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Polymers are one of the most widely used material classes in the world today, and there are many different types of polymers, all with their specific properties and applications. One of the lesser-known classes of polymers is optical polymers (as people tend to focus on the various other properties of polymers), which have found a lot of use in various advanced optical components across the medical, defense, communications, and aerospace industries. Here, we’re going to look at what optical polymers are and some of the specific applications in which they are used.
Like many polymer classes, the area of optical polymers features many different materials, but all materials that fall into this category are known to exhibit properties that are like glass. While they do have a few optical defects compared to glass, they are much more resistant to impact and are more lightweight, hence their use in specific industry applications, such as in optical components in military applications.
Optical polymers typically have two distinct classes. The first is those made of thermoset resins, and the second is those made of thermoplastic resins. Like any polymer, the specific and tailored properties of the polymer are key for each application and the properties of these polymers can be manipulated like most other polymers. The properties that are often tweaked and optimized for optical applications are the density, hardness, rigidity, service temperature, outgassing, conductivity, and resistance to water and radiation. Many of these properties help to determine the spectral transmission and refractive index of the polymer, which are the key selection drivers for their use. Some of the other properties are environment-specific for the intended application.
However, because the polymers often contain more defects than glass, they often need to be coated before use to ensure high optical performance. This can be done via several different coatings depending on the intended application which includes reflective coatings, anti-reflective coatings, anti-abrasion coatings, and anti-static coatings.
The Different Applications
In terms of their use, there are many different applications where they can be used. For example, they can be used in many common optical components that are used across multiple industries, such as in lenses and microlenses, prisms and optical windows. Furthermore, they can be used to construct specialist lenses, such as high aperture aspheric lenses as the polymers can be easily molded and embossed to achieve the desired shape and effects.
The ability to coat the optical polymers does open more options, as the mechanical properties are usually improved as well as the optical performance. Some examples of applications that utilize coated optical polymers include ophthalmic glasses, reading glasses and sunglasses, as well as more complex lenses used in military and defense applications.
While it is not specifically a coating (although you could argue that it is in some form), optical polymers can be used on various optical communication lines as the cladding (i.e. the sheath around the optical fiber which keeps the light along its intended path). Optical polymers have found use in this area in plastic optical fibers, multimode fibers, short-distance optical communication fibers, as well as in some of the specialist optical components that are used within different waveguides.
It is not just lenses and basic optical components that utilize and benefit from the specific properties that optical polymers bring over the glass. They can also be used in a range of high-tech applications as well. One of these areas is sensors. While they have been used in thermal sensors, optical polymer lenses have been more widely used in CMOS image sensors across a range of optoelectronic devices as they are cheaper, easier to make and more flexible than glass lenses. Other high-tech applications include using optical polymers as the photo-resistant material in photolithography methods, using optical polymers as the organic encapsulant in light-emitting diodes (LEDs) – especially high-brightness LEDs (HBLEDs) – as well as in the camera lenses of mobile phones and drones, and in various optical storage devices (CDs, DVDs, etc).
One high-tech area where they are not found is in optical lasers, and this is because optical polymers tend to lose optical power easily, so they are not an ideal choice where optical intensities need to be high. However, their organic structure enables them to be easily integrated with a dye, which means they can be used as an optical filter to absorb specific wavelengths – and these types of filters are used in many technologies from lasers to analytical characterization instruments, and many other applications in between.
Sources and Further Reading
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