U.S. patent application number 15/342357 was filed with the patent office on 2018-05-03 for multi-channel laser system including an acousto-optic modulator (aom) and related methods.
The applicant listed for this patent is Harris Corporation. Invention is credited to Pat O. Bentley, Lee M. Burberry, Michael R. Lange, Catheryn D. Logan, RANDALL K. MORSE, Peter A. Wasilousky.
Application Number | 20180120599 15/342357 |
Document ID | / |
Family ID | 59858474 |
Filed Date | 2018-05-03 |
United States Patent
Application |
20180120599 |
Kind Code |
A1 |
MORSE; RANDALL K. ; et
al. |
May 3, 2018 |
MULTI-CHANNEL LASER SYSTEM INCLUDING AN ACOUSTO-OPTIC MODULATOR
(AOM) AND RELATED METHODS
Abstract
A method may include generating a laser light beam with a laser
source, splitting the laser light beam into a first front side beam
and a back side beam for a back side of an ion trap using a first
beamsplitter, directing the front side beam to a second
beamsplitter using an input telescope, and splitting the first
front side beam into a plurality of second front side beams
directed to a common acousto-optic medium using a second
beamsplitter. The common acousto-optic medium may have a respective
plurality of electrodes coupled to the common acousto-optic medium
for each of the second front side beams. The method may further
include directing the plurality of second front side beams to a
front side of the ion trap using an output telescope, and
generating a respective RF drive signal for each of the plurality
of electrodes using a plurality of RF drivers.
Inventors: |
MORSE; RANDALL K.; (Palm
Bay, FL) ; Wasilousky; Peter A.; (Indialantic,
FL) ; Burberry; Lee M.; (West Melbourne, FL) ;
Lange; Michael R.; (Melbourne, FL) ; Logan; Catheryn
D.; (Melbourne, FL) ; Bentley; Pat O.; (West
Melbourne, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Harris Corporation |
Melbourne |
FL |
US |
|
|
Family ID: |
59858474 |
Appl. No.: |
15/342357 |
Filed: |
November 3, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 2002/008 20130101;
H03K 19/14 20130101; H01S 3/10 20130101; G02F 3/00 20130101; G06N
10/00 20190101; G02F 1/11 20130101; G02F 1/113 20130101; G02B
27/1093 20130101 |
International
Class: |
G02F 1/11 20060101
G02F001/11; G02B 27/10 20060101 G02B027/10 |
Claims
1. A laser system comprising: a laser source configured to generate
a laser light beam; an ion trap; a first beamsplitter configured to
split the laser light beam into a first front side laser light beam
and a back side laser light beam for a back side of the ion trap; a
multi-channel acousto-optic modulator (AOM) comprising a second
beamsplitter to split the first front side laser light beam into a
plurality of second front side laser light beams from the second
beamsplitter, a common acousto-optic medium configured to receive
the plurality of front side laser light beams, and a respective
plurality of electrodes coupled to the common acousto-optic medium
for each of the second front side laser light beams; a plurality of
radio frequency (RF) drivers each configured to generate respective
RF drive signals for each of the plurality of electrodes; an input
telescope configured to direct the front side laser light beam to
the second beamsplitter; and an output telescope configured to
direct the plurality of second front side laser light beams to a
front side of the ion trap.
2. The laser system of claim 1 further comprising at least one
turning mirror to direct the back side laser light beam from the
first beamsplitter to the back side of the workpiece.
3. The laser system of claim 1 further comprising a single-channel
AOM positioned in the light path of the back side laser light beam
between the beamsplitter and the workpiece.
4. The laser system of claim 1 further comprising a single channel
amplitude leveling AOM coupled between the laser source and the
first beamsplitter.
5. The laser system of claim 1 wherein the electrodes comprise
phased array transducer electrodes; and wherein each RF driver is
configured to drive alternating electrodes of the respective phased
array transducer electrodes with different phases.
6. The laser system of claim 5 wherein each RF driver is configured
to drive the alternating electrodes with different phases within a
range of 0.degree. to 180.degree..
