Mode-locked Soliton Fiber Laser Research Articles

Nanosized titanium dioxide saturable absorber for soliton mode-locked thulium-doped fiber laser

We demonstrate the potential of nanosized titanium dioxide (TiO2) in forming ultrashort pulses using a ring cavity thulium-doped fiber laser. A TiO2 polymer composite was transferred onto a microfiber through a spin coating technique to act as a light-absorbing material, saturable absorber (SA). The nonlinear transmission characteristics of this TiO2-SA exhibited 3.8% modulation depth and 17 MW/cm2 saturation intensity at 1.92 µm wavelength. At 1587 mW pump power, the central wavelength, average output power, pulse duration, peak power, and pulse energy were 1925.6 nm, 126.8 mW, 1.5 ps, 6.45 kW, and 11 nJ, respectively. The fabricated TiO2-SA displayed a wide pump power range of fundamental mode-locking at 11.53 MHz without any sign of laser-induced damage threshold or pulse breaking effect. This work has shown the potential use of nanosized TiO2-SA for fabricating broadband nonlinear photonic devices.

Wavelength switchable dissipative soliton mode-locked fiber laser based on Lyot filter

We propose a wavelength switchable mode-locked fiber laser based on a homemade fiber Lyot filter that is comprised of 18-cm-long polarization maintain fiber, polarizer, and polarization controller. The generation of mode-locked operation originates from the principle of NPR by the specific setup of PC + ISO + PMF and polarizer. Due to the Lyot filter, the central wavelength of mode-locked laser can be switched between 1036.6 nm and 1050.5 nm by modulating the polarization state of polarization controller and pump power. The switchable wavelength intervals were about 13.9 nm. Such a switchable mode-locked fiber laser has various potential applications in pulse fiber laser system.

Ti3AlC2 MAX phase thin film as saturable absorber for generating soliton mode-locked fiber laser

We have successfully realized the soliton pulse in a Erbium-doped fiber laser (EDFL) cavity, which was mode-locked by a Titanium Aluminum Carbide (Ti3AlC2) MAX phase based saturable absorber (SA). The SA was obtained by embedding the Ti3AlC2 compound into polyvinyl alcohol (PVA) in form of thin film. The prepared Ti3AlC2 film has a modulation depth of 2% and it was added into an EDFL cavity to generate a stable soliton pulse operating at 1559.7 nm wavelength. The mode-locking operation was successfully observed within a pump power range from 66.3 to 97.6 mW. It has maintained the repetition rate and pulse width at 1.8 MHz and 5.02 ps, respectively. When the pump power reached 97.6 mW, the maximum average output power, pulse energy and peak power were measured to be 8.34 mW, 4.46 nJ and 0.89 kW, respectively. These results unveil the potential of Ti3AlC2 MAX-phase material for implementation as practical and cost-effective SAs.

Optimal conditions for self-starting of soliton mode-locked fiber lasers with a saturable absorber.

With the recently developed single-shot time-stretch dispersive Fourier transform technique, we investigate the buildup process of an all-polarization-maintaining soliton mode-locked fiber laser. Considering the multi-pulse competitions and the evolution of the survived pulse, we find an optimal range of intra-cavity energy for self-starting related to the saturation energy of the employed saturable absorber. Under the conditions, one dominant pulse can build up quickly against the others, and it finally drives to single-pulse operation. The conclusions drawn here hold for other soliton mode-locked lasers.

Soliton mode-locked fiber laser for distance measurements.

Absolute distance measurement is crucial for many applications including metrology, large-scale manufacturing, range finding, and surveying. In this paper, a novel, to the best of our knowledge, technique is introduced for precise distance measurement by including the distance under measurement in a soliton mode-locked fiber ring laser (SMFRL). Consequently, the measured distance can be calculated from the change in the repetition rate of the emitted pulses due to the laser cavity length change. The SMFRL technique is implemented here to measure distances up to 57.4 m with precision of less than 9 µm. Therefore, we believe that the SMRFL technique provides a relatively simple and precise technique to measure relatively long distances.

Ultrafast soliton mode-locked fiber laser at 1560 nm based on Znq2 as a saturable absorber.

