Direct dispersion measurement of highly-erbium-doped optical amplifiers using a low coherence reflectometer coupled with dispersive fourier spectroscopy

The group delay and dispersion, including the erbium ion contributions, of the highly erbium-doped silica planar waveguide amplifier and multicomponent glass fibre amplifiers are directly measured at different pump powers using a low coherence reflectometer and dispersive Fourier spectroscopy. This method derives the refractive index spectra of these amplifiers directly from the produced reflectograms without any physical or mathematical assumptions. The dispersion of the planar waveguide amplifier at 500 mW pumping changes between +300 and -200 ps/km/nm with a 0.4 wt.% erbium concentration.<>     

Specific heat of monolayer films of3He-4He mixtures adsorbed on Grafoil between 0.04 and 4.2 K

The specific heat of mixtures of ³He and ⁴He adsorbed on Grafoil has been measured at four partial monolayer coverages corresponding to areal densities of 0.0279, 0.0419, 0.0485, and 0.066 »^–2 for 0.04 < T < 4.2 K. The ³He concentration in the mixtures was x ₃ = 0, 0.050, 0.091, 0.201, 0.485, 0.650, 0.908, and 0.999. A feature in the specific heat not seen in measurements with the pure isotopes is found for the two intermediate coverages at about 0.4 K. The measurements are analyzed at the higher temperatures using a theoretical virial expansion for two-dimensional gaseous mixtures. The entropy of mixing calculated by numerical integration of the specific heat curves shows that at 4 K the two isotopes are mixed. While mixing effects develop at temperatures below 1 K, the evidence for phase separation as in bulk mixtures is inconclusive.Work supported by the National Science Foundation, Grant DMR-72-03003A03.     

Source of NMR line broadening for3He adsorbed on Grafoil

Pulsed NMR measurements were made of proton resonances in samples of Grafoil sheets soaked in ethyl alcohol. Frequency shifts were observed due to effects of the anisotropy of the magnetic susceptibility of the Grafoil and these shifts can account for line broadening of NMR in helium films on Grafoil at low temperatures.Work supported by a grant from NSF and by contracts with ONR and DOD (Themis Program).     

The piezoelectric semiconductor and acoustoelectronic device development in the sixties

In the 1960s the properties of piezoelectric semiconductors, group III-V zinc-blende and group II-VI wurtzite structure, were explored for the development of acoustoelectronic (AE), devices. Bulk acoustic wave (BAW), delay lines, traveling wave amplifiers, and oscillators were developed. Although these elegant functional devices never made it into the realm of full-scale production and application, the piezoelectric semiconductor developments of the 1960s provided an exciting time for theoretical explanations and creative experimentation to explore device capabilities for electronic systems applications. Delay lines were formed from rectangular parallelepiped blocks of piezoelectric semiconductors with integral input and output transducers depleted of carriers at each end of the block. The ultrasonic traveling wave amplifier was based on the interaction of electrons under a bias field moving with a velocity faster than the piezoelectric field accompanying the acoustic traveling wave. The gain factor in a piezoelectric semiconductor under direct current bias was used to develop oscillators. The main research efforts were carried out by industrial laboratories with government funding support. This paper considers the work with piezoelectric semiconductors during the 1960s with examples from the author's own work.     

Compact solid-state waveguide lasers

Glass waveguide lasers will fill an important niche as optical sources in communication, RF photonics, and optical metrology. This is primarily because waveguide lasers benefit from compact size, low noise, relatively high output powers, long upper-state lifetimes, and simple integration with optical-fiber-based systems. Although we do not expect waveguide lasers and amplifiers to ever supplant fiber and semiconductor lasers and amplifiers in every possible communications application, waveguide lasers have a number of advantages over traditional lasers for these uses. Single-frequency waveguide lasers provide narrow linewidth and high output power in a compact, monolithic package. The narrow linewidth is an important advantage over standard semiconductor lasers, and the compact size makes single-frequency waveguide lasers better suited than fiber lasers or extended-cavity semiconductor lasers for many applications.     

