Professor Ruyan Guo
Growing Ferroelectric Single Crystals with Unique Properties
Ruyan Guo, professor of materials and electrical engineering
Ruyan Guo has a fascination for crystals, and the fortunate capability of producing them on her own. In her lab in Research Unit A, Dr. Guo, professor of electrical engineering and materials research, and her research group use novel methods for producing ferroelectric crystals with a high index of refraction and strong nonlinear optical effects, such as the ability to sense optical signals and alter the phase, intensity, or wavelength of light. These crystals could be used to add information to light in an optical fiber or to code optically transmitted data for security purposes. Ferroelectric fibers can also be used to control the central wavelength of laser light.
To grow her ferroelectric fiber crystals, Dr. Guo uses a technique called Laser Heated Pedestal Growth (LHPG), using a carbon dioxide laser as the power source. Single crystal fibers 100 mm long and with diameters of around 100 microns are drawn out of the intensely defined laser melting zone, where temperatures can reach 3000° C. Such intense laser heating allows for the growth of materials with ultrahigh melting temperatures. Using the laser in an oxidized atmosphere, the crystal growth is contamination-free and much faster than with conventional means — centimeters per hour compared with centimeters per day.
Man Gu, Dr. Guo's graduate research assistant, uses the LHPG technique to grow a family of rare earth (cerium, neodymium, erbium, and ytterbium) -doped single crystal fibers, as well as magnesium oxide and iron-doped lithium niobate single crystal fibers. To verify the quality of the single domain crystals, Guo's research group uses a novel thermal imaging technique called SEAM, for scanning electron acoustic microscopy. Using an acoustically modulated electron beam, SEAM characterizes the ferroelectric domain characteristics of the crystal without damaging the surface.
New Applications in Optical and Photonic Materials
A current topic of research in Dr. Guo's group is attempting to incorporate their ferroelectric fibers into the current silica glass fiber network. So far they have successfully encapsulated lithium niobate crystal in a glass that can taper and splice into silica glass. This development could potentially reduce coupling loss and improve the laser damage threshold in fiber networks, along with phase/dispersion control, wavelength selection, and frequency doubling functions.
Another of Dr. Guo's graduate students, Hongbo Liu, has recently demonstrated a device using bundled crystal fiber as a reference beam modulator to develop a highly sensitive random phase-coded holographic grating multiplexing architecture. Called HRAM, for holographic random access memory, this method for storing memory has been actively studied in recent years for its storage density and high speed. An entire page of information can be stored in a holographic image, compared to a single bit of information in magnetic hard disks and CD-ROMs. Liu's device is a compact system with high image processing capacity, high response speed, and fine control precision.
Post doctoral researcher Yongsu Lee at the optical image furnace
Postdoctoral visiting scholar Dr. Yongsu Lee, from South Korea, uses the optical image furnace in Dr. Guo's lab to grow ferroelectric nonlinear optical single crystal BaTiO3. The optical image furnace is capable of growing crystals of large radial dimensions under pressure and in reduced atmosphere.
And with senior research associate Dr. Jiping Cheng, Dr. Guo is working to understand the mechanics of microwave crystal growth. Dr. Cheng has fabricated zinc oxide single crystal microtubules with stunning crystallographic perfection using a microwave growth mechanism. Though not ferroelectric, zinc oxide has built-in polarization and strong piezoelectricity. They are exploring the unique advantages of the microtubes for UV sensing and for microwave photonic applications.
Dr. Guo received her doctorate in solid state science from Penn State and is on the faculty of the Department of Electrical Engineering. She is involved with optical materials research at both the Center for Optical Technologies and the Electro-Optics Center. Dr. Guo is also a faculty member in Penn State's Center for Dielectric Studies, and the International Center for Actuators and Transducers. She would be happy for potential collaborators to contact her.
