High mobility NMOSFET structure with high-/spl kappa/ dielectric

High-/spl kappa/ NMOSFET structures designed for enhancement mode operation have been fabricated with mobilities exceeding 6000 cm/sup 2//Vs. The NMOSFET structures which have been grown by molecular beam epitaxy on 3-in semi-insulating GaAs substrate comprise a 10 nm strained InGaAs channel layer and a high-/spl kappa/ dielectric layer (/spl kappa//spl cong/20). Electron mobilities of >6000 and 3822 cm/sup 2//Vs have been measured for sheet carrier concentrations n/sub s/ of 2-3/spl times/10/sup 12/ and /spl cong/5.85/spl times/10/sup 12/ cm/sup -2/, respectively. Sheet resistivities as low as 280 /spl Omega//sq. have been obtained.     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

1.65 /spl mu/m-band optical amplification with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping

In order to expand the available bandwidth for wavelength division multiplexing transmission systems, a 1.65 /spl mu/m-band optical fibre amplifier with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping has been demonstrated. The positive gain, 3.8 dB, is the first ever achieved by means of (/sup 2/H/sub 11/2/, /sup 4/S/sub 3/2/) /spl rarr/ /sup 4/I/sub 9/2/ stimulated emission transition.     

Polarization-dependent enhancement of population inversion and of green upconversion in Er:LiNbO/sub 3/ by Yb codoping

We have investigated the polarization dependence of both the population inversion of the /sup 4/I/sub 13/2/ state and the green upconversion to the /sup 4/S/sub 3/2/ state in Er:LiNbO/sub 3/ optical fiber amplifier when codoped with Yb and pumped around 980 nm. The presence of Yb/sup 3+/ enhances the population of the /sup 4/I/sub 13/2/ state of the Er/sup 3+/ ions when pumped at /spl sigma/-polarization (>2.5 times) and at /spl pi/-polarization (>5.5 times), and introduces a broad useful pump band around 940-960 nm at /spl sigma/-polarization, relaxing fabrication tolerances on semiconductor pump sources. An enhancement of green upconversion is also observed by the Yb codoping. Lifetime measurements indicate that, as in glass substrates, nonradiative energy transfer is responsible for these enhancements.     

Theoretical analysis of gain characteristics of Er/sup 3+/-Tm/sup 3+/-codoped tellurite fiber amplifier

The rate and power propagation equations of Er/sup 3+/ and Tm/sup 3+/-codoped tellurite fiber amplifier pumped by 800-nm laser are presented and solved to analyze the dependences of gain at both 1470 and 1530 nm on the codoping concentration of Er/sup 3+/ and Tm/sup 3+/, fiber length, and input signal power. The numerical results show that with pump power of 200 mW and fiber length of 1.5 m, the gain at both 1470 and 1530 nm may reach 12.0 dB when the codoping concentration of Er/sup 3+/ and Tm/sup 3+/ reach 4.0/spl times/10/sup 25/ ions/m/sup 3/, 3.2/spl times/10/sup 25/ ions/m/sup 3/, respectively. The fiber length and codopant concentrations are proposed to make the two channels equivalently amplified.     

Improved-performance, InGaAs/InGaAsP (/spl lambda/=980 nm) asymmetric broad-waveguide diode lasers via waveguide-core doping

Doping the waveguide core (p=2/spl times/10/sup 17/ cm/sup -1/) in asymmetric-waveguide InGaAs/InGaAsP, two-quantum-well diode lasers (/spl lambda/=980 nm) raises the injection efficiency to 90% and decreases the threshold-current density, J/sub th/. For 2 mm long, 100 /spl mu/m wide stripe, uncoated chips J/sub th/ decreases from /spl sim/188 A/cm/sup 2/ to /spl sim/150 A/cm/sup 2/. High characteristic temperatures for J/sub th/ and the slope efficiency are obtained: T/sub 0/=215K and T/sub 1/=600K.     

