Ytterbium-doped Fiber Laser Research Articles

A Narrow-Linewidth Linearly Polarized 1018-nm Fiber Source for Pumping Diamond Raman Laser

A 7.8-GHz linewidth ytterbium-doped fiber (YDF) laser with an output power of 75 W at 1,018 nm is demonstrated based on narrow-bandwidth fiber Bragg gratings. Effective suppression of spectral broadening and amplified spontaneous emission is achieved by optimizing the resonator structure and active fiber parameters. An 1,178-nm diamond Raman output pumped by this narrow-linewidth 1,018 nm source is addressed in this study, which shows a promising application of generating the sodium guide star laser at 589 nm. A single-longitudinal-mode Stokes with an output power of 0.6 W is obtained using this multimode 1,018 nm laser at the pump power of 13 W. The impact of pump spectral linewidth on the effective Raman gain coefficient is analyzed, and the laser threshold of the diamond Stokes resonator increases with the broadening of the pump linewidth.

Gaussian-Shaped Gain-Dopant Distributed Fiber for High Output Power Fiber Amplifier

The remarkable evolution of ytterbium-doped fiber (YDF) lasers and amplifiers is interrupted by a limiting thermo-optical effect called transverse mode instability (TMI). Hereon, we propose a Gaussian-shaped gain-dopant distributed (GSGDD) YDF, which is fabricated by a modified chemical vapor deposition (MCVD) process combined with solution doping technique (SDT). By regulating the solution concentrations of soot layers, the content of Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions presents Gaussian-shaped distribution in the transverse direction while the refractive index profile (RIP) exhibits a stepped profile. The laser performance of this fiber is verified by a bidirectional pumped master oscillator power amplifier (MOPA). Over 3 kW near-single-mode laser output is obtained with the slope efficiency of 84.9%. At the highest power output, there are no Stokes light components in the spectrum and the beam quality M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor is ~1.45 These results suggest that the GSGDD fiber owns great potential to achieve high power output with excellent beam quality.

Experimental study of the Ti-implant surfaces structured by the ytterbium-doped pulsed fiber laser

Relevance. Currently, there are several basic techniques for the dental implant surface structuring. Laser treatment is an extremely promising technique for the surface structuring. This technology allows creating regular implant surface without using chemicals and in just one technological step. The purpose was to present study aimed to compare and evaluate in vivo the stability and osseointegration of dental implants with 2 different surfaces structured by ytterbium-doped pulsed fiber laser operating at 1064 nm.Materials and methods. 60 dental implants were placed in the study. 2 types of dental implant surfaces, namely holes and parallel grooves, were created by the ytterbium laser operating at 1064 nm. A polished dental implant (without laser surface structuring) was also included in the experiment for comparison. The study was carried out on 15 laboratory animals (male rabbits, weight 3.5-4 kg). The implants were placed in the tibia. 4 implants with different surface types but of the same diameter and length were placed in each rabbit.Results. Laboratory animals were sacrificed 1.5 and 3 months after the surgery. The stability of the implants was assessed by RFA (Resonance Frequency Analysis), based on the registration of resonance electromagnetic oscillations of the implant and the surrounding bone when they are exposed to the electromagnetic field (Osstell ISQ). Also, nondecalcified bone blocks were histologically examined using a confocal laser scanning microscope (Carl Zeiss LSM 780) and histomorphometry was performed (BIC-index: Bone-to-implant contact). Bone blocks were prepared according to a special technique: they were soaked and embedded into the plastic and synthetic resin. The obtained blocks were cut into sections, 40-50 µm thick, and stained with toluidine blue.Conclusion. Laser surface structuring of the dental titanium implants is a promising technique. 59 in 60 (98.3%) implants were osseointegrated, there were no signs of inflammation in the bone tissue. The present results allow further studying of dental implants with various surface designs, structured by ytterbium laser.

Tailoring the efficiency and spectrum of a green random laser generated by frequency doubling of random fiber lasers.

