A non-mechanical approach could open the door to a new class of miniaturized, extremely low-cost, robust laser-scanning technologies for military and commercial use
Many essential military capabilities—including autonomous navigation, chemical-biological sensing, precision targeting and communications—increasingly rely upon laser-scanning technologies such as LIDAR (think radar that uses light instead of radio waves). These technologies provide amazing high-resolution information at long ranges but have a common Achilles heel: They require mechanical assemblies to sweep the laser back and forth. These large, slow opto-mechanical systems are both temperature- and impact-sensitive and often cost tens of thousands of dollars each—all factors that limit widespread adoption of current technologies for military and commercial use.
In an advance that could upend this status quo, DARPA’s Short-range Wide-field-of-view Extremely agile Electronically steered Photonic EmitteR (SWEEPER) program has successfully integrated breakthrough non-mechanical optical scanning technology onto a microchip. Freed from the traditional architecture of gimbaled mounts, lenses and servos, SWEEPER technology has demonstrated that it can sweep a laser back and forth more than 100,000 times per second, 10,000 times faster than current state-of-the-art mechanical systems. It can also steer a laser precisely across a 51-degree arc, the widest field of view ever achieved by a chip-scale optical scanning system. These accomplishments could open the door to a new class of miniaturized, extremely low-cost, robust laser-scanning technologies for LIDAR and other uses.
SWEEPER technology is to be developed further through DARPA’s Electronic-Photonic Heterogeneous Integration (E-PHI) program, which has already successfully integrated billions of light-emitting dots on silicon to create an efficient silicon-based laser.
“By finding a way to steer lasers without mechanical means, we’ve been able to transform what currently is the largest and most expensive part of laser-scanning systems into something that could be inexpensive, ubiquitous, robust and fabricated using the same manufacturing technology as silicon microchips,” said Josh Conway, DARPA program manager. “This wide-angle demonstration of optical phased array technology could lead to greatly enhanced capabilities for numerous military and commercial technologies, including autonomous vehicles, robotics, sensors and high-data-rate communications.”
Phased arrays—engineered surfaces that control the direction of selected electromagnetic signals by varying the phase across many small antennas—have revolutionized radio-frequency (RF) technology by allowing for multiple beams, rapid scanning speeds and the ability to shape the arrays to curved surfaces. DARPA pioneered radar phased array technologies in the 1960s and has repeatedly played a key role in advancing them in the decades since.
Transitioning phased-array techniques from radio frequencies to optical frequencies has proven exceptionally difficult, however, because optical wavelengths are thousands of times smaller than those used in radar. This means that the array elements must be placed within only a few microns of each other and that manufacturing or environmental perturbations as small as 100 nanometers can hurt performance or even sideline the whole array. The SWEEPER technology sidesteps these problems by using a solid-state approach built on modern semiconductor manufacturing processes.
DARPA’s Electronic-Photonic Heterogeneous Integration (E-PHI) program
High performance optoelectronic systems, e.g. ultra low-noise lasers and optoelectronic signal sources, are employed in numerous applications such as fiber optic communications, high-precision timing references, LADAR, imaging arrays, etc. Current state-of-the-art ultra-low noise lasers and optoelectronic signal sources use macro-scale photonics for mechanical and thermal noise suppression, and off-chip electronics for feedback control. The benchtop or rack mount component-level assembly of these sources limits photonic coupling efficiency as well as the speed of electronic feedback, and also adds size and weight to the system. Integration of these components in a chip-scale form factor could greatly mitigate these limitations. While silicon is an attractive integration platform due to its capabilities in both electronics and photonics, the indirect bandgap of silicon precludes its use for efficient optical emission. One possible approach to enable high performance optoelectronics on low-cost silicon platform is to heterogeneously integrate III-V photonics with silicon to include efficient III-V optical emitters and other photonic devices with the silicon electronic and photonic platform.
E-PHI seeks to develop the necessary technologies, architectures and design innovations to enable novel chip-scale electronic-photonic/mixed-signal integrated circuits on a common silicon substrate. It is envisioned that E-PHI technology will enable a wide range of novel chip-scale optoelectronic microsystems, including coherent optical systems for sensing (LADAR) and communications, optical arbitrary waveform generators and multi-wavelength imagers with integrated image processing and readout circuitry. To validate the feasibility and viability of electronic-photonic heterogeneous integration technology, E-PHI aims to demonstrate novel high-performance heterogeneous electronic-photonic integrated microsystems. It is anticipated that these E-PHI demonstrator microsystems will provide considerable performance improvement and size reduction versus current, state-of-the-art technologies.
SOURCE - DARPA