Short-pulse Fiber Lasers Research Articles

Floquet Stability of Periodically Stationary Pulses in a Short-Pulse Fiber Laser

Floquet Stability of Periodically Stationary Pulses in a Short-Pulse Fiber Laser

Influence of material thickness and hatching strategies on laser cutting of epoxy mold composites

Glass-filled composites are used for overmolding of electrical components due to their good electrical isolation properties. Laser cutting is a preferred technology to remove excess mold material to achieve a low surface roughness and reduce tool wear. Hatching strategies improve the laser-cutting process of carbon fiber-reinforced polymers toward lower cutting times and a more homogeneous cut surface. The impact of hatching strategies on epoxy mold compounds has been so far unknown as the laser-cutting strategy was based on multiple single passes in previous studies. This work investigates the effects of hatching strategies such as perpendicular hatching, parallel hatching, and a single line, including the influence of material thickness and filler content regarding the cutting time, kerf taper angle, and heat-affected zone, using a 50 W short-pulsed fiber laser for different highly filled epoxy mold compounds. Results show that the use of a hatching strategy is required to cut workpieces at thicknesses of 4 mm or higher due to the sieving size of the filler. Perpendicular hatching needs to be chosen when the aim is a minimal cutting time. The kerf taper angle at the top of the cut is below 4° while hatching leads to a more pronounced kink of up to 25° occurring toward the bottom of the cut. Meanwhile, an increase in filler concentration leads to an increase in cutting time, because of higher thermal conduction, while no effect on the kerf taper angle or the heat-affected zone can be identified.

Nanosecond fiber laser machining of A4SS under different environments: A comparative study

A4 stainless steel (SS) is a suitable metallic material for heat exchangers due to its inherent resistance to harsh environments and a usually difficult to process due to its high strength and superior plasticity. However, many sophisticated machining strategies exist to compete with the material's responsiveness while generating features in the micro-domain. Out of those, short-pulsed fiber laser (SPFL) is the most eminent choice due to its less arduousness. In this research laser micro-machining process (LMMP) is adopted for producing micro-channels on A4SS with the assistance of SPFL. The designed micro-channel structure holds its applicability in heat exchanger applications. Being a thermal process, the current LMMP may have high machining capability regardless of material properties, but at the same time, it has some adverse effects on machined surfaces. This research attempts to scrutinize the impact of SPFL variables on the channel surface’s characteristics by utilizing different characterization equipment. The SPFL-processed surfaces were investigated as a distinct industrial potential in dry, liquid, active, and inactive gas environments by adjusting the crucial variables of the SPFL. Further, the mechanical property, surface, and sub-surface analysis (including the study of functional groups, phases, morphology, and chemical elements) have also been performed to learn more about the varied environmental implications during LMMP-A4SS interactions.

Erbium Oxide as new Saturable Absorber for Short-Pulse Generation at 1.55-micron region

This paper reported on demonstration of Q-switched erbium doped fiber laser (EDFL) by incorporating erbium oxide (Er2O3) film as a saturable absorber (SA). The EDFL was constructed in ring cavity formation, where the Q-switching operation performances are capture out from 10 % port of 10 dB coupler. A stable Q-switched laser obtained at 1564 nm peak wavelength with a repetition rate from 72 kHz to 109 kHz, which corresponds to the pump power trend. Looking into this preliminary finding, the Er2O3 film has a potential to be utilized as an SA for short pulsed fiber laser generation.

Nonlinear optics in carbon nanotube, graphene, and related 2D materials

One- and two-dimensional forms of carbon, carbon nanotube, and graphene, and related 2D materials, have attracted great attention of researchers in many fields for their interesting and useful electrical, optical, chemical, and mechanical properties. In this tutorial, we will introduce the basic physics and the linear optical properties of these 1D/2D materials. We then focus on their nonlinear optical properties, saturable absorption, electro-optic effect, and nonlinear Kerr effect. We will also review and discuss a few key applications using the ultrafast nonlinear phenomena possessed by these 1D/2D materials: (1) short-pulse fiber lasers using saturable absorption, (2) electro-optic modulators, and (3) all-optical signal processing devices.

A contemporary review of optical properties of carbon nanotubes and graphene

Carbon nanotubes and graphene remain the best options for short-pulse fiber lasers.

Enhanced Supercontinuum Generation in Nonlinear Ytterbium-Doped Fiber Amplifier by Seeding at Short Wavelength

The amplification of a short-pulsed fiber laser along a high-power nonlinear fiber amplifier will undergo nonlinear spectral broadening and temporal distortion with the influence of fiber nonlinear effects. Within the same nonlinear Yb-doped fiber amplifier, we experimentally compared the different spectral and temporal evolution processes of tunable chirped picosecond pulses at different wavelengths (ranging from 1030 to 1070 nm). The comparison results indicate that the generated supercontinuum can be significantly enhanced when the amplifier is seeded at a short wavelength. A comprehensive analysis links the phenomenon to the overlap of Yb $^{3+}$ ion gain and the Raman gain, as well as the additional amplified spontaneous emission seeding effect. The phenomena of nonlinear-effect-induced spectral and temporal center dips were also observed and explained. The proposed conclusion can help to thoroughly understand the nonlinear process in fiber amplifiers and contribute to the development of a high-power spectrally flat amplifier-based supercontinuum source.

