Note: Descriptions are shown in the official language in which they were submitted.
CA 02292143 2003-12-08
Power Amplifier for Amplifying a Laser Beam, Method for Producing it
and Use of the Power Amplifier
The invention relates to a power amplifier for amplifying a laser beam, a
method for producing the power amplifier, and use of the power amplifier.
In general, several meters of an optical amplifier fiber, i.e. a glass fiber,
are required for amplifying a laser beam by means of this amplifier fiber.
Conventionally, this amplifier fiber is arranged in the form of an air-cored
coil.
ft is known that the efficiency of a power amplifier can be increased in a
simple manner in that the amplifier fiber is arranged not along a straight
line,
but along a curved line, wherein the best results are obtained if the
curvature
changes along the fine both as to the degree as well as to the sign.
The arrangement of the amplifier fiber as a free coil has the
disadvantage, particularly when using the power amplifier in a vacuum, that
the removal of dissipated heat from the amplifier fiber which is generated,
for
example, as a result of pumped light because of power losses in the amplifier
fiber, is not assured to a satisfactory extent. The results of insufficient
heat
removal are an uneven temperature distribution and possibly overheating of
the amplifier fiber.
It is the objecfi of the invention to
- provide an improved power amplifier of the type mentioned at the
outset, which avoids the disadvantages of the prior art,
- disclose a method for producing such a power amplifier, and
- propose a use of such a power amplifier.
According to fihe present invention, there is provided a power amplifier for
amplifying a laser beam, having an amplifier fiber (10) arranged along a
curved line with a topically changing curvature, characterized in that:
- the power amplifier has a receiving body (12), in which the amplifier
fiber (10) is received,
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the amplifier fiber (10) is arranged on a surface (14) of the receiving body
(12), and
the receiving body (12) has a thermal conductivity for the removal of heat
being generated in the amplifier fiber.
According to the present invention, there is provided a method for
producing such a power amplifier, characterized in that a groove (16) is
created in the receiving body (12) by means of chemical, electro-erosive, or
by non-cutting or cutting mechanical processing.
According to the present invention, there is also provided a use of the
power amplifier in a mobile object, characterized in that the receiving body
(12) is made of a light material.
The following provides a non-restrictive outline of certain features of the
invention which are more fully described hereinafter.
With the power amplifier in accordance with the invention, the amplifier
fiber is not only supported at some points - as in conventional arrangements
-, but is arranged in a groove or recess in a receiving body made of a
material, whose heat conductivity assures a sufficient removal of the heat
being generated in the amplifier fiber. Thus, the amplifier fiber is
essentially
fixed in place over its entire length on or in the receiving body. This
fixation
of the amplifier fiber on or in the receiving body furthermore permits the use
of greater variations in the curvature of the amplifier fiber over a shorter
length than amplifier fibers which are free, or respectively are held only in
spots, and results in an increase in efficiency.
In order to assure perfect functioning of the power amplifier, it is
preferred to avoid the creation of differences in the heat expansion of the
amplifier fiber and the receiving body. For this purpose, materials will be
used for the amplifier fiber and the receiving body, whose coefficients of
heat
expansion are matched to each other.
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In an embodiment where materials with different heat expansion are used
for the amplifier fiber and the receiving body, it is necessary to take care
that
these different heat expansions do not lead to impermissibly great
mechanical stresses or even the breaking of the amplifier fiber. This can
occur if the amplifier is fixed in place over almost its entire length, but
has
zones free of fixation, in which it can move in relation to the receiving
body.
Another advantage of the novel arrangement is that, with a suitable
design and arrangement of the receiving body, the latter can simultaneously
be used as a shielding device against high-energy radiation, particularly for
the amplifier fiber.
With the novel power amplifier, the amplifier fiber is arranged on the
surface of the receiving body, generally in a groove or recess. The maximum
width and depth of the groove here is slightly greater than the diameter of
the
amplifier fiber.
The receiving body preferably has the shape of a plate or a dish.
As already mentioned, the efficiency of such power amplifiers can be
increased if the amplifier fiber is arranged in the form of a curved line,
preferably with a curvature which changes along the line both as to the
degree as well as to the sign. It is particularly advantageous to arrange the
amplifier fiber in a zig-zag shape, or in several approximately parallel
windings, for example in the shape of a spiral, kidney, lobe, dumbbell or
meander. Here, respectively two areas of the amplifier then are located
approximately parallel with each other.
