Note: Descriptions are shown in the official language in which they were submitted.
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Description
Method for determining the eccentricity of a core of an
optical waveguide, as well as a method and apparatus
for connecting optical waveguides
The invention relates to a method for determination of
the eccentricity of a core of an optical waveguide. The
invention also relates to a method and to an apparatus
for connection of optical waveguides.
Prior Art
An optical waveguide normally comprises a glass fiber
with a core, and cladding surrounding the core. The
glass fiber has a higher refractive index within the
core than within the cladding. The refractive index
when plotted over the cross section of the glass fiber
may have a stepped profile or a gradient profile. In
the case of a stepped profile, the refractive index
within the core and that within the cladding each have
values which are independent of the location. There is
a sudden transition from one of the values to the other
at the boundary between the cladding and the core. In
the case of a gradient profile, the refractive index
decreases continuously from the inside outwards within
the core, but once again has a value that is
independent of the location within the cladding. The
values of the refractive index merge continuously into
one another at the boundary between the core and the
cladding.
The basic material of the core and of the cladding of
the glass fiber is normally silicon dioxide. The
refractive index of the core may be increased in
comparison to the refractive index of the cladding, for
example by doping of the silicon dioxide with
germanium. Alternatively, the refractive index of the
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cladding can be reduced in comparison to the refractive
index of the core, for example by doping of the silicon
dioxide with fluorine. Since the core is the optically
denser medium and the cladding is the optically thinner
medium, total internal reflection occurs for light
propagating virtually in the longitudinal direction of
the glass fiber, in a transitional area from the core
to the cladding. An optical signal can therefore be
carried in the core by multiple total internal
reflections on the cladding.
In order to protect the glass fiber, the optical
waveguide also contains a fiber coating surrounding the
glass fiber. Before two optical waveguides can be
welded to one another, this fiber coating must be
removed.
When connecting two optical waveguides, the important
factor is to create a junction point with as little
attenuation as possible. An optical signal passing from
the first to the second of the two optical waveguides
at the junction point should therefore lose as little
power as possible. Any lateral offset of the cores of
the two optical waveguides at the junction point leads
to undesirable attenuation of the optical signal. The
attenuation increases as the offset increases. In order
to produce a junction point with as little attenuation
as possible, the cores of the optical waveguides must
be aligned with respect to one another before or during
the connection process. However, since the cores do not
run centrally in the optical waveguide, the lateral
offset of the cores cannot be determined from the
lateral offset of the cladding of two glass fibers that
are to be connected. Various methods are known for
mutual alignment of the cores of two optical waveguides
that are to be connected. In one known method, the
optical waveguides are first of all joined together
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with a lateral offset at a junction point. The
attenuation of the light passing through the junction
point is then measured and the lateral offset of the
optical waveguides is varied until the attenuation
reaches a value which is as low as possible.
In a group of further methods which are known from the
prior art, the relative position of the cores is
determined directly by optical measurements.
In the document JP 55-096433, the optical waveguides
are illuminated with X-ray radiation. In the documents
US 4,690,493 and US 4,506,947, the optical waveguides
are each illuminated with ultraviolet radiation.
Germanium atoms embedded in the core are in this way
stimulated to emit visible florescent radiation, in
order to increase the refractive index. The optical
waveguide cores that have been made visible in this way
can be aligned by visual monitoring. In all of the
described methods, radiation which has no components in
the visible band is used to stimulate the florescence
of the cores.
In the document US 4,660,972, parallel light is passed
through the optical waveguides from two different
directions. Light entering at the edge of a core is
refracted towards the core, so that the edge of the
core can be seen as a dark contour in the light passing
through. Two adjacent images of the core are produced
on an observation screen, by means of two mirrors and a
beam splitter, from light beams passing through the
optical waveguides in two different directions. The
images of the cores are then aligned with one another
by continuous direct visual checking.
In the document US 4,067,651, a glass fiber is
illuminated with coherent light from a laser. Scattered
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light is produced by scattering of the light on the
glass fiber. The distribution of the refractive index
over the cross section of the glass fiber as defined by
a plane located transversely with respect to the
longitudinal direction of the glass fibers can be
determined from a measurement of the angular
distribution of the intensity of the scattered light on
this plane. However this method is associated with
considerable mathematical complexity.
In the documents JP 59-219707, JP 60-046509,
JP 60-085350, US 4,825,092, US 4,882,497 and
EP 0 256 539 light which has been refracted on optical
waveguides is in each case observed from at least one
direction. Structures produced by the cores in the
intensity distribution are resolved by means of
high-resolution optics. However, the glass fibers
themselves also act as optical lenses. In order to
obtain sharp imaging of the cores on the image plane of
the optics, the optical waveguides must therefore be
positioned relative to the optics such that the object
plane of the arrangement comprising the glass fibers
and optics passes through the cores. The optics must
therefore be focused as a function of the position of
the cores in the optical waveguides.
