Mode-locked Laser Operation Research Articles

Dispersion Management and Pulse Characterization of Graphene-Based Soliton Mode-Locked Fiber Lasers

This paper presents the generation and characterization of femtosecond pulses utilizing graphene-polymethyl-methacrylate (PMMA) thin-film saturable absorber (SA), which is subjected to different lengths of single-mode fiber (SMF) in an erbium-doped fiber laser cavity. The graphene/PMMA-SA is prepared by using a simple transfer procedure of the thin-film on a fiber ferrule. By increasing the SMF length from 0 to 4 m, the corresponding group velocity dispersion of the entire cavity is estimated to change from −0.033 to −0.121 ps2. Analysis of the pulse performance shows that the pulse width behavior varies from 820 fs to 710 fs against different cavity lengths. Similarly, the pulse repetition rate and the spectral bandwidth can be adjusted from 12.5 to 10.0 MHz, and from 8.2 to 5.6 nm, respectively. A comprehensive discussion on the pulse performance is presented, which can contribute to widening the knowledge on the operation of graphene-based soliton mode-locked erbium-doped fiber lasers based on dispersion management by controlling the cavity length.

Saturable absorber based on graphene for a hybrid passive mode-locked erbium-doped fiber laser

We proposed a hybrid passive mode-locked fiber laser based on a saturable absorber fabricated by coating a layer of graphene on a single-mode fiber with inscribed short waveguides. The hybrid mode-locked fiber laser operation is achieved by use of nonlinear polarization rotation and saturable absorption. The output pulses have the center wavelength of 1558 nm, 3-dB bandwidth of 4.6 nm, pulse width of 605 fs, repetition frequency of 20.8 MHz, and signal-to-noise ratio of 60 dB. Compared with the use of nonlinear polarization rotation mode locking alone, the pulse width is compressed by 211 fs, and the signal-to-noise ratio is improved by 5 dB. The advantages of hybrid mode locking mechanism include simple structure and convenient operation, which make the system attractive in ultrafast lasers.

Influence of time-delayed feedback on the dynamics of temporal localized structures in passively mode-locked semiconductor lasers.

In this paper, we analyze the effect of optical feedback on the dynamics of a passively mode-locked ring laser operating in the regime of temporal localized structures. This laser system is modeled by a set of delay differential equations, which include delay terms associated with the laser cavity and the feedback loop. Using a combination of direct numerical simulations and path-continuation techniques, we show that the feedback loop creates echoes of the main pulse whose position and size strongly depend on the feedback parameters. We demonstrate that in the long-cavity regime, these echoes can successively replace the main pulses, which defines their lifetime. This pulse instability mechanism originates from a global bifurcation of the saddle-node infinite-period type. In addition, we show that, under the influence of noise, the stable pulses exhibit forms of a behavior characteristic of excitable systems. Furthermore, for the harmonic solutions consisting of multiple equispaced pulses per round-trip, we show that if the location of the pulses coincides with the echo of another, the range of stability of these solutions is increased. Finally, it is shown that around these resonances, branches of different solutions are connected by period-doubling bifurcations.

The nonlinear optical properties of Zirconium pentatelluride and its application in ultrafast solid-state lasers

The topological Dirac semimetal Zirconium pentatelluride (ZrTe5) has many special properties such as anomalous Hall effect and thermoelectric effect. A fast relaxation time constant of 250 fs indicates its great application potential in ultrafast optics, which has been investigated in a Er-doped passively mode-locking fiber laser. In this paper, the ZrTe5 was adopted as a saturable absorber (SA) to modulate Nd-doped solid-state lasers for ultrafast pulse generation. The nonlinear absorption coefficient of ZrTe5 was measured to be −0.81 cm/GW by Z-scan technique. A pulse width of 18.4 ps with a repetition frequency of 69 MHz was gained in the 1.06 μm passively mode-locking laser. For the 1.34 μm ultrafast laser, a stable pulse sequence with a pulse duration of 17.7 ps was delivered and the corresponding repetition frequency was 71 MHz. Those results revealed that ZrTe5 has an excellent laser modulation performance in ultrafast solid-state lasers. As far as we know, it is the first time the solid-state passively mode-locking laser operation by using ZrTe5 as a SA has been successfully demonstrated.

