A density-functional study of small titanium clusters

The atomic structures and electronic properties of small Ti-N (N=2-10) clusters have been studied by using the density-functional theory with a local spin density approximation. We find that the inner-shells (3s3p) of the titanium atom plays an important role in the formation of the small clusters. We have obtained the ground state of titanium clusters, Ti-7 is found to be a magic cluster, which is in good agreement with the experimental results. Starting with Ti-8 cluster some features of the electronic structure of the titanium bulk have been developed. The ionization potentials and magnetic moments for these small titanium clusters are also presented. (C) 2000 American Institute of Physics. [S0021- 9606(00)30544-X].

High-output very small aperture laser and its near-field distribution properties - art. no. 60200L

A Very-Small-Aperture Laser with a 250 X 500 nm(2) aperture has been created on a 650nm edge emitting LD. The highest far-field output power is 1.9mW and the power per unit emission area is about 15 MW/mu m(2). The special fabrication process and high output power mechanism are demonstrated respectively. The near-field distribution properties are also analyzed theoretically and experimentally.

Subtraction of S-parameters for adiabatic small-signal modulation characteristics of laser diode - art. no. 60201V

An extended subtraction method of scattering parameters for characterizing laser diode is introduced in this paper. The intrinsic small-signal response can be directly extracted from the measured transmission coefficients of laser diode by the method. However the chip temperature may change with the injection bias current due to thermal effects, which causes inaccurate intrinsic response by our method. Therefore, how to determine the chip temperature and keep the laser chip adiabatic is very critical when extracting the intrinsic response. To tackle these problems, the dependence of the lasing wavelength of the laser diode on the chip temperature is investigated, and an applicable measurement setup which keeps the chip temperature stable is presented. The scattering parameters of laser diode are measured on diabatic and adiabatic conditions, and the extracted intrinsic responses for both conditions are compared. It is found that the adiabatic intrinsic responses are evidently superior to those without thermal consideration. The analysis indicates that inclusion of thermal effects is necessary to acquire accurate intrinsic response.

Small-signal and large-signal performance test of high-speed optoelectronics devices

This paper presents measurement methods for determining the reflection coefficients and frequency responses of semiconductor laser diodes, photodiodes, and EA modulator chips. A novel method for determining the intrinsic frequency responses of laser diodes is also proposed, and applications of the developed measurement methods are discussed. We demonstrate the compensation of bonding wire on the capacitances of both the submount and the laser diode, and present a method for estimating the potential modulation bandwidth of TO packaging technique. Initial study on removing the effects of test fixture on large-signal performances of optoelectronic devices at high data rate is also given.

Small-divergence singlemode emitting tapered distributed-feedback quantum cascade lasers

A tapered distributed feedback quantum cascade laser emitting at lambda similar to 8.1 mu m is reported. Utilising a tapered waveguide structure with a surface metal grating, the device exhibited singlemode operation over the temperature range of 100 to 214 K, with sidemode suppression ratio > 20 dB and a nearly diffraction limited far-field beam divergence angle of 5.4 degrees.

Structural studies of NixFe100-x/Mo magnetic multilayers by x-ray small-angle reflection and high-angle diffraction

Magnetic multilayers [NixFe100-x/Mo-30] grown by dc-magnetron sputtering were investigated by x-ray small-angle reflection and high-angle diffraction. Structural parameters of the multilayers such as the superlattice periods, the interfacial roughness, and interplane distance were obtained. It was found that for our NixFe100-x/Mo system, the Mo layer has bcc structure with [110] preferential orientation, while the preferential orientation of the NixFe100-x layer changes from a fee structure with [111] preferential orientation to a bcc structure with [110] preferential orientation with decreasing values of x. An intermixing layer located in the interlayer region between the NixFe100-x and Mo layers exists in the multilayers, and its thickness is almost invariant with respect to an increase of Mo layer thickness and/or a decrease of x in the region of x greater than or equal to 39. The thickness of the intermixing layer falls to zero when x less than or equal to 23.

Fabrication of Windowed Very-Small-Aperture Laser Diodes

A windowed very-small-aperture laser 9VSAL0 source for use in high-resolution near field optical data storage is fabricated. The windowed regions are introduced to avoid shorting the pn junction with metal coating and suppress the COD effect. It facilitates producing VSAL by simplified technology and improves the laser performance. A VSAL with 400nm small sperture is demonstrated by focused ion beam (FIB0 and the output power is 0.3mW at 31mA.