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Strong near field enhancement in THz nano-antenna arrays.

Feuillet-Palma C, Todorov Y, Vasanelli A, Sirtori C - Sci Rep (2013)

Bottom Line: In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies.In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities.This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire "Matériaux et Phénomènes Quantiques", Sorbonne Paris Cité, Université Paris Diderot, CNRS-UMR 7162, FR-75013 Paris, France.

ABSTRACT
A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 10(4)-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

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Related in: MedlinePlus

Possible array optimizations.(a) A figure of merit of a possible detector device build with our THz nano-antenna array. (b) Optimization of the array from the point of view of a SEIRS experiment. The shaded areas correspond to the standard mean deviation of the model.
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f5: Possible array optimizations.(a) A figure of merit of a possible detector device build with our THz nano-antenna array. (b) Optimization of the array from the point of view of a SEIRS experiment. The shaded areas correspond to the standard mean deviation of the model.

Mentions: Consider, for instance, the case where the semi-conductor layer is filled with photoconductive media, such as doped shallow quantum wells as in a typical Quantum Well Infrared Photodetector (QWIP) device25. Another possible example is the micro-bolometer detectors relying on planar antennas26. In this case an important quantity is the contrast C which describes how much of the incident power is coupled inside the detector active medium. The latter, however, is partially dissipated by the metal losses and does not contribute to the photocurrent signal. For the detector the total non-radiative loss is then described by a quality factor 1/Qnr = 1/Qph + 1/Qohm which takes into account both contributions, from the metal 1/Qohm and from the photoconductive media, 1/Qph. In this case we should use Qnr instead of Qohm everywhere in Eq.(2)–(6). The figure of merit of the system is therefore CxQnr/Qph which is also directly proportional to the detector responsivity. If the photoconductive loss is small, 1/Qph ≪ 1/Qohm this figure of merit becomes CxQohm/Qph with C independent from Qph. In this case the optimal responsivity of the detector can be evaluated using the values of C and Q reported in Figure 3(a,b). The result is plotted in Figure 5(a) which provides an optimum filling factor for a detector array of a given thickness. When 1/Qph cannot be neglected with respect to 1/Qohm, Eq.(2) provides a relationship between the contrast C and Qnr, and the optimization can still be performed.


Strong near field enhancement in THz nano-antenna arrays.

Feuillet-Palma C, Todorov Y, Vasanelli A, Sirtori C - Sci Rep (2013)

Possible array optimizations.(a) A figure of merit of a possible detector device build with our THz nano-antenna array. (b) Optimization of the array from the point of view of a SEIRS experiment. The shaded areas correspond to the standard mean deviation of the model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3584925&req=5

f5: Possible array optimizations.(a) A figure of merit of a possible detector device build with our THz nano-antenna array. (b) Optimization of the array from the point of view of a SEIRS experiment. The shaded areas correspond to the standard mean deviation of the model.
Mentions: Consider, for instance, the case where the semi-conductor layer is filled with photoconductive media, such as doped shallow quantum wells as in a typical Quantum Well Infrared Photodetector (QWIP) device25. Another possible example is the micro-bolometer detectors relying on planar antennas26. In this case an important quantity is the contrast C which describes how much of the incident power is coupled inside the detector active medium. The latter, however, is partially dissipated by the metal losses and does not contribute to the photocurrent signal. For the detector the total non-radiative loss is then described by a quality factor 1/Qnr = 1/Qph + 1/Qohm which takes into account both contributions, from the metal 1/Qohm and from the photoconductive media, 1/Qph. In this case we should use Qnr instead of Qohm everywhere in Eq.(2)–(6). The figure of merit of the system is therefore CxQnr/Qph which is also directly proportional to the detector responsivity. If the photoconductive loss is small, 1/Qph ≪ 1/Qohm this figure of merit becomes CxQohm/Qph with C independent from Qph. In this case the optimal responsivity of the detector can be evaluated using the values of C and Q reported in Figure 3(a,b). The result is plotted in Figure 5(a) which provides an optimum filling factor for a detector array of a given thickness. When 1/Qph cannot be neglected with respect to 1/Qohm, Eq.(2) provides a relationship between the contrast C and Qnr, and the optimization can still be performed.

Bottom Line: In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies.In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities.This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire "Matériaux et Phénomènes Quantiques", Sorbonne Paris Cité, Université Paris Diderot, CNRS-UMR 7162, FR-75013 Paris, France.

ABSTRACT
A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 10(4)-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

Show MeSH
Related in: MedlinePlus