The biological world contains a wide variety of sophisticated optical systems (see oemagazine, February 2002, p. 26). Indeed, optical engineers can study and emulate such systems to produce innovative, high-performance designs. The U.S. Defense Advanced Research Projects Agency (DARPA; Arlington, VA) is developing bio-inspired optics under the Bio-Optic Synthetic Systems (BOSS) program for just that purpose (see figure).
A number of efforts funded by the program are currently underway. The crystalline lens in the human eye can change shape, thereby altering its refractive power. This attribute inspired a shape-changing microfluidic lensing system. Using this microfluidic lensing system, a team led by Rockwell Science Center (Thousand Oaks, CA) will demonstrate a 30X zoom on the Pointer unmanned aerial vehicle (UAV). Controlling the overall shape of the lens surface allows the production of optical elements with unmatched performance--essentially the system will exhibit optical zoom capabilities without lateral movement of many lenses. Furthermore, incorporating dynamic control into these lenses permits rapid focusing and the ability to produce a compact zoom lens with a very large optical magnification range.
The spherical lens of the octopus eye features a graded index that compensates for spherical aberration, yielding a wide field of view with optimum focal characteristics. With this inspiration, Case Western Reserve University (Cleveland, OH), in collaboration with the Naval Research Laboratory (NRL; Washington, D.C.), will demonstrate a solid-state dynamic graded-refractive-index lens for a variable field of view. The approach is based on a layer-multiplying co-extrusion technology developed at Case Western that is capable of producing laminates with layer thicknesses on the order of tens of nanometers. The approach allows the designer to vary the index of the laminate during the manufacturing process by selecting materials for each lamina that have differing indices of refraction. Through manipulation of these nanolaminates, the group can dynamically vary the effective index. The NRL group will flight test this lens on the Dragoneye UAV.
Foveation refers to imaging with varying resolution across the field of view. Foveated imaging allows more efficient management of optical information by spatially correcting the aberrations that limit the performance and field of view of the imaging system. The fovea in the human eye provided inspiration for this technology. Using a transmissive spatial light modulator, a team led by the University of Central Florida (Orlando, FL) is developing a foveated imaging system for demonstration on a helicoptor testbed.
The University of Florida (Gainesville, FL) is leading a team in the demonstration of a two-color lens using diffractive optics based on a photon sieve, which is a pattern of sub-wavelength apertures that uses surface plasmons to enhance transmission. The brittlestar uses diffractive optics and provided the inspiration for this system. The approach saves weight and volume and allows a very large field of view with a system design that avoids moving parts.
Millions of years of evolution have resulted in a wide range of highly sophisticated biological optical systems. Photonic and manufacturing technology has evolved to the degree that researchers can finally mimic such systems effectively. The efforts described above borrow from nature to inspire synthetic optical systems with capabilities that greatly exceed the current state of the art. oe
Leonard Buckley is materials chemistry program manager at the Defense Science Office of DARPA, Arlington, VA.
Randall Sands is an independent consultant at Touchstone Consulting, Brookeville, MD.
Dean Scribner is a research physicist at the Naval Research Laboratory, Washington, D.C.
Guido Zuccarello is a chemist at Booz Allen Hamilton, Arlington, VA.