Output Power Of Fiber Laser Research Articles

400-W single-mode single-frequency laser output from homemade tapered fiber

In recent years, the high-power single-frequency fiber lasers have developed rapidly, and they have been used in nonlinear frequency conversion and gravitational wave detection. The main factors limiting the output power of single-frequency fiber lasers are the nonlinear effect and transverse mode instability (TMI) effect. In general, large-core fibers can mitigate nonlinear effects while small-core fibers help to suppress the TMI effect. Owing to the core diameter varying in the longitudinal direction, tapered double clad fiber (T-DCF) is a promising solution to simultaneously suppress the nonlinearity and TMI effects. In the present study, we have fabricated a piece of 2.2-m-long Ytterbium-doped T-DCF. The core diameter and the cladding diameter of this fiber vary gradually from 30.3 μm to 49.3 μm and from 245 μm to 404 μm, respectively. Using this homemade fiber, we constructe an all-fiberized single-frequency master oscillator power amplifier system, which is pumped by laser diodes with a central wavelength of 976 nm. The seed of the system has a central wavelength of 1064 nm, and output power of 30 mW. The T-DCF is coiled on a piece of cooling plate, whose output end is cleaved at a 8° angle. The laser is output to free space and collimated by a free-space collimator. After the collimator, dichroic mirror is utilized to strip out the residual pump power for measuring power, spectrum, time-domain signal and beam quality. The output power increases linearly with the pumping power increasing. When the pumping power is 502 W, the output power reaches 400 W. And there is no stimulated Brillouin scattering (SBS) nor TMI under the power level. The corresponding slope efficiency is 81.7% while the <i>M</i><sup>2</sup> is measured to be 1.29, exhibiting the single-mode output characteristic of the system. When the output power is further increased to 418 W, the TMI effect is observed, which limits further the power scaling of the single-mode output. To the best of our knowledge, this is the highest output power of single-frequency fiber laser based on home-made gain fibers. The results indicate that T-DCFs can simultaneously suppress the nonlinearity and TMI, thus providing a useful reference for further power scaling of single-frequency fiber lasers. Higher output power is expected by optimizing the parameters of T-DCF and the structure of system.

MXene-Ti3C2Tx for watt-level high-efficiency pulse generation in a 2.8 μm mid-infrared fiber laser

We report a watt-level passively Q -switched 2.8 μm mid-infrared multi-mode fiber laser by employing multi-layered two-dimensional MXene- Ti 3 C 2 T x as the saturable absorber (SA). The MXene- Ti 3 C 2 T x is fabricated by selectively etching aluminum layers in Ti 3 AlC 2 . The non-saturable loss, modulation depth, and saturable intensity of the SA at 2866 nm were measured to be 25.0%, 33.2%, and 0.043 GW / cm 2 , respectively. The maximum average output power of the Ti 3 C 2 T x Q -switched fiber laser reached 1.09 W at 28.23% slope efficiency. The pulse repetition rate, shortest pulse width, pulse peak power, and single-pulse energy were 78.12 kHz, 1.04 μs, 13.4 W, and 13.93 μJ, respectively. This is the first demonstration of watt-level pulse generation in a mid-infrared fiber laser using low dimensional materials, to the best of our knowledge. These results indicate that the Ti 3 C 2 T x is a reliable and superior broadband SA for high power mid-infrared pulsed laser generation.

A Comparative Study of Thermal Impact on Erbium Doped Distributed Feedback Fiber Laser Output Power

The temperature dependency of erbium doped distributed feedback fiber laser output performance is experimentally and theoretically investigated with two major pump schemes. The output power declined linearly as temperature increased from 30 °C to 120 °C for 980 nm and 1480 nm pumped test laser while the later exhibited stronger heat susceptibility. Further experiment and analysis identified the temperature induced absorption and emission cross section variation at pump and signal wavelength together with population inversion rate difference are the originations of the thermal sensitivity discrepancy between the two pump setups. Associated theoretical simulation concludes the erbium doped distributed feedback fiber laser thermal output sensitivity is dependent on its gain dynamics and grating structure simultaneously.

