Special Feature

R&D Toward Cost Reduction and Quick Response
to Increasing Demands for Optical Services
Mitsuo Kama, Hiroyuki Tanase†, Yasuo Oda,Masashi Awamori, Tatsuya Nakajima, and Hiroshi Watanabe
Abstract
This article gives an overview of key technologies that will support the large-scale provision of optical services by simplifying optical fiber storage work through the use of connectors and modular products.

1. Issues surrounding the optical access network
The rapid growth in demand for broadband services
has led to an urgent need for quick optical access network installation and simple, easy-to-use, and convenient optical fiber and cable technologies. In addition
to lowering costs while maintaining functions andquality levels, we need new technologies that will
enable us to respond quickly to increasing demandsin the era of mass construction of the optical network.
We must revolutionize the work of field engineers bysimplifying techniques to lower the required skills
and by making optical fiber easier to handle. The following issues are associated with the optical accessnetwork.
• Special skills are required for storing optical fiberin aerial optical closures and optical cabinets.
• Special skills are required for reconnecting optical fiber in aerial optical closures when the customer requests another service.
• Troubleshooting in aerial optical closures andoptical cabinets is difficult.
• Special skills are required for handling opticalcable and fiber inside a house.
If we could eliminate the troublesome work of storingbare optical fiber while ensuring that fiber is not bent
tighter than the allowed bending radius, then weshould be able to greatly reduce the work skills need† NTT Access Network Service Systems Laboratories
Tsukuba-shi, 305-0805 Japan
Email: tanase@ansl.ntt.co.jp

Vol. 5 No. 2 Feb. 2007

ed to handle optical fiber. And if optical fibers could
be connected together using connectors, then thework of reconnecting fibers would become much
simpler. To meet these needs, NTT is researching anddeveloping technologies that do not require workers
to have special skills and optical fiber that can be handled with the same ease as metallic cable (Fig. 1).
2. Recent developments
This section gives an overview of some key technologies (Fig. 2) that have recently been developed tosolve the problems of providing optical access facilities to 30 million subscribers by 2010, which isNTT’s target. They have already been reported separately in NTT Technical Review, but this overview
presents them together to give readers a clearer ideaof how they fit together.
(1) FA connector [1]Our field assembly (FA) connector has a structurethat directly holds the outer sheath of an optical-fiber
drop cable or indoor cable and prevents the opticalfiber itself from being exposed. The interior of the FA
connector includes a ferrule, an optical fiber with apolished tip, and a mechanical splice.
To assemble an FA connector, a worker fixes theouter sheath at the end of an optical-fiber drop cableor indoor cable using the sheath-holding part of theconnector and then attaches the sheath-holding partto a larger holder. Then, using a stripper or fiber cutter, he or she cuts the optical fiber to a specified
length and inserts that strand of fiber into the main25

Special Feature

Achieve 30 million opticalsubscribers by 2010.

No. of opticalsubscribers
30 million
In-home technology
Optical fiber handling technologythat does not require special skills
Cost reduction of opticalaccess network
Cost reduction of opticalcomponents

Access system technology
Establish work procedures that do notrequire skill and experience by simplifying
tools and tasks.
Connector technology for connection points

2005

Fiscalyear

2010

Fig. 1. Development path toward an era of mass optical network construction.

Optical connector
cabinetOptical connector
rosette4-branch opticalsplitterFA connector

Aerial optical closure

ONU

Aerial optical connector

Free-bending optical fiber cord
ONU: optical network unit

Fig. 2. Recently developed key technologies toward 30 million optical access subscribers.

