Q-switched Mode-locked Operation Research Articles

The passive Q-switched and Q-switched mode-locked Nd: GYAP laser based on a novel Bi2O3 saturable absorber

With a newly fabricated Bi2O3 saturable absorber, the passive Q-switched and Q-switched mode-locked laser operations were experimentally demonstrated on a novel Nd: GYAP (Nd: Gd0.1Y0.9AlO3) disordered crystal. For the Q-switched operation, a 358 ns pulse was achieved with a short cavity laser, and a maximum output power of 0.203 W with a slope efficiency of 3.1% was realized. For the Q-switched mode-locked operation, the laser of a maximum output power of 0.264 W and a spectrum of 1.062 nm (FWHM) was also achieved on a 1.78 m Z-folded cavity. The mode-locked pulse has a calculated pulse width of sub-1000 ps and a repetition rate of 90.09 MHz. The research results will open up applications of 2D Bi2O3 saturable absorber and the Nd: GYAP crystal in the field of ultrafast lasers.

Tandem pumped Q-switched mode-locked laser operation of Tm:CYA laser

Tandem pumped Q-switched mode-locked laser operation of Tm:CYA laser

Dual-loss-modulated QML erbium-doped fiber laser with microfiber and NPR technique

We demonstrated a dual-loss-modulated Q-switched mode-locked (QML) erbium-doped fiber laser based on the nonlinear polarization rotation (NPR) technique with a microfiber. The microfiber served as both a highly nonlinear medium and a saturable absorber, which together with the NPR technique enables stable QML operation under significant pump power fluctuations. We evaluated the nonlinear properties of microfibers with different waist diameters. A maximum QML envelope energy of 467.15 nJ is achieved, corresponding to an average single-pulse energy of 4.06 nJ beneath the Q-switched envelope, which is 2.35 times higher than the maximum pulse energy attained with dissipative soliton mode-locking under similar pump power. In addition, the QML laser was verified by numerical simulation based on the coupled Ginzburg-Landau equation. The microfiber's customizable size enables significant variations in non-linear and saturable absorption characteristics, creating the potential for QML pulse regulation. This research provides novel insights for designing QML lasers.

Operation of a passively mode‐locked Tm:YAG laser with tantalum aluminum carbide as a saturable absorber

AbstractIn this paper, a compact diode‐pumped continuous wave (CW) and passively Q‐switched mode‐locked (QML) Tm:YAG lasers operation on the 3F4–3H6 transition is realized by using tantalum aluminum carbide (Ta4AlC3) phase ceramic (MAX) material as a saturable absorber (SA). The first stable QML operation of the mid‐infrared Tm:YAG laser at 2012.38 nm is demonstrated with a Ta4AlC3‐SA. A stable QML Tm:YAG laser was achieved when the absorption pumping power reached 14 W. Under QML mode, Tm:YAG laser generated a maximum average output power of 560 mW at 2012.38 nm with an optical‐to‐optical conversion efficiency of 4%, corresponding to a shortest pulse duration of 541 ps and a high repetition rate of 168 MHz. The experiment shows that Ta4AlC3‐SA is an attractive candidate for diode‐pumped CW and QML mid‐infrared all‐solid‐state lasers emitting around 2.0 μm.

All-fiber low threshold tunable multimode Q-switched mode locked fiber laser using a few mode Er-doped fiber

We report an all-fiber low threshold (70 mW) multimode Q-switched mode-locked (QML) fiber laser at 1.5 m. Nonlinear polarization rotation and a few mode Er-doped fiber (FM-EDF) were both adopted to achieve a low threshold QML operation initially, and the later experimental results showed and verified that the FM-EDF was the key factor of the QML pulses generation. A multimode QML state at 70 mW pump power was obtained with an 18 μs Q-switched pulse width and a 7.41 kHz repetition rate. The repetition rate and pulse width of the mode-locked pulses within the Q-switched envelope were 16.9 MHz and ∼910 ps respectively. The multimode QML fiber laser can be turned from 1561.8 nm to 1575.1 nm owing to the multimode interference and the fiber birefringence filtering effect. The QML pulses with dual-wavelength and three-wavelength were also observed by manipulating the polarization controllers and increasing the pump power. The experimental results showed that multimode QML pulses can be achieved with a short FM-EDF at a lower pump power in an all-fiber multimode cavity. The generated low threshold and tunable QML multimode fiber laser has potential application in measuring and mode-division multiplexed system.

