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Transformer oil is widely used in high-voltage transformers as a cooling and insulation medium. Electrical and thermal stresses expose transformer oil to degradation, which may produce dissolved decay products (DDPs) that are partially adsorbed on the insulation paper and accelerate the degradation of oil and paper. An evanescent field D-shaped plastic optical fibre (POF) sensor was fabricated using the side-polishing technique to detect DDPs in transformer oil. A laser light source and power meter were used in the prototype to measure the output power of the POF sensor. The measurement of DDPs was conducted on seven samples of insulating oil collected from the field. The sensor performance was evaluated based on different sensing areas, and the sensor sensitivity was measured. Results show an excellent correlation between the output power and DDPs. A correlation analysis was conducted amongst sensor output power, transformer oil refractive index and area under the absorbance curve. The performance of the sensor demonstrates improved linearity and sensitivity of 97.49% and 26.6779 µW/RIU, respectively. The POF sensor is easily fabricated, low cost and can be used for real-time monitoring of high-voltage transformers.

A novel all fibre Q-switched Thulium-doped fibre laser (TDFL) is reported which includes a short length of a Thulium–Holmiumco-doped fibre (THDF) as a saturable absorber. A high repetition rate (27.26 kHz) coupled with a low pulse width ( 19 . 06 μ s ) is obtained for single wavelength Q-switched pulse operation at an output wavelength of 1911.5 nm using a pump power of 200 mW. Increasing the pump power from 200 mW to 700 mW results in the repetition rate increasing from 27.26 kHz to 99.67 kHz and the pulse width decreasing from 19 . 06 μ s to 920 ns. The centre wavelength of the single Q-switched pulse was also red shifted from 1911.5 nm to 1932.5 nm with increasing the pump power. A 45 m length single-mode fibre (SMF-28) provided dispersion compensation, and effectively an SMF-THDF-SMF structure is inserted in the cavity which operates in a similar manner to an SMF-MMF-SMF structure, providing a strong multimode interference effect which supports dual-wavelength operation. A stable dual-wavelength Q-switched pulse was achieved at a threshold pump power of 213 mW. The dual-wavelength Q-switched pulse operation was generated at 1911.5 nm and 1914.5 nm with a repetition rate of 8.45 kHz and pulse width of 20 . 02 μ s . The dual-wavelength spacing of this pulse operation was 3 nm, which was in good agreement with calculations based on the multimode interference effect induced by the THDF. The repetition rate increased from 8.45 kHz to 70.65 kHz and the pulse width decreased from 20 . 02 μ s to 870 ns with increasing pump power. At the maximum pump power of 700 mW, the maximum output power was measured as 27.4 mW. The experimental results confirm that the THDF can be utilized as a SA to generate a stable and tunable single-wavelength Q-switched pulse output as well as dual-wavelength Q-switched pulse in the 2 . 0 μ m wavelength region.

A passively Q-switched and mode-locked fiber laser based on thulium-doped fiber laser (TDFL) cavity was demonstrated utilizing nickel oxide (NiO) nanoparticles as a saturable absorber (SA). The NiO synthesis was carried out by using a facile sonochemical method and the prepared NiO thin film was sandwiched between two optical fiber ferrule connectors in the TDFL ring cavity. By controlling the loss and gain in the cavity, stable Q-switching operation was obtained. The repetition rate and pulse width were tunable from 6.71 kHz to 19.58 kHz and from 9.16 μ s to 4.24 μ s respectively, at different pump powers, ranging from 528 mW to 711 mW. The Q-switched TDFL was centered at 1900.52 nm and had maximum pulse energy and slope efficiency of 0.31 μ J and 2.58%, respectively. On the other hand, self-starting mode-locked TDFL was achieved by employing 10 m scandium-doped fiber into the ring cavity and remained stable within a pump power range of 821–967 mW. The TDFL mode-locked had a central wavelength of 1928.81 nm, at a threshold pump power of 821 mW. The repetition rate and pulse width were 8.10 MHz and 61.27 ns, respectively, while the slope efficiency was measured to be 2.20 %.

We reported a newly fabricated saturable absorber (SA) namely Lutetium oxide (Lu2O3) thin film for generating a stable and compact mode-locked Erbium-doped fibre laser (EDFL) operating at 1564 nm. The film SA was synthesized by embedding Lu2O3 into polyvinyl alcohol (PVA) host film. By incorporating the film SA along with 200 m long single mode fibre (SMF) into an EDFL cavity, the mode-locked laser with 0.97 MHz repetition rate stably emerged at an increasing pump power, ranging within 145-187mW. The pulse width was measured to be 2.12 ps. The highest pulse energy and peak power were measured as 7.64 nJ and 3.61 kW respectively and were obtained at 187 mW pump power. The fundamental frequency was examined to have a signal to noise ratio (SNR) of 61 dB. These laser performances suggest that the Lu2O3 film SA is feasible for becoming an alternative passive SA in the 1. 55 μ m region.

