Automatic alignment and locking method and apparatus for fiber optic module manufacturing

A method and apparatus for aligning an optical fiber (120) with an optoelectronic hybrid device (112) and locking the optical fiber in the aligned position are disclosed. A fiber coated with an external layer of gold is threaded through a solder preform (130). The optical fiber (120) rests upon a ceramic substrate (104). The ceramic substrate also supports a device submount (108) that houses the optoelectronic device (112). The ceramic substrate (104) supports a resistor/heater formed of a thin film of nickel-chromium alloy (604). The resistor/heater supports a pad (609) formed of a layer of nickel (610) and a layer of gold (612). Located atop the pad (609) is the solder preform (130). Precise control of heating is provided by applying a predetermined voltage to the resistor/heater (122) for precise time periods, thereby eliminating the necessity of making temperature measurements during heating. As the resistor/heater (122) is energized, the solder preform is liquefied. An open loop search process that utilizes signal strength feedback is used to control the operation of an x-y-z micropositioning stage (328) that precisely positions an arm (306) that supports the optical fiber (120). The alignment system also includes a fixturing setup that includes a probe head (340) having multiple electrical probes (502a, 502b, 504a, 504b) and a vertical rod (506) that applies a downward force to the solder during manufacturing.

FIELD OF THE INVENTION 
The present invention relates to manufacturing of optoelectronic devices, 
and in particular, optical fiber locking and alignment. 
BACKGROUND OF THE INVENTION 
The manufacture of optoelectronic modules, such as optoelectronic receivers 
and optoelectronic transmitters, requires that an optical fiber be 
properly aligned and fixed in an optical subassembly. In an optoelectronic 
receiver, a fiber is aligned with an optical detector, usually a PIN 
photodiode. In an optoelectronic transmitter, an optical fiber is aligned 
with a light-emitting diode (LED) or laser diode. A goal of optical 
alignment is to minimize the amount of attenuation within the subassembly. 
The alignment of the fiber optic member with the LED, laser diode, or 
photodetector is a critical step in the manufacture of an optoelectronic 
hybrid package. The end of an optical fiber is commonly referred to as a 
"fiber pigtail." The arrangement whereby a fiber interfaces with an 
optoelectronic device to form a hybrid optoelectronic package is commonly 
referred to as a "fiber-pigtailed" hybrid package. The process for 
interfacing the fiber to the package is called "pigtailing." 
The methods used to lock optical fibers inside of any type of 
optoelectronic packages must be reproducible, and the materials used must 
be reliable. Further, a successful packaging technique must achieve 
precise optical fiber locking. The alignment and locking of an optical 
fiber in optoelectronic packages intended for avionics applications is 
subject to even more stringent requirements. The methods, apparatus, and 
materials used must produce highly reliable optoelectronic packages. As 
discussed below, current techniques have not sufficiently addressed these 
demands. 
Some prior art methods of attaching an optical fiber inside of an 
optoelectronic package utilize a liquid epoxy to attach the optical fiber 
to a substrate. Since the curing of epoxy can cause movement of the fiber, 
in order to ensure proper positioning, alignment of the fiber must be 
maintained during the solidification process. One disadvantage of epoxy is 
that it takes a long time to cure, which increases assembly time. Also, 
epoxy does not maintain its strength over wide temperature ranges, thereby 
limiting the environments within which it can be used. 
Some methods of attaching an optical fiber inside of an optoelectronic 
package use high melting point bonding materials, such as silicon. The use 
of high melting point bonding materials limits assembly operations before 
the fiber-locking is completed. 
An alternative to using epoxy and expensive, low melting point materials to 
lock optical fibers inside of optoelectronic packages is to use solder as 
the bonding medium. Since some materials tend to degrade during heating, 
the use of solder requires the employment of a method of alignment that 
can be completed rapidly in order to limit the amount of heat applied and 
allow the resulting bond to rapidly cool. Some prior art systems that use 
solder as a bonding medium employ thermocouples to provide feedback 
regarding the amount of heat created within the optoelectronic package. In 
the case of small optoelectronic packages, the use of thermocouples may 
not be practical. It is desirable therefore to provide a method of 
soldering that does not employ thermocouples and, preferably, does not 
require temperature feedback. 
An apparatus that employs solder as the bonding medium is described in 
copending patent application Ser. No. 08/548,179, filed Oct. 25, 1995. 
This patent application discloses an optoelectronic module assembly that 
includes an optical fiber cable assembly and a feedthrough assembly that 
provide high-reliability optical fiber alignment, locking, and sealing. 
The application discloses an optoelectronic package that comprises a 
housing that includes a sidewall with an aperture through the sidewall, 
and a floor with an overlying substrate. A solder lock joint on the 
substrate is formed of a reflowed solder preform. The preform surrounds at 
least part of the metallized portion of the fiber so as to hold the fiber 
in its desired position, in alignment with an optoelectronic device in the 
package. After the fiber is inserted through the preform and aligned 
properly, the preform is heated, causing the preform to melt, flow around 
the fiber, and form the lock joint. While the resulting optoelectronic 
package has high reliability and performance, the method of manufacture is 
slow and labor-intensive. It is desirable to provide a similarly reliable 
package using an automated alignment and locking method and apparatus that 
are suitable for use in a commercial manufacturing environment. 
In summary, methods and apparatus, including the tools and materials, used 
to align and lock optical fibers inside of optoelectronic packages, 
particularly optoelectronic packages intended for avionic use, should 
employ a total integrated solution, which is automated, reliable, and 
repeatable. The present invention is directed to providing such a method 
and apparatus. 
SUMMARY OF THE INVENTION 
In accordance with this invention, an apparatus for aligning an optical 
fiber with an optoelectronic device and a related method are provided. The 
optoelectronic device may be a receiver for receiving light exiting from 
the optical fiber, or an emitter for emitting light into the optical 
fiber. The system employs an instrument for measuring the amount of light 
transmitted between the optical fiber and the optoelectronic device, 
either from the optical fiber to the optoelectronic receiver, or from the 
optoelectronic light emitter into the optical fiber. The system supplies 
electrical current to a resistor overlying a substrate, resulting in the 
formation of heat, which causes melting of a solder preform placed on the 
resistor. While the solder is molten, the optical fiber is aligned with 
the optoelectronic device. The resolidified solder forms a solder lock 
joint. The solder lock joint is the result of a chemical bond between the 
solder, which encloses the optical fiber, and the resistor overlying the 
substrate. 
In accordance with further aspects of this invention, the system includes a 
computer having a monitor and an input device. The computer controls the 
alignment of the optical fiber and electrical current supplied to the 
resistor. The computer receives data from the instrument that measures the 
amount of light transmitted between the optical fiber and the 
optoelectronic device. 