Passively Q-switched and Q-switched mode-locked Nd:Lu0.15Y0.85VO4 lasers at 1.34 µm with a nickel-cobalt layered double hydroxide saturable absorber

A nickel-cobalt (NiCo) layered double hydroxide (LDH) saturable absorber (SA) was successfully fabricated and utilized as a passively mode-locked (PML) laser modulator for the first time. We successfully investigated a 1.34 µm passively Q-switched (PQS) and Q-switched mode-locked (QML) laser operation of Nd:Lu0.15Y0.85VO4 mixed crystal with NiCo-LDH SA, respectively. A stable pulse sequence with a narrowest pulse width of 52 ns and a repetition frequency of 1.18 MHz was obtained, leading to a single pulse energy of 0.72 µJ. Furthermore, for the QML laser operation, an average power of 1.10 W and a calculated pulse width of 25 ps were gained with a repetition frequency of 134 MHz. The results indicate the NiCo-LDH SA has remarkable nonlinear optical properties and promising application prospects in the field of laser modulators at 1.3 µm.

All-fiber all-normal-dispersion passively mode-locked neodymium-doped fiber laser operation at 1064 nm

In this work, we report an all-fiber Nd-doped passively mode-locked fiber laser based on nonlinear polarization rotation mechanism operating in the 1.06 μm region. When the pump power was 300 mW, a pulse with a maximum average output power of 0.63 mW, a narrowest pulse duration of 1.22 ps and a pulse repetition rate of 14.25 MHz was obtained.

High-efficiency mode-locked fiber laser with a switchable oscillating transverse mode in an all few-mode fiber linear cavity.

In this paper, an oscillating transverse mode switchable mode-locked fiber laser with a few-mode fiber linear cavity is proposed and demonstrated. An artificial filter is used to realize the mode gain modulation of the laser. The stable mode-locked pulsed operation with switchable wavelength is easily achieved and the oscillating transverse mode can be flexibly switched between the fundamental mode and high-order mode by adjusting the polarization controller. The mode-locked fiber laser directly oscillates in the high-order mode stably with a slope efficiency of as high as 12%, and the corresponding operating wavelength, repetition rate as well as pulse duration are 1054.07 nm, 22.662 MHz, 31.5 ps, respectively. Besides, a cylindrical vector beam with a high mode purity of 98.6% is obtained by removing the degeneracy of the LP11 mode. This compact and high-efficiency mode-locked fiber laser operating in switchable transverse mode has the potential application for laser processing, particle trapping, bioimaging, and mode division multiplexing system.

SESAM mode-locked Yb:SrLaAlO4 laser

We report on a detailed investigation of continuous-wave and SESAM mode-locked (ML) laser operation of an Yb:SrLaAlO4 laser. Pumped with a high-brightness fiber laser at 976 nm, the ML Yb:SrLaAlO4 laser delivered soliton pulses as short as 38 fs at 1071 nm with an average output power of 86 mW and a pulse repetition rate of ∼59 MHz. The maximum average output power reached 1.05 W at 1054 nm for longer pulses (94 fs), corresponding to a peak power of 146 kW and an optical efficiency of 38.6%. To the best of our knowledge, this is the first demonstration of SESAM ML operation of the Yb:SrLaAlO4 laser.

Dark Pulse Mode-locked Laser based on Aluminum Zinc Oxide coated D-shape fiber as Saturable Absorber

ABSTRACT We have experimentally reported aluminum zinc oxide (AZO) as a novel saturable absorber to generate a mode-locked laser operating in dark pulsed regime. The D-shaped fiber was first prepared by side polishing a single-mode fiber to the 1 dB insertion loss. The AZO was dissolved in isopropyl alcohol and then deposited onto the D-shaped fiber by drop casting method. By carefully optimizing the polarization of the cavity, a dark pulse was achieved, which remained stable within the pump power of 65.7–101.35 mW. Pulse width was 220 ns, and the pulse repetition rate was 1.85 MHz.

