Degree Name

BS in Electrical Engineering


Electrical Engineering Department


Xiaomin Jin


The purpose of this project is to understand free-space optical transmission of signals in the application of transmitting an audio signal. An audio signal will be taken from the headphone output of a computer and used to modulate a current source driving an LED and a laser diode. The optical signal will then be transmitted through free space as well as two different focal length lenses and converted back to an audio signal to measure any attenuation or gain in the original signal. My experimental results showed that the LED was able to transmit up to 10 dB more power than the LD at all frequencies. However, the LD was able to transmit a more consistent power with respect to distance than the LED. The LED had higher average attenuation with respect to distance of 5.8dB/cm, compared to 5.2dB/cm for the LD. This could be because the LD transmits polarized light and the LED does not.