Simplified modeling of transients in gain-clamped erbium-dopedfiber amplifiers

A simple technique for modeling transients in erbium-doped fiber amplifiers (EDFAs) has been applied to a gain-clamped amplifier. Integration of the variables along the length of the amplifier allows the formulation of the problem as a single simple, ordinary, time-dependent differential equation. We demonstrate examples for a typical conventional EDFA and one in which internal out-of-band oscillation is used to clamp the gain     

Effects of sleeping in a chemical protective mask on sleep quality and cognitive performance

PURPOSE: We wanted to determine whether sleep is disrupted when soldiers sleep in a new chemical protective mask, the M40. Sleep quantity and quality, extent of protection provided by the mask during sleep, and next day performance were assessed. METHOD: After several days of training, 9 male soldiers slept with and without the M40 mask on four occasions. RESULTS: Soldiers were able to tolerate the mask for most or all of the night. However, sleep, as assessed by wrist-worn activity monitors, was significantly disturbed. Minutes (mean +/- SEM) of waking significantly increased, from 25 +/- 2.1 to 86 +/- 8.5 per night (p < 0.001), and number of awakenings rose from 8 +/- 0.6 to 20 +/- 0.9 (p < 0.0001). Soldiers reported that it took longer and was more difficult to fall asleep when wearing the mask. Errors on a choice reaction time task increased significantly and subjects reported greater fatigue and sleepiness the day after sleeping in the mask. Protection provided by the masks varied substantially among subjects and declined over the course of the study. Some soldiers were protected throughout the night but others were only protected intermittently. CONCLUSION: We conclude that sleeping in the chemical protective mask should only be done when necessary, given the adverse effects on sleep and daytime function, as well as the variability of protection, of the mask.     

Blood and tissue compatibility of modified polyester: thrombosis, inflammation, and healing

OBJECTIVE: The effects of BRL-32872, azimilide and a selective blocker of the delayed rectifier potassium current, E-4031, were measured at two different basic cycle lengths (BCL), 300 and 1000 ms. Calcium channel antagonists of sarcolemmal (verapamil and nitrendipine) and sarcoplasmic reticulum (ryanodine) membranes were used to investigate whether the inhibition of the calcium current or the calcium release from the sarcoplasmic reticulum could alter the reverse-rate dependence of E-4031 on action potential duration (APD). METHODS: Guinea pig isolated papillary muscles were superfused with a Tyrode solution maintained at 37 degrees C and stimulated at a BCL of 300 or 1000 ms. The standard microelectrode technique was used to record action potential parameters and to study the effects of azimilide, BRL-32872 and E-4031. E-4031 was superfused at increasing concentrations (0.01, 0.03, 0.1 and 0.3 microM) in the absence or in the presence of verapamil (0.3 microM), nitrendipine (0.03 microM) or ryanodine (0.1 microM). RESULTS: BRL-32872 and azimilide induced a self-limited concentration-dependent increase in APD. The effect of BRL-32872 was not dependent on the stimulation frequency whereas the effect of azimilide was significantly reduced at the shorter BCL. E-4031 induced a concentration-dependent increase in APD at both stimulation BCL. The increase in APD was significantly more pronounced in fibres stimulated at a BCL of 1000 ms than in fibres stimulated at a BCL of 300 ms, characterising the reverse-frequency dependent effect of class III antiarrhythmic agents. The reverse-frequency dependence in action potential prolongation induced by E-4031 was significantly reduced in the presence of a low concentration of verapamil (0.3 microM), nitrendipine (0.03 microM), or ryanodine (0.1 microM. CONCLUSION: The results show that BRL-32872, in contrast to azimilide, does not induce the reverse-rate dependency of action potential prolongation typically produced by class III antiarrhythmic agents such as E-4031. Our results also show that reverse-rate dependency induced by E-4031 can be reduced by the simultaneous administration of a low concentration of a calcium channel antagonist or an inhibitor of the release of calcium from the sarcoplasmic reticulum. It is thus suggested that compounds with a suitable balance of potassium and calcium antagonistic activities may have less adverse effects than purely selective potassium channel blockers.     

Low-threshold, transversely excited NdP5O14laser

We have measured the room-temperature lasing behavior of NdP5OI4(NdPP) transverselypumped at 058-wm wavelength by a CW dye laser in an excitation geometrysimulatingthat of an LED or laser diode. For acrystal 760 Nm long, the lowest transversethreshold was 4 mW. From thisthresholdandatheoreticalrelationshipbetween excitation efficiency andpump wavelength, we predict that a threshold of approximately 8.5 mW should be possible for excitation by an edge-emitting 0.8-wm wavelength LED. Usingthin NdP P samples with reflecting back surfaces for better excitation efficiency should lower this threshold by -60 percent, andgiveminimumoptical-to-optical con- version efficiencies of - 3.5 percent.     

Gaussian patterned contacts for improved beam stability of1.55-μm tapered lasers

A Gaussian lateral current-injection profile is approximated by a quasi-random pattern of electrically conducting and insulating regions. This pattern is used for the p-type contact in a laser with a 2.1-mm-long tapered gain region and operating near 1.55-μm wavelength. Lasers with improved stable single lateral modes are obtained with Strehl ratios up to 0.85 for current up to 4.0 A and output power over 1.0 W. Power over 0.5 W can be coupled into a single-mode optical fiber with a cylindrical microlens attached to the output facet to remove the astigmatism of the laser     

Effect of cladding layer thickness on the performance ofGaAs-AlGaAs graded index separate confinement heterostructure singlequantum-well lasers

The thinning of cladding layers of GaAs-AlGaAs graded index separate confinement heterostructure single quantum-well (GRINSCH-SQW) lasers offers several advantages. These advantages include easier fabrication of surface grating-based lasers and ridge lasers, the reduction of growth time and source-material use, and the more effective removal of heat due to lower thermal resistance. Experimental results from GRINSCH-SQW lasers showing that typical cladding thicknesses of 1.5 to 2 μm are much thicker than necessary are presented. Lasers with cladding layers as thin as 4500 Å have not shown any increase in threshold current. Theoretical analysis shows good agreement with the experimental results on the minimum cladding thickness necessary to prevent an increase in the threshold current. The differential quantum efficiency is theoretically considered and is found to be more sensitive to cladding-layer thickness     

Frequency modulation locking in 980 nm strained quantum well lasers

The fundamental and second-harmonic spectral characteristics of frequency modulation locking have been observed in strained-layer InGaAs quantum well Fabry-Perot ridge-waveguide lasers emitting at 980 nm.<>