U.S. patent application number 14/361769 was filed with the patent office on 2014-10-09 for laser-based splicing of glass fibers onto optical components.
This patent application is currently assigned to Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.V.. The applicant listed for this patent is Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e. V.. Invention is credited to Steffen Bohme, Simone Fabian, Thomas Schreiber.
Application Number | 20140298864 14/361769 |
Document ID | / |
Family ID | 47429727 |
Filed Date | 2014-10-09 |
United States Patent
Application |
20140298864 |
Kind Code |
A1 |
Bohme; Steffen ; et
al. |
October 9, 2014 |
Laser-Based Splicing of Glass Fibers Onto Optical Components
Abstract
The invention relates to a method for laser-based splicing of a
glass fiber (1) onto an optical component (3), comprising the
following steps: arranging both surfaces to be spliced
substantially parallel to each other and at a predefined distance
from each other; and aiming a laser beam (4) at the optical
component (3). In order to specify an improved method in which the
properties of the joining partners are maintained to the greatest
extent during splicing, which exhibits high reproducibility and in
particular is suitable for splicing joining partners of different
cross-sections, the invention proposes that the angle of incidence
of the laser beam (4) on the surface of the optical component be
between 15.degree. and 45.degree..
Inventors: |
Bohme; Steffen; (Jena,
DE) ; Schreiber; Thomas; (Jena, DE) ; Fabian;
Simone; (Jena, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.
V. |
Munchen |
|
DE |
|
|
Assignee: |
Fraunhofer-Gesellschaft zur
Forderung der angewandten Forschung e.V.
Munchen
DE
|
Family ID: |
47429727 |
Appl. No.: |
14/361769 |
Filed: |
November 26, 2012 |
PCT Filed: |
November 26, 2012 |
PCT NO: |
PCT/EP2012/004875 |
371 Date: |
May 30, 2014 |
Current U.S.
Class: |
65/392 |
Current CPC
Class: |
G02B 6/32 20130101; G02B
6/255 20130101; G02B 6/2551 20130101 |
Class at
Publication: |
65/392 |
International
Class: |
G02B 6/255 20060101
G02B006/255 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2011 |
DE |
102011119713.7 |
Claims
1. Method for laser-based splicing of a glass fiber (1) onto an
optical component (3), comprising the following steps: arranging
both surfaces to be spliced substantially parallel to each other
and at a predefined distance from each other; and aiming a laser
beam (4) at the optical component (3), characterized in that the
angle of incidence of the laser beam (4) on the surface of the
optical component ranges between 10.degree. and 60.degree.,
preferably between 15.degree. and 45.degree..
2. Method according to claim 1, characterized in that the laser
beam (4) is polarized.
3. Method according to claim 1, characterized in that the distance
between the surfaces to be spliced and/or the angle of incidence of
the laser beam and/or the polarization of the laser beam are
harmonized to each other in such a manner that the laser beam
reflected from the surface of the optical component warms-up the
glass fiber surface to be spliced.
4. Method according to claim 1, characterized in that the laser
beam is generated by means of a CO.sub.2-laser source.
5. Method according to claim 1, characterized in that the laser
beam entirely or partly irradiates an annular zone on the surface
of the optical component (3).
6. Method according to claim 5, characterized in that the width
and/or diameter of the annular zone are varied during the splicing
procedure.
7. Method according to claim 5, characterized in that the diameter
of the annular zone is greater than the fiber diameter.
8. Method according to claim 1, characterized in that the laser
beam is not focused onto the surface of the optical component.
9. Method according to claim 1, characterized in that the
performance of the laser beam as a function of time is varied
during the splicing procedure.
10. Method according to claim 1, characterized in that the glass
fiber is manufactured from pure or endowed silica glass.
11. Method according to claim 1, characterized in that the glass
fiber is a photonic crystal fiber.
12. Method according to claim 1, characterized in that the glass
fiber, viewed in the fiber cross-section, is comprised of areas
having a different endowment.
13. Application of the method according to claim 1 for
confectioning of a glass fiber with a fiber plug.
14. Application of the method according to claim 1 for splicing of
a glass fiber onto an optical component of a fiber laser.
Description
[0001] The invention relates to a method for laser-based splicing
of a glass fiber onto an optical component, comprising the
following steps: [0002] arranging both surfaces to be spliced
substantially parallel to each other and at a predefined distance
from each other; and [0003] aiming a laser beam at the optical
component.
[0004] Splicing as joining method is particularly applied with
fibers and optical components utilized for the proliferation of
optical performances in a kW range (e.g. fiber laser).
[0005] Eligible as optical components, for example, are silica
glass end caps utilized for sealing and environmentally protecting
photonic crystal fibers (PCFs) in which light guidance is partly
accomplished through air ducts. In addition, the end caps provide a
possibility for functionalizing, e.g. an AR coating, or providing
the end cap with a spherical or aspheric surface, and at the same
time they can be utilized as holding or adjusting element. It is
possible that the end caps have a greater diameter than the fiber,
whereby the use of conventional splicing devices is not
feasible.