In the document DE 39 39 497 Al, optical waveguides to
be connected are illuminated with an arc and are caused
to emit light, with the cores in general emitting more
visible light than the cladding. Observation optics are
focused such that the cores are sharply imaged, and can
be aligned with respect to one another. This method is
also used in the documents EP 0 687 928 Al and
US 5,570,446. The cores must remain visible throughout
the entire adjustment process. The optical waveguides
must therefore be kept throughout the entire time
interval of the adjustment process at a temperature
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which is adequate to make the cores visible and to
produce the arc. However, if a temperature such as this
is maintained over a time interval of more than a
plurality of tenths of seconds, this results in
deformation of the optical waveguides, resulting in
increased attenuation. Welding of optical waveguides
using this method therefore requires the adjustment
process to be completed within a time interval of a
plurality of tenths of seconds, and at most within one
second. A correspondingly high computation power must
therefore be provided in a splicer which operates using
the conventional method.
General Description of the Invention
The object of the invention is to specify a method and
an apparatus for connecting optical waveguides, which
allow alignment and welding of optical wavcguide3
without any optical waveguide deformation that would
cause increased attenuation occurring.
According to some aspects of the invention, the object is
achieved by a method for determination of the eccentricity
of the core of an optical waveguide having the features
described herein, by a method for connection of at least
two optical waveguides having the features described
herein, and by an apparatus for connection of at least two
optical waveguides having the features described herein.
The method according to an aspect of the invention for
determining the eccentricity of the core comprises a plurality
of steps. An optical waveguide is provided which has a
core and cladding surrounding the core. In a first
step, a section of the optical waveguide is heated for
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a time interval that is defined in advance, such that a
first light beam is produced by emission of light from
the core and the cladding. A first intensity
distribution, which is caused by the first light beam,
is measured and stored. The position of the center
point of the core is determined from the stored first
intensity distribution. In a second step, the section
is illuminated with light, and a second light beam is
produced by partial refraction of the light on the core
and the cladding. A second intensity distribution,
which is caused by the second light beam, is measured
and stored. The position of the cladding is determined
from the stored second intensity distribution. The
eccentricity is found from the determined position of
the center point of the core and from the determined
position of the cladding, with the eccentricity
indicating the position of the core with respect to the
position of the cladding.
In the first step of the method, the optical waveguides
are thus subjected to a heat source in order to cause
them to emit visible light. Depending on the dopant
substances that are introduced, the core and the
cladding of an optical waveguide have different
emissivity. In general, the core emits more visible
light than the cladding. However, it is also possible
for the core to emit less light than the cladding. The
position of the core is determined from the measurement
of the intensity distribution of the emitted light. In
the second step, illumination is switched on in order
to illuminate the optical waveguide. The position of
the cladding is determined from the measurement of the
intensity distribution of the light passing through the
optical waveguide. The relative position of the core
with respect to the cladding, to be precise the
eccentricity, is determined from a combination of the
results of the two measurements. Using the information
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about the eccentricity, the optical waveguides can be
offset laterally with respect to one another before
connection and, if necessary, can also be rotated about
the longitudinal axis in order to compensate for the
offset of the cores of the two optical waveguides.
The second intensity distribution can be measured
before or after the first intensity distribution. The
second step can thus be carried out before or after the
first step. In the first step, the optical waveguide is
heated only for a few tenths of a second. The two steps
can be carried out within a relatively short time
interval. Only the data of the two intensity
distributions need be stored in this time interval. The
eccentricity can be determined at any time on the basis
of the stored intensity distributions.
An object plane which passes through the section of the
optical waveguide is preferably imaged on an image
plane, with the first intensity distribution and the
second intensity distribution preferably being measured
using the same object plane. The two intensity
distributions can therefore be measured using the same
detection apparatus. In particular, the focusing of the
detection apparatus is not changed between the
measurements.
The object plane can be chosen such that the core and
the cladding are imaged with sufficient clarity on the
image plane. However, since the optical waveguide
itself also acts as a lens, the cladding and the core
that is surrounded by the cladding can in general not
both be imaged with optimum clarity on the image plane.
However, since the eccentricity is defined by the
center points of the core and cladding, fuzzy imaging
of the boundaries of the core and cladding can be
accepted.
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The first intensity distribution and the second
intensity distribution are in each case measured by
recording the intensity values in the same area which
runs transversely with respect to the section of the
optical waveguide. An array of sensor elements for
recording of the intensity values is therefore arranged
at least along a line or curve, with the line or curve
running on a plane which is arranged transversely with
respect to the section of the optical waveguide.
The eccentricity is preferably determined by means of
the center points of the core and cladding. The
position of an intensity extreme is determined from the
first intensity distribution in order to define the
position of a core center point. In particular, the
position of the intensity extreme can be determined
from the position of two flanks. The positions of two
further flanks are determined from the second intensity
distribution, in order to define the position of a
cladding center point. The distance between the core
center point and the cladding center point is
determined in order to define any core eccentricity.
The position of the cladding center point is varied as
a function of the core eccentricity in order to move
the core center point to a previously defined position.
The eccentricity can also be determined with sufficient
accuracy by determination of the core and cladding
center points if the width of the intensity extreme of
the first intensity distribution is relatively high or
the gradient of the flanks of the first or of the
second intensity distribution is relatively shallow.
