Patent ID: 7565082

Claim:
A data transmission system to transmit data through open transmission, the system comprising: a data transmitter, wherein the data transmitter is a portable terminal; and a data receiver, wherein the data transmitter comprises: a laser light source to generate a signal light; a dummy light source to generate a dummy light for judging an optical axis; an optical system to output the signal light and the dummy light on the optical axis, and causing a beam spread of the signal light smaller than a beam spread of the dummy light; a receiving circuit to receive a reception OK signal from the data receiver; and a driving circuit to drive the laser light source to output the signal light for carrying the data responsive to the reception OK signal, wherein the data transmitter is capable of causing the optical axis of the signal light and the dummy light to scan across a photoreceiving part of the data receiver, and wherein the data receiver comprises: a photodetector to optically receive the dummy light and the signal light, said photodetector outputting a first electrical signal when receiving the dummy light and outputting a second electrical signal when receiving the signal light; a level judging apparatus to judge a level of the first electrical signal from the photodetector; a transmitting circuit to transmit the reception OK signal to the data transmitter when the first electrical signal from the photodetector has a level equal to or greater than a predetermined level responsive to a result from the level judging apparatus; a data demodulating circuit for demodulating the second electrical signal from the photodetector when the first electrical signal from the photodetector has a level equal to or greater than the predetermined level and obtaining the data included in the second electrical signal; and a reception result indicator to inform a user of a reception result of the data.