Metamaterial Lenses May Trigger a Disruptive Transformation in Optical Instruments

Recently, a research team from Harvard University has constructed a flat, paper-thin condensing lens by stacking "nanobricks" of titanium dioxide (TiO₂) with a height of approximately 600 nanometers. This new type of lens may bring about a revolutionary change in optical instruments.

Lenses are indispensable components in many optical instruments and electronic products. Traditional lenses are usually made of glass; however, due to their inherent volume and weight, glass lenses often make the instruments bulky—this issue becomes even more pronounced when multiple lenses are required.

Metamaterials have long been a key research focus within the field of photonic crystals. The essence of metamaterials lies in their nanostructures, whose size is smaller than the wavelength of light. These structures can "interact playfully" with photons through different shapes, sizes, and arrangements: they can block, absorb, enhance, or refract photons as needed.

To date, however, metamaterials have not been widely applied in the field of optical lenses. The core reason for this (and also a major difference between metamaterial lenses and glass lenses) is that metamaterials are highly "wavelength-selective" for light. In other words, a lens effective for red light cannot focus green light, and vice versa. Additionally, developing materials suitable for the visible light spectrum (perceivable by the human eye) has proven to be quite challenging. Early metamaterials were primarily silicon-based surface plasmon materials.

Recently, an academic paper published in the journal *Science* has demonstrated that the practical application of metamaterials is now within reach. A research team from Harvard University constructed a flat, paper-thin condensing lens by stacking "nanobricks" of titanium dioxide (TiO₂) with a height of approximately 600 nanometers. Titanium dioxide was chosen mainly because this material exhibits no significant absorption of visible light. This metamaterial lens boasts an effective magnification of up to 170 times, and the resolution of the magnified images is comparable to that of conventional glass lenses. This new type of lens may indeed bring about a revolutionary transformation in optical instruments.

Nevertheless, metamaterial lenses currently can only be applied in instruments that use lasers (a type of electromagnetic wave with a single wavelength). If the challenge of handling composite wavelengths is overcome someday, all optical instruments will undergo a disruptive change. Once this breakthrough is achieved, the size of optical lenses will be significantly reduced, their costs will drop drastically, and our understanding of most existing optical devices will also undergo a disruptive transformation.