Monomode fibre optical light guide - with equal phosphorus oxide content in core and sheath and boron oxide in sheath

A dielectric monomide optical light guide is made of quartz glass with varying dopant contents in the core and sheath areas. Both these areas include a first dopant, which increases the refractive index, in equal proportions. The sheath area contains, in addn. a dopant which reduces the refractive index. This prevent a flattening of the step in the refractive index between core and sheath which would result in a very great attenuation of the monomode light transmission. The light guide is ideal for a broadband transmission of optical signals.