U.S. patent application number 09/897350 was filed with the patent office on 2002-09-05 for switch-mode bi-directional thermoelectric control of laser diode temperature.
Invention is credited to VanHoudt, Paulus Joseph.
Application Number | 20020121094 09/897350 |
Document ID | / |
Family ID | 26955864 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020121094 |
Kind Code |
A1 |
VanHoudt, Paulus Joseph |
September 5, 2002 |
Switch-mode bi-directional thermoelectric control of laser diode
temperature
Abstract
A system for actively heating and cooling an object contains a
thermoelectric device having a Peltier junction. The system is
capable of reversing the direction of DC current flow through the
Peltier junction so that the thermoelectric cooler/heater either
heats or cools the object, as selected. The DC power supply is
preferably operated in switch-mode. The thermoelectric device is
disposed in a laser diode module or in heat-conductive contact with
a laser housing mounting plate in a high-density laser source
bank.
Inventors: |
VanHoudt, Paulus Joseph;
(Berthoud, CO) |
Correspondence
Address: |
Dan Cleveland
Lathrop & Gage L.C.
Suite 302
4845 Pearl East Circle
Boulder
CO
80301
US
|
Family ID: |
26955864 |
Appl. No.: |
09/897350 |
Filed: |
July 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60272997 |
Mar 2, 2001 |
|
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Current U.S.
Class: |
62/3.3 ;
257/E23.082; 62/259.2; 62/3.7 |
Current CPC
Class: |
H01L 35/00 20130101;
F25B 21/04 20130101; F25B 2321/021 20130101; H01L 23/38 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101; H01L 2924/0002
20130101; H01S 5/02415 20130101 |
Class at
Publication: |
62/3.3 ; 62/3.7;
62/259.2 |
International
Class: |
F25B 021/02; F25D
023/12 |
Claims
1. A system for heating and cooling an object, comprising: a first
thermoelectric cooler/heater having a Peltier junction between a
first contact and a second contact; a switch-mode power supply
electrically connected to the first contact and the second contact,
configured for flowing electrical current through the Peltier
junction; and a polarity controller configured for controlling the
direction of electrical current flow through the Peltier
junction.
2. The system as set forth in claim 1, wherein the switch-mode
power supply is configured to provide DC current.
3. The system as set forth in claim 1, wherein the switch mode
power supply is configured to provide pulse-modulated current.
4. The system as set forth in claim 3, including a filter for use
in smoothing the pulse-modulated current.
5. The system as set forth in claim 4, wherein the filter is a
capacitive filter.
6. The system as set forth in claim 5, wherein the capacitive
filter comprises an inductor preceding a capacitor.
7. The system as set forth in claim 1, wherein the object comprises
a laser diode contacting the first thermoelectric
cooler/heater.
8. The system as set forth in claim 7, comprising a heat conductive
block contacting the first thermoelectric cooler/heater, and a
second thermoelectric cooler/heater contacting the heat conductive
block.
9. The system as set forth in claim 8, including control circuitry
operable to maintain each of the first and second thermoelectric
cooler/heaters at different temperatures during system
operation.
10. The system as set forth in claim 1, comprising a closed loop
feedback system including a temperature sensor contacting the
object and configured to provide an input signal useful for
controlling system temperature.
11. The system as set forth in claim 10, wherein the temperature
sensor comprises a thermistor and the input signal comprises a
thermistor voltage signal.
12. The system as set forth in claim 11, including an error
amplifier that operates by comparing the thermistor voltage signal
against a reference voltage representing a desired control
temperature.
13. The system as set forth in claim 12, comprising a digital to
analog converter configured to provide the reference voltage.
14. The system as set forth in claim 1, wherein the control
circuitry includes a thermal process controller adapted to operate
on a temperature signal.
15. The system as set forth in claim 14, wherein the thermal
process controller comprises a PID controller.
16. The system as set forth in claim 14, wherein the thermal
process controller comprises a PI controller.
17. The system as set forth in claim 1, including a polarity
control bridge adapted to electrically activate the thermoelectric
cooler/heater based upon output from the polarity controller.
18. The system as set forth in claim 17, wherein the polarity
control bridge comprises an H-bridge.
19. The system as set forth in claim 1, wherein the control
circuitry includes a thermistor, an error amplifier, a thermal
process controller, and a polarity control bridge forming a first
loop.
20. The system as set forth in claim 19, wherein the switch-mode
power supply is connected to the polarity control bridge for supply
of power thereto.
21. The system as set forth in claim 20, comprising an absolute
value circuit positioned between the thermal process controller and
the switch-mode power supply to form a second loop which is a
subset of the first loop.
22. The system as set forth in claim 21, comprising a third loop
including means for providing feedback based upon output of the
switch-mode power supply, the third loop being operable to adjust
the output of the switch mode power supply according to output from
the thermal process controller.
23. The system as set forth in claim 1 including process control
circuitry configured to adjust power output of the switch-mode
power supply based upon a first input signal from a first feedback
loop.
24. The system as set forth in claim 23, wherein the first feedback
loop is a temperature feedback loop and the input signal is a
voltage signal based upon a temperature of the object.
25. The system as set forth in claim 1, wherein the process control
circuitry is configured to adjust power output of the switch-mode
power supply based upon a second input signal from a second
feedback loop.
26. The system as set forth in claim 25, wherein the second
feedback loop operates by comparing actual output and intended
output of the switch-mode power supply, and by adjusting power
output of the switch-mode power supply to meet the intended
output.
27. The system as set forth in claim 1, comprising a laser diode as
the object, the laser diode and system being mounted on a modular
card, and a plurality of such modular cards mounted adjacent to one
another in a total number not less than twenty modular cards, the
modular cards being identical to one another except that the laser
diodes may emit light at different wavelengths.
