U.S. patent application number 12/334030 was filed with the patent office on 2010-06-17 for method for aligning optical packages.
Invention is credited to Steven Joseph Gregorski.
Application Number | 20100151596 12/334030 |
Document ID | / |
Family ID | 42200235 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100151596 |
Kind Code |
A1 |
Gregorski; Steven Joseph |
June 17, 2010 |
METHOD FOR ALIGNING OPTICAL PACKAGES
Abstract
A method is given for aligning an optical package comprising a
laser, a wavelength conversion device, at least one adjustable
optical component and at least one actuator. The adjustable optical
component may be moved to a command position by applying a pulse
width modulated signal to the actuator. The command position
represents an optimized alignment of the laser and wavelength
conversion device. The actual position of the adjustable may be
measured by measuring an output of a position measuring circuit,
which may measure the voltage amplitude of an oscillation in a
resonator tank circuit during an "off" period of the pulse-width
modulated signal. The resonator tank circuit may comprise a
capacitive element electrically coupled to the electrically
conductive coil. The pulse-width modulated signal may then be
adjusted to compensate for any difference in the actual position
and the command position of the adjustable optical component.
Additional embodiments are disclosed and claimed.
Inventors: |
Gregorski; Steven Joseph;
(Painted Post, NY) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
US
|
Family ID: |
42200235 |
Appl. No.: |
12/334030 |
Filed: |
December 12, 2008 |
Current U.S.
Class: |
438/10 ;
257/E21.002 |
Current CPC
Class: |
G02B 6/4225
20130101 |
Class at
Publication: |
438/10 ;
257/E21.002 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Claims
1. A method for aligning an optical package comprising a laser, a
wavelength conversion device, at least one adjustable optical
component, and at least one actuator, wherein the actuator
comprises a first and second magnetic elements, and the method
comprises: moving the adjustable optical component to a command
position by applying a pulse-width modulated signal to the
actuator, wherein the command position represents an optimized
alignment of the laser and the wavelength conversion device, the
first magnetic element is mechanically coupled to a base of the
optical package and the second magnetic element is mechanically
coupled to the adjustable optical component, the first and second
magnetic elements are in magnetic communication with each other, at
least one of the magnetic elements comprises an electrically
conductive coil wherein the pulse-width modulated signal is applied
to the electrically conductive coil to create a magnetic field of
sufficient strength to move the adjustable optical component in at
least one axis of motion; and measuring an actual position of the
adjustable optical component by measuring an output of a position
measuring circuit, wherein the output of the position measuring
circuit represents a voltage amplitude of an oscillation in a
resonator tank circuit during an "off" period of the pulse-width
modulated signal, the resonator tank circuit comprises the
electrically conductive coil electrically coupled to a capacitive
element, and the voltage amplitude of the oscillation represents
the actual position of the adjustable optical component; and
adjusting the pulse-width modulated signal to compensate for a
difference between the represented actual position and the command
position.
2. The method of claim 1 wherein: the optical package comprises an
optical intensity feedback loop operable to determine the command
position as a function of optical intensity at an output of the
wavelength conversion device.
3. The method of claim 2 wherein the command position is determined
by identifying the position at which the optical intensity at the
output of the wavelength conversion device reaches an approximate
maximum value.
4. The method of claim 2 wherein the command position is determined
during manufacture of the optical package, during operation of the
optical package, or both.
5. The method of claim 1 wherein the resonator tank circuit
comprises an amplifier electrically coupled to the resonator tank
circuit for sustaining the resonator tank circuit oscillation
voltage.
6. The method of claim 5 wherein the amplifier comprises an
operational amplifier, a bipolar junction transistor, or a
field-effect transistor.
7. The method of claim 1 wherein the resonator tank circuit
comprises a ballast inductor which is electrically coupled to the
electrically conductive coil for ensuring that the resonator tank
circuit will oscillate.
8. The method of claim 1 wherein the capacitive element of the
resonator tank circuit comprises a capacitor.
9. The method of claim 1 wherein the position measuring circuit
comprises a rectifier circuit and a filter circuit.
10. The method of claim 9 wherein the output of the position
measuring circuit is measured with an analog-to-digital
converter.
