Mode-locked Soliton Fiber Laser Research Articles

High power femtosecond Bessel-X pulses directly from a compact fiber laser system

We report on high power ultrashort Bessel-X pulses directly from a compact fiber laser system. For spatial profiles, non-diffracting Bessel-like wavepackets were generated with the combination of a collimating lens and a silica-based inverse micro-axicon, which is specially designed and fabricated on the facet of an amplifying fiber doped by ytterbium. For temporal profiles, the seed pulses from a mode-locked dissipative soliton fiber laser at a repetition rate of 56.9 MHz were pre-shaped by a grating pair and a spectral filter. Amplified 18.7 W average power chirped ps pulses were obtained and then dechirped to a duration of 38 fs.

A 31 mW, 280 fs passively mode-locked fiber soliton laser using a high heat-resistant SWNT/P3HT saturable absorber coated with siloxane

We report a substantial increase in the heat resistance in a connector-type single-wall carbon nanotube (SWNT) saturable absorber by sealing SWNT/P3HT composite with siloxane. By applying the saturable absorber to a passively mode-locked Er fiber laser, we successfully demonstrated 280 fs, 31 mW pulse generation with a fivefold improvement in heat resistance.

Formation and evolution of passively mode-locked fiber soliton lasers operating in a dual-wavelength regime

The formation and evolution of dual-wavelength solitons in passively mode-locked fiber soliton lasers are investigated both numerically and experimentally. By solving the Ginzburg–Landau equation and taking the gain profile into account, mode-locked soliton emissions at 1532 and 1555 nm are achieved simultaneously. Numerical results show that the two solitons exhibit the same intensity and duration, indicating that the dual-wavelength pulses possess the soliton energy quantization effect. In the process of pulse–pulse collisions, two solitons pass through each other and maintain their properties, qualitatively distinct from single-wavelength solitons that never overlap each other. The dual-wavelength mode-locked operation evolves into single-wavelength mode locking with the decrease of the pumping strength. The dual-peak gain spectrum of erbium-doped fiber and the birefringence-induced cavity filtering effect play crucial roles in the formation of dual-wavelength solitons. Numerical results agree well with analytical solutions and experimental observations. Our study provides an optional method of measuring the fiber dispersion by means of the dual-wavelength solitons.

Bidirectional passively mode-locked soliton fiber laser with a four-port circulator

We present an all-fiber bidirectional passively mode-locked soliton laser with what we believe is a novel cavity configuration. Using a four-port circulator, we incorporate two different semiconductor saturable absorber mirrors (SESAMs) into the laser cavity, which enables bidirectional mode locking. The laser allows the generation of two independent countercirculating mode-locked pulse trains, each with an individual fundamental repetition rate that can be adjusted by varying the SESAM pigtail length. Two countercirculating pulse trains with repetition rates of 21.3 and 15.2 MHz are obtained simultaneously. By controlling the intracavity loss imposed on these two pulse trains, either one of the two pulse trains can be switched on or off. The bidirectional operation with other repetition rates is also demonstrated.

Bound states of solitons in a fiber laser mode locked with carbon nanotube saturable absorber

We report on the experimental observation of bound states of solitons in an erbium-doped fiber laser passively mode-locked by the carbon nanotube saturable absorber. Bound states of solitons with various pulse separations are obtained. While the tightly bound solitons always exhibit the same set of fixed discrete pulse separations with π or π/2 phase difference, the feature becomes less obvious for the loosely bound solitons. The result that various states of the bound solitons were obtained in the same fiber laser makes a systematic experimental study on them and a comparison of their properties possible. Our results once again show that the bound soliton emission is an intrinsic feature of the mode-locked soliton fiber lasers.

Switchable, dual-wavelength passively mode-locked ultrafast fiber laser based on a single-wall carbon nanotube modelocker and intracavity loss tuning

We demonstrate a dual-wavelength passively mode-locked soliton fiber laser based on the single-wall carbon nanotube saturable absorber. By using a simple scheme of adjusting the intracavity loss, the gain profile of the erbium-doped fiber laser is effectively controlled. Besides operating at a single wavelength, the laser is able to simultaneously generate sub-picosecond pulses at both ~1532 and 1557 nm wavelength. The mode-locking wavelength can also be quickly switched from one wavelength to the other by changing the intracavity loss with a tunable attenuator.

