- This paper shows an optical time domain reflectometry (OTDR) system based on an avalanche photodiode (APD) receiver, a 520 nm laser diode transmitter, a high-speed analog-to-digital converter (ADC) and a commercially available field programmable gate array (FPGA). This approach allows OTDR measurements up to 200 m and provides a spatial resolution of 20 cm. Depending on the number of averaging, the measurement time can be between 5 s and 50 s for a range up to 200 m with a good signal to noise ratio.