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Multiple Soaking with Different SolutionConcentration in Doped Silica PreformFabrication Using Modified ChemicalVapor Deposition and Solution DopingS. M. Aljamimia, M. S. Khairul Anuarb, S. Z. Muhamad-Yassinb, M. I.Zulkiflib, S. Hanifb, N. Tamchekc, Z. Yusoffa & H. A. Abdul-Rashida

a Faculty of Engineering, Multimedia University, Cyberjaya, Selangor,Malaysiab Photonics Department, Telekom Research & Development,Cyberjaya, Selangor, Malaysiac Faculty of Science, Universiti Putra Malaysia, Serdang, Selangor,MalaysiaPublished online: 23 May 2014.

To cite this article: S. M. Aljamimi, M. S. Khairul Anuar, S. Z. Muhamad-Yassin, M. I. Zulkifli, S.Hanif, N. Tamchek, Z. Yusoff & H. A. Abdul-Rashid (2014) Multiple Soaking with Different SolutionConcentration in Doped Silica Preform Fabrication Using Modified Chemical Vapor Deposition andSolution Doping, Fiber and Integrated Optics, 33:1-2, 105-119, DOI: 10.1080/01468030.2013.879238

To link to this article: http://dx.doi.org/10.1080/01468030.2013.879238

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Fiber and Integrated Optics, 33:105–119, 2014

Copyright © Taylor & Francis Group, LLC

ISSN: 0146-8030 print/1096-4681 online

DOI: 10.1080/01468030.2013.879238

Multiple Soaking with Different Solution

Concentration in Doped Silica Preform Fabrication

Using Modified Chemical Vapor Deposition andSolution Doping

S. M. ALJAMIMI,1 M. S. KHAIRUL ANUAR,2

S. Z. MUHAMAD-YASSIN,2 M. I. ZULKIFLI,2 S. HANIF,2

N. TAMCHEK,3 Z. YUSOFF,1 and H. A. ABDUL-RASHID 1

1Faculty of Engineering, Multimedia University, Cyberjaya, Selangor, Malaysia2Photonics Department, Telekom Research & Development, Cyberjaya,

Selangor, Malaysia3Faculty of Science, Universiti Putra Malaysia, Serdang, Selangor, Malaysia

Abstract Incorporation of alumina (Al2O3) into a silica matrix by modified chemical

vapor deposition and a solution doping technique is investigated in this study. Multiplesoaking cycles were used to increase the aluminum content in the core layer. The effect

of alumina retention in silica matrix soot is focused by multiple cycles of soakingwith different solution concentrations, while the effect of the adsorption mechanism is

fixed by maintaining the soot deposition process (such as temperature [1,800ıC],precursor, total gas flow, and soaking time). The deposited soot is examined for

porosity characteristics and effective surface area by a gas adsorption techniquewith Brunauer–Emett–Teller surface area analysis and the surface and cross-section

morphology using scanning electron microscopy. Three different concentrations areused in this work (0.3, 0.7, and 1.2 M) with multiple cycles of soaking. Sintering

and the collapsing process is controlled for each preform. The result shows thatthe alumina content is increased substantially as the number of soaking processes

is increased, which may be due to the retention effect as only a small amount ofadsorption process takes place as indicated by the slight decrease in the surface

area of soot. The collapsed preforms are analyzed using a preform analyzer. Energydispersive x-ray spectrometry is used to check aluminum content and distribution into

the core layer.

Keywords gas adsorption technique with Brunauer–Emett–Teller analysis, modifiedchemical vapor deposition, multiple solution doping process, refractive index profile,scanning electron microscopy–energy dispersive x-ray

Introduction

Incorporation of rare earth (RE) ions in silica optical fiber has been studied since 1964

after Koester and Snitzer published their study on neodymium fiber lasers [1]. One of the

Received 7 October 2013; accepted 23 December 2013.Address correspondence to S. M. Aljamimi, Faculty of Engineering, Multimedia University,

Jalan Multimedia, Cyberjaya, Selangor, 63100, Malaysia. E-mail: salah.foe.mmu@gmail.comColor versions ofone or more of the figures in the article can be found online at www.tandfonline.

com/ufio.

