Ytterbium-doped Fiber Research Articles

Passive mode-locking and Q-switching of ytterbium-doped fiber lasers using Cr2S3 saturable absorbers

Passive mode-locking and Q-switching of ytterbium-doped fiber lasers using Cr2S3 saturable absorbers

Dynamics of h-shape narrow bandwidth dissipative soliton in Yb-doped fiber laser

We demonstrate a narrow bandwidth mode-locked ytterbium-doped fiber laser based on the carboxyl-functionalized graphene oxide (GO-COOH). In the combination of GO-COOH and intracavity filtering effects, the narrow bandwidth spectrum exhibits an h-shape at 1060.76 nm central wavelength with a 3-dB bandwidth of 0.47 nm. Furthermore, the 3-dB bandwidth can be compressed to 0.049 nm by adjusting the polarization controller. The formation of h-shape dissipative soliton has been investigated by applying the dispersive Fourier transformation and numerical simulation. The h-shape narrow bandwidth dissipative soliton we demonstrated provides a new insight for investigating the evolution dynamics of solitons with special shapes.

21 kW, 166 fs pulses from passive mode-locked ytterbium-doped fiber laser employing Bi2O2Te nanosheets as saturable absorber in 1 μm

21 kW, 166 fs pulses from passive mode-locked ytterbium-doped fiber laser employing Bi2O2Te nanosheets as saturable absorber in 1 μm

Switchable mode-locked ytterbium-doped fiber laser based on macrobending loss tuning of figure-eight knot fiber structure

Switchable mode-locked ytterbium-doped fiber laser based on macrobending loss tuning of figure-eight knot fiber structure

Real-time observation of soliton pulsation and explosion in an Yb-doped fiber laser

Nonlinear dissipative systems support pulsating solutions and exhibit many interesting dynamic behaviors. Here, we report various soliton pulsations and explosions in an all-normal dispersion ytterbium-doped fiber laser by utilizing the dispersive Fourier transform technique. By the different soliton dynamics, these phenomena can be classified into single-soliton pulsation and explosion, dual-soliton synchronous and asynchronous pulsation, as well as dual-soliton asynchronous explosion. Solitons exhibit identical periodic fluctuations in the synchronous pulsation while showing the anti-phase behavior in asynchronous pulsation. The dual-soliton asynchronous pulsation might be related to the periodic modulation of the polarization state of solitons. As for the dual-soliton asynchronous explosion, it can be regarded as the asynchronously triggered transient solitons containing periodic explosion through the gain-mediated soliton interactions. These findings may provide new insights into complex dynamics in the field of ultrafast lasers.

20 Watt single-frequency 509 nm laser by single-pass second harmonic generation in an LBO crystal

High power 509 nm continuous-wave (CW) lasers have important applications in science and communication. Here we demonstrate a robust high-power single-frequency 509 nm laser system based on nonlinear phase demodulation technique and single-pass second harmonic generation (SHG) configuration. In experiments, the single-frequency fundamental wave at 1018 nm was linewidth-broadened by an electro-optical modulator and then amplified to 207 W in a ytterbium-doped fiber amplifier. In subsequent single-pass SHG stage, over 20 W CW single-frequency 509 nm laser was generated in a LiB3O5 crystal with a SHG efficiency of 9.7%. To the best of our knowledge, this is the highest reported power for CW single-frequency 509 nm laser, which could be used for advanced underwater optical communication and preparation of cesium Rydberg state.

108 fs high-power mode locked double-clad ytterbium-doped fiber laser using FePS3 saturable absorber

108 fs high-power mode locked double-clad ytterbium-doped fiber laser using FePS3 saturable absorber

Sensitivity Improvements for Picosecond Ultrasonic Thickness Measurements in Gold and Tungsten Nanoscale Films

Picosecond ultrasonics, as a nondestructive and noncontact method, can be employed for nanoscale metallic film thickness measurements. The sensitivity of the system, which determines the measurement precision and practicability of this technique, is often limited by the weak intensity of the ultrasonic signal. To solve this problem, we investigate the distinct mechanisms involved in picosecond ultrasonic thickness measurement for two types of metals, namely tungsten (W) and gold (Au). For thickness measurement in W films, theory and simulation show that optimizing the pump and probe laser wavelengths, which determine the intensity and shape of the ultrasonic signal, is critical to improving measurement sensitivity, while for Au film measurements, where acoustic-induced beam distortion is dominant, the signal intensity can be optimized by selecting an appropriate aperture size and sample position. The above approaches are validated in experiments. A dual-wavelength pump–probe system is constructed based on a passively mode-locked ytterbium-doped fiber laser. The smoothing method and multipeak Gaussian fitting are employed for the extraction of ultrasonic time-of-flight. Subnanometer measurement precision is achieved in a series of W and Au films with thicknesses of 43–750 nm. This work can be applied to various high-precision, noncontact measurements of metal film thickness in the semiconductor industry.

