728592

Research ArticleA New Design for All-Normal Near Zero Dispersion PhotonicCrystal Fiber with Selective Liquid Infiltration for BroadbandSupercontinuum Generation at 1.55m

Partha Sona Maji and Partha Roy Chaudhuri

Department of Physics & Meteorology, Indian Institute of Technology, Kharagpur 721 302, India

Correspondence should be addressed to Partha Sona Maji; [email protected]

Received 21 December 2013; Revised 20 March 2014; Accepted 21 March 2014; Published 16 April 2014

Academic Editor: Luciano Mescia

Copyright 2014 P. S. Maji and P. Roy Chaudhuri. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

A new design of all-normal and near zero flattened dispersion based on all-silica photonic crystal fibers (PCFs) using selectivelyliquid infiltration technique has been proposed to realize smooth broadband supercontinuum generation (SCG).The investigationgives the details of the effect of different geometrical parameters along with the infiltrating liquids on the dispersion characteristicsof the fiber. Numerical investigations establish a dispersion value of 0.48 ps/nm/km around the wavelength of 1.55m. Theoptimized design has been found to be suitable for SCG around the C band of wavelength with flat broadband wavelength band(375 nm bandwidth) and smooth spectrum with only a meter long of the PCF. The proposed structure also demonstrates goodtunable properties that can help correct possible fabrication mismatch towards a better optimization design for various opticalcommunication systems.

1. Introduction

Broadband smooth flattened supercontinuum generation(SCG) has been the target for the researchers for its enormousapplications in the field of metrology, optical sensing, opticalcoherence tomography, wavelength conversion, and so forth[1]. Recent developments for mid-infrared (MIR) SC sourcehave been investigated based on nonsilica fibers [2, 3].Unconventional PCFs based on aperiodic structure have alsobeen investigated [4]. However, achieving flat broadbandsmooth SC sources for IR applications remains challeng-ing [1]. One of the foremost requirements of generatingbroadband flattened SCG is to achieve near zero flatteneddispersion around a targeted wavelength. Photonic crystalfibers (PCFs) [5, 6], which enjoys some unique properties likewide band single mode operation, great controllability overdispersion properties, and higher nonlinearity, has been thetarget host for SCG for the last decades [1]. Researchers haveworked on designing novel dispersion profiles with variableair-hole diameter in the cladding [713] and this designcan be further manipulated for SC generation by pumping

at the near zero wavelength [9, 14]. However, the realizingtechnology of complicated structures or PCF having air-holesof different diameters in microstructure cladding remainstruly challenging. An alternative route of achieving similarperformance is shown to be practicable by filling the air-holeswith liquid crystals [15, 16] or by various liquids such as poly-mers [17], water [18], and ethanol [19]. Tunable photonic bandgap (PBG) effect and long-period fiber grating have beensuccessfully realized with liquid-filled PCFs [20]. Theoreticaldesign of dispersion management by filling the air-holes ofthe PCF with selective liquids for both single wavelength andbroadband wavelength applications has been studied [21, 22].In the present work, a new design of silica based PCF withall-normal near zero chromatic dispersion around the desiredwavelength of 1.55 m through selectively liquid-filled innerair-holes has been proposed and the optimized design hasbeen targeted for achieving smooth and flattened broadbandSC spectra. Asmost of the power resideswithin the core of thePCF, liquid infiltration in air-holes will have the only effect indispersion controllability.We also investigate the temperaturedependence of the liquid-filled PCFs for better optimization

Hindawi Publishing CorporationJournal of PhotonicsVolume 2014, Article ID 728592, 9 pageshttp://dx.doi.org/10.1155/2014/728592

2 Journal of Photonics

design with its tunable property of shifting dispersion peakfor optical communication systems.Themain advantage withthis approach is that we need not require different air-holesin the cladding to realize near zero dispersion at the desiredwavelength; also we can tune the dispersion towards a betteroptimized design by changing the temperature of the liquidand thereby achieving highly smooth and flat broadband SCspectra with only a meter long of the fiber.

