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Cladding-Pumped Optical Fiber Amplifier

1.

INTRODUCTION

In optical fiber systems for analog signal distribution
including CATV systems, increasing the individual output
power of distribution optical amplifiers is one of theefficient measures to effecting cost reduction.
The output signal power of erbium-doped fiber
amplifiers (EDFAs) most commonly used for distributed
amplification is limited by the output power of pumping
laser diodes, and it is around +22 dBm ordinarily. If it
is desired to have higher output powers, a number ofpumping laser diodes must be used, probably raisingproblems of higher cost and bulky equipment.
Here will be presented a compact optical fiber amplifierthat has achieved, by cladding-pumping an Er/Yb
co-doped fiber of double-clad structure using multimodelaser diodes, an optical output power of +31 dBmmaximum.

2.

FEATURES

The optical fiber amplifier developed here by Furukawa
Electric is, as shown in Figure 1, of two-stage
configuration. In the first stage, an EDFA with an ordinary
erbium-doped fiber is used for pre-amplification realizing
low noise, whereas in the second stage, a claddingpumped amplifier is employed to achieve an optical
output power of +31 dBm maximum, whereby backward
pumping is effected using 980-nm multi-mode laser
diodes of Furukawa's in-house product.
Pre-amplifier

Photo 1

Appearance of cladding-pumped optical amplifer for
CATV.

Photo 1 shows the appearance of a cladding-pumped
optical fiber amplifier for CATV.
Figure 2 shows the cross-section of a double-clad
optical fiber for cladding pumping --one of the productsof OFS Fitel-- that features this amplifier. Its silica
cladding where the launched pumping light of multimodepropagates is not circular but star-shaped, with the aimof guiding efficiently, by eliminating skew propagationthat does not contribute to pumping, the pumping lightover the rare earth-doped core. The tapered fiber bundle
shown in Figure 3 --an OFS Fitel product-- is used forcoupling the multimode pumping light into the claddingpumping optical fiber.
Single-Mode Core: Yb3+ or Er3doped (Signal propagation)
Silica Cladding (Pump propagation)
Low-Index Polymer

Power amplifier

Er3doped singleEr3&Yb3doped
mode fiber
cladding-pumped fiber
Input

Fused
Coupler Isolator

Fused
Coupler

Isolator

PowerCombiner

Fused
Isolator Coupler

Output

PDPD

980 nm single mode
pump LD
9xx nm multi mode
pump LD

Figure 1

Figure 2

Cross-section of double-clad optical fiber for
cladding pumping.

Multimode
pump LD
SignalConfiguration of cladding-pumped optical fiber
amplifier.

Figure 3

Schematic of tapered fiber bundle.

Furukawa Review, No. 26

200449

Cladding-Pumped Optical Fiber Amplifier

3.

CHARACTERISTICS

Table 1 shows the basic characteristics of the claddingpumped optical fiber amplifier developed here, andFigure 4 its characteristics. The amplifier uses two
multimode laser diodes with 2.5 W output power in its
cladding amplifier stage, achieving an optical output
power of +31 dBm at an optical pumping powerof 5 W. The noise figure of signal is not more than
5.5 dB, comparable to ordinary EDFAs. Transmission
characteristics including signal distortion, the essential
performance for analogue transmission, have also been
evaluated, and it has been confirmed that composite
second-order distortion (CTB) is –67 dB or less andcomposite triple beat distortion (CTB) is –70 dB or less.
Table 1

Specifications of cladding-pumped optical fiberamplifier.
Specification

Item

Unit

Minimum

Maximum

Wavelength

nm

1545

1560

Input optical signal

dBm

–3

3Output optical signal dBm

31

Noise figure

dB

5.5

CSO

dB– 67CTB

dB–70

Dimensionsmm

Number of LDs
Interface connector
Power supply
Power consumption

33

Total signal output power (dBm)

All these devices including a control circuit capableof mounting up to three pumping laser diodes areaccommodated in a package measuring 150(L) mm
x 125(W) mm x 20(H) mm, thus realizing downsizing.
The amplifier module has adopted D-SuB25pin forinterface connector --an industry-wide standard, inaddition to a single driving power supply of +5 V DC,
and is provided with an RS232 serial communication
port enabling external control of amplifier operation andalarm monitoring. With respect to control method for LDs,
automatic gain control (AGC), automatic level control(ALC), and automatic current control (ACC) are available,
so that the operation mode can be selected dependingon user applications.

3231302928
1549.3 nm
1560.6 nm

272625123456

Pump power (W)Figure 44.

Relationship between pumping power and signal
output power.

CONCLUSION

An optical fiber amplifier based on the cladding-pumping
technology has been integrated with a platform with
control functions to develop a compact, high output
power optical amplifier for CATV, achieving a signal
output power of +31 dBm at a pumping power of 5 Wfrom multimode laser diodes.
It is hoped that the amplifier will be used in variousanalog transmissions.
For more information, please contact:
Technological information:
Optical Components Dept., Information andCommunications Co.
TEL: +81-436-42-1703
FAX: +81-436-42-1789
Others:
Fitel Planning and Coordination Dept., Information andCommunications Co.
TEL: +81-3-3286-3432
FAX: +81-3-3286-3708
Email: fitel@ho.furukawa.co.jp

150 x 125 x 20 (without heatsink)
3D-SuB25pin+5V DCtyp. 60 W (Case temperature: 50°C)

Communication

RS232C serial communication

LD control

Automatic gain control (AGC)
Automatic level control (ALC)
Automatic current control (ACC)

Monitor function

Optical input- and output-power, Amplifier
gain, Reflected power, LD information(Current, Output power, Temperature)

Alarm

Optical input power, Optical output power,
LD, Case temperature, LD drive current

Furukawa Review, No. 26

200450