Soliton Mode-locked Pulse Research Articles

Tungsten trioxide (WO3) film absorber for generating soliton mode-locked pulses in erbium laser

We proposed a new type of passive saturable absorber (SA) based on tungsten trioxide (WO3)- polyvinyl alcohol (PVA) film for generation of soliton mode-locked pulse in the erbium-doped fiber laser (EDFL) cavity. The WO3-PVA has a modulation depth of 20% with a saturable intensity of 0.04 W/cm2. The new SA film was integrated into the cavity to realize a stable mode-locked pulses operating at 1565.08 nm within a pump power range from 50 mW to 225 mW. The pulse repetition rate and pulse width of the soliton laser was 1.85 MHz and 2.69 ps, respectively. The pulse energy of 1.14 nJ and peak power of 0.67 kW were obtained at the maximum input pump power of 225 mW. These results indicate that WO3 is a promising nonlinear optical material for application in generating ultra-fast mode-locked laser. This is the first time that WO3 was utilized as SA in the 1.5 μm region.

Passively Femtosecond Mode-Locked Erbium-Doped Fiber Oscillator with External Pulse Compressor for Frequency Comb Generation

Abstract Optical frequency comb (OFC) sources, for their highly desirable properties, they have revolutionized a wide range of applications specifically orthogonal frequency-division multiplexing (OFDM) system. OFC sources based on femtosecond erbium fiber laser has emerged as the most commonly used in many applications owing to their advantages of low cost, robustness, compactness, high performance, and flexibility. Here, 300 fs soliton mode-locked pulses were achieved using erbium fiber oscillator based on an efficient Graphene saturable absorber and an external all-fiber pulse compressor consisted of erbium-doped fiber amplifier (EDFA) and 200 m long single-mode fiber (SMF). The proposed system works with a central wavelength of 1557 nm at the desirable communication band. The output power of the system and its corresponding pulse energy were 9.29 mW and 1.858 nJ, respectively, at a maximum pump power of 92.6 mW. The designed system is entirely fiber based, with no free-space optics and uses only standard telecommunication equipment. The results of this experiment demonstrate that the simple design of mode-locked fiber oscillator with an external compressor can provide a compact, portable, robust, reliable and high-performance femtoseconds frequency comb.

Mode-locking in Er-doped fiber laser with reduced graphene oxide on a side-polished fiber as saturable absorber

In this work, the generation of highly stable mode-locked pulses from a side-polished fiber (SPF) embedded with graphene oxide (rGO) nanoparticles (NPs) is proposed and demonstrated. The rGO NPs are obtained from a graphene oxide solution prepared using Hummer's technique, before being reduced by a hydrothermal route. The rGO NPs, suspended in the form of a solution, are then drop-casted onto the SPF. The SPF is fabricated by polishing away the cladding layer of a single-mode fiber section, leaving the core exposed and allowing the evanescent field of the signal propagating through the fiber to interact directly with the NPs. The SPF is integrated into an erbium doped fiber laser (EDFL) cavity, and the strong nonlinear optical response and spectral filtering by the rGO NPs as well as total anomalous dispersion of the laser cavity generates highly stable soliton mode-locked pulses with visible Kelly's sidebands at 1544.02 nm. The output pulses have a pulse repetition rate of 16.79 MHz and pulse duration of 1.17 ps throughout the mode-locking operation range of 64.44�280.5 mW. The rGO NP coated SPF in this work demonstrates the viability and performance of the SPF for mode-locked pulse generation via evanescent field interactions. © 2019

Soliton and bound-state soliton mode-locked fiber laser based on a MoS2/fluorine mica Langmuir–Blodgett film saturable absorber