28. A system for heating and cooling an object, comprising: a
thermoelectric cooler/heater having a Peltier junction between a
first junction contact and a second junction contact; a switch-mode
power supply electrically connected to the first junction contact
and the second junction contact, for flowing electrical current
through the thermoelectric cooler/heater through the Peltier
junction; a thermistor for converting a temperature of the object
to a thermistor voltage; an error amplifier for comparing the
thermistor voltage to a reference voltage and producing an error
voltage; a PID controller for processing the error voltage and
producing a PID signal; an absolute value circuit for converting
the PID signal to a negative feedback value for input to the
switch-mode power supply; an H-bridge for reversing the direction
of current through the Peltier junction; a polarity controller for
sensing the polarity of the PID signal and controlling the
H-bridge; and a current-voltage amplifier for converting the
electrical current that flows through the thermoelectric
cooler/heater into a feedback signal for use in controlling the
output of the switch mode power supply.
29. A two-stage thermoelectric temperature control system for
controlling the temperature of a laser diode, comprising: a laser
housing containing a laser diode device; and a first switch-mode
bi-directional thermoelectric cooler/heater disposed in contact
with the laser housing and heat-conductively connected to the laser
diode device.
30. The two-stage thermoelectric temperature control system as set
forth in claim 29, comprising: a heat-conducting mount on which the
laser housing is mounted; and a second switch-mode bi-directional
thermoelectric cooler/heater mounted on the mount.
31. A thermoelectrically controlled high-density laser source bank,
comprising: a plurality of laser diode source modules, each laser
diode source module containing a laser diode and a switch-mode
bi-directional thermoelectric cooler/heater having a Peltier
junction.
32. The thermoelectrically controlled high-density laser source
bank as set forth in claim 31, wherein each laser diode source
module includes: a laser housing containing a laser diode device; a
first switch-mode bi-directional thermoelectric cooler/heater
disposed in contact with the laser housing and heat-conductively
connected to the laser diode device; a heat-conducting mounting
block, on which the laser housing is mounted; and a second
switch-mode bi-directional thermoelectric cooler/heater mounted on
the mounting block.
33. A method of stabilizing temperature in a system having a first
Peltier junction thermoelectric cooler/heater, the method
comprising the steps of: sensing the temperature in the system to
provide a temperature signal corresponding to the temperature; and
selectively activating the first Peltier junction thermoelectric
cooler/heater for heating and cooling purposes to maintain the
temperature within a predetermined temperature range based upon the
temperature signal, wherein the step of selectively activating the
first Peltier junction thermoelectric cooler/heater includes
utilizing a switch-mode power supply.
34. The method according to claim 33, wherein the system includes a
laser diode and the step of sensing the temperature includes
sensing the temperature of the laser diode.
35. The method according to claim 34, including a step of
performing optical telecommunications test operations by energizing
the laser diode concomitantly with the steps of sensing temperature
and selectively activating the first Peltier junction
thermoelectric cooler/heater.
36. The method according to claim 34, wherein the system includes a
heat sink contacting the laser diode and an additional
thermoelectric heater/cooler, the method comprising an additional
step of selectively activating an additional Peltier junction
thermoelectric cooler/heater.
37. The method according to claim 36, wherein the additional step
of selectively activating the additional Peltier junction
thermoelectric cooler/heater includes maintaining the first Peltier
junction thermoelectric cooler/heater and the additional Peltier
junction thermoelectric cooler/heater at different
temperatures.
38. The method according to claim 34, wherein the step of sensing
temperature comprises sensing temperature from a structure selected
from the group consisting of a laser diode and a laser diode
module.
39. The method according to claim 34, wherein the step of sensing
temperature comprises using a thermistor to provide the temperature
signal.
40. The method according to claim 34, wherein the system includes a
thermistor for converting a temperature of the object to a
thermistor voltage, and the step of sensing the temperature
comprises using the thermistor to provide the temperature
signal.
41. The method according to claim 40, wherein the system includes
an error amplifier, and the method includes a step of comparing the
temperature signal to a reference signal to produce an error output
signal.
42. The method according to claim 41, wherein the step of
selectively activating the Peltier junction thermoelectric
cooler/heater comprises integrating the error output signal to
provide and integrated value and providing control signals for use
in heating and cooling operations based upon the integrated
value.
43. The method according to claim 34, wherein the step of
selectively activating the Peltier junction thermoelectric
cooler/heater comprises converting the integrated value into an
absolute value for use as control input to a switch mode power
supply.
44. The method according to claim 34, wherein the step of
selectively activating the Peltier junction thermoelectric
cooler/heater comprises adjusting output of the switch mode power
supply based upon a feedback comparison between desired output and
actual output.
45. The method according to claim 45, wherein the step of
selectively activating the Peltier junction thermoelectric
cooler/heater comprises adjusting output of the switch mode power
supply based upon a feedback comparison between actual and desired
temperature of the object.
Description
RELATED APPLICATIONS
[0001] This application claims benefit of priority to provisional
application serial No. 60/272,997 filed Mar. 2, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to methods, systems and structures for
thermoelectric temperature control, in particular, to
thermoelectric control of laser diodes and other opto-electronic
devices.
[0004] 2. Statement of the Problem
[0005] In many applications, active temperature control improves
the performance of opto-electronic devices. For example, laser
diodes are useful in many fields of technology. They are small and
efficient. They can be directly modulated and tuned. These devices
affect us daily with better clarity in telephone systems, high
fidelity in music, and in many less obvious ways. An important
electrical characteristic of a laser diode is the relation of light
power to laser current, often represented by light-current curves
in graphs in which output light intensity is plotted as a function
of drive current. These curves are used to determine a laser's
operating point (drive current at the rated optical power) and
threshold current (current at which lasing begins). Light
intensity-current curves are strongly dependent on a laser's
temperature. Typically, laser threshold current increases with
temperature. Emission wavelength is strongly dependent on device
temperature. The efficiency of a laser diode is also measured from
light-current curves. The efficiency of the diode decreases with
increasing temperature. Also, the operating lifetime of a laser
diode decreases with increasing temperature.
[0006] In most solid-state detectors, noise decreases with
increasing temperature. Responsiveness also varies with operating
temperature and, therefore, must be stabilized by active
temperature control if a high degree of radiometric accuracy is
required.
