Triple-clad Fiber Research Articles

A Knee-Flexion Angle Optical Fiber Sensor Based on Spherical Fused Triple-Clad Fiber

A Knee-Flexion Angle Optical Fiber Sensor Based on Spherical Fused Triple-Clad Fiber

Modeling of multi-kW in-band pumped triple-clad thulium-doped fiber architecture

We present a model and design for a high-power triple-clad thulium doped fiber specifically for in-band or tandem pumping. This fiber is designed to maximize the output signal power while taking into consideration common effects that limit high-power operation. In-band pumping will allow for thulium fiber lasers to reach multi-kW power levels.

Triple-clad W-type fiber mitigates multipath artifacts in multimodal optical coherence tomography.

Multimodal endoscopic optical coherence tomography (OCT) can be implemented with double-clad fiber by using the presumed single-mode core for OCT and the higher numerical aperture cladding for a secondary modality. However, the quality of OCT in double-clad fiber (DCF) based systems is compromised by the introduction of multipath artifacts that are nt present in single-mode fiber OCT systems. Herein, the mechanisms for multipath artifacts in DCF are linked to its modal contents using a commercial software package and experimental measurement. A triple-clad W-type fiber is proposed as a method for achieving multimodal imaging with single-mode quality OCT in an endoscopic system. Simulations of the modal contents of a W-type fiber are compared to DCF and single-mode fiber. Finally, a W-Type fiber rotary catheter is used in a DCF-based endoscopic OCT and autofluorescence imaging (AFI) system to demonstrate multipath artifact free OCT and AFI of a human fingertip.

High-power 0.4-mJ picosecond CPA system based on an extra-large-mode-area triple-clad fiber.

A high-average-power, high-pulse-energy picosecond chirped pulse amplification (CPA) laser system based on an extra-large-mode-area (XLMA) triple-clad fiber (TCF) was demonstrated. The ultrashort pulses, generated from all-fiber mode-locked oscillator, stretched and then were pre-amplified to 10 W through a series of fiber power amplifiers. Subsequently, the average output power was amplified to 620 W corresponding to a pulse energy of 0.62 mJ via XLMA TCF. Additionally, the amplified pulses were compressed to a pulse duration of 7.6 ps with an average power of 423 W and a compression efficiency of 68.2%. The ultrashort laser is a promising light source for application of water-guided laser processing, albeit with a beam quality factor of 20 and 21 along two orthogonal axes.

All-Fiber Chirped-Pulse Amplifier Emitting 670 fs Pulses With 92 MW Peak Power

We demonstrated an all-fiber chirped-pulse amplifier with a stretcher stage based on a triple-cladding fiber and a final amplification stage based on a newly-developed highly Yb-doped large-mode area fiber with a Ge-doped pedestal. The stretcher fiber was designed to match a diffraction grating compressor in the third-order dispersion and allowed the stretching of 6 ps 1026 nm chirped pulses up to ~500 ps. These pulses were amplified in the developed Yb-doped fiber and then compressed using a transmission grating compressor down to 670 fs duration with 3.5 W average power and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$61.8~\mu \text{J}$ </tex-math></inline-formula> pulse energy, corresponding to a record-high peak power of 92 MW.

Home-made 6.7 kW narrow linewidth triple-cladding fiber laser

Home-made 6.7 kW narrow linewidth triple-cladding fiber laser

High efficiency holmium-doped triple-clad fiber laser at 2120 nm

We developed a new holmium-doped triple-clad fiber (Ho-3CF), reducing the clad diameter to improve the overlap between pump and doped-core, and the holmium concentration to reduce the influence of ion clustering on the laser efficiency. We illustrate here the performance of this fiber in a laser oscillator configuration. The laser emission is centered at 2.12&#x00A0;m by a fiber Bragg grating, and the active fiber is pumped in the clad by a 1.94&#x00A0;m thulium-doped fiber laser. The slope efficiency reaches 73&#x00A0;&#x0025; with respect to absorbed power (60&#x0025; considering coupled power), for a maximum signal power of 62&#x00A0;W delivered on a quasi single spatial mode (M<inline-formula><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula>=1.2). To the best of our knowledge, this slope efficiency is the highest reported for a high power clad-pumped fiber laser emitting at a wavelength higher than 2.1&#x00A0;m. We also analyze experimentally the impact of the pump Numerical Aperture (NA), at the input of the Ho-3CF, on the laser efficiency. Finally, we use our numerical simulation to comment on the best choice of pump wavelength.

