Abstract
Absorption and emission properties between 350nm and 1600nm of the Tm2+ ions in optical fibers were investigated using the Tm2+-Tm3+ co-doped germanosilicate glass fibers and its fiber preform. Strong broad absorption band due to Tm2+ ions was found to appear from 350nm to ~900nm together with the absorption bands due to Tm3+ ions. Broad emission from ~600nm to ~1050nm and the other emission from ~1050nm to ~1300nm, which were not shown in the Tm3+ ions, were found upon the Ar ion laser pumping at 515nm. Both absorption and emission results confirm that the Tm2+ ions in the germanosilicate glass have the 4f-5d energy band from 350nm to ~900nm and the 4f-4f energy level at ~1115nm.
Highlights
Development of high nonlinear optical (NLO) glass fibers is one of issues in making various all-optical devices, such as optical switches and optical tunable filters, in optical communications applications [1,2]
Even though the divalent state of some rare-earth ions, such as samarium and europium, in bulk glasses or in glass fibers using aerosol delivery technique in modified chemical vapor deposition (MCVD) process has been demonstrated [5,6,7,8], and there have been a few reports to obtain the divalent thulium ions in alkaline-earth fluoride crystals by irradiating trivalent thulium (Tm3+) ions with γ-ray or in tetrahydrofuran (THF) solution by reducing TmCl3 with Na naphthalide [9,10], no experimental results have been reported for the Tm2+ ions even in any bulk glasses to the best knowledge
From the absorption and emission properties of the Tm2+-Tm3+ co-doped germanosilicate glass fibers and the preform we have found out that the 4f-5d transitions energy band of the Tm2+ ions in the germanosilicate glass is very different from that in the alkaline-earth fluoride, such as CaF2, crystals
Summary
Development of high nonlinear optical (NLO) glass fibers is one of issues in making various all-optical devices, such as optical switches and optical tunable filters, in optical communications applications [1,2]. Since rare-earth doped fibers are expected to have large nonlinear optical properties, there have been much research activities on development of fibers doped with different rare earth ions [3,4]. Divalent thulium (Tm2+) ions are expected to bring about high optical nonlinearity among rare-earth ions [4]. It is not easy to dope the Tm2+ ions into the glass fiber core because rare-earth ions are usually stable in the trivalent state. The absorption and emission properties of the Tm2+ ions in the germanosilicate glass fibers were investigated and the energy transition levels of the Tm2+ ions in the glass were confirmed
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