2. Liquid-Filled Photonic Crystal Fiber andRelated Issues

Conventional PCFs have cladding structures formed by air-holes with the same diameter arranged in a regular triangularor square lattice. By altering the PCF geometrical parameters,namely, hole-to-hole spacing () and air-hole diameter (),the modal properties, in particular, the dispersion propertiescan be easily engineered [5, 6]. However, the dispersionslope of such PCFs having air-holes of the same diametercannot be tailored in a wide wavelength range. The currentresearch aims to achieve all-normal dispersion close to zeroat a desired wavelength with a flat slope of the dispersioncurve using regular triangular-lattice structure having air-holes of the same size uniformly distributed in the cladding.A common route to realize these goals of flat dispersionaround a specific wavelength is by varying the size of air-holes in different layers and is well known in [712]. Becauseof the fabrication limitation, the concept finds limited useas a practical fiber. This research looks for the achievementof these targets through a regular conventional PCF byincorporating the effects of filling air-hole ring with a liquidof predetermined refractive index (RI). Depending upon therefractive indices of the infiltrating liquid to the air-holes, thelocal refractive indices of the layer can be modified. In thatway, the effect of variable air-hole diameter can be realizedby infiltrating the air-holes with liquids of different refractiveindices. Depending upon the RI of the infiltrating liquid, wecould have the effect of different air-hole diameter.

The fabrication of such a fiber is simplified due to theuniformity of the air-holes in the cladding. To manufacturethese PCFs, onemust first selectively block specified air-holesand infuse the liquid into the unblocked holes. One possibleway is to employ the fusion splicing technique [1820]. Theinner ring of the air-holes can be infiltrated with liquid, firstby fusing the outer rings of air-holes with tailored electricarc energies and fusion times [23] and then by immersingone end of the fiber in a liquid reservoir and applyingvacuum to the other end of the fiber [18]. This can be apossible way to infiltrate liquid in our case. Another way ofselective plug specified air-hole layers in the PCFs is to usemicroscopically positioning tips with glue [24]. Not only air-hole layers but also a single air-hole can be easily blockedby using this technique. In spite of the above methods, onecan also selectively infiltrate the liquid into specified air-hole layers from a macroscopic fiber preform to a connectedmicrostructured PCF by using an applied pressure [21]. Withthe optimized air-hole diameters of the order of 0.60 m, itshould be easy to collapse the air-holes and fill the liquid

into the air-holes with such dimensions. It is also interestingto note that PCFs with similar or smaller air-hole diameterwas realized [25], making the proposed design practicallyachievable. With the advancement of technology, a goodprecision of the PCF parameters can be easily implemented.

There are certain issues related to the infiltration of liquidto the air-holes, such as whether the fluid wets glass and howviscous it is. If the liquid does not wet glass, then surfacetension will oppose entry of the liquid into the air-hole,thereby making the process difficult to realize. The requiredpressure to push such a liquid into the air-holes can beworkedout with the value of its surface tension and contact angle.With an air-hole diameter of the order of 0.60 m, pressureby a vacuum pump will be sufficient.

If the fluid does wet glass, then the air-hole should befilled but the filling-up speed will depend upon viscosity. Itcan be worked out how quickly the air-holes will be filledusing the expressions for Poiseuille flow in a pipe [26]. Inother words, the air-holes can be filled (and how quickly),with the given values for surface tension, contact angle,and viscosity. With the fast advancement of the technology,submicron filling of air-holes will not be very difficult toachieve.

The selective hole filling technique provides a coupleof advantages. Firstly, all the air-holes are of the samediameter, which is easier to be fabricated compared to fiberswith multiple different submicron air-hole sizes. Secondly, aregular PCF with selective infiltration with a liquid provideshuge flexibility for tremendous applications. This is why thepaper pursues selective air-hole filling approach towards thetarget of all-normal near zero dispersion in amicrostructuredoptical fiber. Notably, the technique comes out in designingfibers for various other applications [21, 22, 2732].

3. Analysis Method and DesignOptimization of the PCF

As an initial attempt, we consider a regular PCF with fourrings of air-holes with C

6v symmetry with the central air-holemissing like normal index-guiding PCF as shown in Figure 1.The inner ring of air-holes is infiltrated with a liquid ofcertainRIs.Throughout our design studywe have kept higherair-filing fraction, thereby reducing the confinement loss ofthe structure. As can be seen from our numerical results,we need only a meter long of such a fiber; the propagationloss of the high power spectrum can therefore be highlyreduced. By optimizing the RI value (

) of the infiltrating

liquid combined with PCF geometrical parameters, namely,pitch () and air-hole diameter (), all-normal near zerodispersion around a particular wavelength can be realized.

3.1. Dispersion Analysis. Modal fields as well as dispersionparameters are calculated by using commercially availableCUDOS software along with MATLAB for numerically cal-culating the dispersion relation. The total dispersion () iscomputed with [33]:

=

2 Re [eff]

2.