[0007] Thus, in these and in many other applications, active
temperature control can improve the performance of opto-electronic
devices. It is known in the art to use thermoelectric "Peltier"
devices to cool high-sensitivity transducers and opto-electronic
devices, such as charge coupled devices ("CCDs") and laser diodes,
in an effort to improve their performance. As technical
instrumentation becomes denser, temperature control becomes both
more important and more difficult. For example, it would be more
efficient economically and space-wise to combine many laser source
modules in a photonic test instrument. A high concentration or
density of hot laser sources and associated circuitry, however,
makes it more difficult to regulate cooling and to maintain a
desired uniform temperature. The use of dedicated Peltier cooling
devices does not overcome all of the problems that are presented by
increasing densification; for example, the photonic test system may
need to stabilize at an operating temperature before test
measurements may be performed, or the ambient temperature may be
such that cooling alone is unable to stabilize the system
temperature within a preferred operating range.
SOLUTION
[0008] The present invention helps to solve some of the problems
mentioned above by providing systems and methods for both actively
heating and actively cooling an object to obtain accurate and
precise control of temperature.
[0009] A basic embodiment, for example, comprises a system for
heating and cooling an object that incorporates a first
thermoelectric cooler/heater having a Peltier junction between a
first contact and a second contact. A switch-mode power supply is
electrically connected to the first contact and the second contact,
for flowing electrical current through the Peltier junction. A
polarity controller controls the direction of electrical current
flow through the Peltier junction to provide selective heating and
cooling. The basic embodiment is particularly useful in complex
electro-optical test measurement systems, such as modular laser
diode cards that may be incorporated within high-density optical
source banks for use in testing electro-optical systems.
[0010] A significant advantage is obtained in these systems by
using the switch-mode power supply because these power supplies
operate at much higher efficiencies in these applications than do,
for example, linear or non-switch-mode power supplies. A filter,
such as a capacitive filter, may be used to smooth the pulsed
output from the switch-mode power supply, in order to provide an
essentially non-pulsed power source while maintaining the
efficiency benefit of pulsed power from the switch-mode power
supply. By way of example, a system having an efficiency of
approximately ten percent in usage of power from a linear power
supply might be upgraded to an efficiency of sixty or seventy
percent through the use of a switch-mode power supply. Additional
efficiencies are obtained by using a single Peltier junction for
both heating and cooling purposes by selectively altering the
direction of current flowing through the Peltier junction.
[0011] The control circuitry may comprise various instrumentalities
to accomplish switching of the switch-mode power supply for the
purpose of maintaining the system temperature within a
predetermined temperature range. For example, a polarity controller
may be provided for selectively controlling the direction of
electrical current flow through the Peltier junction in the first
and second directions. A temperature sensor, e.g., a thermistor,
may be configured to provide the polarity controller with an input
signal that is useful for controlling the system temperature. An
error amplifier may be used to provide an output signal by
comparing the thermistor signal against a reference voltage
representing a desired control temperature. An digital-to-analog
converter may be used to provide the reference voltage. A thermal
process controller, such as a proportional integral (PI) or
proportional integral derivative (PID) controller, can integrate
output from the error amplifier to provide control signals based
upon the integrated value of the error amplifier output. A polarity
controller may accept signals from the thermal process controller
for purposes of switching the direction of current from the power
supply. The actual switching operation may be performed, for
example, through the use of an H-bridge under the command of the
polarity controller.
[0012] The circuit components that are described above may be
deployed in a series of loops that together form a closed loop
feedback system for self-regulation of temperature and power
output. For example, the thermistor, the error amplifier, the
thermal process controller, the polarity controller and the
polarity control bridge may be combined to form a first loop. The
switch-mode DC power supply may be connected to the polarity
control bridge for supply of power thereto, and an absolute value
circuit may optionally be positioned to receive control signals
from the thermal process controller. The absolute value circuit may
be used to adapt the process control signals, as needed, for
submission to the switch-mode power supply, whereby a second loop
is formed including the absolute value circuit and the power
supply. A third loop or feedback loop may be provided to measure
the power output of the switch-mode power supply at the
thermoelectric device and adjust the output based upon a comparison
to a signal representing a desired power output.
[0013] The concepts that have been discussed above may be utilized
to provide a two-stage thermoelectric system that, for example, may
be used to control the temperature of a laser diode. One example of
a system of this type may include a laser housing containing a
laser diode device, and a first switch-mode bi-directional
thermoelectric device that is disposed in the laser housing and
heat-conductively connected to the laser diode device. This system
may further include a heat-conducting mount, such as a block or
plate, on which the laser housing is mounted, and a second
switch-mode bi-directional thermoelectric cooler/heater that
resides on the mount. Thus, the two stage system may heat or cool
by virtue of a direct contact with the laser diode package, as well
as through contact with the mounting system for the laser diode
package. The respective switch-mode bi-directional thermoelectric
cooler/heaters may be maintained at different temperatures. These
concepts are particularly useful when a plurality of laser diode
packages are mounted in a high-density photonic test array.
[0014] The instrumentalities that have been described above may be
used in a method of stabilizing temperature in a system having a
Peltier junction thermoelectric cooler/heater. The basic method
includes the steps of sensing the temperature in the system to
provide a temperature signal corresponding to the temperature, and
selectively activating the Peltier junction thermoelectric
cooler/heater to maintain the temperature within a predetermined
temperature range based upon the temperature signal. The sensed
temperature may, for example, be that of a laser diode or a mount
therefor. The laser diode can be energized to perform optical
telecommunications test operations concomitantly with the steps of
sensing temperature and selectively activating the Peltier junction
thermoelectric cooler/heater for heating or cooling purposes. The
heat pump and the heat generator may be selectively activated by
the control circuitry through use of the switch mode power
supply.
