Complete single mode wavelength coverage over 40 nm with a superstructure grating DBR laser

The spectral characteristics of a widely tunable super structure grating distributed Bragg reflector (SSG-DBR) laser are investigated and the design considerations of the grating reflectors are given. By systematically adjusting the control currents of the two reflector sections and the phase section it is experimentally shown that every wavelength in an interval of 40 nm can be reached with a side-mode suppression usually better than 30 dB     

A novel integrated optics wavelength filter in InGaAsP-InP

An InGaAsP-InP integrated optics wavelength selective device is proposed and demonstrated. It utilizes coupling between epitaxial layers with different refractive indices and thicknesses. The device is suitable for integration to form, e.g., a monolithic receiver for wavelength division multiplexed optical communication systems. Design considerations are given. The filter bandwidth and center wavelength can be freely chosen, and bandwidths as narrow as 1.5 nm at 1.3 or 1.55 μm center wavelength are shown feasible. Electrical tuning is possible. Experimental filters show that devices can he fabricated with performance in good agreement with theory, The 22-nm -3-dB bandwidth at 1.12-μm center wavelength presently demonstrated is limited by the measurement system.     

A new random number generator from permutation groups

We describe a new random number generator, RPGM, which is based on the cryptographic system PGM invented by Magliveras in 1976 and subsequently studied by Magliveras and Surkan [10]. PGM relies on a certain method of machine representation for permutation groups. This method allows for encryption and decryption algorithms based on a space-efficient data structure which is called a logarithmic signature for the group. The efficacy of RPGM is studied by means of an extensive analysis of generated data of 100,000 numbers using the Mathieu groupM ₂₄ in its 5-transitive representation on 24 points.     

400 Mbit/s, 372 km coherent transmission experiment using in-lineoptical amplifiers

Reports on an optical transmission experiment using four in-line optical amplifiers. With a net gain of 58000 (47.7 dB) from the amplifiers, the authors were able to increase the longest nonregenerated transmission distance to 372 km. The system penalty associated with the amplifiers was only 1.5 dB     

E center in silicon has a donor level in the band gap

It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity--vacancy pair)--one of the most studied defects in semiconductors--has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.     

Russia's space program: running on empty

To the would-be observer of Russia's space program today, the barrage of confusing claims from experts both inside and outside the country can easily be overwhelming. Apparently, bankruptcy and collapse are imminent: the two top Russian officials, one civilian and one military, have each stated that the nation's space activity is in crisis and might even be forced to a standstill. Yet the industry still produces hardware, the rockets still fly, their ground controllers still operate distant spacecraft, and the cosmonauts aboard Mir still maintain their watch on orbit. Here, the author describes how the Russian space industry is reorganizing itself and has big plans for the future-but even with austerity measures, it needs a major influx of funds not to starve first     

Wavelength dependence of noise figure of a travelling-waveGaInAsP/InP laser amplifier

Heterodyne noise measurements on a travelling-wave semiconductor laser amplifier show that the excess noise factor decreases with increasing wavelength. When the signal wavelength is changed from 1.48 μm to 1.55 μm the noise figure decreases from 10.5 dB to 6.0 dB     

Wide continuous wavelength tuning of a narrow linewidth DBR laser

A continuous wavelength tuning range of 5.4 nm is obtained for a three-section DBR (distributed Bragg reflector) laser by applying one control current in both forward and reverse bias directions. In the reverse direction no significant linewidth broadening is seen due to the absence of injection-recombination shot noise, and a linewidth of less than 3 MHz is obtained over a wavelength span of 1.8 nm. The minimum linewidth observed is 580 kHZ