Mode-locked Yb-doped Fiber Laser Research Articles

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

Yb-doped mode-locked fiber laser with a hybrid structure of NPR and a Lyot filter as the saturable absorber.

Passively mode-locked fiber lasers based on a nonlinear polarization rotation (NPR) have attracted much attention due to their ability to generate short pulses with wide spectra and high peak power. However, environmental perturbations can easily cause the lasers to lose the mode-locked state and make it a challenge for practical application. The aim of this research is to improve the laser stability by inserting a Lyot filter into the mode-locked laser cavity. The experimental results indicate that the mode-locked state can be maintained when the radius of the fiber loop is changed from 7.5 to 1.5 cm, while the signal-to-noise ratio of the fundamental frequency remains almost the same. The tunability of the output power can be achieved by adding a half-wave plate (HWP) in the laser cavity without changing the pump power, while the mode-locked state remains stable. By adjusting the angle of the HWP2, the output power can be adjusted from 3.36 to 66.5 mW at repetition rate of 29.7 MHz.

Dynamics of solitons in NOLM based all-normal dispersion Yb-doped mode-locked fiber laser

The properties of the saturable absorber are critical to the soliton dynamics in the all-normal dispersion Yb-doped mode-locked fiber laser based on the nonlinear optical loop mirror (NOLM). In this paper, it is found that by adjusting the splitting ratio f and cavity length L of the NOLM, self-similar pulse (SSP), soliton molecule (SM), dissipative soliton resonance (DSR), dissipative soliton (DS) and dissipative soliton pair (DSP) can be obtained in such fiber laser system. In addition, the mechanisms and characteristics of these solitons are discussed. These findings will facilitate the in-depth understanding of the characteristics of nonlinear pulses generated by NOLM-based all-normal dispersion Yb-doped mode-locked fiber laser.

Tunable-wavelength broadband spectrum dissipative soliton mode-locked fiber laser

The tunable-wavelength broadband spectrum dissipative soliton (DS) is demonstrated in Yb-doped mode-locked laser using an all-fiber structure saturable absorber (SA), that is, graded index multimode fiber (GIMF)-step index multimode fiber (SIMF)-GIMF with 4.70% modulation depth and 4.55 mW saturation power. Increasing pump power alters intra-cavity balance between loss and gain and nonlinear and dispersion, causing wavelength adjustment and spectrum broadening. The center wavelength shifts towards shorter wavelength with rang of 1037.77–1024.83 nm, corresponding 3-dB bandwidth widens from 6.10 to 9.23 nm and pulse width narrows from 23.80 to 13.38 ps. The signal-to-noise ratio (SNR) is 71.2 dB at the repetition rate of 14.63 MHz. The GIMF-SIMF-GIMF structure has a huge potential to serve as both SA and filter component for the tunable-wavelength broadband spectrum Yb-doped mode-locked fiber laser (MLFL), which is favorable for developing the field of nonlinear microscopy and material processing.

Frequency red shift induced by the enhancement of asymmetric absorption of saturable absorber in a Yb-doped mode-locked fiber laser

The mechanism of frequency red shift from gain spectral center is revealed in a SESAM mode-locked Yb-doped fiber laser for the first time as far as we know, which is due to the asymmetric absorption of SESAM. The phenomenon is demonstrated by numerical simulations and confirmed by experimental results, which is attributed to a greater loss of the frequency components in the temporal rising edge, as a consequence pulses become asymmetric. With the balance between the asymmetric absorption of SESAM and the pulling effect of gain spectral center, pulses in the laser are able to be stabilized and the spectra are ultimately red shifted. The increase of temporal asymmetry, as well as the enhancement of frequency red shift as results of the increase of saturation energy are also demonstrated.

Generation of sub-100 fs pulses from a SESAM-NPE hybrid mode-locked Yb-doped fiber laser at a fundamental repetition rate of 1.15 GHz.

Supercontinuum generation via direct pumping of unamplified high-repetition-rate, sub-100fs pulses with a pulse energy lower than 50pJ is superior in noise performance and features a high acquisition speed. We demonstrate a novel, to the best of our knowledge, gigahertz-repetition-rate, mode-locked Yb-doped fiber laser, where the hybrid mode-locking approach is employed. The laser has a low initiating threshold of 300mW and a broad mode-locking range of 600mW (300-900mW) in terms of pump power. The shortest obtained pulse width of the laser after compression is 95fs, and the highest output pulse energy is 92.9 pJ at a fundamental repetition rate of 1.15GHz. Moreover, the laser's output polarization states are switchable, and it has a polarization extinction ratio of 17.9dB.