Home-made confined-doped fiber with 3-kW all-fiber laser oscillating output

Ytterbium doped fiber lasers (YDFLs) with small volume, good beam quality, good heat dissipation performance and high conversion efficiency are widely used in industrial processing, military, medical and other fields. In past decades, with the development of high-performance double cladding gain fiber and fiber devices, the output power of YDFLs increases rapidly. However, nonlinear effects (NLEs), such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), are produced, which limits the further enhancement of the output power of fiber laser. Large mode area ytterbium-doped fiber (LMAYDF) can effectively increase the nonlinear effect threshold. However, increasing the core diameter will support more high-order modes (HOMs), which may lead the beam quality to deteriorate and induce the mode instability (MI) effect to occur in fiber lasers. Thus, MI and NLEs have become the main limiting factors for the further improving of output power and beam quality in fiber lasers. The confined-doped ytterbium-doped double-clad fiber (CDYDF), by reducing the doping diameter of gain ions in the fiber core, makes the fundamental mode (FM) dominate in mode competition and HOM suppressed to achieve LMAYDF gain control for different modes, thus improving the output power of the fiber laser and maintaining good beam quality. The 33/400 μm confined-doped ytterbium-doped double-clad fiber (CDYDF) is fabricated by modifying the chemical vapor deposition (MCVD) process with solution doping technology (SDT). The Yb<sup>3+</sup> doping diameter ratio is 70% and refractive index profile is close to step-index. Utilizing the master oscillator power amplifier (MOPA) system the beam quality optimization effect of confined-doped fiber is verified and optimized to 1.43 as the power increases while the <i>M</i><sup>2</sup> of seed laser is 1.53. An all-fiber structure counter-pumped fiber oscillator is constructed to test the laser performance of home-made confined-doped fiber. When the pump power is ~4.99 kW, laser power of 3.14 kW with a central wavelength of 1081 nm and line width of 3.2 nm at 3 dB is obtained. Moreover, there is no MI nor SRS in the whole experiment. We demonstrate that it is the highest output power based on home-made confined-doped fiber. The above results indicate that confined-doped fibers have the potential to achieve high-power and high-beam-quality fiber laser output.

Design of a radiation-balanced fiber laser via optically active composite cladding materials

Although the output power of commercial fiber lasers has been reported to exceed 500 kW, the heat generated within fiber gain-media has limited the generation of higher laser powers due to thermal lensing and melting of the gain-media at high temperatures. Radiation-balanced fiber lasers promise to mitigate detrimental thermal effects within fiber gain-media based on using upconverted, anti-Stokes photoluminescence to extract heat from the optical fiber’s core. In this paper, we experimentally demonstrate that Yb(III) ions within $ {\text{YLiF}_4} $YLiF4 (YLF) microcrystals are capable of cooling the cladding of optical fibers. We also present a design for radiation-balanced fiber lasers using a composite fiber cladding material that incorporates YLF nanocrystals as the active photonic heat engine. YLF crystals have the potential to form composite cladding materials to mitigate thermal gradients within the core and cladding based on anti-Stokes photoluminescence. Analytical models of heat transfer within the fiber are presented where the electric-field amplitude within the fiber core is responsible for both the heating of the core and the excitation of Yb(III) ions for anti-Stokes laser refrigeration in the cladding.

Metal-coated fiber sensor for laser radiation power measurements

A technique for measurements of output power of fiber lasers using a metal-coated fiber sensor is proposed. Optical radiation transmitting through the core of a copper-coated silica fiber is partially scattered and, therefore, absorbed in the copper layer. The change of an electrical resistance of the metal coating induced by its heating is measured. This technique can be used for the real-time measurement of output radiation power of fiber laser sources. The measurement range of optical power can be controlled by changing the bend curve radius of the metal-coated fiber. Optical scattering coefficients of the metal-coated fiber core were determined using the proposed theoretical model of the fiber sensor heating.

Optically pumped gas terahertz fiber laser based on gold-coated quartz hollow-core fiber.

