Experimental Study On A PbS Quantum-dot-doped NIR Broadband Fiber Amplifier

Semiconductor nanocrystal quantum dots(QDs)receive great attentions in recent years due to their high quantum yield and adjustable peak wavelength in the absorption-emission light.By regulating the size and size distribution of QDs,we can adjust the bandgap width and the position of the absorption-emission peak wavelengths of QDs obtaining a bandwidth-tunable photoluminescence(PL).However,these unique characteristics are not available for the rare-earth elements.Therefore,using QDs as a gain medium to implement NIR broadband fiber communication amplifiers is a promising topic for extending bandwidth of communication wave band to realize long-distance,high-capacity,high-rate all-fiber communication networks.In this dissertation,we realize experimentally a quantum-dot-doped fiber amplifier(QDFA)which consists of 973-nm pumping laser(LD),isolator(ISO),wavelength division multiplexing(WDM),and QD dopedfibers(QDFs)utilizing the UV-gel as the optical fiber background and PbS QDs as the gain medium doped in the fiber.We achieve a PbS QDs doped fiber amplifier working in near-infrared S-C-L waveband(1470-1620 nm)and with low noise.By using the pressure difference method,the pre-made PbS QDs colloids with different doping concentrations are inputted into the hollow fiber with diameter of 50 ?m,to fabricate QDFs.An optical power meter and fluorescence spectrometer are used to measure the variation of the pumping power,PL intensity with doping concentrations of QDFs,and fiber lengths,respectively.We find the PL intensity of QDF reaching the maximum with the doping concentration of 2 mg/mL and the fiber length of 2.56 cm.Then,we build the QDFA using the suitable QDF and study its optical amplification characteristics(e.g.the gain characteristics and noise figure)by measuring the output signal spectrum.There is evidence to show that such a QDFA has 75-nm bandwidth around the region of 1550-nm wavelength with the switch gain of 16-19 dB(the net gain of 12.26-15.26 dB for the inputted signal power of-23 dBm)and the noise figure of ~3 dB.An obvious excitation threshold and gain saturation phenomenon are observed in the experiment.To achieve a peak PL intensity,a linear relationship between the QD doping concentrations and the fiber length is determined.The reason for widening QDFA bandwidth is closely related to the particle-size distribution of the QDs.Theperformance of bandwidth,C-waveband gain flatness and noise figure of QDFA obtained in this dissertation are better than the conventional erbium-doped fiber amplifiers(EDFAs),while the L-waveband gain flatness is a little lower than the optimized EDFAs.Compared with the QDFA excited by evanescent wave,the QDFA in this dissertation has a lower pumping excitation threshold,a lower pumping power to achieve gain saturation and a higher gain.The QDFA obtained in this dissertation does not involve optimization.In case of optimization for using the QDs with a wider size distribution and the wider-bandwidth signal sources,the obtained performance of the QDFA will be further improved on bandwidth,threshold power,and noise figure.Then,it will have obvious advantage over the conventional EDFAs and QDFA excited by evanescent wave.