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Fiber Optics in Sensors and Contr ol Systems
FIGURE 3.3 Light-emitting diode. 135
LEDs emit light energy over a narrow wavelength (Fig. 3.4a).
Infrared (IR) gallium arsenide LEDs emit energy only at 940 nm
(Fig. 3.4b). As this wavelength is at the peak of a silicon photodiode’s
response, maximum energy transfer between source and detector is
achieved.
A silicon photodetector’s sensitivity to light energy also peaks in
the infrared light spectrum. This contributes to the high efficiency
and long range possible when silicon photodetectors are used in con-
junction with gallium arsenide LEDs.
FIGURE 3.4 (a) LED emission wavelengths. (b) Infrared gallium arsenide LED
emission.