With the arrangement of the amplifier fiber in a groove of the receiving
body and in the just mentioned shape with several windings, the respectively
approximately parallel extending adjoining groove sections, in which
appropriate areas of the amplifier fiber are arranged, are separated from
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each other by a dam, or respectively a wall, made from the material of the
receiving body. The dam is curved in a manner corresponding to the groove,
or respectively amplifier fiber. For fixing the amplifier fiber in place at a
first
groove point, the groove at a second groove point, namely at the point of the
next winding which adjoins the first groove point, is widened by a deformation
of the dam. Because of this, the first mentioned groove point is narrowed to
such an extent, that the amplifier fiber is fixed in place there. The
fastening,
or respectively fixation in place, of the amplifier fiber at further groove
points
takes place correspondingly.
For making the fixation of the amplifier fiber by means of deformation of
the dam in certain areas easier, in a preferred embodiment sifts, which are
provided transversely to the groove, are arranged in the receiving body, by
means of which the dam is divided into easily deformable tabs. These are
then bent in the slit direction in such a way that they cover one of the
adjoining groove sections and the amplifier fiber therein.
Another type of fixation of the amplifier fiber consists in designing the
cross section of the groove in such a way that, at a defined distance from the
groove entrance, it is narrower than at the groove entrance; a dovetail-like
cross section can be considered to be an example of such shaping. The
amplifier fiber is then introduced into the groove by an elastic deformation
of
the dam, or respectively of the wall, and subsequently held in place there.
The amplifier fiber can also be fixed in place on the receiving body by
means of an adhesive or lacquer.
With the method in accordance with the invention for producing a power
amplifier, in which the amplifier fiber is arranged in a groove or recess,
this
groove or recess can be produced by chemical, electra-erosive, or by non-
cutting or cutting mechanical processing.
CA 02292143 2003-12-08
Power amplifiers in accordance with the invention are often employed in
mobile apparatus, for example in terminals for optical data transmission in
space. In this case, the receiving bodies are produced in accordance with the
invention from a material which not only has great heat conductivity, but also
5 is comparatively light, for example of aluminum, an aluminum oxide,
aluminum nitride, beryllium oxide, boric nitride or copper-tungsten; suitable
plastic materials are also usable which, however, do not provide a shielding
effect and for this reason are not suitable in cases in which such a shielding
effect is necessary.
Further properties and advantages of the invention will be described
extensively in what follows by means of exemplary embodiments and with
reference to the drawings. Shown are in:
Fig. 1, portions of a receiving body with an amplifier fiber arranged
therein in a diagram,
Fig. 2, a top view on an amplifier fiber in a spiral-like arrangement,
Fig. 3, a top view on an amplifier fiber in a lobe-like arrangement,
Fig. 4, a top view on an amplifier fiber in a meander-like arrangement,
Fig. 5, a receiving body with a groove which does not change in height,
for receiving the amplifier fiber in a section transversely to the
longitudinal
direction of the groove,
Fig. 6, a receiving body with a groove which does change in height, for
receiving the amplifier fiber in a section transversely to the longitudinal
direction of the groove,
Fig. 7, a receiving body with an amplifier fiber fastened by means of an
adhesive on its surface in a section transversely to the longitudinal
direction
of the groove,
Fig. 8, a receiving body with portions of two windings of an amplifier fiber
received in adjoining sections of a groove in a view from above, and
Fig. 9, a receiving body with an amplifier fiber in a groove, wherein the
dam has been divided into tabs by means of slits.
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ft is pointed out here, that the drawing figures are not to scale, and that
statements, such as "above" and "below", relate to the arrangement in the
respective drawing figure.
Fig. 1 shows an amplifier fiber 10 intended for a power amplifier in
accordance with the invention, which is arranged in a plate-shaped receiving
body 12. The amplifier fiber 10 follows a zig-zag-shaped bent line, wherein
the curvature along the amplifier fiber 10 is not constant, but is changed -
for
increasing the efficiency of the power amplifier - both in the degree as well
as the sign. Here, the amplifier fiber 10 is located in a groove, not
represented in the surface 14 of the receiving body 12. However, it could
also be arranged on the surface 14 of the receiving body 12, or in the
interior
of the receiving body 12.
Figs. 2, 3 and 4 show amplifier fibers 10, whose topical course follows
other curved lines, respectively in several windings, than the amplifier fiber
represented in Fig. 1, namely, in accordance with Fig. 2, a spiral-like line,
in
accordance with Fig. 3, a lobe-like line, and in accordance with Fig. 4, a
meander-like line. The minimum curvature in each case must be of such a
size that any breaking danger of the amplifier fiber 10 is prevented. The
lines
can also be three-dimensional, which is advantageous in respect to
increasing the efficiency of the power amplifier, but considerably complicates
the arrangement in the receiving body.