In this article, we report on an experimentally generated soliton and bound-state soliton passively mode-locked erbium-doped fiber laser by incorporating a saturable absorber (SA) made of MoS2/fluorine mica (FM) that was fabricated with the Langmuir–Blodgett (LB) method. The FM substrate is 20 μm thick and easy to bend or cut, like a polymer. However, it has a higher damage threshold and a better thermal dissipation than polymers. In addition, the LB method can be used to fabricate a thin film with good uniformity. In this study, the modulation depth, saturable intensity, and unsaturated loss of the SA are measured as 5.9%, 57.69 MW/cm2, and 13.4%, respectively. Based on the SA, a soliton mode-locked laser is achieved. The pulse duration, repetition rate, and signal-to-noise ratio are 581 fs, 15.67 MHz, and 65 dB, respectively. By adjusting the polarization controller and pump power, we obtain a bound-state soliton mode-locked pulse. The temporal interval between the two solitons forming the bound-state pulse is 2.7 ps. The repetition rate of the bound-state pulses is proportional to the pump power. The maximum repetition rate is 517 MHz, corresponding to the 33rd harmonic of the fundamental repetition rate. The results indicate that the MoS2/FM LB film absorber is a promising photonic device in ultrafast fiber lasers.

Tm3+-Doped Harmonic Dissipative Soliton Mode-Locked Fiber Laser at 1.93 $\mu$ m Based on Tungsten Disulfide in Anomalous Dispersion Regime

We report a harmonic dissipative soliton $1.93~\mu \text{m}$ thulium fiber laser based on a tungsten disulfide (WS2) saturable absorber (SA) in the anomalous dispersion regime. The multilayer WS2 nanosheets were prepared by liquid phase exfoliation method and the SA was fabricated by dropping WS2 solution onto a gold mirror. The transferred WS2 SA had a modulation depth of 2.5% and a saturation intensity of 0.82 MW/cm2. By incorporating the SA into a linear Tm3+ fiber laser cavity, harmonic mode-locked dissipative soliton laser was achieved at 1930 nm with the spectral width of 8 nm, the pulse energy of 3 nJ, the pulse width of 3.6 ns, and the repetition rate of 56.3 MHz. Based on the experimental results, it is shown that with the presence of harmonic mode-locking in $2~\mu \text{m}$ wavelength region, the multilayer WS2 serving as a SA was verified to be a good candidate for broadband high-energy mode-locking. The order of the harmonic dissipative soliton mode-locked pulses remains the same along with the increasing pump power.

Passively Q-switched and mode-locked Erbium-doped fiber laser with topological insulator Bismuth Selenide (Bi2Se3) as saturable absorber at C-band region

We experimentally demonstrate Q-switched and mode-locked Erbium-doped fiber laser (EDFL) by using topological insulator (TI) Bismuth Selenide (Bi2Se3) as saturable absorber (SA). The fabricated Bi2Se3 SA exhibits modulation depth and saturation intensity at 39.8% and 90.2 MW/cm2, respectively. By incorporating the fabricated Bi2Se3 SA into the laser cavity, Q-switching operation is generated with repetition rate ranging from 23.5 kHz to 68.2 kHz, pulse width ranging from 2.4 μs to 8.6 μs and maximum peak power is calculated at 19.9 mW. Our cavity can also generate soliton mode-locked pulse with repetition rate of 23.3 MHz and pulse width of 0.63 ps by inserting an additional 5 m long single mode fiber (SMF) into the existing laser cavity. Spectral peaks due to Kelly side-bands and four wave mixing (FWM) were observed on the soliton spectrum. Both Q-switching and mode-locking pulses are stable in the laboratory environment, allowing the realization of compact and low cost pulsed fiber laser with Bi2Se3 SA for various photonics applications.

