We report angle-resolved infrared reflectivity measurements from a substantially sub-wavelength thickness, textured, metal-dielectric-metal microcavity. The two-dimensional surface texturing causes the structure to support flat-band, surface plasmon modes exhibiting efficient diffractive coupling to free radiation. Additionally, we observe a transverse magnetic mode that is due to phonon absorption within the dielectric spacer layer of the structure. The nature of these electromagnetic modes, their mutual interactions and the device band structure has been characterized by numerical modelling of the experimental data. With the exception of the phonon mode, the analyzed modes show that absorption of incident radiation predominantly occurs in the metal layers of the structure and at frequencies dictated by the geometry of the patterned top surface.
It is well established that much more radiation may be transmitted through a set of apertures in a metallic screen than a simple calculation from the transmission through the aperture area alone would predict. There has been substantial debate regarding the exact cause of this enhanced transmission, and confusion over the difference between the behaviors of subwavelength apertures as opposed to subwavelength slits. In this study we have analyzed the transmission response of individual slits, using microwave radiation to ensure that transmission is in no part due to direct passage through the metal screen itself. A set of resonant transmission peaks is caused by the excitation of standing-wave-coupled surface plamsons in the finite length slit. It is also found that the high but finite value of the metals’ conductivity influences the transmission response of such slit channels when they are less than 100 microns in width. Indeed there is a strong decrease in transmitted resonant frequency, remarkably tending to zero as the slit width decreases. In addition we have explored the effect of misalignment of the two metal plates that comprise the slit. This modifies resonant frequencies and transmitted intensities through the changing boundary conditions at the slit ends.
It is shown that microwave radiation can be transmitted through a wall of aluminum-alloy bricks even though the width of the gaps between the metallic elements is less than 5% of the radiation wavelength. Up to 90% of the radiation made incident upon the wall is transmitted, with both linear polarizations being passed. Experimental results are compared to theoretical predictions. Proving that the transmission mechanism relies upon self-coupled surface plasmon resonances in what are effectively Fabry-Perot cavities.
Conference Committee Involvement (4)
Emerging Technologies
24 September 2012 | Edinburgh, United Kingdom
Photonic Components and Architectures in Defence Systems
3 September 2009 | Berlin, Germany
Photonic Components and Architectures for Microwave Systems and Displays II
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