Fig. 5 shows a receiving body 12 with a groove 16 for receiving the
cylindrical amplifier fiber 10. The groove 16 is intended to receive an
amplifier fiber which is arranged in a zig-zag-like manner, or respectively in
windings, and is not represented in Fig. 5; and is therefore also embodied in
a zig-zag-like manner, or respectively in windings. Groove sections 16.1,
16.2, 16.3, which adjoin in cross section, are separated by corresponding
wall, or respectively dam, sections 18.1, 18.2, 18.3 of a wall, or
respectively
dam 18, formed by the material of the receiving body 12. The groove 16 is
approximately square in cross section, wherein the lateral lengths a of the
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square are slightly larger than the diameter of the amplifier fiber to be
arranged in the groove 16. Fixation in place of the amplifier fiber in a
groove
16 of such a cross section is provided with the aid of a lacquer or adhesive
and/or by local deformation of the dam 18, such as is described further down
in connection with Fig. 8 and Fig. 9.
A further receiving body 12 with a further groove 14 is represented in Fig.
6. in contrast to the groove in accordance with Fig. 5, which over its height
has the same cross section, or respectively the same width a, the cross
section of the groove 16 in accordance with Fig. 6 is changed. Here, the
groove 1fi has an entry, whose width b is slightly less than the diameter of
the amplifier fiber to be arranged in it, but then widens at least to the
diameter of the amplification fiber to be arranged in it, and narrows again
farther down. Thus, this groove 16 has the approximate shape of a dovetail.
In its cross-sectional shape, the dam 18 is complementary to the groove 16.
Here, the introduction of the amplifier fiber into the groove 16 takes place
by
means of an elastic deformation of the dam 18; this deformation is made
easier by the reduced width c of the narrowest portion of the dam 18.
Following the introduction of the amplifier fiber into the groove 16, the dam
18 again assumes its original shape, so that the amplifier fiber cannot leave
the entry into the groove 16 again because of the reduced width b of the
latter.
Fig. 7 shows a receiving body 12 with an amplifier fiber 10 arranged on
its surface 14, but not in a groove, which is fixed in place by means of a
bead
20 of an adhesive or lacquer.
A receiving body is represented in portions in Fig. 8, which has a groove
16 and an amplifier fiber 10 arranged therein, wherein two groove sections
16.1, 18.2 of the groove 16 and two parts 10.1, 10.2 of the amplifier fiber 10
are arranged parallel. The groove sections 16.1, 16.2 are separated from
each other by an appropriate, also parallel, dam section of the dam 18. This
section of the dam 18 is deformed in four areas 19.1, 19.2, 19.3, 19.4.
CA 02292143 2003-12-08
Because of the deformed areas 19.1, 19.3 of the dam 18, a widening of the
groove section 16.2 results at two places, and simultaneously a narrowing of
the groove section 16.1 at adjoining points, so that a fixation in place of
the
part 10.1 of the amplifier fiber 10 takes place at the two fast mentioned
places. Correspondingly, a widening of the groove section 16.1, as well as a
narrowing of the groove section 16.2, at respectively two points results from
the deformed areas 19.2, 19.4 of the dam 18, and therefore a fixation in
place of the part 10.2 at these two last mentioned points.
Fig. 9 shows a receiving body 12 with a reinforcement fiber 10, which is
arranged in a groove 16. A section 18.1, or respectively 18.2 of the dam 18 is
located on each side of the groove 16. The dam 18 is divided into tabs 22 by
slits 24. The tabs 22 are deformed far fixing the amplifier fiber 10 in place
in
the groove 16 in such a way that the upper free edge area of the tabs 22
projects over the amplifier fiber 10. Only two of the tabs 22 are shown in the
representation in Fig. 9. It is easy to understand that the directions in
which
the deformation of the tabs takes place must be selected to be such that not
only the portions of the amplifier fiber 10 represented in Fig. 9, but also
the
portions thereof not represented are fixed in place.
The invention allows to produce a power amplifier, in which the amplifier
fiber is arranged in a groove or recess. This groove or recess can be
produced by chemical, electro-erosive; or by non-cutting or cutting
mechanical processing.
Power amplifiers in accordance with the invention are employed in mobile
apparatus, for example in terminals for optical data transmission in space. In
this case, the receiving bodies are produced from a material which not only
has great heat conductivity, but also is comparatively light, for example of
aluminum, an aluminum oxide, aluminum nitride, an aluminum alloy,
beryllium oxide, boric nitride or copper-tungsten. Suitable plastic materials
are also usable which, however, do not provide a shielding effect and for this
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reason are not suitable in cases in which such a shielding effect is
necessary.
