APPLIED PHYSICS LETTERS 104, 043302 (2014)

Observation of polymer optical fiber fuse
Yosuke Mizuno,1,a) Neisei Hayashi,1 Hiroki Tanaka,1 Kentaro Nakamura,1,a)and Shin-ichi Todoroki2

1Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku,
Yokohama 226-8503, Japan2
Photonic Materials Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan(Received 2 December 2013; accepted 12 January 2014; published online 27 January 2014)
Although high-transmission-capacity optical fibers are in demand, the problem of the fiber fusephenomenon needs to be resolved to prevent the destruction of fibers. As polymer optical fibers
become more prevalent, clarifying their fuse properties has become important. Here, we
experimentally demonstrate a fuse propagation velocity of 21.9 mm/s, which is 1–2 orders ofmagnitude slower than that in standard silica fibers. The achieved threshold power density andproportionality constant between the propagation velocity and the power density are 1/180 of and17 times the values for silica fibers, respectively. An oscillatory continuous curve instead of
periodic voids is formed after the passage of the fuse. An easy fuse termination method is also
C 2014 Author(s). All article content, except where otherwise noted, is licensed under apresented. V
Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4863413]
Just over a quarter century ago, Kashyap and Blow1,2
published their influential paper on the observation of the optical fiber fuse phenomenon: the continuous self-destructionof a fiber by propagating light. High-power light propagatingthrough the fiber results in local heating and the creation ofan optical discharge that is then captured in the fiber core
and travels back along the fiber toward the light source, consuming the light energy and leaving a train of voids.3 Whilefiber fuse propagation is stunningly beautiful,4 the fiber cannot be used after the passage of the fuse. This effect, alongwith the Shannon limit,5–7 nonlinear effects,8,9 and theoptical amplifier bandwidth,9 is now regarded as a criticalfactor limiting the maximal optical power that can bedelivered.10,11 The fuse properties must be well characterized so that all possible measures are taken to avoid the creation of a fiber fuse.
The fuse properties in various glass fibers, including
standard silica-based single-mode fibers (SMFs),1–4,12–14
microstructured fibers,15 fluoride fibers,16 chalcogenidefibers,16 erbium-doped fibers,17 photonic crystal fibers,18 andhole-assisted fibers,18 are well documented. The fiber fuse isreported to be typically induced at an input optical power of
one to several watts (one to several megawatts per squarecentimeter) and to have a propagation velocity of one to several meters per second. These properties differ according to
the type of glass fiber; the threshold power, for instance, isreported to be much higher in photonic crystal and holeassisted fibers than in silica SMFs,18 and nonlinear saturationof the fuse velocity has been observed in erbium-doped
fibers.17 To date, reports detailing similar properties of nonglass fibers such as polymer optical fibers (POFs) have notbeen published. Several special POFs with relatively low
propagation losses and broadband transmission capabilities
have recently become commercially available,19,20 andextensive studies have investigated the implementation ofa)

Authors to whom correspondence should be addressed. Electronic addresses:
ymizuno@sonic.pi.titech.ac.jp and knakamur@sonic.pi.titech.ac.jp0003-6951/2014/104(4)/043302/4

POF-based high-capacity communication systems19,20 andpossible engineering applications of nonlinear effects inPOFs.21,22 Therefore, there is a pressing need to clarify thefuse properties of POFs.
In this Letter, we characterize the POF fuse and discuss
its unique properties. The propagation velocity of the brightspot is one to two orders of magnitude slower than that instandard silica SMFs. The threshold power density is 1/180
of the reported value for silica SMFs. We find that, after thepassage of the fuse, an oscillatory continuous curve isformed in the POF. We also show that the POF fuse can beeasily terminated by local elastic deformation of the waveguide structure.
The perfluorinated graded-index POF19 employed inthis experiment consists of a core (50 lm diameter), cladding (100 lm diameter), and overcladding (750 lm diameter) encased in polyvinyl chloride. The core and cladding
layers are composed of doped and undoped polyperfluorobutenylvinyl ether, respectively. The refractive index at thecenter of the core is 1.356, whereas that of the cladding
layer is 1.342;23 these values do not depend strongly on theoptical wavelength.24 The polycarbonate reinforcement
overcladding reduces microbending losses and increases
the load-bearing capability. The propagation loss is relatively low (250 dB/km) even at 1.55 lm, and inexpensiveerbium-doped fiber amplifiers (EDFAs) can be used toboost the optical power (the standard polymethyl
methacrylate POF is optimized for visible light transmission, and its propagation loss at 1.55 lm is higher than1  105 dB/km).
Figure 1(a) depicts the experimental setup, in which 7-dBm(5-mW) output light from a 1546-nm distributed-feedback laser
diode (NX8562LB; NEC; 1-MHz linewidth) was amplified by
an EDFA (LXM-S-21; Luxpert Technologies) to up to 23 dBm(200 mW) and injected into a 15-m-long POF. Two optical isolators were inserted to protect the laser and EDFA from reflectedor backscattered light. The end of the silica SMF fitted with an“FC” connector was connected to one end of the POF fitted

