Ultrafast Mode-locking Research Articles

Harnessing tin phthalocyanine for ultrafast mode-locking in an erbium-doped fiber laser

We present the first demonstration, to the best of our knowledge, of a mode-locked erbium-doped fiber laser (EDFL) employing tin phthalocyanines (SnPc) as a saturable absorber (SA). The investigated SA exhibits a notable modulation depth of 18.6%, fabricated via a simple, cost-effective method, wherein the SnPc compound is embedded into a polyvinyl alcohol (PVA) film. Integration of this thin film into the EDFL cavity facilitates the generation of output pulses with a repetition rate of 0.96 MHz and a pulse duration of 2.68 ps. The frequency spectrum showcases a signal-to-noise ratio of up to 73.2 dB, affirming the stability of the mode-locking operation. Operating at a wavelength of 1531.7 nm, this picosecond pulse train holds significant promise for diverse applications, including high-precision optical metrology, frequency-comb generation, and broadband absorption spectroscopy.

Two types of ultrafast mode-locking operations from an Er-doped fiber laser based on germanene nanosheets

As a member of Xenes family, germanene has excellent nonlinear saturable absorption characteristics. In this work, we prepared germanene nanosheets by liquid phase exfoliation and measured their saturation intensity as 0.6 GW/cm2 with a modulation depth of 8%. Then, conventional solitons with a pulse width of 946 fs and high-energy noise-like pulses with a pulse width of 784 fs were obtained by using germanene nanosheet as a saturable absorber for a mode-locked Erbium-doped fiber laser. The characteristics of the two types of pulses were investigated experimentally. The results reveal that germanene has great potential for modulation devices in ultrafast lasers and can be used as a material for creation of excellent nonlinear optical devices to explore richer applications in ultrafast photonics.Graphical

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.

Investigation of nonlinear optical properties of rhenium diselenide and its application as a femtosecond mode-locker

We investigated the nonlinear optical properties of ReSe2. First, we measured the nonlinear absorption coefficient and the nonlinear refractive index of a ReSe2 thin film using open-aperture (OA) and closed-aperture (CA) Z-scan techniques. ReSe2 was shown to possess both saturable absorption and self-defocusing properties. The nonlinear absorption coefficient of ReSe2 was measured to be −(5.67±0.35)×103 cm/GW, and its nonlinear refractive index was −(2.81±0.13)×10−2 cm2/GW at 1560 nm. Next, a fiberized saturable absorber (SA) based on ReSe2 was fabricated with a side-polished fiber platform and was tested as an ultrafast mode-locker capable of producing femtosecond pulses operating at a wavelength of 1560 nm. The estimated modulation depth and saturation power are ∼3.9% and ∼42 W, respectively, for the transverse electric mode, while they are ∼2.4% and ∼53 W for the transverse magnetic mode. Using the prepared SA, stable soliton pulses with a temporal width of ∼862 fs were produced from an erbium-doped fiber ring cavity. To the best of the authors’ knowledge, this is the first demonstration of using a ReSe2-based SA for femtosecond mode-locked pulse generation.

A 1.9 µm femtosecond fiber laser using a 3D printed, all-fiberized graphene/polylactic-acid saturable absorber

We experimentally demonstrate the fabrication of an all-fiberized saturable absorber (SA) suitable for ultrafast mode-locking of a fiber laser operating in the 1.9 µm wavelength region, using three-dimensional (3D) printing technology. An all-fiberized SA was fabricated by 3D-printing a low-cost composite filament of graphene and polylactic-acid (PLA) onto a side-polished fiber. The measured modulation depths of the fabricated SA are ~5% and ~3.5% at 1.9 µm for the transverse electric and transverse magnetic modes, respectively. Using the SA within a thulium (Tm)-holmium-codoped fiber-based ring cavity, it is shown that mode-locked pulses with a temporal width of ~924 fs are readily obtainable. It is believed that this experimental demonstration reaffirms the potential of the graphene/PLA filament-based 3D printing technique for the fabrication of practical wideband SAs.

Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities

Dissipative Kerr solitons in resonant frequency combs offer a promising route for ultrafast mode-locking, precision spectroscopy and time-frequency standards. The dynamics for the dissipative soliton generation, however, are intrinsically intertwined with thermal nonlinearities, limiting the soliton generation parameter map and statistical success probabilities of the solitary state. Here, via use of an auxiliary laser heating approach to suppress thermal dragging dynamics in dissipative soliton comb formation, we demonstrate stable Kerr soliton singlet formation and soliton bursts. First, we access a new soliton existence range with an inverse-sloped Kerr soliton evolution—diminishing soliton energy with increasing pump detuning. Second, we achieve deterministic transitions from Turing-like comb patterns directly into the dissipative Kerr soliton singlet pulse bypassing the chaotic states. This is achieved by avoiding subcomb overlaps at lower pump power, with near-identical singlet soliton comb generation over twenty instances. Third, with the red-detuned pump entrance route enabled, we uncover unique spontaneous soliton bursts in the direct formation of low-noise optical frequency combs from continuum background noise. The burst dynamics are due to the rapid entry and mutual attraction of the pump laser into the cavity mode, aided by the auxiliary laser and matching well with our numerical simulations. Enabled by the auxiliary-assisted frequency comb dynamics, we demonstrate an application of automatic soliton comb recovery and long-term stabilization against strong external perturbations. Our findings hold potential to expand the parameter space for ultrafast nonlinear dynamics and precision optical frequency comb stabilization.

A 3-D printed saturable absorber for femtosecond mode-locking of a fiber laser

In recent years, three-dimensional (3-D) printing has presented a new manufacturing paradigm and attracted considerable attention since it allows for products to be fabricated as solid objects by printing successive layers of material following instructions produced through computer-aided design. Here, for the first time, the 3-D printing technology based on fused deposition modeling is demonstrated to be readily useful in the fabrication of a fiberized saturable absorber (SA) intended for use in ultrafast mode-locking of an all-fiberized laser. The fiberized SA was fabricated on a side polished fiber platform by printing a low-cost composite of graphene and polylactic acid (PLA). The insertion loss and modulation depth of the fabricated SA were measured to be ∼3.8 and 1.2 dB, respectively. The saturation power and the modulation depth for the transverse electric (TE) mode were estimated to be ∼16 W and ∼2.2%, respectively, while the values for the transverse magnetic (TM) mode were ∼24 W and ∼1.5%, respectively. Using the fabricated SA in an erbium fiber ring cavity, stable femtosecond soliton pulses was readily produced at 1560.2 nm. To the best of the authors’ knowledge this is the first experimental demonstration using 3-D printing technology to implement a fiberized saturable absorber.

Femtosecond mode-locking of a fiber laser using a CoSb3-skutterudite-based saturable absorber

We experimentally demonstrate an ultrafast mode-locker based on a CoSb3 skutterudite topological insulator for femtosecond mode-locking of a fiber laser. The mode-locker was implemented on a side-polished fiber platform by depositing a CoSb3/PVA composite. The measured modulation depth and saturation power for the transverse-electric mode input were ∼5% and ∼8.7 W, respectively, and ∼2.8% and ∼10.6 W for the transverse-magnetic mode input. By incorporating this mode-locker into an erbium-doped fiber-based ring cavity, we were able to readily generate mode-locked, soliton pulses having a pulse width of ∼833 fs at 1557.9 nm. The 3-dB bandwidth of the output pulses and time-bandwidth product were ∼3.44 and 0.353 nm, respectively. To the best of the authors’ knowledge, this is the first demonstration of the use of a skutterudite-based saturable absorber for femtosecond mode-locked pulse generation.

A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi_2Te_3 topological insulator

We experimentally demonstrate a femtosecond mode-locked, all-fiberized laser that operates in the 2 μm region and that incorporates a saturable absorber based on a bulk-structured bismuth telluride (Bi(2)Te(3)) topological insulator (TI). Our fiberized saturable absorber was prepared by depositing a mechanically exfoliated, ~30 μm-thick Bi(2)Te(3) TI layer on a side-polished optical fiber platform. The bulk crystalline structure of the prepared Bi(2)Te(3) layer was confirmed by Raman and X-ray photoelectron spectroscopy measurements. The modulation depth of the prepared saturable absorber was measured to be ~20.6%. Using the saturable absorber, it is shown that stable, ultrafast pulses with a temporal width of ~795 fs could readily be generated at a wavelength of 1935 nm from a thulium/holmium co-doped fiber ring cavity. This experimental demonstration confirms that bulk structured, TI-based saturable absorbers can readily be used as an ultra-fast mode-locker for 2 μm lasers.

