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jmansell@aos-llc.com1
Progress Towards Low-Cost Compact Metric Adaptive
Optics SystemsJustin D. Mansell, Brian Henderson, Brennen
Wiesner, Robert Praus, and Steve Coy
Active Optical Systems, LLCwww.aos-llc.com
jmansell@aos-llc.com2
Outline• Introduction & Motivation• Low-Cost Component Development
– DMs, Drive Electronics, & AO Controllers• Optical Setup• System Demonstrations
– PC-interfaced System– Microcontroller System
• Evaluation of the Microcontroller SPGD• Conclusions & Future Work
jmansell@aos-llc.com3
Applications of Adaptive Optics• Laser Wavefront
Control– Intensity Profile Shaping
• Laser Machining• Optical Tweezers
– Atmospheric Aberration Compensation
• Imaging– Astronomy– Target Inspection– Ophthalmology
www.physics.uq.edu.au
www.bme.ogi.edu/ biomedicaloptics
www.kirschnervisiongroup.com
Lick Observatory
jmansell@aos-llc.com4
Barriers to Mass Usage
AO systems can often relax requirements
and increase system functionality
Inertia
Construction of complete active optical
systemsComplexity
Implementation via our unique compact low-
cost hardwareCost
SolutionBarrier
jmansell@aos-llc.com5
What is Low Cost?• Patterson published results of
a $25k system in 2000.– $30k in today’s dollars
• Other vendors are selling:– Low Actuator Count DMs for
~$2k– Drive Electronics for ~$5k– Systems for ~$25k+
• We present here a low-cost metric AO system that is commercially available for $7,500 Patterson et al, Optics Express 6, No. 9, 175-85
jmansell@aos-llc.com6
Outline• Introduction & Motivation• Low-Cost Component Development
– DMs, Drive Electronics, & AO Controllers• Optical Setup• System Demonstrations
– PC-interfaced System– Microcontroller System
• Evaluation of the Microcontroller SPGD• Conclusions & Future Work
jmansell@aos-llc.com8
Polymer Deformable Mirror
25 mm
DM Prior to Packaging Packaged DM
37-pin D-sub Connector
ThorlabsSM1 Adapter
jmansell@aos-llc.com10
Membrane Influence Functions (IFs)
-0.5 0 0.5
-0.5
0
0.5 -1
-0.8
-0.6
-0.4
-0.2
0
Ability to achieve high
spatial frequencies
falls off as ~1/r2
jmansell@aos-llc.com13
Measured Influence Functions
Each Actuator at ~300V Produces ~1 wave at 633nm
jmansell@aos-llc.com16
0
20
40
60
80
100
120
0 100 200 300
Voltage (V)
Dis
plac
emen
t (m
icro
ns)
Electrostatic Snap-Down
1.4”
Parallel Plate Snap-Down Experiment
Mem
bran
e
Ele
ctro
stat
ic P
ad
Translated under Bias
jmansell@aos-llc.com17
Snap-Down ResultsBack of Membrane Electrostatic Pad
Snap-down induced “sputtering” of aluminum coating
Achieved ~40μm of Throw at Snap-Down
jmansell@aos-llc.com18
Resonance Frequency
0
10
20
30
40
50
60
0 500 1000 1500 2000 2500
Frequency (Hz)
Sign
al A
mpl
itude
(a.u
.)
DataFit
Q ~ 2
Because the polymer membranes are currently hand assembled, the resonance frequency changes from device to device.
Tension & Thickness
jmansell@aos-llc.com19
Pellicle Characteristics• Wavefront Quality : λ/2 per inch
– mostly in an astigmatic term
• Demonstrated high reflectivity coatings– Q-Switched damage at 3.3 J/cm2 (235
MW/cm2)– HR coated membrane demonstrated
survivability under 12 kW CW 1064nm
• Available COTS up to 6” in Diameter
Polymer Membrane
Under 12 kW CW 1-μm Light
Thermally Induced Distortion at 1s
jmansell@aos-llc.com20
Static Aberrations• Mounting the pellicle to
the substrate can be tricky.– See Dave Dayton’s results
from yesterday• We have developed a
new mounting process at AOS that has dramatically reduced the aberration amplitude created by this process.
jmansell@aos-llc.com21
Summary of Polymer Membrane DMs
Metal & Dielectric Stacks (12kW cw 1064nm survived, 3.3 J/cm2 Damage Threshold
for Q-Switched)
Coatings6” COTS PartsSize
~40 μm (330VDC at Snap-Down)
Throw~500 HzResonance ValueCharacteristic
jmansell@aos-llc.com22
Potential Applications for Polymer Membrane DMs
• Good for:– Low-Order Quasi-Static Imaging and
Laser Aberration Compensation• Telescopes, Microscopes, Laser
Machining, etc.– Basic Laser Beam Shaping
• Maybe good for:– Vertical Path Atmospheric
(Astronomy)• Probably not good for:
– Large Telescopes– Megawatt Class Lasers– Long Path Free-Space Optical Comm.