The intensity extreme of the core may be relatively
wide, particularly in the case of glass fibers with a
gradient profile. The determination of the eccentricity
makes it possible to define the position of the core
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center point via the position of the cladding center
point. The cladding center point can be positioned,
without having to supply heat to the optical waveguide,
in order to make the core visible.
The eccentricity of the core of an optical waveguide
can also be determined using an alternative method. The
position of a local extreme is determined from the
first intensity distribution in order to define the
position of a core center point. Instead of this, the
positions of two flanks can also be determined from the
first intensity distribution, in order to define the
position of the core center point. The position of a
flank is determined from the second intensity
distribution in order to define the position of a
cladding edge. The distance between the core center
point and the cladding edge is defined from the
position of the extreme or the positions of the two
flanks of the first intensity distribution, and the
position of the flank of the second intensity
distribution. The position of the cladding edge is
varied as a function of the distance in order to move
the core center point to a previously defined position.
The core eccentricity can be determined from the
positions of the core and cladding edge, and from the
diameter of the optical waveguide. Because of the
limited gradient of the flank of the second intensity
distribution, the position of the cladding edge is
defined only roughly. Nevertheless, the cladding edges
of two different optical waveguides for each of which
the position of the flank of the second intensity
distribution is known can be aligned relatively
accurately with respect to one another on the basis of
the two flanks.
The section of the optical waveguide is preferably
heated for only a short time interval, so that there is
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no deformation. If heat were to be supplied for more
than a few tenths of a second, this would result in
deformation of the glass fibers and diffusion of the
dopants that have been introduced, and therefore in
increased attenuation of optical signals. In
particular, the section of the optical waveguide can be
heated by production of an arc or a laser beam for a
time interval of a plurality of tenths of a second, but
for a maximum of one second. The precise value for the
time interval required to make the core visible is
dependent on the basic material and on the doping of
the glass fibers, as well as the thermal power that is
introduced. Only the first intensity distribution need
be recorded during that time interval. The second
intensity distribution can be recorded and the
intensity distributions can be evaluated in order to
determine the positions of the core and cladding, or
the eccentricity of the core, without any further heat
being supplied to that section.
The first and second intensity distributions are
preferably measured by recording intensity values in a
first area, with the first area extending in a first
direction transversely with respect to the longitudinal
axis of the section of the optical waveguide. Sensor
elements for recording of intensity values are thus
arranged at least along one line or curve which extends
in the first direction at a distance from that section
and transversely with respect to the longitudinal axis
of that section. The section of the optical waveguide
can be positioned with respect to the first direction
as a function of the intensity values recorded in the
first area.
The first and second intensity distributions are
preferably measured by in each case recording intensity
values in a second area, with the second area extending
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in a second direction transversely with respect to the
longitudinal axis of the section and transversely with
respect to the first area. Sensor elements for
recording of intensity values are therefore are also
arranged along a line or curve which extends in the
second direction, transversely with respect to the
longitudinal axis of the section, at a distance from
that section of the optical waveguide. The section of
the optical waveguide can be positioned with respect to
the second direction as a function of the intensity
values recorded in the second area.
By way of example, the first direction and the second
direction may be at right angles to one another.
However, the first direction and the second direction
may also include some other angle. Recording of
intensity values along the first direction and along
the second direction makes it possible to position the
section of the optical waveguide on a plane at right
angles to the longitudinal axis.
The intensity values are preferably recorded
simultaneously in the first area and in the second
area. However, the intensity values may also be
recorded in the first area first of all, and then in
the second area. Two appropriately arranged arrays of
sensor elements are required for simultaneous recording
of the intensity values in the first area and in the
second area. A single array of sensor elements is
sufficient for successive recording of the intensity
values in the first area and in the second area. The
array of sensor elements can be arranged in the first
area first of all, and then in the second area.
Alternatively, the light which is incident on the first
area can first of all be recorded with the aid of an
optical system which, for example, comprises a mirror
which can pivot, with the light which is incident on
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the second area then being guided to the array of
sensor elements. However, when the first intensity
distribution is measured successively in the first area
and then in the second area, the section of the optical
waveguide must be heated twice, successively.
The method according to an aspect of the invention for
connection of at least two optical waveguides is carried out
in a plurality of steps. At least two optical waveguides are
provided, which each have a core and cladding
surrounding the core. In a first step, sections of the
at least two optical waveguides are heated for a
limited time interval, such that first light beams are
produced, with one of the first light beams in each
case being produced by emission of light from the core
and the cladding of in each case one of the sections.
First intensity distributions are measured and stored,
with in each case one of the first intensity
distributions being produced by in each case one of the
first light beams. Respective positions of center
points of the cores of the at least two optical
waveguides are determined from the stored first
intensity distributions. In a second step, the sections
of the optical waveguides are illuminated with light
such that second light beams are produced, with in each
case one of the second light beams being produced by
partial refraction of the light on the core and on the
cladding of in each case one of the sections. Second
intensity distributions are measured and stored, with
in each case one of the second intensity distributions
being produced by in' each case one of the second light
beams. Respective positions of the cladding of the at
least two optical waveguides are determined from the
stored second intensity distributions. Any relative
eccentricity is determined from the determined
respective positions of the center points of the cores
of the at least two optical waveguides and the
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determined respective positions of the cladding on the
at least two optical waveguides, with the relative
eccentricity indicating any offset of the respective
cores with respect to any offset of a respective
cladding on the sections of the at least two optical
waveguides. The offset between the cladding on the
respective two sections is then set as a function of
the relative eccentricity, in order to define the
offset between the cores of the respective two
sections. The respective sections of the at least two
optical waveguides are then connected.
