History of the development of optical materials - Lenses
Lens past
In the early days of history, lenses were mainly made of crystal stone through traditional milling and polishing. The main component of crystal is silicon dioxide (SiO2). When pure, it is a colorless and transparent crystal. However, because it inevitably contains elements such as Al and Fe, natural crystals show different colors. As you can imagine, the crystals used by the ancients to make lenses were relatively pure.
Crystal glasses without brackets have been around for a long time in history (different from current crystal glasses)
With the development of history, people's understanding of high-temperature craftsmanship and production technology has become more and more profound, and glass materials have gradually replaced crystal as the main material of lenses. The main reasons are: crystal is quite rare, while glass is relatively easy to obtain; crystal has too many impurities and its optical properties such as density and refractive index are unstable, while glass is relatively pure. Of course, glass is not harmless. Its hardness is not as good as crystal, and ordinary glass is more fragile.
modern and contemporary lenses
By the middle of the 20th century, the lens material ushered in an innovation-resin material. Resin is a typical polymer compound that can change its composition and structure to produce a variety of functions. New materials and combined materials are blooming, and computer-aided design and digital processing are the icing on the cake.
Research on CR39 resin started earliest, and its technology is currently the most mature, with a high market share. Its advantages are high Abbe number (*) while ensuring moderate refractive index, high transparency, strong wear resistance, solvent resistance, chemical resistance and heat resistance. At the same time, due to the mature technology, the lens yield rate is high and the cost is low. However, although the refractive index is moderate, the lenses will still be made very thick when the correction power is high, resulting in heavy weight and insufficient impact resistance, in other words, fragile.
Polycarbonate (PC sheet, polycarbonate) is a typical resin material. It has the advantages of strong impact resistance and low density. However, as a thermoplastic material, its poor processing performance, chemical resistance, and wear resistance are unavoidable defects. PC sheets have a high refractive index and can make relatively thin lenses, but at the same time they have a low Abbe number and severe dispersion at the edge of the lens.
Trivex is also a common resin material that was originally used on armored vehicles. Its biggest features are light weight and good impact resistance. Compared with PC sheets, it has the advantages of chemical solvent resistance and scratch resistance. However, Trivex has a lower refractive index, and its lens thickness is even higher for the same degree of vision correction.
MR materials, some people call them new optical materials, are actually nothing more than fine-tuning the refractive index, Abbe number and impact resistance, so I won’t go into details.
Japanese companies currently have almost a monopoly on high refractive index lenses, but the technology is new and their market share is not high.
Finally, let’s discuss why glass lenses will be replaced? I think there are two reasons: 1. Glass is fragile, and resin materials are more resistant to impact and tension; 2. The density of glass is usually several times that of resin materials, and the refractive index is usually lower than that of resin (common crown glass is about 1.5, The general resin material is around 1.6, and the latest can reach 1.7), so the glass lens will be very heavy. Moreover, some traditional advantages will be replaced, such as the high hardness of glass, which is no longer important because modern coating processes can already ensure the high hardness of lenses. Although there is basically no place for glass in modern lenses, glass materials play an important role in optical instruments such as microscopes, telescopes, cameras and sights due to their excellent optical properties. This also shows that the value of materials is reflected in their function and use.
future lenses
From the above, it is not difficult to see that the development and update of lens materials are all "toothpaste-like", which is nothing more than making some minor optimizations in the fit, quality and comfort of the lenses. But looking at the current lenses, it is not difficult to find that the direction of lens development has shifted to function. Anti-blue light, anti-glare, anti-radiation, anti-splash, anti-pollution, etc., diversification, precision, and functionality are becoming more and more prominent. Even glasses are no longer limited to traditional styles. Rimless glasses, contact lenses, smart glasses, etc. are changing with each passing day. The materials included are even more diverse, such as organic polymer hydrogel, silicone hydrogel, etc. used in contact lenses. Lenses have become thinner and softer, like tinted glasses, sunglasses, etc., and are dyed to serve people's aesthetic needs. However, whether it is for vision correction or aesthetics, the classification of lens materials and functions is constantly being refined.
Rimless glasses require lenses with good impact resistance
Among them, smart glasses are quite eye-catching. With the booming development of AI technology, smart glasses have only taken ten years from concept to beta version. Not only optical materials, but also some electromagnetic materials are used in glasses. In the past, we focused on the combination of multiple elements, but now we have to think about the combination of multiple materials. In the past, there were many examples of using a variety of materials, such as glasses for both far and near vision, but after all, they were all optical materials. But in the future, the question before us is the possible combination of materials in many different fields.
