I'd stick with calling a lightsaber an "IoP" just because a basic weapon doesn't give enough room for uniqueness in DFRPG. How about something like this?
Lightsaber (-whatever)
(+2) Discount Already Applied.
(-1) Marked as a Jedi. You carry the weapon of a Jedi, and those who see it will believe you to be one. This can be either good or bad (see Marked By Power).
(-1) It’s a Beam Of Focused Energy. A lightsaber takes the form of a handle that, when activates, emits an intense beam of focused energy. It inflicts weapon:4 damage on anything it touches, regardless of the force (or lack thereof) behind the blow. Strength and other similar powers do not increase the damage dealt by a lightsaber, though they can be used to overcome an opponent's lightsaber block. [Note that the 'it is what it is' power usually costs nothing; in this case the entire weapon is special. Assume this is the equivalent of a 1-h weapon (w:2) +2 stress (-1 refresh).]
(-?) Cuts Through Anything. Lightsabers ignore all sorts of physical armor, including equipment, Toughness powers, etc. Only force fields, other lightsabers, and certain rare, specially prepared materials can block one.
(-0) Disciplined Fighting Style. Lightsabers require specialized training to use effectively, and can be deadly to those who use them without the proper training and focus. Fighting with a Lightsaber uses Weapons restricted by and modified by the "Lightsaber Dueling" trapping of Discipline.
Then create the following stunt:
Lightsaber Dueling: You are trained in the effective use of lightsabers (this is a new skill trapping; most people can’t handle lightsabers without training). You may use your Weapons (modified and restricted by Discipline) to attack, parry, create blocks, and perform maneuvers with a lightsaber.
Lightsaber Defense: Your lightsaber training is such that you may parry or block attacks that would be impossible for someone wielding a mundane melee weapon. You may block ranged physical and energy-based attacks when wielding a lightsaber. You must already have the Lightsaber Dueling stunt to learn this stunt, and parries or blocks with this stunt are performed as described in Lightsaber Dueling.
Add additional powers and stunts (probably including ones like Eldritch mentioned) to round out lightsaber combat and add in more general Jedi powers.
Or something like that.