We demonstrate a mode-locked nanosecond erbium-doped fiber laser using gold nanoparticles saturable absorber. The gold nanoparticles were obtained through sodium borohydrate reduction method and made into a film structure by embedding into poly (vinyl alcohol). The laser directly produces nanosecond pulses with stable mode locking at a pump threshold of 157 mW. Resultant output pulses have central wavelength, pulse duration and repetition rate of 1561 nm, 436 ns and 1 MHz, respectively. The average output power was measured to be 6.94 mW under the pump power of 245 mW, corresponding to single pulse energy of 6.8 nJ. The experimental results show that gold nanoparticles are a promising material for ultrafast laser systems.

We report for the first time, the application of Lutetium oxide (Lu2O3) thin film as a saturable absorber (SA) in generating a stable and compact Q-switched Erbium-doped fiber laser (EDFL) operating at 1570 nm. The film SA was prepared by embedding the Lu2O3 particles into a polyvinyl alcohol (PVA) host film. By integrating the film SA in a laser cavity, a stable pulsed laser appeared when the input pump power hit the threshold at 26.3 mW. The frequency of the pulsed laser rose from 18.4 kHz to 30.4 kHz, matching the increase of pump power from 26.3 mW to 71.6 mW. The shortest pulse width of 8.47 µs and the highest peak power of 8.98 mW were obtained at the maximum available pump power of 71.6 mW. Meanwhile, the maximum output power and pulse energy were measured at approximately 2.32 mW and 76 nJ, respectively. In addition, the signal to noise ratio (SNR) was 40 dB. These indicators suggest that Lutetium oxide film is a good passive SA that can be used to generate pulsed laser operating at1.55 µm region.

A stable all-fiber passively Q-switched erbium-doped fiber laser emitting at 1559 nm is proposed and demonstrated using an 8-cm-long hafnium–bismuth–erbium co-doped fiber (HBEDF) as a saturable absorber (SA). The HBEDF is fabricated in-house and has a linear absorption of around 5.2 dB at the laser operating wavelength of 1559 nm. The Q-switching pulses are obtained with an input pump power ranging from 50 to 121 mW. It has the pulse repetition rate of 81.57 kHz, the shortest pulse width of 3.31 µs, output power of 10 mW, pulse energy of 123 nJ and peak power of 37.3 mW at the maximum pump power of 121 mW. The corresponding signal-to-noise ratio of the electrical spectrum is measured to be around 70 dB, which indicates the stability of the laser. To the best of our knowledge, this is the first demonstration of the deployment of HBEDF SA in generating a robust and steady pulsed laser in 1.5-micron region.

We demonstrate a Q-switching operation laser at 1.55- and 2-µm region using a homemade 10 cm long of Chromium-doped fiber (CrDF) as a passive saturable absorber (SA). Erbium-doped fiber (EDF) and Thulium-doped fiber (TDF) as a gain medium cooperate in the all-fiber ring cavity configuration. CrDF was fabricated by Modified Chemical Vapour Deposition (MCVD) technique in conjunction with conventional solution doping (SD) method. The CrDF has a saturable absorption of 9% at 1.55-µm region with a saturation intensity of 22 MW/cm2. Therefore, a stable pulse train obtainable within 75–173 mW, with a repetition rate increases from 68.12 kHz to 115.9 kHz. At the maximum pump level, a shorter pulse width, maximum output power, and maximum pulse energy are 3.85 µs, 10.86 mW, and 94.1 nJ, respectively. In TDF laser cavity, the laser pulsing generates from 363 mW to 528 mW, where the repetition rate increases from 13.02 kHz to 27.62 kHz. At maximum pump power, a shorter pulse width, maximum output power, and pulse energy are obtained with 4.48 µs, 6.36 mW, and 230.27 nJ, respectively. Both pulse trains at 1.55- and 2-µm region are stable with a signal-to-noise ratio (SNR) of 71 dB and 44 dB, respectively. These findings are important to the discovery of robust passive saturable absorber development in a form of fiber which has a similar melting point to the rest of the silica fiber in the proposed cavities. Thus, it will be a kick-started to alternative form of passive SAs in developing a future high-power fiber lasers.

In this paper, a stable and robust all-fibre passively Q-switched erbium-doped fibre laser (EDFL) emitting at 1558 nm is described. The proposed laser utilizes an 11 cm long erbium-doped fibre as saturable absorber (SA). The fibre SA features a linear optical absorption of about 13 dB in the Q-switched EDFL operating regime. By elevating the input pump power from the threshold of 60 mW to the maximum available power of 142 mW, a pulse train with a maximum repetition rate of 86 kHz, minimum pulse width of 3.39 µs, maximum average output power of 10.5 mW, maximum pulse energy of 122 nJ and maximum peak power of 36 mW are obtained. The signal to noise ratio (SNR) of the spectrum is measured to be around 70 dB. This fibre SA is simple, reliable, compact and alignment free. Thus it is suitable for making a portable pulse laser source.

This paper reports a generation of short-pulsed thulium-doped fiber laser (TDFL) in Q-switching operation incorporation of homemade graphene oxide (GO) saturable absorber (SA). The GO SA is embedded with a polymer to form a GO film. A piece of the GO film is integrated into the TDFL cavity for generating a self-started Q-switching operation at 1943 nm wavelength. The 3-dB bandwidth, repetition rate, and pulse width of the laser are obtained as 9 nm, 15.76 kHz–25.08 kHz, and 5.08 μs–4.2 μs, respectively. The maximum pulse energy of 0.698 μJ obtainable at 344 mW pump power, with a peak power of 137.4 mW. With a shortest pulse width size at a maximum pump power of 491 mW, the higher peak power is determined about 162 mW. By integrating our stable Q-switched laser with an optical amplifier, numerous applications such as a material cutting with the eye-safe feature can be realized. This shows a small piece of the GO can modulate a light and use for the pulsed laser industry.

