Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-09-22
2002-09-24
Lester, Evelyn A (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S321000, C359S586000, C250S492220
Reexamination Certificate
active
06456416
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process and a device for producing an optical element having a photonic-band structure, particularly an optical element comprising a three-dimensional photonic crystal having a desired crystal structure easily and in a short period of time, and it also relates to an optical element produced by using the process and the device.
Furthermore, the present invention relates to an optical element and an optical demultiplexer. More specifically, it relates to an active optical element and an optical demultiplexer that have achieved an optical switching function by changing a photonic-band structure by switching external fields such as light and an electric field in a photonic crystal.
In the structure called “photonic crystal” in which two types of optical media having different refractive indices are arranged periodically at a wavelength order of light, the relationship between the wave number of light and its frequency, i.e. photon energy, shows a band structure due to periodic changes in the refractive indices. This phenomenon is similar to the phenomenon that electron energy in a semiconductor shows a band structure in a periodic potential.
The photonic crystal is significantly characterized by its optical properties since it is capable of making the so-called “photonic-bandgap” in which light does not transmit in any directions (E. Yablonovitch, Phys. Rev. Lett. 58(20), 2059(1987)) appear and has very high degrees of optical anisotropy and dispersibility. Thus, by taking advantage of such properties, there have been proposed the control of natural light and an optical waveguide, a polarizer and an optical demultiplexer that have a very small radius of curvature at the corner, and expectations are being raised about their applications to a variety of fields.
Heretofore, however, there has not been available an effective process for producing a photonic crystal, particularly a three-dimensional photonic crystal, in which the refractive indices have a periodic structure at the wavelength order of light, in the form of a crystal structure suitable for the application of an optical element. This has been a factor that hinders the commercialization of the photonic crystal and an optical element using the same.
To improve the above situation, there have recently been made several reports on the production of a photonic crystal at the wavelength order of light. Representative among them are on the following three processes.
(1) A process for producing a photonic crystal by removing a solvent from a colloidal solution containing silicon oxide fine particles to crystallize the silicon oxide fine particles. This process takes advantage of the self-arrangement of silicon oxide fine particles, and the photonic crystal produced is called “opal type”. By this process, a crystal having a high repetition number can be produced relatively easily (H. Miguez et al., appl. Phys.
Lett. 71(9), 1148(1997)). However, in this process, the silicon oxide fine particles are not arranged with high reproducibility and high reliability, and a crystal structure cannot be selected freely.
(2) Wood-Pile process (S. Noda et al. Jpn. J. Appl. Phys., 35, L909(1996)). In this process, by using a semiconductor micromachining technique, a structure comprising a plurality of arranged square timbers is formed on each of two substrates, the substrates are bonded to each other in such a manner that the square timbers on one substrate are faced at right angles with the square timbers on the other substrate, and one of the substrates is removed by etching to form a structure comprising two layers of “square timbers”. Similarly, a substrate having “square timbers” arranged on the surface is prepared, and a layer of square timbers is piled up by repeating bonding with accurate positioning and etching. It has been found that a diamond structure which opens a photonic-bandgap in all directions can be formed by this process. This process, however, requires a micromachining process which is complicated and time-consuming, and there is a limit for the number of repeating periods that can be actually formed.
(3) A process called “autocloning” process (Kawakami et al., Japanese Patent Application Laid-Open No. 335758/1998). In this process, a two-dimensional, periodic convexo-concave pattern is formed on a substrate made of quartz or a semiconductor by lithography, and a number of thin films are laminated thereon while the underlying convexo-concave pattern is reproduced by bias sputtering. Thus, a three-dimensional periodic structure is formed both in the surface direction of the substrate on which the convexo-concave pattern has been engraved at the beginning and in the laminating direction perpendicular to the surface. This process is more reliable and more excellent in terms of reliability and reproducibility than the process for producing the opal-type photonic crystal, and does not require a micromachining process which is as complicated and time-consuming as that in the Wood-Pile process. Therefore, this process is capable of producing a photonic crystal which has a relatively large number of periods in the laminating direction. However, since it is inevitable in this process that concave portions come over the concave portions of the pattern of the underlying layer and convex portions come over the convex portions of the pattern of the underlying layer, this process can realize only specific types of crystal structures and therefore cannot attain arbitrary types of crystal structures. In fact, a photonic crystal having a perfect bandgap which opens in all directions cannot be formed by this process.
Other than the above three processes, there has been proposed a process for producing a photonic crystal by taking advantage of an interference pattern of light (Tsunetomo, Koyama, Japanese Patent Application Laid-Open No. 68807/1998). In this process, a laser beam is directed onto a number of thin films laminated one-dimensionally so as to bake the interference pattern on the films, and periodic incisions are made in a perpendicular direction on the surface of the multi-layer film by taking advantage of the fusion, evaporation and ablation occurring on portions where light intensity is high to form a photonic crystal. This process is considered to be an efficient process because it can form a number of periods at a time when a periodic structure is formed by using the interference pattern of a laser. However, even this process is limited in the types of crystal structures it can form.
As described above, the conventional process taking advantage of the self-arrangement of silicon oxide fine particles has problems associated with reliability and reproducibility.
Meanwhile, since other processes require that each layer be laminated with high accuracy to form the periods of a photonic crystal, even if they succeed in the formation of the photonic crystal, it takes long time, the number of repeating periods is limited, and a desired crystal structure cannot be formed freely.
Meanwhile, the application of such a photonic crystal has also been limited heretofore.
That is, except for the three examples that will be given below, the photonic crystal has been conventionally used as a “passive element”, and they have been rarely proposed to be used as an “active element”. In other words, most of the conventionally proposed photonic crystals are determined their optical properties by the refractive-index distribution fixed in space. Therefore, in an optical demultiplexer, for example, the wavelength (frequency) of light to be transmitted in a specific direction is fixed, and the frequency of light to be derived in a specific direction has not been able to be switched. It has also not been possible to dynamically switch the direction of light from one direction of a branch placed in a waveguide to the other direction thereof.
The following three proposals use a photonic crystal as an “active element” having a switching function.
(4) One of the proposals uses a photonic crystal in which
Hiraoka Toshiro
Ichimura Kouichi
Kabushiki Kaisha Toshiba
Lester Evelyn A
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Process and device for producing photonic crystal, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and device for producing photonic crystal, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and device for producing photonic crystal, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2871762