THORLABS TED8000 Series, Руководство по эксплуатации

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4 Optimization of Temperature Control
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4 Optimization of Temperature Control
4.1 Principle Setup and Function
A typical laser diode module comprises
·
the laser diode chip that needs to be temperature controlled;
· the temperature sensor;
·
the TEC element;
· the thermal conductor (copper block) that establishes the thermal contact between the laser
and the TEC, as well between the laser and the temperature sensor and
· the heat sink.
Possible error sources that impact the temperature control
1. The sensor is not in direct thermal contact with the laser chip. The inhomogeneous temperature
within the copper block ("temperature gradient") influences the measurement. Even within the
laser chip a temperature gradient is present. Thus, a correct measurement of the real laser chip
temperature is not possible. Offset and gain errors of the sensor allow only an estimate of the
laser temperature.
Possible optimization: Sensor calibration
2. A change of the internal power dissipation of the laser, e.g. due to change of the laser current,
changes the temperature gradient between laser and sensor as well. This results in a
measurement error depending on the mechanical setup of the laser chip and the sensor. Slow
changes of the ambient temperature, however, will be compensated well by the control loop
since the influence of the ambient temperature on the laser diode can be neglected.
Possible solution: optimized thermal design
3. The transient response after setting a new temperature is limited since the heat transport in the
copper block is relatively slow. Furthermore, the sensor must settle to the laser temperature - it
also has a non-negligible thermal capacity.
Possible optimization: careful adjustment of PID parameters