Bismuth and Bismuth Telluride Thin Films Deposited by MOCVD upon Tapered Fiber Sections as Q-switches for Fiber Lasers

Lasing regimes of ring erbium fiber lasers passively Q-switched by means of fiber tapers coated with thin crystalline films of either Bi2Te3 or Bi as saturable absorbers (SAs) are investigated. 10–15 μm in diameter and 5–10 mm long fiber tapers are prepared by local chemical etching out of a silica light reflecting cladding of the standard SMF-28 optical fiber. Nanometer thick island films of pure Bi and Bi2Te3 are synthesized on the surface of the fiber tapers by applying the metalorganic chemical vapor deposition (MOCVD). The deposited films are then covered with two different polymers: either polyvinyl acetate (PVA) or polydimethylsiloxane elastomer (PDMSE). The fiber section with polymer-coated SA fiber is installed into the ring laser cavity in tandem with the section of an active fiber. For all the samples a stable generation of microsecond pulses in the Q-switch mode at a wavelength of about 1560 nm is observed. To the best of our knowledge, a passively Q-switched fiber laser with nanometer Bi films as a saturable absorber is implemented for the first time. It is established that even a small increase in the temperature of the surrounding medium leads to a significant increase in the transmission coefficient of polymer-coated tapers with deposited SA films, which may be attributed to a decrease in the refractive index of the polymers. The most significant increase in the transmission coefficient with increasing temperature is observed in tapers coated with PVA, which has a refractive index larger than fused silica.