Passively mode-locked fiber laser based on graphene covered single-mode fiber with inner short waveguides

A saturable absorber based on graphene film covered single-mode fiber with inner short waveguides is proposed and demonstrated for passively mode-locked laser operation. The output laser pulses produced have the center wavelength of 1556.9 nm and pulse width of 830.5 fs at the fundamental repetition rate of 18.7 MHz. Such a saturable absorber is highly robust as the graphene film is covered on the surface of single-mode fiber, instead on tapered fiber or side-polished fiber. Moreover, compared with the saturable absorber based on clamping the graphene film between the two fiber connectors in a fiber adaptor, our device provides a large interaction surface area, thus effectively avoiding the thermal damage and ensuring a long time and stable system operation. The device is attractive for high power ultra-short laser pulse generation.

Highly efficient mode-locked and Q-switched Er3+-doped fiber lasers using a gold nanorod saturable absorber

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm2, respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

Sub-100 fs mode-locked Tm:CLTGG laser.

We report on the first sub-100 fs mode-locked laser operation of a Tm3+-doped disordered calcium lithium tantalum gallium garnet (Tm:CLTGG) crystal. Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 69 fs were achieved at a central wavelength of 2010.4 nm with an average power of 28 mW at a pulse repetition rate of ∼87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW.

Kerr-lens mode-locked Tm-doped sesquioxide ceramic laser.

Kerr-lens mode-locked solid-state laser operation at ∼2µm is investigated. Using a Tm3+-doped (Lu,Sc)2O3 "mixed" sesquioxide ceramic as a gain medium, pulses as short as 58 fs are generated at ∼2081nm via soft-aperture Kerr-lens mode locking. The average output power amounts to 220 mW at a pulse repetition rate of 84.8 MHz. The emitted spectrum at the long-wavelength wing extends to >2.2µm which is attributed to vibronic transitions of the Tm3+ ions. The latter is found to be essential for generating pulses with durations in the 50 fs range.

Manipulation of temporal localized structures in a vertical external-cavity surface-emitting laser with optical feedback.

We analyze the effect of optical feedback on the dynamics of an external-cavity passively mode-locked surface-emitting laser operating in the regime of temporal localized structures. Depending on the ratio between the cavity round trip time and the feedback delay, we show experimentally that feedback acts as a solution selector that either reinforces or hinders the appearance of one of the multistable harmonic arrangements of pulses. Our theoretical analysis reproduces well the experiment and allows us to evidence asymmetrical resonance tongues due to the parity symmetry-breaking induced by gain depletion.

Ta2NiSe5 nanosheets as a novel broadband saturable absorber for solid-state pulse laser generation

Two-dimensional (2D) ternary chalcogenides have attracted great attentions because of their novel chemical and physical properties arising from the synergistic effect and stoichiometric variation with the additional third element compared with their binary counterparts. Here, high-quality 2D tantalum nickel selenide (Ta2NiSe5) nanosheets are successfully fabricated by a liquid-phase exfoliation (LPE) method. The ultrafast excited carrier relaxation time and nonlinear optical absorption response are investigated and reveal that the prepared 2D Ta2NiSe5 nanosheets have excellent broadband saturable absorption properties, which are further illustrated by three passively Q-switched (PQS) all-solid-state lasers operating at 1.0, 2.0 and 2.8 µm with the Ta2NiSe5 nanosheet-based saturable absorber (SA). Furthermore, mode-locked laser operation with the pulse width as short as 356 fs is also realized at 1.0 µm. This work not only demonstrates the excellent nonlinear optical proprieties and optical modulation performance of Ta2NiSe5, but also paves the way for exploring the photonic and optoelectronic proprieties of ternary chalcogenide materials.