11. The method of claim 1 wherein the position measuring circuit
comprises an analog-to-digital converter.
12. The method of claim 1 wherein the frequency of the pulse-width
modulated signal is less than the frequency of the resonator tank
circuit oscillation voltage.
13. The method of claim 1 wherein an automatic control system
measures the actual position of the adjustable optical component
and adjusts the pulse-width modulated signal.
14. The method of claim 13 wherein the automatic control system
comprises a microprocessor executing program instructions for
adjusting the pulse-width modulated signal or analog circuit
components for adjusting the pulse-width modulated signal.
15. The method of claim 1 wherein the second magnetic element or
the adjustable optical component is mechanically coupled to the
base of the optical package by a mechanical device providing
sufficient rigidity to keep the adjustable optical component at a
known position in an absence of the pulse-width modulated
signal.
16. The method of claim 15 wherein the mechanical device opposes
the force produced by the actuator.
17. The method of claim 15 wherein the mechanical device is at
least one flexure wire.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure relates to semiconductor lasers,
laser controllers, optical packages, and other optical systems
incorporating semiconductor lasers. More specifically, the present
disclosure relates to a method for aligning optical packages that
include, inter alia, a semiconductor laser and a second harmonic
generation (SHG) crystal or another type of wavelength conversion
device.
[0003] 2. Technical Background
[0004] Short wavelength light sources can be formed by combining a
single-wavelength semiconductor laser, such as an infrared or
near-infrared distributed feedback (DFB) laser, distributed Bragg
reflector (DBR) laser, or Fabry-Perot laser, with a light
wavelength conversion device, such as a second harmonic generation
(SHG) crystal. Typically, the SHG crystal is used to generate
higher harmonic waves of the fundamental laser signal. To do so,
the lasing wavelength is preferably tuned to the spectral center of
the wavelength converting SHG crystal and the output of the laser
is preferably aligned with the waveguide portion at the input facet
of the wavelength converting crystal.
BRIEF SUMMARY
[0005] Waveguide optical mode field diameters of typical SHG
crystals, such as MgO-doped periodically poled lithium niobate
(PPLN) crystals, can be in the range of a few microns. As a result,
the present inventor has recognized that it can be very challenging
to properly align the beam from the laser diode with the waveguide
of the SHG crystal. Accordingly, one object of the present
disclosure is to provide a method for aligning components in
optical packages that utilize a laser diode in conjunction with an
SHG crystal or other type of wavelength conversion device to
generate shorter wavelength radiation (e.g., green laser light)
from a longer wavelength source (e.g., a near-infrared laser
diode).
[0006] In accordance with one embodiment of the present disclosure,
a method is given for aligning an optical package comprising a
laser, a wavelength conversion device, at least one adjustable
optical component, and at least one actuator. The optical package
may contain additional optical components, such as lenses or
mirrors, which facilitate the alignment. The adjustable optical
component may comprise any one or more of these optical components,
either alone or in any combination. This adjustment permits the
alignment of the laser and the wavelength conversion device to be
optimized. The method comprises three basic steps: moving the
adjustable optical component to a command position by applying a
pulse-width modulated signal to an actuator, measuring the actual
position of the adjustable optical component, and adjusting the
pulse-width modulated signal to compensate for any difference
between the command position and the actual position of the
adjustable optical component.
[0007] The adjustable optical component is moved to a command
position by applying a pulse-width modulated signal to the
actuator. The command position represents a position at which the
alignment of the laser and the wavelength conversion device is
optimized. The actuator is comprised of two magnetic elements which
are in magnetic communication with each other. A first magnetic
element is mechanically coupled to a base of the optical package,
and a second magnetic element is mechanically coupled to the
adjustable optical component. At least one of the magnetic elements
comprises an electrically conductive coil, to which the pulse-width
modulated signal is applied in order to effect movement of the
adjustable optical component.
[0008] The method then measures the actual position of the
adjustable optical component by measuring an output of a position
measuring circuit. The position measuring circuit measures the
voltage amplitude of an oscillation in a resonator tank circuit
during an "off" period of the pulse-width modulated signal. The
resonator tank circuit is formed by electrically coupling a
capacitive element to the electrically conductive coil of the
actuator. The voltage amplitude of the oscillation in the resonator
tank circuit represents the actual position of the adjustable
optical component. Thus, the output of the position measuring
circuit represents the actual position of the adjustable optical
component.
