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PRODUCT GUIDE: OPTICAL TIME
DOMAIN REFLECTOMETERS
With the Internet, Ethernet, and metropolitan area networks
(MANs) again beginning to put pressure on the installed capacity
of fiber optics, the importance of test instrumentation cannot
be overstated. That's where the optical time domain reflectometer
(OTDR) comes in. It is the premier instrument in testing a
fiber optic link, for several reasons, first and foremost
its ability to perform and store multiple tests. Such measurements
as splice and connector location, fiber attenuation across
the link, reflectance, and fiber length and break location
can all be determined with an OTDR. If the user is interested
in attenuation of the signal through the fiber's length, he
can obtain only the total of the loss with an optical power
meter. But the OTDR will give him an event map on a monitor,
showing the attenuation across the whole fiber span, as well
as indicating signal level versus distance, the location of
any fusion splices or bend loss and of any breaks in the fiber.
Another factor that sets the OTDR apart is that, because
its principle is like that of a radar and the transmitter
and receiver are on the same instrument, the user needs access
to just one end of a fiber to test a link. Most manufacturers,
however, recommend that the testing be done from both ends
if both are available. Exfo, for one, notes that bidirectional
OTDR averaging is essential for users who must do extensive
fiber link commissioning and documentation, as well as for
those who are sensitive to their cable plant loss budgets.
The basic components of an OTDR include a light source, pulse
generator, coupler, detector, A/D converter, and controller,
in addition to software. The source emits pulses of light
that are directed through the coupler into the fiber under
test. The pulses are averaged and the fiber characterized.
Most manufacturers offer one or more "mini-OTDRs," handheld
or relatively compact instruments that can be taken into the
field.
AGILENT TECHNOLOGIES
www.agilent.com
Agilent's flagship OTDR is the series E6000-B
mini-OTDRs for single-mode networks. Two in the series are
designed for 1310-nm single-mode fiber, and three others for
1310 and 1550 nm. Dynamic range varies, from 28 dB to 45 dB
(1310). A fiber break locator looks exclusively for breaks,
which are displayed quickly. The E6000B combines 16,000 data
points with a minimum sample spacing of 8 cm. The E6010B is
aimed at testing at 1625 nm, with a dynamic range of 40 dB,
and can be used to test the optical supervisory channel capability
of WDM links. A series of modules enables the basic design
to cover the wavelengths 850 nm and 1300 nm. Out-of-band testing
also allows users to do a fiber test while transmitting data
at 1310 or 1550 nm. The series comes in 10 standard models.
•The series of rack
OTDRs ? the E6053A, E6058A, and E6060AÑ based on the design
of the E6000BÑcan be built into a system and controlled remotely
by a PC. Dynamic range varies from 34 dB (1550) to 40 dB (1310).
When used with an optical switch and a PC, these instruments
can be used for commissioning and monitoring a fiber optic
link automatically. With a keyboard and a VGA monitor, these
devices can serve as standalone mini-OTDRs.
•The 8147 is designed
for installation, commissioning and bench applications. Its
"Easy Mode" feature lets the user preprogram complete procedures,
so that with just a few keystrokes, he gets standardized measurements.
Extended in-depth analysis, including two-way measurements,
delta measurements, and comparison of up to four traces, is
available on-line. A return loss graph permits the user to
see the reflectance of individual events at a glance, as well
as the total return loss of the link. The 8147 series comes
in 11 standard versions, with dynamic ranges spanning from
30 dB (1310) to 45 dB (1550).
•The E6091A OTDR
Toolkit II is described by Agilent as ideal for post-processing,
analyzing, and batch processing Bellcore GR-196 bas0ed OTDR
files. Systems employing the E6091 software can transfer data
serially to a PC running Windows 95, 98, or Windows NT. The
data can be saved for use in a spreadsheet or database. Other
features include comparison of up to four traces simultaneously;
Trace Manager, to enable high-speed multiple trace transfer
between the OTDR and PC; and two-way averaging for accurate
loss calculations.
EXFO
www.exfo.com
Exfo says that its FTB-7000B series has
more than 20 models, with instruments suitable for the shorter
distances of local area networks (LAN) and metropolitan area
networks (MAN) as well as the greater distances in long-haul
networks. The company claims links exceeding 200 km can be
characterized using the 45-dB dynamic range model. Single-mode
modules are available at 1310 nm, 1410 nm, 1550 nm, and 1625
nm, and multimode at 850 nm and 1300 nm. A Visual Fault Locator
option gives the user troubleshooting capability in LAN/WAN
and metropolitan networks.
•Exfo recommends
its FTB-9000 optical switch module combined with the FTB-7000
OTDR for batch fiber testing in patch panels or bare ribbon
testing during installation. Dynamic ranges go from 31 dB
to 42 dB. The company offers complete OTDR testing kits, including
multifiber, ribbonized, and bare ribbon configurations. For
unconventional wavelength windows, the company's 1625-nm module
can characterize L-band systems, and the 1400-nm module can
be used with the new fiber that has no water-peak attenuation.
