An integrated tunable microlens, whose focal length may be varied over a range of 3 to 15 mm with total power consumption below 250 mW, is presented. Using thermo-pneumatic actuation, this adaptive optical microsystem is completely integrated and requires no external pressure controllers for operation. The lens system consists of a liquid-filled cavity bounded by a distensible polydimethyl-siloxane membrane and a separate thermal cavity with actuation and sensing elements, all fabricated using silicon, glass and polymers. Due to the physical separation of thermal actuators and lens body, temperature gradients in the lens optical aperture were below 4 °C in the vertical and 0.2 °C in the lateral directions. Optical characterization showed that the cutoff frequency of the optical transfer function, using a reference contrast of 0.2, varied from 30 lines/mm to 65 lines/mm over the tuning range, and a change in the numerical aperture from 0.067 to 0.333. Stable control of the focal length over a long time period using a simple electronic stabilization circuit was demonstrated.

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International audienceThe design, fabrication, and integration of microoptical components for beam focus and steering are demonstrated in an endoscopic optical coherence tomography (OCT) system. The relevant components, a membrane-based microfluidic tunable microlens and an electrostatic 2-D scanning micromirror, are fabricated using silicon and polymer-based microelectromechanical system technologies. All components are assembled inside a 4.5 mu m diameter probe. The design of the optical system, including substantiation of the need for focal length tunability, is presented, along with performance data of an OCT system using these components. A lateral resolution of about 13 mu is achieved, an improvement over fixed-focal length probes. Due to the miniaturization of the measurement head achievable using this optical microsystem, use in conventional endoscopes is possible

We present an efficient, low-cost modulation transfer function (MTF) measurement approach, optimized for characterization of tunable micro-lenses; the MTF may easily be measured at a variety of different focal lengths. The approach uses a conventional optical microscope with an optimized approach for lens illumination and the measurement results have been correlated with a commercial MTF measurement system. Measurements on fixed-focus and tunable micro-lenses were performed; for the latter, resolution for lenses with back focal length of 11 mm was 55 lines/mm, decreasing to 40 lines/mm for a back focal length of 4 mm. In general, it was seen that performance was better for lenses with longer focal lengths.

International audienceNumerous optical imaging techniques have been developed for clinical diagnostics; among these, optical coherence tomography (OCT) has proven to be of considerable utility due to its ability to non-destructively image below the surface of tissue. Endoscopic OCT systems will further extend the capabilities of this approach but require an additional means for scanning in two or three dimensions. We present an integrated optical microsystem which allows scanning of an optical beam in three dimensions (an area scan combined with dynamic focus) suitable for an endoscopic OCT probe. The system is defined by a tunable pneumatically-actuated micro-lens combined with an electrostatically-actuated two-axis micro-mirror, allowing functionality hitherto not achievable