Mode-locked Operation Research Articles

Few-Layered Violet Phosphorene Nanostructures as Saturable Absorbers for Stable Soliton Mode-Locking Operations in an Ultrafast Fiber Laser

Two-dimensional (2D) layered nanosheets of violet phosphorene (VP) have great potential in optoelectronic applications owing to their unique electronic, mechanical, and optical properties. Herein, the nonlinear optical (NLO) properties of liquid-phase-exfoliated (LPE) VP nanosheets based on a side-polished D-shaped fiber (DSF) were experimentally investigated by a homemade dual-balance detection fiber system at the near-infrared band. A strong saturable absorption response was observed. The corresponding modulation depth and saturation intensity were determined as ∼1.57 and ∼68.1 MW/cm2, respectively. As an application, a VP-DSF saturable absorber mode-locked erbium-doped fiber laser was realized for the first time, generating ultrashort pulses with a pulse width of 799 fs. Moreover, the stable soliton molecule mode-locking pulses with a pulse width and time interval of 816 fs and 20.5 ps, respectively, were obtained by adjusting the polarization state in the same laser cavity. The experimental results demonstrated the potential use of VP-based nanomaterials in ultrafast photonics applications.

Nanotubes in Chitin Mode Locker for Passive Mode−Locked Fibre Laser in 2.0 µm Region

This research demonstrated an ultrafast passively mode-locked thulium-holmium doped fibre laser (THDFL) using a carbon nanotube (CNT)-chitin composite film as a saturable absorber (SA). The CNTs were fabricated using ultrasonic-assisted liquid-phase exfoliation, and the chitin biopolymer was derived from oyster mushrooms (Pleurotus Ostreatus). The free-standing SA successfully performed a mode-locking operation at a threshold input pump power of 203 mW with an operating wavelength of 1908.53 nm. The generated mode-locked pulses had repetition rate, pulse width, and signal-to-noise ratio (SNR) values of 16 MHz, 1.1 ps, and 69 dB, respectively. The work demonstrates the potential of CNTs embedded in chitin biopolymer as a sustainable and environmentally friendly SA for a wide range of applications, particularly for pulsed lasers.

Investigation of passively Q-switched and mode-locked operation using Cu nanoparticles doped Indium Selenide as saturable absorber at 1.5-μm region

A reliable Q-switched and mode-locked operation at the 1.5-μm region has been demonstrated using copper nanoparticles (Cu NPs)-doped Indium Selenide (In2Se3). The Cu NPs were produced using pulsed laser ablation (PLA) in a PVA solution before mixed it with In2Se3 solution. Then, the Cu/In2Se3 solution was dry casted into a petri dish and peeled off from the petri dish after it was completely dry to form a free-standing (without substrate) Cu/In2Se3 film as a saturable absorber since this technique offers simplicity and is easy to integrate into the laser cavity. Q-switched pulses were generated at the operating wavelength of 1561.9 nm with a threshold pump power of 24.13 mW. A short pulse width of 2.54 μs, with a repetition rate of 122.60 kHz, attained a maximum pump power of 125.63 mW. The highest pulse energy obtained is 145.84 nJ, with an output power maximum of 17.88 mW on average. A soliton was generated as 100 m SMF integrated into the EDF laser cavity with the center of a wavelength of 1562.2 nm, a pulse width of 3.59 ps, and a peak power of 1.68 kW. These results prove that Cu/In2Se3 shows excellent potential as a SA material that operates in the 1.5-µm region.

MoxTa(1-x)Se2 as saturable absorber for ultrafast photonics

Two-dimension ternary transition metal dichalcogenides have drawn great interests from both the fields of nanotechnology and materials science, due to their extraordinary physical performance, and great potential applications in nanodevice. Here, the applications of MoxTa(1-x)Se2 nanosheets in ultrafast photonics are discussed. The MoxTa(1-x)Se2 nanosheets are prepared by liquid phase exfoliation method. A MoxTa(1-x)Se2-based saturable absorber is fabricated by depositing these nanosheets onto the side surface of d-shaped fiber, which is inserted into a Er-doped fiber laser cavity. By adjusting polarization state and pump power, both harmonic mode-locking and large energy mode-locking operations are realized, respectively. In the former state, a 56th harmonic mode-locking is obtained, which corresponds to a repetition rate of 312.5 MHz. For the later state, the maximum average output power of 12.24 mW and single pulse energy of 2.19 nJ are obtained when the pump power is 500mW. The results demonstrate that MoxTa(1-x)Se2 can be widely used in ultrafast photonics and nonlinear optics.

