Q-switched pulse generation from an all-fiber distributed Bragg reflector laser using graphene as saturable absorber

A Q-switched distributed Bragg reflector fiber laser using a graphene passive saturable absorber is proposed in a cavity consisting of a fiber Bragg grating and Faraday rotator mirror as end mirrors, together with a highly doped erbium-doped fiber as a gain source. The laser has a Q-switched threshold of about 28 mW and a tunable repetition rate of 10.4-18.0 kHz with varying pump power. The shortest pulse width obtained from the system is 3.7 its, with a maximum pulse energy and peak power of 22.2 nJ and 3.4 mW, respectively.     

Q-switched Er-doped fiber laser with low pumping threshold using graphene saturable absorber

We propose a Q-switched Er-doped fiber laser(EDFL) with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol(PVA) thin film as a passive saturable absorber(SA). The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 mW. At maximum 1480 nm pump power of 33.0 mW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56 μs. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 mW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.     

A compact graphene Q-switched erbium-doped fiber laser using optical circulator and tunable fiber Bragg grating

We demonstrate a passively Q-switched tunable erbium-doped fiber laser(EDFL)based on graphene as a saturable absorber(SA).A three-port optical circulator(OC)and a strain-induced tunable fiber Bragg grating(TFBG)are used as the two end mirrors in an all-fiber linear cavity.The Q-switched EDFL has a low pump threshold of 23.8 mW.The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from23.8 mW to 219.9 mW.The minimum pulse duration is 1.7μs and the highest pulse energy is 25.4 nJ.The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.     

Erbium-doped CW and Q-switched fiber ring laser with fiber grating Michelson interferometer

The band-pass characteristic of fiber grating Michelson interferometer is analyzed, which acts as bothband-pass filter and Q-switch. An erbium-doped fiber ring laser based on fiber grating Michelsoninterferometer is implemented for producing single longitudinal mode CW operation with 5 MHz spectrallinewidth and up to 6 mW output power. In Q-switched operation, stable fiber laser output pulses withrepetition rate of 800 Hz, pulse width of 0.6 μs, average power of 1.8 mW and peak power of 3.4 W aredemonstrated. The peak power and average power of the Q-switched pulses are varied with the repetitionrate.     

Wavelength tunable passively Q-switched Yb-doped double-clad f iber laser with graphene grown on SiC

A passively Q-switched tunable Yb-doped double-clad fiber laser is demonstrated with graphene epitaxially grown on SiC.The spectral tuning of the Q-switched fiber laser is implemented by rotating a quartz plate filter inside the cavity.The central wavelength of the fiber laser can be continuously tuned from 1038.54 to 1056.22 nm.The maximum pulse energy of 0.65 μJ is obtained at the pump power of 4.08 W,and the corresponding pulse duration and average output power are 1.60 μs and 35 mW,respectively.     

Q-switched fiber laser using carbon platinum saturable absorber on side-polished fiber

A 1550 nm Q-switched fiber laser using a carbon platinum saturable absorber deposited on side-polished fiber(SPF) is proposed and demonstrated. The SPF is approximately 2 mm with a polarization-dependent loss(PDL)of 0.4 dB and an insertion loss of 2.5 dB. A stable Q-switched output spectrum is obtained at 1559.34 nm with a peak power of ~6 mW, a pulse width of 1.02 μs, pulse energy of 5.8 nJ, average output power of 0.76 mW, and a repetition rate of 131.6 kHz taken at a pump power of 230.0 mW. A signal-to-noise ratio of 49.62 d B indicates that the Q-switched pulse is highly stable.     

Q-Switching Pulse Operation in 1.5-μm Region Using Copper Nanoparticles as Saturable Absorber

We demonstrate a passively Q-switched erbium-doped fiber laser(EDFL)using a copper nanoparticle(CuNP)thin film as the saturable absorber in a ring cavity.A stable Q-switched pulse operation is observed as the CuNP saturable absorber(SA)is introduced in the cavity.The pulse repetition rate of the EDFL is observed to be proportional to the pump power,and is limited to 101.2 kHz by the maximum pump power of 113.7 mW.On the other hand,the pulse width reduces from 10.19 ps to 4.28 ps as the pump power is varied from 26.1 mW to 113.7 mW.The findings suggest that CuNP SA could be useful as a potential saturable absorber for the development of the robust,compact,efficient and low cost Q-switched fiber laser operating at 1.5-μm region.     

