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H2020

TUNEMODE Report Summary

Project ID: 655367
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - TUNEMODE (TUNABLE MODE RANDOM FIBER LASER FOR MODE DIVISION MULTIPLEXING LASER SOURCE)

Reporting period: 2015-12-01 to 2017-11-30

Summary of the context and overall objectives of the project

Project TUNEMODE targets theoretical and experimental study, design optimization, and development of the spatial mode tuning random fibre laser sources for application in spatial division multiplexing (SDM) telecommunication systems. Conventional fibre lasers, based on rare earth elements such as Erbium and Ytterbium, are not optimized for lasing at modes other than the fundamental mode LP01. The proposed concept will use the flexibility of random fibre lasers (RFL) combined with microfibre technology and fibre Bragg grating (FBG) techniques. Moreover, the tunable laser source generating at various spatial modes will have numerous applications beyond telecommunications. The TUNEMODE is an interdisciplinary project that brings together laser science, fibre optics, theory of disordered systems, and optical engineering. The TUNEMODE will be valuable for Europe in the context of addressing the issue of growing bandwidth demand and the need to provide the next leap in capacity-per-fibre.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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 R

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

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. We propose a novel solution based on implementation of RFL in few-mode fibre. Compared to conventional fibre lasers, the RFL has unique features: simple structure without any “mirrors” (laser oscillations occur randomly without requiring the laser cavity); good relative intensity noise (RIN) transfer characteristics due to its incoherent radiation; stable output with little thermal sensitivity; and wide wavelength tenability. The TUNEMODE project aims to produce a novel type of fibre laser: the tunable mode random fibre laser.
Expected results until the end of the project and potential impacts
• new concepts for ultrafast fibre laser using ring cavity
• new concept of localized spatial temporal light structures in a bi-directional Brillouin fibre laser
• new understanding of localized spatial temporal light structures in a bi-directional Brillouin fiber laser
• development and demonstration of two mode fibre laser using ultra-long fibre laser
• development and demonstration of four mode fiber laser using ultra-long fibre laser

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