Multispectral emitter

From Memory Alpha, the free Star Trek reference.

A multispectral emitter is a device for creating wave outputs at or about the frequency of light.

In 2154, a ship used a multispectral emitter to create the holographic illusion of being the Enterprise NX-01. (ENT: "United")

In the same year, a Romulan ship also used this device to be able to mimic other ships. (ENT: "Babel One")