Abstract

Subsequent to the recent demonstration [1] of efficient room temperature infrared-to-blue upconversion in Tm:ZBLAN fibre lasers, there have been several reports on efficient upconversion [2] as well as photodarkening and photobleaching effects in TrmZBLAN fibres [3-5], Preliminary indications of self-mode-locking of such fibre lasers, evidenced by enhanced spectral peaks in the RIN spectra of such lasers at frequencies corresponding to multiples of the longitudinal mode frequency, have been reported by Boot et al[4,6]. In this presentation, we report observation of self-mode-locking of a 482 nm Tm:ZBLAN upconversion fibre laser, evidenced by the generation of a train of CW pulses at 300 MHz, corresponding to the round-trip time of the 33 cm fibre laser cavity. To the best of our knowledge, this report represents the first clear observations of self-mode-locking n a visible upconversion fibre laser. Although the physical mechanism for the mode-locking is still under study, competition between the 1120 nm pump-induced photodarkening (at 482 nm) and saturation of this transient absorption is believed to be the most likely origin of the mode-locking mechanism. As such, we will also present new data on the measurement of transient gain and pump-induced photodarkening (at 482 nm) in TrmZBLAN fibres.

© 1996 Optical Society of America