Letters

Development of Automated Optical Fiber
Cross-connect Equipment
Masato Mizukami†, Mitsuhiro Makihara, Shuichiro Inagaki,and Kunihiko Sasakura
Abstract
We have developed automatic optical fiber cross-connect equipment that provides automatic crossconnection among any of 200 pairs of input and output optical fibers using a fiber-handling robot. Thisequipment allows the cross-connection and management of optical fibers in networks in intelligent
buildings and optical access networks to be performed by remote control. It eliminates the need for manual cross-connection and decreases the operating cost.

1. Importance of automatic optical crossconnection
With the rapid progress of broadband Internet service, optical communication networks have beenextended to offices and homes. It is important todecrease the network operating cost after network
equipment has been installed while offering a highspeed, high-transmission-capacity network that is
highly reliable and economical. This article introduces automated optical fiber cross-connect equipment developed in NTT Microsystem Integration
Laboratories. This equipment eliminates the need for
manual cross-connection and decreases the operatingcost.
1.1 Conventional optical cross-connection andeffectiveness of automation
In intelligent buildings in a metropolitan area network (MAN) and in small-scale facilities in the optical access network, optical cross-connection is necessary for broadband service to be offered through theoptical fibers. Conventionally, optical connectors arejoined manually using an optical connection board
and a patch panel. In this manual connection, mistakes occur due to discrepancies between the actual

physical settings of the connections and their management because these processes are independent.
This reduces reliability. Moreover, manual cross-connection is time-consuming and expensive because
maintenance personnel must be dispatched to remoteplaces to correct mistakes.
1.2 Application of automated optical fiber crossconnect equipment
Figure 1 shows how the automated optical fibercross-connect equipment is used in an optical accessnetwork and a MAN. We investigated cross-connect
equipment that would allow us to reduce the operating costs of cross-connection, especially for smallscale remote unmanned facilities. Introducing thisequipment in the optical access network enables anoptical subscriber cable to be automatically connected and disconnected to an optical cable for a central
office in an instant. Therefore, interruptions to thebroadband communication service can be minimized.
Moreover, no one has to be dispatched to the smallscale facilities in the optical access network. In intelligent buildings on a MAN, it is possible to reconfigure the network flexibly when floor layouts are
remodeled and it is easy to construct private networks
between floors.

† NTT Microsystem Integration Laboratories
Atsugi-shi, 243-0198 Japan
E-mail: mizukami@aecl.ntt.co.jp

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Optical access network

Small-scale facility

Central officeIntelligent buildings

Remoteterminal

Metropolitan area network

RT box
Optical fiber cable

Optical fiber cable
Rural area

Customer premises

Automated optical fibercross-connect equipment

Fig. 1. Application of automated optical fiber cross-connect equipment.

2. Development
2.1 Requirements
Table 1 summarizes the requirements for opticalfiber cross-connect equipment set up in an intelligent
building or in a remote terminal box (RT box). The
system must have several hundred ports so that it canterminate subscriber optical cables in a small-scalefacility. Moreover, the equipment must fit conventional 19-inch and RT-box device racks because it
must be installed efficiently with other telecommunications equipment and communications devices forthe construction of various systems. It should have aswitching time of no more than a few minutes, a low
insertion loss, and optical wavelength transparency.
The switching state must also be maintained even if
the power supply fails (self-holding). In addition, theequipment must satisfy environmental specifications,electromagnetic compatibility (EMC), and earthquake-proof requirements, etc.
Several optical switches such as the laser diodeoptical matrix switch [1] and thermo-optical matrix
switch [2] have been proposed. However, theseswitches do not exhibit self-holding of the optical

Table 1. Requirements for optical fiber cross-connect equipment.

