Effective suppression of nonlinear distortion in optical phase conjugation of optical OFDM signals using backward Raman pumping

ABSTRACT

The use of backward Raman amplification to mitigate nonlinear distortion in optical phase conjugation (OPC) of orthogonal frequency-division multiplexing (OFDM) signals in a fibre communication system is investigated in this paper. A ∼29 dB reduction in the nonlinear distortion is achieved, while comparable conjugated output signal power is maintained through the Raman gain. By numerically solving the nonlinear Schrödinger equation (NLSE) along the fibre, a detailed theoretical model is developed to elaborate the mechanism in Raman-assisted OPC. Different optical network scenarios have been analysed using this model. The mechanism of Raman-assisted OPC is further explained by comparing the power profiles of both the conjugated signal and the nonlinear distortion with those in the conventional scheme. In addition to investigating the nonlinear distortion caused by spurious four-wave mixing (FWM) products, the waveform distortion resulting from pump depletion in the OPC system is also analysed. The linearity in Raman-assisted and conventional OPC systems is characterised and compared. The result shows a power deviation reduction of ∼14 dB through Raman amplification.

KEYWORDS:

• Optical phase conjugation
• nonlinear optics
• optical crosstalk
• optical OFDM
• parametric process

Additional information

Funding

This work was supported by the Research Grants Council of Hong Kong under Projects [416213] and [14206614].

Notes on contributors

Chaoran Huang

Miss Chaoran Huang received her B.Sc. degree in Optical Information Science and Technology from Huazhong University of Science and Technology, China in 2012. She joined the Department of Electronic Engineering of The Chinese University of Hong Kong (CUHK) in 2012 and is currently pursuing her Ph.D. degree. Her research interests mainly focus on fibre optics, optical fibre communications and nonlinear optical signal processing.

Chester Shu

Ir Prof Chester Shu received his Ph.D. degree in Applied Physics from Colum bia University, the USA in 1991. He is a Professor in the Department of Electronic Engineering and the Center for Advanced Research in Photonics at The Chinese University of Hong Kong. His research focuses on optical signal processing for fibre communications and sensing. He has made original contributions to nonlinear processing with specialty fibres and has developed unique approaches for polarisation-insensitive processing and processing of orthogonally polarised signals, wavelength-division processing with time- and wavelength-interleaved laser pulses, phase-sensitive and bit-rate tunable processing for signals in advanced modulation formats. He has published over 300 journal and conference papers, and delivered a number of talks in the field. Ir Prof Shu was a Topical Editor of Optics Letters in the area of fibre communications from 2005 to 2011 and has served in a number of technical programme committees including Optical Fiber Communication Conference and Exhibition/National Fiber Optic Engineers Conference (OFC/NFOEC) and Lasers & Electro-Optics Society (LEOS). He was the Chairman of the Institute of Electrical and Electronic Engineers (IEEE) Hong Kong LEOS (now Photonics Society) Chapter in 2006 and 2007.