Pump optimization experiments of all-fiber few-mode erbium-doped fiber amplifiers for low differential mode gain

Abstract

Mode division multiplexing (MDM) technology has become an effective method to further increase the data capacity of optical fiber transmission systems. Few-mode erbium-doped fiber amplifiers (FM-EDFAs) capable of compensating for the link loss have attracted great attention. FM-EDFAs with low differential mode gain (DMG) are desirable for MDM transmission. Since the refractive index distribution and erbium-ion doping profile of a given FM-EDF are usually changeable, ones have to employ the method of optimizing the pumping power, mode and direction etc. to further reduce the DMG. On the other hand, the FM-EDFAs composed of bulky free-space components require too high alignment accuracy to satisfy the engineering needs. Therefore, it is very necessary to build up all-fiber FM-EDFAs with pump optimization. We build up a four-mode or six-mode all-fiber FM-EDFA with low DMG based on the homemade FMEDF from the project (No.2018YFB1801003) and two six-mode mode-selective photonic lanterns (MSPLs). In order to improve the gain of the higher-order mode signals, we utilize three 1480nm pump lasers corresponding to LP21a, LP21b and LP02 modes, respectively. By optimizing the pump powers, the average modal gains are respectively up to 26.2dB with the DMG of 1.5dB for four-mode (LP₀₁, LP_11a, LP_21a and LP₀₂) signals, and 24.9dB with the DMG of 2 dB for sixmode (LP₀₁, LP_11a, LP_11b, LP_21a, LP_21b and LP₀₂) signals.