Vertical-cavity surface-emitting lasers in the 8-/spl mu/m midinfrared spectral range with continuous-wave and pulsed emission

Continuous-wave (CW) as well as pulsed-laser emission from a midinfrared (/spl lambda/=7.92 /spl mu/m) IV-VI vertical-cavity surface-emitting laser at 1.8 K is presented. The high-finesse microcavity, containing PbSe as an active medium, was optically pumped with a carbon monoxide laser at a wavelength of 5.28 /spl mu/m (1894 cm/sup -1/) in either CW or Q-switched mode. The maximum achieved CW power was 4.8 mW and pulsed peak powers were up to 23 W. Linewidths are considerably narrower than 0.10 cm/sup -1/, corresponding to 0.6 nm.     

Fiber length dependence of phase change induced by laser-diode pumping in Yb/sup 3+/-Al/sup 3+/ co-doped optical fibers

We investigated the fiber length dependence of the phase change near 1580 nm induced by 980-nm pump beam in Yb/sup 3+/-Al/sup 3+/ co-doped optical glass fibers by use of a long-period fiber grating pair. As the pumping power increased, the phase change linearly increased and then was gradually saturated. Both the saturated phase change and the saturation pump power increased with the increase of the fiber length. The saturated phase change in Yb/sup 3+/-Al/sup 3+/ co-doped fibers of 16.7, 33.2, and 43.5 cm was found to be /spl sim/0.5, /spl sim/0.8, and /spl sim/1.0 rad, respectively. The saturation of the phase change is attributed to the saturation of the absorption from the finite ytterbium ions doped in the fibers.     

Multi-watt, high efficiency, diffraction-limited Nd:YAG planar waveguide laser

An efficient, longitudinally diode-pumped, diffraction-limited, Nd:YAG double-clad planar waveguide laser was operated on four transitions of the Nd/sup 3+/ ion. Optimized output powers of 4.3, 3.5, and 2.7 W were obtained for absorbed pump powers of /spl sim/7 W, for the transitions at the lasing wavelengths of 1.064 /spl mu/m, 946 nm, and 1.3 /spl mu/m, respectively. Operation of the weak /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 5/2/ transition, lasing at 1.833 /spl mu/m, was demonstrated at an absorbed pump power threshold of 300 mW and an output power of 400 mW, with a nonoptimized output coupling. Diffraction-limited performance was obtained in both the guided and nonguided axes.     

Fabrication and analysis of high-contrast InGaAsP-InP Mach-Zehnder modulators for use at 1.55-/spl mu/m wavelength

A high-contrast ratio, low voltage-length product, multiple quantum well InGaAsP-InP Mach-Zehnder interferometer is demonstrated and analyzed. An on/off ratio of over 40 dB and voltage-length product of 1.8 V-mm were measured, results which are superior to previous reports of similar MQW structures. Using the Lanczos-Helmholtz beam propagation method, we find that the linear and quadratic electrooptic coefficients for InGaAsP quantum wells are r=(3.9/spl plusmn/1.7) pm/V and s=(5.0/spl plusmn/1.5)/spl times/10/sup -19/ m/sup 2//V/sup 2/, respectively. We also demonstrate active optical alignment of the modulator guides using integrated waveguide light emitting diodes.     

Blue energy upconversion emission in thulium-doped-SiO/sub 2/-P/sub 2/O/sub 5/ channel waveguides excited at 1.064 /spl mu/m

Blue energy upconversion emission in Tm/sup 3+/-doped SiO/sub 2/-P/sub 2/O/sub 5/ channel waveguides off-resonance pumped by infrared radiation is reported. The waveguide samples were excited by a single continuous-wave laser source at 1.064 /spl mu/m. Two distinct blue emission signals around 450 and 480 nm, in addition to red at 660 nm and near-infrared at 800-nm less intense emissions were observed. The upconversion excitation mechanism was assigned to stepwise multiphoton absorption processes followed by nonradiative multiphonon-assisted relaxation processes. Infrared-to-blue conversion efficiencies with respect to the absorbed pump power of /spl sim/6.0/spl times/10/sup -7/ for this off-resonance pumping scheme was measured. The dependence of the infrared-to-blue upconversion mechanism upon the excitation power and thulium content is also examined.     

