New breakthroughs in super-surface technology, boosting the research and development of ultra-thin lenses.

Traditional optical elements usually obtain the ability to manipulate light through their shape or material composition. On the other hand, some optical components can manipulate light in a completely different way, based on what is called a metasurface in physics. These elements can also change the polarization, phase, or amplitude of visible light, but to do this, a flat, ultra-thin nano surface is required.

In various optical system applications, the use of metasurface-based components seems to be an attractive option. This is because they provide ultra-thin alternatives to common optical components such as bulky refractive components and wave plates. However, so far, the manufacturing steps of metasurfaces are expensive, time-consuming, complicated and potentially dangerous, preventing the widespread commercialization of metasurface-based components.

To solve these problems, a research team led by Daniel Andren at Chalmers University of Technology in Sweden is developing a new method of producing metasurfaces. The paper was published on ACS Photonics.

The researchers first used a ready-made standard negative resistance material (polymer resist material), and then spin-coated it on a glass plate and used single electron beam lithography to expose it to make a plate to generate the required surface High aspect ratio nanostructures. After the correct plate is made, this resist material can generate a super-surface, which greatly simplifies the production process and basically becomes a single photolithography step. In this way, the time and expense required for production and processing, as well as any related safety hazards, can be greatly reduced.

In order to verify the principle of this technology, the team produced a flat optical prototype equivalent to a spherical lens. This optical prototype demonstrates narrow focus and high-resolution imaging. More specifically, the researchers created a 1 cm diameter positive lens that is visible to the naked eye, composed of more than 600 million nano-level elements. After testing, the researchers found that the optical element can produce an image that shows the finest details of the target object—just like a normal camera lens, except that the optical element is thousands of times thinner. Other tests have shown that the metasurface is effective, the polarization conversion efficiency is greater than 50%, and it has the function of spanning the entire visible wavelength spectrum.

The team also produced two prototypes of gratings, an abnormal reflection grating and a metasurface cylindrical lens. In addition, they selected various types of substrates in the prototype, in order to prove that this manufacturing method is suitable for both flexible plastic and metal mirror substrates.

Reliability tests show that the metasurface is stable and can be maintained under standard environmental conditions for at least 6 months without any obvious degradation. In terms of stability, the researchers proved that this metasurface can withstand temperatures of at least 100 degrees Celsius. Under the relatively high light intensity of 5 W/cm2 generated by the 532nm continuous laser source, the performance of the metasurface does not significantly decrease.

The researchers predict that their method will eventually promote flat optics to become a strong competitor for bulk optics.