EXFO IQS-2400 WDM Laser Source for IQS-500/600 - Manual (Page 189)

WDM Laser Source 183
D Wavelength and Power
Control, General Principles
Wavelength Control
The source wavelength is influenced mostly by laser temperature and, to a
lesser extent, by laser current intensity. In the IQS-2400 WDM Laser Source,
you can control and stabilize wavelength by modifying the laser
temperature. The laser temperature can be set to any value between
(T
set
–1 °C) and (T
set
+1 °C). T
set
is the temperature that the laser must attain
to generate the central wavelength. Wavelength variation corresponds to
an average of 0.1 nm/°C for a total wavelength tuning range superior or
equal to 2.0 nm.
Note: The displayed wavelength does not take into account the temperature
correction (0 °C correction).
At module startup, the laser is warmed up to 24 °C in order to speed up
stabilization when it is activated. When the laser is deactivated (but
module is still on), the laser temperature is maintained.
Temperature stability and control are essential for wavelength adjustment.
Therefore, the source module includes a thermistor that is placed inside
the laser package and is used to measure internal laser temperature. The
source module also drives the thermoelectric cooler (TEC) used to reach
required temperatures and regulate specific values.
Power Control
To ensure more power stability, the source module is mounted with a
back-facet photodiode measuring a monitor current coming from the rear
facet of the laser. Since the output power is directly proportional to the
monitor current, power is calculated using the monitor current in relation
to the coupling efficiency.
You can control the source power through a change in laser drive current.
A 10.0 dB attenuation range is possible. Wavelength precision will be
maintained throughout the attenuation range.