Er-doped Fiber Research Articles

Programmable spectral peak generation by a mode-locked Er-fiber laser with an intracavity LCOS-SLM filter.

Applying intracavity spectral phase and/or intensity modulation to a mode-locked laser can control the state of circulating pulses in the cavity and produce unique and useful pulse outputs. In this study, a mode-locked Er-doped fiber laser with an intracavity high-resolution liquid crystal-on-silicon spatial light modulator (LCOS-SLM) spectral filter was developed, and programmable narrow linewidth spectral peak generation directly from the oscillator was demonstrated. Furthermore, by simultaneously controlling the intracavity group delay dispersion (GDD), the generation of 20 spectral peaks with a linewidth of 100 pm over a bandwidth of 17 nm was demonstrated. Spectral modulation also affects the temporal waveform, and burst-like pulse trains with intra-burst repetition rates up to 252 GHz were observed.

Spatiotemporal dissipation dynamics: a route to high-beam-quality and high-peak-power spatiotemporal mode-locked fiber lasers

Spatiotemporal mode-locking (STML) opens a new avenue for implementing high-energy, high-peak-power mode-locked fiber oscillators. However, the compromised beam quality poses a critical limitation to their broader applications. This study presents a method for enhancing the beam quality of STML fiber lasers by employing spatiotemporal dissipation involving the quenching and reabsorption effects of multimode erbium-doped fibers. The proposed technique introduces spatiotemporal saturable absorption, achieving high beam quality without the stringent conditions required for Kerr beam self-cleaning (BSC). Integrating spatiotemporal dissipation with Kerr BSC, we demonstrate an all-anomalous-dispersion Er-doped STML fiber laser, which produces solitons with 6.7 nJ pulse energy (the intracavity solitons with 25.8 nJ pulse energy and >52.8kW peak power), sub-500 fs pulse duration, and beam quality with M x 2/M y 2=1.23/1.20. To our knowledge, it is a record peak power for 1.5 µm band soliton lasers. Additionally, the approach enables the generation of noise-like pulses with M x 2/M y 2=1.04/1.13. This work not only advances our understanding of spatiotemporal dissipation dynamics in STML fiber lasers, but also paves the way toward high-performance STML fiber lasers, rendering them very attractive for applications.

Generation of stable dual-wavelength mode-locked pulses using boron nitride saturable absorber in all-polarization-maintaining Er-doped fiber laser

This work demonstrates the generation of stable dual-wavelength mode-locked pulses using boron nitride (BN) as a novel saturable absorber within a polarization-maintaining (PM) Er-doped fiber laser cavity. BN was chosen due to its exceptional properties, including high thermal stability, wide bandgap, and excellent mechanical strength. A drop-casting technique was employed to fabricate the BN-based saturable absorber. The laser generated high-quality dual-wavelength pulses centered at 1566.3 nm and 1575.6 nm with a repetition frequency of 25.3 MHz and a pulse width of 900 ps. The generated laser exhibited excellent stability and a high degree of polarization (DOP) of 99.8 %. These findings contribute to the advancement of dual-wavelength mode-locked fiber laser technology and open new avenues for applications such as dual-frequency comb spectroscopy.

Bidirectional all-PM Er-doped fiber laser based on a self-stabilized interferometer mode-locker

We demonstrate a bidirectional all polarization-maintaining (PM) Er-doped fiber laser based on a self-stabilized interferometer mode-locker. By utilizing mechanical sharing and multiplexing propagation directions, the laser has balanced bidirectional outputs and passively suppresses common-mode noise. We also investigate the intra-cavity pulse dynamics via numerical simulations, which coincides well with experimental observations. The self-stabilized interferometer compensates for the group delay difference between the polarization components induced by linear birefringence. The cross-phase modulation effect in the self-stabilized interferometer leads to asymmetric spectra. In addition, from 10 kHz to 1 MHz frequency range, the integrated RMS phase noise in clockwise (CW) and counter-clockwise (CCW) directions are 0.124 mrad and 0.14 mrad, respectively. The integrated RMS RIN in CW and CCW directions are 439 ppm and 464 ppm. Due to passive common-mode noise cancellation, the repetition frequency difference can be stabilized near 19 Hz in 2500 s gate time. The stability of the repetition frequency difference can reach a minimum value of 4.167 × 10−4 at a gate time of 100 s. This novel bidirectional all-PM Er-doped fiber laser based on a self-stabilized interferometer mode-locker can provide a new scheme for the construction of an all-PM dual-comb system.