In accordance with other aspects of this invention, the resistor is a thin 
metallic film resistor formed of a material that bonds with solder. The 
thin metallic film resistor overlies the substrate and generates heat when 
electrical current is applied. As a result, this resistor is called a 
resistor/heater. Solder placed on the resistor/heater becomes molten when 
the resistor/heater reaches the solder's melting temperature. When this 
occurs, a chemical bond is formed with the metallic resistor/heater. 
In accordance with other further aspects of this invention, a manipulator 
connected to and controlled by the computer aligns the optical fiber with 
the optoelectronic device when the solder is melted. 
In accordance with still other aspects of this invention, the 
resistor/heater is made up of a thin layer of nickel-chromium alloy 
deposited on the substrate, and a thin layer of nickel deposited on 
portions of the nickel-chromium alloy layer. A thin layer of gold is 
deposited on the layer of nickel to form a pad upon which the solder rests 
and to which the solder binds. 
In accordance with yet other aspects of this invention, the solder preform 
has an aperture through which the optical fiber is inserted prior to 
alignment of the optical fiber. The solder preferably is made up of tin 
(Sn) and silver (Ag), preferably in a composition of Sn96.5 Ag3.5 (by 
weight). 
In accordance with yet still other aspects of this invention, the apparatus 
includes a probe head having two device probes that connect to terminals 
of the optoelectronic device. If the optoelectronic device is a light 
emitter, the device probes connect the light source to a source of 
electrical power, which is connected to and controlled by the computer. If 
the optoelectronic device is a light detector, the device probes connect 
the light detector to a current-sensing instrument, which measures the 
amount of photocurrent produced by the light detector, the amount of 
photocurrent being indicative of the amount of light received by the light 
detector. A typical light detector is a PIN photodiode. A typical light 
source is a light-emitting diode (LED). 
In accordance with still further aspects of this invention, the probe head 
includes two resistor probes for connecting the resistor/heater to a power 
source. The probe head also includes a vertical aluminum rod that contacts 
the top surface of the solder preform and stabilizes the preform during 
heating of the resistor/heater. 
In accordance with yet still further aspects of this invention, in order to 
control the temperature and duration of heat applied to the solder, the 
alignment and locking of an optical fiber includes precise control of the 
voltage applied to the resistor/heater. The voltage, which is controlled 
by the computer, begins at a level sufficient to create heat above the 
melting point of the solder. After a predetermined time interval, the 
voltage is decreased slightly. Preferably, the decrease in voltage occurs 
over 20 stages during an interval of 8 seconds. At a predetermined time at 
which the solder becomes molten, automatic manipulation of the optical 
fiber takes place. The automatic manipulation precisely aligns the fiber 
with the optoelectronic device. When the alignment is completed, the power 
applied to the resistor/heater is turned off, allowing the molten solder 
to cool and solidify, locking the optical fiber in place. 
In accordance with still other further aspects of this invention, the 
alignment of the optical fiber with the optoelectronic device includes an 
open loop search for the optimal position of the fiber. The fiber is 
moved, by the manipulator, in small increments in one direction along an 
axis. After each movement, the amount of light transmitted between the 
fiber and the optoelectronic device is measured. At the point where the 
amount of light measured is less than the amount of light measured at the 
immediately previous point, the direction of movement of the fiber is 
reversed. After movement in both directions along an axis is completed, 
the search along that axis is complete. Searches are done along all three 
Cartesian coordinate, i.e., the x, y, and z, axes. Preferably, a coarse 
search, using coarse intervals of movement, is performed prior to melting 
of the solder, and a fine search, utilizing small increments of movement 
is performed while the solder is molten. 
In accordance with yet still other further aspects of this invention, the 
optoelectronic device is contained within an optoelectronic hybrid package 
A preferred optoelectronic hybrid package includes a housing having a 
sidewall with an aperture through the sidewall, and a floor having an 
overlying substrate. The thin film resistor overlies the package 
substrate, and the fiber is secured to the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a pictorial diagram illustrating an exemplary optoelectronic 
hybrid package 102 incorporating a fiber optic interface aligned and 
locked using the method and apparatus of the invention. FIG. 2 is a side 
view of the exemplary optoelectronic hybrid package illustrated in FIG. 1. 
The hybrid package 102 may be an optical receiver or optical transmitter, 
such as specified by the Aeronautical Radio, Inc. (ARINC) 636 standard. 
The following description of the preferred embodiment of the invention is 
based on the exemplary optoelectronic hybrid package 102 illustrated in 
FIG. 1 and FIG. 2. Obviously, changes may be required for other types of 
optoelectronic packages. 
The optoelectronic hybrid package 102 illustrated in FIGS. 1 and 2 includes 
a header assembly 103 having a device floor 106 and sidewalls 118. A 
substrate 104 is mounted on the device floor 106. The substrate 104 is 
preferably a ceramic substrate, which serves as a heat sink that disperses 
heat generated by electronic circuitry mounted on the substrate. A device 
submount 108 is mounted atop the substrate 104. The device submount 108 
includes a block 109 and an optoelectronic device 112 mounted on a side 
110 of the block 109. The optoelectronic device 112 is a light detector, 
such as a PIN photodiode, when the hybrid package 102 is an optical 
receiver. The optoelectronic device is a light emitter, such as an LED or 
laser diode, when the hybrid package is an optical transmitter. A 
cylindrical hermetic feedthrough 114 leads to an aperture 216 formed in 
the package sidewall 118 in alignment with the optoelectronic device 112. 
The hermetic feedthrough 114 is preferably a Kovar tube with a gold-plated 
interior that is braised to the sidewall 118 of the package. An optical 
fiber 120 extends through the hermetic feedthrough and the aperture 216. 
The hermetic feedthrough is more fully disclosed in copending patent 
application Ser. No. 08/548,179, filed on Oct. 25, 1995, the subject 
matter of which is incorporated herein by reference. Preferably, the 
optical fiber 120 is a commercially available sleeved gold metallized 
optical fiber. The sleeving (not shown) is preferably a high-temperature 
plastic that is physically and chemically stable over a wide temperature 
range. 
The optical fiber 120 is held in proper alignment by a fiber lock joint. In 
accordance with the invention, the fiber lock joint is formed by the 
liquefaction and solidification of a solder preform 130. As also described 
more fully below, when the lock joint is formed, the solder bonds to a 
thin film resistor/heater 122 located atop the substrate 104. 
FIGS. 1 and 2 also illustrate the circuitry 134 housed within the hybrid 
package 102. The circuitry 134 is added after aligning and locking the 
optical fiber 120. Prior to installation of the circuitry 134, a hybrid 
package 102 is commonly referred to as an optical header assembly. 
