Bader Aldalali

Large‐Field‐of‐View Wide‐Spectrum Artificial Reflecting Superposition Compound Eyes

In nature, reflecting superposition compound eyes (RSCEs) found in shrimps, lobsters and some other decapods are extraordinary imaging systems with numerous optical features such as minimum chromatic aberration, wide-angle field of view (FOV), high sensitivity to light and superb acuity to motion. Here, we present life-sized, large-FOV, wide-spectrum artificial RSCEs as optical imaging devices inspired by the unique designs of their natural counterparts. Our devices can form real, clear images based on reflection rather than refraction, hence avoiding chromatic aberration due to dispersion by the optical materials. Compared to imaging at visible wavelengths using conventional refractive lenses of comparable size, our artificial RSCEs demonstrate minimum chromatic aberration, exceptional FOV up to 165° without distortion, modest aberrations and comparable imaging quality without any post-image processing. Together with an augmenting cruciform pattern surrounding each focused image, our large-FOV, wide-spectrum artificial RSCEs possess enhanced motion-tracking capability ideal for diverse applications in military, security, medical imaging and astronomy.

Flexible Miniaturized Camera Array Inspired by Natural Visual Systems

We report on a flexible microcamera array inspired by natural visual systems. The camera array is a hybrid artificial visual system that combines the large field of view (FOV) of compound eyes together with the high resolution of mammalian eyes. The camera array allows for maximum flexibility and instantaneous reconfigurability to observe a wide FOV. The microcamera array takes advantage of different fabrication techniques including 3-D printing and ultraviolet (UV) liquid phase photopolymerization, as well as utilizing flexible polymers. The array consists of three miniature cameras, each composed of a 1 mm2 stand-alone image sensor and a 0.9-mm-diameter microlens. The lenses were fabricated by utilizing the surface tension of UV curable transparent polymers on Teflon coated substrates. The structure of the array was fabricated using 3-D printing. The miniaturized cameras were connected by a flexible and stretchable polymer. Images from the cameras in the array were stitched together to provide an FOV of 130°.

Reconfigurable Micro-Camera Array With Panoramic Vision for Surgical Imaging

We present a prototype of a micro-panoramic vision system that includes four micro-cameras controlled simultaneously by mechanical arm-like actuators, structurally similar to umbrella ribs. Each camera rests on an arm that can be oriented at an angle simultaneously with the other three arms. This arrangement offers reconfigurable angle of view and depth perception. Stitching of the images from the four cameras in any one configuration yields a horizontal field of view (FoV) of approximately 45°. Dynamic stitching of panoramas from different configurations can increase the composite horizontal FoV to up to 130° . This micro-camera set is configured in the context of laparoscopic surgery and single-port surgery. Our prototype yields a significantly larger FoV as compared to a commercial laparoscopic camera.

Fabrication of Polydimethylsiloxane Microlenses Utilizing Hydrogel Shrinkage and a Single Molding Step

We report on polydimethlysiloxane (PDMS) microlenses and microlens arrays on flat and curved substrates fabricated via a relatively simple process combining liquid-phase photopolymerization and a single molding step. The mold for the formation of the PDMS lenses is fabricated by photopolymerizing a polyacrylamide (PAAm) pre-hydrogel. The shrinkage of PAAm after its polymerization forms concave lenses. The lenses are then transferred to PDMS by a single step molding to form PDMS microlens array on a flat substrate. The PAAm concave lenses are also transferred to PDMS and another flexible polymer, Solaris, to realize artificial compound eyes. The resultant microlenses and microlens arrays possess good uniformity and optical properties. The focal length of the lenses is inversely proportional to the shrinkage time. The microlens mold can also be rehydrated to change the focal length of the ultimate PDMS microlenses. The spherical aberration is 2.85 μm and the surface roughness is on the order of 204 nm. The microlenses can resolve 10.10 line pairs per mm (lp/mm) and have an f-number range between f/2.9 and f/56.5. For the compound eye, the field of view is 113°.

