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6 Appendix
47
6.2 Setup and Function of a Temperature Controller
When devices are tempered normally, the following components are involved:
·
The component to be tempered (i.e. a laser diode)
·
A sensor measuring the temperature of the component
·
A heat source or sink (air or water / cooling element)
·
A heat conductor connecting the component to the source / sink (copper, aluminium)
·
A "propulsion" to lead the flow of heat (TEC element)
Statements and implications
·
The temperature of the laser can be measured with the sensor.
·
In the copper block, there is a heat flow between laser and TEC element.
·
In the TEC element, there is a heat flow between copper block and heat sink.
·
In the heat sink, there is a heat flow between TEC element and environment.
·
The temperature difference in the TEC element can be controlled by the TEC current.
This has a direct influence on the heat flow in the copper block and in the heat sink.
Hence the temperature of the laser can be influenced by the TEC current. The quantity of heat
flowing from the laser into the copper block and the size of the block impacts the reaction
speed of the setup.
Usually very small components (laser diodes) are tempered with relatively large cooling ele-
ments (TEC elements). Thus the dissipated power must be lead away quickly, and the compon-
ents are to be kept at the same temperature as close as possible.
Demands to the ideal temperature control loop
1. Knowledge of the absolute laser temperature
2. Stability of the laser temperature under any influence
3. Immediate settling to a new laser temperature when changing the set value of the temper-
ature
Influences on the real temperature control loop
To 1:
The sensor cannot be fixed to the laser chip in such a way that it will measure it's temperature
exactly. The reason is, that the temperature in the heat sink has a gradient due to the heat flow.
Further, even within the laser chip the temperature is not homogeneous.As for this, offset and
gain errors of the sensor lead to deviation in laser temperature measurement.
Possible solution: sensor calibration
