performance of the cable. Attenuation should not be excessively increased at the wavelengths used.
results in terms of attenuation: A substantial crushing force of 500N leads only to a residual increase in attenuation of the order of 0.05 db (fiber optic cable type OM3 and @ 850 nm). Furthermore, some mechanical characteristics can be added, such as: • A bending radius of much less than 10 times the optical cable diameter • A tensile strength of much more than 200 N RADIATION RESISTANCE: A KEY ISSUE FOR SPACE APPLICATIONS In space, optical fibers are subjected to ionizing radiation that can cause damage. The high energy ions will break the chemical bonds of the glass that compose the optical fiber. Darkening of the optical fiber occurs due to micro or macro defects. However, optical fiber doped by fluorine is very resistant to radiation (at least until 200 MRad). Another extraterrestrial threat is atomic oxygen (ATOX) which erodes and damages materials including polymer insulated wires and cables. Protective solutions are achieved by wrapping, coating, or isolating wires in aluminum trays, but these solutions add mass to the system and decrease flexibility. Lightweight fiber optical cables that can resist ATOX are a real asset in this field. For space applications, another critical feature for cable materials is low outgassing. Outgassing materials release trapped gas, which can leave residue on instruments and surfaces. To evaluate outgassing, the key material parameters are measured for total mass loss (TML) and collected volatile condensable materials (CVCM). The rate of outgassing increases at higher temperatures
Micro and macro bending on an optical fiber generates leakage modes (sheath mode) and leads to an increase in attenuation performance. This is a well-known phenomenon.
Optical power loss due to macro-bending
Optical power loss due to micro-bending
These mechanical constraints will be combined with environmental constraints including temperature and vibrations, so the structure of the cable must be optimized to minimize their negative effects on optical performances. A way to improve the cable structure is to optimize the extrusion process as well as the adhesion between the different layers of materials. A good knowledge of the different materials used is a real advantage for the design.
In the end, a so-called “tight” structure meets the different requirements and obtains interesting
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