Newport 8000 - Page 49

36 Chapter 3 Laser Diode Driver Module Operation
3.5.3.2 Bandwidth
This setting is used to control noise and laser current modulation rates. Allowable
settings are
Low
,
Low CW
, and
High
.
Low CW
allows a maximum modulation rate
of 30 Hz, and operates with the least noise.
Low
allows up to 10 kHz modulation,
while
High
allows full bandwidth modulation. Modulation is disabled in
Im
and
Po
modes. The MOPA module does not have this setting.
3.5.3.3 Modulate (MOPA Modules Only)
This setting is used to select which laser driver is modulated by the external
modulation input. The choices are
Osc
for the oscillator driver, or
Amp
for the
amplifier driver.
3.5.3.4 Io Lim
As one of the safety features of the Laser modules, the
Io Lim
sets a maximum
allowable current drive for the laser diode. The system will also limit current set
points to this value when operating in the
Io
mode. Two conditions can be generated
when the driver reaches this limit. The lesser of the two is the soft current limit. The
soft limit, indicated by
I
LIMIT
on the status line of the Laser Main Screen, indicates
that the laser module is limiting the current drive to the laser diode, but otherwise
operating as normal. The second condition is a hard limit, which indicates that the
current drive attempted to exceed the current limit faster than the circuitry could limit
it. This condition causes the laser module’s output to be shutdown. Both of these
conditions are monitored in circuitry on the module itself, and in the case of the hard
limit, shutdown is within microseconds of the condition being detected.
3.5.3.5 Vcomp
The voltage compliance setting controls the shutdown of the laser module output
when the forward voltage of the laser exceeds the compliance setting. Like the
current limit described above, the voltage compliance is monitored in circuitry on the
module itself, allowing for shutdown within microseconds of the condition.
3.5.3.6 Im Lim
The photodiode current limit is a software monitored limit on the current delivered
from the photodiode. Because this limit is a software monitored limit, shutdown can
occur up to a second after the condition is true.
3.5.3.7 Po Lim
Like the
Im Lim
, the photodiode power limit is a software monitored limit on the
power delivered from the photodiode. For this limit to function, the user must set a
PD Resp
value other than zero. Because this limit is a software monitored limit,
shutdown can occur up to a second after the condition is true.
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