Nonequilibrium and thermal effects in mode-locked VECSELs

Ultrafast femtosecond timescale dynamics in Vertical External Cavity Surface Emitting Lasers (VECSELs) have recently been employed to achieve record average power and duration mode-locked pulses by employing different types of saturable absorbers and Kerr Lens elements. Microscopic many-body dynamics are expected to dominate when attempting to push pulse durations below 100 fs. We present a preliminary microscopic simulation of ultrafast mode-locking in order to expose the role of hot carrier distributions in establishing ultrafast mode-locking.

A femtosecond pulse erbium fiber laser incorporating a saturable absorber based on bulk-structured Bi_2Te_3 topological insulator

We experimentally demonstrate the use of a bulk-structured Bi(2)Te(3) topological insulator (TI) as an ultrafast mode-locker to generate femtosecond pulses from an all-fiberized cavity. Using a saturable absorber based on a mechanically exfoliated layer about 15 μm thick deposited onto a side-polished fiber, we show that stable soliton pulses with a temporal width of ~600 fs can readily be produced at 1547 nm from an erbium fiber ring cavity. Unlike previous TI-based mode-locked laser demonstrations, in which high-quality nanosheet-based TIs were used for saturable absorption, we chose to use a bulk-structured Bi(2)Te(3) layer because it is easy to fabricate. We found that the bulk-structured Bi(2)Te(3) layer can readily provide sufficient nonlinear saturable absorption for femtosecond mode-locking even if its modulation depth of ~15.7% is much lower than previously demonstrated nanosheet-structured TI-based saturable absorbers. This experimental demonstration indicates that high-crystalline-quality atomic-layered films of TI, which demand complicated and expensive material processing facilities, are not essential for ultrafast laser mode-locking applications.

Few-layer graphene membrane as an ultrafast mode-locker in erbium-doped fiber laser

Single-layer graphene film is fabricated on the copper foil by using chemical vapor deposition method, and the corresponding Raman spectrum is measured. The graphene membrane is transferred to the facet of zirconium oxide of a fiber jumper. The mode-lock Er-doped fiber laser with few-layer graphene membrane as saturable absorber is experimentally studied, which has a ring structure and uses a 10% portion of a fiber coupler as the laser output. The laser generates a pulse train at a 7.69 MHz repetition rate, with a full width at half maximum of 58.8 ps. The corresponding time-bandwidth product is 1.98, indicating that the pulses are chirped. The peak wavelength and 3 dB bandwidth of the laser are 1560.1 nm and 0.27 nm respectively. Through changing the air gap between two the fiber ends, 4 nm wavelength tuning is observed.

Self-Assembled Graphene Membrane as an Ultrafast Mode-Locker in an Erbium Fiber Laser

A self-assembled graphene membrane produced at the liquid/air interface of reduced graphene oxide aqueous suspension is demonstrated as an excellent mode-locker in an erbium-doped soliton fiber laser. Formation of the self-assembled membrane is attributed to hydrophobic nature of graphene and considerable capillary force. Experiments showed that such graphene saturable absorbers with insertion loss less than 6 dB worked well in the laser cavity setup, verifying that the self-assembly method is reliable and practical. Moreover, the method is quite facile, cost-effective, and potentially suitable for large-scale production of graphene mode-lockers.

Testing ultrafast mode-locking at microhertz relative optical linewidth

We report new limits on the phase coherence of the ultrafast mode-locking process in an octave-spanning Ti:sapphire comb.We find that the mode-locking mechanism correlates optical phase across a full optical octave with less than 2.5 microHZ relative linewidth. This result is at least two orders of magnitude below recent predictions for quantum-limited individual comb-mode linewidths, verifying that the mode-locking mechanism strongly correlates quantum noise across the comb spectrum.