Passively Q-switched mode-locked fiber laser with 1-GHz fundamental repetition rate based on zeolite-fabricated Yb–Mg-doped silica glass

We successfully demonstrated a pulse laser with a fundamental repetition rate of 1 GHz in passively Q-switched mode-locked oscillation by using Yb–Mg-doped silica glass fiber (YbMgSGF). The YbMgSGF core glass, fabricated by the zeolite method, showed a Yb2O3 content of 5.46 wt%. To the best of our knowledge, our laser is the first silica-glass-based, Yb-doped fiber laser operating at a fundamental repetition rate of gigahertz. The laser cavity was constructed by a 102-mm-long YbMgSGF as a laser medium and a semiconductor saturable-absorber mirror as a mode-locker. The laser output power reached 5.93 mW, and its slope efficiency and lasing threshold power were 3.6% and 5.3 mW, respectively. The peak wavelength of the oscillation was 1039 nm. We also discuss the conditions to transition from Q-switched mode-locked operation to continuous-wave mode-locked operation. The proposed fiber laser can serve as a seed laser for a master oscillator power amplifier for a high-power, high-efficiency pulsed fiber laser source.

Multiple soliton mode-locking operations of a Holmium-doped fiber laser based on nonlinear polarization rotation

Multiple soliton mode-locking operations are realized in a Holmium-doped (Ho-doped) fiber laser based on nonlinear polarization rotation (NPR) technique. The fundamental mode-locking (FML) operation with a repetition rate of 19.91 MHz and a pulse duration of 974 fs is realized at 2056.1 nm. Bunched solitons operation with up to 7 soliton pulses is firstly implemented in the Ho-doped fiber laser by increasing the pump power. The Ho-doped fiber laser can also evolve into the harmonic mode-locking (HML) operation at ∼ 2056 nm by finely adjusting the intra-cavity parameters. The pulse duration is 965 fs at the highest repetition rate of 139.19 MHz, which is believed to be the first report on the femtosecond HML operation in the Ho-doped fiber lasers.

Picosecond pulses with 40 W peak power from a passively mode‐locked tapered quantum well laser

In this letter, the authors present a monolithic edge emitting diode laser intended as a potential key component for the generation of terahertz radiation in a compact time-domain spectroscopy system. The 6 mm long multi-section InGaAsP double quantum well (DQW) laser, featured with a 3.6 mm long tapered (TP) gain section, operates at a wavelength of ∼832 nm and generates pulses at a fundamental repetition rate of ∼6.3 GHz in passive mode-locking operation. Pulses with 2.6 ps width and 40 W peak power are measured. The generated pulses are not bandwidth-limited and should be compressible for further applications.

Nb2AlC as saturable absorber for a passively mode-locked operation of Tm:YLF laser

The Nb2AlC material has attracted more and more attention in optoelectronics due to its excellent optical properties. Herein, the Nb2AlC-based saturated absorber (SA) was fabricated by ultrasonic thermal dissolution method and spin coating means, and a passively mode-locked (PML) Tm:YLF laser was perfectly demonstrated with the SA. With an incident pump power of 21.63W, a 0.379-W average output power and a 200-ps pulse width were achieved at 1872.1nm, corresponding to a per pulse energy of 3.15nJ and a peak power of 15.75W. In addition, the beam quality factors were measured to be 1.04 and 1.05 in the horizontal direction and vertical direction.

Sub-100 fs watt-level Kerr-lens mode-locked Yb:CaYAlO4 laser with a gigahertz repetition rate

We report a 1.04 GHz high-power Kerr-lens mode-locked Yb:CaYAlO4 laser pumped by a single-mode fiber laser at 976 nm. Based on a bow-tie cavity, stable unidirectional mode-locked operation is obtained with an output coupler of 1.6%. The oscillator delivers pulses with an average power of 1.46 W and with the pulse duration of 99 fs, which, to the best of our knowledge, is the first gigahertz-level Kerr-lens mode-locked laser based on the Yb:CaYAlO4 gain medium. We believe that the watt-level solid-state femtosecond laser at GHz would be an excellent source for developing time-resolved broadband dual-comb spectroscopy.

