Lasers, Optics & Photonics

Biography

Biography: Jair Adriano Lima Silva

Abstract

The resilience towards fi ber dispersion is the main attractive feature of orthogonal frequency division multiplexing (OFDM) signal processing in optical communications systems. Coherent-detection optical OFDM (CO-OFDM) posses many benefi ts that are critical for high data rate fi ber transmission systems. It is extremely robust against chromatic and polarization mode dispersions at the same time that it improves spectral effi ciency eliminating the need for a guard band between the optical carrier and the informationbearing signal. Furthermore, adaptive data rates with diff erent subcarrier mapping levels can be supported using soft ware-defi ned solutions. However, large peak-to-average power ratio (PAPR) of the inherent multicarrier signals is one of the main drawbacks in CO-OFDM systems, as it not only limits the resolution of digital-to-analog converters and power amplifi ers, but also reduces the tolerance to the nonlinearities introduced by Mach-Zehnder (MZM) optical modulators and optical fi bers. Several PAPR reduction techniques such as coding, tone reservation, clipping, peak windowing and partial transmit sequence, have been proposed in the literature. Th ese distinctly techniques provide diff erent degrees of eff ectiveness and tradeoff s that may include increased complexity, reduced spectral effi ciency and performance degradation. Recently, we proposed a PAPR reduction scheme based on constant envelope (CE) signals to improve the tolerance towards MZM modulators and fi ber nonlinearities in direct-detection optical OFDM systems. As a power effi cient technique, it reduced the PAPR to 3 dB using electrical phase modulation (PM). Aft er a successful experimental demonstration in direct-detection optical systems, this CE-OFDM technique was introduced in coherent detection systems as a suitable solution to the aforementioned problems. Unlike the approaches evaluated in the literature, the intermediate electrical constant-envelope signals of this solution were used to modulate the continuous wave laser source, employing a conventional one-branch MZM modulator. Th e infl uence of the electrical phase modulation index h in the performance of CE-OFDM in coherent detection optical systems was treated analytically and its range of validity examined by simulations. A compromise between h and subcarrier mapping was identifi ed according to diff erences in sensitivity related to non-linearities inserted by the MZM. We showed that the proposed scheme outperforms conventional coherent detection OFDM systems.