Khaled Aljasem

Completely integrated, thermo-pneumatically tunable microlens

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.

Fiber optic tunable probe for endoscopic optical coherence tomography

A novel miniaturized fiber optic tunable endoscopic probe based on a pneumatically actuated micro-lens is presented. The probe has a diameter of ∼4 mm and is integrated into a time-domain optical coherence tomography (OCT) system. The integration of the tunable lens with the OCT system leads to a uniformly high lateral resolution and high contrast of the OCT images over the entire scan depth. In addition, the tunable probe can be considered as a platform for integrating multiple microsystems, including particularly scanning micro-mirrors, in a single high-performance endoscopic OCT system.

Scanning and Tunable Micro-Optics for Endoscopic Optical Coherence Tomography

The design, fabrication, and integration of micro-optical 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 μm 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 μm 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.

Highly flexible MTF measurement system for tunable micro lenses

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.

Tunable Scanning Fiber Optic MEMS-Probe for Endoscopic Optical Coherence Tomography

A novel 3D probe for endoscopic optical coherence tomography (OCT) based on tunable and movable MEMS components is presented. A tunable micro-lens and a 2D scanning micro-mirror are integrated into a probe to enable two-dimensional movement with simultaneous dynamic focusing of a beam onto a target. The tunable system is based on a pneumatically actuated micro-lens for the axial movement of the focus position concomitantly with the depth scan of the OCT, whereas an electrostatically actuated micro-mirror is integrated to obtain the 2D lateral scan of the beam. High resolution imaging at high scan rates is expected for the entire scan depth using this concept. Probe design, assembly, and integration into an OCT system are discussed.

Integrated three-dimensional scanner for endoscopic optical coherence tomography

Numerous 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.

Tunable Endoscopic MEMS-Probe for Optical Coherence Tomography

A novel miniaturized tunable endoscopic MEMS probe employable in an endoscopic optical coherence tomography (OCT) system is presented. The probe consists of a pneumatically-actuated micro-lens and a GRIN lens coupled to an optical fiber. Silicon micromachining using polydimethylsiloxane was used to fabricate the lens. The probe has a diameter of 5 mm. The successful integration of the tunable endoscopic probe with an OCT imager promises to be of value in medical diagnostics, particularly for the early detection of internal tumors and cancers.

Pneumatically-Actuated Tunable Microlens for Endoscopic Optical Coherence Tomography

A pneumatically-actuated micro-lens integrated in the sample arm of a time-domain optical coherence tomography (OCT) system is presented. A 50 mum thick polydimethylsiloxane (PDMS) membrane is spun onto the front side of the lens. Deep-reactive ion-etching (DRIE) is applied to create the aperture of the lens. Dynamically shifting the focal length for each A-scan step enhances the axial scan length and the contrast of the backscattered interference signal of the structures beneath the surface. The successful integration of the micro-lens with an OCT system allows its use in endoscopic in-vivo applications.

Tunable multi-micro-lens system for high lateral resolution endoscopic optical coherence tomography

A pneumatically actuated tunable liquid micro-lens is developed for integration in an endoscopic optical coherence tomography (OCT) system allowing dynamic focusing along the scan depth. An evaluation of the optical performance, particularly transverse resolution, is presented and its utility in OCT discussed. A transverse resolution of about 15 mum which does not vary with a scan depth of 9 mm scan depth has been obtained, performance which cannot be obtained with a fixed focal length lens.

Optical coherence tomography using a dynamically focusing tunable micro-lens

A fiber-optic-based, time-domain optical coherence tomography (OCT) system coupled with a pneumatically actuated micro-lens is demonstrated. The OCT system uses a superluminescent diode emitting at a center wavelength of &lgr; ≈ 1300 nm. Microsystem fabrication technologies employing polydimethylsiloxane (PDMS) are used to fabricate the micro-lens with an aperture of 2 mm. A B-scan is carried out while dynamically shifting the focal length of the micro-lens along the axial scan. The OCT scan results show a higher lateral resolution and higher contrast of the backscattered interference signals when using the tunable lens; hence, deeper axial scans are possible. The ability to miniaturize the dimensions of the micro-lens will allow the system to be applicable to en-face optical coherence tomography and endoscopic applications.