Projects - Folded Optical Systems

Annular aspheric mirror elements

Folded Optic technology provides a means for significantly reducing the length of a telescopic lens. The reduction is accomplished by relaying light back and forth between refective surfaces supporting diamond-turned concentric aspheric focal zones. Light enters through an annular aperture and is focused to a centered exit aperture. The number of folds designate the number of reflections: for example, a 4-fold imager has two reflections off each of the two surfaces. An N-fold lens is roughly 1/N the length of a conventional optic, making it an ideal solution for applications where size is a critical issue.

Infrared/Visible lens

The Folded Imager (also referred to as Origami Optics by UCSD) was invented at UCSD and developed with Distant Focus for the DARPA MONTAGE program. The original demonstrators include an eight-fold, a sectioned eight-fold, and a four-fold visible spectrum camera. They were fabricated from diamond-turned calcium fluoride. MITRE and Distant Focus extended the performance range of the optic into LWIR through a hollow-core configuration that uses gold-coated diamond-turned aluminum. The hollow-core configuration has proven to be the most versatile due to its multi-band potential and lower weight for longer focal lengths.

MONTAGE folded optics

Distant Focus’ Folded-Optic technology provides several advantages for long focal-length systems:

  • The compact folded system length is a fraction of that of a comparable traditional optic.
  • Systems can be substantially lighter than a similar conventional optic since it does not require use of heavy glass elements.
  • Fast, aspheric-based design supports high light collection and imaging performance.
  • A fully reflective folded optic is wavelength-independent allowing it to be integrated with multiple sensor types.
  • Folded optics allow stacking multiple cameras on a common axis due to the annular aperture thereby eliminating parallax.
  • Folded-optics can make use of cost efficient molding techniques for large fab quantities.

MONTAGE folded optics

The folded imager can be produced in either a hollow-core or solid-core design. Full annular and sectioned annular configurations are options. The spectral range is determined by the choice of reflection coatings. The obsuration of the annular aperture leads to softer contrast in the mid-frequency range which can be somewhat recovered through digital post-processing.

Distant Focus has licensed the folded optic technology from UCSD. Please contact us to discuss the design and fabrication of a Folded Optic to meet your application needs.

Table with specifications of some previous projects