(1)

Journal of Photonics 3

d

nL

Figure 1: Cross section of the proposed photonic crystal fiber.The shaded regions represent air-holes infiltrated with liquid withrefractive indices

.

Here Re[eff] stands for the real part of the effectiveindices, is the speed of light in vacuum, and is thewavelength.

3.2. Supercontinuum Generation (SCG) Analysis. The SCGwith the liquid filled near zero all-normal dispersion silicabased PCF for smooth flattened broadband spectra hasbeen studied by solving the nonlinear Schrodinger equation(NLSE) [33] describing the pulse propagation through thefiber length. The NLSE takes into account the contribu-tions of the linear effects (attenuation, chromatic dispersion,and high-order dispersions) and the nonlinear effects (self-phase modulation, stimulated Raman scattering, and self-steepening). NLSE for slowly varying pulse envelope (, )in the retarded time frame is given through (2) as follows:

+

2

2

+1

!

= (1

) ([]

2

0

([]

2))

+

(1 +

0

)(

0

() | (, )|

2) ,

(2)

where is the loss coefficient, are the th order dispersion,

0is the input pulse frequency, is the present time frame,

and is the fractional contribution due to delayed Raman

function () [33, 34]. The nonlinear coefficient is given

by (3) as follows:

=

2

2

eff, (3)

where 2is the nonlinear refractive indices of silica and eff

is the effective area at the pumping wavelength .

1.2 1.4 1.6 1.8 2.0 2.2

60

40

20

0

20

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

= 0.85m = 0.90m

= 0.95m = 1.00m

d = 0.62m; nL = 1.33

Figure 2: Computed dispersion of the PCF as a function of pitch() keeping

and fixed.

3.3. Optimization for All-Normal Near Zero Dispersion at theTarget Wavelength. The nonlinear effects in a PCF stronglydepend on the dispersive characteristic and the length of theemployed optical fiber [1]. In particular, with reference toSCG, the shape of the total dispersion curve can be tailoredto obtain a broadband output spectrum.The approach of thepresent research of optimization towards designing near zeroall-normal flat dispersion relies on varying multidimensionalparameter space that consists of the liquidRI (

), the pitch,

and air-hole diameter (). The procedure is followed in threesteps. In the first step, the sensitivity of the variation of theparameters towards the total dispersion has been illustratedby varying one of the design parameters on the dispersionkeeping other parameters constant. In the second stage, wetook one of the parameters fixed (value obtained from the firststep) and optimized the other parameters towards the target.Once one parameter is optimized, we reoptimize the designby adjusting other parameters. In the third stage we selecta practical liquid (wavelength dependent RI) close to theoptimized RI and optimize the other parameters to achievethe target of all-normal near zero dispersion. The first stageof the design optimization is presented as follows. Figure 2shows the effect of on the values. For a particular ,the value of initially increases to reach a maximum andthen starts decreasing. The graph clearly indicates that withan increase of , the maximum of is red-shifted and thedispersion becomes more flatter with wavelengths, while forsmaller wavelengths they are almost parallel without muchchange in the slope. The flatness can be understood fromthe following analogy: the dispersion value from the peakreduces by an amount of 25 ps/nm/km for a wavelengthrange of 794 nm for = 1.00 m, while for the same valuesof dispersion range, the wavelength range comes out to be760 nm for = 0.85 m. This can be attributed to the factthat, for higher , material dispersion dominates, reducing


1.2 1.4 1.6 1.8 2.0 2.2

50

25

0

25

50

75

Disp

ersio

n (p

s/nm

/km

)

nL = 1.33

nL = 1.35

nL = 1.37

nL = 1.39

Wavelength (m)

= 0.9 m; d = 0.62

Figure 3: Dispersion behaviour as calculated for varying values

keeping pitch () and fixed.

the effect of waveguide dispersion. From Figure 3 it can beobserved that both the magnitude and the slope of areaffected for different values of

. An increase of

causes

a blue-shift of the dispersion peak and the dispersion valuesalso increase. The effect of varying the air-hole diameter without changing the other parameters is depicted inFigure 4. It should be noted that we have changed thediameter of all the air-holes including those containing theinfiltrating liquid. An interesting observation can be foundout that, with an increase of , the dispersion seems to beconverging for higher wavelengths while the peak again getsred-shifted but with a steeper slope than that of Figure 2.The convergence can be attributed to the increased effect ofwaveguide dispersion to the total dispersion. Thus, the effectof varying the influences the total dispersion, whereas has the desired effect of modifying the dispersion slope, andvarying

modifies both the slope and dispersion.