105

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106 S. M. Aljamimi et al.

most common techniques of producing silica optical fiber is by using a modified chemical

vapor deposition (MCVD) process. There are generally two methods of incorporating RE

ions into a silica matrix using the MCVD process: the vapor phase and the nonvapor

phase. The vapor phase method is usually much more complex due to the fact that the

desired precursor of dopants (e.g., RE chlorides [RECl3]) has relatively low vapor pressure

compared to the standard precursor of MCVD. The second method is the nonvapor

process, i.e., the liquid phase solution doping process. This technique was first reported by

Stone and Burrus [2] and was further improved by Poole et al. [3]. This technique is used

in this study to incorporate dopants, such as aluminum, into silica matrix since aluminum

increases the solubility of RE ions into the host silica to allow high incorporation of RE

without clustering [4]. In addition, pure silica has high phonon energy that stimulates

non-radiative transitions and leads to shorter fluorescence lifetime. All of this will degrade

the amplification performance of an S-band using thulium-doped silica fiber. Aluminum,

being a glass modifier, can modify the host environment of Si–O bonds and improve

the quantum efficiency of the S-band transition. A higher concentration of aluminum has

been shown to reduce the phonon energy of silica host [5].

In the MCVD process, such precursors as SiCl4 are delivered to a quartz substrate

tube, and these mixtures are oxidized and deposited to the inner tube wall by a high

temperature (1,100ıC–2,100ıC) [4, 6].

For the solution doping process, there are a number of parameters that play a

significant role in determining Al2O3 incorporation inside silica matrix, for example, the

type of solvent, concentration of solution, composition (Al/RE ratio) [7], soaking time [8],

soaking temperature [9, 10], and mechanism by which dopants ions are incorporated into

the soot layer whether by chemical adsorption [11] or by solution retention in a porous

soot layer [12]. In addition, oxidation (after soaking) is also a very important process for

providing better quality and productivity of the fabricated preform.

In RE-doped silica, Al2O3 is the most effective dopant as an index raiser due to the

process simplicity compared to GeO2, the standard index raiser dopant in MCVD. Other

reasons include the ability of Al atoms to dilute the RE in silica matrix, the high vapor

pressure of Al2O3, and less evaporation compared to GeO2 during process [4].

In this article, the study of the aluminum solution penetration/impregnation mech-

anism into the soot is analyzed by chemical adsorption and retention effect. A gas

adsorption technique with Brunauer–Emett–Teller (BET) surface area analysis is used

to examine the surface area, porosity, and pores size distribution of the soot deposited

at 1,800ıC. Multiple soaking processes are used to investigate the incorporation and

retention effect of Al ions into the porous layer. Soot morphology properties are also

analyzed by scanning electron microscopy (SEM). In addition, the effect of different

solution concentrations (0.3, 0.7, and 1.2 M) and relative Al2O3 distribution across the

core of the preform is analyzed using a preform profiler (refractive index profile [RIP]).

This is done while maintaining the deposition temperature, SiCl4 flow, soaking time, and

drying time. Elemental analysis using energy dispersive x-ray spectrometry (EDX) is

used to investigate the aluminum distribution and content across the core layer for each

solution concentration and each soaking cycle.

Experimental Procedure

Several Al2O3-doped silica preforms were prepared using MCVD with a solution doping

process. A high-quality silica tube (Heraeus suprasil [F300] Heraeus Group, Hanau,

Germany) with outer diameter of 25 mm and inner diameter of 19 mm was mounted on the

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MCVD and Multiple Solution Doping Process 107

lathe as the initial step in the fabrication process. The inner surface of the substrate tube

was cleaned by several etching passes using sulfur hexafluoride (SF6). The fabrication

process was followed by deposition of silicon tetra-chloride (SiCl4) and oxygen (O2) at a

high temperature (2,120ıC) by slowly moving an oxygen–hydrogen burner (110 mm/min)

in the same direction of reactant flow and fully sintered into transparent glass, which

makes a thin cladding layer “barrier layer.” This process was followed by the deposition

of a 50-cm-long porous core layer (soot), which consists of the same mixture of SiCl4and O2 with the same burner speed but at a lower deposition temperature of 1,800ıC.

Ethanolic solutions were prepared using aluminum chloride hexahydrate (AlCl3.6H2O)

with three different concentrations of 0.3, 0.7, and 1.2 M. The substrate tube was then

carefully removed from the lathe and vertically soaked in the prepared solutions. The

soot was soaked up to three times in each solution for 90 min per single soak using

the designed solution doping apparatus shown in Figure 1. Each soak cycle consists of

vertical soaking, vertical nitrogen drying, and furnace heat treatment. After each soak,

the impregnated soot layer was dried for 30 min with a small flow of nitrogen stream

(0.5 bar) at room temperature. The soot was then exposed to heat treatment in a furnace,

with a ramp-up rate of 5ıC min�1 up to 600ıC before being cooled to room temperature.