Passive Q-switching in an erbium-doped fiber laser using tungsten sulphoselenide as a saturable absorber

A highly stable Q-switched laser incorporating a mechanically exfoliated tungsten sulphoselenide (WSSe) thin sheet saturable absorber (SA) is proposed and demonstrated. The SA assembly, formed by sandwiching a thin WSSe sheet between two fiber ferrules within the erbium-doped fiber laser, is used to effectively modulate the laser cavity losses. The WSSe-based SA has a saturation intensity of ~0.006 MW∕cm~2 and a modulation depth of 7.8%, giving an optimum Q-switched laser output with a maximum repetition rate of 61.81 kHz and a minimum pulse width of 2.6 μs. The laser's highest output power of 0.45 mW and highest pulse energy of 7.31 nJ are achieved at the maximum pump power of 280.5 mW. The tunability of the cavity's output at the maximum pump power is analyzed with a C-band tunable bandpass filter, giving a broad tunable range of ~40 nm, from 1530 nm to 1570 nm. The output performance of the tunable Q-switched laser correlates well with the gain spectrum of erbium-doped fibers, with the shift in the gain profile as a result of the saturated SA.     

Q-switched ytterbium doped carbon nanotubes fiber laser using multi-walled saturable absorber

A Q-switched ytterbium-doped fiber laser （YDFL） is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide （MWCNTs-PEO） film as a passive saturable absorber （SA）. The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW. The YDFL generates a stable pulse train with repetition rates ranging from 7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW. At 59.55-mW pump power, the lowest pulse width and the highest pulse energy are obtained at 12.18 μs and 143.5 n J, respectively.     

Q-switched ytterbium doped fiber laser using multi-walled carbon nanotubes saturable absorber

A Q-switched ytterbium-doped fiber laser(YDFL)is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide(MWCNTs-PEO)film as a passive saturable absorber(SA).The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film.Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation.The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW.The YDFL generates a stable pulse train with repetition rates ranging from7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW.At 59.55-mW pump power,the lowest pulse width and the highest pulse energy are obtained at 12.18μs and 143.5 nJ,respectively.     

High conversion efficiency,high power density Q-switched fiber laser

An acoustic-optic Q-switched all-fiber laser With a high-repetition-rate, a short pulse width, a wide spectrum, and a high conversion efficiency is experimentally demonstrated. In the laser configuration, a （1＋1）x 1 side-pumping coupler is introduced to perform backward pumping, and a 10/130%tm Yb fiber is adopted. The acoustic-optic component operates in the first direction, achieving a Q-switched pulse with a repetition rate adjustable in the range of 20 kHz-80 kHz. Under a repetition rate of 20 kHz and a pump power of 6.76 W, the fiber laser obtains a highly efficient and stable pulse output, with an average power of 4.3 W, a pulse width of 56 ns, a peak power of 3.83 kW, and a power density of 1.39x 101~ W/cm2. Particularly, the optic-optic conversion efficiency of the laser reaches as high as 64%. Another feature of the pulsed laser is that the high reflection mirror reflects the pump light as well, which brings the secondary absorption of the pump power into the gain fiber.     

Q-Switched Raman Fiber Laser with Molybdenum Disulfide-Based Passive Saturable Absorber

We demonstrate a Q-switched Raman fiber laser using molybdenum disulfide(MoS_2) as a saturable absorber(SA).The SA is assembled by depositing a mechanically exfoliated MoS_2 onto a fiber ferrule facet before it is matched with another clean ferrule via a connector.It is inserted in a Raman fiber laser cavity with a total cavity length of about 8 km to generate a Q-switching pulse train operating at 1560.2 nm.A 7.7-km-long dispersion compensating fiber with 584 ps·nm~(-1)km~(-1) of dispersion is used as a nonlinear gain medium.As the pump power is increased from 395 mW to 422 mW,the repetition rate of the Q-switching pulses can be increased from 132.7 to137.4kHz while the pulse width is concurrently decreased from 3.35μs to 3.03μs.The maximum pulse energy of 54.3nJ is obtained at the maximum pump power of 422 mW.These results show that the mechanically exfoliated MoS_2 SA has a great potential to be used for puise generation in Raman fiber laser systems.     

Zinc-oxide nanoparticle-based saturable absorber deposited by simple evaporation technique for Q-switched fiber laser

A Q-switched erbium-doped fiber laser(EDFL) incorporating zinc-oxide(ZnO) nanoparticles-based saturable absorber(SA) is proposed and demonstrated. To form the SA, the ZnO nanoparticles, which are originally in the powder form, are first dissolved in ethanol and subsequently deposited onto the surface of fiber ferrule by using the adhesion effect with the evaporation technique. By integrating the ZnO nanoparticle-based SA into a laser cavity of an EDFL, a self-started and stable Q-switching is achieved at a low threshold power of 20.24 mW. As the pump power is increased, the pulse repetition rate is tunable from 10.34 kHz to 25.59 kHz while pulse duration decreases from 21.39 μs to 3.65 μs. Additionally,this Q-switched laser has a maximum energy per pulse of 19.34 nJ and an average output power of 0.46 mW. These results indicate the feasibility and functionality of the ZnO nanoparticles-based SA for Q-switched generation, which offers the flexibility and easy integration of the SA into a ring laser cavity.     

Eye-safe,single-frequency pulsed all-fiber laser for Doppler wind lidar

A single-frequency pulsed erbium-doped fiber(EDF) laser with master-oscillator power-amplifier configuration at 1 533 nm is developed. A short-cavity,erbium-doped phosphate glass fiber laser is utilized as a seeder laser with a linewidth of 5 kHz and power of 40 mW. The seeder laser is modulated to be a pulse laser with a repetition rate of 10 kHz and pulse duration of 500 ns. The amplifier consists of two pre-amplifiers and one main amplifier. The detailed characteristics of the spectrum and linewidth of the amplifiers are presented. A pulse energy of 116 μJ and a linewidth of 1.1 MHz are obtained. This laser can be a candidate transmitter for an all-fiber Doppler wind lidar in the boundary layer.     

Diode-Pumped Passive Q-Switched 946-nm Nd：YAG Laser with 2.1-W Average Output Power

We demonstrate a diode-pumped passive Q-switched 946nm Nd: YAG laser with a diffusion-bonded composite laser rod and a co-doped Nd, Cr:YAG as saturable absorber. The average output power of 2.1 W is generated at an incident pump power of 14.3 W. The peak power of the Q-switched pulse is 643 W with 80kHz repetition rate and 40.8 ns pulse width. The slope efficiency and optical conversion efficiency are 17.6% and 14.7%, respectively.     

Generation of Q-Switched Mode-Locked Erbium-Doped Fiber Laser Operating in Dark Regime

We demonstrate a stable Q-switched mode-locked erbium-doped fiber laser(EDFL) operating in dark regime based on the nonlinear polarization rotation technique.The EDFL produces a pulse train where the Q-switching envelope is formed by multiple dark pulses.The repetition rate of the Q-switched envelope can be increased from 0.96 kHz to 3.26 kHz,whereas the pulse width reduces from 211 μs to 86 μs.The highest pulse of 479 nJ is obtained at the pump power of 55 mW.It is also observed that the dark pulses inside the Q-switching envelope consist of two parts:square and trailing dark pulses.The shortest pulse width of the dark square pulse is obtained at 40.5μs when the pump power is fixed at 145 mW.The repetition rate of trailing dark pulses can be increased from 27.62 kHz to 50 kHz as the pump power increases from 55 mW to 145 mW.     

A Q-switched erbium-doped fiber laser based on ZrS_2 as a saturable absorber

A passively Q-switched erbium-doped fiber(EDF) laser is proposed and demonstrated utilizing a zirconium disulfide(ZrS_2)-based saturable absorber(SA). ZrS_2 nanosheets are prepared, whose modulation depth,saturation intensity, and nonsaturable absorbance are measured to be 14.7%, 0.34 MW/cm~2, and 17.4%, respectively. Then, a Q-switched EDF laser is implemented by the ZrS_2-SA. The pulse repetition rate varies from 40.65 to 87.1 k Hz when the pump power changes from 55 to 345 mW. The shortest pulse width is 1.49 μs with pulse energy of 33.5 nJ. As far as we know, this is the shortest pulse width obtained by a ZrS_2-SA so far.     

An efficient intracavity-pumped KTP optical parametric oscillator at 1572 nm

We demonstrate an efficient and eye-safe wavelength intracavity optical parametric oscillator (OPO), based on a KTP crystal inside a Q-switched Nd:YVO4 laser end pumped by a fiber-coupled diode laser. In the acousto-optic Q-switched operation with the pulse repetition rate of 10 kHz, a 1572-nm eye-safe laser with the average power of 237 mW at the incident pump power of 5.64 W is obtained. Under the pulse repetition rate of 5 kHz, the signal light with pulse width of 2 ns and peak power of 18.5 kW is achieved. The conversion efficiency of the average power is 4.2% from pump diode to OPO signal output and the signal pulse duration is about 13 times shorter than that of the depleted pump light.     

Cadmium Selenide Polymer Microfiber Saturable Absorber for Q-Switched Fiber Laser Applications

We demonstrate the generation of a Q-switching pulse train in an erbium-doped fiber laser(EDFL) cavity using a newly developed cadmium selenide(CdSe) based saturable absorber(SA). The SA is obtained by embedding CdSe nanomaterials into a polymethyl methacrylate(PMMA) microfiber. It is incorporated into an EDFL cavity to generate a Q-switched laser operating at 1533.6 nm. The repetition rates of the produced pulse train are tunable within 37-64 kHz as the pump power is varied from 34 mW to 74 mW. The corresponding pulse width reduces from 7.96μs to 4.84μs, and the maximum pulse energy of 1.16 nJ is obtained at the pump power of74 mW.     

Diode end-pumped self-Q-switched and mode-locked Nd,Cr：YAG /KTP green laser

We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr:YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power of 680 mW at 532 nm. The corresponding pulse width of the Q-switched envelope of the green laser is 170±20 ns. The mode-locked pulses have a repetition rate of approximately 183 MHz and the average pulse duration is estimated to be around sub-nanosecond. It is found that the intra-cavity frequency doubling greatly improves the modulation depth and stability of the mode-locked pulses within the Q-switched envelope.