Mode-locked Yb-doped Fiber Laser Research Articles

Generation of coherent multicolor noise-like pulse complex in Yb-doped fiber laser mode-locked by GIMF-SA

We have demonstrated the generation of multicolor noise-like pulse complex in a passively Yb-doped mode-locked fiber laser based on a single mode-graded index multimode-single mode fiber (SMF-GIMF-SMF) device as the saturable absorber (SA). The stimulated Raman scattering (SRS) effect leads to the cascaded generation of the main noise-like pulse (NLP) at 1028.8 nm together with the noise like Raman pulse (RP) at 1076.1 nm. The generated dual wavelength pulses demonstrate the unique properties of mutually synchronization and coherence. The autocorrelation traces show that each of the synchronously mode-locked pulses exhibits a double-scale structure with a narrow peak which consists of a train of quasi-periodic beat pulses with a 35.7 fs pulse width and a pulse separation of about 77.2 fs. The total output power reaches 102.5 mW with 34% of it belonging to the RP. And furthermore, by separating the two pulses with spectral filters, the modulation fringes cannot be observed anymore. These results indicate that the Raman component participates in the mode-locking operation as a 'signal' instead of 'noise'. Such a coherent Raman pulse source provides a novel platform for numerous applications, such as frequency comb spectroscopy and so on.

Tunable and dual-wavelength mode-locked Yb-doped fiber laser based on graded-index multimode fiber device

We have implemented wavelength-tunable and dual-wavelength in an ytterbium-doped passively mode-locked fiber laser using a single mode-graded index multimode-single mode fiber (SMF-GIMF-SMF) device as the saturable absorber (SA) without additional components. Such an all-fiber SA device exhibits fantastic properties with a large modulation depth of 22.9%, a small saturation fluence of 8.3 μJ/cm2, and the transmission curve with a capacity of gain-flattening, which are suitable for the tunable mode-locking generation. Benefiting from the intracavity birefringence-induced filtering effect of the laser cavity, tuning and dual-wavelength operations are obtained. For the tuning operation, the central wavelength of the dissipative solitons (DSs) can be tuned from 1028.5 to 1074.4 nm, with the pulse duration of tens of picoseconds. For the dual-wavelength mode-locking operation, the central wavelengths of dual-wavelength can be switched from 1032.3/1054.1 nm to 1049.3/1072.6 nm. Our results indicate that the SMF-GIMF-SMF device provides a novel platform for wavelength-tunable and dual-wavelength mode-locking in Yb-doped fiber lasers.

Noise-Like Square Pulses in Both Normal and Anomalous Dispersion Regimes

Noise-like square pulses (NLSPs) have been experimentally investigated in both normal and anomalous dispersion regimes. A chirped fiber Bragg grating (CFBG) has been employed as a dispersion management element in the compact linear-cavity mode-locked Yb-doped fiber laser. The net cavity dispersion could be switched from large anomalous dispersion (-2.71 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) to large normal dispersion (+5.33 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), depending on the direction of CFBG inserting in laser cavity. Two kinds of NLSPs with different temporal profiles are achieved in the proposed laser. In anomalous dispersion regime, the square pulse duration can be tuned from 0.91 ns to 5.39 ns, and the maximum square pulse energy is 39.57 nJ. In normal dispersion regime, the top of the pulse is flatter, the square pulse duration can be tuned from 0.89 ns to 5.97 ns, and the maximum square pulse energy is slightly higher, up to 40.17 nJ. The output laser is linearly polarized.

(INVITED)Switchable multi-wavelength mode-locked Yb-doped fiber laser using a polarization maintaining 45°-tilted fiber gratings based Lyot filter

We demonstrate a multi-wavelength mode-locked Yb-doped fiber laser by incorporating a pair of polarization maintaining 45° tilted fiber gratings (PM-45°TFG) based Lyot filter. Thanks to the functions of the polarizer and the comb filtering introduced by the Lyot filter, dissipative soliton (DS) pulses centered at 1035.26 nm, 1044.93 nm, 1055.62 nm, 1066.11 nm and 1076.63 nm can be generated respectively by finely tuning the intracavity polarization controllers (PCs). Moreover, the laser also can operate in a multi-wavelength regime via appropriately adjusting the pump power and polarization orientation. The high nonlinearity induced by the long cavity length leads to the generation of h-shaped mode-locked pulse with a repetition rate of 566.27 kHz. In the absence of any disturbance, the laser can operate steadily, that can potentially be used in various fields including wavelength division multiplexing systems etc.

