Mono or multi-mode optical fibre - has central monomode core with multimode sheath esp. for data transmission

摘要

The optical fibre is capable of working both in single and multimode for data transmission. The fibre is in three coaxial parts. The central element or core of glass (1) has a dia. of d1 with a surrounding sheath (2) of dia. d2 ths having a lower refractive index than the core. A further outer sleeve (3) of transparent plastic, such as silicon resin, has a dia d3 and a still lower refractive index. The dia. d2 is chosen such that d2/2L 0.383(n22 - n23) where n is the respective refractive index and L is wavelength transmitted in multimode. Monomode transmission is by the innermost component and is chosen such that d1/2L 0.383 (n21 - n22)-1/2, multimode transmission being by its surrounding sheath. In a typical case, n1=1.51 n2=1.505 and n3=1.45.