A comparison of one- and higher-dimensional modulation schemes for optical Gigabit transmission

Abstract:
In the last years, multi-dimensional modulation schemes have been presented for the use in optical short-range transmission based on intensity modulation and direct detection (IM/DD). These modulation schemes introduce a higher dimensional signal space in the electrical domain. The so-called carrierless amplitude phase modulation (CAP) is one particular realization of such a higher dimensional modulation scheme. In this contribution, a comparative performance analysis of CAP and multilevel pulse amplitude modulation (PAM) is presented based on numerical simulations. For that, both modulation schemes as well as their resulting transmit signals are initially investigated and compared concerning fundamental properties. In a second step, both modulation schemes are evaluated in terms of overall system performance using a linear transmission system based on IM/DD. As a last step, two different equalizer concepts, namely Tomlinson-Harashima pre-coding (THP) and a decision feedback equalizer (DFE), are compared for the use of PAM in a low-cost short-range IM/DD transmission system.