OPTICAL-PERFORMANCE OF HIGH-ASPECT LIGA GRATINGS

LIGA technology has been used to fabricate linear gratings having free -standing nickel walls a few micrometers wide and as much as 50 mu m h igh, with period on the order of 10 mu m. With additional MEMS process ing steps, such devices are intended for use in a tunable infrared fil ter. Prediction of optical performance is a particularly challenging p roblem for gratings with these parameters and materials and requires a robust Maxwell solver. We have applied our own code, described elsewh ere, in the form of a finite-element implementation of the equivalent variational problem, to examine the optical properties of this class o f gratings. Here, we describe our predicted results for the transmitta nce as a function of wavelength and polarization for various grating p arameters and incident conditions. Measurements of fabricated gratings were also carried out, and the predictions are shown to agree well wi th the measured data. The filter cutoff is shown to be sensitive to th e cone angle of the incident radiation, and the implications of this e ffect for system performance are discussed. (C) 1997 Society of Photo- Optical Instrumentation Engineers.