Abstract

We report a detailed study of the temperature dependence of the behavior of erbium-doped silica fiber amplifiers¹ and lasers.² The important ⁴/_15/2 → ⁴/_13/2 fluorescence spectrum changes significantly in shape, but not position, between 600 and 4 K. At a 1536 wavelength, an increase of 180 % was recorded on cooling from 300 to 77 K. (The integrated fluorescence remained constant.) Concurrently, the absorption around 800 nm shifts to shorter wavelengths. Also, the ground state absorption largely disappears beyond 1545 nm, where the energy level system changes from the three to four level. These effects produce improvements in optimized fiber-amplifier performance when pumped in the GaAIAs diode wavelength region, with temperature-equalized absorption rates and constant pump powers. For 21-mW pump power, the gain at 1536 nm increased from 8 to 13.5 dB when the fiber was placed in liquid nitrogen. At 1550 nm, the saturated small-signal gain did not increase, but the pump power to attain 8 dB reduced from 21 to 13 mW. On cooling, lasing thresholds were also reduced by 50% at 1536 nm but show most dramatic improvement at longer lasing wavelengths by reducing to 15% of the room temperature value.

© 1988 Optical Society of America