- 标题
- 摘要
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- 实验方案
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Microfiber-Knot-Resonator-Induced Partial Elimination of Longitudinal Modes in fiber lasers for in-Tune-Switchable Nanosecond Pulse Generation
摘要： By incorporating a house-made microfiber knot resonator (MKR), mode-locking regime transformation in an erbium-doped fiber (EDF) laser was achieved. With typical nonlinear polarization rotation (NPR) as the mode-locker, ~890 fs soliton pulses could be directly produced from the EDF laser. However, once the MKR was further incorporated in it, the emitted pulse duration fell into the nanosecond regime, and meanwhile the spectral bandwidth dramatically narrowed down around 0.05 nm. This resulted from that the longitudinal laser modes were greatly eliminated by the MKR. The MKR exhibits tightly-packed, extremely narrow transmission teeth, acting as a comb-like, sharp-rolloff bandpass filter. The mode elimination factor could reach ~98.81%. Further manipulating the intra-cavity polarization state, the emission wavelength could be switchable from one of the transmission teeth of the MKR to another, due to the intrinsic polarization-sensitivity of the NPR. Our results demonstrated that MKR could be a useful device in fiber lasers to enable some artificially pre-defined spectral and temporal characteristics through pre-designing on the related parameters of the MKR. This could also provide a route to transform the temporal characteristics through tailoring the spectral profile, i.e., manipulating the permitted longitudinal laser modes, in fiber lasers.
关键词： Microfiber knot,mode-locked,Fiber lasers
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Controllable Generation of Ultrashort Multi-Bound Solitons in a Mode-Locked Erbium-Doped Ring Laser with a Highly-Nonlinear Resonator
摘要： Mode-locked (ML) ultrashort pulse (USP) fiber lasers can be treated as an ideal platform to expand future applications due to a complex nonlinear dynamics with a presence of a high value of a group velocity dispersion and a third-order dispersion in the laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons, and a soliton rain generation. Multi-bound solitons (MBS) generation regime, also known as soliton molecules, is of considerable interest in various fields of applications. For example, the investigation of a MBS generation is very attractive for increasing the data transfer capacity in telecommunications due to coding alphabet extension. The coding concept of MBS suggests a data stream using more than two symbols (2?N symbols, where N is the number of generated solitons in a bound state) [1]. And also, recent research shows that using ultrafast bursts of pulses can improve the quality of laser ablation for medical applications [2]. Moreover, MBS generation can be also used in a coherent pulse staking amplification scheme increasing an amplification efficiency along with a formation of high-energy solitons at a high-repetition-rate [3]. Previously we have obtained a generation of stable low-noise ultrashort multi-bound solitons in a passive mode-locked all-fiber erbium-doped ring laser with a highly-nonlinear resonator [4]. Fig. 1 shows autocorrelation traces and spectrums of MBS generation obtained by pump power variation at a wavelength of 980 nm. The output spectrums are evidently showing high-contrast intensity fringes (up to ~20 dB) and autocorrelation traces having symmetrical form without additional intensity peaks that indicates a stable and strong coherent connection between ultrashort pulses and fixed coherent phase difference in the temporal domain between several identical pulses. It is known that the highest energy of a fundamental soliton in a laser resonator with duration τp is limited by the soliton area theorem Es ~ |β2|/(γ · τp), where γ is the net nonlinear coefficient and β2 is the total cavity dispersion [1]. Soliton energy quantization results in pulse splitting at operation powers higher than the fundamental limit. Here we experimentally demonstrate the formation multi-bound solitons with the controllable number of bound states 7 < N < 17 by pump power variation in the range from ~160 mW to ~377 mW obtained in a highly-nonlinear fiber ring cavity.
关键词： ultrashort pulse,laser ablation,fiber lasers,Mode-locked,coherent pulse staking amplification,soliton molecules,telecommunications,multi-bound solitons
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coherent Beam Combining by Noncollinear Sum-Frequency Generation
摘要： Despite rapid development of fiber laser technologies, highest pulse peak power achievable from fiber lasers eventually approaches limits which are not easy to overcome. Therefore, there is growing interest in methods, which would allow to combine outputs from multiple pulsed fiber lasers into single diffraction-limited beam, and by this enable further scaling. For this reason, numerous coherent and incoherent beam combining methods are being proposed and investigated. Not so well investigated class of beam combining methods is beam combing based on nonlinear interaction. In our earlier work, we have demonstrated beam combining by multiplexing pulses in time, using second-order nonlinear crystal set in noncollinear phase-matching configuration. However, such configuration allows to scale only average power of the beam, leaving pulse energy unchanged (in case of 50 % conversion efficiency). In order to scale pulse energy and peak power, pulses have to be also combined in time, and for this, phase control is needed. Such approach was first proposed by Michailovas et al. and first proof of concept demonstrated by Zhang et al.. However, in previous demonstrations, low-power beams were combined with very low combining efficiency (<0.4 % for 4 beams). Here we apply this method to more realistic scenario and demonstrate combining of pulsed beams from 4 high-power fiber amplifiers with efficiency up to 49 %. Moreover, we demonstrate pulse energy and peak power improvement in the combined beam, exceeding peak-power limitations of single fiber amplifier.
