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Groundbreaking Lens Technology Developed at NTHU
A research team led by Assistant Professor Liu Chang-Hua of NTHU’s Institute of Photonics Technologies has made a major breakthrough in the miniaturization of lenses. Collaborating with a research team at the University of Washington, the team has developed a super-planar lens which uses tens of thousands of nano-pillars arranged in concentric circles to engineer the phase shift of lightwave. Moreover, the lens is thinner than a sheet of paper and can even be peeled off like a sticker and attached elsewhere. It is expected to be used as cameras lenses, mobile phones, and minimally invasive surgical catheters.
 
Their invention of the world's thinnest dielectric super-planar lens has been featured in the top journal Nano Letters, and has received considerable attention from foreign media.
 
A conventional lens is made of a piece of glass a few millimeters in thickness that has to undergo an expensive process of burnishing and polishing. Liu said that in the past two or three years multiple breakthroughs were made in nanotechnology and nano-optics, resulting in the development of dielectric super-planar lens (i.e. metalens). Such lens was typically realized by an array of nano-pillars based on SiO2, TiO2 or Si3N4 to engineer the phase shift of lightwave. However, the fabrication is quite challenging and those nano-pillars are very delicate, as the height of the pillar constituting the lens is at least 5 times its diameter (i.e high aspect ratio).
 
By employing innovative optical design methods, however, Liu’s team can reduce the height of these pillars to the nanometer level, so that the height of the pillar is only 2 times the diameter. The shorter pillar is easier to manufacture, and lenses made with it are lighter and thinner. Thus, the thickness of developed lens can be reduced to approach ~190 nm, one-hundredth that of a human hair, setting a world record for the thinnest dielectric planar lens.
 
Another breakthrough of this innovative work was the use of Van der Waals materials to make nano-pillars for the first time. Liu explained that Van der Waals materials are similar to the graphite used in pencils, which is formed by stacking layers of monoatomic layers connected by a weak Van der Waals force; thus the graphite readily takes to the paper, and can be easily erased.
 
Liu’s team is currently using electron beam microscopy to make super-planar lenses in the laboratory, and has shown that these planar lenses can be useful for imaging applications. However, because thousands of nano-pillars have to be lithographically patterned one by one, the production speed is relatively slow. Liu said that if this technique is adopted by industry, then in the future it will be possible to produce such a lens in a few seconds by using the stepper and transparent media adapter (TMA) currently employed in the semiconductor manufacturing process.
 
Liu said that in addition to such applications as cameras, mobile phone lenses, magnifying glasses, spectacles, and sunglasses, in the future this lighter and thinner lens may also be used to miniaturize various other instruments made up of many lenses, including eyepieces, object lenses, reflectors, and microscopes, and might even be used in tiny medical robots for drilling into human blood vessels.
 
After graduating from NTHU’s Department of Power Mechanical Engineering Liu went to the United States to obtain a Ph.D. in Electrical Engineering at the University of Michigan. He has also conducted postdoctoral research at the Department of Materials Science and Engineering at Northwestern University and the Department of Physics at the University of Washington. Although he was offered a teaching position at a well-known foreign university, he decided to return to Taiwan to teach at NTHU. He said that living in Taiwan has a certain appeal and that the research environment has a lot to offer young professionals, such as Taiwan’s thriving semiconductor industry. “Of course, being close to my family is the most important thing,” he said with a smile.
 
A research team led by Prof. Liu Chang-hua of NTHU’s Institute of Photonics Technologies has developed the world’s thinnest super-planar lens by arranging nano-pillars in concentric circles.

A research team led by Prof. Liu Chang-hua of NTHU’s Institute of Photonics Technologies has developed the world’s thinnest super-planar lens by arranging nano-pillars in concentric circles.


Different arrangements of the nano-pillars have different levels of clarity.

Different arrangements of the nano-pillars have different levels of clarity.

Liu’s new type of super-planar lens uses such semiconductor materials as silica to make micron-scale pillars which can be arranged in concentric circles.

Liu’s new type of super-planar lens uses such semiconductor materials as silica to make micron-scale pillars which can be arranged in concentric circles.


Prof. Liu holding a sample of the thinnest lens.

Prof. Liu holding a sample of the thinnest lens.

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