Passive Mode-locked Fiber Laser Research Articles

Passively mode-locked ytterbium-doped fiber laser operation with few layer MoS2 PVA saturable absorber

A passive mode-locked Ytterbium-doped fiber laser (YDFL) is experimentally demonstrated using a multi-layered molybdenum disufide (MoS2) as a Saturable Absorber (SA). The MoS2 film was obtained based on a liquid phase exfoliation of MoS2 crystal. A small slice of MoS2 film was sandwiched in between two optical ferrules via a fiber adapter and linked into an YDFL cavity to generate a stable mode-locked operation at a wavelength of 1073.86nm with repetition rate of 18.8MHz. At pump power of 202.9mW, the maximum pulse energy of 0.1nJ was achieved with an output power of 1.84mW. The MoS2 film was fabricated through a simple process and it has a modulation depth of 9.7% and saturating intensity of 40 MW/cm2.

Effect of periodic optical pumping on dynamics of passive mode-locked fiber laser

We report on the effect of periodic optical pumping on a passively mode-locked fiber laser (MLFL) based on an erbium-doped fiber (EDF). We investigate the influence of various parameters (including average pump power into the fiber laser, the modulation frequency and duty cycle of the pump, and the polarization state of the light inside the cavity) on the transient response characteristic of the MLFL such as: relaxation oscillation (RO) build-up time (defined as the time delay from the onset of pumping to the generation of passively mode-locked pulses) and the power of the detected RF signal at the fundamental cavity-mode frequency (determined by the ring cavity length), which reflects the stability of mode-locking pulse train.We have found that the RO build-up time is inversely proportional to the average pump power while the RF power of the detected fundamental cavity mode (produced by the ring cavity) is proportional to the average pump power. A change in the duty cycle effectively leads the average pump power to vary, which in turn leads to changes in the transient response. The modulation frequency of the pump is rather related to the stability of the MLFL than its response time. Generally, the lower the modulation frequency, the more stable the mode-locked pulses generated in the fiber laser. Finally, the RO build-up time and, consequently, the pulse-generation time are highly sensitive to the state of polarization in the MLFL cavity.

Dynamic evolution of the dissipative soliton in passively mode-locked fiber laser based on black phosphorus as a new saturable absorber

Black phosphorus (BP) is a promising two dimensional (2D) material due to its electronic and optical properties. Hence, we use BP as a new saturable absorber in passively mode-locked (PML) fiber laser to generate dissipative solitons. Numerical simulations show that under the same conditions, the dissipative soliton generated by PML fiber laser based on BP as a saturable absorber has better physical properties than other 2D materials (such as graphene, transition metal dichalcogenides, topological insulators) as a saturable absorber. With the increase of pump power, dissipative soliton requires more pump power to split into multi-soliton, which means PML fiber laser using BP as a saturable absorber generates the dissipative soliton has high nonlinearity tolerance. According to this paper we can find that BP is an ideal saturable absorber and can be used for ultrashort optical pulse generation.

Dual noise-like pulse and soliton operation of a fiber ring cavity

Passively mode-locked fiber lasers (PML-FLs) are versatile sources that are capable of generating a broad variety of short and ultrashort optical pulses. Besides conservative solitons, PML-FLs allow the generation of different kinds of dissipative structures, usually called dissipative solitons, a concept that also encompasses more complex structures and collective behaviors such as soliton molecules, gas, rain of solitons, etc. In addition to this, PML-FLs are also able to generate even more complex objects, the so-called noise-like pulses (NLPs). A few recent research results revealed a connection between NLPs and solitons, a sign that deterministic ingredients enter into the composition of NLPs, whose nature is traditionally assumed to be random. Although it is usual that a fiber laser is able to generate either solitons or noise-like pulses, depending on pump power and adjustments in the cavity, these two regimes are rarely observed simultaneously. In this paper, a PML-FL in a ring configuration is presented, in which it is possible to observe and verify experimentally the simultaneous presence of NLPs and solitons. Interestingly, these two components are found in different spectral regions, which greatly facilitates their separation and individual study and characterization.

Passive mode-locking of a fiber laser operating in the regime of undumped regular spiking

Computer simulation is used to investigate a new regime of oscillation of fiber lasers in which passive mode-locking takes place simultaneously with the regime of regular undumped spiking induced by an intracavity saturable absorber. Such a superposition regime takes place when part of the output radiation of the laser operating in the regime of spiking is propagated through a fiber-optic delay line and is coupled back into the laser cavity in a time interval equal to the time interval between adjacent spikes. The advantages of the proposed regime of oscillation relative to other means of achieving passive mode-locking in fiber lasers are discussed. The proposed regime is of interest for obtaining reproducible high-energy light pulses.