Large energy polarization convertible solitons in an all-PM mode-locked Yb-doped fiber laser system

In this paper, we have demonstrated an all polarization maintaining (PM) composite ultrafast Yb-doped fiber laser system mode-locked by semiconductor saturable absorber mirror (SESAM), which incorporates the amplifier with the resonant cavity together. Benefiting from this composite laser system, not only the pulse energy is significantly improved, but also polarization convertible solitons are realized. When the pump power is lower than 272 mW, the solitons with the central wavelength of 1029.78 nm and the pulse width of 16.54 ps are transmitting along the fast axis. However, the polarization direction of solitons is switched to slow axis as increasing the pump power to be larger than 272 mW. The maximum output power of the solitons can reach 154.93 mW, corresponding to the pulse energy of 9.53 nJ. To the best of our knowledge, this is the first time to realize 90° polarization conversion for ultrafast solitons in an all-PM fiber laser system. We believe the presented approach reveals a pulse scaling and polarization convertible potential of mode-locked fiber laser.

Generation of 978 nm dispersion-managed solitons from a polarization-maintaining Yb-doped figure-of-9 fiber laser.

Restricted by the narrow gain bandwidth of Yb3+ near 980 nm, it is challenging to generate dispersion-managed (DM) solitons at this wavelength. In this work, we demonstrate the generation of DM solitons at 978 nm in a polarization-maintaining (PM) figure-of-9 fiber laser. Highly coherent pulses with 14.4 nm spectral bandwidth and 175 fs pulse duration are experimentally obtained. To the best of our knowledge, this is the shortest ∼980 nm pulse ever reported in an Yb-doped mode-locked fiber laser. Numerical simulations are performed to reveal the DM solitons' temporal and spectral evolution inside the figure-of-9 cavity under the condition of a narrow gain bandwidth. This robust and cost-effective 978 nm femtosecond laser is a promising light source for applications such as underwater communication and biophotonics.

976 nm all-polarization-maintaining mode-locked fiber laser based on nonlinear polarization evolution.

An all-polarization-maintaining (PM) mode-locked fiber laser based upon nonlinear polarization evolution (NPE) that operates around 976 nm is presented. The NPE-based mode-locking is realized using a special section of the laser which comprises three pieces of PM fibers with specific deviation angles between the polarization axes and a polarization-dependent isolator. By optimizing the NPE section and adjusting the pump power, dissipative soliton (DS) pulses with a pulse duration of ∼6 ps, a spectral bandwidth of >10 nm and a maximum pulse energy of 0.54 nJ are generated. Self-starting, steady mode-locking operation is achievable within a pump power range of ∼2 W. Moreover, by incorporating a segment of passive fiber into the appropriate location in the laser resonator, an intermediate regime between stable single-pulse mode-locking and noise-like pulse (NLP) is realized in the laser. Our work expands the dimension of the research on the mode-locked Yb-doped fiber laser operating around 976 nm.

Passively mode-locked Yb-doped fiber laser based on CNT-film sandwiched between the multimode fiber connectors

We propose and demonstrate a saturable absorber (SA) of composite mode-locked mechanisms based on the Carbon nanotube (CNT) film sandwiched between the multimode fiber (MMF) connectors (CNT-MMF) for achieving passively mode-locked fiber laser. Compared with that CNT-film sandwiched between the single-mode fiber (SMF) connectors (CNT-SMF), the modulation depth is increased 1.48% and the saturation intensity decreases, which is the main reason that the fiber laser based on CNT-MMF-SA can achieve full mode-locked and work for a long time at higher pump power. However, the fiber laser based on the CNT-SMF-SA can only occur the Q-switched mode-locked state and the CNT-film is easily burned out. Further, the structure of the CNT-MMF provides an effective way for obtaining high damage threshold and improving the performance of the fiber laser based on various nanomaterial films. Our work dramatically broadens the design possibilities in terms of technology and provides convenient architectures for the nanomaterial-based mode-locked fiber laser.