Broadband nanotubes-based nonlinear modulators for erbium- and thulium-doped lasers

Carbon-based nanomaterials have become a long-term research hotspot in the fields of material science and nanotechnology. Carbon nanotubes as one-dimensional nanomaterials have shown great application value in the fields of electronics and optoelectronics. Herein, stable mode-locked pulsed lasers in both 1.5- and 2-μm bands were achieved by combining and balancing the stimulated emission effect of rare-earth ions and saturable absorption effect of carbon nanotubes. In the Er-doped fiber laser, pulses with a SNR of 61 dB and a peak power of 2.97 W were achieved at the wavelength of 1565.8 nm. Meanwhile, bound states were observed in the same laser, where the time delay of pulses was adjustable from 9.84 to 21.77 ps by tuning the pump power and polarization state. In the Tm-doped laser, output pulses were obtained at the wavelength of 1921.0 nm with a 60-dB SNR and a 12.82-W peak power. These results demonstrate that carbon nanotubes are ideal candidates for saturable absorber in mode-locked fiber lasers, which can be applied to a variety of applications, including fiber optic sensing, optical communication, and nanoscale processing.

Self – assembled aligned single – walled carbon nanotubes as an anisotropic polarizer and saturable absorber in erbium-doped femtosecond fiber laser

We report the production of a saturable absorber (SA) based on aligned single-walled carbon nanotubes SWCNTs by the self-assembly method. The ultrafast saturation behavior of prepared aligned and random nanostructures shows an increase of modulation depth by 6% due to the alignment method. We also observed the dependence of aligned SWCNTs loss on the polarization direction of laser radiation. All-fiber Er-doped hybrid mode-locked fiber laser was demonstrated based on the aligned /random SWCNTs-based SAs. We achieved the generation of stable stretched pulses with a pulse duration of 490/569 fs and an average output power of 20.7/18.25 mW. We also investigated the advantages of using aligned SWCNTs compared to the typical structure with random tube distribution. We show that the use of aligned SWCNTs film increased the SNR by 24.5, decreased the mode-locking threshold power by 42 mW, and decreased the RIN level by (20-25) dB in the frequency range [∼ 0 Hz- 100 kHz] and ∼ 8 dB in the range [100 kHz – 1 MHz].

Large-energy operation of an Er-doped fiber laser with ZrGeTe4 saturable absorber

ZrGeTe4 as a layered semiconductor material with good stability and optoelectronic properties, and excellent saturable absorption characteristics, but its application in fiber lasers is still insufficient. In order to explore its application in fiber lasers, we prepared ZrGeTe4-PVA thin film by liquid phase exfoliation and performed a series of characterizations. A modulation depth of 13.15 %, a non-saturated loss of 6.4 %, and a saturation intensity of 5.5 MW/cm2 were obtained. Then used the ZrGeTe4-PVA thin film as the saturable absorber (SA) in an Er-doped fiber laser (EDFL), the large-energy operation could be realized. In the case of a cavity length of 234 m, when the pump power was increased to 1229 mW, a maximum single pulse energy of about 32.72 nJ was achieved, with a repetition frequency of 859 kHz. To the best of our knowledge, this is the highest single-pulse energy achieved in an EDFL based on ZrGeTe4-SA. This experiment shows that the ZrGeTe4 is a promising two-dimensional (2D) material with good nonlinear absorption properties, proving that it is a promising pulse modulation of SA and laying a foundation for its subsequent study in fiber lasers.

Interlayer engineered bilayered V₂O₅ NPs as saturable absorbers for infrared ultrashort pulse generation

Interlayer engineering offers a promising approach to modifying the structure of layered vanadium-based oxides, enhancing their saturable absorption effect and making them a desirable choice for developing infrared wavelength-range photonics devices. This experimental work synthesizes interlayer vanadium pentoxide (V2O5) using hydrothermal techniques to produce an excellent saturable absorber (SA). The interlayer engineering strategy enhances strong saturable absorption and self-defocusing effects in V2O5-based SA, enabling the generation of ultrashort pulses in the infrared region. Their superior nonlinear optical characteristics are demonstrated by a modulation depth of 13.9 % and saturation intensity of 0.42 GW cm−1, respectively. By utilizing a transmission coupling fiber-based V2O5-SA inside an Er-doped fiber laser cavity, a passively Q-switched (PQS) laser with a narrow pulse width of 2.78 μs and signal-to-noise ratio (SNR) ∼50 dB is realized for the first time. Furthermore, we explore a V2O5 NPs-SA long-term stability and high damage threshold. The results not only offer additional proof of the capable potential of interlayer V2O5 as a photo-bleaching absorber for realizing pulsed lasers in the NIR band but also cover the method for advancing their probable applications in optoelectronic devices.

