Bandwidth Extension in a Mid-Link Optical Phase Conjugation

Abstract

In this paper, we investigate various designs of distributed Raman amplifier (DRA) to extend amplification bandwidth in mid-link optical phase conjugation (OPC) systems and compare bands 191–197 THz and 192–198 THz giving a total bandwidth of 6 THz using a single wavelength pump. We demonstrate the use of highly reflective fiber Bragg grating (FBG) to minimize gain variation across a WDM grid by optimizing forward and backward pump powers as well as the wavelength of FBGs for original and conjugated channels. Finally, we also simulate OSNR and Kerr nonlinear reduction as a product of signals asymmetry and nonlinear phase shift (NPS) for all channels.

Asymmetry Optimization for 10 THz OPC Transmission over the C + L Bands Using Distributed Raman Amplification

“…Higher order Raman amplification is well known for improving transmission performance through improved noise performance, achieving extended bandwidth even with a single pump wavelength [ 17 ]. At the same time, distributed amplification allows for a precise control of signal power variation across transmission fibre [ 24 ], which is necessary to minimize asymmetry for the OPC system.…”

“…At the same time, distributed amplification allows for a precise control of signal power variation across transmission fibre [ 24 ], which is necessary to minimize asymmetry for the OPC system. In our previous works [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] we compared several designs of distributed Raman amplifiers: first order, second order and dual order using bi-directional and backward-only pumping schemes. Bi-directionally pumped distributed Raman amplification with a single FBG at the end of the transmission span performed best in terms of asymmetry [ 24 ] and relative intensity noise (RIN) [ 30 , 31 , 32 ], which is a key design feature for data transmission in a 60 km span, hence we continue with this design and modifications to meet our bandwidth requirement.…”

“…For example, in [ 15 , 16 ], the fiber nonlinearity compensation using a mid-link OPC can be achieved using a symmetrical chromatic dispersion slope or effective management of dispersion mapping before and after the OPC. Alternatively, in [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], with a purposefully designed distributed Raman amplification scheme, a symmetrical signal power profile along the fiber before and after the OPC was demonstrated to maximize the effectiveness of nonlinearity compensation with a mid-link OPC. In [ 24 ], we numerically optimised the in-span signal power asymmetry for three different advanced Raman amplification schemes using a single channel in the middle of the C-band at 1545 nm and identified that the second-order distributed Raman amplification based on a single-side FBG random distributed feedback laser is the most convenient design to achieve the best signal power profile symmetry.…”

“…Recently, ultra-wideband or multi-band optical transmission assisted by Raman amplification has been a hot topic of discussion [ 25 , 26 , 27 , 28 ], as an efficient tool to fully unlock the potential transmission capacity of single mode fiber (SMF). In this context, the possibility of applying the second-order Raman amplification scheme discussed in [ 17 , 29 , 30 , 31 ] in other transmission bands, using a fiber Bragg grating in another band with appropriate Raman pump wavelengths, becomes particularly interesting. In particular, in [ 17 ] we showed a method for bandwidth extension using a fixed wavelength Raman pump centered at 1366 nm, while using FBGs at different wavelengths for the originally transmitted and the conjugated channels.…”

“…In this context, the possibility of applying the second-order Raman amplification scheme discussed in [ 17 , 29 , 30 , 31 ] in other transmission bands, using a fiber Bragg grating in another band with appropriate Raman pump wavelengths, becomes particularly interesting. In particular, in [ 17 ] we showed a method for bandwidth extension using a fixed wavelength Raman pump centered at 1366 nm, while using FBGs at different wavelengths for the originally transmitted and the conjugated channels. Utilizing this method, we managed transmission over 6 THz with a 5.9% average asymmetry in a 192–198 THz band using 60 km SMF span.…”