Pulse Generation In Fiber Laser Research Articles

Q-switching pulse and mode-locked square-wave pulse generated in a fiber ring laser based on nonlinear polarization rotation

We observe anomalous modes including Q-switching pulses and mode-locked square-wave pulses generated in a dual-gain-media fiber ring laser based on nonlinear polarization rotation in a semiconductor optical amplifier. We disclose the evolution process between them, and present in detail the temporal and spectra profiles of the output pulses. We find that the width of the square-wave pulse can be varied continuously from 500 ps to 165 ns by increasing the semiconductor optical amplifier (SOA) current or rotating the polarization controllers in the ring. The width of the pulse varies along with the temporal profile and spectrum pattern, then we further analyse its width-energy curve. For the first time to our knowledge, when we change the parameter of the ring laser (polarization controllers or variable optical attenuator), the stationary point of the width-energy curve will be shifted to a different position so that change the tuneable range of the pulse width. In addition, the evolution (no peak power clamping effect) and the features (chair-like pulse profile) of the generated square-wave pulse are different than previous reported square-wave pulses. Thus, the proposed scheme can facilitate further investigations of the characteristics of pulse generation in fiber lasers. Additionally, it can also serve as a multi-functional optical source to generate square-wave and Q-switching pulses for potential applications.

Germanene nanosheets for mode-locked pulse generation in fiber lasers

Based on an as-prepared high-quality germanene-polyvinyl alcohol (germanenen-PVA) film, the mode-locked operation and 2th, 4th, 5th and 6th order harmonic mode-locked operations with high stability were generated in an erbium-doped (Er-doped) fiber laser for the first time. The mode-locked pulse with a fundamental of 3.9 MHz and a pulse energy of 2.47 nJ was obtained, corresponding to the signal-to-noise ratio (SNR) of about 90 dB. In addition, the characteristics of four kinds of harmonics with frequencies of 7.8 MHz, 15.7 MHz, 19.6 MHz and 23.5 MHz were also systemically investigated. The results proved that the germanene can be used as an excellent nonlinear photonic device for pulse lasers.

Application prospects of boron nitride as a novel saturable absorber device for ultrashort pulse generation in fiber lasers

For the first time a BN-FM SA has been used in mode-locked fiber lasers, which complements the possibilities of the BN material in mode-locked lasers for ultrashort pulse generation.

Zinc oxide nanoparticles based passive saturable absorber for pulse generation in fiber laser

A stable passive Q-switched pulsed generation in Erbium doped fiber laser by Zinc Oxide nanoparticles embedded in polyvinyl alcohol (ZnONP-PVA)-based saturable absorber is demonstrated in this paper. The surface morphology and thickness profile of the fabricated film were observed using FESEM and 3D measuring laser microscope with the measured thickness of 12 µm. Meanwhile the its optical properties is characterized using Raman spectroscopy. The developed ZnONP-PVA film, has modulation depth of 7.8% and intensity saturation of 88.97 MW/cm2. The threshold input pump power to generate Q-switched pulse is at 45.4 mW and can be tuned until 92.4 mW before the pulse diminished. The operating wavelength of generated pulse is at 1535 nm with 3 dB bandwidth approximately of 2 nm with exclusion of parasitic continuous wave lasing. As the input pump power was tuned from threshold to maximum value, the recorded pulse train of repetition rate is tunable from 73.53 kHz to 103.10 kHz while the pulse width decreases from 6.8 µs to 4.8 µs. The calculated maximum output power and pulse energy at maximum input pump power was 5.14 mW and 49.85 nJ, respectively. The measured signal to noise ratio was 56 dB indicated that the generated pulse by ZnO NP based passive saturable absorber was stable.

Optical Nonlinearity of ZrS₂ and Applications in Fiber Laser.

Group VIB transition metal dichalcogenides (TMDs) have been successfully demonstrated as saturable absorbers (SAs) for pulsed fiber lasers. For the group comprising IVB TMDs, applications in this field remain unexplored. In this work, ZrS2-based SA is prepared by depositing a ZrS2 nanostructured film onto the side surface of a D-shaped fiber. The nonlinear optical properties of the prepared SA are investigated, which had a modulation depth of 3.3% and a saturable intensity of 13.26 MW/cm2. In a pump power range of 144–479 mW, the Er-doped fiber (EDF) laser with ZrS2 can operate in the dual-wavelength Q-switching state. The pulse duration declined from 10.0 μs down to 2.3 μs. The single pulse energy reached 53.0 nJ. The usage of ZrS2 as a SA for pulse generation in fiber lasers is presented for the first time. Compared to the experimental results of dual-wavelength Q-switched fiber lasers with two-dimensional (2D) materials, our laser performance was better. Our work indicates that the group comprising IVB TMD ZrS2 has bright prospects for nonlinear optical applications.

Emerging 2D materials beyond graphene for ultrashort pulse generation in fiber lasers.

Ultrafast fiber lasers have significant applications in ultra-precision manufacturing, medical diagnostics, medical treatment, precision measurement and astronomical detection, owing to their ultra-short pulse width and ultra-high peak-power. Since graphene was first explored as an optical saturable absorber for passively mode-locked lasers in 2009, many other 2D materials beyond graphene, including phosphorene, antimonene, bismuthene, transition metal dichalcogenides (TMDs), topological insulators (TIs), metal-organic frameworks (MOFs) and MXenes, have been successively explored, resulting in rapid development of novel 2D materials-based saturable absorbers. Herein, we review the latest progress of the emerging 2D materials beyond graphene for passively mode-locked fiber laser application. These 2D materials are classified into mono-elemental, dual-elemental and multi-elemental 2D materials. The atomic structure, band structure, nonlinear optical properties, and preparation methods of 2D materials are summarized. Diverse integration strategies for applying 2D materials into fiber laser systems are introduced, and the mode-locking performance of the 2D materials-based fiber lasers working at 1-3 μm are discussed. Finally, the perspectives and challenges facing 2D materials-based mode-locked fiber lasers are highlighted.

