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Basic Concept
Without laser diodes, our daily
life would have a significant lack of entertainment and
telecommunication. Beside the printer technology in this area
the diode laser was the enabler for fast internet connections
and high quality CD’s; Diode lasers differ from most “classical”
lasers in two distinct ways:
Firstly, they do not posses an inherently defined wavelength.
Instead of two defined energy levels, the lasing transition
occurs between two energy bands. Secondly, the pn junction
defines the lasing volume, instead of the resonator in a
classical laser.
The experiments introduce the laser diode and investigates the
variation of the emitted laser wavelength versus temperature and
current. The set-up comprises of a digital slot-in module with a
20 mW pig-tailed laser diode and integrated Peltier cooler. The
change in wavelength by varying the temperature of the laser
diode is measured by means of an optical multichannel analyser (OMA).
The typical shift is approx. 0.25 nm per °C. The temperature
range of the diode laser controller can be varied from 10 to 40°
C, which results in a shift of 7.5 nm.
The use of an oscilloscope is recommended to prevent disturbing
other light and the measurements are carried out with modulated
diode laser light.
Experimental Set-up
The laser diode is mounted inside the slot-in module and
provides an optical fibre output which terminates on the front
panel of the slot-in module. By means of a fibre patch cable, it
is connected to a rotational stage (CON) which allows the
rotation perpendicular to the beam propagation to measure the
spatial distribution of the emitted laser light. In front of the
fibre telescope (FT-2), a pin hole is mounted. Via a second
fibre patch cable, the detected light is fed to the photo
detector slot-in module or to the OMA. The frequency generator
or modulator is used to study the modulation capabilities of the
laser diode with respect to its characteristic curve. Furhermore,
it is used to modulate the laser diode with a rectangular signal
in order to eliminate disturbing environmental light thus,
enhancing the sensitivity of the angle resolved intensity
distribution of the used fibre patch cable. |