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.

Generation of different mode-locked states in a Yb-doped fiber laser based on nonlinear multimode interference.

We demonstrated an ultrafast Yb-doped fiber laser with a single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure based saturable absorber. The GIMF was placed in the groove of an in-line fiber polarization controller to adjust its birefringence, enabling the SMF-GIMF-SMF structure to realize efficient saturable absorption based on nonlinear multimode interference without strict length restriction. By adjusting two intra-cavity polarization controllers, stable dissipation solitons and noise-like pulses were achieved in the 1030 nm waveband with pulse durations of 10.67 ps and 276 fs, respectively. We also realized Q-switched mode-locked pulses in the same fiber laser cavity. By the dispersive Fourier transform method, the real-time spectral evolution in the buildup process of the Q-switched mode-locked state was captured, which showed that the continuous-wave in this laser could gradually evolved into the stable Q-switched mode-locked pulses through unstable self-pulsation, relaxation oscillation and rogue Q-switching stage. To the best of our knowledge, our work reveals the buildup dynamics of the Q-switched mode-locked operation in a fiber laser for the first time. And we also studied the real-time spectral evolution of the stable Q-switched mode-locked pulses, which exhibited periodic breathing property.

2D layered MSe2 (M = Hf, Ti and Zr) for compact lasers: nonlinear optical properties and GHz lasing

Abstract Two-dimensional (2D) ternary transition-metal dichalcogenides (TMDCs) are of great research interest because their superior layer-dependent optical modulation properties. In this work, three different kinds of TMDC nanosheets, including hafnium diselenide (HfSe2), titanium diselenide (TiSe2) and zirconium diselenide (ZrSe2), are prepared by liquid phase exfoliation (LPE) technique. The high-quality material properties of these TMDC nanosheets are confirmed by Raman spectroscopy and X-ray diffraction analysis. Furthermore, the bandgap information of five-layer MSe2 has been investigated via utilizing density functional theory. The calculation results exhibit ultra-narrow bandgap structure (lower than 1.1 eV) for all these three materials, indicating that MSe2 is suitable for broadband photonic applications. By applying the fabricated MSe2 as saturable absorbers, high-performance Q-switched mode-locked laser operation has been realized. The laser gain media are Nd:GdVO4 cladding waveguides fabricated by femtosecond laser direct writing. As a result, the pulsed waveguide lasers are able to deliver approximately 6-GHz laser pulses with a signal-to-noise ratio of over 45 dB. The minimum pulse width is determined to be as short as 26 ps. The results demonstrated in this work exhibit the great potential of TMDCs and waveguide structures in applications of pulsed lasers with compact footprints.

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.

Sequential generation of self-starting diverse operations in all-fiber laser based on thulium-doped fiber saturable absorber

Self-starting Q-switching, Q-switched mode-locking and mode-locking operation modes are achieved sequentially in an all-fiber erbium-doped fiber laser with thulium-doped fiber saturable absorber for the first time. The central wavelengths of Q-switching, Q-switched mode-locking and mode-locking operation modes are 1569.7 nm, 1570.9 nm, and 1572 nm, respectively. The mode-locking operation of the proposed fiber laser generates stable dark soliton with a repetition rate of 0.99 MHz and signal-to-noise ratio of 65 dB. The results validate the capability of generating soliton pulse by doped fiber saturable absorber. Furthermore, the proposed fiber laser is beneficial to the applications of optical communication and signal processing system.

Stable Q-switched mode-locking of an in-band pumped Ho : Y2O3 ceramic laser at 2117 nm

We have demonstrated stable Q-switched mode-locked operation of an in-band pumped Ho : Y2O3 ceramic laser at 2117 nm by using an InGaAs/GaAs-based saturable absorber. An average output power of 330 mW is reached for 2.7 W of absorbed pump power with stable mode-locked pulses having a 98.9-MHz repetition rate and 100% modulation depth embedded inside Q-switched envelopes of ∼1.7-μs duration. The duration of the mode-locked pulses is estimated to be less than 1.5 ns.