[0009] The method next adjusts the pulse-width modulated output so
as to compensate for any difference in the actual position of the
adjustable optical component and the command position.
[0010] Additional features and advantages will be set forth in the
detailed description which follows and, in part, will be readily
apparent to those skilled in the art from that description or
recognized by practicing the embodiments described herein. It is to
be understood that both the foregoing general description and the
following detailed description are intended to provide an overview
or framework for understanding the nature and character of the
present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The following detailed description of specific embodiments
can be best understood when read in conjunction with the following
drawings, where like structure is indicated with like reference
numerals and in which:
[0012] FIG. 1 is a drawing of the optical package according to one
embodiment of the present disclosure;
[0013] FIG. 2 shows an actuator according to one embodiment of the
present disclosure;
[0014] FIG. 3 depicts an electrical schematic of the resonator tank
circuit and the position measuring circuit according to one
embodiment of the present disclosure;
[0015] FIGS. 4a and 4b show the pulse-width modulated signal and
the voltage amplitude of the resonator tank circuit according to
one embodiment of the disclosure; FIG. 4c shows the pulse-width
modulate signal and the output of the position measuring circuit
according to one embodiment of the disclosure; and
[0016] FIG. 5 depicts the relationship between the actual position
of the adjustable optical component and the voltage amplitude of
the oscillation in the resonator tank circuit according to one
embodiment of the disclosure.
DETAILED DESCRIPTION
[0017] A method for aligning an optical package 10 according to one
embodiment can be illustrated with reference to FIG. 1. The optical
package 10 comprises a laser 20, a wavelength conversion device 30,
at least one adjustable optical component 40A, 40B, and at least
one actuator 60 is given. The adjustable optical components 40A,
40B are moved to command positions by applying a pulse-width
modulated signal to the actuator 60. The command positions
represent an optimized alignment of the laser 20 and the wavelength
conversion device 30. Referring now to FIGS. 1 and 2, the actuator
60 comprises a first and second magnetic elements 100A, 100B. The
first magnetic element 100A is mechanically coupled to a base 120
of the optical package 10, and the second magnetic element 100B is
mechanically coupled to the adjustable optical component 40A, 40B.
The first magnetic element 100A and the second magnetic element
100B are in magnetic communication with each other. At least one of
the magnetic elements 100A, 100B comprises an electrically
conductive coil 140 to which the pulse-width modulated signal is
applied. The application of the pulse-width modulated signal to the
electrically conductive coil 140 creates a magnetic field of
sufficient strength to move the adjustable optical components 40A,
40B in at least one axis of motion.
[0018] Referring to FIG. 3, the actual positions of the adjustable
optical components 40A, 40B can be measured by measuring an output
450 of a position measuring circuit 350. In the embodiment
described herein, the position measuring circuit 350 comprises a
rectifier circuit 330 and a filter circuit 340. The output 450 of
the position measuring circuit 350 represents a voltage amplitude
440 of an oscillation in a resonator tank circuit 320 during an
"off" period 410 of the pulse-width modulated signal 300. The
resonator tank circuit 320 comprises the electrically conductive
coil 140 electrically coupled to a capacitive element 327. The
voltage amplitude 440 of the oscillation in the resonator tank
circuit 320 represents the actual position of the adjustable
optical component 40A, 40B.
[0019] To align the optical package 10, the pulse-width modulated
signal 300 is adjusted to compensate for the difference between the
represented actual position and the command positions.
[0020] The particular embodiment of the optical package 10
disclosed herein is for illustrative purposes only. Those skilled
in the art will recognize that numerous embodiments of the optical
package are possible and are taught in readily available technical
literature relating to the design and fabrication of frequency or
wavelength-converted semiconductor laser sources. In the embodiment
depicted in FIG. 1, the near infrared light emitted by the laser 20
is coupled into a waveguide portion of the wavelength conversion
device 30 by optical components 40A, 40B that are adjustable in the
X and Y dimension, such as a suitable lens or mirror which may
comprise one or more optical elements of unitary or multi-component
configuration. The optical package illustrated in FIG. 1 is
particularly useful in generating a variety of shorter wavelength
laser beams from a variety of longer wavelength semiconductor
lasers and can be used, for example, as a visible laser source in a
laser projection system.