104, 043302-1

C Author(s) 2014
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Appl. Phys. Lett. 104, 043302 (2014)

where r is the radial distance from the core center, R is thecore radius, and g is the refractive index profile coefficient.
Consequently, the maximal power density I can be calculated as
ð 2p

ðrdh

P 0
I ¼ lim 2 ð2p
r!0 p r

0

ðR
dh

00

 g !
rrdr
1
RP gþ2: (2)¼ g !
p
R2 gr
1
rdr
R

By assuming g  2 in the graded-index POF,19 Eq. (2) can befurther simplified as
I¼

FIG. 1. (a) Schematic of the experimental setup. The silica SMFs are indicated by blue lines. (b) Composite photograph of the fiber fuse propagating
along the POF; photographs were taken at 1-s intervals. The light wasinjected from the right-hand side, while the fuse propagated from the lefthand side. The fiber arrangement was that of Todoroki4 to allow a directcomparison between the POF and silica SMF. (c) Magnified view of thepropagating fuse. The light was injected from the left-hand side.

with an “SC” connector via an FC/SC adaptor (couplingloss  0.3 dB).21,22 We confirmed that the fiber fuse can be initiated in the same way as in glass fibers1–4,12–18 by external stimuli such as heating, bending, or bringing the fiber output end
into contact with an absorbent material. For the demonstration
discussed here, we used a POF end surface polished roughlywith 0.5-lm alumina powder.
From observations of the propagation of the fuse along
the POF (Fig. 1(b)), the propagation velocity was calculated
to be approximately 24 mm/s, which is extremely slow incomparison to Todoroki’s4 result for a silica SMF. The optical power of the propagating light was calculated using themeasured power of the injected light, the coupling loss at theSMF/POF interface, and the propagation loss in the POF tobe approximately 75 mW, corresponding to a maximal power
density of 7.6 kW/cm2 (Refer to the next paragraph for calculation method). A magnified view of the fuse propagation
along a straight portion of the POF is shown in Fig. 1(c)(70.5 mW, 22.8 mm/s).
Here, we derive an equation for the maximal power density I in the core when light with a certain power P isinjected into the graded-index POF. We consider a refractiveindex in the core that takes a parabolic profile.19 Under theassumption that all modes propagate with equal attenuation
without coupling, the optical power profile is given, in thesame way as the refractive index profile, by25
 g !
rpðrÞ ¼ pð0Þ 1 ;
(1)
R

2P;
p R2

(3)

which indicates that the maximal power density in thegraded-index POF with an incident power P is equal to theaverage power density in a step-index POF of the same core
diameter with twice the incident power. For instance, forP ¼ 75 mW and R ¼ 25 lm, I is calculated to be 7.6 kW/cm2.
We found that the fuse propagation velocity in thePOF, measured at 1.55 lm, had an almost linear dependence
on the maximal power density with a slope of 1.59
 106 mms1 MW1 cm2 (Fig. 2(a)). The power density at
which the fuse ceased, i.e., the threshold power density, was
6.6 kW/cm2 at a propagation velocity of 21.9 mm/s. Comparing
these results with those of silica SMFs (Fig. 2(b); results12 at
1.48 lm and the theoretical line13 at 1.55 lm) revealed that at1.55 lm the slope in the POF data (corresponding to the efficiency of the velocity control) was 17 times as steep as that inthe silica SMF (9.41  104 mms1 MW1 cm2), and thethreshold power density of the POF was 180 times lower
than that of the silica SMF (1.2 MW/cm2). The minimal propagation velocity achieved at 1.55 lm was 11 times as low asthat experimentally obtained in a silica SMF at 1.48 lm(250 mm/s).14Digital micrographs taken after the passage of the fusedisclose the extent of the damage to the fiber. The fuse wasinitially triggered by exploiting the rough surface at the endof the POF (Fig. 3(a)) and was verified to be induced at thecenter of the core, which supports the assumption in our calculation that the maximal power density in the fiber crosssection affects the fuse induction and can be used to determine the threshold power density. The passage of the fuse(Fig. 3(b)) appeared as a continuous black carbonized curvethat oscillated periodically along the length of the POF,
which is considerably different from the bullet-shaped voids
observed in glass SMFs. The oscillation period was approximately 1300 lm, which is in general agreement with the theoretical oscillation period of the ray.26 Figure 3(c) shows theposition where the fuse ceased after the incident opticalpower was reduced to that below the threshold; since thefuse remained at this point for several seconds, it melted a
relatively large area of the POF, which resulted in theobserved bending.
Optical propagation loss in the POF after the passageof the fuse was measured for incremental cutbacks from30 cm to 20 cm (Fig. 3(d)) and a fixed input power ofThis article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
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Appl. Phys. Lett. 104, 043302 (2014)

