This is a 9 MHz photodiode circuit that was used to test the LED's. The LED was placed directly in front of the detector window while the output was monitored with a oscilloscope. A slide showing the circuit used to drive the LED would be appropriate here, but the setup is quite simple. A 9-volt battery was used for bias, a resistor for current limiting, and a signal generator for modulation. The signal generator can be applied across either the resistor or the LED. If a signal generator with bias adjustment were used, the battery and resistor would be optional.