[0021] Referring again to FIG. 1, the adjustable optical components
40A, 40B are particularly helpful because it is often difficult to
focus the output beam emitted by the laser 20 into the waveguide
portion of the wavelength conversion device 30. For example,
waveguide optical mode field diameters of typical SHG crystals,
such as MgO-doped periodically poled lithium niobate (PPLN)
crystals, can be in the range of a few microns. The adjustable
optical components 40A, 40B cooperate with the laser 20 to generate
a beam spot 80 of appropriate size on the input face 90 of the
wavelength conversion device 30. In the embodiment shown in FIG. 1,
a first adjustable optical component 40A is configured to be
adjusted only in the direction of the "X" axis, and a second
adjustable optical component 40B is configured to be adjusted only
in the direction of the "Y" axis. Thus, in this embodiment, the
adjustable optical components 40A and 40B cooperate with each other
to actively align the beam spot 80 with the waveguide portion of
the wavelength conversion device 30 by altering the position of the
beam spot 80 on the input face 90 of the wavelength conversion
device 30 until it is aligned with the waveguide portion of the
wavelength conversion device 30.
[0022] In the embodiment of FIG. 1, the adjustable optical
components 40A and 40B comprise a pair of lenses. However, as those
skilled in the art will recognize, other types of optical
components may be used, such as mirrors. Also, the adjustable
optical component may comprise other optical components in the
optical package, including but not limited to the laser 20 or the
wavelength conversion device 30.
[0023] In the embodiment described herein, two optical components
are adjusted in order to align the optical package 10. However, it
is contemplated that only one adjustable optical component 40A, 40B
can be used. As an illustrative example, the optical package may
comprise two lenses, one of which is adjustable and one of which is
fixed. The only adjustable optical component in such a system could
be one of the lenses. The remaining optical components (i.e., the
laser 20, the wavelength conversion device 30, and the other lens)
could be fixed and would not be adjustable. Furthermore, in this
type of system the sole adjustable component may be moved in either
one axis of motion, two axes of motion, three axes of motion, etc.
A separate actuator may be required to effect movement in each axis
of motion. Other embodiments may permit any one of the other
optical components in the optical package to be adjusted, while
keeping the other optical components fixed. As another example, the
laser 20 may be the adjustable optical component, while the
remaining optical components of the optical package 10 would be
fixed.
[0024] In other embodiments, it is contemplated that two or more
optical components may be adjusted in order to optimize the
alignment of the optical package 10. These adjustable optical
components may comprise any combination of the optical components
present in the optical package 10. As an illustrative example, in
an optical package 10 comprising a laser 20, a wavelength
conversion device 30, and two lenses, all the components may be
adjustable. In an alternative embodiment, one of the lenses and the
laser may be adjustable. Many combinations of adjustable optical
components 40A, 40B are possible. Furthermore, of the two or more
adjustable optical components 40A, 40B, any one of them may be
adjustable in either one, two, or three axes of motion, independent
of the other adjustable optical components 40A, 40B. Continuing
with the illustrative example, the laser may be adjustable in two
axes of motion, while one of the lenses may only be adjustable in
one axis of motion. Those skilled in the art will recognize that
many combinations of adjustable optical components 40A, 40B are
possible, as well as their corresponding adjustability in up to
three axes of motion.
[0025] When referring to the movement of the adjustable optical
component 40A, 408, the embodiment described herein contemplates
the definition of the term "axis of motion" to include any
direction that is parallel to the laser beam 70, perpendicular to
the laser beam 70, or which may have both a parallel and
perpendicular component with respect to the laser beam 70. In the
embodiment described herein, the movement of the adjustable optical
component 40A, 40B may be in one direction perpendicular to the
laser beam 70, or in two directions perpendicular to the laser beam
70 and to each other.
