Imaging freeform optical systems designed with NURBS surfaces

The designs of two imaging freeform systems using nonuniform rational basis-spline (NURBS) optical surfaces are described. The first system, a 10  deg×9  degf/2 three-mirror anastigmat has four times higher spatial resolution over the image plane compared with the equivalent conventional rotational aspheric design, and 2.5 times higher resolution compared with a 10th-order XY polynomial freeform design. The mirrors for the NURBS freeform design have more than twice the asphericity than the conventional rotational and XY polynomial designs. In the second system, a Ritchey–Chretien telescope followed by a two-mirror NURBS freeform corrector is compared to a four-mirror Korsch telescope, for imaging to a visible-infrared imaging spectrometer. The freeform corrector design had 70% smaller spot sizes over the field and eliminated the large tertiary required in Korsch type design. Both of these NURBS freeform designs are possible due to a custom optical design code for fast accurate NURBS optimization, which now has parallel raytracing for thousands of NURBS grid points.United States. Air Force (Contracts FA8721-05-C-0002 and FA8702-15-D-0001

A multifunctional structures approach for deployable in-space optomechanics

Thesis (Ph. D.)--University of Rochester. Department of Mechanical Engineering, 2018The DISCIT (Deployable In-Space Coherent Imaging Telescope) research effort at MIT LL (MIT Lincoln Laboratory) seeks to develop a 0.7 m diameter deployable sparse-aperture primary-mirror telescope that leverages advances in HSC (high strain composite) deployable structures and piezoelectric actuation technologies. A system such as DISCIT could provide affordable, high-resolution, persistent space-based imaging in a low-SWaP (size, weight, and power) design over existing technologies. A key challenge with deploying a sparsely filled primary in an imaging telescope is the precision required to collocate the mirror segments relative to the other optical components. DISCIT addresses this in two ways: (1) the primary mirror segments are deployed and coarsely positioned using flexible HSC hinges to achieve better than 2.5 m piston and axial positional repeatability and 20 rad pitch and roll angular repeatability, and (2) the mirror segments are then phased using piezoelectric actuation stages mounted beneath each mirror to accomplish the final precision alignment of the optical system. Therefore, the HSC hinges only need positional and angular repeatability within the capture range of the piezoelectric actuation stages. The research presented within this dissertation expands upon the underlying DISCIT architecture of HSC hinges by integrating piezoelectric patch actuators with the structure itself to induce in-plane strains for post-deployment shape correction, creating a multifunctional structure for deployable in-space optomechanics. An outline of multifunctional and deployable structures is first presented, providing an overview of deployables for in-space applications and the techniques traditionally used. A look at how DISCIT implements HSCs for precision deployables follows and the novel, active HSC hinge with integrated actuation is introduced. Both simulation and experimental testing were used to design the active HSC hinge, starting with mechanical testing of the composite material for developing a finite element model and an experimental assessment of two piezoelectric patch actuator types after bending to validate their appositeness for HSC actuation. The development and validation of the finite element model is described along with a custom algorithm that was written for selectively placing the actuators to control specific degrees of freedom for precision optical alignment. Experimental testing and results are presented which examine the deployment precision of a HSC hinge without and with the piezoelectric actuators, and additionally characterizes the actuation performance and compares with the aforementioned finite element model. To achieve precision optical alignment a preliminary closed loop controller is demonstrated for a single degree of freedom on the active HSC hinge. A summary of accomplishments, results, and a discussion of future work concludes this dissertation

Imaging freeform optical systems designed with NURBS surfaces

The designs of two imaging freeform systems using nonuniform rational basis-spline (NURBS) optical surfaces are described. The first system, a 10  deg×9  degf/2 three-mirror anastigmat has four times higher spatial resolution over the image plane compared with the equivalent conventional rotational aspheric design, and 2.5 times higher resolution compared with a 10th-order XY polynomial freeform design. The mirrors for the NURBS freeform design have more than twice the asphericity than the conventional rotational and XY polynomial designs. In the second system, a Ritchey–Chretien telescope followed by a two-mirror NURBS freeform corrector is compared to a four-mirror Korsch telescope, for imaging to a visible-infrared imaging spectrometer. The freeform corrector design had 70% smaller spot sizes over the field and eliminated the large tertiary required in Korsch type design. Both of these NURBS freeform designs are possible due to a custom optical design code for fast accurate NURBS optimization, which now has parallel raytracing for thousands of NURBS grid points.United States. Air Force (Contracts FA8721-05-C-0002 and FA8702-15-D-0001