Modulation Schemes for Single-Laser 100 Gb/s Links: Multicarrier

Abstract

We evaluate multicarrier modulation methods for 100 Gb/s single-wavelength data center interconnects. We consider two different orthogonal frequency-division multiplexing (OFDM) techniques: DC-biased OFDM (DC-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM). We also consider two different techniques for bit loading and power allocation: fixed bit loading with preemphasis and optimized bit loading and power allocation. We first present a semianalytical performance and complexity evaluation of these OFDM methods including the effects of linear filtering, clipping, and quantization. We then include the effects of chromatic dispersion and chirp, as well as intensity and shot noises. Performance is quantified in terms of the required average optical power to achieve a target bit-error probability for a given modulator bandwidth. Complexity is quantified in terms of the resolution and sampling rate required of digital-to-analog (DAC) and analog-to-digital (ADC) converters, as well as the number of signal processing operations required. For each OFDM technique, we adjust the clipping ratio to minimize the optical power requirement. For DC-OFDM, taking into account the DAC frequency response reduces the optical power requirement up to 2 dB. ACO-OFDM is more power efficient and requires lower DAC/ADC resolution than DC-OFDM, but ACO-OFDM requires prohibitively high sampling rates owing to its poor spectral efficiency.