1(b)) with the stack-
and-draw technique (Fig. 3(a)). The fiber dimensions (meas-
ured from a scanning electron microscope picture—Fig. 3(b))
are: d
7.4 lm, K7.1 lm, and d
5.9 lm.
Prior to the experimental investigation, we have carried
out numerical simulations with the use of structural parameters
of the fabricated fiber in order to verify the impact of the tech-
nology induced geometry change on guiding characteristics.
As expected, the decrease (in comparison to the optimum val-
ues given in the previous paragraphs) of the core diameter, to-
gether with the increase of the air-hole diameter, results in an
improved basic cell isolation (with the calculated XT level of
approximately 60 dB at a coupling length of approximately
1250 m) at the expense of low confinement loss of the cladding
modes (<0.001 dB/km). This enhanced isolation was also con-
firmed experimentally with the measured central-to-outer core
FIG. 1. (a) MCFs’ basic cell; (b) 7 core MCF design; (c) 19 core MCF design;
and (d) electric field distributions of the fundamental mode propagating in the
core (FM
) and three cladding modes (CL
) propagating in
the basic cell with the lowest confinement loss.
081106-2 Ziolowicz et al. Appl. Phys. Lett. 105, 081106 (2014)
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XT of below 60 dB at a distance of approximately 1 km.
Furthermore, the results of macrobend loss measurements
(measured for the central core of the MCF) confirm the fiber
bend insensitivity but also indicate a seeming gain effect dur-
ing increasing the number of turns or decreasing the bend ra-
dius as presented in Fig. 4(a). This phenomenon can be
explained by cladding modes’ coupling to the fundamental
core mode during bending, which is also a result of the high
basic cell isolation in the fabricated fiber, and can be elimi-
nated by tailoring air-hole size and lattice constant to the opti-
mum values. Dispersion characteristics were measured in a
free space Michelson interferometer configuration.
experimentally measured dispersion curve (Fig. 4(b))ischar-
zero dispersion slope coefficient S
¼0.097 ps/(nm
km), and
a dispersion of 18.42 ps/(nm km) at 1550 nm wavelength
which prove high telecommunication potential of the presented
FIG. 3. (a) Initial stacked preform assembly and (b) an SEM image of the
fabricated fibers cross section.
FIG. 2. (a) Dispersion curves for
¼8.2 lm and different values of
and (b) MFD and MCF-SMF
overlap in the function of d
¼8.2 lm with the dotted line rep-
resenting MFD for the structure with-
out air-holes. (c) Normalized electric
field intensity distribution after a
distance of the coupling length in two
cores for strong core isolation—
¼8.2 lm, d
¼5.6 lm, and
K¼8.2 lm and (d) normalized electric
field intensity distribution after a dis-
tance of the coupling length in two cores
for weak core isolation—d
¼8.2 lm,
¼4.6 lm, and K¼8.2 lm. (e) XT
(dashed line) and confinement loss of
cladding modes (solid lines) for
¼8.2 lmandK¼8.2 lminthe
function of d
081106-3 Ziolowicz et al. Appl. Phys. Lett. 105, 081106 (2014)
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The transition from existing large-capacity transmission
networks based on single core fibers to future networks based
on MCFs requires development of MCFs with characteristics
compatible with ITU-T recommendations for single core
fibers. While several uncoupled core hole-assisted MCFs
were already reported,
our research is unique due to
the remarkable compliance of the designed fiber with obliga-
tory telecommunication standards in terms of transmission
loss, macrobend insensitivity, and dispersion characteristics.
Furthermore, our fiber can be manufactured with the use of
common and undemanding stack-and-draw method and can
be spliced to the standard SMF-28 fibers with low loss. The
above features make our solution ready for implementation
in telecommunication links already in the near future.
Moreover, with the developed fiber Bragg grating inscription
the reported fiber may find applications in fiber
optic filters, lasers, and sensors.
This research was partially supported by the National
Centre for Research and Development within the research
Projects PBS1/B3/12/2012 and POIG.01.03.01-06-085/12,
by the Polish Agency for Enterprise Development within
the Innovative Economy Programme as the key Project
POIG.01.04.00-06-017/11, as well as by the Polish National
Science Centre within the Project 2013/09/D/ST7/03961. This
research project has been also supported by the European
Commission under the 7th Framework Programme through the
“Space” action of the “Cooperation” Programme, BEACON
Grant No. 607401.
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ber of turns for different bend radii and (b) results of chromatic dispersion
measurement referenced to the specification of standard SMF-28eþfrom
081106-4 Ziolowicz et al. Appl. Phys. Lett. 105, 081106 (2014)
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... The theoretical and experimental MCFs as shown in Table 1 proves that placing air-holes between cores is an effective and reliable approach to reduce the crosstalk [19]. ...
