Pick out the correct staments about optical fibres from the following:
S1: Optical fibres are used for the transmission of optical signals only
S2: Optical fibres are used for transmission of optical electrical signals
S3: The intensity of light signals sent through optical fibres suffer very small loss
S4: Optical fibres effectively employ the principle of multiple total internal reflections
S5: Optical fibres are glass fibres coated with a thin layer of a material with lower refractive index