A soliton-locked Erbium-doped fiber laser is demonstrated for the first time using a pure Antimony (Sb) film as a saturable absorber (SA). The SA device is fabricated by depositing a 5 μm Sb layer onto a polyvinyl alcohol thin film via Physical vapor deposition process. Self-starting soliton mode-locked pulses train with a constant repetition rate of 0.99 MHz is obtained as the pump power increased from 101 mW to 142 mW. The laser operates at 1559 nm with a pulse width of 3.53 ps. At the pump power of 142 mW, the maximum peak power and pulse energy are calculated as 5.83 kW and 20.59 nJ, respectively. The obtainable pulse is very stable with a signal-to-noise ratio (SNR) of 70 dB. Our experimental results manifest that the pure Sb thin film-based SA is able to generate mode-locked pulsed laser at the 1.55-micron laser regime.

Stable and compact Q-switched and mode-locked thulium-doped fiber laser (TDFL) is demonstrated by employing Antimony (Sb) film Saturable absorber (SA) in the ring cavity. The Sb film SA is fabricated by sputtering a thin layer of Sb element onto polyvinyl alcohol (PVA) thin film. Self-pushed TDFL Q-switched with repetition rate and pulse width of 14.5 kHz to 23.5 kHz and 11.6 μ s to 4.9 μ s respectively are obtained, as the pump power raises from the threshold (271 mW) to its maximum (399 mW). The TDFL Q-switched spectrum is centered at 1947 nm wavelength. At the maximum pump power (399 mW), the maximum peak power and the maximum pulse energy are obtained at 24.4 mW and 120.12 nJ respectively. Meanwhile, self-starting mode-locked TDFL emerges as the pump power varies from 454 mW to 582 mW. The TDFL mode-locked output spectrum is centered at 1914 nm wavelength. A nearly constant repetition rate of 8.65 MHz and pulse width of 64 ps are observed, as the pump power lifted to the maximum (582 mW). The results verify that the pure Sb PVA film SA is viable to construct stable and reliable short pulse laser in the 2-micron regime.

In this paper, we report a nanosecond mode locked erbium doped fiber laser (EDFL) using zinc oxide (ZnO) nanoparticles as a saturable absorber (SA) for the first time. Due to its excellent optical properties, in particular a high nonlinear optical response and fast recovery time, ZnO nanoparticles can be used as a saturable absorber device for pulsed laser generation. For easy integration into the laser cavity, the ZnO nanoparticles were imbedded into a polymer film using a seeding solution technique. 400 ns mode locked pulse train was successfully obtained at a relatively low threshold pump power of 45.4 mW. The output laser operates at the fundamental frequency of 1 MHz with a center wavelength of 1558.34 nm. The highest pulse energy and peak power achieved by the laser are estimated at 11.6 nJ and 27.3 mW respectively at the maximum available pump power of 142 mW. The results show that the SA derived from ZnO nanoparticles is capable of producing nanosecond mode locked EDFL for possible applications that require high pulse energy and medium output power.

We demonstrate a Q-switched all-fiber laser operating at 2-µm region by adding a piece of 8 cm long holmium doped fiber (HDF) as a fiber saturable absorber (SA) in Thulium doped fiber laser (TDFL) ring cavity. Doping of Ho ions into yttria-alumina silica glass was done through conventional Modified Chemical Vapor Deposition (MCVD) technique in conjunction with solution doping process. The fabricated HDF has a linear absorption of 3 dB with a core diameter and a numerical aperture of 10 µm and 0.18, respectively. A self-started Q-switching operation begins at 418 mW pump level and continually dominant until 564 mW pump level. As the pump power increases, stable pulse train presence from 30.61 kHz to 38.89 kHz while the pulse width reduces from 3.18 µs to 2.27 µs. Both maximum output power and maximum peak power are obtained at 5.05 mW and 57.2 mW, respectively, while the maximum pulse energy is calculated to be 129 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is 50 dB. Our work may contribute to the discovery of stable, robust, and economic SA for pulse fiber laser generation at 2-µm region.

A passive Q-switched and mode-locked ytterbium-doped fibre laser (YDFL) pulse generation using a nickel oxide thin film as a saturable absorber is reported. The nickel oxide nanoparticle thin film ...