7. The laser system of claim 5 wherein an RF power level associated
with each RF drive signal has a constant power.
8. The laser system of claim 1 wherein the second beamsplitter
comprises a high efficiency diffractive optical element (DOE) and a
set of telecentric beam forming optics associated therewith.
9. A laser system comprising: a laser source configured to generate
a laser light beam; an ion trap; a first beamsplitter configured to
split the laser light beam into a first front side laser light beam
and a back side laser light beam for a back side of the ion trap; a
multi-channel acousto-optic modulator (AOM) comprising a second
beamsplitter to split the first front side laser light beam into a
plurality of second front side laser light beams from the second
beamsplitter, the second beamsplitter comprising a high efficiency
diffractive optical element (DOE) and a set of telecentric beam
forming optics associated therewith, a common acousto-optic medium
configured to receive the plurality of front side laser light
beams, and a respective plurality of electrodes coupled to the
common acousto-optic medium for each of the second front side laser
light beams; a plurality of radio frequency (RF) drivers configured
to generate respective RF drive signals for each of the plurality
of electrodes; an input telescope configured to direct the front
side laser light beam to the second beamsplitter; an output
telescope configured to direct the plurality of second front side
laser light beams to a front side of the ion trap; at least one
turning mirror to direct the back side laser light beam from the
first beamsplitter to the back side of the ion trap; and a
single-channel AOM positioned in the light path of the back side
laser light beam between the beamsplitter and the ion trap.
10. The laser system of claim 9 further comprising a single channel
amplitude leveling AOM coupled between the laser source and the
first beamsplitter.
11. The laser system of claim 9 wherein the electrodes comprise
phased array transducer electrodes; and wherein each RF driver is
configured to drive alternating electrodes of the respective phased
array transducer electrodes with different phases.
12. The laser system of claim 11 wherein each RF driver is
configured to drive the alternating electrodes with different
phases within a range of 0.degree. to 180.degree..
13. The laser system of claim 11 wherein an RF power level
associated with each RF drive signal has a constant power within
.+-.0.1%.
14. A method comprising: generating a laser light beam with a laser
source; splitting the laser light beam into a first front side
laser light beam and a back side laser light beam for a back side
of an ion trap using a first beamsplitter; directing the front side
laser light beam to a second beamsplitter using an input telescope;
and splitting the first front side laser light beam into a
plurality of second front side laser light beams directed to a
common acousto-optic medium using a second beamsplitter, wherein a
respective plurality of electrodes is coupled to the acousto-optic
medium for each of the second front side laser light beams;
directing the plurality of second front side laser light beams to a
front side of the ion trap using an output telescope; and
generating respective RF drive signals for each of the plurality of
electrodes using a plurality of radio frequency (RF) drivers.
15. The method of claim 14 further comprising directing the back
side laser light beam from the first beamsplitter to the back side
of the ion trap using at least one turning mirror.
16. The method of claim 14 wherein a single-channel acousto-optic
modulator (AOM) is positioned in the light path of the back side
laser light beam between the beamsplitter and the workpiece.
17. The method of claim 14 wherein a single-channel amplitude
leveling acousto-optic modulator (AOM) is coupled between the laser
source and the first beamsplitter.
18. The method of claim 14 wherein the electrodes comprise phased
array transducer electrodes; and wherein generating the respective
RF drive signals comprises generating the respective RF drive
signal to drive alternating electrodes of respective phased array
transducer electrodes with different phases.
19. The method of claim 18 wherein each drive signal is configured
to drive the alternating electrodes with different phases within a
range of 0.degree. to 180.degree..
20. The method of claim 18 wherein an RF power level associated
with each RF drive signal has a constant power.
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of optical
devices, and, more particularly, to acousto-optic modulators for
lasers and related methods.
BACKGROUND
[0002] Acousto-optic modulators, sometimes referred to as Bragg
cells, diffract and shift light using sound waves at radio
frequency. These devices are often used for Q-switching, signal
modulation in telecommunications systems, laser scanning and beam
intensity control, frequency shifting, and wavelength filtering in
spectroscopy systems. Many other applications lend themselves to
using acousto-optic devices.
