Optical fibers in medical equipment

1.    Types of optical fibers

Optical fibers can carry energy at the various wavelengths, from ultraviolet (UV) to infrared (IR). There are fibers with a high OH ion concentration for a better transmission in the UV-VIS range (200-700 nm) and fibers with a low OH ion concentration for a better transmission in the VIS-IR range (400-200 nm).

For each fiber two NA (numerical aperture) types are available: NA 0.22 fiber and NA 0.37 fiber. A higher NA can be achieved either by doping the cladding glass (e.g. with germanium) or by employing a hard plastic clad instead of a glass cladding. In the first instance, we shall have quarz-quarz fibers, in the second quarz-plastic fibers.

The diameter of the core can vary from 50 to 1500 microns. Thinner fibers are employed in surgery and dermatology applications, whilst thicker fibers are used in aesthetic and physiotherapy applications.

2.    Coatings

An optical fiber, being made of glass, is fragile and needs a protective coating in order to be handled easily. Various materials are used for coating, but in our equipment the most used are nylon, tefzel and polyamide. The first two provide better elasticity, the latter is more rigid but can tolerate higher temperatures (up to 300°C).

3.    Jackets

Jackets provide protection against mechanical damage at various protection levels, from simple silicone jackets or C-Flex (for fibers that undergo sterilization) to jackets with Kevlar/aramid fibers for tensile strength, high-flexible PVC jackets with plastic lining and steel jackets (metal armor) with high tensile and compression strength (mostly used in veterinary).

Jackets come in various colours (white, grey, black, green, red, blue, etc.) to match the handpiece and the laser source. 

4.    Optical fiber connectors

A connector terminates the end of an optical fiber and enables easy connection and disconnection to a laser source or a handpiece. At present, standard SMA connectors in stainless steel are generally used for low wattages (up to 5-6 W) and freestanding fiber end for high-power applications.

5.    Biocompatibility

Optical fibers for medical applications must be certified for biocompatibility. In particular, ISO 10993 describes all tests that must be carried out on optical fibers in order to use them in contact with human tissues. The employment of these biocompatibility-certified fibers and the implementation of a company quality system allows us to supply optical fibers with a CE medical mark.