Mode-locked Fiber Laser Operating Research Articles

Utilization of Te as a saturable absorber for mode-locked 2.8 µm Er3+: ZBLAN fiber laser

In this manuscript, we present the experimental realization of a mode-locked Er3+: ZBLAN (ZrF2- BaF2- LaF3- AlF3- NaF) fiber laser operating at mid-infrared (mid-IR) 2.8 μm band, achieved through the utilization of Tellurium (Te) as the saturable absorber (SA). An exploration of their nonlinear optical absorption properties at 2.8 μm was undertaken employing a dual-channel detection methodology. Our investigation reveals that the Te-SA prepared exhibits a significant broadband saturable absorption response, thereby confirming its suitability as SA for passive mode-locked fiber laser at 2.8 μm. The peak average output power pulse and energy of the mode-locked Er3+: ZBLAN fiber laser are 41.2mW and 1.632nJ, respectively. These measurements were conducted at a repetition rate of 25.25 MHz, accompanied by a signal-to-noise ratio (SNR) of 60 dB at a transmit pump power of 600 mW. This is the first demonstration of a mode-locked fiber laser operating in the 2.8 µm mid infrared band using Te-SA.

Polarization-dependent covalent organic framework saturable absorber and application of femtosecond fiber laser therein

Covalent organic frameworks (COFs) are materials that can be used in a wide variety of applications because of the nature of their ordered, crystalline, low-density, and porous structures. This work demonstrates the use of a π-electron-extended porphyrin/pyrene-linked COF (PorPh-PyTA-COF) as a saturable absorber (SA) in the 1.5 μm spectral region. The nonlinear optical absorption properties of this COF SA were studied and demonstrated a modulation depth of 0.8 % and saturation intensity of 0.5 kW/cm2. Using the COF SA, the operation of a mode-locked erbium-doped fiber laser was realized with a pulse duration of 506 fs at 1570 nm. This is believed to be the first report of a COF-based mode-locked fiber laser operating in the near-infrared spectral range. Additionally, a 3.7 dB polarization-dependent loss was measured in the COF SA and its role in the mode-locking process was also discussed.

O-band mode-locked praseodymium-doped fluoride fiber laser using nickel phosphorus trisulfide

In this work, we demonstrated a mode-locked fiber laser operating in the O-band region using nickel phosphorus trisulfide (NiPS3) as a saturable absorber (SA) for the first time. An arc-shaped fiber was coated with a layer of NiPS3 to serve as the SA which was then integrated into a praseodymium (Pr3+)-doped fluoride fiber laser (PDFFL) cavity for signal emission at 1.3 µm. The mode-locked laser operates at a center wavelength of 1302.3 nm, around the zero-dispersion wavelength. The mode-locked PDFFL has a repetition rate and signal-to-noise ratio (SNR) of 0.403 MHz and 55 dB, respectively. Ultrashort pulses of 370 fs were generated using the NiPS3-SA with a pulse energy of 17.1 nJ and a peak power of 46.2 kW. The NiPS3-SA in our work has shown the potential of this 2D nanomaterial ability to generate mode-locked pulses at 1.3 µm, which was rarely explored.

Improvement of peak power of dissipative soliton resonance pulse in a thulium-doped fiber laser

Single pulse energy and pulse width can be theoretically increased indefinitely without pulse-breaking in a dissipative soliton resonance pulse (DSR) generated from a mode-locked fiber laser when the peak power is keeping in a certain value. But in some applications, both high pulse energy and high peak power are needed in one single pulse. To improve the peak power of the DSR pulse, the characteristics of DSR pulses were investigated and found that the position of the gain fiber is a factor to influence the peak power and the pulse width. Here, we demonstrate a thulium-doped mode-locked fiber laser operating in the DSR regime with a nonlinear amplifying loop mirror (NALM). When changing the position of the gain fiber, the peak power of DSR pulse could be improved from 0.38 W to 1.42 W with the same pump power. This approach provides a method for increasing the pulse energy and efficiency in mode locked fiber lasers, which may meet some special application.

Widely Tunable Actively Mode-Locked Bi-Doped Fiber Laser Operating in the O-Band

Here, we propose an all-fiber actively mode-locked Bismuth (Bi)-doped fiber laser based on the use of an acousto-optic modulator. The mode-locked Bi-doped fiber laser produces 13ns pulses with a repetition rate of 1.683MHz at 1340nm. Higher harmonic mode-locking is achieved simply by changing the operating frequency of the acousto-optic modulator. The output power of the laser is 7mW and this is further amplified to 101mW using an external Bi-doped fiber amplifier. A peak power of 4.6W with a pulse energy of 60nJ is achieved after the master oscillator power amplifier. The stability of the laser is studied using an RF spectrum analyzer and an SNR of more than 60dB at the fundamental frequency of 1.683MHz was recorded. Furthermore, wavelength tuning of the Bi-doped fiber laser is explored and demonstrated from 1300 to 1370nm.

