We discuss a new simple InGaAs/InAlAs avalanche photodiode (APD) with a planar buried multiplication region. Some of the advantages compared to standard APDs are: 1. The thickness of the avalanche and the charge control regions are accurately controlled by molecular beam epitaxy (MBE) growth in contrast to the standard diffusion process; 2. InAlAs is the multiplication material (avalanching faster electrons) instead of InP (avalanching slower holes); 3. InAlAs avalanche gain has a lower noise figure than that for InP; 4. A guard ring is not required; 5. Fabrication is as simple as that for a p-i-n detector; 6. The APD has high wafer uniformity, and high reproducibility; 7. The InAlAs breakdown voltage is lower than InP, and its variation with temperature is three times lower than that for InP; 8. Excellent aging and reliability including Telcordia GR-468 qualification for die and modules; 9. High gain-bandwidth product as high as 150GHz; and 10.High long range (LR-2) bit error rate (BER) 10<sup>-12</sup> receiver sensitivity of -29.0dBm at 10Gb/s, -28.1dBm at 10.7Gb/s and -27.1dBm at 12.5Gbs.
A holographic technique ('light-in-flight' (LIF) holography) is described, which combines classic off-axis holography with the latest ultrashort-pulse laser technology to produce three-dimensional images with femtosecond temporal resolution. The LIF holography can be used to study the distortions of pulses moving through optical fibers (Abramson, 1987), visualize relativistic effects (Abramson, 1985), measure the shape and deformation of fast moving objects, and make observations through nonrigid scattering media (Spears et al., 1989). The technique can also be applied in ultrafast optical science, metrology, and medical imaging.
Electronic holography and speckle interferometry are combined with femtosecond gating techniques to form images of absorbing structures embedded in organic tissue. The method takes advantage of the inherent instability of living tissue.