[0003] In such acousto-optic devices, a piezoelectric transducer,
sometimes also referred to as an RF transducer, is secured to an
acousto-optic bulk medium as a transparent optical material, for
example, fused silica, quartz or similar glass material. An
electric RF signal oscillates and drives the transducer to vibrate
and create sound waves within the transparent medium which effect
the properties of an optical field in the medium via the photo
elastic effect, in which a modulating strain field of an ultrasonic
wave is coupled to an index of refraction for the acousto-optic
bulk medium. As a result, the refractive index change in amplitude
is proportional to that of sound.
[0004] The index of refraction is changed by moving periodic planes
of expansion and compression in the acousto-optic bulk material.
Incoming light scatters because of the resulting periodic index
modulation and interference, similar to Bragg diffraction.
[0005] Acousto-optic modulators are preferred in many applications
because they are faster than tiltable mirrors and other mechanical
devices. The time it takes for the acousto-optic modulator to shift
an exiting optical beam is limited to the transit time of the sound
wave. The acousto-optic modulators are often used in Q-switches
where a laser produces a pulsed output beam at high peak power,
typically in the Kilowatt range. This output could be higher than
lasers operating a continuous wave (CW) or constant output
mode.
[0006] Examples of acousto-optic modulator devices and similar
acousto-optic systems are disclosed in commonly assigned U.S. Pat.
Nos. 4,256,362; 5,923,460; 6,320,989; 6,487,324; 6,538,690;
6,765,709; and 6,870,658, the disclosures of which are hereby
incorporated by reference in their entireties.
[0007] Some applications using acousto-optic devices modulate the
intensity of an optical beam. This modulation may create small
deviations in the output angle of the diffracted beam because of
the local thermal transients introduced when the RF modulation
waveform to the device is turned ON and OFF. These thermal
transients may negatively impact the resolution and location of the
focused spot, which may be produced. One advantageous approach
which may be used to help enhance the resolution of acousto-optic
devices is set forth in U.S. Pat. No. 7,538,929 to Wasilousky,
which is assigned to the present Applicant and is hereby
incorporated herein in its entirety by reference. Wasilousky
discloses an acousto-optic modulator which includes an
acousto-optic bulk medium and transducer attached to the
acousto-optic bulk medium and famed as a linear array of
electrodes. A transducer driver is connected to each electrode and
is coherently phase driven to alter the angular momentum
distribution of an acoustic field and alternately allow and inhibit
phase matching between the optical and acoustic field and produce a
desired intensity modulation of an optical wavefront.
[0008] Despite the existence of such configurations, further
advancements in laser systems using acousto-optic modulators may be
desirable in certain applications.
SUMMARY
[0009] A laser system may include a laser source configured to
generate a laser light beam, an ion trap, a first beamsplitter
configured to split the laser light beam into a first front side
laser light beam and a back side laser light beam for a back side
of the ion trap, and a multi-channel acousto-optic modulator (AOM).
The multi-channel AOM may include a second beamsplitter to split
the first front side laser light beam into a plurality of second
front side laser light beams from the second beamsplitter, a common
acousto-optic medium configured to receive the plurality of front
side laser light beams, and a respective plurality of electrodes
coupled to the common acousto-optic medium for each of the second
front side laser light beams. The system may further include a
plurality of radio frequency (RF) drivers each configured to
generate an RF drive signals for each of the plurality of
electrodes, an input telescope configured to direct the front side
laser light beam to the second beamsplitter, and an output
telescope configured to direct the plurality of second front side
laser light beams to a front side of the ion trap.
[0010] More particularly, the laser system may further include at
least one turning mirror to direct the back side laser light beam
from the first beamsplitter to the back side of the workpiece.
Also, a single-channel AOM may be positioned in the light path of
the back side laser light beam between the beamsplitter and the
workpiece. Furthermore, a single channel amplitude leveling AOM may
be coupled between the laser source and the first beamsplitter.
