Tm³⁺ doped tellurite glass for S band amplifiers

Abstract

In the past, much effort has been devoted solely to the development of fiber amplifiers operating in the C(1530-1560nm) and L(1560-1610nm) bands based on Er-doped fiber amplifiers. However, with the rapid increase in data transmission, the demand for a larger bandwidth to handle a larger transmission capacity has become vital. We report on the spectroscopy and gain measurements in a thulium (Tm³⁺) doped tellurite glass for broadband amplification in the S band (1440-1530nm).

The composition presented here is LTT: 25Li₂O+5TiO₂+70TeO₂. Based on DTA measurement, the glass transition temperature of T_g is ~270°C and there is no apparent crystallization. The 1470nm fluorescence profile is independent of concentration and the full width at half maximum is ~106nm which is at least 30nm broader than that reported in fluoride ZBLAN glass. The 1470nm transition is ~97 % radiative, the effect of OH quenching is minor and the glass can accept large dopant levels. The ³H₄-³F₄ transition is self-terminating unless the lower ³F₄ level is depopulated. Our results on a 2000ppm Tm³⁺-Ho³⁺ codoped LTT glass shows a 33% reduction in the lifetime of the ³F₄ state without affecting the lifetime of the ³H₄. It is estimated that a Ho³⁺ concentration of 10,000ppm is required.

A multimode LTT fiber doped with 2000ppm of Tm³⁺ with a NA of ~0.45 and a core diameter of 40µm has been fabricated. The background loss is 3dB/m at 1µm. Gain measurements were performed in free space configuration using 800nm from a Ti:Sapphire laser as a pump source and a HP tunable laser diode between 1470nm and 1580nm as the signal source. The pump power incident on the fiber was ~1W uncorrected for coupling losses whilst the signal power was maintained at -55dBm. A 0.30m length fiber shows gain extending to a longer wavelength (1560nm) than that reported in ZBLAN. An average gain of 4dB was measured at 1470nm and the gain increases with pump power with a pump efficiency of ~3.5dB/W. The gain figure and pump efficiency will improve significantly in a single mode fiber.

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Identifiers

ORCID for J. Nilsson: orcid.org/0000-0003-1691-7959

ORCID for W.S. Brocklesby: orcid.org/0000-0002-2123-6712

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