DARPA seeks proposals on photonic delays as a building block for optical computing

Scientists at the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., are trying to find compact, robust ways to control the flow of photons in future applications of optical computing.

By John Keller

ARLINGTON, Va.—Scientists at the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., are trying to find compact, robust ways to control the flow of photons in future applications of optical computing.

Toward this goal, DARPA is asking industry for proposals on developing a chip-scale, integrated photonic platform with fiber-like losses for optical delay applications in an initiative called Integrated Photonic Delay—iPhoD, for short (DARPA solicitation number DARPA-BAA-08-33).

If successful, the iPhoD program will enable unprecedented integrated optical delay performance and complexity, and will build the framework of a scalable, integrated photonic platform technology able to handle and manipulate photons with throughput efficiency and precision approaching that of electrons within electronic integrated circuits, DARPA officials say.

The ability to generate long optical delays with low intrinsic loss would be useful for high-precision military applications such as high-time-bandwidth product analog optical signal processors and delay lines for wideband RF systems, optical buffers for all-optical routing networks, and ultra-stable optical interferometers for sensing applications, DARPA officials say.

Although fiber-based optical delays that meet DARPA’s technical requirements are available in the commercial market, these devices can lack the kinds of compactness, environmental robustness, manufacturing scalability, and precision for the applications DARPA scientists have in mind.

Many multi-tap delay line applications like finite impulse response filters can require the precision splitting and combining of hundreds of high-resolution time delays, which cannot be easily implemented in fiber-based architectures, DARPA experts point out.

These kinds of high-resolution wideband signal processing applications, they say, demand high throughput efficiency to be most useful. For these RF filtering applications, as well as for RF/digital signal storage/buffering and many other interferrometric optical sensing applications, microsecond range time delays and beyond is necessary.

To date, low-loss optical fiber is the only guided-wave delay medium capable of providing these long delays with acceptable unamplified transmission loss, DARPA scientists say, yet the size constraints, precise differential time delay control requirements, and on-chip/off-chip optical signal routing complexity and management of these fiber-based devices make them inappropriate for many military applications.

To fill the gap, the iPhoD program seeks to develop robust ultralow-loss single-mode, single-polarization, compact integrated photonic waveguide technology with accompanying coupler, splitter, and optical via technologies.

The iPhoD project will be a three-phase program that will demonstrate a small, ultralow-loss integrated photonic platform, culminating in an optical delay application demonstration.

The technical challenges of the iPhoD program include developing the science and technology necessary to understand and overcome the important loss contributions in today’s integrated optical waveguides. DARPA solicits the most compelling approaches capable of bridging the gap between optical fiber and integrated optic waveguide transmission losses.

DARPA is seeking research proposals for integrated photonic delay technologies that will lead to the ability to fabricate dense, high-performance, cost-effective optical delay processors.

Areas of interest are ultralow-loss waveguide design, fabrication, and testing; high-efficiency input/output coupling and 3D layer-to-layer coupling; high-precision, on-chip optical splitting/combining and trimming; and optical delay application demonstration.

More information on the iPhoD program is available online at www.fbodaily.com/archive/2008/04-April/23-Apr-2008/FBO-01558150.htm. A PDF with program details is available online at www.fbo.gov/utils/view?id=e048922826cf8066fe8adecb06b213eb.

For more information, contact DARPA’s Dr. Ronald Esman by phone at 571-218-4691, or by e-mail at ronald.esman@darpa.mil. Also contact Steve F. Pappert by phone at 571-218-4679 or by e-mail at spappert@darpa.mil. Submit initial questions by e-mail to BAA08-33@darpa.mil.

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