Jong-hyeon Chang

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.

Microelectrofluidic iris for variable aperture

This paper presents a variable aperture design based on the microelectrofluidic technology which integrates electrowetting and microfluidics. The proposed microelectrofluidic iris (MEFI) consists of two immiscible fluids and two connected surface channels formed by three transparent plates and two spacers between them. In the initial state, the confined aqueous ring makes two fluidic interfaces, on which the Laplace pressure is same, in the hydrophobic surface channels. When a certain voltage is applied between the dielectric-coated control electrode beneath the three-phase contact line (TCL) and the reference electrode for grounding the aqueous, the contact angle changes on the activated control electrode. At high voltage over the threshold, the induced positive pressure difference makes the TCLs on the 1st channel advance to the center and the aperture narrow. If there is no potential difference between the control and reference electrodes, the pressure difference becomes negative. It makes the TCLs on the 1st channel recede and the aperture widen to the initial state. It is expected that the proposed MEFI is able to be widely used because of its fast response, circular aperture, digital operation, high aperture ratio, and possibility to be miniaturized for variable aperture.

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.

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.

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.

Four zoom lens design for 3D laparoscope by using liquid lens

Laparoscopic lens module that is capable of zooming is presented. The lens module has a high magnification and a high resolution such as four zoom and 2M pixels full HD image. The lens module consists of two lens sets to get 3-D images. Each lens module has several lenses less than conventional laparoscope but has 8 lenses and two liquid lenses. The total length of module is 19 mm long and the diameter is less than 5 mm. The separated distance of two lens center is 5 mm and two lens modules are inserted into the 11mm diameter laparoscope. The lens module is designed by Code V™ by using the 2M pixels CMOS sensor that the pixel size is 1.75 μm. The merit of this fluidic lens design is being convertible between a convex and concave shape. The effective focal length of zoom-out and zoom-in modes is 3.24 mm and 12.94 mm respectively. The modulation transfer function of zoom-out and zoom-in modes is 40% and 30% at 140 lp/mm frequency. We have a diffraction of element at near stop to improve image resolution. Also the resolution of zoom-in mode is improved by using liquid iris. The F-number of a two modes is 4.4 and 5.8 and the optical distortion is 10% and 0.5%. It is expected that the z-direction resolution by this laparoscope is less than 2 mm

A tunable optical IRIS based on electromagnetic actuation for a high-performance mini/micro camera

This paper presents a tunable iris based on electromagnetic actuation for a tiny high-performance camera in mobile devices such as smart phones and pads. To investigate the effect of a magnetic field on a ferrofluid, the contact angle modification and transportation of a sessile ferrofluid droplet are tested using a neodymium magnet and electric coil. The variation of the contact angle of the ferrofluid droplet is 21.3° for the neodymium magnet and 18.1° for the electric coil based on electromagnetic induction. And the transportation of the ferrofluid droplet is also demonstrated using the neodymium magnet and electric coil. As the concept proof, the pretest of a tunable iris operated by electromagnetic actuation is conducted by using a hollow cylinder cell. In the initial state, the ferrofluid is in the relax state, so the cylinder cell shows the largest aperture (4.06 mm). When an electrical current is applied to an electric coil wound around the outside of the cylinder cell, the ferrofluid initially placed in the hydrophobic sidewall inside the cylinder cell is actuated and pulled to the center. The aperture under the current is modified from 4.06 mm at 0 A to 3.2 mm at 2 A. Finally, the envisioned tunable iris consisted of two connected circular microchannels is realized using a MEMS technology. The iris size is 9×9×2 mm3, and the variation of the aperture diameter is from 1.72 mm at 0 A to 1.09 mm at 2.6 A.

Microelectrofluidic lens for variable curvature

This paper presents a tunable liquid lens based on microelectrofluidic technology which integrates electrowetting and microfluidics. In the novel 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. The previous electrowetting lens in which the contact angle changes at the side wall has a certain limitation of the curvature variation because of the contact angle saturation. Although the contact angle saturation also appears in the surface channel of the MEFL, the low surface channel increases the Laplace pressure and it makes the MEFL to have full variation of the optical power possible. The magnitude of the applied voltage determines the lens curvature in the analog mode MEFL as well as the electrowetting lens. Digital operation is also possible when the control electrodes of the MEFL are patterned to have an array. It is expected that the proposed MEFL is able to be widely used because of its full variation of the optical power without the use of oil and digital operation with fast response.

Optical probe design with extended depth-of-focus for optical coherence microscopy and optical coherence tomography

In this report, Optical probe system for modality, optical coherence tomography (OCT) and optical coherence microscope (OCM), is presented. In order to control the back focal length from 2.2 mm to 27 mm, optical probe is designed using two liquid lenses and several lenses. The narrow depth of focus (DOF) in microscope is extended by phase filter such as cubic filter. The filter is modified so that DOF is extended only In the OCM mode. The section for the extended DOF of probe is controlled by iris. Therefore in OCT mode, the phase filter does not affect on the DOF of lens. In OCM mode, the Gaussian light and modified light will affect the DOF. The probe dimension is less than 4 mm diameter and less than 60 mm long. The scan range of system is 0.88 mm wide, 1 mm deep in the OCT and 510 μm wide, 1 mm deep in the OCM mode. The lens curvature and iris aperture are operated by digital microelectrofluidic lens and iris.

Design of an optical probe compatible for multimodal imaging

This study introduces a multimode compatible forward scanning optical probe which includes tunable iris and varifocal lens based on micro-electro-fluidics. Concept development and optical design is carried out for the optical probe. The result shows that it can be adaptively used as a multimodal imaging tool for both optical coherence tomography and microscopy. It also has been proved that an optical depth scanning with the designed probe can provide optical coherence tomography with high resolution without any mechanical movement of the optics.