Check out an explanation for Kylo Ren's lightsaber design in Star Wars: The Force Awakens, which is pretty much what everyone thought when we first seen it in the teaser -- that Kylo didn't really have a clue how to construct one.
Though Kylo's weapon evokes an ancient feel, its components are modern. Its crude appearance suggests construction by an inexperienced hand.
The stressed crystal barely contains the power of the weapon, necessitating lateral plasma vents that become the crossguard quillons.
It's also stated that Kylo used a "cracked kyber crystal" which explains the “ragged, unstable appearance” and "unstable plama blade matrix."
And the reason for the crossguard blades? They help balance the power of Kylo's lightsaber.
Here is a pic. Click to enlarge:
"Star Wars: The Force Awakens" is directed by J.J. Abrams from a screenplay by Lawrence Kasdan and Abrams. Kathleen Kennedy, J.J. Abrams, and Bryan Burk are producing, and John Williams returns as the composer.
Actors John Boyega, Daisy Ridley, Adam Driver, Oscar Isaac, Andy Serkis, Domhnall Gleeson, Max von Sydow, Lupita Nyong'o and Gwendoline Christie will join the original stars of the saga, Harrison Ford, Carrie Fisher, Mark Hamill, Anthony Daniels, Peter Mayhew, and Kenny Baker in the new film.