| 摘要 |
An optical communication system using digital pulse position modulation employs a mode locked laser with a mode locking frequency equal to the time slot frequency of the modulation and means dependent on groups of consecutive digits of the data to be transmitted to select pulses from the laser for transmission. In one example, 4-bit groups from the data for transmission select one out of 20 pulses from the laser thus leaving a guard interval of 4 time slot periods between position modulated pulses. An encoder and a decoder for converting between digitally encoded data and position modulated pulses are described. These use a counter driven by clock pulses at the time slot frequency to supply inputs alternately to two encoding logic circuits or two multiplexers. |
