Optics Communications 285 (2012) 4353–4358

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Optics Communications

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Analysis of multimode BDK doped POF gratings for temperature sensing

Yanhua Luo a,b,n, Wenxuan Wu a, Tongxin Wang a, Xusheng Cheng c, Qijin Zhang a,Gang-Ding Peng b, Bing Zhu c

a CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, Anhui Key Laboratory of Optoelectronic Science and Technology,

University of Science and Technology of China, Hefei, Anhui 230026, Chinab School of Electrical Engineering, University of New South Wales, Sydney 2052, NSW, Australiac Department of Electronic Engineering and Information Science, University of Science and Technology of China, Hefei, Anhui 230026, China

a r t i c l e i n f o

Article history:

Received 13 May 2012

Received in revised form

21 June 2012

Accepted 22 June 2012Available online 5 July 2012

Keywords:

Polymer optical fiber

Polymer optical fiber gratings

Multimode

Temperature sensor

BDK

18/$ - see front matter & 2012 Elsevier B.V. A

x.doi.org/10.1016/j.optcom.2012.06.051

esponding author at: School of Electrical En

ales, Sydney 2052, NSW, Australia. Tel.: þ61

1 2 93854036.

ail address: yhluo3@mail.ustc.edu.cn (Y. Luo)

a b s t r a c t

We report a temperature sensor based on a Bragg grating written in a benzil dimethyl ketal (BDK)

doped multimode (MM) polymer optical fiber (POF) for the first time to our knowledge. The thermal

response was further analyzed in view of theory and experiment. In theory, with the order of the

reflected mode increasing from 1st to 60th order, for MM silica fiber Bragg grating (FBG) the

temperature sensitivity will increase linearly from 16.2 pm/1C to 17.5 pm/1C, while for MM polymer

FBG the temperature sensitivity (absolute value) will increase linearly from �79.5 pm/1C to

�104.4 pm/1C. In addition, temperature sensitivity of MM polymer FBG exhibits almost 1 order larger

mode order dependence than that of MM silica FBG. In experiment, the Bragg wavelength shift will

decline linearly as the temperature rises, contrary to that of MM silica FBG. The temperature sensitivity

of MM polymer FBG is ranged from �0.097 nm/1C to �0.111 nm/1C, more than 8 times that of MM

silica FBG, showing great potential used as a temperature sensor.

& 2012 Elsevier B.V. All rights reserved.

1. Introduction

POFs have attracted much attention due to their flexibility,ease of use, large deformation limit, clinical acceptability forin-vivo biosensing, etc [1–9]. In addition, due to larger thermo-optic coefficient of polymers [10–13], they are much more sensitiveto temperature than those of silica fiber [14]. So temperaturesensors with POF FBGs show a much greater wavelength shift forcertain temperature change than their silica counterparts, whichwill either allow the simpler and cheaper use with lower resolu-tion, or alternatively enable the sensing of small temperaturechanges [15]. And optical devices based on POF gratings willallows device properties to be readily controlled thermally due tohigh temperature sensitivity [15]. Hence, since the first MM POFgratings inscribed in 1999 [16], gratings written in POF havereceived a lot of attentions for their unique characters [10,11,13,17–19] and numerous studies on POF gratings in the application oftemperature sensing have been conducted [10,12,15,20–22]. Most ofthem are based on single mode (SM) poly(methyl methacrylate)(PMMA) POF gratings [10,12,15,20,22,23]. The temperature sensi-tivity of the gratings in SM PMMA POF has been studied previously

ll rights reserved.

gineering, University of New

2 93855509;

.

[10,12,23], with a negative temperature coefficient of between�146 pm/1C and �360 pm/1C significantly larger in magnitudethan that observed for FBGs in silica fibers, which is around 10 pm/1C[20]. Later on, X. Chen et al. found that in the SM eccentric-coredPMMA POF gratings, the temperature sensitivity is about�50.1 pm/1C [22]. In addition, it has been found that gratings inSM PMMA microstructured optical fibers (mPOF) have a differentthermal response with a much lower magnitude of temperaturesensitivity between �52 pm/1C and �95 pm/1C [15,20]. And C.Zhang et al. found that for the few mode TOPAS cyclic olefincopolymers (TOPAS) mPOF Bragg gratings, they own the maximumpositive temperature sensitivity of �810 pm/1C, which is the largestsensitivity yet observed for POF gratings [24]. Recently, the negativetemperature sensitivity of �60 pm/1C and �36.5 pm/1C has alsobeen measured for SM TOPAS mPOF gratings [25,26].