This process was repeated for each soak cycle. The substrate tube was then remounted

on the lathe and MCVD process was resumed.

The soot was then subjected to an oxidation process at a temperature of 1,500ıC

with oxygen flow at 1,000 sccm. The porous layer experienced several sintering stages in

the presence of oxygen and helium at temperature ranges from 1,800ıC to 2,000ıC and

fully sintered at the temperature of 2,200ıC. The temperature of the sintering process

was increased gradually to ensure the soot is sintered to fine transparent glass. At the

end of the fabrication, the tube-collapsing process was performed at 2,200ıC to obtain a

solid preform. Table 1 gives the summary of fabrication parameters.

Fabricated preforms were scanned using a preform analyzer to investigate the RIP

of every preform of the intended solution. Small samples of the collapsed preforms were

analyzed using EDX on SEM to check aluminum distribution and concentration within the

core layer. In addition, one preform was prepared with the above-mentioned parameters,

but without the soaking and collapsing processes, to analyze the soot morphology and

pore size distribution using SEM and the gas adsorption technique, respectively.

Figure 1. Solution doping apparatus.

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108 S. M. Aljamimi et al.

Table 1

Summary of fabrication parameters

Preforms fabricatedMCVD C

solution doping

parameters P1 P2 P3

Cladding deposition

temperature

2,120ıC 2,120ıC 2,120ıC

Core deposition

temperature

1,800ıC 1,800ıC 1,800ıC

SiCl4 flow 100 sccm 100 sccm 100 sccm

Sintering

temperature

1,900ıC–2,100ıC 1,900ıC–2,100ıC 1,900ıC–2,100ıC

Collapse

temperature

2,200ıC 2,200ıC 2,200ıC

Soaking time 90 min 90 min 90 min

Solution 0.3 M 0.7 M 1.2 M

N2 drying 30 min 30 min 30 min

Furnace drying

temperature

600ıC 600ıC 600ıC

Oxidation

temperature

1,500ıC 1,500ıC 1,500ıC

Oxidation O2 flow 1,000 sccm 1,000 sccm 1,000 sccm

Results and Discussion

Soot Characterization by Gas Adsorption Technique with BET Analysis

and SEM

Figure 2a presents the nitrogen gas adsorption isotherm curve for the deposited soot

at 1,800ıC. This curve is the first indicator that explained features of deposited soot,

and it can be classified as Type III [13]. According to the International Union of Pure

and Applied Chemistry, the pore width of soot consists of mainly mesopores (2–50 nm)

and partly macropores (>50 nm). Type III isotherm also suggests the existence of a

multi-layer pore structure. Besides that, the pore shape could consist of slit- or wedge-

shaped pores with a shallow pore volume and pore diameters ranging from 4–50 nm,

as indicated in Figure 2b. Figure 2b represents the differential pore volume distribution

using the density functional theory (DFT), an alternative approach to interpret adsorption

data on porous materials [14]. From the DFT, the porosity of deposited soot at 1,800ıC

is mostly distributed in the mesopores range (pore widths in the range from 2–50 nm)

with an average pore size of 31 nm. As shown in this result, pores with a size larger

than 50 nm were found to be too shallow and can be assumed as nonporous.

The BET equation (Eq. (1)), uses the information from the isotherm to determine

the surface area of the sample, where X is the weight of nitrogen adsorbed at a given

relative pressure (P=Po); Xm is monolayer capacity, which is the volume of gas adsorbed

at standard temperature and pressure (STP); and C is constant; STP is defined as 273 K

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MCVD and Multiple Solution Doping Process 109

Figure 2. (a) Isotherm curve for soot deposited at 1,800ıC, (b) pore size distribution for soot

deposited at 1,800ıC, and (c) BET multi-point plot for soot surface area estimation.

and 1 atm [13]:

1

XŒ.P0=P / � 1�D

1

XmCC

C � 1

Xm

P=Po: (1)

Ideally in multi-point BET analysis, a minimum of three data points in the P=Po range

of 0.025 to 0.30 should be used to determine the surface area using the BET equation.

