Apparatus and method for bonding optical elements by non-contact soldering

The present invention relates to bonding of optical elements such as an optical waveguide, an optical collimator, an optical attenuator, an optical isolator, etc., and in particular, to an apparatus and method for bonding the optical elements by non-contact soldering to prevent moisture from penetrate into inside the optical elements by performing soldering without being in direct contact with a bonding portion of optical elements and by sealing up completely a gap formed in the bonding portion between the housings during packaging or bonding optical elements. The apparatus for bonding optical elements comprising: at least two optical elements, an inside of which being provided with optical systems while an outside of which being surrounded by housings; alignment apparatus which fixes one end of the each optical element and aligns optical system of the optical elements; laser light sources disposed respectively at both end of the housings, illuminating the laser beams such that the beams are not focused on outer surface of the housings; lead-supplying units disposed respectively at both upper end of the laser light sources, supplying the lead on the laser beams; and a controller for controlling the laser light sources and the lead supplying units.

CLAIM OF PRIORITY 
This application makes reference to, incorporates the same herein, and 
claims all benefits accruing under 35 U.S.C .sctn.119 from an application 
entitled Apparatus And Method For Bonding Optical Elements By Non-Contact 
Soldering earlier filed in the Korean Industrial Property Office on Aug. 
28, 1997, and there duly assigned Serial No. 97-41906 by that Office. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to bonding of optical elements such as an 
optical waveguide, an optical collimator, an optical attenuator, an 
optical isolator, etc., and in particular, to an apparatus and method for 
bonding the optical elements by non-contact soldering. 
2. Description of the Related Art 
There are several known methods of soldering electronic devices and optical 
elements. A first method is to heat a portion to be bonded by means of an 
electric iron and then supply lead. A second method is to place a 
high-frequency induction heater around the optical elements and apply 
constant heat to the portion to be bonded by high-frequency heating. A 
third method is to perform soldering by using a laser light source as a 
heat source, which is available where the electric iron cannot be used due 
to the high packaging density or there is mass production due to many 
portions to be bonded, as shown, for example, in U.S. Pat. No. 4,963,714 
to Joseph R. Adamski et al. entitled Diode Laser Soldering System. Lastly, 
a fourth method, which is available where there are many different 
portions to be bonded, is to apply heat to the portions to bonded by 
changing a light path using a prism. Here, the lead used in the first and 
second methods is in the form of a wire. The third and fourth methods, 
however, utilize lead powder plastered around the portions to be bonded. 
The soldering processes according to the known methods are frequently 
applied to electronic devices. However, in order to apply such a soldering 
process to optical devices, the following should be considered: 
(1) A possible contact during application of the heat to the bonding 
portions may affect the alignment of the optical elements; 
(2) Bonding portions of the optical elements should be kept symmetric to 
prevent misalignment of the optical elements due to thermal expansion; 
(3) Heat should be uniformly applied to symmetrical bonding portions to 
prevent misalignment of the optical elements; 
(4) The bonding portions should be filled completely with lead to secure 
reliability of the optical elements; and 
(5) Reproducibility and mass production of the optical elements should be 
guaranteed. 
My examination of weak points in connection with the respective soldering 
methods mentioned above based on the foregoing considerations shows that 
neither the first nor second soldering methods meet all of the foregoing 
five points of consideration. Regarding the third soldering method, while 
meeting symmetry of optical elements arranged in a plane, it does not meet 
the foregoing considerations as to symmetry in three-dimensional space. 
Regarding the forth soldering method, while making connection of desired 
portions possible, it cannot secure the symmetry. 
In short, though very useful to the electronic devices, the conventional 
soldering methods are not suitable for optical elements due to the 
misalignment problem. That is to say, during application of heat to the 
bonding portions, if the lead contacts the surface of the bonding 
portions, the optical elements may be misaligned. Further, the laser beam 
applied to the bonding portions of the optical elements cannot be kept 
symmetric, which causes the misalignment of the optical elements due to 
the thermal expansion and non-uniform distribution of heat. As a result, 
the properties of the optical elements are affected, thus lowering 
reliability of the products. In addition, the reproducibility and mass 
production of the optical elements are also lowered. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide an apparatus 
and method for bonding optical elements by non-contact soldering, in which 
the interior of the bonding portions of the optical elements is sealed up 
completely to prevent moisture from penetrating into the optical elements. 
