3-TRANSITION CASCADE ERBIUM LASER AT 1.7, 2.7, AND 1.6 MU-M

We report on an upconversion cascade laser in an erbium-doped ZBLAN fi ber emitting simultaneously on the three transitions S-4(3/2) --> I-4( 9/2) at 1.7 mu m, I-4(11/2) --> I-4(13/2) at 2.7 mu m, and I-4(13/2) - -> I-4(15/2) at 1.6 mu m. At moderate pump powers, the laser transitio n at 1.6 mu m supports 2.7-mu m lasing and permits a slope efficiency at 2.7 mu m of 15% versus launched pump power. Above the threshold of upconversion lasing at 1.7 mu m, the slope efficiency at 2.7 mu m incr eases to 25.4%. Taking pump excited-state absorption into account, thi s value represents more than 90% of the theoretical slope efficiency. A transversely single-mode output power of 99 mW is achieved at 2.7 mu m. (C) 1997 Optical Society of America.