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JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 24, DECEMBER 15, 2014

Fiber-Optic Interferometry Using Narrowband Light
Source and Electrical Spectrum Analyzer: Influence
on Brillouin Measurement
Yosuke Mizuno, Member, IEEE, Neisei Hayashi, and Kentaro Nakamura, Member, IEEE

Abstract—We observe an interference pattern using a simple
fiber-optic interferometer consisting of an electrical spectrum analyzer and a narrowband light source, which is commonly employedfor observing the Brillouin gain spectrum. This interference pattern expands well beyond the frequency range corresponding to
the Brillouin frequency shift in silica fibers (11 GHz at 1.55 μm).
Using both silica single-mode and polymer optical sensing fibers,
we then experimentally prove that the distinctive noise in a selfheterodyne-based Brillouin measurement with an unoptimized polarization state originates from the interference between the reference light and the Fresnel-reflected light. This noise can be almost
completely suppressed by employing a delay line that is longer thanthe coherence length of the light source and by artificially applying
a high loss near the open end of the sensing fiber.
Index Terms—Brillouin scattering, fiber-optic interferometry,
nonlinear optics, polymer optical fiber.

I. INTRODUCTIONUBSTANTIAL efforts have been directed toward the studyof Brillouin scattering in optical fibers [1] in the last
40 years, and a number of related applications have been developed, including lasing [1], microwave signal processing [2],core alignment [3], optical memory [4], slow light generation[5], and distributed strain and temperature sensing [6]–[10]. To
improve the performance of these applications, Brillouin scattering properties have been investigated not only in standard
silica glass fibers [11], [12] but also in various specialty fibers,
such as tellurite fibers [13], [14], bismuth-oxide fibers [14],chalcogenide fibers [15], photonic crystal fibers [16], and fibers
doped with rare-earth ions (erbium, thulium, etc.) [17], [18].
Each fiber type has its own distinctive features; for instance, theBrillouin scattering power in tellurite and chalcogenide fibers is
far higher than that in other fibers, whereas the Brillouin scattering power in erbium-doped fibers at 1.55 μm can be tuned
by controlling the 980-nm pump power. However, all of theseglass fibers are fragile and require careful handling; in sensing

S

Manuscript received August 21, 2014; revised October 23, 2014; accepted
October 23, 2014. Date of publication October 28, 2014; date of current version
November 14, 2014. This work was supported in part by Grants-in-Aid forYoung Scientists (A) under Grant 25709032 and for Challenging Exploratory
Research under Grant 26630180 from the Japan Society for the Promotionof Science and by research grants from the General Sekiyu Foundation, theIwatani Naoji Foundation, and the SCAT Foundation. The work of N. Hayashi
was supported by a Grant-in-Aid for JSPS Fellows under Grant 25007652.
The authors are with the Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 Japan (e-mail: ymizuno@sonic.
pi.titech.ac.jp; hayashi@sonic.pi.titech.ac.jp; knakamur@sonic.pi.titech.ac.jp).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JLT.2014.2365187

applications, they cannot be used to measure strains larger thanroughly 3%.
Our approach to overcome these problems exploits Brillouinscattering in polymer (or plastic) optical fibers (POFs) [19],[20], which can offer extremely high flexibility and can endure100% strain [21]. Though we have successfully observed andcharacterized Brillouin scattering in POFs [22]–[28], the power
is quite low because of the large core, multimode nature, andrelatively high propagation loss. For more detailed characterization, Brillouin measurements should be performed with amaximal signal-to-noise (SN) ratio.
In general, Brillouin scattering can be classified into two
types: spontaneous scattering (with lower scattering power) andstimulated scattering (with higher scattering power). To date,stimulated Brillouin scattering (SBS) has been detected by theso-called pump-probe technique [29]–[32], which measures thechange in scattering power as a function of the frequency difference between the pump and probe lightwaves. Because lock-in
detection can be employed relatively easily, the SN ratio of the
SBS measurement is sufficiently high even in POFs [25]. However, in measuring spontaneous Brillouin scattering (SpBS) withstandard self-heterodyne detection, lock-in detection cannot beeasily applied. As a result, the peculiar structure of the noise
floor overlaps the Brillouin gain spectrum (BGS) and prevents
the correct detection of the BGS and/or the Brillouin frequency
shift (BFS). By compensating the noise floor of an electrical
spectrum analyzer (ESA), the SN ratio was improved to someextent [33]. However, the SpBS measurement still suffers fromthis noise floor structure, especially when the polarization state
is not precisely optimized. Clarifying the origin of this noise will
enhance not only the SN ratio of the SpBS measurement (especially in POFs) but also the performance of self-heterodynebased Brillouin sensors, such as Brillouin optical correlationdomain reflectometry (BOCDR) [10], [13], [33], [34].
In this study, we observe an interference pattern with a simple Mach–Zehnder interferometer consisting of an ESA and anarrowband light source, which is generally employed to observe the BGS, and show that the interference pattern expands
the frequency range corresponding to the BFS in silica singlemode fibers (SMFs; 11 GHz at 1.55 μm). We then experimentally prove, using a silica SMF and a POF as the fiber
under test (FUT), that the aforementioned distinctive noise in
the SpBS measurement with an unoptimized polarization state
originates from interference between the reference light andFresnel-reflected light. We also show that this noise can be almost completely suppressed by employing a delay line that is0733-8724 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications standards/publications/rights/index.html for more information.