[0015] Additional objects and advantages will be apparent to those
skilled in the art upon reading the following detailed description
in association with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A more complete understanding of the invention may be
obtained by reference to the drawings, in which:
[0017] FIG. 1 depicts a switch-mode bi-directional thermoelectric
control system for heating and cooling an object through use of a
bi-directional switch mode thermoelectric cooler;
[0018] FIG. 2 shows a block diagram of switch-mode bi-directional
thermoelectric control system for controlling temperature of a
laser diode in a laser-diode source bank of a photonic tester;
[0019] FIG. 3 shows a block diagram of a high-density optical
source bank in which an embodiment of a bi-directional switch mode
thermoelectric cooler is utilized;
[0020] FIG. 4 depicts a cross-sectional view of an exemplary,
general-purpose laser diode-mounting fixture in which the relative
locations and dimensions of bi-directional switch mode
thermoelectric device are shown;
[0021] FIG. 5 depicts a top view of the laser diode-mounting
fixture shown in FIG. 4;
[0022] FIG. 6 depicts a laser-diode-mounting fixture in which a
laser diode package is mounted on an aluminum block;
[0023] FIG. 7 provides additional detail with respect to the laser
diode package shown in FIG. 6;
[0024] FIG. 8 depicts a capacitive filter for use in smoothing the
output of the switch-mode power supply; and
[0025] FIG. 9 depicts a power output curve from a switch mode or
pulsed DC power supply that has been smoothed over time by action
of the circuit shown in FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] A system in accordance with preferred embodiments of the
invention provides a solid-state bi-directional thermoelectric
device that provides both active heating and active cooling of
circuitry that requires operational temperature control by
mechanisms beyond normal convectance, in order to perform within
specifications.
[0027] A basic embodiment, for example, comprises a system for
heating and cooling an object that incorporates a first
thermoelectric cooler/heater having a Peltier junction between a
first contact and a second contact. A switch-mode power supply is
electrically connected to the first contact and the second contact,
for flowing electrical current through the Peltier junction. A
polarity controller controls the direction of electrical current
flow through the Peltier junction to provide selective heating and
cooling.
[0028] The preferred use of a switch mode power supply, especially
one that is capable of pulse modulating DC current, provides a
significant advantage in the cooling heating and system. This
advantage exists because the same amount of heating or cooling
effect may be obtained with less power dissipation into heat. For
example, measurements on test systems have shown that the switch
mode power supply may dissipate 10% of its power into heart,
whereas a non-switching DC supply dissipates from 60% to 70% of its
power. The reduced amount of power dissipation permits, for
example, a greater density of laser channel sources to be used in
proximity to one another in optical test systems and other
applications where heat dissipation is a limiting design factor
that limits the amount of densification that may be attained.
[0029] A thermoelectric device in accordance with these principles
is useful in a large number of various types of applications,
especially in high performance or tight tolerance electrical
testing equipment. Various types of temperature sensors may be used
to measure the temperature of the object being heated or cooled.
The DC electrical current is provided in various ways, preferably
by a switch-mode DC power supply. Control of the direction of flow
of the DC electrical current through the Peltier junction is
effected using any of a large number of different solid-state and
analog control systems. The invention is described herein in
relation to its use for controlling the temperature of laser diodes
in a high-density laser source bank. It is understood, however,
that the invention is useful in a large number of technical
applications in which temperature, heating and cooling must be
accurately and precisely controlled. Therefore, although the
invention is described herein with reference to FIGS. 1-7, it is
understood that the embodiments described herein are not intended
to limit the scope of the invention, which is defined in the claims
below.
[0030] A "switch mode" DC power supply is one that permits
selective modulation of the DC current, e.g., as a series of
positive or negative pulses such as consist of the positive
amplitude of a sine wave or an analogous square wave. This pulsing
capability significantly reduces Thomson effect heating, which
cannot be entirely avoided in a Peltier device. It is not necessary
to provide pulse-mode power to directly to the Peltier junction. In
fact, it is preferred to filter the pulse-mode output and thereby
provide a smoothed power output by averaging the total power to
fill in the gaps between pulse spikes. This concept of
filtering-to-average- obtains the efficiency benefit of pulsed-mode
(i.e., switch-mode) supply while providing optimum power delivery
to the Peltier junction thermoelectric cooler/heater in the form of
a relatively steady-state current.
[0031] The term "Peltier junction thermoelectric cooler/heater" is
used generally in the specification to include both electrical
conductors and semiconductors. Any two dissimilar types of material
in contact with one another may be used to form the Peltier
junction. These materials especially include dissimilar
electrically conductive metals. It is well known, however, that two
dissimilar semiconductors, for example, n-type and p-type
materials, may also be utilized to provide a Peltier effect in
thermoelectric cooler/heaters. A particularly preferred Peltier
junction thermoelectric cooler/heater comprises n and p-doped
silicon.
[0032] The term "bi-directional" is used in the specification to
denote that the direction of flow of DC current through the Peltier
junction of a thermoelectric cooler/heater in accordance with the
invention is selectively controllable and reversible. As a result,
a thermoelectric cooler/heater may be used either to heat or to
cool. The combination of a switch-mode DC power supplied and the
capability to select and reverse the direction of current flow
through the Peltier junction is obtained through novel circuitry,
as described below.
[0033] FIG. 1 depicts a system 100 for heating and cooling an
object 102, such as a laser diode, in accordance with one aspect of
the invention. System 100 includes a thermoelectric device 104
comprising a first electrical junction contact 106 and a second
electrical junction contact 108 in contact with each other, thereby
forming a Peltier junction 110 between first electrical junction
contact 106 and second electrical junction contact 108. System 100
further comprises a switch-mode DC power supply 112 and a polarity
controller 114 for controlling the direction of electrical current
flow through Peltier junction 110. DC power supply 112 is
electrically connected to first junction contact 106 and to second
junction contact 108 so that it may provide pulse-modulated DC
current through Peltier junction 110.
[0034] The polarity controller 114 may have various types of
structures and operating techniques to accomplish the function of
selectively reversing current flow through Peltier junction 110.
Preferably, thermoelectric device 104 includes a heat sink 116
having a large total heat capacity relative to the heating and
cooling requirements of object 102. The heat sink 116 may be made
of identical material with respect to the second junction contact
108, or it may be a separate component heat-conductively connected
by connector 117, as depicted in FIG. 1. A feature of a system in
accordance with the invention is that the direction of flow through
thermoelectric cooler/heater 104 and through Peltier junction 110
can be changed to effect heating or cooling. In FIG. 1, the flow of
current indicated by the arrows of electrical lines 120, 122 is
from first junction 106 to second junction 108. In this
configuration, heat flows from first junction 106 to second
junction 108 into heat sink 116, thereby cooling object 102. In
accordance with the invention, the direction of current flow is
reversible, so that heat flows from second junction 108 to first
junction 106, thereby heating object 102.
