I. Campillo

Enhanced millimeter-wave transmission through subwavelength hole arrays

We explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.

Left-handed extraordinary optical transmission through a photonic crystal of subwavelength hole arrays

Metamaterial structures are artificial materials that show unconventional electromagnetic properties such as photonic band-gap, extraordinary optical transmission and left-handed propagation. Up to now, relations of photonic crystals and negative refraction have been shown as well as of photonic crystals and sub-wavelength hole arrays. Here we report a left-handed metamaterial engineered by a combination of sub-wavelength hole array plates periodically stacked to form a photonic crystal structure. It is shown the possibility of fine-tuning the metamaterial in order to permit extraordinary optical transmission and left-handed behaviour. Our work demonstrates the feasibility of engineering left-handed metamaterials by just drilling holes in metallic plates and brings together single structure photonic crystals, extraordinary optical transmission and left-handed behaviour.

Enhanced millimeter wave transmission through quasioptical subwavelength perforated plates

In this paper, we show that the phenomenon of extraordinary transmission through arrays of subwavelength holes, present in the optical regime, is also present in the millimeter wave range. After presentation of the theoretical foundations of the enhanced transmission, measurements of the transmission response have been performed on different samples by using a millimeter wave quasioptical vector network analyzer in the range between 45 and 110 GHz. The prototypes have been fabricated in Aluminum plates with several thickness and different hole diameters drilled by using a laser machine. Good agreement between theory and experiment is obtained, with clear signals of the existence of resonant transmission at wavelengths close to the period of the array. Possible applications in frequency selective surfaces and near-field imaging are envisaged.

Negative refraction in a prism made of stacked subwavelength hole arrays

Metamaterial structures are artificial materials that show unconventional electromagnetic properties such as negative refraction index, perfect lenses, and invisibility. However, losses are one of the big challenges to be surpassed in order to design practical devices at optical wavelengths. Here we report negative refraction in a prism engineered by stacked sub-wavelength hole arrays. These structures exhibit inherently an extraordinary optical transmission which could offer a solution to the problem of losses at optical wavelengths. It is shown the possibility to obtain negative indices of refraction starting from near to zero values. Our work demonstrates by a direct experiment the feasibility of engineering negative refraction by just drilling sub-wavelength holes in metallic plates and stacking them.

Molding Left- or Right-Handed Metamaterials by Stacked Cutoff Metallic Hole Arrays

A novel periodic structure, made of an arbitrary number of stacked subwavelength hole arrays, exhibiting simultaneously electromagnetic band gap, extraordinary transmission and a longitudinal left handed propagation is presented in this paper. If the longitudinal period of the stacked structure is chosen adequately, it is possible under normal incidence to mold the electromagnetic wave properties inside the structure from right-handed to left-handed wave propagation passing through a zero-group velocity band. The transmission response of the fabricated prototype has been measured with a millimeter wave quasioptical vector network analyzer in the range between 40 GHz and 110 GHz confirming the possibility to tune the left- or right-handed characteristics of the propagating waves. These results can give rise to interesting applications such as novel lenses and other quasioptical structures.

Extraordinary transmission and left-handed propagation in miniaturized stacks of doubly periodic subwavelength hole arrays

Metallic plates embedded between dielectric slabs and perforated by rectangular arrays of subwavelength holes with a dense periodicity in one of the directions support extraordinary transmission (ET) phenomena, viz. strong peaks in the transmittance frequency dependence. Stacks of such perforated plates support ET phenomena with propagation along the stack axis that is characterized by the left handed behavior. The incorporation of the dielectric materials and dense periodicity allows significantly reducing the illuminated area of the perforated plate required experimentally to observe the ET phenomena as compared to the areas required in the case of free standing rectangular hole arrays. This facilitates the experimental investigation of ET under excitation in the Fresnel zone of Gaussian beams.

Dual-band low-profile corrugated feeder antenna

A dual-operating-band planar horn antenna having very low profile is presented in this paper. By opening a subwavelength aperture into a corrugated conducting plate, good return losses and a narrow radiated beam in each of the two desired operating frequency bands can be measured. This behavior is very similar to that observed in optical wavelengths where enhanced transmission was measured through apertures etched in metallic corrugated plates. Here, the double-corrugated structure has been scaled into the microwave frequency range and the excitation has been done by a conventional closed metallic waveguide placed in the rear part of the structure. In this way, a new concept of a very low profile feeder is proposed with potential wireless applications.

Planoconcave lens by negative refraction of stacked subwavelength hole arrays.

This work presents the design of a planoconcave parabolic negative index metamaterial lens operating at millimeter wavelengths fabricated by using stacked subwavelength hole arrays. A staircase approximation to the ideal parabola profile has been done by removing step by step one lattice in each dimension of the transversal section. Theory predicts power concentration at the focal point of the parabola when the refractive index equals -1. Both simulation and measurement results exhibit an excellent agreement and an asymmetrical focus has been observed. The possibility to design similar planoconcave devices in the terahertz and optical wavelengths could be a reality in the near future.

Regular and anomalous Extraordinary Optical Transmission at the THz-gap

In this paper Anomalous Extraordinary Transmission (ET) is reported for s-polarization of low loss doubly periodic subwavelength hole arrays patterned on polypropylene (PP) substrates by conventional contact photolithography at the so-called THz-gap (1-10 THz). The unexpected enhanced transmittance for s-polarization (i.e. without spoof plasmons) was previously numerically demonstrated in subwavelength slits arrays. However, subsequently no experimental work has been devoted to this unexpected Extraordinary Transmission neither in subwavelength slits nor in subwavelength holes. Here, numerical study and experimental results of the Anomalous ET and the symmetric and antisymmetric transmittance modes associated with the already well-known p-polarization ET are shown alongside a systematically analysis of the frequency peaks as a function of hole size for both incident polarizations.

Increase of the transmission in cut-off metallic hole arrays

In this letter, the phenomenon of extraordinary transmission through arrays of subwavelength holes in the microwave range is demonstrated. It is also shown that the magnitude of the transmission is strongly dependent on the number of holes in the sample. Prototypes have been designed and fabricated in an Al plate. The transmission response is measured with a millimeter wave quasi-optical vector network analyzer in the range between 40 and 70GHz. These measurements show a resonant total transmission at wavelengths close to the period of the array which depends strongly on the number of resonant holes. These results can give rise to interesting applications such as frequency selective surfaces and other quasi-optical structures.