TRANSMISSION
Multimode stepindex all silica fibers are generally fibers with pure silica core and doped cladding. The OH content of the core will determine the transmission performances: high OH content will be better for UV+visible and low OH better for nearIR+visible.

UV SOLARISATION
High UV power launched into a fiber rapidly alter the transmission characteristics in a non reversible manner. This is called "solarisation". For such application it is necessary to use special solarisation resistant fibers.

NUMERICAL APERTURE
Standard NA of all silica fibers is 0.22+0.02 which gives an acceptance angle of 25.4°. For some applications it is interesting to have smaller NAs such as 0.10 to 0.12 for a small and more precise output spot or instead to have bigger NAs to improve bending insensitivity. In some cases it can be interesting to splice fibers with different NAs to optimize input and output parameters.

BUFFER
Silica is normally very resistant (2000Kpsi). However surface flaws normally weaken fibers. A hard polymer buffer (see HCS general information) applied to the cladding during fiber draw improves considerably fatigue resistance by reducing propagation of the flaws.

COATING
This is the mechanical protection applied to the fiber during drawing process. It is different from protective structures which can be added afterward by the cabler.
The choice of coating is important and determine the environment behaviour of the fiber. Commonly used materials are ETFE and Polyimide.
ETFE is soft and easy to strip for terminations but it's temperature range is -65°C to +125°C.
Polyimide is a hard material applied in thin layer with very good temperature performance (-65°C to +350°C and up to 400°C for short period) and high power injection. UV and radiation resistance are also improved.