Note: Descriptions are shown in the official language in which they were submitted.
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HEADER ASSEMBLY HAVING
INTEGRATED COOLING DEVICE
BACKGROUND
Technological Field
This invention is generally concerned with the field of opto-electronic
systems
and devices. More specifically, embodiments of the present invention relate to
a
transistor header that includes various features directed to the enhancement
of the
reliability and performance of various electronic devices, such as lasers,
included in
the transistor header.
Related Technolo~y
Transistor headers, or transistor outlines ("TO"), are widely used in the
field
of opto-electronics, and may be employed in a variety of applications. As an
example, transistor headers are sometimes used to protect sensitive electrical
devices,
is and to electrically connect such devices to components such as printed
circuit boards
("PCB")
With respect to their construction, transistor headers often consist of a
cylindrical metallic base with a number of conductive leads extending
completely
through, and generally perpendicular to, the base. A glass hermetic seal
between the
2o conductive leads and the base provides mechanical and environmental
protection for
the components contained in the TO package, and electrically isolates the
conductive
leads from the metallic material of the base. Typically, one of the conductive
leads is
a ground lead that may be electrically connected directly to the base.
Various types of devices are mounted on one side of the base of the header
2s and connected to the leads. Generally, a cap is used to enclose the side of
the base
where such devices are mounted, so as to form a chamber that helps prevent
contamination or damage to those device(s). The specific characteristics of
the cap
and header generally relate to the application and the particular device being
mounted
on the base of the header. By way of example, in applications where an optical
device
3o is required to be mounted on the header, the cap is at least partially
transparent so to
allow an optical signal generated by the optical device to be transmitted from
the TO
package.
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Although transistor headers have proven useful, typical configurations
nevertheless pose a variety of unresolved problems. Some of such problems
relate
specifically to the physical configuration and disposition of the conductive
leads in
the header base. As an example, various factors conspire to compromise the
ability to
precisely control the electrical impedance of the glass/metal feedthru, that
is, the
physical bond between the conductive lead and the header base material. One
such
factor is the fact that there is a relatively limited number of available
choices with
respect to the diameter of the conductive leads that are to be employed.
Further, the
range of dielectric values of the sealing glass typically employed in these
configurations is relatively small. And, with respect to the disposition of
the
conductive leads, it has proven relatively difficult in some instances to
control the
position of the lead with respect to the through hole in the header base.
Yet other problems in the field concern those complex electrical and
electronic
devices that require many isolated electrical connections in order to function
properly.
Typically, attributes such as the size and shape of such devices and their
subcomponents are sharply constrained by various form factors, other
dimensional
requirements, and space limitations within the device. Consistent with such
form
factors, dimensional requirements, and space limitations, the diameter of a
typical
header is relatively small and, correspondingly, the number of leads that can
be
2o disposed in the base of the header, sometimes referred to as the
input/output ("I/O")
density, is relatively small as well.
Thus, while the diameter of the header base, and thus the I/O density, may be
increased to the extent necessary to ensure conformance with the electrical
connection
requirements of the associated device, the increase in base diameter is
sharply limited,
if not foreclosed completely, by the form factors, dimensional requirements,
and
space limitations associated with the device wherein the transistor header is
to be
employed.
A related problem with many transistor headers concerns the implications that
a relatively small number of conductive leads has with respect to the overall
3o performance of the device wherein the transistor header is used.
Specifically, devices
such as semiconductor lasers operate more efficiently if their driving
impedance is
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balanced with the impedance at the terminals. Impedance matching is often
accomplished through the use of additional electrical components such as
resistors,
capacitors and transmission lines such as microstrips or striplines. However,
such
components cannot be employed unless a sufficient number of conductive leads
are
available in the transistor header. Thus, the limited number of conductive
leads
present in typical transistor headers has a direct negative effect on the
performance of
the semiconductor laser or other device.
In connection with the foregoing, another aspect of many transistor headers
that forecloses the use of, for example, components required for impedance
matching,
1o is the relatively limited physical space available on standard headers. In
particular,
the relatively small amount of space on the base of the header imposes a
practical
limit on the number of components that may be mounted there. In order to
overcome
that limit, some or all of any additional components desired to be used must
instead be
mounted on the printed circuit board, some distance away from the laser or
other
is device contained within the transistor header. Such arrangements are not
without
their shortcomings however, as the performance of active devices in the
transistor
header, such as lasers and integrated circuits, depends to some extent on the
physical
proximity of related electrical and electronic components.
The problems associated with various typical transistor headers are not,
2o however, limited solely to geometric considerations and limitations. Yet
other
problems relate to the heat generated by components within, and external to,
the
transistor header. Specifically, transistor headers and their associated
subcomponents
may generate significant heat during operation. It is generally necessary to
reliably
and efficiently remove such heat in order to optimize performance and extend
the
25 useful life of the device.
However, transistor headers are often composed primarily of materials,
Kovar~ for example, that are not particularly good thermal conductors. Such
poor
thermal conductivity does little to alleviate heat buildup problems in the
transistor
header components and may, in fact, exacerbate such problems. Various cooling
3o techniques and devices have been employed in an effort to address this
problem, but
with only limited success.
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By way of example, solid state heat exchangers may be used to remove some
heat from transistor header components. However, the effectiveness of such
heat
exchangers is typically compromised by the fact that, due to variables such as
their
configuration and/or physical location relative to the primary components) to
be
cooled, such heat exchangers frequently experience a passive heat load that is
imposed by secondary components or transistor header structures not generally
intended to be cooled by the heat exchanger. The imposition on the heat
exchanger of
such passive heat loads thus decreases the amount of heat the heat exchanger
can
effectively remove from the primary component that is desired to be cooled,
thereby
to compromising the performance of the primary component.
