Note: Descriptions are shown in the official language in which they were submitted.
CA 02379417 2002-O1-15
Description
Optical coupling device
The invention relates to an optical coupling
device for injecting light between two optical-
waveguide end faces, it being possible to vary the
geometrical position of the one optical-waveguide end
face, for example, an optical fiber, with respect to
the other optical-waveguide end face, for example a
fiber-optic chip, with the aid of a variable-length
element which, via a holding device, carries the one of
the two optical waveguides, and is fastened to the
other optical waveguide through two holding blocks.
An optical coupling device is known, for
example, from WO 98/13718. Such coupling devices are
used in optical filters according to the phased-array
principle with an injection face, which light enters at
a specific geometrical position, the geometrical
position influencing the output wavelength of the
optical filter. Optical filters according to the
phased-array principle are used, in particular, as
multiplexers or demultiplexers in optical wavelength-
multiplex operation (WDM), since they have a low input
attenuation and high crosstalk suppression. The optical
filter has, as its essential component, a plurality of
curved optical waveguides of different length, which
form a phase-shifter region.
German Patent Application DE 44 22 651.9
describes that the central wavelength of a phased-array
filter can be established through the position of an
injection optical waveguide, which guides the light
into the optical waveguide. In this way, the central
wavelength of the optical filter can be adjusted
accurately through the geometrical positioning of the
injection optical waveguide or the injection fiber.
Since it is therefore desirable for the optical
waveguides to be shifted reJ.ative to one another, the
optical waveguides cannot be adhesively bonded directly
to one another.
In the optical coupling device cited in the
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introduction, the holding blocks are fastened to the
chip, and the optical fiber is held on the variable-
length element. In this case, the variable-length
element may oscillate or bend, which causes temporary
or permanent deadjustment of the fiber, even though a
certain degree of guiding is provided.
It is therefore an object of the invention to
ensure improved guiding of the variable-length element
parallel to its extension direction and to avoid
deadjustment during operation.
To achieve this object, the optical coupling
device mentioned in the introduction is characterized
in that the variable-length element, or the holding
device, is held by a spring element, which is spongily
or porously designed and which is supported directly or
indirectly on at least one of the holding blocks and
allows movements of the variable-length element, or the
holding device, in the length direction of the
variable-length element, in which the variable-length
element is extended or shortened, and prevents movement
of the variable-length element perpendicular to the
length direction of the variable-length element. The
variable-length element, which is necessarily fastened
further away to the other optical waveguide, that is to
say the chip, presses against the holding device for
the fiber, in order to permit the relative movement of
the f fiber with respect to the chip . The spring element
is configured in such a way that residual movement
perpendicular to the plane is maximally suppressed. The
effect achieved by this is that the movement of the
fiber relative to the chip takes place very exactly
parallel to the chip face and virtually no deadjustment
perpendicular thereto occurs.
Since the spring element is spongily or
porously designed and the wall thickness of the spring
element is hence reduced in comparison with the wall
thickness of the solid material, the desired elasticity
or spring characteristic is imparted to the spring
element. Through selection of the ratio between the
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remaining wall thickness and the hole size, it is
advantageously possible to vary the elasticity in wide
ranges.
In the invention, it is furthermore
advantageous that the holding block can be adhesively
bonded to the second optical waveguide (optical-
waveguide chip) very close to the fiber, so that large
levers are avoided. Undesired movements in the
directions perpendicular to the desired extension of
the variable-length element are thereby reduced
significantly.
An advantageous configuration of the device
according to the invention is characterized in that the
variable-length element, the holding device and the
spring element are arranged between the two holding
blocks, and in that the holding device is designed
integrally with the variable-length element and the
spring element is designed separately therefrom. In
this case, it is advantageous that the material of the
spring element can be selected without having to take
into account the requirements placed on the material of
the variable-length element.
Another advantageous configuration of the
device according to the invention is characterized in
that the variable-length element, the holding device
and the spring element are arranged between the two
holding blocks, and in that the holding device, the
variable-length element and the spring element are
designed integrally. This configuration has production-
technology advantages and also has advantages relating
to the operational reliability and the life of the
arrangement.
Another advantageous configuration of the
device according to the invention is characterized in
that the variable-length element, the holding device
and the spring element are arranged between the two
holding blocks, and in that the holding device and the
spring element are designed integrally and the
variable-length element is designed separately
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therefrom. Here again, it is possible to produce the
holding devices and the spring element without having
to pay attention to the material of the variable-length
element.
