Temperature controllers are designed to regulate temperature and remove heat for temperature-sensitive elements such as laser diodes. This is accomplished by either cooling or heating a Thermo-Electric Cooler (TEC) device by applying either a positive or negative current and voltage. They are also often referred to as Peltier devices, heat pumps or heat exchangers.
Temperature controllers apply a current and voltage to a TEC element. This can have two primary functions. The first function is to remove heat from the laser diode or another thermal load element. Cooling the laser diode is necessary to maintain its lifetime. For example, a GaAs laser diode operating in the NIR typically often has a lifetime of 10,000 hours at 25 degrees C. As a rule of thumb, for every 10 degrees C higher operating temperature the laser diode has, the lifetime will decrease by a factor of 2. A laser diode often produces many Watts or Joules of thermal energy (heat) causing self-heating, even with effective heat sinking with low thermal resistance. Thus, a temperature controller is necessary to maintain the lifetime of the semiconductor device.
The second function is to stabilize the temperature of the laser diode, which is important for power stability. Laser diodes, like many semiconductor materials, generally operate less efficiently at higher temperatures. Lower efficiency due to heating of the junction results in reduced optical power. Thus, it is important to regulate the temperature using a laser diode controller. The temperature controller applies a varying current to the Peltier element as a function of the feedback signal from the thermistor in the form of a resistance. The thermistor is a sensing element that is used to measure the temperature at a certain point. A thermistor's electrical resistance varies directly as a function of resistance according to an exponential function with constants describing the properties of the specific thermistor. The current controller measures the resistance of the thermistor by applying a small current, usually on the order of several micro-Amperes, and reads the voltage across the thermistor.
Opt Lasers™ temperature controllers are available with a wide range of maximum currents and voltages to remove heat from the laser diode and stabilize its temperature. Temperature controllers are used in conjunction with a TEC element and a laser diode current driver to operate the laser diode.