unit of the FA connector. Finally, the worker connects
the optical fiber using the mechanical splice inside
the connector and fixes the sheath-holding part to themain unit of the FA connector to complete the assembly. Once the conventional mechanical splice technique has been applied, the unit can be easily and reliably assembled on the spot without the use of special
tools. This method also achieves high reliability: it
can achieve a connection loss of only about 0.3 dBand it satisfies the requirements for outdoor conditions in terms of temperature characteristics in prolonged high temperature and humidity.
The FA connector consists of a plug and a socket26(FA connector plug and FA connector socket), as
shown in Fig. 3. These can be connected directly toeach other without the need for an adaptor. They aredesigned to be connected and disconnected manytimes. The FA connector socket can also be connected to (and disconnected from) an SC connector plug,
which conforms to the JIS C 5973 standard. Moreover, because its structure is designed to change theoutput direction of an optical-fiber drop cable orindoor cable by 90º while reducing overall cable
length, the FA connector socket will easily fit in themost commonly used outlet box (shallow-type switch
box conforming to JIS C 8435), as shown in Fig. 4.
NTT Technical Review

Special Feature

FA connector plug

FA connector socket

FA connector plug
Sheathholding part

Main unit

FA connector socket
SheathMain unit
holding part

Optical-fiber drop cable

Optical-fiber indoor cable

FA connector plug

FA connector socket

Fig. 3. Typical structures of FA connector plug and socket.

FA-connector-socket (for outlet use)

Main unit

Color panel
Main unit

Optical-fiberindoor cable

FA-connector-socketunit (for outlet use)

Optical-fiberindoor cable

Unit

Fig. 4. Typical structures of FA connector socket (for outlet use).

(2) Optical cabinet [1]In existing outdoor optical cabinets, optical fibers
are connected by either fusion or mechanical splicing. Consequently, they must provide storage spacefor surplus fiber to allow repeated cutting and splicing. Storing this delicate reserve fiber after a connection has been made or after troubleshooting in theevent of a failure takes time and skill. An optical cabinet that incorporates an FA connector as a connection point solves such problems in existing outdoor
optical cabinets. It improves operability and alsoenables the cabinet size to be reduced because it
improves maintainability (Fig. 5).
The FA connector has enabled a 40% reduction in
the man-hours required to perform connecting andstoring work in the cabinet and has enabled the volVol. 5 No. 2 Feb. 2007

ume to be reduced to only about 35% of that of existing products. The FA connector socket also allows
connection and disconnection of an SC connector
plug, which makes troubleshooting at connection
points inside optical cabinets much simpler andstreamlines maintenance operations. There is no needto store bare optical fiber, which reduces the numberof components needed for storing optical fiber andimproves the cost efficiency.
(3) Optical connector rosette [1]The optical connector rosette, which is installedinside the user’s home as shown in Fig. 2, uses an FA
connector socket at the connection point inside therosette, resulting in a smaller unit (Fig. 6). As in thecase of the optical cabinet, the man-hours for connection and storage work in the rosette were reduced by27

Special Feature

Outdoor optical cabinet (existing)

Optical connector cabinet

Optical fiber

Optical-fiber indoor cable
FA connector plug

Fiber storage trays

Allows simple
connection/disconnection.

Optical-fiber dropcable
Optical-fiber
Mechanical spliceindoor cable

FA connector socket
Optical-fiber drop cable

Fig. 5. Outdoor optical cabinet and optical connector cabinet.

Optical rosette (existing)

Optical connector rosette

Optical fiber Fiber storage section

Optical-fiber indoor cable
FA connector socket

MechanicalspliceAllows simple
connection/disconnection.

Optical-fiber indoor cable

Connector direction canbe set within a range of SC connector
plug
180° at 45° intervals.

Fig. 6. Optical rosette and optical connector rosette.