As suggested above, the physical location of the heat exchanger or other
cooling device has various implications with respect to the performance of the
components employed present in the transistor header. On particular problem
that
arises in the context of thermoelectric cooler ("TEC") type heat exchangers
relates to
~5 the fact that TECs have hot and cold junctions. The cold junction, in
particular, can
cause condensation if the TEC is located in a sufficiently humid environment.
Such
condensation may materially impair the operation of components in the
transistor
header, and elsewhere.
Another concern with respect to heat exchangers is that the dimensions of
2o typical transistor headers are, as noted earlier, constrained by various
factors. Thus,
while the passive heat load placed on a heat exchanger could be at least
partly offset
through the use of a relatively larger heat exchanger, the diametric and other
constraints imposed on transistor headers by form factor requirements and
other
considerations place practical limits on the maximum size of the heat
exchanger.
25 Finally, even if a relatively large heat exchanger could be employed in an
attempt to offset the effects of passive heat loads, large heat exchangers
present
problems in cases where the heat exchanger, such as a TEC, is used to modify
the
performance of transistor header components such as lasers. For example, by
virtue
of their relatively large size, such heat exchangers are not well suited to
implementing
3o the rapid changes in laser performance that are required in many
applications because
such large heat exchangers heat up and cool down relatively slowly. Moreover,
the
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performance of the laser or other component may be further compromised if the
heat
exchanger is located relatively far away from the laser because the rate at
which heat
can be transferred with respect to the laser or other component is at least
partially a
function of the distance between the component and the heat exchanger.
s In view of the foregoing discussion, what is needed is a transistor header
having features directed to addressing the foregoing exemplary concerns, as
well as
other concerns not specifically enumerated herein. An exemplary transistor
header
should implement a relatively high I/O density without increasing the relative
diameter of the header. Moreover, the exemplary transistor header should be
io configured to precisely control the electrical impedance and permit
location of various
components in relatively close proximity to the active components, such as a
laser,
within the header without violating applicable form factors or other geometric
and
dimensional standards. Finally, the exemplary transistor header should include
features directed to facilitating a relative improvement in heat management
capability
~5 within the transistor header.
BRIEF SUMMARY OF AN EXEMPLARY EMBODIMENT OF THE INVENTION
In general, embodiments of the invention are concerned with a transistor
header including various features directed to enhancing the reliability and
performance of various electronic devices, such as lasers, included in the
transistor
2o header.
In one exemplary embodiment, a transistor header is provided that includes a
substantially cylindrical metallic base as well as a platform disposed in a
substantially
perpendicular orientation with respect to the base and extending through both
sides of
the base. The platform is constructed from an insulating material such as a
ceramic.
25 The platform is hermetically sealed to the base, and flat surfaces defined
by the
platform on either side of the base are configured to receive multiple
electrical
components. Moreover, the platform includes a plurality of conductive
pathways)
extending between the ends of the platform so that components on opposite
sides of
the base may be electrically connected with each other. On one end of the
platform, a
3o connector is provided that is in electrical communication with some or all
of such
conductive pathways.
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In this exemplary embodiment, a laser is disposed on top of a TEC, which, in
turn, is mounted to the platform. A cup having a transparent portion is
situated on the
base cooperates with the platform and the base to define a hermetic chamber
enclosing the laser and the TEC. Power is supplied to the TEC by way of a
laser
control system that communicates both with a light intensity measuring device
optically coupled to the laser and with a temperature sensing device thermally
coupled
to the laser.
In operation, power is supplied to the laser by way of the connector on the
platform and the laser emits light through the transparent portion of the cup.
The light
to intensity measuring device and the temperature sensing device provide data
on the
light intensity of the laser as a function of laser temperature and transmit
the data to a
control circuit which adjusts the power applied to the TEC, thereby raising or
lowering the temperature of the laser as necessary to meet the laser
performance
requirements.
These and other, aspects of embodiments of the present invention will become
more fully apparent from the following description and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the manner in which the above-recited and other advantages and
features of the invention are obtained, a more particular description of the
invention
2o briefly described above will be rendered by reference to specific
embodiments thereof
which are illustrated in the appended drawings. Understanding that these
drawings
depict only typical embodiments of the invention and are not therefore to be
considered limiting of its scope, the invention will be described and
explained with
additional specificity and detail through the use of the accompanying drawings
in
which:
Figure lA is a perspective view illustrating various aspects of the device
side
of an exemplary embodiment of a header assembly;
Figure IB is a perspective view illustrating various aspects of the connector
side of an exemplary embodiment of a header assembly;
Figure 2A is a perspective view illustrating various aspects of the device
side
of an alternative embodiment of a header assembly;
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Figure 2B is a perspective view illustrating various aspects of the connector
side of an alternative embodiment of a header assembly;
Figure 3A is a perspective view illustrating various aspects of the device
side
of another alternative embodiment of a header assembly;
Figure 3B is a perspective view illustrating various aspects of the connector
side of another alternative embodiment of a header assembly;
Figure 4A is a top perspective view of an exemplary embodiment of a header
including active devices mounted on a TEC disposed within a hermetic chamber;
Figure 4B is a bottom perspective view of the exemplary embodiment
to illustrated in Figure 4A;
Figure 4C is a cross-section view illustrating various aspects of the
exemplary
embodiment presented in Figures 4A and 4B;
Figure 4D is a cross-section view taken along line 4D-4D of Figure 4C and
illustrates various aspects of an exemplary arrangement of a TEC in a header
t5 assembly;
Figure 4E is a side view illustrating aspects of an exemplary electrical
connection scheme for the header assembly and a printed circuit board;
Figure 4F illustrates various aspects of an alternative platform/TEC
configuration where the TEC is located outside the hermetic chamber; and
2o Figure 5 is a schematic diagram illustrating various aspects of an
exemplary
embodiments of a laser control system.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Reference will now be made to figures wherein like structures will be
provided with like reference designations. It is to be understood that the
drawings are
25 diagrammatic and schematic representations of various embodiments of the
claimed
invention, and are not to be construed as limiting the scope of the present
invention in
any way, nor are the drawings necessarily drawn to scale.
