| 摘要 |
In a frequency shift keyed direct detection (FSKDD) optical (e.g. infra-red) transmission system, a first light source 21 is intensity modulated with a lower frequency part 25 of an information signal and a second light source 22 is frequency modulated with a higher frequency part 24 of that signal. The frequency modulation is then converted to intensity modulation to provide a composite intensity modulated signal carrying both the high and low frequency parts. The technique overcomes the problem of poor low frequency response of solid state light sources. The conversion between modulation types may be effected in the high frequency branch of the transmitter or at the receiver (Fig.2). <IMAGE>
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