关键词： noncollinear sum-frequency generation,fiber lasers,pulse energy scaling,peak power scaling,coherent beam combining
更新于2025-09-12 10:27:22
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Optimal laser beam configurations for laser cutting of metal sheets
摘要： The most recent developments in high power laser sources and handling optical systems create new options for optimizing the cutting process. However the selection of an optimal configuration is not evident since in laser cutting of metal sheets, the interaction between the laser and the material is geometrically complex. From an energetic point of view, parameters such as wavelength, polarization and beam shape can be optimized for different materials and thicknesses and, in theory, can significantly increase process efficiency. This paper offers an overview of possible techniques for such optimization and discusses their practical implications.
关键词： segmented polarization,beam shaping,laser cutting,fiber lasers,polarization,cutting speed
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Pump-Power-Noise Influence on Mode Instabilities in High-Power Fiber Laser Systems
摘要： Transverse mode instability (TMI) is still the most limiting effect for the further average-power scaling of fiber lasers and amplifiers with excellent beam quality. For the modal energy transfer to happen, a phase shift between the thermally-induced refractive index grating and the modal interference pattern in the fiber is essential. In former experimental and theoretical studies it has been shown that such a phase shift can be induced by changes of the pump power. Thus, the investigation of the influence of pump-power noise on the TMI threshold is of high relevance since this noise could act as the main trigger for TMI. To experimentally examine this behavior, white noise with a bandwidth of 2 kHz was generated and transferred via an arbitrary waveform generator to the pump-diode driver. The connected laser diode pumped a 1.1 m long Large Pitch Fiber (LPF) with an active core of ~65 μm from the counter-propagating direction. The TMI threshold of the free-running system was measured according to [5] to be 256 W. The above mentioned frequency range of the white noise was chosen because it was found that only frequency components below 2 kHz have an significant impact on the TMI threshold of the particular system. To investigate the influence of the pump-power noise on the TMI threshold we varied the amplitude of the generated pump noise and measured the latter by sending a partial reflex of the pump beam onto a photodiode. The relative intensity noise (RIN) serves as a measure of the pump-noise amplitude and was calculated by integrating the power spectral density of the measured noise trace. Afterwards, the TMI threshold was determined according to [5] for different RINs, i.e., pump-noise amplitudes. The results are illustrated in Fig. 1. As can be seen, the fiber laser system started with a TMI threshold of 256 W (no artificial noise, RIN = 0.209 %, close to the measured dark noise) and could be decreased by almost a factor of three to 89 W (RIN = 2.927 %) by steadily increasing the pump-noise amplitude. Thus, the experiments have revealed that pump-power noise significantly influences the TMI threshold of fiber laser systems and, thus, likely acts as the main trigger for TMI. The nonlinear decrease of the TMI threshold with increasing pump-power noise (i.e., RIN), as shown in Fig. 1, can be explained with the nonlinearity with which the strength of the energy transfer grows with increasing average power. This correlation together with the current investigations on seed-power noise will also be discussed at the conference. From the experiments it can be concluded that developing low-noise pump sources and drivers could increase the TMI threshold of fiber lasers and amplifiers and, thus, it has the potential to enable a further average-power scaling of these systems with excellent beam quality.
关键词： Transverse mode instability,pump-power noise,fiber lasers,TMI,RIN
更新于2025-09-12 10:27:22
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Direct oscillation of ultrafast HOM in Yb-doped fiber laser
摘要： We experimentally demonstrated direct oscillation of high order modes (HOMs) in a mode-locking Yb-doped fiber laser, in which a pair of mode-selective couplers act as an efficient mode conversion centered around 1064 nm.
关键词： Fiber,Lasers,Pulsed,HOMs
更新于2025-09-12 10:27:22
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - A novel kind of pulsating soliton in mode-locked fiber lasers
摘要： We find a novel kind of pulsating soliton with broadened Kelly sidebands. By simulation, we find the wavelength of the soliton oscillates due to the interaction with the unsynchronized resonant dispersive wave.
关键词： Fiber lasers,Optical solitons,Nonlinear optics
更新于2025-09-12 10:27:22
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Optical microfiber-based ultrafast fiber lasers
摘要： Optical microfibers drawn from conventional fibers have attracted considerable interests and have found many novel applications. Here, we review recent advances in ultrafast fiber lasers based on optical microfibers. Starting with characteristics and fabrication of optical microfibers, which are closely related to ultrafast fiber lasers, we show that characteristics of large portion of evanescent field, tailorable dispersion, high optical nonlinearity, very low optical loss and full compatibility with conventional fibers are greatly beneficial to novel ultrafast fiber lasers. We then highlight recent works on ultrafast fiber lasers based on optical microfibers in terms of fast saturable absorbers made from optical microfiber-supported nanomaterials, dispersion management and high optical nonlinearity, as well as some other novel ultrafast fiber lasers. Finally, we briefly discuss future opportunities for optical microfiber-based ultrafast fiber lasers, such as high-order dispersion management, nonlinearity management and applications for sensing and measurement.