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.

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.

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.

C+L band wavelength and bandwidth tunable fiber laser incorporating carbon nanotubes

Spectral wavelength and bandwidth tunable mode-locking ultrafast fiber laser has widespread applications in the fields of optical telecommunication, spectroscopy, pump-probe measurements, and so on. Here, we report an single-wall carbon nanotube (SWCNT)-based wavelength and bandwidth tunable mode-locked fiber laser operation in the C[Formula: see text]L band. The output spectral wavelength and bandwidth can be continuously tuned by adjusting the intra-cavity tunable filter with a wavelength tuning range spanning [Formula: see text]70 nm (from 1539.8 nm to 1610.1 nm) and bandwidth from 0.5 nm to 4.5 nm, respectively. Our results provide a compact, mode-locked fiber laser wider in tuning range than the other systems for various applications requiring variable spectral wavelength or bandwidth.

Wavelength and duration tunable dissipative soliton resonance fibre laser

We report on a wavelength and duration tunable mode-locked Yb-doped fibre laser operating in a dissipative soliton resonance (DSR) regime at a sub-megahertz repetition rate. The DSR regime has the advantage of avoiding pulse splitting. Hence, it is suitable for obtaining a high output pulse energy. In the experiment, by extending the cavity length to 219.36 meters, a DSR pulse output with a repetition rate of 923 kHz is achieved. For the case of the DSR operating at 1032 nm, the maximum single-pulse energy is 113 nJ. The output pulse duration can be changed from 389 ps to 1.25 ns by controlling the pump power. A wavelength-tuned range of 73 nm (1007–1080 nm) is further realized by adjusting the intra-cavity spectral filter.

Low-amplitude, drifting sub-pulses hiding in background of noise-like pulse generated in fiber laser.

We report a puzzling dynamic observed in a passively mode-locked fiber laser operating in the noise-like pulse regime, in which low-amplitude sub-structures emerge and drift away from the main waveform of the NLP pulse packet. The peak amplitudes of the drifting sub-pulses are orders of magnitude lower than the main packet when the NLP is monitored with a low-speed detecting system, a fact that makes the sub-pulses entirely hide in the background of the pulse train as the oscilloscope trace is displayed in a coarse amplitude resolution. Moreover, the presence of the low-amplitude sub-pulses cannot be detected in ordinary characteristics like optical spectrum, radio-frequency spectrum, and autocorrelation trace. We speculate that such a dynamic may extensively exist in fiber lasers operating in the noise-like pulse regime, and is just overlooked in the previous research efforts due to the difficulty to observe it. The discovery of this intriguing dynamic is informative for investigating the mechanisms of noise-like pulse.

High-energy mode-locked holmium-doped fiber laser operating in noise-like pulse regime.

An all-fiber mode-locked holmium-doped fiber laser operating in the noise-like pulse regime is reported. Employing a nonlinear amplifying loop mirror as the artificial saturable absorber, the laser generates pulses with energy up to 280nJ, which is, to the best of our knowledge, the highest pulse energy ever achieved from mode-locked holmium-doped fiber lasers. We also discover a peculiar mode-locking operation mode using the laser. The peculiar mode falls into the category of a noise-like pulse, while it possesses a number of unique features (strong spikes in the optical spectrum, high temporal coherence, and chair-like pulse profile) that are not observed in previous research works regarding noise-like pulse lasers.

Nanosecond Pulses Generation with Samarium Oxide Film Saturable Absorber**Supported by the INTI Research Grant Scheme 2018 under Grant No INTI-FITS-01-06-2018.

Nanosecond pulse generation is demonstrated in a mode-locked erbium-doped fiber laser (EDFL) utilizing a samarium oxide (Sm2O3) film. The Sm2O3 film exhibits a modulation depth of 33%, which is suitable for mode-locking operation. The passively pulsed EDFL operates stably at 1569.8 nm within a pumping power from 109 to 146 mW. The train of generated output pulses has a pulse width of 356 nm repeated at a fundamental frequency of 0.97 MHz. The average output power of 3.91 mW is obtained at a pump power of 146 mW, corresponding to 4.0 nJ pulse energy. The experimental result indicates that the proposed Sm2O3 saturable absorber is viable for the construction of a flexible and reliably stable mode-locked pulsed fiber laser operating in the 1.5 μm region.

