Trend in Optical Fibers and Cables for Fiber-To-The-Home

ABSTRACT 

The configuration of optical fiber cables deployed in 

Japan and the requirements for FTTH are described. 

The optical fiber used in FTTH is introduced, and 

bending loss improvement and transmission range 

expansion are described. Optical fiber cables which 

meet the requirements peculiar to FTTH are also 

introduced and reviewed. 

Key words: FTTH, optical fiber cable, FTTX, 

Japan 

I. INTRODUCTION 

In Japan, "e-Japan Strategy" was formulated in January 

2001 with the goal of making Japan "the most 

advanced IT nation in the world by 2005" [1] . Today, 

the improvement of Japanese broadband infrastructure 

is accelerated by the strategy, and broadband 

networks are available for the lowest cost and the 

fastest speed in the world. The number of broadband 

subscribers including Fiber To The Home (FTTH), 

Digital Scriber Line (DSL), cable internet, and wireless 

such as Fixed Wireless Access (FWA) has 

reached about 20 million. Today DSL subscribers 

account for about 70% of total broadband subscribers, 

but its quarterly increment tends to reduce. In contrast, 

the number of FTTH subscribers reached about 2.9 

million in March 2004, and its quarterly increment 

tends to increase. Thus it is anticipated that the 

number of FTTH subscribers will surpass the num- 

Feature Articles: Optical Fiber Communications 

Trend in Optical Fibers and Cables for 

Fiber-To-The-Home 

Takahiro Hamada , Shoichiro Matsuo , Kuniharu Himeno 

Fujikura Ltd. Optics and Electronics Laboratory, Japan 

ber of DSL subscribers in the near future [2] . 

In order to support the continuing spread of FTTH 

cost reduction of materials used in FTTH and simplification 

of construction are required. As a result 

optical fibers and cables with performances peculiar 

to FTTH are desired. In the next section, we describe 

the configuration of optical fiber cables deployed in 

Japan and requirements for them. In section 3 and 4, 

we introduce the optical fiber used in FTTH, and 

describe its bending loss improvement and transmission 

range expansion. In the rest of the report, we 

introduce optical fiber cables which meet the requirements 

peculiar to FTTH. 

II. CONFIGURATION OF OPTICAL 

FIBER CABLES FOR FTTH IN JAPAN 

The typical configuration of optical fiber cables for 

FTTH in Japan is shown in Fig.1. An access line 

from the network center to the subscriber consists of 

the duct cable installed under the ground near the 

network center, the aerial cable installed between 

poles, the drop cable branched from the aerial cable, 

and the indoor cable in the subscriber. 

The duct cable should have a smaller diameter and 

house fibers with a high density since the cable is 

especially installed in existing duct in metropolitan 

area. The aerial cable should have a long length on 

a drum to reduce connection points of the cables 

and should be light in weight for easy installation. 

The drop cable requires low cost since the cable 

China Communications December 2005 59

60 


cost directly account for a cost per subscriber, and 

should be able to be handled easily for quick and 

economical installation. 

A surplus optical fiber took out from the cables is 

wound and stored in a closure or a cabinet. In 

particular, the fiber in the drop cable is required to 

be able to be bent small to downsize the closure 

and the cabinet. Furthermore, a fiber in an indoor 

cable may be bent with a small curvature for wiring 

along a wall and for storage. 

Fig�� Fig�� Fig�� Fig�� Fig�� Configuration Configuration of of cables cables in in in FTTH� FTTH� FTTH� FTTH� FTTH� 

3. OPTICAL FIBER USED IN FTTH 

The structure of a silica optical fiber, which is the 

most popular optical fiber in telecommunications, is 

shown in Fig.2. The fiber consists of a cladding 

which is made from silica and a core whose refractive 

index is raised slightly higher than that of the 

Fig�� Fig�� Fig�� Fig�� Fig�� Structure Structure of of silica silica optical optical fiber� fiber� fiber� fiber� fiber� (a) (a) dimensions� dimensions� dimensions� dimensions� dimensions� (b) 

(b) 

refractive refractive index index profile� profile� profile� 

profile� profile� 

cladding by doping germanium. 

