Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - RANPOFIL (Science and applications of random polymer fiber lasers)

Teaser

To simplify the structure of RFLs, in 2010, Turitsyn’s group has reported a novel type of RFLs in the randomly distributed refractive index inhomogeneities throughout the length of the silica fibre due to the Raman amplified Rayleigh backscattering in different types of...

Summary

To simplify the structure of RFLs, in 2010, Turitsyn’s group has reported a novel type of RFLs in the randomly distributed refractive index inhomogeneities throughout the length of the silica fibre due to the Raman amplified Rayleigh backscattering in different types of cavities with and without conventional point-action reflector. However, the backscattering coefficient defined the part of the scattered radiation that is scattered back into the core of the optical fibre per unit length is as small as ~4.5×10-5 km-1. Therefore, I proposed one kind of new RFLs with high backscattering coefficient to decrease the pump threshold (reducing the power consumption) and pump fibre length (allowing building smaller devices easily integrable). RANPOFIL project aimed to build a new polymer RFLs configuration to enhance the performances of RFLs. Polymer optical fibres (POFs) have two merits: (1) high Rayleigh backscattering coefficient; (2) high negative thermo-optical coefficient. Thus the random lasing emission wavelength can been easily be controlled through temperature. Therefore, the new RPFLs with low pump threshold, short pumped fibre length, high stimulated Raman gain and controlled random lasing emission is designed based on stimulated Raman scattering in the POFs. First, we coated laser dye-doped polymethyl methacrylate on the surface of a bare polymer optical fiber (POF) to fabricate new POFs. Coherent random lasers were obtained for the gain POFs under the pump. The mechanism for the random lasers is based on the refractive index heterogeneity scattering of the coating gain polymer. Second, we used the band-gap of liquid crystal to control the random lasing emission wavelength. Third, we researched the glassy behavior in a RL with complex energy level structure in the electrospun polymer fibre system. Meanwhile, we also reported whispering gallery mode (WGM) lasing emission when a 532 nm pulse laser beam radially excited the single electrospun polymer fiber (EPF) created by this method. Last, we demonstrated the realization of a high-polarization RFL output based on the hybrid Raman and Erbium gain with the tailored effect provided by a 45°-tilted fiber Bragg grating (45°-TFBG), revealing an improvement in the polarization extinction ratio (PER) and achieving a PER of ~15.3 dB. The aim of RANPOFIL is to create two-way transfer of critical knowledge between the EU partners and me, and to train me in an area of high practical relevance. The project gives me an opportunity to establish long-term research links and networks with the EU partners, and to enhance my academic career in China after the project completion.

Work performed

1. Work performed
In 2017-2019, I carried out research on polymer fibre random lasers: (1) Developing a comprehensive nonlinear model to analyse random lasing emission mechanism; (2) Using dip coating technique, I fabricated POF. I prepared a dye-coated POF and studied the RL properties emitted by the POF at different receiving positions, coating thicknesses, and lengths based on the pump light radiation mode effect; (3) Proposing a new organic/inorganic hybrid laser dye to enhance lasing lifetime. In addition, I report the experimental evidence of the glassy behavior in a random laser with more complex energy level structure; (4) Demonstrating the new mechanism of “band gap + scattering” to control random lasing in the cholesteric liquid crystal (CLC). Dye-doped polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy were fabricated, and mirrorless lasing with an electrically tunable wavelength was successfully achieved.
2. Main results achieved so far
(1) To simplify the fabrication procedures and decrease the cost of polarizers, the ultraviolet (UV) inscribed 45°-TFBG has been fabricated as a polarizer in a standard commercial SMF that possesses significant advantages, e.g. low-cost, effective and all fiber system, over traditional polarizers. In principle, the TE light through such grating shows large transmission loss whereas the TM-light loss remains small due to Brewster’s Law. Therefore, the 45°-TFBGs have been applied in optical communications and fiber laser systems as a broadband polarizer. The result was published at Optics Express.
(2) Our work mainly focuses on the influence of the pump radiation mode on the characteristics of the RL emitted from the axial and radial directions in the gain POFs with different coating thicknesses under the 532-ns laser-end pump. The mixed solution was applied to the bare POF surface instead of the end face by dip-coating. There is a whispering gallery modes laser has been found in our experiment. Meanwhile, the dye-doped POF system pump exhibits good photo stability and self-healing properties. The results were published at Physica Scripta and Journal of Physics D: Applied Physics.
(3) The POSS groups suppress the photo-bleaching effect to improve the luminous stability in the organic/inorganic hybrid laser system. And the phase transition between a continuous wave paramagnetic regime (below threshold) and spin-glass regime (above threshold) representing RSB phenomenon has been observed. The results have been published in Annalen der Physik (Inside Cover) and Nanophotonics.
(4) Based on the “band gap and scattering” mechanism, the random lasing wavelength can be tuned at 80 nm in the CLC. Meanwhile, the broad tuning range (∼110 nm) of PSCLC lasers, coupled with their stable emission performance, continuous tunability, and easy fabrication, has been obtained in the PSCLC. The results have been published at Phtonics Resarch.
3. Overview of the results and their exploitation and dissemination
Through two years research, I have controlled the random lasing emission in the liquid crystal and extended the random lasers in the polymer optical systems. In addition, the statistical dynamics of random lasers has been researched. Supported by the Marie Curie research fellowship I have published 12 high-impact papers including Nanophotonics, Photonics Research, Optics Express, ACS Sensors, Annalen der Physik.

Final results

This project gives me an opportunity to become a research leader through increased knowledge and research links, advanced training, and acquired skill in organizing and managing research activities. I can be assured to possess vital multidisciplinary research skills and knowledge. Successful completion of RANPOFIL research-oriented tasks requires the participant to considerably increasing his knowledge of methodologies and the foundational science behind relevant analytical techniques. Skills learned within the RANPOFIL program ensure that I am uniquely qualified to attain and fulfill significant roles in the vital cross-discipline area of fibre laser and fibre fabrication technology. This invaluable experiences enable me to gain deep insight on RFL. This knowledge is required of a team leader in the challenging area of fiber optics. The industrial placement also has a great impact on the rapid commercialisation of the developed novel laser systems and shed some light on technology transfer and industrial partnership from scientific research to commercial application.

Website & more info

More info: https://scholar.google.com/citations.