Digital Holography as Computer Vision Position Sensor with an Extended Range of Working Distances.

Area of Science:

• Optics and Photonics
• Computer Vision
• Metrology

Background:

• Traditional computer vision methods face limitations in micro-scale applications due to finite depth-of-field and fixed working distances.
• Refractive imaging systems are constrained by the physical properties of lenses, restricting their operational range and resolution.
• Digital holography offers a lensless alternative, overcoming these inherent limitations of conventional imaging.

Purpose of the Study:

• To apply digital holography for artificial visual in-plane position sensing.
• To achieve an extra-large range-to-resolution ratio for displacement measurements.
• To extend the applicability of computer vision in scenarios with demanding working distances.

Main Methods:

• Utilizing digital holography, a lensless imaging technique that records and numerically reconstructs optical wavefronts.
• Employing a pseudoperiodic pattern on the object to enable subpixel resolution and a wide field-of-observation displacement range.
• Reconstructing the object numerically by backward propagation of the recorded wavefront, allowing arbitrary adjustment of object distance.

Main Results:

• Demonstrated an in-plane resolution of 50 nm in X and Y, and 0.002 degrees in rotation (theta).
• Achieved measurements over a working distance range exceeding 15 cm.
• Defined an operational workspace of 12x10x150 mm³ for the sensing system.

Conclusions:

• Digital holography significantly expands the application scope of computer vision, particularly for micro-scale measurements.
• The lensless nature of digital holography removes the depth-of-field and working distance constraints of refractive systems.
• This technique provides a powerful solution for high-resolution, long-range in-plane position sensing.