J. L. Jewell

Vertical-cavity surface-emitting lasers: Design, growth, fabrication, characterization

The authors have designed, fabricated, and tested vertical-cavity surface-emitting lasers (VCSEL) with diameters ranging from 0.5 mu m to>50 mu m. Design issues, molecular beam epitaxial growth, fabrication, and lasing characteristics are discussed. The topics considered in fabrication of VCSELs are microlaser geometries; ion implementation and masks; ion beam etching packaging and arrays, and ultrasmall devices. >

Generation of subpicosecond solitonlike optical pulses at 0.3 THz repetition rate by induced modulational instability

We report the generation of 0.5 ps full width at half‐maximum optical pulses at >0.3 THz (tunable) repetition rate via an induced modulational instability in a single‐mode fiber. A 1.319‐μm neodymium:yttrium aluminum garnet laser is chosen as the carrier wave and the initial modulation on this carrier is introduced by mixing it with an external‐grating‐cavity InGaAsP laser. The use of this all‐optical modulating scheme and the nonlinear optical propagation effect in fiber (i.e., modulational instability) allows one to reach into the terahertz regime, which is about two orders of magnitude beyond the fastest data limited by the finite response of electronics.

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.

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.

High-power cw vertical-cavity top surface-emitting GaAs quantum well lasers

We have devised a novel vertical‐cavity top surface‐emitting GaAs quantum well laser structure which operates at 0.84 μm. The laser combines peripheral current injection with efficient heat removal and uses only the epitaxially grown semiconductor layers for the output mirrors. The structure is obtained by a patterned deep H+ implantation and anneal cycle which maintains surface conductivity while burying a high resistance layer. Peripheral injection of current occurs from the metallized contact area into the nonimplanted nonmetallized emission window. For 10‐μm‐diam emitting windows, ∼4 mA thresholds with continuous‐wave (cw) room‐temperature output powers ≳1.5 mW are obtained. Larger diameter emitting windows have maximum cw output powers greater than 3 mW. These are the highest cw powers achieved to date in current injected vertical‐cavity surface‐emitting lasers.

Fabrication of Microlasers and Microresonator Optical Switches

We have microfabricated low‐threshold, high‐speed vertical‐cavity lasers and optical switches by optimizing the mirror design, crystal growth, and ion etching of microresonators. By minimizing the sidewall ion damage in electrically pumped microlasers, we have defined large arrays of 3‐μm‐diam surface‐emitting devices with threshold currents below 1.5 mA. Ion beam etching was also used to define 0.5–1.5 μm wide all‐optical microresonator switches with recovery times as low as 30 ps and controlling energies as low as 0.6 pJ.

Lasing characteristics of GaAs microresonators

Lasing characteristics of optically pumped 1.5‐μm‐diam GaAs‐AlAs microresonators are reported. Room‐temperature thresholds of 9 pJ were observed. Uniform outputs were obtained from a simultaneously driven 2×2 array.

Vertical cavity single quantum well laser

We have achieved room‐temperature pulsed and cw lasing at 980 nm in an optically pumped vertical cavity structure grown by molecular beam epitaxy containing only a single quantum well (SQW) of In0.2Ga0.8As. Limited gain due to the extremely short active material length of 80 A implies that losses due to absorption, scattering, and mirror transmission are extremely low. Using 10 ps pump pulses at 860 or 880 nm, the estimated energy density absorbed in the spacer was ∼12 fJ/μm2 at threshold, indicating a carrier density approximately four times that required for transparency. Continuous wave pumping yielded an estimated threshold absorbed intensity of ∼7 μW/μm2.

Transverse modes, waveguide dispersion, and 30 ps recovery in submicron GaAs/AlAs microresonators

We have studied room‐temperature optical gating of ∼5 ps pulses in GaAs/AlAs microresonators with diameters ranging from 500 A compared to a large ∼10 μm nearby region.

Electrodispersive multiple quantum well modulator

The electric-field dependence of optical absorption has been studied extensively for bulk and multiple-quantum-well(MQW) semiconductors. In bulk semiconductors, it is known as the Franz-Keldysh effect. More recently, in MQW semiconductors, it is called the quantum confined Stark effect (QCSE)[1] and turns out to be much larger than in bulk semiconductors. Main consequences of the QCSE are broadening and red-shift of exciton absorption peaks. Direct modulation of optical absorption by the QCSE leads to an electro-optic modulator which has demonstrated fast optical modulation[2]. Major drawbacks of this absorption modulator are poor contrast and/or low absolute transmission. Moreover, since the wavelength of the light is usually close to an exciton peak, there is always strong absorption. This limits the maximum optical intensity to be handled by the modulator to a level below that of exciton saturation.