Nonlinearities Originated in a Red RC-LED and Their Impact on Spectrally Efficient Modulation

Nonlinear signal distortions originated in a resonant-cavity light emitting diode (RC-LED) are investigated. Using laboratory measurements and offline processing, the RC-LED´s nonlinear behavior is investigated for multilevel pulse amplitude modulation (M-PAM) and carrierless amplitude and phase modulation with the help of a Volterra-series expansion. Dynamic nonlinearities are identified which are strongly dependent on the modulation format used. The impact of these nonlinearities is then investigated for a short-range gigabit transmission link, consisting of a RC-LED and 30 m of step-index polymer optical fiber. It is shown that dynamic nonlinearities are a dominat source of signal impairments when using M-PAM at lower baud rates and that the performance of M-PAM can be considerably improved with a Volterra-series extension of a decision feedback equalizer (DFE) compared with a regular DFE.