FIG. 3 and FIG. 4 are elevational side and top plan views, respectively, of 
an alignment fixturing setup 302 suitable for use in an automatic 
alignment and locking system formed in accordance with the invention of 
the type illustrated in FIGS. 7 and 8, and described below. The alignment 
system fixturing setup is usually employed prior to installation of 
circuitry 134, i.e., when the hybrid package 102 is empty. The header 
assembly with a substrate 104, a device submount 108, and a hermetic 
feedthrough is secured to an alignment nest fixture 304 on the fixturing 
setup 302. The alignment nest fixture 304 holds the header assembly 
securely in place relative to the fixturing setup 302. A fiber manipulator 
306, which comprises an outwardly extending arm having an inverted 
V-shaped groove at its outer end, grips the optical fiber 120 between the 
sidewall 118 of the hybrid package and the location of the solder preform 
130 and aligns the optical fiber 120 relative to the optoelectronic device 
112. 
If necessary, the position of the alignment nest fixture can be positioned 
along Cartesian coordinate, i.e., x, y, z, axes, by an adjustment 
subfixture 320. The adjustment subfixture 320 is mounted on a base 309 and 
includes an x-axis adjustment control 322, a y-axis adjustment control 
324, and a z-axis adjustment control 326. The x and y axes are horizontal 
and the z-axis is vertical. The adjustment subfixture supports a table 317 
on which the alignment nest fixture 304 is mounted. While various 
commercially available adjustment subfixtures can be used, one suitable 
subfixture is an XYZ Micropositioning Stage produced by Photon Control of 
Cambridge, England. 
Two subsystems manipulate and align the optical fiber 120 with respect to 
the optoelectronic device 112. A manual alignment subsystem 310 allows 
manual manipulation of the fiber manipulator 306 and, thus, the optical 
fiber, along Cartesian coordinate, i.e., x, y, and z, axes. In this 
regard, the manual alignment subsystem 310 includes an x-axis micrometer 
adjustment control 312, a y-axis micrometer adjustment control 314, and a 
z-axis micrometer adjustment control 316. These controls allow an operator 
to manually position the fiber manipulator 306 to obtain a coarse 
alignment of the optoelectronic device 112 and the optical fiber 120. 
Preferably, a microscope (not shown) is used to magnify the area where the 
optical fiber 120 and the optoelectronic device 112 meet to assist manual 
alignment. 
The manual alignment subsystem 310 is mounted on a bracket 311. Mounted on 
the bracket 311 is a y-axis support 313. The y-axis support 313 supports a 
y-axis table 315 that is movable along a horizontal axis only. The 
position of the y-axis table 315 is controlled by the y-axis micrometer 
control 314. More specifically, the housing of the y-axis micrometer 
control is supported by an arm 318 attached to the y-axis support. The 
movable element of the y-axis micrometer control is attached to the y-axis 
table. The y-axis table is supported along opposing edges by bearings that 
lie in V-shaped grooves. 
Mounted on the y-axis table 315 is an x-axis support 319. The x-axis 
support 319 supports an x-axis table 321 that is movable along a 
horizontal axis only. The horizontal x-axis lies orthogonal to the 
horizontal y-axis. The position of the x-axis table is controlled by the 
x-axis micrometer control 312. More specifically, the housing of the 
x-axis micrometer control 312 is supported by an arm 323 attached to the 
x-axis support 319. The movable element of the x-axis micrometer control 
is attached to the x-axis table 321. The x-axis table is supported along 
opposing edges by bearings that lie in V-shaped grooves. 
Mounted on the x-axis table 321 is a z-axis support 325. The z-axis support 
325 supports a z-axis table 327 that is movable along a vertical axis 
only. The position of the z-axis table is controlled by the z-axis 
micrometer control 316. More specifically, the housing of the z-axis 
micrometer control is supported by an arm 329 attached to the z-axis 
support 325. The movable element of the z-axis micrometer control is 
attached to the z-axis table. The z-axis table is supported along opposing 
edges by bearings that lie in V-shaped grooves. The fiber manipulator 306 
is mounted on the z-axis table 327. While various commercially available 
products can be used to form the manual alignment subsystem 310, one 
suitable product is the X-Y-Z Micropositioner stage manufactured by Line 
Tool Company of Allentown, Pa. 
An automated micropositioning stage 328 controls the position of the 
bracket 311 and, as a result, the position of the optical fiber 120, via 
the manual alignment subsystem 310. While various types of 
micropositioning stages 328 can be used, one commercially available 
product is the Klinger UT 100.50 PP linear translation stage manufactured 
by Newport Corp. of Irvine, Calif. The automated micropositioning stage 
328 provides an x-axis, a y-axis, and a z-axis fine position control. As 
described further below, the automated micropositioning stage 328 is 
connected to, and controlled by, a computer. 
As illustrated in FIG. 3, the alignment fixturing setup 302 also includes a 
probe head 340 whose vertical position is controlled by a probe lever 342. 
More specifically, the probe head 340 is mounted on one end of a 
dogleg-shaped arm 341. The other end of the dogleg-shaped arm 341 is 
hingedly attached to the lower end of a bracket 343. The bracket 343 is 
mounted on a support 345. The probe lever 342 is hingedly attached to the 
top of the bracket. A link 347 connects the inner end of the probe lever 
342 to the dogleg-shaped arm 341. The probe head 340 overlies the region 
where the optical fiber 120 meets the optoelectronic device 112. When the 
probe lever 342 is raised and lowered, the probe head is raised and 
lowered, thereby establishing or disestablishing contact between probes 
supported by the probe head 340 and corresponding points on the 
optoelectronic hybrid 102, described below. 
As illustrated in FIG. 1, the hybrid package 102 includes four electrical 
terminals--two resistor terminals 124 and two device terminals 126. The 
two resistor terminals 124 rise above the resistor/heater 122 on the 
ceramic substrate 104. The resistor terminals 124, which are located on 
opposite sides of the solder preform 130, are connected to the 
resistor/heater 122. The two device terminals 126 reside on the top 
surface 111 of the device submount 108. The device terminals 126 are 
electrically connected to the optoelectronic device 112. 
FIG. 5 is a perspective, upwardly looking view of the probe head 340. The 
probe head supports two resistor probes 502a and 502b, two device probes 
504a and 504b, and a rod 506, all vertically oriented. The resistor probes 
502a and 502b are positioned such that, when the probe head 340 is 
lowered, the resistor probes 502a and 502b come into electrical contact 
with the resistor terminals 124. The two device probes 504a and 504b are 
positioned such that when the probe head 340 is lowered the device probes 
504a and 504b come into contact with the device terminals 126. Preferably, 
gold-plated contacts are located at the bottoms of the probes 502a, 502b, 
504a, and 504b. The rod 506 is formed of oxidized aluminum and located 
midway between the resistor probes 502a and 502b in the probe head 340. 
