It specifies a way to wirelessly transfer data via infrared radiation. The IrDA specifications include standards for both the physical devices and the protocols they use to communicate with each other. The IrDA standards have arised from the need to connect various mobile devices together. IrDA devices communicate using infrared LED's. Many CCD cameras are sensitive to this wawelength too.
Signal continues into a filter.
There is a direct relationship between the energy of the incoming radiation, and the charge that the optics part of the receiver generates. Speeds for IrDA v. 1.0 range from 2400 to 115200 kbps. Data format is the same as for a serial port - asynchronously transmitted word, with a startbit at the beginning. With fixed length and speed of 38400 bps, each bit would take 3 pulses. The NRZ signal in the figure is the original data signal without modulation.