All-fiber Ring Laser Research Articles

783 MHz fundamental repetition rate all-fiber ring laser mode-locked by carbon nanotubes

We demonstrate a 783 MHz fundamental repetition rate mode-locked Er-doped all-fiber ring laser with a pulse width of 623 fs. By using carbon nanotubes saturable absorber, a relatively low self-starting pump threshold of 108 mW is achieved. The laser has a very compact footprint less than 10 cm × 10 cm, benefiting from the all-active-fiber cavity design. The robust mode-locking is confirmed by the low relative intensity noise and a long-term stability test. We propose a new scheme for generating high repetition rate femtosecond optical pulses from a compact and stable all-active-fiber ring oscillator.

Fast dual-comb spectroscopy based on a dual-wavelength all-fiber ring laser with high repetition rate

We demonstrate fast dual-comb spectroscopy based on a high-repetition-rate dual-wavelength erbium-doped fiber laser with a large repetition rate difference. It can operate in three different dual-wavelength states with repetition rate differences of 4.32, 2.74 and 3.635 kHz, respectively. To the best of our knowledge, the corresponding refresh time can be as low as 231 μs, which is the fastest in dual-comb spectroscopy using a single fundamentally mode-locked all-fiber laser. The high repetition rate of approximately 154.68 MHz provides a maximum optical frequency bandwidth of 4.37 THz. Dual-comb spectroscopy was used to measure the transmittance curve of the Fabry–Perot etalon.

Ultrafast Tm-doped fiber laser based on hybrid fiber coupler

Tm-doped ultrafast fiber lasers have been widely used in scientific research and industrial applications. Here, with the usage of an novel integrated fiber coupler, we describe a reduced laser configuration to achieve compact and high-performance all-fiber Tm-doped mode-locked fiber laser. This novel fiber component can be used as wavelength division multiplexer (WDM), output coupler (OC) and optical modulator at the same time, fabricated by magnetron-sputtering vanadium dioxide (VO2) saturable absorber (SA) on a optical coupler. The bare coupler was laboratory-tapered performing WDM and OC simultaneously. With above-mentioned device, a mode-locked Tm-doped fiber laser was constructed. Fundamental solitons were formed and generated with a short pulse width of 478 fs and a high repetition rate of 160 MHz. In addition, Short-term and long-term laser stability was confirmed by the noise analysis and 4-h running test. 336 fs RMS time jitter ([10 kHz - 10 MHz]) and 0.036% RMS relative intensity noise ([1 Hz - 10 MHz]) was acquired. This new integrated design at 2 μm region simplifies implementation of the ultrafast Tm-doped fiber laser and paves the way for developing compact and high-performance all-fiber ring laser.

Harmonic mode-locked noise-like pulses under a Q-switched envelope in an erbium doped all-fiber ring laser.

We report for the first time, to the best of our knowledge, harmonic mode-locked noise-like pulses under a Q-switched envelope in an all-fiber erbium doped ring laser cavity, mode locked using the nonlinear polarization rotation (NPR) technique. For a cavity with a fundamental repetition rate of 1.33 MHz, stable mode-locked noise-like pulses, with few nanoseconds durations, single pulse energies around 30-40 nJ, and Q-switched repetition rates up to 31 kHz, were produced and characterized from the fundamental to the eighth harmonic. The formation and evolution of Q-switched harmonic mode-locked noise-like pulses were preceded by the formation of Q-switched mode-locked noise-like pulse bunches. This is also the first report on noise-like bunches under a Q-switched envelope, to our knowledge. Our studies also provide further insights into the interplay of different physical mechanisms involved in the production of such ultrashort pulses. Such sources should prove especially useful for efficient supercontinuum generation and laser micromachining.

Experimental and theoretical study on the dissipative soliton energy quantization effect in the negative dispersion regime

We present experimental and simulation results on the dissipative soliton energy quantization effect in the negative dispersion regime of an all-fiber Er-doped ring laser. A fiber filter is inserted into the cavity to facilitate the energy flow out of the cavity under net negative dispersion value conditions, and a single-dissipative soliton operation with the maximum pulse energy of 0.135 nJ is achieved. The dissipative soliton splitting occurred when the pump power is increased by dual-pulse, triple-pulse, and four-pulse operations. Simulations based on the extended nonlinear Schrödinger equation have been performed to confirm the multiple-dissipative soliton generation and soliton energy quantization in a net negative dispersion mode-locked fiber laser. These experimental and simulation results will help to improve the pulse energy in the negative dispersion regime and provide a more unified theory for the understanding of the mode-locking regimes in negative dispersion lasers.