MIZUNO et al.: FIBER-OPTIC INTERFEROMETRY USING NARROWBAND LIGHT SOURCE AND ELECTRICAL SPECTRUM ANALYZER:

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longer than the coherence length of the light source and by artificially applying a considerable loss near the open end of the
FUT.
II. PRINCIPLES
A. Brillouin Scattering
SpBS in optical fibers is caused by acoustic-optical interaction, generating backscattered Stokes light, the spectrum ofwhich is referred to as the BGS [1]. The central frequency of the
BGS shifts downward relative to the incident pump frequency
by an amount termed as BFS. At 1.55 μm, the BFS is reported
as 10.8 GHz for silica SMFs [1] and 2.8 GHz for perfluorinated graded-index POFs [22]. The BFS depends on strain andtemperature [11], [12], [23], [26], which is the basic operating
principle of Brillouin-based distributed sensors, such as Brillouin optical time-, frequency-, and correlation-domain analysis (BOTDA [6], [35], [36], BOFDA [8], [37], [38], BOCDA[9], [39], [40], respectively) and Brillouin optical time- andcorrelation-domain reflectometry (BOTDR [7], [41], [42] andBOCDR [10], [13], [33], [34], respectively).
Because the BFS values in optical fibers are not sufficiently
smaller than the frequency resolution of a typical optical spectrum analyzer (OSA; 10 GHz), an ESA is often employedwith a self-heterodyne scheme to observe the BGS with a muchhigher frequency resolution. However, self-heterodyne detection is known to broaden the observed BGS by double theamount of the 3-dB linewidth of the pump light [43], leading topossible incorrect measurements. Therefore, a light source withan output linewidth sufficiently narrower than the linewidth of
the BGS should be utilized. The Brillouin linewidth is typically30 MHz in silica SMFs [1] and 100 MHz in POFs [22] at
1.55 μm (depending on the pump power [24], [43]). Therefore, alaser diode (LD) with 1-MHz linewidth is suitable. Moreover,the Brillouin scattering power measured by self-heterodyne detection is highly dependent on the relative polarization state
between the Stokes light and reference light, which sometimes
leads to unstable measurements [33], [44], [45].
B. Fiber-Optic Interferometry
Fiber-optic interferometry can be used as a self-heterodyne
detection system for SpBS measurement. In general, when the
output of a broadband light source is injected into an optical interferometer, its transmission spectrum exhibits an interference
pattern with periodic peaks and dips. Suppose the interferometeris composed of one type of fiber. Then, the period of the interference pattern Δf is inversely proportional to the difference
between the two path lengths ΔL as
c
,
(1)
Δf =
nΔL
where c is the velocity of light in vacuum and n is the refractive
index (of the fiber core in this case). Therefore, by measuring
Δf, the change in either refractive index or path length canbe derived. To date, a number of studies have been publishedrelating to sensing based on this principle [46]–[50]. However,these studies commonly used broadband light sources (suchFig. 1. Schematic of Mach–Zehnder interferometer used in the experiment,
containing the distributed-feedback laser diode (DFB-LD), ESA, PC, and PD.