[0026] For the purposes of describing and defining the present
invention, it is noted that there will be varying degrees of
"optimized" alignment between the laser 20 and the wavelength
conversion device 30. For example, although an "optimized"
alignment may be established as the one configuration where the
output of the wavelength conversion device 30 is at an absolute
maximum, it is also contemplated that a particular alignment state
may qualify as an "optimized" alignment if the optical output of
the wavelength conversion device 30 merely exceeds a given
threshold. That given threshold may be presented as a given optical
power level, a percentage of maximum power, etc.
[0027] Referring now to FIG. 2, the actuator 60 comprises two
magnetic elements 100A and 100B. The first magnetic element 100A
comprises an electrically conductive coil 140. The first magnetic
element 100A is coupled to a base 120 of the optical package 10,
while the second magnetic element 100B is coupled to the adjustable
optical component. The magnetic elements are in magnetic
communication with each other such that the application of a
pulse-width modulated signal to the electrically conductive coil
140 produces a magnetic field of sufficient strength to move the
adjustable optical component 40A, 40B in at least one axis of
motion.
[0028] It to be understood that a magnetic element can be any
structure that comprises a material upon which an attractive or
repulsive force can be generated due to the presence of a magnetic
field, including but not limited to a permanent magnet, a structure
(like an electromagnetic coil) that comprises a permanent magnet, a
metal that responds to a magnetic field, a structure that comprises
a metal that responds to a magnetic field, or combinations thereof.
Where the magnetic element is an electrically conductive coil 140,
it is contemplated that although typical electrically conductive
coils comprise a wire (or other suitable electrical conductor)
wound a number of time around a ferrite core, other methods of
creating an electrically conductive coil can be gleaned from
conventional or yet-to-be-developed teachings in the art.
[0029] In the embodiment described herein, the first magnetic
element 100A comprises an electrically conductive coil 140, and the
second magnetic element 100B comprises a permanent magnet. An
alternative embodiment may reverse the magnetic elements: the first
magnetic element 100A (coupled to the base 120) may comprise the
permanent magnet, and the second magnetic element 100B (coupled to
the adjustable optical component 40A, 40B) may comprise the
electrically conductive coil 140. It is to be understood that many
combinations of magnetic elements are possible in order to achieve
the same purpose.
[0030] In one embodiment, a flexure wire 130 holds the second
magnetic element 100B (and the corresponding adjustable optical
component 40A, 40B) in place while still affording movement by the
actuator 60. One end of the flexure wire 130 is mechanically
coupled to the second magnetic element 100B and the other end of
the flexure wire is mechanically coupled to the base 120 of the
optical package 10. The flexure wire provides mechanical rigidity
to the adjustable optical component 40A, 40B and keeps it in a
"rest position" in the absence of a pulse width modulated signal.
Application of a pulse width modulated signal creates a movement of
the adjustable optical component 40A, 40B, the force of which is
opposed by the flexure wire 130. As the adjustable optical
component 40A, 40B moves further away from the "rest position," tie
opposing force generated by the flexure wire 130 increases. In this
fashion, the magnitude of the pulse-width modulated signal controls
the position of the adjustable optical component 40A, 40B. The
force generated by the actuator 60 either repels or attracts the
adjustable optical component 40A, 40B. Those skilled in the art
will recognize that other mechanical devices may be substituted for
the flexure wire 130, including but not limited to coil springs,
mechanical guides, or any other component or assembly which keeps
the second magnetic element 40B and the adjustable optical
component 40A, 40B in a known "rest position" in the absence of the
pulse-width modulated signal. These other embodiments may achieve
the same effect of providing mechanical rigidity as well as
opposing the force generated by the actuator 60.
