An optronic data core was a device made up of a tech cube and enhancement module, which enabled the creation of holodeck technology.

After a group of Hirogen and the crew of the USS Voyager called a cease-fire following a deadly World War II-set holodeck war game in 2374, Captain Kathryn Janeway gave an optronic data core to a young Hirogen as a trophy. It was hoped that the Hirogen would use the data core in order to create an unlimited supply of prey for their hunts, thus allowing them to re-form their civilization rather than becoming dispersed across the Delta Quadrant. The Hirogen accepted the trophy and evacuated Voyager. (VOY: "The Killing Game, Part II")

Optronics
opti-cable • optronic coupler • optronic data core • optronic data stream • optronic emitter • optronic integrator • optronic pathway • optronic relay • optronic weapons array