response and gain [see gain in Fig. 2(a), the smaller corresponds

to F5 that has less fiber length]. To prove the tailoring capacity

of the device, the spectral response from the first four fibers is

converted in a ‘‘W like shape’’ by a proper tuning of the tem-

perature. In Figure 2(b), the Brillouin spectra from each fiber

and their superposition response (continuous line) when F1 and

F2 are at 58�C and F3–F5 at 20�C are plotted. The first two

BFS peaks, i.e., F1 and F2 are moved to the right and hence

peaks mB2 and mB3 become one, which is broader than the origi-

nal peak F3. The resultant second peak is twice the bandwidth

of peak 2 or 3 (30 MHz at 3 dB). The reject bands are placed at

10.756 GHz and 10.834 GHz, respectively, from the pump

wave. A third reject band, that is the gap between mB4 and mB5,has 170 MHz of bandwidth and centre at 10.965 GHz from the

pump [Fig. 2(b)].

By varying the temperature in the SBAD, the reject band or

the bandwidth is tuned, then a specific behavior in the spectral

response of the device is obtained. The Brillouin gain distribu-

tion from F1 to F4 at temperature variations between 54�C and

64�C is depicted in Figure 3. Figure 4 shows the bandwidth

value between mB2 and mB3 as a function of the increment in

temperature that is similar to the dependence of BFS on the

temperature [1].

4. CONCLUSIONS

An optical active device based on the composition of the Bril-

louin gain spectral response is presented. It is made by the

proper connection of serial and parallel pieces of fiber. The

fibers have different lengths, optical and geometrical characteris-

tics, in addition to the tuning effect of the temperature that con-

fers a great flexibility and several degrees of freedom to reach

the required Brillouin spectral response. We have developed

devices with Brillouin spectrum responses that can be used as

narrow optical filters, e.g., Brillouin optical amplifiers and nar-

row comb lasers that are the more significance. The proposed

method can be a powerful tool to use in all-optical devices to

handle optical signals in optical communications and signal

processing.

ACKNOWLEDGMENTS

This work was supported by the Spanish Ministry of Education

under Grant BES-2005-8287 of project TEC2007-67987-CO2-01.

REFERENCES

1. J.M. Lopez-Higuera (Ed.), Handbook of optical fiber sensing tech-

nology, Wiley, New York, 2002.

2. J. Pelayo, D. Subias, F. Villuendas, R. Alonso, I. Garces, C. Heras,

P. Blasco, and F. Lopez, Brillouin optical spectrum analyzer, Pat-

ent ES2207417-A1, 2002.

3. X.P. Mao, R.W. Tkach, A.R. Chraplyvy, and R.M. Derosier,

Stimulated Brillouin threshold dependence on fiber type and uni-

formity, IEEE Photon Tech Lett 4 (1992), 66–69.

4. K. Shiraki, M. Ohashi, and M. Tateda, Performance of strain-free

stimulated Brillouin scattering suppression fiber, J Lightwave Tech

14 (1996), 549–554.

5. N. Shibata, R. Waarts, and R. Braun, Brillouin-gain spectra for sin-

gle-mode fibers having pure-silica, GeO2-doped and P2O5-doped

cores, Opt Lett 12 (1987), 269–271.

6. N. Yoshizawa and T. Imai, Stimulated Brillouin scattering suppres-

sion by means of applying strain distributed to fiber with cabling,

J Lightwave Tech 11 (1993), 1518–1522.

7. J. Hansaryd, F. Dross, M. Westlund, and P.A. Andrekson, Increase

of the SBS threshold in a short highly nonlinear fiber by applying

a temperature distribution, J Lightwave Tech 19 (2001),

1691–1697.

8. C.A. Galindez, F.J. Madruga, A. Ullan, and J.M. Lopez-Higuera,

Technique to develop active devices by modifying Brillouin gain

spectrum, Electron Lett 45 (2009), 637–638.

9. G.P. Agrawal, Non linear fiber optics, 3rd ed., Academic Press,

Orlando, FL, 2001.

VC 2010 Wiley Periodicals, Inc.