The probe head 340 illustrated in FIG. 5 includes five vertically oriented 
cylindrical holes. The probes 502a, 502b, 504a, and 504b and the rod 506 
are slidably inserted into corresponding ones of the cylindrical holes 
508. The sliding design allows the probes and the rod to move 
independently relative to the probe head 340. Independent vertical 
movement helps to ensure that the probes and the rod make contact in the 
manner hereinafter described when the probe head is lowered. Preferably, 
the probes are spring-loaded downwardly. 
One suitable probe is a QA Technology 075-PRP2540L/075-SDN250S-G probe 
assembly manufactured by QA Technology of Hampton, N.H. This probe 
assembly includes a receptacle extending through the top of the 
cylindrical hole 508 and a spring-loaded contact extending through the 
bottom of the hole 508. The probe assembly held in place by a press fit. 
The rod 506 is held in place by friction. A set screw or cam can also be 
used to hold the rod in place. As will be readily appreciated by those 
skilled in this art and others, the use of cylindrical tubes to allow 
vertical movement of the probes and friction to resist vertical movement 
of the rod when the head is lowered should be considered as exemplary, not 
limiting, since a variety of alternative ways of accomplishing the same 
result are available. 
FIG. 6A is a partial elevational view showing the probe head 340 and the 
mating of individual probes with their respective terminals when the probe 
head is lowered. As illustrated in FIG. 6, the resistor terminals 124 rise 
above the resistor/heater 122, which lies above the ceramic substrate 104. 
The resistor probes 502a and 502b are aligned with and make electrical 
contact with the resistor terminals 124, when the probe head is lowered. 
Likewise, the device terminals 126 rise above the top surface 111 of the 
device submount 108. The device probes 504a and 504b are aligned with and 
make electrical contact with the device terminals 126, when the probe head 
is lowered. 
Additionally, the rod 506 is positioned such that, when the probe head 340 
is lowered, the rod 506 contacts the top of the solder preform 130. The 
rod 506 applies downward pressure on the top of the solder preform 130 
sufficient to resist vertical movement of the solder preform during 
heating of the solder preform in the manner described below. Boiling of 
the flux during heating of the solder can create such vertical movement. 
The rod 506 thereby functions to stabilize the solder preform 130 during 
manufacture, thereby minimizing misalignment. 
FIG. 6A also illustrates the details of the thin film resistor/heater 122, 
which, as noted above, lies on the ceramic substrate 104. The ceramic 
substrate 104 preferably is formed of high-purity alumina. The top of the 
alumina ceramic substrate is polished to a 1-microinch (maximum) surface 
finish. The bottom has a lapped 10-microinch (nominal) surface finish. The 
resistor/heater is formed by a layer of nickel-chromium alloy 604 that 
lies on the top surface of the ceramic substrate 104. Preferably, the 
nickel-chromium alloy layer is about 1,250 angstroms in thickness and 
approximately rectangular shaped. 
The resistor terminals 124 are rectangular and oriented such that their 
longitudinal axes lie approximately parallel to each other and parallel to 
the longitudinal axis of the optical fiber 120. Each resistor terminal 124 
comprises a layer of nickel 606 that lies atop the nickel-chromium alloy 
layer 604, and a gold layer 608 that lies atop the nickel layer. The gold 
and nickel layers have the same approximate width and length. The nickel 
layer 606 preferably has a thickness of approximately 5000 angstroms. The 
preferred thickness of the gold layer is approximately 3250 angstroms. 
An approximately circular pad 609 is generally centered on the 
nickel-chromium alloy layer 604, midway between the resistor terminals 
124. The pad 609 comprises a nickel layer 610 lying atop the 
nickel-chromium alloy layer 604, and a gold layer 612 overlying the nickel 
layer 610. The nickel layer 610 and gold layer 612 have approximately the 
same thicknesses as the nickel layer 606 and the gold layer 608, 
respectively, of the terminals 124. The diameter of the pad is 
approximately 0.060 inch. 
Preferably, the nickel-chromium alloy layer 604, the nickel layers 606 and 
610, and the gold layers 608 and 612 are formed by sputter deposition with 
no break in vacuum between each material deposition. After deposition, the 
nickel-chromium alloy layer 604 is unsolderable when heated above the 
melting point of the solder. 
The solder preform 130 is preferably formed of SnAg solder. When molten, an 
intermetallic alloy is formed by the tin of the solder and the nickel 
layer 610 of the pad 609. In one actual embodiment of the invention, the 
solder preform comprises Sn96.5 Ag3.5, and has a melting temperature of 
221.degree. C. A small amount of solder flux, such as Indium Corporation 
of America No. 5R solder flux, is used to assist in adhering the solder 
preform 130 to the pad 609. Since molten SnAg solder can erode nickel 
under certain conditions, certain criteria must be met when practicing the 
invention. Specifically, the maximum temperature and the duration of the 
heating must be chosen so as to minimize the erosion of the nickel layer 
610. In addition, the nickel layer 610 must be thick enough to withstand 
whatever erosion occurs while the molten solder is in contact with the 
nickel. Also, because the resistance of the nickel-chromium alloy 
resistor/heater 122 changes with time when power is applied, power must be 
carefully controlled and applied over a short period of time in order to 
maintain precise control over the temperature and duration of the heat 
provided by the resistor/heater. How this is accomplished is described 
below. 
In addition to a bond being created between the solder preform and the 
resistor/heater 122 when heat is generated, a bond between the optical 
fiber 120 and the solder preform is created. More specifically, nickel 
underlayer 624 and gold overlayer 626 surround the optical fiber 120. When 
heat is created by applying power to the resistor/heater 122, an 
intermetallic alloy is formed by the tin of the solder and the nickel 
underlayer 624 of the optical fiber. 
FIGS. 6B through 6D illustrate alternative configurations of the solder 
preform 130 and rod 506. FIG. 6B illustrates a substantially flat solder 
preform 130 positioned above and extending beyond the circular pad 609. 
The optical fiber 120 is positioned adjacent and above the solder preform 
130. The rod 506 illustrated in FIG. 6B includes a two-pronged fork 630 at 
the lower end of the rod 506. A horizontal base 631 of the fork 630 is 
approximately perpendicular to the vertical orientation of the rod 506. 
Two side prongs 632 extend vertically downward from the ends of the fork 
base 631. The rod 506 is positioned so that the side prongs 632 of the 
fork 630 applies downward pressure on the top of the solder preform 130 
sufficient to resist vertical movement of the solder preform during 
heating of the solder preform in the manner described below. 
FIG. 6C illustrates an inverted U-shaped solder preform 130 surrounding the 
optical fiber 120. An inverted U-shaped solder preform 130 may be 
positioned on the circular pad 609 after the optical fiber 120 is manually 
positioned above the circular pad 609. As described above, the rod 506 
applies downward pressure on the top of the solder preform 130 sufficient 
to resist vertical movement of the solder preform during heating of the 
solder preform in the manner described below. 