Reference is first made to Figures lA and 1B together, which illustrate
perspective views of one presently preferred embodiment of a header assembly,
3o designated generally at 200. In the illustrated example, the header
assembly 200
includes a substantially cylindrical metallic base 10. The base 10 includes
two
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flanges 90 used to control angular or rotational alignment of the header 200
to a
receptacle (not shown) on a higher level opto-mechanical assembly. The base
can be
formed of Alloy 42, which is an iron nickel alloy, as well as cold-rolled
steel, or
Vacon VCF-25 Alloy. The base 10 also includes a ceramic platform 70 extending
s perpendicularly through the base as shown. The ceramic platform is
hermetically
sealed to the base to provide mechanical and environmental protection for the
components contained in the TO package.
The hermetic seal between the base 10 and the platform 70 is created by
electrically insulating glass-to-metal seals. Alternatively, the platform 70
may
to incorporate two additional ceramic outer layers to electrically isolate the
outermost
conductors. In this second case, a metal braze or solder can be used to
hermetically
seal the platform 70 to the metal base. This solution overcomes the principal
shortcomings of glasses, namely their low strength, brittleness, and low
thermal
conductivity.
is The platform 70 is structured to house multiple electrical components 50
and
100, and active devices 60 on either side of the base. In the illustrated
embodiment,
the active device 60 comprises a semiconductor laser, and the components 50
and 100
are resistors, capacitors, and inductors that are used to balance the driving
impedance
of the laser with the component impedance. As it is important for a
semiconductor
20 laser to be precisely positioned perpendicularly to the base 10, platform
70 is,
therefore, precisely positioned perpendicularly with respect to the base 10.
Where active device 60 comprises a semiconductor laser, a small deviation in
the position of active device 60, in relation to base 10 can cause a large
deviation in
the direction of the emitted laser beam. Accurate perpendicularity between the
25 platform and the base can be achieved by incorporating a vertical pedestal
feature in
the base material, as shown on Figure lA. The vertical pedestal houses the
photodiode
30 in the embodiment shown in Figure lA. Such feature can be machined,
stamped,
or metal injection molded directly with the base thus providing a stable and
geometrically accurate surface for mating with the platform.
3o The platform 70 further includes multiple electrically isolated conductive
pathways 110 extending throughout the platform 70 and consequently through the
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base 10. The conductive pathways 110 provide the electrical connections
necessary
between electrical devices or components located throughout the platform 70.
The
conductive pathways 110 form a connector on that side of the base that does
not
include the semiconductor laser 60, also referred to herein as the "connector
side" of
the base. Note in connection with the foregoing that the side of the base
where the
active device 60 is located may in some instances be referred to herein as the
"device
side" of the base.
The connector formed by the conductive pathways 110 is used to electrically
connect the header assembly 200 to a second electrical subassembly, such as a
printed
1o circuit board, either directly (for example, by solder connection) or
indirectly by an
intermediary device such as a flexible printed circuit. The semiconductor
laser 60 is
electrically connected to the electrical components 50 and 100 via the
conductive
pathways 110. In one embodiment, the platform 70 is itself a printed circuit
board
having conductive pathways 110 formed therein.
~5 The use of advanced ceramic materials, examples of which include aluminum
nitride and beryllia, allows the header assembly 200 to achieve substantially
lower
thermal resistances between the devices inside the package and the outside
world
where heat is ultimately transferred. As discussed in further detail below in
the
context of an alternative embodiment of the invention, a cooling device, such
as a
2o thermoelectric cooler ("TEC"), a heat pipe or a metal heat spreader, can be
mounted
directly on the platform, thereby providing for a very short thermal path
between the
temperature sensitive devices on the platform and a heat sink located outside
the
header assembly.
As is further shown in Figures lA and 1B, the header assembly 200 can
2s additionally include two conductive leads 40 extending through and out both
sides of
the base 10. The conductive leads 40 are hermetically sealed to the base 10 to
provide
mechanical and environmental protection for the components contained in the TO
package between the conductive leads 40 and the base 10. The hermetic seal
between
the conductive leads 40 and the base 10 is created, for example, by glass or
other
30 comparable hermetic insulating materials that are known in the art. The
conductive
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leads 40 can also be used to electrically connect devices and/or components
located
on opposite sides of the base.
In the illustrated embodiment at least, the conductive leads 40 extend out
from
the side of the base 10 that does not contain the semiconductor laser 60, in a
manner
s that allows for the electrical connection of the header assembly 200 with a
specific
header receptacle located on, for example, a printed circuit board. It is
important to
note that conductive pathways 110 and conductive leads 40 perform the same
function
and that the number of potential conductive pathways 110 is far greater than
the
potential number of conductive leads 40. Therefore, alternative embodiments
can
to incorporate even more conductive pathways 110 than shown in the illustrated
embodiment.