At relative pressures higher than 0.5, there is the onset of capillary condensation, and at

relative pressures that are too low, only monolayer formation occurs. When the BET

equation is plotted, the graph should be linear with a positive slope. The slope and y-

intercept can be obtained using least-squares regression. The monolayer capacity Xm

can be calculated with Eq. (2). Once Xm is determined, the total surface area St can be

calculated with Eq. (3), where Lav is Avogadro’s number, Am is the cross-sectional area

of the adsorbate and equals 0.162 nm2 for an absorbed nitrogen molecule, and Mv is the

molar volume and equals 22,414 mL [13]:

Xm D1

s C iD

C � 1

Cs

; (2)

S DXmLavAm

Mv

: (3)

Figure 2c shows the BET multi-point plot of the deposited soot at 1,800ıC. From the

BET equation and the multi-point plot, the surface area of the deposited soot was found

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to be 20.14 m2g�1. This number is relatively low compared to the soot surface area

reported from Dhar et al. [15] and classical data for mesoporus silica [16]. Both reported

values are in the range of 112.00 to 195.01 m2g�1. In the Dhar et al. case, the soot

was deposited at 1,200ıC, while in this work, the deposition temperature is much higher

(1,800ıC) and with no POCl3 involved. POCl3 usually is used to reduce the viscosity

of the glass during the MCVD process, which could lead to a different surface area

value. Furthermore, the deposition direction in this work is in the forward direction;

thus, the effect of temperature is higher compared to [15]. At higher temperatures, the

deposited soot was found to be of finer particles, averaging a size from hundreds of

nanometers to a few microns, as reported by Cheung et al. [17] with simulation results

Figure 3. (a) Cross-sectional view on substrate tube, (b) agglomerated soot with random distri-

bution in size and structure, (c) close-up image of soot surface (magnification of 20,000�), and

(d) close-up image of soot surface (magnification of 40,000�).

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MCVD and Multiple Solution Doping Process 111

at temperature 1,700ıC. The gas adsorption technique reveals some level of restrictions

for the adsorption performance process for this type of soot in terms of soot multi-layer

formation, pore shape and size, and effective surface area.

Furthermore, two samples of deposited soot were taken for the analysis of the

soot morphology and network structure. Figure 3a shows a cross-sectional view of

the deposited soot onto the inner wall of the substrate. The image shows the forma-

tion of multi-layer soot with a total thickness of about 5 �m with various sizes of

agglomerated soot. This can be explained by the thermophoretic process, where variation

of agglomerated soot size deposited is subject to the thermophoretic process, which is

governed by temperature difference, gravitational force, and total flow rate. In terms

of density, the deposited layer shows a low degree of density, possibly due to high

temperature, low precursor flow, and low total gas flow. Figure 3b shows the upper view

of the deposited soot at a magnification of 1,200�. It can be noticed that there are small

hole structures distributed uniformly. Figures 3c and 3d show the images of the void

structure at magnifications of 20,000� and 40,000�, where random build-up of voids in

the soot network can be seen. In this work, the void dimension is also random in size,

area, and volume, as labeled in Figure 3c. It could be postulated that the void of an

agglomerated soot network is the result of the thermophoretic deposition process, void of

a soot network with an open or a closed structure interconnected to form a 3D structure.

Preform Characterization

RIP. The RIP of Al2O3 was measured along the collapsed preform length for each

preform. Since Al2O3 has a higher refractive index than silica, the refractive index across

the preform core reflects the Al distribution across the deposited soot. The refractive index

difference (�n) was found to be uniform without a central dip due to the strong retention

of SiO2 with Al2O3 during the sintering process. The retention force prevents Al2O3

from evaporating compared to GeO2, which can evaporate during sintering process [18].

The RIPs for single, double, and triple soak cycles for each solution concentration are

illustrated in Figures 4a, 4b, and 4c, respectively. It can be seen that when the number

of soak cycles is increased, the proportion of Al RIP increases appreciably. At the same

time, an increment of Al solution concentrations results in distinct RIP increments in

each preform. However, the amount of Al that penetrates into the soot is dependent on

the soot porosity and voids among the silica network.

From the �n results in Table 2, the increment percentage of �n from the second

soak to the third soak is approximately half of the increment percentage obtained from

the first soak to the second soak. This indicates that aluminum penetration through the

soot becomes more difficult for the triple soak cycle compared to the first and second

soak cycles.

