Fig. 1. Effects of heat treatment time on photoluminescence spectra of PbSe quantum dot-doped glass samples^[20]. (a) The first heat treatment time; (b) the second heat treatment time

Fig. 2. Absorption spectra and photoluminescence (PL) spectra^[24]. (a) Absorption spectra of P1.5 glasses heat treated at different temperatures for 24 h; (b) PL spectra of P1.5, P1, and Z2 glasses heat treated at different temperatures for 24 h

Fig. 3. Spectra of PbSe quantum dots glass samples^[27]. (a) Optical absorption spectra of PbSe quantum dots glass samples, where the inset is a magnified spectrum of the area within the rectangle (1000‒1400 nm); (b) normalized emission spectra of glass samples under excitation at 550 nm, where the inset is the dependence of the PL peak wavelength on B₂O₃ concentration

Fig. 4. Measurement results of network structure of PbSe quantum dot glasses and schematic of the difficulty level of ion diffusion in different glass network structures^[27].(a) Fourier transform infrared spectroscopy (FT-IR) spectra of PbSe quantum dot-doped glass samples; (b) ¹¹B magic angle spinning nuclear magnetic resonance spectra of glass samples 5B₂O₃(BS5) and 20B₂O₃(BS20); (c) schematic illustration showing the difficulty level of ion diffusion in three-dimensional glass network structure and three-dimensional glass network structure; (d) schematic illustration showing the difficulty level of ion diffusion in two-dimensional glass network structure and two-dimensional glass network structure

Fig. 5. Optical microscopy image, Raman spectrum and ion distribution schematic of PbS quantum dot glass^[28]。(a) Optical microscopy image of PbS quantum dot glass-doped with AgNO₃;_{(b) Raman mapping for the Raman peaks at 2300 cm^-1 (b), 1840 cm^-1 (c), and 1375 cm^-1 (d) of AgNO3-doped glasses irradiated at a laser power of 1.8 W and a scanning speed of 5 μm/s, where the box and arrows in (a) are guide marks for the Raman mapping zone, and the scale bars in (a)‒(d) represent 20 mm; (e) schematic illustration of the formation of three characteristic zones in the irradiated area after irradiation at laser power of 1.8 W and a scanning speed of 5 μm·s^-1, where the horizontal dotted arrow is a guide mark for the eyes and shows the direction of detection of EPMA; (f) ion distribution around the focal center measured by electron probe micro-analyzer (EPMA)}

Fig. 6. PbSe quantum dot-doped glass fiber^[29-31]. (a) Schematic illustrations of the fabrication process of quantum dot fiber; (b)‒(d) transmission electron microscopy (TEM) images of PbSe quantum dot-doped glass fiber; (e) comparison between PbSe quantum dot fiber (QDF) and conventional SiO₂ single mode fiber

Fig. 7. PL spectra of PbSe QDF^[30]. (a) PL-emission intensity of QDF as a function of fiber length for the different annealing conditions; (b) PL spectra of QDF with different lengths; (c) PL spectra of the identical QDF

Fig. 8. Melt-in-tube technique and PbS quantum dot-doped glass fiber prepared by the technique^[32-33]. (a) Schematic of melt-in-tube technique; (b)(c) digital photographs of glass preform before and after drawn by melt-in-tube technique; (d) high-definition transmission electron microscopy (HRTEM) image of the PbS quantum dot-doped glass fiber heat treated at 560 ℃ for 10 h; (e) HRTEM image of a single quantum dot in the PbS quantum dot-doped glass fibers

Fig. 9. Schematic of element-migration path and element distribution of PbS quantum dot glass fiber^[32-33]。(a) Schematic illustrations of element-migration pathways in PbS quantum dot-doped glass fiber^[32]; the distribution of representative elements measured by line scanning electron probe micro-analyzer (EPMA) across the cross-section of heat-treated fiber: (b) before optimization^[32]; (c) after optimization^[33]

Fig. 10. PL spectra and lifetime decay curves of PbS quantum dot-doped glass fiber^[33]. (a) PL spectra of PbS quantum dot-doped glass fiber heat-treated at different temperatures for 5 h; (b) PL spectra of fiber heat-treated at 390 ℃ for different duration; (c) lifetime decay curves of fiber heat treated at different temperatures for 5 h

Fig. 11. Structure characterization and spectrum of PbSe quantum dot fiber^[34].(a) A TEM photograph showing PbSe quantum dots in the optical fiber preform; (b) spectral variations of attenuation of the PbSe quantum dot-doped optical fiber; (c) emission spectrum from the PbSe quantum dot-doped optical fiber upon pumping with the 1064 nm Nd∶YAG laser

