S. L. McCall

Whispering-gallery mode microdisk lasers

A new microlaser design based on the high‐reflectivity whispering‐gallery modes around the edge of a thin semiconductor microdisk is described and initial experimental results are presented. Optical confinement within the thin disk plane results in a microresonator with potential for single‐mode, ultralow threshold lasers. Initial experiments use selective etching techniques in the InP/InGaAsP system to achieve 3–10 μm diameter disks as thin as 500 A suspended in air or SiO2 on an InP pedestal. Optically pumped InGaAs quantum wells provide sufficient gain when cooled with liquid nitrogen to obtain single‐mode lasing at 1.3 and 1.5 μm wavelengths with threshold pump powers below 100 μW.

Optical bistability in semiconductors

Optical bistability has been observed in a semiconductor for the first time. The bistable etalon consists of a GaAlAs‐GaAs‐GaAlAs molecular‐beam‐epitaxially‐grown sandwich with 90% reflectivity coatings. The bistability is primarily dispersive with the nonlinear refractive index arising from light‐induced changes in exciton absorption. Using light of frequency just below the exciton peak, we observed bistability from 5 to 120 °K with 40‐ns turn‐off and subnanosecond turn‐on times with 1 mW/μm2 holding intensity.

Threshold characteristics of semiconductor microdisk lasers

This letter describes the threshold characteristics of InGaAs/InGaAsP microdisk lasers with optical emission near a wavelength λ=1.52 μm. More than 5% of the total spontaneous emission feeds into the lasing mode as the microdisk diameters reach 2 μm.

Room‐temperature excitonic optical bistability in a GaAs‐GaAlAs superlattice étalon

The quantum wells provided by a superlattice increase the binding energy of the free excitons in GaAs, permitting 300 K bistable operation of a superlattice etalon. The superlattice consists of 61 periods of 336 A GaAs and 401 A Ga0.73Al0.27As. The intensities required are about 1 mW/ ( μm)2 and the switching times are 20–40 ns, similar to the low‐temperature pure GaAs values. Room‐temperature operation of semiconductor etalons enhances the likelihood of all‐optical logic and switching.

Surface-Emitting Microlasers for Photonic Switching and Interchip Connections

Vertical-cavity electrically pumped surface-emitting microlasers are formed on GaAs substrates at densities greater than two million per square centimeter. Two wafers were grown with ln0.2Ga0.8As active material composing three 80 ? thick quantum wells in one and a single quantum well (SQW) 100 ? thick in the other. Lasing was seen in devices as small as 1 .5 ?m diameter with <0.05 ?m3 active material. SQW microlasers 5 x 5 ?m square had room-temperature cw current thresholds as low as 1.5 mA with 983 nm output wavelength. 10 x 10 ?m square SQW microlasers were modulated by a pseudorandom bit generator at 1 Gb/s with less than 10-10 bit error rate. Pulsed output >170 mW was obtained from a 100?m square device. The laser output passes through the nominally transparent substrate and out its back side, a configuration well suited for micro-optic integration and photonic switching and interchip connections.

Directional light coupling from microdisk lasers

We describe methods for directional coupling of light output from whispering‐gallery mode microdisk lasers. Patterned asymmetries in the shape of microdisk resonators provide control of both direction and intensity of light output without dramatically increasing laser thresholds.

GaAs‐AlAs monolithic microresonator arrays

Monolithic optical logic devices 1.5–5 μm across are defined by ion‐beam assisted etching through a GaAs/AlAs Fabry–Perot structure grown by molecular beam epitaxy. They show reduced energy requirements (more than an order of magnitude smaller than the unetched heterostructure), uniform response over small arrays, negligible crosstalk at 3 μm center‐center spacing, ∼150 ps recovery time, and thermal stability at 82 MHz operating frequency. All experiments were performed at room temperature.

Instability and regenerative pulsation phenomena in Fabry‐Perot nonlinear optic media devices

Fabry‐Perot nonlinear optic devices may undergo regenerative pulsations. Such effects may be used to convert cw laser power into a train of light pulses.

Optical bistability and differential gain between 85 and 296 °K in a Fabry‐Perot containing ruby

Bistability, differential gain, discriminator, clipper, and limier actions were observed using a plano‐concave Fabry‐Perot cavity containing ruby. Input powers were approximately 20 mW from a cw ruby laser. Operation wa anticipated near 77 °K where the R1 transition was nearly resonant with the laser. However, the device functioned at room temperature. The refractive index of ruby depends on the fractional ground‐state population. Driving the R lines leads to a nonlinear refractive index due to dispersive contributions from nonresonant pump and charge‐transfer bands, which explains the room‐temperature operation.

Room‐temperature lasing action in In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes

We report room‐temperature operation of electrically pumped whispering‐gallery mode In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes with emission at wavelength λ=1.0 μm and threshold current Ith=5 mA. Because the lasing modes do not overlap the diode’s central region, carrier density is not efficiently pinned by above‐threshold stimulated emission.