Q1. (Total 25 marks ) (2) The core and cladding refractive indexes of a step index silica fiber are n, =1.4675 and n, =1.4628 respectively . The cladding diameter of the fibre is 125 um. If the core diameter of the fibre is 9 um, what is the numerical aperture of the fiber? Is this fibre a single mode fibre or a multimode fibre at 1550mm ? Is it a single mode fibre or a multimode fibre at 850mm ? At which wavelength , the fibre loss is lower ? What is the single mode cutoff wavelength of the fibre ? Why ? What is the type of dispersion at 1550mm ? What are the two types of dispersion at 850mm