Focal length measurement of a microlens-array by grating shearing interferometry.

Area of Science:

• Optics and Photonics
• Interferometry
• Microlens Technology

Background:

• Accurate focal length measurement is crucial for microlens array (MLA) performance in optical systems.
• Existing methods can be complex or require specialized equipment.
• A need exists for a simple, accurate, and accessible focal length measurement technique for MLAs.

Purpose of the Study:

• To introduce a straightforward grating shearing interferometry technique for determining the focal length of microlens arrays (MLAs).
• To demonstrate the feasibility and accuracy of this novel measurement method.
• To analyze the measurement uncertainty and establish the achievable accuracy.

Main Methods:

• Utilizing grating shearing interferometry with a Ronchi grating and CCD sensor.
• Employing a He-Ne laser, condenser, and collimator to generate a plane wavefront.
• Transforming the plane wavefront to a spherical wavefront using the MLA and analyzing interference stripe patterns.

Main Results:

• Successfully measured the focal length of a microlens array (MLA) using the developed technique.
• Interference stripes were generated and detected by the CCD sensor by overlapping diffractive patterns.
• The focal length was determined by analyzing the period change of the interference stripes.

Conclusions:

• The developed grating shearing interferometry technique offers a simple and effective method for MLA focal length measurement.
• The experimental validation confirmed the feasibility of the technique, achieving a measurement accuracy of 2%.
• This method provides a valuable tool for optical metrology and the characterization of microlens arrays.