An emissive display device, including: a reflective electrode and a transparent electrode. The invention provides a simple, elegant casement window lock having an extended operating range, is economical to manufacture, and uses few parts. 6 Pas at normal temperature before curing is filled in a space around the dispersion compensating fiber 1 within the housing 2 and then the filling material is cured. A photodetector unit receives a reflected component of the first light spot to form a first electrical signal and a reflected component of the second light spot to form a second electrical signal.