Wavelength-Tunable Er$^{3+}$-Doped fs Mode-Locked Fiber Laser Using Short-Pass Edge Filters

We demonstrate a wavelength-tunable Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped femtosecond mode-locked soliton fiber laser by incorporating a short-pass edge filter into a ring cavity. When the filter is thermo-optically tuned toward shorter wavelengths to strongly attenuate the wavelengths longer than the cutoff, the constituting wavelengths of the mode-locked fiber laser move to shorter wavelengths and the laser center wavelength can be tuned over 1539.7 ~ 1560 nm. The cavity dispersion is preset in the deep soliton region to keep small fluctuations of laser pulsewidth when the laser wavelength is tuned.

Fiber Dispersion Measurement With a Swept-Wavelength Pulse Light Source

A new fiber dispersion measurement method by utilizing a periodically swept-wavelength pulse light source is proposed and demonstrated. The periodic pulse timing variation of the pulse train induced by wavelength sweeping can be directly detected by a radio-frequency spectrum analyzer. Experiments by using an asynchronous mode-locked fiber soliton laser as the swept-wavelength pulse source have been successfully carried out to demonstrate the feasibility.

Laser Dynamics of a 10 GHz 0.55 ps Asynchronously Harmonic Modelocked Er-Doped Fiber Soliton Laser

Laser dynamics of a 10 GHz 0.55 ps asynchronously harmonic modelocked Er-doped fiber soliton laser are investigated both theoretically and experimentally. Theoretical analyses based on the master equation model solved by the variational method have indicated that all the pulse parameters of the laser output will exhibit complicated slow periodic variations in the asynchronous soliton modelocking (ASM) mode. New experimental methods based on analyzing directly the RF spectra of the ASM laser output have been developed to accurately determine the sinusoidal variation of the pulse timing and the pulse center wavelength for the first time. It is found that the pulse center wavelength variation can be as large as 1 nm half-peak-to-peak and the pulse timing variation can be as large as 3 ps. The consistency among all the experimental data and theoretical prediction is carefully examined and the results indicate that the ASM pulse dynamics observed experimentally are in good agreement with those obtained from the theoretical analyses.

A passively mode-locked femtosecond soliton fiber laser at 15 μm with a CNT-doped polycarbonate saturable absorber

We report a new 1.5 mum femtosecond fiber soliton laser incorporating a polymer saturable absorber that consists of polycarbonate (PC) with carbon nanotubes (CNTs). We installed the polymer in a fiber laser with a cavity length of 5.1 m, in which an erbium-doped fiber was used as the gain medium. Stable passive mode-locking was achieved for a pump power of 303 mW at 39 MHz, and a pulse width of 115 fs with an average output power of 3.4 mW was obtained.

Passively harmonic mode-locked erbium-doped fiber soliton laser with a nonlinear polarization rotation

Based on the nonlinear polarization rotation technique, we report on a stable passive 23rd harmonic mode-locked erbium-doped fiber soliton laser for the first time to the best of our knowledge. In this laser, 23 solitons are uniformly distributed in the cavity simultaneously, and all solitons have the same energy and duration. The increase of the coupler output enhances the dispersive radiation, and the longer cavity strengthens the interaction between solitons and dispersive waves. The two above factors play the key function to generate the 23rd harmonic mode-locked operation.

177 fs erbium-doped fiber laser mode locked with a cellulose polymer film containing single-wall carbon nanotubes

A mode-locked soliton erbium-doped fiber laser generating 177fs pulses is demonstrated. The laser pumped by a 85mW, 980nm laser diode emits 7mW at 1.56μm at a pulse repetition rate of 50MHz. Passive mode locking is achieved with a saturable absorber made of a high-optical quality film based on cellulose derivative with dispersed carbon single-wall nanotubes. The film is prepared with the original technique by using carbon nanotubes synthesized by the arc-discharge method.

Spatiotemporal analytical model for coupled-cavity soliton fiber lasers

A closed-form analytical model for the spatiotemporal processes giving rise to soliton pulse formation and compression in an additive-pulse mode-locked coupled-cavity fiber laser systems is presented. The model is based on a modified nonlinear Schrödinger equation for solitons. Perturbation techniques coupled with Fourier transform methods are employed to simplify the solution to the nonlinear Schrödinger equation. The contributions of Gaussian white noise, random noise, group velocity dispersion, and self-phase modulation to the mode-locking process and system performance are described. The model is used to analyze the temporal and spectral characteristics of a 1.55-µm mode-locked soliton fiber laser with a pulse width of 25 ps and a pulse repetition rate of 4 ns, accurately.

