Laser radar has a variety of applications in remote sensing and inspection, including rangefinding, terrain-mapping, and industrial inspection. Design of such systems is nontrivial and, until recently, presented a challenge to an end user not specializing in the technology. To address this issue, a modular prototype laser-radar design unit, the APL-1, has been developed specifically to allow inexperienced users to easily develop and field a custom system.
Designed by H. N. Burns Engineering Corp. (Orlando, FL) for the Johns Hopkins University Applied Physics Laboratory (APL; Laurel, MD) and commercialized by International Photonics (Orlando, FL), the unit features an indium gallium arsenide diode laser operating at 905 nm, a silicon avalanche-photodiode (APD) detector with a 6.7-mrad field of view, associated diagnostic equipment, and full documentation and training. All major subsystems—laser transmitter, receiver, and range counter—are plug-in modules that can be easily replaced by user-designed circuits, which allows system integrators to test custom subsystems. Internal signals for each module are ported out to SMA connectors on the edge of the module, so that intermediate signals such as laser current, preamplifier output, and APD bias voltage can be sampled without affecting system operation or damaging circuitry.
The package includes theoretical background and training courses, as well as full documentation, enabling an untrained engineer to develop a system from the design table to the field. "It's an interesting teaching tool," says APL laser radar researcher Timothy Cole. "It's an analog rather than a digital system—it presents data as analog signals rather than digital outputs—so users have to learn a certain amount of theory to extract range data. At the same time, it’s very simple to work with."