Frequency doubling of random fiber lasers could provide an effective way to realize visible random lasing with the spectrum filled with random frequencies. In this paper, we make a comprehensive study on the efficiency and spectral manipulation of a green random laser generated by frequency doubling of an ytterbium-doped random fiber laser (YRFL). To tailor the efficiency of green random lasing generation, the ytterbium-doped random fiber lasing is filtered at different spectral positions, and then amplified to watt-level to serve as the fundamental laser source for frequency doubling in a periodically poled lithium niobate (PPLN) crystal. We found that by selecting different spectral components of ytterbium-doped random fiber lasing, the temporal intensity fluctuations of the filtered radiations vary dramatically, which plays an important role in enhancing the efficiency of frequency doubling. By fixing the filtering radiation wavelength at 1064.5 nm and tuning the central wavelength of YRFL, we experimentally demonstrate that, compared to the filtered radiation in the center of the spectrum, the efficiency of frequency doubling can be nearly doubled by utilizing the filtered ytterbium-doped random fiber lasing in the wings of the spectrum. As a result, the conversion efficiency of the generated green random laser at 532.25 nm can be more than 11% when the input power of the polarized 1064.5 nm fundamental light is 2.85W. For spectral manipulation, we realize a spectral tunable green random laser in the range of 529.9 nm to 537.3 nm with >100 mW output power for the first time by tuning the wavelength of YRFL and the temperature of PPLN simultaneously. The system can be naturally modified to simultaneously realize the efficiency enhancement and wavelength tuning, thus providing a new route to generate high efficiency and tunable visible random laser via frequency doubling that are potentially useful for imaging, sensing and visible light communication applications.

Hybrid nanocomposite film provides FWM and Fabry Perot Filter: Towards multi-wavelength fiber laser generation in 1 µm region

We report on the demonstration of a multi-wavelength ytterbium-doped fiber laser (YDFL) by exploiting a nanocomposite film to act as both a Fabry-Perot (FP) filter and a nonlinear material inside the ring cavity. The proposed filter is formed by combining an FP structure based on a large core diameter single-mode fiber (SMF) with a nanocomposite film. The nanocomposite film was prepared by coating gold nanostars with zinc-oxide nanorods/multi-walled carbon nanotubes (ZnO-NRs@Au-NSs/MWCNTs) embedded into polyvinyl alcohol (PVA) polymer. Moreover, the fabricated hybrid nanocomposite film exhibits a high nonlinear optical response that fulfilling the requirement to induce the FWM effect employed to suppress the mode-competition. Four lasing lines of uniform power-symmetry distribution with a spacing of ~160 GHz have been generated by appropriately adjusting the pump power strength to 230 mW. The results suggest that ZnO-NRs@Au-NSs/MWCNTs nanocomposite film could be a promising filter for stable multi-wavelength generations at room temperature.

Switchable Ytterbium Fiber Laser Based on a Symmetrical Long-Period Fiber Grating

In this study, a switchable ytterbium-doped fiber laser based on symmetrical long-period fiber grating (LPFG) is presented. The LPFG is used as a wavelength-selective filter (WSF). Utilizing this WSF, the laser can emit one, two, or multiple stable output beams by adjusting the temperature on the LPFG from 20 °C to 600 °C. In addition, switching is also possible by adjusting the curvature of the LPFG from 0.399 to 0.709 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The symmetrical LPFG was fabricated by combining the cladding shaping with the thermal core expansion techniques by using a CO2-laser LZM-100 glass-processing system. The experimental results show a side-mode suppression ratio (SMSR) of 49 dB and a linewidth of 0.06 nm, within the range from 1038 to 1080 nm. In conclusion, the main achievement of this switchable laser is the high SMSR and stable output for high values of temperature, using a repeatable, simple, easy construction, and cost-effective laser tuning technique.

A 1.0-µm pulsed generation in ytterbium-doped fiber laser with Gadolinium oxide as a saturable absorber

A passively Q-switched and mode-locked laser was successfully demonstrated, the saturable absorber based on Gadolinium oxide was inserted into the ytterbium-doped fiber laser to generate pulses at the 1.0 µm region. By adjusting the pump power of the laser to 146.46 mW, the laser resonator generates a Q-switched pulse at the center wavelength of 1033.84 nm. The maximum achievable pump power of 175.83 mW has produced a 6.93 µs pulse width, 71.43 kHz repetition rate, and 6.23 nJ pulse energy. Later, the incorporation of a 200 m single-mode fiber has triggered a self-started mode-locked laser. The pulse centered at the peak wavelength of 1033.54 nm. The generated pulse was in the range of 146.46 mW to 183.18 mW with a repetition rate of 0.98 MHz. These results proved an outstanding non-linear optical property of Gadolinium oxide, which offers its compatibility with a near-infrared photonics device.