Light can be confined within the core by the coreto 

-cladding index difference. The structure is characterized 

by the core diameter 2a and the relative 

refractive index difference Light confined in the 

fiber propagates at a very small attenuation, e.g. 0. 

2-0.3 dB/km. The cladding diameter is 125 µm, and 

the cladding is coated with plastic resin to a diameter 

of 250 µm. 

The optical fiber has two main categories; a multimode 

fiber and a single-mode fiber. The 

core diameter of the multimode fiber is 50 

µm and the fiber is easy to connect with each 

other and with an inexpensive light source, 

so that the fiber is applied to short distance 

communications. The single-mode fiber 

whose core diameter is about 10 µm is applied 

to high-speed and/or long-distance communications 

since more sophisticated techniques 

are required to connect with each 

other and with optical devices. 

The fiber with an index profile as shown in 

Fig.2 can be operated as a single-mode fiber 

when the normalized frequency V defined as the following 

equation is less than 2.405 at a wavelength of . 

(1) 

(2) 

Possible combinations of parameters which 

result in single-mode operation are infinitely. 

However, the dimensions and properties of "the 

single-mode fiber" for telecommunications are 

defined in ITU-T Recommendation G.652. 

In Japan, the single-mode fiber complying G. 

652 are used even in FTTH whereas FTTH 

covers short distance and requires economical 

materials. This is because arc-fusion splice and 

connector for the fiber have been highly developed 

and the cost of optical devices for the fiber 

has become reasonable. 

3.1 Solution for small bending radius 

An optical fiber for a drop cable or an indoor 

China Communications December 2005

cable should be able to be bent in a smaller curvature 

as described in Section 2. However, the fiber bent in 

a small radius causes transmission loss, which is 

called the bending loss. 

A single-mode fiber with a smaller mode field 

diameter (MFD) has a lower bending loss. MFD may 

be reduced by enhancing the refractive index of the 

core and reduce the core diameter so as to keep the 

single-mode conditions shown in Eq. (1). 

We have developed FutureGuide ® -SR15, which 

can achieve a negligibly low bending loss at a bending 

radius of 15 mm by slightly enhancing the 

refractive index of the core. This allowable bending 


radius is a half of that of the conventional singlemode 

fiber (C-SMF). The wavelength dependences 

of the bending losses for FutureGuide ® -SR15 and C- 

SMF are shown in Fig.3 [3] . 

The bending loss for FutureGuide ® -SR15 is about 

one-tenth of that for C-SMF. The bending loss at 

longer wavelength increases as shown in Fig.4 since 

the MFD at a longer wavelength becomes larger. 

The characteristics of FutureGuide ® -SR15 and 

ITU-T recommendation G.652.B are shown in Table 

1. The allowable bending radius of FutureGuide ® - 

SR15 is a half of that of ITU-T recommendation G. 

652.B. The typical MFD of FutureGuide ® - 

SR15 is smaller than that of ITU-T recommendation 

G.652.B. However, 

FutureGuide ® -SR15 is applicable to all regions 

in FTTH and even in trunk lines since 

all characteristics of FutureGuide ® -SR15 

complies with G.652.B. 

3.2 Solution for wideband transmission 

Wavelengths used for the optical communications 

are defined as shown in Fig.4. Even 

Fig�� Fig�� Fig�� Fig�� Fig�� Wavelength Wavelength dependence dependence dependence of of binding binding loss loss on 

on 

in FTTH, Wavelength Division Multiplex- 

FutureGuide 

FutureGuide FutureGuide 

ing (WDM) 

is used to 

construct 

passive optical 

networks 

(PON) to 

save the 

number of 

optical fibers 

per 

subscriber. 

In WDM for 

FTTH, Ctransmission 

band is used 

for downstreamtransmission 

® �SR�� SR�� SR�� SR�� SR�� and and C�SMF C�SMF C�SMF C�SMF C�SMF at at ø�� ø�� ø�� ø�� ø�� mm mm and and �� turn� turn� turn� turn� turn� 

Table.1 Characteristics of FutureGuide ® -SR15 and ITU-T recommendation G.652.B. 


