nt of two fibre ends Waveguide loss and then through the use of a transparent adhesive with refractive index which matched that of the fibre, the joint is made permanent. The alignment of the fibre and the mechanical strength are achieved by using capillaries or a V-groove. The performance obtained with mechanical splicing is in the range of 0.2dB to 0.3dB. Which splicing technology is used depends on the application but fusion is simpler to use and it is very popular. Figure 53.5 State of the art loss of single mode fibre In optics the term dispersion is used to indicate the dependence of the refractive index of the material on the wavelenght of the radia- tion. This dependence is a basic characteristic of the material. The conversion and radiation loss. This loss can be controlled by in- effect of dispersion on a pulse of light propagating in the fibre is to creasing the radius of the core and the index difference, An. Bending increase the width of the pulse and the understanding of dispersion loss depends on the size of the core and the bend radius. The bending and its effects is fundamental in understanding optical fibre trans- loss can be represented as in Equation 53.9. mission. Optical energy propagates along the waveguide with a velocity (53.9) known as the group velocity, u given by Equation 53.11 where, in this equation, the denominator is known as the group index. R is the radius of curvature of the bend and R the critical (53.11) curvature given by Equation 53.10, with a being the fibre radius. Clearly 0 then the is independent of dn group velocity (53.10) wavelength and is equal to the phase velocity. An optical pulse consists of a number of wavelengths (frequencies) and since each of them propagates with different group velocity they arrive at the end of a fibre of length L each delayed by T given by Equation 53.12. Looking at the equation for R the approach to minimising abli is to use the largest possible An and operate at the shortest possible wavelength. This implies that operation at long wavel