Very narrow linewidth asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers

Asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector (RW-DBR) lasers are demonstrated with a spectral linewidth as low as 39 kHz for an output power of 24 mW. The fabrication requires only a single standard epitaxial growth of a laser structure while the use of a thin top cladding layer allows for a shallow reactive ion etch of the distributed Bragg reflector. These RW-DBR lasers have a threshold current of 12.4 mA, a slope of 0.3 W/A, and over 40 dB side-mode suppression at a wavelength of 1010 nm.     

MQW wavelength-tunable DBR lasers with monolithically integrated external cavity electroabsorption modulators with low-driving voltages fabricated by selective-area MOCVD

The design and operation of multiple-quantum-well (MQW) wavelength-tunable distributed Bragg reflector (DBR) InGaAs QW lasers with nonabsorbing gratings and monolithically integrated external cavity electroabsorption modulators fabricated by selective-area MOCVD are presented. Uncoated devices exhibit CW threshold currents as low as 10.5 mA with slope efficiencies of 0.21 W/A from the laser facet. Wavelength tuning of 7 nm is obtained by injection current heating of the DBR section. These devices also exhibit extinction ratios of 18 dB from the modulator facet at a low modulator bias of 1 V, when measured with a broad-area detector. When coupled to a singlemode fiber, these devices exhibited high extinction ratios of 40 dB at a modulator bias of 1.25 V.     

Wavelength-tunable asymmetric cladding ridge-waveguide distributedBragg reflector lasers with very narrow linewidth

Narrow-linewidth ridge-waveguide distributed Bragg reflector (DBR) lasers with asymmetric cladding are demonstrated. This design requires only a single epitaxial growth of an asymmetric cladding laser structure while the grating and the ridge waveguide are fabricated after the growth. These lasers have a threshold current as low as 9 mA, a slope efficiency of 0.3 W/A, and a T₀ of 100 K. Wavelength tuning of 8 nm is achieved by current injection heating of the DBR section. A spectral-linewidth minimum of 36 kHz is achieved at an output power of 20 mW and is limited by linewidth rebroadening due to current injection in both the gain section and DBR section     

Experimental-theoretical Landau energy level data and its use in making p-Ge laser transition assignments

Landau energy levels are determined from cyclotron resonance absorption data and compared to theoretical calculations. Energy level diagrams are presented to graphically display the nonequal energy level spacings and identify absorption transitions. This information is then used to make transition assignments responsible for the p-Ge laser signals seen by V. N. Shastin et al. and C. Kremser et al. This work suggests that the p-Ge laser yields signals via the following transitions: (a) the expected cyclotron transitions for Δn=1, (b) harmonic cyclotron transitions for Δn=2, 3, (c) light-to-heavy hole transitions and (d) light hole to acceptor level transitions. The material of this paper should be of aid in the study of the pumping-oscillation cycle of the p-Ge laser.     

Establishment of a dynamic model for the p-Ge far IR laser

Using new experimental data from modeling the p-Ge laser pulse plus literature data, basic laser parameters are obtained so that one can solve the laser equations of Pantell and Puthoff to obtain formulas for calculating all laser quantities of interest. Values, calculated using the formulas, such as gain, saturation intensity, pump population differences, power generated, output coupling, efficiency, etc. are in excellent agreement with available experimental data. This work contributes to problems in determining laser line transitions, the laser cycle, and the optimization of the laser performance.     

Design of a novel MRI compatible manipulator for image guided prostate interventions

This paper reports a novel remotely actuated manipulator for access to prostate tissue under magnetic resonance imaging guidance (APT-MRI) device, designed for use in a standard high-field MRI scanner. The device provides three-dimensional MRI guided needle placement with millimeter accuracy under physician control. Procedures enabled by this device include MRI guided needle biopsy, fiducial marker placements, and therapy delivery. Its compact size allows for use in both standard cylindrical and open configuration MRI scanners. Preliminary in vivo canine experiments and first clinical trials are reported.     

High performance laser with nanopatterned active layer by selective area epitaxy

Lasers containing a nanopatterned active layer demonstrating excellent threshold characteristics are presented. The nanopatterned active layer is fabricated using high-resolution electron beam lithography and selective-area metal organic chemical vapour deposition crystal growth. Results demonstrating an order of magnitude improvement over previous results are reported.     

Scaling the Aspect Ratio of Nanoscale Closely Packed Silicon Vias by MacEtch: Kinetics of Carrier Generation and Mass Transport

Metal‐assisted chemical etching (MacEtch) has shown tremendous success as an anisotropic wet etching method to produce ultrahigh aspect ratio semiconductor nanowire arrays, where a metal mesh pattern serves as the catalyst. However, producing vertical via arrays using MacEtch, which requires a pattern of discrete metal disks as the catalyst, has often been challenging because of the detouring of individual catalyst disks off the vertical path while descending, especially at submicron scales. Here, the realization of ordered, vertical, and high aspect ratio silicon via arrays by MacEtch is reported, with diameters scaled from 900 all the way down to sub‐100 nm. Systematic variation of the diameter and pitch of the metal catalyst pattern and the etching solution composition allows the extraction of a physical model that, for the first time, clearly reveals the roles of the two fundamental kinetic mechanisms in MacEtch, carrier generation and mass transport. Ordered submicron diameter silicon via arrays with record aspect ratio are produced, which can directly impact the through‐silicon‐via technology, high density storage, photonic crystal membrane, and other related applications.     

The Effect of Nanotube Content and Orientation on the Mechanical Properties of Polymer–Nanotube Composite Fibers: Separating Intrinsic Reinforcement from Orientational Effects

We have measured the mechanical properties of coagulation‐spun polymer–nanotube composite fibers. Both the fiber modulus, Y, and strength, σ_B, scale linearly with volume fraction, V_f, up to V_f ～10%, after which these properties remain constant. We measured dY/dV_f = 254 GPa and dσ_B/dV_f = 2.8 GPa in the linear region. By drawing fibers with V_f < 10% to a draw ratio of ～60%, we can increase these values to dY/dV_f = 600 GPa and dσ_B/dV_f = 7 GPa. Raman measurements show the Herman's orientation parameter, S, to increase with drawing, indicating that significant nanotube alignment occurs. Raman spectroscopy also shows that the nanotube effective modulus, Y_Eff, also increases with drawing. We have calculated an empirical relationship between the nanotube orientation efficiency factor, η_o, and S. This allows us to fit the data for Y_Eff versus η_o, showing that the fiber modulus scales linearly with η_o, as predicted theoretically by Krenchel. From the fit, we estimate the nanotube modulus to be; Y_NT = 480 GPa. Finally, we show that the fiber strength also scales linearly with η_o, giving an effective interfacial stress transfer of τ = 40 MPa and a nanotube critical length of l_c=1250 nm. This work demonstrates the validity of the Cox‐Krenchel rule of mixtures and shows that continuum theory still applies at the near‐molecular level.     

High-power high-Modulation-speed 1060-nm DBR lasers for Green-light emission

We report on the static and dynamic performance of high-power and high-modulation-speed 1060-nm distributed Bragg reflector (DBR) lasers for green-light emission by second-harmonic generation. Single-wavelength power of 387 mW at 1060-nm wavelength and green power as high as 99.5 mW were achieved. A thermally induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. Measured rise-fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the lasers suitable for >50-MHz green-light modulation applications.