Efficient tunable laser operation of Tm:KGd(WO/sub 4/)/sub 2/ in the continuous-wave regime at room temperature

Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined.     

Electronic changes of refractive index in intensively pumped Nd:YAG laser crystals

Refractive index changes accompanying changes in population of electron levels of Nd/sup 3+/ ions in a Nd:YAG laser crystal under intensive diode and laser pumping have been studied using a highly sensitive polarization interferometer. An electronic change of the index due to population of the /sup 4/F/sub 3/2/ level is measured to be high (comparable with the thermal component) in the crystal under QCW diode-stack pumping (at 808 nm). The electronic component increased dramatically under pumping by an additional laser (at 266 nm) due to population of a higher-lying level /sup 2/F(2)/sub 5/2/. Analytical estimation reveals a predominating contribution of the well-allowed 4f-5d inter-shell transitions in polarizability of the excited levels /sup 4/F/sub 3/2/ and /sup 2/F(2)/sub 5/2/ both at a testing wavelength of 633 nm and at a wavelength of the strongest laser transition 1064.2 nm.     

High-power broadly tunable Ho/sup 3+/-doped silica fibre laser

Tuning of the 2.1 /spl mu/m Ho/sup 3+/-doped silica fibre laser is demonstrated for the first time. The /sup 5/I/sub 7//spl rarr//sup 5/I/sub 8/ transition provides tuning over 144 nm, from 2019 to 2163 nm, and a maximum pump-limited output power of 1.58 W at 2100 nm was produced.     

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.     

Wideband DHBTs using a graded carbon-doped InGaAs base

We report an InP/InGaAs/InP double heterojunction bipolar transistor (DHBT), fabricated using a mesa structure, exhibiting 282 GHz f/sub /spl tau// and 400 GHz f/sub max/. The DHBT employs a 30 nm InGaAs base with carbon doping graded from 8/spl middot/10/sup 19//cm/sup 3/ to 5/spl middot/10/sup 19//cm/sup 3/, an InP collector, and an InGaAs/InAlAs base-collector superlattice grade, with a total 217 nm collector depletion layer thickness. The low base sheet (580 /spl Omega/) and contact (<10 /spl Omega/-/spl mu/m/sup 2/) resistivities are in part responsible for the high f/sub max/ observed.     

Laser emission and amplification at 1.3 mu m in neodymium-doped fluorophosphate fibres

Laser emission and amplification have been studied in the 1.3 mu m spectral region on the /sup 4/F/sub 3/2/-/sup 4/I/sub 13/2/ transition in Nd/sup 3+/-doped fluorophosphate singlemode fibres. Pumping at 800 nm yields an extracted laser power of 10 mW at 1.323 mu m. A gain higher than 3 dB was obtained at the same wavelength in the amplifier experiment.<>     

Amplification and lasing at 1.3 mu m in praseodymium-doped fluorozirconate fibres

Light emission from the /sup 1/G/sub 4/ to /sup 3/H/sub 5/ transition around 1.3 mu m of Pr/sup 3+/ has been studied in fluoride glass (ZBLAN) fibres. Pumping at 1064 nm yields extracted laser power of a few mW at 1.294 mu m. Gain curves centred at 1.295 mu m have been obtained, with gross gains of more than 15 dB at 1.319 mu m. Changes of the output ASE with pumping conditions are explained by excited state absorption or energy transfer from the /sup 1/G/sub 4/ upper level of the transition.<>     

Spectroscopic and stimulated emission characteristics of Nd/sup 3+/ in transparent Y/sub 2/O/sub 3/ ceramics

Nd:Y/sub 2/O/sub 3/ ceramic materials have been synthesized using the vacuum sintering technique with the raw materials prepared by the nanocrystalline methods. The TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. The radiative spectral properties of Nd:Y/sub 2/O/sub 3/ ceramic have been evaluated by fitting the Judd-Ofelt model with the absorption and emission data. Individual Stark levels for /sup 2s+1/L/sub J/ manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd:Y/sub 2/O/sub 3/ ceramic. Laser performance studies reveal two stimulated emission channels at 1074.6- and 1078.6-nm wavelengths with stimulated emission cross sections of 7.63/spl times/10/sup -20/ and 6.35/spl times/10/sup -20/ cm/sup 2/. With 1.5 at % Nd:Y/sub 2/O/sub 3/ ceramic acting as a laser medium, we obtained a slope efficiency of 32% with 160-mW output power and pump threshold of 200 mW at 1078.6 nm.     