[0035] There will now be shown a system in accordance with other
aspects that demonstrate, by way of example, additional detail with
respect to control circuitry for use in governing the operation of
the Peltier thermoelectric device and control the temperature of an
object. A switch-mode power supply is electrically connected to the
thermoelectric device for flowing electrical current through the
thermoelectric cooler/heater through the Peltier junction. A
thermistor may be used to convert a temperature of the object to a
thermistor voltage. An error amplifier may be used to compare the
thermistor voltage to a reference voltage and produce a
corresponding error voltage. A PID controller may be used to
process the error voltage and produce a corresponding PID signal.
An absolute value circuit may be used to convert the PID signal to
a negative feedback value for input to the switch-mode power
supply. An H-bridge may be used to reverse the direction of current
through the Peltier junction. A polarity controller may be used to
sense the polarity of the PID signal and control the H-bridge. A
current-voltage amplifier may be used to convert the electrical
current that flows through the thermoelectric device into a
feedback signal for use in controlling the output of the switch
mode power supply.
[0036] FIG. 2 shows a block diagram of bi-directional switch-mode
thermoelectric control system 200 in accordance with the invention
for controlling temperature of a laser diode in a laser-diode
source bank of a photonic tester. System 200 includes a thermistor
and associated circuitry 202, such as bridge circuitry, for
converting a temperature of an object 204 to a thermistor voltage.
Object 204 is, for example, a laser diode, another light source
such as a light emitting diode, or a mounting block on which a
laser diode housing is mounted. Typically, a thermistor having a
nominal resistance of 10 K ohms is used in the thermistor and
associated circuitry 202. Suitable thermistors are commercially
available. For example, a Dale 1T1002-5 is one such thermistor. An
error amplifier 206 compares the thermistor voltage to a reference
voltage corresponding to a desired reference temperature. Suitable
error amplifiers are commercially available, for example, from
Analog Devices, model AD706. The reference voltage is created with
a digital-to-analog converter, for example, a 12-bit Linear Tech
LTC8043 or a 16-bit LTC1595. The difference between the thermistor
voltage and the reference voltage is an error voltage. This
difference is provided as the output of error amplifier 206 and the
input of a thermal process controller 208. Preferably, thermal
process controller 208 is a PID controller, for example, a
controller from Analog Devices, model ADS706. The controller 208
may also be a proportional-integral controller.
[0037] Additional system components can be added to the control
system 200 to accommodate recognized needs. For example, it may be
the case that a power supply requires a negative control voltage
input to regulate the power output. In this case, an optional
absolute value circuit 210 converts the output of thermal process
controller 208 so that it is always negative because the
switch-mode DC power supply, described below, requires negative
feedback regardless of whether the thermoelectric device 216 is
heating or cooling. Absolute value circuit 210 is commercially
available, for example, from Analog Devices, model AD706. Voltage
output from the polarity controller 208 also flows along electrical
path 211 to polarity controller 212, which is a voltage comparator
for determining whether the voltage is positive or negative
corresponding to a temperature above or below the reference
temperature. Polarity controller 212 controls an H-bridge 214 in a
way that changes the direction of current through the
thermoelectric device 216. Suitable comparators are commercially
available for use as polarity controller 212; for example, Linear
Tech LT1017CS8. H-bridge 214 is a set of transistors used to change
the direction of current flowing to thermoelectric device 216. A
suitable, commercially available H-bridge is a Fairchild FDS6990
utilizing MOSFETs.
[0038] The output of absolute value circuit 210, that is, a
negative feedback voltage value, is transmitted along electrical
lines 218 to switch-mode (pulse-modulated) power supply 220.
Switch-mode power supply 220 converts the low power negative
feedback voltage into DC current at a higher power level. In the
preferred embodiment, the output current in electrical line 221 has
a value in a range of from about 0 to 1.3 amps, with a
corresponding voltage in a range of from about 0 to 13 volts.
H-bridge 214 controls the direction of the current flow through the
Peltier junction of thermoelectric cooler/heater 216. Depending on
the direction of current flow through the Peltier junction at any
given time during operation, thermoelectric cooler/heater 216
functions as a heater or a cooler. Numerous types of thermoelectric
cooler/heaters suitable for use in accordance with the invention
are commercially available. A laser diode module typically includes
a laser housing containing a laser diode and a thermoelectric
temperature controller. An example of a commercially available
laser module is the Lucent D2525P. A commercially available
thermoelectric cooler/heater 216 suitable for controlling the
temperature of a mounting block (on which a laser module is
disposed) is a Melcor CP1.0-63-05L.
[0039] System 200 also includes I-V amplifier 224 that converts the
current which flows through the Peltier junction in thermoelectric
cooler/heater 216 into a voltage that is used in a minor control
loop by being transmitted back through electrical line 225 to power
supply 220. The output of I-V amplifier 224 and the output of
absolute value circuit 210 are compared. If the outputs are not the
same, then the output of power supply 220 is corrected.
[0040] The circuitry represented in FIG. 2 provides efficiency and
good control of a switch-mode bi-directional thermoelectric
cooler/heater in accordance with the invention. It is understood
that analog or digital circuits using different devices in a
different order may be used to accomplish the same function without
departing from the scope of invention.
[0041] There will now be shown a thermoelectrically controlled
high-density laser source bank, comprising a plurality of laser
diode source modules, each laser diode source module containing a
laser diode and a switch-mode bi-directional thermoelectric
cooler/heater having a Peltier junction. The laser source bank may
further include a laser housing containing a laser diode device, a
first switch-mode bi-directional thermoelectric cooler/heater
disposed in the laser housing and heat-conductively connected to
the laser diode device, a heat-conducting mounting block on which
the laser housing is mounted, and a second switch-mode
bi-directional thermoelectric cooler/heater mounted on the mounting
block.
[0042] In the prior art, adequate control of laser diode
temperature was one of the hindrances against assembling and
operating laser source banks having large numbers of laser sources,
and has prevented the accumulation of high density source banks
having more than about eight to seventeen channels in a single box.
