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Tool Used: ModeSYS

Due to its relaxed alignment tolerances and low cost, step-index (SI) plastic optical fiber (POF) is an attractive technology for short-distance data interconnects. Furthermore, PAM-4 modulation with DSP equalization at the receiver can help overcome the inherent bandwidth limitations of POF at Gb/s data rates [1],[2].

Based partially on work presented in [1] and [3], Figure 1 illustrates the topology in ModeSYS that implements end-to-end 1-Gb/s PAM-4 transmission over 1-mm diameter SI-POF. ModeSYS simulates the fiber using a computationally efficient model based on the Gloge power-flow equation, while MATLAB co-simulation models the transmitter and receiver DSP using functions from the OptSim DSP library for MATLAB. The transmitter generates an electrical PAM-4 signal with Nyquist pulse shaping and pre-emphasis filtering, and the receiver DSP uses an LMS equalization algorithm to recover the transmitted symbols and analytically estimate the BER.

Figure 2 depicts the optical eyes at the POF input and output, showing eye closure due to intermodal dispersion and mode coupling. Figure 3(a) illustrates the recovered eye diagram after the receiver¡¯s analog-to-digital conversion and equalization, which has compensated for the eye closure, while Fig. 3(b) depicts the analytically estimated BER in comparison with an ideal PAM4 reference curve. The BER of 2.35 ¡Á 10^-4 is below an FEC threshold of 3.7 ¡Á 10^-3 [4],[5].