L-Band Tunable and Dual-Wavelength Mode-Locked Fiber Laser With NCF-GIMF-Based SA

A hybrid structure of no-core fiber and graded-index multimode fiber (NCF-GIMF) is demonstrated, which can be used as both the saturable absorber (SA) and the wavelength selective element. By employing such a device, an L-band wavelength tunable Er-doped mode-locked laser is realized and stable single solitons of ~1.7 ps, with continuously tunable wavelengths from 1574 to 1601.1 nm, are generated. Moreover, dual-wavelength mode-locked laser operation at 1575.4 and 1603 nm is achieved, with a pulse duration of 1.2 and 1.7 ps, respectively. The proposed device is simple and compact and represents an effective approach for tunable and dual-wavelength mode-locked fiber laser operation.

Improved optical damage threshold graphene Oxide/SiO2 absorber fabricated by sol-gel technique for mode-locked erbium-doped fiber lasers

In this study, a mode-locked erbium-doped fiber (EDF) laser based on solid-state graphene oxide (GO)-doped sol-gel glass saturable absorber (SA) was designed and tested. The GO-based SA was fabricated for the first time using low-temperature sol-gel technique. Compared to traditional ways of fabricating SAs, the SAs-doped sol-gel glass showed outstanding advantages in terms of high optical damage threshold. The optical damage threshold of SAs-doped sol-gel glass reached as high as 50.69 GW/cm2. X-ray diffractometry (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and annex-energy spectrometry (EDS) identified the main component of prepared sol-gel glass as compact amorphous silicon dioxide. The application of GO-doped sol-gel glass to EDF laser yielded stable mode-locked fiber laser operation. The pulse duration, maximum output power and peak power were recorded as 582 fs, 17.58 mW and 1.30 kW, respectively. Overall, these data indicated that the proposed sol-gel method is promising for fabricating practical SAs for mode-locked fiber lasers.

Widely tunable multi-wavelength passively mode-locked Yb-doped fiber laser operation in an all-normal-dispersion regime

We have demonstrated the generation of widely tunable spectral multi-wavelength all-normal-dispersion (ANDi) Yb-doped fiber laser based on nonlinear polarization evolution (NPE) as the passively mode-locking mechanism. An easy-controlling tunable passband filter fabricated through a phase-shift long-period grating (PS-LPG) is employed to tune and control the wavelength in the laser cavity. By combining the character of the emission cross section of Yb-doped fiber, the tunable spectral ranges of the dual- and triple-wavelength pulses output is up to ∼20 nm and ∼7 nm, respectively. To our knowledge, it’s the widest of tuning spectral range in the both dual- and triple-wavelength ANDi Yb-doped fiber laser with controllable and all-fiber format filter. The proposed method may provide a simple way to obtain a broad spectral range with multi-wavelength output in fiber laser systems.

Ultraviolet-enhanced supercontinuum generation with a mode-locked Yb-doped fiber laser operating in dissipative-soliton-resonance region.

We experimentally demonstrate an all-fiber, ultraviolet-enhanced, supercontinuum generation in a specifically designed seven-core photonic crystal fiber pumped by a picosecond Yb-doped master oscillator power amplifier (MOPA). The MOPA source is seeded by a giant-chirped Yb-doped mode-locked fiber laser operating in the dissipative-soliton-resonance (DSR) region. The DSR is achieved by using a nonlinear optical loop mirror (NOLM) with a fundamental repetition rate of 4.5 MHz and a central wavelength of 1035 nm. An extremely wide optical spectrum spanning from 350 nm to 2400 nm is obtained with a total output power of 6.86 W.

Electronic initiation and optimization of nonlinear polarization evolution mode-locking in a fiber laser

We describe a system for automated modelocking and optimization of a fiber laser oscillator employing nonlinear polarization evolution. Using four liquid crystal variable retarders, we fully control the fiber launch and output polarization states, enabling compensation for mechanical and environmental perturbations to the fiber cavity. We demonstrate mapping of the modelocking regions for an ANDi fiber oscillator and demonstrate that local and global optimization algorithms can be used to maintain the laser in the same operating state. This technique enables robust operation of nonlinear polarization evolution modelocked fiber lasers, rivaling the stability of PM fiber lasers while maintaining the advantages of the NPE modelocking mechanism.