Comparative analysis of the effects of internal lasing oscillation and external light injection on semiconductor optical amplifier performance

One of the key differences of a semiconductor optical amplifier (SOA) with internal lasing oscillation (ILO) from a SOA with external light injection (ELI) lies in a carrier-sharing mechanism. Since the internal lasing mode shares the same pool of carriers with the signals, the carriers (or photons) withdrawn from the circulating laser mode speed up the gain recovery. On the other hand, the external light injected into the SOA shortens the carrier recovery time through optical pumping without any carrier sharing involved. To find out a better scheme, we have made a comparative investigation on the effects of the ILO and ELI on the SOA performance. It turns out by way of simulation that the ELI scheme provides faster gain recovery, shorter carrier lifetime, and higher saturation power when the external injection power is higher than the internal lasing power. The performance enhancement is not so pronounced with the carrier-sharing mechanism, as the internal lasing mode itself gives rise to severe longitudinal spatial hole burning (LSHB). Nevertheless, the ILO scheme is preferable for linear-amplification applications. We also examine the use of the ELI for low-crosstalk optical amplifiers. It is found that the ELI scheme does not bring in a very strong resonance peak in the crosstalk, which appears in a SOA with ILO due to relaxation oscillations of the lasing mode. In comparison to the ILO in SOAs, the ELI into SOAs is likely to leave more optical gain for multi-channel amplification without any sacrifice on the crosstalk.     

Mössbauer spectroscopy of the high-pressure phase of pure iron;ɛ-Fe

Hyperfine Interactions - First off-line tests at the ion trap facility SHIPTRAP took place. The facility is being set up to deliver very clean and cooled beams of singly-charged recoil ions (Rare...     

Tungsten microcone arrays grown using nanosecond pulsed-Nd:YAG laser in a low-pressure He-gas atmosphere

Tungsten microcone arrays with a high aspect ratio are formed by the cumulative nanosecond pulsed-Nd:YAG laser irradiation of single-crystal tungsten under low pressure in an inert atmosphere. The morphology of the microcones and their density were strongly affected by the number of laser pulses. The microcones grew to a length of 20 μm with a diameter of about 1.5 μm at the tip after irradiation with more than 1200 pulses under our experimental conditions. They may have potential applications for emission cathodes in a field-emission display (FED) and in microelectronic devices. Received: 8 January 2001 / Accepted: 13 June 2001 / Published online: 2 October 2001     

Synthesis and thermal properties of disiloxane-arylene polymers by dehydrocoupling polymerization of bis(dimethylsilyl)arylene with water

Disiloxane-arylene polymers having phenylene, biphenylene, and fluorenylene groups as arylene units were synthesized by dehydrocoupling polymerization of corresponding bis(silane) derivatives with water. The reactivity of Si-H was not affected by the structure of aromatic groups in the reaction. The polymers containing biphenylene and fluorenylene units are amorphous and show higher glass transition temperatures than the polymer from 1,4-bis(dimethylsilyl)benzene.     

Radiative carrier recombination dependent on temperature and well width of InGaN/GaN single quantum well

Photoluminescence (PL) spectra and time-resolved PL are measured from around 10 to 300 K for the InGaN/GaN single quantum wells (SQWs) with well widths of 1.5, 2.5, 4 and 5 nm. For the SQWs with the well widths of 1.5 and 2.5 nm, the peak position of PL exhibits an S-shaped shift with increasing temperature. The radiative recombination time τ_RAD begins to increase at the temperature for the position to change from the red-shift to the blue-shift. The steep increase of τ_RAD is observed beyond the temperature from the blue-shift to the red-shift. For the SQWs with the well widths of 4 and 5 nm, the peak position of PL exhibits a monotonic red-shift. τ_RAD decreases at first and then increases with temperature. It is about 100-times longer in the low temperature region and about 10-times longer at room temperature as compared with those of the SQWs with narrower widths.     

8-Hydroxyquinoline derivative as a fluorescent chemosensor for zinc ion.

8-Hydroxyquinoline derivative 1 as a fluorescent chemosensor for Zn2+ was synthesized. Because Cd2+ is often found with Zn2+ in the environment and can form fluorescent complexes with chelating fluorophores, a potentially important property of chemosensors for Zn2+ is their selectivity for Zn2+ over Cd2+. The Zn2+ or Cd2+ complexes of 1 gave an emission band from the 1:1 complex, but the fluorescence intensity for Cd2+ was a half of that for Zn2+. Ligand 1 is suited for use as a fluorescent chemosensor for Zn2+.     

Rattling in the Quadruple Perovskite CuCu3V4O12

Of particular interest is a peculiar motion of guest atoms or ions confined to nanospace in cage compounds, called rattling. While rattling provides unexplored physical properties through the guest–host interactions, it has only been observed in a very limited class of materials. Herein, we introduce an A‐site‐ordered quadruple perovskite, CuCu₃V₄O₁₂, as a new family of cage compounds. This novel AA′₃B₄O₁₂‐type perovskite has been obtained by a high‐pressure synthesis technique and structurally characterized to have cubic Im$\bar 3$ symmetry with an ionic model of Cu²⁺Cu²⁺₃V⁴⁺₄O₁₂. The thermal displacement parameter of the A‐site Cu²⁺ ion is as large as U_iso≈0.045 Ų at 300 K, indicating its large‐amplitude thermal oscillations in the oversized icosahedral cages. Remarkably, the presence of localized phonon modes associated with rattling of the A‐site Cu²⁺ ion manifests itself in the low‐temperature specific heat data. This work sheds new light on the structure–property relations in perovskites.     

Calibration transfer employing univariate correction and robust regression

This paper proposes a new method for calibration transfer, which was specifically designed to work with isolated variables, rather than the full spectrum or spectral windows. For this purpose, a univariate procedure is initially employed to correct the spectral measurements of the secondary instrument, given a set of transfer samples. A robust regression technique is then used to obtain a model with low sensitivity with respect to the univariate correction residuals. The proposed method is employed in two case studies involving near infrared spectrometric determination of specific mass, research octane number and naphthenes in gasoline, and moisture and oil in corn. In both cases, better calibration transfer results were obtained in comparison with piecewise direct standardization (PDS). The proposed method should be of a particular value for use with application-targeted instruments that monitor only a small set of spectral variables.