Then, we started the second stage of the optimizationprocedure as the following. For this step we tried to keep nearer to 1.0 m such that we could have smaller effectivearea which in turn will enhance nonlinearity. Starting with/ = 0.7 and

= 1.35, the values of the are changed

progressively to get a near zero profile of the dispersion.To have higher values of nonlinear coefficient, we keptthe values around 0.90 m. Then the values of air-holediameter and

are changed progressively to either raise

or lower the dispersion and change the slope. During theprocess we tried to keep the values of the parameters suchthat the values of the parameters remain practically feasible.Following the above steps, we have obtained an all-normalnear zero dispersion in the wavelength around 1570 nm with value of 0.41 ps/nm/km with = 0.90 m and =0.59 m and

= 1.331 as demonstrated in Figure 5.

Having obtained a preliminary design using an artificial,dispersionless liquid, we continuewith the third optimization

1.2 1.4 1.6 1.8 2.0 2.2

50

40

30

20

10

0

10

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

d = 0.58md = 0.62m

d = 0.66md = 0.70m

= 0.9 m; nL = 1.33

Figure 4: Variation of dispersion as a function of air-hole diameter() when pitch () and

remain constant.

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

120

100

80

60

40

20

0

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

= 0.90m; d = 0.59m; nL = 1.331

Figure 5: All-normal near zero dispersion with =0.40 ps/nm/km near 1570 nm with = 0.90 m,

= 1.331, and

= 0.59 m.

stage.We select oil (calling it as oil number 1)whoseRI is closeto the above optimized value in the target communicationwavelength band and is given by Cauchy (4) (available withM/S Cargile lab., USA [35]).

Cauchy equation for oil number 1 is known to be [35]

1 () = 1.3336794 +

219396

2+

3.562146 10

9

4,

(4)

where are in Angstrom.


1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

100

80

60

40

20

0

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

Designed dispersionZero dispersion

Figure 6: The optimized design of the all-normal near zerodispersion with = 0.51 ps/nm/km near 1550 nm with =0.90 m, = 0.57 m with oil #1.

1.2 1.4 1.6 1.8 2.0 2.2

600

450

300

150

0

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

With liquidWithout liquid

Figure 7: The effect of liquid infiltration in the first air-hole ringupon dispersion. Not only the dispersion values but also the slope ofthe graph has been drastically altered.

With this liquid an all-normal near zero dispersion PCFwith value of 0.48 ps/(nm.km) around 1550 nm of wave-length has been achieved with the designing PCF parametersof = 0.90 m with = 0.57 m as shown in Figure 6.Now as we see the / value is higher than the accepted valuefor endlessly single-mode operation. To achieve our target,we needed to make a tradeoff between a pure single-mode

1.6 1.8 2.01.0 1.2 1.4 2.2 2.4100

75

50

25

0

25

50

75

100

Disp

ersio

n (p

s/nm

/km

)

Optimized dispersionLiquid material dispersionSilica material dispersion

Wavelength (m)

Figure 8: The contribution of the material dispersion of theliquid and background silica material dispersion towards the totaldispersion.

guiding and few higher order mode guiding. Our numericalstudy reveals that with our present optimize value the nexthigher order mode can coexist with the fundamental one;however the confinement loss of the mode is found out to beabout hundred times of magnitude higher than that of thefundamental mode throughout the spectral range considered(specially at the pumping wavelength) and hence would leakaway with propagation within a very short length of thedesigned fiber. This would make the designed fiber an effec-tively single-mode fiber.The effect of liquid infiltration upondispersion has been presented in Figure 7. The figure clearlyreveals the determining effect of the liquid infiltration in theair-holes as not only a drastic change but also a slope reversalof the dispersion could be observed. Total dispersion alongwith the contribution of the material dispersion of the liquidand background silica material towards the total dispersionhas been shown in Figure 8 for the above optimized structure.The new control technique applied to the design of PCFs withdesired dispersion properties can be widely used for specificapplications such us control of SCG, sensors, and broadbandtransmission [1].

