Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-03-25
2002-10-22
Parker, Kenneth (Department: 2877)
Optical waveguides
With optical coupler
Particular coupling structure
C385S016000, C385S052000
Reexamination Certificate
active
06470119
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical coupling means for coupling light between two waveguide end surfaces which are arranged opposite one another.
Coupling means of the named type are used to couple light supplied in an optical waveguide into another waveguide. An example is a coupling means for coupling light supplied in a strip-type waveguide, e.g. an optical fiber, into a strip-type or layer-type waveguide that is integrated on a substrate.
For example, the integrated waveguide can be a coupling-in waveguide of an optical multi-channel filter. An example of such a filter is a filter according to the phased-array design, with a coupling-in surface in the form of an end surface of the layer-type integrated input waveguide of this filter, through which light enters into the input waveguide at a particular geometrical position, whereby the geometrical position influences an output wavelength of the optical filter.
Such optical filters according to the phased-array principle are used in particular as multiplexers or demultiplexers in optical wavelength multiplex operation (WDM), since they comprise a low insertion damping and a high cross-talk suppression.
An optical filter according to the phased-array principle comprises, as an essential component, several optical waveguides of differing optical length that are coupled to the layer-type coupling-in waveguide and that run in a curved fashion, with the waveguides forming a phase-shifter arrangement. The layer-type coupling-in waveguide distributes the light onto the waveguides of differing optical length.
In WO 96/00915 A1 (GR 94 P 1417 DE), it is specified that the center wavelength of a phased-array filter can be determined by the position of the supplying waveguide, which conducts the light into the coupling-in waveguide of the filter. In this way, the center wavelength of this filter can be adjusted precisely by means of the geometrical positioning of the end surface of the supplying strip-type waveguide in relation to the end surface of the coupling-in waveguide of the filter.
After the adjustment of the center wavelength, the end surface of the supplying waveguide and the end surface of the coupling-in waveguide of the filter are fixed relative to one another, e.g. in that the supplying waveguide is glued fixedly to the substrate of the filter.
Given a conventional manner of construction of such a filter, the center wavelength and channel spacing are determined by the layout of the filter and by the process technology.
With respect to many applications, there is a need for a filter that can be tuned or matched. With such a filter, it is purposely possible to select one of several channels, or the center wavelength of a filter comb can be matched to the requirements of operation, in order for example to compensate for the ageing of transmitting lasers.
Apart from classical monochromators, piezo-controlled Fabry-Perot resonators are predominantly offered on the market as tunable or matchable optical filters. These are manufactured in a micromechanical construction, and are for this reason expensive and not suitable for mass production and application.
Mach-Zehnder interferometers can be tuned (see N. Nakato et al.: “128-Channel Polarisation-Intensive Frequency-Selection Switch using High-Silica Waveguides on Si,” IEEE Photonics Technology Letters 2, p. 441 (1990)), but are periodic filters. For narrow-band applications, a cascading of several such filters, matched to one another, is thus necessary. The matching of a filter constructed in this way thereby becomes very expensive, because for this purpose a corresponding number of control currents must be regulated.
Phased-array filters can in principle be tuned by modifying the optical path length in the individual waveguides of the phase-shifter region of this filter, e.g. by means of thermo-optical and/or electro-optical effects (see EP 0 662 621 A1 (GR 94 P 1013 DE)).
SUMMARY OF THE INVENTION
The invention is based on the object of providing optical multichannel filters, easily tuned, with a strip-type or layer-type coupling-in waveguide comprising an end surface, in particular phased-array filters.
Advantageously, with the inventive coupling means it is possible to adapt a particular output wavelength of the filter, e.g. the center wavelength of a filter comb, to the requirements of the operation, in order for example to compensate for the modification of the transmitting lasers.
A particular advantage of the invention is that not only such tunable optical multi-channel filters, including multi-channel filters according to the spectrograph principle, but rather also optical intensity modulators and waveguide switches, can be realized.
The shifting means of the inventive coupling means can advantageously be realized in miniaturized form, i.e. with dimensions that are on the order of magnitude of the dimensions of the waveguide end surfaces.
The inventive coupling means advantageously comprises a compact construction, and thus has sufficient stability to ensure that the adjustment of a strip-type waveguide is maintained in relation to the position of another waveguide, in particular of a layer-type waveguide, and no worsening of the insertion damping thereby takes place.
The inventive shift means is preferably and advantageously constructed in such a way that, relative to a support point that is fixed relative to one of the two end surfaces, the expansion element expands and/or contracts in a direction parallel to the one end surface, and thereby moves the other end surface relative to the fixed support point. A fixed reference point is thereby given to which the expansion and/or contraction are oriented. The end surface that is moved relative to the fixed support point can be the end surface of a waveguide in which the light is supplied to the coupling means, and/or the end surface of a waveguide in which the light is conducted away from the coupling means.
The other end surface is advantageously mounted in a mounting element that can be moved parallel to the one end surface, which element is connected fixedly with the expansion element. It is thereby advantageous for the mounting element and the expansion element to be constructed in one piece, since in this way the assembly expense is reduced.
Preferably and advantageously, the mounting element is made of a ceramic material, and comprises a continuous opening in which a waveguide comprising the other end surface is housed and fixed.
In order to prevent the mounting element from being able to oscillate about the support point with the expansion element, it is advantageous to provide a guide means for the linear guiding of the mounting element parallel to the one end surface. Such a guide means preferably comprises two glide surfaces positioned opposite one another and arranged fixedly relative to an end surface, between which the mounting element is arranged and along which the mounting element can be moved parallel to the one end surface.
In a preferred and advantageous embodiment of the inventive coupling means, the displacement means can be controlled externally. For this purpose, this embodiment is advantageously constructed in such a way that the displacement means comprises a control means with which the expansion and/or contraction of the expansion element can be controlled.
The coupling means that can be controlled in this way is preferably fashioned in such a way that the expansion element is made of piezoelectric material and the control means produces an electrical field that acts on the piezoelectric material with a field strength that can be modified in a controllable fashion, and/or in such a way that the expansion element is made of material with a thermal expansion coefficient, and the control means comprises a means for the controlled heating and/or cooling of the expansion element.
In a further preferred embodiment of a controllable coupling means, the displacement means comprises a positioning motor that is fixed relative to the one end surface, and comprises an expansion elem
Albrecht Helmut
Bayersdorfer Bernhard
Heise Gerhard
Michel Herbert
Reichelt Achim
Mooney Michael P.
Parker Kenneth
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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