Brief Review of Recent Developments in Fiber Lasers

This review covers the recent achievements in high-power rare earth (RE)-doped fiber lasers, Raman fiber lasers, and Brillouin fiber lasers. RE-doped fiber lasers have many applications such as laser cutting, laser welding, laser cleaning, and laser precision processing. They operate in several wavelength ranges including 1050–1120 nm (ytterbium-doped fiber lasers), 1530–1590 nm (erbium- and erbium–ytterbium-doped fiber lasers), and 1900–2100 nm (thulium- and holmium-doped fiber lasers). White spaces in the wavelength spectrum, where no RE-doped fiber lasers are available, can be covered by Raman lasers. The heat power generated inside the laser active medium due to the quantum defect degrades the performance of the laser causing, for example, transverse-mode instability and thermal lensing. It can even cause catastrophic fiber damage. Different approaches permitting the mitigation of the heat generation process are considered in this review. Brillouin fiber lasers, especially multiwavelength Brillouin fiber lasers, have several important applications including optical communication, microwave generation, and temperature sensing. Recent progress in Brillouin fiber lasers is considered in this review.

Linewidth compression of a single longitudinal mode ytterbium-doped fiber laser based on femtosecond laser fabricated fiber Bragg gratings.

We demonstrate a single longitudinal mode distributed Bragg reflection (DBR) fiber laser by directly fabricating fiber Bragg gratings (FBGs) on an ytterbium-doped fiber (YDF) using a femtosecond laser. A simple optical self-injection feedback method was used to effectively compress the linewidth and reduce relative intensity noise (RIN) of a single longitudinal mode DBR fiber laser. Further, we investigated the effect of self-injection feedback cavity length and reflectivity on linewidth compression and determined that the linewidth tends to decrease with the increase of the external cavity photon lifetime. By a self-injection feedback, the laser linewidth was compressed from 31.8kHz to 1.4kHz. Meanwhile, the relaxation oscillation peak from -103.2d B/H z at 1.51MHz was suppressed to -122.3d B/H z at 0.16MHz. This low-noise narrow linewidth single longitudinal mode fiber laser is expected to be a promising candidate for applications such as active detection of neutral atmosphere and distributed fiber sensing.

Investigations of a 1018 nm gain-switched Yb-doped fiber oscillator.

In this paper, we investigate a 1018nm gain-switched ytterbium-doped fiber oscillator at a low repetition rate in terms of theory and experiment. Theoretically, a numerical model applicable to a 1018nm gain-switched ytterbium-doped fiber laser was established. The influence of the pump peak power and active fiber lengths on the 1018nm gain-switched ytterbium-doped fiber laser was numerically simulated. Experimentally, a compact 1018nm all-fiber-structured pulsed laser oscillator is constructed, in which a pulse width of 110ns and a single-pulse energy of 0.1mJ were obtained. Moreover, the experimental results are in agreement with the numerical simulation ones. To the best of our knowledge, this is the first time that gain-switching technology has been applied to 1018nm fiber lasers to generate nanosecond pulsed lasers. The model and experimental results can provide a reference for the engineering design of the same type of low repetition rate fiber lasers below the kilohertz level.

