Low frequency noise in 6H-SiC MOSFET's

The noise spectra for n-channel, depletion-mode MOSFETs fabricated in 6H-SiC material were measured from 1-10⁵ Hz at room temperature. Devices were biased in the linear regime, where the noise spectra was found to be dependent upon the drain-to-source bias current density. At a drain-to-source current of 50 μA for MOSFETs with a W/L of 400 μm/4 μm, the measured drain-to-source noise power spectral density was found to be A/(f^λ), with A being 2.6×10^-12 V², and λ being between 0.73 and 0.85, indicating a nonuniform spatial trap density skewed towards the oxide-semiconductor interface. The measured Hooge parameter (α_H) was 2×10^-5. This letter represents the first reported noise characterization of 6H-SiC MOSFET's     

Improved catastrophic optical mirror damage level in InGaAs/AlGaAslaser diodes

9.2 W continuous wave (CW) optical power at a heatsink temperature 10°C and 12.2 W in a regime with stabilised temperature of the laser chip is demonstrated from a 100 μm aperture InGaAs/AlGaAs (λ=1.03 μm) laser diode with 0.4 μm wide GaAs waveguide. Thus, record-high optical power densities of 30 MW/cm² and 40 MW/cm² correspondingly are achieved at the front facet without catastrophic optical mirror damage (COMD)     

High-performance long-wavelength (λ~1.3 μm) InGaAsPNquantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the λ=1.2- to 1.3-μm wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at λ=1.295 μm exhibited a record low threshold current density (J_TH) of 2. 5 kA/cm². Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J_TH =1.9 kA/cm² at λ=1.27 μm and J_TH=1.27 kA/cm² at λ=1.2 μm. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 μm     

High contrast GaInAs:Fe photoconductive optical AND gate fortime-division demultiplexing

A high-contrast, three port optical AND gate based on the photoconductive effect in Ga_0.47In_0.53As:Fe and operating in the λ=1.3-5 μm wavelength range is demonstrated. A 250:1 optical power contrast ratio (or 48 dB in electrical power after detection) is obtained in an optical-to-optical time division demultiplexing of a 100 MHz pulse train by a 6.25 MHz clock, both at λ=1.3 μm, with the demultiplexed output pulses at λ=1.5 μm     

High-power VCSEL arrays for emission in the watt regime at roomtemperature

Selectively oxidized InGaAs vertical-cavity surface emitting lasers (VCSELs) at an emission wavelength of λ=980 mm are investigated for high-power applications. Densely packed arrays consisting of 19 single devices with an active diameter of 50 μm emit 1.08 W of continuous-wave (CW) optical output power at room temperature. At 10°C, heat sink temperature the output power increases to 1.4 W, which corresponds to a chip size averaged power density of 1 kW·cm². Low divergence angle of less than 16° full-width at half-maximum (FWHM) and the circularly symmetric far-field pattern allow for simple focusing of the beam with power densities above 10 kW·cm²     

3.5-mm-square InGaAs p-i-n photodiodes and their application tooptical-axis arrangement between 1.3-μm laser diodes and a SMF

InGaAs p-i-n photodiodes (PD) with 3.5-mm×3.5-mm-large photosensitive area have been fabricated using chlorine-vapor-phase-epitaxial (C-VPE) growth. They showed high responsivity of 0.95 A/W (λ=1.3 μm) and 1.2 A/W (λ=1.55 μm) and good homogeneity in the whole area. Long-term reliability was confirmed through high-temperature aging tests at 150°C up to 5200 hours. A PD with two pairs of parallel electrodes (PE-PD) was applied to optical-axis arrangement between 1.3-μm laser diodes (LD's) and a single mode fibre (SMF). The beam position of a LD was detected in error within ±20 μm using PE-PD prior to coupling of a LD beam into a SMF. Total inspection time was reduced to one third the original time     

2-Gbit/s signal amplification at λ=1.53 μm in anerbium-doped single-mode fiber amplifier

The gain, saturation power, and noise of an erbium-doped single-mode traveling-wave fiber amplifier operating at a wavelength λ=1.53 μm are characterized. In continuous-wave (CW) measurements amplification at 2 Gbit/s was demonstrated with up to 17-dB gain for 1×10^-9 bit error rate at 1.531 μm and a 3-dB full bandwidth of 14 nm. From the determination of the fiber-amplifier's output signal-to-noise ratio versus input signal power during data transmission, it was concluded that, with signal levels used here, signal-spontaneous beat noise limited the receiver sensitivity improvement. With the fiber amplifier acting as an optical preamplifier of the receiver, the best sensitivity was -30 dBm, obtained after installing a polarizer at the fiber amplifier output to reject half of the applied spontaneous emission power. This sensitivity was 6 dB better than without the fiber amplifier, proving that the fiber amplifier can be used as a preamplifier     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

