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.

最近，一篇发表在《科学》杂志上的学术论文表明，超材料的实际应用现在触手可及。来自哈佛大学的研究团队通过堆叠约600纳米高的二氧化钛（TiO₂）“纳米砖”，构建了一种平坦的、纸薄的聚焦透镜。选择二氧化钛主要是因为这种材料对可见光没有显著的吸收。这种超材料透镜的有效放大倍数高达170倍，放大图像的分辨率可与传统玻璃透镜相媲美。这种新型透镜确实可能在光学仪器中带来革命性的变革。

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.