We experimentally demonstrate, for the first time, a 2.8μm femtosecond mode-locked fluoride fiber laser (MLFFL) with switchable pulsed-state including monopulse, dipulse, harmonic mode-locking and soliton molecules. Specifically, through adjustments to the cavity parameters, the mode-locking operation from monopulse to dipulse within a specific pump power range can be realized, with the maximum output power of 165mW and 175mW, respectively. Further increasing the pump power, the operating regime of the oscillator switches to second-order harmonic mode-locking, where the pulse fundamental repetition rate is ~155MHz with the output power of 330mW. In this case, bound soliton molecule can also be acquired by appropriately optimizing the orientation of the waveplates while keeping the pump power fixed. In particular, with increased pump power, multiple states of bound soliton molecule pairs can be achieved as well. The laser system is simple in structure, self-starting and good stability. Our experimental results may provide solutions for practical applications which requiring different pulse state switchable.
Broadband supercontinuum generation in highly GeO2 doped fibers holds significant appeal for researchers due to their distinct advantages. In this study, we propose employing a low repetition rate noise-like pulse mode-locked fiber laser as the pulse seed for mid-infrared supercontinuum generation in such fibers. Utilizing only one amplifier stage to amplify the noise-like pulse, we achieved a broadband supercontinuum with a 20dB bandwidth spanning from approximately 652nm to 3350nm in a highly GeO2 doped fiber with a core GeO2 concentration of 98%, even with an output power as low as 297mW. To the best of our knowledge, this represents the widest supercontinuum achieved in highly GeO2 doped fibers to date. Additionally, we observed that further increases in pump power resulted in damage to the core of the highly GeO2 doped fibers. This posed a challenge in expanding the spectral range of the output supercontinuum by simply increasing the peak pulse power. This conclusion is of significant reference value for research on supercontinuum generation based on highly GeO2 doped fibers.
Mid-infrared conventional solitons and soliton molecules are generated in a polarization-maintaining erbium-doped fluoride fiber oscillator, where a semiconductor saturable absorber is used as the mode locker and a polarization beam splitter is employed for getting linearly polarized output pulses. By rotating the half-wave plate in front of the polarization beam splitter to change the output coupling ratio, the system is switchable between conventional solitons and soliton molecules. conventional solitons with a pulse duration of 120 ps, a maximum average power of 248 mW, and a repetition rate of 44.5 MHz are obtained when the oscillator operates in the single-pulse mode-locked state. By decreasing the output coupling ratio, the operating regime of the oscillator switches to the soliton-molecule mode-locked state, in which soliton-triplets equally distributed at a repetition rate of 44.5 MHz with a signal-to-noise ratio of 78 dB and a temporal separation of 60 ps are obtained. Our work offers a scheme to realize switchable operations between the conventional soliton and the soliton molecule in the mid-infrared polarization-maintaining mode-locked fiber laser.
In this paper, a high power Tm3+-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system with the center wavelength is 1940 nm is demonstrated. The maximum laser power was measured to be 200 W with a slope efficiency of 56.2% at the 793 nm pump power of 368.6 W. Power stability of the laser output over 60 min is measured to be ~0.12%, which indicate a relatively stable laser operation of the TDFL. The output power is limited by the available pump power for the lack of amplified spontaneous emission, parasitic oscillation or self-pulsing effects even at the maximum output power level, showing further power scaling should be possible with increase the pump power.
We have proposed and implemented a scheme for Spiral Phase Plate (SPP) with continuous surface fabrication on fiber tips. By combining Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) system and bitmap (BMP) format processing method, we fabricated a SPP with the topological charge of 1 on the fiber tip, and experimentally analyzed the diffraction and interference properties of the generated vortex beam. The experimental results were in good agreement with the simulation results, which indicated the SPP fabricated by this method had good optical properties and high reliability. This work could be valuable for fiber communication and information encryption.
In this work, we propose a theory of ultrafast dual wavelength pulsed laser modulation. The modulation effect of modulated light on signal light is studied based on a four-level cross absorption modulation system with the principle of in band relaxation and inter band Pauli incompatibility in single-layer graphene. The study find that the signal saturation absorption decreases with the increase of modulation intensity; in addition, modulation light and signal light also affect each other's transmittance. The model of dual wavelength synchronous laser based on modulation theory can obtain stable output. Under the guidance of this model, we have built passively Q-switched synchronous erbium-doped, and ytterbium doped fiber lasers. With the increase of pump power, the repetition rate of synchronous pulses changes from 24.50 kHz to 39.90 kHz. The laser has potential applications in Raman scattering spectroscopy, multicolor pump detection spectroscopy and nonlinear frequency conversion.
An all-fiber mid-infrared enhanced supercontinuum laser source, spanning from ~2 μm to ~4.2 μm, was demonstrated in an erbium-doped ZBLAN fiber amplifier. A 2 μm low repetition rate noise like-pulse mode-locked fiber laser was adopted as the pulse seed for the system. Thanks to using a new-type homemade silica-fluoride fiber pump combiner, the 2.8 μm pulses in the supercontinuum were amplified in the erbium-doped ZBLAN fiber amplifier with all-fiber structure. Due to soliton self-frequency shift, long wavelength components were generated and a 1.4 W mid-infrared enhanced supercontinuum with up to 97% of the power beyond 2.7 μm was obtained in the erbium-doped ZBLAN fiber. This research demonstrated a compact and simple in-amplifier mid-infrared supercontinuum generation with all-fiber structure.
Recently, ultrafast optical modulators (OMs) based on atomic transition-metal dichalcogenides (TMDs) film have been intensively explored. Benefited from their remarkable nonlinear saturable absorption properties, TMDs based OMs could be employed as critical devices for pulsed lasers systems to transit continuous wave into pulse trains in laser cavity. Herein, the few-layer TMDs films were grown by chemical vapor deposition (CVD) method in possession of uniform thickness, large areas and high crystal quality. Then two types TMDs based OMs were fabricated by integrating single TMDs film or van der waals heterostructures (VdWHs) on the target substrates. As for VdWHs based OMs, different few-layer TMDs films were vertically stacked in turns on the target substrates to form heterointerfaces, which has been demonstrated with ultrafast carrier relaxation time between neighbor layers recently and is favor for ultrafast pulse generation. In our experiments, the nonlinear optical properties of two types TMDs based OMs were systematically investigated by measuring their nonlinear saturable absorption curves and further compared by embedded them into same fiber laser systems. The results indicate that the VdWHs based OMs owns more excellent nonlinear optical properties (such as larger modulation depth, smaller saturable intensity) and offers a feasible strategy to engineer desired ultrafast photonics devices by modifying the structure of VdWHs.
We propose two schemes for achieving tungsten disulfide (WS2)-based saturable absorber (SA) and saturable absorber mirror (SAM). By utilizing the pulsed laser deposition method, we grow the WS2 film on microfiber to form an evanescent field interaction SA device. Incorporating this SA device into a common ring-cavity erbium-doped fiber (EDF) laser, stably passive mode-locking can be achieved with pulse duration of 395 fs and signal-to-noise ratio of 64 dB. We also produce a fiber tip integrated WS2-SAM by utilizing the magnetron sputtering technique (MST). This new type of SAM combines the WS2 layer as SA and gold mirror as high reflective mirror. By employing the WS2-SAM, we construct the linear-cavity EDF lasers, and achieve passive mode-locking operation with pulse duration of ∼1 ns and SNR of ∼61 dB. We further achieve stably passive Q-switching operation with pulse duration of ∼160 ns and pulse energy of 54.4 nJ. These fiber-integrated SAs and SAMs have merits of compactness and reliability, paving the way for the development of new photonic devices such as SAs for pulsed laser technology.
We have demonstrated the dissipative solitons generated in an ytterbium-doped fiber laser cavity using graphene oxide as the saturable absorber. The lasing light, centered at 1077.2 nm, has a 3 dB spectral bandwidth of ∼1.12 nm . Under different launched pump powers and appropriate polarization orientations, harmonic mode-locked of second- and third-order pulse trains have been achieved; the corresponding 3-dB bandwidth and pulse duration have been detected.
We demonstrate a saturable absorber (SA) based on cladding-filled graphene in a specially designed and manufactured photonic crystal fiber (PCF) for the first time. The saturation absorption property is achieved through the evanescent coupling between the guided light and the cladding-filled graphene layers. To boost the mutual interaction, the PCF is designed to contain five large air holes in the cladding and small-core region. Employing this graphene-PCF SA device, we construct an erbium-doped all-fiber laser oscillator and achieve mode-locked operation. This device can pave the way for high power and all-fiber applications of photonics with graphene with some unique advantages, such as single-mode operation, nonlinearity enhancement, high-power tolerance, environmental robustness, all-fiber configuration, and easy fabrication.
Long period fiber grating (LPFG) upon all-solid photonic bandgap fiber with a bandgap at 1.068 to 1.180 μm is fabricated by high-frequency CO 2 laser pulse irradiation. The resonance wavelength is 1335.76 nm with a modulation depth of 15 dB and a 3-dB bandwidth of 2.6 nm. Bending response of the LPFG is dependent on the axial orientations and the input polarization states. The maximum bending sensitivity is achieved at 52 nm/m . The temperature response is weakly dependent on the polarization state, and is achieved around 20.47 pm/°C at a 0-deg polarization azimuth. The bending measurement error resulting from temperature can be negligible within the range of 0.4 to 0.82 m −1 . It is be beneficial to avoiding cross-sensitivity of temperature in bending measurements.
We investigate on a multi-wavelength operation erbium-doped fiber laser Q-switched by a graphene-based saturable absorber. Stable pulses were generated with the widths from 6.9 to 1.5 μs, energies from 40.4 to 130.2 nJ and repetition rates from 68.32 to 132.9 kHz, when the pump power increased from 142.32 to 441.86 mW. A fiber Bragg grating with five reflective peaks was inserted into the fiber ring through an optical circulator, resulting in a stable output of five-lasing-wavelength output. The laser can perform as a low-cost and easy-built all fiber light source, and has potential applications in the fields where pulses at multi-wavelength operation are needed, i.e., temperature or strain fiber sensors.
In this paper, we drew a 500 m-long PCF taper directly on the industry drawing tower. The fiber taper has a uniform
cross-section structure with OD from 170 μm to 70 μm, and demonstrates very good beam quality. The optical
attenuation of PCF taper was measured. The optical attenuation is ~5 dB/km near 1200 nm, but the water absorption
peak around 1400 nm and the attenuation beyond 1600 nm are still large. The zero dispersion wavelength (ZDW) was
calculated to be ~1090 nm at the taper input end, and shifted to ~870 nm at the taper output end. The PCF taper was
pumped with a picosecond laser source at wavelength of 1064 nm, and generated 200 mW output power of SC covering
from ~450 nm to 1600 nm.
KEYWORDS: Signal attenuation, Fiber lasers, High power lasers, Single mode fibers, Fabrication, Glasses, Step index fibers, Cladding, Silica, Structured optical fibers
We fabricated a new type of multicore fiber using the PCVD process and stack-and-draw method. The fabrication
process is described in detail in this work. The fiber core is composed with 91 GeO2-doped micro-rods arranged in the
hexagon shape and the largest core diameter of the fabricated fibers is measured up to 50μm, very suitable for low loss
splicing with the multimode fiber. For the fiber with 125μm glass diameter, the attenuation is measured only 3dB/km at
1060nm and lower than 10dB/km at 1550nm, the water-loss peak at 1383nm is about 110dB/km; the mode properties of
our fiber were also measured, which show the fundamental mode characteristic with good Gaussian configuration. The
large single mode area can deduce the nonlinear effect in the high power delivery. Our multicore fiber might have the
potential application such as the delivery of high power, the multiparameter fiber sensor, etc. according to our design.
A 145-m long microstructured optical fiber taper was fabricated on the industry drawing tower. The fiber taper had good uniformity of structure as the outer diameter decreased from 110 to 80 μm. Its optical attenuation was measured 52 dB/km at 1060 nm, and the zero dispersion wavelengths along the slow axis were calculated decreasing from 1000 to 915 nm. Watt-level supercontinuum spanning from 430 to 2050 nm was obtained as the fiber taper pumped by a 1064 nm picosecond laser source. The nonlinear mechanism of spectral broadening is carefully investigated with the support of numerical simulations.
Two kinds of supercontinuum (SC) sources are successfully generated by propagating 200-fs unamplified and amplified
pulses through a 0.85-m long nonlinear photonic crystal fiber (PCF), respectively. The spectra bandwidth of
amplified-femtosecond-pumped SC is about 870 nm spanning 480 nm to 1350 nm, which is flat to 1.2dB over 100 nm
spreading from 550nm to 650 nm. With the same PCF, SC spectra pumped by unamplified-femtosecond-pulses are
narrower and unevener. A detailed simulation is carried out to help us understand the mechanism of supercontinuum
evolution. For pump wavelength located at the zero dispersion wavelength of the PCF, spectra are broadened by the
interaction between SPM and higher-order dispersion at early stage. With increasing the pump power, the spectra are
broadened by fission of higher solitons and parametric four-wave mixing (FWM). When the peak power is up to
mega-watt, FWM plays a notable role in flattening and further broadening the supercontinuum spectra in short
wavelength side. An effective way to generate a flat SC laser source pumped by femtosecond pulses is also
demonstrated.
Microchip-laser-pumped supercontinuum (SC) is successfully generated through a 30-m long photonic crystal fiber
(PCF). The spectra bandwidth of SC is 850 nm spanning from 550 nm to 1300 nm. The -15dB-flat bandwidth is 400 nm
spanning from 600 nm to 1000 nm. It is easy to achieve a much more flat SC with the sacrifice of spectra bandwidth. A
detailed simulation is carried out to help us understand more about the supercontinuum generation process. The primary
mechanism of spectral broadening is identified as parametric four-wave mixing (FWM) combined with stimulated
Raman scattering (SRS). These findings also demonstrate an effective way to generate a flat supercontinuum laser source.
Rod-type photonic crystal fibers (PCFs) bring enormous advantages in Q-switched fiber laser with high pulse energy, short pulse width and good beam quality for its large mode area and short fiber length. In this paper, an acoustic-optic Q-switched photonic crystal fiber laser was investigated by using a 1m-long Yb-doped large mode area rod-type photonic crystal fiber as gain medium. A maximum pulse energy of 0.78 mJ (21.7 KW peak power) and the shortest pulse width of 20 ns were obtained at low repetition rates. A maximum 1033.6 nm average power of 14.5 W was demonstrated at 65 KHz with a slope efficiency of 56%. Further improvements would be obtained by optimizing the experiment configuration so as to achieve shorter pulse width and higher pulse energy.
An Yb-doped double-cladding photonic crystal fiber (DC-PCF) superfluorescent source (SFS) is presented experimentally for the first time, which is pumped at 976nm by a diode laser (LD) with the end-coupling method. We employ a single-stage SFS in double-pass forward configuration and get the maximum output power of 1.649W with a slope efficiency of 56.7%. The peak wavelength and the 3dB bandwidth are 1067.6nm and 22.4nm, respectively.
In this paper a large mode area Yb3+-doped double cladding photonic crystal fiber laser is reported. The laser's output power reaches as high as 4.3W. The slope efficiency and the maximum optical-to-optical efficiency of laser output are 69.4% and 59.7%, respectively, with respect to absorbed pump power. Single transverse mode operation is obtained at central wavelength of 1072.3nm and the measured mode distribution agrees with the simulation by using scalar beam propagation method.
A bidirectionally pumped spectrum pre-sliced multi-wavelength fiber source is presented in the paper. Two 980nm laser diodes (LDs) are engaged to provide the pump power. An optimized double pass Mach-Zehnder interferometer with extinction ratio larger than 41dB is utilized as the comb filter. The extinction ratio of the fiber source is larger than 24.5dB in the whole C band, and almost reaches 29dB at 1530nm. Integral power of each channel is 0.58mW at 1550nm under 112.3mW total pump power. Channel spacing and bandwidth are 0.81nm and 0.30nm, respectively.
KEYWORDS: Fiber lasers, Fiber Bragg gratings, Reflectivity, Mirrors, High power lasers, Cladding, High power fiber lasers, Signal attenuation, Lithium, Physics
An all-fiber Yb-doped double-clad fiber laser based on distributed Bragg reflection (DBR) with fiber Bragg gratings (FBGs) is demonstrated. The single transverse-mode wavelength-stable output at 1 .06 µ m is up to 1.18W, with a slope efficiency of 68% and an optical-to-optical conversion efficiency of more than 50%
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