We present the use of a large stroke deformable membrane mirror for focus control over a range of 123 μm in a commercial confocal microscope at 0.5-0.64 NA. The MEMS mirror is much faster than lens or stage translation allowing synchronization to x-y scanning for agile control over the 3D shape of the surface that is scanned. We describe a novel, low-actuator-count MEMS mirror designed specifically for focus control in scanning laser microscopes and present images taken with the mirror deployed on an Olympus Fluoview FV300.
We present the use of a large-stroke deformable membrane mirror at 45° incidence to achieve a very compact optical
system capable of fast multi-layer focusing in an optical disc unit. The MEMS mirror replaces a lens translation
mechanism and liquid crystal compensator, resulting in a single optical element to control both focus depth and
compensation of attendant focus-dependent spherical aberration. We outline the membrane optical requirements in
terms of stroke and aberration compensation required for multi-layer focusing for current DVD and BD standards.
We demonstrate an adjustable range of at least 1.6 μm peak wavefront spherical aberration correction at a membrane
displacement of 7 μm, which should be sufficient capability for quadruple layer BDXL™ discs.
In this paper we describe a process for creating thin SU-8 2002 films between 1.5 μm and 3.0 μm thick that are hardbaked
and can withstand a release etch in either aqueous or plasma silicon etchants. Resulting films are characterized
using both wafer bow and membrane bulge tests to monitor in-plane stress and Young's modulus. We explore the
influence on final film stress of several process variables including hard bake temperature, exposure dose, film thickness,
and various temperature profiles. We observe resultant film stress in the range of 13.8 to 32 MPa, and Young's modulus
in the range of 2.1 to 5.2 GPa for free-standing membranes. Illustrative process recipes are described for both patterned
and un-patterned SU-8 2002 membrane devices.
SU8-2002 deformable membrane mirrors for primary focus control and compensation of focus-induced spherical
aberration have been fabricated using a surface micromachining process with dry etching of silicon in XeF<sub>2</sub>. This
process has a higher yield and realizes larger mirrors with a twofold improvement in stroke, relative to a wet release
etch process previously described. The use of 3 mm x 4.24 mm elliptical mirrors for 45° incidence focus control in
microscopy is described.
This paper describes deformable membrane mirrors designed for focus control and aberration compensation in vital
microscopy and shows microscope images obtained using these mirrors. The mirrors are metalized polymer membranes
ranging from 1-3 mm in diameter using the photo-cured epoxy SU-8 2002, constructed using a die-bonding process.
They are electrostatically actuated using three concentric electrodes to provide large displacement while minimizing
We have built 1 mm circular and 1 mm × 1.4 mm elliptical surface micro-machined SU-8 2002 deformable mirrors for
focus control. The SU-8 2002 membrane layers are 2.25 μm thick with gold as the reflective coating on their surfaces.
Three annular electrodes were used for electrostatic actuation. Stable deflection was observed up to 6.8 μm for a 1 mm ×
1.4 mm elliptical mirror with an air gap of 14 μm. The frequency response of the membrane exhibited a 3 dB frequency
larger than 10 kHz.
This paper describes a method to extend the range of motion of a deformable, continuous membrane mirror beyond the limit of open-loop electrostatic instability through feedback control. The feedback scheme employs capacitive sensing directly at the mirror actuation electrodes and is based on frequency modulation of a coupled ring oscillator using a differential measurement technique. Analysis of the system shows that the range of stable deflection depends on the relative dynamics of the device and the feedback control circuitry. Experimental results demonstrate stable closed-loop deflection of our silicon nitride membrane test device to 69% of the air gap and confirm the dependence of the maximum stable displacement on overall loop dynamics.
This paper describes a method to extend the range of motion of a deformable, continuous membrane mirror beyond the
limit of open-loop electrostatic instability through the use of a feedback control scheme. The feedback scheme is based
on capacitive sensing of the mirror. The sensing is achieved by coupling the actuation electrodes to a ring oscillator.
We use a differential technique, where the frequency of the coupled oscillator is compared to a reference ring oscillator.
Analysis of the system using a simplified parallel-plate model shows that the range of stable deflection depends on the
dynamics of the device and control circuitry, and suggests that stable full-gap displacement can be achieved under
certain conditions. Experimental results are provided, showing stable closed-loop deflection of our silicon nitride test
device to 61% of the air gap, consistent with the predictions of our model.