However, the study of MM polymer FBG for temperature sensinghasn’t yet been reported although numerous MM POF gratings havealready been fabricated [16,27,28]. Whereas temperature sensors ofMM polymer FBGs will have a lot of merits of both MM FBGs andPOF gratings, such as easy coupling [27,29,30], noise reduction byfitting 410 narrow peaks instead of 1 broad envelope and correla-tion of multi-peaks of different height requires algorithm of imagerecognition [31], high temperature sensitivity, good biocompatibil-ity, etc [27,32,33]. Therefore, applications of MM polymer FBGs fortemperature sensing would be of great interest and have greatpotential. In this work, BDK doped MM polymer FBG was fabricated,

Y. Luo et al. / Optics Communications 285 (2012) 4353–43584354

and for the first time used for temperature sensing. Furthermore,temperature sensing properties of such MM polymer FBG wereinvestigated systematically in theory and experiment.

2. Experiments

2.1. POF fabrication

POF doped with BDK was fabricated according to the previousreport [34]. Fiber parameters and grating fabrication conditionsare listed in Table 1.

2.2. POF gratings fabrication

According to the previous work [35], POF gratings werefabricated in a short section of photosensitive POF doped withBDK with sagnac ring system. After 4 min 69 mW/cm2 355 nmillumination, the reflection spectrum of MM polymer FBG formedas shown in Fig. 1. The Bragg wavelength of the maximumreflection mode is around 1567.8 nm, the reflection intensity isabout 14.4 dB above the noise level. The full-width at half-maximum (FWHM) of the reflection peak was 0.13 nm. Further-more, the effective refractive index of the core could be deducedabout 1.477.

3. Thermal response of MM polymer FBG in theory

According to the Bragg reflection condition, the index mod-ulation period L and the propagation constants of forward (b1)

Table 1Description of grating formation process.

POF specification Grating formation process

Cladding (methyl methacrylate (MMA)–

butyl acrylate (BA): 69/31 wt%)

355 nm frequency-tripled Nd:YAG

pulse laser frequency: 10 Hz

Core (MMA–BA–BDK: 62.4/28/9.6 wt%) Pulse width: 6 ns

Index difference: �0.011 Average power intensity:

69 mW/cm2

Dfiber, � 300 mm Grating length: 6 mm

Dcore, �23 mm Phase mask period: 1.0614 mm

Fig. 1. Reflection spectrum of FBG in POF doped with BDK after 4 min 355 nm UV

exposure.

and backward (b2) propagating modes has the following rela-tionship [29]:

b1�b2 ¼2pL

ð1Þ

For reflection to the same mode, b1 ¼�b2 ¼ b. Then the Braggreflection condition is simplified to be b¼ p=L [29]. For graded-index MM fiber, the number of propagating modes is usuallycalculated by the following equation [29]:

M¼1

2a2k2n2

1D ð2Þ

where a is the core radius; k is the wave number; n1 is therefractive index of the core; D is the maximum relative indexdifference.

Due to the characteristics of the interfacial-gel polymerization atthe fabrication process of POF [32,36,37], the POF fabricated shouldbe a graded index POF. In the case of our MM POF, the number ofmodes is 26 at 1.57 mm. However, some of these modes have almostthe same propagation constant. Therefore, the concept of principalmode was introduced: the modes having the same propagationconstant is classified into the same principal mode [38,39].The propagation constant for the Nth principal mode is approxi-mated by the equation [29]:

b¼2pl

n1

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1�4D

Nþ1

V

rð3Þ

where V is the normalized frequency: V ¼ 2paNA=l, and NA is thenumerical aperture. In addition, for the higher order mode, theshorter the Bragg wavelength should be [29].