Aluminium zinc oxide as a saturable absorber for passively Q-switched and mode-locked erbium-doped fiber laser

Transparent conductive oxides (TCOs) are widely integrated in the field of optoelectronics since they are optically transparent and electrically conductive at the same time. Indium tin oxide (ITO) is a well-developed TCO, but due to its high cost, aluminum zinc oxide (AZO) is now emerging as a promising low-cost replacement for ITO. This work reports on AZO thin film prepared with polyvinyl alcohol (PVA) as a host material. The AZO–PVA thin film was incorporated into an erbium-doped fiber laser (EDFL) as a saturable absorber for the first time. Both Q-switched and nanosecond pulse mode-locked operation were experimentally achieved. The Q-switched EDFL operated at the center wavelength of 1559.6 nm, which had the shortest pulse width of 2.2 µs, the maximum repetition rate of 86 kHz and the highest pulse energy of 47.3 nJ. The mode-locked was achieved at the center wavelength of 1560.4 nm.

Real-time observation of Q-switched mode-locking in a tin selenide modulated ultrafast fiber laser

We build a compact ultrafast Er-doped fiber laser based on the tin selenide (SnSe) saturable absorber (SA). Stable continuous-wave and Q-switched mode-locking operation states are realized. By utilizing the time-stretch dispersive Fourier transform, we explore the distinct evolution process of the Q-switched mode-locking operation in a SnSe SA modulated ultrafast Er-doped fiber laser from a real-time horizon. The real-time spectrum displays an interesting breathing process. Inside a single Q-switching envelope, the real-time spectra exhibit entirely different profiles, intensities and bandwidths. Our results can facilitate the understanding of the intrinsic mechanism of the Q-switched mode-locking pulse dynamics in ultrafast fiber lasers.

Tunable Q-switched mode-locked Cr:LiSAF laser

We have achieved stable passively Q-switched mode-locked (QML) operation in a Cr: LiSAF laser. In the experiments, a 10 mm long, %1.5 Cr-doped LiSAF crystal was pumped by two 150 mW single-mode diodes at 660 nm. An AlGaAs based saturable Bragg reflector (SBR) with a central wavelength of 850 nm and a modulation depth of 0.8% was used for initiating and sustaining QML operation. The QML laser was self-starting and robust against environmental fluctuations. In QML operation, the system produced sub-5-ps long mode-locked pulses at 150–200 MHz, inside 2–2.5 μs long Q-switched envelopes with 30–70 kHz repetition rate. The modulation depth of mode-locking stayed around 50%. We have also observed variation of mode-locked pulse parameters within the Q-switched envelope and also from Q-switched pulse to pulse. At an absorbed pump power level of around 280 mW, the QML pulses had an average power of 50 mW, whereas the estimated peak power of the mode-locked pulses were around 0.5 kW. Simple rotation of an intracavity birefringent tuning plate (BRF) enabled tuning of the central wavelength of the pulses between 835 and 865 nm. To our knowledge, this study is the first work focusing on QML operation in Cr: LiSAF lasers. The findings in this initial study is an initial attempt to understand the dynamics of QML operation in Cr:LiSAF. Further work will focus on reducing the mode-locked pulsewidths to sub-1-ps level and also on increasing the modulation depth of mode-locking for further peak power scaling.

Q-switched mode-locked multimode fiber laser based on a graphene-deposited multimode microfiber

We report Q-switched mode-locked (QML) pulses generation in an Yb-doped multimode fiber (MMF) laser by using a graphene-deposited multimode microfiber (GMM) for the first time, to the best of our knowledge. The single-wavelength QML operation with the central wavelength tunable from 1028.81 nm to 1039.20 nm and the dual-wavelength QML operation with the wavelength spacing tunable from 0.93 nm to 5.79 nm are achieved due to the multimode interference filtering effect induced by the few-mode fiber and MMF structure and the GMM in the cavity. Particularly, in the single-wavelength QML operation, the fifth harmonic is also realized owing to the high nonlinear effect of the GMM. The obtained results indicate that the QML pulses can be generated in the MMF laser, and such a flexible tunable laser has promising applications in optical sensing, measuring, and laser processing.