4. Numerical Analysis for SCG withthe Optimized Near Zero All-NormalDispersion PCF

NLSE, as mentioned in (2), is solved numerically by usingthe split step Fourier transformbased beampropagation codedeveloped by COSTP11 [36]. In our study, we have consideredthe pumping of laser power pulses with hyperbolic secant


1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75

0

50

100

Inte

nsity

(dB)

200

150

100

50

Wavelength (m)

Figure 9: Evolution of the spectrum as the pulse propagates alongthe fiber. The input pulse and the output spectrum after each 25 cmof propagation.

field profile emerging from a laser with full width at halfmaximum (FWHM) of 1.5 ps. In our calculations we setthe pump wavelength of = 1.55 m, the closest tozero in the normal dispersion regime, in order to generatethe broadest spectra. Consequently, the spectral wideningis dominated by self-phase modulation (SPM) followed byoptical wave breaking and the noise-sensitive soliton dynam-ics are suppressed by pumping in the normal dispersionregion in such fibers. The soliton effect, for example, solitonfission, is completely removed, giving rise to the smoothspectra. Optimization of the all-normal dispersion fiberdesign allowed us to generate ultrabroadband, flat top, andsmooth SC generation. An effective area of 4.03m2 andnonlinear coefficient = 27.3W1km1 are achieved in theoptimized PCF with = 0.90 m and = 0.57 m at thepumping wavelength. The input pulse power has been keptto be 4.0 kW with FWHM of 1.5 ps. A possible source forsuch a pump can be the commercially available Er3+, Yb3+doped silicate based fiber laser emitting around 1550 nm ofwavelength [37]. The calculated values of higher order betasare presented in Table 1. The spectrum evolution of the fiberafter it evolves through each 25 cm of the fiber with theabove parameters has been shown in Figure 9. The spectrumspreads for awidewavelength range, ranging from 1300 nm to1750 nm. The intensity is calculated using the usual notationwith Intensity (dB) = 10 log

10(). It can be observed that

as the pulse propagates through the fiber the peak powerreduces, creating new peaks on both sides of the input pulsealmost symmetrically. The evolution of the spectrum as afunction of propagation distance has been shown in Figure 10which clearly shows the spreading of the pulse taking almostsymmetrically around the pumping wavelength. The graphclearly indicates that after travelling a distance of 1.2 meters,the broadband spectrum spread for a wide wavelength range

Table 1:The values of used for simulation for the optimized PCF.

Higher order betas Beta values

2(ps2/km) 0.069276

3(ps3/km) 3.59804 103

4(ps4/km) 6.57756 104

5(ps5/km) 2.82896 106

6(ps6/km) 2.82896 1010

7(ps7/km) 1.45745 1012

8(ps8/km) 2.91289 1014

1.8

1.7

1.6

1.5

1.4

1.3

0 0.2 0.4 0.6 0.8 1

Z (m)

Propagation, spectral domain

Wav

eleng

th (

m)

Figure 10: Propagation of the spectrum as it travels through thefiber.

from 1300 nm to 1750 nm. One of the most notable featuresof the SC spectrum is the spectral broadening which isaccompanied with an oscillating nature covering the wholespectrum. The spectrum consists of many small peaks. Thisparticular nature is a typical pattern due to self-phase modu-lation (SPM), which is assumed to be dominating nonlineareffect for the spectral broadening. The multipeak structurein the system is the result of interference between the sameoptical frequencies in the pulse and the relatively smootherSC generation results from the combination effect of SPMand all-normal near zero flat dispersion nature of the fiber.We have calculated the spectral width of the broadband flatSC spectrum according to Begum et al. [14], where they havecalculated the FWHM at the negative value of the intensitypoints corresponding to the peak maximum value. With thesame analogy, numerical calculations show a bandwidth of375 nm with our optimized fiber. However with another way,the intensity bandwidth can be calculated at 20 dB fromthe peak point. The numerical calculation shows a 20 dBbandwidth of spectral width of 285 nm that can be achievedwith a fiber length of 1.2 meter as shown in Figure 11.


1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75

0

50

100

Inte

nsity

(dB)

200

150

100

50

Wavelength (m)

Figure 11: Optical spectrum with the optimized fiber after propaga-tion of 1.2meter. A FWHMof 375 nm is obtainedwith the optimizedfiber.