Throughout the multiple concentrations and multiple soaking cycles process, several

observations can be noticed, such as a higher Al concentration leads to high refractive

index difference and multiple soaking cycles with heat treatment between soaking cycles

enables higher retention of Al in the core but with a wider core diameter. From RIP

results, it is clearly observed that a higher concentration of Al leads to a wider core

diameter and less depression in the thin deposited cladding layer (barrier layer). For the

low Al concentration (0.3 M), the depression in the cladding layer is distinguished, and

this depression decreases when the concentration is increased to 0.7 M. For the highest Al

concentration (1.2 M), the index difference is high and the depression cladding region is

shallow. The reason for this phenomena, however, is still under further investigation, but

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Figure 4. Al2O3 RIP as a function of multiple soaking cycles in solution concentrations of:

(a) 0.3 M, (b) 0.7 M, and (c) 1.2 M.

it could be related to the diffusion from the core to the cladding layer due to the ionic

mobility of the Al ions during the sintering and collapsing processes. Since the high

solution concentrations (0.7 and 1.2 M) have a higher number of Al ions than the

low solution concentration (0.3 M), there is a high tendency of Al ions to diffuse to

the deposited cladding layer.

SEM-EDX. EDX has been used to analyze the aluminum’s distribution and content

across the core layer of collapsed performs for each solution concentration and soaking

cycle. During EDX measurement, the detector was able to detect and measure the

Al concentration for the different solution concentrations and multiple soaking cycles,

except the sample with the lowest concentration of 0.3 M, and a single soak cycle was

not detected. EDX linescan measurements were carried out at a middle circumferential

position for each polished sample to investigate the Al distribution profile across the core

layer. For further investigation, the points and identification (points&id) measurement

technique was performed point by point with a fixed interval among the points to cover

Table 2

Summary of �n for different concentrations and multiple soaking cycles

Refractive index

difference (�n) of Al2O3

Increment percentage

of �n

Solution

concentration

First

soak

cycle

Second

soak

cycle

Third

soak

cycle

From first

soak to second

soak cycle (%)

From second

soak to third

soak cycle (%)

0.3 M 1:44 � 10�3

1:97 � 10�3

2:2 � 10�3 37 17

0.7 M 2:7 � 10�3

4:5 � 10�3

6:0 � 10�3 67 33

1.2 M 5:4 � 10�3

8:1 � 10�3

10:0 � 10�3 50 23.5

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MCVD and Multiple Solution Doping Process 113

the whole length of the core diameter. The purpose of this measurement is to check the

aluminum retained as weight percentage in the collapsed core layer.

For a high Al concentration (1.2 M), the EDX linescans for single, double, and

triple soak cycles are compared and summarized in Figure 5a. Al distribution around

the core region has a similar pattern for RIPs where Al increased gradually, reached the

maximum values (peak), then decreased gradually. It can be observed from the figure

that the repeated soak cycles increased the amount of Al across the core layer and

widened the core diameter, which is in agreement with RIP pattern. Figure5b shows the

Al content across the collapsed core layer as weight percentage (wt%) for each soak

cycle. The average peak content of Al weight percent incorporated into the perform core

increased from �1.8 wt% for a single soak cycle, to �3 wt% for a double soak cycle,

to �4.33 wt% for a triple soak cycle. The core diameter examined by EDX is about 1,

1.2, and 1.6 mm for single, double, and triple soak cycles, respectively.

For medium Al concentration (0.7 M), the EDX linescans for single, double, and

triple soak cycles are compared in Figure 6a and Al content as weight percent in Figure 6b.

The averaged peak content of Al weight percent incorporated into the preform core

increased from �0.90 wt% for a single soak cycle, to �1.3 wt% for a double soak cycle,

to �2.5 wt% for a triple soak cycle. The core diameter examined by EDX is about 0.90,

1, and 1.1 mm for single, double, and triple soak cycles, respectively.

For the lowest Al concentration (0.3 M), linescan and points&id measurement were

performed for double and triple soak cycles only, shown in Figure 7. The averaged peak

content of Al weight percent incorporated into the perform core increased from �0.6 wt%

for a double soak cycle to �1.03 wt% for a triple soak cycle. The core diameter examined

by EDX is about �0.76 and �0.88 mm for double and triple soak cycles, respectively.

