Letters

Optical Wiring Technology for Home Networks
for a Service-ready and Low-cost FTTH ServiceHiroshi Aoyama, Hiroshi Tanaka, Yasuhiko Hoshino,and Yasuo Oda†
Abstract
The rapid increase in demand for NTT’s B-FLET’S service (high-speed Internet access via FTTH
(fiber to the home)) has led to the need for rapid and inexpensive service construction. Therefore, wedeveloped a cable sheath connector and a connector-based optical cabinet and connector-based opticalrosette. We used a new optical fiber that can be bent with a small radius and cable sheath connector technology for these products to create a zero-storage optical fiber system.

1. Background
There are now more than 100 million broadband
subscribers worldwide and Japan ranks second withover 15 million. Demand for broadband services has
increased since 2001 and the market is now wellestablished. Moreover, growth is expected to accelerate in the coming years. The majority of broadband
users in Japan currently use DSL (digital subscriberline), which uses a DSL modem on a metallic telephone line. The number of ADSL (asymmetric DSL)
lines has risen to more than 11.2 million because
ADSL offers a high-speed access line service at a lowcost. NTT offers not only ADSL service, but also an
FTTH (fiber to the home) service called B-FLET’S[1], [2], which has a higher transmission speed thanother broadband services. There were more than 1.14
million subscribers to the FTTH service at the end of2003. This is four times the previous year’s number(0.31 million), which shows that FTTH is achieving
rapid market penetration. To ensure widespread availability of optical fiber services, we must construct an
optical communications infrastructure and ensurethat customers get a quick response to requests forservice. Then, once the infrastructure is in place, wemust be able to wire up subscribers’ homes rapidly† NTT Access Network Service Systems Laboratories
Tsukuba-shi, 305-0805 Japan
E-mail: y.oda@ansl.ntt.co.jp

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and inexpensively. To cope with these demands, wedeveloped several key optical components toimprove the efficiency of home optical networks.
2. Concept
To provide FTTH, we must deploy optical fiber upto and inside a customer’s premises. However, there
are several problems with the present FTTH wiring
system (Fig. 1). One problem is that in the opticalcabinet currently used to terminate an optical fiber
drop cable, the jacket of the optical fiber must be
removed because fiber connection is achieved byusing a mechanical splice*1. This leaves the spare
fiber in the bare state, so we must be very carefulwhen we place it in the cabinet. Another problem isthat when we want to find a disconnection, we must
cut the connection in the cabinet and connect an SC
connector pigtail to the fiber to test it. The situation issimilar when we want to perform a test in an opticalrosette*2. We have now developed optical components that eliminate the need to store surplus lengthsof optical fiber, which may become required for
repeated cutting and splicing, by using plug-andsocket connectors in the optical cabinet, rosette, and*1 splice: splice here means an optical joint of the fibers, which isachieved with a narrow gap between the facets of the fiber.
*2 rosette: a small terminal box for installing the connection part ofan optical fiber in a customer’s home.

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Customer’s premises

Indoor optical fiber cable

Optical fiber drop cable

Optical fiber staples

PCONU
Optical cabinet
Outlet box
ONU

Optical rosette
ONU: optical network unit

Fig. 1. Example of optical wiring on a customer’s premises.

outlet box. Furthermore, we used a new optical fiberthat can be bent with a small radius for the connector.
3. Outline of components
3.1 Cable sheath connector (FA connector)
Our cable sheath connector (called a field assembly(FA) connector) can be assembled simply. The FA

connector can sheathe an optical fiber drop cabledirectly, so there is no need to remove the fiber cablejacket. A ferrule, a polished optical fiber, and amechanical splice are installed in the FA connector inadvance (Fig. 2).
The FA connector can be assembled very simply bya service engineer visiting the customer’s home. To
assemble an FA connector, the end of the jacket of theFA connector plug

FA connector socket

Optical fiber drop cable or indoor optical fiber cable

Optical fiber drop cable or indoor optical fiber cable

Fixed cable sheath part

Fixed cable sheath part
Connection point

Connection point

Optical fiber
FerruleFerruleOptical fiber

Built-in optical fiber(polished)
Split sleeve
Mechanical splice

Built-in optical fiber(polished)
Mechanical spliceFig. 2. Basic structure of FA connector.

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optical fiber drop cable is attached to the fixed cablesheath part and then installed in a holder. Then thefiber is cut to a regulation length with a stripper and afiber cutter. After that, the fiber is inserted into themain part of the FA connector and fibers are connected with the installed mechanical splice. Finally, thecable sheath part is fixed in the main FA connector
part. The mechanical splice is a conventional technology, so we did not have to develop any new tools
for connection and could make a simple assembly
technique with low loss and high reliability.
The FA connector consists of a plug and a socket(FA connector plug and FA connector socket), which
can be connected directly to each other (Fig. 3). TheFA connector socket can also be connected to an SC
connector plug, which conforms to JIS C 5973,
directly without an adapter. Furthermore, because its
structure is designed to bend the optical fiber drop
cable by 90°, which reduces its size, it will fit in themost commonly used outlet box (conforming to JIS C8435) and can also be used in the B-FLET’S service
for condominium network systems (Fig. 4).
Another feature of the FA connector is that it satisfies outdoor environment condition requirements

FA connector plug

FA connector socketMain part
Fixed cable sheath part

These parts areused duringassembly andremoved afterward.