Here, we discuss the temperature dependence of reflectionwavelengths of our Bragg grating in graded-index MM POF.The temperature dependence of the Bragg wavelength is given bythe differentiation of Eq. (3). For simplicity, we assume that thesecond term in the square root of Eq. (3) is much smaller than theunity and that the numerical aperture is approximated by NA¼

n1

ffiffiffiffiffiffiffi2Dp

, then the following equation is obtained [29]:

dldT¼

l2

2n1L2

dLdTþ

l2

2n21L�l2ðNþ1Þð3n2�2n1Þ

2pan21

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2n1ðn1�n2Þ

p" #

dn1

dT

þl2ðNþ1Þ

2pan1

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2n1ðn1�n2Þ

p dn2

dTð4Þ

where n2 is the refractive index of the POF cladding. As listed inTable 2, dn1=dT for BDK doping core and dn2=dT for no dopingcladding are almost the same value of �1�10�4

1C�1 [14,40].As the thermal expansion coefficient is a small value of 5�10�5

1C�1 [14], the absolute value of the first term in Eq. (4) isone order less than that of the second term. In addition, as thesevalues are small, the reflection peaks have similar temperaturedependence.

Due to dn1=dT � dn2=dT , Eq.(4) can be simplified into

dldT¼

l2

2n1L2

dLdTþ

l2

2n21L

dn1

dTþ

3l2ðNþ1Þðn1�n2Þ

2pan21

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2n1ðn1�n2Þ

p dn1

dTð5Þ

where n1 is larger than n2. According to Eq. (4), with the modeorder increasing, the changing speed of the Bragg wavelengthupon the temperature change will increase linearly, that is to say,with the mode order increasing, the temperature sensitivity of thePOF gratings will increase linearly.

According to Eq. (5), when the temperature has a change DT,the Bragg wavelength will have a shift Dl, which is given by

Dl¼l2

2n1L2

dLdTþ

l2

2n21L

dn1

dTþ

3l2ðNþ1Þðn1�n2Þ

2pan21

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2n1ðn1�n2Þ

p dn1

dT

" #*DT ð6Þ

Table 2Relevant parameters of MM silica FBG and MM polymer FBG.

Parameters MM silica FBG Reference MM polymer FBG Reference

Core diameter (mm) 50 [29] 23 This work

Core index 1.4709 [29] 1.477 This work

Grating period (nm) 534 [29] 530.7 This work

Operating wavelength (mm) 1.55 [29] 1.57 This work

Index difference 0.0137 [29] 0.011 This work

Thermal optic coefficient (1C) 1�10�5 [29] �10�10�5 [14]

Thermal expansion coefficient (1C) 0.55�10�6 [29] 5�10�5 [14]

Fig. 2. Relationship between the temperature sensitivity of MM silica FBG and

MM polymer FBG, and the order of the reflected mode.

Fig. 3. Dependence of the Bragg wavelength shift upon temperature change for

1st order mode of MM silica FBG and MM polymer FBG.

Y. Luo et al. / Optics Communications 285 (2012) 4353–4358 4355

Substituting the parameters in Table 2 into Eq. (5), the tempera-ture sensitivity of MM silica and polymer FBG can be given by

dldT¼ 0:01613þ2:2� 10�5

ðNþ1Þ ð7Þ

and

dldT¼�0:07862�4:2� 10�4

ðNþ1Þ ð8Þ

respectively, where the value of positive and negative represents theshift direction of the Bragg wavelength when the temperaturechanges. Compared with Eqs. (7) and (8), it is obviously shown thatthe temperature sensitivity of MM polymer FBG is the negativevalue while that of MM silica FBG is the positive value, indicatingwith the temperature increasing, the Bragg wavelength of MMpolymer FBG blueshifts while that of MM silica FBG redshifts.In addition, for the same order of reflected mode, the temperaturesensitivity of MM polymer FBG is almost 5 times higher than that ofMM silica FBG. Furthermore, the mode order influence upon thetemperature sensitivity of MM polymer FBG is almost 1 order largerthan that of MM silica FBG.

Fig. 2 shows the relationship between the temperature sensi-tivity and the order of the reflected mode for both MM silica FBGand MM polymer FBG. Seen from Fig. 2, the temperature sensi-tivity of MM polymer FBG presents the negative value and that ofMM silica FBG the positive value. With the order of the reflectedmode increasing from 1st to 60th order, for MM silica FBG thetemperature sensitivity will increase linearly from 16.2 pm/1C to17.5 pm/1C, while for MM polymer FBG the temperature sensi-tivity will increase linearly from �79.5 pm/1C to �104.4 pm/1C.Compared with MM silica FBG, MM polymer FBG exhibits evidentlymode order dependence.

