Fiber Laser Wavelength Research Articles

Ultra-compact all-in-fiber-core Mach-Zehnder interferometer.

Optical Mach-Zehnder interferometers (MZIs) are useful components in a variety of optical applications, including optical modulation; signal processing; and physical, chemical, and biological sensing. We introduce here a novel, assembly-free all-in-fiber-core MZI, which is directly written with a femtosecond laser. By introducing a positive refractive index-modified zone in half of the fiber core, the original single-mode fiber section is converted into a few-mode fiber section, where a strong coupling between the two lowest-order guided modes is generated, resulting in a well-defined interference spectrum in transmission. This device promises many significant advantages over existing approaches such as ease of fabrication, stability, small insertion loss, robustness extremely broad operating bandwidth, and precise and controllable cavity lengths. These advantages make this device strikingly attractive with the potential for extensive adoption in fiber communications, signal processing, sensors, and laser wavelength control.

Stable dual-wavelength thulium-doped fluoride fiber laser at S-band region with WS2 as birefringence element

In this work, the generation of dual-wavelength fiber laser at S-band region has been demonstrated with thulium-doped fluoride fiber as gain medium and WS2 thin film as a stabilizer. The generated dual-wavelength fiber laser is achieved in the simple ring cavity with WS2 acted as a birefringence element to suppress mode-hopping and mode competition. A stable dual wavelength fiber laser of spacing approximately 1.17nm is achieved at the pump power of 76.44mW. An OSNR of 31.9dB and maximum peak power difference of 0.5dB are attained at oscillating wavelengths of 1500.08nm and 1501.25nm. The proposed DWFL exhibits maximum wavelength drifting as low as 0.06nm and 0.05nm at 1500.8 08nm and 15001.25nm respectively. This indicates the WS2 is highly potential to be used in optoelectronics technology.

Mode-Locking Thulium-Doped Fiber Laser With 1.78-GHz Repetition Rate Based on Combination of Nonlinear Polarization Rotation and Semiconductor Saturable Absorber Mirror

We experimentally demonstrate a passively mode-locking thulium-doped fiber laser based on the combination of the nonlinear polarization rotation (NPR) and the semiconductor saturable absorber mirror (SESAM). In contrast to SESAM mode-locking merely, the fiber lasers based on NPR working together with SESAM have more advantages. By using two mode-locking mechanisms, the nonlinear effect can be enhanced tremendously; then, the threshold of high-order harmonic mode-locking (HML) pulse trains can be decreased, and the pulses width can be compressed. The shapes of the pulses can also be reshaped better, and the HML pulse trains stability can be improved. The high repetition rate of 1.78 GHz is obtained by both NPR and SESAM in the experiment. Because of the variation of the gain-and-loss distribution in the cavity, the output wavelength of mode-locking fiber laser can be tuned from 1839 to 1890 nm, and the multiwavelength HML is also observed in the experiment.

Fibre laser cutting of polycaprolactone sheet for stents manufacturing: A feasibility study

The role of the stent is temporary and it is limited to the intervention and shortly thereafter. Bioresorbable polymer stents were introduced to overcome this problem, making the stent manufacturing process rather difficult considering the complexity of the material. The stent forecast sale makes constant technology development necessary on this field. The adaptation of the laser manufacturing industry to these new materials is costly, thus further studies employing different sorts of lasers are necessary. This paper aims to explore the feasibility of 1.08µm wavelength fibre laser to cut polycaprolactone sheet, which is especially interesting for long-term implantable devices, such as stents. The laser cut samples were analysed by Differential Scanning Calorimetry (DSC), Tensile Stress Test, and Optical Microscopy in order to study the effects of the laser process over the workpiece. The parameters measured were: taper angle, dimensional precision, material structure changes and mechanical properties changes. Results showed a dimensional precision above 95.75% with a taper angle lower than 0.033°. The laser ablation process has exhibited a minor influence upon material properties. Results exhibit the feasibility of fibre laser to cut polycaprolactone, making the fibre laser an alternative to manufacture stents.