Effect of intracavity loss on output stability and reliability of solid-state mode-locked lasers with SESAM

Mode-locked lasers have been widely used, but high-quality stable operation is still the key factor affecting their reliability. We present a numerical simulation of the dynamics of a passively mode-locked laser using saturable absorbers, and the effects of gain and loss on output stability are discussed. The results reveal that, in the case of a sudden and intense disturbance, the laser loses its lock, and the mode-locking state can be restored by stabilizing the cavity loss, whereas the mode-locking state of the laser is more robust to the slowly changing cavity loss. The laser output energy, spectrum, and pulse width vary with the cavity loss. If slow-varying cavity losses occur during mode-locked laser operation, the laser energy, pulse width, and spectrum must be monitored in real time when there is a high requirement for energy stability, pulse width, and spectral stability.

Reverse saturable absorption in Ti3C2 MXene nanosheets for dissipative soliton resonance mode-locking operation in Er-doped fiber laser

In this paper, Ti3C2Tx MXene nanosheets were prepared using a low-power ultrasonic-assisted liquid phase exfoliation method. The Ti3C2Tx nanosheets based saturable absorber deposited on the tapered microfiber possessed the typical saturable absorption and reverse saturable absorption with the surface evanescent field. With a home-made femtosecond excitation source at 1550 nm, the modulation depth was determined as 4.8% with a saturation intensity of 18.7 MW/cm2. By inserting our as-prepared saturable absorber into an Erbium-doped fiber laser (EDFL), two types of mode-locked pulses operating in the stable conventional soliton (CS) and dissipative soliton resonance (DSR) regimes were realized at the fundamental repetition frequency of 7.39 MHz, respectively. The pulse width of the CS pulse was 1.185 ps with a central wavelength of 1560.6 nm. While the pulse width of the DSR pulses varied from 2.07 ns to a maximum of 8.13 ns with the increase of the pump power. Our work reveals the reverse saturable absorption effect of Ti3C2Tx could play a key role in the DSR pulse generation, which may benefit the application of the pulse modulation and optical communication with the two-dimensional materials.

Wideband ultrafast mode-locked praseodymium- and erbium-doped fiber lasers using zinc phosphate at 1.3- and 1.5 µm

The nonlinear optical behavior of novel zinc phosphate-based saturable absorber (SA) was investigated for the first time in this work. Zinc phosphate was synthesized and coated over an arc-shaped fiber to work as a SA. The zinc phosphate SA was then optically characterized for linear and nonlinear optical absorption. Linear absorption of the zinc phosphate SA was 3.3 dB at 1301 nm and 3.9 dB at 1561 nm. The nonlinear optical analysis of the zinc phosphate SA showed a modulation depth of 18 %. The SA was then incorporated in a praseodymium (Pr3+) doped fluoride fiber laser (PDFFL) to achieve stretched pulse mode-locked pulses at 1.3 µm. Ultrashort pulses of 452 fs were obtained from the mode-locked PDFFL with a repetition rate of 0.4 MHz. A high pulse peak power of up to 29.6 kW was obtained at a maximum pump power of 196 mW. Also, incorporating SA in an erbium-doped fiber laser (EDFL) resulted in mode-locked laser operation at 1561 nm. The soliton mode-locked EDFL pulses of 900 fs duration and 19.14 MHz repetition rate were achieved at C-band. These demonstrations validate the wideband saturable absorption of zinc phosphate to generate short pulses in the femtosecond regime.

Mode-locked operation in thulium-holmium doped fiber laser based on Cr2AlC MAX phase SA coated arc-shaped fiber

Mode-locked operation in thulium-holmium doped fiber laser based on Cr2AlC MAX phase SA coated arc-shaped fiber

Q-switched and vector soliton pulses from an Er-doped fiber laser with high stability based on a γ-graphyne saturable absorber.

As a Dirac material, an allotrope of graphene, namely γ-graphyne (γ-GY), is proved to have excellent nonlinear optical properties. Unfortunately, the saturable absorption properties and ultrafast photonics applications of γ-GY at the 1.5 μm band, which play vital roles in optical communication, have not been reported so far. Herein, γ-GY nanosheets (NSs) are prepared by an improved mechanochemical method, and a saturable absorber (SA) is fabricated by a laser-induced deposition method. The modulation depth (MD) and saturable fluence at 1.5 μm are found to be 5.40% and 23.46 μJ cm-2, respectively. Consequently, by inserting the as-prepared SA into an Er3+-doped fiber laser (EDFL), Q-switching and mode-locking operation with high stability are realized. Also, the mode-locking pulses are verified to be polarization-locked vector solitons (PLVSs) based on further study. With increasing pump power, the phase difference between the two orthogonal components increases, leading to the evolution of state of polarization (SOP). Additionally, the degrees of polarization (DOPs) are measured and all reach more than 97%, meaning high polarization stability. Therefore, this work not only broadens the application scope of γ-GY in ultrafast photonics, but also provides an important foundation for the study of soliton dynamics.