All-normal dispersion ytterbium-doped fiber laser mode locked by nonlinear multimode interference.

We report a mode-locking operation using a nonlinear multimode interference (MMI)-based saturable absorber in an ytterbium-doped fiber laser under an all-normal dispersion configuration. The MMI is observed in a step-index single mode-multimode-single mode (SMS) fiber structure. The intensity and wavelength-dependent transmission of the SMS structure has been studied numerically to understand the Kerr-induced saturable absorber properties of MMI in a step-index fiber. Numerical investigations show that presence of a narrow-band wavelength-tunable spectral filter is necessary for a nonlinear MMI-based saturable absorber to be effective for mode locking. A single-pulse mode-locking operation in the laser is realized at a very low pump power of ${\sim}{56.3}\;{\rm mW}$ at which the laser generates 180 ps duration pulses at ${\sim}{9}\;{\rm MHz}$ repetition rate with measured signal-to-noise ratio of ${\sim}{50}\;{\rm dB}$. This all-fiber integrated laser operates in multi-pulse and noise-like rectangular pulse regimes at increased pump power.

Ultra-high speed random bit generation based on Rayleigh feedback assisted ytterbium-doped random fiber laser

In this paper, we propose an ultra-high speed random bit generator without the time-delay signature based on an ytterbium-doped random fiber laser (YRFL) with Rayleigh scattering feedback. The spectrum of the YRFL has a relatively broad bandwidth (0.35 nm) and the lasing temporal intensity shows random fluctuations without cavity induced time-delay signatures (TDS), which are essential for ultra-high speed random bit generation The chaotic signal and its time-delayed signal sampling at 40 Giga samples per second (GS/s) are converted to digital 8-bit signals. By selecting 5 least significant bits from each 8-bit digital signal and using bitwise exclusive-OR operation, we experimentally achieve 200 Gbps physical random bit generation based on ytterbium-doped random fiber laser with the verified randomness. The combination of broadband emission and free of TDS makes random fiber lasers new promising sources for high performance random bit generation in a simple and compact configuration, which has a great potential in cryptography and secure communication applications.

All-fiber Mach–Zehnder interferometric comb filter based on macrobend single-mode optical fiber for selecting lasing performance in 1-micron region

We report on a new method to select between tunable single- and multi-wavelength switchable lasing performances in continuous-wave (CW) ytterbium-doped fiber laser (YDFL). The wavelength selection and switching techniques are based on the whispering gallery mode (WGM) effect in a Mach–Zehnder interferometric comb-filter formed by bending a standard single-mode fiber (SMF) into a balloon like shape. By incorporating the proposed comb-filter into the laser ring cavity and adjusting the SMF’s bending diameter to control the spectral cavity losses, the single-wavelength lasing was tuned from 1065.26 to 1048.6 nm. Furthermore, by appropriately rotating the polarization controller (PC) cascaded with the filter, the laser can be switched between the dual-and triple-wavelength lasing operations. Two sets of switchable triple-wavelength lasing operations around 1045 nm were obtained with a side-mode suppression ratio (SMSR) of 26.9 dB and 22.4 dB, respectively. To the best of our knowledge, this is the first demonstration of a balloon-like interferometer based comb-filter using a bare bending SMF. The experimental results indicate that the proposed filter provides a promising method to achieve tunable single- or switchable multi-wavelength YDFL.

Molybdenum Carbide Buried in D-Shaped Fibers as a Novel Saturable Absorber Device for Ultrafast Photonics Applications.

