| 摘要 |
PURPOSE:To remove a noise or disturbance by optically modulating separately a noninverted and inverted transmitting signals with linearly polarized lights having mutually orthogonal polarizing planes transmitting them, separately detecting these signals, optically demodulating them and then, obtaining the difference between the signals. CONSTITUTION:A signal A, which PCM-encodes an audio signal and causes the signal to be a pulse string, is inputted. Then, one part of the signal is kept as it is and the other part is inverted by an inverter 3. The both of them are separately added to light emitting diodes 4 and 5 and outputted as an AM modulating light. Both outputs are passed through polarizer 6 and 7, in which polarizing surfaces P1 and P2 are differ ent almost by 90 deg., and optical signals B1 and B2, for which a linear polarizing surface is different by 90 deg., are sent. The optical signals B1 and B2 are detected to analyzers 8 and 9, whose polarizing surfaces are the P1 and P2, and inputted to light receiving elements 10 and 11. Then, the optical signals are demodulated. Next, the optical signals are inputted to a differential amplifier 12 and a difference signal C is obtained. Then, the signals are D/A converted and returned to the original audio signal. Thus, the noise of a transmitting system or the disturbance due to a light from an external part is canceled and the transmission of high reliability is executed. |