5. Tunable Properties of Inner RingLiquid-Filled PCFs

It is well known that the dispersion can be tailored in a PCFaccording to the requirement by changing the geometricalparameters. However, once a design is fixed and fabricatedthe dispersion of that particular fiber is also fixed. So, tohave a different or optimized design we need another fiber tobe fabricated. Now here comes the advantage of liquid-filledPCF. Fluid-filled PCFs have created novel opportunities fortunable dispersion control, with applications in tunable delaylines, nonlinear optics, and long period grating designs [38].Here in this type of selective liquid infiltrated PCF, we canchange the RI of the infiltrating liquid by changing the tem-perature of the infiltrating liquid and can tune the dispersionproperties according to the requirement. As the temperaturecoefficient of the liquids available with M/s Cargile lab [35]is of the order of 4 104/C which is much larger thanthat of fused silica, the smaller changes of temperature willaffect the RI of the liquid only. We have considered theoptimized design shown in Figure 6 and we demonstrate thetunability property of the liquid by changing the temperatureof the liquid. Figure 12 shows the dispersion characteristicsfor five different temperature of the liquid. It can be seenfrom the figure that with the increase of the temperaturethe peak value of the dispersion shifts away from the zerodispersion value.The peak dispersion and the correspondingvariation of the peak dispersion wavelength for differenttemperature are demonstrated in Figure 13. The peak dis-persion value with temperature shows a linear relationshipwith a negative slope of 0.31084 ps/nm/km/C. Wavelengthcorresponding to peak dispersion for different temperaturehas been presented in Figure 13(b). The graph presents alinear relationship between the corresponding wavelengthwith temperature with a positive slope of 0.65 nm/C. Sowe can tune the temperature of the liquid according to therequirement to obtain an optimized/required design. Ournumerical calculations demonstrate that around the temper-ature of 23.5C,we could achieve an all-normal flat dispersionPCF with a peak value of 0.089 ps/nm/km around 1550 nmof wavelength. This design will be more demanding for thecurrent target of all-normal flat dispersion around 1550 nm.

1.2 1.4 1.6 1.8 2.0 2.2

40

30

20

10

0

Wavelength (m)

Disp

ersio

n (p

s/nm

/km

)

@21C@23C@25C

@27C@29C

Figure 12: Dispersion curves for the liquid-filled PCF operated atvarious temperatures.

So with the tunability property of the infiltrating liquid wecan easily tune the peak dispersion just by changing thetemperature of the liquid for a fabricated PCF.

6. Conclusion

We have demonstrated a new design of all-normal near zerodispersion PCF based on selectively liquid infiltration andexplored its properties for flattened broadband SC generationin near IR wavelength regions. We have studied the effectof individual PCF parameters, namely, and , along withinfiltrating liquid (

) towards the target of all-normal near

zero dispersion PCF around the communication wavelengthwindow. Our study reveals that varying influences the totaldispersion, whereas has the desired effect of modifyingthe dispersion slope and varying

modifies both the slope

and the dispersion. Based on the above findings, we haveachieved an all-normal near zero dispersion PCF with value of 0.48 ps/(nmkm) around 1550 nm of wavelengthwith the designing PCF parameters of = 0.90 m with =0.57 mand oil number 1. Our study reveals that by adjustingthe different parameters, near ZDW can be tuned accordingto the requirement. With the above designed PCF, we haveobtained a smooth and broadband spectra ranging from1350 nm to 1725 nm, that is, for a bandwidth of 375 nmwith 1.2meter length of the fiber. We have also demonstrated the tun-ability properties of the optimized PCF.The peak wavelengthcorresponding to all-normal flat dispersion can be well tunedby the refractive index of the liquid which can be controlledby the operation temperature. By changing the operationaltemperature to 23.5C we could achieve a peak dispersionof 0.089 ps/nm/km around 1550 nm of wavelength with ouroptimized design. The tunability of the liquid-filled PCF canbe utilized for wide wavelength range applications and also


20 22 24 26 28 30

2.0

1.5

1.0

0.5

0.0

0.5

1.0Pe

ak d

isper

sion

(ps/

nm/k

m)

Temperature of the liquid (C)Calculated valuesLinear fit

(a)

20 22 24 26 28 30

Temperature of the liquid (C)Calculated valuesLinear fit

1543

1542

1541

1540

1539

1538

1537

Peak

disp

ersio

n w

avele

ngth

(nm

)

(b)

Figure 13: (a) Peak dispersion values of the liquid-filled PCF operated at variant temperatures. (b) Peak dispersion wavelength of the liquid-filled PCF operated at variant temperatures.

to correct possible fabrication mismatches in the geometryof PCF structures. The significance of this work is that itprovides a new type of dispersion engineered silica basedPCF for near Infrared (IR) SC source with flat broadbandspectrum with about a meter long of the fiber which can beuseful for applications inmetrology, spectroscopy, andopticalcoherence tomography in the near infrared region.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

The authors would like to thank Dr. Boris Kuhlmey, Univer-sity of Sydney, Australia, for providing valuable suggestionsin understanding the software for designing and studyingthe properties of different structures. Thanks are also dueto Dr. Alessandro Tonello of Xlim Institute, UMR CNRSLimoges Cedex, France, for providing valuable suggestionin developing and understanding the NLSE codes. Theauthors acknowledge sincerely the Defence Research andDevelopment Organization, Govt. of India and CRF of IITKharagpur for the financial support to carry out this research.

