US Patent 7366420 Optical transmission device

An optical transmission device for providing stable communication with a partner device by reducing errors in optical axis misalignment. Such errors are caused by uneven distribution of the light intensity in a received light beam resulting from atmospheric microscopic fluctuations. A cross pattern filter having at least two cross patterns is used at a partner transmission device side with respect to an incident direction detecting means, and arranged so that a cross pattern generated on the position detecting photodetector by the cross pattern filter and parting lines for dividing a position detecting photodetector do not overlap with each other, but intersect with each other.