Anti-aliasing phase reconstruction via a non-uniform phase-shifting technique

Area of Science:

• Optical metrology
• Signal processing

Background:

• Conventional phase-shifting techniques suffer from frequency aliasing and ripple artifacts due to insufficient phase shifts.
• Harmonics in fringe signals can alias with the fundamental frequency, degrading phase map accuracy.

Purpose of the Study:

• To present a novel anti-aliasing phase-measuring technique to suppress ripple-like artifacts.
• To enable accurate phase and harmonic coefficient estimation even with a limited number of fringe patterns.

Main Methods:

• Theoretical analysis of phase shifts and their greatest common divisor (GCD) to understand aliasing.
• Development of an iterative least-squares fitting procedure assuming identical harmonic characteristics across fringe patterns.
• Utilizing non-uniform phase shifts to minimize aliasing effects.

Main Results:

• The proposed method effectively separates high-order harmonics from as few as 4 fringe patterns.
• Significant suppression of ripple-like phase errors caused by frequency aliasing was demonstrated.
• Accurate estimation of fringe phases and harmonic coefficients was achieved.

Conclusions:

• The anti-aliasing technique overcomes the limitations of conventional methods by addressing frequency aliasing.
• This approach provides a robust solution for accurate phase measurement in optical metrology.
• The method is effective even with a small number of fringe patterns and non-uniform phase shifts.