InSb-based saturable absorbers for ultrafast photonic applications.

Sb-related III-V compounds have recently gained great research interest owing to their excellent optical and electrical characteristics, which provide many possibilities in photonics and electronics. This study investigated the application of InSb films in ultrafast photonics. An InSb film was fabricated on the tapered zone of a microfiber, and its saturation intensity, modulation depth, and non-saturable loss were determined as 119.8 MW cm-2, 23.5%, and 27.3%, respectively. The structure of the electronic band and density of states of InSb were theoretically calculated. Notably, mode-locked and Q-switched fiber lasers were realised by incorporating the InSb-microfiber device into two different Er-doped fiber cavities. In the Q-switching state, the narrowest pulse duration was measured as 1.756 μs with a maximum single-pulse energy of 221.95 nJ and a signal-to-noise ratio of 60 dB. In the mode-locking operation, ultrafast lasers with a high signal-to-noise ratio (70 dB), a pulse width as narrow as 265 fs and a repetition rate of 49.51 MHz were acquired. Besides, the second-harmonic mode-locked state was built with an output power of 13.22 mW. In comparison with the reported laser performance with 2D materials as saturable absorbers, the InSb-based mode-locked and Q-switched fiber lasers proposed herein exhibit better comprehensive performance.

All-solid-state Acousto-optic Mode-locked Laser Operating at 660 nm

All-solid-state Acousto-optic Mode-locked Laser Operating at 660 nm

Ultrafast Yb:CALGO laser oscillator based on cross-polarization pumping with a cost-efficient multi-mode diode

We demonstrate a multimode diode-pumped Yb:CALGO laser oscillator based on bandwidth-optimized cross-polarization pumping targeting sub-30-fs operation. In our first proof of principle experiment we achieved mode-locked operation at 83 MHz repetition rate with 0.4 W of average power and a 33-nm-bandwidth optical spectrum supporting sub-40-fs pulses. This concept offers a simple and cost-efficient alternative to green-pumped Ti:sapphire lasers.

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.

Polarization-multiplexed dual-comb fiber laser based on an all-polarization-maintaining cavity configuration

In this study, we present a polarization-multiplexed, erbium-doped dual-comb fiber laser based on an all-polarization-maintaining cavity configuration. We observed that the dual-comb fiber laser easily realized the self-starting mode-locking operation due to the non-linear amplifying loop mirror (NALM) with a non-reciprocal phase shifter. Furthermore, owing to the sharing of the NALM part, the two outputs from this laser configuration had similar center wavelengths, with small different repetition rates (∆frep). In the free-running operation, the standard deviation of relative stability for Δfrep of 2.09 kHz was measured to be 1.59 Hz, and the full width at half-maximum of the relative beat note between the two frequency combs in the optical frequency domain was approximately 1 kHz. These results show that the two frequency combs from this laser configuration have high relative stability and mutual coherence.

Revealing the Evolution from Q-Switching to Mode-Locking in an Erbium-Doped Fiber Laser Using Tungsten Trioxide Saturable Absorber

Passively Q-switching and mode-locking technologies can generate short pulses with durations that differ by several orders of magnitude widely used in different applications. Recently, Q-switching and mode-locking realized in an identical laser cavity with saturable absorbers was reported. The analysis of pulse conversion is helpful for us to further understand the pulse dynamics of a laser. In this paper, the pulse evolution from Q-switching, Q-switched mode-locking to mode-locking, is demonstrated by using a tungsten trioxide saturable absorber in a ring-cavity erbium-doped fiber laser. Firstly, self-started Q-switching at 1563 nm is observed, the repetition rate continuously increases, and the duration decreases when the pump power increased. Then, with an adjusting intra-cavity state of polarization under a high pump power level, stable Q-switched mode-locking pulses evolved from Q-switching, are observed. The amplitude of the emerged pulse sequence with a period of 36.8 ns, determined by cavity length, is modulated by the Q-switched envelope with the period of 10.3 μs. By optimizing the intracavity polarization carefully, stable continuous wave mode-locking operation is achieved eventually. To the best of our knowledge, this is the first experimental demonstration of Q-switching and mode-locking, respectively, in an identical transition-metal-oxides-based pulsed fiber laser without modification of cavity structure.