Combining Eqs. (5)–(8), when the temperature has a changeDT, the shift (Dl) of the Bragg wavelength for MM silica FBG and

MM polymer FBG can be given as

Dl¼ ½0:01613þ2:2� 10�5ðNþ1Þ�DT ð9Þ

and

Dl¼ ½�0:07862�4:2� 10�4ðNþ1Þ�DT ð10Þ

respectively. That means that if the temperature change is thesame, the Bragg wavelength of MM silica FBG and MM polymerFBG shifts in opposite direction. For the same order of thereflected mode, the shift value of MM polymer FBG is almost5 times larger than that of MM silica FBG. Furthermore, the modeorder influence upon the shift of the Bragg wavelength of MMpolymer FBG is almost 1 order larger than that of MM silica FBG.

Take the 1st order mode for example, as shown in Fig. 3. Fig. 3shows that the shift of the Bragg wavelength vs the temperaturechange for 1st order mode of MM silica FBG and MM polymerFBG. Seen from Fig. 3, the 1st order Bragg wavelength of MMpolymer FBG will blueshift while that of MM silica FBG redshiftwhen temperature increases. When the temperature changeincreases from 0 to 60 1C, the shift of the 1st order Braggwavelength of MM silica FBG will increase linearly from 0 to1.0 nm, while that of MM polymer FBG will decrease linearly from0 to �4.8 nm, showing larger shift compared with MM silica FBG.

4. Thermal response of MM polymer FBG in experiment

The thermal response of MM polymer FBG was performedwith the experimental setup similar to the report before [23].Both ends of MM polymer FBG were sticked using epoxy glue

Fig. 5. (a) Peak intensity vs temperature for modes a, b, c, and d. (b) The

relationship between the Bragg wavelength of modes a, b, c and d, and

temperature, and its corresponding linear fitting curve.

Y. Luo et al. / Optics Communications 285 (2012) 4353–43584356

vertically on a metal panel. Then the sensing part of MM polymerFBG was put into the oven, whose temperature was controlled bythe PID method. The accuracy of the temperature measurementwas 71 1C, and it took about 2 min for the heating system toreach the desired temperature and 5 min for the stabilizing of thetemperature. The reflection spectra of MM polymer FBG wererecorded by an optical spectrum analyzer (Agilent AQ6317C),when the thermal test was carried out. A tunable laser source(ANDO AQ4321D) was adopted for MM polymer FBG character-ization, which was launched into the POF through a 3 dB Y-typesilica fiber coupler.

Change in the Bragg grating spectra was recorded as tempera-ture was changed (Fig. 4). The solid line and dash line in Fig. 4represent the reflection spectra at 16.81C and 23.41C, respectively.(The reason why the reflection spectra in Fig. 2 and Fig. 4 changedis attributed to both the reset of the coupling end and differenceof the operating temperature.) The spectra had more than 10peaks. Thereinto, four peaks a, b, c and d are chosen forcomparison, which are at 1570.537, 1569.485, 1568.463 and1567.547 nm, respectively. Similarly to the thermal response ofSM POF [23], as the temperature increases to 23.4 1C, thespectrum moves to the left, where the shift is about 0.6 nm. Thenpeaks a, b, c and d changed into a’, b’, c’ and d’, which shows thatnot only the Bragg wavelength shifts but also the peak intensitychanges. The former change is mainly due to the temperature-caused refractive index or physical length change [41], while thelatter changes in the amplitude of different reflected modes is dueto the displacement of the peak wavelength of the reflectedmodes [42,43] as well as the drift of the coupling end.

