Q-switched Mode-locked Pulses Research Articles

GENERATION OF Q-SWITCHED AND SOLITON MODE-LOCKED PULSES WITH BISMUTH TELLURITE SATURABLE ABSORBER

We demonstrated Q-switched and soliton mode-locked pulses operating at 1569.51 nm and 1564.45 nm, respectively by using a newly developed Bismuth Telluride Polyvinyl Alcohol (Bi2Te3 PVA) film as saturable absorber (SA). By incorporating the SA into an Erbium-doped fiber laser (EDFL) cavity, Q-switched pulses were obtained within a pump power range from 101.90 to 175.82 mW. At the maximum pump power, the laser operated at repetition rate of 92.76 kHz and pulse width of 4.76 µs while producing the highest single pulse energy of 39.4 nJ. By incorporating an additional 200 m long single-mode fiber into the laser cavity, stable soliton mode-locked pulses were generated. It operated at repetition rate of 0.97 MHz with a pulse width of 2.97 ps and a signal-to-noise ratio (SNR) of 50.89 dB.

Mode-locked and Q-switched mode-locked fiber laser based on a ferroferric-oxide nanoparticles saturable absorber.

We demonstrated an ultrafast erbium-doped fiber laser (EDFL) based on ferroferric-oxide (Fe3O4) nanoparticles as a saturable absorber (SA). The investigated SA was based on magnetic fluid deposited on the end face of a fiber ferrule connector. When the SA was inserted into an EDFL cavity, a stable 2.93 ps mode-locked pulse can be achieved by adjusting the intra-cavity polarization controller. The pulse had a central wavelength of 1572.39 nm and a 3 dB bandwidth of 1.39 nm. We also obtained Q-switched mode-locked pulses at 1593.4 nm. The repetition frequency and the temporal width of the Q-switched pulse envelope varied with the pump power. When the pump power reached 225 mW, the maximum average output power and the pulse envelope energy were up to 4.51 mW and 235.5 nJ. To the best of our knowledge, this is the first time that mode-locked and Q-switched mode-locked pulses have been obtained in a fiber laser based on Fe3O4 nanoparticles.

7 W mid-infrared supercontinuum generation up to 4.7 μm in an indium-fluoride optical fiber pumped by a high-peak power thulium-doped fiber single-oscillator.

In this letter, a high-power supercontinuum (SC) generation is achieved in an InF3 fiber with a maximum all bands output power of 7 W and spectrum extension up to 4.7 μm. An actively Q-switched mode-locked (QML) Tm3+-doped fiber single-oscillator has been used to pump the fluoride fiber. At the average power level of 15 W, the most energetic QML pulse provided by the fiber laser had an energy of 88 μJ and an estimated peak power of 60 kW. To the best of our knowledge, this is the first experimental demonstration of a Watt-level range supercontinuum generation in an InF3 fiber pumped by a single-oscillator laser system.

调Q和调Q锁模脉冲共存双波长光纤激光器

调Q和调Q锁模脉冲共存双波长光纤激光器

Self Q-switched mode-locking in compact red Pr3+-doped ZBLAN fiber laser

The self Q-switching mode-locking effect in compact red fiber laser has been investigated. The Q-switched mode-locking state can keep operating with a pump power ranging from 120.5 mW to 564.8 mW. The maximum average output power of this self Q-switched mode-locking laser is 22.5 mW, and the central wavelength of the output optical spectrum is 635.9 nm with a 3 dB bandwidth of 2.4 nm, as well as the fundamental repetition rate of mode-locking pulse trains being 25.8 MHz. This work can provide an attractive method for Q-switched mode-locking pulse generation in visible fiber lasers.

Q-Switched Pulse and Mode-Locked Pulse Generation From a Yb3+-Doped Fiber Laser Based on Bi2Se3

The Q-switched pulse and mode-locked pulse were investigated in an all-normal dispersion Yb-doped fiber laser (YDFL) based on the topological insulators (TIs) with mixing of polyvinyl alcohol (PVA) to produce Bi2Se3 /PVA film or deposition on the end facet of fiber to manufacture TI-compatible fiber. Through the dark Bi 2Se3/PVA films with large nonsaturable loss, the YDFL was operated in the Q-switched state. The repetition rate and the duration of the Q-switched pulses increased and declined, respectively, with the pump power to show 2.2 μs duration and 137.8 kHz repetition rate at the highest pump power. Moreover, the mode-locked pulses, with a 16 MHz repetition rate and 380 ps pulsewidth, were generated at high pump power by using the light Bi2Se3/PVA film. By means of a Bi2Se3 compatible fiber, through optical deposition of the Bi2Se3 nanoplatelets on the end facet of the fiber, the mode-locked YDFL was generated at low-threshold pump power and revealed more stabilized operation state up to two hours.