High-power P-i-N diode with local lifetime control using palladium diffusion controlled by radiation defects

We demonstrate for the first time a high-power P-i-N diode with local lifetime control using palladium (Pd) diffusion. Low-temperature (600/spl deg/C-700/spl deg/C) diffusion of Pd is stimulated by radiation defects resulting from alpha-particle irradiation (/sup 4/He/sup 2+/: 10 MeV, 10/sup 12/ cm/sup -2/). The region of maximal radiation damage of Gaussian shape is decorated by substitutional Pd after diffusion from a palladium silicide surface layer through the P/sup +/--P region into the N-base close to the anode junction. Significantly lower leakage current compared to that of standard /sup 4/He/sup 2+/ irradiation and very good ruggedness under fast recovery (di/dt/spl ap/500 A//spl mu/s, V/sub R//spl ap/2 kV) is demonstrated for Pd diffusion at 600/spl deg/C.     

Mode Propagation in a Nonuniform Cylindrical Medium (Correspondence)

A simplified form of the coupling coefficient C(/spl beta//sub p/, /spl beta//sub q/) resulting from a coupled mode theory analysis of wave propagation in a nonuniform medium is derived. It is found for most situations of interest that C(/spl beta//sub p/, /spl beta//sub q/) is proportional to 1/(/spl beta//sub p/-/spl beta//sub q/) and the power transfer between two modes is proportional to 1/(/spl beta//sub p/ - /spl beta//sub q/)/sup 4/. /spl beta//sub p/ and /spl beta//sub q/ are the two different modal propagation constants. For a dielectric rod C(/spl beta//sub p/, /spl beta//sub q/) is a simple line integral around the rod boundary. Approximate forms are presented for optical waveguides.     

Demonstration of 1789 V, 6.68 m/spl Omega/ /spl middot/ cm/sup 2/ 4H-SiC merged-PiN-Schottky diodes

The design, fabrication and characterisation of a high performance 4H-SiC diode of 1789 V-6.6 A with a low differential specific-on resistance (R/sub SP/spl I.bar/ON/) of 6.68 m/spl Omega/ /spl middot/ cm/sup 2/, based on a 10.3 /spl mu/m 4H-SiC blocking layer doped to 6.6/spl times/10/sup 15/ cm/sup -3/, is reported. The corresponding figure-of-merit of V/sub B//sup 2//R/sub SP/spl I.bar/ON/ for this diode is 479 MW/cm/sup 2/, which substantially surpasses previous records for all other MPS diodes.     

Asymmetric broad waveguide diode lasers (/spl lambda/ = 980 nm) of large equivalent transverse spot size and low temperature sensitivity

980-nm InGaAs-InGaAsP diode lasers of asymmetric broad-waveguide (BW) transverse structure are demonstrated. Single-transverse-mode devices have equivalent (transverse) spot sizes of 0.8 /spl mu/m (i.e., significantly larger than for symmetric BW structures), which are obtained at no price in device-parameter temperature sensitivity. Built-in discrimination against the first-order transverse mode allows fundamental-transverse-mode operation in relatively narrow beams (/spl theta//sub /spl perp// = 34/spl deg/). For 2-mm-long 100-/spl mu/m-wide-stripe uncoated devices with double-quantum-well active regions, the threshold-current density is as low as 190 A/cm/sup 2/, while the characteristic temperatures for the threshold-current density T/sub 0/, and the external differential quantum efficiency T/sub 1/ are high: 183 K and 650 K, respectively.     

Ridge-width dependence on high-temperature continuous-wave quantum-cascade laser operation

We report continuous-wave (CW) operation of quantum-cascade lasers (/spl lambda/=6 /spl mu/m) up to a temperature of 313 K (40/spl deg/C). The maximum CW optical output powers range from 212 mW at 288 K to 22 mW at 313 K and are achieved with threshold current densities of 2.21 and 3.11 kA/cm/sup 2/, respectively, for a high-reflectivity-coated 12-/spl mu/m-wide and 2-mm-long laser. At room temperature (298 K), the power output is 145 mW at 0.87 A, corresponding to a power conversion efficiency of 1.68%. The maximum CW operating temperature of double-channel ridge waveguide lasers mounted epilayer-up on copper heatsinks is analyzed in terms of the ridge width, which is varied between 12 and 40 /spl mu/m. A clear trend of improved performance is observed as the ridge narrows.     

