Experimental demonstration of scene-based cophasing in optical synthetic aperture imaging using the SPGD algorithm.

Area of Science:

• Optical astronomy
• Spaceborne imaging systems
• Adaptive optics

Background:

• Large-aperture telescopes require precise alignment of sub-apertures for high-resolution imaging.
• Cophasing methods, particularly for piston-tip-tilt error, are crucial for synthetic aperture imaging.
• Existing methods often rely on models or lack simultaneous multi-aperture correction.

Purpose of the Study:

• To propose and demonstrate a scene-based cophasing technique for synthetic aperture imaging.
• To address the challenge of simultaneous piston-tip-tilt correction across multiple sub-apertures.
• To evaluate the performance of the stochastic parallel gradient descent (SPGD) algorithm in a model-less cophasing scenario.

Main Methods:

• Development of a tabletop synthetic aperture imaging system with 37 sub-apertures.
• Implementation of the stochastic parallel gradient descent (SPGD) algorithm for scene-based cophasing.
• Simultaneous optimization of 111 actuators for piston-tip-tilt control using extended scenes (static and dynamic).

Main Results:

• Successful reduction of piston-tip-tilt errors in all experimental measurements.
• Significant improvement in image sharpness was observed.
• Demonstrated model-less cophasing capability using extended scenes.

Conclusions:

• The proposed scene-based SPGD cophasing technique effectively improves image quality in synthetic aperture imaging.
• The method shows promise for high-resolution spaceborne Earth observation.
• Scene dynamics influence the correction rate, highlighting an area for future research.