We present detail investigation of the domain evolution in lithium niobate and lithium tantalate during backswitched electric field poling which allowed to produce micro- and nanoscale domain patterns by applications of voltage to lithographically defined strip electrodes. In situ optical observation of the domain kinetics during poling and high- resolution visualization by SEM and SFM of the static domain patterns on polar surfaces and cross-sections have been used. We separated and studied the main stages of domain evolution. The important role of backswitching as a powerful tool for high-fidelity domain patterning in thick wafers and for production of quasi-periodic nanoscale domain patterns has been demonstrated. We have proposed several variants of domain manipulation during backswitched poling: the frequency multiplication of the domain patterns, domain 'erasing' and 'splitting', formation of oriented arrays of nanoscale domains. We have demonstrated the production of lamellar domain patterns with period down to 2.6 microns in 0.5-mm-thick wafers and strictly oriented quasi-periodic domain arrays consisting of the individual nanodomains with diameter down to 30 nm and density up to 100 per square micron.
In nonlinear optics applications employing quasi- phasematching, short pitch domain gratings are generally required for the generation of visible and ultraviolet light. The conventional electric-field poling method enables the fabrication of periodically-poled lithium niobate (PPLN) down to generally 6 micron-pitch domains in 0.5-mm-thick substrates. While such PPLN is useful for first-order second harmonic generation (SHG) of green wavelengths, shorter periods for blue and UV SHG have been difficult to obtain in 0.5-mm-thick substrates. Here we describe an enhanced electric-field poling technique for ferroelectric materials which utilizes spontaneous flip-back towards high-resolution and high-yield domain patterning.
Laser-based displays and illumination systems are applications which can capitalize on the brightness and efficiency of semiconductor lasers, provided that there is a means for converting their output into the visible spectrum. Semiconductor laser manufacturers can adjust their processes to achieve desired wavelengths in several near-infrared bands; an equally agile conversion technology is needed to permit display and illumination system manufacturers to choose visible wavelengths appropriate to their products. Quasi- phasematched second harmonic generation has the potential to convert high-power semiconductor laser output to the visible with 50% optical-to-optical conversion efficiency in a single-pass bulk configuration, using electric-field-poled lithium niobate. Lithographically- defined electrode structures on the positive or negative polar faces of this crystal are used to control the formation of domains under the influence of electric fields applied using those electrode structures. The quality of the resulting domain patterns not only controls the efficiency of quasi-phasematched second harmonic generation, but also controls the degree of resistance to photorefractive damage. We present a model which is used to identify the optimum electrode duty cycle and applied poling field for domain patterning and compare the predicted domain duty cycle with experimental results. We discuss factors which contribute to inhomogeneous domain pattern quality for samples poled under otherwise ideal conditions and our progress in limiting their influence. Finally, we present optical characterization of a 2.4 mm long 500 micrometers thick sample which produced an average second harmonic power of 1.3 W of 532 nm green from a 9 W average power Q-switched 1064 nm Nd:YAG laser in a loose- focus single-pass configuration.
Deviations from ideal alignment and end finish can result in lossy fiber optic connections. Models of amodal fiber-to-fiber interconnects (where the optical energy has no modal structure) commonly used by connection system designers assume independence of the misalignment parameters. This paper describes a method of studying the interaction of these parameters using both computer modeling and laboratory data. The initial results show a coupled relationship existing between several pairs of misalignment parameters. In these instances the net loss due to combinational misalignments was significantly different than the linear addition of the individual loss values.
KEYWORDS: Phase only filters, Signal attenuation, Polymers, Connectors, Local area networks, Polymer optical fibers, Data communications, Polymethylmethacrylate, Sensors, Light emitting diodes
The purpose of this paper is to compare the cost and performance trade-offs of polymer optical fiber networks with glass fiber networks and networks on other media. The discussion also includes distance versus attenuation and bandwidth limits for higher data rate transmission over polymer fibers. Finally we describe the performance of a 10 Mb/s Ethernet system built and tested using a modular approach incorporating a prototype snap-lock connection system designed for low cost high volume applications. Low cost is achieved through the use of larger diameter polymer optical fiber which facilitates the use of molded plastic components and simple crimp-on fiber terminations integrated receivers and visible red LEDs.
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