Thus, in the first step, the optical waveguides are
heated for a limited time interval, and the first
intensity distributions are measured. As soon as the
intensity values of the first intensity distributions
have been stored, the supply of heat is interrupted.
This makes it possible to avoid deformation of the
optical waveguides in the vicinity of the junction
point. In the second step, the sections of the optical
waveguides are illuminated, and the second intensity
distributions are measured. As soon as the intensity
values of the second intensity distribution have been
recorded, the illumination can also be switched off.
The relative eccentricity is given by the difference
between the offset of the cores, to be more precise the
offset of the core center points, and the offset of the
cladding, to be more precise the offset of the cladding
center points, and thus allows the offset of the cores
to be set via the offset of the cladding.
The position of a local extreme is preferably
determined from in each case one of the first intensity
distributions, in order to define the position of in
each case one core center point. The position of the
local extreme, for example, of an intensity peak, can
be determined in particular from the positions of two
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flanks. The positions of two further flanks are
determined from in each case one of the second
intensity distributions, in order to define the
position of in each case one cladding center point. In
order to define the relative eccentricity of in each
case two of the sections, a first offset is determined
between the core center points of the respective two of
the sections, a second offset is determined between the
cladding center points of the respective two of the
sections, and the difference between the first offset
and the second offset is formed. The offset of the
cladding center points is set in order to define the
offset of the core center points.
The flanks of the first and second intensity
distributions, which result from the edges of the cores
and cladding, in general have only a limited gradient
because of the unclear imaging of the optical
waveguides. The edges of the cores and cladding can
therefore not be defined very precisely. However, the
positions of the core and cladding center points can be
determined more reliably since a rising flank and a
falling flank are in each case arranged essentially
axially symmetrically about the position of a core or
cladding center point.
The in each case one first intensity distribution and
the in each case one second intensity distribution of
one of the sections are preferably measured by
recording intensity values in the same area, which
extends transversely with respect to one of the
sections. It is therefore possible to use the same
array of sensor elements in order to record the first
intensity distribution and the second intensity
distribution for in each case one of the sections.
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The first intensity distribution and the second
intensity distribution are preferably measured by
recording the intensity values in first areas, with in
each case one of the first areas receiving light from
one of the sections, and extending transversely with
respect to the longitudinal axis of that one of the
sections in a first direction. An array of sensor
elements for recording of the intensity values is
arranged at a distance from the optical waveguides, and
extends in a first direction transversely with respect
to the longitudinal axis of one of the sections.
The first intensity distributions and the second
intensity distributions are preferably measured by
recording intensity values in second areas, with in
each case one of the second areas receiving light from
one of the sections, extending transversely with
respect to the longitudinal axis of that one of the
sections, and extending in a second direction
transversely with respect to one of the first areas. An
array of sensor elements for recoding of the intensity
values is arranged at a distance from the optical
waveguides, and extends in a second direction
transversely with respect to the longitudinal axis of
one of the sections.
The first direction and the second direction may be at
right angles to one another, or may include some other
angle. Since the first intensity distribution and the
second intensity distribution are recorded for in each
case one of the sections in the first area and in the
second area, the positions of the core and of the
cladding can be defined on a plane which runs
transversely with respect to the longitudinal axis of
in each case one of the sections.
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The apparatus according to an aspect of the invention for
connection of at least two optical waveguides which each
have a core and cladding surrounding the core comprises a
plurality of components. A heat source is provided in
order to heat respective sections of the optical
waveguides and in order to produce first light beams,
which are in each case produced by emission of light
through the core and through the cladding on one of the
sections. A holding apparatus is provided in order to
fix the sections of the optical waveguides, with the
holding apparatus also being designed for positioning
of the sections. An illumination device is provided for
illumination of the sections of the optical waveguides
and in order to produce second light beams, which are
each produced by refraction of light on the core and
the cladding of one of the sections. A detection device
is provided in order to measure first intensity
distributions, which are produced by the first light
beams, and in order to measure second intensity
distributions, which are produced by the second light
beams. Furthermore, a memory unit is provided for
storage of the first and second intensity
distributions. A control device is provided in order to
control the holding apparatus, and is designed to set
an offset of the cladding as a function of the stored
first and second intensity distributions, in order to
produce a previously defined offset between the cores.