Passively mode-locked Yb-doped all-fiber oscillator using self-made strain-compensated semiconductor mirrors as saturable absorbers

We report a linear-cavity mode-locked Yb-doped fiber laser using self-made semiconductor saturable absorber mirrors (SESAMs). The SESAMs are grown by means of metalorganic chemical vapor deposition, with a design of high modulation depth using strain-compensated multiple quantum wells. We choose two kinds of self-made SESAMs with different periods of top reflector in the linear cavity, and they can both be applied to stable mode-locking operation without damage. The output characteristics of the mode-locked oscillator indicate that SESAMs with high modulation depth are beneficial for mode-locked fiber lasers and the modulation depth can limit the pulse width of the output pulses.

Optimizing noise characteristics of mode-locked Yb-doped fiber laser using gain-induced RIN-transfer dynamics

Abstract Gain-parameter-dependent transfer functions and phase-noise performances in a mode-locked Yb-doped fiber laser are measured in this study. It is discovered that the corner frequency in the amplitude and phase domains is determined by the absorption coefficient of the gain fiber, when the total absorption and other cavity parameters are fixed. This shows that an oscillator using gain fiber with higher dopant concentration accumulates more phase noise. Furthermore, we present net cavity dispersion-dependent transfer functions to verify the effect of dispersion management on the frequency response. We derive a guideline for optimizing mode-locked fiber laser design to achieve low phase noise and timing jitter.

Stable mode-locked Yb-fiber laser with a 6 MHz repetition rate tuning range

For the precise measurement, a femtosecond mode-locked Yb-doped fiber laser with a 6 MHz repetition rate tuning range at a fundamental repetition rate of 26 MHz was reported, corresponding to 23% tuning ratio. With chirped fiber Bragg grating, the mode-locked fiber laser could run at different dispersion regimes. The influence of the net cavity dispersion on output characteristics and repetition rate tunability was studied. In a range of negative cavity dispersion, the mode-locked fiber laser could output the nearly same spectrum when the repetition rate was tuned, and the output spectrum was nearly Gaussian-type. Based on this result, a simple scheme, spatial optical path structure, and optimized cavity parameters was designed, which promised the large tunable range and stable mode-locking. The mode-locked fiber could stably output 3.23 mW ultrashort laser pulses with 347 fs dechirped pulse duration. Furthermore, the Yb-fiber laser was locked to the Rb atomic clock so that the repetition rate could be stabilized. The Allan deviation is 2×10−10 when the average time was 1 s.

Spectral filtering effect on multi-pulsing induced by chirped fiber Bragg grating in dispersion-managed mode-locked Yb-doped fiber lasers

Abstract We numerically and experimentally investigate the multi-pulsing mechanism in a dispersion-managed mode-locked Yb-doped fiber laser. Multi-pulsing occurs primarily owing to the inherent filtering effect of the chirped fiber Bragg grating. The spectral filtering effect restricts the spectral broadening induced by self-phase modulation and causes extra loss, leading to a decreased pump power threshold for the multi-pulsing state. Numerical simulations show that multi-pulsing emerges at a lower pump power when the spectral filter bandwidth becomes narrower. In the experiment, the spectral width increases as the net cavity dispersion approaches zero. Pulses with wider spectral widths experience more loss from the spectral filtering effect, leading to a decreased pump power threshold for multi-pulsing. Therefore, the net cavity dispersion also has an impact on the multi-pulsing threshold. Based on this conclusion, we devise a strategy to obtain single-pulsing operation with the shortest pulse width and the highest pulse energy.

NCF–GIMF device as SA and filter utilized in tunable single- and dual-wavelength Yb-doped mode-locked fiber laser

In this letter, by incorporating hybrid structure of no-core fiber (NCF)-graded index multimode fiber (GIMF) as the saturable absorber (SA) and spectral filter simultaneously, not only the switchable noise-like pulses (NLPs) but also the tunable single- and dual-wavelength dissipative solitons (DSs) are obtained from a net normal dispersion Yb-doped mode-locked fiber laser. The NCF–GIMF​ device plays a crucial role in the pulse generation and the wavelength tuning. By means of being stretched, the transmission peak of the NCF–GIMF device can be tuned over 60 nm which is responsible for the wavelength tuning of the oscillator. As the SA, the NCF–GIMF device affords variable saturable absorption properties during the stretching process which are suitable for the ultrafast soliton generation. Based on this device, the center wavelengths of the NLPs are demonstrated to be switchable from 1034.6 nm to 1072.2 nm. The single wavelength DSs with the pulse width at the level of tens of picoseconds can be tuned from 1026.3 nm to 1080 nm. Additionally, the dual-wavelength asynchronized DSs with a spectral interval of 21 nm have a wavelength-tunable range of 13 nm. This all-fiber ultrafast Yb-doped laser with tunable and flexible outputs can satisfy diverse application needs.

