An optical ?bre transmission system consists of a circular LED source, a 2-metre length of optical ?bre and a circular PIN diode detector. Both the source and detector are positioned 100 µm from the ends of the ?bre. Detailed data for the source, a glass ?bre, a polymer ?bre and the detector are given below. Use this data to perform the following calculations.
(a) The total power Ps emitted by the source in all directions (use eqn [15.23b]).
(b) The numerical aperture and maximum angle of acceptance of the glass ?bre.
(c) The numerical aperture and maximum angle of acceptance of the polymer ?bre.
(d) The source and detector are linked by the glass ?bre; calculate the power input to the ?bre, the ?bre transmission factor, and power output from the ?bre. (Hint: use PIM/R=KSM and POM/PIM = T.)
(e) The source and detector are now linked by the polymer ?bre; calculate the power input to the ?bre, the ?bre transmission factor, and power output from the ?bre.
(f) For both the glass system of (d) and the polymer system of (e), calculate the power incident on the detector and the detector output current. (Hint: use PD/POM = KMD.)
LED source Radiance = 10 W cm-2 sr-1 Diameter = 200 µm Centre wavelength = 810 nm Glass ?bre Multimode step index Core diameter = 100 µm Core refractive index = 1.5 Core-cladding index difference = 0.015 Attenuation at 810 nm = 5 dB km -1 Fibre length = 2m Polymer ?bre Multimode step index Core diameter = 1.0 mm Core refractive index = 1.65 Core cladding index difference = 0.04 Attenuation at 810 nm = 500 dB km-1 Fibre length = 2m PIN diode detector Diameter = 2.0 mm Centre wavelength = 810 nm Responsivity at 810 nm = 0.55 A W-1.