The platform 70 further includes steps and recessed areas that permit
mounting devices with various thicknesses flush with the metal pads on the
ceramic.
This allows the use of the shortest electrical interconnects, wire bonds for
example,
15 having improved electrical performance and characteristics.
The photodiode 30 is used to detect the signal strength of the semiconductor
laser 60 and relay this information back to control circuitry (see Figure 5)
of the
semiconductor laser 60. In the illustrated embodiment, the photodiode can be
directly
connected to the conductive leads 40. Alternatively, the photodiode can be
mounted
2o directly onto the same platform as the laser, in a recessed position with
respect to the
light emitting area. This recessed position allows the photodiode to capture a
fraction
of the light emitted by the laser, thus allowing the photodiode to perform the
same
monitoring function. In yet another configuration, as shown in Figure 4C, a
monitor
photodiode 1004 with an angled facet can be mounted in a plane behind the
laser
25 diode. The angled facet deflects the light emitted from the back-facet of
the laser
upwards toward the sensitive area of the detector.
The configurations of the monitoring photodiode discussed in the previous
paragraph allow for eliminating the need of conductive leads 40, and lends
themselves
to simplified electrical connections, such as wire bonds, to the conductive
pathways
30 110 of the platform 70. In an alternative embodiment, the photodiode light
gathering
can be increased by positioning an optical element on the base for focusing or
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redirecting light, such as a minor, or by directly shaping and/or coating the
base metal
to focus additional light onto the photodiode
As is further shown in Figures lA, the base 10 includes a protruding portion
45 that is configured to releasably position or locate a cap (not shown) over
one side
of the base 10. A cap can be placed over the side of the base 10 containing
the
semiconductor laser 60 for the purpose of protecting the semiconductor laser
60 from
potentially destructive particles. A transparent cap is preferable for the
illustrated
embodiment so as to allow the laser light to escape the region between the cap
and the
base 10.
Reference is next made to Figures 2A and 2B, which illustrate perspective
views of an alternative embodiment of a header assembly, designated generally
at
300. This alternative embodiment shows an optical receiver 360 mounted
horizontally on the platform 370 perpendicularly bisecting the base 310 of the
header
assembly 300. The optical receiver can be a photodetector or any other device
is capable of receiving optical signals. The optical receiver 360 is mounted
flat on the
platform 370 and detects light signals through the side facing away from the
base 310.
This type of optical receiver is sometimes referred to as an "edge detecting"
detector.
The base 310 and platform 370 are described in more detail with reference to
Figures
lA and 1B. The platform 370 contains electrical components 350, 400 on either
side
20 of the base for operating the optical receiver 360. The platform 370 also
includes
conductive pathways 410 for electrically connecting devices or components on
either
side of the base 310. This embodiment of a header assembly does not contain
conductive leads and therefore all electrical connections are made via the
conductive
pathways 410.
2s Reference is next made to Figures 3A and 3B, which illustrate perspective
views of yet another alternative embodiment of a header assembly, designated
generally at 500. This alternative embodiment also shows an optical receiver
530
mounted vertically on the base 510. The optical receiver can be a
photodetector or
any other device capable of receiving optical signals. This is an optical
receiver 530
3o which detects light signals from the top of the device. The base 510 and
platform 570
are described in more detail with reference to Figures lA and 1B. The platform
570
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contains electrical components 550, 600 on either side of the base for
operating the
optical receiver 530. The platform 570 also includes conductive pathways 510
for
electrically connecting devices or components on either side of the base 510.
This
embodiment of a header assembly does not contain conductive leads and
therefore all
electrical connections are made via the conductive pathways 410.
Directing attention now to Figures 4A through 4D, various aspects of an
alternative embodiment of a header assembly, generally designated at 700, are
illustrated. The embodiment of the header assembly illustrated in Figures 4A
through
4D is similar in many regards to one or more of the embodiments of the header
assembly illustrated in Figures lA through 3B. Accordingly, the discussions of
Figures 4A through 4D will focus primarily on certain selected aspects of the
header
assembly 700 illustrated there. Note that in one embodiment of the invention,
header
assembly 700 comprises a transistor header. However, header assembly 700 is
not
limited solely to that exemplary embodiment.
As indicated in Figures 4A through 4D, header assembly 700 generally
includes a base 702 through which a platform 800 passes. Platform 800 may
comprise a printed circuit board or, as discussed herein, may comprise other
materials
and/or configurations as well. The platform 800 is configured to receive a
cooling
device 900 upon which various devices and circuitry are mounted. Note that
while it
2o may be referred to herein as a "cooling" device 900, the cooling device 900
may,
depending upon its type and the application where it is employed, serve both
to heat
and/or cool various components and devices. Finally, a cap 704 mounted to, and
cooperating with, base 702, serves to define a hermetic chamber 706 which
encloses
cooling device 900 and the mounted devices and circuitry.
As discussed in further detail below, a variety of means may be employed to
perform the functions disclosed herein, of a cooling device. Thus, the
embodiments
of the cooling device disclosed and discussed herein are but exemplary
structures that
function as a means for transferring heat. Accordingly, it should be
understood that
such structural configurations are presented herein solely by way of example
and
3o should not be construed as limiting the scope of the present invention in
any way.