High-pulse-energy high-brightness Q-switched Tm3+:Ho3+-codoped triple-clad polarization- maintaining fiber laser

A Q-switched polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser is under investigation with special focus on important optical parameters enabling efficient frequency conversion into mid-infrared (mid-IR). An active fiber of 5 m length is used in a single-oscillator free-space cavity arrangement and operated in continuous-wave and pulsed operation. In Q-switched regime at a repetition rate of 63 kHz, high pulse energies up to 760 μJ were obtained while reaching pulse widths as low as 45.6 ns, resulting in pulse peak powers of 15.7 kW with an average output power of 48 W. In addition, an M x,y 2 &lt; 1.2 and a FWHM of 290 pm for the emission spectrum was measured.

Yb-Doped Triple-Clad Fiber for Nearly 10 kW Level Tandem-Pumped Output

Yb-Doped Triple-Clad Fiber for Nearly 10 kW Level Tandem-Pumped Output

High-power cladding pumped Raman fiber amplifier with a record beam quality.

In this Letter, a high-power, high-brightness all-fiberized Raman amplifier based on a cladding-pumping scheme is presented for the first time, to the best of our knowledge. The triple-clad passive fiber is employed as Raman gain fiber in the laser system. The maximum output power is 762.6 W emitting at 1130 nm. To the best of our knowledge, this is the highest power in the fields of cladding-pumped Raman amplifiers. Through a cladding-pumping process, the beam quality parameter ${{\rm M}^2}$M2 improves from 6.12 of seed laser to 2.24 at maximum output power of 762.6 W, while the best ${{\rm M}^2}$M2 is 1.9 at 267.2 W. It is also the best beam quality of Raman laser with brightness enhancement in any kind of configuration (graded-index fiber or multi-clad fiber, laser or amplifier, all-fiber or free-space configuration) with power of over 100 W.

Diode-pumped triple-clad fiber MOPA with an output power scaling up to 4.67 kW.

In this Letter, we have demonstrated a triple-cladded fiber (TCF)-based master oscillator power amplifier (MOPA), with an output power scaling up to 4.67 kW, an optical-to-optical efficiency of 78%, and a beam quality factor ${{\rm M}^2}$M2 of 1.57. The MOPA output power was limited by stimulated Raman scattering (SRS) of which our design yielded a 31.2 dB suppression ratio at the 4.67 kW output power. Such a unique design of a TCF-based structure allows a wide range of flexibility over fiber parameters, mitigation of nonlinear effects, low-loss splice integration, reliable high-power pump guiding in turn, and an ease in overall thermal management at multi-kW output power levels. Together with direct diode-pumping configuration, TCF-based designs promise thermally and mechanically robust, compact, and highly efficient MOPA systems of a superior beam quality.

Amplification of a radially polarized beam in a thermally guiding ytterbium-doped fiber rod

Amplification of a radially polarized beam from an Yb:YAG seed laser at 1030 nm in a very-large-core triple-clad ytterbium-doped fiber configured as a thermally guiding fiber rod amplifier is demonstrated. The amplifier yielded a maximum output power of 10.7 W (limited by available pump power) with corresponding single-pass gain of 6.4 dB, while the radial polarization purity was maintained over the full range of pump power with a measured polarization extinction ratio of 100:1. The amplified output beam displayed the characteristic donut-shaped intensity profile with negligible beam distortion as evidenced by a measured beam propagation factor (M2) of 2.1 ± 0.1. A simplified model for propagation of a radially polarized beam in a thermally guided fiber rod is developed to provide insight into the underlying design principles and to establish a strategy for scaling output power. The power scaling limitations of this approach are considered.

Yb-Doped Aluminophosphosilicate Triple-Clad Laser Fiber With High Efficiency and Excellent Laser Stability

We fully demonstrated an ytterbium (Yb) doped triple-clad laser fiber with intense pump absorption, high efficiency, and laser stability. P5+/Al3+ molar ratio in the central region of fiber core was specially designed to be ∼1.08 for compensating P2O5 evaporation, while the ratio in the outer region was set as ∼0.92 for obtaining a flattened refractive index profile. Applying a two-stage deposition process, one-time collapse technique, low-temperature multi-times sintering, and suitable flow of pure POCl3 during sintering and collapsing process were instrumental in decreasing and offsetting element evaporation. Measured in an all-fiber master oscillator power amplifier configuration, the 7-m-long fiber obtained 1.39 kW near-single-mode laser output at 1079.6 nm with a slope efficiency of 85.2% and a beam quality M 2 of 1.36. Output laser spectrum with no sign of nonlinear-related peaks and a narrow 3-dB-bandwidth of ∼0.33 nm was obtained. The fiber-based laser setup was kept at the maximum power for 1 h with power degradation less than 0.21%. The results demonstrated Yb-doped aluminophosphosilicate triple-clad fiber is a highly competitive candidate for commercial high-power laser and high-power narrow-linewidth fiber laser.