1.3 μm passively Q-switched mode-locked laser with Fe3O4 nanoparticle saturable absorber

Fe3O4 nanoparticles (FONP) are made into saturable absorbers and assembled into the resonant cavity, for the first time, and passively Q-switched mode-locked (QML) pulse output is realized in a 1.3 μm all-solid-state laser. When the pump power increases to 8 W, the repetition frequency of the Q-switched pulse increases from 47 kHz to 116 kHz, the pulse width changes from 1.137 μs to 767 ns, and the corresponding single pulse energy is 1.2 μJ. At the same time, the passively QML operation was observed on the oscilloscope, with a pulse repetition frequency of 154.5 MHz and a pulse width of 660 ps. Our experiments demonstrate that FONP exhibits good nonlinear optical characteristics in the 1.3 μm waveband, and has the potential to realize giant ultrashort and multiwavelength tunable pulse output in all-solid-state pulsed lasers.

Passively Q-Switched Mode-Locked Tm,Ho:CaYAlO4 Laser Based on Double-Walled Carbon Nanotube Saturable Absorber

A passively Q-switched mode-locked (QML) operation in Tm, Ho: CaYAlO4 bulk laser was demonstrated experimentally by employing double wall carbon nanotube (DWCNTs) as a saturable absorber. The laser is pumped by a self-made wavelength tunable Ti: sapphire laser, and the pump threshold of Tm, Ho: CaYAlO4 laser was measured as 677 mW by using transmittance of 1.5% output coupler. A stable Q-switched mode-locked operation state was achieved when the absorption pumping power reached 1958 mW. And when the pumping power reached 2.6 W, a maximum output power was 64 mw with central wavelength of 2085 nm, the corresponding repetition frequency of mode-locked pulse was 98.04 MHz, and the modulation depth in Q-switching envelopes is close to 100%.

Watt-Level Dual-Wavelength Q-Switched Mode-Locked All-Solid-State Tm:CYA Laser

A passively Q-switched mode-locked all-solid-state Tm:CaYAIO4 (Tm:CYA) laser with a MoS2 saturable absorber is demonstrated for the first time. Employing a typical X-type cavity and output coupling mirror of 9%, when the laser diode (LD) pump power is higher than 8.5W, the laser enters into a stable Q-switched mode-locked operation, further increasing the pump power into a dual-wavelength operating state, the corresponding typical center wavelengths are 1863nm and 1877nm. When the pump power reaches 20W, the maximum output power is 1.15W, the frequency of mode-locked pulse is 103.7MHz, and the modulation depth of mode-locked pulses in the Q envelope is close to 100%. The results prove that MoS2 SA is suitable for 2 μm high power mode locking.

Q-switched mode-locked Nd:GGG waveguide laser with tin disulfide as saturable absorber

We demonstrate a Q-switched mode-locked waveguide laser operation with high fundamental repetition rate based on the few-layer tin disulfide (SnS2) as a saturable absorber. The excellent nonlinear optical property of SnS2 enables efficient pulsed laser generation. By using Nd:GGG ridge waveguide, the fundamental repetition rate up to 17.9 GHz has been achieved for the mode-locked pulses with duration as short as 30 ps. In addition, this Nd:GGG-based waveguide laser exhibits excellent lasing properties (maximum output power of 115 mW at 1064 nm) by modulation of SnS2, suggesting promising application as miniature ultrafast light sources.

Watt-level continuous-wave and high-repetition-rate mid-infrared lasers based on a Er3+-doped Ca0.8Sr0.2F2 crystal

A 3 at% Er3+:Ca0.8Sr0.2F2 mixed crystal was grown successfully with a Ca:Sr molar ratio of about 4:1. This was applied as a laser gain medium and pumped by diode laser, obtaining a continuous-wave output power of 1.41 W with a slope efficiency of 39.2%, thus exceeding the Stokes limit by about 5%. Furthermore, with Mn+1XnTx (MXene) as a saturable absorber, passive Q-switched mode-locking operation was experimentally demonstrated for the first time, to the best of our knowledge. Mode-locked pulses under the Q-switched pulse envelope had a high repetition rate of 103.2 MHz at a center wavelength of 2,796.7 nm.