62 


from a network center to a subscriber, and O-trans- sintering the glass particles. 

mission band is used for upstream transmission from It has been reported that the fiber without OH 

the subscriber to the network center. In addition, the absorption peak can be made by optimization of 

new system that uses C-transmission band for broad- dehydration conditions and fiber structure in the 

casting and O-transmission band and S-transmission 1980s 

band for optical communications has started to be 

deployed. WDM-PON using more wavelengths is in 

research towards a future FTTH system. 

In C-SMF, E-transmission band is not used for 

[5-7] . Recently, this type of fiber, "low water 

peak fiber," has been commercialized and 

standardized. We also have developed FutureGuide ® - 

SR15E, which have both low bending loss and low 

water peak. The spectral attenuations of 

FutureGuide ® -SR15E and C-SMF are 

shown in Fig.5. FutureGuide ® -SR15E 

has a low OH absorption and can be 

used for optical communications at Etransmission 

band [3,8] . 

Exposing an optical fiber to hydrogen 

may result in the increase of an 

attenuation at 1383 nm [9,10] . Therefore, 

the upper attenuation value of a low- 

Fig�� Fig�� Fig�� Fig�� Fig�� Wavelengths Wavelengths used used for for for the the optical optical communication� 

communication� 




water-peak fiber after hydrogen aging 

optical communications due to possible larger 

attenuation at 1383 nm. The attenuation at 

1383 nm results from the second overtone 

of the fundamental Si-OH vibration at 2700 

nm. OH groups in a preform must be eliminated 

for decreasing the attenuation at 1383 

nm. 

An optical fiber preform is made of SiO2 from SiCl through the thermal oxidation 

4 

and/or the hydrolysis reaction. 

As for the perform synthesis methods 

using the thermal oxidation reaction, such as 

the MCVD and the PCVD methods, the reduction of 

OH-groups contained in raw material, a substrate 

and a jacketing tubes, and modification of the apparatus 

for tighter gas leak have been attempted to 

reduce the absorption at 1383 nm [4] test (IEC60793-2-50) is defined by ITU-T G.652.C 

and G.652.D. The attenuations of FutureGuide 

. 

As for the perform synthesis methods using the 

hydrolysis reaction, such as the VAD and the OVD 

methods, OH-groups in glass particles generate 

inherently. Therefore, when a preform is made by the 

hydrolysis, OH-groups in the preform is eliminated 

by the dehydration process in which a soot perform 

is heated in the presence of Cl or SOCl before 

2 2 ® - 

SR15E and ITU-T G.652.D are shown in Table 2. 

The characteristics of FutureGuide ® -SR15E other 

than those shown in Table 2 are the same as the 

characteristics of FutureGuide ® -SR15 shown in Table 

1. FutureGuide ® -SR15E has an allowable bending 

radius of 15 mm and is compliant with ITU-T Recommendation 

G.652. As a result, FutureGuide ® Fig�� Fig�� Fig�� Fig�� Fig�� Spectral Spectral attenuations attenuations of of FutureGuide FutureGuide 

- 

SR15E can be used for broadband WDM transmission 

line in access and core networks. 

® �SR��E �SR��E �SR��E �SR��E �SR��E and and and C�SMF� C�SMF� C�SMF� 

C�SMF� C�SMF� 


Increasing the relative-index difference 

between the core and the cladding results 

in decreasing a bending loss but decreasing 

a MFD. If two fibers with Gaussian 

electric fields and with MFDs of 2W and 1 

2W , the connection loss in dB, Ls, 

2 

between the fibers can be calculated by 

Eq. (3). 