FIG. 2. (a) Propagation velocity of the fiber fuse in a POF measured at 1.55 lm as a function of the maximum power density in the core. Measured data areshown as blue circles, and the red line is a linear fit. The slope of the line is 1.59  106 mms1 MW1 cm2, and the threshold intensity is 6.6 kW/cm2.
(b) Propagation velocities of the fiber fuse as a function of the power density. The measured data for the silica SMF at 1.48 lm (data extracted from the literature12) are shown as green circles, and the green line is a linear fit (slope of 1.17  105 mms1 MW1 cm2); the theoretical threshold power density13 is1.16 MW/cm2. The blue line is a theoretical prediction13 for the silica SMF at 1.55 lm (slope of 9.41  104 mms1 MW1 cm2). The data in (a) are also
reproduced for comparison.

10 dBm (10 mW) at 1.55 lm. A loss of 1.4 dB/cm indicates
that, unlike silica SMFs,1–4,12–14 light can propagate
through the POF for several tens of centimeters after thepassage of the fuse. We believe this is because undamaged
regions remain in the core and cladding layers as thesediameters are relatively large, which is a unique characteristic of POFs. Yet this propagation loss is somewhat significant for communication applications, and so once the fuseis induced, it is crucial to stop the propagation as soon as
possible.

Several methods for terminating fiber fuses have beendeveloped for glass fibers,18,27–29 which are, in principle,
also applicable to POFs. One method is to thin the outer
diameter of the fiber at a certain position while maintaining
the core diameter;28 this can reduce the internal pressure andarrest the propagating fuse via deformation. In silica
SMFs, this structure is fabricated using hydrofluoric acid as
an etchant,28 but in a POF, chloroform could be used to etchthe overcladding layer.30 An even easier method, which wepresent here, is to pressure-bond a small metal ring around

FIG. 3. (a) Digital micrograph of thePOF end at which the fuse was initiated by exploiting the rough surface.
(b) The path of the fuse in the POF.
(c) The point at which the fuse was terminated by decreasing the input opticalpower. (d) The dependence of the output power on the cut-back length. The
open circles are measured points, andthe solid line is a linear fit. The slopeof the line is 1.4 dB/cm. (e) Image ofthe fuse termination in the POF at theposition of a nickel ring.

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Mizuno et al.

the fiber; this method is only applicable to POFs with anextremely high flexibility.31 The optical power of the particular propagating mode that provides the bright spot withenergy is decreased below the threshold by deformation, andthe propagating fuse is thus terminated. The resulting
induced optical loss is negligibly low, and an image of thefuse termination at the position of the ring (Fig. 3(e)) showsthat bending did not occur. Once the ring is detached, thepolymer material will return to the original configuration(elastic deformation).
In conclusion, we have experimentally demonstrated a
POF fuse propagation velocity of 21.9 mm/s, which is 1–2
orders of magnitude slower than that in standard silica fibers.
The achieved threshold power density and proportionality
constant between the propagation velocity and the power
density are 1/180 of and 17 times the values for silica fibers,
respectively. We have found that a unique oscillatory continuous carbonized curve is formed after the passage of thefuse, which can be terminated easily. Future work will focus
on understanding the detailed mechanism of the initiationand propagation of the POF fuse. We believe that theseresults serve not only as a valuable guideline for the development of POF-based high-capacity transmission systems andengineering applications of nonlinear effects in POFs butalso as a strong impetus for the on-going research relating tofiber fuses and material sciences.
The authors thank Hirotsugu Yoshida (Sekisui ChemicalCo., Ltd.) for his helpful discussions, Richard Nedelcov(Department of Language Arts, Tokyo University of theArts) for his English editing, and Akitoshi Okino, TakahiroIwai, Ken Kakegawa, Yosuke Watanabe, Yukiko Ishihara,
Yoshitaka Utsunomiya (Department of Energy Sciences,
Tokyo Institute of Technology), Hideki Hosoda, Tomoya
Inamura, Masaki Tahara, Taku Aoki, Hyunbo Shim,Masatoshi Ii, Wei Qiu, Kazunari Minakawa, and Mingjie
Ding (Precision and Intelligence Laboratory, Tokyo Instituteof Technology) for the experimental assistance they offered.
This work was partially supported by a Grant-in-Aid forYoung Scientists (A) (No. 25709032) from the Japan Society
for the Promotion of Science (JSPS) and by research grants
from the General Sekiyu Foundation, the Iwatani Naoji

Appl. Phys. Lett. 104, 043302 (2014)

Foundation, and the SCAT Foundation. N.H. acknowledges
a Grant-in-Aid for JSPS Fellows (No. 25007652).
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