This paper considers a range of plasmonic-black-metal polarizers suitable for ultra-short pulses. The polarizers consist of
a metal surface being nanostructured with a periodic array of ultra-sharp grooves with periods of 250-350 nanometers,
and groove depths around 500 nanometers. The surfaces can be designed such that practically all incident light with
electric field perpendicular to the groove direction is absorbed. The efficient absorption is due to incident light being
coupled into gap-plasmon polaritons that propagate downwards in the gaps between groove walls towards the groove
bottom, where it is then subsequently absorbed during propagation. Reflection is largely avoided due to an adiabatic
groove taper design. The other polarization, however, is very efficiently reflected, and the main point of this paper is that
the reflection is with negligible dispersive stretching even for ultra-short pulses of 5-10 femtoseconds temporal width in
the visible and near-infrared. Temporal pulse shapes after reflection are calculated by decomposing the incident laser
pulse into its Fourier components, multiplying with the reflection coefficient in the frequency domain, and then Fouriertransforming
the product back to the time-domain. Reflection of pulses is compared for polarizers based on different
metals (gold, nickel, chromium). Polarizers are studied for two groove-array designs and two directions of light
incidence, center wavelengths 650 nm and 800 nm, and pulse widths 5 fs and 10 fs for the incident pulse.
KEYWORDS: Waveguides, Near field scanning optical microscopy, Wave propagation, Near field optics, Near field, Finite element methods, Interfaces, Dielectrics, Free space optics, Telecommunications
The excitation of surface plasmon-polariton (SPP) waveguide modes in 500-nm-wide and 550-nm-high dielectric
ridges deposited on a thin gold film is characterized at telecommunication wavelengths, by application of a
scanning near-field optical microscope (SNOM), and by utilizing the finite element method (FEM). Different
tapering structures for coupling in SPPs, excited at the bare gold-air interface, are investigated with a SNOM,
and the dependence of in coupling efficiency on tapering length is characterized by means of FEM calculations.
The performance of this in coupling method is compared to an alternative excitation scheme, where the effective
index of SPPs in the tapering region is matched to the index of the incident beam, thereby exciting SPPs directly
in the dielectric tapering structure. Single-mode guiding and strong lateral mode confinement of dielectric-loaded
SPP waveguide (DLSPPW) modes are demonstrated by characterizing a straight DLSPPW section with a SNOM
and with the effective index method (EIM). The propagation loss of DLSPPW modes is characterized for different
wavelengths in the telecommunication region, by application of a SNOM, and the results are compared to EIM
calculations.
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