(3) 

Obviously, the connection loss is minimized when 

W =W . When an optical fiber with an enhanced 

1 2 


IV. NEW OPTICAL FIBER IN 

DEVELOPMENT FOR FURTHER 

BENDING LOSS IMPROVEMENT 

We so far have described fibers with a simple refractive-index 

profile called as the step-index profile as 

shown in Fig.2 (b). In addition to the requirements 

for an indoor cable as described in section 2, the 

cable is desired to be able to be handled without 

worrying about bending just like a metal 

cable [11] core refractive index for 

reduction of bending loss 

is connected with C- 

SMF, connection loss increases 

according as the 

MFD difference between 

those two fibers. 

A fiber with improved 

bending loss for an indoor 

cable should be connected 

with C-SMF applied in a 

drop cable and an optical 

network unit (ONU) in a 

subscriber. Therefore, we 

should consider not only 

bending loss but also MFD of the fiber so as to 

maintain its MFD as large as that of C-SMF, 9.2 µm. 

We have proposed an improved bending loss fiber 

with a refractive index profile as shown in Fig.6 

. In this section, we introduce the 

fiber which has a new refractive-index 

profile so as to achieve advanced bending 

loss properties. 

[12] Table 2. Attenuations of FutureGuide 

. 

The feature of the profile is that "trench" with a lower 

refractive-index than that of the fused silica locates 

between the inner cladding around the core and the 

outer cladding. The index trench at the edge of the 

mode field works to confine the mode field stronger 

® -SR15E. 

Fig�� Fig�� Fig�� Fig�� Fig�� Schematic Schematic of of trench trench trench index index profile� profile� profile� profile� profile� 

than the step index profile even if MFD of the fiber is 

the same as that for a fiber with the step index profile. 

As a result, a fiber with optimized parameters of 1 ~ 

3 and r2 ~r shown in Fig.6 can achieve improved 

3 

bending loss and connection loss properties com- 


64 


pared with the step index profile. 

As an example, simulated and measured bending 

loss at 1650 nm as a function of bending radius for 

fibers with the trench-index and step-index profiles 

Fig�� Fig�� Fig�� Fig�� Fig�� Simulated Simulated Simulated and and measured measured bending bending loss loss at at ��nm ��nm ��nm ��nm ��nm as as a a func� func� func� func� func� 

tion tion of of bending bending radius radius for for for fibers fibers with with trench�index trench�index trench�index trench�index trench�index and and step�index step�index step�index step�index step�index 

profiles� profiles� profiles� profiles� profiles� 

are shown in Fig.7. The bending loss of the fiber with 

a trench index profile is lower than that 

of the fiber with a step index profile. A 

mechanical splice loss between the 

fiber and C-SMF is 0.15 dB in average 

and 0.03 dB in standard deviation, 

which is acceptable for practical use. 

V. EASY-HANDLING Ø0.5 

-MM OPTICAL FIBER 

It has been necessary to simplify the 

installation of cables and to reduce 

construction time to popularize FTTH. 

A fiber with thicker coating than the 

conventional fiber with a diameter of 

0.25 mm is expected to ease the handling 

in installation and connection. 

However, commercially available connection 

tools and devices for FTTH are 

specialized for Ø 0.25-mm fiber. 

The schematic of structure for the 

easy-handling Ø0.5-mm optical fiber is shown in 

Fig.8. Two layers of UV curable resin and a thin layer 

of colorant are applied to Ø0.125 mm silica fiber, and 

the outer diameter of this fiber is Ø0.25 mm. The 

low-bending-loss single-mode fiber 

(FutureGuide ® -SR15) is employed as 

the silica fiber in order to reduce bending 

radius in storage and loss. 

The outer surface of this fiber is coated 

with colored UV curable resin, and the 

final diameter is 0.5 mm. This layer is 

designed to be easily strippable from 

the Ø0.25-mm fiber but to be stably 

attached to the fiber. As a result, the 

existing commercially available splice 

tools and devices can be applied to the 

new fiber. The characteristics of Ø0. 

5mm optical fiber are shown in Table 3. 

