Ultrathin cameras using annular folded optics

Abstract

We present a reflective multiple-fold approach to visible imaging for high-resolution, large aperture cameras of significantly reduced thickness. This approach allows for reduced bulk and weight compared with large high-quality camera systems and improved resolution and light collection compared with miniature conventional cameras. An analysis of the properties of multiple-fold imagers is presented along with the design, fabrication, and testing of an eightfold prototype camera. This demonstration camera has a 35 mm effective focal length, 0.7 NA, and 27 mm effective aperture folded into a 5 mm total thickness.

Design strategies to simplify and miniaturize imaging systems

“…If playing on the refractive index, the bending, and the position of the pupil is not sufficient to provide a good optical quality, the traditional approach consists of increasing the number of optical surfaces, which often leads to increasing the number of optical components. However, a method which increases the number of optical surfaces while using a single optical component has already been proposed: the design is based on a folded imaging system which reflects the optical path multiple times with concentric reflectors [18,19]. The limitation of such folded systems is that the field of view is narrowed as the number of reflective surfaces increases.…”

“…We can quote, for example, systems involving curved detectors [1], multichannel systems inspired by the compound eyes of insects [2][3][4][5][6][7], multichannel systems based on the TOMBO principle [8], lenseless imagery [9][10][11][12][13][14][15][16][17], and folded imaging systems [18,19]. Therefore, choosing the suitable system for a given application among all these concepts is often not obvious for an optical designer.…”

Ultrathin four-reflection imager

“…One method of significantly increasing focal length and magnification without a corresponding increase in track length consists of reflecting the optical path multiple times with concentric reflectors, thus constraining the optical propagation to occur within a thin optical element. This concept is based on an extension of traditional reflective telescope design [1,2] with additional reflectors to minimize track length and an enlarged diameter to maintain light collection [3].…”

“…These challenges can be met by (1) the use of multiple aspheric reflectors optimized to correct the aberrations caused by the geometry, (2) an enlarged diameter to allow multiple concentric reflections, improve light collection, and offset the diffraction effects caused by the annular aperture, and (3) self-alignment of multiple surfaces through use of single-point diamond turning (SPDT) to fabricate concentric annular aspheric reflectors with minimal rechucking. An eight-reflection imager was previously demonstrated experimentally in [3] by diamond turning a single side of a calcium fluoride (CaF 2 ) lens blank and coating the substrate with patterned silver reflectors. The eight-reflection imager of [3] achieved an effective focal length (EFL) of 35 mm in a physical track of just 5 mm, providing a well-corrected image over a field of view (FOV) of 6:67°.…”

“…An eight-reflection imager was previously demonstrated experimentally in [3] by diamond turning a single side of a calcium fluoride (CaF 2 ) lens blank and coating the substrate with patterned silver reflectors. The eight-reflection imager of [3] achieved an effective focal length (EFL) of 35 mm in a physical track of just 5 mm, providing a well-corrected image over a field of view (FOV) of 6:67°.…”