This is the light saber wielded by Sabine in the TV series Star Wars: Rebels.
it is Mandalorian made by Tarre Vizsla leader of the House Vizsla of Mandalore
you can find info about him here:
http://starwarsrebels.wikia.com/wiki/Tar_Vizsla
The Dark Saber is one of a kind originally built by Tarre Vizsla and was used to unite all of Mandalore.