COUPLED-WAVE ANALYSIS OF LAMELLAR METAL TRANSMISSION GRATINGS FOR THEVISIBLE AND THE INFRARED

We theoretically and experimentally investigate the response, in the v isible and in the near infrared, of micrometer- and submicrometer-peri od lamellar metal transmission gratings in vacuum and on silica and Ga As substrates. We use a coupled-wave analysis to characterize the grat ing response as a function of wavelength, period, grating profile, and dielectric constant of the metal and the substrate. Losses to the met al, which have been neglected in prior studies, are shown to be as lar ge as 80% of the incident optical power. Absorption in the metal and t he substrate, associated with complex refractive indices, leads to a b roadening and a reduction in amplitude of Rayleigh wavelength resonanc e features in the transmission efficiency and reduces the extinction b etween orthogonal polarizations in the wire-grid polarizer limit. The results of transmission and photocurrent studies performed on metal-se miconductor-metal photodiodes fabricated on GaAs or GaAs-AlGaAs hetero structure substrates demonstrate the rigorous nature of the coupled-wa ve analysis, indicate experimental limitations for the application of an infinite grating approximation to model finite-period structures, a nd provide evidence for the presence of surface electromagnetic waves in the forward-diffracted optical intensity distribution. Qualitative agreement is also obtained between coupled-wave analysis results and t ransmission data reported in the literature for gold gratings on silic a.