The active heating and cooling provided by switch-mode
bi-directional thermoelectric cooler/heaters in accordance with the
invention contribute to the feasibility of building and operating
high-density laser diode source banks.
[0043] FIG. 3 is a block diagram of an optical test system 300
illustrating, by way of example, a modular structure that operates
according to preferred principles of the invention. An optical
source array 302 is comprised of a plurality of individual
channels, such as channel 303, which each contain a corresponding
plurality of elements. The optical source array 302 contains a
total of N such channels, where N may be, for example, 100 or 200
channels as needed for test purposes. The optical source array 302,
as depicted in FIG. 3, consumes less power and occupies a smaller
footprint than prior devices. An additional advantage is that the
array 302 may be selectively configured to meet the demands of
specific test purposes and need not be provided with too many
channels. Additional channels may be selectively added or removed
to meet future demands.
[0044] The individual channels of the optical source array 302 are
modularly constructed to meet the needs of specific test
situations. By way of example, in the optical source array 302, a
laser source module bank 304 includes a plurality of individual
laser source module cards, e.g., card 306 including a laser diode
or any other type of optical telecommunications laser source. An
example of a commercially available laser source module is the 515
module available from ILX Lightwave of Boulder, Colo. A modulation
switch circuitry bank 308, e.g., comprising individual switch
circuitry 310, permits selective laser modulation according to
permitted system modulation functions, such as sine wave, square
wave, triangular or sawtooth wave, and rectangular wave function
modulations, for each laser source module card. A thermal control
bank 312 is formed of the previously described individual Peltier
thermoelectric devices 314, as shown in FIGS. 1 and 2. These
devices compensate for temperature variances in the individual
laser diodes of the laser source module array 304 in providing a
stable pulse modulated laser output. In each channel, the laser
source module cards, such as card 306, preferably include the
switch circuitry 310 and the thermoelectric devices 314 as integral
components, however, selected portions of the switch circuitry 310
and the thermoelectric devices 314 may be provided as separate
modular cards with compatible plug-in connectors. The
thermoelectric devices heat or cool the laser diodes. The laser
diode and system electronics are preferably mounted on a modular
card. A plurality of such modular cards can be mounted adjacent to
one another in a total number not less than twenty modular cards,
e.g., to form an optical source array 302 comprising forty-eight,
one-hundred or more adjacent cards. The modular cards forming the
optical source array 302 are preferably identical to one another
except that the laser diodes may emit light at different
wavelengths.
[0045] A channel option array 316 comprising individual channel
option cards, such as card 318, may be selectively added using
commercially available components to provide shutter control for
each laser, a variable optical attenuator, a polarization
controller a polarization scrambler, a power monitor, or a
wavelength reference. These devices may be used individually,
selectively combined in series, or not used at all, depending upon
test needs.
[0046] In cases where the channel option card 318 is a power
monitor card, it is preferred to use a tap coupler, e.g., a 99%/1%
coupler where power measurement is made on the 1% tap. Prior power
monitor devices monitor current at a laser chip on the laser source
card and use this measurement to stabilize the power output of the
laser. Prior techniques are, therefore, only sensitive to laser
effects that can affect power stability; however, these techniques
are insensitive to power changes that derive from changes in the
other optical and circuitry elements connected to the laser.
Placing a power monitor downstream of the laser in the position of
card 118 advantageously permits monitoring and/or selective
adjustment of laser power output based upon the total channel laser
power output.
[0047] Where, for example, the channel option card 318 is a
polarization controller or polarization scrambler, the card
operates upon polarized light from the laser source card 306 to
align polarization in a controlled manner to optimize external
modulation power and to control polarization dependent dispersion
and polarization-dependent loss. A polarization scrambler generates
all states of polarization in a certain time interval, which
averages out polarization-dependent effects. By way of example, one
commercially available device that can be used as both a
polarization alignment device and a polarization scrambler is the
model PCS-3X-PC/APC-7 available from General Photonics.
[0048] Where, for example, the channel option card 318 is a
wavelength reference, or wavelength lock, an optical filter and
power meter provide feedback that measure and stabilize the laser
frequency from laser source card 306. The feedback signal is
derived using the intensity or phase of light that is reflected
from or transmitted to the filter.
[0049] Where, for example, the channel option card 318 is a
shutter, the shutter mechanism, such as a mechanically actuated
fiber switch in a V-groove mount, is preferably used to disrupt or
transmit laser emissions from the laser source card 306 without
having to change the current at the laser. This ability avoids the
necessity of deenergizing and reenergizing the laser, which
requires a long settling time to stabilize laser emissions upon
reenergization. By way of example, commercially available shutter
devices include model FOSW 1-1-L-PC-L-1 shutter from Lightwave
Link, which has a 50 ms switching time.
[0050] Where, for example, the channel option card 318 is a
variable optical attenuator, such as the OZ Optics model
DD-100-11-1550-9/125-S-40- -3D3S-1-0.5-485:1-6-MC/SPI, the
attenuator is used to reduce the intensity of light in the channel
303 to much lower and stable power levels than the laser source
card 306 can achieve alone with a reduction in current. The
individual channel attenuator reduces the power level of the
channel for whatever level is needed for the system under test by
producing a combined comb using one device before the comb is
delivered to a system under test.
[0051] Each channel in the optical source array 302 shares a common
electrical/optical backplane 320 and a common electrical/optical
backplane 322, which respectively provide compatible electrical or
optical couplings that mate with corresponding couplings on the
individual channels. The specific manner of connectivity is not
critical, so long as the connectors provide the optical and
electrical pathways that are required for module compatibility with
optical test system 300.
[0052] An optional but preferred multiplexer (MUX) 324 combines the
individual channel emissions from the optical source array 302 to
provide a combined comb including the combined emissions. For
example, a commercially available MUX is model
AWG-NG48x1-100G-1.5-FC/APC from PIRI. The creation of a wavelength
comb within a single instrument advantageously facilitates
operations on the combined comb within the test system 300, as
opposed to prior techniques requiring a separate device that
occupies an additional footprint. Comb operations are, accordingly,
simplified and expanded, as a single programmable controller is
enabled to direct these functions in a more versatile manner than
could be obtained from separate devices. An additional advantage is
that fiber management and integrity is controlled within the
enclosure of test system 300, reducing set-up time and the risk of
fiber damage.
