Abstract
This paper presents a real-time, coherent optical OFDM transmitter based on a field programmable gate array implementation. The transmitter uses 16QAM mapping and runs at 28 GSa/s achieving a data rate of 85.4 Gb/s on a single polarization. A cyclic prefix of 25% of the symbol duration is added enabling dispersion-tolerant transmission over up to 400 km of SSMF. This is the first transmission experiment performed with a real-time OFDM transmitter running at data rates higher than 40 Gb/s. A key aspect of the paper is the introduction of a novel method for OFDM symbol synchronization without relying on training symbols. Unlike conventional preamble-based synchronization methods which perform cross-correlations at regular time intervals and let the system run freely in between, the proposed method performs synchronization in a continuous manner ensuring correct symbol alignment at all times.
Highlights
Orthogonal frequency division multiplexing (OFDM) [1] has attracted much interest within the field of optical communications
This paper presents a real-time, coherent optical OFDM transmitter based on a field programmable gate array implementation
A cyclic prefix of 25% of the symbol duration is added enabling dispersion-tolerant transmission over up to 400 km of SSMF
Summary
Orthogonal frequency division multiplexing (OFDM) [1] has attracted much interest within the field of optical communications. While first OFDM experiments were based on offline processing, practical applications call for real-time, highly optimized signal processing. Such OFDM transmitters (Tx) [5,6,7] and receivers (Rx) [8] were demonstrated by employing state-of-the-art field programmable gate arrays (FPGA) along with high speed data converters. The latest real-time implementations of high speed optical OFDM transmitters include the work published in [6] and [7] where line rates of 101.5 Gb/s and 93.8 Gb/s were reported, respectively. The results of [7] were achieved with polarization multiplexed CO-OFDM and 4QAM mapping Both papers considered back-to-back systems without transmission. Unlike conventional preamble-based synchronization methods which perform cross-correlations at regular time intervals and let the system run freely in between, the proposed method performs synchronization in a continuous manner ensuring correct symbol alignment at all times
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