1.9 μm square-wave passively Q-witched mode-locked fiber laser.

We propose and demonstrate the operation of Q-switched mode-locked square-wave pulses in a thulium-holmium co-doped fiber laser. By using a nonlinear amplifying loop mirror, continuous square-wave dissipative soliton resonance pulse is obtained with 4.4 MHz repetition rate. With the increasing pump power, square-wave pulse duration can be broadened from 1.7 ns to 3.2 ns. On such basis Q-switched mode-locked operation is achieved by properly setting the pump power and the polarization controllers. The internal mode-locked pulses in Q-switched envelope still keep square-wave type. The Q-switched repetition rate can be varied from 41.6 kHz to 74 kHz by increasing pump power. The corresponding average single-pulse energy increases from 2.67 nJ to 5.2 nJ. The average peak power is also improved from 0.6 W to 1.1 W when continuous square-wave operation is changed into Q-switched mode-locked operation. It indicates that Q-switched mode-locked operation is an effective method to increase the square-wave pulse energy and peak power.

Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.

In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum. The operation regime of the laser can be controlled by adjusting the amplifier pump powers and the polarization controllers. To the best of the authors' knowledge, this is the first demonstration of a single mode-locked cavity where narrowband DSR pulses and broadband NLPs alongside Q-ML pulse bunches can be selectively generated by employing two NALMs.

Multi-operational tuneable Q-switched mode-locking Er fibre laser

A wavelength-spacing tuneable, Q-switched mode-locking (QML) erbium-doped fibre laser based on non-linear polarization rotation controlled by four waveplates and a cube polarizer is proposed. A mode-locked pulse train using two quarter-wave plates and a half-wave plate (HWP) is obtained first, and then an extra HWP is inserted into the cavity to produce different operation regimes. The evolutions of temporal and spectral dynamics with different orientation angles of the extra HWP are investigated. A fully modulated stable QML pulse train is observed experimentally. This is, to the author’s best knowledge, the first experimental work reporting QML operation without adding an extra saturable absorber inside the laser cavity. Multi-wavelength pulse laser operation, multi-pulse train continuous-wave mode-locking operation and pulse-splitting operations are also reported at certain HWP angles. The observed operational dynamics are interpreted as a mutual interaction of dispersion, non-linear effect and insertion loss. This work provides a new mechanism for fabricating cheap tuneable multi-wavelength lasers with QML pulses.

Cr:ZnS saturable absorber passively Q-switched mode-locking Tm,Ho:LLF laser.

We first report on a diode-end-pumped passively Q-switched mode-locking Tm,Ho:LLF laser at 2053 nm by using a Cr:ZnS saturable absorber. A stable Q-switched mode-locking pulse train with a nearly 100% modulation depth was achieved. The repetition frequency of the Q-switched pulse envelope increased from 0.5 to 12.3 kHz with increasing pump power from 1 to 4.36 W. The maximum average output power of 145 mW was obtained, and the width of the mode-locked pulse was estimated to be less than 682 ps with a 250 MHz repetition frequency within a Q-switched pulse envelope of about 700 ns.

Integrated Fiber-Optic Device Based on a Combination of a Piezoelectric Transducer and a Bulk-Structured Bi2Te3 Topological Insulator for Q-Switched Mode-Locking of a Fiber Laser

We propose a single, integrated fiber-optic device that possesses both passive Q-switching and active mode-locking functions. The structure of the integrated fiber-optic device consists of a bulk-structured Bi2Te3 topological insulator (TI) layer sandwiched between the surface of a piezoelectric transducer and the flat side of a side-polished fiber. The Bi2Te3 TI is used as a saturable absorption material to induce Q-switching while the piezoelectric transducer is used to produce an acousto-optical modulation function for mode-locking. The integrated fiber-optic device is used within an erbium fiber ring cavity to readily produce stable Q-switched mode-locked pulses at 1559 nm. Control of the modulation index of the acousto-optic modulation part together with the pump power was also shown to be able to change the laser operating regimes among CW, Q-switching, Q-switched mode-locking, and mode locking.