[0031] FIG. 3 depicts one configuration of the resonator tank
circuit 320 and the position measuring circuit 350. The resonator
tank circuit 320 comprises the electrically conductive coil 140 and
a capacitive element 327. The capacitive element 327 may comprise a
capacitor. In addition, as will be described herein, the resonator
tank circuit 320 may also comprise a ballast inductor 326. If the
ballast inductor 326 is not present in the circuit, it may be
electrically replaced by a short circuit. A pulse-width modulated
signal 300 is applied to the electrically conductive coil 140
(which is part of the resonator tank circuit 320) in order to move
an adjustable optical component to a command position. The
resulting electrical current in the electrically conductive coil
140 creates a magnetic field which operates to produce a force
between the magnetic elements 100A, 100B sufficient to move the
adjustable optical component 40A, 40B. In the embodiment described
herein, the pulse-width modulated signal 300 creates a positive or
negative electrical current in the electrically conductive coil
140. The corresponding magnetic field produced by the electrically
conductive coil 140 will also be of two polarities. If the second
magnetic element 100B is a permanent magnet, the polarity of the
magnetic field will determine whether the magnetic force between
the magnetic elements 100A, 100B is attractive or repulsive. In
this fashion, the pulse-width modulated signal 300 controls the
polarity and strength of the magnetic force between the magnetic
elements 100A, 100B of the actuator 60. The frequency of the
pulse-width modulated signal 300 may be higher than the mechanical
response time of the actuator 60 so that the actuator 60 acts as a
low-pass filter. In this fashion, the application of a pulse-width
modulated signal 300 to the actuator 60 results in smooth movement
of the adjustable optical component 40A, 40B.
[0032] Referring to FIGS. 3 and 4a, the pulse-width modulated
signal 300 applied to the electrically conductive coil 140
comprises two distinct time periods: an "on" period 400 and an
"off" period 410. During the "on " period 400, the pulse width
modulated signal 300 connects the electrically conductive coil 140
to a power supply, which causes the electrical current in the
electrically conductive coil 140 to increase. During the "off"
period 410, the pulse-width modulated signal 300 disconnects the
power supply (not shown) from the electrically conductive coil 140
and allows the electrical current to begin to decay. By applying
the pulse-width modulated signal 300 in this fashion, an average
electrical current is passed through the electrically conductive
coil 140 which may be adjusted by changing the duty cycle of the
pulse-width modulated signal 300, as is well known to those skilled
in the art. Because the force of the magnetic field generated by
the electrically conductive coil 140 and the magnetic element 100A,
100B is related to the amplitude of the current passing through the
electrically conductive coil 140, the movement of the adjustable
optical component 40A, 40B is effected by adjusting the duty cycle
of the pulse-width modulated signal 300.
[0033] Referring again to FIG. 3, the resonator tank circuit 320 is
formed by electrically coupling a capacitive element 327 to the
electrically conductive coil 140. The capacitive element 327 causes
the resonator tank circuit 320 to oscillate during the "off" period
410 of the pulse-width modulated signal 300. The voltage amplitude
440 of the oscillation in the resonator tank circuit 320 decays if
any resistance is in the circuit, due to, for example, any
resistance in electrically conductive coil 140. Thus, in the
embodiment described herein, a feedback amplifier 310 provides a
mechanism to sustain the voltage oscillation during the "off"
period 410, thus causing the voltage amplitude 440 of the
oscillation to remain substantially constant. Those skilled in the
art will appreciate that a number of amplifier circuits may be used
for sustaining the oscillation of the resonator tank circuit,
including, but not limited to, amplifier circuits comprising an
operational amplifier, a bipolar junction transistor, or a
field-effect transistor.
[0034] According to one embodiment, the position measuring circuit
350 comprises a rectifier circuit 330 and a filter circuit 340. The
output 450 of the position measuring circuit 350 is a signal which
represents the voltage amplitude 440 in the resonator tank circuit
320 during the "off" period 410 of the pulse-width modulated signal
300. The output 450 during the "off" period 410 may be measured by
an analog-to-digital converter. Many other types of circuits are
possible which perform the same function. Other embodiments may
include similar measuring circuits, as is known to those skilled in
the art. Such circuits may include, for example, measuring the
voltage amplitude 440 of the resonator tank circuit 320 directly
with a fast analog-to-digital converter.
[0035] In one embodiment, the resonator tank circuit 320 may also
comprise a ballast inductor 326 which is electrically connected to
the electrically conductive coil 140. The ballast inductor 326
insures that there is a minimum amount of inductance in the
resonator tank circuit 320 in the event the inductance of the
electrically conductive coil 140 becomes very small, such as may
occur when the two magnetic elements 100A, 100B are in very close
proximity to one other.
