O-band And Ultra-broad Band Quantum Dot Fiber Amplifiers

Fiber amplifier is one of the key components of optical fiber communicationsystem. Higher bandwidth requirements of fiber amplifier are highly valued for thegrowing demands for information exchange. For now, bandwidth of a variety of rareearth-doped fiber amplifiers including commercial erbium-doped fiber amplifier(EDFA) has covered only part of the optical fiber communication bands(1200-1700nm). Especially, for the1310nm optical communication window,O-band optical fiber amplifier is scarce. The appearing of Quantum Dots (QDs) hasbrought great hope to solve this problem. QDs have ultra-wideband emission andsize effect and have great potential to serve as the gain medium in bandwidth tunablefiber amplifiers.In this thesis, we proposed a new "O-band and ultra-wideband quantum dotsfiber amplifiers" which use PbS QDs as the gain medium and a2x2taper coupler asthe carrier respectively. By "controlling the synthesis conditions" and "multi-sizedQDs doping", QDs with ideal emission spectra were obtained. Then, QDs-dopedsol-gel solution was applied over the cone to form a new "cladding". Based onevanescent wave, the signal light followed will be amplified when the PbS QDs inthe taper region are excited by pump light. The main works and innovations are asfollows:(1)By improving the existing organometallic synthetic routes, we obtainedsmall PbS QDs with emission peak at1310nm at relatively low temperature40℃,which were characterized by TEM and Fluorescence Spectroscopy. Moreover, theeffect of synthesis temperature and reaction time on the fluorescence spectra wasalso studied. Reaction temperature of this method was easily controlled and thepreparation condition was mild. The resulting quantum dots have symmetryfluorescence spectrum. By applying those QDs to the fiber coupler, we fabricatedO-QDFA which showed a flat gain spectrum in the1260-1360nm.The impact ofpump power on amplifier performance was also studied, and a24dB maximumswitching gain with400mW980nm pumping was achieved. Considering the system losses, the net gain was up to5.5dB.(2)The hydrophobic PbS QDssynthesized in the organic phase were modified with a home-made amphiphilicpolymer so that the QDs could be easily dispersed into alcohol solution, which madepossible the formation of high-quality silica thin films doped with QDs in the"cladding".(3)With multi-sized QDs doping method, polymer modified QDs ofdifferent sizes with emission peaks located at1550nm and1310nm respectivelywere mixed and resulted in the broadening of the fluorescence spectra. TheQDs-doped silica sol was applied to the self-made taper coupler to makeultra-wideband optical fiber amplifier. The amplifier showed a400nm (1200-1600nm) bandwidth with70mW980nm pumping and the switching gain was higherthan14dB. Moreover, to explore the best doping ratio of the two sized QDs, we alsostudied the effect of different ratios of the two QDs on the amplification of the fiberamplifiers.The research provides experimental bases to the realization of the O-band andultra-broad band fiber amplifiers needed in the1310nm window and high speedoptical fiber communication systems.