Another object of the present invention is to provide an apparatus and 
method for bonding optical elements by non-contact soldering, capable of 
minimizing property variations of the optical elements. 
To achieve the foregoing objects, an apparatus for bonding optical elements 
according to the present invention comprises: a couple of optical elements 
having optical systems therein and which is surrounded by housings; an 
alignment apparatus which fixes one end of the each optical element and 
aligns the optical systems of the optical elements; laser light sources 
arranged respectively at predetermined ends of the housings for 
illuminating a laser beam such that the beam is not focused on the outer 
surface of the housings; lead-supplying units arranged respectively at the 
upper ends of the laser light sources for supplying the lead on the laser 
beam; and programmable logic control (PLC) which auto-controls the laser 
light sources and the lead supplying units. 
To achieve the foregoing objects, a method for bonding optical elements 
according to the present invention comprises steps of: fixing a couple of 
optical elements to an alignment apparatus for aligning the optical 
systems of the optical elements; illuminating laser beams from plural 
laser light sources such that the beams are not in contact with 
cross-sections of bonding portions of the optical elements which are 
arranged between housings of the optical elements; after a predetermined 
time, supplying lead from lead supplying units on the laser beams; 
dissolving the lead by the laser beams so that the lead flows into gaps 
formed in bonding sections between the housings; after a predetermined 
time, breaking off a driving force of the lead supplying units under 
auto-control of a programmable logic control (PLC); and, after a 
predetermined time, breaking off the laser beams under control of the PLC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 the apparatus for bonding optical elements 
according to a preferred embodiment of the present invention includes 
optical elements 26 and 28 with various built-in optical systems, 
alignment apparatus 22 and 24 for the optical elements, continuously 
operable laser light sources 10a and 10b, lead-supplying units 14a and 
14b, and lead 16a and 16b. Further, a housing 30 for protecting the 
optical system from the ambient environment is provided at the outer 
circumference of optical element 26. Likewise, a housing 32 is provided at 
the outer circumference of optical element 28. Through (via) holes 34 are 
formed symmetrically on both sides of housing 32, and the lead 16a and 16b 
for fixing housings 30 and 32 are input through via holes 34, while one 
end of optical element 26 is fixed to alignment apparatus 22 and one end 
of the optical element 28 is fixed to alignment apparatus 24. 
The continuously operable laser light sources 10a and 10b are arranged at 
both sides of the optical elements 26 and 28 with a predetermined spacing. 
Laser light sources 10a and 10b illuminate laser beams 12a and 12b, 
respectively, such that the foci of the laser beams 12a and 12b are not in 
contact with outer surface of the housing 32, to apply heat to a bonding 
portion 40 (see FIGS. 2 and 3 for more detail on bonding portion 40) and 
dissolve lead 16a and 16b, thereby making optical elements 26 and 28 
fixed. A diameter of the foci 20a and 20b of the beams 12a and 12b 
illuminated from the laser light sources 10a and 10b is about 0.5 
mm.about.3 mm, and an electric power of the beam illuminated from the 
laser light sources 10a and 10b is about 15 W.about.40 W. Lead-supplying 
units 14a and 14b, supplying lead 16a and 16b which are in the form of 
wire, are arranged at the upper end of the each laser light source 10a and 
10b. Lead-supplying units 14a and 14b supply lead 16a and 16b on laser 
beams 12a and 12b. Here the term "on laser beams" is defined as supplying 
lead, in the form of a thin wire from nozzles of the lead supplying units 
at a speed and amount controlled by a programmable logic control based on 
the size of the bonding portion, in contact with the laser beam until it 
reaches the point of focus of the laser beam so that the lead is dissolved 
and flows into the bonding portion. That is to say, lead-supplying units 
14a and 14b supply lead 16a and 16b so that the lead 16a and 16b comes in 
contact with the beams 12a and 12b without the lead 16a and 16b being 
directly contacted with the surfaces of bonding portion 40 prior to being 
dissolved. Laser light sources 10a and 10b and lead-supplying units 14a 
and 14b are automatically controlled by PLC (Programmable Logic Control) 
42. Namely, PLC 42 controls the turning on and off (ON/OFF) of laser light 
sources 10a and 10b and controls the supplying time of lead 16a and 16b so 
that lead 16a and 16b are supplied symmetrically at left and right side of 
optical elements 26 and 28. 
