High-precision linearity standard for high-power optical-fiber power meters

A high-precision linearity standard for high-power optical fiber power meters (OFPMs) at 1550 nm is developed using an integrating sphere and an InGaAs photodiode connected to a picoammeter. Its linearity is evaluated in the superposition method, where optical signals are superposed in the integrating sphere using a two-core ferrule to avoid high loss and high-power instability of an otherwise used fiber coupler. The uncertainty (k=1) of this standard´s linearity at 1 W with reference power 1 mW is less than 0.002 dB. Test OFPMs´ linearity is calibrated by comparison with this standard within an extended uncertainty (k=2) of 0.005 dB at 1 W.