Fabrication and laser performance of triple-clad Yb-doped aluminophosphosilicate fiber

Abstract We fabricated an Yb-doped triple-clad fiber consisting in adding to aluminophosphosilicate core and F300-pump cladding, low-refractive-index fluorine doped silica cladding, and demonstrated its laser performance based on an all-fiber oscillator. MCVD system, all-gas-phase chelate precursor doping technique, and a simple overcladding process were applied to make Yb-doped aluminophosphosilicate triple-clad fiber preform. Ultra-thin substrate tube and a two-stage deposition process were proposed to decrease and offset elements evaporation. The outer region of fiber core was tested with ∼1050 ppm Yb2O3, ∼10,800 ppm Al2O3, and ∼9950 ppm P2O5, while the central region was doped with ∼600 ppm Yb2O3, 8100 ppm Al2O3, and ∼7000 ppm P2O5, respectively (ppm is in molar here). Two-stage deposition process and triple-clad design results in pump absorption from Yb3+ ions about 0.67 dB/m at 915 nm. Tested in an all-fiber oscillator configuration forward-pumped by 915 nm laser diodes, 28 m-long triple-clad fiber presented 560 W laser output with optical-to-optical efficiency of 68.7%, and the corresponding beam quality M2 is ∼1.18. The results indicate all-gas-phase chelate precursor doping technique in combination with overcladding technique is potential to manufacture high power triple-clad fiber, and ultra-thin substrate tube as well as two-stage deposition process are very effective ways to decrease and offset element evaporation.

Side coupler applied in a multi-pumped Yb-doped triple-clad fiber laser

A ytterbium (Yb)-doped side multi-pumped fiber amplifier operating at 1.08 µm is demonstrated. Firstly, we present a novel (2 + 1) × 1 side-pumped fiber coupler which is fabricated by two tapered 105/125 µm double-clad fibers and a 20/50/400 µm triple-clad Yb-doped fiber and the relationship between the fused depth and coupling efficiency is analyzed. Secondly, a new method is adopted to fabricate the (2 + 1) × 1 side coupler. The coupling efficiency of the side coupler for a 975 nm pump light can reach up to 95% and the signal light insertion loss is less than 0.04 dB. Then, four (2 + 1) × 1 side-pump couplers are fabricated on a 25 m long triple-clad gain fiber in sequence. Based on these couplers, an all-fiber side multi-pumped fiber amplifier with an output power of 645 W and optical–optical efficiency of 65% is achieved in the experiment. In addition, the scheme ensures that the temperature of the fiber is reduced to meet safety levels. Finally, by increasing the number of the side couplers to improve the pump power, the output power of the amplifier will be higher.

1.2 kW clad pumped Raman all-passive-fiber laser with brightness enhancement.

An all-fiber clad pumped Raman fiber laser (FL) oscillator with a CW power of 1.2kW and an efficiency of 85% is presented. To the best of our knowledge, this laser is the highest power and the highest efficiency Raman FL demonstrated in any configuration with brightness enhancement (BE). To the best of our knowledge, it is also the first greater than kilowatt FL of any kind that does not utilize rare-earth doping in the oscillator fiber (all passive fiber). The beam quality (BQ) of the Raman laser was M2=2.75 at 1kW, and the pump-Stokes BE factor was approximately 7. The laser consists of a specially designed triple-clad fiber which confines the low BQ pump power into the multi-mode inner clad, while generating the Raman signal in the large-mode-area core. The second Stokes is inhibited by selecting the appropriate inner clad-to-core area ratio and by the oscillator's selective fiber Bragg grating reflectors.

250 W clad pumped Raman all-fiber laser with brightness enhancement.

We report a strictly all-fiber clad pumped Raman fiber laser with a CW power of 250W. To the best of our knowledge, this is the highest power Raman fiber laser demonstrated in any configuration allowing brightness enhancement. In addition, this is the first report of a Raman clad pumped all-fiber laser. The brightness of the pump source was enhanced by a factor of ∼3.8. This result was achieved by the design of a novel triple-clad fiber, with tight pump power inner confining clad that both maximized the Raman gain and inhibited the second Stokes radiation. We discuss power-increase effects on the beam quality, efficiency, and brightness enhancement.

