Considerations for tolerancing aspheric optical components

Area of Science:

• Optical Engineering
• Metrology
• Aspheric Optics

Background:

• Optical designs commonly include surface form and centering tolerances for aspheric surfaces.
• Unlike spherical surfaces, form and centering errors are intrinsically coupled for aspheric surfaces.
• Existing standards lack clear definitions for interpreting these tolerances, especially for aspheric surfaces with form errors.

Purpose of the Study:

• To analyze the compatibility of form and centering tolerances for aspheric surfaces using the best-fit surface position definition.
• To identify problems associated with the best-fit surface position method for aspheric optics.
• To propose and evaluate alternative definitions for aspheric surface position.

Main Methods:

• Analysis of the coupling between form and centering errors in aspheric surfaces.
• Investigation of the best-fit surface position definition and its sensitivity to power error and form errors.
• Development and consideration of alternative surface position definitions.

Main Results:

• The best-fit surface position definition is sensitive to power error and form errors, particularly when the aspheric departure derivative is small.
• Conditions for compatibility between form and centering tolerances under the best-fit definition were analyzed.
• Alternative definitions were proposed to overcome the limitations of the best-fit approach.

Conclusions:

• Current methods for defining aspheric surface position have limitations that impact optical design and metrology.
• Proposed alternative definitions offer more robust interpretations of surface position for aspheric optics.
• Revised definitions are crucial for accurate tolerancing and manufacturing of aspheric components.