D. J. Channin

Optical waveguide modulation using nematic liquid crystal

Devices are demonstrated for modulating light in optical waveguides using nematic liquid crystals. 100% modulation and response times of 35 μsec are achieved. Coupling of light into waveguide modes of a liquid layer is demonstrated.

Fast electro‐optic waveguide deflector modulator

We describe a high‐speed deflector‐modulator based on an electro‐optically induced thick phase grating in optical waveguides of single‐crystal epitaxial ZnO film on Al2O3 substrates. 40% of the beam is diffracted into first order with response times of 3 nsec. The extinction ratio in the deflected beam is greater than 95%. We predict 80% diffraction, response times of < 1 nsec, and power requirements of approximately 1 mW/MHz for an optimized geometry.

Low‐loss epitaxial ZnO optical waveguides

Optical waveguide losses below 5 dB/cm have been measured on single‐crystal epitaxial ZnO films grown on Al2O3. These films promise to be useful in a variety of active integrated optic applications. Comparison of the details of loss measurements with carrier density and mobility measurements gives information on possible loss mechanisms.

Scattering in ZnO-Sapphire Optical Waveguides

Optical waveguide loss due to scattering in epitaxial ZnO-sapphire films was studied by measuring the dependence of attenuation on mode number and on optical wavelength. Analysis of the results in terms of wave-optical scattering theory enabled the bulk and surface scattering contributions to be determined. The bulk scattering showed the lambda(-4) dependence characteristic of Rayleigh scattering. A white noise spectrum of surface roughness was found to be in good agreement with surface scattering observed in most of the waveguides studied. The attenuation coefficients derived from the data were related to specific aspects of the waveguide fabrication process and allowed rational improvements resulting in a decrease in loss from 20 dB/cm to 1 dB/cm.

Triode optical gate: A new liquid crystal electro‐optic device

A new liquid crystal field effect electro‐optic device is described. Light transmission induced by voltage pulses across two electrodes is modulated or gated by voltage on a third electrode. The three‐terminal gating characteristics are applicable to scanning and multiplexing arrays of devices for displays or light valves. A novel enhancement mode is also demonstrated.

Rapid turn‐off in triode optical gate liquid crystal devices

A liquid crystal field‐effect light valve with high‐speed turn‐off operation is described. The three‐terminal device is symmetric in its turn‐on/turn‐off operation and uses digital rather than multifrequency addressing.

High-speed electrooptic waveguide grating modulator using epitaxial ZnO

The results of a detailed study of electrooptic waveguide grating modulators are presented. Using low-loss epitaxial ZnO on sapphire waveguides with deposited interdigital electrodes diffraction percentages up to 80 percent at 80 V with rise times below 3 ns are observed. Capacitive power requirements on the order of 4 mW/MHz are predicted. A theoretical description which includes carrier and piezoelectric effects is given and is shown to be adequate for designing this type of modulator. The grating waveguide modulator spatially separates the diffracted from the main beam and thus can be used for switching. In addition, the spatial separation allows a number of these to be cascaded on a common waveguide. These features make it probable that grating modulators will find a variety of uses in integrated optics.

1.3 &#181;m LPE- and VPE-grown InGaAsP edge-emitting LED&#769;s

Comparably high performance has been obtained from both vapor-phase and liquid-phase epitaxy InGaAsP/InP 1.3 μm edge-emitting LEDs. Best results include 135 μW of optical power coupled into a 50 μm core 0.2 NA graded-index fiber, spectral half-widths ∼600 Å, rise/fall times ∼2 ns, ac modulation rates ∼200 MHz, and reliable operation in excess of 17 000 h @70°C and 3000 h @120°C. Asymmetries in the far-field patterns of these devices are also discussed.

Self-oscillations and dynamic behavior of aged InGaAsP laser diodes

The pulse response of vapor-phase grown InGaAsP/InP 1.3 μm laser diodes was studied before and after accelerated aging. Dynamic behavior, including self-sustained oscillations, was found to be largely unaffected by the aging process. This indicates that these lasers can be preselected for specified modulation characteristics that will remain constant over the operating life of the diode.

Low-loss epitaxial ZnO optical waveguides*

Optical waveguide losses below 5 dB/cm have been measured on single-crystal epitaxial ZnO films grown on Al2O3. These films promise to be useful in a variety of active integrated optic applications. Comparison of the details of loss measurements with carrier density and mobility measurements gives information on possible loss mechanisms