•The ToolBox software
in the FTB-7000B module has two modes: auto mode and advanced
mode. The first has preset test parameters and a choice of
single- or dual-wavelength OTDR testing. The second allows
the user to manually set all acquisition parameters, including
index of refraction and helix factor.
•The FTB-100B mini-OTDR
has an internal memory of 70 traces, and additional storage
capacity of up to 6000 traces. The module is available at
four wavelengths: 1310 nm, 1410 nm, 1550 nm, and 1625 nm.
Dynamic ranges to up to 45 dB. It contains an InGaAs detector
power meter that can measure in dB, dBm, and watts. The trace
has 52,000 data points, and a sampling resolution down to
8 cm.
•Exfo's FTB-400
Universal Test System comes in two configurations: a two-slot
OTDR and loss testing combination that has more than 500 OTDR
and loss capabilities, and a seven-slot configuration that
has more than 1000 testing combinations, including polarization
mode dispersion, DWDM modules, ribbon test kits, switches
for high-fiber-count testing, and OTDR and loss testing. It
has more than 20 OTDR modules, mated to four single-mode and
two multimode wavelengths.
TEKTRONIX
www.tektronix.com
Tektronix calls its line of mini-OTDRs its
"next-generation entry" into long-haul fiber installations
of 300 km and up, but says it also addresses short- and mid-range
fiber optic networks. The line, called NetTek™  OTDR,
combines OTDRs and optical power meter modules with the NetTek
Analyzer, the control and display platform that houses these
modules. There are nine OTDR modules, with wavelengths ranging
from 850/1300 nm to 1550/1625 nm, and dynamic range from 34
dB to 44 dB.
•Tektronix says
that the OTDRs address virtually every prevailing mode, wavelength,
and fiber optic network, and both in-band and out-of-band
measurements. The NetTek platform simultaneously accepts up
to four OTDRs plus an optical power meter. The platform is
designed to accommodate an expanding line of measurement modules,
including the YBT250, used for Base Station testing, and others
currently in development.
•The NetTek platform
has standard internal memory of 7 MB available for storage
and running WinCe applications. A floppy disk and a 128-MB
memory card are optional. A port supports standard PCMCIA
memory cards. Display range is 0 to 320 km for single-mode
fiber and 0 to 32 for multimode. The OTDRs can operate with
pulse widths from 10 nanoseconds to 20 microseconds. Thirty-two
thousand measurement points is standard.
•NetTek OTDR modules
use TektronixÕs IntelliTrace Plus technology, which automatically
optimizes test parameters so the user does not have to.
FOTEC
www.fotec.com
Fotec says that its Fiber U OTDR converts
any Windows PC into a full-function optical time domain reflectometer.
It consists of a mainframe and separate optical plug-in units
for measuring characteristics of either single-mode or multimode
fiber. Dynamic ranges are 25 dB for the 850/1300-nm multimode
devices and 28/27 dB for the 1310/1550-nm single-mode devices
and the combination multimode/single-mode device. Fotec says
the unit can be ordered in a field kit with carrying case
and launch cable. It can read from 2 to 180 kilometers, and
display 8 traces simultaneously.
NOYES
www.noyes-fiber.com
Noyes's M600 line of mini-OTDRs has user-installable
modules for testing multimode (850/1300 nm) and single-mode
(1310/1550 nm) fiber links. For the multimode M600-K-MM1-xx
dynamic range is 21/23 dB; for the single-mode M600-K-SM1-yy
it is 26 dB; for the multimode/single-mode M600-QUAD-xx-yy
it is 21 dB (850 nm), 23 (1300 nm), 26 (1310 nm), and 26 (1550
nm).
•The standard mainframe
includes a color LCD display, a floppy disk drive, and nonvolatile
memory that can store up to 50 traces. The software supports
trace manipulations such as two-way averaging, trace overlay,
graphing, and batch printing. Pulsewidth and range can be
set automatically or manually for maximum flexibility. The
M600 can automatically increment and include a fiber number
in each file name to speed up identification.
ANDO
www.ando.com
Ando's AQ7250 mini-OTDR is described by
the company as offering a range of functions and capabilities
ideal for field use. The single-mode unit's wide dynam ic
range of 41.5 dB (1310 nm) and 39.5 dB (1550 nm) enables measurement
of cables over extra-long distances, the company says, and
its high measuring speed means that it can measure a splice
loss of 0.5 dB from 70 km away in just 20 seconds. The screen
updates a minimum of twice per second in preview mode, allowing
real time checking of changes in the state of optical fibers
in less than a second. On batteries the AQ7250 has an operational
life of about eight hours under normal service conditions,
so the user can get a full day's work on one charge.
Automatic detection of splice losses, return losses, and
other items exceeding preset levels is possible. When calculations
are complete, the list screen is displayed, enabling the user
to view distances to splice points, splice loss, return loss,
and total losses, and other items at a glance.
•Ando also offers
the AQ7410 and AQ7410B reflectometers for measuring high-resolution
return loss distribution of waveguides and optical modules.
Using a wavelength-tunable narrow-band light source unit,
it is possible to obtain optical loss distributions of waveguides
and optical modules by observing Rayleigh backscattered light.
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