S PE C I A LT Y F I B E R S

Polymer fiber fuse characterization
improves propagation possibilities
YOSUKE MIZUNO, NEISEI HAYASHI, HIROKI TANAKA, KENTARO
NAKAMURA, and SHIN-ICHI TODOROKI

Detailed characterization of a polymer
fiber ‘fuse’ increases understandingof high-power propagation limits
and expands fiber applications madepossible by unique attributes inducedby the fuse process.

several watts (one to fuse properties of POFs and potenseveral megawatts per tially exploit their properties for newsquare centimeter) and applications.
to have a propagationvelocity of one to sev- Fundamental characterizationeral meters per second. For our experimental investigation
To date, reports de- of polymer fiber fuse characteristics,
tailing similar proper- we used a perfluorinated graded-inties of nonglass fibers such as poly- dex POF with a propagation loss of
mer or plastic optical fibers (POFs) ~250 dB/km at 1.55 μm. Output lighthave not been published. Several spe- from a 1546 nm laser was amplified
cial POFs with relatively low propaga- using an erbium-doped fiber amplifition losses and broadband transmis- er (EDFA) and injected into the POF
sion capabilities have recently become through its end face, which was polcommercially available, and extensive ished roughly with alumina powder.
studies have investigated the implemen- a)POFc) Lighttation of POF-based
Ignition
0.0 s
high-capacity communication systems
1.0 s
and possible engi2.0 s
neering applications
EDFAof nonlinear effects
Laser
Isolator
Isolator POF
3.0 s
in POFs.3 Therefore,
1546 nmMax. output
there is a pressing
7 dBm
4.0 s
23 dBm
20 mm(5mW)
need to clarify the(200 mW)

Just over a quarter of a century ago,
Kashyap and Blow published their influential paper on the observation of
the optical fiber fuse phenomenon: thecontinuous self-destruction of a fiber
by propagating light.1 High-power
light propagating through the fiber results in local heating and the creationof an optical discharge that is then captured in the fiber core and travels backalong the fiber toward the light source,
consuming the light energy and leaving
a train of voids. While fiber fuse propagation is stunningly beautiful, the fiber cannot be used after the passageof the fuse. This effect is thus, alongwith the Shannon limit and nonlinear
effects, looked on as one of the criticalfactors limiting the maximal
optical power that can be deFIGURE 1. Anlivered by the fiber.
experimental setup (a),The fuse properties in varia composite photograph(b), and a magnified viewous glass fibers including stan(c) show the fiber fusedard silica single-mode fibers
propagating along the2(SMFs), silica multimode fiPOF; photographs werebers, and photonic crystal fitaken at 1 s intervals. A
bers are well documented.
movie is available atThe fiber fuse is reported tohttps://www.youtube.com/
be typically induced at an inwatch?v=t0k_B6EOQhg.
put optical power of one toLaser Focus World

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Fuse

LightMarch 201549

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S PE C I A LT Y F I B E R S c on tin ued

From observations of the propagation of the fuse along the velocity achieved at 1.55 μm was 11 times as low as that exPOF, the propagation velocity was calculated to be ~24 mm/s perimentally obtained in a silica SMF at 1.48 μm (250 mm/s).
(see Fig. 1).4 The fuse propagation velocity in the POF had an
A detailed theoretical analysis has proven that the slower
almost linear dependence on the maximal power density. The propagation velocity is attributed to the lower thermal conpower density at which the fuse ceased (that is, the thresh- ductivity in the POF, and that the lower threshold power denold power densi- sity is a result of the lower temperature—at which the optiIntensity (a.u.)ty) was 6.6 × 10−3 cal absorption is maximal—and the higher absorption at that
1.2
MW/cm2 at a prop- temperature.5
agation velocity of
1.0
21.9 mm/s.
Spectral and microscopic analysis
0.8Comparing these A comparison of the emission spectrum of the bright spot
results with those propagating along the POF (due to a 300 mW incident pow0.6of silica SMFs re- er) to that of the blackbody-like spectra of an incandescent
0.4
vealed that at 1.55 light bulb and sunlight shows that, although the POF fuse
0.2
μm the threshold spectrum has some characteristic peaks, all three spectra are
power density of similar (see Fig. 2).
0.0
200
400
600
8001000
the POF was 180
This would indicate that the bright spot of the POF fuse origWavelength (nm)times lower than inates not from plasma emission but from thermal radiation,
FIGURE 2. In an emission spectrum ofthat of the silica because if the bright spot of the POF fuse is indeed a plasma,
the bright spot of the POF fuse, the aqua,
SMF (which was the emission spectrum will generally contain some line-shaped
green, and red dashed curves represent~1.2 MW/cm2). In components. Spectra theoretically calculated using Planck’s
the normalized blackbody radiation spectra
addition, the min- law indicate that the temperature of the bright spot is about
calculated theoretically at 2600, 3600,
imal propagation 3600 K (also verified using Wien’s displacement law).
and 4600 K.
Digital micrographs taken after the passage of the fuse disclose the extent of the damage to the fiber (see Fig. 3). The
fuse initially triggered by exploiting the rough surface at theend of the POF was verified to be induced at the center of thecore. The passage of the fuse appeared as a continuous black
carbonized curve that oscillated periodically along the lengthof the POF, which is considerably different from the bulletshaped voids observed in glass fibers.
The oscillation period was ~1300 μm, which is in generalagreement with the theoretical oscillation period of the ray.
This indicates that the bright spot travels only along the optical path of the propagating mode with the highest energy and
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March 2015

