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04 Apr 2008
An imaging device combining a fluidic lens with a set of fixed glass lenses can operate as a camera and as a microscope.
A highly versatile imager which is able to function as a regular camera with an ultrawide autofocusing range, and as a microscope with 3 µm resolution, has been developed by a US team. The device exploits the wide tuning range of a fluidic lens, as well as fixed lenses to correct optical aberrations (Optics Letters 33 291).
"We normally consider cameras and microscopes as two very different systems," Frank Tsai from the University of California, San Diego, told optics.org. "Our approach using fluidic lenses can enable the same device to function as a camera and as a microscope. This has never been achieved before."
The system consists of a specially constructed membrane-based fluidic lens along with three glass lenses arranged in a so-called Cooke triplet formation, which is known to eliminate most of the optical distortion or aberration at the outer edge of glass lenses. A CMOS image sensor completes the device, which has a total volume of less than 1 cm3.
The team used the device to photograph objects 15 m away and then to focus on objects as close as 1 cm from the camera. "This is the widest focusing range achieved with a single camera," said Tsai. "We have demonstrated a tuning range as wide as 200 diopters, which is 15 times the tuning range of the lens in human eyes."
The team drew part of their inspiration from biological vision systems. While most animal eyes provide high acuity within a narrow field of view, an imaging device requires high acuity over the entire image field. However, the flat surface of the CMOS image sensor is unable to correct the field curvature in the same way as an animal's retina can. "As a result, we have to combine the bio-inspired fluidic optics with conventional fixed lenses to correct these optical artefacts," explained Tsai.
"Decades of accumulated knowledge in optics design has made conventional fixed lenses highly effective at correcting artefacts like aberration and chromatic dispersion, while varying the lens shape is an elegant tuning mechanism seen in many animals," said Tsai. "A hybrid system combining the extended functionality of fluidic lenses with the artefact correction of fixed lenses provides the most versatile and high-performance imaging system."
Creating a repeatable and well controlled fabrication process for fluidic lenses remains a challenge for the team, who claim to have introduced new materials and processing technology to improve the quality of their lens.
"A further challenge is the design of optical systems that contain fluidic lenses," Tsai commented. "Designers need to understand the properties and constraints of fluidic lenses and figure out effective ways to optimize the performance. Current optical design handbooks do not have sufficient information to guide them."
The team now plans to apply this technology to minimally invasive surgical procedures such as laparascopic surgery, as well as several commercial applications. "The ultimate goal of our bio-inspired fluidic imaging is to create a paradigm shift of the world of imaging," said Tsai.
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