[0006] If joining partners with different cross-sections, specific
waveguide structures and/or different endowments, e.g. PCFs, are
connected mechanically stable and without losses in quality of
material, then a CO.sub.2 laser is preferably used as heat source.
The reason is that the laser wavelength of a CO.sub.2 laser is very
well absorbed by the materials of the joining partners (usually
silica glass). Moreover, contamination due to process gases or
sedimentation of electrode or wire material occurring in
conventional processes is thereby ruled out. And a quick change
between components to be differently spliced is also feasible, if
process parameters are already known, without requiring a change of
electrodes or gas nozzles, for example, which are subject to wear
and tear or without requiring a "running-in" of the process.
[0007] A method of this kind is disclosed, for example, in EP 1 128
960 B1 according to which the surface of an optical component is
irradiated with a laser beam having a nearly vertical angle of
incidence, and thus warmed-up.
[0008] But it has become evident that a method of this kind is not
suitable for splicing of special fibers, e.g. PCFs, as well as
fibers manufactured from different materials, e.g. Panda fibers and
passive/active single-mode fibers of low guidance, because often
much too high temperatures occur which destroy or adversely affect
the material structure of a special fiber.
[0009] During splicing of PCFs onto optical components, it is
required that the air ducts extend up to the splicing point and be
not destroyed, i.e. collapse, before in order to maintain the
optical properties.
[0010] For special fibers comprised of different or differently
endowed materials, however, it is important to maintain the
material properties during the splicing procedure that are
attributable to the different composition of the fiber. Too high
temperatures during splicing may entail diffusion or degassing
processes which adversely affect the optical properties of a
fiber.
[0011] Now, therefore, it is the object of the present invention to
specify a method improved versus state of the art, in which the
properties of the joining partners are maintained to the greatest
extent during splicing, which exhibits high reproducibility and in
particular is suitable for splicing joining partners of different
cross-sections.
[0012] This object is achieved by providing for an angle of
incidence of the laser beam onto the surface of the optical
component that ranges between 10.degree. and 60.degree., preferably
between 15.degree. and 45.degree..
[0013] The angle of incidence within the purport of the present
invention is the angle between the laser beam direction and the
surface normal of the optical component.
[0014] Within the purport of the present invention, the term "glass
fiber" not only covers a single optical fiber, but also a bundle of
fibers, the individual fibers of which are simultaneously to be
spliced onto the optical component.
[0015] By way of the present invention, it is achieved that only
part of the laser performance takes effect on the glass fiber
surface to be spliced, because only part of the laser energy, owing
to the Fresnel reflection, is reflected from the surface of the
optical component and can reach to the surface of the glass fiber.
By way of an appropriate choice of the distance between the surface
of the optical component and the glass fiber, the angle of
incidence of the laser beam and/or polarization of the laser
radiation, both surfaces can be brought to the optimal temperature
for splicing in a unique process step without exposing the surfaces
to an undesired and too high a thermal load. In particular, by way
of the present invention, selected areas of the glass fiber can
remain thermally unloaded to a great extent, even though the
distance between the glass fiber and the optical component is very
small. For example, only the material at the surface of the optical
component can be warmed-up until softening, whereas the surface of
the glass fiber is only warmed-up to the extent sufficient to
establish a stable splice connection, but without this leading to a
relevant softening of the material of the glass fiber. In this
case, the structure of the glass fiber is reliably maintained
during the splicing procedure.
[0016] It is also possible that the glass fiber already contacts
the optical component during splicing, i.e. that the distance
between the joining partners is zero, rather than bringing it in
contact with it only after reaching the splicing temperature as is
common practice.
[0017] A preferred embodiment of the method provides for generating
the laser beam with a CO.sub.2 laser source. The high absorption of
the CO.sub.2 laser wavelength by the joining partners causes
excellent incipient melting of the same. Besides, by way of an
appropriate choice of the laser performance, it is feasible to
control the temperature of the joining partners to be achieved
infinitely and very precisely which leads to very good and
reproducible results.
[0018] It is further preferred that the laser beam is configured as
an annular beam. Accordingly, the laser beam irradiates an annular
zone on the surface of the optical component. This annular zone can
be irradiated entirely. Likewise, it is possible to irradiate ring
segments only. This can be accomplished by means of appropriate
optics through beam forming. Alternatively, it is possible to guide
the laser beam continuously via the annular zone on the surface of
the optical component. Thereby, only an annular area at the surface
of the optical component is heated-up and reflected onto the
surface of the glass fiber, whereby the interior area of the glass
fiber is only slightly subjected to thermal loads, depending on set
laser performance, polarization, the angle of incidence of the
laser beam and on the distance of the joining partners. This is
advantageous especially for PCFs which often have an interior area
with air ducts so that a collapse of the inner structure during
splicing can be counteracted.