Continuous-wave operation of GaInAs-AlGaAsSb quantum cascade lasers

We report on the demonstration of continuous-wave (CW) operation of GaInAs-AlGaAsSb quantum cascade (QC) lasers. By placing a 2.5-/spl mu/m-thick gold layer on both sides of the laser ridge to extract heat from the active region in the lateral direction, together with mounting the device epilayer down, we have achieved CW operation of GaInAs-AlGaAsSb QC lasers composed of 25 stages of active/injection regions. The maximum CW operating temperature of the lasers is 94 K, and the emission wavelength is around /spl lambda//spl sim/4.65 /spl mu/m. For a device with the size of 10/spl times/2000 /spl mu/m/sup 2/, the CW optical output power per facet is 13 mW at 42 K and 4 mW at 94 K. The CW threshold current density is 1.99 kA/cm/sup 2/ at 42 K, and 2.08 kA/cm/sup 2/ at 94 K, respectively.     

High-temperature 4.5-/spl mu/m type-II quantum-well laser with Auger suppression

Laser emission at 4.2-4.5 /spl mu/m has been observed at temperatures up to 310 K in pulsed optical pumping experiments on type-II quantum-well (QW) lasers with four constituents in each period (InAs-Ga/sub 1-x/In/sub x/Sb-InAs-AlSb). The characteristic temperature, T/sub 0/, is 41 K, and a peak output power exceeding 2 W/facet is observed at 200 K. The power conversion efficiency per facet of /spl ap/0.2% up to 200 K is within a factor of 2 of the theoretical value. The 300 K Auger coefficient of 4/spl times/10/sup -27/ cm/sup 6//s extracted from the threshold pump intensity demonstrates that Auger losses have been suppressed by a factor of four.     

High-gain quantum-dot semiconductor optical amplifier for 1300 nm

Using an AlGaAs-GaAs waveguide structure with a six-stack InAs-InGaAs "dots-in-a-well" (DWELL) gain region having an aggregate dot density of approximately 8/spl times/10/sup 11/ cm/sup -2/, an optical gain of 18 dB at 1300 nm has been obtained in a 2.4-mm-long amplifier at 100-mA pump current. The optical bandwidth is 50 nm, and the output saturation power is 9 dBm. The dependence of the amplifier parameters on the pump current and the gain recovery dynamics has also been studied.     

Integrated semiconductor vertical-cavity surface-emitting lasers and PIN photodetectors for biomedical fluorescence sensing

Vertical-cavity surface-emitting lasers (VCSELs), optical emission filters, and PIN photodetectors were fabricated as part of a monolithically integrated near-infrared fluorescence detection system. The integration of these micro-fabricated components with micro-arrays, flow channel arrays, and biochips can drastically reduce cost and enable parallel sensing architectures. An optoelectronic design is presented that integrates VCSELs, optical filters, and photodetectors through a modification to a typical VCSEL structure. System designs were simulated and compared, leading to several innovative approaches for integrated sensors. The laser and detector modules were characterized independently and subsequently integrated to form a complete sensor. VCSELs with oxidation apertures measuring 4, 7, 14, and 20 /spl mu/m showed a lasing wavelength of /spl lambda/=773 nm, threshold current densities from 6400 to 1300 A/spl middot/cm/sup -2/, and maximum output powers of 0.6-4 mW, with transverse single-mode and multimode operation. PIN photodetectors were fabricated with integrated emission filters. Quantum efficiencies above 85% were observed with a dark current of 500 fA/(mm detector diameter). Complete sensor units were tested and near-infrared fluorescent molecules (IR-800) were detected. A theoretical detection limit of 10/sup 5/ fluorophores//spl mu/m/sup 2/ was determined. The compact parallel architecture, high-power laser, and low-noise photodetector make this sensor a good candidate for biomedical fluorescence-based sensing applications.