1.55 μm silicon-based reflection-type waveguide-integrated thermo-optic 2 × 2 switch

In this work a waveguide-integrated 2 × 2 switch operating at the infrared communication wavelength of 1550 nm is proposed and theoretically discussed. The device is based on the total internal reflection (TIR) phenomenon and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapour deposition (PECVD) techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be therefore achieved at the interface by acting on the temperature. The device is integrated in a 4 μm-wide and 3 μm-thick single-mode rib waveguide. The substrate is a silicon-on-insulator (SOI) wafer with an oxide thickness of 500 nm. We calculated an output crosstalk always better than 24 dB and insertion losses as low as 3.5 dB.     

GaSb-based mid-infrared 2–5 μm laser diodes

Laser diodes emitting at room temperature in continuous wave regime (CW) in the mid-infrared (2–5 μm spectral domain) are needed for applications such as high sensitivity gas analysis by tunable diode laser absorption spectroscopy (TDLAS) and environmental monitoring. Such semiconductor devices do not exist today, with the exception of type-I GaInAsSb/AlGaAsSb quantum well laser diodes which show excellent room temperature performance, but only in the 2.0–2.6 μm wavelength range. Beyond 2.6 μm, type-II GaInAsSb/GaSb QW lasers, type-III ‘W’ InAs/GaInSb lasers, and interband quantum cascade lasers employing the InAs/Ga(In)Sb/AlSb system, all based on GaSb substrate, are competitive technologies to reach the goal of room temperature CW operation. These different technologies are discussed in this paper. To cite this article: A. Joullié, P. Christol, C. R. Physique 4 (2003).     

Distinction investigation of InGaAs photodetectors cutoff at 2.9 μm

Using double heterojunction structure with linearly graded In_xAl_1–xAs as buffer layer and In_0.9Al_0.1As as cap layer, wavelength extended In_0.9Ga_0.1As detectors with cutoff wavelength of 2.88 μm at room temperature have been grown by using gas source molecular beam epitaxy, their characteristics have been investigated in detail and compared with the detectors cutoff at 2.4 μm with similar structure as well as commercial InAs detectors. Typical resistance area product R₀A of the detectors reaches 3.2 Ω cm² at 290 K. Measured peak detectivity reaches 6.6E9 cm Hz^1/2/W at room temperature.     

Welding of polymers using a 2 μm thulium fiber laser

Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing.     

1.53 μm electroluminescence from ErF3-doped organic light-emitting diodes

Near-infrared (NIR) organic light-emitting devices (OLEDs) are demonstrated by employing erbium fluoride (ErF₃)-doped tris-(8-hydroxyquinoline) aluminum (Alq₃) as the emitting layer. The device structure is ITO/N,N′-di-1-naphthyl-N,N′-diphenylbenzidine (NPB)/Alq₃: ErF₃/2,2′,2″-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole) (TPBI)/Alq₃/Al. Room-temperature electroluminescence around 1530 nm is observed due to the ⁴I_13/2–⁴I_15/2 transition of Er³⁺. Full width at half maximum (FWHM) of the electroluminescent (EL) spectrum is ～50 nm. NIR EL intensity from the ErF₃-based device is ～4 times higher than that of Er(DBM)₃Phen-based device at the same current. Alq₃–ErF₃ composite films are investigated by the measurements of X-ray diffraction (XRD), absorption, photoluminescence (PL) and PL decay time. Electron-only devices are also fabricated. The results indicate that energy transfer mechanism and charge trapping mechanism coexist in the NIR EL process.     

InGaAsP/InP photodetectors targeting on 1.06 μm wavelength detection

InP-based InGaAsP photodetectors targeting on 1.06 μm wavelength detection have been grown by gas source molecular beam epitaxy and demonstrated. For the detector with 200 μm mesa diameter, the dark current at 10 mV reverse bias and R₀A are 8.89 pA (2.2 × 10⁻⁸ A/cm²) and 3.9 × 10⁵ Ω cm² at room temperature. The responsivity and detectivity of the InGaAsP detector are 0.30 A/W and 1.45 × 10¹² cm Hz^1/2 W⁻¹ at 1.06 μm wavelength. Comparing to the reference In_0.53Ga_0.47As detector, the dark current of this InGaAsP detector is about 570 times lower and the detectivity is more than ten times higher, which agrees well with the theoretical estimation.     