jmansell@aos-llc.com24
Drive Electronics
ElectronicsPCB
6” 6”
3”
USB Interface
32-Channel Output up to 295 V(scalable to more output channels
and from 8-bit to 16-bits in 2-bit increments)
Packaged Electronics(Internally 3.2x4” Boards)
Optional BNC Input
(not shown)
jmansell@aos-llc.com25
Converting the Drive Electronics into an AO Controller
• The USB interface chip we chose to use was an inexpensive (~$10) microcontroller that was designed for low-cost applications like toys.
• During the development, we discovered that it had integrated ADCs and sufficient computational capability to do metric adaptive optics.
jmansell@aos-llc.com26
Outline• Introduction & Motivation• Low-Cost Component Development
– DMs, Drive Electronics, & AO Controllers• Optical Setup• System Demonstrations
– PC-interfaced System– Microcontroller System
• Evaluation of the Microcontroller SPGD• Conclusions & Future Work
jmansell@aos-llc.com27
Optical Setup Picture
PSFCamera
DM
Drive Electronics with Microcontroller AO
BS
Lens
Photodiode and Pinhole
BS
Photodiode Input
jmansell@aos-llc.com29
Rise Time
~10% to 90% Fall Time = 144 μs
Rise Time Oscillation ~3.7 kHz
200 μs / div200 μs / div
jmansell@aos-llc.com30
Outline• Introduction & Motivation• Low-Cost Component Development
– DMs, Drive Electronics, & AO Controllers• Optical Setup• System Demonstrations
– PC-interfaced System– Microcontroller System
• Evaluation of the Microcontroller SPGD• Conclusions & Future Work
jmansell@aos-llc.com31
Stochastic Parallel Gradient Descent (SPGD) Algorithm
1. Start with a pointin the error space.
2. Take a step in a random direction to another point.
3. Find the “optimum” position based on the gradient.
4. Repeat to 2
4
1 2
3
Starting PointTrial Step (V’)
Final Position (V’’)
jmansell@aos-llc.com32
SPGD Algorithm Math
( )dVMMVV stepinitial −+= η''
( )
actuators ofnumber theis and 1, to1- fromvector
number random a is rand(...)size, step maximum theis
, where'
N
NranddVdVVV
+
Δ•Δ=
+=Take a Random Trial Step
Take a Step Based on the Trial Result
Step Size
Gain
jmansell@aos-llc.com33
Brute-Force Searching Algorithm• Choose each actuator and scan over the
entire 255 count range in 5 count intervals and set it to the best value.
• After scanning all the actuators, repeat the scan.
jmansell@aos-llc.com34
PC-Based Optimization
Added Controls for Optimization Testing in the Existing Drive
Electronics Software
jmansell@aos-llc.com35
Typical Point Spread Functions
Before AO (Mirror Under Optimal Focal Bias) After AO
NOTE: Fringing due to the window on the camera
jmansell@aos-llc.com36
Outline• Introduction & Motivation• Low-Cost Component Development
– DMs, Drive Electronics, & AO Controllers• Optical Setup• System Demonstrations
– PC-interfaced System– Microcontroller System
• Evaluation of the Microcontroller SPGD• Conclusions & Future Work
jmansell@aos-llc.com37
Average Results (30 ms delay, 20 averages, 16s)η=
0.1
η=0.
2η=
0.3
η=0.
4η=
0.5
Δ=4 Δ=6 Δ=8 Δ=10 Δ=12
Key: Average / Std. Dev.
jmansell@aos-llc.com38
Definition of Output Parametrization
Time (s)
Phot
odio
de S
igna
l (V)
10% to 90% Rise Time
Final Value = Average over the last 0.2 seconds
Converged RMS = RMSover the last 0.2 seconds
jmansell@aos-llc.com42
Effect of Sample Delay on Final Value
1.9
2
2.1
2.2
2.3
2.4
2.5
0 5 10 15 20 25 30
Delay (ms)
Con
verg
ed F
inal
Ph
otod
iode
Val
ue (V
)
~18 ms
jmansell@aos-llc.com43
Conclusions• We have developed low cost:
– DMs ($1,500)– USB Interfaced Drive Electronics ($5,000)– Metric Adaptive Optics Systems ($7,500)
• We characterized the parameters of our microcontroller SPGD metric AO system to find the effect of – the gain (η), – the step size (Δ), – and the measurement delay.
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