FIG. 6D illustrates a U-shaped solder preform 130. The rod 506 in FIG. 6D 
is T-shaped, having a horizontal base 633 sized approximately to the width 
of the solder preform 130. The T-shaped rod 506 applies downward pressure 
on the top of the solder preform 130 sufficient to resist vertical 
movement of the solder preform during heating of the solder preform in the 
manner described below. 
FIGS. 7 and 8 are block diagrams of automatic alignment and locking systems 
for optoelectronic receiver and optoelectronic transmitters, respectively, 
according to the invention. The diagrams, which are generally similar, 
include the electronic components of the system and the mechanical 
components that are electronically controlled. The manually controlled 
elements of the alignment fixturing setup 302 shown in FIGS. 3 and 4 and 
described above are not depicted in detail. They are shown in block form 
with only the probe head 340 and the probes 502a, 502b, 504a, and 504b 
being broken out. 
The automatic alignment and locking systems shown in FIGS. 7 and 8 include 
a computer 704 connected to a monitor 706, a keyboard 708, a digital bus 
710, such as an IEEE 488 bus, and an optional printer 712. A stepping 
motor controller 714 that controls a stepping motor power driver 716 is 
connected to the digital bus 710. The stepping motor controller 714 and 
stepping motor power driver 716 form part of and control operation of the 
micropositioning stage 328. As described above, the micropositioning stage 
328 controls the position of the manual alignment subsystem 310. The 
manual alignment subsystem 310 controls the position of the fiber 
manipulator 306, which, in turn, controls the position of the optical 
fiber 120. If the chosen XYZ microprocessing stage 328 is the Klinger NT 
100.50PP linear translation state referenced above, a suitable stepping 
motor controller is the Klinger MC4 and a suitable stepper motor driver is 
the Klinger MD4 also produced by Newport Corp. of Irvine, Calif. 
FIGS. 7 and 8 also include a microscope 730 positioned to view the region 
where the optical fiber 120 is to be aligned with the optoelectronic 
device 112, a video camera 732 positioned to view the output of the 
microscope 730, and a video monitor 734 for displaying the pictures 
captured by the video camera 732. A work light 735 is provided to 
illuminate the image area. As noted above, the microscope 730, camera 732, 
and video monitor 734 allow an operator to manually adjust the alignment 
fixturing setup 302 (if necessary) and the manual alignment subsystem 310. 
FIGS. 7 and 8 also include a switch 722, a resistance measuring digital 
multimeter 724 and a power supply 726. The switch controls the application 
of power produced by the power supply 726 to the resistor probes 502a and 
502b. The computer 704 controls the power generated by the power supply 
726. The resistance measuring digital multimeter measures the resistance 
of the heater/resistor and supplies this information, in digital form, to 
the computer 704. More specifically, the resistor probes 502a and 502b of 
the probe head 340 are electrically connected to a three-position toggle 
switch 722. The toggle switch 722 allows the probes to be switched between 
the resistance measuring digital multimeter 724, and the power supply 726. 
A suitable digital multimeter having a resistance measuring function is 
the 197A multimeter produced by Keithley Instruments of Cleveland, Ohio. A 
suitable power supply is HP 6033A power supply produced by Hewlett-Packard 
Corp. The switch 722, a multimeter 724, and power supply 726 combination 
allows the resistance across the resistor/heater 122 to be measured, and, 
alternatively, electrical power to be applied to the terminals 124 of the 
resistor/heater 122. 
The foregoing description has described the components that are common to 
the optoelectronic receiver automatic alignment and locking system shown 
in FIG. 7 and the optoelectronic transmitter automatic alignment and 
locking system shown in FIG. 8. In addition to the foregoing components, 
the optoelectronic receiver automatic alignment and locking system (FIG. 
7) includes a current-measuring digital multimeter 728, which may also be 
a Keithley 197A multimeter, electrically connected to the device probes 
504a and 504b. The output of the current-measuring digital multimeter is 
applied to the computer 704. The current-measuring digital multimeter 728 
measures the photocurrent produced by the optoelectronic device 112, which 
is preferably a PIN photodiode, when the device receives light from the 
optical fiber 120. The photocurrent is measured in microamperes. Rather 
than being separately connected to the computer, as shown in FIG. 7, the 
power supply 726, the resistance-measuring digital multimeter 724, the 
current measuring digital multimeter 728, and the stepper motor controller 
714 could all be connected to the computer 704 via a common data bus. 
In addition to the foregoing components, the optoelectronic receiver 
automatic alignment and locking system illustrated in FIG. 7 includes a 
precision current source 721 and an LED 720 powered by the precision 
current source 721. The LED 720 is coupled to one end of a fiber optic 
patch cord 723. The other end of the fiber optic patch cord 723 is coupled 
to the remote end of the optical fiber 120 to be aligned by a suitable 
optical coupling mechanism 725. The LED 720 provides the light that is 
detected by the optoelectronic device 112, i.e., the PIN diode, during 
alignment and locking of the optical fiber 120 in the manner described 
below. 
The automatic alignment and locking system for an optoelectronic 
transmitter (FIG. 8) also includes a precision current source 821. 
However, rather than being used to supply power to an LED that lights the 
remote end of the optical fiber 120 to be aligned, the precision current 
source 821 is connected to the device probes 504a and 504b to supply 
current to the optoelectronic device 112, which, in the case of a 
transmitter, is an LED. Further, the current-measuring digital multimeter 
is eliminated. As with the precision current source 721 shown in FIG. 7, a 
suitable current source is an ILX Lightwave LDX-3207 manufactured by ILX 
Lightwave of Bozeman, Mont. 
In addition, rather than including a precision power source, an LED, and a 
coupling medium at the remote end of the optical fiber 120 to be aligned, 
the optoelectronic transmitter alignment and locking system shown in FIG. 
8 includes an optical head 852 and an optical power meter 854. The optical 
head 852 is optically coupled to the remote end of the optical fiber 120 
to be aligned, and the electrical output of the optical head is connected 
to the optical power meter 854. The optical power meter produces a digital 
output representative of the light received by the optical head 852 from 
the optical fiber 120 to be aligned. The digital output of the optical 
power meter 854 is supplied to the computer 704, preferably via a common 
digital data bus. 
Prior to describing how the computer 704 controls the various elements 
shown in FIGS. 7 and 8 and described above, the nature of the solder 
preform 130 and how it melts and reforms are described. In this regard, 
attention is directed to FIGS. 9A and 9B. 
FIGS. 9A and 9B illustrate an optical fiber 120 passing through a solder 
preform 130 both before and after alignment and reflow of the solder 
preform according to the invention. The solder preform 130 comprises a 
solid piece of solder, preferably SnAg solder, having a generally 
horizontal, approximately cylindrical aperture 628 extending through it. 
