Fibre optic wedge type cavity random laser

Abstract

In this work, a fibre optic wedge type cavity, with arbitrarily distributed scattering centres, is employed to construct a flexible, cost effective and low threshold random laser. The wedge cavity is obtained through the triangular-shaped of air holes that are naturally formed during the drawing of a four-core optical fibre within a single cladding of 125 µm in diameter. The sharp edge corners of the triangular shaped of the air holes are filled with a phenol-rhodamine 6G mixture to form the laser gaining medium to take the advantage of the strong optical cavity confinement due to the geometry of the structure. Randomly distributed air-bubbles are naturally formed in different sizes and shapes during the filling process of the phenol-rhodamine 6G mixture, which serve as the scattering centres to form the random laser’s gaining medium. By making fine spatial tuning of the excitation beam spot, that is, by moving the beam spot towards the apex of the wedge, a single mode lasing is obtained at 585 nm, with 1.4 nm of the FWHM.