We experimentally evaluate high-speed intensity modulation/direct detection (IM/DD) transmissions with a 1.55-μm broadband electro-absorption modulated laser and pulse amplitude modulations (PAM). We demonstrate 80 Gb/s/λ PAM-4 and 96 Gb/s/λ PAM-8 transmissions with low-complexity digital equalizers at the receiver. Performance comparison with different types of equalizers are performed, including linear symbol-spaced feed-forward equalizer (FFE), fractional (half-symbol) spaced FFE and decision feedback equalizer (DFE), with different tap number. It is found that for both cases, a 6-tap symbol-spaced FFE is sufficient to achieve a stable performance with bit-error-rate below the 7% overhead hard decision forward error correction (7%-OH HD-FEC) threshold over a 4 km standard single mode fiber link. Practical considerations including comparison between adaptive and static equalizer implementation and tolerable fiber chromatic dispersion are discussed.
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- Distributed feedback laser (DFB)
- Direct detection
- Electroabsorption modulator
- Optical interconnects