[0036] The frequency of the oscillation in the resonator tank
circuit 320 depends primarily on the inductance of the ballast
inductor 326 and the electrically conductive coil 140, as well as
the capacitive element 327. The frequency of the oscillation may
change somewhat as the inductance of the electrically conductive
coil 140 changes. However, the position measuring circuit 350 may
be designed to not be affected by the change in frequency. In the
embodiment described herein, the frequency of the oscillation in
the resonator tank circuit 320 may be greater than the frequency of
the pulse-width modulated signal 300.
[0037] Referring to FIGS. 4A and 4B, the pulse-width modulated
signal 300 and its relationship to the resonator tank circuit
voltages 420, 430 are shown. The pulse-width modulated signal 300
may have an "on" period 400 and an "off" period 410. During the
"on" period 400, the resonator tank circuit voltage 420 may, as
shown in the embodiment herein, remain relatively constant.
However, during the "off" period 410, the resonator tank circuit
voltage 430 may oscillate. FIGS. 4A and 4B depict the relationship
between these two signals. FIG. 4B shows a close-up of the
resonator tank circuit oscillation voltage, illustrating the
frequency of oscillation of the resonator tank circuit voltage 430
during the "off" period 410.
[0038] The voltage amplitude 440 of the oscillation in the
resonator tank circuit 320 during the "off" period 410 depends on
the distance between the two magnetic elements 100A, 100B. As the
distance between the two magnetic elements 100A, 100B changes, the
electrical inductance of the electrically conductive coil 140
changes. As a consequence, the voltage amplitude 440 of the
oscillation in resonator tank circuit 320 also changes. Thus, the
measurement of the voltage amplitude 440 of the oscillation in the
resonator tank circuit 320 is an indirect measurement of the
position of the adjustable optical component 40A, 40B.
[0039] Referring now to FIGS. 3 and 4A-C, the embodiment described
herein includes a position measuring circuit 350 which may comprise
a rectifier circuit 330 and a filter circuit 340. The position
measuring circuit 350 measures the voltage amplitude 440 of the
oscillation in the resonator tank circuit 320 during an "off"
period 410 of the pulse-width modulated signal 300 by rectifying
(through the rectifier circuit 330) and filtering (through the
filter circuit 340) the voltage of the resonator tank circuit 320.
The output 450 of the position measuring circuit 350 during the
"off" period 410 is a substantially DC (direct current) voltage
which represents the voltage amplitude 440 of the resonator tank
circuit 320. As previously discussed, because the voltage amplitude
440 represents the position of the adjustable optical component
40A, 40B, the output 450 of the position measuring circuit 350 also
represents the position of the adjustable optical component 40A,
40B. Those skilled in the art will recognize that a variety of
circuits may be used to measure the voltage amplitude 440. Such
circuits may include, by way of illustrative example, an
analog-to-digital converter or a voltage integrator circuit.
[0040] Referring to FIG. 5, the relationship between the voltage
amplitude 440 of the oscillation in the resonator tank circuit 320
and the actual position of the adjustable optical component 40A,
40B is given as an illustrative example. The relationship may be
substantially linear. In one embodiment, the flexure wire 130
maintains the adjustable optical component 40A, 40B at an
approximate position of 75 .mu.m in the absence of a pulse-width
modulated signal 300. Applying a pulse-width modulated signal 300
may move the adjustable optical component up to 20 .mu.m in either
direction, depending on the polarity of the pulse-width modulated
current. This movement results in the output 450 of the position
measuring circuit 350 to vary approximately from +1500 mV to -1500
mV. It is to be understood that other voltage ranges and position
ranges are possible.
[0041] According to the embodiment described herein, the
pulse-width modulated signal 300 may be adjusted in order to
compensate for a difference between the actual position of the
adjustable optical component 40A, 40B (as measured by the position
measuring circuit 350) and the command position. Such an adjustment
may include, for example, increasing or decreasing the duty cycle
of the pulse-width modulated signal 300. In addition, this
adjustment may be performed as frequently as is required by the
application. Furthermore, the method may be repeated any number of
times to periodically or continuously maintain the adjustable
optical component at the command position.
