Arbitrary high speed qam optical transmitter

Arbitrary High Speed QAM Optical Transmitter using FPGA and 34GBd DAC
Vitor B. Ribeiro, Luis P. F. de Barros, Luis H. H. de Carvalho, Anderson C. Bravalheri, Luis R. Monte, Pedro P. G.
Cardoso and Julio C. R. F. Oliveira
CPqD Foundation, Optical Communications Systems, Photonics Division, Campinas, Brazil
{vribeiro, lbarros, lhecker, abraval, lmonte, julioc}@cpqd.com.br

Abstract— In this paper we present a high speed
N-QAM transmitter capable of generating constellations up to
25GBd using a high-speed DAC and FPGA. Electrical generation of 4-QAM, 16-QAM and 64-QAM is achieved with proposed
DAC/FPGA structure. A high quality optical generation of
DP-QPSK (4-QAM) and DP-16QAM signal is demonstrated. The main issues related to electrical and optical generation are discussed and solutions for the common pitfalls are outlined.
Keywords-component; Optical Communications; Quadrature
Amplitude Modulation; High-Speed Digital to Analog Converter;
Digital Signal Processing.

I.

INTRODUCTION

There has been significant interest in high speed electronic digital signal processing (DSP), in recent years, for overcoming transmission impairments in coherent optical systems.
Chromatic dispersion (CD), polarization mode dispersion
(PMD), frequency offset (FO) and laser phase noise can be mitigated using digital filters [1-2]. Those techniques are usually implemented in the receiver side and improved system capacity not only by impairment mitigation, but also for handling well polarization multiplexing (PM) and high order modulation formats [3]. In order to further improve system capacity the DSP is being used in the transmitter side [4-7].
Pre-filtering the signal makes possible to increase spectral efficiency (SE) by applying orthogonal frequency division multiplexing (OFDM) [5], Nyquist filtering [4,6] and other pulse shaping techniques [7]. Moreover the transmitter can generate arbitrary N-quadrature amplitude modulation (NQAM)