Optical waveguides – Integrated optical circuit
Reexamination Certificate
1999-11-16
2001-10-30
Ngo, Hung N. (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S015000, C385S129000, C385S031000
Reexamination Certificate
active
06310991
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an integrated optical circuit having a silicon substrate and waveguides disposed thereon.
BACKGROUND INFORMATION
Integrated optical circuits are needed in communications engineering for various purposes, such as for the distribution, combining, spectral partitioning or switching of information-modulated light fluxes. In addition, it is also possible to implement other circuits with the aid of optical structures, such as computer circuits.
At present, integrated optical circuits are constructed using waveguides made of polymers or III-V compound semiconductors which are structured by lithographic processes.
Suitable as the optically active elements of such circuits are, inter alia, photonic crystals which, because of their small geometrical dimensions, require a waveguide pattern into which they are inserted in order to develop their full effect. Such waveguide patterns are usually strip waveguides made of polymer or semiconductor material.
These waveguide patterns can be produced in a complementary structure which, through its form, prevents the propagation of the photon pulses in the matter and, through selective built-in defects, allows propagation into otherwise completely reflecting matter. In this context, there is not a step change (sudden change) in refractive index as in the guiding of waves in optical waveguides formed by doping or in the form of strip waveguides, instead—theoretically stated—forbidden bands limit the state solution of the eigensolutions desired for specific wavelengths for propagating these waves. These waveguides are described, for example, in a reference by A. Mekis et AL in Physical Review Letters, Volume 77, No. 18, p. 3787.
SUMMARY
An object of the present invention is to provide an integrated optical circuit in which such waveguides are used for various functions and which can be manufactured with the requisite precision.
This objective is achieved according to the present invention, in that at least one photonic crystal is provided as a waveguide. Further waveguides may be provided in the form of strip waveguides, an insulating layer being disposed between the strip waveguides and the silicon substrate, and the photonic crystal extending from a plane below the lower boundary surface of the waveguides to beyond the upper boundary surface of the waveguides.
The commercially available material “silicon on insulator”, for example from the manufacturer SOITEC SA., Grenoble, France, can advantageously be used to manufacture the circuit according to the present invention. This material has good transmission properties for wavelengths of 1.55 &mgr;m. Silicon has a very high dielectric constant of 12 for such waveguides, which can also be used in the case of photonic crystals. Special photonic crystals, inserted with very low insertion loss at defined locations of the circuit, ensure the functioning of the circuit, for example as a computing circuit, it being possible for the entire circuit to be made very small. Thus, for example, 6 periods of the lattice of the photonic crystals with a lattice spacing of ⅓ of the wavelength are sufficient to achieve an attenuation of 35 dB.
One advantageous embodiment of the circuit according to the present invention is that the at least one photonic crystal is formed by needles having a high dielectric constant in the form of a two-dimensional periodic lattice with imperfections. However, it is also perfectly possible for the at least one photonic crystal to be formed by a body having a high dielectric constant with holes of low dielectric constant in the form of a two-dimensional periodic lattice with imperfections photonic crystals formed in this manner are described, for example, in German Patent No. 195 33 148.
Depending on the specific requirements, the needles may stand on the insulating layer, which is less thick in the region of the photonic crystal than under the waveguides, or the needles may stand on the silicon substrate.
An advantageous further development of the circuit according to the present invention is that the spaces between the needles are filled with non-linearly optical material, and that the refractive index of the non-linearly optical material is adjustable by a voltage applied to field electrodes. It is thus possible to control, for example, the behavior of filters designed as integrated optical circuits; See also German Patent No. 195 42 058.
In a further advantageous embodiment the needles or holes are at an angle with respect to the optical axis. This allows the branching of light in one part of the wavelength range into a further plane of the integrated optical circuit. An alternative thereto is provided by another embodiment of the present invention, in which the at least one photonic crystal, due to the arrangement of the imperfections, represents a branch filter in which branched-off light of a selected wavelength range escapes laterally. The laterally emerging light can be guided further in various manners.
In another example embodiment of the present invention, laterally emerging light of different wavelength ranges is capable of being focused on different locations of a parallel-extending photonic crystal. Thus, a plurality of computing planes can be connected in a simple manner.
REFERENCES:
patent: 6134369 (2000-10-01), Kurosawa
patent: 6175671 (2001-01-01), Roberts
patent: 6204952 (2001-03-01), Hinkov et al.
patent: 19526734-A1 (1997-01-01), None
patent: WO-95/30917 (1995-11-01), None
patent: WO-96/27225 (1996-09-01), None
Cheng et al; “Fabrication pf Photonic Band-Gap Crystals”; Journal of Vacuum Science and Technology; vol. 13, No. 6, 1995, pp. 2696-2700.*
Koops; “Photonic Crystals Built By Three-Dimensional Additive Lithography Enable Integrated Optics of High Density”, SPIE, vol. 2849, 1996; pp. 248-256.
Dultz Wolfgang
Koops Hans Wilfried
Deutsche Telekom AG
Kenyon & Kenyon
Ngo Hung N.
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