This work reports on the use titanium dioxide doped fiber (TiO2DF) as a passive saturable absorber (SA) in generating stable and self-starting mode-locked pulse laser in Erbium doped fiber laser (EDFL) ring cavity. The TiO2DF SA is a self-made fiber with 20 cm in length. It has a core diameter of 45 μm, the numerical aperture (NA) of 0.21, core composition of Silica-Titanium (Si-Ti) and cladding composition of Silica Oxides (SiO2). The TiO2DF SA has a wide-band linear absorption profile which also covers the mode-locked laser operating wavelength of 1553 nm. The TiO2DF serves as a great SA due to the presence of anatase crystalline form of TiO2 which provide saturable optical losses in the laser cavity. Results show that reliable mode-locked pulse is observed as the pump power raises from 106 mW to 142 mW. Within this range of pump power, a nearly constant repetition rate within the range of 0.984 MHz to 0.990 MHz is obtained. The actual pulse width seen from the autocorrelator is about 9.74 ps. Both, the maximum peak power of 878 mW and the maximum pulse energy of 8.56 nJ are calculated at the maximum pump power (142 mW). The fundamental frequency of the EDFL mode-locked pulse laser has a signal to noise ratio (SNR) of 54 dB. Our demonstration shows that the TiO2DF-SA is reliable and quite promising in generating EDFL mode-locked pulse laser.

A dark pulse generation is demonstrated in a fiber laser configured with a 20 cm long HBEDF and multilayer Black Phosphorus as a gain medium and saturable absorber, respectively. Dark pulses fiber laser at 1.5 µm region was obtained when the pump power exceeds the threshold of 147 mW. Meanwhile, the spectrum of the dark pulse is centred at 1556.40 nm, with the 3 dB bandwidth of 0.12 nm and the separation between adjacent pulses is 1145 ns, corresponding to the cavity length of 211 m. The pulse width was measured to be around 320 ns. The radio-frequency spectrum of the dark pulse, which was measured within the 20 MHz range. More than 17 harmonics were observed within this range, which indicates the mode-locking operation of the laser. The fundamental frequency was obtained at 1.1 MHz, which agreed with the oscilloscope trace. Furthermore, it shows a signal to noise ratio of about 36.58 dB, which indicates good stability. The maximum output power of 0.78 mW and pulse energy of 0.78 nJ were obtained at 187 mW pump power.

In this paper, we present a Q-switched fibre laser at 1069 nm which is induced by an 8 cm long Hafnium bismuth erbium co-doped fibre (HBEDF) saturable absorber (SA). The pulsating laser has a maximum repetition rate of 67 kHz at 175 mW pump power. We obtained the narrowest pulse width of 3.48 μs, the maximum pulse energy of 70.2 nJ, the maximum output power of 4.7 mW and the maximum peak power of 20.1 mW. The Q-switched laser is simple and may found practical applications in medicine and remote sensing.

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of ...

We experimentally demonstrated a passive, stable mode-locked ytterbium-doped fiber laser (YDFL) based on black phosphorus (BP) as saturable absorber (SA). The BP-SA was prepared by mechanically exfoliation of the crystal and transferred the acquired thin layer onto the end surface of a standard FC/PC fiber connector. By incorporating the BP-SA into the YDFL cavity, a stable mode-locked operation was obtained at 1033.76 nm wavelength with a repetition rate of 10 MHz. The maximum pulse energy of 2.7 nJ and peak power of 0.83 kW were obtained at the maximum pump power of 200 mW. The experimental results indicate that the BP SA can be used successfully to generate stable mode-locking pulse at 1 μm region.

A passive mode-locked Ytterbium-doped fiber laser (YDFL) is experimentally demonstrated using a multi-layered molybdenum disufide (MoS 2 ) as a Saturable Absorber (SA). The MoS 2 film was obtained based on a liquid phase exfoliation of MoS 2 crystal. A small slice of MoS 2 film was sandwiched in between two optical ferrules via a fiber adapter and linked into an YDFL cavity to generate a stable mode-locked operation at a wavelength of 1073.86 nm with repetition rate of 18.8 MHz. At pump power of 202.9 mW, the maximum pulse energy of 0.1 nJ was achieved with an output power of 1.84 mW. The MoS 2 film was fabricated through a simple process and it has a modulation depth of 9.7% and saturating intensity of 40 MW/cm 2 .

This paper demonstrates the integration of quantum dot (QD) cadmium selenide (CdSe) nanoparticles, which is embedded into polymethyl methacrylate (PMMA) film into an ytterbium-doped fiber laser (YDFL) cavity to produce Q-switched and mode-locked fiber lasers. The QD CdSe based film functions as a saturable absorber (SA). For Q-switching operation, stable pulse is generated within 970–1200 mW pump power, with tunable repetition rate and pulse width of 24.5–40.5 kHz and 6.8–3.7 µs, respectively. Maximum pulse energy and peak power are obtained about 1.1 µJ and 0.28 W, respectively. As we tune the polarization state of the laser cavity and use a single QD CdSe film, the mode-locking operation could also be generated within 310–468 mW pump power with repetition rate of 14.5 MHz and pulse width of 3.5 ps. Maximum pulse energy and peak power are obtained about 2 nJ and 0.11 W, respectively. These results may contribute to continuous research work on laser pulse generation, providing new opportunities of CdSe material in photonics applications.

