Transmitting binary ones and zeros via IR (infrared) light is not as complicated as it may appear at first glance. Just as radio stations transmit information using radio waves, infrared devices transmit data using the infrared frequencies of the electromagnetic spectrum. Also, just as you need a compatible device to listen to a radio broadcast, you must have a device capable of understanding and translating incoming infrared signals. All sending and receiving IR devices contain small, dark windows called IR ports. Inside these ports, transceivers (a combination of a receiver and transmitter) send and receive data using the IR frequency. After a device's CPU (central processing unit) sends the binary ones and zeros to the software controlling the IR transmission process, that information is converted into pulses of IR light. The software then forwards the data to the device's transceiver, which transmits the IR signals to another IR port. The receiving device's IR software converts the infrared transmission back into binary digits. IR devices transmit the binary ones and zeros according to a protocol set by the IrDA (Infrared Data Association; http://www.irda.org). For high-data transmissions, such as from a laptop to a printer, both devices must be within a few feet of each other and the IR ports must be within each other's line of site. The data is sent in a 30-degree wide cone from one IR port to another. Depending on the IR software, a pulse of light could represent a digital one, while the absence of a pulse of light could represent a digital zero. High-speed IR devices don't actually transmit data in a serial string of ones and zeros, however. Rather, bits of data are sent in groups to speed up the transmission process.
reference:(http://www.smartcomputing.com/articles/archive/r0403/30r03/30r03.pdf?guid=) *note: Search More You Damned Fool!!!