... The particularity of our design is the air-hole placement which forms a groove-like structure around the cores, which can evidently prevent the leakage of core energy and isolate the light from other cores. The air-holes are placed in such a manner to minimize their number and achieve minimum crosstalk.The MCF structures having air-holes all around the cores are also good in manufacturability [18,19]. Subsequently, six different MCF designs have been considered in this work; two designs with 31-cores as shown in Figures 1 and 2 and four designs with 37-cores with different horizontal and diagonal core pitch as shown in Table 2. Figure 1 shows the cores along the edges have no air-holes as proposed in Refs [23,24] to minimize the micro-bending losses in outer cores using minimum CT and core pitch. ...
... These fibers commonly exhibit a single core. However, there are several scenarios where multiple cores are desired, such as Space-division multiplexing (SDM) [109] and sensing. Multicore fibers can be manufactured by similar technologies than SMF such as the stack and drawn process [110]. ...
... Multicore fibers can be manufactured by similar technologies than SMF such as the stack and drawn process [110]. Alternatively, the microstructured hole arrangement of Photonic Crystal Fibers (PCFs) can also be applied [109]. These fibers, when spliced and fused with common optical fibers can behave as sensors [111]. ...
Full-text available
The consolidation of laser micro/nano processing technologies has led to a continuous increase in the complexity of optical fiber sensors. This new avenue offers novel possibilities for advanced sensing in a wide set of application sectors and, especially in the industrial and medical fields. In this review, the most important transducing structures carried out by laser processing in optical fiber are shown. The work covers different types of fiber Bragg gratings with an emphasis in the direct-write technique and their most interesting inscription configurations. Along with gratings, cladding waveguide structures in optical fibers have reached notable importance in the development of new optical fiber transducers. That is why a detailed study is made of the different laser inscription configurations that can be adopted, as well as their current applications. Microcavities manufactured in optical fibers can be used as both optical transducer and hybrid structure to reach advanced soft-matter optical sensing approaches based on optofluidic concepts. These in-fiber cavities manufactured by femtosecond laser irradiation followed by chemical etching are promising tools for biophotonic devices. Finally, the enhanced Rayleigh backscattering fibers by femtosecond laser dots inscription are also discussed, as a consequence of the new sensing possibilities they enable.
... For the manufacturing of hole-assisted MCFs, the most commonly used method is the stackand-draw method [26][27][28], which can be applied to make the designed NA-PCF. For example, Xia et al. have successfully used the stack-and-draw method to produce hole-assisted MCF with a length of more than 1km in 2012 [10]. ...
Full-text available
Drawing on the flexibility of photonic crystal fiber (PCF) for air-hole design, we propose a novel homogeneous nanorod-assisted multi-core PCF (NA-PCF) for multi-core fiber (MCF) communication system. High refractive index nanorods are introduced in the center of the fiber cores and a periodical arrangement of air-holes further surrounded them. The air-holes and the nanorods work together to greatly suppress the crosstalk (XT) between the cores. By comprehensively balancing the influence of various parameters on XT, single-mode cutoff wavelength (cc) and the effective mode field area (Aeff), simulation results show that the NA-PCF has a Aeff of about 70.26m2, XT of about -50.58dB/km, relative core multiplicity factor(RCMF) of 4.7 and cc of 1530nm. This designed fiber structure targets applications in large-capacity long-distance MCF communication.
The design of homogenous trench-assisted multi-core fiber with M-type cores and a cladding diameter of 200 μm is proposed by numerical simulations. The M-type core is introduced to reduce the inter-core crosstalk (XT) of a 19-core fiber to below -30 dB/100 km with a low cost of cutoff wavelength. At the same time, the trade-off between the XT suppression and the effective area of the fundamental mode is mitigated to ensure the effective area is larger than 70 μm2 to suppress the non-linear effects. The study of the effects of the high-index ring of the M-typed core on the XT, effective area, and power fraction shows the potential in improving the fiber performance by a well-designed micron structure of the core. The bending performance shows this design can operate with low loss and crosstalk, and an effective area of over 70 μm2 at a bending radius from 15 mm to 500 mm. The proposed design provides the possibility to improve the MCF performance for long-haul transmission.
In this paper, we present a novel design of trench-nanopore-assisted double-clad few-mode fiber, which can support 14 linearly polarized (LP) modes. The trench-nanopore structure is introduced to effectively split adjacent modes and decrease bending loss. We evaluate the impact of parameters on the effective modal index (neff), the minimum effective refractive index difference (minΔneff) and modal effective area (Aeff) by using the finite element. The bending loss and broadband performance of the entire C+L bands, including neff, Δneff, differential mode delay (DMD) and dispersion, are also investigated. The simulated results show that all modes supported by the designed fiber are completely separated with Δneff between adjacent modes larger than 6 × 10–4 over the whole C+L-band. Bending loss is lower than 10−5 dB/m. The designed trench-nanopore-assisted fiber has the potential applications for short-haul mode division multiplexing systems to improve transmission capacity.