Study of nonlinear laser-matter interactions in 2D materials has promoted development of photonics applications. As a typical MXene material, molybdenum carbide (Mo2C) has attracted much attention because of its graphene-like structure. Here, a type of D-shaped fiber (DF)-buried Mo2C saturable absorber (SA) fabricated by magnetron-sputtering deposition (MSD) and sol-gel technique is reported. The Mo2C material was buried between the bottom DF and the upper amorphous silica fabricated by sol-gel technology. Therefore, the DF-based SA effectively solves the problem of material shedding and aging, thus improving the stability and damage threshold of the fiber laser. Application of the SA in erbium-doped fiber laser and stable passive Q-switched operation with a maximum pulse energy of 430.47 nJ is realized. By adjusting the polarization state and pump power, high-power mode-locked pulses are generated with a pulse duration and output power of 199 fs and 54.13 mW, respectively. Further, bound-state soliton pulses are obtained with a pulse width of 312 fs and soliton interval of 1.26 ps for the first time based on MXene materials. Moreover, by application of the SA in ytterbium-doped fiber lasers, a stable dissipative soliton mode-locked pulse is obtained with a pulse width of 23 ps. These results indicate that the DF-based buried Mo2C as a novel SA provides a reliable method for all-fiber and multifunctional high-power ultrafast laser.

High-pulse-energy multiphoton imaging of neurons and oligodendrocytes in deep murine brain with a fiber laser

Here we demonstrate high-pulse-energy multiphoton microscopy (MPM) for intravital imaging of neurons and oligodendrocytes in the murine brain. Pulses with an order of magnitude higher energy (~ 10 nJ) were employed from a ytterbium doped fiber laser source at a 1-MHz repetition rate, as compared to the standard 80-MHz Ti:Sapphire laser. Intravital imaging was performed on mice expressing common fluorescent proteins, including green (GFP) and yellow fluorescent proteins (YFP), and TagRFPt. One fifth of the average power could be used for superior depths of MPM imaging, as compared to the Ti:Sapphire laser: A depth of ~ 860 µm was obtained by imaging the Thy1-YFP brain in vivo with 6.5 mW, and cortical myelin as deep as 400 µm ex vivo by intrinsic third-harmonic generation using 50 mW. The substantially higher pulse energy enables novel regimes of photophysics to be exploited for microscopic imaging. The limitation from higher order phototoxicity is also discussed.

Stable evanescent wave mode-locked laser based on a photonic-crystal-fiber-induced Mach-Zehnder filter as a gain-tilt equalizer.

In this paper, a switchable multichannel ytterbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) has been experimentally demonstrated. The MZI is fabricated by splicing a short piece of nonlinear photonic-crystal fiber (NLPCF) between two segments of a single-mode fiber. MZI-based NLPCF gathering with the intracavity birefringence polarization controller offers functions as both the selective comb filter and the mode locker. The laser can emit a single, dual, triple, or quadruple channel that can be varied in the spectral span around1030-1050 nm by only adjusting the pump power or polarization state. A stable evanescent wave, picosecond mode-locking generation with variable repetition rate (24.5 to 18.23 MHz and 34.64 MHz) has been realized via only inserting the polarization controller and adjusting its state inside the cavity. To the best of the authors' knowledge, this the first demonstration of a passive filter based on a NLPCF-MZ interferometer to generate switchable mode-locked pulses delivered from a single laser oscillator.

Narrow-linewidth high-efficiency single-frequency ytterbium-doped fiber laser with highly linear polarization at 1064 nm.

We present a linearly polarized single-longitudinal-mode (SLM) ytterbium-doped fiber laser with a polarization extinction ratio (PER) of over 35 dB and a narrow linewidth of less than 4.5 kHz. The very high PER is obtained by utilizing the polarization evolution effect at the optical fiber and the high-performance polarizing beam splitter. The SLM is achieved by using a segment of polarization-maintaining ytterbium-doped fiber as a narrowband filter. In addition, a high optical signal-to-noise ratio of 50 dB and a good slope efficiency of 60.5% are achieved. Using an ytterbium-doped fiber amplifier, a linearly polarized SLM laser system with a high power of over 2.5 W is demonstrated at 1064 nm.