Fig. 2. (a) Observed expansion of the interference pattern. Each electrical
spectrum was measured at a driving current of 11.0 (black), 11.1 (purple), 11.2
(dark blue), 11.4 (light blue), 11.9 (green), 12.7 (yellow), 13.8 (orange), and16.2 mA (red). (b) Corresponding optical spectra of the LD output.

as super continuum sources, amplified spontaneous emission
outputs, super luminescent light emitting diodes, and sweptsource lasers) and OSAs. No reports have been provided on theuse of narrowband light sources and ESAs.
III. EXPERIMENTS
A. Mach–Zehnder Interferometry
To verify the operation of the fiber-optic interferometer using a narrowband light source and an ESA, we implemented astandard Mach–Zehnder interferometer (see Fig. 1). We used a
distributed-feedback LD (NX8562LB, NEC; 1.55 μm; 10 mW
output) with a 3-dB linewidth of 1 MHz, corresponding to acoherence length of approximately 200 m. The laser output was
divided and guided into two arms; a polarization controller (PC)was inserted in one arm to control the relative polarization state,while a delay line was inserted in the other arm to control thepath-length difference. The two beams were then coupled, converted into an electrical signal with a photo diode (PD), andobserved with an ESA.
Fig. 2(a) shows the measured electrical spectra when the LD
driving current was gradually increased around its threshold(11 mA). The path-length difference ΔL was 1.15 m. Theinterference pattern expanded to a larger frequency range as
the LD output of the optical spectrum increased, as shown in
Fig. 2(b).
Fig. 3(a)–(d) show the measured interference patterns around
2 GHz when the path-length difference ΔL was 0.51 m, 1.15 m,
11.2 m, and 1 km, respectively. The polarization state was adjusted to maximize the interferometric visibility (or amplitudeof the interference pattern). The frequency intervals of the interference patterns were 401.1 MHz (ΔL = 0.51 m), 178.6 MHz(ΔL = 1.15 m), and 18.2 MHz (ΔL = 11.2 m). The theoretical interval for ΔL = ∼ 1 km, which is 0.2 MHz, was not

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Fig. 5. Measured interference pattern around 11 GHz when the path-length
difference was 1.15 m. The polarization state was adjusted to maximize thevisibility.
Fig. 3. Measured interference patterns around 2 GHz when the path-length
difference was (a) 0.51 m, (b) 1.15 m, (c) 11.2 m, and (d) 1 km. The polarization
state was adjusted to maximize the visibility. The additional trend in (a) indicatesthe spectrum when the polarization state was adjusted to minimize the visibility.

Fig. 6. Schematic of the self-heterodyne-based experimental setup for Brillouin measurement, containing the distributed-feedback laser diode (DFB-LD),
EDFAs, ESA, PCs, and PD.

Fig. 4. Frequency interval plotted as a function of the path-length difference.
The circles are measured data, and the blue line is a theoretical line calculatedusing (1).

observed regardless of the polarization state, because ΔL wasmuch longer than the coherence length (200 m). Fig. 3(a) also
displays the electrical spectrum measured when the polarization
state was adjusted to minimize the visibility. The pattern was nolonger observed. Thus, the interference pattern was almost completely suppressed by optimizing the polarization state; however,
the emergence of the interference pattern cannot be avoided inmany practical cases, such as cases where adaptive polarization
control cannot be performed or where polarization diversity [44]or polarization scrambling [33], [45] is employed.
The relationship between the frequency interval and the pathlength difference was in extremely good agreement with thetheoretical calculations (see Fig. 4). This result implies thatthe basic operation of fiber-optic interferometry (such as themeasurement of path-length difference) can be achieved in the
spectral domain by using a narrowband light source (including a

cost-effective DFB-LD) and an ESA. The applicable frequencies
range from several megahertz (corresponding to the coherence
length of the light source) to several gigahertz (corresponding to
the upper limit of the measurable frequency of a standard ESA).
This method is free from errors caused by power fluctuations,leading to higher stability than that of the well-known powerdomain fringe-counting techniques using a narrowband lightsource and an optical power meter (or an oscilloscope) [51]–[53].
Fig. 5 shows the interference pattern near 11 GHz for ΔL =1.15 m. The interference pattern expands well beyond the range
where the BGS in a standard silica SMF is observed at 1.55 μm.
Therefore, this interference pattern should have a significant
effect on the Brillouin measurement when the polarization state
is not optimized.
B. Brillouin Measurement in Silica SMFs
First, we investigated the influence of the interference patternon the Brillouin measurement using a 13.2-m-long silica SMF as
the FUT. The experimental setup used in the experiment, which
is based on self-heterodyne detection, is depicted in Fig. 6.
All optical paths were composed of silica SMFs. The DFB-LD
output (same as that described in the preceding section) was
divided into two beams: one was used as pump light, and the

MIZUNO et al.: FIBER-OPTIC INTERFEROMETRY USING NARROWBAND LIGHT SOURCE AND ELECTRICAL SPECTRUM ANALYZER:

Fig. 7.

