Variable aperture controlled by microelectrofluidic iris.

This Letter presents an adaptive liquid iris based on microelectrofluidic technology with experimental results. In the microelectrofluidic iris (MEFI), the electrostatic force generated by electrowetting in a surface channel unbalances the Laplace pressure acting on two fluidic interfaces between air and a light-absorbing liquid in two connected surface channels in a chamber. Then, the changed net pressure makes the iris aperture of the liquid diaphragm adjustable. The present MEFI was designed to have a tunable range from 4.2 to 0.85 mm in diameter and a tuning ratio of 80%. The MEFI was fabricated with a transparent electrode patterned on three glass plates and two channel spacers. Concerning the optical and interfacial properties of the MEFI for its operation, an aqueous near-infrared dye used in optical coherence tomography (OCT) was forced into a ring shape as the driving liquid in the hydrophobic chamber. By switching the segmented concentric control electrodes in steps, digital operation of the MEFI was successfully observed with clear aperture stops. The measured turnaround speed was 80 mm/s, which is significantly higher than that for other comparable adaptive liquid irises. Due to a scalable aperture range with fast response, the concept of MEFI is expected to be widely applied in various optical systems that require high-quality imaging, as well as in real-time diagnostic OCT.

Adaptive optical probe design for optical coherence tomography and microscopy using tunable optics.

We present a tunable, adaptive optical imaging probe for multimodal imaging such as optical coherence tomography and microscopy. The probe is compatible with forward-looking scanning laser imaging devices such as an endoscope. The lens configuration includes a tunable iris and two varifocal lenses, both driven by microelectrofluidics, as well as several conventional fixed focus lenses. The modulation transfer function and spot size in the focal plane is evaluated, and we show using optical simulations that there are three possible imaging modes with different transverse resolutions and focal depths.

Zoom lens design using liquid lens for laparoscope.

Traditional laparoscopic optical systems consisting of about 30 lenses have low optical magnification. To magnify tissue during surgical operations, one must change from one laparoscope to another or use a magnifying adapter between the laparoscope and the sensor. Our work focuses on how to change the sag of a liquid lens while zooming from 1 × zoom, to 2 × , and 4 × in an optical design for a laparoscope. The design includes several lenses and two liquid lenses with variable focal lengths. A pair of laparoscopes for 3-D stereoscopy is placed within a tube 11 mm in diameter. The predicted depth resolution of tissue is 0.5 mm without interpolation at 4 × zoom.

Varifocal liquid lens based on microelectrofluidic technology.

This Letter presents a tunable liquid lens based on microelectrofluidic technology. In the microelectrofluidic lens (MEFL), electrowetting in the hydrophobic surface channel induces the Laplace pressure difference between two fluidic interfaces on the lens aperture and the surface channel. Then, the pressure difference makes the lens curvature tunable. In spite of the contact angle saturation, the narrow surface channel increases the Laplace pressure to have a wide range of optical power variation in the MEFL. The magnitude of the applied voltage determines the lens curvature in the analog mode MEFL. Digital operation is also possible when the control electrodes of the MEFL are patterned to have an array. The lens aperture and maximum surface channel diameter were designed to 3.2 mm and 6.4 mm, respectively, with a channel height of 0.2 mm for an optical power range between +210 and -30 D. By switching the control electrodes, the averaged transit time in steps and turnaround time were as low as 2.4 ms and 16.5 ms, respectively, in good agreement with the simulation results. It is expected that the proposed MEFL may be widely used with advantages of wide variation of the optical power with fast and precise controllability in a digital manner.

Varifocal liquid-filled microlens operated by an electroactive polymer actuator.

We designed, fabricated, and characterized varifocal microlenses, whose focal length varies along with the deformation of a transparent elastomer membrane under hydraulic pressure tailored by electroactive polymer actuators. The microfluidic channel of the microlens was designed to be embedded between silicon and glass so that transient fluctuation of the optical fluid and elastomer membrane is effectively suppressed, and thus the microlens is optically stabilized in a reduced time. Multilayered poly(vinylidene fluoride-trifluoroethylene-clorotrifluoroethylene) actuators were also developed and integrated onto the microfluidic chambers. We demonstrated that the developed microlenses are suitable for use in microimaging systems to make their foci tunable.