US Patent 7352512 Compact self-compensating beam splitter apparatus and method of using

In accordance with an embodiment of the present invention, an optical system includes two tilted planar elements each having two surfaces for which the sign of the slopes of at least three of the four surfaces that an incident beam encounters are the same and which, when inserted into the path of the incident beam produces an output beam having no angular deviation and essentially no lateral deviation from the incident beam path.