Supercontinuum generation by nonlinear polarization rotation mode-locked fiber laser with pulse type switchable

We report on the generation of a supercontinuum (SC) by nonlinear polarization-rotating (NPR) mode-locked fiber laser, which includes a pulsed switchable NPR mode-locked fiber laser, an Er-doped fiber amplifier, and high nonlinear fiber (HNLF). In the experiment, by adjusting the polarization controller (PC) angle and pump power, we obtained three different pulses. They are traditional soliton bunch pulses, the coexistence of soliton bunch pulses and square pulses, and multi-longitudinal mode noise like square pulses. All three pulses can generate SC with spectrum width be about of 1000 nm. We fixed the pump power in the laser and observed the influence of amplifier power on the spectrum width and output power of SC. The SC width of soliton bunch pulse reaches 950.9 nm, the SC of soliton bunch pulse and square pulse coexisting pulse is 1009.7 nm, and the SC spectrum width of multi-longitudinal mode noise like square pulse is 887.1 nm. Our results demonstrate the generation of SC with three types of switchable pulses, opening up possibilities for various application requirements.

Mo4/3B2T2/Co3O4 vdW heterostructure as saturable absorber for ultrafast pulse generation

VdW heterostructure have garnered significant interest in ultrafast laser generation because of their attractive saturable absorption properties, holding promise for applications in optics, medicine, and optoelectronics. In this study, the saturable absorption of Mo4/3B2T2/Co3O4 vdW is investigated for the first time. Mo4/3B2T2/Co3O4 vdW SA is successfully applied to passively mode-locked Er-doped fiber lasers. Due to the excellent saturable absorption properties of Mo4/3B2T2/Co3O4 vdW SA, stable mode-locked fiber lasers can be realized in the same cavity, including fundamentally conventional soliton, bound soliton, and harmonic soliton. Among them, the conventional soliton operates at a repetition rate of 11.16 MHz with a high SNR of 56.26 dB. Bound soliton is observed with a soliton pulse separation of 5.26 ps. Furthermore, 3rd-, 5th-, 8th-, 10th-, 12th-, 15th-, and 17th-order harmonic solitons are observed, corresponding to repetition rates of 33.48 MHz, 55.8 MHz, 89.28 MHz, 111.6 MHz, 133.92 MHz, 167.4 MHz and 189.72 MHz, respectively. For vdW heterostructure, the saturable absorption properties are strongly modulated by the interlayer coupling, which may be introduced by the Fermi level recombination and photogenerated carrier migration between the heterostructure. We established a model to understand the saturable absorption properties of the Mo4/3B2T2/Co3O4, which suggests the enhancements of the saturable absorption are attributed to the carrier migration between Mo4/3B2T2 and Co3O4. The results indicate that Mo4/3B2T2/Co3O4 vdW heterostructure can be used as an excellent nonlinear optical material, which can be used as SA in ultrafast pulse generation.

Robust Edge States of Quasi-1D Material Ta2NiSe7 and Applications in Saturable Absorbers.

The helical edge states (ESs) protected by underlying Z2 topology in two-dimensional topological insulators (TIs) arouse upsurges in saturable absorptions thanks to the strong photon-electron coupling in ESs. However, limited TIs demonstrate clear signatures of topological ESs at liquid nitrogen temperatures, hindering the applications of such exotic quantum states. Here, we demonstrate the existence of one-dimensional (1D) ESs at the step edge of the quasi-1D material Ta2NiSe7 at 78 K by scanning tunneling microscopy. Such ESs are rather robust against the irregularity of the edges, suggesting a possible topological origin. The exfoliated Ta2NiSe7 flakes were used as saturable absorbers (SAs) in an Er-doped fiber laser, hosting a mode-locked pulse with a modulation depth of up to 52.6% and a short pulse duration of 225 fs, far outstripping existing TI-based SAs. This work demonstrates the existence of robust 1D ESs and the superior SA performance of Ta2NiSe7.

