Signal Processing for Improved Spatial Resolution Measurements
Summary:
With BMDO SBIR funding, Brimrose Corporation has developed a novel “photoelectromotive-force” detector that eliminates the large, electronic filter banks now used in Doppler radar systems. Such a system, when applied in the field of optical path-length measurement, has been demonstrated to improve spatial resolution by more than two orders of magnitude. Manufacturers of optics equipment, data storage equipment, integrated circuits, semiconductors, thin-film coatings, and maintenance management equipment would find such a technology valuable for its improved resolution and lower cost. The technology may also improve the resolution of other imaging techniques, including ultrasound, sonar, and laser radar. Brimrose has created a laboratory prototype and plans to have products ready in 2002.
Technology Description:
With BMDO SBIR funding, Brimrose Corporation (Baltimore, MD) has developed a novel “photoelectromotive-force” detector that can improve spatial resolution in Doppler radar and other imaging systems. Such a system, when applied in fields of optical path-length measurement, has been demonstrated to improve spatial resolution by more than two orders of magnitude.
Brimrose's processing technology improves spatial resolution by overcoming the fundamental resolution limits of time delay measurements and interferometry, two common methods for making distance measurements. Time delay measurements are limited in resolution by the coherence and the frequency of the signal (an incoherent signal blurs resolution, while a low frequency signal is so spread out in time that time delays can’t be pinpointed). Interferometry improves precision through the use of coherent lasers, but requires precisely aligned mirrors that increase the cost of the system. Furthermore, interferometer-based distance measurement system can only offer resolutions no better than nanometer scale.
The “photoelectromotive-force” detector produces an output voltage proportional to the difference frequency between two laser signals. By adapting this detector, Brimrose implemented a microwave radar signal processing technique called coherence frequency domain reflectometry (CFDR) to the optical spectrum. CFDR achieves greater accuracy by sending out “chirped” signals, signals whose frequency varies with time. By comparing the frequency of the measuring signal with that of a reference signal, CFDR can provide a distance measurement that approaches the theoretical limits for an electromagnetic wave (or any other type of wave). To achieve this precision, though, a sensor is needed that can directly detect the frequency difference between the two signals. Without Brimrose's photoelectromotive-force sensor, which produces an output voltage proportional to the frequency of the optical beat signal, additional mathematical processing is needed to determine the frequency content of the signal. In addition to slowing down the signal analysis, this extra processing introduces some aliasing that blurs the distance measurement.
When applied to Doppler radar imaging, this processing technique can measure distance differences of 100 nanometers from more than 300 meters away. The processing module is also simpler (as it doesn't require a readout laser), lighter and faster than current processors.
MDA Origins:
BMDO funded SBIR Phase I and Phase II research to improve the performance of radar signal time-integrator by using photorefractive semiconductors. Such an approach could save valuable space and weight on in-flight air and missile systems and mobile ground-based radar systems, while also offering enhanced resolution.
Spinoff Applications:
In addition to the BMDO-funded work in Doppler radar, this optical processor has been modified for use in testing equipment, where very precise displacement measurements are crucial. The makers of optics equipment, data storage equipment, integrated circuits, semiconductors, thin-film coatings, and maintenance management equipment might all find use for a measurement device based on this technology.
In measuring the thickness of integrated circuit layers, for instance, this technology could have immense advantages over methods now in use, as it could offer a greater resolution and eliminate the possibility of calibration errors. For maintenance management, such a technology can monitor the vibration levels of a particular machine in operation for any changes that would indicate potential trouble. For topographic measurement, it could gauge the roughness of the surface to determine depth.
Another use is for measuring dispersion in newly-manufactured and existing fiber-optic lines. Today, fiber-optic manufacturers must measure dispersion by cutting a length of fiber over a kilometer long and testing a sample signal. This costly and awkward procedure can be replaced with a photorefractive-based system that can take measurements of both chromatic and polarization dispersion using lengths of fiber as small as one centimeter.
The technology may also improve the resolution of other imaging techniques, including ultrasound, sonar, and laser radar. So the performance of medical, atmospheric, non-destructive testing, and other imaging technologies could be improved based on these designs. Also, the technology can be integrated into other forms of commercial Doppler radar and pulsed Doppler radar systems for aircraft guidance, air traffic control, weather pattern monitoring and warning, remote sensing, and obstacle finding and avoidance.
Commercialization:
Brimrose is currently seeking outside investment to bring this technology to market. The primary markets will be in manufacturers for fiber-optic, semiconductor, and data-storage equipment, where the device can be used for testing purposes. Brimrose has received one patent for this technology.
Company Profile:
The Brimrose Corporation of America was founded in 1979 as a research and development facility for x-ray equipment. In the late 1980s, the company had switched focus to electro-optic technology for fiber-optic components and test equipment. The company, located in Baltimore, Maryland, has also developed optics equipment for medical diagnostic instrumentation and defense equipment. It employs 60 people.
Contact Information:
Brimrose Corporation of America
Corporate headquarters
5024 Campbell Blvd
Baltimore MD 21236
Tel:410-931-7200
Fax:410-931-7206
web: www.brimrose.com
Chen Chia Wang (principal investigator)
Brimrose Corporation of America (research lab)
7720 Belair Road
Baltimore MD 21236
Tel:410-668-5800
Fax:410-668-4835
email: ccwang@brimrose.com
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