The apparatus according to an aspect of the invention is
therefore designed to determine a first intensity distribution
and a second intensity distribution in two successive
steps, and to position the ends of two optical
waveguides relative to one another as a function of the
first intensity distribution and the second intensity
distribution. The heat source supplies heat to the
optical waveguides only during the measurement of the
first intensity distribution. In contrast, the heat
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source is switched off during the measurement of the
second intensity distribution, during the evaluation of
the measurement results, and during the positioning of
the optical waveguides. The illumination device
illuminates the optical waveguides with visible light
during the measurement of the second intensity
distribution, and is switched off during the
measurement of the first intensity distribution. The
illumination device is preferably switched on during
the evaluation of the measurement results and the
positioning of the optical waveguides since the
cladding edges are preferably aligned by visual
inspection. However, fully automatic positioning, which
is carried out with the illumination device switched
off, is likewise feasible, on the basis of the
measurements of the first and second intensity
distributions. The measurement of the second intensity
distribution, the evaluation of the measurement results
and the positioning of the optical waveguides are
carried out without any thermal load on the optical
waveguides, because the heat source is switched off.
The requirements for the speed of evaluation and the
positioning speed for a splicer which contains the
apparatus according to the invention are
correspondingly reduced.
The heat source is preferably designed to produce an
arc. In particular, the heat source comprises welding
electrodes for production of the arc. The heat source
can therefore be used not only for production of the
first light beams but also for the welding of the
optical waveguides.
The holding apparatus is preferably designed for
positioning of the sections of the optical waveguides
in a longitudinal direction and in two lateral
directions. The longitudinal direction is defined by
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longitudinal axes of the optical waveguides to be
connected. The two lateral directions are oriented
transversely with respect to the longitudinal
direction, preferably at right angles to it, and
include any desired angle, but preferably 60 or 90 .
An appropriate number of actuators are provided in the
holding apparatus for the positioning of the end
sections in the three directions, and in this case the
actuators can be operated by the control device.
The detection device preferably has at least one
detection apparatus with imaging optics and with a
sensor which comprises an array of sensor elements. The
imaging optics have an object plane, which passes
through the sections of the optical waveguides, and an
image plane, which passes through the array of sensor
elements. The object plane is set such that the cores
and the cladding of the sections are imaged with
sufficient clarity on the image plane.
In general, it is not possible to completely clearly
image both the cores and the cladding. This is because
the optical waveguides themselves also act as lenses.
The beam path which describes the imaging of the
cladding depends only on the optical characteristics of
the imaging optics. The beam path which describes the
imaging of the core in contrast depends on the optical
characteristics of the imaging optics and on the
optical characteristics of the cladding, surrounding
the core, of the optical waveguide. Since there is no
need for completely clear imaging of the cores and of
the cladding for determination of the eccentricity or
of the relative eccentricity, the first intensity
distribution and the second intensity distribution can
be measured using the same setting for the object
plane, that is to say using the same imaging optics
focusing. It is advantageous to measure the first
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intensity distribution and the second intensity
distribution using the same focusing because, in this
case, the imaging characteristics, that is to say the
association between areas on the object plane and areas
on the image plane, are the same for both measurements.
The sensor preferably contains an array of sensor
elements arranged over an area, in order to record
intensity values of the first and second intensity
distributions. A longitudinal section through the
sections of the optical waveguides can be imaged on an
array such as this. The intensity values of the first
and second intensity distributions for in each case one
of the sections are determined using those sensor
elements which are arranged along a line running
transversely with respect to the longitudinal direction
of the section.
The sensor may also just contain an array, arranged in
the form of a line, of sensor elements for recording of
intensity values of the first and second intensity
distributions. One such sensor can record only
intensity values for a first or a second intensity
distribution relating to in each case one of the
sections. The first and second intensity distributions
of different sections must therefore be measured
successively.
The detection device preferably has at least two
detection apparatuses, each having one optical axis.
The optical axes of a first and second of the at least
two detection apparatuses are preferably oriented
transversely with respect to one another and
transversely with respect to the longitudinal axis of
the sections. The use of the at least two detection
apparatuses makes it possible to unambiguously define
the positions of the core and of the cladding on a
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plane running transversely with respect to the longitudinal axis.
The sections of the at least two optical waveguides are preferably
arranged in beam paths which each run between the light source of the
illumination
device and one of the at least two optical imaging systems. A dedicated light
source can be provided for each of the optical imaging systems. However, it is
also
possible to provide one illumination device with only one light source and a
corresponding number of mirrors for production of the desired beam paths.
According to one aspect of the present invention, there is provided a
method for determining the eccentricity of a core of an optical waveguide,
to comprising the following steps: providing an optical waveguide which has a
core
and a cladding surrounding the core; heating of a section of the optical
waveguide
for a predetermined time interval such that a first light beam is produced by
emission of light from the core and from the cladding; measuring a first
intensity
distribution, which is produced by the first light beam, and storing a
measurement
of the first intensity distribution; determining a position of a center point
of the core
from the stored first intensity distribution measurement; illuminating the
section with
light such that a second light beam is produced by partial refraction of the
light on
the core and the cladding; measuring a second intensity distribution which is
produced by the second light beam, and storing a measurement of the second
intensity distribution; determining a position of the cladding from the stored
second
intensity distribution measurement; and determining the eccentricity from the
determined position of the center point of the core and from the determined
position
of the cladding, with the eccentricity indicating the position of the core
with respect
to the position of the cladding.
