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A Compact Erbium Doped Fiber Amplifier with
Fast Transient Control

1.

INTRODUCTION

Conventionally, high-capacity, point-to-point transmissions have been realized by the implementation of wavelength division multiplexing (WDM) systems in telecommunications trunk lines. Recently, however, such technologies as optical add drop multiplexing (OADM) and photonic cross connect (PXC) have been developed to realize
the ring and mesh configuration of optical networks,
thereby aiming at implementing transparent photonic networks without resort to using opto-electric conversion.
Such a configuration is expected not only to improve theefficiency and reliability of transmission but also to offer
more flexible services as well as to reduce the costs ofinvestment and maintenance. Because, in such systems,
dynamical switching of optical signals with arbitrary wavelengths are effected at each node, erbium doped fiberamplifiers (EDFA) employed are required to give unconventional fast response to the transient conditions.
Moreover, because equipment space in the terminal offices is limited, it is essential to improve the mounting density of transmission equipment, and this raises an increasing need for compact EDFAs.
Against this background, we have developed a compact EDFA with fast transient control measuring 70 × 90× 15 mm, the maximum compactness in the same industry. The product will be presented below.

2.

FEATURES

The EDFA developed here consists of a pumping laser
module and a variable optical attenuator, enabling highperformance operation with a saturated output power of
not less than 17 dBm and a variable gain range of notless than 10 dB. The optics comprise a small diameter
erbium doped fiber (EDF) with reduced length due to highconcentration doping and downsized optical components
such as compact isolator. In addition, the small packagemeasuring 70 × 90 × 15 mm has been realized thanks tothe two-stage layout for the control circuit. See Photo 1. It
is possible to externally change the control mode and tomonitor alarms through RS232 serial communication. Thecontrol modes include automatic gain control (AGC),
automatic level control (ALC), and automatic current con-Photo 1

Compact size erbium doped fiber amplifier with fasttransient control.

trol (ACC), allowing the user to select a suitable mode
depending on applications.

3.

TRANSIENT RESPONSE
CHARACTERISTICS OF EDFA

When an EDFA is not fast enough in responding to changes in the number of input channels, the output signal levelshows transient fluctuations causing degradation in transmission quality in terms of bit error rate (BER) and so on.
In order to maintain constant the gain for the surviving
channels, it is essential to effect fast control of the pumping laser diode. Performance indexes to represent suchtransient response include the following three items, andthe developed EDFA is satisfactory in terms of theseindexes. See Table 1 and Figure 1.
1) Gain excursion
2) Settling time3) Gain error
Table 1

Transient response performance (at Pout: 17 dBm,Gain: 23 dB).

Event type

Gain excursion

Settling time

Gain error

15 dB Add

0.4 dB

122 µs0.36 dB

15 dB Drop

1.2 dB

118 µs0.36 dB

Furukawa Review, No. 28

200561

A Compact Erbium Doped Fiber Amplifier with Fast Transient Control

4.

CONCLUSION

Table 2 shows the general characteristics of the EDFA
developed here. It is hoped that the product will find wideapplications, making contribution to the development ofphotonic network.
For further information, please contact:
Optical Components Department, Telecommunications
CompanyTEL: +81-436-42-1703
FAX: +81-436-42-1789
Planning and Coordination Department,
Telecommunications Company
TEL: +81-3-3286-3432
FAX: +81-3-3286-3708
Email: fitel@ho.furukawa.co.jp

GLOSSARY
WDM: Wavelength Division Multiplexing
A transmission technology which enables increasing thetransmission capacity of optical fibers by several to several tens times. More specifically, optical signals of slightly
different wavelength are multiplexed and the multiplexed
signal is propagated along a single optical fiber.

Figure 1

Measured transient response (Left: add, Right: drop).

Table 2

General characteristics of the EDFA.

Item

Specification

NoteWavelength

C band1530~1564 nm

Output power≥ 17 dBm

Pin=-13~-3 dBm

Variable gain range≥ 10 dB

Gain excursion≤ 1.5 dB

Transient settling time≤ 200 µs

Return loss

≤ -40 dB

1⇔32 ch(15 dB add/drop)1⇔32 ch(15 dB add/drop)

OADM: Optical Add-Drop Multiplexer
When installed at the nodes in a ring network, this opticalmultiplexer can add and/or drop some of the opticalchannels that are multiplexed by WDM.
PXC: Photonic Crossconnect
This system makes it possible to separate the optical signals transmitted from multiple fibers at the respective
demultiplexers and allocate them by channel to output
fibers.
EDFA: Erbium Doped Fiber Amplifier
An optical amplifier using erbium-doped fiber (EDF)
pumped by a laser diode. It takes advantage of the factthat the gain band of erbium coincides with the signal
wavelength band of 1.55 µm generally used for opticaltransmission, and that EDF is highly compatible with ordinary transmission optical fibers.

Furukawa Review, No. 28

200562