Numerical comparison of pumping methods for high-power Er/Yb-codoped fiber lasers

The amplified spontaneous emission (ASE) in the Yb band and thermal damage are the main obstacles to the power scaling of high-power Er/Yb-codoped fiber lasers (EYDFLs) and amplifiers. In this paper, three popular pumping methods, i.e., off-peak pumping, core pumping with ytterbium-doped fiber laser, and cascade co-pumping, the conquering of these obstacles is investigated and compared based on numerical simulation. The influence of the pump wavelength is systematically analyzed. Performances, including thermal effects, optimal fiber length, and maximum applicable pump power and expectable output power are compared for EYDFLs with these pumping methods. The results show that off-peak pumping and core pumping can alleviate the Yb ASE problem and increase the achievable output power to some extent. We believe this improvement fundamentally originated from the lower absorption coefficient that alleviates the bottlenecking effect. The Yb ASE problem is still inevitable for these two methods, whereas the cascade co-pumping method can completely extricate a EYDFL from the restrict of this problem and push the power to the thermal damaged limitation.

1.3 kW Continuous Wave Output Power of Ytterbium-Doped Large-Core Fiber Laser

A very efficient key cladding-pumped trivalent ytterbium (Yb3+) doped fiber laser has been developed. The whole fiber laser system generated 1.3 kW of continuous-wave (CW) maximum output power with very high efficiency at 1.1 μm and near the diffraction beam quality (M2 = 1.27). The measure slop efficiency is 76% and shows no limit of temperature and nonlinear effects. In a preliminary proof of principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped fiber laser with a diameter core and a numerical aperture of 0.09 has been demonstrated. When pumped to the ends of both fibers, they have strong beam quality and display no signs of rolling over even at the highest output power. The large core ytterbium doped fiber laser (YDFL’s) is end pumped with diodes stack source through opposite ends of fiber. This design of fiber can delivers maximum output power which is restricted mostly by accessible pump power.

Passively mode-locked laser at 1μm region based on tungsten trioxide (WO3) saturable absorber

Stable and efficient mode-locked operation at 1065 nm was demonstrated using tungsten trioxide (WO3) thin film as a saturable absorber (SA). The WO3 thin film composite was prepared by a low cost and simple method and it has a modulation depth of 20 %. As the SA film was inserted into a Ytterbium-doped fiber laser (YDFL) cavity. The mode-locked laser operated in normal dispersion regime and generated pulses at 1065 nm with 3-dB bandwidth of 1 nm. The YDFL operated at fixed repetition rate of 10 MHz with pulse width of 1.67 ps. The maximum average output power of 21.64 mW and pulse energy of 2.16 nJ were recorded at a pump power of 162 mW.

Simulation for efficiency improvement of a thuilium Q-switched ytterbium-doped all-fiber laser.

We theoretically explore the mechanism in a thulium Q-switched ytterbium-doped all-fiber fiber laser using a set of rate equations to model the correlations between the photons and the five energy levels of thulium involved in the Q switching mechanism. We demonstrate that by coupling with a gain-switched resonator, the Q-switched laser is stabilized up to the maximum pulsing rate that is limited by the lifetime of level 3H5. To the best of our knowledge, this is the first study that revealed that level 3H5 plays an essential role in reinitialization, achieving sequential pulses, and limiting the maximum repetition rate.

Single-frequency all-polarization-maintaining ytterbium-doped bidirectional fiber laser.

We reported an all-polarization-maintaining single-frequency ytterbium-doped bidirectional fiber laser for the first time, to the best of our knowledge. Single-frequency operation was achieved by a stable dynamic grating in the active fiber of a proper length owing to the bidirectional operation of the laser. The fiber laser possesses a linewidth of 7.43 kHz, a slope efficiency of 47.9%, and a great long-term stability.

Sub-nanosecond gain-switched Ytterbium-doped fiber laser pumped by 1030 nm dissipative soliton resonance mode-locked fiber laser

In this work we report on a tandem pumped gain-switched Yb-doped fiber laser. We used an amplified dissipative soliton resonance mode-locked fiber laser with the wavelength of 1030 nm as a source of high repetition rate pulsed pump, incorporated with a CW diode laser at the wavelength of 976 nm in hybrid pump scheme. Sub-nanosecond narrow line-width gain-switched pulses with peak power of 10 kW at 1064 nm have been achieved. The line-width of the gain-switched laser is less than 0.06 nm and the repetition rate is 683 kHz.