William B. Lawler

Low-cost compact MEMS scanning ladar system for robotic applications

Future robots and autonomous vehicles require compact low-cost Laser Detection and Ranging (LADAR) systems for autonomous navigation. Army Research Laboratory (ARL) had recently demonstrated a brass-board short-range eye-safe MEMS scanning LADAR system for robotic applications. Boeing Spectrolab is doing a tech-transfer (CRADA) of this system and has built a compact MEMS scanning LADAR system with additional improvements in receiver sensitivity, laser system, and data processing system. Improved system sensitivity, low-cost, miniaturization, and low power consumption are the main goals for the commercialization of this LADAR system. The receiver sensitivity has been improved by 2x using large-area InGaAs PIN detectors with low-noise amplifiers. The FPGA code has been updated to extend the range to 50 meters and detect up to 3 targets per pixel. Range accuracy has been improved through the implementation of an optical T-Zero input line. A compact commercially available erbium fiber laser operating at 1550 nm wavelength is used as a transmitter, thus reducing the size of the LADAR system considerably from the ARL brassboard system. The computer interface has been consolidated to allow image data and configuration data (configuration settings and system status) to pass through a single Ethernet port. In this presentation we will discuss the system architecture and future improvements to receiver sensitivity using avalanche photodiodes.

A 32x32 pixel focal plane array ladar system using chirped amplitude modulation

The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered light is focused onto an array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. Pixel read-out is achieved using code division multiple access techniques as opposed to the usual time-multiplexed techniques to attain high effective frame rates. The raw data is captured with analog-to-digital converters and fed into a PC to demux the pixel data, compute the target ranges, and display the imagery. Last year we demonstrated system proof-of-principle for the first time and displayed an image of a scene collected in the lab that was somewhat corrupted by pixel-to-pixel cross-talk. This year we report on system modifications that reduced pixel-to-pixel cross-talk and new hardware and display codes that enable near real-time stereo display of imagery on the ladars control computer. The results of imaging tests in the laboratory will also be presented.

MEMS-scanned ladar sensor for small ground robots

The Army Research Laboratory (ARL) is researching a short-range ladar imager for small unmanned ground vehicles for navigation, obstacle/collision avoidance, and target detection and identification. To date, commercial ladars for this application have been flawed by one or more factors including, low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. In the prior year we conceived a scanned ladar design based on a newly developed but commercial MEMS mirror and a pulsed Erbium fiber laser. We initiated construction, and performed in-lab tests that validated the basic ladar architecture. This year we improved the transmitter and receiver modules and successfully tested a new low-cost and compact Erbium laser candidate. We further developed the existing software to allow adjustment of operating parameters on-the-fly and display of the imaged data in real-time. For our most significant achievement we mounted the ladar on an iRobot PackBot and wrote software to integrate PackBot and ladar control signals and ladar imagery on the PackBots computer network. We recently remotely drove the PackBot over an inlab obstacle course while displaying the ladar data real-time over a wireless link. The ladar has a 5-6 Hz frame rate, an image size of 256 (h) × 128 (v) pixels, a 60° x 30° field of regard, 20 m range, eyesafe operation, and 40 cm range resolution (with provisions for super-resolution or accuracy). This paper will describe the ladar design and update progress in its development and performance.

Chirped AM ladar for anti-ship missile tracking and force protection 3D imaging: update

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a chirped amplitude modulation ladar to provide range and velocity measurements for tracking of targets handed over to it by the distributed aperture system IRST (DAS-IRST) under development at the Naval Research Laboratory (NRL) under Office of Naval Research (ONR) sponsorship. By using an array receiver based on Intevac Inc.s Electron Bombarded Active Pixel Sensor (EBAPS) operating near 1.5 μm wavelength, ARLs ladar also provides 3D imagery of potential threats in support of the force protection mission. In Phase I, ARL designed and built a breadboard ladar system for proof-of-principle static platform field tests. In Phase II, ARL is improving the ladar system to process and display 3D imagery and range-Doppler plots in near real-time, to re-register frames in near real-time to compensate for platform and target lateral motions during data acquisition, and to operate with better quality EBAPS tubes with higher quantum efficiency and better response spatial uniformity. The chirped AM ladar theory, breadboard design, performance model results, and initial breadboard preliminary test results were presented last year at this conference. This paper presents the results of tests at the Navys Chesapeake Bay Detachment facility. The improvements to the ladar breadboard since last year are also presented.

Anti-ship missile tracking with a chirped amplitude modulation ladar

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. ARL is developing a ladar based on its patented chirped amplitude modulation (AM) technique to provide unambiguous range and velocity measurements of targets handed over to it by the IRST. Using the ladars range and velocity data, false alarms and clutter objects will be distinguished from valid targets. If the target is valid, its angular location, range, and velocity, will be used to update the target track until remediation has been effected. By using an array receiver, ARLs ladar can also provide 3D imagery of potential threats in support of force protection. The ladar development program will be accomplished in two phases. In Phase I, currently in progress, ARL is designing and building a breadboard ladar test system for proof-of-principle static platform field tests. In Phase II, ARL will build a brassboard ladar test system that will meet operational goals in shipboard testing against realistic targets. The principles of operation for the chirped AM ladar for range and velocity measurements, the ladar performance model, and the top-level design for the Phase I breadboard are presented in this paper.

