Creating The Future Of Optics And Photonics: UCF Provides An Overview Of The Research Underway In The College Of Optics And Photonics

Introduction

Formed in 1986 as the Center for Research and Education in Optics and Lasers (CREOL) at the University of Central Florida, this program was the first photonic program in the United States to achieve the status of a full college headed by a dean. The College of Optics and Photonics is now internationally recognized as one of the top academic and research programs in optics and photonics in the world. Today, the college offers interdisciplinary graduate programs leading to M.S. and Ph.D. degrees in optical science and engineering. CREOL and the Florida Photonics Center of Excellence (FPCE) are research centers within the college.

The research activities of the College faculty span the spectrum from basic science to prototype development, and the faculty vigorously pursues joint research projects with industry, academia, and government laboratories. Some areas of study within the college are: nanophotonics, biophotonics, imaging and displays, and ultra high-speed optical communications. This article provides insight into the top trends in the photonics field and the research topics currently being investigated at the college.

New Visualization Displays

Emergence of several trends such as the increased availability of wireless networks, miniaturization of electronics and sensing technologies, and novel input and output devices is giving rise to user interfaces suitable for use across a wide range of applications. The research group led by Dr. Jannick Rolland, associate professor of optics, ECE & computer science, is designing visualization hardware, focusing on deployable displays and displays worn on the body to support mobile users. Low field of view designs, suitable for integration into eyeglasses are expected to become a viable option for mobile displays. Eyeglass-based displays, which are well suited for mobile applications, are likely to receive social acceptance.

Bessel Beam Imaging

Bessel beams that propagate without being subject to diffractive spreading produce a narrow light beam for a long distance. This property can be used for high resolution imaging over a few millimeters depth of focus. Endoscopic optical coherence tomography (EOCT), which combines OCT with endoscopic techniques, has attracted interest because of its high resolution when compared to ultrasound imaging. Dr. Jannick Rolland's group has adapted an axicon as a focusing lens in the narrow endoscope to achieve high lateral resolution over long depth range of imaging because axicon lenses are optical elements that produce Bessel beams along the optical axis instead of the usual Airy spot of a conventional lens.

Optical Frequency Combs

The generation of stabilized optical frequency combs is becoming increasingly important for many applications related to ultra high speed communications and signal processing. For example, the possibility of being able to exactly synthesize the optical electric field, using Fourier concepts, or the ability to send uniquely coded optical signals that would be difficult to intercept or interpret. Optical frequency combs would allow for unique methods of ultra high data transfer between users, providing security, robustness, and high spectral efficiency.

The Ultrafast Photonics group, led by Dr. Peter Delfyett, university trustee chair professor of optics, ECE & physics, has made important advances in the generation of optical frequency combs from semiconductor lasers. They have developed a novel dispersion managed modelocked ring diode laser that produces optical pulses of 185 fsec in duration — the shortest optical pulses generated to date from a diode laser.

Working with MIT Lincoln Labs, Delfyett's group have demonstrated a unique modelocked diode laser that generates an optical frequency comb with ~100 frequency components on a 5 GHz grid, where the linewidth of each component of the comb is ~ 300 kHz and the generated pulse train possesses less than 8 fsec of timing jitter. The timing stability demonstrated by this laser is the lowest reported to date of any actively modelocked laser.

Additionally, the group has extended the dispersion management concept of their ring laser to a novel amplification scheme called eXtreme Chirped Pulse Amplification (X-CPA) where the temporal duration of a modelocked pulse is stretched by a factor of ~16,000 before it is amplified — and then subsequently recompressed — to obtain high peak power optical pulses. The resulting peak power generated from this system is 1.4 kW and represents the highest peak power generated to date from a modelocked semiconductor diode laser.

Nanophotonics And Chemistry

Combining knowledge in chemistry and nanoscience, Dr. Florencio Hernández, assistant professor of chemistry & optics, has developed a non-invasive glucose sensor. Based on the Tollen's test, he generates gold nanospheres in solution using glucose. The number of gold nanospheres generated in solution increases directly proportional with the glucose concentration. The higher the glucose concentration, the higher the number of nanoparticles generated, thus the higher the extinction efficiency of the solution. The linear dependence of the extinction efficiency of the gold nanoparticles solution with glucose concentration and high sensitivity and selectivity of the method makes this new sensor suitable for direct applications in biomedical sensing.

Wide Bandgap Photonic Devices

Zinc Oxide-based (ZnO) compounds have been shown to have an exciton binding energy of ~ 60meV, roughly twice that of GaN, enabling epilayers to maintain relatively efficient electroluminescence up to temperatures of 650K. Prior research has demonstrated the ability to tune the band gap of ZnO to higher or lower energies by alloying with Mg or Cd, respectively. This has opened up the potential for heterostructure devices offering high efficiency optical emitters and detectors.