[0011] In accordance with one example embodiment, the electrodes
may comprise phased array transducer electrodes, and each RF driver
may be configured to drive alternating electrodes of the respective
array transducer electrodes with different phases. More
particularly, each RF driver may be configured to drive the
alternating electrodes with different phases within a range of
0.degree. to 180.degree.. By way of example, an RF power level
associated with each RF drive signal may have a constant power. By
way of example, the second beamsplitter may comprise a high
efficiency diffractive optical element (DOE) and a set of
telecentric beam forming optics associated therewith.
[0012] A related method may include generating a laser light beam
with a laser source, splitting the laser light beam into a first
front side laser light beam and a back side laser light beam for a
back side of an ion trap using a first beamsplitter, directing the
front side laser light beam to a second beamsplitter using an input
telescope, and splitting the first front side laser light beam into
a plurality of second front side laser light beams directed to a
common acousto-optic medium using a second beamsplitter. A
respective plurality of electrodes may be coupled to the common
acousto-optic medium for each of the second front side laser light
beams. The method may further include directing the plurality of
second front side laser light beams to a front side of the ion trap
using an output telescope, and generating respective RF drive
signals for the electrodes using a plurality of RF drivers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic block diagram of a laser system
including a multi-channel acousto-optic modulator (AOM) in
accordance with an example embodiment.
[0014] FIG. 2 is a schematic block diagram of a laser system for
use with an ion trap including a multi-channel AOM in accordance
with an example embodiment.
[0015] FIGS. 3 and 4 are schematic circuit diagrams illustrating
different electrode connection configurations and associated
driving signals therefor which may be used with the systems of
FIGS. 1-2.
[0016] FIGS. 5-6 are flow diagrams illustrating method aspects
associated with the systems of FIGS. 1-2, respectively.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] By way of background, excessive noise levels from laser
sources in optical illumination systems generate instabilities and
errors. In particular, systems that manipulate the quantum states
of particles, atoms and electrons, typically require extreme
stability. Beam pointing errors correlate to noise in quantum state
manipulation systems. Moreover, beam pointing stability due to
thermal transients in the bulk material of active acousto-optic
devices in an optical illumination system affect many applications,
but especially those designed for quantum state illumination.
[0018] Turning initially to FIG. 1 and the flow diagram 70 of FIG.
5, a laser system 130 which provides multi-channel operation and
associated method aspects are now described. By way of background,
typical multi-channel acousto-optic (AO) devices suffer from
excessive beam pointing errors due to data dependent thermal
transients generated in the ultrasonic transducer and bulk optical
substrate material. Moreover, beam pointing errors correlate to
noise in quantum state manipulation systems. In addition,
inter-channel acoustic crosstalk is a major source of data
dependent variation in the modulated optical beam intensity.
[0019] Current passive approaches may minimize the magnitude of
beam deflection due to thermal transients generated when channel
data is switched on and off (i.e., no auxiliary heating
electrodes). This reduces the magnitude of the time average thermal
gradients produced by the aggregate array during normal operation,
leading to reductions in polarization corruption and gross beam
offset. In addition, it does not address beam intensity
fluctuations produced by inter-channel acoustic strain field
interaction.
[0020] Beginning at Block 71, the multi-channel system 130
illustratively includes a laser source 131 which generates a first
laser light beam 141, at Block 72. In accordance with one example
embodiment, a Paladin Advanced 355 nm mode locked UV laser source
from Coherent, Inc. of Santa Clara, Calif. may be used, although
other suitable laser sources may also be used in different
embodiments. A diffractive/refractive beam splitter 142 divides the
first laser light beam 141 into a plurality of second laser light
beams 143, at Block 73, which in the illustrated example is four,
although other numbers of beams (e.g., 8, 32, etc.) may be used
depending upon the given application. The second laser light beams
143 are received by a common phase modulation acousto-optic medium
133 of a multi-channel AOM 132. That is, the acousto-optic medium
133 is common to all of the second laser light beams, i.e., the
same acousto-optic medium is used to modulate each of the second
laser light beams. The acousto-optic medium 133 may include a
piezoelectric transducer and bulk acousto-optic medium (e.g.,
silica, quartz, glass, etc.), as discussed above. However, it
should be noted that the phase-capable multi-channel AOM 132 need
not be used in all embodiments, and that an amplitude modulation
AOM may instead by used in other configurations, for example.
