Design of phase-shifting algorithms by fine-tuning spectral shaping

Area of Science:

• Optical Metrology
• Interferometry
• Signal Processing

Background:

• Phase Shifting Interferometry (PSI) relies on Phase Shifting Algorithms (PSAs) to estimate modulating wavefronts from interferometric measurements.
• Traditional PSAs, like the Schwider-Hariharan (SH-PSA), were developed to mitigate specific errors such as detuning.
• Existing PSAs aim to reduce various data error sources affecting demodulated phase accuracy.

Purpose of the Study:

• To propose a novel technique for designing PSAs.
• To leverage the Frequency Transfer Function (FTF) for PSA design.
• To fine-tune spectral zeroes of PSAs to match a target FTF spectrum.

Main Methods:

• Utilizing the Frequency Transfer Function (FTF) as a design tool for PSAs, a practice gaining traction from Electrical Engineering.
• Developing a technique to adjust (tune) the spectral zeroes of a PSA.
• Monitoring changes in the FTF magnitude plot as spectral zeroes are tuned.

Main Results:

• A new PSA design methodology based on spectral zero tuning is presented.
• The proposed method allows for the approximation of a template FTF spectrum.
• The tuning process provides a way to systematically improve PSA performance by observing FTF magnitude changes.

Conclusions:

• The spectral zero tuning technique offers a promising approach for designing improved PSAs.
• This method facilitates the creation of PSAs with tailored Frequency Transfer Functions.
• The FTF magnitude serves as a critical indicator for guiding the PSA design process.