G. R. Olbright

Near-infrared high-gain strained layer InGaAs heterojunction phototransistors : resonant periodic absorption

We report high‐gain phototransistors on GaAs substrates at wavelengths for which GaAs substrates are transparent, and hence, are promising for optoelectronic interconnect, optical‐logic device, neural network, and lightwave communication applications. Using a new technique called resonant periodic absorption we have achieved high‐optical gain at previously inaccessible wavelengths (≳925 nm). Resonant periodic absorption is achieved in an asymmetric microresonator consisting of a strained‐layer InGaAs/GaAs heterojunction phototransistor sandwiched between distributed Bragg reflectors. By aligning the optical intensity maxima with the InGaAs quantum wells in the collector region of the phototransistor, we dramatically enhance the optical absorption.

Linewidth, tunability, and VHF-millimeter wave frequency synthesis of vertical-cavity GaAs quantum-well surface-emitting laser diode arrays

The authors report the measurement of the laser linewidth, wavelength tunability, and generation of microwave frequencies between individually addressable elements of a vertical-cavity GaAs quantum-well surface-emitting laser diode array (lasing in the wavelength range 850-865 nm). Using heterodyne techniques, the authors obtain a deconvolved 65 MHz laser linewidth from the 109 MHz beat signal. The laser linewidth corresponds to a semiconductor laser linewidth enhancement factor alpha =5.7, which is in excellent agreement with that obtained independently from optical gain measurements and corresponding calculated refractive index changes. The authors measured heterodyne beat frequencies of 2-20 GHz. The bandwidth was limited by the microwave amplifiers. A simple calculation shows that a tuning range of 65 MHz to 3 THz can be achieved.<<ETX>>

Optical switching in N × N arrays of individually addressable electroabsorption modulators based on Wannier–Stark carrier localization in GaAs/GaAlAs superlattices

We report room- and low-temperature (10-K) electroabsorption measurements in N × N arrays of individually addressable superlattice electroabsorption modulators based on Wannier–Stark carrier localization. Our data exhibit excellent array uniformity over an area encompassing several hundred modulators. We demonstrated electroabsorption changes as large as |Δα| ≃ 22 000 cm−1, electrorefraction changes as large as |Δn| ≃ 0.1 (corresponding to a π/2 phase shift for an ≈2-μm-thick superlattice), optical bistability with contrast ratios >6:1, and relaxation self-oscillations (oscillatory amplitude modulation of an incident cw beam) in an inductive electro-optic circuit. We developed the capability of demonstrating a new electro-optical component technology for integrating two-dimensional source arrays with ultralow-energy optical switching arrays.

Hybrid integration of bipolar transistors and microlasers: Current‐controlled microlaser smart pixels

We describe the hybrid integration of GaAs/AlGaAs heterojunction bipolar transistors with GaAs/AlGaAs (850 nm operation) and InGaAs/AlGaAs (980 nm operation) vertical‐cavity microlasers to form ultra‐low‐drive‐current microlaser smart pixels. We achieved a single‐mode, low divergence, 1 mW output with a 70 μA base injection current and digital electronics matched input impedance. The integration technology is appropriate for the integration of optoelectronic integrated circuits to GaAs and Si microelectronics circuits.

Many-body effects in the luminescence of highly excited indirect superlattices

Experimental and theoretical investigations of the optical-excitation-dependent spatially indirect photoluminescence of GaAs/AlAs type II superlattices are reported. Simultaneous blue and red shifts of the indirect photoluminescence peaks are observed and analyzed, using many-body theory. The relevant microscopic mechanisms are exchange and correlation effects in the excited electron and hole plasmas as well as energy renormalizations due to the optically induced space-charge potential, the latter being the dominant effect. Comparison of theory and experiment allows us to extract the individual renormalization effects in the electron and hole plasmas.

Generation of tunable near-infrared amplified femtosecond laser pulses and time-correlated white-light continuum

We report the generation of kilohertz-rate, amplified, sub-100-fsec-duration laser pulses tunable from 785 to 825 nm. A novel two-stage amplification scheme is used to produce amplified, tunable optical pulses, with microjoule energies. Diffraction-limited focusing of the amplified laser pulses in ethylene glycol to peak intensities greater than 1013 W/cm2 results in the efficient generation of white-light continuum pulses with a bandwidth extending from 0.4 to 1.0 μm. This tunable laser system is well suited for sensitive femtosecond spectroscopic measurements in the near infrared, and its tunability may easily be extended to cover the wavelength range 600–900 nm.

Micro-optic and microelectronic integrated packaging of vertical-cavity lasers

The applications for optoelectronic integrated circuits demand high performance optoelectronic devices or smart pixels. The stringent requirements on these smart pixels require that packaging technology be developed concurrently to the development of the optoelectronic components. We discuss the packaging requirements of smart pixels based on vertical-cavity microlasers. We present a novel microlens/macrolens combination which allows high power densities to be focused to a diffraction-limited spot using present VCSEL technology. Finally, we discuss the applications for microlaser-based spatial light source arrays.

Commercial manufacturing of vertical-cavity surface-emitting laser arrays

Optoelectronic integrated circuits based on arrays of vertical- cavity surface emitting lasers (VCSELs) are evolving into functional chips enhancing the performance of fiber optic networks, optical data storage, laser printing and scanning, visual displays, and optoelectronic computing and other systems. This evolution involves the development of advanced manufacturing technology germane to packaged arrays of VCSELs comprising micro- optic lens arrays and interface electronics. In this paper we describe Photonics Researchs LASE-ARRAY commercial manufacturing efforts. Specifically we will discuss commercial manufacturing advancements in molecular beam epitaxial growth, full-wafer processing, interface electronics, microoptic lens arrays, packaging and implementation of statistical process control. Yield and reliability will also be discussed. Last we discuss emerging applications for the LASE-ARRAY technology.

Electron/hole energy shifts in narrow GaAs/AlAs quantum wells: Inhomogeneous broadening due to half‐monolayer well‐width fluctuations

We use absorption, photoluminescence, and x‐ray diffraction spectra of two GaAs/AlAs type II heterostructures, whose GaAs well thicknesses differ by ≂4 A to obtain a direct measurement of the individual quantum confinement energy shifts of the heavy hole, light hole, and electron levels. We find that excitonic absorption linewidths are dominated by inhomogeneous broadening that arises from half‐monolayer well‐thickness fluctuations. For self‐consistency these shifts are applied to separately determine the individual valence‐band and conduction‐band offsets.

Optical gain and ultrafast nonlinear response in GaAs/AlAs type‐II quantum wells

We describe the femtosecond optical gain nonlinearities for the unusual case of electrons which are distributed between the direct‐GaAs and indirect‐AlAs layers in a GaAs/AlAs type‐II multiple quantum‐well (MQW) structure. Due to the spatial separation of electrons from the holes, we observe a significant increase in the gain lifetime (≳150 ps) in type‐II MQWs, as compared to type ‐I MQWs (∼50 ps). In addition, we investigate the effect of a longitudinal electric field on Γ‐X energy splitting in type‐II structures. Finally, at early times we observe an ultrafast nonlinear optical response in the gain/absorption spectra which we attributed to electron‐hole scattering without carrier loss.