Nano-crystallization and highly oriented crystal line patterning of Sm3 +-doped Bi2GeO5 and Bi4Ge3O12 in bismuth germanate-based glasses

Glasses based on the system of Sm2O3-Bi2O3-GeO2 were prepared, and their electronic polarizabilities and formation behavior of Bi2GeO5 (monoclinic) and Bi4Ge3O12 (cubic) crystals were clarified. The glasses showed large electronic polarizabilities (αO2-(n)) and optical basicities (Λ(n)), e.g., αO2-(n)=2.783Å3 and Λ(n)=1.070 for 50Bi2O3-50GeO2 glass, indicating a basic nature in the glasses. The small addition of Sm2O3 was found to be effective for the control of the crystallization of Bi2O3-GeO2 glasses. Sm3+-doped Bi2GeO5 nanocrystals with an ellipsoidal shape (a(long)~32nm b(short)~20nm) and Sm3+-doped Bi4Ge3O12 nanocrystals with a spherical shape (~7nm) were formed in the glass-ceramics of 5Sm2O3-45Bi2O3-50GeO2 and 5Sm2O3-31Bi2O3-54GeO2-10B2O3, respectively. Highly oriented crystal lines consisting of Bi2GeO5 or Bi4Ge3O12 were patterned at the glass surface by continuous wave Yb:YVO4 fiber laser (wavelength: 1080nm) irradiations, suggesting the possibility of the design and control of spatially selected crystallization in Bi2O3-GeO2 based glasses.

1-μm-wavelength ytterbium-doped fiber laser based on the third harmonic reflection in secondary-type-In Bragg gratings.

In this Letter, a 1-μm-wavelength fiber laser is proposed through the use of the ytterbium-doped active fiber and the third harmonic Bragg reflectors. Benefiting from the ratio below 0.5 between the core diameter of the fiber and the Talbot length of the UV fringes, enabling the formation of the secondary-type-In grating, the reflector with reflectivity higher than 95% at two-thirds of the designing Bragg wavelength can be fabricated within 2 min. Inherited by the lower temperature and strain sensitivity of the third harmonic grating, the laser has good wavelength stability and could be used as a reliable laser resource. In addition, this Letter can also be expected to provide great flexibility in fiber laser wavelength design.

Unusual anti-thermal degradation of bismuth NIR luminescence in bismuth doped lithium tantalum silicate laser glasses.

For application of bismuth laser glasses in either fiber amplifier or laser, their performance stability in long run should be understood especially in extreme conditions. However, so far, there are few reports on it. Here, we found, after the cycle experiments on heating and cooling, that the proper increase of lithium content in lithium tantalum silicate laser glass can lead to unusual anti-thermal degradation of bismuth NIR luminescence, which completely differs from the scenario in germanate glass. FTIR, 29Si MAS NMR spectra, absorption and dynamic photoluminescence spectra are employed to unravel how this happens. The results illustrate that it should be due to the decrease of polymerization of silicate glass network, which in turn allows the regeneration at 250°C, and therefore, the content increase of bismuth NIR emission centers. In the meanwhile, we noticed though Bi luminescence can be thermally quenched its peak does not shift along with temperature, which seldom appears in laser materials. The unique property might guarantee the unshift of Bi fiber laser wavelength once such glass was made into fiber devices even as the environmental temperature changes. The role of lithium is discussed in the evolution of glass structures, the suppression of glass heterogeneity, and the thermal stability of Bi luminescence, and it should be helpful to design homogeneous silicate laser glass with outstanding thermal stability.

Nucleation and Crystal Growth in Laser-Patterned Lines in Glasses

Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

Phase-shifted fiber Bragg grating inscription by fusion splicing technique and femtosecond laser

A new method for phase-shifted fiber Bragg grating (PS-FBG) inscription in single mode fiber by fusion splicing technique and femtosecond laser is presented. The PS-FBG is produced by exposing the fusion spliced fiber with femtosecond laser through a uniform phase mask. The transmission spectrum of the PS-FBG shows a nonlinear red shift during the inscription process, and two or three main dips can be observed due to the formation of one or two FBG-based Fabry–Pérot structures by controlling the exposure intensity and time of the laser. For a peak power density of 4.8×1013W/cm2, the induced refractive index modulation can reach to 6.3×10−4 in the fiber without sensitization. The PS-FBG's temperature, strain and pressure characteristics are also experimentally studied. These PS-FBGs can be potentially used for multiple wavelength fiber lasers, filters and optical fiber sensors.

