Passively Q-switched Er3+-doped fiber lasers using colloidal PbS quantum dot saturable absorber

Short-pulsed Q-switched fiber laser using graphene oxide quantum dots based as saturable absorber

In this work, we report the experimental study of a Q-switched optical fiber laser based on graphene oxide quantum dots (GOQDs) as saturable absorber (SA). GOQDs are fabricated by carbonization and exfoliation electrospun polyacrylonitrile (PAN) fibers. The results of Fourier Transform Infrared Spectroscopy (FTIR) showed bands caused by the CHs and C[bond, double bond]O groups associated with the GOQDs. The Raman spectrum showed the typical G and D bands of GOQDs. The size of the GOQDs, calculated by Transmission Electron Microscopy (TEM) was 6 nm; additionally, by high resolution TEM (HRTEM), an interplanar distance of 0.19 nm corresponding to the (002) direction of the graphene oxide was calculated. The SA was achieved using the photodeposition technique of the GOQDs onto the core of a single-mode optical fiber. The nonlinear characterization (NLC) of the GOQDs was carried out using the P-scan technique with a high-gain erbium-doped fiber amplifier (EDFA) at a wavelength of 1550 nm. The obtained results showed a saturable absorption behavior with a value of β = - 1.178 x 10 - 6 ( m / W ) and a non-linear susceptibility of I m ( χ ( 3 ) ) ≈ - 1.573 x 10 - 7 ( e s u ) . The experimental results of the SA, based on GOQDs as a switching device in a fiber laser, showed a typical behavior of a Q-switched laser by generating a pulsed emission at a wavelength of 1599 nm, a frequency from 2 to 16 kHz, and a maximum average output power of 1.3 mW.

Wavelength-tunable noise-like fiber laser based on PbS quantum dot saturable absorber film

A wavelength-tunable noise-like pulse (NLP) erbium-doped fiber laser incorporating PbS quantum dot (QD) polystyrene (PS) composite film as a saturable absorber (SA) is experimentally demonstrated. The wavelength tuning is implemented via a Lyot filter consisting of a segment of polarization-maintaining fiber (PMF) and a 45° tilted fiber grating. By adjusting the polarization state of the ring cavity, the laser can deliver NLP with a continuous wavelength-tunable range from 1550.21 to 1560.64 nm. During continuous wavelength tuning, the output power varies between a range of 30.88-48.8 mW. Worthwhile noting is that the output power of 48.8 mW is the reported highest output power for wavelength-tunable NLP operation in an erbium-doped fiber laser using composite film as a saturable absorber.

Highly efficient mode-locked and Q-switched Er3+-doped fiber lasers using a gold nanorod saturable absorber

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm², respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

PbS Quantum Dots Saturable Absorber for Dual-Wavelength Solitons Generation

PbS quantum dots (QDs), a representative zero-dimensional material, have attracted great interest due to their unique optical, electronic, and chemical characteristics. Compared to one- and two-dimensional materials, PbS QDs possess strong absorption and an adjustable bandgap, which are particularly fascinating in near-infrared applications. Here, fiber-based PbS QDs as a saturable absorber (SA) are studied for dual-wavelength ultrafast pulses generation for the first time to our knowledge. By introducing PbS QDs SA into an erbium-doped fiber laser, the laser can simultaneously generate dual-wavelength conventional solitons with central wavelengths of 1532 and 1559 nm and 3 dB bandwidths of 2.8 and 2.5 nm, respectively. The results show that PbS QDs as broadband SAs have potential application prospects for the generation of ultrafast lasers.

Passively Q-switched erbium-doped fiber laser utilizing tungsten oxide as a saturable absorber

We demonstrated a passively $Q$Q-switched fiber laser utilizing tungsten oxide (${\rm WO_{3}}$WO₃) thin film as a saturable absorber (SA). The ${\rm WO_{3} {\text -} SA}$WO₃-SA was sandwiched as a polymer composite film between fiber ferrules in an erbium-doped fiber cavity. ${\rm WO_{3}}$WO₃ exhibits high nonlinear optical response characterized by an appropriate modulation depth of 10% and a saturation intensity of ${100}\;{{\rm MW/cm}^2}$100MW/cm². The fiber cavity starts to generate a stable pulse train whereby as the pump power increases from 45 to 165 mw, the repetition rate increases from 16.75 to 56.3 kHz, while the pulse width decreases from 13.8 to 4.3 µs. The $Q$Q-switched laser generated maximum pulse energy of 6.6 nJ obtained at 165 mW, which was the maximum pump power available by the used laser diode. This is, to the best of our knowledge, the first demonstration of a $Q$Q-switched fiber laser based on the ${\rm WO_{3} {\text -} SA}$WO₃-SA, which could contribute as a new potential SA material in the field of pulsed fiber lasers.