Volume Holograms

The research led by Dr. Winston Schoenfeld, assistant professor of optics & photonics and leader of the Nanophotonics Device Group, is using liquid phase epitaxy aims to create high resistivity ZnO substrates with high quality relative to the hydrothermally grown material currently available. Additionally, research is aimed at enhanced performance of light emitting diodes (LEDs) through device development and advanced packaging concepts. Medical and biomedical applications for LEDs are also being studied, with particular focus on areas such as photodynamic treatment of acne, tomography, and aged-related macular degeneracy treatment.

Volume holograms have the potential for replacing components in many applications including conventional optics (beam splitters, polarizers, attenuators, narrow-band filters, and dispersive elements including integrating several functions on a chip), laser systems (attenuators, mode selectors, beam combining), optical communications (WDM filters, add/drop, equalizers), and data storage (unlimited reading). Photo-Thermal Refractive (PTR) glass is particularly attractive as a medium for volume holograms because it is unaffected by ionizing and optical radiation and tolerates temperatures up to 400 C with distortions below 10^-4. Dr. Leon Glebov, senior research scientist and leader of the Photo-Induced Processing Laboratory, has developed fabrication technology for PTR glass and has demonstrated a new approach for single-transverse-mode semiconductor lasers, coherent coupling of physically-separated semiconductor lasers, and spectral beam combining based on the use of thick Bragg gratings recorded PTR glass. This approach may enable a new architecture for high power, narrow emission bandwidth laser systems with near-diffraction limited divergence.

Extreme UltraViolet (EUV) Optical Sources

EUV is considered the wave of the future for the manufacture of small-scale computer chips. Currently, computer production relies on ultraviolet-light lasers to imprint tiny technical features on computer chips; many expect the use of extreme ultraviolet-light lasers to revolutionize the industry and enable optical lithography to continue the progression of Moore's Law. Dr. Martin Richardson, Northrop Grumman professor of X-ray photonics and leader of the Laser Plasma Laboratory, is developing EUV sources by shooting nanosecond laser pulses into loaded micro-droplets to generate 13.5nm radiation. The efficiency and power levels have been rapidly improving so that this source is expected to be in commercial use by 2010.

Novel Display Devices And Adaptive-Focus Lenses

Liquid crystals are revolutionizing display devices and imaging systems. Dr. Shin-Tson Wu, provost-distinguished professor of optics and leader of the Liquid Crystals Displays Lab, is developing new display devices for a variety of applications, including transflective LCDs for cell phones, laptop computers, desktop monitors, and wide-view technology for high definition LCD TVs. In parallel, he is developing adaptive-focus liquid crystal lens for bio-inspired dynamic foveated imaging to mimic human vision, tunable-focus liquid lens for camera zoom lens and eyeglasses, high birefringence and low viscosity liquid crystal materials for laser beam steering, and other bio-photonics applications such as adaptive color camouflage and nonlinear optical effects of bacteria-rhodopsin films.

Laser-Doping For Photonics Device And Sensor Applications

Laser doping is a unique process for doping wide bandgap (WBG) semiconductors with both n-type and p-type dopants. A research team led by Dr. Aravinda Kar, professor of optics, MMAE, ECE and physics, and leader of the Laser-Aided Manufacturing, Materials and Micro-processing Laboratory, is using laser doping of silicon carbide (SiC) to fabricate efficient light-emitting diodes (LEDs). SiC has been identified as the WBG semiconductor of choice for high temperature, high power, and high frequency electronic device fabrication because of its superior properties such as chemical inertness, radiation hardness, high thermal conductivity, and high electric breakdown strength which make it suitable for numerous advanced applications including advanced power generation systems.

An n-type 6H-SiC substrate has been doped with conventional (Al and N) as well as unconventional (Cr) dopants using the laser doping technique for fabricating white LEDs. The laser-fabricated LED exhibits an excellent color rendering index. The color temperature is 5338oK, which is very close to the incandescent lamp (or black body) and lies between the bright midday sun (5200 oK) and average daylight (5500 oK). Optimization of laser doping to achieve higher dopant concentration levels is anticipated to increase quantum output by increasing the radiative recombination rate and driving SiC to a direct bandgap semiconductor behavior.

Conclusion

The diversity of technologies and the wide range of research taking place at The College of Optics and Photonics illustrate how optics and photonics can affect almost any application. The industry is rapidly evolving, with new discoveries being reported daily. Today's prominent technology trends will be tomorrow's commercial, off-the-shelf products. Just as the 20th Century was the Age of Electronics, enabled by photonics, the 21st Century is the Age of Photonics, enabled by electronics.

About the Author

Dr. James Pearson is director of research and administration at CREOL & FPCE, The College of Optics and Photonics, and also special assistant to the director of research at the University of Central Florida. Pearson thanks the authors of the individual topics, identified in the articles, for their contribution to this summary of current trends at the college.