LED doubles as emitter and detector


Posted on Sep 10, 2012

Figure 1 shows the relative responsivity and emission spectra for an Infineon (www.infineon.com) SFH409 LED. This infrared GaAs LED has peak emission at 940 nm with a half-peak bandwidth of 50 nm. In detection mode, it peaks at 920 nm with a half-peak bandwidth of 55 nm. As Figure 1 shows, the wavelength of peak responsivity is shorter than the peak-emission wavelength, and a fair amount of overlap exists between the two curves. Thanks to this overlap, the LED is useful as a transducer. Figure 2 shows a half-duplex application that exploits the LED.






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