The wavelength used for most fiber optic systems falls in which region and is invisible to the human eye?

• A. Ultraviolet, invisible
• B. Solar, visible
• C. Infrared, invisible
• D. Visible, visible

Answer: (C)

Light carried in fiber optics is chosen to travel with minimal loss and distortion, and that typically happens in the infrared region. Infrared lies just beyond what our eyes can see, so it’s invisible to humans, which helps avoid interference from ambient light. In silica fiber, there are low-loss windows around 850 nm for shorter links and around 1310 nm and 1550 nm for longer links, which is why those wavelengths are widely used for data transmission. Ultraviolet would be absorbed more and can cause damage or excessive attenuation, while visible light is more prone to scattering and interference from lighting in the environment. So, infrared, invisible to the eye, is the region that best suits most fiber optic systems.