[0021] The AOM 132 further includes multiple transducers, each
comprising respective electrodes 134, for each of the second laser
light beams 143 coupled to the common acousto-optic medium 133. The
laser system 130 further illustratively includes a plurality of RF
drivers 136 each configured to generate the requisite RF drive
signals for their respective phased array transducer electrodes
134, at Block 74, which illustratively concludes the method of FIG.
7 (Block 75).
[0022] Referring additionally to FIGS. 3 and 4, each RF driver 136
may be configured to drive alternating electrodes of the respective
array of transducer electrodes 134 with different phases. More
particularly, two example configurations for driving alternating
electrodes 40 of the array of transducer electrodes 34 with
different phases are now described. In the first configuration
(FIG. 3), the first and third driving signals (shown on the right
hand side of FIG. 3) provided to corresponding odd numbered
electrodes are 180.degree. out of phase with the second and fourth
driving signals provided to corresponding even numbered electrodes.
In the second configuration (FIG. 4), first and second drive
signals are respectively connected to odd and even electrodes in an
interdigitated fashion as shown, and as before these drive signals
are 180.degree. out of phase to one another. In this way, directly
adjacent electrodes are driven at opposite phases to one another.
However, it should be noted that the RF drive signals need not
always be 180.degree. out of phase, i.e., they may be somewhere
between 0.degree. and 180.degree. to vary the level of phase
matching occurring in the AO diffraction process.
[0023] Such a bi-phase configuration helps to eliminate beam
deflection due to thermal transients generated when channel data is
switched on and off, i.e., by using phase modulation only. More
particularly, a bi-phase approach maintains the RF Signal "ON" and
only flips the phase of the drive signal to alternating elements,
as opposed to a conventional amplitude modulation approach in which
optical modulation is achieved by turning the RF signal "ON" and
"OFF".
[0024] The present approach may accordingly reduce time average
thermal gradients produced by the aggregate array during normal
operation since the RF power level is essentially constant or
stationary, which helps to minimize polarization corruption and
gross beam offset. This further helps to reduce beam intensity
fluctuations produced by inter-channel acoustic crosstalk by
minimizing changes in the adjacent channel strain field due to
changes in local channel data.
[0025] By way of example, the transducer electrodes 134 may be
implemented as metalizations on the piezoelectric AO medium 133,
which are spaced apart 500 .mu.m or less at their centers, and more
particularly 450 .mu.m or less. However, other dimensions may be
used in different embodiments.
[0026] Accordingly, employing a phase modulation capable
acousto-optic modulator or transducer structure in a multi-channel
device configuration provides significant advantages. More
particularly, phase modulation used with pulse code (ON/OFF)
modulation provides inherently better pointing stability, since the
RF power applied to the device remains substantially constant at
all times, even during data input bit transitions. Moreover, the
effects of inter-channel acoustic crosstalk are reduced since the
integrated optical effect resulting from changes in the localized
strain field due to adjacent transducer operation are reduced. This
technique may be particularly appropriate when reduced "ON/OFF"
contrast is acceptable, e.g., mask generation involving
photoresist. However, in addition to a photoresist layer of a
semiconductor device, other optical targets 138 may also be used
with the system 130, such as an ion trap(s), micromachining
workpiece, etc.
[0027] Turning now to FIG. 2 and the flow diagram 80 of FIG. 6, a
multi-channel laser system 230 which may incorporate the
multi-channel AOM 132 described above, or alternately an array of
conventional transducers, for quantum state applications is now
described. By way of background, quantum state manipulation
illumination systems control both the optical amplitude and phase
in an interferometric application. However, this requires
significant improvements in crosstalk and beam pointing
stability.