OPTICAL FIBER ARTERIAL PULSEWAVE SENSOR

Sunghoon Eom,1 Jaehee Park,1 and Jonghun Lee21 Department of Electronic Engineering, Keimyung University,1000 Sindang-Dong, Dalseo-Gu, Daegu 704-701, South Korea;Corresponding author: jpark@kmu.ac.kr2 Division of Advanced Industrial Science and Technology, DGIST,Daegu Technopark Venture, Gongdanbuk2gil, Dalseo-Gu, Daegu704-230, Korea

Received 24 August 2009

ABSTRACT: An optical fiber arterial pulse wave sensor is proposedusing an in-line Michelson interferometer that is a hollow optical fiberspliced to a single-mode fiber at one end and cleaved at the other end.

The proposed optical fiber arterial pulse wave sensor consists of an

Figure 4 Bandwidth between mB2 and mB3 as a function of the temper-

ature. Measured data (circles) and theoretical approximation (line)

Figure 3 Measured BGS curve setting F1 and F2 at 54�C (line), 56�C(line-*), 58�C (line-h), 60�C (line-l), 62�C (line-D), and 64�C (line-*)

and F3–F5 at 20�C

1318 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 6, June 2010 DOI 10.1002/mop

in-line Michelson interferometer and steel reinforcement enclosed in a

heat-shrinkable tube. The sensor was directly attached onto a wrist andsignals corresponding to arterial pulse waves successfully obtained. The

signal-to-noise ratio of the sensor signals was better than 20 dB.VC 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:

1318–1321, 2010; Published online in Wiley InterScience

(www.interscience.wiley.com). DOI 10.1002/mop.25200

Key words: arterial pulse waves sensor; in-line Michelson

interferometer; optical fiber sensor

1. INTRODUCTION

Oriental doctors use the palpation of the arterial pulse as a diag-

nostic tool when examining patients. Thus, great attention has

been paid to the character of the normal arterial pressure pulse

wave and to the changes that occur as a result of disease, such

as diabetes, obesity, hypertension, and heart disease [1].

As a result, various arterial pulse wave sensors have already

been developed, including a noninvasive pulse meter using a

Doppler microwave [1], photoelectric method using an light-

emitting diode [2], and pressure meter using a compression cuff

[3]. Yet, as none of these sensors is suitable for long-term con-

tinuous monitoring, ultrasonic pulse wave sensors [4] and piezo-

electric sensors [5, 6] have been investigated for this purpose.

Although these sensors have a high flexibility, they suffer from

low elecromechanical coupling. Meanwhile, fiber-optic sensors

have recently attracted attention for biomedical applications,

because of the very high resolution and accuracy, the miniature

geometry of their sensing element, and their immunity to elec-

tromagnetic interference. As a result, a fiber-optic sensor has al-

ready been developed for use in venous occlusion plethysmogra-

phy [7], a fiber-optic pressure microsensor created for balloon

catheters [8], and a optical fiber sensor embedded into medical

textiles for healthcare monitoring [9], all of which show a high

performance. Accordingly, this article explored the use, an

optical fiber arterial pulse sensor with a high sensitivity for

continuous monitoring. The sensor was developed using an

in-line Michelson interferometer [10], which has a similar struc-

ture to a fiber Fabry-Perot interferometer [11] and twofold

higher sensitivity than a fiber Fabry-Perot sensor [12].

2. PRINCIPLE AND FABRICATION

The in-line Michael interferometer uses a hollow optical fiber

(HOF) [13] with an air-hole around the center axis, as shown in

Figure 1. The interferometer is composed of a HOF joined to a

single-mode fiber (SMF) at one end and cleaved at the other

end. The SMF is used as the guiding fiber, whereas the hollow

fiber is used as the sensing fiber. Fresnel reflections are gener-

ated at the splicing point and end of the hollow fiber. The inter-

ference fringe of the two reflections is obtained using a sensor

integrator, and the interference signal and phase shift [11] are

Ir ¼ IiðR1 þ R2 þ 2ffiffiffiffiffiffiffiffiffiffiR1R2

p Þ cosU; (1)

