Characterization for vision science applications of a bimorph deformable mirror using phase-shifting interferometry

Abstract

The wave front corrector is one of the three key elements in adaptive optics, along with the wave front sensor and the control computer. Low cost, compact deformable mirrors are increasingly available. We have tested the AOptix bimorph deformable mirror, originally developed for ultra-high bandwidth laser communication systems, to determine its suitability for vision science applications, where cornea and lens introduce optical aberrations. Measurements of the dynamic response of the mirror to a step input were obtained using a commercial Laser Doppler Vibrometer (LDV). A computer-controlled Twyman-Green interferometer was constructed to allow the surface height of the deformable mirror to be measured using Phase-Shifting Interferometry as a function of various control voltages. A simple open-loop control method was used to compute the control voltages required to generate aberration mode shapes described by the Zernike polynomials. Using this method, the ability of the deformable mirror to generate each mode shape was characterized by measuring the maximum amplitude and RMS error of each Zernike mode shape up to the fifth radial order. The maximum deformation amplitude was found to diminish with the square of the radial order of the Zernike mode, with a measured deformation of 8 microns and 1.5 microns achieved at the second-order and fifth-order Zernike modes, respectively. This deformation amplitude appears to be sufficient to allow the mirror to correct for aberrations up to the fifth order in the human eye.

Characterization of a bimorph deformable mirror using stroboscopic phase-shifting interferometry

“…We have tested three bimorph DMs manufactured by AOptix (Campbell, CA), each having similar characteristics with the exception of small manufacturing differences [9,10]. One of these units has been successfully employed in an AO system for in vivo retinal imaging [11].…”

Bimorph deformable mirror: an appropriate wavefront corrector for retinal imaging?

“…It is also interesting to compare our data with the ones obtained by our earlier open-loop characterization method (cf. Figure 13) [5]. Although we find general agreement between the open-loop data and the results produced by our closed-loop system, there is some difference between the amplitudes achieved for individual Zernike modes.…”

“…We have previously characterized this device with "open-loop" control [5]; here, we describe its performance in "closed-loop" control mode. The latter reflects the intended application in AO imaging and also permits an analysis of controller optimization.…”

Optical Characterization of a Bimorph Deformable Mirror

“…The use of a similar instrument for dynamic characterization of millimeter-sized MEMS devices was first described by Hart, et al [13]. A previous incarnation of this instrument employed continuous-wave illumination, allowing static surface profiles to be measured [5]. A typical surface profile measurement of the DM obtained using this instrument is displayed in Figure 4 The interferometer was outfitted with a pulsed diode laser to allow the DM surface profile to be measured in response to time-varying voltage inputs.…”

“…We described an open-loop method for characterizing the static deformation characteristics of this DM in an earlier publication [5], and demonstrated the ability of this DM to reproduce aberrations described by the Zernike polynomials up to the 5 th order. Dalimier and Dainty [6] recently compared this DM and two others, demonstrating the ability of the three DMs to correct for the aberrations found in a typical human eye.…”