The Al content wt% profile has the same pattern as the Al linescan distribution

profile. It has a rather constant maximum value in the middle of the core and decreases

sharply toward zero at the sides. The Al distribution is quite uneven, especially for the first

and second soak cycles, and it improved with slightly even distribution for the third soak,

where Al occupies almost the entire available surface area and voids, which maintains

its retention among silica network.

It can be noticed that during the third soak, a lesser amount of Al was engrossed into

the soot, because the porous and voids were already filled during the first and second

soak cycles. Furthermore, the soot has small surface area of 20.14 m2g�1, so less Al

can be incorporated during the third soak cycle through surface area adsorption. The

mechanism of Al incorporated in each soak/heat treatment cycle was discussed in [19],

which suggested that during the first soak/heat cycle, the amount of Al is controlled by

the amount of solution that can penetrate into the interstices of the silica soot network.

After the solution drains out, some slits of AlCl3.6H2O and ethanol remain trapped in the

interstices. Heat treatment is applied to remove excess ethanol, and at 600ıC, all AlCl3trapped previously in the soot has been converted to Al2O3. For the second soak/heat

cycle, a new amount of Al is deposited on top of the first deposit, perhaps occupying the

surface area not covered during the first soak/heat cycle. In the third soak/heat cycle,

the available penetration pathways would be more restricted, so less Al is expected to be

deposited.

According to the DFT analysis of the soot sample deposited at 1,800ıC, the porosity

is distributed in the mesoporous range, which has poor surface area of 20.14 m2g�1.

In this case, most Al will be adsorbed to the soot surface area during the first soak

cycle and heat treatment at 600ıC. Then the soot surface area was found decreased to

1.97 m2g�1 after the first soak cycle as obtained by BET surface area analysis. During

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114 S. M. Aljamimi et al.

(a)

(b)

Figure 5. (a) EDX line-scans results of Al distribution across the core layer for solution

concentration of 1.2 M and (b) Al wt% profile across the core layer for solution concentration

of 1.2 M as a function of number of soak cycles.

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MCVD and Multiple Solution Doping Process 115

(a)

(b)

Figure 6. (a) EDX linescan results of Al distribution along the core for solution concentration

of 0.7 M and (b) Al wt% profile across the core layer for solution concentration of 0.7 M as a

function of number of soak cycles.

the second soak cycle, the adsorption process becomes more restricted for Al compared

to the first soak cycle. Al will find less space of voids to occupy among the silica

network, so fewer adsorption processes take place. The soot surface area is measured

after the second soak cycle by BET surface area analysis and was found to decrease to

1.61 m2g�1; this suggests that the amount of Al incorporated in the second soak cycle is

probably by the retention effect among voids and a minimal adsorption process for the

available surface area from the first soak cycle. Al will face more restricted pathways

to utilize its retention during the third soak cycle and will try to occupy the available

space of void among silica networks. Multiple soaking processes reveal that the retention

effect has a major function for incorporation of Al into the voids among a soot network.

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116 S. M. Aljamimi et al.

Figure 7. Al linescan and content (wt%) profile across the core layer for solution concentration

of 0.3 M as a function of number of soak cycles.

Moreover, the increment of the core diameter is caused by the amount of Al that was

incorporated into the core during multiple soaking cycles, which might diffuse to the

deposited cladding layer.

The RIP and EDX measurements have provided preliminary insight on aluminum

distribution in collapsed preforms with different intended solution concentrations. It is

also clear that higher aluminum concentration and multiple soaking cycles lead to a

higher RIP and wider core diameter.

Conclusion

Solution doping at the porous soot stage of MCVD is a commonly used technique to

introduce Al2O3 and other dopants into the core region of silica performs. In this study,

silica soot deposited at 1,800ıC on the substrate tube has been analyzed. A Gas adsorbtion

techinque was used to provide information about the type of isotherm and soot porosoity

range (mesoporous). Soot suface area was analyzed by BET analysis, founded initially as

20.14 m2g�1. This intial surface area was decreased after the first and second soak cycles

to 1.97 and 1.61 m2g�1, respectively. SEM was used to analyze the soot morphology and

silica network, where soot and voids were found to be random in size.

High incorporation of Al2O3 into the core layer was achieved by using multiple

soaking cycles, which yields a higher refractive index difference across the core layer. A

significant increment in terms of �n was obtained for each solution concentration during

several soaking cycles. This study suggested that the retention effect plays a major role

in incorporating Al into the voids among a silica network than the adsorption process

through the surface area of the soot, since the surface area is small (20.14 m2g�1).