Mode-locked Yb-doped fiber laser based on mode coupler

We demonstrate a mode-locked Yb-doped fiber laser (YDFL) that enables fiber high-order mode (HOM) oscillation inside the ring cavity, by using a pair of mode selective couplers (MSCs) as an effective mode converter, the optical fiber HOM is obtained. The central wavelength of MSC is located at 1064 nm, which can achieve 80 nm mode conversion bandwidth and 94% high-order mode purity. A mode-locked pulsed fiber laser with a 3 dB spectral width of 7.4 nm, a pulse repetition frequency of 10.9 MHz, and a radio frequency signal-to-noise ratio of 55 dB is obtained, and the slope efficiency of the output power is 2.3%. These results show that the HOM can be directly oscillated by the cascaded MSCs in the fiber laser and participated in the mode-locking process to obtain a pulsed HOM laser.

Noise-like square pulses in a linear-cavity NPR mode-locked Yb-doped fiber laser

We have first experimentally demonstrated the generation of noise-like square pulses (NLSPs) in a linear-cavity mode-locked Yb-doped fiber laser. The mode-locking mechanism is based on nonlinear polarization rotation (NPR) in our simple and compact linear-cavity configuration, in which a fiber-pigtailed polarization beam splitter (PBS) is used as a mode-locking element. The pulse duration of square pulses can be tuned from 2.92 ns to 12.06 ns with the amplitude remaining constant, and the maximum output average power is 75.4 mW with the slope efficiency of 23.69%, under our pump-power condition.

Mode-locked femtosecond polarization-maintaining Yb-doped fiber laser with a figure-nine configuration

In the present work, we demonstrated a mode-locked polarization-maintaining (PM) Yb-doped fiber laser based on the figure-of-nine configuration to generate ∼100 fs pulses at 1μm. For the dispersion management, a pair of gratings was inserted into the laser resonator to compensate the group delay dispersion (GDD). The stable, self-started passive mode-locking operation was realized with a pulse duration of 122 fs and a full width at half maximum (FWHM) spectral width of 14.1 nm (3 dB bandwidth). The output power was 21 mW at a repetition rate of 34.4 MHz, corresponding to a pulse energy of 0.61 nJ and a peak power of 4.85 kW. Moreover, the theoretical investigation based on the nonlinear Schrodinger equation was implemented to explore the mode-locking properties. Numerical analyses were almost in agreement with the experimental results.

Simulation for Generation of Several Types of Pulses in an Yb-Doped Mode-Locked Fiber Laser

We numerically demonstrated six types of pulses in an Yb-doped fiber laser, including dissipative soliton (DS), dissipative soliton resonance (DSR), multipulse, noise-like pulse (NLP), breathing soliton and soliton explosion. The influence of cavity conditions on DSR pulse properties is discussed systematically. It is found that the change of the saturation power of saturable absorber (SA) could transform DSR into various types of pulses. Saturation power of SA and injected signal affect the number and shape of multipulse. Furthermore, the influence of the saturation power of SA and intra-cavity dispersion on pulse type is diagrammed intuitively. By properly adjusting the transmission curve of SA, breathing soliton and soliton explosion can be obtained as well.

Route to stable dispersion-managed mode-locked Yb-doped fiber lasers with near-zero net cavity dispersion.

We numerically investigate the stability of a dispersion-managed mode-locked Yb-doped fiber laser of near-zero net cavity dispersion. The instability is primarily due to the filtering effect of the chirped fiber Bragg grating. The size of the unstable region is dependent on the modulation depth of the saturable absorbers. At modulation depth higher than 30%, stable mode-locking can operate throughout the dispersion region. Based on the simulation results, stable mode-locking around zero cavity dispersion is experimentally viable by a SESAM with a 34% modulation depth. The fiber laser can generate laser pulses with a 17-nm spectral bandwidth and a 139-fs dechirped pulse duration.

Hybrid structure based on no-core and graded-index multimode fibers as saturable absorber for a self-starting mode-locked Yb-doped fiber laser

We demonstrate an all-fiber ytterbium (Yb)-doped mode-locked oscillator using a hybrid structure based on no-core fiber graded-index multimode fiber (NCF-GIMF) as the saturable absorber (SA). The proposed SA exhibits unique characteristics such as large-power tolerance, high modulation depth of 24.7%, and low saturation intensity of 11.01MW/cm2, which help to achieve a stable mode-locking operation. The all-normal and self-starting oscillator generates stable ultrafast pulses with a repetition rate of 21.35 MHz, pulse energy/average output power of 120 pJ/2.7 mW, and a pulse duration of 2.4 ps at a central wavelength of 1034.2 nm. The output pulses are then dechirped to 300 fs using an external grating compressor and possess high stability with a radio frequency spectrum of 58 dB. These results show that the NCF-GIMF-based SA can be used as an effective photonic device for high energy wave breaking free pulse generation.