342 W narrow-linewidth continuous-wave thulium-doped all-fiber laser

High-power narrow-linewidth rare-earth-doped fiber lasers, which are well known for their high beam quality and high efficiency properties, have rapidly developed in the last decade, due to the needs of a vast range of applications such as nonlinear frequency conversion, and incoherent spectral beam combination to further scale up the total output power of fiber lasers. At the same time, many efforts have also been made to extend the operating wavelength of narrow-linewidth fiber laser toward the longer mid-infrared wavelength region, which was motivated by a large number of promising applications such as atmosphere monitoring, and pump source for mid-infrared optical parametric oscillator. In most cases, thulium-doped fiber lasers operate efficiently in a wavelength range of 1.8-2.1 m, which could be considered as being one of the most important sources of narrow-linewidth laser radiation that has been developed and intensively investigated in the last several years. Here, we demonstrate a high-power narrow-linewidth continuous-wave thulium-doped all-fiber laser based on master-oscillator power-amplifier (MOPA) configuration. The MOPA yields 342 W of narrow-linewidth laser output at the central wavelength of 2000.3 nm with a 3-dB spectral bandwidth of 90 pm. The beam quality factor is measured to be M2 of 1.15 at an output power of 300 W. No indication of stimulated Brillouin scattering could be observed at the highest output power level, and the output power is only currently limited by 793 nm available pump power. This kind of high-power narrow-linewidth thulium-doped all-fiber MOPA represents a promising achievement in the generation of high-power laser source via incoherent spectral beam combination.

Effect of high-temperature preheating on the selective laser melting of yttria-stabilized zirconia ceramic

Selective laser melting (SLM) is one of the current rapid fabrication technology methods which has wide potential application in the aerospace, medical, consumer products and automotive industries. Currently, ceramic materials are not used as widely as metal and polymer materials due to the high melting point, high-temperature strength and low thermal conductivity, which influence the microstructure and density of ceramic samples during SLM fabrication. The most effective method of reducing cracks is the preheating at high temperature of the ceramic powder during SLM process. This paper presents the selective melting of yttria-stabilized zirconia (ZrO2–Y2O3 93–7) ceramic using a 1μm wavelength fibre laser with high-temperature preheating at 1500–2500°C, and an additional CHEVAL Nd-YAG laser for the preheating of the powder bed before scanning. In this paper, the influence of different laser powers and different scanning velocities on the microstructure, relative density and deformation of the ceramic sample is investigated; in particular, the effect of preheating on the morphology of the micro-cracks is discussed. Experimental results show that high-temperature preheating in 10mm diameter range is possible with the Nd-YAG laser, and that orderly cracks are transformed into disordered little cracks by the high-temperature preheating. With preheating to 1500°C, 2000°C and 2500°C, the relative density of the sample made by mixing fine powder (9–22.5μm, 20wt%) and coarse powder (22.5–45μm, 80wt%) is increased by 84% (without preheating) to 90–91%. The transformation of the monoclinic and cubic structures to a tetragonal structure is observed during the process of melting and cooling, and increasing the preheating temperature to 1500°C, 2000°C and 2500°C is more suited to the formation of tetragonal crystals.

Highly fluorescent silver nanoclusters in alumina-silica composite optical fiber

An efficient visible fluorescent optical fiber embedded with silver nanoclusters (Ag-NCs) having size ∼1 nm, uniformly distributed in alumina-silica composite core glass, is reported. Fibers are fabricated in a repetitive controlled way through modified chemical vapour deposition process associated with solution doping technique. Fibers are drawn from the transparent preforms by conventional fiber drawing process. Structural characteristics of the doped fibers are studied using transmission electron microscopy and electron probe micro analysis. The oxidation state of Ag within Ag-NCs is investigated by X-ray photo electron spectroscopy. The observed significant fluorescence of the metal clusters in fabricated fibers is correlated with electronic model. The experimentally observed size dependent absorption of the metal clusters in fabricated fibers is explained with the help of reported results calculated by ab-initio density functional theory. These optical fibers may open up an opportunity of realizing tunable wavelength fiber laser without the help of rare earth elements.

