Twenty years ago (when building community wireless networks was all the craze, at least here), we played with free-space optics and in course of that found out that random soviet (4mm!) green LED from parts bin makes exceptionally good receiver for the red laser LED from cheap laser pointer (driven by bunch of paralleled up HC04 gates). The contraption was not really practical, but across few meters of lab bench had higher bandwidth than we could measure with the surplus 50MHz CRO we had there.