An explanation of operation the mechanism and the method thereof regarding 
the bonding apparatus for optical elements by the non-contact soldering 
process with reference to FIGS. 1 through 6 is as follows: 
First of all, optical element 26 is fixed and positioned to alignment 
apparatus 22 and optical element 28 is fixed and positioned to alignment 
apparatus 24, as represented in FIG. 1. After the foregoing procedure, the 
alignment apparatus aligns the optical systems (not shown), which are 
packed inside optical elements 26 and 28, automatically or manually. After 
the optical systems are aligned at an optimum position, PLC 42 controls 
laser light sources 10a and 10b. Then, laser light sources 10a and 10b 
illuminate laser beams 12a and 12b, such that the beams are not in contact 
with the surfaces of both the housing 30 of optical element 26 and the 
housing 32 of optical element 28. That is to say, laser light sources 10a 
and 10b illuminate beams 12a and 12b, as represented in FIGS. 1 and 2, so 
that the beams can be focused within the domain where the foci of the 
beams are not in contact with the surfaces of bonding portion 40 of the 
optical elements. In other words, the illumination position of laser beams 
12a and 12b are the bonding portion 40 of the optical elements and the 
laser light sources 10a and 10b may apply heat at its maximum provided 
that optical elements 26 and 28 arc put at vicinity of the focal length of 
beams 12a and 12b. Here, the diameters of foci of beams 12a and 12b at 
their focal length are about 0.5 mm.about.3 mm. Though they depend on 
usage, 2.5 mm is applied in the embodiment of the present invention. The 
illumination time of beams 12a and 12b illuminated from laser light 
sources 10a and 10b consists of three steps to improve bonding reliability 
of lead 16a and 16b. 
After a predetermined time, namely, after laser light sources 10a and 10b 
heat up, in the vicinity of 100.degree. C., the cross-section of bonding 
portion 40 sufficiently for a preliminary heating time "T1", increasing 
affinity of the lead 16a and 16b, PLC 42 automatically controls 
lead-supplying units 14a and 14b as represented in FIGS. 4 through 6. 
Then, lead-supplying units 14a and 14b supply lead 16a and 16b on laser 
beams 12a and 12b. Namely, lead-supplying units 14a and 14b supply lead 
16a and 16b at a constant velocity for a primary heating time "T2" as 
represented in FIGS. 4 through 6. Then lead 16a and 16b, right before it 
touches bonding portion 40, come into contact with laser beams 12a and 12b 
in the first place and be dissolved, thereby being melted and flowed into 
the through holes 34 of the bonding portion 40. Here, lead-supplying units 
14a and 14b supply lead 16a and 16b on beams 12a and 12b at a velocity of 
about 5 mm/sec. After that, under control of PLC 42, lead supplying units 
14a and 14b break off supplying lead 16a and 16b at a velocity of about 
-25 mm/sec at the stage when the primary heating time "T2" elapses. In 
succession, laser light sources 10a and 10b illuminate beams 12a and 12b, 
thereby post-heating for the post-heating time "T3" so that lead 16a and 
16b supplied already at bonding portion 40 are maintained in a stable 
formation, under control of PLC 42 as represented in FIGS. 4 through 6. 
Then, PLC 42 turns off laser light sources 10a and 10b after the lapse of 
the post-heating time "T3". By the foregoing, optical elements 26 and 28 
are bonded in manner of a non-contact soldering process as represented in 
FIG. 3. Here, in general, when the preheating time is too long, with 
respect to the preheating time, the primary heating time, and the 
post-heating time of the laser beam illumination time of laser light 
sources 10a and 10b, a problem may occur that plated portions on the 
cross-sections of bonding portion 40 of the optical elements may burn out 
or all fluxes may evaporate away. So, in the embodiment of the present 
invention, time is controlled at a ratio of preheating time: primary 
heating time: post-heating time=1 sec: 1.5 sec.about.1.7 sec: 1.5 sec, 
respectively. 
While there have been illustrated and described what is to be considered to 
be the preferred embodiment of the present invention, it will be 
understood by those skilled in the art that various changes and 
modifications may be made, and equivalents may be substituted for elements 
thereof without departing from the true scope of the present invention. 
Therefore, it is intended that the present invention not be limited to the 
particular embodiment disclosed as the best mode contemplated for carrying 
out the present invention, but that the present invention includes all 
embodiments falling within the scope of the appended claims.