Multi-wavelength Ultra-long Raman Fibre Laser Based on Rayleigh-scattering Feedback A.E. El-Taher (1) * , D.V. Churkin (2) , P. Harper (1) , S.A. Babin (2) , J.D. Ania-Castanon (3) , S.K. Turitsyn (1) (1) Photonics Research Group, Aston University, Birmingham, B4 7ET, UK, * eltaheae@aston.ac.uk (2) Institute of Automation and Electrometry, SB RAS, Novosibirsk 630090, Russia. (3) Instituto de Óptica, CSIC, C/ Serrano 121, Madrid 28006, Spain Abstract We experimentally demonstrate a Raman fiber laser with linear cavity based on point-action fibre Bragg grating reflectors and random distributed feedback via Rayleigh scattering in the long fibre providing stable multiple wavelengths (close to ITU grid) output at Watts level. Introduction Multi-wavelength fibre lasers have attracted great interest due to their wide applications in wavelength division multiplexing (WDM) systems, instrument testing, optical fiber sensors, and spectroscopy. For telecommunication applications the dense wavelength-devision-multiplexing (DWDM) is the most important solution for high-capacity transmission. Several techniques have been proposed to generate stable multi-wavelength laser operation based on different kinds of amplifiers: semiconductors optical amplifier 1 , erbium-doped fibre amplifiers 2 and Raman fibre amplifiers 3 with a multichannel filter inserted inside the cavity. The simplest multi-wavelength in-fibre laser cavity can be constructed by wavelength- selective reflectors such as fibre Bragg gratings (FBGs) in conjunction with a broad-band reflectors in linear scheme, the other simple type is fibre ring laser where the lasing wavelengths can be defined by FBGs as well. One of interesting possibilities to provide broad- band feedback is the Rayleigh scattering (RS) due to inhomogeneities naturally present within the glass structure of the fibre. Although the total backward radiation is very weak (<0.1%), the effect may be accumulated over a long distance. When the backscattered radiation is amplified a fibre laser without any regular reflectors could be constructed. Using that concept a one- dimensional laser with RS-based random distributed feedback has been demonstrated where the Rayleigh scattering is amplified through the stimulated Raman scattering to provide distributed amplification 4 . The cylindrical fibre waveguide geometry provides transverse confinement and effectively one-dimensional random distributed feedback leading to the generation of stationary near-Gaussian beam with a narrow bandwidth similar to conventional lasers. Recently, a stable CW generation on 5 lines simultaneously has been obtained in the linear cavity having 5 FBGs separated by 5-10 nm. The setup is proposed for sensing applications 5 . Further, it was shown that using random distributed feedback, the independent lasing on the wavelengths separated by 1 nm only is also possible if FBGs are placed at different fiber side 6 . In this paper we extend this study and demonstrate 22 lines with wavelengths close to : Angle end : Angle connector : splice point SMF TW 1% FBGs WDM Pump @1455nm Fig. 1: Experimental set-up ECOC 2010, 19-23 September, 2010, Torino, Italy 978-1-4244-8535-2/10/$26.00 ©2010 IEEE P1.21