[0042] Referring again to FIG. 1, in another embodiment, the
optical package 10 comprises an optical intensity feedback loop
comprising a partially reflective mirror 95, an optical detector
110, and a microcontroller 115. The mirror 95 reflects a portion of
the optical output of the wavelength conversion device 30 to an
optical detector 110. The optical detector 110 measures the optical
intensity of the reflected output and communicates the measure to
the microcontroller 115. In this system, the microcontroller 115
determines the command position by identifying points at which the
optical intensity reaches an approximate maximum value. The command
position may be determined either during the manufacture of the
optical package 10, during the operation of the optical package 10,
or both.
[0043] It is contemplated that an automatic control system may
perform each step in the method, including applying a pulse-width
modulated signal to an actuator to move the adjustable optical
component 40A, 40B to a command position, measuring the actual
position of the adjustable optical component 40A, 40B, and
adjusting the pulse-width modulated signal 300 to compensate for a
difference in the command position and actual position. Such a
control system may be comprised of a microprocessor executing
program instructions to adjust the pulse width-modulated signal
300, or it may be comprised of discrete analog components connected
together in such a fashion to adjust the pulse-width modulated
signal 300. Those skilled in the art will recognize that there are
numerous methods to implement such a control system by using
various combinations of digital and analog components. Furthermore,
the automatic control system may be implemented in a single
integrated circuit, either by itself or combined with other
circuits.
[0044] The embodiments described herein permit the adjustable
optical components 40A, 40B to be kept at the command positions,
notwithstanding any external force which, without this method, may
cause the adjustable optical component 40A, 40B to move away from
the command position. Such external forces may include gravity or
the stress in the optical package 10 caused by a temperature
change. Also, this force may be the result of vibration or shock to
the optical package 10 or any of its components.
[0045] Although the embodiments described herein refer to "a
laser," "the laser," "a wavelength conversion device," and "the
wavelength conversion device," it is contemplated that the optical
package may comprise more than one laser or more than one
wavelength conversion device. As an illustrative example, an
optical package may comprise two lasers and two corresponding
wavelength conversion devices. The alignment of each
laser/wavelength conversion device pair may be optimized according
to the principles described herein.
[0046] It is noted that recitations herein of a component of the
present disclosure being "configured" to embody a particular
property are structural recitations as opposed to recitations of
intended use. More specifically, the references herein to the
manner in which a component is "configured" denotes an existing
physical condition of the component and, as such, is to be taken as
a definite recitation of the structural characteristics of the
component.
[0047] It is noted that terms like "preferably" and "typically,"
when utilized herein, are not utilized to limit the scope of the
claimed invention or to imply that certain features are critical,
essential, or even important to the structure or function of the
claimed invention. Rather, these terms are merely intended to
identify particular aspects of an embodiment of the present
invention or to emphasize alternative or additional features that
may or may not be utilized in a particular embodiment of the
present invention.
[0048] For the purposes of describing and defining the present
invention it is noted that the terms "substantially" and
"approximately" are utilized herein to represent the inherent
degree of uncertainty that may be attributed to any quantitative
comparison, value, measurement, or other representation. For
example, the voltage amplitude of the oscillation in the resonator
tank circuit may, under some conditions, remain substantially
constant. The terms "substantially" and "approximately" are also
utilized herein to represent the degree by which a quantitative
representation may vary from a stated reference without resulting
in a change in the basic function of the subject matter at issue.
For example, the output of the position measuring circuit may vary
approximately from +1500 mV to -1500 mV.
[0049] Having described the invention in detail and by reference to
specific embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims. More
specifically, although some aspects of the present invention are
identified herein as preferred or particularly advantageous, it is
contemplated that the present invention is not necessarily limited
to these preferred aspects of the invention.
[0050] It is noted that one or more of the following claims utilize
the term "wherein" as a transitional phrase. For the purposes of
defining the present invention, it is noted that this term is
introduced in the claims as an open-ended transitional phrase that
is used to introduce a recitation of a series of characteristics of
the method and should be interpreted in like manner as the more
commonly used open-ended preamble term "comprising."
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