Abstract

An optical method is proposed for extending the focal depth of an imaging system. The theoretical analysis and experimental results illustrate that the focal depth can be significantly increased by using an encoded light source. In the conventional conclusion, the focal depth is only dependent on the N.A. of the imaging system, but we point out that it is also related to the degree of complex coherence at the object plane, which equals that of Fourier transformation of the intensity distribution of the light source. Therefore, as a kind of inverse source problem, the required focal depth could be achieved by designing a proper light source. As an example, a gratinglike source is used to demonstrate the exactness of the method we propose.

© 1991 Optical Society of America