A Ti3C2 MXene based saturable absorber (SA) was demonstrated as an optical modulator to enable Q-switching and mode-locking in a Thulium-Holmium doped fiber laser (THDFL) cavity. Two different SA configurations were studied, with one SA in the form of a polyvinyl alcohol (PVA) polymer host thin film and the other one with the Ti3C2 MXene deposited along with a D-shaped fiber. For the case of the Ti3C2-PVA SA, only Q-switched was obtained at the threshold pump power of 126.4 mW. The generated Q-switched pulses had a center wavelength of 1961.4 nm with a maximum repetition rate and pulse energy of 42.5 kHz and 37.4 nJ and a minimum pulse duration of 2.4 mu s. For the Ti3C2 MXene coated D-shaped fiber SA, mode-locking was achieved at a pump power of 209.9 mW with a center wavelength of 1915.9 nm and having a repetition rate and pulse width of 12.6 MHz and 1.89 ps, respectively. The experimental results indicate that the Ti3C2 MXene based SA could generate Q switched pulses when in the form of a thin film but can only be used as a mode-locker when the SA material is coated along the surface of the D-shaped fiber.

This research demonstrates mode-locked erbium-doped fiber laser (EDFL) and thulium-holmium doped fiber laser (THDFL) using hafnium diselenide (HfSe2) as saturable absorber (SA). The Kelly's sidebands were observed in both spectra, showing that both lasers operated in an anomalous dispersion region. A polarization controller was used to achieve reliable mode-locking operation at a threshold power of -46 mW and -254 mW for the EDFL and THDFL respectively. The center wavelengths obtained for the EDFL and THDFL were 1557 nm and 1912 nm, respectively. In EDFL, the output soliton generates 0.75 ps of pulse width and a repetition rate of 14.8 MHz, while THDFL has a pulse width of 1.15 ps and a repetition rate of 12.5 MHz. The pulses were highly stable for both gain mediums, verified by the signal-to-noise ratio (SNR) of 68 dB and 63 dB for EDFL and THDFL, respectively. In addition, there were no significant changes during the three-hour stability test, suggesting a longterm stability. This work shows a low-cost laser with possible application in C-band and near the 2.0 mu m region.

This study demonstrates the potential of cadmium telluride (CdTe), a part of the quantum dot (QD) family, as a saturable absorber (SA) to generate ultrashort pulses at the C-band region. The SA was fabricated by drop-casting the CdTe material onto the exposed core of the D-shaped fiber. The nonlinear property of the fabricated SA has a modulation depth of 1.87% and saturation intensity of 6.0 kW cm(-2). The mode-locked laser was generated after the SA was integrated into the erbium-doped fiber laser (EDFL) cavity at a threshold pump power of 192.1 mW giving a center wavelength of 1559 nm and a pulse duration of 770 fs. The maximum average output and peak power were measured to be 2.8 mW and 0.208 kW, respectively. The mode-locked fiber laser generated a signal-to-noise ratio (SNR) of 67.7 dB, proving that the generated mode-locked pulses were very stable. The current work indicates that the novel CdTe device can provide stable mode-locked lasers in the C-band region.

Vanadium carbide (V2C), a member of the MXene family, promises numerous possibilities in ultrafast laser technology with substantial applications in various optical industries. In this work, MXene V2C was deposited onto a tapered fiber using the drop-casting technique and incorporated into a thulium/holmium doped fiber laser cavity for generating mode-locked outputs in the 2.0 mu m region. The fabricated SA exhibited nonlinear optical properties such as saturation intensity and modulation depth of 2.07 MW/cm(2) and 7.57%, respectively. The findings of the mode-locked characteristics showed a central wavelength of 1937 nm with a signal-to-noise ratio (SNR) of 73 dB. Correspondingly, the laser-generated mode-locked pulses with output power, pulse energy, and peak power of 2.71 mW, 235.2 pJ, and 0.14 kW, respectively. The results suggest that the mode-locked laser obtained based on the MXene V2C could be applied to the field of photonics.

Passive mode-locking pulse generation in a Thulium-Holmium doped fiber laser (THDFL) with molybdenum tungsten disulfide-reduced graphene oxide (MoWS2-rGO) nanocomposite saturable absorber (SA) was demonstrated for operation in 2.0 mu m wavelength regions. Mode-locked pulse was achieved by the evanescent wave interaction with the MoWS2-rGO based SA embedded on a side polished fiber. The THDFL produces mode-locked pulses centered at 1908.6 nm with a repetition rate and pulse duration of 11.9 MHz and 1.5 ps, respectively. A high signal to noise ratio (SNR) of 48 dB as well as minimal power and wavelength fluctuations indicates the excellent stability of the mode-locking operation. To the best of our knowledge, it is the first demonstration of MoWS2-rGO used as a SA in the THDFL system. The proposed laser would benefit various domains, mainly medicine, for its operation in the eye-safe 2.0 mu m wavelength region.