Properties of Scalable Chirped-Pulse Optical Comb in Erbium-Doped Ultrafast All-Fiber Ring Laser

We report on a scalable chirped-pulse Er-doped all-fiber laser, passively mode-locked by single-wall carbon nitride nanotubes. The average output power is ~15 mW, which corresponds to a peak power of ~77 W, and pulse energy of ~1.9 nJ and was achieved using a single amplification stage. We observed chirped-pulse generation with a duration of ~24.6 ps at a relatively low repetition rate of ~7.9 MHz, with a signal-to-noise ratio of ~69 dB. To characterize the short-term stability of the obtained regime, we have measured the relative intensity noise of the laser, which is <−107 dBc/Hz in the range of 3 Hz–1000 kHz. It should be noted that the standard deviation of root mean square of average power does not exceed a magnitude of 0.9% for 3 h of measurement.

Single- and dual-wavelength noise-like pulses generation in a Nd-doped all-fiber ring laser based on nonlinear polarization rotation

Single- and dual-wavelength noise-like pulses (NLP) with the uncompressed pulse duration about 1 ps were demonstrated for the first time in a Nd-doped all-fiber ring laser based on nonlinear polarization rotation (NPR). NLP with pulse width of 1.79 ps and pulse repetition rate of 14.29 MHz has been obtained under the maximum pump power of 297 mW as the laser operating at a single-wavelength of 1062.66 nm. In addition, 952.56 fs uncompressed NLP with pulse energy of 0.088 nJ was generated with the dual-wavelength of 1062.63 and 1064.78 nm. To our knowledge, our results proved for the first time that NPR mode-locking Nd-doped all-fiber ring laser can generate the NLP with the uncompressed pulse width about 1 ps, which would be of great interest as a seed source for all-fiber amplifiers for the generation of ultrashort large-energy pulses.

All-fiber integrated saturable absorber-tunable wavelength filter for Q-switching laser in both C- and L-bands.

We proposed and experimentally demonstrated combining a nonlinear optic saturable absorber and a wideband-tunable spectral filter in a single graphene oxide (GO) film deposited fiber optic device. The GO film was prepared on the cleaved facet of an optical fiber applying two sequential processes: the electrical deposition to make a thick GO film using an arc fusion splicer, followed by the laser pulse drilling to form a multi-layered GO film. The GO deposited fiber facet and a pristine fiber facet formed an asymmetric Fabry-Perot interferometer (FPI), whose spectral response was flexibly controlled by adjusting the air gap between them. An all-fiber ring laser cavity was built using the proposed device as a tunable saturable absorber along with erbium-doped fiber as a gain medium in the L-band. Stable Q-switching laser pulse trains were successfully generated, whose pulse duration was in the order of a few microseconds and its peak wavelength was tunable over 40nm from 1564 to 1604nm covering both C-and L-bands. At a certain condition, we also obtained Q-switching pulses simultaneously lasing at the double wavelengths, 1573.3 and 1586.7nm. Detailed device fabrication processes and laser characteristics are described to elucidate the high potential of 2-dimensional material films in nonlinear optics.

An investigation into self-pulsing behavior in an Er-doped ring laser

We observe a strong self-pulsing phenomenon in an all-fiber Er-doped ring laser. With an increase in the pump power, the generated pulse gradually evolves from a sine-wave pulse to a typical mode-locking pulse train. The self-mode-locked laser pulse obtained has a pulse-repetition rate in the megahertz region and a maximum average output power of around 1 mW. The self-pulsing evolving dynamics can be analyzed using coupled-wave rate equations by simultaneously considering the interaction of two adjacent Er-ions and the reabsorption loss of the ground-state energy levels.

Incipient mode locking dynamics in an all-normal dispersion ytterbium-doped fiber ring laser

In this work we study experimentally the temporal dynamics of an all-normal dispersion all-fiber ring laser far from stable mode locking. Temporal mapping relying on segmented memory capabilities of a fast oscilloscope is used for this purpose. A regime is found where radiation fills the cavity and is characterized by peaks that successively emerge, grow in amplitude while compressing temporally, before decaying abruptly, and localized low-intensity components mediating their interactions across the cycles. The highest-amplitude peaks ephemerally dominate intracavity radiation, before being superseded by other emerging peaks. As radiation covers the whole period and no permanent pulse ever emerges, the regime can be viewed as an intermediate stage between continuous-wave and mode locking operations. The interest of using segmented memory possibilities for proper characterization of this unconventional regime is highlighted.