Ultrashort Pulse Soliton Fiber Laser Generation With Integration of Antimony Film Saturable Absorber

A soliton-locked Erbium-doped fiber laser is demonstrated for the first time using a pure Antimony (Sb) film as a saturable absorber (SA). The SA device is fabricated by depositing a 5 μm Sb layer onto a polyvinyl alcohol thin film via Physical vapor deposition process. Self-starting soliton mode-locked pulses train with a constant repetition rate of 0.99 MHz is obtained as the pump power increased from 101 mW to 142 mW. The laser operates at 1559 nm with a pulse width of 3.53 ps. At the pump power of 142 mW, the maximum peak power and pulse energy are calculated as 5.83 kW and 20.59 nJ, respectively. The obtainable pulse is very stable with a signal-to-noise ratio (SNR) of 70 dB. Our experimental results manifest that the pure Sb thin film-based SA is able to generate mode-locked pulsed laser at the 1.55-micron laser regime.

Large-area highly crystalline WSe2 atomic layers for ultrafast pulsed lasers.

Large-area and highly crystalline transition metal dichalcogenides (TMDs) films possess superior saturable absorption compared to the TMDs nanosheet counterparts, which make them more suitable as excellent saturable absorbers (SA) for ultrafast laser technology. Thus far, the nonlinear optical properties of large-scale WSe2 and its applications in ultrafast photonics have not yet been fully investigated. In this work, the saturable absorption of chemical vapor deposition (CVD) grown WSe2 films with large-scale and high quality are studied and the use of WSe2 films as a broadband SA for passively mode-locked fiber lasers at both 1.5 and 2 μm ranges is demonstrated. To enhance the light-material interaction, large-area WSe2 film is tightly transferred onto the side wall of a microfiber to form a hybrid structure, which realizes strong evanescent wave interaction between light and WSe2 film. The integrated microfiber-WSe2 device shows a large modulation depth of 54.5%. Using the large-area WSe2 as a mode-locker, stable soliton mode-locked pulse generation is achieved and the pulse durations of 477 fs (at 1.5 μm) and 1.18 ps (at 2.0 μm) are demonstrated, which suggests that the large-area and highly crystalline WSe2 films afford an excellent broadband SA for ultrafast photonic applications.

Ultrathin quartz plate-based multilayer MoS2 for passively mode-locked fiber lasers (invited)

We have grown ultrathin quartz plate-based multilayer molybdenum disulfide (MoS2) by chemical vapor deposition (CVD). When employed as saturable absorber (SA), the prepared MoS2 device exhibits remarkable merits (e.g. uniform thickness, high quality of crystal lattice high damage threshold easy fabrication and good practicability). The modulation depth, saturable intensity, and non-saturable loss of this SA device are measured to be 16.1%, 0.438 MW/cm2 and 44.6% respectively. By incorporating the SA into a typical ring cavity erbium-doped fiber laser, stable passive soliton mode-locked pulse is achieved with the repetition frequency of 0.987 MHz, the signal noise ratio (SNR) of 71.4 dB and the pulse duration of 2.17 ps. The experimental results demonstrate our MoS2-SA device to be an effective mode locker, and it is promising to be used in ultrafast photonics.

Stretched and soliton femtosecond pulse generation with graphene saturable absorber by manipulating cavity dispersion

Graphene is at the center of a significant research effort for ultrafast photonics due to its unique optical properties. Here, we demonstrated the generation of stretched and soliton femtosecond mode-locking pulses in an erbium doped fiber laser (EDFLs) by using graphene saturable absorber and managing the net cavity dispersion. The novelty of this work arises due to the simple fabrication of the graphene SA and the realization of two types of mode-locking pulse by manipulating the cavity dispersion. At total cavity dispersion of −0.028ps2, stretched pulses train was successfully obtained. The laser has a pulse width of 750fs at repetition rate of 35.1MHz and pulse energy of 0.054nJ at maximum output power of 1.9mW. By varying the net cavity dispersion so that the anomalous dispersion has been achieved with total dispersion of −0.3ps2, soliton mode locked pulse train was successfully obtained. The laser has a pulse width of 820fs at repetition rate of 11.5MHz and pulse energy of 0.42nJ at output power of 4.85mW. These results make the proposed EDFLs suitable for applications in optical communications, metrology, environmental sensing, and biomedical diagnostics.

