| 摘要 |
<p>1486421 Photo-electric communication systems COMMUNICATIONS PATENTS Ltd 22 Nov 1974 [3 Dec 1973] 55933/73 Heading G1A [Also in Division H4] In a television transmission system, modulated light carries the television signal along optical fibres to individual subscribers or to a distribution point from which ordinary cables can be used. The signal carried is a modulated r.f. signal. Individual programmes can be transmitted over respective optical fibres, or multiplexed into a common fibre; frequency division can also be used. Each subscriber may have a receiver able to discriminate between the various programmes, or may have an optical fibre or electric cable link to a programme exchange to control which programme is sent to him. The optical source may be an LED or an injection laser, e.g. a Zn or Al doped GaAs Burras diode, and the detector may be a pn diode. The source can be pulsed.</p> |