A mode-locked fiber laser was developed by using bis(8-hydroxyquinoline) zinc (Znq2) as a saturable absorber (SA). Znq2 is an organic metal chelate with several advantages such as good saturable absorption, relatively high damage threshold, and an easy, low-cost, and simple fabrication process. The developed SA based on Znq2 has a linear absorption (at 1560 nm), modulation depth, and saturation intensity of 1.2 dB, 16.6 %, and 95MW/cm2, respectively. The laser cavity produced a very stable soliton mode-locking operation at 1560.6 nm with pulse duration, repetition rate, and SNR of 1.46 ps, 3.5 MHz, and 60.6 dB, respectively. This work is the first, to the best of our knowledge, to report Znq2 as a mode locker.

Stabilization of a Harmonic Mode-Locking by Shifting the Carrier Frequency

Harmonically mode-locked soliton fiber lasers have been intensively investigated in recent years due to their wide range of applications. Drawback of these lasers is relatively large timing jitter which is significantly higher than the timing jitter in lasers operating at fundamental frequency. We report the stabilizing frequency shift effect in harmonic mode-locking ring soliton fiber laser that is studied theoretically and numerically. It is known that a harmonic mode-locking regime in a fiber laser occurs due to interpulse repulsion, which leads to a uniform distribution of pulses in the cavity. We demonstrate that the frequency shift contributes to an increase in the hardness of interpulse interactions and can led to stabilization of the periodic arrangement of pulses. The experiment carried out confirms the theoretical predictions and the results of numerical simulation.

Two key frontier issues on picosecond pulses generated by mode-locked fiber lasers

Narrowband dissipative soliton mode-locked fiber lasers can produce transform-limited picosecond pulses. Unfortunately, due to the limitation of allowable nonlinear phase shift for the intracavity pulse, the repetition rate of the pulses generated by such lasers cannot be reduced by increasing the cavity length; the pulse energy is only below 0.1 nJ. These seriously restrict the practical application of such picosecond pulsed fiber lasers. In this paper, we propose a method that allows the cavity length to be increased to reduce the repetition rate of the narrowband dissipative soliton picosecond fiber laser pulses by extracting the pulse energy out of the cavity with a coupler to suppress the accumulation of nonlinear phase shift of the intracavity pulses. Using this method, the laser repetition rate was successfully reduced from 35.2 MHz to 1.77 MHz, and the pulse time-frequency characteristics remained unchanged. We also propose a method to suppress spectral broadening in picosecond pulse fiber amplification based on inter-stage FBG notch filtering. By simply using the inter-stage notch filter, the output pulse spectrum width after the first-stage fiber amplifier can be narrowed, allowing the second-stage fiber amplifier to further increase the pulse energy, and also, the pulse can be reshaped to be nearly Gaussian-shaped, allowing the second-stage fiber amplifier to increase the pulse energy higher by using the Gaussian pulse characteristics of the smaller spectral broadening slope. Using this method, on the premise of keeping the RMS spectral width within 0.4 nm, after a 10 ps pulse passes through a standard single-mode fiber amplifier, the pulse energy can be increased from 0.2 nJ to more than 10 nJ.

Investigation on soliton mode-locked fiber laser with PbSe quantum dot as gain medium by numerical simulation

A soliton mode-locked lead selenide (PbSe) quantum-dot-doped fiber laser (QDFL) is proposed and investigated by numerical simulation for the first time. Buildup dynamics in time and spectral domains are studied. Output properties starting from Gaussian and noise-like signals are characterized. The optimum quantum-dot-doped fiber lengths are revealed under various PbSe quantum dot doping concentrations. The evolutions of the pulse and spectrum in the resonator at the steady state are discussed. The results obtained facilitate the understanding of the operating principle of QDFL for solving emission wavelength problem.

Pump-controlled wavelength switchable dissipative soliton mode-locked Yb-doped fiber laser using a 45° tilted fiber grating

We demonstrate a pump-controlled wavelength switchable Yb-doped fiber laser (YDFL) by nonlinear polarization rotation (NPR) for the first time. The polarizer replaced by a 45° tilted fiber grating (45°-TFG) combines with a section of polarization maintaining fiber (PMF) to form a fiber-based birefringent filter. Stable dissipative soliton (DS) with center wavelength of 1068.39 nm is generated under the mode-locked threshold of 277 mW. The operating wavelength switching between 1046.51 nm and 1067.90 nm can be realized via increasing the pump power simply while keeping the polarization controllers (PCs) in a fixed state. The laser maintains stable mode-locking operation at each wavelength, which can be regarded as a type of multi-wavelength ultrafast light source with precise control and integration potential.

