Letters

Aerial Optical Fiber Interconnection Method
for Connecting Fibers of Different Carriers
Kimio Ando, Yuji Aoyagi, and Masashi Awamori†
Abstract
In response to demands to interconnect optical fibers owned by different carriers, we have developed
a simple optical fiber interconnection method. Each carrier uses our cord converter to terminate a fiberin a standard connector. These connectors can then be connected together simply, without either carrier
working on or handling fibers belonging to another carrier. We have also designed an aerial optical closure that can be mounted on a utility pole to accommodate several such connectors.

1. Background
Every year, the number of carriers offering opticalfiber services increases. NTT’s regional operatingcompanies, NTT East and NTT West, already provide
the B-FLET’S service. Although optical fiber is in
the process of being supplied to some user premises,some route sections still have no optical fibers. On
the other hand, some optical fibers that are already inplace remain unused. Carriers with no optical fiber on
certain routes have recently asked to lease these
unused optical fibers (Fig. 1). In response to thisdemand, we have developed two products for interconnecting the optical fibers of different carriers.
† NTT Access Network Service Systems Laboratories
Tsukuba-shi, 305-0805 Japan
E-mail: awamori@ansl.ntt.co.jp: Optical fiber cable owned by carrier A: Optical fiber cable owned by carrier B
Carrier A building
Carrier A has surplus Pole
Carrier B Optical mainof optical fiber.
equipment distribution frame Pole
ClosureClosureClosurePole
Customer
ClosureApplies tocarrier Bfor service

ClosureRoute without optical fiber facility of carrier B
Conventional facility configuration

Carrier A building
Carrier B Optical mainequipment distribution frame

ClosureClosureClosureClosureCustomer

ClosureLeases optical fiber on this route from carrier A

Suggested facility configuration

Fig. 1. Example of optical fiber facility configuration.

Vol. 1 No. 2 May 2003

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Letters

Carrier B
aerial optical closure

Carrier B
optical fiber cable

Connection patterns
Pattern 1 Carrier A
optical fiber

Connection point

Carrier A
Carrier A
aerial optical closure optical fiber cable

SpliceCarrier A
Aerial drop optical fibercable

Carrier B
optical fiber

Connection point(splice)
Pattern 2 Carrier A
Carrier B
Cord with adequate Cord with adequate
Carrier A connector attached connector attached Carrier B
optical fiber
optical fiber
SpliceConnection point(connector joint)

Carrier B
Aerial drop optical fiber
cableFig. 2. Example of optical fiber cable connection configuration at a pole.

The conventional way to connect fibers of two different carriers is to connect together one aerial drop
optical fiber belonging to each carrier (Fig. 2). There
are two patterns of doing this: 1) one carrier splices
together a single optical fiber belonging to each carrier or 2) each carrier splices a connector onto its own
fiber and one of the carriers connects them. Boththese methods have problems. In the first case, single
optical fibers are exposed near the splicing point,
which could lead to higher loss over the transmission
route. Moreover, carriers have complained that theirfibers have been damaged by another carrier working
on them. In the second case, even though the intercarrier splice is eliminated, the connectors are stillleft exposed. To solve these problems, we have developed i) a cord converter and ii) an aerial optical closure to accommodate SC connectors.

by one.
2. The connector should be a standard one thatany carrier can easily procure, attach, anddetach. We chose to use the SC connector (Fig.
3).
3. The need to work on another carrier’s facilities
should be eliminated.
4. Interconnection should be done as close to autility pole as possible.
3. Conventional method of attaching an SC connector
The usual way to attach an SC connector to a fiber
cord is shown in Fig. 4. First, the SC connector isspliced onto the end of a short section of optical fiber

2. Design goals
In designing these products, we had the following
goals.
1. It should be possible to lease optical fibers one
Cord with SC connector
attached (pigtail)

Splicing point

Fig. 3. SC connector.
Single optical fiber
conductor

Optical fiber
cable

Single optical fiber conductor is exposed, which degrades performance.