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Definition of the “pump path” when a silica SMF was used as the FUT.

Fig. 9. Measured electrical spectra around 10.8 GHz when the path-length
difference was 3.05 m before (green) and after (black) the bending loss wasapplied near the FUT end. The polarization state was adjusted to maximize(solid) and minimize (dotted) the Brillouin peak power.

Fig. 8. Measured electrical spectra around 10.8 GHz when the path-length
difference was (a) 0.20 m, (b) 1.15 m, (c) 3.05 m, and (d) 1 km. In (a)–(c),the polarization state was adjusted to maximize (colored) and minimize (black)the interferometric visibility. In (d), the polarization state was adjusted for thehighest (colored) and lowest (black) noise floor.

other was used as reference light. The pump light was amplified
to 20 dBm with an erbium-doped fiber amplifier (EDFA) andinjected into the FUT, generating backscattered Stokes light.
The reference light was amplified to 3 dBm with another EDFA
to enhance the SN ratio and coupled with the Stokes light. The
optical beat signal was converted into an electrical signal andobserved with an ESA as BGS. The relative polarization state
between the Stokes light and the reference light was adjustedwith two PCs. A delay line was inserted in the reference path tocontrol the path-length difference ΔL between the pump pathand reference path. Here, we define the “pump path” as the pathalong which the light Fresnel-reflected at the end of the FUT
propagates (see Fig. 7).
Fig. 8(a)–(d) show the measured electrical spectra around10.8 GHz when the path-length difference ΔL was 0.20 m,
1.15 m, 3.05 m, and 1 km, respectively. The spectral peakobserved at 10.87 GHz is the BGS in the silica SMF [1]. In
Fig. 8(a)–(c), the polarization state was adjusted to maximize
and minimize the interferometric visibility. In Fig. 8(d), the polarization state was adjusted for the highest and lowest noise
floor because the height of the noise floor is positively corre-

lated with the visibility in this experiment. In Fig. 8(a), the BGS
was detected even though it overlapped the interference pattern(its dip can be observed at 10.65 GHz) because the theoretical frequency interval of 1.0 GHz was much broader than the
Brillouin linewidth (though the SN ratio was lower). In Fig. 8(b)and (c), the frequency intervals were 178.3 and 67.3 MHz, respectively, overlapping the BGS and resulting in erroneous BGS
measurement. These interference patterns were drastically mitigated by properly adjusting the polarization state. In Fig. 8(d),as 1 km was much longer than the coherence length of theLD, the interference pattern was not observed regardless of thepolarization state.
One method for suppressing the influence of the interference
pattern is to weaken the Fresnel reflection at the FUT end. Fig. 9shows the measured electrical spectra for ΔL = 3.05 m before
and after a bending loss (>60 dB; Fresnel reflection reduced by>120 dB) was applied near the FUT end. Using this method,
the interference pattern was almost completely diminished, andthe polarization state adjustment was the sole contribution to theBrillouin peak power, which is an ideal situation for Brillouinmeasurement.
C. Brillouin Measurement in POFs
Next, we performed similar experiments using POF as the
FUT. The same experimental setup (see Fig. 6) was employed.
The pump power was amplified to 25 d Bm, and the reference power was 3 dBm. The POF used in the experiment was a
3.57-m-long perfluorinated graded-index POF with a core diameter of 50 μm, a core refractive index of 1.35, an outer diameterof 500 μm, a numerical aperture of 0.185, and a propagation lossof 250 dB/km at 1.55 μm. Both ends of the POF were cut perpendicular to the fiber axis, and one end was butt-coupled [22]to the pigtail (silica SMF) of the optical circulator. As shown in
Fig. 10, Fresnel reflection occurs at two points: the SMF/POF
interface and the open end of the POF. Considering that the light,
which is Fresnel-reflected at the open end, drastically attenuates

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Fig. 10.

JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 24, DECEMBER 15, 2014

Two possible pump paths when a POF was used as the FUT.

