Rotation-, shift-, and magnification-insensitive periodic-pattern-defects optical detection system

The paper presents a new periodic-pattern-defects optical detection system using an omnidirectional bandpass spatial filter, which is insensitive to object shift, rotation, and magnification variations. The system is based on the spectral difference between periodic patterns and defects, and is designed to block the repetitive periodic regular pattern spectra and pass the defect information carrying spectra. A computer simulation shows that the minimum detectable defect size using this optical system is about one-twentieth that of the periodic pattern pitch; this system is characterized by its ability to detect defects at any location and rotation, and is insensitive to object magnification by the frequency domain operation characteristics.