Fluorescence and laser operation in single-mode Ti-diffusedNd:MgO:LiNbO3 waveguide structures

The spectral properties of the guided-wave Nd fluorescence and results of laser oscillation in Ti-indiffused single-mode Nd:MgO:LiNbO ₃ waveguides and waveguide cavities, respectively, are reported. The splitting and polarization behavior of the fluorescence lines around 0.9, 1.08, and 1.37 μm were studied. Using a single-mode diode laser as a pump source (λ_p=814.6 nm), an oscillation threshold in an 8-mm-long structure of 2.1-mW absorbed pump power has been obtained. An output power up to 310 μW (limited by the available pump power), a slope efficiency of 16% at power levels >150 μW, and an emission linewidth of 0.21 nm (at λ_s=1085 nm) have been measured     

Arrays of microdischarge devices having 50-100 μm squarepyramidal Si anodes and screen cathodes

Microdischarge devices having (50-100 μm)² pyramidal Si anodes and metal screen cathodes have been operated continuously at Ne gas pressures up to 1350 Torr and voltages below 95 V. More than 34 μW of output power is produced by a single device in a solid angle of ~5×10^-2 sr for a Ne pressure of 500 Torr. 3×3 arrays of these devices have been fabricated     

10W near-diffraction-limited peak pulsed power from Al-free, 0.98μm-emitting phase-locked antiguided arrays

10 W peak-pulsed power emitted in a beam pattern 2×diffraction limit (DL) is obtained from a 40-element, 200 μm-aperture Al-free phase-locked antiguided array (λ=0.98 μm). 60% of the power resides in the central lobe, and the external differential quantum efficiency is 54%, for 1 mm-long optimised facet-coated devices     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C     

10-μm GaAs/AlGaAs multiquantum well scanned array infraredimaging camera

A long-wavelength infrared imaging camera that uses a GaAs/Al_xGa_1-xAs quantum-well infrared photodetector (QWIP) array is demonstrated. Excellent noise equivalent temperature difference sensitivity (NEΔT<0.1°C) has been achieved. The long-wavelength cutoff for the QWIP used in this camera is at λ _c=10.7 μm with the peak response being at λ_p =9.8 μm. A peak detectivity of 2×10¹⁰ cm√Hz/W has been achieved at 77 K as well as an excellent pixel-to-pixel uniformity of 2%. Since GaAs has a more mature growth and processing technology as well as higher uniformity than HgCdTe, it shows great promise for the fabrication of large two-dimensional arrays     

Pressure-dependent Sellmeier coefficients and material dispersionsfor silica fiber glass

The pressure-dependent Sellmeier coefficients are essential to characterize the optical design parameters for the optical fiber communication systems under deep sea environmental conditions. These coefficients are calculated for densified silica glass for the first time to compute the pressure dependence of material dispersion at any wavelength from the ultraviolet (UV) to 1.71 μm. The zero dispersion wavelength λ₀ (1.2725 μm at 0.1 10⁶ N m ^-2) varies linearly with pressure, and dλ₀/dP is 0.0027 nm/(10⁶ N m^-2). The calculated value is approximately one-third of the experimental value of 0.0076 nm/(10⁶ N m^-2) for a germanium-doped dispersion shifted fiber having λ₀=1.5484 μm and -0.0070 nm/(10⁶ N m^-2) for a pure silica-core fiber cable having λ₀ =1.2860 μm. Since, the refractive indexes are increased with pressure, the negative value of shift of the zero-dispersion wavelength is erroneous. The explanations are due to Ge-doping in silica glass, a possible temperature fluctuation of 0.16°C in the pressure-dependent measurement system of the zero dispersion wavelength and different experimental conditions of the silica glass and the optical fibers. This anomaly can also be attributed to the internal strain development at the core-cladding and fiber-jacketing boundaries due to pressure, which shows a larger experimental value. It accounts for the experimental values satisfactorily     

Leaky mode propagation in planar multilayer birefringentwaveguides: longitudinal dielectric tensor configuration