Yb-Doped Mode-Locked Fiber Laser Based on an All-Fiber Interferometer Filter

An interference filter is designed by fusing a segment of multi-core fiber (MCF) between two segments of multimode fibers (MMFs), which is then spliced between two segments of single mode fibers (SMFs). The light is split into the cladding and different cores of the MCF through the first segment of MMF, which is then coupled back into the core of SMF by the second segment of MMF. When the lengths of MCF are selected to be 4 mm and 10 mm, the 3 dB bandwidths of the filters around 1060 nm are 8.40 nm and 4.84 nm, respectively. Applying these filters in an Yb-doped fiber laser mode-locked by nonlinear polarization rotation, stable pulses have been obtained. Compared with the reported interference filters, the filter proposed in this paper has the advantages of simple fabrication process, compact structure and high environmental stability.

Ultra-Broadband NPE-Based Femtosecond Fiber Laser

A dissipative soliton mode-locked Yb-doped fiber laser is investigated experimentally and numerically from the point of view of generating ultra-broadband ultrashort pulses. An energy up to 2.2 nJ and a spectral bandwidth over 60 nm (at the −10 dB level) were obtained experimentally without dispersion compensation in the cavity. Almost a 100-fold compression coefficient has been achieved, so the resulting pulse duration was 149 fs. The numerical simulation has shown that a further scaling up to 3.5 nJ and a 100 nm spectral bandwidth is possible by reducing the low power transmission coefficient of the NPE-based SAM and increasing the amplification. At the same time, the tolerance of the SAM to a low power radiation is responsible for the transition to a multi-pulse operation regime.

Wavelength-tunable mode-locked fiber laser based on an all-fiber Mach–Zehnder interferometer filter

Wavelength-tunable dissipative solitons and amplifier similaritons have been obtained by inserting all-fiber Mach–Zehnder interferometer (MZI) filters with different free spectral ranges (FSRs) in a Yb-doped mode-locked fiber laser. The MZI filter is fabricated by splicing one segment of seven-core fiber (SCF) between two segments of single-mode fibers. The bandwidth of the filter depends on the FSR of the modulated interference curve and consequently depends on the tapered fiber diameter. Inserting MZI filters with bandwidths in a fiber laser and applying a tensile strain on the tapered SCF, both wavelength-tunable dissipative solitons and amplifier similaritons have been obtained.

Sideband-free dispersion-managed Yb-doped mode-locked fiber laser with Gires–Tournois interferometer mirrors

High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the near-zero dispersion region of mode-locked fiber lasers. Here, we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors. Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror, the pump power, and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity. By optimizing these three parameters, the laser can generate a sideband-free, Gaussian-shaped spectrum with a 13.56-nm bandwidth at -0.0232 ps2 net cavity dispersion, which corresponds to a 153-fs pulse duration.

Mode-locked Yb-doped fiber laser with graded-index multimode fiber as saturable absorber with gain management

We experimentally demonstrate a novel, linear-cavity mode-locked Yb-doped fiber laser based on the graded-index multimode fiber (GIMF) as saturable absorber, and propose the use of varying gain levels by doubling gain fiber length to mitigate the technical difficulty of multimode fiber as a saturable absorber in the length accuracy requirements. It provides a more flexible solution to achieve a highly stable mode-locked fiber laser based on GIMF. By analogy to dispersion management, we refer to this scheme as gain management. By adopting the two mechanisms of flexible GIMF length and gain management simultaneously, a stable mode-locked pulse train with the repetition rate of 10.96 MHz and pulse duration of ∼83.4 ps at 1064.07 nm was generated. Stable pulse bunches with pulse numbers up to 12 in a single bunch were obtained when increasing the pump power. The proposed gain management method opens a promising way for practical highly stable mode-locked technology based on nonlinear multimode interference mechanism.

90-fs Yb-doped fiber laser using Gires-Tournois interferometers as dispersion compensation

This paper reports a Yb-doped mode-locked femtosecond fiber laser based on a nonlinear amplifying loop mirror (NALM). The improved NALM structure ensures the high repetition rate of 97 MHz and the maximum output power of 126 mW. The Gires-Tournois interferometers (GTI) are used as dispersion compensation devices in laser resonator. The pulse output with full width half maximum (FWHM) of 26 nm and a dechirped pulse duration of 90 fs is obtained. As far as we know, this is the relatively short pulse in an improved NALM mode-locked Yb-doped fiber laser.

The route to a 200 MHz, all-PM femtosecond Yb-doped fiber laser with a high output coupling ratio.