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Rather, any other structure or combination of structures effective in
implementing the
functionality disclosed herein may likewise be employed.
With continuing attention to Figures 4A and 4B, and directing attention also
to
Figures 4C and 4D, further details are provided concerning various aspects of
platform 800. In the illustrated embodiment, platform 800 is disposed
substantially
perpendicularly with respect to base 702. In particular, base 702 includes a
device
side 702A and a connector side 702B, and platform 800 passes completely
through
base 702, so that an inside portion 801A of platform 800 is disposed on device
side
702A of base 700 and outside portion 801B of platform 800 is disposed on
connector
side 702B of base 702. However, this arrangement of platform 800 is exemplary
only, and various other arrangements of platform 800 may alternatively be
employed
consistent with the requirements of a particular application.
In the illustrated embodiment, platform 800 includes a f rst feedthru 802
having a mufti-layer construction that includes one or more layers 804 of
conductive
~5 pathways 806 (see Figure 4A). In general, conductive pathways 806 permit
electrical
communication among the various components and devices (removed for clarity)
disposed on platform 800, while also permitting such components and devices to
electrically communicate with other components and devices that are not a part
of
platform 800. Moreover, conductive pathways 806 cooperate to form a connector
810
2o situated on the outside portion 801 B of platform 800, on the connector
side 702B of
base 700. In general, connector 810 facilitates electrical communication
between
header assembly 700 and other components and devices such as, but not limited
to,
printed circuit boards (see Figure 4E). In one embodiment, connector 810
comprises
an edge connector, but any other form of connector may alternatively be used,
25 consistent with the requirements of a particular application. As discussed
in further
detail below, first feedthru 802 may include cutouts 811 or other geometric
features
which permit direct access to, and electrical connection with, one or more
conductive
pathways 806 disposed on an inner layer of first feedthru 802.
In addition to the first feedthru 802, platform 800 further includes a second
3o feedthru 812 to which the first feedthru 802 is attached. Note that in the
exemplary
illustrated embodiment, first feedthru 810, with the exception of conductive
pathways
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806, may comprise a material that is generally resistant to heat conduction,
such as a
ceramic with low thermal conductivity, such as alumina for example. Low
thermal
conductivity ceramics may be more desirable in some instances than high
thermal
conductivity ceramics, such as aluminum nitrade or beryllia, due to the
relatively
lower cost of such low thermal conductivity ceramics, as well as the ease with
which
such low thermal conductivity ceramics can be brazed to various metals such as
may
be used in the construction of header assembly 700. In contrast, second
feedthru 812
in the illustrated embodiment comprises a material that is generally useful as
a heat
conductor, such as a metal. Various copper-tungsten alloys are examples of
metals
to that are suitable in some applications. Thus, platform 800 is generally
configured to
combine heat conductive elements with non-heat conductive elements so as to
produce a desired effect or result concerning the device wherein platform 800
is
employed.
In connection with the foregoing, it should be noted further that ceramics and
metals are exemplary materials only and any other material or combination
thereof
that will facilitate implementation of the functionality disclosed herein may
alternatively be employed. Moreover, other embodiments of the invention may
employ different arrangements and numbers of, for example, conductive and non-
conductive feedthrus, or feedthrus having other desirable characteristics.
2o Accordingly, the illustrated embodiments are exemplary only and should not
be
construed to limit the scope of the invention in any way.
With respect to their configurations, the geometry of both first feedthru 802
and second feedthru 812 may generally be configured as necessary to suit the
requirements of a particular application or device. In the exemplary
embodiment
illustrated in Figures 4A through 4D, second feedthru 812 incorporates a step
812A
feature which serves to, among other things, provide support for cooling
device 900
and, as discussed in further detail below, to ensure that devices mounted to
cooling
device 900 are situated at a desirable location and orientation. As further
indicated in
Figure 4D, for example, second feedthru 812 defines a semi-cylindrical bottom
that
3o generally conforms to the shape of cap 704 and contributes to the stability
of cooling
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device 900, as well as providing a relatively large conductive mass that aids
in heat
conduction to and/or from, as applicable, cooling device 900 and other
devices.
As suggested earlier, platform 800 also serves to provide support to cooling
device 900. Directing renewed attention now to Figures 4A through 4D, details
are
provided concerning various aspects of cooling device 900. In particular, a
cooling
device 900 is provided that is mounted directly to platform 800. In an
exemplary
embodiment, cooling device 900 comprises a thermoelectric cooler ("TEC") that
relies for its operation and usefulness on the Peltier effect wherein
electrical power
supplied to the TEC may, according to the requirements of a particular
application,
1o cause selected portions of the TEC to generate heat and/or provide a
cooling effect.
Exemplary construction materials for the TEC may include, but are not limited
to,
bismuth-telluride combinations, or other materials with suitable
thermoelectric
properties.
Note that the TEC represents an exemplary configuration only, and various
other types of cooling devices may alternatively be employed as required to
suit the
dictates of a particular application. By way of example, where active
temperature
control of one or more electronic devices 1000, aspects of which are discussed
in
more detail below, is not required, the TEC may be replaced with a thermally
conductive spacer or similar device.
2o In addition to providing heating and/or cooling functionality, cooling
device
900 also includes a submount 902 that supports various electronic devices 1000
such
as, but not limited to, resistors, capacitors, and inductors, as well as
optical devices
such as mirrors, lasers, and optical receivers. Thus, cooling device 900 is
directly
thermally coupled to electronic devices 1000.
