Sensing fabrication errors in diffraction gratings using high dynamic range imaging.

Area of Science:

• Optics and Photonics
• Materials Science
• Metrology

Background:

• Diffraction gratings are crucial optical components with stringent quality requirements.
• Detecting subtle fabrication errors is essential for grating performance.
• Existing microscopic techniques have limitations in identifying certain types of defects.

Purpose of the Study:

• To design and demonstrate a simple, cost-effective instrument for identifying and characterizing fabrication errors in diffraction gratings.
• To achieve high dynamic range detection of scattered light from gratings.
• To overcome limitations of traditional microscopic inspection methods.

Main Methods:

• Utilized an uncooled charge-coupled device (CCD) camera for light detection.
• Employed a high dynamic range imaging process to analyze scattered light.
• Focused on detecting light in the focal plane of a lens positioned relative to the grating under test.

Main Results:

• The instrument achieved a dynamic range of approximately nine orders of magnitude.
• Successfully identified small, periodic fabrication errors in test diffraction gratings.
• Demonstrated superior sensitivity compared to conventional microscopic techniques for specific defect types.

Conclusions:

• The developed instrument offers a simple and effective solution for detecting fabrication errors in diffraction gratings.
• High dynamic range imaging with a CCD camera provides a powerful tool for grating metrology.
• This method enhances the ability to identify critical grating defects that impact optical performance.