Hybrid discrete Fourier transform (DFT)-spread orthogonal frequency division multiplexing (OFDM)-digital filter multiple access (DFMA) passive optical networks (PONs) are proposed, for the first time, where digital signal processing (DSP)based digital filtering is applied to individual DFT-spread OFDM signals from various optical network units (ONUs), and a single FFT operation and its following data recovery processes are implemented in a pipelined approach in the optical line terminal (OLT). The proposed networks maintain all salient features associated with previously reported hybrid OFDM-DFMA PONs, more importantly, they additionally reduce the upstream signal peak-to-average power ratios (PAPRs) by >2dB. As a direct result, in comparison with the hybrid OFDM-DFMA PONs, the proposed PONs increase the upstream system power budget by >3dB and reduce the minimum required DAC/ADC quantization bits by at least 1 bit.

The performance of InP modulators is investigated for duobinary and differential phase-shift key transmission. We demonstrate that despite nonlinear phase-voltage characteristics and residual absorption, InP devices give excellent performance comparable to ideal Mach-Zehnder modulators. 02005 Optical Society of America OCIS codes: (060.2330) Fiber optics communications (250.7360) Photonic integrated circuits

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