The elimination of zero-order diffraction of 10.6 μm infrared digital holography

A new method of eliminating the zero-order diffraction in infrared digital holography has been raised in this paper. Usually in the reconstruction of digital holography, the spatial frequency of the infrared thermal imager, such as microbolometer, cannot be compared to the common visible CCD or CMOS devices. The infrared imager suffers the problems of large pixel size and low spatial resolution, which cause the zero-order diffraction a severe influence of the reconstruction process of digital holograms. The zero-order diffraction has very large energy and occupies the central region in the spectrum domain. In this paper, we design a new filtering strategy to overcome this problem. This filtering strategy contains two kinds of filtering process which are the Gaussian low-frequency filter and the high-pass phase averaging filter. With the correct set of the calculating parameters, these filtering strategies can work effectively on the holograms and fully eliminate the zero-order diffraction, as well as the two crossover bars shown in the spectrum domain. Detailed explanation and discussion about the new method have been proposed in this paper, and the experiment results are also demonstrated to prove the performance of this method.     

Investigation on different ESD protection strategies devoted to 3.3 V RF applications (2 GHz) in a 0.18 μm CMOS process

ESD protection for radio frequency (RF) applications must deal with good ESD performance, minimum capacitance, zero series resistance and good capacitance linearity. In order to fulfill these requirements, different ESD protection strategies for RF applications have been investigated in a 0.18 μm CMOS process. This paper compares different ESD protection devices and shows that a suitable ESD performance target for RF applications (200 fF max, 2 kV HBM) can be reached with a diode network scheme. The optimization of the diodes is then a key point which is detailed. A trade-off has to be found between the ESD performance, the voltage drop during ESD and the parasitic capacitance. Poly as well as shallow trench isolation (STI) bounded diodes have been studied and it appears clearly that a solution based on poly bounded diodes is the best choice.     

Dielectrophoretic adhesion of 50–300 μm particles under ambient atmospheric conditions

The SPABRINK EU project required temporary adhesion of coloured solid “ink” particles to form an image. We use dielectrophoretic force to attach ink particles under the field from a voltage applied to an interdigitated electrode on the image carrying surface.Finite element modeling results were compared in terms of an “adhesion factor” that included the density of particles as well as dielectric constant. In our experiments 50–300 μm alumina, silica sand and polymer particles were shown to adhere to a vertical plane electrode structure under laboratory ambient atmosphere.     

Investigation on Tm3+-doped silicate glass for 1.8 μm emission

A Tm³⁺-doped silicate glass (SiO₂–CaO–Na₂O–K₂O) with good thermal stability is prepared by the melt-quenching method. Intense 1.8 μm emission is obtained when pumped by an 808 nm laser diode. Based on the measured absorption spectra, radiative properties are predicted using Judd–Ofelt theory and Judd–Ofelt parameters Ω_λ (λ=2, 4, 6), as well as absorption and emission cross-sections are calculated and analyzed. The difference between the measured Tm³⁺:³F₄ lifetime and the calculated lifetime is also discussed. The emission property together with good thermal property indicates that Tm³⁺-doped silicate glass is a potential kind of laser glass for efficient 2 μm laser.     

15 μm Quantum Well Infrared Photodetector for thermometric imagery in cryogenic windtunnel

Quantum Well Infrared Photodetector (QWIP) usually suffer from a too moderate quantum efficiency and too large dark current which is often announced as crippling for low flux applications. Despite this reputation we demonstrate the ability of QWIP for the low infrared photon flux detection. We present the characterization of a state of the art 14.5 μm QWIP from Alcatel-Thales III–V Lab. We developed a predictive model of the performance of an infrared instrument for a given application. The considered scene is a cryogenic wind tunnel (ETW), where a specific Si:Ga camera is currently used. Using this simulation tool we demonstrate the QWIP ability to image a low temperature scene in this scenario. QWIP detector is able to operate at 30 K with a NETD as low as 130 mK. In comparison to the current detector, the operating temperature is 20 K higher. The use of a QWIP based camera would allow a huge simplification of the optical part.     

Linewidth enhancement factor of InAs/InP quantum dot lasers around 1.5 μm

Linewidth enhancement factor (LEF) of InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) emitting around 1.5 μm is investigated both above and below the threshold. Above the threshold, LEFs at three different wavelengths around the gain peak of 1.53 μm by the injection locking technique are obtained to be 1.63, 1.37 and 1.59. Then by Hakki–Paoli method LEF is found to decrease with increased current and shows a value of less than 1 below the threshold. These small LEF values have clearly indicated that our developed InAs/InP QDs are perfect and promising gain materials for QD MWLs, QD mode-locked lasers (QD MLLs) and QD distributed-feedback (QD DFB) lasers around 1.5 μm.     

A high-power continuous-wave diffraction-limited Nd:GdVO4 laser operating at 1.34 μm

High-power and high beam quality continuous-wave (CW) Nd:GdVO₄ lasers operating at 1.34 μm were experimentally demonstrated. The lasers consisted of either one or two crystals, which were both end-pumped by high-power fiber-coupled diode lasers. With one crystal, the maximum CW output power generated was 8.4 W. When two crystals were used, a maximum output power of 15.7 W was achieved with the incident pump power of 76.2 W, showing a slope efficiency of 26.2% and an optical-to-optical efficiency of 20.6%. The beam divergence at an output power of 15 W was measured to be about two times that of the diffraction limit.     