[0019] In particular it is possible to vary the shape and/or size
of the annular zone during the splicing procedure. This can be
accomplished by altering the focus of the laser radiation
(variation of the ring width). Likewise, laser optics and the
optical component can be moved relatively towards each other.
Without changing the angle of incidence, the diameter of the
annular zone will thus change. This variation serves for a
selective (timed) temperature control at the surfaces of the
joining partners during the splicing procedure.
[0020] In a preferred practical example of the present invention,
the diameter of the annular zone is greater than the diameter of
the glass fiber. Thereby it can be achieved that the surface of the
optical component is more strongly heated-up for the purpose of
softening, whereas the glass fiber is only slightly warmed-up in
order to establish a stable splice connection. The glass fiber is
not hit directly by the laser radiation, and an undesired adverse
impact on the glass fiber due to thermal load is avoided.
[0021] In a still further preferred embodiment, the laser beam is
not focused onto the surface of the optical component so as to be
able to accomplish a more homogeneous incipient melting of the
surface of the optical component over a wider area. Furthermore, it
is thus made possible to reduce the portion of laser radiation
reflected to the surface of the glass fiber. In this manner, by way
of appropriately adjusting the laser performance, angle of
incidence, and focusing the laser beam as well as the distance
between the joining partners, it is possible to control thermal
load of the surface of the glass fiber virtually independent of
that of the optical component.
[0022] With a preferred configuration of the inventive method, the
performance of the laser beam as a function of time is varied
during the splicing procedure. For example, the laser performance
is initially increased continuously from a start value up to a
finish level. And then, the warmed-up and/or incipiently molten
surfaces of the joining partners are brought into contact with each
other to establish the splice connection. Upon establishing the
connection, the performance of the laser beam as a function of time
can be continuously decreased. A slow "ramping-up" of the laser
performance can be utilized for a gentle warm-up of the joining
partners in the area of the splice point. Likewise, a steady
reduction in laser performance takes the effect that undesired
material strains and stresses as well as relevant mechanical
deformation which would adversely affect the quality of the optical
connection are avoided in the area of the finished splice.
[0023] The inventive method is especially suitable for splicing of
special fibers, e.g. PCFs, as well as fibers made of different
materials or having differently endowed areas, e.g. Panda fibers or
passive/active single-mode fibers of low guidance. The inventive
method ensures that the material structure of special fibers is not
destroyed or adversely affected during splicing.
[0024] The invention is described now on the basis of a preferred
practical example, where:
[0025] FIG. 1 shows a schematic side view of two joining
partners.
[0026] FIG. 1 schematically shows a glass fiber 1 having a surface
2 to be spliced. Located in an arrangement facing the surface 2 to
be spliced is an optical component 3. Glass fiber 1 and optical
component 3 are manufactured from silica glass. In FIG. 1, for
example, an end cap splice is produced at a PCF.
[0027] The surface 2 to be spliced is arranged substantially
parallel to the surface of the optical component 3 and at a
distance from it.
[0028] A laser beam 4 is aimed at the section of the surface of the
optical component 3 which is to be connected with the glass fiber
1, and it has an angle of incidence .alpha. which should range
between 15.degree. and 45.degree..
[0029] The laser beam 4 is a laser beam formed as an annular beam
from a CO.sub.2 laser source not shown here, which for the sake of
clarity is only represented schematically by the dashed lines
designated with number 4. Radiation 4 in this practical example has
a cone shell shape which is generated either by beam forming by
means of suitable optical components or by continuous deflection of
the laser beam 4. The laser beam 4 irradiates an annular zone 5,
the diameter of which is greater than that of glass fiber 1. Glass
fiber 1 is not hit directly by the laser beam 4.
[0030] As one may recognize in FIG. 1, the laser beam is not
focused onto the surface of the optical component 3. The slightly
divergent bundle of beams of the laser beam 4 hits onto the surface
of the optical component 3 and there it irradiates the annular zone
5 which on account of defocusing has a corresponding width.
[0031] The surface of the optical component 3 is heated by the
laser radiation 4 up to the softening of the material.
[0032] Part of the laser beam 4, dependent upon laser beam focusing
and angle of incidence .alpha., is reflected from the surface of
the optical component 3 and directed to the surface 2 of glass
fiber 1 where it causes a warm-up of glass fiber 1 without this
leading to a softening and thus to a destruction of the structure
of glass fiber 1. However, warming-up the fiber 1 is required to
ensure a stable splice connection.
[0033] When the glass fiber 1 and the optical component 3 have
reached the relevant desired temperature, they are brought into
contact in order to establish the splice connection (not shown
here).
* * * * *