All-fiber wavelength-tunable bandpass filter based on core-mode conversion for mode-locked laser

We propose an all-fiber configuration of tunable bandpass filter (TBPF), consisting of a mode selective coupler (MSC) and an acoustically induced fiber grating (AIFG). Either the MSC or the AIFG can act as high-order mode converters in a few-mode fiber. The working wavelengths of the MSC and the AIFG are chosen to achieve complete conversion cycle between the core-mode linearly polarized (LP01) mode and the LP11 mode. The tunability of the TBPF is achieved by changing the frequency of the radio frequency signal. An all-fiber tunable ring laser based on the TBPF is used to generate a stable continuous-wave laser with 3-dB bandwidth of around 0.8 nm. The tunable wavelength ranges from 1530 to 1580 nm. Furthermore, the TBPF is introduced into the cavity of a mode-locked fiber laser. Wavelength-tunable mode locking pulses are obtained at central wavelengths from 1530 to 1560 nm.

Tm-doped all-fiber structured femtosecond laser mode-locked by a novel Chem-Te saturable absorber

We succeed in developing a chemically synthesized tellurium nanocrystals (Chem-Te) thin film by liquid phase peeling technique, and demonstrate this material is an effective saturable absorber (SA) for realization of stable mode-locking in an all-fiber structured thulium-doped laser cavity. By integrating this SA into an all-fiber structured ring laser cavity, we obtained the mode-locked pulses at the repetition rate of 11.17 MHz, the achieved pulses spectral bandwidth FWHM (full width at half maximum) of 5.26 nm and the pulses duration of 890 fs with 620 mW pump power at 1560 nm, the fundamental mode-locked laser output power as high as 5.35 mW. In addition, by further increasing the pump power, the second-order and third-order harmonic mode-locked pulses train of this fiber laser were also observed. To the best of our knowledge, this is the first report on the novel Chem-Te material saturable absorption property realization in 2 μm-band fiber laser system.

Simulation of ultrashort pulse generation in an all-fiber erbium-doped ring laser with a highly nonlinear cavity

The generation of ultrashort pulses in an all-fiber erbium ring laser with a highly nonlinear cavity is mathematically modeled. It is shown that ultrashort pulses with the characteristics of both stretched pulses and solitons are generated in a highly nonlinear fiber cavity. The evolution of the width, energy, and spectral width of the ultrashort pulses in the fiber laser is obtained in the mathematical analysis. It is shown that an ultrashort pulse in a highly nonlinear cavity has a minimum width of about 200 fs, a maximum spectral width at half-height of about 17 nm, and a maximum energy of about 180 pJ. The modeling results are verified by comparing them with experimental data.

Multibound Soliton Formation in an Erbium-Doped Ring Laser With a Highly Nonlinear Resonator

We have studied the generation of low-noise ultrashort multibound solitons in the telecommunication spectral window in an erbium-doped all-fiber ring laser with a highly-nonlinear resonator mode-locked by a nonlinear polarization evolution effect. The multibound soliton generation is obtained with more than 20 bound dechirped pulses with a duration of ~ 240 fs at a repetition rate of ~ 11.3 MHz (with a signal-to-noise ratio of ~ 73.3 dB), the relative intensity noise is $\sim 1.3\cdot 10^{\mathbf {-8}}$ with a time averaging window of ~ 100 s.

Spatial-mode switchable EDF laser based on low modal-crosstalk mode MUX/DEMUX

We report an all-fiber ring laser that emits three linearly polarized (LP) modes based on the intracavity mode multiplexer/demultiplexer (MUX/DEMUX). The low modal-crosstalk all-fiber mode MUX/DEMUX consisting of cascaded mode-selective couplers (MSCs) multiplex/demultiplex multiple spatial modes. The output mode lasing of the Erbium-doped fiber (EDF) laser can be switched among the three LP modes by employing combination of a mode MUX and a simple N × 1 optical switch. The slope efficiencies, optical spectra and mode profiles are investigated.