Based on the time-independent rate equations and nonlinear Schrödinger equation, we simulate a 200 MHz all-polarization-maintaining (PM) mode-locked Yb-doped fiber laser. The cavity round trip evolution toward stable mode locking is present. Additionally, the gain coefficients along the gain fiber as well as the pulses, chirp, and spectra at different locations in the cavity are examined. The effects of chirped fiber Bragg grating parameters on the pulse shape and spectrum profile are also investigated. According to the calculations, we experimentally realize a 200 MHz femtosecond fiber laser with 115 mW output power. The timing jitter and integrated relative intensity noise are measured as 158 fs (1 kHz to 10 MHz) and 0.0513% (1 Hz to 300 kHz), respectively. Eventually, an amplified average power of 610 mW and 79 fs compressed pulses with a peak power of approximately 28 kW are obtained. The exhibited all-PM femtosecond fiber laser system can be adopted as the foundation for an optical frequency comb.

Dissipative dual-wavelength pulses synchronously mode-locked in a compact fiber laser

Exploiting the reflect pulse from the polarization beam splitter, synchronously mode-locked dual-wavelength dissipative sub-pulses have been obtained both numerically and experimentally in an Yb-doped passively mode-locked fiber laser. Numerical simulation results show that, the synchronous two sub-pulses are in fact the leading and trailing edges of the pulse circulating in the cavity, thus they are bounded together tightly and exhibit the same repetition rates all the time. However, different from the bound soliton in anomalous dispersion, the proposed dual-wavelength pulses behavior is unique. Owing to the liner chirp of the pulses, the interval between these two sub-pulses could be changed. When the pulses are passing through a segment of fiber with anomalous dispersion in the simulation or a pair of gratings in the experiment, the time interval can be getting even closer until the pulses are merged. In addition, the time interval can be extended when the pulses are passing through a segment of normal-dispersion fiber. Moreover, the central wavelengths of the two sub-pulses and the interval between them can be varied by fine tuning the cavity parameters, such as the pump power, the orientation of the wave plates or the central wavelength of the filter. Experimental results from an Yb-doped mode-locked fiber laser based on nonlinear polarization rotation agree very well with the simulation results.

Tunable Dual-Wavelength with Twin-Pulse Dissipative Solitons in All-Normal Dispersion Yb-Doped Fiber Laser.

A tunable dual-wavelength with two separated twin-pulse dissipative solitons (DSs) of Yb-doped mode-locked fiber laser in the all-normal-dispersion (ANDi) regime is firstly reported and demonstrated in this paper. A Sagnac loop is used as an all-fiber format spectral filter in the laser cavity, and stable twin-pulse DSs with different wavelength mode-locked lasers are achieved by the nonlinear polarization evolution (NPE) effect. By adjusting the polarization state of the Sagnac loop, the spectral ranges of the dual-wavelength can be tuned from 1031.3 nm to 1041.5 nm and from 1067.1 nm to 1080.9 nm, respectively. However, the pulse space between the two separated twin-pulse DSs is maintained, i.e., 41.63 ns. Furthermore, the twin-pulse can regress to the single-pulse when the pump power keeps dropping. It has been observed that the highest energy of the two twin-pulse DSs output is 23.36 nJ at a repetition rate of 2.282 MHz with a maximum pump power of 560 mW.

Stable and high energy ytterbium-doped mode-locked fiber laser based on a franckeite-polymer film modulator

As a novel material with narrow band gap and natural van der Waals heterostructures (vdWH), francketie has potential applications in the field of optoelectronic fields. However, few studies have applied its nonlinear optical absorption properties to ultrafast fiber lasers. Here, we synthesized francketie nanosheets via the liquid-phase exfoliation (LPE) method. By incorporating the polyvinyl alcohol (PVA), a franckeite-PVA saturable absorber (SA) was fabricated to achieve a mode-locked Yb-doped fiber laser (YDFL) for the first time to the best of our knowledge. The saturation intensity and modulation depth of the SA were measured about 75 MW∕cm2 and 7%, respectively. The proposed franckeite-based YDFL demonstrates stable mode-locked operation with the maximum single energy of 5.35 nJ and the pulse duration of 1.57 ns. Our experimental results fully prove that franckeite may have wide potential for designing ultrafast photonics devices with low cost, high stability and excellent performance.