Numerical simulation of two-soliton and three-soliton molecules evolution in passively mode-locked fiber laser

In this paper, we have studied the dynamic evolution and output characteristics of soliton molecules in the passively mode-locked Yb-doped fiber laser through numerical simulation. Under two different intra-cavity average dispersion values (5.142 ps2/km, -4.461 ps2/km), with the increase of small signal gain (g0) or gain saturation energy (Esat). Soliton molecules will not always maintain the state of two-soliton molecules or three-soliton molecules, but will occur at intervals. We have obtained specific multi-soliton molecules partitions, and studied the effects of g0 and Esat on the pulse duration, peak power and pulse energy of soliton molecules in these regions. Simulation results have theoretical significance for the practical application of soliton communication.

Pump-controlled wavelength switchable dissipative soliton mode-locked Yb-doped fiber laser using a 45° tilted fiber grating

We demonstrate a pump-controlled wavelength switchable Yb-doped fiber laser (YDFL) by nonlinear polarization rotation (NPR) for the first time. The polarizer replaced by a 45° tilted fiber grating (45°-TFG) combines with a section of polarization maintaining fiber (PMF) to form a fiber-based birefringent filter. Stable dissipative soliton (DS) with center wavelength of 1068.39 nm is generated under the mode-locked threshold of 277 mW. The operating wavelength switching between 1046.51 nm and 1067.90 nm can be realized via increasing the pump power simply while keeping the polarization controllers (PCs) in a fixed state. The laser maintains stable mode-locking operation at each wavelength, which can be regarded as a type of multi-wavelength ultrafast light source with precise control and integration potential.

Dual-mode and two-signal-wavelength femtosecond optical parametric oscillator based on LiB3O5.

We demonstrate a tunable femtosecond dual-beam-mode (cylindrical vector beam [CVB] and Gaussian beam [GB]), dual-signal-wavelength optical parametric oscillator based on a temperature-tuned lithium triborate crystal, synchronously pumped by a frequency-doubled mode-locked Yb-doped fiber laser. When fixing the CVB wavelength at 780 nm, the central wavelength of the GB signal could be continuously tuned from 664 to 722 nm. The maximum total signal output power is 515 mW at a 4 W pump with dual-wavelength operation (664 and 780 nm). All the measured signal pulse durations are around 150 fs. Moreover, sum-frequency-generation with Gaussian mode tuning from 548 to 588 nm is obtained, with the maximum power of 52 mW at 548 nm. Thanks to the dual-channel configuration, the wavelengths of a CVB and GB can be tuned independently. Such a flexible and versatile configuration makes it a practical tool for many applications such as high-resolution microscopy and high-capacity optical communication.

Discrete evolution of temporal separation and relative phase for bound solitons in a mode-locked Yb fiber laser

We report experimental measurements of structural soliton pairs in a mode-locked Yb-doped fiber laser. The quantization of the temporal separation and relative phase between the pair of dissipative solitons is clearly observed and, most interestingly, the transitions between different states as the pump power is varied show abrupt jumps. This is a clear signature of the discrete nature of the stable pair states. The typical separations are of the order of 1 ps and the separation changes are of the order of 100 fs, while the relative phase of the pulses jumps between π/2 → π/4 → π/2 as the pump power is increased.

MXene saturable absorber enabled hybrid mode-locking technology: a new routine of advancing femtosecond fiber lasers performance

Abstract MXene is a promising two-dimensional (2D) material that is widely used in electro-photonic devices due to its unique properties. In this contribution, V2CT x , a novel MXene, was employed as a saturable absorber (SA) for hybrid passively mode-locked fiber lasers. An ultra-stable and self-starting mode-locked laser system with low threshold can be achieved using V2CT x nanosheets and nonlinear polarization evolution (NPE). Signal to noise ratio increased 13 dB compared with using only NPE SA. A 72 fs pulse duration is easily achieved from this hybrid mode-locked fiber laser system. To the best of our knowledge, this is the shortest pulse duration generated from the Yb-doped mode-locked fiber lasers using a hybrid or 2D SAs. This study proves that MXene V2CT x nanosheets can be developed as suitable SAs and served as potential advanced ultrafast photonic devices in the future.