Mode volume

In telecommunication, mode volume is the number of bound modes that an optical fiber is capable of supporting.

Note: The mode volume M is approximately given by V ²/2 and (V ²/2)[g /(g +2)] respectively for step-index and power-law profile fibers, where g is the profile parameter, and V is the normalized frequency greater than 5.

Source: from Federal Standard 1037C and from MIL-STD-188