An optically pumped gas terahertz fiber laser based on gold-coated quartz hollow-core fiber is demonstrated. When the terahertz fiber laser is filled with methanol gas and pumped by a piezoelectric-ceramic-transducer-adjusted transversely excited atmospheric pressure carbon dioxide laser, a continuous 2.52THz laser with the output power of 110mW is obtained. Attributed to the adjustment of the piezoelectric ceramic transducer in the carbon dioxide laser, the fluctuation of the terahertz fiber laser output power is controlled within ±5%. The result confirms the possibility of a compact flexible optically pumped gas terahertz fiber laser.

Plane-by-plane femtosecond laser inscription of first-order fiber Bragg gratings in fluoride glass fiber for in situ monitoring of lasing evolution

We report the femtosecond laser inscription of fiber Bragg gratings (FBGs) in an Er-doped fluoride glass fiber used for lasing at a mid-infrared wavelength of 2.8 µm. The lasing evolution is discussed in terms of the FBG reflectivity, wavelength transition to the Bragg wavelength, and output power of the mid-infrared fiber laser. A first-order and short (2.5-mm-long) Bragg grating showed a reflectivity of 97%, because of a laser-induced index modulation of 1.1 × 10-3. This modulation was sufficient to saturate this system's output power. The laser oscillator is designed to lase in the atmospheric window of 2799-2800 nm slope. Further, this oscillator's efficiency is as high as 29.1% for the launched pump power over the range of 0.4-4.6 W and at a lasing wavelength of 2799.7 nm. This oscillator also exhibited a FWHM bandwidth of 0.12 nm.

Passively Q-switched fibre laser based on a saturable absorber of siloxane

A passively Q-switched fiber laser using a novel saturable absorber (SA) of Siloxane has been demonstrated. The modulation depth of the SA is measured to be 4.87%. Based on such an SA, the Q-switched operation in the laser has been achieved. The average output power of the Q-switched fiber laser is 0.78 mW with a pulse repetition rate of 21.3 kHz. The pulse energy goes up to 36.62 nJ when the pump power of the laser is 200 mW. The Q-switched laser exhibits the performances of self-starting, good stability, and high pulse energy. To the best of our knowledge, it is the first demonstration of the passively Q-switched laser based on a siloxane SA.

5 kW all-fiber 1018 nm laser combining

The scheme of tandem pumping has drawn a lot of interest in fiber laser field for their outstanding characteristics, which include high-brightness, low quantum defect, and great potential for power scaling. The 1018 nm laser can be used as an efficient tandem pumping source for high-power ytterbium fiber laser, but it is difficult to improve signal fiber laser output power. One of the efficiency methods to break through this limitation is beam combining. In this paper, based on 19 single-mode 1018 nm fiber lasers and a 191 fiber combiner, we setup an all-fiber schematic laser combining system, and achieve 5 kW laser output with 1018 nm.

More than 400 W random fiber laser with excellent beam quality.

We report on the demonstration of a high power, high beam quality random fiber laser. It is a half-open cavity based on 130-m-long large mode area step-index fiber with a core diameter of 20μm and a numerical aperture of 0.08. The random laser cavity, whose central wavelength is 1120nm, is pumped by a 1070nm Yb-doped fiber oscillator. The maximum output power is 418W with respect to the injected pump power of 588W, corresponding to the optical-to-optical efficiency of 71%. The output power, spectral, and temporal characteristics are carefully presented and discussed, showing that such a cavity can export high power random laser stably and effectively. The far field beam quality is also measured, and the profile is nearly a Gaussian shape. This work provides an impactful method to advance the output power of random fiber lasers.

Evaluation of 976 nm Multimode Single Emitter Laser Diodes for Efficient Pumping of 100 W+ Yb-doped Fiber Laser

<p>Experimental evaluation of spectral and power-current (P-I) characteristics of fiber coupled single emitter multimode laser diodes used for development of efficient pumping assembly is reported. Fiber coupled laser diodes emitting around 976 nm are best suited for pumping Yb-doped fiber lasers because of excellent coupling efficiency and reduced thermal load. We have experimentally investigated emission spectrum of fiber coupled multimode laser diodes at different temperatures and drive currents. It is found that peak emission wavelength shifts towards the longer wavelength with increase in temperature and drive current. P-I characteristics of fiber coupled laser diodes have been obtained and presented for drive current from 0.4 A to 11.5 A. Based on experiment, we have constructed spectrally matched laser diode assembly for efficient pumping of 100 W fiber laser. It requires very precise control of temperature and drive current to maintain the emission spectrum. Total 162 W power is pumped in to the Yb-doped fiber laser cavity through multi-mode pump combiners and we have obtained 110 W fiber laser output power @1070 nm. The achieved optical-to-optical efficiency is 68 per cent.</p>

