Spectrally-efficient all-optical OFDM by WSS and AWG

Abstract

We report on the transmission experiment of seven 12.5-GHz spaced all optical-orthogonal frequency division multiplexed (AO-OFDM) subcarriers over a 35-km fiber link, using differential quadrature phase shift keying (DQPSK) modulation and direct detection. The system does not require chromatic dispersion compensation, optical time gating at the receiver (RX) or cyclic prefix (CP), achieving the maximum spectral efficiency. We use a wavelength selective switch (WSS) at the transmitter (TX) to allow subcarrier assignment flexibility and optimal filter shaping; an arrayed waveguide grating (AWG) AO-OFDM demultiplexer is used at the RX, to reduce the system cost and complexity.

25 Gbit/s per User Coherent All-Optical OFDM for Tbit/s-Capable PONs

“…Figure 2 shows the experimental setup used to generate the five orthogonal phase-locked 12.5 GHz spaced AO-ODFM subcarriers, using a wavelength-selective switch (WSS) and a flat and stable optical comb. The optical comb is generated by the cascade of a tunable laser, a 12.5 GHz clock-driven Mach-Zehnder modulator, a 12.5 GHz clockdriven optical phase modulator, a SSMF compressing span, and finally an optical delay line synchronizing the optical pulse peaks with the electrical signal, as explained in detail in [21]. In the experiment we have replaced the AWG at the TX with a WSS, with a second-order super-Gaussian transfer function, to provide suitable signal shaping and flexible subcarrier multiplexing [23].…”

“…In this kind of AO-OFDM architectures, the AO-OFDM subcarrier spacing, which also equals the modulation rate, spectral range (FSR) of the cyclic AWG [15,21] employed in the architecture. In this case, a splitter-based overlay is possible, such as in legacy G-PON and XG-PON infrastructures.…”

Enhancing the Anti-Dispersion Capability of the AO-OFDM System via a Well-Designed Optical Filter at the Transmitter

“…In Ref. [8], the ICI and Inter-Symbol Interference (ISI) of the AO-OFDM system based on the Gauss-shaped filter were not affected by dispersion, and the frequency domain waveform of the Gauss-shaped filter is discussed in this article. Compared with Ref.…”

“…Compared with Ref. [8], it was closer to a Sinc-shaped filter, and we already made a formula derivation, so we will not discuss the relationship between the ICI, ISI, and CP of the system without dispersion. We will mainly discuss why the AO-OFDM system based on the Gauss-shaped filter was more resistant to dispersion.…”

“…Due to higher spectrum utilization and more flexible carrier allocation strategies, the AO-OFDM system can be regarded as one of the core technologies of the next generation of optical networks with more flexibility and elasticity [1][2][3][4][5][6]. At present, AO-OFDM systems typically use optical arrayed waveguide gratings (O-AWGs) and wavelength-selective switches (WSSs) based on liquid crystal on silicon (LCoS) as the core components for generating orthogonal sub-carriers [7][8][9][10][11][12]. The WSS is a key component of a reconfigurable optical adding/dropping multiplexer and a key all-optical routing element in a wavelength-reconfigurable network.…”