Nonlinearity mitigation for high-speed optical OFDM transmitters using digital pre-distortion

Yuan Bao,Guifang Li,Jianping Li,Bai-Ou Guan,Xinhuan Feng,Zhaohui Li

doi:10.1364/oe.21.007354

Abstract

Optical orthogonal frequency-division multiplexing (OOFDM) signal is sensitive to nonlinear distortions induced by optical modulators. We propose and experimentally demonstrate a digital pre-distortion (DPD) algorithm to linearize the optical modulators including electro-absorption modulated lasers (EML) and Mach-Zehnder modulators (MZM) used in high-speed OOFDM transmitters. By using an adaptive DPD algorithm with a learning structure, the inverse transfer function of a modulator, which is based on a polynomial model, has been obtained. In the experiment, the performance improvements with and without considering the memory effects of the DPD model are illustrated. The two typical kinds of high-speed OOFDM signals with a bit rate up to 30-Gb/s have been implemented experimentally. The results show that the nonlinear distortion induced by optical modulators can be compensated by using the DPD algorithm to substantially improve the optical modulation index.

Highlights

Optical orthogonal frequency-division multiplexing (OOFDM) has been considered as a promising candidate of future large-capacity optical networks [1, 2]
We propose and experimentally demonstrate a digital pre-distortion (DPD) algorithm to linearize the optical modulators including electro-absorption modulated lasers (EML) and Mach-Zehnder modulators (MZM) used in high-speed OOFDM transmitters
The results show that the nonlinear distortion induced by optical modulators can be compensated by using the DPD algorithm to substantially improve the optical modulation index

Summary

Introduction

Optical orthogonal frequency-division multiplexing (OOFDM) has been considered as a promising candidate of future large-capacity optical networks [1, 2]. Optical feed-forward compensation technique has been proposed to reduce the nonlinear distortion induced by uncooled distributed-feedback (DFB) laser diodes in radio-over-fiber (ROF) systems [3]. This linearization approach requires delay alignment of the error cancellation loop, which can be quite complicated. Optical modulator optimization for OFDM transmitter is proposed to overcome the nonlinear distortion of MZM and increase the optical power efficiency [8]. This DPD algorithm only discusses the MZM and is not suitable for other optical modulators. The differences between nonlinear characteristics of intensity modulated MZM and EML are demonstrated and the effective region of DPD algorithm is discussed

OOFDM transmitter and polynomial-based DPD algorithm

Experimental setup and results

Findings

Conclusion