We experimentally demonstrate a passive, stable and low cost Q-switched erbium-doped fiber laser based on molybdenum disulfide (MoS2) and black phosphorus (BP) saturable absorber (SA). Both MoS2 and BP SAs are prepared by mechanically exfoliating the crystal and fixing the acquired flakes onto the end surface of a standard FC/PC fiber connector. By integrating either MoS2 or BP SA into the laser cavity, a stable Q-switched operation is achieved at wavelengths of 1551.4 or 1552.9 nm respectively. Using the MoS2 SA, the repetition rate of the output laser increases from 14.25 to 38.43 kHz as the 980 nm pump power rises from 57 to 170 mW while its pulse width reduces from 10.7 to 5.02 μs. The maximum pulse energy was 141.3 nJ. On the other hand, with the BP SA, the repetition rate and pulse width fall in the ranges of 9.1–44.33 kHz and 20.75–7.04 μs respectively, as the pump power grows from 50 to 170 mW. The laser with the BP SA, produces the maximum pulse energy of 134 nJ. The experimental results indicate that MoS2 and BP SAs can be used to generate stable Q-switching pulses at 1.5 μm region successfully.

We demonstrate all-fiber dual-wavelength Q-switched and mode-locked erbium-doped fiber laser (EDFL) by utilizing the thulium-holmium-doped fiber (THDF) as a fiber saturable absorber (SA) and also a Mach-Zehnder interferometer (MZI) element. The 19 cm long THDF has a core diameter of 11.5 µm, refractive index difference of 0.005, and cutoff wavelength of 1810 nm. Stable dual-wavelength Q-switching operation was generated at 1555.14 nm and 1557.64 nm with free spectral range (FSR) of 2.5 nm. The repetition rate of 14.45–78.49 kHz was obtained between 12 and 100 mW pump power. At maximum pump power, the maximum output power and pulse energy were 2.58 mW and 32.87 nJ, respectively. By adding 195 cm long SMF in the same cavity, the stable dual-wavelength mode-locking operation was started at 166 mW and continue stable to 201 mW pump power. This mode-locking operation produced stable dual-wavelength pulses at 1530.34 nm and 1532.84 nm with a repetition rate of 1 MHz with a pulse duration of 128 ns and signal-to-noise ratio (SNR) of 62 dB. It shares the same value of FSR in Q-switching operation. The highest output power of 1.57 nJ corresponds to the maximum output power of 1.57 mW was obtained. Our results validate the linear absorption characteristic at C-band region and multimode fiber effect of THDF can be utilized as SA to generate stable all-fiber dual-wavelength pulsed lasers. Remarkably, these findings expand a fiber gain medium application in short pulse generation.

We report the generation of mode-locked thulium-holmium doped fiber laser (THDFL) at 1979 nm. This is a first demonstration of mode-locked by using Titanium Dioxide (TiO 2 ) film as a saturable absorber (SA). A piece of 1 mm×1 mm TiO 2 film was sandwiched in between two fiber ferrule in the cavity. Fabrication process of TiO 2 film incorporated a TiO 2 and a polyvinyl alcohol (PVA). The stable 9 MHz repetition rate of mode-locked mode operation with 58 dB SNR was generated under pump power of 902–1062 mW. At maximum pump power, the mode-locked THDFL has output power and pulse energy of 15 mW and 1.66 nJ, respectively. Our results demonstrate the TiO 2 can be used promisingly in ultrafast photonics applications.

We demonstrate a Q-switched Erbium-doped fibre laser (EDFL) utilizing cobalt oxide (Co3O4) nanocubes film based saturable absorber (SA) as a passive Q-switcher. Co3O4 nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application. It has saturation intensity and modulation depth of 3 MW/cm2 and 0.35%, respectively. The proposed laser cavity successfully generates a stable pulse train where the pulse repetition rate is tunable from 29.8 to 70.92 kHz and the pulse-width reduces from 10.9 to 5.02 μs as the 980 nm pump power increases. This result indicates that the Co3O4 is excellent for constructing an SA that can be used in producing a passively Q-switched fibre laser operating at a low pump intensity. To the best of our knowledge, this is the first demonstration of Co3O4 film based fibre laser.

Copper nanoparticles was utilized and coated with an organic polymer, chitosan to develop thin film saturable absorber (SA) for the formation of passively Q-switched pulses in an erbium doped fiber laser (EDFL). The CuNP/chitosan thin film able to generate stable Q-switching lasing output at operating wavelength of 1557 nm. At maximum pump power of 90.44 mW, the generated pulse indicates a maximum repetition rate of 91.24 kHz, minimum pulse width of 3.60 µs and maximum pulse energy of 74.53 nJ. These results demonstrated the potential performance of CuNP/chitosan based saturable absorber compared to other copper based saturable absorber.Copper nanoparticles was utilized and coated with an organic polymer, chitosan to develop thin film saturable absorber (SA) for the formation of passively Q-switched pulses in an erbium doped fiber laser (EDFL). The CuNP/chitosan thin film able to generate stable Q-switching lasing output at operating wavelength of 1557 nm. At maximum pump power of 90.44 mW, the generated pulse indicates a maximum repetition rate of 91.24 kHz, minimum pulse width of 3.60 µs and maximum pulse energy of 74.53 nJ. These results demonstrated the potential performance of CuNP/chitosan based saturable absorber compared to other copper based saturable absorber.

