| 摘要 |
PURPOSE:To obtain an optical transmission system without the limitation of the Law of Electromagnetic Waves and the leakage, by PCM-modulating a sound signal, irradiating the signal as an optical signal, receiving this optical signal and demodulating and reproducing the signal. CONSTITUTION:A sound signal spoken by a caller to a microphone 9 is A/D- converted to a PCM modulation signal at a pulse modulation circuit. A light illumination drive circuit 10 drives a light emitting element 11 in synchronizing with this signal to a pulsive optical signal X into space. A marker signal generating circuit 12 generates a code signal specifying a recipient before the call with the application of a channel switch 13, and when the call is finished, a call end code is generated to drive the circuit 10. At the reception side, a PCM modulation pulse is detected at an optical signal detection circuit 15 from a signal received at a photodetector 8 and the pulse is inputted to a demodulation circuit 14. The circuit 14 demodulates the PCM modulation signal into the sound signal comprising analog signals, and the sound signal is amplified at a low frequency amplifier 19 to drive a speaker 20. A marker signal discriminating circuit 21 activates the amplifier 19 when the code is coincident with a recipient code of itself. |
