As a first approximation, I don't see how a wavelength of less than 2 [Planck distances](http://en.wikipedia.org/wiki/Planck_length) could exist. The question is: Are there any other limits that would come into play before that? 

For example:

- Would the energy density cause the photon to turn into a black hole or something like that?
- Would the energy of the photon exceed the total mass+energy of the universe?