Theoretical study of filtered and amplified PRBS phase modulation for SBS suppression in a 2.5 kW, 10 GHz monolithic fiber amplifier

We report a theoretical and experimental study on stimulated Brillouin scattering (SBS) suppression in a monolithic fiber amplifier with filtered and amplified pseudo-random binary sequence (PRBS) phase modulation. Theoretically, we use a time-dependent three-wave coupled nonlinear system considering both active fiber and passive fiber to describe the acoustic phonon, laser, and Stokes characteristics in a fiber amplifier. The SBS threshold power after filtered PRBS phase modulation is numerically evaluated to obtain the optimal parameters, and the time-averaged distributions of the counter-pump power, laser power, and Stokes power at different positions along the fiber length of the fiber system are simulated. Also, we established a four-stage fiber amplifier system to verify our theory. The configuration of the fiber amplifier system includes a filtered and amplified PRBS phase-modulated single-frequency fiber laser, a three-stage pre-amplifier, and a counter-pumping main stage, subsequently. 2.5 kW output power with an FWHM linewidth of 9.63 GHz is accomplished by a domestic ytterbium-doped double-clad fiber with core/cladding diameters of 20.2/400 µm. The reflectivity of the main stage is 0.049‰ at the maximum output power, which indicates the proposed architecture is under the SBS threshold. The experiments verify the accuracy of the theoretical model, which provides a reliable reference for evaluating the SBS suppression capability of the high-power narrow-linewidth fiber amplifier phase modulated by the filtered and amplified PRBS signal.

Four bits data sequence generators based ytterbium doped fiber amplifiers for upgrading maximum Q factor and minimum BER

Abstract We have simulated four bits data sequence generators based ytterbium-doped fiber amplifiers for upgrading max. Q factor and min. BER. Optical power variations against time duration after fiber cable length of 250 km with the bits sequence generators of 0101, 1000, and 1010 respectively are simulated. As well as the electrical power/total received power variations against frequency after photodetector receiver with the bits sequence generators of 0101, 1000, and 1010 respectively are discussed in details. Moreover, the signal power amplitude level with the time period duration after photodetector receiver/3R regenerator with the bits sequence generators of 0101, 1000, and 1010 respectively are clarified to show the max. Q factor and min. BER values for each case.

Novel Bidirectional Output Ytterbium-Doped High Power Fiber Lasers: From Continuous to Quasi-Continuous.

Traditional ytterbium-doped high-power fiber lasers generally use a unidirectional output structure. To reduce the cost and improve the efficiency of the fiber laser, we propose a bidirectional output fiber laser (BOFL). The BOFL has many advantages over that of the traditional unidirectional output fiber laser (UOFL) and has a wide application in the industrial field. In theory, the model of the BOFL is established, and a comparison of the nonlinear effect in the traditional UOFL and the BOFL is studied. Experimentally, high-power continuous wave (CW) and quasi-continuous wave (QCW) BOFLs are demonstrated. In the continuous laser, we first combine the BOFL with the oscillating amplifying integrated structure, and a near-single-mode bidirectional 2 × 4 kW output with a total power of above 8 kW is demonstrated. Then, with the simple BOFL, a CW bidirectional 2 × 5 kW output with a total power of above 10 kW is demonstrated. By means of pump source modulation, a QCW BOFL is developed, and the output of a near-single mode QCW laser with a peak output of 2 × 4.5 kW with a total peak power of more than 9 kW is realized. Both CW and QCW output BOFL are the highest powers reported at present.

40 W of supercontinuum generated by a self-pulsed pump-sharing oscillator-amplifier.

We demonstrate an all-fiber supercontinuum (SC) source delivering up to 40W of average power ranging from 750to 2200nm. The laser source is based on a self-Q-switched pump-sharing oscillator-amplifier. The self-Q-switched master oscillator generates giant pulses, amplified in the high-power stage. Finally, a passive fiber acts as a nonlinear stage, improving the spectrum flatness as well as the spectral broadening. To the best of our knowledge, this is the first time that a pump-sharing oscillator-amplifier is used for SC generation and is based on the use of a submeter Ytterbium-doped fiber length inside the oscillator.