Simultaneous Measurement of Strain and Temperature Using a Single Emission Line

In this study, we present and demonstrate a novel sensor system for simultaneous measurement of strain and temperature through a unique combination of a long period grating and a fiber laser based on a fiber Bragg grating. In order to achieve this, a new erbium-doped fiber laser structure is created, showing an optical signal-to-noise ratio of 55 dB and a peak power measured on the optical spectrum analyzer between −5 and 0 dBm. The strain and the temperature information can be obtained by using a unique emission line through monitoring both the fiber laser wavelength shift and the change of the power level, both of which showing a clear linear behavior.

Broadband Graphene Saturable Absorber for Pulsed Fiber Lasers at 1, 1.5, and 2 μm

Ultrafast fiber lasers with broad spectral coverage are in great demand for a variety of applications, such as spectroscopy, and biomedical diagnosis. Graphene is an ideal ultrawide-band saturable absorber. We report broadband (up to ~1000 nm) ultrafast pulse generation from three fiber lasers mode-locked by a single graphene saturable absorber device. The mode-locked pulses were based on Yb-, Er- and Tm:Ho-doped fiber lasers at the central wavelength of 1035, 1564, and 1908 nm, respectively. The maximum output energy is up to 16.2 nJ at 1908 nm. It is the first time that ultrafast fiber lasers covering 1, 1.5, and 2 μm spectral region are mode-locked with a single graphene device. Our results validate the intrinsic broadband operation property of graphene devices for all major fiber laser wavelengths from 1 to 2 μm.

Brillouin scattering properties of lanthano-aluminosilicate optical fiber.

Utilizing measurements on a lanthano-aluminosilicate core optical fiber, the specific effects of lanthana (La2O3) on the Brillouin characteristics of silica-based oxide glass optical fibers are described. Lanthana is an interesting species to investigate since it possesses a wide transparency window covering the common fiber laser and telecom system wavelengths. As might be expected, it is found that the properties of lanthana are very similar to those of ytterbia (Yb2O3), namely, low acoustic velocity, wide Brillouin spectral width, and a negative photoelastic constant, with the latter two properties affording significant reductions to the Brillouin gain coefficient. However, lanthana possesses thermo-acoustic and strain-acoustic coefficients (acoustic velocity versus temperature or strain, TAC and SAC, respectively) with signs that are opposed to those of ytterbia. The lanthano-aluminosilicate (SAL) fiber utilized in this study is Brillouin-athermal (no dependence of the Brillouin frequency on temperature), but not atensic (is dependent upon the strain), which is believed to be, to the best of our knowledge, the first demonstration of such a glass fiber utilizing a compositional engineering approach.

Microstructure study on selective laser melting yttria stabilized zirconia ceramic with near IR fiber laser