Suppressing mode instabilities by optimizing the fiber coiling methods

Suppressing mode instabilities (MI) by optimizing the fiber coiling methods has been studied numerically. By employing our semi-analytical model, the MI threshold of two typical high power fibers in various coiling methods has been calculated. It reveals that fiber laser systems with gain fibers being coiled in cylinder shape has higher MI threshold than those with gain fibers being coiled in spiral shape, and MI-free output power of fiber lasers can be scaled up to above 3 kW even with the typical commercial fibers in the co-pumped configurations.

High-power ultralong-wavelength Tm-doped silica fiber laser cladding-pumped with a random distributed feedback fiber laser.

We demonstrated a high-power ultralong-wavelength Tm-doped silica fiber laser operating at 2153 nm with the output power exceeding 18 W and the slope efficiency of 25.5%. A random distributed feedback fiber laser with the center wavelength of 1173 nm was employed as pump source of Tm-doped fiber laser for the first time. No amplified spontaneous emissions or parasitic oscillations were observed when the maximum output power reached, which indicates that employing 1173 nm random distributed feedback fiber laser as pump laser is a feasible and promising scheme to achieve high-power emission of long-wavelength Tm-doped fiber laser. The output power of this Tm-doped fiber laser could be further improved by optimizing the length of active fiber, reflectivity of FBGs, increasing optical efficiency of pump laser and using better temperature management. We also compared the operation of 2153 nm Tm-doped fiber lasers pumped with 793 nm laser diodes, and the maximum output powers were limited to ~2 W by strong amplified spontaneous emission and parasitic oscillation in the range of 1900–2000 nm.

Diode-Pumped 1178-nm High-Power Yb-Doped Fiber Laser Operating at 125 C

We demonstrate a high-power Yb-doped fiber laser operating at 1178 nm based on commercial silica double-cladding fiber and laser diode (LD) pumping regime at 976 nm. It is experimentally proved that heating the active fiber is an efficient way to suppress amplified spontaneous emission (ASE) and to increase the parasitic lasing threshold in long-wavelength Yb-doped fiber lasers. By adopting output coupling fiber Bragg grating (OC FBG) with high reflectivity and heating the Yb-doped fiber to 125 $^{\circ}\text{C}$ , a record output power of 31 W is obtained, and the corresponding slope efficiency is $\sim$ 44% with respect to the pump power. To the best of our knowledge, it is the highest output power of Yb-doped fiber lasers, which adopt commercial double-cladding active fiber and operate in the range beyond 1160 nm. Furthermore, it is first experimentally proved that the parasitic lasing threshold is related to the power of the backward ASE and the length of the active fiber.

Beam quality in spectral beam combination based on multi-layer dielectric grating

Owing to damage, thermal issues, and nonlinear optical effects, the output power of fiber laser has been proven to be limited. Beam combining techniques are the attractive solutions in order to achieve high-power high-brightness fiber laser output. Designing such a high-power laser system relies on coherent and incoherent combination of radiation from multiple laser channels into a single beam with enhanced brightness. Spectral beam combination is a promising alternative way that allows each array to be overlapped in near-and far-field without spatial interference, thus relaxing the requirements for linewidth controlling and phase locking of individual array and practically allowing power and brightness to be scaled with the potential to combine a large number of channels. Spectral beam combination implementations can be divided into two subsets: serial and parallel, based on the combining elements. For scaling high power, we pursue spectral beam combining with parallel subsets as an alternative to other beam combination implementation. In the spectral beam combining system based on multi-layer dielectric grating, the combined beam suffers the degradation in beam quality, which is caused by the optical dispersion, and also by the random error due to the misalignment of arrays or the thermal-optic effect of grating in the experimental system. In this paper, we strictly derive the equation of M2 variation caused by the optical dispersion in both single-grating structure and dual-grating structure. And also, we discuss how the laser linewidth, beam size, spectral separation of two adjacent channels, distance between two adjacent channels and the period of grating influence the desired beam quality in detail, separately, in the single-grating structure and the dual-grating structure. The results show that with the value of M2 fixed, the finite beam size gives rise to a laser bandwidth decreasing in single-grating structure combination, whereas the beam size induces a laser bandwidth to increase in dual-grating structure combination. If M2 1.2, the laser bandwidth of dual-grating system can be over several sub-nanometers, rather than several tens of pm as in the single grating design.

