A Review of Polymers and Plastic High Index Optical Materials

The industry of plastics has grown rapidly since its inception in the 1940s, the use of plastics as an optical material only really started to pick up in the 1970s and has had a much slower underlying growth than for the commodity industry e.g. packaging, closures, etc. After that, in this industry the advantage of material consistency and uniformity, full three dimensional machining capability and mass production are exploited to the full.

However, plastics in general are weaker and more costly than traditional materials and people still retain a ‘bad image’ of them because of their previous misuse. In the past, and to a certain extent today, plastic engineering components have been designed to directly replace components in traditional engineering materials, leading to poor performance and costly reproduction. For effective material substitution, the designer using plastics has to appreciate their benefits as well as their limitations. Today, designs are being produced that are not only unique to plastics but are also out-performing designs in traditional materials.

In a comparable way, prejudices prevent consumers trusting plastic lenses. Although they realize benefits such as thinner and lighter design, they worry about clarity and transparency, and the most common question is if plastic lenses harm their eyes or obstruct their vision.

Furthermore, in recent years the industry has confused consumers rather than informing them. Optical properties, like refractive index and Abbe value are not clearly defined by manufacturers (i.e. a given “n” is nd or ne?). Many people ask themselves why high index plastic lenses must be always multicoated? Another similar question is why high index plastic lenses mainly are designed as aspheric? Is chromatic dispersion more or less affected by the refractive index? What is the relation between Abbe value and chromatic performance of these materials?

Consequently, this review has to investigate mainly the above questions in order to search and estimate the performance of new plastic high index materials and to compare with traditional lens materials.