Stable soliton pulse generation from a SnSe2-based mode-locked fiber laser

Based on an as-prepared high-quality tin diselenide-polyvinyl alcohol (SnSe2-PVA) film, a stable passively erbium-doped (Er-doped) soliton mode-locked fiber laser at 1561.38 nm was realized. The output performances were investigated experimentally. At the pump power of 310 mW, the shortest pulse duration of 1.197 ps was obtained with a fundamental frequency of 3.45 MHz, corresponding to the peak power of 317 W, which is much higher than previous reports of SnSe2 mode-locked fiber lasers. The results show that SnSe2 can offer an exciting platform for stable high peak power and ultrashort pulse generation.

Few-layer silicene nanosheets as saturable absorber for subpicosecond pulse generation in all-fiber laser

Two-dimensional silicene nanosheets is an emerging material in many fields. However, there is a lack of research on nonlinear optical applications of silicene nanosheets so far. Here, we demonstrate a subpicosecond soliton mode-locked erbium-doped fiber laser using microfiber-based silicene nanosheets as a saturable absorber for the first time, to the best of our knowledge. Few-layer silicene nanosheets, which were prepared by liquid-phase exfoliation method, have a modulation depth is 20% and the saturation intensity is 5.78 MW/cm2. Stable soliton pulses were generated at 1531.48 nm with a 3-dB bandwidth of 2.84 nm, a pulse duration of 937 fs, and a time-bandwidth product of 0.34. Our results indicate that few-layer silicene nanosheets could be used as an excellent photonic device for short-pulse laser, and promote the applications of silicene-based nonlinear photonics.

Soliton Mode-Locked Large-Mode-Area Tm-Doped Fiber Oscillator

We report a passively mode-locked fiber oscillator based on thulium-doped large-mode-area (LMA) fiber. Reliably mode-locking soliton operation can be readily achieved after the suppression of the higher-order modes by using mode field adapters in combination with coiling fiber method. The laser delivers 600-fs level pulses at $2~\mu \text{m}$ with an average power of up to 243 mW and a repetition rate of ~53.7 MHz. The output corresponds to a maximum pulse energy of 4.5 nJ, >5 times larger than that of a similar homemade mode-locked Tm laser with the LMA fibers replaced by single mode fibers, coinciding with theoretical prediction. The successful demonstration of our soliton mode-locked LMA fiber laser at $2~\mu \text{m}$ offers another strategy for high performance ultrafast fiber sources at mid-infrared region.

基于非线性放大环镜和Lyot滤波器的多波长与耗散孤子锁模态开关型掺铥光纤激光器

基于非线性放大环镜和Lyot滤波器的多波长与耗散孤子锁模态开关型掺铥光纤激光器

Experimental study on dissipative soliton fiber laser with dynamically tunable polarization trajectory

In this paper, a dissipative soliton mode-locked fiber laser is established based on carbon nanotube in order to study the polarization dynamics of dissipative soliton by using a commercial polarimeter. Under the pump power of 160 mW, stable dissipatives soliton are observed to have a limited cycle polarization trajectory shown on Poincare sphere, indicating the periodic modulation of anisotropy in cavity. The stable dissipative soliton possesses a high signal noise ratio of 57.7 dB at fundamental frequency. Moreover, the fast oscillation of state of polarization leads to a lower degree of polarization (DOP). In addition, the polarization controllers are employed to compensate for the birefringence in the cavity to adjust the ratio between cavity length and birefringence length. As a result, we can observe the polarization evolving from the polarization locked attractor to the limited cycle attractor by adjusting polarization controllers. It is noted that this dynamic polarization trajectory can be manually controlled. By comparing polarization attractor with DOP, it is clear that the size of trajectory shown on Poincare sphere is inversely proportional to DOP. We expect our work to be conducible to studying the physics in lasers and creating a new type of polarization tunable laser.

