Agilent Technologies 8504B - Page 69

FINAL TRIM SIZE : 7.5 in x 9.0 in
P
erforming
Guided
Setups
and
Calibrations
Performing
Manual
Calibrations
Reduce
the
eects
of
chromatic
dispersion
at
1550
nm
Y
ou can
turn o
the
use
of
chromatic
dispersion
correction
data.
This
allows
you
to use
your own
correction
methods
.
When
making measurements
at 1550
nm, the
amount
of
chromatic
dispersion
experienced
by the
light traveling
in the
reference
path
will
be
less
than
that
in
the path
of the
device being
tested.
This
is
due
to
that
fact
that,
in
most
cases
, light
traveling
in
the
path
with
the
device
being
tested
is
all
in
ber
.
However
, part
of
the
reference
path
is
in
an
open
beam
(inside
the
8504B).
This
mismatch in
dispersion
results
in
a
broadening
and
subsequent
drop
in
the
peak value
of
the
displayed
reection
\impulse".
The
peak
value
decreases
monotonically
as
a
function
of
the
length
of
the
dispersion
mismatch.
This
eect
is
consistent
and
has
been
corrected
out
by
the precision
reectometer
.
The
instrument
assumes
a
dispersion
coecient
of
17
ps/(nm)(km). The
result of
this correction
leaves a
residual
error
on
the
order
of
6 0.3
dB.
If the
path to
the
device
being
tested
is
both
in
ber
and
an
open
beam,
the
eects
are very
dicult to
remove from
the
measurement;
subsequent uncertainties
due
to
chromatic
dispersion
can
approach
5
dB
.
External
sources
can
be
used
In
addition
to
the
internal
1300
nm
and
1550 nm
sources,
you
can
use
an
external
source
for measurements
.
(The
external
source
input
is
provided
as
a
convenience
for users
with
very
advanced
applications
.
It
is
not
meant
for
the
typical
user.)
The
external
source
must
be
able
to
be
modulated
with
a
27
kHz
signal.
When using
an
external
source
,
normal
calibration
and
correction
features
are
not applied
to the
measurement
data.
Refer
to
\T
o
calibrate
for
an
external
source"
to learn
how
to
calibrate
the
precision
reectometer
for
use
with
an
external
source
.
2-22
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