Laser-induced damage threshold (LIDT) is investigated at several wavelengths in the high-purity silica optical fiber. The finite element method (FEM) is used to study transmission mode, LIDT, temperature distribution, and thermal stress distribution of the fiber. Our results show that the center of the front surface is subjected to severe thermal effects under laser irradiation and consequently, and it is susceptible damage. The variations in temperature and thermal stress are identified as increasing with laser fluences, which show a similar tendency. When laser fluences surpass the LIDT, such as 35 GW / cm2, the temperature at the front surface center shows a sudden growth and the melting damage appears, and no stress damage occurs at this time. Notably, the melting effect of high purity fused silica optical fiber is simulated by numerical calculation based on ray optics for the first time. Our research can provide systematic FEM simulations for the LIDT of silica optical fibers.
The sensitive parameters affecting the dark current characteristics are further studied by using InAs/GaSb type II superlattice (T2SL) pBpp structure long wavelength Infrared photodetectors.Generation of recombination (G-R), surface leakage current and tunneling current are the main components of dark current. Using pBpp structure can suppress them effectively, thereby decreasing dark current. Based on the k ∙ p method, the band structure of InAs/GaSb T2SL and InAs/AlSb T2SL can be obtained by solving the 8-band k ∙ p model. We have calculated different doping levels of pBpp detector and different layer thicknesses of pBpp detector. For pBpp device, we consider the dark current for different contact layer doping and different absorber layer doping. We also study the influence of different contact layer thicknesses and different absorber layer thicknesses on dark current. The dark current of pBpp detector is dominant by tunneling current at low temperature, and diffusion is the main limiting mechanism in dark current at high temperature, for barrier layer inhibits generation-recombination contribution. Eventually, the dark current of a pBpp structure has been calculated for versus voltage at 77 K.
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