From the Al2O3 RIP, the distribution of Al was found to be higher at the center of

the preform. The preform core indicates no “central dip” in all of Al concentrations

(0.3, 0.7, and 1.2 M) with multiple soak cycles. Core diameters were increased as the

number of soaking cycles were increased, which was verfied by EDX measurement.

Depression of the deposited cladding layer was distinguished for a low concentration

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MCVD and Multiple Solution Doping Process 117

(0.3 M) and tended to decrease as the solution concentrations and the number of soaking

cycles were increased.

The effective result and analysis of this study is important to provide full informa-

tion about solution doping parameters, multiple soaking cycle procedures, the effect of

different solution concentration on RIP, and the Al distribution profile across the core

layer, which can enhance the quality of fabricated performs.

Funding

The authors would like to thank Telekom Research & Development for providing the

funding (RDTC 11076) to perform this work.

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Biographies

S. M. Aljamimi received his B.Eng. in electronics engineering, majoring in telecom-

munication, from Multimedia University Malaysia in 2011. He is working toward his

M.Eng.Sc. in optical fiber fabrication and photonics while working as a research officer

at Multimedia University.

M. S. Khairul Anuar received his B.Sc and M.Sc. in physics from University

Malaya in 2000 and 2004, respectively. He joined Telekom Research & Development in

2004 under the Optical Material Devices Group (Optical Fibre) for 2 years and switched

to the Laser Diode Fabrication (LD Group). From 2007 to the present, he joined the

MCVD Group due to his interest in optical fibers. His work focuses on understanding

the fabrication of optical fiber preforms, including chemistry, thermophoretic of particle

transport, fluid flow, and preforms characterization.

S. Z. Muhamad-Yassin graduated from University of Malaya in 2004 with a bach-

elors in science physics with honors. In 2009, received his M.Eng.Sc. from Universiti

Teknologi Mara in optical amplifiers. From 2009 until now, he is a research officer at

Telekom Research & Development. Most of his research involves the evolution of the

fabrication and characterization of rare earth optical fiber performs.

M. I. Zulkifli graduated from University of Malaya in 1999 with a bachelors in

science physics with honors. He then joined the same university as a tutor at the Center

for Science Foundation for 6 years. He joined Telekom Research & Development in 2005,

focusing on optical fiber preforms using the MCVD technique. He is now serving as a

research officer at Telekom Research & Development, and most of his research involves

the fabrication and characterization of rare earth optical fiber performs.

S. Hanif received his diploma in electronic engineering from Polytechnic of Kota

Bharu, Kelantan, in 1999. He joined Telekom Research & Development in 2001 in the

Calibration Unit; in 2008, he joined the Telekom Malaysia Research and Development–

Multimedia University laboratory as a Technical Assistant.

N. Tamchek received his B.S. (in 2001) in physics from Kanazawa University,

Japan, and his M.Sc. (in 2004) and Ph.D. (in 2010) in photonics from the University of

Malaya, Kuala Lumpur, Malaysia. He is currently a lecturer at the Department of Physics,

University Putra Malaysia. He joined the MCVD Laboratory at Telekom Research &

Development in 2009. His work has focused on development and fabrication of photonics

devices using flame hydrolysis deposition and MCVD system. He is also involved with

the development of photonic devices for telecommunication and sensors.

Z. Yusoff received his B.Eng. in electronics and communications from the University

of York, UK, in 1999. He then completed his Ph.D. in optical communications from the

University of Southampton, UK, in 2004. He has been a member of the academic staff of

the Faculty of Engineering, Multimedia University (MMU), since 1999. He is currently

an associate professor, the Chairman for Center for Advanced Devices and Systems, and

the Deputy Director of Research Management Center. He is a recipient of a number

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MCVD and Multiple Solution Doping Process 119

of research grants from various sources worth almost RM 6 million. To date, he has

published over 60 research papers in international journals and conferences.

H. A. Abdul-Rashid received his B.Eng. in electrical and electronic engineering

from University College, London, in 1997 and his M.Eng.Sc. in signal processing from

Multimedia University in 2002. He later received his Ph.D. from Multimedia University

in optical communication systems in 2007. He has been with the Faculty of Engineering,

Multimedia University, since 1998. He currently lectures at the faculty besides leading

a research team at the Center for Photonics and Electronic Devices (CPED) in specialty

fiber fabrication, optical amplifiers, fiber sensors, and fiber lasers.

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