References

[1] J. M. Dudley, G. Genty, and S. Coen, Supercontinuum gener-ation in photonic crystal fiber, Reviews of Modern Physics, vol.78, no. 4, pp. 135184, 2006.

[2] J. Swiderski, F. Theberge, M. Michalska, P. Mathieu, and D.Vincent, High average power supercontinuum generation in

a fluoroindate fiber, Laser Physics Letters, vol. 11, pp. 015106015109, 2014.

[3] G. Sobon, M. Klimczak, J. Sotor et al., Infrared supercontin-uum generation in soft-glass photonic crystal fibers pumped at1560 nm, Optical Materials Express, vol. 4, pp. 715, 2014.

[4] A. di Tommaso, M. de Sario, L. Mescia, and F. Prudenzano,Numerical analysis of aperiodic photonic crystal fiber struc-tures for supercontinuum generation, Optical Engineering, vol.51, pp. 03500310350037, 2012.

[5] J. Broeng, D. Mogilevstev, S. E. Barkou, and A. Bjarklev,Photonic crystal fibers: a new class of optical waveguides,Optical Fiber Technology, vol. 5, no. 3, pp. 305330, 1999.

[6] P. S. J. Russell, Photonic-crystal fibers, Journal of LightwaveTechnology, vol. 24, no. 12, pp. 47294749, 2006.

[7] K. Saitoh,N. J. Florous, andM.Koshiba, Theoretical realizationof holey fiber with flat chromatic dispersion and large modearea: an intriguing defected approach,Optics Letters, vol. 31, no.1, pp. 2628, 2006.

[8] N. Florous, K. Saitoh, and M. Koshiba, The role of artificialdefects for engineering large effective mode area, flat chromaticdispersion, and low leakage losses in photonic crystal fibers:towards high speed reconfigurable transmission platforms,Optics Express, vol. 14, no. 2, pp. 901913, 2006.

[9] K. Saitoh and M. Koshiba, Highly nonlinear dispersion-flattened photonic crystal fibers for supercontinuum generationin a telecommunication window, Optics Express, vol. 12, no. 10,pp. 20272032, 2004.

[10] K. Saitoh,M.Koshiba, T.Hasegawa, and E. Sasaoka, Chromaticdispersion control in photonic crystal fibers: application toultra-flattened dispersion,Optics Express, vol. 11, no. 8, pp. 843852, 2003.

[11] F. Poletti, V. Finazzi, T.M.Monro,N.G. R. Broderick,V. Tse, andD. J. Richardson, Inverse design and fabrication tolerances ofultra-flattened dispersion holey fibers, Optics Express, vol. 13,no. 10, pp. 37283736, 2005.


[12] T.-L. Wu and C.-H. Chao, A novel ultraflattened dispersionphotonic crystal fiber, IEEE Photonics Technology Letters, vol.17, no. 1, pp. 6769, 2005.

[13] X. Zhao, G. Zhou, L. Shuguang et al., Photonic crystal fiberfor dispersion compensation,Applied Optics, vol. 47, no. 28, pp.51905196, 2008.

[14] F. Begum, Y. Namihira, T. Kinjo, and S. Kaijage, Supercontin-uumgeneration in square photonic crystal fiberwith nearly zeroultra-flattened chromatic dispersion and fabrication toleranceanalysis, Optics Communications, vol. 284, no. 4, pp. 965970,2011.

[15] C. Zhang, G. Kai, Z. Wang et al., Transformation of a trans-missionmechanism by filling the holes of normal silica-guidingmicrostructure fibers with nematic liquid crystal, Optics Let-ters, vol. 30, no. 18, pp. 23722374, 2005.

[16] T. T. Alkeskjold, J. Lgsgaard, A. Bjarklev et al., Highly tunablelarge-core single-mode liquid-crystal photonic bandgap fiber,Applied Optics, vol. 45, no. 10, pp. 22612264, 2006.

[17] B. J. Eggleton, C. Kerbage, P. S. Westbrook, R. S. Windeler, andA. Hale, Microstructured optical fiber devices,Optics Express,vol. 9, no. 13, pp. 698713, 2001.

[18] C. Martelli, J. Canning, K. Lyytikainen, and N. Groothoff,Water-core fresnel fiber, Optics Express, vol. 13, no. 10, pp.38903895, 2005.