Short pulse fiber lasers mode-locked by carbon nanotubes and graphene

One and two dimensional forms of carbon, carbon nanotubes and graphene, have interesting and useful, not only electronic but also photonic, properties. For fiber lasers, they are very attractive passive mode lockers for ultra-short pulse generation, since they have saturable absorption with inherently fast recovery time (<1ps). In this paper, we review the photonic properties of graphene and CNT and our recent works on fabrication of fiber devices and applications to ultra-short pulse mode-locked fiber lasers.

Short pulsed gain-switched fiber laser with improved efficiency utilizing unabsorbed pump recovery.

A simple solution for increasing the slope efficiency of a gain-switched fiber laser based on Yb-doped active fiber is presented. By adding a fiber amplifier stage, which recovers the unabsorbed pump light from the gain-switched oscillator, a significant increase in slope efficiency is achieved. The pulses at 1030-nm wavelength have an FWHM of 28 ns and a peak power of 2.3 kW.

Eyesafe high peak power pulsed fiber lasers limited by fiber nonlinearity

We present design and performances of several eye-safe high peak power fiber lasers operating either around 1550nm or 2000nm. They share the limitations by nonlinear effects either Stimulated Brillouin Scattering for single frequency lasers or Kerr related effects for short pulse amplifiers. Performances above 1kW peak power for single frequency lasers and 26nJ for short pulse fiber lasers are reported. The influence of the saturation power of the fibers on the non-linearity is discussed and applied to a comparison between Erbium and Ytterbium co-doped fibers and Thulium doped fibers. The Brillouin gain properties in these fibers are also compared.

High-Accuracy Calibration of CMM Using Temporal-Coherence Fiber Interferometer with Fast-Repetition Comb Laser

A coordinate measuring machine (CMM) is a measuring system with the means to move probing system and capability to determine spatial coordinates on working surface. CMM is used in many industry fields from few micrometers of work pieces to a 5-meter truck. The verification method of CMM is done following international standard. The artifacts for calibrated reference length are the end standards, such as gauge block and step gauge, or laser interferometer for large size CMM. The current laser interferometer is operated by continuous laser and interference fringe counting. One constraint of continuous laser is an incremental measurement. The measurement path cannot be interrupted during the measurement period. We developed a new absolute interferometer system from a short-pulse mode-locked fiber laser. A Fabry–Pérot etalon (FPE) is used to select high-frequency parts of repetition-frequency modes of the mode-locked comb laser at the wavelength of 1.55 μm. The 5-GHz repetition-modified laser beam, which is realized by a new fiber-type FPE, is transmitted to a fiber-type Michelson interferometer. The interference fringes exhibit a temporal coherence interference and can be used for measuring spatial positioning. The temporal coherence between different pairs of modified pulse trains is referred to as absolute length standards. The performance of CMM was determined directly from different positions of two interference fringe patterns.

High Speed Laser Micro Drilling for Aerospace Applications

To realize a reduced fuel consumption of civil jet transport aircrafts, hybrid laminar flow control (HLFC) is a key technology in aerospace industry. For drag reduction caused by boundary layer suction, small holes at the leading edges of the aircraft wings and tail planes are needed. Much effort has been spend in drilling of small holes into different materials. Nevertheless, the economically drilling of small holes in the range of 50 to 100μm in diameter on large areas is up to date crucial. Apart from processing time this is also due to the demand of close tolerances in case of suction holes. Additionally, minimization of the thermal distortion when drilling large areas gets more challenging. This paper deals with the transfer of the laser drilling process to an adequate system technology for the fabrication of large suction inserts using a short pulsed fiber laser with a power of 200W at a pulse repetition rate of 200kHz. The laser combined with a galvanic scanner and a plane field optic leads to a precise and fast drilling over an area of 100mm x 100mm. Using a precise stage several of these drilling fields can be placed side by side to machine the complete panel area. The amount of drilled through-going holes and their roundness as well as the distortion of the panel is influenced by the applied drilling sequence and energy input. As a result, round micro holes down to 30μm in diameter can be produced with a drilling rate of more than 400 holes per second in 0.8mm thick titanium sheets.

Characterization of nonlinear saturation and mode-locking potential of ionically-doped colored glass filter for short-pulse fiber lasers

The nonlinear saturable absorption of an ionically-doped colored glass filter is measured directly using a Z-scan technique. For the first time, we demonstrate the potential of this material as a saturable asborber in fiber lasers. We achieve mode-locking of an ytterbium doped system. Mode-locking of cavities with all-positive and net-negative group velocity dispersion are demonstrated, achieving pulse durations of 60 ps and 4.1 ps, respectively. This inexpensive and optically robust material, with the potential for broadband operation, could surplant other saturable absorber devices in affordable mode-locked fiber lasers.