about 40% through improved workability because
there is no need to store bare optical fiber. 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 45º steps
to suit the installation environment. Use of an FA
connector here has enabled us to reduce the volumeof the rosette by as much as 60% compared withexisting products while simplifying troubleshooting
at connection points inside optical rosettes andimproving maintainability.
(4) Free-bending optical fiber cord [2]Optical fiber that can be wired simply and neatly
without special skills in much the same way as metallic cord will be an important factor in satisfying user28

needs as optical services are rapidly deployed on alarge scale. To this end, we have developed a freebending optical fiber cord that can be bent, folded,and tied as needed just like a metallic cord [2], [3]. It
consists of holey fiber, a cord cover to protect thefiber, and a dustproof connector. The holey fiber isbased on hole-assisted fiber (HAF), which has a highly refractive glass at its core and glass containing
holes in its cladding. This design produces a strong
light-confinement effect, which means that there islittle bending loss even when the cord is bend with avery small bending radius. The cord cover has anouter diameter of 4 mm and a structure that reduces
the load on the inner optical fiber when the cord isbent or stepped upon. It features a flexible material
NTT Technical Review

Special Feature

Application to opticalcabling in house
Right-angle bend

Application to optical LAN
Bundled state

RouterSwitchPC

Optical data socket

ONU
Optical rosetteMedia adaptor

UTP cable

Free-bending optical fiber cord

Free-bending optical fiber cord
UTP: unshielded twist pair cable

Fig. 7. Application examples of free-bending optical fiber cord.

Drop cable
Termination
board

Drop connector case

Aerial optical connector

Termination
board

Splitterstorage case

Aerial opticalconnector

Splitter moduleFig. 8. Wiring format of new aerial optical closure.

conducive to bending to facilitate handling and toallow the tying or bundling of excess cord without
affecting communications or leaving kinks after untying. The dustproof connector is compatible with SC
connectors and features a shutter mechanism to protect the tip of the optical fiber from dust.
If a house is equipped with an optical socket like an
optical connector rosette, this free-bending opticalfiber cord can simplify home wiring of optical fiber,
enabling home users without specialized knowledge
to install it just like electrical or telephone wiring.
Free-bending optical fiber cord can also be used forwiring optical local area networks (Fig. 7).
(5) Aerial optical closure [2]Work in an aerial closure involves connecting optical fiber using a fusion or mechanical splice, so a long
length of optical fiber must be stored in a tray. The
optical fiber must be handled carefully during theVol. 5 No. 2 Feb. 2007

storage work because it is thin and fragile. This storage work is also time consuming and thus poses anobstacle to large-scale optical service construction.
Moreover, once a joint has been cut, it must be reconnected to a new optical fiber when the customer
requests another service. To solve these problems, wehave developed an aerial optical closure that uses
connector-based connections [2], [4]. It has the following internal wiring format. An aerial optical connecter (described below and shown in Fig. 10) is
attached to optical fiber wired from an optical cable,
and it is wired to a terminal board and connected tothe input side of a splitter module. Next, the opticalfibers on the output side of the splitter module are
wired to the drop connector case. These are connected to the drop-cable and run into a customer’s residence (Fig. 8). Connectors are attached to input/output optical fibers of the splitter beforehand, and these29

Special Feature

Existing aerial optical closure

New aerial optical closure

Fig. 9. Storage formats inside aerial optical closures.

designed for assembly in the field by workers. It canbe installed easily in a short time with no special tools
and its use for making connections within an aerial
optical closure enables the time required for connecting and storing optical fiber to be reduced by about40%.
3. Conclusion
Fig. 10. Appearance of aerial optical connector.

fibers are protected. Therefore, storage work
becomes very simple. This aerial optical closure:• Reduces the need for storing bare optical fiberand hence simplifies the storage of optical fiber(Fig. 9)• Makes connection work easy by using a connector• Simplifies storage work by modularizing thesplitter function• Eliminates the need for special protection for
optical fibers.
All in all, storage and connection work is greatly
improved compared with the existing system. Achange of service can be implemented just by disconnecting and reconnecting optical connectors and theoptical fiber can be handled as easily as metallic
cable. The above technical features are expected tomake a great contribution to large-scale optical service construction and to simplify maintenance workin the future.
The connector discussed above is shown in Fig. 10[2], [5]. It is based on the FA connector (1). It is used
for connecting fiber within an aerial optical closure in
the aerial section of optical fiber cables running froman NTT switching station to customer houses and it is30