Study of a harmonic mode lock stability under external continuous-wave injection

In this paper, we investigate experimentally the effect of an injected continuous external optical laser in a stable passive harmonic mode-locked fiber laser operating in the anomalous dispersion regime. Under specific conditions, the continuous-wave significantly increases the stability of the harmonic mode-locked regime. This occurs for a discrete set of wavelengths and below a critical injected power.

Molybdenum Disulphide Tape Saturable Absorber for Mode-Locked Double-Clad Ytterbium-Doped All-Fiber Laser Generation**Supported by the PPP Grant Scheme of University of Malaya under Grant No PG098-2014B.

We demonstrate the generation of passive mode-locked double-clad ytterbium-doped fiber laser operating in a 1-micron region. We prepare the saturable absorber from commercial crystal of molybdenum disulphide (MoS2). Without chemical procedure, the MoS2 is mechanically exfoliated by using a clear scotch tape. A few layers of MoS2 flakes are obtained on the tape. Then, a piece of 1 × 1 mm tape containing MoS2 thin flakes is inserted between two fiber ferrules and is integrated in the ring cavity. Stable mode-locking operation is attained at 1090 nm with a repetition rate of 13.2 MHz. Our mode-locked laser has a maximum output power of 20 mW with 1.48 nJ pulse energy. These results validate that the MoS2 has a broad operating wavelength which covers the 1-micron region, and it is also able to work in a high-power cavity.

Spectral-doublet rectangular pulses in passive mode-locked fiber lasers with anomalous dispersion

It has been found by numerical simulation that dissipative soliton resonance in passive mode-locked fiber lasers with anomalous dispersion can result in the formation of rectangular pulses with a spectral doublet. With an increase in the pump power and hence in the length of the pulses, the width of the peaks of the spectral doublet decreases, and their position remains unchanged. As a consequence, the generation of a single pulse in the laser resonator turns out to be stable, and the regime of a high-energy rectangular pulse with a doublet spectral structure is observed. The mechanisms involved in this regime are analyzed.

On-field measurement trial of 4×128 Gbps PDM-QPSK signals by linear optical sampling

Linear optical sampling is a promising characterization technique for advanced modulation formats, together with digital signal processing (DSP) and software-synchronized algorithm. We theoretically investigate the acquisition of optical sampling, when the high-speed signal under test is either periodic or random. Especially, when the profile of optical sampling pulse is asymmetrical, the repetition frequency of sampling pulse needs careful adjustment in order to obtain correct waveform. Then, we demonstrate on-field measurement trial of commercial four-channel 128Gbps polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signals with truly random characteristics by self-developed equipment. A passively mode-locked fiber laser (PMFL) with a repetition frequency of 95.984MHz is used as optical sampling source, meanwhile four balanced photo detectors (BPDs) with 400MHz bandwidth and four-channel analog-to-digital convertor (ADC) with 1.25GS/s sampling rate are used for data acquisition. The performance comparison with conventional optical modulation analyzer (OMA) verifies that the self-developed equipment has the advantages of low cost, easy implementation, and fast response.

Ultrafast erbium-doped fiber laser mode-locked with a black phosphorus saturable absorber

We experimentally demonstrate a passive mode-locked erbium-doped fiber laser (EDFL) using a multi-layer black phosphorus saturable absorber (BPSA). The BPSA is fabricated by mechanically exfoliating a BP crystal and sticking the acquired BP flakes onto scotch tape. A small piece of the tape is then placed between two ferrules and integrated into an EDFL cavity to achieve a self-started soliton mode-locked pulse operation at 1560.7 nm wavelength. The 3 dB bandwidth, pulse width, and repetition rate of the laser are 6.4 nm, 570 fs, and 6.88 MHz, respectively. The average output power is 5.1 mW at pump power of 140 mW and thus, the pulse energy and peak power are estimated at 0.74 nJ and 1.22 kW, respectively. The BPSA was constructed in a simple fabrication process and has a modulation depth of 7% to successfully produce the stable mode-locked fiber laser.