VI. DROP CABLE 

In Japan, the typical drop cable wired from an aerial 

Fig�� Fig�� Fig�� Fig�� Fig�� Schematic Schematic Schematic of of the the structure structure for for Ø�� mm mm mm optical optical fiber fiber in� in� in� in� in� 

crease crease in in handling� handling� handling� 

handling� handling� 


decreasing the number of manufacturing process and 

reducing the cable diameter. For easy installation, 

the cable has been designed so as to take the fiber out 

easily. The Ø0.5-mm optical fiber described in the 

previous section also will be employed in the cable. 

The cable can be separated off the supporting wire 

without special tools thanks to the notch between the 

supporting wire and the cable in order to improve the 

handling for the installation. In addition, the fiber 

can easily be taken out the cable thanks to the notch 


Table.3 Characteristics ofØ0.5-mm optical fiber. in the center of the cable. 

Central value The cable size has been reduced to 5 mm 

Attenuation 

1.31 µm 0.340 dB/km 2 mm. The strength member is made of 

1.55 µm 0.193 dB/km the plastic material. The sheath has good 

Handling property 

flame-resistance and reduced environmental 

burdens by employing non-halogen 

material. 

VII. AERIAL CABLE 

Aerial cables are popular in Japan. The 

length of an aerial cable on one drum 

should be elongated to reduce connection 

points of the cables for installation 

cable to a subscriber contains one optical fiber as 

cost reduction. In addition the cable should be 

shown in Fig.9. The drop cable has been designed in 

consideration of cost reduction and easy installation. 

The cost reduction of the cable has been achieved by 

light in weight for easy installation. The key 

points of the cable design are described as follows. 

[13] 1.55 µm 3.8 dB 

Crush test 490 N/10cm 

Fiber strength 

Connection effect 

1.55 µm 

20 %/min 

1.55 µm 

0.01 dB 

5.2 GPa 

36 dB 

Temperature depen 

dence of optical loss 

-30 1.55 µm

66 


(a) 24-fiber aerial cable (b) 100-fiber aerial cable 

Fig�� Fig�� Fig�� Fig�� Fig�� Structure Structure of of aerial aerial aerial cable� cable� cable� cable� cable� 

Steel messenger 

4-fiber ribbons 

Central member 

Sheath 

Rip cord 

Fig.10. In Japan, aerial cables with up to 640 fibers 

are available. Downsizing the SZ-slotted rod in the 

cable contributes to reducing cable diameter and 

weight. The fiber ribbon in the cable can be split 

into individual fibers with a special splitting tool in 

order to connect with another aerial cable or a drop 

cable for distribution. 

VIII. DUCT CABLE 

Fig�� Fig�� Fig�� Fig�� Fig�� Structure Structure of of ��fiber ��fiber ��fiber ��fiber ��fiber duct duct cable� cable� cable� 

cable� cable� 

SZ-slotted rod with 5 slots 

A duct cable should have a 

smaller diameter and house the 

fiber with a high density since 

the cable is installed especially 

in existing duct in metropolitan 

area. For example, ultra small 

diameter multi-core duct cable 

shown in Fig.11 can permit to 

house 1000-fiber in 29-mm 

diameter. 

IX. CONCLUSION 

Optical fibers and cables dedicated 

to FTTH in Japan have been introduced and 

reviewed. Those will contribute to construct FTTH 

systems efficiently and speedy. Those technologies 

may contribute construction of FTTX also in other 

countries. Further research and development will 

continue in order to solve problems in FTTH or 

FTTX construction. 

8-fiber 

ribbons 

Tension 

member 

Sheath 

Slotted 

core 

Water 

blocking 

tape 

Rip cord 

REFERENCE 

[1] Ministry of Internal Affairs 

and Communi-cations, 

Information and Communications 

Policy Site, Japan, 

"MPHPT Communications 

News Sept. 10,2001,Vol.12, 

No.11," http://www.soumu. 

go.jp/joho_tsusin/eng/Releases/NewsLetter/Vol12/ 

Vol12_11.html. 

[2] Ministry of Internal Affairs 

and Communica-tions, Information 

and Communications 

Policy Site, Japan, "2004 

WHITE PAPER Information 

and Communications in Japan," 


http://www.johotsusintokei.soumu.go.jp/ 

whitepaper/eng/WP2004/2004-index.html. 

