Abstract: The present invention relates to an optical power and extinction ratio controlling device and method. An optical signal output from a light source is detected and optical power and extinction ratio of the light source are controlled. In detail, a feedback signal is provided to the light source to automatically control the bias current based on a DC signal output by a photodetector detecting the optical signal. Therefore, the optical output of the light source is maintained. Also, an optical signal output by the photodetector is converted into a predetermined times DC signal, and a feedback signal is provided to the light source to automatically control the modulation current based on the DC signal. Therefore, the extinction ratio of the light source is maintained. As a result, the extinction ratio is automatically maintained to satisfy the change of condition and the characteristic of light source, thereby maintaining quality optical outputs.