[0053] The optical pathway proceeds from the multplexer 324 to a
series of optional modular service channel WDM processors 326 and
328, which are coupled with corresponding service channel sources
330 and 332 for conventional data transmission signal processing,
e.g., for WDM-TDM handshake recognition relating to endpoint
interpretation of the channels in the combined comb.
[0054] A beam splitter 334, e.g., a 99%/1% splitter, provides light
from the combined comb to an auto-calibration device 336, which
includes an optical filter and power meter that provide feedback
for measurement and stabilization of the laser frequency. The
feedback signal is derived using the intensity or phase of light
that is reflected from or transmitted to the filter at emission
wavelengths corresponding to the design wavelengths for the
channels of laser source array 304. Power control of individual
laser source cards in the laser source array 304 may, thus, be
regulated after MUX processing to form a combined comb.
[0055] An optional variable optical attenuator 338, such as the OZ
Optics model DD-100-11-1550-9/125-S-40-3D3S-1-0.5-485:1-6-MC/SPI,
operates on the combined comb downstream of MUX 324 reduce the
intensity of light in the combined comb to much lower and stable
power levels than the laser source array 304 can achieve alone with
a reduction in current. The individual channel attenuator reduces
the power level of the channel for whatever level is needed for the
system under test and operates on the combined comb using one
device before the comb is delivered to a system under test.
[0056] A polarization controller or polarization scrambler 340
operates upon the combined comb downstream of MUX 324 to align
polarization in a controlled manner to optimize external modulation
power and to control polarization dependent dispersion and
polarization-dependent loss. A polarization scrambler generates all
states of polarization in a certain time interval, which averages
out polarization-dependent effects and identifies minimum and
maximum transmission orientations. By way of example, a
commercially device that can be used as both a polarization
alignment device and a polarization scrambler is model
PCS-3X-PC/APC-7, which is available from General Photonics.
[0057] A splitter 342 divides the optical pathway for the combined
comb into a polarized output segment leading to polarizer 344 and a
non-polarized segment 346. The segment leading to polarizer 344 is
in optical communication with an optical power measurement module
148, which monitors the power output in the combined comb at
different polarization states. Optical connectors 350 and 352 are
present to receive optical input from other sources external to the
optical test system 300, such as a system power monitor 354 or a
general-purpose power monitor 356.
[0058] The non-polarized segment 346 is advanced by a splitter 358
or a series of such splitters leading to an output panel 360
including a plurality of optical connectors 362 and 364. The panel
360 may be provided on the front or rear of the optical test system
300, or two or more such panels 360 may be present on both the
front and rear or the sides.
[0059] The foregoing discussion has focused primarily upon the
optical pathway within the optical test system 300, and the
discussion of electronics has until now not included a discussion
of the control circuitry. A master control circuit 366 preferably
includes a central processing unit, magnetic or optical data
storage, random access memory, and program logic, as required to
interact with other system components of the optical test system
300 during normal system control operations in the intended
environment of use. For example, master control circuit 366 may
include a conventional motherboard for a personal computer, as well
as any other circuitry and data storage devices that are commonly
used with computers. Modulation control module 368 is provided to
drive laser source emissions from the laser source array 306
according to system needs. The modulation control module 368 may
also be incorporated as part of the master control circuit 366. The
modulation control module 368 is provided with a plurality of N
connectors, such as connector 370, for use in coupling with an
external modulation input source 384. These connectors may be
optical or electrical connectors, and the number N corresponds to
the number N of channels in the optical source array 302. Thus, the
external modulation input source 372 may be configured to drive
modulation of the optical source array 302 in a manner that is not
provided for by the electronics in the modulation control module
368.
[0060] The electronics on modulation control module 368 include a
function generator that accepts instructions from the master
control circuit 366 to drive individual elements (e.g., laser
source card 306) of the laser source bank 304 in a predetermined
manner that is compatible with test practices. This function
generator may be switched to an OFF mode to accept external inputs.
In an ON mode, the function generator provides sine waves,
triangular or sawtooth waves, square waves, and any other wave form
that is known or useful to those skilled in the art. The modulation
depths are selectively adjustable from 0 to 100%. The modulation
control module preferably provides signals with a plurality of
these waveforms for availability to each channel in the optical
source array 302, and individual channels are intelligent in the
sense that they are programmed by instructions from the master
control circuit 366 to accept one of the provided waveforms to
energize the laser.
[0061] An optical or magnetic disk drive 374, such as a Zip drive,
is used to provide software upgrades to master control circuit 366,
as well as to log the performance of optical test system 300. These
functions may also be accomplished using a modem or network
connection to an appropriate server, e.g., an Internet server, or
other suitable terminus.
[0062] A front panel display 378, e.g., a 10 inch color liquid
crystal display or plasma display panel, provides a graphical user
interface showing all of the source channels in the optical source
array 302, their emission power levels, and the emission
wavelengths. An intuitive command set is provided for interaction
with the master control circuit 366 to allow rapid modifications to
the system setup. Single source commands are provided to adjust the
properties of individual lasers on each channel. Comb commands are
provided to adjust the properties of the complete comb. Modulation
functions are provided to adjust the operation of the modulation
control module 368.
[0063] Optical test system 300 is compliant with any number of data
transmission protocols that are commonly used in networking and
optical test systems. External interfaces 378 exist for connections
to other devices that use these protocols, such as RS-232, GPIB,
and Ethernet. Furthermore, these interfaces preferably include a
modem connection for either an internal or external modem, which
interfaces with the manufacturer of optical test system 300 for
trouble-shooting purposes. The modem may also provide real-time
test measurement data summaries to remote locations or a telephony
network.
[0064] Except for those components that are specifically noted
above as being external to optical test system 300, all system
components that have previously been described are preferably
internal to a single box 380, and are provided as modular cards or
boards that may easily be replaced or renewed on a
component-by-component basis. This feature provides an extremely
compact modular system that occupies a small volume footprint and
can be upgraded for small incremental costs over a period of many
years.
