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Coaxial Uncooled DFB Laser Diode Module for
C-WDM Applications

1.

INTRODUCTION

Recent years have seen widespread use of the coarsewavelength division multiplexing (C-WDM) system, since
the recent growth of broadband access has made it
essential to increase the capacity of metro systems. In theC-WDM system, wavelength multiplexing is effected at acertain wavelength interval (e.g. 20 nm) that is coarser
than that of ordinary WDM systems, thereby the transmission capacity per single fiber is increased. Recently, theC-WDM systems are being introduced into analog communications as well as into digital communications,including CATV and mobile communications systems. InCATV systems optical fibers are used in the links nearer
to the base station for the purpose of capacity increase.
In mobile communications systems also, optical repeaters
are used for dead zones of poor radio wave reception
such as in tunnels and underground malls. Against thisbackground, Furukawa Electric has developed a coaxial
uncooled DFB laser module for C-WDM applications, andbegan products shipping.

2.

2.2 Wavelength Lineup
A broad wavelength lineup of 18 wavelengths is provided
with an interval of 20 nm ranging from 1270 nm to 1610
nm.
2.3 Specifications for Digital Applications
Table 1 shows the specifications for digital communications. The product amply satisfies the characteristics for
2.5-Gb/s modulation, and thus can deal with 2.5-Gb/s
digital modulation. Figure 2 shows a typical eye diagram
during 2.5-Gb/s modulation.
Table 1 Specifications for digital communications.
ItemSpec.

Condition

Spectrum width

nm

≦1.0

2.5 Gb/s,-20 dB width

Rise time

ps

≦0.10

20-80 %

Fall time

ps

≦0.15

20-80 %FEATURES

2.1 StructureFigure 1 shows the appearance of the product. The package is a coaxial type without built-in temperature control
function, and three flange types are available including
horizontal, vertical and flangeless types. The pigtail fiber
has a flame-retardant coating of Hytrel †, and is compatible with various connectors. Also, a single or semi-double
stage optical isolator is built in.

Figure 2 Eye pattern at 2.5-Gb/s modulation.

2.4

Specifications for Repeater Applications in
Mobile Communications
In mobile communications where the frequency bands ofthe second generation (i.e. 800 MHz) and the third generation (i.e. 1.9 GHz and 2.2 GHz) are used, the laser modules to be applied to optical repeaters are required tohave such performance as high output (4 mW), low thirdorder inter-modulation distortion (IMD3) and low relative
intensity noise (RIN). Typical specifications for the thirdgeneration are shown in Table 2.
Figure 1 Appearance of coaxial DFB LD module.
† Hytrel is a registered trademark of DuPont.

Furukawa Review, No. 30

200623

Coaxial Uncooled DFB Laser Diode Module for C-WDM Applications

Table 2 Specifications for repeater applications in mobile communications.
Item

Spec.

Cut-off frequency

GHz

Typ.3

IMD3dBc≦-56

RINdB/Hz≦-145

IsolationdB≦30

Table 3 Specifications for CATV return-path applications.
ItemCondition

Spec.

Condition
2 tone, f1=13 MHz,f2=19 MHz,OMI=10 %/tone

IMD2dBc≦-50

IMD3dBc≦-60

2 tone, f1=2.2 GHz,
f2=2.2025 GHz,
OMI=20 %/tone

Spurious noisewith carrier

dBc

Typ.-55

f=2.2 GHz

Spurious noise
without carrier

dBc

Typ.-50

1 tone, f=19 MHz,OMI=10 %/tone,
SMF: 20 km

RINdB/Hz≦-150

f=5〜200 MHz

IsolationdB≧502.5 Specifications for CATV Return-path Applications
In CATV return-path the adoption of a semi-double stage
optical isolator and an angled PC connector is standardized since stringent measures against reflected light areneeded. Also, low inter-modulation distortion and low
spurious noise are required together with low RIN. Table 3
shows the typical specifications.

3.

CONCLUSIONS

Furukawa Electric has brought into market the coaxial
uncooled DFB laser module for C-WDM applications having a broad wavelength lineup of 18 wavelengths ranging
from 1270 nm to 1610 nm with an interval of 20 nm. The
product can deal with both the digital and analogue communications, thus satisfactorily meeting customer needs.
For further information, please contact:
Optical Devices Department, R&D Div.
TEL: +81-436-42-1617
FAX: +81-436-42-1736

Furukawa Review, No. 30

200624