According to another aspect of the present invention, there is provided
a method for connecting at least two optical waveguides, comprising the
following
steps: providing the at least two optical waveguides, respectively comprising
a core
and a cladding surrounding the core; heating of respective sections of the at
least
two optical waveguides for a limited time interval, such that first light
beams are
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produced, with one of the first light beams in each case being produced by
emission
of light from the core and the cladding of in each case one of the sections;
measuring first intensity distributions, with in each case one of the first
intensity
distributions being produced by in each case one of the first light beams and
storing
measurements of the first intensity distributions; determining respective
positions of
center points of the cores of the at least two optical waveguides from the
stored first
intensity distributions measurements; illuminating the sections of the optical
waveguides with light such that second light beams are produced, with in each
case
one of the second light beams being produced by partial refraction of the
light on
lo the core and on the cladding of in each case one of the sections; measuring
second
intensity distributions, with in each case one of the second intensity
distributions
being produced by in each case one of the second light beams, and storing
measurements of the second intensity distributions; determining respective
positions of the cladding of the at least two optical waveguides from the
stored
second intensity distributions measurements; determining a relative
eccentricity
from the determined respective positions of the center points of the cores of
the at
least two optical waveguides and the determined respective positions of the
cladding of the at least two optical waveguides, with the relative
eccentricity
indicating an offset of the respective cores with respect to an offset of the
respective
cladding of the sections of the at least two optical waveguides; subsequently
adjusting the offset of the respective cladding between the claddings as a
function
of the relative eccentricity in order to define the offset between the cores;
and
subsequently connecting the respective sections of the at least two optical
waveguides.
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Brief Description of the Figures
Figure 1 shows a refinement of the apparatus for
connection of two optical waveguides according to the
present invention.
Figure 2A shows an arrangement for recording of
intensity values of the first intensity distribution
according to one refinement of the present invention.
Figure 2B shows an arrangement for recording of
intensity values of the second intensity distribution
according to one refinement of the present invention.
Figure 3A shows a cross section through an optical
waveguide.
Figure 3B shows a longitudinal section through an
arrangement of two optical waveguides.
Figure 4A shows a first intensity distribution
determined using the method according to the invention.
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Figure 4B shows a second intensity distribution
determined using the method according to the invention.
Explanation of Exemplary Embodiments
Figure 1 shows one refinement of the apparatus for
connection of two optical waveguides. The figure shows
-a splicer for fusion welding of two optical waveguides.
Each of the optical waveguides 11 and 12 comprises a
glass fiber with a core and cladding surrounding the
core. The splicer comprises a holding apparatus, which
is designcd for fixing and positioning of the optical
waveguides 11 and 12, with the holders 51, 52 and 53.
The optical waveguides 11 and 12 which are inserted
into the holding apparatus have sections 110 and 120,
on which the glass fibers are exposed by removal of the
fiber coatings. The end areas 1101 and 1201 of the
sections 110 and 120 are arranged opposite one another.
The holders 51 and 52 each have V-shaped grooves, which
are used to secure the optical waveguides 11 and 12
against horizontal sliding. The holder 51 is designed
for positioning of the optical waveguide 11 in a
vertical lateral direction Y. The holder 52 is designed
for positioning of the optical waveguide 12 in a
horizontal lateral direction X. The holder 53 is
designed for positioning of the optical waveguide in a
longitudinal direction Z by movement along the groove
in the holder 52. The splicer also comprises a heat
source for heating of the respective sections 110 and
120. The heat source comprises two welding electrodes
21 and 22, which are arranged opposite one another, for
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production of an arc around the end areas 1101 and 1201
of the optical waveguides 11 and 12. The radiation
power of the arc is sufficient to weld the optical
waveguides. The splicer also comprises a detection
device with the detection apparatuses 31 and 32. Each
of the two detection apparatuses 31 and 32 is designed
to record first and second light beams, which originate
from the sections 110 and 120 of the optical waveguides
11 and 12. The splicer also comprises an illumination
device with light sources 41 and 42. The sections 110
and 120 are arranged in the beam paths between a
respective one of the light sources 41 and 42 and one
of the detection apparatuses 31 and 32. The splicer
furthermore comprises the control device 60 for
controlling the heat source, the illumination device,
the detection apparatus and the holding apparatus. The
control device 60 is designed for positioning of the
optical waveguides 11 and 12 as a function of intensity
distributions recorded by the detection apparatuses.
According to the invention, the control device is
designed to carry out a method having a plurality of
steps. In a first step, the heat source is switched on
for a short time interval. A voltage which leads to the
formation of an arc is therefore applied to the welding
electrodes 21 and 22. Dopants, for example, germanium
or fluorine, are incorporated in the glass fibers in
order to produce different refractive indexes in the
core and cladding. The emissivity also varies as a
function of the doping, so that the cores and cladding
of the glass fibers are caused to emit light to
different extents in the sections 110 and 120. At the
same time, the sections 110 and 120 are heated by the
radiation power of the arc. The arc is switched off
again after just a few tenths of a second, in order to
avoid deformation of the optical waveguides 11 and 12,
which would result in increased attenuation of optical
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signals. In the time interval in which the heat source
is switched on and the cores of the optical waveguides
are caused to emit visible light, first intensity
distributions of the light emitted from the cores and
cladding in the sections 110 and 120 are measured by
the two detection apparatuses 31 and 32, and are stored
in memory units 71 and 72.