1 Gb/s VCSEL/CMOS flip-chip 2-D-array interconnects and associated diffractive optics

980-nm substrate-emitting oxidized-aperture VCSELs with threshold currents in the 150 /spl mu/A to 500 /spl mu/A range have been developed for optoelectronic interconnects. 8/spl times/8 VCSEL arrays with 125 /spl mu/m pitch have been flip-chip bonded to CMOS driver circuitry having 0.5 /spl mu/m gate size. InGaAs/InP 8/spl times/8 detector arrays have been flip-chip bonded to provide good responsivity and high speed detection in dense arrays with 125 /spl mu/m pitch. Data rates as high as 1.1 Gb/s have been demonstrated with the incorporation of refractive coupling optics between transmitter and receiver arrays. Studies have been conducted of crosstalk and alignment sensitivity of these optoelectronic interconnect arrays. Design and modeling techniques have been demonstrated for the development of diffractive optics for optoelectronic interconnects. Special techniques have been developed to deal with very short working distances and subwavelength feature in the diffractive optics. Fan-out performance up to 7/spl times/7 with accurately controlled intensity weights has been demonstrated with diffractive optics. The use of diffractive optics in optoelectronic interconnects with fan-out and/or fan-in can make the interconnect an integral part of the optoelectronic processing algorithm.

Performance of high-frame-rate, back-illuminated CCD imagers

A second generation of high-frame-rate 512 X 512 and 1024 X 1024 pixel CCD imagers has been fabricated. These thinned, back-illuminated frame transfer imagers, designed for optical signal-processing applications, employ a split-frame transfer into dual storage registers and multiple output ports for increased frame rates. Reported here are measured characteristics of 16-port 512 X 512 and 32-port 1024 X 1024 imagers from the second design/fabrication cycle. Data are presented characterizing quantum efficiency, dynamic range, antiblooming control operation, high-speed performance, and on-chip correlated-double-sampling amplifier noise.

Brassboard development of a MEMS-scanned ladar sensor for small ground robots

The Army Research Laboratory (ARL) is researching a short-range ladar imager for navigation, obstacle/collision avoidance, and target detection/identification on small unmanned ground vehicles (UGV).To date, commercial UGV ladars have been flawed by one or more factors including low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. ARL built a breadboard ladar based on a newly developed but commercially available micro-electro-mechanical system (MEMS) mirror coupled to a lowcost pulsed Erbium fiber laser transmitter that largely addresses these problems. Last year we integrated the ladar and associated control software on an iRobot PackBot and distributed the ladar imagery data via the PackBots computer network. The un-tethered PackBot was driven through an indoor obstacle course while displaying the ladar data realtime on a remote laptop computer over a wireless link. We later conducted additional driving experiments in cluttered outdoor environments. This year ARL partnered with General Dynamics Robotics Systems to start construction of a brass board ladar design. This paper will discuss refinements and rebuild of the various subsystems including the transmitter and receiver module, the data acquisition and data processing board, and software that will lead to a more compact, lower cost, and better performing ladar. The current ladar breadboard has a 5-6 Hz frame rate, an image size of 256 (h) × 128 (v) pixels, a 60° × 30° field of regard, 20 m range, eyesafe operation, and 40 cm range resolution (with provisions for super-resolution or accuracy).

0.5-/spl mu/m CMOS orthogonal encoding readout cell for active imaging systems

We propose a novel continuous-time simultaneous-readout scheme for active imaging systems based on orthogonal modulation of photodetector signals. The superimposed-continuous-time approach presented here differs from the conventional scheduled-discrete-time scheme in that the photodetector signals are summed in a common bus and read concurrently. We show how that our proposed architecture may be advantageous, particularly in applications where bandwidth requirements for a time-multiplexed scheme are highly demanding. The active readout cell presented here is the kernel of the proposed orthogonal encoding architecture. We describe the cell operation principle, its properties and major design challenges. A 0.5-/spl mu/m CMOS test chip has been fabricated to demonstrate functionality of the readout architecture. Test results show it to be a viable option for highly-integrated active imaging systems.

Low-cost compact ladar sensor for ground robots

The Army Research Laboratory (ARL) is researching a short-range ladar imager for small unmanned ground vehicles for navigation, obstacle/collision avoidance, and target detection and identification. To date, commercial ladars for this application have been flawed by one or more factors including, low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. The ARL conceived a scanned ladar design based on a newly developed but commercial MEMS mirror and a pulsed Erbium fiber laser. The desired performance includes a 6 Hz frame rate, an image size of 256 (h) × 128 (v) pixels, a 60° × 30° field of regard, 20 m range, eyesafe operation, and 40 cm range resolution (with provisions for super-resolution or accuracy). The ladar will be integrated on an iRobot PackBot. To date, we have built and tested the transceiver when mounted in the PackBot armmounted sensor head. All other electronics including the data acquisition and signal processing board, the power distribution board, and other smaller ancillary boards are built and operating. We are now operating the ladar and working on software development. This paper will describe the ladar design and progress in its development and performance.