关键词： Dispersion management,Saturable absorbers,Ultrafast fiber lasers,Optical microfibers,Optical nonlinearity
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Label-Free Multiphoton Microscopy in Human Tissue Enabled by an Er:Fiber-Laser Based Tunable Source
摘要： Multiphoton microscopy (MPM) is an important bio-imaging tool. Different modalities can serve as a contrast agent, such as second-/third-harmonic generation (SHG/THG) and two-/three-photon excitation fluorescence (2PEF/3PEF). Ultrafast lasers with flexible wavelength tunability are crucial for driving MPM bio-imaging, and the conventional solution relies on ultrafast Ti:sapphire lasers plus an optical parametric oscillator/amplifier. Recently, we have demonstrated that ultrafast fiber lasers are a potential solution to implementing compact, robust, and wavelength tunable femtosecond sources for driving MPM. To realize wavelength tunability we employ self-phase modulation (SPM) in optical fibers to broaden a narrowband input spectrum of Yb-/Er-doped fiber lasers (YDFLs/EDFLs) up to >400-nm wide with well-isolated spectral lobes; filtering the leftmost/rightmost lobes leads to nearly transform-limited pulses [1–6]. Such a SPM-enabled spectral selection (SESS) allows us to obtain wavelength widely tunable femtosecond pulses for MPM [2,5,6]. In this submission, we representatively demonstrate label-free harmonic generation microscopy (HGM) in human skin and brain tissues. Figure 1(a) depicts a scanning microscope driven by an EDFL-based SESS source. The EDFL operates at 31-MHz repetition rate and generates 290-fs pulses centered at 1550 nm. The narrowband EDFL [blue curve in Fig. 1(a)] is coupled into 9-cm optical fiber (10-μm mode-field diameter and -10 fs2/mm group-velocity dispersion at 1550 nm). The output spectrum is shown as the red curve in Fig. 1(b) under 85-nJ coupled pulse energy. We use optical filters to select the leftmost spectral lobe peaking at 1250 nm, which leads to 11.7-nJ, 47-fs pulses. Then we employ these pulses to drive a scanning microscope and conduct HGM in human skin and brain tissues. Figure 1(c) shows the dermal papilla at the junction of epidermis and upper dermis in human skin. Basal cells are visualized by THG (cyan hot) due to optical inhomogeneity at the interface (e.g., cell membrane); SHG (red hot) originates from the non-centrosymmetric structure of collagen fibers. In Fig. 1(d), neural network and brain vasculature in human brain tissue can be visualized by THG and SHG, respectively [Fig. 1(d)]. THG contrast inside the vasculature shows also red blood cells. In conclusion, we report on MPM deep-tissue imaging enabled by an EDFL-based SESS source. It is noteworthy that besides HGM excited by 1250-nm femtosecond pulses demonstrated here, the SESS source also supports 1300-/1700-nm illumination for 3PEF of green/red fluorescent protein (GFP/RFP) [7,8]. Such a fiber-based solution can be applied to many important applications, such as histopathology, morphology, and neuroscience.
关键词： ultrafast fiber lasers,Multiphoton microscopy,self-phase modulation,bio-imaging,harmonic generation microscopy
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - DSTMS-Based Ultrabroadband Terahertz Time-Domain Spectroscopy
摘要： DSTMS organic electro-optic crystal is a very promising and efficient THz-wave generation material. It allows for both very high THz electric fields generation, exceeding several GV/m using optical rectification of femtosecond laser pulses, as well as the possibility for extremely broad bandwidth extending well beyond 10 THz. However, the usual laboratory THz systems based on these crystals exploit very bulky and expensive fs laser systems, which are not desired for industrial THz imaging and spectroscopy applications. Recently, some compact system employing organic crystals were demonstrated, however they use a conventional photoconductive antenna as a THz-wave detector. Here we present a compact THz time-domain spectroscopy system based on a relatively low-cost and small-size femtosecond fiber lasers operating at 1560 nm. As the THz generation and detection material, we choose the organic crystal DSTMS (4-N,N-dimethylamino-4’-N’-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate), since it reaches the highest overall efficiency and the flattest spectrum among the presently known state-of-the-art organic crystals. The developed terahertz system is capable of achieving frequencies up to 20 THz with a high dynamic range of more than 60 dB. We use a commercial femtosecond laser with pulse length of 18 fs, 200 mW average power, 40 MHz repetition rate and 1560 nm wavelength as pump beam. We achieve a very large frequency bandwidth reaching 20 THz, profiting from using DSTMS as both THz generator and THz coherent detector material.
关键词： DSTMS,organic crystal,terahertz time-domain spectroscopy,THz-wave generation,femtosecond fiber lasers
更新于2025-09-12 10:27:22