In one exemplary embodiment, the electronic devices 1000 include a laser
1002, such as a semiconductor laser, or other optical signal source. With
regard to
devices such as laser 1002, at least, cooling device 900 is positioned and
configured to
ensure that laser 1002 is maintained in a desired position and orientation. By
way of
example, in some embodiments of the invention, cooling device 900 is
positioned so
3o that an emitting surface of laser 102 is positioned at, and aligned with, a
longitudinal
axis A-A of header assembly 700 (Figure 4C).
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Note that although reference is made herein to the use of a laser 1002 in
conjunction with cooling device 900, it should be understood that embodiments
employing laser 1002 are exemplary only and that additional or alternative
devices
may likewise be employed. Accordingly, the scope of the invention should not
be
construed to be limited solely to lasers and laser applications.
In at least some of those embodiments where a laser 1002 is employed, a
photodiode 1004 and thermistor 1006 (see Figure 4D) are also mounted to, or
proximate, submount 902 of cooling device 900. In general, photodiode 1004 is
optically coupled with laser 1002 such that photodiode 1004 receives at least
a portion
to of the light emitted by laser 1002, and thereby aids in gathering light
intensity data
concerning laser 1002 emissions. Further, thermistor 1006 is thermally coupled
with
laser 1002, thus permitting the gathering of data concerning the temperature
of laser
1002.
In some embodiments, photodiode 1004 comprises a 45 degree monitor
is photodiode. The use of this type of diode permits the related components,
such as
laser 1002 and thermistor 1006 for example, to be mounted and wirebonded on
the
same surface. Typically, the 45 degree monitor diode is arranged so that light
emitted
from the back of laser 1002 is refracted on an inclined surface of the monitor
diode
and captured on a top sensitive surface of the monitor diode. In this way, the
monitor
2o diode is able to sense the intensity of the optical signal emitted by the
laser.
Note that in those embodiments where a laser 1002 is employed, cap 704
includes an optically transparent portion, or window, 704A through which light
signals generated by the laser 1002 are emitted. Similarly, in the event
electronic
device 1000 comprises other optical devices, such as an optical receiver, cap
704
z5 would likewise include a window 704A so as to permit reception, by the
optical
receiver, of light signals. As suggested by the foregoing, the construction
and
configuration of cap 704 may generally be selected as required to suit the
parameters
of a particular application.
In view of the foregoing general discussion concerning various electronic
3o devices 1000 that may be employed in conjunction with cooling device 900,
further
attention is directed now to certain aspects of the relation between such
electronic
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devices 1000 and cooling device 900. In general, cooling device 900 may be
employed to remove heat from, or add heat to, one or more of the electronic
devices
1000, such as laser 1002, in order to achieve a desired effect. As discussed
in further
detail herein, the capability to add and remove heat, as necessary, from a
device such
s as laser 1002, may be employed to control the performance of laser 1002.
In an exemplary embodiment, the heating and cooling, as applicable, of
electronic devices 1000 is achieved with a cooling device 900 that comprises a
TEC.
Various aspects of the arrangement and disposition of electronic devices 1000,
as welt
as cooling device 900, serve to enhance these ends. By way of example, the
fact that
to electronic devices 1000 are mounted directly to cooling device 900 results
in a
relatively short thermal path between electronic devices 1000 and cooling
device 900.
Generally, such a relatively shorter thermal path between components
translates to a
corresponding increase in the efficiency with which heat may be transferred
between
those components. Such a result is particularly useful where devices whose
operation
is and performance is highly sensitive to heat and temperature changes, such
as lasers,
are concerned. Moreover, a relatively short thermal path also permits the
transfer of
heat to be implemented relatively more quickly than would otherwise be the
case.
Because heat transfer is implemented relatively quickly, this exemplary
arrangement
can be used to effectively and reliably maintain the temperature of laser 1002
or other
2o devices.
Another aspect of at least some embodiments relates to the location of cooling
device 900 relative, not just to electronic devices 1000, but to other
components,
devices, and structures of header assembly 700. In particular, because cooling
device
900 is located so that the potential for heat transmission, whether radiative,
2s conductive, or convective, from other components, devices, and structures
of header
assembly 700 to cooling device 900 is relatively limited, the passive heat
load
imposed on cooling device 900 by such other components and structures is
relatively
small. Note that, as contemplated herein, the "passive" heat load generally
refers to
heat transferred to cooling device 900 by structures and devices other than
those upon
3o which cooling device 900 is primarily intended to exert a heating and/or
cooling
effect. 'thus, in this exemplary embodiment, "passive" heat loads refers to
all heat
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loads imposed on cooling device 900 except for those heat loads imposed by
electronic devices 1000.
The relative reduction in heat load experienced by cooling device 900 as a
consequence of its location has a variety of implications. For example, the
reduced
heat load means that a relatively smaller cooling device 900 may be employed
than
would otherwise be the case. This is a desirable result, particularly in
applications
such as header assemblies where space may be limited. As another example, a
relatively smaller cooling device 900, at least where cooling device 900
comprises a
TEC, translates to a relative decrease in the amount of electrical power
required to
io operate cooling device 900.
Another consideration relating to the location of cooling device 900 concerns
the performance of laser 1002 and the other electronic components 1000
disposed in
hermetic chamber 706. In particular, the placement of cooling devices 900,
such as
TECs that include a "cold" connection, in hermetic chamber 706 substantially
~5 forecloses the occurrence of condensation, and the resulting damage to
other
components and devices of header assembly 700, caused by the cold connection,
that
might otherwise result if cooling device 900 were located outside hermetic
chamber
706.
