The SPIE Spotlight eBook, shown and linked on the left, provides an overview of emerging varifocus technologies. Sarah Lukes' additional publications in active optics may be found h ere .

Publications and their relevant figures are separated into three main sections. The imaging demonstrations show images taken in a confocal microscope, wide-field microscope, and with an optical disc system. Deformable mirrors are used to perform focusing and zoom. Their surface shapes may be altered to correct both low and high order spherical aberration as discussed in the spherical aberration section below. The control system section has papers on a capacitive sensing control scheme for greater focusing of the mirrors.

Imaging Demos

confocal microscopy

Lukes, S. J. and Dickensheets, D.L. “Agile scanning using a MEMS focus control mirror in a commercial confocal microscope,” SPIE BiOS Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XXI, 89490W-89490W-11, (2014). (selected as Translational)

Fig. 11 compares image quality of Drosophila in a confocal microscope using the automated stage versus a deformable mirror for focusing over 120 micron range at 0.6 numerical aperture.
Fig. 12 shows oblique planes at different angles using a deformable mirror that is syncronized with the fast scan axis of a confocal microscope.
Fig. 13 shows that the surface shape of a deformable mirror can be optimized to correct spherical aberration. This improves contrast and brightness of a bee stinger, as well as improves the axial point spread function.

Lukes, S. J. and Dickensheets, D.L. "MEMS mirror for flexible z-axis control in a commercial confocal microscope," IEEE/LEOS Intl. Conf. on Optical MEMS and Nanophotonics, pp. 148-149, Banff, AB (2012).

Fig. 4 compares images of a spinal cord of a chick embryo both with z-stage translation and a deformable mirror for focusing over a 40 micron range.
Fig. 5 shows an oblique plane image of fungus with 55 micron depth using a deformable mirror for focusing.

Wide-field microscopy

Lukes, S. J. and Dickensheets, D. L. "SU-8 2002 surface micromachined deformable membrane mirrors," IEEE JMEMS, 22(1):94-106, 2013.

Fig. 11 shows USAF target images in a wide-field microscope. Fig. 11a shows 140 microns change in focus without any correction of spherical aberration. Fig. 11b shows the improved image quality when spherical aberration of the MEMS mirror is corrected with electronic control of its surface shape.

Lukes, S. J. and Dickensheets, D. L. "SU-8 focus control mirrors released by XeF2 dry etch," Conf. Proceedings in SPIE MOEMS and Miniaturized Systems X, 7930, 793006-6 (2011).

Fig. 8 shows images of a USAF target in a wide-field microscope.

Optical Discs

Lukes, S. J. and Dickensheets, D. L. "MEMS focus control and spherical aberration correction for multilayer optical discs," SPIE MOEMS and Miniaturized Systems XI, 82520L (2012).

Fig. 4 shows interferograms with correction of 1.6 micron single-pass spherical aberration on a defocus optical path difference of 10 micron with a 3-mm-diameter deformable mirror.

Spherical Aberration

Open access: Lukes, S. J., Downey, R., Kreitinger, S., and Dickensheets, D. L. "Four-zone varifocus mirrors with adaptive control of primary and higher-order spherical aberration," J. of Applied Optics., 55, 5208-5218, 2016.

Fig. 7 shows independent control of defocus and the range of primary, secondary, and tertiary spherical aberration that a 4-mm-diameter, circular-boundary deformable mirror can achieve.
Fig. 8a shows the spherical aberration capability of a 5-degree-incidence-angle, elliptical-boundary deformable mirror. Fig. 8b also shows the mirror's composite Zernike spectra.
Fig. 9 shows the spherical aberration capability of 10- and 45-degree-incidence-angle deformable mirrors.

Fig. 8 and Fig. 9 show improved point spread functions by balancing spherical aberration over 120 micron focal range in a 0.6 numerical aperture confocal microscope.
Fig. 6 shows surface shape with corresponding voltages and zernike coefficients of a 3-mm-diameter deformable mirror with 4 microns of displacement.

Lukes, S. J. and Dickensheets, D. L. "SU-8 2002 surface micromachined deformable membrane mirrors," IEEE JMEMS, 22(1):94-106, 2013.

Fig. 11b shows improved image quality of 228 line pairs/mm when spherical aberration of the MEMS mirror is corrected with electronic control of its surface shape.

Lukes, S. J. and Dickensheets, D. L. "MEMS focus control and spherical aberration correction for multilayer optical discs," SPIE MOEMS and Miniaturized Systems XI, 82520L (2012).

Fig. 5 shows surface profiles of a deformable mirror with different voltages applied and the corresponding defocus, primary spherical aberration, and secondary spherical aberration.
Fig. 6 shows spherical aberration and spherical aberration with balancing defocus added introduced to the optical system by the surface shape of the deformable mirror.
Fig. 4 shows interferograms with correction of 1.6 micron single-pass spherical aberration on a defocus optical path difference of 10 micron with a 3-mm-diameter deformable mirror.

Control System

Lukes, S. J., Himmer, P. A., Moog, E. J., Shaw, S. R., and Dickensheets, D. L. "Feedback-stabilized deformable membrane mirrors for focus control," J. of Micro/Nanolithography, MEMS, and MOEMS 8(4), 043040 (7 pp.), 2009.

Capacitive sensing scheme that improved the open-loop displacement from 43% of the air gap to a closed-loop displacement of 61% of the air gap for a deformable mirror.

Lukes, S. J., Lutzenberger, B. J., Dunbar, E., Shaw, S. R., and Dickensheets, D. L. "Variable-focus SU-8 membrane mirror with enhanced stroke using feedback control," IEEE/LEOS Intl. Conf. on Optical MEMs and Nanophotonics, pp. 141-142, Clearwater Beach, FL (2009).

Capacitive sensing scheme that improved the open-loop displacement from 49% of the air gap to a closed-loop displacement of 75% of the air gap for a deformable mirror.