Design method of freeform off-axis reflective imaging systems with a direct construction process.

Area of Science:

• Optical Engineering
• System Design
• Infrared Optics

Background:

• Designing unobscured, off-axis reflective imaging systems presents significant challenges.
• Traditional methods often require complex optimization or result in obscurations.
• Freeform optics offer potential for compact and high-performance designs but require advanced design methodologies.

Purpose of the Study:

• To propose a novel method for designing freeform off-axis reflective imaging systems.
• To develop a special algorithm for calculating freeform surface data points.
• To demonstrate the effectiveness of the method through a high-performance LWIR system design.

Main Methods:

• A novel algorithm calculates data points on unknown freeform surfaces using rays from multiple fields and pupil coordinates.
• These points are used to construct three-dimensional freeform surfaces for imaging systems.
• The method directly yields an unobscured design, suitable as a starting point for optimization.

Main Results:

• A freeform off-axis three-mirror imaging system was designed using the proposed method.
• The system achieved high performance with an F/1.49 aperture and 64mm entrance pupil diameter.
• The system demonstrated an 8° × 9° field-of-view (FOV) and diffraction-limited performance in the long-wavelength-infrared (LWIR) spectrum.

Conclusions:

• The proposed method enables the direct design of unobscured freeform off-axis reflective imaging systems.
• The technique provides a robust starting point for further optical system optimization.
• The successful design of an LWIR system validates the method's capability for high-performance imaging applications.