Er-doped Tellurite glasses for planar waveguide power amplifier with extended gain bandwidth

Abstract

ABSTRACT:Tellurite glass compositions doped with erbium and erbium/ytterbium optimised to support extended gain bandwidth with significant amplification have been fabricated, and their thermal, optical absorption, excitation and luminescence properties investigated. Each rare-earth dopant concentration was set at 1x10 20 cm -3 . Broad emission cross-section bandwidths up to 50nm FWHM were observed, with fluorescence lifetimes of ~3ms. Collinear pump probe measurements on ~4mm thick bulk samples revealed peak gains of up to 2.1dB/cm at a wavelength of 1535nm in the co-doped material, with an incident pump intensity of only I inc~8 kWcm -2 at a wavelength of 974nm. At equivalent absorbed pump powers between co-doped and single doped materials the relative gain was 1.25dB/cm (I inc~4 kWcm -2 ) and 0.9dB/cm (I inc~8 kWcm -2 ) respectively, demonstrating efficient energy transfer from the ytterbium to erbium ions. Excited state absorption at longer wavelengths was observed and characterised and its implication on realising sufficient gain in the wavelength band of interest is discussed.

Er-doped planar waveguides for power amplifier applications

“…Figure 2 illustrates the measured gain for the two samples, in-band pumped at 1480 nm, as a function of time at discrete probe wavelengths. A comparison of the gain for the same samples pumped at 974 nm is given in Figure 3, measured as per the setup described in [6]. Clearly the stronger absorption of the 974 nm pump provided a higher inversion and therefore higher gain.…”

“…Tellurites glasses on the other hand typically have phonon energy levels <800 cm -1 , meaning the 4 I 11/2 level of Er 3+ ions has a modest lifetime that can allow back-transfer of energy to a Yb 3+ co-dopant, alternatively the stored population in this level can be extracted parasitically via excited state absorption (ESA), energy transfer upconversion (ETU), or simply radiatively to the ground state. Presented last year at this conference [6] we explored Teullurite compositions based on a zinc oxide glass former, magnesium oxide modifier, and borate additive to capitalise on the more energetic stretching vibrations of the B-O -bonds [7], up to about 1400 cm -1 . This indeed assisted efficient absorbed pump energy transfer by Yb 3+ to Er 3+ , however it was at the expense of the 4 I 13/2 level lifetime, reducing it to ~3 ms.…”