Formation of Low Threshold Voltage Microlasers

Vertical cavity surface emitting lasers (VCSELs) with threshold voltages of 1.7V have been fabricated. The resistance-area product in these new vertical cavity lasers is comparable to that of edge-emitting lasers, and threshold currents as low as 3 mA have been measured. Molecular beam epitaxy was used to grow n-type mirrors, a quantum well active region, and a heavily Be-doped p-contact. After contact definition and alloying, passive high-reflectivity mirrors were deposited by reactive sputter deposition of SiO2/Si3N4 to complete the laser cavity

Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes

Room-temperature continuous and pulsed lasing of vertical-cavity, single-quantum-well, surface-emitting microlasers is achieved at ~983nm. The active Ga[sub][0-8]In[sub][0-2]As single quantum well is 100 [angstroms] thick. These microlasers have the smallest gain medium volumes among lasers ever built. The entire laser structure is grown by molecular beam epitaxy and the microlasers are formed by chemically assisted ion-beam etching. The microlasers are 3-50-μm across. The minimum threshold currents are 1.1 mA (pulsed) and 1.5 mA (CW)

Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers

Vertical-cavity electrically driven lasers with three GaInAs quantum wells and diameters of several μm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength

Effects of rf Current on Spin Transfer Torque Induced Dynamics

The impact of radiofrequency (rf) currents on the direct current (dc) driven switching dynamics in current-perpendicular-to-plane nanoscale spin valves is demonstrated. The rf currents dramatically alter the dc driven free layer magnetization reversal dynamics as well as the dc switching level. This occurs when the frequency of the rf current is tuned to a frequency range around the dc driven magnetization precession frequencies. For these frequencies, interactions between the dc driven precession and the injected rf induce frequency locking and frequency pulling effects that lead to a measurable dependence of the critical switching current on the frequency of the injected rf. Based on macrospin simulations, including dc as well as rf spin torque currents, we explain the origin of the observed effects.Comment: 5 pages, 4 figure

Microsolvation of Mg2+, Ca2+: Strong influence of formal charges in hydrogen bond networks

A stochastic exploration of the quantum conformational spaces in the microsolvation of divalent cations with explicit consideration of up to six solvent molecules [Mg (H 2 O) n )]2+, (n = 3, 4, 5, 6) at the B3LYP, MP2, CCSD(T) levels is presented. We find several cases in which the formal charge in Mg2+ causes dissociation of water molecules in the first solvation shell, leaving a hydroxide ion available to interact with the central cation, the released proton being transferred to outer solvation shells in a Grotthus type mechanism; this particular finding sheds light on the capacity of Mg2+ to promote formation of hydroxide anions, a process necessary to regulate proton transfer in enzymes with exonuclease activity. Two distinct types of hydrogen bonds, scattered over a wide range of distances (1.35–2.15 Å) were identified. We find that in inner solvation shells, where hydrogen bond networks are severely disturbed, most of the interaction energies come from electrostatic and polarization+charge transfer, while in outer solvation shells the situation approximates that of pure water clusters

Low-Voltage-Threshold Microlasers

We have reduced the voltage required for threshold in vertical cavity surface emitting lasers (VCSEL) to 1.7 V [l], the lowest yet reported for a CW-operating VCSEL [2,3]. Room-temperature current threshold was 3 mA pulsed, 4 mA CW. This advance in VCSEL technology leads to manageable heat dissipation for high packing densities. It was achieved in a structure which can be further optimized for high wallplug efficiency and high powers. Furthermore the thickness of the molecular beam epitaxially (MBE) grown portion of the structure was reduced by about 1.5 μm compared to conventional VCSELs, resulting in decreased MBE costs, significantly shallower processing depths and easier integration of VCSELs with transistors or other electronics. The (resistance x area) products of our VCSELs are nearly as low as those reported for high-power edge-emitting lasers. MBE was used to grown-doped Al_(0.15)Ga_(0.85)As/GaAs bottom mirror layers, the active region containing 3 GaAs quantum wells, and a 1-μm-thick p-doped top contact layer. 12 pairs of alternating SiO_2/Si_3N_4 layers formed a high-reflectivity mirror which completed the laser cavity. The reactive sputter-deposited mirrors produce reflectivities of 98.3% for 9.5 pairs [3]. Individual laser elements were defined by ion milling of mesas through the p-n junction, followed by planarization with SiO_2 to define the current path. Then, Au-Zn p-contacts were deposited around the mesa tops and alloyed for current injection. A final ion-milling step was used to isolate individual contacts. In this way microlasers with diameters ranging from 7.5-25 μm were fabricated and measured

Microlasers for photonic switching and interconnection

Vertical-cavity, surface-emitting lasers have great potential owing to their inherent two-dimensional geometry and very small gain nedium volumes which are essential to low threshold currents. Possible applications are optical switching/computing, photonic interconnection, high/low power laser sources, image processing, optical neural networks, etc. Driven by these high promises, there have been numerous reports on vertical cavity surface emitting laser diodes using InGaAs/GaAs/A1As, GaAs/AlGaAs structures. In this paper, we report characteristics of discrete InGaAs microlasers and monolithic two-dimensional arrays of microlasers. The advantages of optics for communications of data over distances longer than nearby gates have been argued previously. We proposed and demonstrated a photonic interconnect scheme using microlasers with planar optics which will be robust, accurate, and easily alignable