The aperture 628 is sized to receive an optical fiber 120 with enough 
space around the optical fiber 120 to allow for coarse alignment of the 
fiber prior to melting of the solder. As illustrated in FIG. 9A, the 
solder preform 130 is preferably a vertically oriented cylindrical shape, 
with flat bottom and top surfaces. The flat bottom surface lies on the 
heater/resistor 122 in the position described above. The flat top surface 
receives the bottom of the rod 506 when the probe head 340 is lowered, as 
described above. The solder preform 130 must contain enough solder to 
produce a sufficiently strong fiber lock joint. In one actual embodiment 
of the invention, the solder preform contains 28 mg of solder. 
As noted above, the solder preform 130 rests on the gold layer 612 of the 
pad 609. See FIG. 6. An optical fiber 120 inserted through the aperture 
628 in the solder preform 130 is aligned in the manner herein described. 
Thereafter, the heater/resistor is energized, causing the solder to melt. 
The melted solder is allowed to cool and resolidify. The resolidified 
solder creates a fiber lock joint, as illustrated in FIG. 9B. The solder 
is bonded to the nickel layer 610 (FIG. 6) and the optical fiber 120 is 
bonded to the solder. 
FIG. 10 is a flow diagram illustrating the operation of an automatic 
alignment and locking system formed in accordance with the invention. As 
illustrated in FIG. 10, the method 1002 of employing the automatic 
alignment and locking system begins, at step 1004, with an operator 
inputting system-operating parameters to the computer 704. The 
system-operating parameters are described below. At step 1006 the operator 
loads an optoelectronic hybrid package 102 onto the alignment nest fixture 
304 (FIG. 3) of the alignment fixturing setup. At step 1008, an operator 
loads an optical fiber 120 and a preform 130 by feeding the optical fiber 
120 through the hermetic feedthrough 114 mounted in the package sidewall 
118 of the optoelectronic hybrid package 102 and through the hole in the 
preform, and positions the preform onto the gold layer 612 of the pad 609. 
Prior to loading the preform 130, a thin layer of flux is applied to the 
preform 130 or to the pad 609. Next, at step 1010, the probe head is 
lowered. 
After the above manual steps take place, the resistance of the 
resistor/heater 122 is measured to determine if the resistance of the 
resistor/heater lies within an acceptable range of resistance values. This 
occurs at step 1012. The switch 722 (FIG. 7) is set to connect the 
resistor probes 502a and 502b to the resistance-measuring digital 
multimeter 724, which measures the resistance of the resistor/heater 122. 
At step 1014, the measured resistance is read by the computer 704 and 
displayed on the monitor 706. At step 1016, a test is made by the computer 
to determine if this resistance is within a predetermined acceptable 
range. If the resistance is outside the acceptable range, either the 
resistor/heater 122 is bad or the contact with the resistor probes 502a 
and 502b is poor. After corrective action is taken, the process loops back 
to step 1012 and the resistance is again measured and displayed. In one 
actual embodiment of the invention, the predetermined acceptable 
resistance range is 12 to 18 ohms. 
If, at step 1016, the resistance is within the acceptable range, the switch 
722 (FIG. 7) is reset to connect the power supply 726 to the resistor 
probes 502a, 502b. This occurs at step 1018. As a result, current flows 
through the resistor/heater 122, when the power supply 726 is turned on by 
the computer. At step 1020, the LED 720 (FIG. 7) or 850 (FIG. 8) is turned 
on. In the case of the optoelectronic receiver automatic alignment and 
locking system (FIG. 7), this is accomplished by turning on the precision 
current source 721 either manually or by a suitable computer-produced 
control signal (not shown) connected to the remote LED 720. In the case of 
the optoelectronic transmitter automatic alignment and locking system, 
this is accomplished by the computer turning on the precision current 
source 821 connected to the optoelectronic device 112 mounted in the 
device submount 108 of the optoelectronic package. 
At step 1024, a test is made to determine if light is passing through the 
optical fiber 120. This test is accomplished by the computer receiving a 
current measurement from the current measuring digital multimeter 728 
(FIG. 7) or from the optical power meter 854 (FIG. 8). If, at step 1024, a 
response is not observed by the computer, at step 1026, the fiber position 
and probe contact points are checked. This is done manually. If, as shown 
at step 1028, a determination is made that either the fiber position 
and/or the probe contacts are satisfactory, the probe head is raised (if 
necessary), the appropriate corrective action takes place and the process 
returns to step 1008, where the probe head 340 is lowered into place. If, 
at step 1028, the fiber position and probe contacts are determined to be 
satisfactory, at step 1030, the optoelectronic package 102 is removed. 
Then the process cycles to step 1006, where the new optoelectronic package 
is loaded into the alignment nest. 
If, at step 1024, a proper light response is observed by the computer, at 
step 1032, a pre-locking automatic alignment subroutine occurs. A suitable 
pre-locking automatic alignment subroutine is illustrated in FIG. 11 and 
described below. After the pre-locking automatic alignment subroutine is 
finished, at block 1034, a test is made to determine if the LED coupled 
power reading by either the current-measuring digital multimeter 728 (FIG. 
7) or the optical power meter 854 (FIG. 8), lies above a predetermined 
lower value. In one actual embodiment, the predetermined lower value is a 
signal indicating that the received light power is greater than 20 .mu.W. 
If not above this value, processing loops back to step 1026. If, at step 
1034, the LED coupled power reading is determined to be above the 
predetermined lower value, the program cycles to a final alignment and 
locking subroutine 1036. A suitable final alignment and locking subroutine 
is illustrated in FIG. 13 and described below. During the automated final 
alignment and locking subroutine, the solder preform 130 is heated, the 
optical fiber 120 is finely aligned with the optoelectronic device, and 
the solder is cooled, locking the optical fiber in its final, aligned 
position. 
Two basic searching techniques can be used to align an optical fiber with 
an optoelectronic device--a closed loop technique and an open loop 
technique. In a closed loop technique, the fiber is moved by steps a fixed 
distance in each direction along a particular axis, and data is acquired 
at each step. Upon completion of movement, the maximum signal position is 
identified. The fiber is then moved to the maximum position. The process 
is then repeated for another axis. After alignment along all axes, the 
fiber is in its final position. This technique is necessary when the light 
emitter is a multitransverse mode laser diode, which has many "side-lobes" 
in its emission output patterns. 
In an open loop technique, the fiber 120 is moved along an axis in each 
direction step by step. At each step of the movement, the current signal 
strength is compared with the signal strength from the previous step. If 
the signal strength in the current step is greater than the signal 
strength in the previous step, movement is continued in the current 
direction. If the signal strength decreases, the direction of fiber 120 
movement is reversed. Movement ends when the fiber is at the location 
where the signal strength is the greatest. An open loop search can be used 
only for optoelectronic devices that do not have multiple peaks in a 
search path. The present invention utilizes an open loop searching 
algorithm to align the optical fiber 120 with the optoelectronic device 
112 both during prealignment (FIG. 11) and during final alignment (FIG. 