Passively Q-switched mode-locked Tm, Ho:LLF laser with a WS2 saturable absorber

Using few-layer tungsten disulfide (WS2) doped polyvinyl alcohol as a saturable absorber for the initiation of the pulse generation, we experimentally demonstrate stable passively Q-switched mode-locked operations of Tm, Ho:LiLuF4 laser at 1895 nm for the first time. The laser is designed with an X-type four-mirror cavity and pumped by a Ti:sapphire laser operated at 785 nm, and its continuous operation is initiated when the absorbed pump power is 143 mW. When the absorbed pump power reaches 2.645 W, we obtain a maximum output power of 985 mW and a crystal slope efficiency of 39.8% by linear fitting. When the saturable absorber WS2 is inserted in the cavity, the threshold of the absorbed pump power is increased to 234 mW. With the increase of the pump power, Q-switch pulse sequence is first observed. When the absorbed pump power reaches 1.39 W, the stable operation of the Q-switched mode locked pulse is realized. A maximum average output power of 156 mW is achieved at an absorbed pump power of 2.6 W, which corresponds to a 25 kHz Q-switched repetition rate and a 300 μs-long pulse envelope. In this case, the modulation depth in Q-switching envelopes is close to 100%. After the passively Q-switched mode-locked is obtained stably, the mode-locked pulses inside the Q-switched pulse envelope have a repetition rate of 131.6 MHz, corresponding to a mode locked pulse energy of 1.19 nJ and a cavity length of 1.14 m. According to the definition of the rise time and considering the symmetric shape of the mode locked pulse, we can assume that the duration of the pulse is approximately 1.25 times more than the rise time of the pulse. Then the width of the mode locked pulse is estimated to be about 878 ps. These experimental results show that WS2 is a promising broadband saturable absorption material for generating a 2 μm-wavelength mid-infrared solid-state laser pulse. By increasing the pump power and reducing the loss of WS2 material, it is possible to realize a continuous mode locking operation which has a narrower pulse duration. The mode-locked mid-infrared pulses are very stable and have a lot of potential applications such as ultrafast molecule spectroscopy, mid-IR pulse generation, laser radar, atmospheric environment monitoring, etc.

Generation of Q-switched mode locking controlled rectangular noise-like soliton bunching in a Tm-doped fiber laser.

We report on an interesting phenomenon of the combination of Q-switched mode locked pulses (QSMLP) and rectangular noise-like pulses (RNLP) as a unit in a Tm-doped ring fiber laser which contains a Fabry-Perot (F-P) subcavity based on the nonlinear polarization evolution (NPE) technique. The RNLP and QSMLP are independently generated in the ring cavity and F-P subcavity, respectively. A notable characteristic is that the physical parameters of RNLP, e.g. repetition rate and pulse duration, are controlled by QSMLP. Thus, they form as a composite bunching, which is termed as "Q-switched mode locking controlled rectangular noise-like soliton bunching (QRNSB)". Further investigation shows that the existence of QRNSB only occurs in high pumping conditions, while both fundamental mode-locking pulses and the coexistence of QSMLP and solitons are achieved in low pumping ones. Our work can enrich the understanding of the nonlinear dynamics in fiber lasers.

As-grown uniform MoS2/mica saturable absorber for passively Q-switched mode-locked Nd:GdVO4 laser

Molybdenum disulfide (MoS2) has recently attracted growing attention due to its distinctive properties and potential applications in optoelectronics and electronics. Here, large-area and high-quality MoS2 film with uniform thickness was obtained by thermally decomposing ammonium thiomolybdate. Besides, it is firstly demonstrated that the as-grown MoS2/mica can be directly inserted into Nd:GdVO4 laser cavity as saturable absorber for the output of diode-pumped passively Q-switched mode-locked pulse trains. Using the MoS2 saturable absorbers, the stable Q-switched mode-locked pulse trains with high modulation depth were realized, suggesting that the broadband MoS2 SA could potentially be employed in mode-locking laser system

A Fiber Laser Using Graphene-Integrated 3-D Microfiber Coil

We demonstrate a state variable fiber pulse laser based on a graphene-integrated microfiber device. A 3-D microfiber coil integrated with graphene acts as a polarization-sensitive saturable absorber. By adjusting the polarization controllers, stable Q-switched pulses and mode-locked rectangular pulses are observed. To our knowledge, this is the first study conducted to achieve switching between rectangular pulses and Q-switched pulses while keeping the pump power constant. The rectangular pulses have a pulsewidth and repetition rate of ∼10 ns and ∼940 kHz, respectively, and the Q-switched pulses have a pulsewidth and repetition rate of ∼40 $\mu\mbox{s}$ and ∼4.8 kHz, respectively.

Generation and evolution of mode-locked noise-like square-wave pulses in a large-anomalous-dispersion Er-doped ring fiber laser.