Fig. 4. Conventional connection method.

72

NTT Technical ReviewLetterscord. Together, these are known as a pigtail. Then, theend of the fiber is bared and spliced to the end of asingle optical fiber from the cable.
4. Optical fiber cord converter
In our method, shown in Fig. 5, the SC connector isattached to a fiber cord in a clean manufacturing environment. The other end of the cord can later beattached to an optical fiber cable by simple mechanical means. We developed two converters to handle
either i) one or two single fibers or ii) a 4-fiber tape.
Both types contain a filter (which can be optionallyomitted) that cuts off the wavelength of a test light(1.55 or 1.65 µm), which allows easier maintenanceand testing of optical facilities along with transmission and subscriber loop tests.

5. Aerial optical closure for accommodating
SC connectors
Since NTT did not have a suitable closure, wedeveloped an aerial optical closure to accommodate
SC connectors(Figs. 6 and 7).
Its structure
was designed
to connect andaccommodate
eight aerial
drop opticalfiber cables. To
shorten thedevelopment
p e r i o d , w e Fig. 6. Aerial optical closure for accommodating SC connectors.
Cable cross- section

Connector
Optical fiber cord Cord converter(SC connector)

1.2 mmφ copper
supporting wireCable
Fibers(1-, 2-, or 4-fibers)

6.0 mm or less

Details of cord converter
Attaching
2.0 mm orless
Cable
Optical Optical fiber cord Optical fiber Cable
fiber cord (Dimensions: 12 × 12 × 50)(4-conductor)

Cable
Optical fiber cord
Optical fiber Cable
Opticalfiber cord
(Dimensions: 6 × 6 × 42.5)

Tension members(non-inductive material)(1- or 2-conductor)

Fig. 5. SM aerial drop optical fiber cable with connector cord at one end.

SM aerial drop optical fiber(optical fiber cord)
SC adapter
Wiring guide
SM aerial drop optical fiber(cord converter)
SM aerial drop optical fiber(cable)

Carrier A sideconnection point
Carrier B sideconnection point(when 5 to 8 fibers are accommodated)

SM aerial drop
optical fiber(cord converter)
Carrier A side Carrier B side
cable slot
cable slot
(when 1 to 4 fibers are accommodated)

Cord-mounting plate

Fig. 7. Inside view of the closure.

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LettersClosure
Kimio Ando
Research Engineer, First Promotion Project,NTT Access Network Service Systems Laboratories.

Pole(Example)
Mounting plate

Fig. 8. Back of the closure.

Yuji Aoyagi
Research Engineer, Optical Access Network
Project, NTT Access Network Service Systems
Laboratories.

Table 1. Specifications of the closure.
Size

210 [H] × 140 [W] × 45 [D] (mm)Maximum capacity
8 (16 fibers.)
number of connections
Connectors

SC optical connector(conforming to JIS C 5973)

Applicable cable

1-, 2-, or 4-fiber single mode aerial drop
optical fiber cable with connectors at one
end

WeightAbout 1 kg

Masashi AwamoriFirst Promotion Project, NTT Access NetworkService Systems Laboratories.

employed existing closure parts used by NTT. The
cord-mounting plate has mounting holes to match thepegs on the cord converter for easy installation. TheSC adapter mates the female ends of two SC connectors. The closure accommodates four of theseadapters. The closure carefully guides and holds thefibers so they are not bent or damaged. It has amounting plate on the back (Fig. 8) to enable it to be
attached to a pole. Table 1 lists the main specifications of this closure.
6. Future outlook
Technological innovation and competition have led
to rapid progress in the telecommunications field.
Movements towards innovation are particularly
expected in the field of optical fiber facilities. We willcontiave to work on the development of access line
technology in order to achieve a network with theflexibility to satisfy future demands.

74NTT Technical Review