Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-11-05
2001-09-04
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S201300, C250S307000
Reexamination Certificate
active
06285020
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of optics, and in particular to the enhanced transmission of light through a thin metal film perforated with one or more apertures.
BACKGROUND OF THE INVENTION
As discussed in detail in U.S. patent applications Ser. No. 08/979,432, filed Nov. 26, 1997 (“the '432 Application”), Ser. No. 09/168,265, filed Oct. 8, 1998 (“the '265 Application”), and Ser. No. 09/208,116, filed Dec. 9, 1998 (“the '116 Application”) (collectively referred to herein as “the Previous Applications”, each of these Previous Applications being incorporated herein by this reference), light transmission through one or more subwavelength-diameter apertures provided in a thin metal (i.e. conductive and opaque in the wavelength of interest) film can be greatly enhanced by arranging the holes in a periodic array and/or by providing a periodic surface topography on the metal film (surface features such as dimples or protrusions) in conjunction with the aperture(s). This enhancement, which can be as large as a factor of 1,000, occurs when light incident on the conductive film interacts resonantly with a surface plasmon mode.
The present invention is a light transmission apparatus wherein the light transmission efficiency is even further enhanced in comparison to previous optical transmission apparatus. In addition, the invention includes a novel near-field scanning microscope, a novel mask technology for sub-wavelength lithography, a wavelength-selective filter and light collecting device utilizing the improved enhanced light transmission apparatus.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, an apparatus for enhanced light transmission through a perforated metal film is provided. The apparatus comprises a metal film having a first surface and a second surface, at least one aperture provided in the metal film and extending from the first surface to the second surface, and first and second dielectric layers. The first dielectric layer is provided substantially adjacent to the first metal film surface, and the second dielectric layer is provided substantially adjacent to the second metal film surface. The respective refractive indices of the first and second dielectric layers are substantially equal. Light incident on one of the surfaces of the metal film interacts with a surface plasmon mode on at least one of the surfaces of the metal film thereby enhancing transmission of light through the at least one aperture in the metal film. The apparatus may have a single aperture or a plurality of periodically arranged apertures, and the metal film surface may be provided with or without a periodic surface topography for further enhanced transmission. Wavelength-selective optical filters, spatial optical filters, light collectors, near-field scanning optical microscope probes and photolithographic masks are also provided.
Accordingly, an object of the invention is to provide an apparatus which provides enhanced light transmission through one or more apertures utilizing two dielectric layers substantially adjacent to the surfaces of the metal film and having substantially equal refractive indices, such that the transmission is enhanced in comparison to the transmission through the apertures in the absence of such refractive index-matched layers.
Another object of the invention is to provide an apparatus which provides enhanced light transmission through a single aperture.
A further object of the invention is to provide an apparatus which provides enhanced light transmission at selected wavelengths through one or more apertures.
A still further object of the present invention is to provide a wavelength-selective optical filter with one or more apertures which provides enhanced light transmission.
A still further object of the present invention is to provide a spatial optical filter which provides enhanced light transmission.
A still further object of the present invention is to provide a light collector with one or more apertures which provides enhanced light transmission.
A still further object of the present invention is to provide a near field scanning optical microscope probe with one or more apertures which provides enhanced light transmission.
A still further object of the present invention is to provide a photolithographic mask with one or more apertures which provides enhanced light transmission.
Other objects of the present invention will become more readily apparent in light of the following description in conjunction with the accompanying drawings.
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Ebbesen Thomas W.
Kim Tae Jin
Krishnan Ajit
Lezec Henri Joseph
Thio Tineke
Isztwan Andrew G.
Le Que T.
NEC Research Institute Inc.
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