Spatial-mode switchable, multi-wavelength all-fiber erbium-doped fiber (EDF) laser based on low modal crosstalk mode multiplexer/demultiplexer (MUX/DEMUX)

We experimentally demonstrate an all-fiber erbium-doped fiber ring laser based on a Sagnac interferometer with a low modal crosstalk mode multiplexer/demultiplexer (MUX/DEMUX). Three linearly polarized (LP) modes are generated by mode MUX/DEMUX, which consists of cascaded mode-selective couplers. The proposed fiber laser can simultaneously achieve spatial-mode switching and multi-wavelength tuning. In the experiment, single-, dual-, and triple-wavelength lasing outputs for LP01, LP11, LP21 and hybrid modes are obtained. The stabilities for LP01, LP11, LP21 and hybrid modes are investigated in more than 20 min, 16 min, 12 min and 16 min, respectively. Moreover, the mode intensity profiles, the OSNRs of the lasing output and the slope efficiencies are also measured.

All-fiber narrow-linewidth ring laser with continuous and large tuning range based on microsphere resonator and fiber Bragg grating.

We demonstrate an all-fiber single-longitudinal-mode (SLM) narrow-linewidth ring laser stabilized by a microsphere resonator and fiber Bragg gratings (FBGs) with a large continuous wavelength tuning range from 1540 nm to 1570 nm. In the experiment, stable lasing with a linewidth smaller than 5 kHz was obtained. The laser wavelength was linearly and continuously tuned in the range of 0.15 nm by increasing the pump power and discretely tuning with a step of 0.1 nm by stress-controlled FBGs. The tuning range of the proposed laser configuration was determined by the FBG, and the SLM state was ensured by the coupling between the few-mode tapered fiber and the microsphere, which was simpler in alignment than other ring lasers utilizing microresonators.

Q-switching and mode locking pulse generation from an all-fiber ring laser by intermodal acousto-optic bandpass modulation

Q-switched and mode-locked (QML) pulse generation from an all-fiber ring laser based on intermodal acousto-optic bandpass modulation is reported. The modulator relies on full-acousto-optic mode re-coupling cycle induced by a standing flexural acoustic wave, with a transmission response that is controlled by amplitude modulation of the acoustic wave signal. The Q factor of the cavity is controlled by a rectangular pulse wave with variable frequency and duty cycle, whereas mode locking is achieved by amplitude modulation derived from a standing flexural acoustic wave. The best QML pulses were obtained at 0.5 kHz repetition rate, with a pump power of 549.2 mW, at the optical wavelength of 1568.2 nm. A maximum overall energy of 2.14 µJ at an average output power of 1.07 mW was achieved, corresponding to a burst of mode-locked sub-pulses of 100 ps pulse duration within a QML envelope of 3.5 µs.

Thulium-Doped Silica Fibers with Enhanced Fluorescence Lifetime and Their Application in Ultrafast Fiber Lasers

In this work we report on the thulium-doped silica-based optical fibers with increased fluorescence lifetime of the 3F4 level thanks to the modification of the local environment of thulium ions by high content of alumina. The determination of the cross-relaxation energy-transfer coefficients from the measurements of the fluorescence lifetimes of the 3F4 and 3H4 energy levels of Tm3+ ions in the experimentally prepared optical fiber is provided as well. Preforms of optical fibers were prepared either by conventional solution-doping of Tm3+ and Al3+ ions or by dispersion-doping of Tm3+ ions with alumina nanoparticles. Optical fibers were characterized by means of Tm, Al, and Ge concentrations, refractive index profiles, optical spectral absorption and luminescence, and by time-resolved fluorescence spectroscopy. Highly aluminium-codoped thulium silicate optical fibers exhibited fluorescence lifetimes of over ~500 μs with maximum value of 756 μs, which means a fluorescence lifetime enhancement when compared to the thulium-doped fibers reported elsewhere. We show an application of the thulium-doped fiber in a compact all-fiber ring laser that is passively mode-locked by using graphene-based saturable absorber. The output pulsewidth and repetition rate were 905 fs and 32.67 MHz, respectively.

High-energy ultrashort-pulse all-fiber erbium-doped ring laser with improved free-running performance

We report on stable stretched-pulse generation with a pulse duration (at FWHM) ∼180 fs at a central wavelength of 1560 nm with an average output power of 30 mW at a repetition rate of ∼11.3 MHz (with the signal-to-noise ratio at a fundamental frequency ∼59 dB) with an Allan deviation of a pulse repetition frequency of ∼5.75·10−9 for a 1 s interval and a relative intensity noise of <−101 dBc/Hz<−101 dBc/Hz (30–1000 kHz). This corresponds to a <14.7 kW maximum peak power and a <2.6 nJ maximum available pulse energy obtained immediately from the highly nonlinear all-fiber laser resonator.