Enhanced 2.0 μm emission in Ho3+/Yb3+ co-doped silica-germanate glass

A detailed investigation on thermal and spectroscopic properties of different Ho³⁺/Yb³⁺ concentration ratios in silica-germanate glasses is displayed. According to the measurement of thermal properties, the host glass possesses high transition temperature (585 °C) as well as the large ΔT(155 °C). The 2.0 μm fluorescence can be obtained from all the samples. Maximum stimulated emission cross-section of around 2.0 μm is 0.56 × 10⁻²⁰ cm² of Ho³⁺ as calculated by McCumber theory. Besides, the underlying mechanism is analyzed by means of fluorescence spectra. Thus, desirable thermal properties and spectroscopic characteristics of Ho³⁺/Yb³⁺ co-doped silica-germanate glass is a promising material in 2.0 μm emission.     

2.7 μm fluorescence radiative dynamics and energy transfer between Er3+ and Tm3+ ions in fluoride glass under 800 nm and 980 nm excitation

A detailed study of the fluorescence radiative dynamics and energy transfer processes between Er and Tm ions in the Er³⁺/Tm³⁺ doped fluoride glass is reported. The fluorescence properties of 2.7 μm emission, other infrared and visible emissions are investigated under different selective laser excitations. Three Judd–Ofelt intensity parameters, energy transfer microparameters and efficiency have been determined and discussed. It is found that present Er³⁺/Tm³⁺ doped fluoride glass possesses large calculated emission cross section (8.98×10^–21 cm²) around 2.7 μm. The more suitable pumping scheme for laser applications at 2.7 μm laser is 980 nm excitation for Er³⁺/Tm³⁺ doped fluoride glass.     

Positive influence of Tm3+ on effective Er3+: 3 μm emission in fluoride glass under 980 nm excitation

Er³⁺ and Tm³⁺ singly doped and codoped new fluoride glasses were prepared by traditional melt-quenching method. Efficient 3 μm emission was obtained under 980 nm laser excitation. It is worthy to notice that one of the two ions can be the sensitizer to the other one by depressing the Er³⁺: 1.5 μm emission through the energy transfer process from Er³⁺:⁴I_13/2 level to Tm³⁺:³F₄ level. On the basis of measured absorption spectra, the Judd-Ofelt intensity parameters and radiation emission probability were calculated to evaluate the spectroscopic properties. Additionally, the micro-parameters together with the phonon assistance of Er³⁺:⁴I_13/2 → Tm³⁺:³F₄ and Er³⁺:⁴I_11/2 → Tm³⁺:³H₅ processes were quantitatively analyzed by using Dexter model. The theoretical micro-parameters results meet well with the experiments which indicates that Er³⁺/Tm³⁺ codoped fluoride glass is a potential kind laser glass for 3 μm laser.     

Absolute line intensities measurements and calculations for the 5.7 and 3.6 μm bands of formaldehyde

The goal of this study is to achieve absolute line intensities for the strong 5.7 and 3.6 μm bands of formaldehyde and to generate, for both spectral regions, an accurate list of line positions and intensities. Both bands are now used for the infrared measurements of this molecule in the atmosphere. However, in the common access spectroscopic databases there exists, up to now, no line parameters for the 5.7 μm region, while, at 3.6 μm, the quality of the line parameters is quite unsatisfactory. High-resolution Fourier transform spectra were recorded for the whole 1600–3200 cm^?1 spectral range and for different path-length-pressure products conditions. Using these spectra, a large set of H₂CO individual line intensities was measured simultaneously in both the 5.7 and 3.6 μm spectral regions. From this set of experimental line strength which involve, at 5.7 μm the ν₂ band and, at 3.6 μm, the ν₁ and ν₅ bands together with nine dark bands, it has been possible to derive a consistent set of line intensity parameters for both the 5.7 and 3.6 μm spectral regions. These parameters were used to generate a line list in both regions. For this task, we used the line positions generated in [Margulés L, Perrin A, Janeckovà R, Bailleux S, Endres CP, Giesen TF, et al. Can J Phys, accepted] and [Perrin A, Valentin A, Daumont L, J Mol Struct 2006;780–782:28–42] for the 5.7 and 3.6 μm, respectively. The calculated band intensities derived for the 5.7 and 3.6 μm bands are in excellent agreement with the values achieved recently by medium resolution band intensity measurements. It has to be mentioned that intensities in the 3.6 μm achieved in this work are on the average about 28% stronger than those quoted in the HITRAN or GEISA databases. Finally, at 3.6 μm the quality of the intensities was significantly improved even on the relative scale, as compared to our previous study performed in 2006.