Transcript Chirped Amplitude Modulation Ladar for Range and Doppler

Chirped Amplitude Modulation Ladar for Range
and Doppler Measurements and 3-D Imaging
Barry Stann, Brian Redman, William Lawler, Mark Giza,
John Dammann, Army Research Laboratory
Dr. Keith Krapels, Office of Naval Research
SPIE Defense & Security Symposium
April 2007
The work presented here was jointly sponsored by CDR Keith Krapels, Ph.D.,
Office of Naval Research, and the Army Research Laboratory.
ONR Ladar Concepts of Employment
Cruise Missile Tracking
Coarse Range:
Range-Doppler Tracking:
Y
3D Imaging for Force Protection
Coarse Range:
3D Imaging:
Chirped AM Ladar System Block Diagram
Chirped AM Range-Doppler Measurement Theory
Frequency
Transmitted/LO
fIF
Received
fstop
fD
Dt
fstart
Time
Tchirp
Slow Time = Chirp-to-Chirp
Intermediate Frequency (IF) Signals for Each Chirp
2D
FFT
Fast Time = Samples within a Chirp
ONR Ladar Field Test Setup at CBD
256X256X256 Image at 295 m
Range-Velocity Plot
(V=1.566 m/s, Range=2.166 km)
ONR Advanced Breadboard Ladar (2006)
High Power Long Pulse EDFA
•Erbium amplifier contract start delayed
•Image tube wore-out before October field test at
Fort A.P. Hill
•New field test planned with new image tube and
high power EDFA when available
FOPEN Breadboard Ladar
•NVESD foliage penetration
data collection
•Military targets
•Ground-to-ground
•Multi-aspect
•100 m range
•FOPEN breadboard ladar
•1.55 µm, 1 W diode laser
•31 mm receiver aperture
•100m range
•128x128x128 Image
•1 s frame time
•.5 m range resolution
FOPEN Ladar Illuminator
•Quintessence Photonics Diode Laser
•1550 nm
•1 W
•Single transverse mode
•Separate Osc./Amp. Sections
facilitate modulation
•Amp. Section < 4 A
•Osc. Section < .7 A
•Efficiency > 20 %
•Illuminator Characteristics
•Modulated Output Power ~ .7 W
•Bandwidth = 440 MHz
•Buck converters for TE cooler
and Oscillator drivers
•1 W Mini-Circuits Amp drives
oscillator
•RF Drive = 4-5 mW
Laser
Osc. driver
RF amp.
TE cooler
driver
ONR/FOPEN Breadboard Components
Frequency synthesizer:
• 400 MHz bandwidth
• Oscillator and delayed local oscillator
• Programmable thru PC (bandwidth, center
frequency, chirp period, delay)
• Low cost parts
• Can be made smaller (4”X4”) and cheaper
• Better synthesizer chip will be available
Receiver:
Computer:
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Window control of system parameters
Processes 128x128x128 image in 1 s
Displays 3-D image in stereo
Diagnostic windows available
Target tracking possible
• 330 MHz demodulation bandwidth
• Uses Intevac InGaAs image tube
• 250 Vp-p local oscillator voltage added to tube
cathode to anode voltage
• Eliminated LO voltage interference with CMOS
sensor over bandwidth
• PC control of cathode to anode voltage
• PC control of CMOS sensor parameters
• Fan sufficient for rf amplifier cooling
Illuminator:
• Built around Quintessence Photonics 1.55 µm laser diode
(oscillator/amplifier)
• Uses Analog Technologies laser and TE cooler drivers
(chopper designs)
• 5 W input yields 330 mW light power
• 330 MHz modulation bandwidth
• Contains Mini-Circuits amplifier for modulating laser
• Cost for illuminator is $ 1.5 k
FOPEN Breadboard Ladar Initial Results
•~25 m range
• S/N~20
• little time on tube
Top of ladder
Side view
Breadboard Issues/required fixes
•Short tube lifetime, heating to install ground plane
•Lossy receive lens, poor focus (2X)*
•Non-delivery of high current laser driver (3X)*
•Illumination field > Receiver FOV (2X)*
•ROIC noisy over most of FPA (3X)*
•Other system/circuitry clean-up (1.5X)*
(*Potential S/N increase (NX))
Imaging with Improved FOPEN Breadboard
19”
24”
Wood Crate at 85 m (front)
Wood Crate at 85 m (side)
Ladar Image (front)
Ladar Image rotated 90 deg.
Desired Image Tube Redesign
Cathode
Cathode
MSM Array
CDMA ROIC
CMOS Sensor
MSM Detector
Chirp
Chirp
Chirp
Present tube design
•Narrowband filter required to attenuate solar
background
•Conversion efficiency is low
•RF amp requires high prime power and is expensive
•Ladar frame-rate limited to low Hz
•RF bandwidth limits range resolution to .5 m
•High RF fields can disrupt operation of CMOS sensor
Revised tube design
•Conversion efficiency is high
•Maximum tube gain can be exploited
•RF amplifier is low power
•Video frame-rates are possible
•GHz RF bandwidths achievable (.1 m range resolution)
•MSM detector rejects solar background
CONCLUSIONS
•ONR advanced breadboard will be field tested with high power
Erbium amplifier when available
•FOPEN ladar enables extensive check-out of various changes and
improvements to the ONR receiver
•The diode laser (Quintessence Photonics) is a great source for
short-range ladar applications using the chirped AM architecture
•The FOPEN ladar demonstrates that large format (128x128x128
pixels) 100 m imaging is possible with Intevac image tube and low
power diode source
•Redesign of the Intevac image tube is required for a viable ladar
system