Electron energy distribution in CO2laser discharges

Electrical plasma parameters of the CO2laser were investigated by probe and high-frequency techniques. The electron energy distribution function was measured by the second derivative method. The relatively high-pressure effect on the electron probe current was taken into account when analyzing the experimental curves. The influence of the addition of N2, He, Xe and the influence of CO2dissociation on the plasma discharge properties were studied. Calculations of the pumping rates to vibrational levels taking part in creating inversion show that the influence on output power of a CO2laser usually observed with the addition of N2and He cannot be explained by a changing of the electron component of the plasma. The increase of output power and efficiency with addition of Xe to the CO2laser is connected with an essential changing of plasma parameters of the electron component.     

Band tailing and the spontaneous spectra of compensated epitaxial GaAs laser junctions

The spectra of the spontaneous emission from GaAs laser diodes fabricated by vapor-phase epitaxy and containing a high degree of compensation in the p-type side of the junction are, in many respects, similar to those previously reported for the cathodoluminescence of homogeneous p-type material. The temperature dependence of the spectra of these diodes supports a model where the emission is attributed to radiative transitions between a narrow band of states near the conduction-band edge and an exponential distribution of states extending the valence band into the forbidden gap. An increase in temperature then results in an increase or a decrease in the radiative power output depending on the position of the quasi-Fermi level for electrons relative to the above narrow band of states and a distribution of nonradiative levels below it.     

Efficient power extraction at TRAPATT harmonics

Using silicon planar diodes in a coaxial cavity that closely approximates to- Evans's TRAPATT circuit, microwave power up to the fourth harmonic has been extracted efficiently with a very low subharmonic content. The efficiency at the fundamental (1 GHz) and the third harmonic (3 GHz) were almost identical at 35% and 34%, respectively.     

Active RC networks using a parallel T

A method of independent control over the positions of the poles and zeros of an active RC network is described, Secondorder transfer functions can be realised by using these circuits. The adjustments of their characteristics after the construction are very easy. A simple experiment shows good agreement with the theory.     

InGaAs-InP P-I (MQW)-N surface-normal electroabsorption modulatorsexhibiting better than 8:1 contrast ratio for 1.55-μm applicationsgrown by gas-source MBE

We report growth of In_0.53Ga_0.47 As-InP multiple quantum well (MQW) modulators operating at 1.55 μm for fiber-to-the-home applications. By employing a 200-period InGaAs-InP MQW stack in the intrinsic region of a p-i-n structure and working in reflection, we have been able to realize surface-normal modulator devices that exhibit better than an 8:1 contrast ratio. This is the highest contrast ratio reported to date for this type of device working at this wavelength     

Cut-off frequency in radially inhomogeneous single-mode fibre

The limit for single-mode operation in a graded-index fibre has been obtained by calculating the normalised cut-off frequency of the TE01 mode, The affect of diffusion at the core-cladding boundary has been estimated.     

Effect of dip in the referctive index on the cut-off frequency of a single-mode fibre

The normalised frequency for single-mode cut-off in an optical fibre has been calculated as a function of the dip in the refractive index at the centre of the core. For a particular class of profiles, dip width up to 40% have a negligible effect on the propagation characteristics.