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Port capacity

200 × 200 non-blocking

SizeShould fit in 19-inch rack and in racks used in small-scale remoteunmanned facilities

Optical characteristics

Insertion loss: less than 1 dB
Return loss: more than 40 dB
Wavelength independent

Self-holding

Possible (when the power supply is cut)

Switching time

1 min. (average)

Operation temperatureand humidity

Temperature: 5–45°C, Humidity: 20–70%

EMC

VCCI class A

Earthquake-proof

Fully operable after a category 7 earthquake

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connection and their optical performances are worse
than those of an optical connector. Furthermore, it isdifficult to achieve several hundred non-blocking
optical cross-connections with these switches.
2.2 Configuration of automated cross-connect
equipment
To meet all of the above requirements, we deviseda robotics-based handling method in which a fiberhandling robot connects and disconnects optical connector plugs to and from optical adaptors to achieve
the cross-connection of optical fibers (Fig. 2). A
100 × 100 automated optical fiber cross-connect system was previously developed [3], but for use in bothan optical access network and a MAN, we developed
a new configuration for the automated optical fibercross-connect equipment. The equipment comprisesa control-terminal PC and the optical fiber cross-connect module. In the terminal PC, operation and maintenance software controls the equipment, issues
cross-connection commands, and manages the equipment. The cross-connection module consists of an
optical connection part, robot mechanism, and controller. Two or more cross-connect modules can beinstalled in one device rack, and as many as four
modules can be controlled by one controller.
To satisfy environmental requirements, the positioning error due to thermal expansion caused bytemperature changes should be corrected. To ensure
electromagnetic compatibility, we designed a sealed
housing that prevents electromagnetic waves fromescaping. As earthquake-proofing measures, wedeveloped an earthquake-proof mechanism in themodule and a restoration procedure in the operationand maintenance software.
2.3 Optical cross-connect module
Figure 3 shows the inside of the automated opticalfiber cross-connect module and fiber-handling robot.
The module can connect any of the 200 input opticalfibers to any of the 200 output fibers by exchanging
optical jumper cords. Cross-connections are made byexchanging one plug for another. First, the robot hand
disconnects two target plugs, each of which has ajumper cord, and arranges them on the arrangement
board. The cord is rewound into the fiber storage cartridge so that it does not become tangled with othercords. Next, the robot hand grasps one of the target
plugs and connects it to the target adaptor in the connection board. It then connects the other plug in thesame way.
To make the module compact, the optical connection part, optical fiber storage cartridge, and robot
mechanism were newly developed. For high connection density in the optical connection part, wedesigned a housing to accommodate two 25-port
optical adaptors in two staggered rows and stacked
two housings vertically. The optical fiber storage cartridge was designed to be compact while accommodating multiple fibers.
Cross-connecting fibers on a densely packed connection board requires robot fingers that can accessthe whole area of the connection board. We designed
a long finger using the finite element method. As aresult, 200 × 200 port cross-connection is possible
because the packaging density is twice that of conControl software

Opticalcrossconnect
moduleController

PC for remote control

Fig. 2. Configuration of the automated optical fiber cross-connect equipment.

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Robot mechanism

Housing

Optical connection part

Optical adaptor
Optical connector
plug
Optical jumper
cordFinger partConnection
board

Rewindmechanism

Transfermechanism

Optical I/O fibers

Optical fiber storage cartridge

Optical I/O fibers

Fig. 3. Configuration of the automated optical-fiber cross-connect module.

ventional automatic equipment. We confirmed thatthe equipment could be installed in a 19-inch rack orin an RT-box device rack.
2.4 Operation and maintenance software
The operation and maintenance software installedin the control-terminal PC is connected with the optical cross-connect module by a local area network(LAN) or RS-232C line. This software has twomodes: operating and maintenance.
In the operating mode, a telecommunication line
control function connects and disconnects the control-terminal PC to and from the controller’s communication line. An equipment registration function registers information about the input and output equipment to which the optical cross-connect module isconnected. An earthquake-proof function performs a
restoration procedure after an earthquake. An optical
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cross-connection function handles the connection
and disconnection of specific optical fibers.
The maintenance mode has functions for i) displaying sensors installed in the module, ii) examining
mechanisms, iii) initializing various mechanism elements such as the rewind and robot mechanisms, andiv) batch processing that is continuously executed in
the order of the setting sequences. These functions
enable an inexperienced terminal operator to operate
the equipment via a simple graphical user interface.
3. Performance of the equipment
We evaluated the performance of the equipment.
The main results are summarized in Table 2. The
optical characteristics of the newly developed opticalparts unit were equivalent to those of an MU-type
optical connector, and it passed the long-term reliaNTT Technical Review

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Table 2. Results of performance evaluation test.
Test
Optical device

