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.

MDZ081

MDZ081

Surgical vascular handpiece, with zoom, for VIS-NIR lasers (532, 650, 700-1100 nm) and powers up to 30W. Available in different configurations covering spot sizes from 0.5 to 8 mm with AN 0.22 optical fibers. Spot sizes can be selected by means of a regulation ring. The optical group is protected by a sealed safety glass.

Ergonomical and easy-to-handle design, aluminium body and stainless steel spacer with a flat or round-shaped end. The handpiece is currently equipped with a Ø400 or Ø600µm optical fiber (other types of optical fiber are available on request) and a SMA connector with anti-screwback design.

It can be customized with regulation rings in various colours (neutral, green, red, blue, smoky grey). Other types of coating are also available (PVC with Kevlar, stainless steel with PVC or black silicone) for the protection of the optical fiber.

MDZ081  

Manipolo chirurgico-vascolare zoom per laser VIS-NIR (532, 650, 700-1100nm) e potenze fino a 30W. Ha diverse configurazioni che gli consentono di coprire spot da 0,5 a 8mm di diametro con fibre ottiche AN 0,22. La regolazione dello spot avviene attraverso la ghiera di regolazione. Il gruppo ottico è protetto da una finestra di protezione sigillata. E' ergonomico e maneggevole con il corpo in alluminio ed il distanziale in acciaio che può avere punta piatta o sferica. E' fornito di serie con fibra ottica Ø400 o Ø600µm ed attacco SMA (altri tipi di fibra ottica disponibili a richiesta) con blocco antisvitamento. E' personalizzabile attraverso varie colorazioni della ghiera di regolazione: neutrale, verde, rosso, blu, fumè. Sono inoltre disponibili diversi tipi di guaine (PVC con kevlar, acciaio con PVC o silicone nero) per la protezione della fibra ottica.

Optical fibres

Optical fibers are based on the principle of total internal reflection that was observed in a water jet by Swiss physicist Jean Daniel Colladon in the early 1840s, and later by French physicist Jacques Babinet who observed the same phenomenon in a glass rod.  The first practical application was the use of total internal reflection as a medium for light propagation in fountain lighting. In the 20^th century, research focused on developing fiber bundles for image transmission, to be used in internal medical examination. The first fiber optic semi-flexible gastroscope was patented by  Basil Hirschowitz, C. Wilbur Peters and Lawrence E. Curtiss in 1956, and Curtiss himself produced the first glass-clad fibers. In 1965 Charles K. Kao' and George A. Hockham, working at STL, the research center of the British company STC (Standard Telephones and Cables) were the first to suggest that the attenuation in the fibers available at the time was actually caused by glass impurities that could be removed, rather than by physical effects such as scattering. They promoted the idea that fibers would be a practical and efficient communication medium when the attenuation could be reduced below 20 dB/km. This was achieved in 1970 by researchers Robert D. Maurer, Donald Keck, Peter Schultz and Frank Zimar, working for American glassmaker Corning Glass Works (now Corning Inc.). They produced a fiber with 17 dB/km attenuation by doping silica with titanium.

Total internal reflection

An optical fiber is a medium for telecommunication that includes a core surrounded by a cladding, both made from silica glass SiO₂ doped with various materials in order to obtain a refractive index of the core n1 greater than the refractive index of the cladding n2. The difference between these two refractive indexes, thanks to the phenomenon of total internal reflection, allows light to propagate along the fiber.

Attenuation (or signal loss)

The optical fiber is totally immune to electromagnetic interference, but light attenuations can occur due to impurities in the glass (loss due to absorption) and to physical effects inside the glass fiber itself (scattering). Such attenuations are measured in dB/km and can vary according to the wavelength of the light beam.

Attenuation can also be caused, in addition to light absorption and scattering, by excessive bending of the fiber during use: when a critical bend radius of the fiber is reached, the light ray will partially disperse in the cladding as its angle of incidence becomes higher than the acceptance angle of the fiber.

Numerical aperture

Another important fiber parameter is the Numerical Aperture (NA): it represents the maximum acceptance angle of the fiber for an incident ray.  If the angle of the intersection is too large, the light ray will not be totally reflected back into the core but partially lost in the cladding.

Applications for optical fibers

Optical fibers are used in telecommunications for data transmission over long distances and at increasing speeds. Technological developments in the last 20 years brought an increasing use of optical fibers in lightning as well as image and energy transmission both in the medical field (surgery, endoscopy, physiotherapy) and in the industrial sector (systems for vision, cutting, welding/soldering, drilling etc.).