Improvements for determining the modulation transfer function of charge-coupled devices by the speckle method

Area of Science:

• Optics and Photonics
• Image Sensors
• Metrology

Background:

• Accurate measurement of the modulation transfer function (MTF) is crucial for characterizing imaging systems.
• The speckle method is a common technique for MTF determination, but it is susceptible to uncertainties.
• Non-uniformities in the illumination field and charge-coupled device (CCD) response can introduce errors, especially at low spatial frequencies.

Purpose of the Study:

• To present and evaluate two novel corrections for the speckle method to minimize MTF uncertainty in CCD characterization.
• To address systematic errors in both low and high spatial frequency regions.
• To reduce experimental errors associated with CCD positioning.

Main Methods:

• Development of a low-spatial-frequency correction to attenuate power spectral density values caused by non-uniformities.
• Investigation of the impact of CCD-aperture distance on MTF in the high-spatial-frequency region.
• Proposal and validation of a simple correction for CCD positioning errors.

Main Results:

• The low-frequency correction effectively reduces errors from field and CCD response non-uniformities.
• In the high-frequency region, a 1 mm variation in CCD-aperture distance can lead to >10% root-mean-square error in MTF.
• The proposed CCD positioning correction reduces experimental error to 0.43%.

Conclusions:

• The developed corrections significantly enhance the reliability of MTF measurements using the speckle method for CCDs.
• Accurate control of CCD-aperture distance is critical for high-frequency MTF accuracy.
• The proposed methodology offers a practical solution for minimizing experimental uncertainties in MTF determination.