Optical waveguides – Planar optical waveguide
Reexamination Certificate
1998-10-30
2001-01-23
Healy, Brian (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S014000, C385S130000, C385S131000, C385S141000, C065S385000, C065S386000, C065S388000, C065S389000
Reexamination Certificate
active
06178281
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for the manufacture of optical components, at least one three-dimensional optical waveguide structure being produced in a light-sensitive substrate by locally subjecting the substrate to an exposure so that a difference in refractive index between the substrate and the at least one optical waveguide structure is created. The present invention also relates to an optical component.
BACKGROUND INFORMATION
Optical components having integrated optical waveguide structures are known. These optical waveguide structures possess a difference in refractive index as compared to the substrate surrounding them, so that they are suitable for guiding light waves. A conventional method is described, for example, in U.S. Pat. No. 5,136,677, in which the chalcogenide glasses are subjected locally to an exposure in order to produce the optical waveguide structure. An exposure occurs here in relatively thin substrates, in the light wave transmission direction of what will later be optical waveguide structures. It is also known from U.S. Pat. No. 5,136,677 that intersecting optical waveguide structures can be created in a substrate using two different light sources, and that the optical properties of the optical waveguide structures can be influenced using interference phenomena.
It is known, in order to allow the optical waveguide structures, once produced, to guide electromagnetic waves, for example light waves, that they must have a refractive index which is typically a few percent higher than the substrate surrounding the optical waveguide structure. In addition, the dimensions for the optical waveguide structures lying perpendicular to the light wave propagation direction must be selected so that they are on the order of the wavelength of the light to be guided, typically from 1 to 10 &mgr;m. Using the difference in refractive index between the optical waveguide structure and the substrate, and the dimensions of the optical waveguide structures, it is possible to establish the number of modes of light waves being transmitted for a given wavelength being guided. This defined refractive index difference, with the necessary small dimensions, can be achieved with the conventional methods for the manufacture of optical waveguide structures only at the cost of substantial losses.
The optical waveguide structures are usually produced in integrated optical components which are configured, for example, as amplifiers, splitters, couplers, multiplexers, or switches. For this purpose, optical fibers, for example glass fibers, which feed signals in and out are coupled to the optical waveguide structures in the optical components. The problem arises here that the glass fiber cross section must be coupled to the optical waveguide cross section. The effective cross section for common glass fibers is 5 to 10 &mgr;m. With integrated optical components, it is advisable to work with smaller cross sections, for example in order to increase the energy density in the optical waveguide structures or to spatially delimit light guidance so that the physical size of the integrated optical components can be reduced. Because of the difference in cross sections at the coupling point, attention must be paid to the numerical aperture, which describes the angular region from which an optical fiber can accept incident light. Light which is incident at a limit value greater than one corresponding to the numerical aperture cannot be guided, and is lost. On the other hand, the small cross section of the optical waveguide structures in the integrated optical components necessarily results in an increase in the numerical aperture, so that light signals sent out from the integrated optical components can be only partially transferred into the coupled glass fibers.
In order to mitigate this problem and the losses associated therewith, it is known to provide a so-called “taper” between the optical waveguide structures and the glass fibers, as a transitional structure. This is intended to effect a continuous transition for the effective cross sections of the glass fibers and the optical waveguide structures, and for the numerical aperture.
The taper can be only incompletely configured using the conventional manufacturing methods for optical waveguide structures, in which optical waveguide structures are produced in, for example, glass, polymer, or Ormocer substrates or in surface layers of silicon wafers using ion exchange, a local change in the stoichiometry of oxides or oxynitrides, or a local filling of etched or stamped valley structures. Because of the limited depth of the layer thickness, cross-sectional adaptation can be accomplished only by expanding the waveguide cross section while the depth remains the same. The refractive index is often defined by the material properties, and is therefore constant over the entire taper. The result can be that the taper becomes entirely or partially multimodal, i.e. that propagation directions which cannot be received by the adjacent optical waveguide or glass fibers become possible within it.
SUMMARY OF THE INVENTION
The method according to the present invention has an advantage that highly precise optical waveguide structures, configured in particular as tapers, with which optical waveguide structures and glass fibers can be coupled in low-loss fashion, can be created with simple technical means. Because an exposure occurs at least twice, at different angles of incidence for the light perpendicular to the light wave propagation direction of the optical waveguide structure, the substrate surrounding what will later be the optical waveguide structure experiences a diminution in refractive index, the optical waveguide structure being defined using a mask which preferably has a width which varies in the light wave propagation direction; as a result, three-dimensional optical waveguide structures can be achieved which have not only an expansion of the optical waveguide cross section but also an increasing depth. It is thereby possible, very advantageously, to create cross sections of optical waveguide structures, in the coupling region to glass fibers, with which it is possible to adapt the effective cross sections of the optical waveguide structures and the glass fibers.
A preferred exemplary embodiment of the present invention provides for the angles of incidence of the exposure in the light wave propagation direction to be variably adjustable. This allows a further optimization of the cross-sectional adaptation via the taper, for example by the fact that the latter has a cross section which is triangular when viewed in cross section and expands in trumpet-like manner from the optical waveguide structure toward the glass fiber.
In a further preferred exemplary embodiment of the present invention, provision is made for the mask to have, outside the optical waveguide structure, a transparency which varies in the light wave propagation direction. This advantageously makes it possible to vary the difference in refractive index between the optical waveguide structure and the substrate surrounding the optical waveguide structure in defined manner, so that, in particular in the case of an increase in the cross section of the optical waveguide structure, the difference in refractive index decreases in defined manner to ensure that the optical waveguide structure is monomodal in the light wave propagation direction as the cross section increases.
Provision is also made, in a preferred exemplary embodiment of the present invention, for the angle of incidence of the exposure to be established so as to result in buried optical waveguide structures. The result of this is that additional covering of the optical waveguide structure that is produced, to prevent external influences, is no longer necessary. The entire process for manufacturing the optical components having the optical waveguide structures is thereby simplified.
Provision is moreover made, in a preferred exemplary embodiment of the present invention, for the exposure to be accom
Blechschmidt Jörg
Graf J{umlaut over (u)}rgen
Loeffler Peter
Sautter Helmut
Schink Rainer
Healy Brian
Kenyon & Kenyon
Robert & Bosch GmbH
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