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.

MoS2 saturable absorber for single frequency oscillation of highly Yb-doped fiber laser

In this Letter, a single-frequency fiber laser using a molybdenum disulfide (MoS2) thin film as a saturable absorber is demonstrated. We use a short length of highly Yb-doped fiber as the gain medium and a fiber ferrule with MoS2 film adhered to it by index matching gel (IMG) that acts as the saturable absorber. The saturable absorber can be used to discriminate and select the single longitudinal modes. The maximum output power of the single-frequency fiber laser is 15.3 mW at a pump power of 130 mW and the slope efficiency is 15.3%. The optical signal-to-noise ratio and the laser linewidths are ～60 dB and 5.89 kHz, respectively.

Theoretical study of the temperature distribution in high power gain fiber of gradient doping

Thermal effect in the gain fiber is one of the main factors which restrict the power improvement of high power fiber amplifiers. Previous studies have shown that the temperature distribution is closely related to the doping concentration along the gain fiber. In order to reduce the maximum temperature of the gain fiber, we propose to use doping concentration varying along the gain fiber as a method to disperse the thermal effect of the fiber laser and improve the laser output power. Based on the rate equation model and thermal conduction model, the thermal distributions and output powers of several different gradient doping gain fibers are simulated in the cases where the output powers are approximately the same. Our study shows that compared with the conventional constant doping gain fiber, linear doping of the rare earth ion along the gain fiber can reduce the maximum temperature of the gain fiber as well as the temperature of the fusion point greatly, thus improving the stabilities of the fusion point and the fiber laser amplifier. In the case of cosinoidal doping, the gain fiber can not only reduce the temperature of the fusion point but also make the temperature have a periodic distribution along the gain fiber, which can suppress the stimulated Brillouin scattering effect effectively. The exponential doping of the gain fiber can also reduce the maximum temperature and the temperature of the fusion point, which is beneficial to the further scaling of the fiber laser output power. At the same time, it can make the gain of the signal light have a uniform distribution along the gain fiber, which suppresses the mode instability effect and improves the output beam quality of the fiber laser. These conclusions also hold true when the pump power changes. Therefore, the gradient doping of the gain fiber proposed in this paper can optimize the temperature distribution along the fiber and improve the stability of the fusion point. Besides, it can improve the beam quality of the output laser and suppress the nonlinear effect and mode instability effect. The results indicate that the gradient doping of the gain fiber is an effective and feasible way to improve the output power of fiber amplifier. Last but not the least, it is possible to produce the gradient doping gain fiber by the laser heated pedestal growth method and the direct nanoparticle deposition technique. The investigation can present a reference for designing the gain fiber in high-power fiber laser systems.

Passively Q-Switched Er-Doped Fiber Lasers Using Alcohol

A passively Q-switched Er-doped fiber laser using a simple and cost-effective saturable absorber (SA) of alcohol has been demonstrated. The SA is made through filling anhydrous alcohol in the gap between the end-facets of two optical patch cords, which are inserted into a cannula. The modulation depth of the SA with 820-μm alcohol layer is measured to be 18%. Based on such an SA, the Q-switching operation in the Er-doped fiber laser has been achieved. The average output power of the Q-switched fiber laser is 30.3 mW with the pulse repetition rate of 81.9 kHz, and thus, the pulse energy is up to 348.6 nJ. To the best of our knowledge, it is the first demonstration of the passively Q-switched laser based on an alcohol SA. This provides the further evidences indicating the possibility of organic liquid as effective SAs for pulsed lasers.