The experimental results of the reflection intensity and theBragg wavelength for the modes of a, b, c and d in MM polymerFBG has been given in Fig. 5 (a) and (b), respectively. Seen fromFig. 5(a), with the temperature increasing, the reflection inten-sities for the modes of a, b, c and d fluctuate from 7.0 to 12.4 dB,6.4 to 15.3 dB, 8.0 to 16 dB and 2.9 to 13 dB due to the displace-ment of the peak wavelength of the reflected modes [42,43] aswell as the drift of the coupling end. Seen from Fig. 5(b), the Braggwavelengths decrease with the temperature increasing. In addi-tion, the thermal response of the Bragg wavelengths that arestudied using the linear regression can be expressed as

la ¼�0:097Tþ1572:210 ðfor mode aÞ

lb ¼�0:104Tþ1571:286 ðfor mode bÞ

lc ¼�0:105Tþ1570:247 ðfor mode cÞ

ld ¼�0:111Tþ1569:488 ðfor mode dÞ ð11Þ

Fig. 4. Reflection spectra of MM polymer FBG at 16.8 1C and 23.4 1C.

where la, lb, lc and ld refer to the Bragg wavelengths of modes a,b, c and d at different temperatures. The adjusted R-squaredvalues are 0.998, 0.997, 0.999 and 0.997, showing good linearproperty of regression. The rms deviations of the data are 0.0615,0.0744, 0.0454 and 0.0932 nm for modes a, b, c and d, resulting inthe rms temperature error of 0.63, 0.72, 0.43 and 0.84 1C over thewhole measurement range as implied by Eq. (11), respectively.Seen from Eq. (11), the temperature sensitivity of the modes a, b,c and d are �0.097, �0.104, �0.105 and �0.111 nm/1C, respec-tively. The temperature sensitivity in experiment is more than8 times that of MM silica FBG [29], showing great potentialused for temperature sensing. In addition, that the valuesobtained from the experiment are not completely matched withthe values from the theory is due to the difference in materials,mode order, etc.

As for the higher order mode, the shorter the Bragg wave-length should be [29], so the order of the modes a, b, c and dincreases in turn. Therefore, the higher the mode, the highertemperature sensitivity it is, which is in good accordance with theresult in the above theory. Furthermore, although the value fordifferent modes are different, the difference is very small, which isless than 13%. So for reflection to the neighboring modes, thetemperature sensitivity should be more close to each other, inwell accordance with the theory results in Fig. 2.

Fig. 6. Dependence of the Bragg wavelength shift upon temperature change in

BDK doped MM polymer FBG for modes a, b, c and d.

Y. Luo et al. / Optics Communications 285 (2012) 4353–4358 4357

Furthermore, deducing from Fig. 5(b), the shift of the Braggwavelengths decreased with the temperature change increasingas shown in Fig. 6. In addition, the shift of the Bragg wavelengthsvs the temperature change using the linear regression can beexpressed as

Dla ¼�0:097DTþ0:040 ðfor mode aÞ

Dlb ¼�0:104DTþ0:045 ðfor mode bÞ

Dlc ¼�0:105DTþ0:022 ðfor mode cÞ

Dld ¼�0:111DTþ0:059 ðfor mode dÞ ð12Þ

where la, lb, lc and ld refer to the corresponding shift of the Braggwavelengths of modes a, b, c and d with different temperaturechanges. The adjusted R-squared values are 0.998, 0.998, 0.999 and0.997, showing good linear property. The rms deviations of the dataare 0.0458, 0.0554, 0.0338 and 0.0694 nm for modes a, b, c and d,resulting in the rms temperature change error of 0.47, 0.53, 0.32 and0.63 1C over the whole measurement range as implied by Eq. (12),respectively. Seen from Eq. (12) the shift of the Bragg wavelengthupon the temperature change for the modes a, b, c and d are�0.097, �0.104, �0.105 and �0.111 nm/1C, respectively. TheBragg wavelength shift upon the temperature change in experimentis more than 8 times that of MM silica FBG [29]. For the higher ordermode, the larger the shift of the Bragg wavelength upon thetemperature change should be [29], in well accordance with thetheory results in Fig. 3.

