Fig. 1. (a) TEM images and (b) size distribution of PbS QDs

Fig. 2. Energy level diagram of PbS QDs

Fig. 3. Experimental setup of QDFA

Fig. 4. (a) Measured absorption spectrum and transmissivity of UV-gel background; (b) measured PL-emission and absorption spectra of PbS QDs

Fig. 5. (a) Measured pumping power in QDF as a function of fiber length; (b) attenuation of QDF varying with wavelength

Fig. 6. PL peak intensity of QDF as a function of fiber length under different doping concentrations

Fig. 7. Relationship between Lopt and doping concentration

Fig. 8. Output signal spectra of QDFA under different pumping powers, where the illustration is output spectrum for zero pump

Fig. 9. Signal gain of QDFA as a function of wavelength under different pumping powers

Fig. 10. Signal gain as a function of pumping power under different wavelengths, the insert shows the partial enlargement

Fig. 11. Signal gain as a function of fiber lengthunder different wavelengths

Fig. 12. Signal gain and NF of QDFA