Step Index & Graded Index Fiber
step index fiber
It is an optical fiber which has a core of constant refractive index.there are two types of step index fibers:single mode si and multi mode si fiber
single mode step index fiber has only one mode of EM propagation (HE11) an has a core diameter of about 8-12 Um. and multi mode si has many mode of propagation and has a core of diameter of about 50 Um which allow many no of modes through it.
single mode step index has an adv of lower inter modal dispersion as there is only one mode present there is very low chance of dipersion multimode fiber has high intermod dispersion due to large no of propagating modes in it and moreover due to varying group velocities of propagating modes results in dispersion and as a result it restricts bandwidth in multi mode fiber
adv of multi mode over si fibers:
use of spatial non coherent sources i.e. use of led over laser diode
large NA and larger core diameter results in easy optical power transmission and easy connecting of same fibers
lower tolerance of fiber connectors
Graded index fiber
has a core of varying refractive index it has a high value n at the core which dec radially towards the cladding has a multimode graded index fiber
multimode graded index fiber under parabolic index profile shows a parabolic transmission of rays through it
through geometrical optics,large no of refractions are observed due to varying refractive index from core to cladding
multimod graded index fiber hav a lower intermodal dispersion as compared to multimode step index however there are many modes of propagation but all are normalised through index grading
rays travelling through core hav a shorter path but move with a lower vel due to high n value. thus despite of all this it follows parabolic transmission and provide considerable bandwidth as compared to multi mode step index
It is an optical fiber which has a core of constant refractive index.there are two types of step index fibers:single mode si and multi mode si fiber
single mode step index fiber has only one mode of EM propagation (HE11) an has a core diameter of about 8-12 Um. and multi mode si has many mode of propagation and has a core of diameter of about 50 Um which allow many no of modes through it.
single mode step index has an adv of lower inter modal dispersion as there is only one mode present there is very low chance of dipersion multimode fiber has high intermod dispersion due to large no of propagating modes in it and moreover due to varying group velocities of propagating modes results in dispersion and as a result it restricts bandwidth in multi mode fiber
adv of multi mode over si fibers:
use of spatial non coherent sources i.e. use of led over laser diode
large NA and larger core diameter results in easy optical power transmission and easy connecting of same fibers
lower tolerance of fiber connectors
Graded index fiber
has a core of varying refractive index it has a high value n at the core which dec radially towards the cladding has a multimode graded index fiber
multimode graded index fiber under parabolic index profile shows a parabolic transmission of rays through it
through geometrical optics,large no of refractions are observed due to varying refractive index from core to cladding
multimod graded index fiber hav a lower intermodal dispersion as compared to multimode step index however there are many modes of propagation but all are normalised through index grading
rays travelling through core hav a shorter path but move with a lower vel due to high n value. thus despite of all this it follows parabolic transmission and provide considerable bandwidth as compared to multi mode step index