Temporal decay of photon emission from avalanche photodiodes (APDs) is demonstrated. The steep rise of the reverse voltage can cause a higher probability of photon emission. For a silicon avalanche photodiode, the photon emission has a broad spectral distribution from 500 to 1100 nm with two peaks at 750 and 994 nm, respectively. The number of emitted photons increases by 44 Mcount/(s mA sr) as the APD's reverse current increases. This suggests that the reverse current, instead of the reverse voltage, applied to the APD is the main determinant of the photon emission. It is furthermore shown that the distribution of the photon emission is a super-Poisson distribution.
We numerically analyze and compare the mode and dispersion properties of three different microstructured optical fibers with the same square array of different-shaped air holes: rhombic, square, and circular. We use a full vectorial finite-difference method. The analysis shows that the properties of microstructured optical fibers depend on the hole area, hole shape, and wavelength to different extents. The effects of air hole shapes on the properties of microstructured optical fibers can be treated as the perturbations for sufficiently small air filling factors. For larger air filling factors the properties of microstructured optical fibers are clearly affected by the air hole shape. This dependence is useful for understanding the properties of microstructured optical fibers.