Dressing of Hybrid Bond CBN Wheels Using Short-Pulse Fiber Laser

A systematic research analysis has been applied to study the effect of dressing parameters on grinding forces, work piece roughness and wheel wear of a hybrid bond CBN grinding wheel. This paper presents some of the results achieved by the comparison between a conventional SiC dressed wheel and a grinding wheel dressed by means of a short-pulse fiber laser. The results show high technological potential for the laser dressing method compared to conventional dressing. Lower grinding forces and specific energy, with relatively the same surface roughness and lower total grinding wear (wear by dressing plus wear by grinding) are the biggest advantages of the laser dressing method over the conventional method. However, the economic aspects of laser dressing (investment on laser source and associated add-ons) at the moment, cannot justify the integration of such systems on the grinding machine for all types of applications. The next challenge is optimization of the laser dressing process to increase the efficiency of the process and expand the possible applications both from a technical and commercial point of view.

Compositional dependence of g-factor and damping constant of (Gd100-xREx)FeCo alloy films (RE = Yb, Tm, Er)

Time domain magnetization dynamics of (Gd100-xREx)FeCo (RE = Yb, Tm, Er) alloy films with various compositions were measured by pump-probe method using a high energy ultra short pulse fiber laser, and their g-factors and damping constants were estimated. The g-factor of GdFeCo became large near the angular moment compensation point CA, which is qualitatively consistent with the simple mean field model. On the other hand, the damping constants took a maximum near magnetization compensation point, which is not described by the mean field model. Substitution of Tm or Er for Gd results in the significant increase of damping constant; (Gd90Tm10)FeCo and (Gd90Er10)FeCo exhibit roughly 3-6 times large damping constant compared to GdFeCo, while (Gd90Yb10)FeCo has almost the same damping constant as GdFeCo. This means that the damping constant is significantly modified by the orbital moment of RE atoms.

Dispersion and nonlinear phase-shift compensation in high-peak-power short-pulse fiber laser sources using photonic-crystal fibers

Photonic-crystal fibers (PCFs) with a specifically designed dispersion profile and nonlinearity are shown to enable an accurate broadband compensation of the stretcher-compressor dispersion in fiber laser sources of high-peak-power ultrashort light pulses. We demonstrate that the nonlinear phase shift in such systems can partially compensate for the fourth-order dispersion, allowing the stretcher—compression group delay to be compensated up to the fourth-order dispersion terms by using a sequence of only two fibers—a standard optical fiber and a PCF.

Evolution and applications of high power, ultra short pulse fiber laser

Evolution and applications of high power, ultra short pulse fiber laser

Designing dispersion-compensating photonic-crystal fibers using a genetic algorithm

A genetic algorithm is combined with a fully vectorial finite-element solver to design photonic-crystal fibers (PCFs) for a broadband dispersion compensation in a generic stretcher–compressor system of an ytterbium fiber laser. Two types of PCFs are compared in terms of their dispersion-compensation capability, optical nonlinearity, and confinement loss. Fibers of the first type are standard PCFs where a solid core is surrounded by a triangular uniform lattice of identical air-holes. In PCFs of the second type, the solid core is surrounded by a dual-scale cladding, where the inner part comprises air-holes of different diameters, while the outer cladding consists of large-diameter air-holes. Second-type PCFs are shown to provide a much more accurate dispersion compensation. The influence of fiber-fabrication tolerances on the precision of dispersion compensation in short-pulse fiber laser systems is examined.

Tailoring the dispersion properties of photonic crystal fibers

Photonic crystal fibers (PCFs) have had a substantial impact on nonlinear fiber optics and shortpulsed fiber laser systems due to their novel dispersion properties. The large normal or anomalous waveguide dispersion available in such fibers opens up a number of new opportunities not accessible with standard fiber technology. In this contribution, the fundamentals of PCF dispersion are briefly reviewed along with earlier results. In addition, some of our recent work on dispersion tailoring to facilitate nonlinear processes, and dispersion control in lasers will be presented.

Clad-pumped Er3+/Yb3+-codoped short pulse fiber laser with high average power output exceeding 2W

A clad-pumped short pulse Er3+/Yb3+-codoped fiber laser based on master oscillator and power amplifier (MOPA) structure, integrating the performances of broad-band tunable wavelength, uniform output power spectrum, high repetition rate and high average power to together, is proposed and demonstrated. Combining the cavity parameter optimization of the fiber master oscillator and power fiber amplifier with gain saturation characteristic of erbium-doped fiber, we achieved a lasing output with uniform output power and continuously tunable wavelength in the range from 1535 to 1530nm (i.e. 35nm band width). The maximum output power fluctuation is no more than 0.5 dBm, the average power is about 2 W, pulse repetition rate is greater than 10 GHz and pulse width is less than 30 ps in the whole tunable wavelength band width. Furthermore, the laser has advantages of good performance, simple all-fiber structure and convenient operation.