Q. Deng

Low-threshold vertical-cavity surface-emitting lasers based on oxide-confinement and high contrast distributed Bragg reflectors

The interest in low-threshold vertical-cavity surface-emitting lasers (VCSELs) is increased by the demonstration of the small size, low loss optical mode due to oxide-confinement in the Fabry-Perot microcavity laser. Intense recent work in this area has resulted in numerous record breaking demonstrations of low-threshold current, high wall-plug efficiency, and high speed. In this paper, we discuss the impact of the dielectric cavity design to enhance control of the optical mode. We argue that high contrast dielectric mirrors can become an important design approach, especially for small apertures limited by diffraction loss. Experimental results are compared for different types of mirror and aperture designs.

Randomly oriented Angstrom‐scale microroughness at the Si(100)/SiO2 interface probed by optical second harmonic generation

Femtosecond pulses from a Kerr–Lens mode‐locked Ti:sapphire laser are used to generate second harmonic from a series of native‐oxidized Si(100)/SiO2 and hydrogen‐terminated Si(100) samples prepared with systematically varied interfacial microroughness with root‐mean‐square feature heights ranging from 0.6 to 4.3 A. Rotationally anisotropic second harmonic signals using different polarization configurations were measured in air and correlated with atomic force microscopy measurements. The results demonstrate rapid, noncontact, noninvasive measurement of Angstrom‐level Si(100)/SiO2 interface roughness by optical second harmonic generation.

Self-consistent Green’s function approach to the analysis of dielectrically apertured vertical-cavity surface-emitting lasers

Dielectrically apertured vertical-cavity surface-emitting lasers are modeled using a Green’s-function-based optical solver that allows calculation of the full-vector lasing modes and their threshold conditions. The laser is separated into subsystems consisting of a planar microcavity, a dielectric aperture, and an active gain medium. The exact Green’s function solution for a radiating point source in the planar microcavity is then used to construct an eigenvalue equation for the self-consistent lasing modes. The derived eigenvalue equation is numerically solved to evaluate threshold dependence on aperture and cavity design. Results show a low threshold for thin oxide apertures placed at field antinodes, as well as for tapered oxides with thin tapers placed at field nodes.

Controlled spontaneous lifetime in microcavity confined InGaAlAs/GaAs quantum dots

Controlled spontaneous lifetimes are demonstrated in InGaAlAs/GaAs quantum dots confined in planar microcavities. Due to their independent and spectrally sharp light emission, the quantum dot emitters provide an excellent means for studying the spontaneous lifetime dependence on microcavity tuning, while maintaining experimental parameters such as temperature and pump intensity constant. The measured lifetime changes are compared with calculated results and show good agreement.

Temperature dependence of the transverse lasing mode in vertical‐cavity lasers

Experimental data are presented along with calculations which describe the near‐threshold transverse modes in AlAs/GaAs/InGaAs vertical‐cavity surface‐emitting lasers with two different Bragg reflector systems. The Bragg reflector systems are composed of either AlAs/GaAs quarter‐wave stacks or a combination of AlAs/GaAs and ZnSe/CaF. The temperature dependence of the lasing mode is studied for three different structures, and it is shown that higher‐order lasing modes are favored with strong cavity detuning when the cavity resonance exists at a wavelength greater than the bulk emission peak. Important aspects of the lasing behavior are described by calculating the spontaneous mode which occurs at the lasing wavelength.

Native‐oxide laterally confined whispering‐gallery mode laser with vertical emission

Data are presented demonstrating whispering‐gallery mode lasing in a diode with native‐oxide lateral confinement and vertical emission. The vertical emission is obtained from distributed Bragg reflectors that confine the mode in the normal direction, and that results in a real wave vector component normal to the crystal surface external to the cavity.

Ring and stripe oxide‐confined vertical‐cavity surface‐emitting lasers

Ring and stripe oxide‐confined vertical‐cavity surface‐emitting lasers are studied. Interesting coupling effects are observed due to the nonzero propagation velocity of the optical mode in the plane of the cavity. The stripe geometries appear interesting due to the very low threshold and provide a convenient means for increasing the aperture size while maintaining uniform current pumping. The ring laser provides a means of obtaining well defined multiple spots in the far field.

SELF-CONSISTENT EIGENMODE ANALYSIS OF THE DIELECTRICALLY APERTURED FABRY-PEROT MICROCAVITY

Analysis is presented to calculate the eigenmode of a Fabry–Perot microcavity containing an optically thin dielectric aperture. The treatment yields the eigenmode field distribution, frequency, and threshold susceptibility. It is also suggested that self-focusing phenomena in large area vertical-cavity surface-emitting lasers can arise due to aperture formation by the complex susceptibility of a quantum well active region.

SPONTANEOUS LIFETIME CONTROL OF QUANTUM DOT EMITTERS IN APERTURED MICROCAVITIES

Data are presented on modified spontaneous emission rates in quantum dot microcavity arrays. Three-dimensional optical confinement is achieved using apertured microcavities with square aperture sizes varied from 5 to 1 μm on a side. A maximum measured increase in the on-resonance spontaneous emission rate over that off resonance is ∼50%, and we identify this enhancement with apertured modes of the microcavity. Oscillations in the spontaneous emission rate versus wavelength correspond to spectral resonances in the higher order aperture modes.

Tunneling transport and diffusion in weakly coupled quantum dot ensembles

The lateral tunneling rate and carrier diffusion in weakly coupled quantum dots are analyzed. In the weak coupling limit, localization of charge within a single dot is obtained through superposition of the lowest-energy eigenstates of coupled dots. The free evolution of the wave function leads to tunneling, but with a time dependence that includes dephasing. Idealized quantum dot boundary conditions are used to estimate tunneling times, and these are compared with recent experiments.