Polymer optics are popular with manufacturers and engineers in various industries due to their flexibility in the manufacturing process and relatively low cost per unit. Polymer optics also allow for various enhancements that can improve their performance. One such enhancement is the usage of optical coatings. Optical coatings are used in various applications, from automotive lighting (reflective coatings) to health care and other imaging industries (anti-reflective coatings).
An optical coating consists of a combination of thin film layers that create interference effects used to enhance transmission or use reflection properties within the optical system. The performance of a coating is based on the number of layers, differences in refractive index at the layer interfaces, and thickness of the individual layers. Commonly used types of optical coatings are:
- Hard coatings
- Reflective coatings
- Anti-reflective coatings
In this article you will discover how optical coatings are applied, how these coatings enhance your optics, and which optical coatings can be used for the custom polymer optics that we deliver.
Applying optical coatings to polymer optics
An optical coating can be applied to a plastic optic in a number of ways. One of the most popular methods is the dip and spray application. Additionally, hard coatings can be applied through a spin application. These methods require a catalyst to cure the resin and flash off any active solvents in the resin. Normally these catalysts are light (IR/UV) or thermal based.
Let’s take a closer look at some of the coatings which can be applied to our polymer optics.
One of the few drawbacks of machined, molded or diamond-turned optical plastics is that the material is prone to abrasion, scratches, and chemical attack. Luckily this can be solved by applying a coating, which will not interfere with the integrity of the plastic optic. When a hard coating is applied, the optical product becomes extremely tough and scratch-resistant. Understanding exactly how much more durable your optics will become because of the coating is important for specifying durability requirements.
A hard coating can effectively help protect a polymer optic by improving abrasion and chemical resistance. Hard coatings can pass ASTM D1044 test Taber Abrasion (Δ % Haze) with levels of <7 after 500 revolutions. They will also hold up against chemical attacks from sodium hydroxide, 1% solutions of hydrochloric acid, and acetone, to name a few.
Reflective coatings are used to minimize loss while reflecting lasers and other light sources. During reflection, absorption and scattering can cause decreased throughput or even potential laser-induced damage. Reflective coatings are commonly used in laser optics applications, such as folding a laser’s beam path and laser cavity end mirrors.
At Addoptics we commonly use Al (aluminum) combined with Sio2 (serving as a protective layer). But silver or gold coatings are also a possibility. Metallic surfaces can reflect light due to loosely attached electrons which freely oscillate with incident light waves, without much hindrance. However, all metals will absorb some amount of incident light. As such, metallic mirror coatings are susceptible to damage when using high power lasers.
For optimal lens performance, an anti-reflective coating can help. This is most commonly used for imaging applications. An anti-reflection (AR) coating will immensely improve the efficiency of the optic by enhancing contrast, increasing transmission, and eliminating ghost images. Above all, most anti-reflection coatings are resistant to physical and environmental damage. As such, AR coatings are an optimal choice for transmissive optics.
Please note that when specifying an AR coating for your particular project you must be aware of the spectral range of your optical system. An anti-reflection coating can greatly improve the performance of a system, but when using the coating at wavelengths outside the design wavelength range, this could potentially decrease the performance of the system.
Coating your custom optics
Addoptics offers smart manufacturing of optics as a service. We can provide custom optics within a couple of days. Without high investment costs, expensive tooling, or a minimum order quantity. For optical engineers, our service enables you to experience design freedom, while remaining within budget. Explore new possibilities with our custom optics in combination with optical coatings.