Application of Cr2Si2Te6 saturable absorber in Er-doped fiber laser for generating dual-wavelength mode-locked pulse

As a typical two-dimensional (2D) ferromagnetic insulator (FI), the Cr2Si2Te6 (CST) has performance ferromagnetic properties. The previous investigation has shown that quantum mechanical simulation can get structure and electronic properties of CST, and the indirect gap value of CST is 0.6 eV by establishing its layered calculation. It implies that the CST is an excellent optical modulator due to larger infrared radiation absorption interval. Based on that, some groups conducted the research of fiber laser based on CST saturable absorber (SA). However, the exploration and application of 2D CST in optics is still in the early stage. In this investigation, the CST was utilized as a SA in an Er-doped fiber laser. The dual-wavelength mode-locked pulse could be observed when the pump power was adjusted from 25 to 140 mW. The CST was applied in Er-doped fiber as SA for generating dual-wavelength mode-locked pulse for the first time. It exhibits performance optical properties that provide a significant reference for exploring the application of 2D materials in ultrafast laser.

Tunable and switchable multi-wavelength mode-locked fiber lasers induced by an optimized hybrid mode-locked composite filtering effect.

A multi-wavelength mode-locked fiber laser can generate different wavelengths from a single laser cavity, offering potential as a dual-frequency comb and serving as an ideal light source for terahertz wave generation. We present an optimized hybrid mode-locked Er-doped fiber laser with flexible outputs: switchable and tunable dual-wavelength mode-locking, along with stable tri-wavelength mode-locking, which is achieved by introducing 0.69 m polarization-maintaining fiber and bent 200 m single-mode fiber to enhance intra-cavity birefringence and nonlinear effect to optimize the hybrid mode-locking effect, that is, build the composite filter effect. The dual-wavelength mode-locking not only covers a tunable wavelength range of 5 nm but also provides tunable wavelength intervals of 4-26 nm due to the composite filter effect. The formation dynamics of the tri-wavelength mode-locking can be switched either pair-by-pair or one-by-one. This approach enables the realization of wavelength interval tunable dual-wavelength mode-locking in mode-locked fiber lasers simply by introducing fiber without additional actions. Such a simple, compact fiber laser with tunable wavelength capabilities holds significant potential for diverse applications.

Narrow bandwidth mode-locked fiber laser with the GIMF-based saturable absorber

We have demonstrated the realization of the nearly transform-limited conventional solitons (CSs) with narrow spectral bandwidth in an Er-doped linear-cavity fiber laser, which is mode-locked by the graded index multimode fiber (GIMF)-based saturable absorber (SA). To our knowledge, this is the first report of the GIMF-based SA in the narrow bandwidth soliton generation. Simultaneously, the wavelength tunability of 0.48 nm and controllable Kelly sidebands for the narrow bandwidth solitons can be realized by the polarization controller (PC). Thereby, the minimum spectral bandwidth of the CSs reaches to be 0.1 nm, accompanied by the pulse duration of 20.8 ps and pulse energy of 1.07 nJ. Our work provides a compact and low-cost alternative for the narrow bandwidth solitons and offers a promising platform in the fields such as spectroscopy, quantum optics and other fields.

790–1000 nm continuously-tunable fiber-based femtosecond laser source

We report a 790–1000 nm tunable femtosecond laser source by second harmonic generation (SHG) of a 1580–2000 nm soliton self-frequency shift (SSFS) fiber laser. The SSFS fiber laser with an all polarization-maintaining fiber configuration consists of passively mode-locked figure-9 Er-doped fiber oscillator, two-stage fiber amplifiers and a nonlinear fiber, delivering femtosecond Raman solitons in a tunable range of 1580 to 2016 nm. The tunable Raman solitons are further injected into a specifically-designed chirped periodically-poled lithium niobite (CPPLN) crystal for efficient SHG, and therefore femtosecond pulses with wide wavelength tuning from 790 to 1000 nm are obtained. The shortest pulse duration is < 100 fs at 890 nm, and the average power is 7.55 mW with a repetition rate of 44.9 MHz. This is, to the best of our knowledge, the first demonstration of a < 1000 nm broadband tunable fiber-based femtosecond source almost covering the whole short-wavelength near-infrared spectrum, which may have important applications in the nonlinear microscopy, biomedical imaging, and material processing.

