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Glossary
70
Clock
A signal that provides a timing reference.
Clock recovery
Recovering the clock from the incoming data.
dB
Decibel: a method of expressing power or voltage ratios. The decibel scale is
logarithmic. It is often used to express the efficiency of power distribution
systems when the ratio consists of the energy put into the system divided by
the energy delivered (or in some cases, lost) by the system. One milliwatt is
usually the reference for 0 decibels. The formula for decibels is:
(level/reference)
level
dB
= 10@log
+ 10 log
level
dB
reference
level
In the electrical domain:
P out
+ 10log
P ref
dB
dB
= 10@log(P
power
power
out
= 10@log(V
2 ref
V
+ 1mW
= 20 log(V
50ohm
/50 W=1 mW
V2
ref
In optical:
P o
dBm
= 10@log(P
power
o
+ 10log
P ref
dBm
power
P
= 1 mW = 0 dBm
ref
+ 1mW + 0dBm
P
ref
dBm
The symbol for power level in decibels relative to 1 mW.
DFB laser
Distributed Feedback Laser-a type of laser designed for stable single-mode
operation. Internal waveguides select one of several possible laser modes and
suppress all others.
Demodulation
A process whereby a modulated signal is returned to its original form.
DWDM
Dense Wavelength Division Multiplexing-a higher capacity version of
WDM, which is a way to increase the capacity of fiber optic transmission
systems through multiplexing up to 40 wavelengths of light.
Deterministic jitter
The difference between the maximum and minimum deviations from the
expected timing positions of data after removing the random jitter.
V 2 out
R
2 ref
V
+ 20log
+ 10log
/P
)
R
ref
2
/R/V
2/R)
out
ref
/V
)
out
ref
/P
)
ref
OI1125 E/O Transmitter Instruction Manual
V out
V ref
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