Researchers Fabricate Novel PBG Composite Glass Materials

9/9/1999 - 42-99r
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Researchers at the Naval Research Laboratory (NRL) have fabricated photonic bandgap (PBG) nanochannel glass materials for use in the development of a new class of extremely compact and efficient opto-electronic devices. The new devices will have widespread use in both military and commercial applications. The research team consists of Dr. Armand Rosenberg, Ms. Elizabeth Bolden, and Dr. Brian Justus, of the Optical Sciences Division. This work is funded by the Office of Naval Research.

According to Dr. Rosenberg, "Structures that exhibit photonic bandgap optical effects are composed of alternating layers or rows of dissimilar materials. The thickness of the alternating layers is on the order of the wavelength of light. By manipulating the structures of these materials, it becomes possible to engineer materials with customized optical properties, suitable for a variety of applications. A major application area is controlling the propagation of light in opto-electronic devices, similar to how the flow of electrons is controlled in semiconductor devices. The size of present optical and opto-electronic devices could be greatly reduced and their efficiency increased if the propagation of light could be better controlled and optical losses due to scattering are eliminated. The novel PBG materials we have developed will enable the miniaturization of such optical and opto-electronic devices. In addition, new devices will be possible based on the unusual combinations of optical and electrical properties of these novel PBG materials, which are not found in nature."

The fabrication process for these nanochannel glass materials begins by inserting an etchable glass rod into a glass tube and drawing them at high temperatures to yield filaments having a reduced overall diameter. The filaments are stacked and re-drawn, further reducing their diameter. Finally, sections of the nanochannel glass are wafered and polished. Etching the wafers results in a glass matrix containing a regular array of sub-micron diameter holes. Additional processing can be performed, such as filling the holes with another dielectric or semiconductor material. The PBG nanochannel glass material resulting from this process is, as Dr. Rosenberg states, "a fundamental building block of what is, in effect, the optical analog of electronic integrated circuitry."

The research team reports their present goal is to optimize the properties of the two-dimensional PBG crystals currently fabricated at NRL. The NRL team has already demonstrated PBG nanochannel glass materials with photonic band gaps varying from infrared to ultraviolet wavelengths. According to Dr. Justus, co-inventor of the nanochannel glass materials, "The specific optical properties of these PBG materials are highly dependent on their physical characteristics, such as the symmetry, structure and composition of the layered materials. Slight modification of these characteristics can significantly enhance the observed photonic band gap effects."

The research team reports, "photonic bandgap structures embedded with nonlinear optical materials show promise in the development of optical switches and limiters having improved performance." Optical limiters can be used to protect the human eye against accidental or hostile damage from lasers.Optical Sciences Division researchers, Drs. Horn-Bond Lin and Anthony Campillo, have recently reported the first demonstration of optical limiting in such a structure. In a related project, Drs. James Shirk and Richard Pong, also of NRL's Optical Sciences Division, are developing more advanced optical limiters that are fabricated by introducing phthalocyanine nonlinear absorbing materials, developed by Dr. Art Snow of NRL's Chemistry Division, into the nanochannel structure of the PBG materials. Research team members report, "the optical limiters resulting from this process are projected to give 100- to 1000-fold better eye protection than is currently possible."

"We envision that the payoffs resulting from this research will include the fabrication of next- generation optical sensors and miniaturized optical systems; high-speed opto-electronic components for high-bandwidth communication; low noise, high gain optical amplifiers; thresholdless/low-threshold lasers; identification systems based on engineered optical properties; and efficient directional antennas for RF/microwave devices," concluded Dr. Rosenberg.

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