What is "d-beam"

The D-Beam was originally manufactured by Interactive Light, as a stand-alone unit, around 1996. It was then purchased by Roland, for their own equipment. The D-Beam Controller is a Roland Synthesizers interface that controls sound and effects via hand movements interacting with an infrared beam of light. Although controlled in a similar manner to a theremin, it should not be confused with one. The theremin operates with radio frequencies.

It was first introduced in the Roland MC-505 in 1998.