Full characterization of packaged Er-Yb-codoped phosphate glass waveguides

We present a procedure for the characterization of packaged Er-Yb-codoped phosphate glass waveguides. The procedure is based on precise measurements of the output optical powers when the waveguide is diode-laser pumped at 980 nm. The dependence of these optical powers on the input pump power is then fitted to the results from a numerical model that describes in detail the propagation of the optical powers inside the waveguide. The best fit is obtained for the following parameters: the signal wavelength scattering losses are /spl alpha/(1534)=8.3/spl times/10/sup -2/ dB/cm, the Yb/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 5.4/spl times/10/sup -25/ m/sup 2/ and 7.0/spl times/10/sup -25/ m/sup 2/, the Er/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 1.6/spl times/10/sup -25/ m/sup 2/ and 1.2/spl times/10/sup -25/ m/sup 2/, the Yb/sup 3+/--Er/sup 3+/ energy-transfer coefficient is 1.8/spl times/10/sup -23/ m/sup 3//s and the cooperative-upconversion coefficient is 8/spl times/10/sup -25/ m/sup 3//s. An approximate method is introduced that allows the determination of the absorption and emission cross section distributions for the erbium /sup 4/I/sub 13/2//spl hArr//sup 4/I/sub 15/2/ transition from the amplified spontaneous emission power spectrum.     

The influence of pump wavelength on Er:YAG Green-emitting laser characteristics

Mathematical modeling is used to study the influence of pump wavelength on the emission of an Er(0.5 at.%):YAG laser on the transition /sup 4/S/sub 3/2//spl rarr//sup 4/I/sub 15/2/ (561 nm). Three pump wavelengths (direct pumping: 488 nm, upconversion pumping: 800 and 810 nm) are investigated and the corresponding laser emission regimes are discussed. For upconversion pumping, we find an optimum pump wavelength and optimum resonator losses for lowering of the continuous-wave emission threshold.     

Studies of CW laser oscillation on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

In this paper, we report on studies of a continuous-wave laser at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) used to pump the iodine was produced by a radio frequency excited electric discharge. The electric discharge was sustained in He-O/sub 2/ and Ar-O/sub 2/ gas mixtures upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(/sup 2/P/sub 1/2/) state. The results of experimental studies for several different flow conditions, discharge arrangements, and mirror sets are presented. The highest laser output power obtained in these experiments was 520 mW in a stable cavity composed of two 99.995% reflective mirrors.     

Fabrication of ultrathin and highly flexible InP-based membranes for microoptoelectromechanical systems at 1.55 /spl mu/m

In this letter, tunable microcavities have been fabricated to evaluate their tunability in dependence on the membrane thickness. The membrane thickness has been decreased from 615 nm down to a record thickness of 123 nm yielding in a maximum mechanical tunability of 15.15 nm/V/sup 2/. Furthermore, a three-period /spl lambda//4 InP/air-gap high reflective mirror (R > 99.8% at 1.55 /spl mu/m) with a record wide stopband of more than 1100 nm has been fabricated. These results are achieved thanks to specific metal-organic vapor-phase epitaxy growth parameters.     

Path to the measurement of positive gain on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

Laser action at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O/sub 2/(a/sup 1//spl Delta/) which is produced using wet-solution chemistry. The system difficulties of chemically producing O/sub 2/(a/sup 1//spl Delta/) have motivated investigations into gas phase methods to produce O/sub 2/(a/sup 1//spl Delta/) using low-pressure electric discharges. We report on the path that led to the measurement of positive gain on the 1315-nm transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) was produced in a flowing electric discharge. Atomic oxygen was found to play both positive and deleterious roles in this system, and as such the excess atomic oxygen was scavenged by NO/sub 2/ to minimize the deleterious effects. The discharge production of O/sub 2/(a/sup 1//spl Delta/) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was upstream of a continuously flowing supersonic cavity, which was employed to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(/sup 2/P/sub 1/2/) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the gain measurements.     

Characterization and reliability of dual high-k gate dielectric stack (poly-Si-HfO/sub 2/-SiO/sub 2/) prepared by in situ RTCVD process for system-on-chip applications

We investigate for the first time the possibility of integrating chemical vapor deposition (CVD) HfO/sub 2/ into the multiple gate dielectric system-on-a-chip (SoC) process in the range of 6-7 nm, which supports higher voltage (2.5-5 V operation/tolerance). Results show that CVD HfO/sub 2/-SiO/sub 2/ stacked gate dielectric (EOT =6.2 nm) exhibits lower leakage current than that of SiO/sub 2/ (EOT =5.7 nm) by a factor of /spl sim/10/sup 2/, with comparable interface quality (D/sub it//spl sim/1/spl times/10/sup 10/ cm/sup -2/eV/sup -1/). The presence of negative fixed charge is observed in the HfO/sub 2/-SiO/sub 2/ gate stack. In addition, the addition of HfO/sub 2/ on SiO/sub 2/ does not alter the dominant conduction mechanism of Fowler-Nordheim tunneling in the HfO/sub 2/-SiO/sub 2/ gate stack. Furthermore, the HfO/sub 2/-SiO/sub 2/ gate stack shows longer time to breakdown T/sub BD/ than SiO/sub 2/ under constant voltage stress. These results suggest that it may be feasible to use such a gate stack for higher voltage operation in SoC, provided other key requirements such as V/sub t/ stability (charge trapping under stress) can be met and the negative fixed charge eliminated.     