[3] K. Ichii, N. Yamada, M. Fujimaki, K. Harada, 

K. Tsurusaki: "Characteristics of low macrobending 

loss SMF (FutureGuide(r)-SR15E) with low water 

peak," Proc. 2004 IEICE General Conference, B-10- 

2, 2004. 

[4] P. Matthijsse, D. R. Simons: "Towards the 

low limits of 1383 nm loss in PCVD enabled 

single mode fibre production," OFC 2004, TuB5, 

2004. 

[5] T. Moriyama, O. Fukuda, K. Sanada, K. Inada, 

T. Edahiro and K. Chida: "Ultimately low OH 

content V.A.D. optical fibres," Electronics Letters, 

vol. 16, pp. 698-699, 1980. 

[6] F. Hanawa, S. Sudo, M. Kawachi and M. Nakahara: 

"Fabrication of completely OH-free V.A.D. fibre," 

Electronics Letters, vol. 16, pp. 699-670, 1980. 

[7] K. Kosaka, T. Moriyama, M. Miyamoto, R. 

Yamauchi and O. Fukuda: "Fabrication of ultra lowloss 

and low-OH VAD single mode fibers," ECOC'84, 

pp. 292-293, 1984. 

[8] T. Nunome, H. Kutami, M. Saito, M. Fujimaki 

and K. Harada: "Optical fiber with low attenuation 

at the water peak for broadband communications," 

Proc. 2001 IEICE Society Conference, SB-12-2, 2001. 

[9] K. Mochizuki, Y. Namihira and H. Yamamoto: 

"Transmission loss increase in optical fibres due to 

hydrogen permeation," Electronics Letters, vol. 19, 

pp. 743-745, 1983. 

[10] K. H. Chang, D. Kalish and M. L. Pearsall: 

"New hydrogen aging loss mechanism in the 1400 

nm window," OFC/IOOC '99, PD22-1-3, 1999. 

[11] J. Zhou, K. Nakajima, K. Tajima, K. Hogari 

K. Sato, I. Sankawa: "Application of PCF to 

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premises," Technical report of IEICE, OFT2002- 

81, 2003. 


[12] S. Matsuo, M. Ikeda and K. Himeno: "Bend- 

Insensitive and Low-Splice-Loss Optical Fiber for 

Indoor Wiring in FTTH," OFC2004, ThI3. 

[13] M. Sugimoto, K. Nishizawa, A. Takahashi: 

"Sield Trial of Newly Optical Drop and Indoor 

Cable," Proc. 2005 IEICE General Conference, B- 

10-10, 2005. 

[14] H. Iwata, S. Tomita, K. Hogari: "Novel Optical 

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IWCS 1999 Proc., pp. 20-24, 1999. 

BIOGRAPHY 

Takahiro Hamada was born in Fukuoka, Japan, 

in 1971. He received the B.E. degree in applied 

chemistry from Kyushu Institute of Technology , 

Fukuoka, Japan in 1994, and the M.E. degrees in 

electrical engineering from Shizuoka University, 

Shizuoka, Japan in 1996.He has been with Fujikura 

Ltd. Chiba, Japan, since 1996 and has been working 

on the development of optical fibers process 

technology. 

Shoichiro Matsuo was born in Fukuoka, Japan, 

in 1964He received the B.E. and M.E. degrees in 

electrical engineering from Kyusyu University, 

Fukuoka, Japan in 1988 and 1990. He jointed 

Fujikura Ltd. in 1990, where he has been working on 

design and development of optical fibers. 

Kuniharu Himeno was born in Fukuoka, Japan, 

in 1962. He received the B.E. degree in electrical 

engineering from Kyushu University, Fukuoka, Japan 

in 1984.He has been with Fujikura Ltd. Chiba, 

Japan, since 1984 and has been working on the 

design and development of specialty fibers such as 

apolarization-maintaining optical fiber.

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