THORLABS PICO D, User Manual

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2.5.3.3.1 Digital status: _SYSTEM_ERROR
When digital status signal _SYSTEM_ERROR is TRUE - LOW (0 V) the PICO D unit
has an internal error,
e.g . overheating, and should not be used. In case of an error,
the laser is forced to an off state irrespective of the logical status of
_OPTICAL_POWER_ENABLE (as for all other control signals).
When digital status signal _SYSTEM_ERROR is FALSE - HIGH (5 V) the unit is in
normal operation mode.
The _SYSTEM_ERROR may be TRUE during the startup phase. This is quite nor-
mal.
_SYSTEM_ERROR’s that occur during operation can only be reset by switching off
the PICO D unit.
2.5.3.3.2 Digital status: _WAVELENGTH_ERROR
This signal indicates the electronic controller error. When _WAVELENGTH_ERROR
is TRUE - LOW (0 V) the electronic error will be approximately more than
±
15pm.
When digital status signal _WAVELENGTH_ERROR is FALSE - HIGH (5 V) the er-
ror will approximately
±
15 pm in wavelength. Since it is the electronic error other op-
tical effects are not included, for example mode hops, drift etc.
2.5.3.3.3 Digital status: _OPTICAL_POWER_ERROR
When digital status signal _OPTICAL_POWER_ERROR is TRUE - LOW (0 V) the
output optical power from the unit does not follow (
i.e. too low) the set optical power
(applied voltage to the analog OPTICAL _POWER control signal, see 2.5.4.2).
When digital status signal _OPTICAL_POWER_ERROR is FALSE - HIGH (5 V) the
difference between output optical power and set wavelength is within specifications.
If the +OPTICAL_POWER (see 2.5.4.2) is increased beyond the voltage
corresponding to a maximum recommended laser diode drive current, the _OPTI-
CAL_POWER_ERROR will change its logical state to TRUE - LOW (0 V). A further
increase of +OPTICAL_POWER will, for some laser units, further increase the
optical output power. The increase will vary from individual to individual. The PICO D
control electronics will protect the laser diode, however it is not recommended to
operate the laser if the _OPTICAL_POWER_ERROR is TRUE - LOW (0 V).
2.5.3.3.4 Digital status: _TEMPERATURE_ERROR
When digital status signal _TEMPERATURE_ERROR is TRUE - LOW (0 V) the unit
has not (yet) the right laser cavity working temperature. The PICO D unit can be
used but optical power and wavelength may be out of specifications.
When digital status signal _TEMPERATURE_ERROR is FALSE - HIGH (5 V) the
unit has the correct laser cavity working temperature.
2.5.3.3.5 Digital status: _MODE_HOP_DETECT
The _MODE_HOP_DETECT signal is normally HIGH. A detected mode hop will pull
this signal low within 10
µ
s of the mode hop event. The signal is hold low for at least
100
µ
s. Multiple mode hops within the “hold low” period of time would not be de-
tected. Neither may mode-hops be detected if the PICO D is operated at maximum
tuning speed.