Effect of facet coatings on far fields of semiconductor lasers

A theoretical expression is derived for the far fields of semiconductor lasers with coated facets. It is shown that the far fields are different for uncoated, antireflection-coated and high-reflection-coated lasers. The correction factor for the far fields is shown to depend on the transmission coefficient of the facets.     

Mode-hopping noise in index-guided semiconductor lasers and its reduction by saturable absorbers

Mode-hopping noise in index-guided semiconductor lasers is investigated. It is found that random switching between lasing modes and output power differences in those modes cause mode-hopping noise. An effective method to suppress such mode-hopping noise is proposed. High Te doping to an n-type GaAlAs cladding layer completely suppresses the noise. Te in GaAlAs forms a DX center that acts as a saturable absorber. This property stabilizes the laser mode and prevents mode competition. The minimum loss difference between lasing and nonlasing modes to suppress mode-hopping noise is also discussed.     

Finite-difference time-domain analysis of laser diodes integratedwith tapered beam-expanders

Waveguide properties of laser diodes integrated with horizontally tapered beam-expanders are analyzed by the finite-difference time-domain method. The taper length dependence of the radiation loss and fiber-coupling efficiency are clarified. Lower loss and higher fiber-coupling efficiency are achieved in the exponentially tapered beam-expander compared with a linearly tapered one having an equivalent length     

Numerical analysis of /spl alpha/ parameters and extinction ratios in InGaAsP-InP optical modulators

The /spl alpha/ parameters and extinction ratios of InGaAsP-InP electroabsorption (EA) modulators and Mach-Zehnder (MZ) modulators are theoretically investigated. The bound states of excitons in quantum wells (QWs) under electric field are calculated through the finite-difference method, and quasi-bound states are obtained by the transfer-matrix method. Reducing the heights of the potential barriers of the QWs is prerequisite to achieving small values of the /spl alpha/ parameter for EA modulators and low driving voltages for MZ modulators. Bulk EA modulators are shown to inherently have relatively small /spl alpha/ parameters; however, they also require a tradeoff between the extinction ratio and the insertion loss. The /spl alpha/ parameters of symmetrical and /spl pi/-phase-shifted MZ modulators in the single- and dual-drive cases are also discussed.     

Analysis of wall conditioning by using plasma impact desorption in the tandem mirror GAMMA 10

A method for evaluating wall condition by using plasma impact desorption (PID) technique has been developed and successfully applied to the tandem mirror GAMMA 10 as a monitor for wall conditioning. A magnetically shielded quadrupole mass spectrometer was installed in the vacuum chamber of the GAMMA 10 central cell. The behaviour of the partial pressure of various gas molecules desorbed by ICRF-heated plasma discharges were analyzed. The predominant increase of the partial pressure due to PID (ΔP_PID) was hydrogen (M = 2) and a small amount of impurity as CO (M = 28), CH₃ (M = 15), H₂O (M = 18) and CO₂ (M = 44) was observed in the wall-conditioning discharges. The reduction of hydrogen pressure as well as ΔP_PID of the above impurities was observed with the progress of wall conditioning. This behavior has a good correlation with the increase of partial pressures due to electron-impact desorption measured at the same period. The relation between ΔP_PID and the charge-exchange flux was investigated.     

N-Type Doping to an Active-Short Cavity DBR Laser to Expand Its Continuous Tuning Range

We propose the use of a short-cavity distributed Bragg reflector (DBR) laser with a modified active DBR structure, which has an n-type-doped active single quantum well, and that achieves fast wavelength switching that is potentially applicable for optical packet switching networks. The laser exhibits 6.4-nm continuous tuning by moderating a steep gain change at a low DBR injection current. Furthermore, 32-nm continuous tuning has also been achieved for an integrated laser with an eight-channel array.     

Roxithromycin inhibits cytokine production by and neutrophil attachment to human bronchial epithelial cells in vitro

We evaluated the effect of roxithromycin on cytokine production and neutrophil attachment to human airway epithelial cells. Roxithromycin suppressed production of interleukin 8 (IL-8), IL-6, and granulocyte-macrophage colony-stimulating factor. It inhibited neutrophil adhesion to epithelial cells. Roxithromycin modulates local recruitment and activation of inflammatory cells, which may have relevance to its efficacy in airway diseases.     

Optical line shape functions in quantum-well and quantum-wirestructures

Line shape functions in quantum-well and quantum-wire structures are theoretically analyzed taking non-Markovian relaxation processes into account. For high carrier density (as in laser operation), the line shape functions in low-dimensional systems have a strong convergent characteristic because the carrier-carrier coupling, i.e. the system-reservoir coupling, becomes stronger in the lower-dimensional systems. In particular, the line shape of the quantum wire can be approximated by the Gaussian function. In the case of low carrier density, the lower-dimensional systems have smaller homogeneous broadening widths because of longitudinal optical phonon localization; the transverse relaxation times are 0.1 ps (bulk), 0.3 ps (quantum well), and 0.7 ps (quantum wire)     

Suppression of leakage current in InGaAsP/InP buried heterostructure lasers by InAlAs strained current-blocking layers

InGaAsP/InP buried heterostructure (BH) lasers with InAlAs strained current-blocking layers are proposed. For use as a current-blocking material with a bandgap energy larger than that of InP, InAlAs is superior to InGaP. This is because a wide bandgap can be obtained in the InAlAs without large bandgap shrinkage caused by tensile strain. A two-dimensional simulation shows that the leakage current in BH lasers with thin pnpn blocking layers is suppressed up to 85 degrees C by employing 100 AA In/sub 1-x/Al/sub x/As(x>or=0.54) layers.<>     

Dependence of linewidth enhancement factor on crystal orientationin strained quantum well lasers

The linewidth enhancement factor a in strained quantum well (QW) lasers is estimated theoretically for various crystallographic directions. It is found that the a factor in a strained In_0.7Ga_0.3As-InP QW laser on a (111) substrate is less than 1.4, much lower than for conventional strained QW lasers on (001) substrates