C.1 Laser diode

The Lumix LU045M200 is a laser diode mounted on a 14-pin butterfly chip and connected to a single-mode optical fiber (see Fig. C.1). It has a power of 200 mW and a wavelength of 845 nm. The optical fiber has a Fiber Bragg Grating (FBG) that filters the light to produce a better monochromatic wave. Apart from the laser diode, the chip also has a photodiode, a thermistor and a Thermoelectric Cooler (TEC). The photodiode measures the intensity of light that is produced into the optical resonator cavity of the laser. The thermistor measures the temperature of the laser and the TEC is a device that uses the Peltier effect to refrigerate the laser chip. The laser diode is driven at constant current by a laser diode controller (Thorlabs IP500), which also displays the instantaneous intensity of the laser radiation read by the photodiode. A TEC controller (Thorlabs TCM1000T) controls the temperature of the laser by reading it from the thermistor and performing a proportional/integral (PI) feedback on the TEC. There is one laser driver and one TEC controller for each laser and they are assembled in the so called laser controller box.

Figure C.1: Laser diode mount. Only 8 pins of the butterfly chip are needed to measure and control the intensity and the temperature of the laser diode. The controllers (intensity and temperature) read the signals and perform the feedbacks.
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JM Huguet 2014-02-12