CeFO Publications

@article{bauer_afocal_2024,

title = {Multiconfiguration afocal freeform telescopes},

author = {A. Bauer and C. Zhang and Y. Liu and J.P. Rolland},

doi = {https://doi.org/10.1364/OE.516961},

year  = {2024},

date = {2024-02-12},

urldate = {2024-02-12},

journal = {Optics Express},

volume = {32},

issue = {4},

pages = {6154-6167},

abstract = {An approach to designing multiconfiguration afocal telescopes is developed and demonstrated. Freeform surfaces are used to maximize the achievable diffraction-limited zoom ratio while staying in a compact volume for a two-position multiconfiguration afocal optical system. The limitations of these systems with three-mirror beam paths are discussed and subsequently overcome by introducing an additional degree of freedom. In a four-mirror beam path system, the goal of a 5x zoom ratio is achieved with a compensated exit pupil and diffraction-limited performance. A significant benefit in optical performance when using freeform surfaces is shown compared to more conventional surface types.},

keywords = {CeFO, CeFO design},

pubstate = {published},

tppubtype = {article}

}

@article{Moein2021-2,

title = {Freeform optics for variable extended depth of field imaging },

author = {S. Moein and T. J. Suleski},

url = {https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-24-40524&id=464994},

year  = {2021},

date = {2021-11-19},

urldate = {2021-11-19},

journal = {Optics Express},

volume = {29},

number = {24},

pages = {40524-40537},

abstract = {Imaging depth of field is shallow in applications with high magnification and high numerical aperture, such as microscopy, resulting in images with in- and out-of-focus regions. Therefore, methods to extend depth of field are of particular interest. Researchers have previously shown the advantages of using freeform components to extend depth of field, with each optical system requiring a specially designed phase plate. In this paper we present a method to enable extended depth-of-field imaging for a range of numerical apertures using freeform phase plates to create variable cubic wavefronts. The concept is similar to an Alvarez lens which creates variable spherical wavefronts through the relative translation of two transmissive elements with XY polynomial surfaces. We discuss design and optimization methods to enable extended depth of field for lenses with different numerical aperture values by considering through-focus variation of the point spread function and compare on- and off-axis performance through multiple metrics.},

keywords = {CeFO, CeFO design, imaging},

pubstate = {published},

tppubtype = {article}

}

@article{liu_cubesat_21,

title = {Freeform hyperspectral imager design in a CubeSat format},

author = {Y. Liu and A. Bauer and J. P. Rolland},

doi = {https://doi.org/10.1364/OE.439530},

year  = {2021},

date = {2021-10-25},

journal = {Optics Express},

volume = {29},

issue = {22},

pages = {35915-35928},

abstract = {A freeform pushbroom hyperspectral imager design was investigated as a combination of a freeform reflective triplet imager and a freeform reflective triplet spectrometer used in double-pass. The design operates at about F/2 with a 15-degree cross-track field-of-view and a 30 mm entrance pupil diameter. The design process led to achieving a small volume of less than 2 liters that fits comfortably within a 3U CubeSat geometry, exemplifying the compactness of this hyperspectral imager. We report the freeform sag departures and maximum slopes of the freeform surfaces, as well as the manufacturing tolerances together with an evaluation of the system stray light, all of which highlight the feasibility of a design in this class to be manufactured. This design uniquely positions itself on the landscape of compact hyperspectral imagers.},

keywords = {CeFO, CeFO design},

pubstate = {published},

tppubtype = {article}

}

@article{bauer_21,

title = {Roadmap for the unobscured three-mirror freeform design space},

author = {Aaron Bauer and Jannick P. Rolland},

doi = {https://doi.org/10.1364/OE.433643},

year  = {2021},

date = {2021-08-03},

urldate = {2021-08-03},

journal = {Optics Express},

volume = {29},

number = {17},

pages = {26736-26744},

abstract = {In rotationally symmetric lens design, there are rule-of-thumb boundaries on field-of-view and aperture for well-known design forms that provide valuable information to the designer prior to starting a design. In the design space of unobscured three-mirror imagers, freeform optics have been shown to provide a significant benefit over conventional surface shapes, but the degree to which they improve the performance for any given combination of field-of-view, entrance pupil diameter, and F-number remains unknown. Thus, designers of these systems are not afforded any pre-design information to inform their specification decisions. Here, we designed over 200 systems to establish a first-of-its-kind roadmap of specification ranges over which an unobscured three-mirror imager using freeform surfaces can achieve diffraction-limited performance in the visible spectrum. The scalability of the findings to the infrared regions of the spectrum is also addressed.},

keywords = {CeFO, CeFO design},

pubstate = {published},

tppubtype = {article}

}

@article{Shadalou2021_3,

title = {Tunable illumination for LED-based systems using refractive freeform arrays},

author = {Shohreh Shadalou and William J. Cassarly and Thomas J. Suleski},

url = {https://doi.org/10.1364/OE.441304},

doi = {10.1364/OE.441304},

year  = {2021},

date = {2021-00-00},

urldate = {2021-00-00},

journal = {Optics Express},

volume = {29},

number = {22},

pages = {35755-35764},

abstract = {Tunable illumination with high uniformity can improve functionality for multiple application areas. In lighting applications, dynamic illumination has been achieved by applying axial movement to the source(s) or other optical elements, resulting in poor uniformity, or using a liquid lens that adds design complexity. Advances in high-precision manufacturing methods have facilitated the practical implementation of freeform optical components, enabling new design approaches for illumination systems. This paper explores the use of arrays of varifocal transmissive freeform Alvarez lenses for an LED-based illumination system. The design is initialized using paraxial geometrical optics concepts and then refined for a 1mm-by−1 mm white LED source through a multi-step optimization. Design procedures are discussed, and simulation results are presented for an example illumination system that varies from a small circular spot mode to a large square uniform flood mode through millimeter-scale lateral translation between the Alvarez lens arrays.},