Fig. 12. Fabrication process of PbS quantum dot-doped silica fiber (PQDF) and its refractive index difference^[37]. (a) Fabrication process of PQDF; (b) refractive index difference of the PQDF, where the inset is cross-section of the fiber

Fig. 13. Structure characterization and spectrum of PbS quantum dot fiber^[37]. (a) High-resolution transmission electron microscopy (HRTEM) images of PbS quantum dots fiber, where the inset is the size distribution of PbS quantum dots; (b) lattice image; (c) selected-area electron diffraction (SAED) pattern; (d) detailed statistics for maximum size distribution; (e) optical loss spectrum of the PQDF; (f) luminescence spectra of the PQDF with different pump powers, where the inset is luminescence intensity versus pump power of three active centers

Fig. 14. Refractive index profile and fluorescence spectra of the PbS-doped ring-core fiber^[38]. (a) Refractive index profile of the PbS-doped ring-core fiber and the cross-sectional microscopic image of the fiber; (b) fluorescence spectra of the fiber

Fig. 15. Absorption spectrum and bleaching relaxation curves of PbS quantum dot glass and train of mode-locking pulses of the laser^[39-40]. (a) Absorption spectra of silicate (1 and 2) and phosphate (3) glasses containing PbS quantum dots of 3.8, 4.3, and 4.2 nm in mean diameter, respectively, where the insert is the transmission spectra of these glasses, and the arrows indicate pump and probe wavelengths at 1048 nm; (b) bleaching relaxation for PbS quantum dots of 3.8 nm in diameter, and pump fluences are 0.58 and 1.4 mJ/cm², where open triangular symbols indicate bleaching relaxation at high pumps; (c) bleaching relaxation for PbS quantum dots of 4.3 nm in diameter, and pump fluences are 0.77 and 1.4 mJ/cm²; (d) bleaching relaxation for PbS quantum dots of 4.2 nm in diameter, and pump fluences are 0.46 and 0.72 mJ/cm²; (e) train of mode-locked pulses from the Cr-Tm-Ho∶YSAG laser with the PbS quantum dots-based saturable absorber

Fig. 16. Configuration schematic of the laser and train of mode-locking pulses^[41]. (a) Configuration schematic of Tm∶KYW laser; (b) a single Q-switched pulse consisted of a train of mode-locking pulses; (c) a train of mode-locking pulses at the frequency of 185 MHz within a Q-switched pulse envelope

Fig. 17. Schematic of optical amplification experimental system and optical gain of PbS quantum dot-doped glasses^[24]. (a) Schematic of optical amplification experimental system, where a represents 1330 nm or 1550 nm laser diode (LD) as probe beam, b represents 808 nm LD as excitation source, c represents chopper, d represents mirror, e represents lens, f represents sample, g represents filter, h represents InGaAs p-i-n detector, and i represents digital oscilloscope; (b) optical gain (I/I₀) of PbS quantum dot-doped glasses as a function of pumping power, where (1) represents Z2 glasses heat-treated at 600 ℃ for 24 h, (2) represents P1 glasses heat-treated at 580 ℃ for 24 h, (3) represents P1.5 glasses heat-treated at 550 ℃ for 24 h,and the insert shows the amplified signals of P1 glasses heat-treated at 580 ℃ for 24 h

Fig. 18. Response curve and nonlinear switch test results of PbSe quantum dot fiber^[34]. (b) Response time of the PbSe quantum dot-doped optical fiber, pumping wavelength is 1064 nm and the response is detected at 1500 nm (y-axis: voltage; and x-axis: time); detected output signal at 1500 nm when the continuous wave pump at 1064 nm with 0 mW (c) and 550 mW (d) power (y-axis: voltage; and x-axis: time)

Fig. 19. Experimental setup schematic and output signal spectrum of quantum dot fiber amplifier^[43]. (a) Experimental setup of quantum dot fiber amplifier (QDFA); (b) spectral distribution of PbSe quantum dot-doped fiber amplifier output signal at different pump powers

Fig. 20. Gain spectra of PbS QDFA^37]. (a) Net gain spectra of QDFA at different pump powers; (b) net gain versus pump power at three active centers; (c) on-off gain spectrum and net gain spectrum with 120 mW pumping

Fig. 21. Configuration schematic and mode transmission results of OAM amplifier^[38]. (a) Setup of OAM amplifier, where a represents polarization controller, b represents collimator, c represents spiral phase plate, d represents quarter-wave plate, e represents lens, f represents dichroic mirror (DM), g represents objective, h represents beam-splitter, i represents linear polarizers, and j represents right-angle prism mirror; (b) beam profile before entering the input side of the fiber; (c) interference before entering the input side of the fiber; (d) beam profile after exiting the output side of the fiber; (e) interference after exiting the output side of the fiber