Overcoming the project challenges requires joint efforts of research experts across a number of relevant disciplines, ranging from laser science to high-speed optical communication techniques. The tunability of a fibre laser is an important feature in communication applications. TUNEMODE extends tunability beyond the usual tuning of the wavelength to the very important tuning of the spatial laser modes. Conventional fibre lasers operate at fundamental mode LP01. Standard approaches to developing a fibre laser for an SDM system are based on the use of conventional cavity configurations such as ring or linear cavity, distributed feedback (DFB), or distributed Bragg reflector (DBR) laser cavity. Most components for these cavity setups are composed of single-mode fibre, which create difficulties, because this SMF will act as a filter for higher-order modes and increase the complexity of the research. TUNEMODE demonstrated a novel solution based on implementation of RFL in few-mode fibre. The overview of the results and their exploitation and dissemination are listed below
1) SMF-based RFL for the purpose of characterizing the random laser
a) Self-pulsing in Bi-directional Ring Cavity Ultra-long Raman Fiber Laser
The experiment examine random mode characteristics in Random fibre laser and also ultra-long fibre laser based on SMF and TRUEWAVE fibre. The main objective is to characterize the stability of the random and ultra-long fibre laser in the time domain and thus, this RFL will utilize a 1450 nm Raman pump. Ultra-long Raman fibre laser is of significant interest due to its application in many areas such as telecommunication and sensing. In this work, we find a self-pulsing ultra-long Raman fibre laser in bi-directional ring cavity configuration. Three laser cavities with different total cavity length are investigated, which generates the pulse repetition rate of approximately 25MHz, 14MHz and 10MHz, for cavity length 28km, 56km and 76km, respectively. Broader spectral bandwidth is observed for shorter laser cavity at the similar pump power of 2.48W. The highest signal-to-noise ratio of 46dB and 47dB are attained for laser cavities with 56km and 76km at 1.62W and 1.97W pump powers, respectively. This work presents the novelty in its alternative prospect with previous works which employed linear laser cavity configuration and another gain medium to attain self-pulsing Raman fibre laser.
b) Localized Spatial-Temporal Light Structures In A Bi-Directional Brillouin Fiber Laser
Stimulated Brillouin scattering (SBS) in optical fibre is a nonlinear effect that results from the interaction between intense pump light and acoustics wave in the optical fibre. A deeper understanding of cascaded SBS in optical fibre is important to the applications of optical communication, optical sensor and waveguide circuit. The conventional Brillouin fibre laser is been analyst by using an optical spectrum analyzer and this limit the information of Brillouin characteristics. The generation of the cascaded Brillouin fibre laser is normally using bi-directional cavity to allow multi Stokes generation. The complexity of SBS cavity in fibre laser system makes their theoretical and experimental analysis technically and conceptually challenging. Here, using a real-time spectral measurement technique to reveal localize spatial-temporal light structures in a bi-directional Brillouin fibre laser. The spatial-temporal measurement shows partially mode-locked characteristic of the generation. A good qualitative consistency between the simulation and experimental results is evidence that can open too many applications of Brillouin fibre laser
2) Development of an RFL using two-mode graded-index fibre.
a) Two-mode fibre Bragg Grating Fabrication
The project was successfully fabricated the two and four mode fiber Bragg grating in few mode fibre. The few mode FBG is been used as mode filter in the random fibre laser in this project
b) Dual mode Output in Random Few Mode Fibre Laser
The project is successfully demonstrated in the first time two mode Random fibre laser using Few Mode fibre. All of these modes will be characterized in terms of output performance, with the most important factor being the stability for each mode. The outcome of this objective is expected to be a novel type of laser with strong potential for commercialization and big academic and industrial impact.