The technologies described in this report areextremely important for mass construction of theoptical access network and are expected to simplify
field work greatly. As optical services spread rapidly
and become familiar to users, “ease of use” will
become an even more important factor. To support therapid construction of the optical network and reduce
the total cost, we will continue our R&D efforts
toward skill-free and low-cost optical products andtechnologies.
References
[1]

[2]

[3]

[4]

[5]

H. Aoyama, H. Tanaka, Y. Hoshino, and Y. Oda, “Optical Wiring
Technology for Home Networks for a Service-ready and Low-cost
FTTH Service,” NTT Technical Review, Vol. 3, No. 4, pp. 33–37,2005.
O. Yamaguchi, “Trends in Optical Access Network Technologies
Toward ‘30 Million Optical Subscribers by 2010’,” NTT TechnicalReview, Vol. 4, No. 4, pp. 21–28, 2006.
M. Kama, H. Aoyoma, H. Tanaka, and Y. Oda, “Bendable OpticalFiber Cord for Do-it-yourself Optical Wiring,” NTT Technical Journal, Vol. 18. No. 4, pp. 65–67, 2006 (in Japanese).
M. Awamori, H. Tanase, K. Terakawa, T. Nakajima, M. Toyonaga,
and M. Kama, “Optimal Aerial Optical Closures for Large-scale Optical Network Construction,” Proc. of the IEICE Society Conference,
B–10–13, 2006 (in Japanese).
T. Nakajima, K. Terakawa, M. Awamori, H. Tanase, M. Toyonaga,
and M: Kama, “Aerial Optical Connectors for Large-scale Optical
Network Construction,” Proc. of the IEICE General Conference,
B–10–7, 2006 (in Japanese).

NTT Technical Review

Special Feature

Mitsuo Kama

Masashi Awamori

Senior Research Engineer, Second Promotion
Project, NTT Access Network Service SystemsLaboratories.
He received the B.E. degree in electrical engineering from Tokyo Metropolitan University,
Tokyo, in 1984. He joined NTT R&D Department in 2002. Since then, he has been activelyengaged in developmental research on opticalaccess network systems technology.

Research Engineer, Second Promotion Project,
NTT Access Network Service Systems Laboratories.
He received the associate degree in electricalengineering from Ishikawa National College ofTechnology, Ishikawa, in 1994. He joined NTT
R&D Department in 2001. Since then, he has
been actively engaged in developmental researchon aerial optical closure technology and opticalfiber connecting technology.

Hiroyuki Tanase

Tatsuya Nakajima

Research Engineer, Second Promotion Project,
NTT Access Network Service Systems Laboratories.
He received the B.E. degree in mathematics ofscience and engineering from Sophia University,
Tokyo, in 1993. He joined NTT R&D Department in 2005. Since then, he has been activelyengaged in developmental research on aerial
optical closure technology and optical fiber connecting technology.

Research Engineer, Second Promotion Project,
NTT Access Network Service Systems Laboratories.
He received the B.E. degree in civil engineering from Waseda University, Tokyo, in 2000. He
joined NTT R&D Department in 2005. Sincethen, he has been actively engaged in developmental research on aerial optical closure technology and optical fiber connecting technology.

Yasuo Oda

Hiroshi Watanabe

Research Engineer, Second Promotion Project,NTT Access Network Service Systems Laboratories.
He received the B.E. degree in electro-information engineering from Nagasaki University,Nagasaki, in 1992. He joined NTT R&D Department in 2004. Since then, he has been activelyengaged in developmental research on opticalfiber splicing technology and home network
wiring technology.

Research Engineer, Second Promotion Project,NTT Access Network Service Systems Laboratories.
He received the B.E. and M.E. in applied
physics of engineering from the University ofTokyo, Tokyo, in 1996 and 1998, respectively.
He joined NTT R&D Department in 2004. Since
then, he has been actively engaged in developmental research on optical fiber splicing technology and home network wiring technology.

Vol. 5 No. 2 Feb. 2007

31