A micro camera utilizing a microlens array for multiple viewpoint imaging

We present the concept and realization of a micro plenoptic camera to achieve multiple viewpoint imaging with one single image capture and without moving the camera. The micro plenoptic camera is based on lightfield photography where the camera captures the 4- dimensional lightfield and images it onto a 2- dimensional CCD sensor through the use of a microlens array. The microlens array was fabricated using the photoresist reflow process. We realized both a simulated micro camera with a 2mm aperture, a 69×69 microlens array of 50µm pitch size and a 5 megapixel CCD, as well as an experimental camera with a 15.2mm aperture, a 97×97 microlens array of 240µm pitch size and a 1 megapixel CCD.

Fabrication of polydimethylsiloxane microlens arrays on curved surfaces

We report on polydimethlysiloxane (PDMS) microlens arrays on curved surfaces. The mold of the microlens arrays was formed using the photoresist reflow method on top of SU-8 islands connected to each other by a thin layer of SU-8. The mold was transferred to PDMS using a double transfer method. Stress simulation determined that when placed on a curved surface the flexible polymer connecting the microlens arrays endured the most stress minimizing the optical deformation of the microlens arrays. Focal point results demonstrate uniformity of the microlenses within an array with an estimated focal length of 330 μm.

Reconfigurable, panoramic vision micro camera array

We present a prototype of a micro panoramic vision system that includes five micro-cameras controlled simultaneously by mechanical arm-like actuators, structurally similar to umbrella ribs. Each camera rests on an arm that can be oriented at an angle simultaneously with the other four arms. This arrangement offers reconfigurable angle of view and depth perception. Stitching of the images from individual cameras yields a horizontal field of view of 360°. This micro-camera set is configured in the context of laparoscopic surgery and single-port surgery.

A bio-inspired cylindrical lens based on reflection from an array of micro-mirrors fabricated on a cylindrical flexible substrate

Most optical systems utilize refractive lenses to focus light. These lenses have low transmission and suffer chromatic aberration because the refractive index is a function of wavelength. Focusing light by reflective curved surfaces (e.g., spherical mirrors) could address these two issues. However, this is hard to implement in micro-optical systems since the imager, with similar dimensions to other components, would inherently be on the same side of the curved mirror as the light source, thus blocking the incoming light. Some natural visual systems, however, rely on a configuration of distributed mirrors to focus light [1]. Inspired by such systems, we designed and realized a cylindrical lens based on reflection from an array of micro-mirrors fabricated on a cylindrical flexible substrate.

Micro Cameras Capable of Multiple Viewpoint Imaging Utilizing Photoresist Microlens Arrays

We present micro cameras that provide multiple viewpoint imaging from one single image capture and without moving the camera. The micro cameras are based on lightfield photography where the camera captures the 4-D lightfield and images it onto a 2-D charge-coupled device (CCD) sensor through the use of a microlens array. The microlens array was fabricated using the photoresist reflow process. Two micro cameras were realized. One camera has a 15.2-mm aperture, a 97 × 97 microlens array of 230-μm pitch size, and a 1-megapixel CCD and is capable of 100 different viewpoints with a viewing angle of approximately 20°. The other camera has a 9-mm aperture, a 56 × 42 microlens array of 80-μm pitch size, and a 5-megapixel CCD and is capable of around 1000 different viewpoints with a viewing angle of approximately 4.7°. The resolution of the images rendered from the two cameras is 97 × 97 and 56 × 42 pixels, respectively.

Surface profiling and characterization of microlenses utilizing a Shack-Hartmann wavefront sensor

We report on the characterization of microlenses utilizing the three-dimensional (3D) surface profile obtained from a Shack-Hartmann wavefront sensor. This method can be applied to most types of microlenses, especially liquid ones. Both a solid and a liquid microlens were characterized. The surface data was analyzed and then exported into Zemax to compute their optical properties. The wavefront error of the liquid lens tested increased from 0.44 to 2.41 waves as its focal length was tuned from 10.1 to 4.3 mm. The surface profiles can also be used to study the effect of gravity on microlenses and surface wetting for optimizing the lens fabrication procedure.