In addition to the heat transfer effects that may be achieved by way of the
20 location of cooling device 900, and the relatively short thermal path that
is defined
between cooling device 900 and the electronic devices 1000 mounted to submount
902 of cooling device 900, yet other heat transfer effects may be realized by
way of
various modifications to the geometry of cooling device 900. In connection
with the
foregoing, it is generally the case that by increasing the size of cooling
device 900, a
25 relative increase in the capacity of cooling device 900 to process heat
will be realized.
In this regard, it should be noted that it is the case in many applications
that
the diameter of base 702 is o8en constrained to fit within certain
predetermined form
factors or dimensional requirements and that such form factors and dimensional
requirements, accordingly, have certain implications with respect to the
geometric and
3o dimensional configuration of cooling device 900.
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By way of example, the diametric requirements placed on base 702 may serve
to limit the overall height and width of cooling device 900 (see, e.g., Figure
4D). In
contrast however, the overall length of header assembly 700 is generally not
so rigidly
constrained. Accordingly, certain aspects of cooling device 900, such as its
length for
s example, may desirably be adjusted to suit the requirements of a particular
application. In the case of a TEC, for example, such a dimensional increase
translates
into a relative increase in the amount of heat that cooling device 900 can
process. As
noted earlier, such heat processing may include transmitting heat to, and/or
removing
heat from, one or more of the electronic components 1000, such as laser 1002.
t0 Moreover, various dimensions and geometric aspects of cooling device 900
may be varied to achieve other thermal effects as well. By way of example, in
the
event cooling device 900 comprises a TEC, a relatively smaller cooling device
900
will permit relatively quicker changes in the temperature of electronic
devices 1000
mounted thereto. In the case where electronic device 1000 comprises a laser,
this
is capability is particularly desirable as it lends itself to control of laser
performance
through the vehicle of temperature adjustments.
Turning now to consideration of the power requirements for cooling device
900, at least where it comprises a TEC, and electronic devices 1000, it was
suggested
earlier herein that those devices typically rely for their operation on a
supply of
2o electrical power. Generally, the TEC must be electrically connected with
platform
800 so that power for the operation of the TEC, transmitted from a power
source (not
shown) to platform 800, can be directed to the TEC. Additionally, power is
supplied
to electronic devices 1000 by way of platform 800, and electronic devices 1000
must,
accordingly, be connected with one or more of the conductive pathways 806 of
25 platform 800.
The foregoing electrical connections and configurations may be implemented
in a variety of ways. Various aspects of exemplary connection schemes are
illustrated
in Figures 4A, 4B and 4E. With reference first to Figure 4B, the underside of
submount 902 of cooling device 900 is connected with conductive elements 814
3o disposed on the underside of first feedthru 802, by way of connectors 816
such as, but
not limited to, wire bonds. Such conductive elements 814 may be electrically
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connected with selected conductive pathways 806 (see Figure 4A) and/or
connector
810, that are ultimately connected with an electrical power source (not
shown).
Directing attention next to Figure 4A, details are provided concerning various
aspects of the electrical connection of electronic devices 1000 disposed on
submount
902. As noted earlier, and illustrated in Figure 4A, some embodiments of
platform
800 include one or more cutouts 811, or other geometric feature, that permits
direct
connection of electronic devices 1000, such as laser 1002 to one or more
conductive
pathways 806 disposed within first feedthru 802 of platform 800. This
connection
may be implemented by way of connectors 818 such as bond wires, or other
1o appropriate structures or devices. In addition to the aforementioned
connection, and
as illustrated in Figure 4E, at least some embodiments of the invention
further include
a flex circuit 820, or similar device, which serves to electrically
interconnect platform
800 of header assembly 700 with another device, such as a printed circuit
board.
With attention now to Figures 4A through 4D, details are provided concerning
is various operational aspects of header assembly 700. In general, power is
provided to
laser 1002 and/or other electrical components 1000 by way of connector 810,
conductive pathways 806, and connectors 818. In response, laser 1002 emits an
optical signal. Heat generated as a result of the operation of laser 1002,
and/or other
electronic components 1000, is continuously removed by cooling device 900,
which
2o comprises a TEC in at least those cases where a laser 1002 is employed in
header
assembly 700, and transferred to second feedthru 812 upon which cooling device
900
is mounted. Ultimately, second feedthru 812 transfers heat received from
cooling
device 900 out of header assembly 700.
Because cooling device 900 is disposed within hermetic chamber 706, the cold
25 junction on cooling device 900, where it comprises a TEC, does not produce
any
undesirable condensation that could harm other components or devices of header
assembly 700. Moreover, the substantial elimination of passive heat loads on
cooling
device 900, coupled with the definition of a relatively short thermal path
between
electronic components 1000, such as laser 1002, and cooling device 900,
further
3o enhances the efficiency with which heat can be removed from such electronic
components and, accordingly, permits the use of relatively smaller cooling
devices
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900. And, as discussed earlier, the relatively small size of cooling device
900
translates to a relative decrease in the power required to operate cooling
device 900.
Yet other operational aspects of embodiments of the invention are considered
in
further detail below in the context of the discussion of a laser control
system.