Bound States of Dissipative Solitons in the Single-Mode Yb-Doped Fiber Laser

We present results of our research on the observation of a bound state of double dissipative-soliton operation of a passive mode-locked Yb-doped fiber laser based on the nonlinear polarization rotation mechanism through the proper adjustment of the wave plates. The generated dissipative solitons with large net positive cavity Group Velocity Dispersion (GVD) are characterized by their spectral profile of sharp peaks near edges, which are distinct from those of the conventional solitons in fiber lasers. By using an artificial saturable absorber, we have obtained stable single and double bound-state dissipative solitons. In all-normal-dispersion Yb-doped single-mode fiber lasers, the bound state of double dissipative solitons with a full-width at half-maximum of 7 ps, and a fixed pulse separation of 8 ps independent of the experimental conditions is achieved for the first time, to the best of our knowledge. Our result once again shows that the passively mode-locked fiber laser with large normal dispersion can help to explore dissipative soliton dynamics.

Corrigendum: Can silicon carbide serve as a saturable absorber for passive mode-locked fiber lasers?

Scientific Reports 5: Article number: 16463; published online: 12 November 2015; updated: 10 March 2016 The original version of this Article contained typographical errors in the spelling of the authors Chao-Kuei Lee and Chih-I Wu which were incorrectly given as Chao-Kuei Leeb and Chih-I Wua respectively.

Vector Passive Harmonic Mode-locking Fiber Laser Based on Topological Insulator Bi2Se3 Interacting with Fiber Taper

I propose a vector passive harmonic mode-locked fiber laser based on topological insulator Bi2Se3 interacting with a fiber taper with a diameter of 7 μm. The particles of topological insulator are deposited uniformly onto the fiber taper with light pressure effect. By incorporating the fabricated saturable absorber into an Er-doped fiber laser cavity, stable mode-locked fiber is obtained. Due to the intense evanescent field of the fiber taper, strong confinement of light enhances the nonlinearity of the laser cavity, and passive harmonic mode-locking is performed. I observe a maximum harmonic mode-locking of 356th, corresponding to a frequency of 3.57 GHz. The pulse duration is 824 fs, and the full width at half maximum of the spectrum is about 8.2 nm. The polarization dependent loss of the saturable absorber is ~ 2.5 dB in the wavelength range of the C band. As the cavity contains no other polarization dependent device, the mode-locked laser is functioning in the vector state. The harmonic order vs pump power is investigated. To the best of our knowledge, this report is the highest frequency mode-locked fiber laser based on Bi2Se3. Experimental results indicate that the topological insulator Bi2Se3 functioning with a thin fiber taper is effective for vector harmonic mode-locking.

Impact of Sampling Source Repetition Frequency in Linear Optical Sampling

We report the repetition frequency constraint of a passively mode-locked fiber laser (PMFL) for linear optical sampling based M-ary phase-shift keying (PSK) constellation characterization, based on the commonly used Viterbi–Viterbi carrier phase estimation algorithm. Referred to the error vector magnitude (EVM) value by the conventional high-speed electronic coherent detection, we put forward a benchmark of EVM $_{\rm {RMS\_{}error}}$ to evaluate the accuracy of constellation characterization by linear optical sampling. Due to the repetition frequency constraint of the PMFL, the EVM $_{\rm {RMS\_{}error}}$ will reach an ultimate value of 0.25% for the purpose of PSK constellation characterization, while it is insensitive to the signal symbol rate. The analytical results of a typical 28-GBaud QPSK signal well agree with those of the simulation and the experiment, therefore providing guidance for the repetition frequency optimization of PMFL-based linear optical sampling.

Can silicon carbide serve as a saturable absorber for passive mode-locked fiber lasers?

The study presents a novel demonstration of a passively mode-locked erbium-doped fiber laser (EDFL) that is based on a silicon carbide (SixC1−x) saturable absorber. When the C/Si composition ratio is increased to 1.83, the SixC1−x film transforms from two-photon absorption to nonlinear saturable absorption, and the corresponding value reaches −3.9 × 10−6 cm/W. The Si-rich SixC1−x film cannot mode lock the EDFL because it induced high intracavity loss through two-photon absorption. Even when a stoichiometric SiC is used, the EDFL is mode locked, similar to an EDFL operating under weak nonlinear-polarization-rotation condition. A C-rich SixC1−x film containing sp2-orbital C–C bonds with a linear absorbance of 0.172 and nonlinear absorbance of 0.04 at a 181 MW/cm2 saturation intensity demonstrates nonlinear transmittance. The C-rich SixC1−x saturable absorber successfully generates a short mode-locked EDFL pulse of 470 fs. The fluctuation of the pulse-train envelope dropps considerably from 11.6% to 0.8% when a strong saturable-absorption-induced self-amplitude modulation process occurs in the C-rich SixC1−x film.

