Fig. 1. Three-mode power detection unit. (a) Schematic diagram; (b) prototype

Fig. 2. LP modes excited by MSPL. (a) LP₀₁; (b) LP_11a; (c) LP_11b

Fig. 3. Power detection error measured in two calculation ways by changing input power of signal

Fig. 4. Mode transmittance curves for different polarization states

Fig. 5. Experimental system of three-mode optical amplification for FM-EDFA

Fig. 6. Variations of modal gain and DMG with LP_11b-mode pump power