FIGURE 3. A digital micrograph shows the POF end at which thefuse was initiated (a), the path of the fuse in the POF (b), and thepoint at which the fuse was terminated by decreasing the optical
input power (c).
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The position wherea)the fuse ceased (andremained for severalseconds) after the incident optical pow3 mm
er was reduced below
threshold resulted inVoidsVoidsc)
the POF melting over b)
a large area and fiber
bending (see Fig. 3).
The propagation
500 µm500 µmbehavior of the POF
fuse was also invese)
tigated at a power d)density up to several
tens of kW/cm2 (corresponding to a subwatt power source).65 mm
1 mm
As the propagation velocity is raised in proFIGURE 4. Shown are the path of the POF fuse at a power density
portion to the incident of 42 kW/cm2 (a), two example micrographs (b, c) of the POF fusepower density—reach- path containing voids, and the path of the POF fuse (d) with a burst
ing 41 mm/s at 67 kW/ at a power density of 67 kW/cm2 and its magnified view (e).
cm2—spiral propagation of damage is observed (see Fig. 4).
The diameter of the spiral oscillation
is about 200 μm, which is larger thanthe core/cladding diameter (around 100μm), indicating that the overcladding layer was thermally damaged at this highpower density. Gas bubbles were alsoobserved. The bubbles formed randomly
at places where the curvature of the fusepassage was maximal, and were somewhat similar to the void train observedin glass fibers. The formation was, however, so irregular that sometimes bubbles
were not observed.
At 67 kW/cm2, a burst induced by aconsiderable amount of generated gas
was newly observed. The higher the incident power was, the more frequently the burst was observed. Therefore, it
is difficult to make the POF fuse propagate for a relatively long distance (longer than several tens of centimeters) at apower density higher than 100 kW/cm2(or at a power higher than ~1 W).

Opportunities
Unlike the process within glass fibers,
light and electric current can simultaneously propagate through the POF after
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S PE C I A LT Y F I B E R S c on tin ued

the passage of the fuse because the generated continuous carbonized curve iselectrically conductive while the opticalpropagation loss is 1 to 2 dB/cm—sufficiently low for centimeter-order lightpropagation. This characteristic provides
a possible scheme for a long photoelectric interaction length.
The optical propagation loss is, however, somewhat significant for communication applications, and so once thefuse is induced, it is crucial to stop thepropagation as soon as possible. Several
methods for terminating fiber fuses havebeen developed for glass fibers. Some ofthese methods 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; this canreduce the internal pressure and arrest
the propagating fuse via deformation.
In silica SMFs, this structure is fabricated using hydrofluoric acid as an etchant,

but in a POF, chloroform could be used REFERENCES
1. R. Kashyap and K.J. Blow, Electron. Lett. 24,to etch the overcladding layer.
47 (1988).
An even easier method that we have de2. S.-i. Todoroki, Fiber Fuse: Light-induced
veloped is to pressure-bond a small metal
Continuous Breakdown of Silica Glass Opticalring around the fiber. While this method
Fiber, NIMS Monographs (Springer Japan,2014).
is only applicable to POFs with extremely
3. Y. Koike and M. Asai, NPG Asia Mater. 1, 22
high flexibility, the optical power of the(2009).
particular propagating mode that pro- 4. Y. Mizuno et al., Appl. Phys. Lett. 104,vides the bright spot with energy is de043302 (2014).
creased below the threshold by defor- 5. Y. Mizuno et al., Sci. Rep. 4, 4800 (2014).
6. Y. Mizuno et al., IEEE Photon. J. 6, 6600307
mation, and the propagating fuse is thus
(2014).
terminated. The resulting induced optical loss is negligibly low, and bending Yosuke Mizuno is an assistant profesdoes not occur after the fuse termination. sor, Neisei Hayashi is a research associOnce the ring is detached, the polymer ate, Hiroki Tanaka is a PhD student, andKentaro Nakamura is a professor inmaterial returns to the original config- the Precision and Intelligence Laboratory
uration owing to its elastic deformation. at Tokyo Institute of Technology (TokyoWe believe that a more thorough char- Tech), 4259 Nagatsuta-cho, Midori-ku,
acterization of fiber fuses will serve not Yokohama, Kanagawa 226-8503 Japan;
email: ymizuno@sonic.pi.titech.ac.jp; http://
only as a valuable guideline for the de- titech.ac.jp. Shin-ichi Todoroki is a prinvelopment of POF-based high-capacity cipal researcher in the Photonic Materials
transmission systems, but also advance Unit, National Institute for Materials Science
the engineering of nonlinear and other (NIMS), 1-1 Namiki, Tsukuba-city, Ibaraki
305-0044 Japan; http://www.nims.go.jp.
novel POF fiber designs.

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