Equipment

Performance

Optical characteristics

Insertion loss: less than 0.5 dB
Return loss: more than 45 dB

Reliability

Satisfied Telcordia GR-326 standard

Optical characteristics

Insertion loss: less than 1 dB
Return loss: more than 40 dB

Switching time (average)

Less than 1 min. (to exchange one pair of fibers)

Operating range oftemperature and humidity

Temperature: 5–45°C, Humidity: 20–70%

EMC

VCCI class A

Earthquake-proof

Fully operable after a category 7 earthquake (simulated below thefloor of the NTT test building)bility test specified by the Telcordia GR-326 standard. The initial insertion loss of the equipment wasless than 1 dB, and the return loss was more than 40dB. A pair of optical jumper cords could beexchanged in one minute or less on average. Theequipment operated perfectly under room temperature changes from 5 to 45°C. The EMC characteristics satisfied class A of the VCCI (Voluntary Control
Council for Information Technology Equipment)
standard. It could also be operated after a simulated
category seven earthquake (on the Japanese scale)
was applied below the floor (acceleration input: 10m/s2) on which the equipment was standing.
The evaluation results confirm that the automatedoptical fiber cross-connect equipment is suitable forpractical use in intelligent buildings and opticalaccess networks.
References
[1]

[2]

[3]

M. Ikeda, S. Oku, Y. Suzuki, and M. Okayasu, “Lossless 4x4 Monolithic LD Optical Matrix Switches,” International Topical Meeting on
Photonic Switching, pp. 792, 2D1, 1992.
R. Nagase, A. Himeno, M. Okubo, K. Kato, K. Yukimatsu, and M.
Kawachi, “Silica-based 8x8 Optical Matrix Switch Module withHybrid Integrated Driving Circuits and its System Application,” IEEE
J. Lightwave Technol. 12, No. 9, pp. 1631-1639, Sep. 1994.
K. Sasakura, J. Yamaguchi, T. Yoshizawa, K. Kobayashi, and K.
Kaneko, “Automated optical fiber cabling system for Intelligentbuildings,” Proc. 48th IWCS, pp. 364-368, 1999.

Masato Mizukami

Shuichiro Inagaki

Senior Research Engineer, Network Hardware
Integration Laboratory, NTT Microsystem Integration Laboratories.
He received the B.E., M.E., and D.Eng.
degrees in precision engineering from Kanazawa
University, Kanazawa, Ishikawa, in 1988, 1990,and 1997, respectively. He joined NTT in 1990
and is currently engaged in R&D of an automated optical fiber cross-connect system. He is amember of the Japan Society for Precision Engineering (JSPE) and the Society of Instrument andControl Engineers of Japan.

Senior Research Engineer, Network Hardware
Integration Laboratory, NTT Microsystem Integration Laboratories.
He received the B.E. degree in electronic engineering from the University of Electro-communications, Tokyo in 1979. In 1979, he joined theElectrical Communication Laboratories, Nippon
Telegraph and Telephone Public Corporation(now NTT), Tokyo, Japan. Since then, he has
been engaged in R&D of electrical and opticalconnection equipment for communications. He isa member of IEICE and an associate member ofIEEE.

Mitsuhiro Makihara

Kunihiko Sasakura

Senior Research Engineer, Network Hardware
Integration Laboratory, NTT Microsystem Integration Laboratories.
He received the B.S. and M.S. degrees inmechanical engineering from Kyushu Institute ofTechnology, Kitakyushu, Fukuoka in 1987 andthe University of Tokyo, Tokyo in 1989, respectively. In 1989, he joined NTT Applied Electronics Research Laboratories, Tokyo, Japan. He isengaged in research on optical switching equipment for optical communications. He hasreceived the JSPE technology development
award. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan and the Japan Society ofMechanical Engineers.

Senior Research Engineer, Supervisor, Network Hardware Integration Laboratory, NTTMicrosystem Integration Laboratories.
He received the B.E. degree from Shizuoka
University, Shizuoka in 1980 and the same year
he joined Musashino Electrical Communication
Laboratories, Nippon Telegraph and Telephone
Public Corporation (now NTT), Tokyo, Japan.
He has been active in R&D of optical connectors,
inspection systems for optical connectors, andmore recently optical fiber cabling systems. He isa member of the Japan Society of Precision Engineering.

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