Nowadays, fibre optic sensors have been widely used to detect temperature, pressure, vibration and other physical properties. To design high performance fibre optics sensors, sensing elements such as light propagation need to be investigated for parameters such as absorbance, transmittance and scattering. In this study, the backscattered light is studied and modelled using MATLAB based on Brillouin and Rayleigh scattering. The scattering effects on the output power and Stokes power are clearly seen where both powers reduce with the increase of fibre length. The Rayleigh power in terms of Coherent Rayleigh Noise is studied where broader source linewidth, higher spatial resolution and lower group velocity produce less noise. The less fluctuation due to noise can be attributed to the less temporal and spatial fluctuations of the optical pump power or pump current. The output from this research can benefit experimental studies to design fibre optic sensors in future.

We investigated the spectral and coherence signatures of threshold in random lasers with incoherent feedback consisting of alumina colloidal nanoparticles suspended in rhodamine 6G methanol solution under nanosecond-pulsewidth pumping, based on measurement of temporal and spatial coherence properties and comparison with emission spectra. Feedback in this random laser was provided by multiple scattering from the alumina particles, and the effects of particle concentration and scattering length were studied for the weakly scattering and diffusive scattering regimes. At threshold, in each regime, the visibility of the interference fringes jumped abruptly, coinciding with a substantial increase in peak emission intensity and decrease in the linewidth of a single dominant emission peak. � 2014 IOP Publishing Ltd.