These are the results for a handful of common LEDs. The superbright red LED's are the clear winners with a cutoff of at least 2 MHz. The most likely reason that the superbright LEDs are also fast is a correlation between efficiency of carrier recombination and speed. There are many other fairly inexpensive but much faster components which can be used in place of LEDs'. For example, 1.3 and 1.5 micron lasers used to drive fiber optic communication channels routinely go into the GHz range, and superluminescent diodes routinely go into the hundreds of MHz. The ideal component is probably not yet available, a 5 or 10 micron laser that operates at room temperature. However, such a component will probably be available in the next few years.#