Another advantageous configuration of the
device according to the invention is characterized in
that the variable-length element, the holding device
and the spring element are arranged between the two
holding blocks, and in that the holding device, the
spring element and the holding block connected thereto
are designed integrally and the variable-length element
is designed separately therefrom.
Another advantageous configuration of the
device according to the invention is characterized in
that the spring element is formed by slots in the
variable-length element, or the holding device, which
lie in a plane parallel to the end faces and
perpendicular to the length direction of the variable-
length element. These slots can be employed
particularly advantageously whenever the variable-
length element, the holding device and the spring
element, or alternatively at least the holding device
and the spring element, are designed integrally with
one another. The direction of the slots is also
advantageous since, if the slots are rotated through
90°, for example, stability in the critical direction
perpendicular to the chip plane is no longer
sufficiently guaranteed.
Another advantageous configuration of the
device according to the invention is characterized in
that an even number of slots are provided. Tilting
tendencies can thereby be minimized.
Another advantageous configuration of the
device according to the invention is characterized in
that the spring element is formed by bores in the
variable-length element, or the holding device, which
lie in a plane parallel to the end faces and
perpendicular to the length direction of the variable-
length element. Such bores are easy to machine-produce,
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it being possible to set the spring constant of the
spring element through the size of the bores.
Another advantageous configuration of the
device according to the invention is characterized in
that the length of the variable-length element is
selected in such a way that the spring element is under
prestress in the starting position of the variable-
length element. This guarantees that, if it is designed
separately from the variable-length element, the
holding device follows the variable-length element when
the latter contracts.
Another advantageous configuration of the
device according to the invention is characterized in
that the two holding blocks are connected to one
another by a link, the arrangement. consisting of the
two holding blocks, the variable-length element, the
holding device and the spring element being provided
with greater stability.
Another advantageous configuration of the
device according to the invention is characterized in
that the two holding blocks are connected to one
another by a frame, a respective link being provided at
the top and at the bottom between the two holding
blocks, and the links being produced in one piece with
the holding blocks, so that they can be adhesively
bonded with the latter to the chip.
Lastly, another advantageous configuration of
the device according to the invention is characterized
in that the holding device has a ferrule in which the
optical waveguide, or the optical fiber, is fastened.
It would admittedly also be possible to fasten the
fiber to the resilient element without a ferrule, for
example by adhesive bonding in a V-groove.
Nevertheless, it is preferable to use a ferrule owing
to the accuracy of the fit and the avoidance of aging
phenomena in the adhesive for adhesively bonding the
fiber in the V-groove.
An exemplary embodiment of the invention will
be described with the aid of the appended drawing,
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which shows a side view of the exemplary embodiment of
the coupling device according to the invention.
The figure shows a side view of a coupling
device according to an exemplary embodiment of the
invention, in which two holding blocks 4, 6 are
fastened, for example adhesively bonded, on an optical-
waveguide chip 2. One of the holding blocks 4 carries a
variable-length element 8. A fiber 10 is fastened to a
holding device 12. The variable-length element 8 is
clamped or adhesively bonded between the one holding
block 4 and a holding part 12 for the fiber 10.
The variable-length element 8, or the holding
part 12, is supported on the holding block 6 via a
spring element 14. The spring element is formed by
outer slots 16 and inner slots 18. The slots 16, 18 can
also be replaced by bores. In the vicinity of the
spring element 14, the material may also be spongily or
porously designed.
For the spring element 14, it is only necessary
for the wall thickness of the spring element to be
reduced in comparison with the wall thickness of the
solid material, in order to impart the desired
elasticity or spring characteristic to the spring
element 14. Through selection of the ratio between the
remaining wall thickness and the hole size, it is
possible to vary the elasticity in wide ranges.
In the exemplary embodiment that is shown, the
two holding blocks 4, 6 are connected to one another
via a link 20, which lies in the plane of the fiber-
optic chip 2. The two holding blocks 4, 6 can also be
connected to one another via a frame, which stands
perpendicular to the face of the fiber-optic chip 2,
which ensures that the coupling device overall is
stabilized. In this exemplary embodiment, the links can
be produced in one piece or adhesively bonded to one
another.