5. Conclusion

Temperature sensing properties of BDK doped MM polymerFBG have been studied in theory and experiment for the first time.In theory, with the order of the reflected mode increases from 1stto 60th order, for MM silica FBG the temperature sensitivity willincrease linearly from 16.2 pm/1C to 17.5 pm/1C, while for MMpolymer FBG the temperature sensitivity will increase linearlyfrom �79.5 pm/1C to�104.4 pm/1C. The mode order influenceupon the shift of the Bragg wavelength of MM polymer FBG isalmost 1 order larger than that of MM silica FBG. When thetemperature change increases from 0 to 60 1C, the shift of the 1storder Bragg wavelength of MM silica FBG will increase linearlyfrom 0 to 1.0 nm, while that of MM polymer FBG will decrease

linearly from 0 to �4.8 nm, showing higher shift compared withMM silica FBG. In experiment, the Bragg wavelength shift willdecline as the temperature rises, contrary to that of MM silicaFBG. The temperature sensitivity of MM polymer FBG is largerthan �0.097 pm/1C, more than 8 times that of MM silica FBG.All these results show that MM BDK doped polymer FBG has greatpotential for the temperature sensing field.

Acknowledgments

The authors gratefully acknowledge the financial support byNational Natural Science Foundation of China (No. 21074123,91027024 and 50973101), an International Science Linkages (ISL)Australia China Special Fund project (CH060036) from the Depart-ment of Industry, Innovation, Science and Research (DIISR),Australia and Open Fund of State Key Laboratory of InformationPhotonics and Optical Communications (Beijing University ofPosts and Telecommunications) and wish to express their thanksto the referees for critically reviewing the manuscript and makingimportant suggestions.

References

[1] H. Poisel, D. Kalymnios, K. Krebber, P. Scully, M. Werneck, J. Zubia, POFSensors—applications in every days life, in: 2007 33rd European Conferenceand Exhibition of Optical Communication (ECOC), (IEEE, 90489 Nuernberg,Wassertorstrasse 10, Germany), 2007, pp. 1–4.

[2] G. Emiliyanov, J.B. Jensen, O. Bang, P.E. Hoiby, L.H. Pedersen, E.M. Kjær, OpticsLetters 32 (2007) 460.

[3] S. Kiesel, K. Peters, T. Hassan, M. Kowalsky, IEEE Photonics Technology Letters20 (2008) 416.

[4] G.E. Town, W. Yuan, R. McCosker, O. Bang, Optics Letters 35 (2010) 856.[5] C. Markos, W. Yuan, K. Vlachos, G.E. Town, O. Bang, Optics Express 19 (2011)

7790.[6] W. Yuan, G.E. Town, O. Bang, IEEE Sensors Journal 10 (2010) 1192.[7] F.M. Cox, A. Argyros, M.C.J. Large, Optics Express 14 (2006) 4135.[8] J. Jensen, P. Hoiby, G. Emiliyanov, O. Bang, L. Pedersen, A. Bjarklev, Optics

Express 13 (2005) 5883.[9] A. Dupuis, N. Guo, Y. Gao, N. Godbout, S. Lacroix, C. Dubois, M. Skorobogatiy,

Optics Letters 32 (2007) 109.[10] H.Y. Liu, H.B. Liu, G.D. Peng, P.L. Chu, Optics Communications 219 (2003) 139.[11] J.M. Yu, X.M. Tao, H.Y. Tam, Optics Letters 29 (2004) 156.[12] H.Y. Liu, G.D. Peng, P.L. Chu, IEEE Photonics Technology Letters 13 (2001) 824.[13] D.J. Webb, K. Kalli, C. Zhang, M. Komodromos, A. Argyros, M. Large,

G. Emiliyanov, O. Bang, E. Kjaer, Proceedings of SPIE 6990 (2008) 69900L-1.[14] G.D. Peng, P.L. Chu, Proceedings of SPIE 4929 (2002) 303.[15] H. Dobb, K. Carroll, D.J. Webb, K. Kalli, M. Komodromos, C. Themistos,

G.D. Peng, A. Argyros, M.C.J. Large, M.A. van Eijkelenborg, Q. Fang,I.W. Boyd, Proceedings of SPIE 6189 (2006) 618901-1.

[16] G.D. Peng, X. Xiong, P.L. Chu, Optical Fiber Technology 5 (1999) 242.[17] Z. Xiong, G.D. Peng, B. Wu, P.L. Chu, IEEE Photonics Technology Letters 11

(1999) 352.[18] H.Y. Liu, H.B. Liu, G.D. Peng, P.L. Chu, Optics Communications 266 (2006) 132.[19] X. Chen, C. Zhang, D.J. Webb, B.V. Hoe, G.V. Steenberge, K. Kalli, F. Berghmans,

H. Thienpont, W. Urbanczyk, K. Sugden, G.-D. Peng, Proceedings of SPIE 7653(2010) 76533A-1.

[20] K.E. Carroll, C. Zhang, D.J. Webb, K. Kalli, A. Argyros, M.C.J. Large, OpticsExpress 15 (2007) 8844.

