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refractive index
cladding
core
cladding
optical fibre
refractive index (core): 1.5
angle of incidence: 0°
refractive index (cladding): 1.3
point of incidence
1.5
1.6
−60
0
60
1.3
1.4
upper
lower
straight optical fibre
curved optical fibre
The light ray has escaped to the cladding because the angle of incidence is smaller than or equal to the critical angle.
The light ray cannot leave the fibre from the other end.