Shear horizontal BG surface acoustic waves on piezoelectrics: a historical note

In December of 1968 Jeffrey Bleustein of Yale University published an article predicting the existence of a new type of transverse surface acoustic wave (SAW) that could propagate on the surface of a piezoelectric crystal. This was followed within 20 days by the publication of an article by Yuri Gulyaev in January of 1969 predicting the same basic surface wave propagation. The wave took on the name Bleustein-Gulyaev or BG-wave, joining the names of Rayleigh, Love, Sezawa, and Stonely for distinct types of SAW. But is there more to the story than this? Were there works preceding those of Bleustein and Gulyaev which signaled an interest in exploring a new surface wave mode on piezoelectrics? What about the work of Shimizu, Nakamura, and Ohta, who in April of 1969 published both theoretical and experimental verification of the existence of such a wave independent of the knowledge of the Bleustein and Gulyaev papers? This paper explores the early roots and characteristics of the shear horizontal surface wave on a piezoelectric.     

High-reliability SAW bandpass filters for space applications

High-reliability surface-acoustic-wave (SAW) bandpass filters have been developed for use in transponders for more than 25 earth-orbital and deep-space satellite programs. SAW filters have been incorporated in several NASA standard TTandC transponders and NASA standard tracking and data relay satellite system (TDRSS) user transponders. The author gives examples of the electrical performance, summarizes the manufacturing processes, and discusses qualification testing for these SAW devices. He identifies reliability problems encountered and their solutions.     

Electrostatic-Discharge Awareness & Control?An R&M 2000 Issue

As weapon systems become more sophisticated to meet multiple complex hostile threats, there will be an increasing reliance upon a high density of analog and digital microelectronic components, modules, and subsystems. Hybrid microelectronics are moving toward submicron geometries for semiconductor components, multilayer interconnects, and higher component densities on larger area substrates. This miniaturization increases the susceptibility of microelectronic circuitry to electrical overstress (EOS) and electrostatic discharge (ESD). Since EOS and ESD directly affect reliability and maintainability, procedures must be developed to account for them in engineering design, manufacturing, and testing. Over the past several years, there has been a concerted effort to raise ESD awareness at all levels of design and production at Motorola and other electronic firms. This paper briefly describes what measures should be considered and presents examples of their implementation at Motorola to increase reliability, lower costs, and reduce maintainability factors.     

Low-temperature heat capacity of helium films adsorbed on copper

Heat capacity measurements are described for films of pure⁴ He and a 12%He ³ mixture ofHe ³ andHe ⁴He adsorbed on copper, for 0.1<T<1.2 K.He ⁴ heat capacity isotherms show a step-type behavior as a function of coverage for the first two layers, while the mixture isotherms only show the first step. A comparison is made with recent multilayer data for helium films on Vycor published by other authors.Work supported by the National Science Foundation.     

The experimental and theoretical characterization of the SAW propagation properties for zinc oxide films on silicon carbide

The surface acoustic wave (SAW) propagation properties of zinc oxide (ZnO) films on silicon carbide (SiC) have been theoretically and experimentally characterized in the film thickness-to-acoustic wavelength ratio range up to 0.12. The experimental characterization of the SAW propagation properties was performed with a linear array of interdigital transducer (IDT) structures. The measurements characterized the velocity and propagation loss of two surface modes, a generalized SAW (GSAW) mode with velocities between 6000 and 7000 m/s, and a high velocity Pseudo-SAW (HVPSAW) mode with velocities between 8500 and 12 500 m/s. The experimentally determined characteristics of the two waves have been compared with the results of calculations based on published data for SiC and ZnO. Simulation of wave characteristics was performed with various values of the elastic constant C(13), which is absent in the published set of material constants for SiC, within the interval permitted by the requirement of positive elastic energy in a hexagonal crystal. The best agreement between the measured and calculated propagation losses of the HVPSAW has been obtained for C(13) near zero. Although for the GSAW mode the calculated velocity dispersion has been found nearly insensitive to the value of C (13) and consistent with the experimental data, for the HVPSAW, some disagreement between measured and calculated velocities, which increased with ZnO film thickness, has been observed for any C(13 ) value. Theoretical analysis of HVPSAW has revealed the existence of a previously unknown high velocity SAW (HVSAW). The displacement components of this wave have been analyzed as functions of depth and confirmed its pure surface, one-partial character.