[0028] Beginning at Block 81, the system 230 illustratively
includes a laser source 231, such as those described above, which
is configured to generate a laser light beam (Block 82). The output
of the laser source 231 may optionally be provided to a single
channel amplitude leveling AOM 251, which helps reduce noise from
the laser source. The output of the AOM 251 is split into a first
front side laser light beam 252 and a back side laser light beam
253 for a back side of an ion trap 238 by a beamsplitter 260, at
Block 83. The front side laser light beam 252 passes through an
input telescope 245 to the multi-channel AOM 132, at Block 84. As
noted above, the AOM 132 includes the diffractive/refractive
beamsplitter 142 or diffractive optical element (DOE) to split the
front side laser light beam 252 into a plurality of front side
laser light beams 246, at Block 85. In the illustrated example,
four such beams are shown, but in other embodiments different
numbers of beams may be used, as noted above. Additional beam
forming optics between the beamsplitter 142 and the common AO
medium 133 are incorporated to allow telecentric beam positioning
and adjustment of individual beam waist dimensions along the
centerline and midpoint of each transducer.
[0029] The modulated front side laser light beams 254 output by the
AOM 132 are passed through an output telescope 247 and directed to
the front side of an ion trap 238, at Block 86. The back side laser
light beam 253 is directed to a first turning mirror 255, and then
through first and second focusing optics 256, 257 (although
different numbers of optical focusing stages may be used in
different embodiments) to a single channel AOM 258. The output of
the single channel AOM 258 is directed by turning mirrors 259 and
260 to the back side of the ion trap 238 in the example
implementation. Furthermore, respective RF drive signals are
generated for the phased array transducer electrodes 134 using the
plurality of RF drivers 136, at Block 87, as similarly described
above, or using simplified drive signals when conventional
transducers are employed. The method of FIG. 6 illustratively
concludes at Block 88.
[0030] In accordance with one example implementation, an integrated
multi-channel AOM assembly 132 may be provided including a high
efficiency DOE or beamsplitter 142, a set of telecentric beam
forming optics, a thermally compensated N channel AOM including the
common AO medium 133 and in one embodiment transducers employing an
array of phased electrodes 134, and in certain applications, a
counter propagating illumination beam. As noted above, the input
beam may be split into N separate optical beams, each of which may
be independently modulated in phase and amplitude, with a frequency
shift on the first order diffracted beam equal to the acoustic
frequency. The resultant individual beam pointing stability is not
only suitable for precision photolithography tools, but also
addressing applications such as illuminating atoms in an ion trap
architecture quantum computer, micro-machining and 3D printing, for
example.
[0031] A highly engineered integrated module approach may be used
to achieve the highly uniform, stable, low cross-talk multi-channel
beam illumination system needed for high precision manipulation of
quantum states of individual atoms. This integrated module approach
may be used at various interaction wavelengths. It should be noted
that the noise diverting approach using the first order beam as a
noise dump described above with respect to FIG. 1 may also be
employed in the systems 130 and 230 in some embodiments, if
desired.
[0032] In one or more of the foregoing embodiments, separate active
heating elements may be included to help improve performance, if
desired. One such configuration is set forth in U.S. Pat. No.
6,765,709 to Montgomery et al., which is assigned to the present
Assignee and is hereby incorporated herein in its entirety by
reference. Furthermore, additional techniques may also be employed
for noise reduction in some embodiments, such as described in the
co-pending applications: attorney docket no. GCSD-2898 (62086)
entitled CONTROL SYSTEM USING A PHASE MODULATION CAPABLE
ACOUSTO-OPTIC MODULATOR FOR DIVERTING LASER OUTPUT INTENSITY NOISE
TO A FIRST ORDER LASER LIGHT BEAM AND RELATED METHODS; and attorney
docket no. GCSD-2900 (62087) entitled MULTI-CHANNEL ACOUSTO-OPTIC
MODULATOR (AOM) AND RELATED METHODS. Both of these applications are
assigned to the present Applicant Harris Corporation and are hereby
incorporated herein in their entireties by reference.
[0033] Many modifications and other embodiments will come to the
mind of one skilled in the art having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. Therefore, it is understood that the disclosure is not to
be limited to the specific embodiments disclosed, and that
modifications and embodiments are intended to be included within
the scope of the appended claims.
* * * * *