HP 86037B, Инструкция по эксплуатации

Страница: 15 / 204

1-9
Quick Start
Measuring Fiber Devices
f
m
is 2 GHz.
S
0
is 0.07 ps/(nm2×km).
λ
SPAN
is 60 nm.
L is 70 km.
Substituting these values into the above equation, we have:
Note that 0.85 nm is the maximum allowed step size. Steps shorter than 0.85
nm are permitted. The 0.85 nm step size results in about 70 steps for the mea-
surement.
You can reduce the measurement time using the following techniques:
• Sacrifice accuracy for measurement speed by choosing a lower modulation fre-
quency.
For the example above, if we make fm equal to 1 GHz, the step size can be
increased to 1.7 nm. This results in about 35 steps for the measurement and
thereby halving the measurement time.
• Make a survey measurement with a wide wavelength range and a lower modu-
lation frequency, for example, 500 MHz. Then, raise the modulation frequency,
for example, to 2 GHz, but narrow down
λ
SPAN
by zooming into the wavelength
range of interest.
In the above equation, a reduction of
λ
SPAN
by a factor of 2 will increase the
maximum allowed step size (
∆λ
)
MAX
by 2. The number of steps,
∝ λ
SPAN
/
(
∆λ
)
MAX
, and therefore the measurement time, will decrease by a factor of 4.
In this example, reducing the measurement span from 60 to 30 nm increases
the maximum allowed step size from 0.85 nm to 1.7 nm. The measurement
time decreases from about 9 minutes to about 2 minutes and 15 seconds.
(∆λ)
M A X
=
5 0 0
0 .0 7 p s
n m
2 .
K M
X 2 G H z X 6 0 n m X 7 0 k m