[21] D.J. Webb, K. Kalli, K. Carroll, C. Zhang, M. Komodromos, A. Argyros, M. Large,G. Emiliyanov, O. Bange, E. Kjaer, Proceedings of SPIE 6830 (2007) 683002-1.

[22] X. Chen, C. Zhang, D.J. Webb, G.-D. Peng, K. Kalli, Measurement Science andTechnology 21 (2010) 094005.

[23] X. Cheng, W. Qiu, W. Wu, Y. Luo, X. Tian, Q. Zhang, B. Zhu, Chinese OpticsLetters 9 (2011) 020602.

[24] C. Zhang, D.J. Webb, K. Kalli, G. Emiliyanov, O. Bang, E. Kjær, Bragg gratinginscription in TOPAS microstructured polymer optical fibre, in: Proceedingsof the 16th International Conference on Polymer Optical Fiber, UK, 2007.

[25] W. Yuan, D.J. Webb, K. Kalli, K. Nielsen, H.K. Alessio Stefanil, Rasmussen,O. Bang, Proceedings of SPIE 7753 (2011) 77538X.

[26] I.P. Johnson, W. Yuan, A. Stefani, K. Nielsen, H.K. Rasmussen, L. Khan,D.J. Webb, K. Kalli, O. Bang, Electronics Letters 47 (2011) 271.

[27] I.P. Johnson, D.J. Webb, K. Kalli, M.C.J. Large, A. Argyros, Proceedings of SPIE7714 (2010) 77140D-1.

[28] I.P. Johnson, D.J. Webb, K. Kalli, W. Yuan, A. Stefani, K. Nielsen,H.K. Rasmussen, O. Bang, Proceedings of SPIE 8073 (2011) 80732V-1.

[29] T. Mizunami, T.V. Djambova, T. Niiho, S. Gupta, Journal of LightwaveTechnology 18 (2000) 230.

Y. Luo et al. / Optics Communications 285 (2012) 4353–43584358

[30] C. Lu, Y. Cui, Journal of Lightwave Technology 24 (2006) 598.[31] W. Ecke, Applications of Fibre Bragg Grating Sensors, Institute of Photonic

Technology, Perth, 2008.[32] Y. Luo, B. Yan, M. Li, X. Zhang, W. Wu, Q. Zhang, G.-D. Peng, Optical Fiber

Technology 17 (2011) 201.[33] I.P. Johnson, K. Kalli, D.J. Webb, Electronics Letters 46 (2010) 1217.[34] W. Wu, Y. Luo, X. Cheng, X. Tian, W. Qiu, B. Zhu, G.D. Peng, Q. Zhang, Journal

of Optoelectronics and Advanced Materials 12 (2010) 1652.[35] Y.H. Luo, Q.J. Zhang, H.Y. Liu, G.D. Peng, Optics Letters 35 (2010) 751.[36] F. Zhang, X. Wang, Q. Zhang, Polymer 41 (2000) 9155.

[37] Q. Zhang, P. Wang, Y. Zhai, Macromolecules 30 (1997) 7874.[38] Y. Suematsu, K. Iga, Hikari Faiba Tsuusin Nyuumon, 3rd ed., Tokyo, Japan,

1989 (in Japanese).[39] K. Kitayama, S. Seikai, N. Uchida, IEEE Journal of Quantum Electronics QE-16

(1980) 356.[40] Z. Zhang, P. Zhao, P. Lin, F. Sun, Polymer 47 (2006) 4893.[41] M.B.J. Diemeer, Optical Materials 9 (1998) 192.[42] T.V. Djambova, T. Mizunami, Japanese Journal of Applied Physics 39 (2000) 1566.[43] R.M. Cazo, O. Lisboa, H.T. Hattori, V.M. Schneider, C.L. Barbosa, R.C. Rabelo,

J.L.S. Ferreira, Microwave and Optical Technology Letters 28 (2001) 4.