The PANDA segmented ring-core (SERC) few-mode fiber (FMF) can further enhance its characteristic of separating the eigenmodes by dividing the RC into several ring-sectors (RSs) with variable angles and decreasing refractive indices in the azimuthal direction. The novel PANDA SERC FMF with an appropriate choice of parameters can support 10 fully separated eigenmodes, where minimum effective index differences min(∆neff) between adjacent eigenmodes can reach 3.5 × 10⁻⁴ over the whole C + L band. Moreover, the group velocity dispersion (GVD), effective mode areas and losses of the fiber are within the range of (-42, 20) ps/nm/km, (31, 75) μm² and (0.4, 0.56) dB/km over the whole C + L band. Numerical results show that the designed fiber has excellent bending resistance, while the splice losses between standard step-index fiber and PANDA SERC FMF are within the range of 0.62-1.05 dB at 1550 nm. Consequently, the proposed fiber can provide a promising way to design the fully degeneracy-lifted polarization-maintaining (PM) FMF for the mode-division multiplexing (MDM) transmission.
The space division multiplexing system is helpful to break through the transmission limitations of traditional optical communication systems. Inter-fiber separation and the number of alternating dielectric layers of Bragg fibers array (BFA) are considered with view to applying BFA to space division multiplexing system. The simulation results indicate that BFA with improper inter-fiber separation will result in topological edge state, thus leading to strong crosstalk and high confinement loss, and its crosstalk is hard to decrease with the increase of alternating dielectric layers. The confinement loss of each Bragg fiber in BFA with proper inter-fiber separation is greatly lower than that of traditional Bragg fiber with the same parameters. Our optimized BFA can be realized with low crosstalk of below -30 dB for 55.4 km propagation. In addition, the arrangement analysis of BFA in this paper provides some constructive suggestions for the application of traditional Bragg fiber in optical devices design such as BFA laser and omnidirectional emitting laser.
We present a steering wheel-type ring depressed-core few-mode fiber (SWTR-DC-FMF) that features a central depressed step-index core and a novel SWTR structure consisted of two symmetrical high-index parts and low-index parts, respectively. The DC and SWTR make great contribution to separate the non-degenerated LP modes and spatial modes in the circular symmetry core, resulting in fully improved mode spacing. The designed fiber is able to support 10 spatial modes with the minimum effective index difference (Min Δneff) between adjacent spatial modes larger than 1.93 × 10-4 and the Min Δneff between adjacent LP modes above 1.51 × 10-3 at the same time, facilitating potential fiber spatial mode multiplexing transmission with less multiple-input multiple-output (MIMO-less) digital signal processing technique. The broadband performance including neff, Δneff, effective mode area (Aeff) and differential mode delay (DMD) is comprehensively investigated over the whole C and L band. Moreover, the birefringence and fabrication tolerance are discussed. The designed fiber targets emerging applications in short-reach weakly coupled space-division multiplexing (SDM) optical networking to increase transmission capacity and spectral efficiency and further reduce the system complexity effectively.
This paper presents a study on the propagation of modes of electromagnetic wave through a homogeneous multicore fiber. Complete view for fundamental modes for each core and other linearly polarized modes are obtaining here. Coupling between fundamental modes and other different cladding modes are presented in this paper. This study includes the coupling coefficient between multiple modes under periodic perturbation conditions for hexagonal seven core configuration.
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Optical communication technology has been advancing rapidly for several decades, supporting our increasingly information-driven society and economy. Much of this progress has been in finding innovative ways to increase the data-carrying capacity of a single optical fibre. To achieve this, researchers have explored and attempted to optimize multiplexing in time, wavelength, polarization and phase. Commercial systems now utilize all four dimensions to send more information through a single fibre than ever before. The spatial dimension has, however, remained untapped in single fibres, despite it being possible to manufacture fibres supporting hundreds of spatial modes or containing multiple cores, which could be exploited as parallel channels for independent signals.
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A new type of optical fiber called heterogeneous multi-core fiber (heterogeneous MCF) is proposed towards future large-capacity optical-transport networks and the design principle is described. In the heterogeneous MCF, not only identical but also non-identical cores, which are single-mode in isolation of each other, are arranged so that cross-talk between any pair of cores becomes sufficiently small. As the maximum power transferred between non-identical cores goes down drastically, cores are more closely packed in definite space, compared to a conventional, homogeneous multi-core fiber (homogeneous MCF) composed of only identical cores.
