Energy transition characterization of 1.18 and 1.3 μm bands of bismuth fiber by spectroscopy of the transient oscillations

Abstract

The experimental evidence of laser transition type in bismuth-doped silica fibers operating at different spectral bands is presented. Spectrally resolved transient (relaxation) oscillations studied for a Bi-doped fiber laser at room and liquid-nitrogen temperatures allow to identify the three- and four-level energy bands. 1.18 μm short-wavelength band is found to be a three-level system at room temperature with highly populated terminal energy level of laser transition. The depopulation of ground level by cooling the fiber down to liquid-nitrogen temperature changes the transition to four-level type. Four-level energy transition distinguished at 1.32 μm exhibits the net gain at room temperature.

Nonlinear fibre-optic devices pumped by semiconductor disk lasers

“…The gain and pump conversion efficiency demonstrated by the Bi-doped fibres to date are sufficient for several types of optical amplifiers [116,119]. The broad pump absorbing spectral band allows Bi-doped fibre to share the same pump source with a Raman-amplifier [114,117,118].…”

Preparation of optical media with NIR luminescent Bi+ impurity centers by ion exchange

“…The Near Infrared (NIR) photoluminescence (PL) of bismuth doped glasses attract a considerable attention since its discovery because of the intense broadband emission, matching the telecommunication window diapason and long lifetime (several hundreds of microseconds). However, the nature of multiple NIR emissive centers in Bi‐containing glasses is not clear, and it is believed, that the investigation of bismuth‐containing NIR PL centers in crystals can be more informative .…”

Picosecond bismuth-doped fiber MOPFA for frequency conversion

“…Bismuth-(Bi-) doped fiber continues to attract attention because of its broad gain bandwidth that covers the spectral region between ytterbium and erbium-doped fiber. While the nature of the active center responsible for laser behavior in Bi-doped fiber is still unclear, and the subject of ongoing study [1][2][3], Bi-doped fiber already shows promise as a platform for lasers and amplifiers for new applications. Continuous wave Bi-doped fiber laser systems operating around the 1:18 μm band have been reported [4,5] and passively mode-locked Bi fiber laser systems operating in this wavelength range have been demonstrated in systems employing carbon nanotubes [6] or semiconductor saturable absorber mirrors (SESAMs) [7,8].…”

“…Full details of the fiber used are given in [10]. As reported in [3], achieving appreciable gain in bismuth fiber operating in the 1:18 μm band requires cryogenic cooling to force four-level laser behavior. As such, in this work our active fibers are cooled through submersion in liquid nitrogen.…”