In a second step, the illumination device is switched
on for a specific time interval. The light produced by
the light sources 41 and 42 is refracted on the cores
and cladding of the exposed glass fibers. While the
illumination device is switched on, the two detection
apparatuses 31 and 32 measure second intensity
distributions of the light which is partially refracted
by the cores and cladding on the sections 110 and 120,
and store them in the memory units 71 and 72.
In a third step, the successively measured and stored
first and second intensity distributions are evaluated,
and the cladding on the sections 110 and 120 is aligned
relative to one another in order to set an offset,
defined in advance, between the cores of the sections
110 and 120.
Figures 2A and 2B each show an arrangement for
recording of intensity values. The sections 110 and 120
are arranged on the object plane 3111 of the imaging
optics 311. The sensor 312 is arranged on the image
plane 3112 of the imaging optics 311. The imaging
optics 311 are shown in the form of a convex lens, but
may also comprise an arrangement of lenses and mirrors.
The object plane 3111 runs in the longitudinal
direction of the optical waveguide 11 or 12. The
imaging optics 311 image an area, in the form of a
line, of the object plane 3111 on an area, in the form
of a line, of the image plane 3112. Light beams from in
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each case one of the cross sections of the sections 110
and 120 are thus respectively imaged on an area, in the
form of a line, on the image plane 3112. The sensor 312
comprises a two-dimensional, that is to say area,
arrangement of sensor elements for recording of
intensity values. The sensor can thus record at least
the intensity values of light beams from first and
second cross sections of the sections 110 and 120. In
order to align the sections 110 and 120 with respect to
one another on the basis of the intensity values
recorded by the sensor 312, first and second intensity
distributions are measured for light beams from first
and second cross sections, with in each case one of the
first and second cross sections being arranged in a
respective one of the sections 110 and 120. A first and
a second intensity distribution are therefore in each
case measured for each of the two sections 110 and 120.
An offset of the cladding 112 and 122 on the optical
waveguides 11 and 12 is then set, in order to define an
offset of the cores 111 and 121.
Figure 2A shows a beam path for measurement of a first
intensity distribution. The object plane 3111 of the
imaging optics 311 passes through the cores 111 and 121
of the sections 110 and 120 which are heated by a heat
source and caused to emit light. First light beams Lll
and L12 originating from the cores 111 and 121 are
refracted only slightly because they strike the edges
of the cladding 112 and 122 virtually at right angles,
and, in consequence, they are focused on the image
plane 3112. Light which originates from areas of the
object plane 3111 located outside the core are in
contrast refracted to a greater extent by the edges of
the cladding 112 and 122, and are not focused on the
image plane 3112.
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Figure 2B shows a beam path for the measurement of a
second intensity distribution. The object plane 3111 of
the imaging optics 311 passes through the cladding 112
and 122 of the sections 110 and 120 illuminated by the
light source 41 or 42. Second light beams L21 and L22
originating from the edges of the cladding 112 and 122
are focused by the imaging optics 311 on the image
plane 3112. Light which is refracted by the sections
110 and 120 is not focused on the image plane 3112.
However, this light leads to central maxima in the
center of the second intensity distributions, whose
positions do not depend on the positions of the cores
111 and 121.
The focusing of the imaging optics 311 is not changed
between the measurement of the first intensity
distribution and the measurement of the second
intensity distribution. That is to say, since both
intensity distributions are based on the same imaging
of the object plane 3111 on the image plane 3112, it is
possible to associate spatially resolved structures
with one another in the two intensity distributions.
Figure 3A shows one of the optical waveguides 11 and 12
and one of the sections 110 and 120, in the form of a
cross section. A respective one of the cores 111 and
121 is surrounded by respective cladding 112 and 122. A
respective one of the cores 111 and 121 has one of the
core center points K1 and K2. A respective one of the
claddings 112 and 122 has one of the cladding center
points M1 and M2. The cores K1 and K2 have the
eccentricities or offsets El and E2 with respect to the
cladding Ml and M2. Respective coordinates for lower
core edges K11 and K21, upper core edges K12 and K22,
lower cladding edges M11 and M21 and upper cladding
edges M12 and M22 are illustrated with respect to a
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first direction X and a second direction Y on the
cross-sectional plane.
If the eccentricities El and E2 and the positions of
the cladding Ml and M2 are known, then the positions of
the cores K1 and K2 are defined. A respective one of
the eccentricities El and E2 can be determined from the
first and second intensity distributions for light
beams from a cross section of one of the sections 110
and 120.
The cores Kl and K2 can then be positioned via the
cladding Ml and M2.