This paper demonstrated the nanosecond pulse laser operation at 1.55 and 2 μm wavelength regions using a newly develop chromium-doped fiber (CrDF) as a saturable absorber (SA) to convert efficiently continuous-wave laser operation to nanosecond pulse laser operation. The laser uses an erbium-doped fiber (EDF) and thulium-doped fiber as the gain medium. A piece of 10 cm long CrDF was integrated into both laser cavities to generate nanosecond pulse laser operation. In 1.55 region generation, an additional single-mode fiber (SMF) 100 m long was added into the EDF laser cavity. Stable pulse generation occurred at a repetition rate of 1 MHz with a pulse width of 432 ns and a signal-to-noise ratio (SNR) of 66 dB. The highest peak power of 24 mW was obtained at 142 mW pump power. In 2 μm region generation, the obtained repetition rate was 10 MHz with a pulse width and SNR of 59 ns and 41 dB, respectively. The highest peak power was only 8.3 mW. By looking into the findings, the newly developed CrDF SA has a potential to be further enhanced toward better generation of ultrashort pulse fiber lasers.

We demonstrate a passively Q-switched erbium doped fiber laser (EDFL) based on quantum dots (QD) CdSe as a saturable absorber (SA). The synthesized CdSe powder was embedded into a poly(methyl methacrylate) (PMMA) using emulsion polymerization process. The film is sandwiched between two fiber connector via an adapter to form a fiber-compatible SA device. By integrating the SA device into the EDFL ring cavity, the stable Q-switched operation is achieved at 1559.35 nm as the pump power is varied within 30–118 mW. The laser has a pump threshold of 20.4 mW. The pulse repetition rate shows an increasing trend from 33.2 to 68.45 kHz, whereas the pulse width exhibits a decreasing trend from 10.04 to 4.30 μs as the pump power is increased from 30 to 118 mW. The highest pulse energy of 11.83 nJ is obtained at a pump power of 118 mW. These results indicate that QD CdSe is a promising SA for Q-switching laser operation.

A passively Q -switched ytterbium-doped fiber laser (YDFL) operating at 1062 nm was demonstrated by using a segment of 20 cm titanium dioxide-doped fiber saturable absorber ( TiO 2 DF SA). The Q -switched YDFL emerged stably with tunable repetition rates ranging from 32 kHz to 53 kHz as the pump power rose from 109 mW to 233 mW. Within this range of pump power, a maximum output power of 10.1 mW, maximum peak power of 75 mW, and maximum pulse energy of 191 nJ were obtained. The narrowest pulse width of 2.55 μs was attained at the maximum pump power of 233 mW, while the signal-to-noise ratio of the fundamental frequency was 47 dB. This demonstration reveals that the proposed TiO 2 DF SA is feasible for constructing a flexible and reliably stable Q -switched pulsed fiber laser in the 1-micrometer region.

A passively Q-switched Ytterbium-doped fiber laser (YDFL) based on MoS2 saturable absorber (SA) is demonstrated. A few layers of MoS2 are mechanically exfoliated from a natural MoS2 crystal using a scotch tape and the resulting SA is sandwiched between two fiber ferrules to form a fiber compatible Q-switcher. The saturation intensity, non-saturable intensity, and modulation depth of the MoS2 SA are 23.5 MW/cm2, 23.0, and 11.3%, respectively. By introducing the MoS2 SA into the YDFL cavity, a stable pulse laser is generated at 1070.2 nm wavelength with a threshold pump power of 49.57 mW. The repetition rate of the Q-switched pulses ranges from 3.817 to 25.25 kHz, as the 980 nm pump power increases from 49.57 to 87.2 mW. The highest pulse energy is 295.45 nJ at a pump power of 87.2 mW.

A simple all fiber passive mode-locked thulium-doped fiber (TDF) linear cavity laser operating at 1901.6 nm with an incorporation of homemade graphene oxide paper (GOP) based saturable absorber is proposed and practically demonstrated. The TDF linear cavity laser generates mode-locking pulse at a threshold pump power of 540 mW. By varying the pump power from the threshold power to 1052 mW, pulse repetition rates remain constant at 82.4 MHz. At the maximum pump power of 1052 mW, the pulse width is estimated as 12.66 ps, whereas the pulse energy is calculated as 83.1 pJ.

This paper describes the all-fiber dual-wavelength thulium ytterbium co-doped fiber laser by using a newly developed octagonal shaped double-clad thulium-ytterbium co-doped fiber as gain medium in conjunction with spatial filtering effect. The thulium ytterbium co-doped fiber laser operates at wavelengths of 1990.64 nm and 1998.92 nm with a signal to noise ratio of more than 34 dB as the 980 nm multimode pump power is increased above a threshold value of 1.5 W. The slope efficiency of the dual-wavelength laser is measured to be around 26.16%, which is comparable with the conventional thulium laser pumped by 800 nm single mode pump.