Fig. 11. Measured electrical spectra around 2.8 GHz when the path-length
difference was (a) 0.05 m, (b) 4.15 m, (c) 8.30 m, and (d) 1 km. The polarization
state was adjusted so that the visibility was maximized (colored) and minimized(black).

when it returns from the POF to the silica SMF because of theserious mode-field diameter mismatch [22], we define the main
“pump path” (used to calculate the path-length difference ΔL)
as the path along which the Fresnel-reflected light propagates at
the SMF/POF interface.
Fig. 11(a)–(d) show the measured electrical spectra around
2.8 GHz when ΔL was 0.05 m, 4.15 m, 8.30 m, and 1 km,
respectively. The spectral peak observed at 2.81 GHz is the
BGS in the POF [22]. The polarization state was adjusted tomaximize and minimize the visibility. In Fig. 11(b) and (c), themeasured frequency intervals were 49.3 and 24.4 MHz, respectively, which overlapped the BGS in a manner analogous to thesilica SMF case. However, unlike the silica SMF case, weakinterference patterns were observed even for ΔL = 0.05 m (seeFig. 11(a); the theoretical frequency interval is 4.1 GHz) andΔL = ∼ 1 km [see Fig. 11(d); beyond the coherence length].
The measured frequency intervals for both path lengths were31.8 MHz, which corresponds to two lengths of the 3.57-mlong POF (n = 1.35). Therefore, we conclude that these interference patterns were caused by the interference between twopump waves Fresnel-reflected at the SMF/POF interface and at
the open end of the POF.

Fig. 12. Measured electrical spectra when ΔL was (a) 0.05 m and (b) 1 km,
after the open end of the POF was angled-cut. The polarization state was adjusted
so that the noise floor was highest (colored) and lowest (black).

Subsequently, we cut the open end of the POF at an angle
to suppress the Fresnel reflection (note that applying a highbending loss to POFs is difficult [20]), and we measured theelectrical spectra when ΔL was 0.05 m and 1 km, as shownin Fig. 12(a) and (b), respectively. The polarization state wasadjusted for the highest and lowest noise floor. Even when thenoise floor was high, the interference patterns were greatly suppressed. The polarization state adjustment was not influenced
by the interference pattern. However, to maximize the SN ratio of the BGS measurement (i.e., the difference between the
Brillouin peak power and the noise floor), the suppression of
the Rayleigh noise (tail of the Rayleigh-scattered light spectrum) is more important than the enhancement of Brillouin peak
power [54]. Note that Rayleigh noise is a phenomenon unique
to POFs with a low BFS. As the polarization state for maximal
Brillouin peak power is generally different from that for minimal Rayleigh noise, the optimized BGS with the highest SN
ratio in Fig. 12(a) differs from that in Fig. 12(b).
D. Discussion
When the polarization state cannot be adaptively optimized,
the interference pattern emerges as a serious problem in observing the BGS. In the case of silica SMFs, the interference pattern
can be mitigated either by adjusting the fiber length difference
between the pump and reference paths or by applying a highbending loss near the SMF end (or by cutting the end at anangle). When the former method is used, a delay line, which
is longer than the coherence length of the light source, should
be inserted into one of the paths because shortening the pathlength difference requires considerable effort. In BOCDR, we
often insert a long delay line in the reference path to control
the order of the correlation peak [10], [34], which is also desirable from the aspect of SN ratio enhancement. On the other
hand, in the case of POFs, the interference pattern cannot be
sufficiently suppressed by adjusting the path-length difference
or by suppressing the Fresnel reflection at the open end; these
two measures must be taken simultaneously. The suppressionof the Fresnel reflection at the open end can be achieved either
by cutting the end at an angle, immersing the end into indexmatching oil or water (n = ∼ 1.32 at 1.55 μm [55]), or using asufficiently long POF to attenuate the Fresnel-reflected light.

MIZUNO et al.: FIBER-OPTIC INTERFEROMETRY USING NARROWBAND LIGHT SOURCE AND ELECTRICAL SPECTRUM ANALYZER:

For the BGS measurement, the polarization state adjustment
has three roles: maximization of the Brillouin peak power, minimization of the Fresnel-induced interference pattern, and minimization of the Rayleigh noise (especially in the case of POFs).
These three behaviors are independent of one another; for instance, a minimized interference pattern generally does not leadto a maximized Brillouin peak power. Therefore, by suppressing the influence of the interference pattern using one of theaforementioned methods, the polarization state can be adjusted
solely to maximize the Brillouin peak power in silica SMFs or
to minimize the Rayleigh noise in the case of POFs [54]. This
interference pattern suppression results in BGS and BFS detection with the highest SN ratio, even when the polarization statecannot be arbitrarily adjusted.
IV. CONCLUSION
We clarified the origin of the distinctive noise in SpBS measurements with an unoptimized polarization state and presented
a strategy for detecting the BGS with as high an SN ratio as
possible. First, using a Mach-Zehnder interferometer consisting of an ESA and a narrowband light source, we demonstrated an interference pattern that expanded well beyond the11 GHz range. Then, using a silica SMF and a POF as the
FUT, the distinctive noise in the SpBS measurement was shown
to originate from the interference between the reference lightand the Fresnel-reflected light. Moreover, this noise is almost
completely suppressed by inserting a delay line longer than thecoherence length of the light source and by applying a considerable loss near the open end of the FUT. We believe thatthese results will be a significant guideline for characterizing theBrillouin properties in various fibers with a high SN ratio as
well as for developing high-performance fiber-optic Brillouindevices and systems in the near future.
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Yosuke Mizuno (M’14) was born in Hyogo, Japan, on October 13, 1982. Hereceived the B.E., M.E., and Dr.Eng. degrees in electronic engineering from the
University of Tokyo, Tokyo, Japan, in 2005, 2007, and 2010, respectively.
From 2007 to 2010, he was engaged in Brillouin optical correlation-domainreflectometry for his Dr.Eng. degree at the University of Tokyo. From 2007 to
2010, he was a Research Fellow (DC1) of the Japan Society for the Promotionof Science (JSPS). From 2010 to 2012, as a Research Fellow (PD) of JSPS,
he worked on polymer optics at the Tokyo Institute of Technology, Japan. In
2011, he stayed at BAM Federal Institute for Materials Research and Testing,
Germany, as a Visiting Research Associate. Since 2012, he has been an Assistant Professor with the Precision and Intelligence Laboratory, Tokyo Instituteof Technology, where he is active in fiber-optic sensing, polymer optics, andultrasonics.
Dr. Mizuno received the Funai Research Award 2010, the Ando Incentive
Prize for the Study of Electronics 2011, the NF Foundation R&D Encouragement Award 2012, and the Challenging Research Award 2013. He is a memberof the Japanese Society of Applied Physics and the Institute of Electronics,
Information, and Communication Engineers of Japan.

Neisei Hayashi was born in Gunma, Japan, on April 13, 1988. He received
the B.E. degree in advanced production from the Gunma National College
Technology (GNCT), Gunma, Japan, in 2011, and the M.E. degree in electronicengineering from the Tokyo Institute of Technology, Tokyo, Japan, in 2013.
Since 2013, he has been working toward the Dr.Eng. degree in polymer optics
with the Tokyo Institute of Technology. From 2008 to 2010, he studied a ringwandering phenomenon for his B.E. degree at the GNCT. From 2011 to 2013, heworked on nonlinear optics in polymers for his M.E. degree at Tokyo Institute ofTechnology. In 2013, he became a Research Fellow (DC1) of the Japan Society
for the Promotion of Science (JSPS)His research interests include fiber-optic
sensing, polymer optics, and ultrasonics.
Mr. Hayashi received the TELECOM System Technology Award for Student
2012. He is a member of the Japanese Society of Applied Physics and theInstitute of Electronics, Information, and Communication Engineers of Japan.

Kentaro Nakamura (M’00) was born in Tokyo, Japan, on July 3, 1963. Hereceived the B.E., M.E., and Dr.Eng. degrees from Tokyo Institute of Technology, Tokyo, Japan, in 1987, 1989, and 1992, respectively. Since 2010, he has
been a Professor with the Precision and Intelligence Laboratory, Tokyo Instituteof Technology. His research interests include applications of ultrasonic waves,measurement of vibration and sound using optical methods, and fiber-optic
sensing.
Dr. Nakamura received the Awaya Kiyoshi Award for encouragement ofresearch from the Acoustical Society of Japan (ASJ) in 1996 and the Best Paper Awards from the Institute of Electronics, Information and Communication
Engineers (IEICE) in 1998 and from the Symposium on Ultrasonic Electronics
in 2007 and 2011. He also received the Japanese Journal of Applied Physics
Editorial Contribution Award from the Japan Society of Applied Physics (JSAP)in 2007. He is a member of the ASJ, the JSAP, the IEICE, and the Institute ofElectrical Engineers of Japan.