Fully silicided NiSi gate on La/sub 2/O/sub 3/ MOSFETs

We have fabricated the fully silicided NiSi on La/sub 2/O/sub 3/ for n- and p-MOSFETs. For 900/spl deg/C fully silicided CoSi/sub 2/ on La/sub 2/O/sub 3/ gate dielectric with 1.5 nm EOT, the gate dielectric has large leakage current by possible excess Co diffusion at high silicidation temperature. In sharp contrast, very low gate leakage current density of 2/spl times/10/sup -4/ A/cm/sup 2/ at 1 V is measured for 400/spl deg/C formed fully silicided NiSi and comparable with Al gate. The extracted work function of NiSi was 4.42 eV, and the corresponding threshold voltages are 0.12 and -0.70 V for respective n- and p-MOSFETs. Electron and hole mobilities of 156 and 44 cm/sup 2//V-s are obtained for respective n- and p-MOSFETs, which are comparable with the HfO/sub 2/ MOSFETs without using H/sub 2/ annealing.     

Measurement of gain, group index, group velocity dispersion, and linewidth enhancement factor of an InGaN multiple quantum-well laser diode

Gain, group index, group velocity dispersion (GVD), temperature variation of refractive index, and linewidth enhancement factor of an In/sub 0.15/Ga/sub 0.85/N/In/sub 0.02/Ga/sub 0.98/N multiple quantum-well blue laser diode was measured using the Fourier transform method as a function of wavelength from 400 to 410 nm. At the lasing wavelength (403.5 nm), the group index is 3.4, the GVD (dn/sub g//d/spl lambda/) is -37 /spl mu/m/sup -1/, the temperature variation of refractive index dn/dT is 1.3/spl times/10/sup -4/ K/sup -1/, and the linewidth enhancement factor is 5.6.     

Multiwavelength diode-cladding-pumped Nd/sup 3+/-doped germano-aluminosilicate fiber laser

Simultaneous multiwavelength oscillation at 1060 and 1090 nm has been produced from a free-running Nd/sup 3+/-doped multicomponent silica fiber laser. As a result of co-doping with both Al/sub 2/O/sub 3/ and GeO/sub 2/, the Nd/sup 3+/ ions are situated at separate sites relating to either Al/sup 3+/-rich or Ge/sup 4+/-rich regions of the germano-aluminosilicate glass. The slope efficiency of the combined /spl sim/1-/spl mu/m output was /spl sim/52% (56%) with respect to the launched (absorbed) pump power. The 1060-nm emission reaches threshold first because of the greater number of Nd/sup 3+/ ions that are located at Al/sup 3+/-rich sites. On chopping the pump light the relaxation oscillations relating to the 1090-nm emission are antiphase with the oscillations observed with the 1060-nm emission. A degree of spectral overlap exists between the fluorescence emitted from Nd/sup 3+/ ions located at each site. Power equalization (to /spl sim/1 W each) of the 1060- and 1090-nm emissions was carried out by way of Raman amplification that occurred either internally or externally to the Nd/sup 3+/-doped silica fiber laser.     

DRAM plate electrode bias optimization for reducing leakage current in UV-O/sub 3/ and O/sub 2/ annealed CVD deposited Ta/sub 2/O/sub 5/ dielectric films

A new plate biasing scheme is described which allowed the use of 65% higher supply voltage without increasing the leakage current for the UV-O/sub 3/ and O/sub 2/ annealed chemical-vapor-deposited tantalum pentaoxide dielectric film capacitors in stacked DRAM cells. Dielectric leakage was reduced by biasing the capacitor plate electrode to a voltage lower than the conventionally used value of V/sub cc//2. Ta/sub 2/O/sub 5/ films with 3.9 nm effective gate oxide, 8.5 fF//spl mu/m/sup 2/ capacitance and <0.3 /spl mu/A/cm/sup 2/ leakage at 100/spl deg/C and 3.3 V supply are demonstrated.<>     

Semiconductor laser pumping of continuous-wave Pr/sup 3+/-doped ZBLAN fibre laser

Blue semiconductor laser pumped continuous-wave laser oscillation of a Pr-doped ZrF/sub 4/-BaF/sub 2/-LaF/sub 3/-AlF/sub 3/-NaF fibre in the red spectral range is reported for the first time. The pump power is provided by a frequency-doubled optically pumped semiconductor laser system. When pumped with 300 mW at a wavelength of 479.7 nm, the Pr/sup 3+/-laser emitted 94 mW of output power at a wavelength of 635 nm. Threshold pump power and slope efficiency with respect to the incident pump power were determined to be 49.7 mW and 41.5%, respectively.     

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.