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An LED Model for Intensity-Modulated Optical Communication Systems

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3 Author(s)
Elgala, H. ; Dept. of Electr. Eng. & Sci., Jacobs Univ., Bremen, Germany ; Mesleh, R. ; Haas, H.

Modulating the intensity of light-emitting diodes (LEDs) with analog signals, especially in the case of the bipolar optical orthogonal frequency-division-multiplexing (O-OFDM) signal, leads to significant signal degradation due to LED nonlinearity. The LED transfer function distorts the signal amplitude and forces the lower peaks to be clipped at the LED turn-on voltage. Additionally, the upper peaks are purposely clipped before modulating the LED to avoid chip overheating. The induced distortion can be controlled by optimizing the bias point or backing-off the average O-OFDM signal power. In this letter, a model that incorporates amplitude distortion and that provides a parameterized upper clipping is proposed. Through Monte Carlo simulations, the model can be used to determine the optimum bias point and to optimize the O-OFDM signal power. In this context, a novel concept of soft-clipping of the upper peaks is presented. It is shown that soft-clipping is an effective approach to reduce nonlinearity distortion and to enhance symbol error performance.

Published in:

Photonics Technology Letters, IEEE  (Volume:22 ,  Issue: 11 )