Two simple applications of this trainer are described here an analogue and a digital link. The circuits employed represent one method of realising two links respectively. There are several other means of building more efficient analogue and data links. This is left to the ingenuity of the opto electronics designer and experimenter. The circuits shown have been tested and have been found to perform satisfactorily. These may however require minor changes from one kit to another. Misalignment and dirt particles in the optical path can also cause variations in performance. The SMA terminations on the patch cord are polished to minimise coupling losses. The opto electronic devices in the SMA adopter and the SMA connectors in the patch cord have been aligned to obtain maximum optical power coupling. The performance of the link is determined by the transfer factor, which is the ratio of the receiver photocurrent to the transmitter LED forward current. For this trainer, this ratio is typically 100 to 200 microamperes of receiver photocurrent per milli ampere of transmitter LED forward current when using the 1-meter PMMA simplex cable. Factors like bandwidth/baud rate will be determined by the actual external components used.