In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, we experimentally demonstrate the formation of noise-like square-wave pulse, which shows quite different features from conventional dissipative soliton resonance (DSR). The corresponding temporal and spectral characteristics of a variety of operation states, including Q-switched mode-locking, continuous-wave mode-locking and Raman-induced noise-like pulse near the lasing threshold, are also investigated. Stable noise-like square-wave mode-locked pulses can be obtained at a fundamental repetition frequency of 195 kHz, with pulse packet duration tunable from 15 ns to 306 ns and per-pulse energy up to 200 nJ. By reducing the linear cavity loss, stable higher-order harmonic mode-locking had also been observed, with pulse duration ranging from 37 ns at the 21st order harmonic wave to 320 ns at the fundamental order. After propagating along a piece of long telecom fiber, the generated square-wave pulses do not show any obvious change, indicating that the generated noise-like square-wave pulse can be considered as high-energy pulse packet for some promising applications. These experimental results should shed some light on the further understanding of the mechanism and characteristics of noise-like square-wave pulses.

Experimental investigation on Q-switching and Q-switched mode-locking operation in gold nanorods-based erbium-doped fiber laser

We report on the generation of Q-switched and Q-switched mode-locked (QML) pulses in an erbium-doped fiber ring laser by using a polyvinyl alcohol (PVA) -based gold nanorod (GNR) saturable absorber (SA). The PVA-based GNR SA has a modulation depth of ∼4.8% and a non-saturable loss of ∼26.9% at 1.5 μm. A Q-switched pulse train with a repetition rate varying from 18.70 to 39.85 kHz and a QML pulse train with an envelope repetition rate tuning from 20.31 to 31.50 kHz are obtained. Moreover, the lasing wavelengths of the Q-switched pulses can be flexibly tuned by introducing a narrow bandwidth, tunable filter into the laser cavity. The results demonstrate that the GNRs exhibit good optical performance and can find a wide range of applications in the field of laser technology.

Passively Q-switched mode-locked Tm:LLF laser with a MoS2 saturable absorber

A passively Q-switched mode-locked (QML) Tm:LiLuF4 (LLF) laser with a MoS2 saturable absorber (SA) is demonstrated for the first time, to our best knowledge. For the Q-switching mode, the maximum average output power and Q-switched pulse energy are 583 mW and 41.5 μJ, respectively. When the absorbed power is greater than 7.4 W, the passively QML pulse is formed, corresponding to an 83.3-MHz frequency. The modulation depth in Q-switching envelopes is approximately 50%. Results prove that MoS2 is a promising SA for Q-switched and QML solid-state lasers.

Generation of low repetition rate sub-nanosecond pulses in doubly QML Nd:Lu0.5Y0.5VO4 and Nd:YVO4 lasers with EO and transmission SSA

By employing the mixed crystal Nd:Lu 0.5 Y 0.5 VO 4 and the single crystal Nd:YVO 4 as the laser media, the characteristics of the QML laser doubly modulated by electro-optic (EO) modulator and transmission semiconductor saturable absorber (T-SSA) are studied. Under the same cavity parameters, the properties of the low repetition rate sub-nanosecond pulses generated from Nd:Lu 0.5 Y 0.5 VO 4 and Nd:YVO 4 laser are compared. The experimental results show that Nd:Lu 0.5 Y 0.5 VO 4 laser can generate shorter pulse width than Nd:YVO 4 laser, and meanwhile, needs lower pump power to generate low repetition rate sub-nanosecond pulses. The shortest pulse durations obtained from the doubly QML Nd:Lu 0.5 Y 0.5 VO 4 and Nd:YVO 4 lasers are estimated to be 204 and 294 ps, with the corresponding peak power of 3.4 and 3.04 MW, respectively. • Doubly QML laser with EO modulator/semiconductor saturable absorber is realized. • Properties of Nd:Lu 0.5 Y 0.5 VO 4 and Nd:YVO 4 crystals are comparatively studied. • Nd:Lu 0.5 Y 0.5 VO 4 can generate shorter Q-switched envelope and mode-locking pulse. • Nd:Lu 0.5 Y 0.5 VO 4 can produce low repetition rate sub-ns pulses at lower pump power.

Watt-level passively Q-switched mode-locked YVO4/Nd:YVO4 laser operating at 1.06µm using graphene as a saturable absorber

Abstract High-quality monolayer graphene films with large area were grown on Cu foils by the chemical vapor deposition (CVD) technique. For the first time, graphene saturable absorbers (SAs) with well-defined layer numbers were fabricated by controlling of transfer process precisely. Using the graphene SAs, stable Q-switched mode-locking pulse trains with a nearly 100% modulation depth were realized in a diode-pumped YVO4/Nd:YVO4 laser. At the pump power of 6.0 W, the average output power reached a high value of 1.6 W. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser using graphene SA, suggesting that the low-cost, broadband graphene SA could potentially be employed in practical high-power mode-locking laser system.