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We designed and fabricated a low-crosstalk seven-core fiber with transmission losses of 0.17 dB/km or lower, effective areas larger than 120 μm<sup>2</sup>, and a total mean crosstalk to the center core of -53 dB after 6.99-km propagation (equivalent to -42.5 dB after 80 km), at 1550 nm. We also investigated the signal-to-noise ratio (SNR) achievable in uncoupled multi-core transmission systems by regarding the crosstalk as a virtual additive white Gaussian noise. The SNR under existence of crosstalk in the fabricated multi-core fiber (MCF) was estimated to be 2.4 dB higher than that in a standard single-mode fiber (SSMF) in the case of 80-km span, and 2.9 dB higher in the case of 100-km span; which are the best values among MCFs ever reported, to the best of our knowledge. The SNR penalties from crosstalk in this MCF were calculated to be 0.4 dB for 80-km span and 0.2 dB for 100-km span. We also investigated SNR penalty from crosstalk in the more ordinary case of an MCF with SSMF cores, and found that the total mean crosstalk to the worst core after one 80-km span should be less than about -47 dB for 0.1-dB penalty, about -40 dB for 0.5-dB penalty, and about -36 dB for 1-dB penalty.
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We demonstrate mode-division multiplexed WDM transmission over 50-km of few-mode fiber using the fiber's LP01 and two degenerate LP11 modes. A few-mode EDFA is used to boost the power of the output signal before a few-mode coherent receiver. A 6×6 time-domain MIMO equalizer is used to recover the transmitted data. We also experimentally characterize the 50-km few-mode fiber and the few-mode EDFA.
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In this paper, the concept of supermode is introduced for long-distance optical transmission systems. The supermodes exploit coupling between the cores of a multi-core fiber, in which the core-to-core distance is much shorter than that in conventional multi-core fiber. The use of supermodes leads to a larger mode effective area and higher mode density than the conventional multi-core fiber. Through simulations, we show that the proposed coupled multi-core fiber allows lower modal dependent loss, mode coupling and differential modal group delay than few-mode fibers. These properties suggest that the coupled multi-core fiber could be a good candidate for both spatial division multiplexing and single-mode operation.
In this Letter we present, for the first time to our knowledge, the results of fiber Bragg grating (FBG) inscription in a novel microstructured multicore fiber characterized by seven single-mode isolated cores. A clear Bragg reflection peak can be observed in all of the 7 cores after one inscription process with a KrF nanosecond laser in a Talbot interferometer set up. We furthermore perform a numerical analysis of the effective refractive indices of the particular modes and compare it with the FBG inscription results. An experimental analysis of the strain and temperature sensitivities of all of the Bragg peaks is also included.
We describe and explain the design methods for the cores, trench layers and core number in multi-core fibers (MCFs) in detail. According to such method, we propose relative optimized design schemes for heterogeneous trench-assisted multi-core fiber (Hetero-TA-MCF), inside which cores are arranged in one-ring structure. This Hetero-TA-MCF is a kind of bend-insensitive MCF with high density of cores and ultra-low crosstalk.
A seven-core few-mode multicore fiber in which each core supports both the LP01 mode and the two degenerate LP11 modes has been designed and fabricated for the first time, to the best of our knowledge. The hole-assisted structure enables low inter-core crosstalk and high mode density at the same time. LP01 inter-core crosstalk has been measured to be lower than -60 dB/km. LP11 inter-core crosstalk has been measured to be around -40 dB/km using a different setup. The LP11 free-space excitation-induced crosstalk is simulated and analyzed. This fiber allows multiplexed transmission of 21 spatial modes per polarization per wavelength. Data transmission in LP01/LP11 mode over 1 km of this fiber has been demonstrated with negligible penalty.
We demonstrate an experimental study of the chromatic dispersion properties for a series of microstructured fibers (MSFs) dedicated for a supercontinuum generation. With white-light interferometry application we analyze experimentally how the small variations of structural parameters, i.e. an air-hole diameter and a lattice constant, influence dispersion characteristics in different groups of MSFs. Our study provides useful information on how to design the fiber which is less sensitive to the fabrication imperfections. Moreover those investigations are the initial step to the development of the customized or tunable supercontinuum light sources based on MSFs with slightly changed structural parameters which can generate light with a different spectrum range, adapted to a proper application.
Mode-division multiplexing over 33-km few-mode fiber is investigated. It is shown that 6×6 MIMO processing can be used to almost completely compensate for crosstalk and intersymbol interference due to mode coupling in a system that transmits uncorrelated 28-GBaud QPSK signals on the six spatial and polarization modes supported by a novel few-mode fiber.