Switchable dissipative soliton resonance and noise like pulses regimes in a mode-locked double-clad thulium doped fiber laser

We report an experimental study of switchable rectangular pulses generation in a passively mode-locked double-clad thulium-doped fiber laser operating in the anomalous dispersion regime. A fiber loop mirror and a polarization imbalanced nonlinear optical loop mirror (NOLM) forms the linear cavity. The loop in the NOLM includes a quarter-wave retarder, which allows switching between two regimes of rectangular pulse generation. The laser generates rectangular noise-like pulses (NLPs) or dissipative soliton resonance (DSR) pulses with 1.18 MHz repetition rate at ∼1990 nm. At the maximum pump power of 10 W, rectangular pulses with energy of up to 540 nJ in DSR operation and 482 nJ in NLP operation were obtained with output average power of 640 mW and 571 mW, respectively.

SESAM mode-locked Tm:LuYO3 ceramic laser generating 54-fs pulses at 2048 nm.

Mode-locked laser operation near 2.05 µm based on a mixed sesquioxide Tm:LuYO3 ceramic is demonstrated. Continuous-wave and wavelength-tunable operation is also investigated. Employing a GaSb-based semiconductor saturable absorber mirror as a saturable absorber, a maximum average output power of 133 mW is obtained for a pulse duration of 59 fs. Pulses as short as 54 fs, i.e., eight optical cycles are generated at a repetition rate of ∼78MHz with an average output power of 51 mW. To the best of our knowledge, this result represents the shortest pulse duration ever achieved from Tm-based solid-state mode-locked lasers.

High power diode pumped solid-state femtosecond laser systems

We demonstrate high power direct diode-pumped femtosecond laser based on a commercially available configuration and pumped by multi-diode laser modules delivering high brightness and average power. The multi-diode modules employ beam-combining scheme preserving linear polarization and focusing properties of individual laser diodes. Stable passive Kerr lens modelocked (KLM) laser operation was demonstrated, producing 30 fs pulses at ∼300 mW average output power. A simple approach to numerical modelling of KLM laser operation in cases when longitudinal pump beam exhibits strong astigmatism is also discussed.

Generation of Q-switched and mode-locked pulses using neodymium oxide as saturable absorber

Generations of Q-switched and mode-locked pulses were successfully demonstrated in an erbium-doped fiber laser (EDFL) cavity using Neodymium oxide (Nd2O3) as saturable absorber (SA). Nd2O3 nano-powder was mixed with aqueous solution of polyvinyl alcohol (PVA) to form a thin film after a drying process. The thin film was used to form a SA device. A stable Q-switched EDFL pulses operating at a wavelength of 1558.5 nm were successfully obtained by incorporating the device into the laser cavity. The pulse’s repetition rate rose from 89.45 to 104 kHz while the pulse width shrunk from 2.56 to 2.19 µs as the pump power was varied from the threshold of 91.17 to 142.08 mW. The output power steadily increased from 9.57 to 13.94 mW with a slope efficiency of 8.42% as the pump power was raised in the same range. Meanwhile, a stable mode-locked laser operating in soliton regime was also realized as the additional 100 m SMF was incorporated into the laser cavity. The laser operated at a central wavelength of 1559 nm with visible Kelly sidebands. The soliton pulses operated at a fixed repetition rate of 1.809 MHz with a pulse width of 4.62 ps as the pump power was varied within 25.03 to 75.92 mW. The peak power of the mode-locked laser increased from 0.37 kW to 1.26 kW as the pump power was varied within the pump power range. The finding reveals the outstanding optical nonlinearity of Nd2O3, which can open new potential in pulsed laser development for various applications including, optical communication, material processing, biomedical diagnostic etc.

Continuous-wave mode-locked Tm:YAG laser with GaAs-based SESAM

Passive mode-locked laser operation at 2012 nm based on Tm:YAG and GaAs-based saturable absorber mirrors is demonstrated. Continuous-wave mode-locking performance was observed, resulting in a pulse width of 47.9 ps and 117 mW average output power at 97.7 MHz. The mode-locked laser exhibits an excellent stability with a remarkably high extinction ratio of 72 dB above carrier.