DARPA wants photonic integrated circuits

High-energy photons emission (abstract illustration). (Photo: GiroScience/Shutterstock.com)

The U.S. Defense Advanced Research Projects Agency (DARPA) Microsystems Technology Office is soliciting research proposals for the development of a new class of atom-based systems using integrated photonics and trapped atoms to enable high-performance, robust, portable clocks and gyroscopes.

The military researchers are asking industry to develop relatively simple portable photonic integrated circuits (PICs) for high-performance position, navigation and timing (PNT) devices as an alternative to GPS for when satnav signals are not available.

A PIC or integrated optical circuit, similar to an electronic integrated circuit, integrates multiple photonic (having to do with light) functions, providing capabilities for information signals imposed on optical wavelengths, typically in the visible spectrum or near-infrared, 850–1650 nanometers.

A-PhI Program

The Atomic-Photonic Integration (A-PhI) program seeks to develop trapped-atom based, high-performance PNT devices, reducing the complexity of these atomic systems by using PICs. According to the DARPA document, the PICs will replace the optical assembly behind devices such as sensitive and accurate angle sensors and clocks, while still enabling the necessary trapping, cooling, manipulation and interrogation of atoms.

A-PhI aims to demonstrate that compact PICs can replace the optical bench of conventional free-space optics for high-performance trapped-atom gyroscopes and trapped-atom clocks without degrading the performance of the underlying physics package.

Physics

Atomic systems using trapped atoms have the potential to be made portable while maintaining their accuracy due to the atomic trap’s small size and the inherent isolation a trap offers an atomic system from the environment, especially from acceleration.

Currently, these systems are bulky, heavy, and not notably portable, because of the complexity of the optical systems used to create the trap.
In the past, efforts to miniaturize the hundreds to thousands of optical components in such benchtop systems have relied on removing optical elements, miniaturizing the remaining elements, and tightly integrating them in a small package.

The products deliver degraded performance with the need to maintain very tight optical alignment, causing both poor environmental robustness and poor tolerance to design errors. Effective miniaturized atomic systems cannot be achieved at a reasonable cost with this approach.

Recent developments in PIC research suggest that on-chip optical frequency combs based on microresonators, optical frequency synthesis, novel on-/off-chip coupling, wavelength demultiplexers, and on-chip phased arrays for dynamic manipulation of light fields can replace optical systems with readily manufacturable, low-cost chips without the alignment sensitivity of conventional free-space optics.

Gyroscopes

A-PhI also seeks to develop proof-of-concept trapped atom gyroscopes, a matter-wave analog of the interferometric fiberoptic gyroscope. Such a miniaturization effort could generate an order of magnitude improvement in angular sensitivity and dynamic range over current free-space products.

A-PhI hopes to develop portable, high-performance, navigation and timing systems: the miniaturization of the optics of atomic systems without a decrease in performance.

Subsequent work, the RFP asserts, will be required to incorporate the necessary compact and robust lasers and electronics to achieve a fully functioning, high-performance, portable PNT system.