keywords = {CeFO, CeFO design, freeform, Illumination},

pubstate = {published},

tppubtype = {article}

}

@article{takaki2020,

title = {Off-axis conics as base surfaces for freeform optics enable null testability},

author = {N. Takaki and J. C. Papa and A. Bauer and J. P. Rolland},

doi = {https://doi.org/10.1364/OE.389426},

year  = {2020},

date = {2020-04-13},

journal = {Optics Express},

volume = {28},

number = {8},

pages = {10859-10872},

abstract = {When conducting interferometric tests of freeform optical surfaces, additional optical components, such as computer-generated holograms or deformable mirrors, are often necessary to achieve a null or quasi-null. These additional optical components increase both the cost and the difficulty of interferometric tests of freeform optical surfaces. In this paper, designs using off-axis segments of conics as base surfaces for freeforms are explored. These off-axis conics are more complex base surfaces than typically-used base spheres but remain null-testable. By leveraging off-axis conics in conjunction with additional orthogonal polynomial departures, designs were found with up to an order-of-magnitude of improvement in testability estimates relative to designs that use base spheres. Two design studies, a three-mirror telescope and a wide field-of-view four-mirror telescope, demonstrate the impact of using off-axis conics as the base surface.},

keywords = {CeFO, CeFO design},

pubstate = {published},

tppubtype = {article}

}

@article{Alonso2019b,

title = {Effects on the OTF of MSF structures with random variations},

author = {Kevin Liang; Miguel A. Alonso },

doi = {10.1364/OE.27.034665},

year  = {2019},

date = {2019-11-11},

urldate = {2019-11-11},

journal = {Optics Express},

volume = {27},

number = {24},

pages = {34665-34680},

abstract = {In diamond-machined freeform manufacturing processes, a tool-tip often leaves behind characteristic mid-spatial frequency (MSF) structures on the optical surface. Unwanted movement between the tool-tip and the part results in MSF structures with random variations. Here, we analyze the effects of these MSF structures on the system’s optical performance and derive simple analytic estimates for the optical transfer function in terms of the parameters of these structures. These expressions are expected to aid in MSF tolerancing.},

keywords = {CeFO design},

pubstate = {published},

tppubtype = {article}

}

@article{BauerARRI,

title = {All-reflective electronic viewfinder enable by freeform optics},

author = {A. Bauer and M. Pesch and J. Muschaweck and F. Leupelt and J. P. Rolland},

url = {https://doi.org/10.1364/OE.27.030597},

year  = {2019},

date = {2019-10-14},

journal = {Optics Express},

volume = {27},

number = {21},

pages = {30597-30605},

abstract = {Refractive eyepiece design forms are often limited by chromatic aberrations and require a mix of glass types to achieve sufficient correction, thus they are not conducive to manufacture in volume. Reflective surfaces are inherently achromatic and can be produced in volume, but rotationally symmetric reflective surfaces are either used with lossy obscurations or are incapable of correcting rotationally variant aberrations when used in an unobscured form. Freeform optics enable unobscured reflective design forms with excellent image quality. Here, we document the design, fabrication, and assembly of an all-reflective high-end electronic viewfinder that shows the applicability of freeform surfaces to eyepiece design forms.},

keywords = {CeFO design, CeFO related},

pubstate = {published},

tppubtype = {article}

}

@article{LIANG2019,

title = {Validity of the perturbation model for the propagation of MSF structure in 2D},

author = {Kevin Liang and G.W. Forbes and Miguel A. Alonso},

editor = {Optical Society of America},

url = {https://doi.org/10.1364/OE.27.003390},

doi = {10.1364/OE.27.003390},

year  = {2019},

date = {2019-02-04},

journal = {Optics Express},

volume = {27},

number = {3},

pages = {3390-3408},

abstract = {Assessment of the performance degradation caused by the mid-spatial frequency (MSF) structure on optical surfaces often relies on a perturbation method that dovetails with the familiar sequence of models based on geometrical and physical optics. In the case of imaging systems, the perturbative step yields estimates of wavefronts in the exit pupil which are, in turn, used to extract performance measures such as MTF, PSF, and Strehl ratio. To date, the validity of that perturbation appears to be poorly understood. We present methods to estimate the errors of this approach and thereby arrive at a rule of thumb for its accuracy: the error is approximately equal to the RMS of the MSF structure at its source multiplied by the square of the ratio between a particular Fresnel zone size and a characteristic length of the MSF structure.},

keywords = {CeFO, CeFO design, CeFO manufacturing},

pubstate = {published},

tppubtype = {article}

}

@article{Takaki_degen,

title = {Degeneracy in freeform surfaces described with orthogonal polynomials},

author = {N. Takaki and A. Bauer and J. P. Rolland},

url = {https://doi.org/10.1364/AO.57.010348},

doi = {10.1364/AO.57.010348},

year  = {2018},

date = {2018-12-10},

journal = {Applied Optics},

volume = {57},

number = {35},

pages = {10348-10354},

abstract = {Orthogonal polynomials offer useful mathematical properties for describing freeform optical surfaces. Their advantages are best leveraged by understanding the interactions between variables such as tip and tilt, base sphere and conic variables, and packaging variables that define the problem of design for manufacture. These interactions can cause degeneracy, which can complicate the interpretation of design specifications in manufacturing and, consequently, negatively impact the cost of fabrication and assembly. Optimization constraints to break degeneracy during design are also discussed.},

keywords = {CeFO, CeFO design},

pubstate = {published},

tppubtype = {article}

}