U ¼ 4pnLk

; (2)

respectively, where Ii is the incident light power, Ir1 is the

reflected light power at the splicing point, Ir2 is the reflected

light power at the end of the hollow fiber, R1(Ir1/Ii) is the reflec-

tance of the mirror at the splicing point, R2(Ir2/Ii) is the reflec-

tance at the other end, n is the refractive index of the fiber, L is

the length of the sensing fiber, and k is the wavelength of the

laser source. The optical fiber arterial pulse wave sensor (Fig. 2)

consists of an in-line Michelson interferometer and steel rein-

forcement enclosed in a heat-shrinkable tube. When this sensor

is directly attached and fixed onto a wrist, the mechanical dis-

placement of the skin due to the arterial pulse induces optical

length changes in the interferometer. The optical length changes

then cause a phase shift of the interference signal. The phase

shift [14] is given by

DU ¼ 4pnk

DLþ 4pLk

Dn

¼ 4pnLk

2v

E� n2½ð3v� 1Þb12 þ ðv� 1Þb11�

2E

� �apðtÞ;

(3)

where m is Poisson’s ratio, E is Young’s modulus, p(t) is the

arterial pulse signal, a is the mechanical coupling coefficient,

ej are the strain components, and bij are the elements of the

strain-optic tensor of the optical indicatrix [15] given by

D1

n2

� �i

¼X3j�1

bijej: (4)

The first-term results from the effect of the physical change

of the optical fiber length, whereas the second term represents

the strain-optic effect because of the change of the refractive

index of the fiber. This equation shows that the interference out-

put signal is a function of the arterial pulse signal.

The fabrication of the proposed optical fiber arterial pulse

wave sensor is easy and inexpensive. First, to produce an in-line

Michelson, a SMF is joined to a HOF using an electric arc

fusion splicing system. The fusion splicing system is operated at

a lower arc current and for a shorter duration than when making

a normal splice, as several splicing pulses are needed to con-

struct the proposed interferometer. After splicing, the HOF is

cleaved to the desired cavity length. Finally, the in-line Michel-

son interferometer and steel reinforcement are inserted into a

heat-shrinkable tube and the tube made to shrink by heating. To

evaluate the measurement performance, the proposed arterialFigure 1 In-line Michelson interferometer

Figure 2 Optical fiber arterial pulse wave sensor

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 6, June 2010 1319

pulse wave sensor was fabricated using a hollow fiber with a 4-

lm air-hole and a 10-mm long interferometer.

3. EXPERIMENT RESULTS

The experimental setup (Fig. 3) is used to test the proposed arte-

rial pulse wave sensor consisted of a 1.3 lm DFB laser diode

(LD), photodiode (PD), 3-dB coupler, oscilloscope, a LD drive

and temperature controller, and the proposed arterial pulse wave

sensor including an in-line Michelson interferometer. The light

emitted from the light source was propagated inside the fiber

through the 3-dB coupler to reach the arterial pulse wave sensor.

As a result of interference at the sensor, the interference signal

Figure 3 Experimental setup

Figure 4 Arterial pulse waves: (a) a 25-year-old man in normal state, (b) a 25-year-old man after light exercise, and (c) a 21-year-old woman in

normal state

1320 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 6, June 2010 DOI 10.1002/mop

was returned to the photodetector (PD), converted into an elec-

trical signal, and finally displayed on the oscilloscope. When the

sensor was fixed onto a wrist using an elastic bandage, the me-

chanical displacement of the skin surface because of the heart-

beat caused a change in the optical length of the optical fiber

sensor. The phase shift of the interference signal, resulting from

the optical length variations, was then used to monitor the arte-

rial pulse waves.

Figure 4 shows the output interference signals when the opti-

cal fiber arterial pulse wave sensor was directly attached to a

wrist using an elastic bandage. Figure 4(a) shows the arterial

pulse wave (top) of a 25-year-old man in a normal state, where

the average amplitude of the pulses was about 250 mV, and the

arterial pulse rate was around 1.163 per second. Meanwhile, Fig-

ure 4(b) shows the arterial pulse wave (middle) after light exer-

cise, where the average amplitude of the pulses was about 340

mV, and the arterial pulse rate was around 1.54 per second. The

pulse rate and amplitude relative to the blood pressure in a nor-

mal state were higher than those after light exercise. However,

the drift of the operating point of the interferometer and environ-

mental noise yielded an uncertainty in the amplitude of the arte-

rial pulse. Thus, if the operating point is fixed and the environ-

mental noise removed, the blood pressure can be measured from

the amplitude. Figure 4(c) shows the arterial pulse wave (top) of

a 21-year-old woman in a normal state. The pulse rate was about

1.67 per second and the amplitude was around 335 mV. The sig-

nal-to-noise ratio (signal amplitude after the sensor was fixed

onto the wrist/signal amplitude before the sensor was fixed onto

the wrist) of the sensor signals was better than 20 dB. In addition

to the drift effect of the operating point and environmental noise,

polarization fading and a sensor position dependency appeared.