While, as noted earlier in connection with the discussion of Figures 4A
through 4D, certain effects may be achieved by locating cooling device 900
within
hermetic chamber 706, it is nevertheless desirable in some cases to locate the
cooling
device outside of the hermetic chamber. Aspects of an exemplary embodiment of
such a configuration are illustrated in Figure 4F, where an alternative
embodiment of
1o a header assembly is indicated generally at 1100. As the embodiment of the
header
assembly illustrated in Figure 4F is similar in many regards to one or more of
the
embodiments of the header assembly discussed elsewhere herein, the discussion
of
Figure 4F will focus primarily on certain selected aspects of the header
assembly
1100 illustrated there.
Similar to other embodiments, header assembly 1100 includes a base 1102
having a device side 1102A and a connector side 1102B, through which a
platform
1200 passes in a substantially perpendicular orientation. The platform 1200
includes
an inside portion 1202A and an outside portion 1202B. One or more electronic
devices 1300 are attached to inside portion 1202A of platform 1200 so as to be
2o substantially enclosed within a hermetic chamber 1104 defined by a cap 1106
and
base 1102. In the event that electronic device 1300 comprises an optical
device, such
as a laser, cap 1106 may further comprise an optically transparent portion, or
window,
1106A to permit optical signals to be transmitted from and/or received by one
or more
electronic devices 1300 disposed within hermetic chamber 1104.
With continuing reference to Figure 4F, platform 1200 further comprises a
first feedthru 1204, upon which electronic devices 1300 are mounted, joined to
a
second feedthru 1206 that includes an inside portion 1206A and an outside
portion
1206B. The outside portion 1206B of second feedthru 1206 is, in turn,
thermally
coupled with a cooling device 1400. In the illustrated embodiment, cooling
device
1400 comprises a TEC. However, other types of cooling devices may
alternatively be
employed.
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In operation, heat generated by electronic devices 1300 is transferred,
generally by conduction, to second feedthru 1206. The heat is then removed
from
feedthru 1206 by way of cooling device 1400 which, in some embodiments,
comprises a TEC. As in the case of other embodiments, a TEC may also be
employed, if desired, to add heat to electronic devices 1300.
Thus positioned and arranged, cooling device 1400 is able not only to
implement various thermal effects, such as heat removal or heat addition, with
respect
to electronic devices 1300 located inside or outside hermetic chamber 1104,
but also
operates to process passive heat loads, which may be conductive, convective
and/or
radiative in nature, imposed by various components such as the structural
elements of
header assembly 1500. As noted herein in the context of the discussion of
various
other embodiments, variables such as, but not limited to, the geometry,
placement,
and construction materials of platform 1200 and cooling device 1400 may be
adjusted
as necessary to suit the requirements of a particular application.
~s As suggested earlier, at least some embodiments of the cooling device may
be
usefully employed in the context of a laser control system. Directing
attention now to
Figure 5, various aspects of an exemplary embodiment of a laser control
system,
indicated generally at 2000, are illustrated.
As indicated in Figure 5, laser control system 2000 includes a temperature
2o sensing device 2002, such as a thermistor, which is thermally coupled with
a laser
2004, such as a semiconductor laser. Laser control system 2000 further
includes a
light intensity sensing device 2006, such as a photodiode, that is optically
coupled
with laser 2004. Further, a TEC 2008 is thermally coupled with laser 2004. In
at
least one embodiment, such thermal coupling is achieved by mounting laser 2004
2s directly to a submount of TEC 2008. Laser control system 2000 further
includes a
control circuit 2010 configured to receive inputs from temperature sensing
device
2002 and light intensity sensing device 2006, and to send corresponding
control
signals to a power source 2012 in communication with TEC 2008.
In general, operation of laser control system 2000 proceeds as hereafter
3o described. In particular, the intensity of the optical signal emitted by
laser 2004 is
sensed, either directly or indirectly, by light intensity sensing device 2006.
Light
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intensity sensing device 2006 then transmits, from time to time, a
corresponding
signal to control circuit 2010. In at least some embodiments, the temperature
of laser
2004 may be regulated by TEC 2008 so as to achieve wavelength stabilization.
This
can be achieved by way of control circuit 2010 and power source 2012.
Additionally, temperature sensing device 2002 is positioned and configured to
measure the temperature of laser 2004 and transmit, from time to time, a
corresponding signal to control circuit 2010. Based upon inputs received from
temperature sensing device 2002 and light intensity sensing device 2006,
control
circuit 2010 is able to implement changes to the temperature of laser 2004 by
way of
to power source 2012 and TEC 2008.
In particular, because TEC 2008 may be configured to add and/or remove heat
from laser 2004, laser control system 2000 thus affords the ability to, among
other
things, change and/or maintain the temperature of laser 2004 as desired or
required by
a particular application. Thus control circuit 2010 cooperates with TEC 2008
to
t 5 control both the direction and amount of heat flow with respect to laser
2004. In this
way, various operational parameters of the signal emitted by laser 2004 may
desirably
be adjusted.
That is, embodiments of laser control system 2000 are capable of not only
maintaining the temperature of active devices such as laser 2004 below a
critical
2o value at which laser 2004 performance begin to degrade and reliability
becomes an
issue, but embodiments of laser control system 2000 also enable control of the
temperature of active devices such as laser 2004 at a given value independent
of
ambient temperature conditions, so as to achieve certain ends such as, in the
case of
laser 2004 operation for example, wavelength stabilization.
25 The present invention may be embodied in other specific forms without
departing from its spirit or essential characteristics. The described
embodiments are
to be considered in all respects only as illustrative and not restrictive. The
scope of
the invention is, therefore, indicated by the appended claims rather than by
the
foregoing description. All changes which come within the meaning and range of
3o equivalency of the claims are to be embraced within their scope.
What is claimed is:
