Er-doped Fiber Laser Research Articles

Wavelength tunable Q-switched Er-doped fiber laser based on ZrSe2

We demonstrated a passively Q-switched Er-doped fiber laser based on the ZrSe2/PVA film. Here, the layer structure ZrSe2 platelets were produced by the liquid-phase exfoliation method. By means of nonlinear optical transmittance measurement, the modulation depth and saturation intensity of the ZrSe2/PVA SA were 31% and 4.75 MW/cm2, respectively. The Q-switched pulses revealed the highest repetition rate and pulse energy around 43.7 kHz and 139.8 nJ with the pump power at 346 mW. Based on the invisible filter, we produced the wavelength-tunable and dual-wavelength Q-switched pulses after insertion of the in-line polarizer inside the cavity. Through the proper adjustment of the polarization controller, a tuning wavelength of from 1544.3 to 1563.5 nm, a tuning range of around 19.2 nm, and the smallest tuning interval of around 1 nm have been achieved.

Large-energy mode-locked Er-doped fiber laser based Cr2Si2Te6 as a modulator

Ultrafast photonic devices based on two-dimensional (2D) materials attract the attentions of researchers. In order to expand the range and diversity of ultrafast lasers and advanced photonics, it is necessary to explore new 2D materials with excellent nonlinear absorption properties. Ferromagnetic insulators (FIs) have the suitable band structure and they can be stripped into single layer structure easily, however, few related works have been reported. In this work, Cr2Si2Te6 (CST) thin film modulator was prepared through the method of liquid-phase exfoliation (LPE) and investigated its nonlinear optical properties and application in obtaining large energy mode-locking pulse output. The modulation depth and saturable intensity of the CST were 4.40% and 12.51 MW/cm2, respectively. Transferring it into the ring cavity, the all-fiber laser can generate a large energy pulse with a center wavelength of 1558.53 nm and a repetition frequency of 1.61 MHz. The energy of single pulse was 53.03 nJ. The maximum average output power was 85.54 mW under the pump power of 1659 mW. To our knowledge, the energy of single pulse is the highest among the reported all-fiber lasers with FIs saturable absorbers (SAs). Our experimental results proved that CST-SA has excellent modulation properties, which provides a basis for future research.

Ternary transition metal dichalcogenides for passively Q-switched Er-doped fiber laser applications

A ternary transition metal dichalcogenide based saturable absorber was proposed and employed to generate the Q-switching pulses in a fiber laser. The fabricated MoxTa1−xSe2-based saturable absorber exhibits excellent nonlinear optical absorption properties with saturable intensity of 19.25 MW/cm2 and modulation depth of 19.89%. After incorporating the MoxTa1−xSe2-based saturable absorber into a fiber laser cavity, this fiber laser worked at passively Q-switched state. Moreover, by enhancing the pump power up to 900 mW, the output power was enhanced to 11.86 mW and the pulse width was reduced down to 2.2 μs. The repetition frequency was adjustable in the extent of 94.15–196.31 kHz, and the signal-to-noise ratio was as large as 73 dB. Our results indicate that the proposed MoxTa1−xSe2 materials possess remarkable nonlinear optical characteristics that can be considered as a powerful candidate for pulsed lasers applications.

Harmonically mode-locked Er-doped fiber laser at 1.3 GHz using a V2AlC MAX phase nanoparticle-based saturable absorber

We experimentally demonstrate a harmonically mode-locked erbium (Er)-doped fiber laser using a V2AlC-based saturable absorber (SA) at the 1.55 μm wavelength region. The prepared SA was fabricated using a side-polished fiber with V2AlC MAXphase nanoparticles via liquid-phase exfoliation (LPE). The derived saturation intensity and modulation depth of the V2AlC-based SA were approximately 63 MW/cm2 and 18%, respectively. The repetition rate was tuned from 14.98 MHz to 1.3 GHz (86th harmonic) by adjusting the pump power. The 86th harmonic mode-locked pulses at approximately 1.3 GHz repetition rate were generated with a temporal width and supermode suppression ratio of approximately 863 fs and 30 dB, respectively. These results demonstrate the application of the V2AlC MAX phase in giga-hertz frequency ultrafast fiber lasers.

Robust, fast and sensitive near-infrared continuous-filtering Vernier spectrometer.

We present a new design of a robust cavity-enhanced frequency comb-based spectrometer operating under the continuous-filtering Vernier principle. The spectrometer is based on a compact femtosecond Er-doped fiber laser, a medium finesse cavity, a diffraction grating, a custom-made moving aperture, and two photodetectors. The new design removes the requirement for high-bandwidth active stabilization present in the previous implementations of the technique, and allows scan rates up to 100 Hz. We demonstrate the spectrometer performance over a wide spectral range by detecting CO2 around 1575 nm (1.7 THz bandwidth and 6 GHz resolution) and CH4 around 1650 nm (2.7 THz bandwidth and 13 GHz resolution). We achieve absorption sensitivity of 5 × 10-9 cm-1 Hz-1/2 at 1575 nm, and 1 × 10-7 cm-1 Hz-1/2 cm-1 at 1650 nm. We discuss the influence of the scanning speed above the adiabatic limit on the amplitude of the absorption signal.

Coupling scheme for graphene saturable absorber in a linear cavity mode-locked fiber laser.

A saturable absorber based on a graphene layer covered single-mode fiber with inner short waveguides is proposed and demonstrated for a linear cavity Er-doped mode-locked fiber laser. A pair of short waveguides is written in the fiber by using femtosecond micromachining technology, and the propagating light is guided by one short waveguide to the cladding-air interface and interacts with the graphene layer in the form of evanescent waves before being collected back to the core by another short waveguide, and, as a result, the saturable absorption is excited. The designed saturable absorber is used in the passively mode-locked fiber laser to generate traditional soliton mode-locked pulse output with the center wavelength of 1564.9 nm and pulse width of 758 fs at the fundamental frequency of 22.58 MHz. The fabricated saturable absorber device is stable in operation, compact in structure, safe for thermal damage, and can effectively overcome the shortcomings of poor robustness of the saturable absorbers based on a tapered fiber and D-shaped fiber. This provides a new optical coupling scheme for saturable absorbers based on 2D materials such as graphene and has great potential application in the field of ultrashort pulse lasers.

Enhanced optical nonlinearities in Ti3C2 MXene decorated Fe3O4 nanocomposites for highly stable ultrafast pulse generation

In the present work, we proposed a facile strategy to synthesize the Fe3O4/Ti3C2 MXene composite. The morphology and structures of Fe3O4/Ti3C2 MXene were investigated to confirm the interaction. Moreover, the conventional open- and closed-aperture (OA/CA) Z-scan experiments were implemented to work out the nonlinear optical properties at 1 μm. The large effective nonlinear absorption coefficient βeff, nonlinear refractive index n2, third-order susceptibility |χ(3)| were −4.39 cm MW−1, -2.9 × 10−3 cm2 GW−1, 1.5 × 10−10 esu, respectively. In addition, based on the photogenerated carrier separation and transfer model, a set of rate equations was established to interpreter the nonlinear optical dynamics. The recovery lifetimes were estimated in ∼10 ps level, while the carrier separation and transfer times were in sub-ps level. Furthermore, the tapered-microfiber Fe3O4/Ti3C2 MXene composite was employed as the saturable absorber in the Er-doped fiber laser (EDFL) and the Yb-doped fiber laser (YDFL). In the EDFL, a conventional soliton operation was realized at 1555 nm with a minimum pulse duration of 773 fs and a high signal-to-noise ratio (SNR) of 72 dB. While in the YDFL, a dissipative soliton was achieved with a pulse duration of 677 ps and a high SNR of 82 dB. Our work confirmed that Fe3O4/Ti3C2 MXene hybrid possesses excellent nonlinear optical properties and benefits the ultrafast photonics applications.

Spatio-temporal dynamics of conventional soliton and breathing soliton in an anomalous dispersion fiber laser

The evolutions of conventional soliton (CS) and breathing soliton (BS) dynamics in an anomalous dispersion Er-doped fiber laser are investigated experimentally and numerically. Based on the dispersive Fourier transform technique, the evolution processes of CS buildup and extinction are observed and discussed. It was found that a transitional unstable stage exists during the buildup and extinction process. In the same laser, BS state is also reached. Simulation results of CS and BS evolutionary dynamics are anastomotic with experimental results. The results may contribute to better understanding of the complex pulse dynamics in ultrafast fiber lasers.

Vector harmonic mode-locking by acoustic resonance

For an Er-doped fiber laser, for the first time, to the best of our knowledge, we demonstrate both experimentally and theoretically a novel mechanism of harmonic mode-locking based on the electrostriction effect leading to excitation of the torsional acoustic modes in the transverse section of the laser. The exited torsional acoustic modes modulate the fiber birefringence that results in synchronization of oscillations at the harmonic modes and the linewidth narrowing with the increased signal-to-noise ratio of 30 dB. By adjusting the in-cavity birefringence based on tuning the polarization controller, we enable the selection of the harmonic mode to be stabilized.

Femtosecond laser direct inscribed 45° tilted fiber grating for a net-normal-dispersion mode-locked Er-doped fiber laser

The application of a femtosecond laser direct inscribed 45° tilted fiber grating (TFG) in a net-normal-dispersion mode-locked Er-doped fiber laser, as an in-fiber polarizer, has been systematically studied. The 45° TFG with a grating length of ~ 12.6 mm and a grating period of ~ 2.2 μm has a polarization dependent loss of ~ 9.8 dB and supports various types of dissipative soliton (DS) outputs. The achieved single DS mode-locked pulse centered at 1570.55 nm has a 3 dB bandwidth of 15.64 nm and a pulse duration of ~ 4.68 ps. By simply employing a section of single-mode fiber, the output pulse duration can be dechirped to ~ 250 fs. The fundamental repetition rate is 25.47 MHz and the maximum pulse output power is 24.04 mW. By appropriately adjusting the intra-cavity polarization states and increasing the pump power, the bound-state DS, as well as a harmonic mode-locked DS, can be generated. The bound-state pulse is composed of two identical DS pulses with a temporal interval of ~ 26.27 ps. The second- and third-order harmonic mode-locked DS pulses with repetition rates of 50.93 MHz and 76.40 MHz are obtained for pump powers of 298 mW and 528 mW, respectively. Our results indicate that the feasibility and versatility of the femtosecond laser inscribed 45° TFG to realize nonlinear polarization evolution mode-locking in various operation regimes. Combined with the flexibility of the femtosecond laser direct inscription technique, such a 45° TFG paves a promising route for the development of robust, compact and high-energy ultrafast all-fiber lasers.

Q-Switched and Mode-Locked Er-doped fiber laser based on MAX phase Ti2AlC saturable absorber

MAX phase materials, exhibiting excellent antioxidation, corrosion resistance and high electrical and optical conductivity, attract much attention. The nonlinear optical properties of the MAX phase Ti2AlC was demonstrated by measuring the saturable absorption of Ti2AlC- polyvinyl (PVA) film. The modulation depth of the Ti2AlC-PVA film is calculated to be 2.21%. Stable Q-switched and mode-locked pulses train were achieved in Erbium-doped fiber ring cavity by using Ti2AlC-PVA film as a saturable absorber. The maximum single pulse energy of the Q-switched laser was 92.8 nJ, and the pulse width of the mode-locked laser was 680 fs. This study shows the great potential of MAX phase materials for ultrashort laser pulses generation and provides some valuable design guidelines for the preparation of SAs based on MAX phase materials.

Fast tunable all-polarization-maintaining supercontinuum fiber laser for CARS microscopy

We have demonstrated a compact fiber laser with broad and fast wavelength tunability for coherent anti-Stokes Raman scattering (CARS) microscopy. Originated from an Er-doped fiber laser, the Stokes pulses can be tuned from 1015 to 1060 nm within 300 μs from supercontinuum of a tapered high nonlinear fiber, while pump pulses at 790 nm were obtained by second harmonic generation. The two beams were then sent to microscopes for CARS detection of oil, ethanol and mouse ear samples. This fast and broadly tunable fiber laser in the all-polarization-maintaining architecture would be promising to implement rapid label-free histology in clinical translation.

Dual-wavelength mode-locked Er-doped fiber laser in a spectral filter free cavity

We present the experimental investigation of a dual-wavelength passively mode-locked Er-doped fiber laser with strict polarization control. The configuration includes a double-pass amplifier with a Faraday mirror and twisted fiber. We observe that including double-twist fiber cancels circular and linear birefringence and allows obtaining dual-wavelength emission varying the losses in the cavity. In contrast, results including single-twist fiber which only emits single-wavelength due to large circular birefringence.

Nonlinearity managed passively harmonic mode-locked Er-doped fiber laser based on carbon nanotube film.

We examine the implication of intracavity nonlinearity for harmonic mode locking (HML) by exploiting highly nonlinear fiber in a carbon nanotube film mode-locked Er-doped fiber laser. It is found that the reasonably large nonlinearity is of benefit to increase the extent of harmonic order while the excessive nonlinearity leads to some peculiar multi-pulse patterns such as noise-like pulse and soliton rain. Via appropriate nonlinearity management, nearly 4 GHz repetition rate pulses at the 91st harmonic with 936 fs pulse duration are delivered under the pump power of 280 mW. The pulse stability is evidenced by the super-mode suppression ratio of 35.6 dB. To the best of our knowledge, it is the highest repetition rate yet reported for a passively HML fiber laser based on a film-type physical saturable absorber. Furthermore, the laser exhibits steep pumping efficiency slope of ${\gt}{19}\;{\rm MHz/mW}$, which is also a record among all of the passively HML fiber lasers.

Sech-Shape Time-Stretched Dissipative Solitons in Anomalous Dispersion Cavity Fiber Lasers

New pulse dynamics, which generates time-stretched dissipative soliton, has been analyzed in theory and demonstrated in experiment. With introducing non-equilibrium saturable absorber (SA) into the laser cavity, the time-dependent loss of SA can balance the intracavity dispersion, while gain and nonlinearity assist to stabilize the pulse. The pulse envelop is in exact sech-shape and the duration can be stretched to sub-microsecond by the cavity dispersion. To verify the dynamics, a mode-locked Er-doped fiber laser (EDFL) is fabricated, in which a piece of Tm-doped fiber (TDF) serves as the non-equilibrium SA. The laser delivers stable nanosecond pulse and its temporal intensity is in exact sech 2 shape. The pulse duration is invariant with the pump power but determined by the cavity length. As large as 155nJ mode-locked pulse has been generated. Furthermore, such mode-locked pulse can serve as ideal pump source to optical parametric oscillators, and will have wide applications in optical communication, material processing and biomedicine technology.

Generation of single-,dual-wavelength mode-locked operations based on ZrSe2 as saturable absorber in an Er-doped fiber laser

In this experiment, the Zirconium Diselenide (ZrSe2) was successfully manufactured as the saturable absorber (SA), the modulation depth and saturable intensity of 3.94% and 13.38 MW/cm−2, for demonstrating single-, dual-wavelength pulses within an Er-doped fiber laser (EDFL). The pulse duration of single-wavelength pulses was approximately 1.65 ps. The central wavelengths of dual-wavelength pulses were 1559.4 and 1559.8 nm. The results fully suggested that ZrSe2 nanosheets have widely potential in ultra-fast pulse lasers due to its excellent saturable absorber characteristics.

All-fiber passively mode-locked laser based on an electron beam evaporation grown Co2+:ZnSe film saturable absorber

We experimentally demonstrated an all-fiber mode-locked erbium-doped laser based on Co2+:ZnSe (Cobalt, Zinc Selenide) thin film as the saturable absorber (SA), which was grown on the fiber taper by electron beam (e-beam) evaporation technology. The modulation depth, non-saturable loss and saturation intensity were found to be ∼12%, 76% and 1.89 MW/cm2, respectively. The X ray diffraction (XRD) results showed that the Co2+:ZnSe thin film was provided with the cubic zinc blende structure. The scanning electron microscope (SEM) and atomic force microscopy (AFM) images showed the prepared thin film has a smooth and uniform surface. When the fiber-taper Co2+:ZnSe SA was inserted into an erbium-doped fiber laser cavity, a stable mode-locked pulse was obtained. The mode-locked pulses had a pulse repetition rate of 17.83 MHz and pulse duration of ∼4 ns throughout the mode-locked operation range of 200-600 mW. The recorded maximum average output power was ∼4.88 mW. The signal to noise ratio (SNR) was obtained to be 64.9 dB, which indicates the favorable stability of the mode-locked pulse. These results demonstrate the Co2+:ZnSe thin film grown on a fiber taper has high optical quality and implementation of stable pulse operation on passively mode-locked Er-doped fiber lasers.

Complex soliton patterns formation in a multi-wavelength Er-doped fiber laser

We report on the emission of complex soliton patterns from a multi-wavelength mode-locked Er-doped fiber laser through nonlinear polarization rotation (NPR). The optical spectrum exhibits three distinct well-separated spectral peaks centred at 1567 nm, 1585 nm, and 1616 nm. It is mainly attributed to the linear losses and the nonlinear birefringence filtering inside the cavity. Each wavelength in the spectrum contributes by its own soliton dynamics to a composite-state soliton regime. This is verified by using an external optical tunable filter with 0.5 nm filter bandwidth to filter out the lasing at each wavelength. By controlling the cavity parameters, this regime still can be operated in harmonic states.

Generation of a 59 fs pulse with a 550 nm spectral range in a mode-locked Er-doped single-mode fiber laser system

We demonstrated a compact broad spectrum ultrashort fiber laser system that employed a similariton laser as a seed and fiber-optic nonlinearities in an erbium-doped fiber amplifier to broaden the optical spectrum. The system generated a stable 59 fs ultrashort pulse with a spectral bandwidth beyond 550 nm (i.e. 1490–2030 nm). The mode-locked oscillator produced an 85.9 fs similariton pulse at the wavelength of 1553 nm. The maximum average output power of the laser system was 251 mW. This new type of standard single-mode fiber-format energetic ultrashort system was suitable as a source for biological tissue imaging, broad-band spectroscopy, and optical frequency combs.

Design and Dispersion Control of Microstructured Multicore Tellurite Glass Fibers with In-Phase and Out-of-Phase Supermodes

High nonlinearity and transparency in the 1–5 μm spectral range make tellurite glass fibers highly interesting for the development of nonlinear optical devices. For nonlinear optical fibers, group velocity dispersion that can be controlled by microstructuring is also of great importance. In this work, we present a comprehensive numerical analysis of dispersion and nonlinear properties of microstructured two-, four-, six-, and eight-core tellurite glass fibers for in-phase and out-of-phase supermodes and compare them with the results for one-core fibers in the near- and mid-infrared ranges. Out-of-phase supermodes in tellurite multicore fibers are studied for the first time, to the best of our knowledge. The dispersion curves for in-phase and out-of-phase supermodes are shifted from the dispersion curve for one-core fiber in opposite directions; the effect is stronger for large coupling between the fields in individual cores. The zero dispersion wavelengths of in-phase and out-of-phase supermodes shift to opposite sides with respect to the zero-dispersion wavelength of a one-core fiber. For out-of-phase supermodes, the dispersion can be anomalous even at 1.55 μm, corresponding to the operating wavelength of Er-doped fiber lasers.