DARPA's Chip-Sized Digital Optical Synthesizer to Aim for Routine Terabit-per-second Communications

DARPA’s new Direct On-chip Digital Optical Synthesizer program seeks to do with light waves what researchers in the 1940s achieved with radio microwaves. Currently, optical frequency synthesis is only possible in laboratories with expensive racks of equipment. If successful, the program would miniaturize optical synthesizers to fit onto microchips, opening up terahertz frequencies for wide application across military electronics systems and beyond.

“The goal of this program is to make optical frequency synthesis as ubiquitous as microwave synthesis is today,” said Robert Lutwak, DARPA program manager. “There are significant challenges, but thanks to related DARPA programs POEM, Quasar, ORCHID, PULSE and E-PHI and other advanced laboratory research, technology is at the tipping point where we’re ready to attempt miniaturization of optical frequency synthesis on an inexpensive, small, low-power chip.”

The basic concept is to create a “gearbox” on a chip that produces laser light with a frequency that is a precise multiple of a referenced radio frequency, such as is readily available within most existing DoD and consumer electronic systems. The ability to control optical frequency in a widely available microchip could enable a host of advanced applications at much lower cost, including:

* High-bandwidth (terabit per second) optical communications
* Enhanced chemical spectroscopy, toxin detection and facility identification
* Improved light detection and ranging (LiDAR)
* High-performance atomic clocks and inertial sensors for position, navigation and timing (PNT) applications
* High-performance optical spectrum analysis (OSA)

Today, optical communications employ techniques analogous to those of pre-1940 AM radio, due to the inability to control frequency precisely at optical frequencies, which are typically 1,000 times higher than microwaves. The higher frequency of light, however, offers potential for 1,000-fold increase in available bandwidth for communications and other applications.

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