Nonlinear Absorption Properties of Cr2Ge2Te6 and Its Application as an Ultra-Fast Optical Modulator

In this manuscript, the nonlinear absorption properties of Cr₂Ge₂Te₆ and its application in ultra-fast optical modulation are investigated. Typical parameters, namely, nonlinear absorption coefficient (β), saturation intensity, and modulation depth are measured to be ~1.66 × 10⁻⁹ m/W, 15.3 MW/cm², and 5.8%, respectively. To investigate the feasibility of using the Cr₂Ge₂Te₆ as an ultra-fast optical modulator, a ring-cavity passively mode-locked Er-doped fiber laser has been constructed. The output power/pulse, duration/pulse, and repetition rate/signal-to-noise ratios for the stable mode-locked operation are 2.88 mW/881 fs/19.33 MHz/48 dB, respectively, which proves that the Cr₂Ge₂Te₆ has outstanding nonlinear optical properties and advantages in performing as an ultra-fast optical modulator. Further, the experimental results provide valuable references and open new avenues for developing two-dimensional, material-based, ultra-fast optical modulators and advanced photonic devices based on Cr₂Ge₂Te₆.

Tunable passively Q-switched Dy3+-doped fiber laser from 2.71 to 3.08 μm using PbS nanoparticles

We present the first widely tunable passively Q-switched Dy³⁺-doped ZBLAN fiber laser around 3 μm pumped at 1.1 μm using PbS nanoparticles as the saturable absorber (SA) to our knowledge. At 2.87 μm, the modulation depth and saturation intensity of the SA were measured to be 12.5% and 1.10  MW/cm², respectively. Stable Q-switching was achieved over a wavelength range of 2.71-3.08 μm (∼370  nm), which is a record tuning range from a pulsed rare-earth-doped fiber laser, to our knowledge. A maximum output power of 252.7 mW was obtained, with a pulse energy of 1.51 μJ, a pulse width of 795 ns, and a repetition rate of 166.8 kHz. This demonstration implies that Dy³⁺ is a promising gain medium for tunable pulsed sources in the 3 μm band and shows for the first time, to the best of our knowledge, the potential of PbS as a mid-infrared SA.

Passively Q-switched Nd-doped fiber laser based on PbS/CdS core/shell quantum dots as a saturable absorber

In our work, PbS/CdS core/shell quantum dots with an absorption peak of 1043 nm were successfully employed as a modulator for achieving a passively Q-switched Nd-doped fiber laser. The saturation intensity and modulation depth of the film-type modulator were 7.6  MW/cm² and 4.1%, respectively. Due to the protection of the CdS shell, the PbS core exhibited good photo-chemical stability, which led to the generation of stable passively Q-switched operation. The maximum average output power was 7.88 mW with a minimum pulse width of 235.7 ns. To our knowledge, this was the first demonstration focusing on the combination of quantum dot and Nd-doped fiber laser; in addition, 235.7 ns was the narrowest pulse width of a passively Q-switched Nd-doped fiber laser. Our results highlighted the excellent nonlinear absorption properties of PbS/CdS core/shell quantum dots and give significant guidance for future optical applications of quantum dots and demonstrations of pulsed Nd-doped fiber lasers.

Stable passively Q-switched erbium-doped fiber laser incorporating a PbS quantum dots polystyrene composite film based saturable absorber

We demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) using PbS quantum dots in polystyrene films (QDPFs) as saturable absorbers (SAs). Compared to other SAs, PbS QDPFs have advantages of broad absorption range, high quantum yield, low cost, and facile preparation. We have successfully generated stable Q-switched pulses with an average output power of 40.19 mW, a single pulse energy of 586.1 nJ, a repetition rate of 68.04 kHz, a pulse width of 3.9 μs, and a signal-to-noise ratio of 50.5 dB under 660 mW pump power. The output of the EDFL has been monitored for 5 consecutive hours under laboratory conditions to show stable operation of the laser system.

Mode-locked Er-doped fiber laser based on PbS/CdS core/shell quantum dots as saturable absorber

Previously, PbS/CdS core/shell quantum dots with excellent optical properties have been widely used as light-harvesting materials in solar cell and biomarkers in bio-medicine. However, the nonlinear absorption characteristics of PbS/CdS core/shell quantum dots have been rarely investigated. In this work, PbS/CdS core/shell quantum dots were successfully employed as nonlinear saturable absorber (SA) for demonstrating a mode-locked Er-doped fiber laser. Based on a film-type SA, which was prepared by incorporating the quantum dots with the polyvinyl alcohol (PVA), mode-locked Er-doped operation with a pulse width of 54 ps and a maximum average output power of 2.71 mW at the repetition rate of 3.302 MHz was obtained. Our long-time stable results indicate that the CdS shell can effectively protect the PbS core from the effect of photo-oxidation and PbS/CdS core/shell quantum dots were efficient SA candidates for demonstrating pulse fiber lasers due to its tunable absorption peak and excellent saturable absorption properties.