Figure 3B shows a longitudinal section through the two
sections 110 and 120. The two sections 110 and 120 are
illustrated with a considerable offset in one of the
lateral directions X and Y. The eccentricities El and
E2 are given by the differences between in each case
one of the core center points K1 and K2 and the
corresponding one of the cladding center points Ml and
M2. The difference between the offset AK of the core
center points K1 and K2 and the offset AM of the
cladding center points M1 and M2 is the relative
eccentricity AE. If the relative eccentricity AE and
the offset of the cladding center points AM are known,
then the offset AK of the core center points K1 and K2
is defined. The relative eccentricity AE can be
determined from the first and second intensity
distributions of the two sections 110 and 120. An
offset AK of the cores Kl and K2 can then be defined
via the offset AM of the cladding Ml and M2. Instead of
the eccentricities, the distances Dl and D2 between in
each case one of the core center points K1 and K2 and
one of the cladding edges M11, M12, M21 and M22 can
also be used in order to align the cores 111 and 121
via the cladding edges M11, M12, M21 and M22.
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The sensors 311 and 312 illustrated in figures 2A and
2B are arranged in first and second areas B1 and B2,
which each extend the sections 110 and 120 over a
certain distance in the longitudinal direction Z and in
one of the lateral directions X and Y.
Figure 4A shows one of the first intensity
distributions Ill and 112. That one of the first
intensity distributions Ill and 112 is produced by a
first light beam from a cross section of one of the
sections 110 and 120. The first light beam is produced
by light which is emitted from one of the cores 111 and
121 and from the corresponding cladding 112 and 122 on
one of the sections 110 and 120. The light is caused to
be emitted by heat being supplied to the sections 110
and 120. That one of the first intensity distributions
Ill and 112 is plotted against one of the directions X
and Y. This results in the illustrated profile with a
central intensity peak KE1, which is bounded by two
flanks KF1 and KF2. The position of one of the core
center points Kl and K2 with respect to one of the
directions X and Y can be determined from the position
of the intensity peak KE1.
Figure 4B illustrates one of the second intensity
distributions 121 and 122. The one of the second
intensity distributions 121 and 122 is produced by a
second light beam from a cross section of one of the
sections 110 and 120. The second light beam is produced
by light which is produced by an illumination device
and is refracted on the sections 110 and 120, or passes
by at the side. The one of the second intensity
distributions 121 and 122 is plotted against one of the
directions X and Y. This results in the illustrated
profile with the two flanks MF1 and MF2. The position
of one of the cladding center points Ml and M2 with
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respect to one of the directions X and Y can be
determined from the position of the flanks MF1 and MF2.
The intensity peak R which is also illustrated in
Figure 4B is caused by scattered light from the
illumination device, which has entered the beam path of
the detection apparatus by being reflected on the glass
fibers. In the case of the apparatus used for this
graph, the directions X and Y include only an angle of
60 . The reflection is shifted towards the center if
the angle is 90 .
If the first intensity distributions Ill and 112 for
each of the two directions X and Y are known, it is
possible to define the positions of the core center
points K1 and K2 and their offset AK on the plane
covered by X and Y. If the second intensity
distributions 121 and 122 for each of the two
directions X and Y are known, the positions of the
cladding center points Ml and M2 and their offset AM
can be defined on the plane covered by X and Y. If the
first and second intensity distributions I11, 112, 121
and 122 for each of the two directions X and Y are
known, the eccentricities El and E2 and the relative
eccentricity AE can be defined. The relative
eccentricity AE is given by the difference between the
offset AK of the core center points K1 and K2 and the
offset AM of the cladding center points Ml and M2.
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In one possible variation of the method, the positions
of the cores 111 and 112 and of the cladding 112 and
122 can be determined from the first intensity
distributions. However, in general, the cladding is
illuminated less strongly than the core, so that the
position of a cladding edge can be determined with less
accuracy than the position of a core edge. Furthermore,
fluorescent impurities may be located on the surface of
the optical waveguide, and make it more difficult to
determine the position of the cladding edge.
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List of Reference Symbols
11,12 Optical waveguide
110,120 Sections of the optical waveguide
1101,1201 End surfaces of the sections
111,121 Cores of the glass fibers
112,122 Cladding of the glass fibers
21,22 Heat source, welding electrodes
31,32 Detection device, detection apparatuses
311 Imaging optics
313 Optical axis of a detection apparatus
3111 Object plane
3112 Image plane
312 Sensor
3121 Array of sensor elements
41,42 Illumination device, light sources
51,52,53 Holding apparatus, holders
60 Control device
71,72 Memory units
X,Y Lateral directions
Z Longitudinal direction
Lll, L12 First light beam
L21, L22 Second light beam
B1, B2 First and second areas
Iii, 112 First intensity distributions
121, 122 Second intensity distributions
K1, K2 Core center points
Kll, K21 Lower/left core edges
K12, K22 Upper/right core edges
M1, M2 Cladding center points
M11, M21 Lower/left cladding edges
M12, M22 Upper/right cladding edges
KE1 Intensity peaks of Ill and 112
KF1, KF2 Flanks produced by edges of the cores
MF1, MF2 Flanks produced by edges of the cladding
Dl, D2 Distance from the core center point to
the cladding edge
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R Reflection