Thus, to improve the performance of the proposed sensor, the

polarization fading and environmental noise need to be elimi-

nated, and the operating point of the interferometer fixed at one

point. To remove the sensor position dependency, a new structure

needs to be designed for the proposed arterial pulse wave sensor.

4. CONCLUSIONS

A fiber-optic arterial pulse wave sensor was developed using an

in-line Michelson interferometer. The in-line Michelson interfer-

ometer is a HOF joined to a SMF at one end and cleaved at the

other end. The optical fiber arterial pulse wave sensor consists

of an in-line Michelson interferometer and steel reinforcement

enclosed in a heat-shrinkable tube. When the fiber-optic arterial

sensor was attached onto a wrist using an elastic bandage, sig-

nals corresponding to arterial pulse waves were successfully

obtained. The signal-to-noise ratio of the sensor was better than

20 dB. However, an uncertainty was yielded due to polarization

fading, environmental noise, the operating point drift, and sensor

position dependency. Thus, for more accurate monitoring, new

technologies and a new sensor structure to eliminate these noises

need to be developed.

ACKNOWLEDGMENT

This work was supported by the Daegu Gyeongbuk Institute of

Science and Technology.

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pressure microsensor for biomedical applications, Sens Actuators A

66 (1998), 150–154.

9. A. Grillet, D. Kinet, J. Witt, M. Schukar, K. Krebber, F. Pirotte,

and A. Depre, Optical fiber sensors embedded into medical textiles

for healthcare monitoring, IEEE Sensor J 8 (2008), 1215–1222.

10. S. Kim, J. Park, and W. Han, Optical fiber Ac voltage sensor,

Microwave Opt Technol Lett 51 (2009), 1689–1691.

11. Y. Yeh, C. Lee, R. Atkins, W. Gibler, and H. Taylor, Fiber optic

sensor for substrate temperature monitoring, J Vac Sci Technol A

8 (1990), 3247–3250.

12. J. Bae, J. Park, and C. Lee, Fiber-optic interferometric temperature

sensor using a hollow fiber, Proceedings of Asia Optical Communi-

cation and Optoelectronic Conference (AOE), 2007, pp. 133–135.

13. K. Oh, S. Choi, Y. Jung, and W. Lee, Novel hollow optical fibers

and their applications in photonic devices for optical communica-

tions, J Lightwave Technol 23 (2005), 524–532.

14. G. Hocker, Fiber-optic sensing of pressure and temperature, Appl

Opt 18 (1979), 1445–1448.

15. G. Hocker, Fiber optics acoustic sensors with composite structure:

An analysis, Appl Opt 18 (1979), 3679–3683.

VC 2010 Wiley Periodicals, Inc.

Q-FACTOR INVESTIGATION OFANTENNAS OVER METAMATERIALSSUBSTRATES

S. Collardey, A. Sharaiha, W. Abdouni, C. Niamien,and A.-C. TarotInstitut d’Electronique et de Telecommunications de Rennes,UMR CNRS 6164, I.E.T.R., Groupe Antennes andHyperfrequences, Bat 11 D, Campus de Beaulieu, Universite deRennes 1, 35042 Rennes Cedex, France; Corresponding author:sylvain.collardey@univ-rennes1.fr

Received 31 August 2009

ABSTRACT: In this article, antennas over metamaterials substratesare investigated with the radiating Q factor determined by using a

time-domain method. The main objective is to illustrate theelectromagnetic behavior of this kind of complex structure by calculatingits energy budget (stored and radiated energies). An example of a patch

antenna using such materials is analyzed and experimental results arepresented. VC 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett

52: 1321–1325, 2010; Published online in Wiley InterScience

(www.interscience.wiley.com). DOI 10.1002/mop.25213

Key words: antenna; Q factor; metamaterials; efficiency

1. INTRODUCTION

The trend is to reduce more and more the size of antennas inte-

grated in the design of new communication systems. To our

knowledge, the reduction of antenna dimensions will result in a

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 6, June 2010 1321