Purpose– The purpose of this paper is to explore selective laser melting of yttria-stabilized zirconia (YSZ) ceramic by a 1 μm wavelength fibre laser; investigate the influence of different laser powers and different scanning velocities on the microstructure, the relative density, the deformation of ceramic sample and the micro-hardness; and analyze the crystal structure transformation during the fabrication.Design/methodology/approach– During the fabrication, the 5 mm × 5 mm × 5 mm YSZ ceramic samples are fabricated by rapid prototyping (RP) machine MCP Realizer SLM 250; density and microscopic photographs show the ceramic melting situation. The density of cubic sample with different laser powers and different scanning velocities is measured by Archimedes method. The microstructure of samples and powder is observed by SEM. The micro-hardness is measured by the Vickers micro-hardness equipment, and the crystal structure transition is studied by XRD.Findings– It is possible to melt YSZ powder completely with near-IR fibre laser, and the relative density of 5 mm × 5 mm × 5 mm cubic sample is 88 per cent, and the micro-hardness could reach 1,209 ± 262 HV500. The influence of laser power on the volume deformation is more sensitive than the scanning speed at the same energy density. The small pores and the obvious orderly cracks can be observed in the cross-section of sample; the uneven distribution of laser energy input is the main reason of the formation of orderly cracks. The transformation from monoclinic and cubic crystal to tetragonal crystal occurred during the melting process. Heat treatment (1400°C for 30 min) cannot significantly improve the density of the sample, but it can restore the colour of ceramic.Research limitations/implications– Particularly serious due to the deformation of the ceramic material, the authors cannot prepare a large ceramic sample and measure its macroscopic mechanical properties.Originality/value– This paper describes the manufacture of YSZ ceramic sample by SLM technology with a 1 μm wavelength fibre laser, and preliminary studies show the microscopic structure, distribution of laser parameters and crystal transformation.

Single Polarization, Dual Wavelength Fiber Laser Based on a 3-Stage All Fiber Lyot Filter

We have demonstrated a switchable dual wavelength fiber ring laser with a high degree of polarization output by using an intracavity 3-stage all fiber Lyot filter. The filter is formed by concatenating four 45° tilted fiber gratings separated by polarization maintaining fibers with a length ratio of 1:2:4 (20, 40, and 80 cm), giving a compact integrated configuration with reduced bandwidth. Switchable dual wavelength or single wavelength output at 1533.5 and 1563.3 nm has been achieved. The output lasing is considerably stable owing to the in-phase mode-selecting function of the multistage Lyot filter, and has a very high degree of polarization higher than 99.9%.

Laser Transmission Bonding of Silicon with Titanium and Copper Layer for Wafer-Level Packaging

For packaging of silicon components with high spatial selectivity and small heat affected zone (HAZ) laser transmission bonding (LTB) of silicon-silicon compounds using the intermediate layer system copper-titanium is investigated. The bonds are realized by using a cw-thulium fiber laser (wavelength 1940 nm). Several process parameters, like laser intensity, feed rate and contact pressure, are analyzed and optimized during the investigation. Also varying layer thicknesses for titanium and copper are compared in order to analyze their influence on the LTB process. Results are examined regarding the tensile strength measured by using tensile test. Occuring bond failures during the experiments are described and methods for avoiding these are discussed. Micrographs are analyzed in order to investigate the bond zone by SEM. Specimens bonded with corresponding standard bond process using the same layer system and bond geometry are used in order to compare the results.

Crystallization and photoluminescence properties of α-RE2(WO4)3 (RE: Gd, Eu) in rare-earth tungsten borate glasses

Glasses with the compositions of 22.5RE2O3–47.5WO3–30B2O3 (mol%) (RE: Gd, Eu) were prepared by a conventional melt quenching method, and α-Gd2(WO4)3 and α-Eu2(WO4)3 crystals were synthesized through their crystallization. The two types of WO4 tetrahedra present in α-RE2(WO4)3 provide the Raman bands at 931–934cm−1 for WIIO4 tetrahrdra with much distortions and at 946–950cm−1 for WIO4 tetrahedra with a near regular symmetry. The crystallized samples containing α-Eu2(WO4)3 exhibit strong red emissions under the excitation at 396 and 467nm, although the base glass has no photoluminescence emission. α-Gd2(WO4)3 and α-Eu2(WO4)3 crystals were patterned on the glass surface by irradiations of a continuous wave Yb:YVO4 fiber laser (wavelength: 1080nm).

Non-ablative texturing of silicon surface with a continuous wave fiber laser

Laser surface texturing based on ablation has been widely used, but hardly any reports can be found on non-ablative laser surface texturing. Silicon is highly transparent to the infrared wavelength of fiber laser (λ = 1090 nm) and thus regarded as an unsuitable tool for the purpose of surface texturing. However, we succeeded in using a continuous wave fiber laser to produce regular arrays of sub-micron bumps on silicon surface. The approach is shown to be based on laser-induced oxidation of silicon.