Which pair is a recognized singlemode fiber standard?

• A. OS3 OS4
• B. SM1 SM2
• C. OS1 OS2
• D. OM1/OM2

Answer: (C)

Singlemode fiber standards are defined by ITU-T and the recognized pair is OS1 and OS2. These two designations specify singlemode fiber with different application notes: OS1 is typically used for indoor/outdoor installs with specific attenuation and bend-radius requirements, while OS2 is geared toward outdoor, long-haul use with even tighter performance targets. Both are singlemode, meaning they have a 9 µm core that supports a single propagation mode for lower dispersion over long distances.

OM1/OM2, in contrast, are multimode fiber categories (larger cores used for shorter links), so they aren’t the singlemode option. SM1/SM2 and OS3/OS4 are not standard, widely adopted pairings for singlemode fiber in typical practice, so OS1 OS2 is the correct recognized pair.