Real-time transition dynamics between multi-pulsing states in a mode-locked fiber laser

We experimentally studied the transition dynamics between consecutive multi-pulsing states, specifically the build-up and annihilation of soliton pulses between a double pulsing and a three-pulse state, utilizing the dispersive Fourier transform technique. The birth of an additional pulse in a mode-locked soliton fiber laser in a multi-pulsing regime arises from a dispersive wave-induced narrow-band pulse that experiences strong intensity fluctuations, while the other soliton pulses maintain their shapes. During the decaying process to a double pulsing state, it is observed that all the pulses undergo a unique breathing behavior before settling into a steady state.

Soliton mode-locked Er-doped fiber laser by using Alq3 saturable absorber

This paper demonstrated a mode-locked fiber laser based on Alq3 as passive saturable absorber (SA) in a simple all-fiber Erbium-doped fiber laser (EDFL) cavity. By incorporating Alq3 into the fiber laser cavity, a stable mode-locked pulsing was achieved. The laser pulses have a pulse width of 1.6 ps with a soliton spectrum centered at 1561.5 nm. The pulses train exhibits a very stable output with a high signal to noise ratio (SNR) of 41.5 dB. The results suggest that Alq3 is a promising nonlinear optical material, which could be as an ultra-fast mode-locker. To the best of our knowledge, this is the first demonstration of Alq3 as a mode-locker in an EDFL setup.

The use of polarization-imbalanced NOLM to improve the quality of the spectrum compression

In the present work, we investigated the polarization-imbalanced non-linear optical loop mirror (NOLM) for compressing the soliton spectrum as well as removing the sidebands. In the passive mode-locked soliton fiber laser, the spectra of solitons are usually accompanied with dispersive waves that can form spectral sidebands. The sidebands are the result of a constructive interference between the soliton and dispersive waves that take place at frequencies in which the phase difference is 2π. These sidebands may contain a significant part of the energy of the output spectrum, it is important first clean the spectrum by removing the sidebands and then compress the spectrum to have an optimal soliton profile. Our NOLM consists of a nearly symmetrical coupler with a 51/49 coupling ratio, and a fiber loop which consists of two 50-m pieces of SMF-28 fibers twisted in opposite directions. The maximum transmission of the NOLM at high power was 34%. At the NOLM output we reached a spectral compression of more than 50% for different values of input power. Although the sidebands around 1555 nm and 1570 nm were totally cleaned, nearly 5% of the sidebands were remaining around 1560 nm and 1567 nm. In order to get stronger spectral compression, the signal at the NOLM output was first amplified then sent into 1 km of SMF-28. For minimum input power the full width at half maximum (FWHM) bandwidth of the spectrum decreased from 5.5 nm to 0.67 nm. For higher input power the FWHM decreased from 4.23 nm to 0.59 nm.

Dual-wavelength mode-locked erbium-doped fiber laser based on tin disulfide thin film as saturable absorber

The use of tin disulfide (SnS2) as a candidate material for saturable absorption in nonlinear optical devices is investigated in this article. A dual-wavelength soliton mode-locked fiber laser is demonstrated using a fabricated SnS2 thin film as a saturable absorber within an erbium-doped fiber laser cavity. The laser generates two peaks centered at 1536.7 and 1562.6 nm, with a pulse width of 5.3 ps. The experimental results indicate that the SnS2 thin film has the required absorption characteristics to realize good mode-locked operation. Thus, we confirm that SnS2 has great potential to be used in multiwavelength ultrafast fiber laser applications.

Pulse-repetition-rate tuning of a harmonically mode-locked fiber laser using a tapered photonic crystal fiber.

Strong enhancement of optoacoustic interactions in the micrometer-sized core of a photonic crystal fiber (PCF) enables stable, harmonic mode locking of a soliton fiber laser at GHz frequencies. Here we report that by tapering the PCF during the draw, the optoacoustic gain bandwidth can be broadened to ∼47 MHz, more than 3 times wider than in the untapered fiber. This made possible broad pulse-repetition-rate tuning over 66MHz (from 2.042 to 2.108GHz) of an optoacoustically mode-locked soliton fiber laser. Within this tuning range, the harmonically mode-locked pulse trains at the laser output were observed to be quite robust, with better than 40dB supermode suppression ratio, sub-ps pulse timing jitter, and <0.2%relative intensity noise. This gigahertz-rate, near-infrared soliton fiber laser has remarkable pulse-rate tunability and low noise level, and has important potential applications in frequency metrology, high-speed optical sampling, and fiber telecommunications.