| 摘要 |
The use of multi-level signalling in optical links may provide an improvement in system capacity compared to conventional binary signalling. Unlike conventional electronic or radio systems, in optically amplified links where optical noise is dominant equally spaced signalling levels are not optimum. For these links, the use of signalling levels with quadratic spacing can provide the lowest bit error rate for a given signal power, allowing a 6 dB reduction in launched optical power. The invention described is an arrangement to produce multi-level optical signalling with quadratic spacing. A multi-level optical signal generator for generating a multi-level optical signal in optical links in response to two or mote electrical signals. A light source arrangement provides a respective optical signal for each electrical signal utilising either separate light sources corresponding to each electrical signal or preferably, a single light source and a beam splitter. Each optical signal is modulated in response to its respective electrical signal and the signals are combined to produce the multi-level optical signal, preferably with quadratic spacing. |
