Generation and transmission of 854 Gb/s real-time 16QAM coherent optical OFDM signals over 400 km SSMF with preamble-less reception

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.

Timing, carrier frequency and phase recovery for OFDM and Nyquist signals using a mean modulus algorithm

“…For instance, the constant modulus algorithm (CMA) [15] is frequently used for polarization demultiplexing. In [2] and [13], it has been shown to also work for recovering frequency and timing information. The CMA cost function is defined by (16) is used as a cost function instead of the one for the CMA, square root operations can be avoided at the price of additional square operations.…”

“…In particular, it is shown that our mean modulus algorithm (MMA) is well suited for both Nyquist and OFDM signals. It can be used to extract clock, carrier frequency and phase while featuring a low computational complexity [2] [13].…”

PAPR reduction technique by inserting a power-concentrated subcarrier for CO-OFDM

“…Optical OFDM has been a promising technology for next-generation optical communication systems due to its high spectral efficiency using high-order modulation enabling dynamic data rate adaptation [6][7][8][9][10][11][12]. Additionally, optical OFDM shows extreme robustness to fiber dispersion [6][7][8][9][10][11][12][13][14][15][16].…”

Blind symbol synchronization for direct detection optical OFDM using a reduced number of virtual subcarriers

“…A number of synchronization techniques designed specifically for multi-gigabit per second optical OFDM have been developed in recent years [4][5][6][7][8]. Giddings et al [4] proposed overlaying a pattern of DC levels on OFDM symbols with a square waveform whose period is equal to the symbol length.…”