In this paper we show how the optical properties of a metallic film can be tailored by one-dimensional periodically nanostructuring it which, in turn modifies the surface plasmon properties. The interaction of light with the surface plasmons can be used for two apparently opposite effects: trapping incident radiation into small volumes (in reflection gratings) and transmitting light very efficiently (in transmission gratings). A physical picture of the mechanisms involved, as well as dependences of the transmission and reflection spectra on wavelength, absorption and geometrical parameters of the grating, are provided.

Transmission and focusing of light in one-dimensional periodically nanostructured metals

This letter describes the use of nanotransfer printing (nTP) for forming three-dimensional (3D) structures with feature sizes between tens of nanometers and tens of microns over areas of several square millimeters. We demonstrate three different approaches-deep etching through printed hard masks, direct transfer of three-dimensional structures, and purely additive fabrication of multilayer stacks-for using nTP to fabricate a range of complex 3D nanostructures, including closed channels, suspended beams, and nanochannel stacks, that would be difficult or impossible to build with other methods.

Three-Dimensional and Multilayer Nanostructures Formed by Nanotransfer Printing

A broadband wire grid polarizer (400) for the visible spectrum has a plurality of elongated elements (1240) supported on a substrate (1210). A region (1250) having a lower refractive index than the refractive index of the substrate is disposed between the elements and the substrate to reduce the longest wavelength at which resonance occurs.

Broadband wire grid polarizer for the visible spectrum

The optical response of regularly arranged noble metal wires with nanoscopic cross sections (nanowire gratings) strongly depends on the polarization direction of the incident light. We use silver and gold nanowire gratings produced by electron beam lithography to study this effect by optical extinction spectroscopy. For a polarization direction perpendicular to the wire axis, the excitation of a dipolar plasmon mode dominates the extinction spectrum. The spectral position of the plasmon resonance can be tuned by an appropriate choice of nanowire geometry and material. For a polarization direction parallel to the wire axis, the profile of the extinction spectrum varies mainly as a function of the grating constant. In particular, a transmission maximum for small grating constants is found. By combining the surface plasmon excitation and grating effect for orthogonal polarization directions, a spectrally selective polarizer with an extinction ratio of 26 is demonstrated.

Optical properties of Ag and Au nanowire gratings

We present a semi-analytical model that quantitatively predicts the transmission, the absorption and the resonance locations of one-dimensional lamellar metallic gratings with subwavelength slit apertures. The model relies on the fact that subwavelength apertures perforated in metallic films behave like monomode waveguides and provide Airy-like formulae for the transmission and reflection coefficients. Limitations are outlined for too shallow grating depths.

https://iopscience.iop.org/article/10.1088/1464-4258/2/1/309/pdf

One-mode model and Airy-like formulae for one-dimensional metallic gratings

We theoretically and experimentally investigate the response, in the visible and in the near infrared, of micrometer- and submicrometer-period lamellar metal transmission gratings in vacuum and on silica and GaAs substrates. We use a coupled-wave analysis to characterize the grating response as a function of wavelength, period, grating profile, and dielectric constant of the metal and the substrate. Losses to the metal, which have been neglected in prior studies, are shown to be as large as 80% of the incident optical power. Absorption in the metal and the substrate, associated with complex refractive indices, leads to a broadening and a reduction in amplitude of Rayleigh wavelength resonance features in the transmission efficiency and reduces the extinction between orthogonal polarizations in the wire-grid polarizer limit. The results of transmission and photocurrent studies performed on metal–semiconductor–metal photodiodes fabricated on GaAs or GaAs–AlGaAs heterostructure substrates demonstrate the rigorous nature of the coupled-wave analysis, indicate experimental limitations for the application of an infinite grating approximation to model finite-period structures, and 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 transmission data reported in the literature for gold gratings on silica.

Coupled-wave analysis of lamellar metal transmission gratings for the visible and the infrared

Photocurrent and transmission studies for 543<λ<1523 nm of metal‐semiconductor‐metal (MSM) photodetectors on semi‐insulating GaAs substrates demonstrate a polarization and wavelength dependence of the coupling of light into the metal electrodes. Devices with electrode periods of 400 and 800 nm were investigated and differences as large as 85% in efficiency between orthogonal polarizations were measured for the 400 nm devices. Modeling of the energy transmission through lamellar periodic structures using a Greens function formalism and incorporating dispersion of the substrate dielectric constant produces semiquantitative agreement with the measurements. Suggestions for future MSM photodetector design are discussed.

Polarization and wavelength dependence of metal‐semiconductor‐metal photodetector response

The effect of grating diffraction on metal‐semiconductor‐metal photodetector temporal response is shown to be significant, and largest for devices with electrode periods less than the optical wavelength. This is related to a polarization dependence of the initial photogenerated carrier densities and distributions. With subpicosecond illumination, the measured difference in peak temporal signal for orthogonal polarizations was up to three times larger than that of the time‐integrated photocurrent, and risetimes differed by as much as 30%. Transmission efficiencies obtained from coupled‐wave analysis of metal grating structures on GaAs show excellent agreement with the time‐integrated photocurrent measurements.

D. Landheer

Papers

Coupled-wave analysis of lamellar metal transmission gratings for the visible and the infrared

Polarization and wavelength dependence of metal‐semiconductor‐metal photodetector response

Polarization dependence of the temporal response of metal‐semiconductor‐metal photodetectors