Intermodal nonlinear effects mediated optical event horizon in short-length multimode fiber

The group-velocity-led optical event horizon (OEH) in optical fibers provides a convenient way to efficiently control a weak dispersive pulse by a comparatively strong solitonic pulse. State-of-the-art experiments demonstrating OEH make use of two different light sources, which increases the system complexity and cost. Here, we propose an elegant and cost-effective approach to observe the OEH through intermodal nonlinear interaction between azimuthally symmetric ${\text{LP}}_{01}$ and ${\text{LP}}_{02}$ modes of a specially designed triple-clad multimode fiber through only a single pump. The simultaneous control over dispersion and the walk off of ${\text{LP}}_{01}$ and ${\text{LP}}_{02}$ modes of the designed fiber pave the way for the OEH interaction. The ${\text{LP}}_{02}$ mode possesses anomalous dispersion, while the ${\text{LP}}_{01}$ mode exhibits normal dispersion over the wavelength range of interest. Depending upon the location of the input pump wavelength, the ${\text{LP}}_{02}$ soliton can reflect a weak copropagating ${\text{LP}}_{01}$ dispersive pulse, which possesses the same carrier wavelength as the soliton. The findings of this work might be useful for all-optical switching and also for the optical transistor action, where the increased feasibility is obtained by the fact that the proposed approach does not require separate input wavelengths for the soliton and the dispersive pulse. Moreover, a tunable pump source can be used to observe either a redshift or a blueshift in the dispersive pulse.

Research on the temperature sensing characteristics of triple cladding quartz specialty fiber based on cladding mode resonance

A triple-cladding quartz specialty fiber (TCQSF) temperature sensor based on cladding mode resonance is made. The sensor is fabricated by just splicing a short, few-centimeter-long segment of TCQSF between two standard single-mode fibers (SMFs), so the sensor structure is simple. In order to explain its sensing principle in detail, we assume that the TCQSF is equivalent to three coaxial waveguides based on coupling mode theory. Utilizing the scalar method and the relationship between Bessel function and mode field distribution of step-index circular symmetry waveguide, the mode field distribution of these waveguides and their characteristic equation can be easily obtained. Then the dispersion curves of each mode which is transmitted in the three waveguides can be calculated. The intersection between the fundamental core mode LP01(rod) in the rod waveguide and the cladding mode LP01(tube) in the tube waveguide I indicates that the two modes have the same propagation constant, and satisfy the phase-matching condition when the wavelength is 1563.7 nm which is known the resonant wavelength. And only when the sensor length is equal to the beatlength, can the light be coupled completely from the core to the fluorine-doped silica cladding. Thus, the cladding mode resonance phenomenon occurs and a band-stop filter spectrum will be obtained. Then the sensor is applied to the simulation calculation of the temperature sensing characteristics. With increasing temperature, both the refractive index of each layer and the sizes of the axial and radial fibers will change, which will finally lead to a big difference on the dispersion curves of LP01(rod) and LP01(tube). Therefore, the resonant wavelength shift of the sensor can be obtained by just calculating the dispersion curves of these two modes at different temperatures, and the scope of curvature sensitivity is 70.76-97.36 pm/℃. Finally, a straight forward experiment is performed to prove the temperature sensing properties. Experimental results show that the sensor has a sensitivity in temperature of 73.74 pm/℃ at 35 ℃-95 ℃, which is completely consistent with the theoreticaly calculatied results. Thus, the proposed sensor has the advantages of simple structure, easy fabrication, highly sensitivity, controlled cladding mode excitation, and so on. It can be used in industrial production, biomedical and other temperature sensing areas.

Comparative Study of Triple-Clad Dispersion-Shifted, Dispersion-Flattened and Dispersion-Compensated Fiber for Broadband Optical Network Application

AbstractIn this paper, comprehensive analyses of triple-clad fibers are presented. The geometry of multiple-clad fibers has been considered as a four-layer cylindrical structure. The geometry consists of a core and three claddings. We have analyzed and compared different types of triple-clad refractive index profiles on the basis of dispersion, mode distribution and propagation constant. To enhance the optical characteristics of these three fibers, we have developed a combined formulation which is applicable for single-clad, double clad and triple-clad optical fibers. In optical fibers, two or more claddings are required for dispersion shifting, dispersion flattening and other specialized applications. Thus, an analysis of design dispersion-shifted, dispersion-flattened and dispersion-compensated fibers is presented. We have used a boundary match method for evaluating propagation wave vectors and guided modes.