(Invited) Solution Exfoilated Black Phosphorus and Its Applications

Black phosphorus (BP), has recently attracted much attention all over the world and demonstrated great potential in novel nanoelectronics owing to its direct and narrow bandgap. Regarding to the scale production of BP and its related electronic devices, solution exfoliation reveals superior advances when compared with mechanical exfoliation. Remarkably, liquid-phase exfoliated BP flakes and quantum dots (QDs) exhibit exciting properties in solar cells, electronic, and optical devices. The exfoliation of BP in diverse solvents have been demonstrated. The solution exfoliated BP flakes can be an effective electron transport layer in organic photovoltaics (OPVs). The BP QDs can be incorporated in the active layer of OPV to enhance its power conversion efficiencies. In addition, the BP flakes exhibit nonlinear optical properties which can be an excellent saturable absorber for high energy pulse generation in fiber laser.

(Invited) Solution Exfoilated Black Phosphorus and Its Applications

Black phosphorus (BP), has recently attracted much attention all over the world and shown great potential in novel nanoelectronics owing to its direct and narrow bandgap. Regarding to the scale production of BP and its related electronic devices, solution exfoliation reveals superior advances when compared with mechanical exfoliation. Remarkably, liquid-phase exfoliated BP flakes and quantum dots (QDs) exhibit exciting properties in solar cells, electronic, and optical devices. The exfoliation of BP in diverse solvents have been demonstrated. The solution exfoilated BP flakes can be an effective electron transport layer in organic photovotaics (OPVs). The BP QDs can be incorporated in the active layer of OPV to enhance its power conversion efficiencies. In addition, the BP flakes exhibit nonlinear opical properties which can be an excellent saturable absorber for high energy pulse generation in fiber laser.

Polarization and Thickness Dependent Absorption Properties of Black Phosphorus: New Saturable Absorber for Ultrafast Pulse Generation.

Black phosphorus (BP) has recently been rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of BP flakes. We observe that both the linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness in BP, completely different from other typical two-dimensional layered materials (e.g., graphene and the most studied transition metal dichalcogenides). We then use the nonlinear optical properties of BP for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 μm. We observe that the output of our BP based pulsed lasers is linearly polarized (with a degree-of-polarization ~98% in mode-locking, >99% in Q-switching, respectively) due to the anisotropic optical property of BP. Our results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.).

Black Phosphorus–Polymer Composites for Pulsed Lasers

Black phosphorus (BP) is a very promising material for telecommunication due to its direct bandgap and strong resonant absorption in near‐infrared wavelength range. However, ultrafast nonlinear photonic applications relying on the ultrafast photocarrier dynamics as well as optical nonlinearity in black phosphorus remain unexplored. In this work, nonlinear optical properties of solution exfoliated BP are investigated and the usage of BP as a new saturable absorber for high energy pulse generation in fiber laser is demonstrated. In order to avoid the oxidization and degradation, BP is encapsulated by polymer matrix which is optically transparent in the spectrum range of interest to form a composite. Two fabrication approaches are demonstrated to produce BP‐polymer composite films which are further incorporated into fiber laser cavity as nonlinear media. BP shows very fast carrier dynamics and BP‐polymer composite has a modulation depth of 10.6%. A highly stable Q‐switched pulse generation is achieved and the single pulse energy of 194 nJ is demonstrated. The ease of handling of such black phosphorus‐polymer composite thin films affords new opportunities for wider applications such as optical sensing, signal processing, and light modulation.

Mechanism of high-energy pulse generation without wave breaking in mode-locked fiber lasers

The mechanism and intrinsic conditions of high-energy wave-breaking-free pulse generation in fiber lasers mode-locked by a nonlinear polarization rotation technique are investigated numerically and experimentally. Both numerical and experimental results show that the pulses along the two orthogonal polarization axes of the fiber have a large difference in pulse energy. The numerical simulations show that the ratio of the energy of two components is limited and ranges from about 8 to about 65. The slope of the instantaneous frequency at the central position of the pulse decreases rapidly with the increase of the pulse duration and energy, whereas the slope at the pulse edge changes slightly. The accumulation of instantaneous frequency throughout the pulse width approaches a constant in a higher pulse energy regime. Understanding the mechanism and intrinsic conditions of the wave-breaking-free pulse generation could be useful in generating high-energy pulses delivered from fiber lasers.

Nanosecond square pulse generation in fiber lasers with normal dispersion

We report on the generation of nanosecond square pulses in a passively mode-locked fiber ring laser made of purely normal dispersive fibers. Different to the noise-like pulse operation of the laser, the generated square pulses are stable and have no internal structures. We show that the formation of the square pulse is due to the combined action of the pulse peak clamping effect caused by the cavity and the almost linear pulse propagation in the normal dispersive fibers.

Pulse generation in fiber lasers with frequency shifted feedback

Lasers with frequency shifted feedback may spontaneously generate periodic trains of short optical pulses. Frequency shifts as small as several kilohertz per roundtrip are shown to sustain pulsing at the cavity fundamental frequency in Er/sup 3+/- and Nd/sup 3+/-fiber lasers with intracavity acousto-optic frequency shifters. A numerical model based on the split step Fourier method suggests that this pulse mode of operation may be attributed to the Kerr-type nonlinearity of the optical fiber. >