[19] S. Yiou, P.Delaye, A. Rouvie et al., StimulatedRaman scatteringin an ethanol coremicrostructured optical fiber,Optics Express,vol. 13, no. 12, pp. 47864791, 2005.

[20] C.-P. Yu and J.-H. Liou, Selectively liquid-filled photoniccrystal fibers for optical devices, Optics Express, vol. 17, no. 11,pp. 87298734, 2009.

[21] K. M. Gundu, M. Kolesik, J. V. Moloney, and K. S. Lee, Ultra-flattened-dispersion selectively liquid-filled photonic crystalfibers, Optics Express, vol. 14, no. 15, pp. 68706878, 2006.

[22] C. P. Yu, J. H. Liou, S. S. Huang, and H. C. Chang, Tunabledual-core liquid-filled photonic crystal fibers for dispersioncompensation, Optics Express, vol. 16, no. 7, pp. 44434451,2008.

[23] L. Xiao,W. Jin,M. S.Demokan,H. L.Ho, Y. L.Hoo, andC. Zhao,Fabrication of selective injectionmicrostructured optical fiberswith a conventional fusion splicer,Optics Express, vol. 13, no. 22,pp. 90149022, 2005.

[24] A.Witkowska, K. Lai, S. G. Leon-Saval, W. J.Wadsworth, and T.A. Birks, All-fiber anamorphic core-shape transitions, OpticsLetters, vol. 31, no. 18, pp. 26722674, 2006.

[25] W. H. Reeves, J. C. Knight, P. S. J. Russell, and P. J. Roberts,Demonstration of ultra-flattened dispersion in photonic crys-tal fibers, Optics Express, vol. 10, no. 14, pp. 609613, 2002.

[26] E. W. Washburn, The dynamics of capillary flow, PhysicalReview, vol. 17, pp. 273283, 1921.

[27] J. H. Liou, S. S. Huang, and C. P. Yu, Loss-reduced highlybirefringent selectively liquid-filled photonic crystal fibers,Optics Communications, vol. 283, no. 6, pp. 971974, 2010.

[28] N. Vukovic, N. Healy, and A. C. Peacock, Guiding propertiesof large mode area silicon microstructured fibers: a route toeffective single mode operation, Journal of the Optical Societyof America B: Optical Physics, vol. 28, no. 6, pp. 15291533, 2011.

[29] N. Healy, J. R. Sparks, R. R. He, P. J. A. Sazio, J. V. Badding, andA. C. Peacock, High index contrast semiconductor ARROWand hybrid ARROW fibers, Optics Express, vol. 19, no. 11, pp.1097910985, 2011.

[30] Y. Miao, B. Liu, K. Zhang, Y. Liu, and H. Zhang, Temperaturetunability of photonic crystal fiber filled with Fe

3O4nanopar-

ticle fluid, Applied Physics Letters, vol. 98, no. 2, pp. 021103021105, 2011.

[31] M.-Y. Zhang, S.-G. Li, Y.-Y. Yao, B. Fu, and L. Zhang, A darkhollow beam from a selectively liquid-filled photonic crystalfibre, Chinese Physics B, vol. 19, no. 4, pp. 047103047106, 2010.

[32] W. Qian, C.-L. Zhao, J. Kang, X. Dong, Z. Zhang, and S. Jin,A proposal of a novel polarizer based on a partial liquid-filledhollow-core photonic bandgap fiber, Optics Communications,vol. 284, no. 19, pp. 48004804, 2011.

[33] G. P. Agrawal, Nonlinear Fiber Optics, Optics and PhotonicsSeries, Academic Press, SanDiego, Calif, USA, 4th edition, 2007.

[34] Q. Lin and G. P. Agrawal, Raman response function for silicafibers, Optics Letters, vol. 31, no. 21, pp. 30863088, 2006.

[35] http://www.cargille.com/.[36] http://www.ufe.cz/costp11/.[37] D. Jackson, Towards high-power mid-infrared emission from

a fibre laser, Nature Photonics, vol. 6, pp. 423431, 2012.[38] B. T. Kuhlmey, B. J. Eggleton, and D. K. C. Wu, Fluid-filled

solid-core photonic bandgap fibers, The Journal of LightwaveTechnology, vol. 27, pp. 16171630, 2009.

Submit your manuscripts athttp://www.hindawi.com

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

ComputationalMethodsinPhysics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttp://www.hindawi.com

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of

Documents

728592