In this paper we examine leaky mode propagation in a general five-layered c-rotated optical structure with longitudinal dielectric tenser configuration that can be considered a useful pattern for many actual waveguides. The dependence of the leaky mode propagation on the longitudinal angle φ (between the optical c-axis and laboratory axis) is shown and the dispersion characteristics for different types and thicknesses of buffer and metal layer are reported. The guided mode losses at the wavelength λ=0.633 μm assume the lowest values (about 1 dB/cm) for an Ag layer and for φ=0°. Furthermore, we investigate the variation in the propagation characteristics of the leaky and guided modes with respect to the source wavelength. We obtain the transition wavelength from (G) guided modes to lowest order (L¹ ) leaky mode, having the ordinary component that leaks into the substrate; the transition wavelength to a higher order (L²) leaky mode, which has both ordinary and extraordinary leaky components and the leaky cutoff wavelength. As an example, for φ=10° and an Ag metal layer, the first-order G₁₁ mode transforms from guided to leaky L₁₁¹ at λ_gl≃0.9 μm. The losses exhibit a change of several dB near the wavelength transition from guided to leaky mode (e.g. The attenuation constant of the G₁₁ mode changes from 0.26×10² dB/cm at λ=0.633 μm to 0.18×10 ⁵ dB/cm at λ=0.95 μm where its ordinary component is a leaky one). A similar change is found near the transition wavelength from a lowest-order mode to the highest-order leaky mode     

Room-temperature long-wavelength (λ=13.3 μm) unipolarquantum dot intersubband laser

Long-wavelength (λ=13.3 μm) unipolar lasing at 283 K from self-organised In_0.4Ga_0.6As/GaAs quantum dots, due to intersubband transitions in the conduction band, is demonstrated for the first time. The threshold current density under continuous wave operation is 1.1 kA/cm² for a 60 μm×1.2 mm broad-area plasmon-enhanced waveguide device and the maximum power output is ≈ μW. The long intersubband relaxation time in quantum dots, together with the short lifetime in the ground state, due to interband stimulated emission, help to achieve the necessary population inversion and gain     

GaAs/AlGaAs quantum-well, long-wavelength infra-red (LWIR) detectorwith a detectivity comparable to HgCdTe

The authors achieved the first high responsitivity R_v=30000 V/W, high detectivity D*=1×10¹⁰ cm √(Hz)/W GaAs/AlGaAs multiquantum-well superlattice detector which is sensitive in the long wavelength infra-red (LWIR) spectral region. This detector operates at λ=8.3 μm and at a temperature of T=77 K     

Design and characterization of superlattice infrared photodetectoroperating at low bias voltage

In this paper, we investigate the performance and characterization of a 15-period superlattice embedded between two thick AlGaAs barriers. The structure can operate at low bias voltage with less power consumption for 8-10 μm long-wavelength infrared detection. In our design, one barrier is used to reduce the dark current and the other one is designed to enhance the collection efficiency of photoelectrons at the collector contact. The fabricated detector can be operated at a bias voltage lower than 0.1 V and exhibits a pronounced photovoltaic response. The spectral response shows voltage dependence around 0 V. At high bias voltage (>25 mV) the spectral lineshape is independent of bias and is around 8-10 μm with peak wavelength at 9.3 μm. At lower bias voltage the response is shifted toward shorter wavelength range. The peak responsivity was found to be 12 mA/W at λ_p =8.7 μm and zero bias and 85 mA/W at λ_p=9.3 μm and 0.1 V. Background limitation can be achieved up to 65 K with bias voltage less than 0.1 V. The measured noise power spectral density of the dark current at 77 K shows the characteristics of full shot noise rather than generation-recombination noise. The peak detectivity is determined to be D^*=3.5×10⁹ cm√(Hz)/W at 77 K and 0.1 V. In comparison with a conventional 30-period QWIP, our detector has the advantages of better performance at low bias voltages with lower power consumption and a tunable feature of spectral range     

Generation of frequency-tunable light and frequency reference gridsusing diode lasers for one-petahertz optical frequency sweep generator

Generation of frequency-tunable light and frequency reference grids in a wide frequency span for a diode laser based optical frequency sweep generator has been performed. Frequency tuning and noise characteristics in nonlinear frequency conversions have been discussed. By using AlGaAs, InGaAsP lasers and their frequency conversions in the type II angle phase-matching KTP crystal, highly coherent frequency-tunable outputs have been obtained from 600 THz (0.5 μm) to 170 THz (1.7 μm). Use of the DFB lasers ensures the continuous tuning with a frequency range as wide as 1 THz. Atomic potassium and molecular iodine absorption resonances have been employed as frequency references for stabilizing the frequencies of lasers and the generated light with the frequency stability of 10^-9-10^-10. Optical frequency comb generation has been realized at the 0.8 μm wavelength with a two-sided sidebands span of 4 THz. We have also proposed and demonstrated specific frequency-tunable systems based on sum and difference-generations of diode lasers     

Ultra-sensitive autocorrelation of 1.5 μm light with singlephoton counting silicon avalanche photodiode

1.5 μm two-photon absorption in a single photon counting silicon avalanche photodiode at record continuous-wave levels below 100 μW is reported. Autocorrelation of a 10 GHz, 1.67 picosecond pulse-train using this device demonstrates 1.5 × 10^-3 (mW)² peak-power times average-power sensitivity without the use of lock-in detection