270 MHz passively mode-locked Er-doped fiber laser using single walled carbon nanotube polymer film.

We demonstrated a short-cavity mode-locked erbium-doped fiber laser based on single walled carbon nanotube polymer composite film saturable absorber with a maximum fundamental repetition rate of 270.5 MHz. To the best of our knowledge, this is the highest fundamental repetition rate among mode-locked erbium-doped ring fiber lasers based on nanomaterial polymer composite films. Samples with non-saturable loss range from 13.2% to 60% and modulation depth from 1.63% to 7.08% are prepared by controlling carbon nanotube concentration and film thickness. We systematically investigate the impacts of saturable absorbers on mode-locking repetition rate. Our results show that when the laser repetition rate continuously increases from 15.45 MHz to 270.5 MHz, samples with higher non-saturable loss will push forward the mode-locking threshold and eventually lose mode-locking. In addition, the increased modulation depth will enhance the pulse shaping ability and result in a shorter pulse. Our results may help for high repetition rate mode-locked fiber laser design and improve the laser characteristics. The demonstrated laser may support applications such as frequency comb, etc.

Epitaxy of Antimonene Thin Films with Screw Dislocations for the Application of Saturable Absorbers.

The exotic optoelectronic properties of antimonene, including strain-induced tunable bandgaps, broad nonlinear refractive response, etc., have evoked profound upsurges for decades. As the screw dislocations break the crystal symmetry and modify interlayer coupling, it is highly desirable to investigate the optical prospects of antimonene with screw dislocations. Herein, controllable epitaxy of spiral β-antimonene is achieved on Fe3GaTe2 substrates. By fine-tuning growth temperatures, the evolutions of spiral β-antimonene with non-centrosymmetric stacking are investigated via scanning tunneling microscopy. The effects of interfacial strain and dislocation motion during screw-dislocation-driven growth are also studied. Additionally, a modulation depth of 40.8% and mode locking at 1558 nm with a pulse width of 290 fs are observed in Er-doped pulsed fiber lasers generated with spiral Sb-based saturable absorbers, revealing superior performance that far outstrips reported Sb-based saturable absorbers to date. Our work sheds light on the preparation of Sb films with screw dislocations and demonstrates a promising approach toward fabricating ultrafast optical devices.

Demonstration of a 0.8 W continuous wave bulk laser around 2 μm in a Tm3+:Ga-rich BGG glass

Efficient lasing of Ga-rich BGG bulk glasses doped with Tm3+ is demonstrated. Two BGG bulk samples with Tm3+ ion concentrations of 1.27×1020 cm−3 and 2.54×1020 cm−3 were tested for their laser performance. In-band pumping was realized using a continuous-wave (CW) homemade Er-doped fiber laser at 1600 nm. A maximum slope efficiency of 27.7% was demonstrated with respect to the absorbed pump power. The emission cross-section was retrieved from the laser efficiency data for three different lasing wavelengths and compared with the theoretical calculations. The power scaling potential of the Tm3+:BGG glass was investigated and a maximum output power of 0.8 W was achieved.

Generation of Bright–Dark Pulse Pairs in the Er-Doped Mode-Locked Fiber Laser Based on Doped Fiber Saturable Absorber

This study reports new types of passive mode-locked Er-doped fiber laser (EDFL) based on a segment of doped fiber saturable absorber (DFSA) with Tm/Ho-doped fiber (THDF), Yb-doped fiber (YDF), and Er-doped fiber (EDF). By employing THDF-SA, a bright pulse sequence with a fundamental repetition rate of 17.86 MHz was obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, and second-harmonic pulses, were obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in both polarization directions was verified. Furthermore, using EDF-SA and YDF-SA, dark pulses and dark–bright pulses were obtained. A comparison of the three experiments revealed that THDF-SA effectively reduces the mode-locked threshold and improves the average output power. Compared with bright pulses, dark pulses offer several advantages such as resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL can find broad application in long-distance transmission, precision measurement, and other fields.

GHz-rate 57-fs acousto-optic mode-locking fiber laser based on cascaded all-fiber pulse compression.

We demonstrate a compact ultrafast fiber laser system that can deliver 1.87 GHz pulse train at 1550 nm with a pulse energy of 52 pJ and an ultrashort pulse duration of 57 fs. While an acousto-optic mode-locking fiber laser was used as the seed light source at GHz rate, a stage of Er-doped fiber amplifier boosted the laser power to ∼320 mW, giving a pulse energy of ∼170 pJ. Then, a pulse compression setup was constructed, providing a high compression ratio of ∼10 with a total efficiency of ∼32%. In the cascaded compression configuration, multiple fiber samples with alternately normal and anomalous dispersion were fused together, providing efficient nonlinear spectral broadening while suppressing excessive pulse broadening over propagation. This GHz-rate ultrafast fiber laser, with compact configuration, broad optical spectrum, and high time-resolving ability could be used as the seed light source for constructing high-rate, high-power ultrafast laser systems and may find a few applications in optical measurements and microwave photonics.