The authors demonstrate the generation of soliton mode-locked pulses from an erbium-doped fibre ring laser incorporating molybdenum disulphide (MoS2) saturable absorber (SA) with a net anomalous dispersion. The MoS2 SA is prepared by mechanically exfoliating MoS2 crystal and fixing the acquired MoS2 flakes onto the end surface of a standard FC/PC fibre connector. A self-started mode-locked soliton pulse is generated by fine-tuning the rotation of the polarisation controller at the threshold pump power of 50 mW. Its solitonic behaviour is verified by the presence of Kelly sidebands in the output spectrum. The central wavelength, 3 dB bandwidth, pulsewidth, and repetition rate of the laser are 1598.94 nm, 5.4 nm, 0.83 ps, and 17.1 MHz, respectively. The maximum pulse energy is 74 nJ at pump power of 110 mW with the output power of 1.26 mW. The MoS2 SA was constructed in a simple fabrication process and has a modulation depth of 11.3% to successfully produce the stable soliton mode-locked fibre laser.

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO2) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO2 is a new potential SA material for pulsed laser applications.

We fabricate a free-standing few-layer molybdenum disulfide (MoS2)–polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a soliton mode-locked Erbium-doped fiber laser (EDFL). A stable self-started mode-locked soliton pulse is generated by fine-tuning the rotation of the polarization controller at a low threshold pump power of 25 mW. Its solitonic behavior is verified by the presence of Kelly sidebands in the output spectrum. The central wavelength, pulse width, and repetition rate of the laser are 1573.7 nm, 630 fs, and 27.1 MHz, respectively. The maximum pulse energy is 0.141 nJ with peak power of 210 W at pump power of 170 mW. This result contributes to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

Spent coffee ground (SCG) was demonstrated as saturable absorber (SA) for Wideband Q-switched fiber lasers generation. The SCG SA has a broad linear absorption that covers from 1000 nm to 2000 nm wavelength and a modulation depth of 30% at 1.55-µm region. Through purification process, the finer SCG powder is obtained, and be embedded with a polyvinyl alcohol for thin film formation. To realize Q-switching operation lasers, a fabricated SCG film was integrated into three different fiber laser cavities including ytterbium-doped fiber laser, erbium-doped fiber laser, and thulium-doped fiber laser. A peak wavelength has obtainable at 1031 nm, 1563 nm, and 1976 nm for 1-, 1.55-, and 2- µm regions, respectively. The shortest pulse width of 4.80 µs and maximum pulse energy of 0.152 µJ are observed from the YDFL cavity. RF spectrum shows the signal-to-noise ratio for all regions is above 35 dB, indicates a stable pulsing generation. Our technique opens the door for unlimited materials SA from environmentally friendly resources which contribute to sustainable effort.

A dark pulse multi-wavelength mode-locked fibre laser was demonstrated via the enhanced zirconia-yttria-aluminium co-doped silica fibre (Zr-EDF) as a gain medium with the utilisation of black phosphorus as saturable absorber (BPSA). A self-started dark pulse was accomplished by increasing the pump power and carefully rotating a polarisation controller (PC). Five lasing lines of multi-wavelength were generated with small constant channel spacing of 0.6 nm. The measured fundamental repetition rate was 1 MHz with a pulse duration of 3.46 ps. At output power 9.89 mW, the calculated pulse energy was 9.89 nJ, whereas the optical signal to noise ratio (OSNR) was as high as 74.8 dB, which confirmed the stability of the dark pulse train.

We demonstrated a rare-earth element of lutetium oxide (Lu2O3) as a passive saturable absorber (SA) for generating Q-switching operation laser at 1-micron region. The laser cavity is all-fiber ring configuration with a single-clad ytterbium-doped fiber as a gain medium. Under drop-casting fabrication method, the Lu2O3 film with a 20 μm thickness has a linear absorption of ∼ 5 dB. A stable pulse train with a typical pattern of repetition rate (26.25 kHz–46.68 kHz) and pulse width (9.36 μs to 4.59 μs) presence along the increment of pump power from 116 mW to 151 mW. At maximum pump power, the single pulse envelope has a pulse energy of 128.8 nJ with 42 dB signal-to-noise ratio (SNR). The maximum output power is 6 mW and the laser consistently has a peak wavelength at 1067.8 nm. Exploring a new alternative material for saturable absorber is one of direction for better pulse all-fiber laser development, especially at 1-micron region wavelength.

Thulium oxide (Tm2O3) film is demonstrated to work as a passive saturable absorber (SA) for stable pulse generation at 1.55-µm region. The Tm2O3 film was fabricated from a commercially available Tm2O3 embedded into polyvinyl alcohol (PVA) as a film host. The obtained Tm2O3 film has an absorption at 1.55-µm region, which corresponds to energy level diagram of thulium. The Tm2O3 film is switched into the all-fibre ring cavity configuration. Self-started Q-switching operation obtained from 84.13 mW until 159.03 mW pump power. The repetition rate increases from 43.82 kHz and stop at 62.70 kHz, while the pulse duration narrowed from 14.00 µs to 9.50 µs. The stability of the pulse train can be confirmed through signal-to-noise ratio (SNR) of fundamental frequency. The maximum output power and pulse energy is 3.90 mW and 6.22 nJ, respectively. As a result, these findings confirm Tm2O3 can be utilised as a potential passive SA to generate laser pulsing at 1.55-µm region.