Soliton mode‐locked erbium‐doped fibre laser with mechanically exfoliated molybdenum disulphide saturable absorber

The authors demonstrate the generation of soliton mode-locked pulses from an erbium-doped fibre ring laser incorporating molybdenum disulphide (MoS2) saturable absorber (SA) with a net anomalous dispersion. The MoS2 SA is prepared by mechanically exfoliating MoS2 crystal and fixing the acquired MoS2 flakes onto the end surface of a standard FC/PC fibre connector. A self-started mode-locked soliton pulse is generated by fine-tuning the rotation of the polarisation controller at the threshold pump power of 50 mW. Its solitonic behaviour is verified by the presence of Kelly sidebands in the output spectrum. The central wavelength, 3 dB bandwidth, pulsewidth, and repetition rate of the laser are 1598.94 nm, 5.4 nm, 0.83 ps, and 17.1 MHz, respectively. The maximum pulse energy is 74 nJ at pump power of 110 mW with the output power of 1.26 mW. The MoS2 SA was constructed in a simple fabrication process and has a modulation depth of 11.3% to successfully produce the stable soliton mode-locked fibre laser.

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.

Soliton dynamic patterns of a passively mode-locked fiber laser operating in a 2 μm region

We experimentally report on the soliton dynamics in a passively mode-locked thulium-doped fiber laser based on the nonlinear amplifying loop mirror with all-abnormal dispersion. In fundamental mode-locked regime, stable soliton mode-locked pulses, with central wavelength of 1965.67 nm and repetition rate of 1.72 MHz, have been observed. In addition, by changing the pump power and appropriately rotating the intra-cavity polarization controllers, several distinctive multi-soliton operations and interactions have been observed, such as different types of soliton rain, the release of solitons, the conversion between soliton rain and soliton release, and the emission of quasi-rectangular pulses.

Multi wavelength mode-lock soliton generation using fiber laser loop coupled to an add-drop ring resonator

The add-drop ring resonator system is the fundamental building block of optical transmission and communication systems. An add-drop microring resonator (MRR) consisting of a \(120\,\upmu \hbox {m}\) diameter loop of optical waveguide was used to filter the input spectrum of a mode-locked laser. The experimental setup is used to generate soliton mode-locked laser pulse, where we used the experimental data to model and simulate the propagation of the mode-locked soliton laser pulse within the MRR. The transmission characteristics of the through and drop ports output signals from this system are described in this paper. As results, multi-wavelength mode lock soliton with full width at half maximum and free spectral range (FSR) of 8 pm and 0.67 nm were generated respectively. The FSR of the input signals are enlarged significantly by the system, thus separating signal wavelengths by a resonator has been investigated. In the proposed scheme, FSR-spaced signals are leveraged as a means of obtaining higher bandwidth output signals while using an add-drop MRR.

Soliton Mode-Locked Erbium-Doped Fiber Laser Using Non-Conductive Graphene Oxide Paper

A femtosecond mode-locked soliton erbium-doped fiber laser (EDFL) is demonstrated using a commercially available nonconductive graphene oxide paper as a saturable absorber. The paper that is sandwiched between two fiber ferrules acts as a mode-locker. The EDFL generates a soliton mode-locked pulse train with a repetition rate of 15.62 MHz and pulsewidth of 680 fs. It is observed that the fiber laser has a low pulsing threshold as well as low damage threshold. The pulse energy and peak power are 0.0085 nJ and 11.85 W, respectively. The easy fabrication of graphene oxide paper should promote its potential application in ultrafast photonics.

Broadband saturable absorber for 10-fs pulse generation

We demonstrate the fabrication of a broadband saturable absorber with a silver bottom mirror. The reflectivity bandwidth of the absorber shows the potential for generating sub-10-fs pulses. With a Ti:sapphire laser we obtained self-starting Kerr-lens mode-locked pulses as short as 10 fs at the cavity stability limit and selfstarting soliton mode-locked pulses of 16 fs over the full cavity stability regime.