John C.C. Fan always likes to have a few dishes cooking at the same time. That’s why he divided up the workings of his company, Kopin Corp., into several different product lines. First came low-power transistors for wireless devices; next came miniature display screens for camcorders, cell phones and other handheld devices. Last summer Fan introduced Kopin’s latest entrée: a light-emitting diode that exploits nanotechnology to generate more light with less power.