13). 
FIG. 11 is a flow diagram illustrating a pre-locking automatic alignment 
subroutine suitable for use in the method of operation shown in FIG. 10. 
The pre-locking automatic alignment subroutine illustrated in FIG. 11 
includes three coarse alignment routines 1042, 1044, and 1046 followed by 
three fine alignment routines 1048, 1050, and 1052, all of which are 
substantially identical except for axial (x, y, z) and numerical distance 
(coarse, fine) differences. As a result, only one alignment routine, 
illustrated in FIGS. 12A and 12B, is described in detail. 
The alignment routine illustrated in FIGS. 12A and 12B is based on an open 
loop search algorithm. Beginning at any point along the axis to be 
searched, i.e., the x, y, or z axis, at step 1204, the power value, P, 
measured at the beginning position is inputted. P represents the PIN 
photocurrent as measured by the current measuring digital multimeter 728 
(FIG. 7) in the case of an optoelectronic receiver, or the LED coupled 
power as measured by the optical power meter 854 (FIG. 8) in the case of a 
photoelectronic transmitter. The input P value is stored as a saved P 
value. At step 1206, the fiber 120 position is changed along the axis in a 
first direction by a predetermined increment. The predetermined increment 
is based on whether the alignment routine is a coarse or fine alignment 
routine. While the coarse and fine alignment routines for each axis could 
have a different incremental value, preferably the same coarse and fine 
values are used along all of the axes. In one actual embodiment of the 
invention, the coarse alignment increment is 10 .mu.m and the fine 
alignment increment is 1 .mu.m. At step 1208, the process pauses to allow 
for fiber movement to be completed before new data is acquired. In one 
actual embodiment, a pause time of 0.46 second is employed for coarse 
alignment, and a pause time of 0.18 second is employed for fine alignment. 
At step 1210, a new P value is measured and input. At step 1212, the new P 
input value is compared with the saved P value. If the new P value is 
greater than or equal to the saved P value, at step 1214, the old saved P 
value is replaced with the new P value, and the process loops back to step 
1206. As a result, the search continues in the same direction. 
If, at step 1212, the saved P value is greater than the new P value, the 
optimal position has been passed. When this occurs, at step 1216, the 
fiber 120 is returned to the prior position along the chosen (same) axis. 
Thereafter the process pauses, at step 1218, to allow the fiber to return 
to its prior position before data is acquired. Then, at step 1220, P is 
measured and input. Then the old saved P value is replaced with the new P 
value. At step 1222, the direction of searching is reversed. More 
specifically, the fiber is moved by the predetermined increment in the 
opposite direction along the chosen axis. After a pause at step 1224, a 
new P value is measured and input at step 1226. Next, at block 1228, a 
test is made to determine if the new P value is equal to or greater than 
the saved P value. If the new P value is equal to or greater than the 
saved P value, the old saved P value is replaced with the new P value. 
Then the process cycles to step 1222 and the loop is repeated. 
If, at block 1228, the saved P value is found to be greater than the new P 
value, at step 1232, the optical fiber is returned to its prior position 
along the chosen axis, and the process is finished. 
The end result of the routine or process illustrated in FIGS. 12A and 12B 
and described above is to position the optical fiber at the location along 
the chosen axis where the maximum amount of light is transferred between 
the optoelectronic device 112 and the optical fiber. As shown in FIG. 11, 
the open loop search process is executed along all axes, i.e., along the 
x, y, and z axes. Coarse alignment along all three axes is followed by 
fine alignment along all three axes. Alternatively, other sequences can be 
used. For example, the alignment sequence may comprise a coarse alignment 
along the y-axis, a coarse alignment along the x-axis, a fine alignment 
along the y-axis, a fine alignment along the x-axis, a coarse alignment 
along the z-axis, and a fine alignment along the z-axis. Alternatively, 
only a single alignment process, i.e., a fine or coarse alignment process 
only along each axis could be implemented, with the obvious loss of speed 
of alignment or resolution. 
Careful control of the voltage applied at the resistor terminals 124 is 
necessary to achieve the proper temperature for melting the solder preform 
without detrimentally impacting the other elements of the optoelectronic 
package. More specifically, the temperature and duration of heat produced 
by the power applied to the resistor terminals must be sufficient to melt 
the solder with minimum material erosion. Further, overheating, which can 
also cause flux to char, if flux is used with the solder, must be avoided. 
FIG. 13 illustrates a process for controlling the application of voltage 
to the resistor/heater in accordance with the invention that achieves 
these desired results. Prior to describing FIG. 13, attention is directed 
to FIG. 14, which is a graph illustrating changes in voltage and 
temperature that occur over time as power is applied. 
In one actual embodiment of the invention, the solder preform 130, which 
consisted of Sn96.5 Ag3.5, had a melting temperature of 221.degree. C. The 
nominal resistance of the resistor/heater 122 of this embodiment of the 
invention was 15 ohms. It was experimentally found that applying 17.5 
volts to the resistor/heater 122 caused the desired 221.degree. C. 
solder-melting temperature to be achieved. Since the actual resistivity 
value of a resistor/heater 122 varies from a nominal value, e.g., 15 ohms, 
the resistance R.sub.m of each resistor/heater 122 should be measured 
before applying current. The following formula can be used to calculate 
the voltage (V.sub.a) required to achieve the same power dissipation: 
EQU V.sub.a =(17.5.sup.2 /15).multidot.R.sub.m !.sup.1/2 (1) 
The table below illustrates the voltage value and time schedule used by the 
preferred embodiment of the invention to achieve proper heating of the 
solder preform without excessive material erosion. In the table, the 
values in the column labeled "VOLTAGE" actually represent the control 
signals transmitted from the computer 704 to the power supply 726. 
Depending on the nature of the chosen power supply, minimal delays may 
exist between the computer control signal and the actual voltage applied 
to the resistor/heater 122. The "STEPS" column indicates the number of 
voltage change steps that occur during a particular interval. The purpose 
of the steps is described below. 
TABLE 1 
______________________________________ 
VOLTAGE VALUE AND TIME SCHEDULE 
VOLTAGE TIME Range NUMBER OF STEPS 
______________________________________ 
0 to V.sub.a 
From 0th to 8th second 
1 
V.sub.a to 0.94 V.sub.a 
From 8th to 16th second 
20 
0.94 V.sub.a to 0 
After the 16th second or the 
1 
final second after the fine 
alignment at the preform molten 
state 
______________________________________ 
FIG. 14 is a graphical representation of the voltage value and time 
schedule set forth in the above table. The solid line 1404 represents the 
voltage applied to the heater/resistor 122 over time. The dotted line 1406 
represents the temperature applied to the solder preform 130. As 
summarized in the above table, and illustrated in FIG. 14, at 0, V.sub.a 
is applied to the heater/resistor. After a short ramp-up period, the 
voltage remains constant at V.sub.a during the interval 1420. The constant 
voltage is denoted as a single step. During this interval, the temperature 
ramps up. See line 1406. At point 1408, during time intervals 1422 and 
1424, the voltage is reduced to 0.94 V.sub.a. The reduction occurs in a 
stepwise manner that includes 20 steps. 