Stable operating region in a harmonically actively mode-locked fiber laser

We theoretically study the recovery of a harmonically actively mode-locked soliton fiber laser from pulse dropout. In such lasers, a large number of pulses propagate simultaneously in the cavity. In order to obtain stable operation, pulses that are dropped due to changes in environmental conditions should recover, while other pulses that propagate in the cavity should remain stable. Soliton perturbation theory is used to find stability conditions for the noise in a time slot where a steady state pulse exists and in a time slot where a pulse is dropped. In the stable operating region of the laser, noise is stable in the presence of a pulse while noise becomes unstable in time slots where a pulse is dropped. Such a stability condition ensures that the laser can recover from accidental pulse dropout. A good agreement between the results of a reduced model and the results of a comprehensive numerical simulation was obtained. The results of this paper may enable to improve the stability of actively mode-locked fiber lasers.

Soliton interaction in a fiber ring laser

We have experimentally investigated the soliton interaction in a passively mode-locked fiber ring laser and revealed the existence of three types of strong soliton interaction: a global type of soliton interaction caused by the existence of unstable cw components, a local type of soliton interaction mediated through the radiative dispersive waves, and the direct soliton interaction. We found that the appearance of the various soliton operation modes observed in the passively mode-locked fiber soliton lasers are the direct consequences of these three types of soliton interactions. The soliton interaction in the laser is further numerically simulated based on a pulse tracing technique. The numerical simulations confirmed the existence of the dispersive-wave-mediated soliton interaction and the direct soliton interaction. Furthermore, it was shown that the resonant dispersive-wave-mediated soliton interaction in the laser always has the consequence of causing random irregular relative soliton movement and the experimentally observed states of bound solitons are caused by the direct soliton interaction. In particular, as the solitons generated in the laser could have a profile with long tails, the direct soliton interaction could extend to a soliton separation that is larger than 5 times the soliton pulse width.

Periodic soliton amplitude variation caused by unstable dispersive waves in a laser

A high-frequency periodic soliton amplitude variation is experimentally observed in a passively mode-locked soliton fiber laser when the modulation instability of the dispersive waves becomes obvious. This experimental result suggested that the influence of the dispersive waves on a soliton is non-negligible when the dispersive waves become unstable. Numerical simulation confirmed the experimental observation. Possible mechanism of soliton-unstable dispersive wave interaction in a laser was elaborated.

Fiber-laser-based frequency comb with a tunable repetition rate

A phase-locked, self-referenced frequency comb generated by a mode-locked fiber soliton laser with a tunable repetition rate is presented. The spacing of the frequency comb is set by the laser's repetition rate, which can be scanned from 49.3 MHz to 50.1 MHz while one tooth of the comb is held phase-locked to a stable RF source. This variable repetitionrate frequency comb should be useful for wavelength and length metrology, synchronization of different fiber laser-based frequency combs, and the generation of precise swept wavelength sources.

Observation of quantum-limited timing jitter in an active, harmonically mode-locked fiber laser

We report on the observation of quantum-limited timing jitter in a harmonically mode-locked soliton fiber laser with an ultralow-noise local oscillator. The effects of amplitude and phase modulation on the spectrum are described and compared with theory.

Passive harmonic mode-locked soliton fiber laser stabilized by an optically pumped saturable Bragg reflector

Stabilization of passive harmonic mode locking is achieved for what is believed to be the first time in an Er-Yb soliton fiber laser by optical pumping of the semiconductor saturable absorber above the bandgap. The results show 35-dB mode suppression of undesired harmonics.

Dispersion management in a harmonically mode-locked fiber soliton laser

Harmonically mode-locked Er-fiber soliton lasers have become a reliable source of high-repetition-rate picosecond pulses in high-speed communications and photonic analog-to-digital conversion systems because of their low-noise, dropout-free operation. We have fabricated such a laser with a strongly dispersion-managed cavity and modeled its operation, and we have found that dispersion management significantly extends the power range over which uninterrupted single-pulse production is attained and dramatically decreases the effects of amplified spontaneous emission on the phase noise of the laser.