As illustrated inFigure 4a an "opposed" or "through beam" configuration points the light transmitter and the receiver directly at each other. Although much of the light launched by the transmitter may never reach the distant receiver assembly,sufficient light is detected to passinformation. Since there is only air between the transmitter and receiver, it is the most commonly used configuration to transmit information over long distances.Most optical communications systems rely on this configuration. Remote controllers for televisions, VCRs, audio systems and computers all rely on this direct light link method, since it makes the most efficient use of the transmitted light.
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