The subject-matter of my dissertation is on the field of opto-electronics; it gives a possible solution to the problematics of semiconductor lasers' optical power control. Semiconductor lasers or laser diodes are fairly unstable devices. Beside the common semiconductor temperature stability issues they produce even more interesting phenomena, which are derivable from laser physics. This is why among others the light of a laser diode will be extremely temperature-dependent too. Certain measuring tasks, for example in multi-wavelength reflectometry, can be done mostly with laser diodes because of their narrow optical bandwidth, but accurate measurements need stable optical power. My goal was to design a laser diode control circuit, which can hold steadily and temperature-independently the adjustable optical power of a low-power laser diode commonly used in multi-wavelength reflectometry applications. I realized this with the feedback of built-in monitor photodiode's signal. Comparing to a variable reference it gives the control signal of the parallel regulator. The circuit also capable of intensity modulation of laser diode's light. My circuit is working and fulfilling its duties adequately. The perfected version is probably going to be used in the OMT Laboratory's own bi-wavelength reflectometer device which is under development.