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CRANBURY, N.J., Jan. 4, 2008 -- Princeton Lightwave Inc. (PLI), a maker of optical semiconductor components and subsystems, has received a two-year $3.5-million contract from DARPA to develop focal plane arrays (FPAs) with single-photon sensitivity for use in three-dimensional imaging systems at 1.06 µm.

The modules are intended for use as the optical engines at the core of 3-D imaging flash ladar systems such as those demonstrated in DARPA’s Jigsaw 3-D imaging laser radar program.  PLI will develop FPA modules that use InP-based Geiger-mode avalanche photodiodes (GmAPDs) to achieve single-photon sensitivity and perform time-of-flight ranging measurements on a per-pixel basis.

The GmAPD, also commonly known as a single-photon avalanche diode (SPAD), is an avalanche photodiode structure that, when operated above its breakdown voltage, can generate a macroscopic current pulse in response to the absorption of a single photon.

The operation of the PDA requires a specialized readout integrated circuit (ROIC) designed for the 3-D imaging application. On a per-pixel basis, the ROIC senses the GmAPD output current pulse corresponding to the absorption of a single photon and assigns a time stamp indicating the interval between the launch of a short-duration ranging laser pulse and the photon detection event.

The per-pixel time-of-flight information is translated to distance, as in conventional ladar measurements, and provides the third spatial dimension to complement the 2-D image provided by pixel location in the detector array.

PLI said it will hybridize the GmAPD PDAs and ROICs using flip-chip bonding, and a high optical fill factor will be achieved using an array of microlenses mated to the back-illuminated PDA chip.

Mark Itzler, PLI’s CTO and principal investigator for the program, said, “We’ve been developing single-photon-counting technology for several years, and 3-D imaging is an excellent application for it since we can leverage our expertise in both semiconductor device design and module packaging. By the time we complete this two-year development program, we expect to see product-scale demand for these sensors to provide 3-D imaging capability in a variety of defense systems.”

The GmAPD FPA technology, initially demonstrated by MIT Lincoln Laboratory under DARPA sponsorship of the Jigsaw program, has a number of highly desirable features, PLI said. Since single photon detection in a GmAPD provides a macroscopic current pulse that can be sensed using digital thresholding circuitry, the device technology provides a direct -- and noiseless -- “photons-to- bits” conversion process. Among the benefits of single-photon sensitivity is the ability to obtain 3-D image data using low-power pulsed sources and the collection of 3-D images even in situations involving very large source attenuation. In particular, the Jigsaw program demonstrated the feasibility of using the GmAPD FPA technology to create 3-D images of objects obscured by forest canopy and camouflage netting, PLI said.

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Jan 2008
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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