Even though the voltage drops, the temperature continues to rise. At point 
1423, the resistor/heater 122 reaches a temperature (221.degree. C.) that 
causes the solder preform 130 to melt. At this point, an open loop 
automatic fine alignment routine of the type shown in FIG. 12 and 
described above begins. As will be better understood from viewing FIG. 13 
and the following discussion, the fine alignment routine finely aligns the 
optical fiber 120 along the x and y axes, which are the axes lying 
orthogonal to the z-axis. 
At point 1425 the final fine alignment routine ends. Typically, this occurs 
within two seconds of beginning the fine alignment process (point 1423). 
If the final fine alignment process completes before the scheduled end of 
the heating period (point 1225), voltage is continued to be applied and 
reduced in the stepwise manner described above. At the end of the heating 
period, if final fine alignment is completed, the voltage is turned off 
(point 1425). After a short ramp-down period, the voltage drops to zero. 
If the final fine alignment process requires time beyond the 20th step 
(time intervals 1422 and 1424), the voltage is maintained at 0.94 V.sub.a 
until alignment is completed and, then, is reduced to 0. 
The total solder molten time interval 1424 must be limited in order to 
avoid dissolving all of the nickel adhesion layer located between the 
solder preform and the nickel-chromium alloy layer 604. See FIG. 6. The 
maximum allowable period is 5 seconds for the parameters set forth in the 
foregoing table and described above. After the voltage ends, the solder 
preform temperature gradually returns to room temperature during time 
interval 1426. 
As will be appreciated by those skilled in this art and others, the voltage 
and time schedule to be used in an actual embodiment of the invention will 
depend on the resistance of the heater/resistor 122, the rate of heat 
dissipation of optoelectronic package 102, the thickness of the nickel 
layer 610, and the melting temperature of the solder preform 130, as well 
as other variables. The length of time that solder is molten must be 
sufficient to allow fine alignment of the optical fiber 120. Further, the 
thickness of the nickel layer 610 must be adequate for the nickel layer to 
survive erosion while molten solder is in contact with the nickel layer. 
Because the resistance of nickel-chromium alloy changes when it is heated 
for some period of time, minimizing the time of heating reduces the 
introduction of complexities in the soldering process, specifically, 
changes in the amount of voltage that must be applied. 
FIG. 13 is a flow diagram illustrating a final alignment and locking 
subroutine 1036 suitable for achieving the voltage value and time schedule 
illustrated in FIG. 14 and described above. At step 1304, the computer 704 
causes the power supply to output voltage V.sub.a. At step 1306, the 
process waits for the temperature of the resistor/heater 122, and 
correspondingly the temperature of the solder preform 130, to rise. Steps 
1304 and 1306 occur during the time interval 1420 illustrated in FIG. 14. 
At step 1308, at a time represented by point 1408 in FIG. 14, a test is 
made to determine if the predetermined time to solder melting has elapsed. 
If the predetermined time has not elapsed, at step 1314, the voltage is 
decreased by an amount represented by (V.sub.a -V.sub.b)/M, where V.sub.b 
represents the voltage at point 1410 in FIG. 14 (0.94 V.sub.a), and M 
represents the number of steps between points 1408 and 1410. At step 1316, 
the process waits the step time interval while maintaining a constant 
voltage. 
At step 1318, a test is made to determine if the end of the heating period 
has been reached, i.e., if point 1410 has been reached. If not, the 
process cycles to step 1308. When, at step 1308, the predetermined time to 
solder melting has elapsed, which is point 1409 in FIG. 14, at step 1310, 
fine alignment routines of the type shown in FIGS. 12A and 12B and 
described above occur along the x and y axes. Then, at step 1312, a test 
is made to determine if the heating period has ended. If not, the process 
cycles to step 1314. When the heating period ends, step 1312 or 1318, the 
computer turns off the power supply. See step 1320. 
The table below lists the values of some of the key software-controlled 
parameters of the pre-locking automatic alignment subroutine 1032 and the 
automated final alignment and locking subroutine 1036 utilized in one 
actual embodiment of the invention. Some of these values have been set 
forth above. 
TABLE 2 
______________________________________ 
KEY SOFTWARE CONTROLLED AMETERS 
Default 
Parameters 
Definition Value 
______________________________________ 
Wait time Waiting time after V.sub.a is applied to the 
8 seconds 
power supply 
Dwell time 
Time for voltage to change from V.sub.a to 
8 seconds 
0.94 .multidot. V.sub.a 
Voltage steps 
The number of steps to change from V.sub.a 
20 
to 0.94 .multidot. V.sub.a 
Temperature C. 
The room temperature 23.degree. C. 
Molten Expected time for final fine alignment 
2 seconds 
alignment time 
Coarse wait time 
Wait time after each 10 .mu.m stage of 
0.46 second 
coarse alignment in the x, y, and z 
directions for data acquistion 
Fine wait time 
Wait time after each 1 .mu.m stage of fine 
0.18 second 
alignment in the x, y and z directions 
for data acquisition 
______________________________________ 
The wait time parameter is the time interval 1420 in FIG. 14. The dwell 
time parameter is the time for the voltage output to change from V.sub.a 
to 0.94.multidot.V.sub.a, or the time between points 1408 and 1410. This 
is equivalent to the combination of time interval 1422 plus the time 
interval 1424. The voltage steps parameter is the number of steps during 
which the voltage V.sub.a is reduced to 0.94.multidot.V.sub.a. In the 
situation where fine alignment of the optical fiber 120 occurs faster than 
the expected time for fine alignment (molten alignment time), the program 
could be modified to end when alignment is complete, since it is not 
necessary to actually obtain a voltage of 0.94.multidot.V.sub.a. In such a 
program, the voltage can be reduced to 0 when fine alignment is completed. 
The molten alignment time parameter is the expected time needed for fine 
alignment, i.e., the time interval 1424 shown in FIG. 14. The coarse and 
fine wait times are the times required for fiber repositioning to occur 
before new data is acquired. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that various changes can be made therein 
without departing from the spirit of the invention. For example, the 
schedule of voltage and time control could be changed, or the steps 
carried out in other ways designed to accomplish the same functional 
result. Hence, it is to be understood that within the scope of the 
appended claims the invention can be practiced otherwise than as 
specifically described herein.