Study On The Fiber-Type Random Laser Based On A Cylindrical Waveguide With A Disordered Cladding Layer

In a conventional laser cavity, scattering and disordered structure can’t be avoided which impeded the generation of the laser, however, it can realize random laser. High laser thresholds and non-directional limits the application of the traditional random laser. Compared with the traditional random medium, directional lasing output with high effiency and low threshold was successfully realized because of the fiber optical waveguide structure can limit the light scattering along the radial; In addition, different fiber waveguide can provide convenient, extensive amplification (such as Raman pump, the absorption energy levels of rare earth ions pump) and feedback mechanisms (such as Rayleigh scattering and grating reflection), which is not only an excellent platform to study the random laser, but also a flexible means for random laser’s optimization and regulation.For the above reasons, a novel type of optical fiber waveguide structure which was based on a cylindrical waveguide with a disordered cladding layer was proposed. The structure which is made from a capillary coated with a disordered layer at its internal surface and filled with a gain (dye laser) solution in the core region can achieve the random laser with the low threshold and tunableness. It can form a stable laser structure depending on the separation between the gain and scattering. The details are as follows:First, a theoretical simulation of the new waveguide structure is completed through software simulation design, which contains mode field characteristics and power characteristics to improve the laser characteristics and experimental parameters. It proved that a cylindrical waveguide with a disordered cladding layer supports the multi-mode transmission. In addition, the higher of the disorder parameter of random scattering layer, the higher capacity of waveguide structure restrain photons stronger.Secondly, this paper introduces the production of a randon lasser based on the cylindrical waveguide with a random laser cladding. We need to make a special fiber. The particular random cavity is maded as a carrier to fill the gain medium by the existing hollow capillaries and scattering particles mixed with the adhesive solution. Rhodamine B is selected as the gain medium. The gain control system is designed to complete the experimental system of random laser.And then, the characteristics of random lasers based on the cylindrical waveguide with a random laser cladding is studyed. Different wavelengths output can be achieved by changing the Irradiated position of the pump or varying the concentration of the gain medium. Remove the particles from the new waveguide structure, there is only fluorescence and no lasing phenomenon. The random cladding in this optical fiber structure provides multiple scattering and restrict the most light in the gain region, promote the formation of the random lasing modes. The system provides an open channel which is flexible to choose the filled-material and scattering mechanisms.Finally, the output power of random laser is sensitive to the concentration of microfluidic scatterer which exists the potential applications in the field of optical sensing. The concentration of scattering particle in the gain medim effects the output intensity of the laser. The random lasing intensity decreases exponentially with increase of particle concentration in the core, providing a potential way of small particle sensing using RLs.