Abstract: We have found that it is possible to make a multistage optical fiber amplifier having a substantially flat gain band of spectral width of 40 nm or more, excellent noise figure (e.g.,<4 dB) and output power. Such amplifiers can advantageously be used, for instance, in multichannel WDM systems and analog CATV systems. A significant aspect of the amplifier is the provision of an optical loss element (exemplarily a multi-grating optical fiber filter) that provides, at least at one wavelength in the gain band, an attenuation of more than G/3 dB, where G is the average amplifier gain (in dB) in the gain band. A further significant aspect of the amplifier is the use of relatively longer amplifier fibers, which facilitates attainment of high output power and low noise figure. Exemplarily, the amplifier is a 2-stage amplifier comprising silica-based Er-doped amplifier fiber, with three-Gaussian filters between the stages.

Abstract: A high quality oxide layer has been formed on a GaN surface by a method that involves preparation of the GaN such that the surface is essentially atomically clean and essentially atomically ordered, and that further involves exposing the surface to evaporant from a GGG (gallium gadolinium garnet) evaporation source. MOS structures comprising the GaN/oxide combination have shown low leakage current, as well as charge accumulation and depletion.

Abstract: A method for efficiently generating thermal positions from a source of energetic positrons, consisting of a method for increasing the emission efficiency of the positron source, and a method for increasing the efficiency of a positron moderator. In an advantageous case the combined improvements lead to an about ten-fold increase in generated thermal positrons. The method for improving the source efficiency consists in reducing the self-absorption of positrons, typically emitted from radioactive atoms incorporated into a substrate by means of diffusion, by the source. This is accomplished by providing for a backing layer having a relatively small diffusion constant for the radioactive species, and a thin diffusion layer having a relatively large such diffusion constant, with the diffusion layer deposited onto the backing layer.