L. A. Coldren

Growth of single‐crystal sapphire‐clad ruby fibers

Single‐crystal Cr‐doped Al2O3 fibers can be grown by a floating‐zone technique from small source rods locally melted at the end by a CO2 laser. By using the same laser to melt and regrow only the surface of the fiber, the Cr concentration in this surface layer can be reduced by a factor of 100 or more by selective evaporation.

Effect of bias field in a zinc‐oxide‐on‐silicon acoustic convolver

A monolithic acoustic surface wave parametric signal processor, fabricated with sputtered zinc oxide on an oxidized epitaxial n ‐on‐n+ silicon substrate, is demonstrated. The dependence of the convolution output signal strength on applied gate bias is analyzed, and it is found that the maximum output occurs just before the semiconductor surface inverts, at which time the high‐frequency capacitance‐voltage characteristic has its maximum slope.

Zinc‐oxide–on–silicon acoustically scanned imager with positive sensitivity and storage capabilities

The use of remotely launched acoustic surface waves to scan image information on a zinc‐oxide–on–silicon monolithic geometry is demonstrated. The dynamic range for the readout can be greatly enhanced by using pulsed bias signals which invert the surface of the n‐on‐n+ silicon substrate. Images may also be stored in the form of trapped charge replicas in the zinc oxide, and subsequently they may be nondestructively read out using the scanning surface waves.

Acoustic waveguide with a cladded core geometry

A new type of acoustic waveguide analogous to the clad optical fiber waveguide is described and experimental results are given. Modes exist in this structure which confine the acoustic energy to approximately the core due to the lower acoustical velocity in this region. The waveguide is excited with specially electroded bulk shear transducers bonded to the end surfaces. In the ∼100−MHz region both radial and torsional type modes may be attractive for long−delay (near 1 msec) low−loss serial memory applications.

Zinc oxide on silicon memory cells scanned by acoustic surface waves

The use of parametrically mixed acoustic surface waves to remotely scan and process the contents of zinc−oxide−on−silicon charge storage cells is demonstrated. The write, erase, and store characteristics of the memory cells are investigated. The signal−processing capability of the device is illustrated by the correlation of a line of stored information with a biphase coded input signal.

cw monolithic acoustic surface wave amplifier incorporated in a Δv/v waveguide

Room‐temperature cw operation is reported for an acoustic surface wave amplifier which uses a 25‐μm‐wide thin film of InSb deposited on LiNbO3. The device also illustrates the use of a thin semiconductor or metal film as a waveguiding structure which exhibits very little dispersion. A cw gain of 23 dB was observed at 340 MHz with a group delay factor (1/τ)∂τ/∂f = −8.3 × 10−7 MHz−1.

Interior‐surface acoustic waveguiding in capillaries

Capillary tubing, used as a waveguide for surface acoustic waves confined to the interior surface, is shown to be a guiding structure that has a number of properties useful for long‐delay‐line applications. Very clean rf pulse transmission has been achieved, with spurious bulk modes stripped away by absorption at the outer surface. Low dispersion is available with bore diameters of a few Rayleigh wavelengths. In a fused silica structure flame‐drawn to a half‐meter length, the propagation loss was experimentally found to be limited by material bulk attenuation constants.

Acoustic surface wave Δv/v waveguides on anisotropic substrates

Accurate measurements of the phase and group velocity dispersion curves have been made for Δv/v waveguides on (001) 〈 110 〉 Bi12GeO20. The measurements are shown to be in good agreement with the results of a simple theory which includes the effect of substrate anisotropy. Results indicate that the acoustic energy is bound more tightly to waveguides fabricated on crystal orientations where anisotropy provides a reduced diffraction loss for unguided waves.

Noise figure calculation for the Rayleigh wave amplifier

The noise figure of a Rayleigh wave amplifier is calculated using the impedance field method of noise calculation. The coupling of noise in the semiconductor to the acoustic wave is obtained from a normal mode formula. The results indicate that relatively low noise figures should be obtainable, and that trapping phenomena can be the major source of noise excitation.