1 MHz, 273 W average power Ytterbium-doped rod-type fiber chirped pulse amplification system

Ytterbium-doped ultrafast fiber lasers are widely used in scientific research, industrial processing, medical diagnosis, and other fields due to their excellent beam quality and high power output. The larger mode area allows the fiber to transmit higher peak-pulse power. The commercial rod-type Ytterbium-doped fiber with a core diameter of 85 μm, produced by NKT in Denmark, can produce ultra-short pulses on the order of 100 watts and 100 microjoules. Based on this rod-type fiber, we construct a chirped-pulse amplification (CPA) system in which the high-efficiency transmission gratings and temperature-tunable chirped fiber Bragg grating (CFBG) are used to compensate for dispersion. We investigate the effect of power input on the amplified power and pulse compression quality, and find that higher power input slows down the gain saturation and improves amplification efficiency. At power inputs of 20 W and 30 W, we obtain power outputs of 305 W and 323 W respectively, with an amplification efficiency of about 80%. To reduce the accumulation of nonlinear phase shift, we use circular polarization amplification. At low power outputs (less than 160 W), the effect of nonlinear phase accumulation on the compressed pulse is negligible, and the increase in power input increases the amplification efficiency. When the power output exceeds 200 W, the cumulative increase of nonlinear phase shift reduces the pulse compression quality, which implies that the input power is appropriately reduced to the power range between 5 W and 20 W. With a power input of 20 W and pump power of 429 W, the power output can reach 305 W. After pulse is compressed by using a diffraction-grating pair, this rod-type fiber CPA system can deliver 1 MHz, 264 fs pulses with 273 W in average power. These results provide an important experimental basis for optimizing the performance of high-power and high-energy ultrafast fiber lasers.

Gain-Managed Nonlinear Amplification in Erbium-Doped Fibers

This experiment aimed to characterize Gain-Managed Nonlinear amplification (GMN) in Erbium-doped fibers. This effect has so far been presented in Ytterbium-doped fibers and only simulated on Erbium-doped fibers.

Suppression effect of auxiliary laser on stimulated Raman scattering effect of high-power Yb-doped fiber laser amplifier

<sec>A novel technique to suppress the stimulated Raman scattering (SRS) effect in high-power ytterbium-doped fiber amplifier is proposed and theoretically investigated by introducing an auxiliary laser to manipulate the gain distribution in the amplifier.</sec><sec>By injecting an auxiliary laser with shorter wavelength than the signal into the amplifier, the auxiliary laser, owing to its larger stimulated emission cross-section, initially extracts a significant portion of the laser gain. At this point, the gain of the longer-wavelength signal laser is suppressed to a certain extent. As the pump power is depleted in the rear segment of the gain fiber, the amplified auxiliary laser, which has larger absorption cross-section than the signal, is gradually absorbed by the active fiber and transfers its power to the signal laser. This process enhances the gain of the long-wavelength signal laser, enabling it to be rapidly amplified at the end of the amplifier. Compared with the amplification of the singular signal laser, the introduction of an extra auxiliary laser shifts the high-gain region of the signal laser to the rear portion of the amplifier, thereby reducing the effective length and alleviating the interaction strength between the signal laser and Stokes wave, in order to obtain a higher SRS threshold.</sec><sec>The SRS threshold of a 20 μm/400 μm fiber amplifier is investigated by using numerical simulation under different wavelengths of the auxiliary laser and different power ratios of the signal laser to auxiliary laser. The results indicate that incorporating an auxiliary laser with an appropriate wavelength and power level can significantly reduce the interaction strength between the signal and Stokes wave, thereby enhancing the SRS threshold of the amplifier efficiently. Specifically, in a 1080 nm fiber amplifier utilizing a 20 μm/400 μm ytterbium-doped large mode area fiber, if the total power of the 1080 nm signal and 1040 nm auxiliary laser is set to 200 W, while with a power ratio of 1:25, the SRS threshold increasing from 3.14 kW (singular signal laser) to 8.42 kW can be anticipated. Moreover, based on the auxiliary laser amplification technique that suppresses the SRS effect, the output power enhancement of fiber lasers with the structure of master oscillator power amplifier (MOPA) is also analyzed. This technical solution is relatively straightforward to implement and can be seamlessly integrated with other techniques aimed at reducing the SRS effect, which is promising to promote further power scaling of all-fiber amplifier.</sec>

Low differential phase noise ytterbium-doped fiber amplifier system for coherent beam combination

A two-channel ytterbium-doped fiber amplifier system with active phase-locking reaches a differential phase noise of only 40 mrad (X/160) at 200-W channel power. Frequencies above 30 Hz did not require noise suppression, thus simplifying advanced beam-shaping through coherent beam combination.

2 × 3 kW bidirectional output fiber oscillator employing spindle-shaped ytterbium-doped fiber

2 × 3 kW bidirectional output fiber oscillator employing spindle-shaped ytterbium-doped fiber