Generation of soliton and bound soliton pulses in mode-locked erbium-doped fiber laser using graphene film as saturable absorber

We report an observation of soliton and bound-state soliton in passive mode-locked fibre laser employing graphene film as a passive saturable absorber (SA). The SA was fabricated from the graphene flakes, which were obtained from electrochemical exfoliation process. The graphene flakes was mixed with polyethylene oxide solution to form a polymer composite, which was then dried at room temperature to produce a film. The film was then integrated in a laser cavity by attaching it to the end of a fibre ferrule with the aid of index matching gel. The fibre laser generated soliton pulses with a 20.7 MHz repetition rate, 0.88 ps pulse width, 0.0158 mW average output power, 0.175 pJ pulse energy and 18.72 W peak power at the wavelength of 1564 nm. A bound soliton with pulse duration of ~1.04 ps was also obtained at the pump power of 110.85 mW by carefully adjusting the polarization of the oscillating laser. The formation of bound soliton is due to the direct pulse to pulse interaction. The results show that the proposed graphene-based SA offers a simple and cost efficient approach of generating soliton and bound soliton in mode-locked EDFL set-up.

Bound States of Dispersion-Managed Solitons From Single-Mode Yb-Doped Fiber Laser at Net-Normal Dispersion

The bound states of multiple dispersion-managed solitons (DMSs) were experimentally investigated from a net-normal-dispersion passive mode-locked Yb-doped fiber laser based on the nonlinear polarization rotation mechanism through the proper adjustment of the waveplate at certain pump power. The long-term operation of the bound double DMSs has been experimentally verified and reveals the possible application in the fields of optical communication. In addition, we observed multiple bound solitons and the bound states of the multiple solitons whose intensity autocorrelation traces were similar to that operating at single and double bound soliton states. By means of the grating pairs at the outside laser cavity for pulse compression, the bound states of multiple solitons below 1 ps can be experimentally retrieved. The observed results in this paper illustrate that the passive mode-locked fiber laser around zero cavity dispersion can provide the platform to explore the fundamental physics of soliton dynamics.

High power L-band mode-locked fiber laser based on topological insulator saturable absorber

We demonstrate a passive mode-locked Er:Yb doped double-clad fiber laser using a microfiber-based topological insulator (Bi(2)Se(3)) saturable absorber (TISA). By optimizing the cavity loss and output coupling ratio, the mode-locked fiber laser can operate in L-band with high average output power. With the highest pump power of 5 W, 91st harmonic mode locking of soliton bunches with average output power of 308 mW was obtained. This is the first report that the TISA based erbium-doped fiber laser operating above 1.6 μm and is also the highest output power yet reported in TISA based passive mode-locked fiber laser.

Ultrawide broadband photonic source based on a new design of mode-locked erbium-doped fibre laser

Pulses with a spectral width of 134 nm at −6 dBm nm−1 and 223 nm at −20 dBm nm−1, covering L-band and U-band and longer wavelengths (even beyond 1700 nm), are achieved by means of a new design of passive mode-locked erbium-doped fibre laser. This source includes a C/L-band filter inside a ring cavity with an L-band erbium-doped fibre amplifier as active medium and its output pulses are amplified by means of a second L-band amplifier. It is demonstrated that output spectra are clearly broadened due to the presence of the C/L band filter.

Passive harmonic hybrid mode-locked fiber laser with extremely broad spectrum.

We demonstrate a harmonic mode-locking Erbium-doped fiber laser which is cooperatively mode-locked by nonlinear polarization evolution (NPE) and semiconductor saturable absorber mirror (SESAM). Via effective dispersion and nonlinearity optimization, 8th harmonic at a repetition rate of 666.7 MHz is obtained. The output pulses has a full spectrum width at half maximum (FWHM) of 181 nm and duration of 218 fs. The pulses are compressed to 91 fs by external chirp compensation. The average power of the direct output pulse at an available pump power of 1.5 W is 136 mW, which exhibits a single-pulse energy of 0.2 nJ. The cavity super-mode suppression is up to 60 dB and the signal-to-noise ratio of the 8th harmonic is over 75 dB.