In this work, a WTe2 coated tapered fiber was used as a saturable absorber (SA) to induce mode locking in a thulium/holmium doped fiber (THDF) laser through evanescent field interaction. The WTe2 was drop-casted onto the tapered fiber to form an SA which had a modulation depth of 18.08%, saturation intensity of 0.14 MW/cm(2), and non-saturable absorption of 81.92%. Mode locked pulses were obtained at a wavelength of 1909.81 nm with a pulse width of 1.77 ps, and a 3 dB bandwidth of 2.2 nm. It has a signal-to-noise ratio of 52 dB and a repetition rate of 11.54 MHz at a pump power of 436.4 mW. The maximum output power, pulse energy, and peak power obtained were 3.51 mW, 303.9 pJ, and 0.17 kW respectively. The use of evanescent field coupling in the tapered fiber with the WTe2 nanoparticles allows the realization of high-power mode locking applications.

In this work, a simple yet efficient method of growing magnetic binary metal oxides of CuO/Fe2O3 nanoparticles on reduced graphene oxide (rGO) sheets using the hydrothermal method was demonstrated. The rGO-CuO/Fe2O3 nanocomposite was characterized by X-ray diffraction (XRD), Raman, field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscopy (HRTEM) analysis. The nonlinear optical absorption characteristics of the rGO-CuO/Fe2O3 nanocomposite exhibited a modulation depth and saturation intensity of 12.5% and 1.0 kW/cm2, respectively. The rGO-CuO/Fe2O3 nanocomposite in the solution form were drop-casted onto a microfiber to form a saturable absorber (SA) which was then incorporated into a Thulium-Holmium (Tm/Ho) co-doped fiber laser (THDFL) cavity. The mode-locked output was generated at 1917 nm with pulse duration of 1.34 ps and repetition rate of 11.36 MHz. The obtained RF spectrum revealed that the mode-locked laser was stable with a signal to noise ratio (SNR) of about 63 dB. This work demonstrated the capability of rGO-CuO/Fe2O3 nanocomposite as an SA to induce stable mode-locking in a THDF fiber laser cavity.

A mode-locked Thulium-Holmium doped fiber laser (THDFL) with a Germanium Selenide (GeSe) saturable absorber (SA) is demonstrated for operation in the 2.0 mu m wavelength region. The SA device is fabricated by drop-casting the GeSe onto an arc-shaped fiber which is then incorporated into the THDFL to induce mode-locked pulses. Stable mode-locking is attained at 1908.78 nm, with pulse duration of 1.67 ps and output power of 2.74 mW at a maximum pump power of 476 mu W. The results of this work show that the GeSe can be a viable alternative for ultrafast photonics applications in the 2.0 mu m. region.

High responsivity, large-area plasmonic-enhanced nanostructure photodetector based on multilayer (ML) molybdenum disulfide (MoS2) deposited on p-type Silicon (Si) substrates is reported. A large area ML-MoS2 is deposited onto the Si photodetector (PD) using a modified membrane filtration method. This large area ML-MoS2 and Au NSs on the p-Si form a cavity-like structure that dramatically enhances the incident light path. The increase of incident light path due to light trapping effect enhances the electron-hole pair generation tremendously. The plasmonic-enhanced ML MoS2 on Si PD has achieved a stable and repeatable photoresponse up to 37 A W-1, whereas the detectivity is around 10(12) Jones at the broad wavelengths (405-780 nm) with a modulation frequency of 1 kHz. The enhancement of photoresponsivity is 8, 5.3 and 11 times with 5 V bias at an incident wavelength of 405 nm, 650 nm and 780 nm respectively as compared to the bare p-Si PD. The experimental results also show that the plasmonic-enhanced ML-MoS2 on Si PD exhibited fast photoresponse (rise time of similar to 1 mu s and fall time of similar to 18 mu s), which is much higher compared to typical transition metal dichalcogenide PD or single layer MoS2 based PD. These excellent performances show that the plasmonic-enhanced MoS2 structure is highly potential to apply in Si photovoltaics, visible range photodetection, and visible bio/chemical sensing application.

In this work, tungsten disulphide (WS2) based heterojunction photodetector device is fabricated on top of silicon (Si) substrate by using simple drop casting method. The device is characterised for its optoelectronic properties in the visible range of light illumination at 465 nm. The current-voltage (I-V) measurement is performed to attain I-V curves of various laser powers (282.6 μW, 589.2 μW, 889.9 μW, 1.07 mW and 1.265 mW). The photocurrent is found to be highly dependent on the laser power. Time based responses are calculated at 3.0 V DC bias voltage for various modulation frequencies (1 Hz, 50 Hz, 100 Hz, 500 Hz, 1 kHz, 3 kHz and 5 kHz). The fabricated device has high responsivity of 66.85 mA/W for an incident laser power of 1.265 mW and detectivity of 1.1763 × 10 9 Jones for an incident laser power of 282.6 μW. Raman shifts are observed at 351.38 cm -1 and 420.54 cm -1 , confirming the successful growth of WS 2 and verification of a non-stoichiometric WS 2 layer by the energy-dispersive X-ray (EDX) spectroscopy. These results are very promising towards further development for optoelectronic applications.