[0065] External optical and electrical systems can also be provided
for use in combination with the optical test system 300. For
example, each channel in optical source array 302 is preferably
provided with an optical connector, such as connector 382, that
accepts a fiber optic coupling for connection with an additional
optical source system, such as external microwave modulation system
384, which may, for example, be an optical test mainframe. In this
manner, additional sources may be combined into the comb that is
processed through MUX 324.
[0066] Similarly, external optical devices may be provided
downstream of the optical test system 300, e.g., a generic device
386, with power measurements being obtainable at any point from the
downstream pathway by a simple tap, such as tap 388, for feedback
to the optical power measurement module 348 through one of
connectors 350 or 352. Further splitters, such as 2.times.2
splitter and 1.times.1 splitter 392 may be used as needed to branch
the optical pathway to other equipment 394, which may include
measurement systems such as power meters and the like, or it may
branch to open system architecture or networks. Other pathway
branches, for example, lead to test equipment, which may include
1.times.N switches for the testing of, for example, erbium doped
fiber amplifiers (EDFA) or other DWDM system components.
[0067] Any of the components of optical test system 300 that have
been previously described may benefit from the use of a
thermoelectric device of the type shown in FIGS. 1 and 2 where the
performance of the component would benefit from controlled heating
and cooling.
[0068] According to still further aspects and instrumentalities of
the thermoelectric control system and its preferred embodiments,
there will now be shown a two-stage thermoelectric temperature
control system for controlling the temperature of a laser diode.
The system comprises a laser housing containing a laser diode
device and a first switch-mode bi-directional thermoelectric
cooler/heater disposed in the laser housing and heat-conductively
connected to the laser diode device. The laser housing may be
mounted on a heat-conducting mount, and a second switch-mode
bi-directional thermoelectric cooler/heater can be mounted on the
mount or in contact with the laser diode. Separate control
circuitry may be adapted in the manner shown above to operate the
first and second switch-mode bi-directional thermoelectric
cooler/heater at different temperatures.
[0069] FIG. 4 and FIG. 5 depict a cross-sectional and a side
elevational view, respectively, of an exemplary, general-purpose
laser diode-mounting fixture 400 in which the relative locations
and dimensions of thermoelectric cooler/heaters in accordance with
the invention are shown. A wall 404 defines an inside space 406, an
exterior space 407, an inside surface 408, and an opening 410. A
mounting block 412 is disposed on the inside surface 408 covering
opening 410. A plurality of switch-mode bi-directional
thermoelectric devices 414 and 416, such as the Peltier junction
thermoelectric devices 104 shown in FIG. 1, are operably coupled
with appropriate control and drive circuitry for selective heating
and cooling of the general purpose laser diode-mounting fixture
400. These thermoelectric devices 414 and 416 are attached to
inside surface 408 above and below opening 410, respectively,
between inside surface 408 and mounting block 412. Thereby,
thermoelectric devices 414, 416 are heat-conductively connected to
mounting plate 412, which typically comprises aluminum. A laser
module plug connector 420 is provided in mounting plate 412 for
coupling with a laser diode package. The laser module plug
connector 420 is disposed substantially within inside space 406. A
portion 422 of laser module plug connector 420 is disposed towards
the exterior 407 and opening 410. A third switch-mode
bi-directional thermoelectric cooler 424 in accordance with the
invention is located within laser module 420 where it actively
heats and cools the laser diode module 420. The outer surface of
wall 404 forms a plurality of heat-dissipative fins 426 having an
increased surface area for communicating heat energy between the
wall 404 and the environment of use.
[0070] FIG. 6 depicts an alternative laser diode mounting system
600. A thermoelectric device 602 is preferably a Peltier junction
device of the type shown as thermoelectric device 104 in FIG. 1. An
aluminum heat-conducting block 604 is positioned between the
thermoelectric device 602 and a laser diode package 606. The
thermoelectric device 602 is in direct contact with an aluminum
heat conductive plate 608. The thermoelectric device 602 and the
aluminum heat conductor 604 preferably have hollow interiors to
accommodate electrical conductors for the proper operation of the
laser diode package 606 and mounting system 600.
[0071] FIG. 7 provides additional detail with respect to the laser
diode package 606 shown in FIG. 6. A thermoelectric device 700 is
preferably a Peltier junction device of the type shown as
thermoelectric device 104 in FIG. 1. The thermoelectric device 700
is in direct contact with a heat sink 706 and a laser diode 704. A
heat shield 708 is provided to shield adjacent devices from radiant
heat effects.
[0072] FIG. 8 is a circuit diagram showing a particularly preferred
capacitive filter 800 that may be interposed on line 21 between the
switch-mode power supply 200 and the H-bridge 214 (see also FIG.
2). The capacitive filter 800 comprises, in series, and inductor
802 and a capacitor 804. The capacitor 804 may be connected to
ground 806 or, alternatively, a voltage that enhances the
capacitive effects of the capacitor 804.
[0073] FIG. 9 depicts the intended result of the capacitive filter
800 where the pulse mode power supply 216 (see FIG. 8) produces a
series of pulses, such as pulses 900 and 902. The capacitive filter
800 operates upon these pulses by averaging them to form a smoothed
filter output curve 904thatis preferably a continuous curve that is
essentially steady-state over an interval of time. The integral
controller 208 (see FIG. 2) may cause the switch-mode power supply
220 to vary the amplitude and/or width of these pulses to either
raise or lower the power magnitude of curve 904.
[0074] The preceding discussion is intended to illustrate various
embodiments of the invention by way of example, and not by way of
limitation. For example, although the above discussion emphasizes
the importance of heating and cooling laser diodes, it is also
understood that any number of high performance electronic systems
may also benefit from heating and cooling through the use of a
bi-directional Peltier junction. Furthermore, the associated
circuitry that is described above may be replaced by functionally
equivalent circuitry without departing from the broad principles of
the invention. Accordingly, the inventors hereby state their
intention to rely upon the Doctrine of Equivalents, in order to
protect their full rights in the invention.
* * * * *