Main part
Fixed cable sheath part

FA connector socket

FA connector plug

Fig. 3. Constituent elements and completed FA connector plug and socket.
Mounting unit

FA connector socket

Outlet box

Mounting unit
Main part

SC connector plug

Indoor optical fiber cable

FA connector socket(installed in outlet box)

SC connector plug

Fig. 4. Example of structure of FA connector socket (outlet type).

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related to temperature characteristics and continuous
temperature/humidity cycle characteristics. This will
enable it to be used in outdoor optical cabinets as wellwith long-term reliability.
3.2 Optical cabinet and optical rosette
Our new optical cabinet (Fig. 5) and optical rosette(Fig. 6) are based on a common design that uses theFA connector.
The existing optical cabinet must provide storage
space for surplus optical fiber to allow repeated cutting and splicing. The new optical cabinet accommoExisting optical cabinet

Optical fiber

Fiber storage part

dates the FA connector, so there is no need to store
bare optical fiber. This allows easy connection
between an optical fiber drop cable and an indoor
optical fiber cable. It can be used as a connection
point for testing because the FA connector socket
allows connection/disconnection to/from an SC connector plug, so it improves testing efficiency and lets
us make a compact outdoor optical cabinet. The new
optical cabinet thus provides easier maintenance thanthe existing one and its volume is 65% smaller. This
will reduce the cost of the B-FLET’S service system.
The new optical rosette is similar to the optical cabNew optical cabinet
Indoor opticalfiber cable

FA connector plug

FA connector
allows simple
connection anddisconnection.

MechanicalspliceOptical fiber drop cable

FA connector socket
Optical fiber drop cable

Indoor optical fiber cable

Fig. 5. Comparison of existing and new optical cabinets.

Existing optical rosette

New optical rosette
Indoor optical fiber cable

Optical fiber
Fiber storage part

FA connector socket
FA connector
allows simple
connection anddisconnection.

Mechanical splice
Indoor optical fiber cable

Direction can be selected
in 45° steps within 180°.
SC connector plug

Fig. 6. Comparison between existing and new optical rosettes.

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Lettersinet. By using the FA connector, we reduced the system’s volume by 60% and reduced the system costand increased the efficiency for finding disconnection points and performing maintenance. The rosetteallows a choice of five exit directions for the indoor
optical fiber cable because the FA connector orientation in the optical rosette can be changed in 45° steps
to suit the installation conditions.

Hiroshi Aoyama
Senior Research Engineer, Second Promotion
Project, NTT Access Network Service Systems
Laboratories.
He received the B.E. degree in mechanicalengineering from Saitama University, Saitama in
1986. He joined NTT R&D Department in 2004
and is actively engaged in developmental
research on optical fiber splicing technology andhome network wiring technology.

4. Conclusion
We improved the efficiency of the construction andmaintenance of an optical network on a customer’s
premises and made a compact low-cost system byusing cable sheath connector technology. In future,
we will attempt to use a free-bend optical fiber thatenables a smaller bending radius and employ it in ourproducts. This should make optical network construction as efficient as metallic network construction
and will strongly support the B-FLET’S service strategy.
References[1][2]

http://www.ntt-east.co.jp/product_e/05/index.html
http://www.ntt-west.co.jp/service_guide/5great/great02.html

Hiroshi Tanaka
Research Engineer, Media Utilization Group,
Access Media Project, NTT Network Service
Systems Laboratories.
He received the B.E. degree in electrical engineering from Nihon University, Tokyo in 1989.
He joined NTT R&D Department in 1998 and isactively engaged in developmental research on
metallic cable splicing technology and home network wiring technology.

Yasuhiko HoshinoResearch Engineer, Second Promotion Project,
NTT Access Network Service Systems Laboratories.
He graduated in mechanical engineering fromNagaoka College of Technology, Nagaoka,Niigata in 1986. He joined NTT R&D Department in 2003 and is actively engaged in developmental research on optical fiber splicing technology and home network wiring technology.

Yasuo Oda
Research Engineer, Second Promotion Project,
NTT Access Network Service Systems Laboratories.
He received the B.E. degree in electrical information engineering from Nagasaki University,Nagasaki in 1992. He joined NTT R&D Department in 2004 and is actively engaged in developmental research on optical fiber splicing technology and home network wiring technology.

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