In this paper, we demonstrated and compared several fibre-based saturable absorbers (SAs) used in the generation of stable Q-switched fibre lasers in the 1-micron region, using 1.5 m long Ytterbium-doped fibre (YDF) as the gain medium. The tested fibre SAs consist of four segments; (1) 8 cm long Hafnium bismuth erbium-doped fibre (HBEDF), (2) 12 cm long Ytterbium-doped fibre (YDF), (3) 20 cm long Titanium dioxide-doped fibre (TDDF) and (4) 11 cm long Thulium-doped fibre (TDF). The fibre segments were joint with a single-mode fibre (SMF28) of approximately 10 cm at both of their ends via fusion splicing to become useful fibre-based SAs. The Q-switched fibre lasers stably operated at ~1060 nm wavelength. Among these fibre SAs, the highest pulse energy (191 nJ) was achieved through the TDDF SA, while the shortest pulse width (1.97 ms) and the highest pulse frequency (74.2 kHz) were obtained via the YDF SA. These fibre SAs provide simple operation, high stability and high thermal damage threshold which are desirable for high power laser operations.

We demonstrated a reliable and stable Q-switched ytterbium-doped fiber laser centered at 1069 nm by employing a segment of 11 cm thulium-doped fiber (TDF) as a saturable absorber (SA) in the ring cavity. The fiber SA has an optical absorption of 1.35 dB at the Q-switched operating regime. As we increased the pump power from 109 mW to the maximum available pump power of 206 mW, a consistent Q-switched laser with output power ranging from 1.8 to 4.8 mW was attained. The pulse width narrowed from 4.9 to 2.87 μs, whereas the repetition rate increased from 40 to 60.2 kHz. In addition, maximum pulse energy of 80.7 nJ and a maximum peak power of 28.1 mW were obtained at the maximum pump power. The signal to noise ratio (SNR) was around 47 dB. Our experimental study shows that a segment of TDF can be used as a Q-switcher in the 1 μm fiber laser cavity to facilitate a reliable and robust microsecond pulse generation.

We demonstrate the generation of Q-switched pulses from an ytterbium-doped fiber laser (YDFL) using quantum dot (QD) CdSe as a passive saturable absorber (SA). The CdSe QD is fabricated by the synthesis of CdO, Se, and manganese acetate and paraffin oil and oleic acid as the solvent and surfactant, respectively. The CdSe QD is then doped into poly-methyl-methacrylate (PMMA) via an emulsion polymerization process. A PMMA-hosted CdSe QD thin flake with a homogeneous end surface is then formed and placed between two ferrules and assembled in a YDFL cavity to achieve the Q-switching operation with a repetition rate of 24.45 to 40.50 kHz while varying the pump power from 975 to 1196 mW. The pulse width changes from 6.78 to 3.65 μs with a maximum calculated pulse energy at 0.77 μJ at a pump power of 1101 mW. This work may be the first demonstration of CdSe QD-based Q-switching in an all-fiber configuration that should give proportional insight into semiconductor QD materials in photonics applications.

We report a simple way to generate Q-switched and mode-locked pulses by incorporating black phosphorus (BP) as a saturable absorber (SA) in an erbium-doped fiber laser (EDFL) cavity. The preparation of BP-based SA is facilitated by a mechanical exfoliation method. Stable mode-locked pulses with a repetition rate of 1 MHz and energy of 7.35 nJ energy per pulse are generated under a maximum pump power of 250 mW in the ring cavity.

Q-switched thulium-doped fiber laser (TDFL) is demonstrated using pencil-core flakes as a saturable absorber (SA) for the first time. The SA was fabricated by exfoliating pencil-core flakes on adhesive tape surface, then repeatedly folded over the tape until the flakes homogenously deposited on the tape. A small piece of the tape is sandwiched between two ferrules and incorporated in TDFL cavity to realize a stable Q-switching pulse train. By increasing the 1552-nm pump power from 389 to 431 mW, the repetition rate of the TDFL increases from 14.95 to 34.60 kHz while the pulse width decreases from 6.70 to 4.69 μs. The maximum pulse energy of 46.05 nJ is generated with repetition rate and pulse width of 21.25 kHz and 6.27 μs, respectively. To the best our knowledge, this is a first demonstration SA from mundane object as alternative to commercial bulk graphite for Q-switched fiber laser.

A tunable and low-threshold thulium (Tm)-doped fiber (TDF) laser is demon- strated using a new silica-based nanoengineered TDF in a linear configuration, in con- junction with 1552-nm pumping. The TDF used in these experiments had a Tm-doped nanoengineering yttrium-alumina-silica glass core with a diameter of 13.43 � m and 0. 21 NA, which is surrounded by a pure silica inner cladding with normal acrylate polymer resin coating. The nanoengineered TDF was fabricated using a modified chemical vapor deposition (MCVD) process, in conjunction with a solution-doping technique. The fabricated fiber shows an absorption loss of 165 dB/m at 793 nm. A maximum lasing slope efficiency of 26.2% was obtained at a 1910-nm wavelength using the fabricated fiber with an optimum length of 5 m. The maximum output power of 138 mW was achieved at the maximum pump power of 1100 mW. The lowest pump power threshold of 693 mW for a 1552-nm wave- length was obtained at a TDF length of 7 m. The operating wavelength of the laser could be continuously tuned from 1890 to 1910 nm with an optical signal-to-noise ratio better than 43 dB, whereas the slope efficiency of the laser varies from 16.4% to 19.7%.