Saturable Absorber Device Research Articles

Generation of short microwave pulse trains based on a hybrid mode-locked optoelectronic oscillator.

A novel approach, to the best of our knowledge, for generating short microwave pulse trains based on a hybrid mode-locked optoelectronic oscillator (HML-OEO) is proposed and demonstrated. In the proposed scheme, a saturable absorber (SA) device is inserted into the active mode-locked OEO (AML-OEO) to compress the pulse width of the microwave pulse trains. Numerical simulations and experimental results show that the HML-OEO generates a short microwave pulse train with a repetition rate of 98.994 kHz through fundamental frequency mode locking, and its pulse width is compressed by about 50% compared to the AML-OEO. Additionally, in the experiment, microwave pulse trains with different repetition rates are generated by second-, third-, fourth-, and fifth-order harmonic mode locking, respectively. Compared to the AML-OEO, the HML-OEO achieves pulse compression effects of 49.3%, 49.8%, 49.4%, and 49.9%, respectively. Notably, compared to the AML-OEO, the proposed scheme also exhibits outstanding performance in frequency stability.

Molten fluoride salt-assisted synthesis of titanium carbide (Ti2C) MXene and its application for 2 µm mode-locking in a thulium-doped fiber laser

Titanium carbide (Ti2C), a new two-dimensional material named MXenes, has attracted interest due to its potential applications in numerous fields. Of the many unique characteristics of Ti2C MXene, its nonlinear properties are attractive for optoelectronic applications, specifically for ultrafast laser generation. In this work, a Ti2C MXene was fabricated by etching a MAX phase precursor titanium aluminum carbide (Ti2AlC) using a mixture of lithium fluoride and hydrochloric acid, eliminating the risk of using the harmful hydrofluoric acid. The Ti2C MXene was prepared in solution form and then dropped onto a reduced core diameter of tapered fiber before being used as a saturable absorber (SA). The SA device was inserted into a thulium-doped fiber laser to generate stable mode-locked pulses at a center wavelength of 1951 nm with a pulse width of 1.67 ps. The mode-locked laser was highly stable when tested over time, with peak optical power fluctuations of as little as 0.005 dB measured. The results show that the Ti2C MXene exhibit outstanding performance for ultrafast laser generation.

Molybdenum gallium carbide coated D-shape fiber for nanosecond dark pulse generation in erbium-doped fiber laser

Molybdenum gallium carbide (Mo2Ga2C), a material belongs to MAX phase group, has garnered significant interest in a wide range of scientific field, including material science, engineering, and laser physics. It is chemically and structurally promising since it exhibits a low shear modulus, superconducting behaviour, and high mechanical stability. Here, we prepared a saturable absorber (SA) based on Mo2Ga2C coated D-shape fiber using solution casting technique. It exhibits outstanding saturable absorption of 7.2%, allowing it to generate dark pulse laser in an erbium-doped fiber laser cavity. We analyzed the laser’s performance and obtained a dark pulse with a pulse energy, peak power, and average output power of 3.9 nJ, 27.5 mW, and 7.3 mW, respectively. This foundational work may introduce a new material as an alternative SA device in fiber laser cavity.

Generation of stable femtosecond pulses using MoS2−xSex as the saturable absorber in Er-doped fiber laser

A new transition-metal dichalcogenide (Janus TMDs), molybdenum selenide sulfide (MoS[Formula: see text]Se[Formula: see text]), has attracted wide attention due to its unique and highly stable alloy structure, high carrier mobility and the ability to modulate the band gap based on composition. In this work, MoS[Formula: see text]Se[Formula: see text] nanosheets were prepared through liquid phase exfoliation and further prepared as a saturable absorber (SA). The nonlinear optical response was investigated by the homemade balanced twin-detector measurement system, revealing the potential of MoS[Formula: see text]Se[Formula: see text]-SA in ultrafast photonics. The SA devices exhibited good saturation absorption characteristics. By applying it to the Er-doped fiber laser, a stable mode-locked fiber laser based on MoS[Formula: see text]Se[Formula: see text]-SA was successfully achieved. The pulse width was measured to be 509 fs, with a spectral width of 6.33 nm and a maximum output power of 7.44 mW in the mode-locked state. This is the first reported instance of achieving mode-locking operation in the Er-doped fiber laser using MoS[Formula: see text]Se[Formula: see text]-SA, indicating its great potential for applications in ultrafast photonics.

Generation of Different Mode-Locked States in Nonlinear Multimodal Interference-Based Fiber Lasers

A novel mode-locking method based on nonlinear multimode interference (NLMI) using a distributed large-core (105 μm) graded-index multimode fiber (GIMF)-based saturable absorber (SA) capable of generating four pulse modes is proposed. The distributed SA geometry consists of two GIMFs located at different positions in the resonant cavity. The coupling and joint operation not only facilitate resistance to pulse fragmentation but also provide a sophisticated and widely tunable transmission with saturable and reverse saturable absorption phenomena. Based on this, dissipative soliton (DS), dissipative soliton resonance (DSR), wedge-shaped, and staircase pulses are achieved without additional filters. The DS has accessible output power, pulse energy, bandwidth, and duration of up to 15.33 mW, 2.02 nJ, 22.63 nm, and ~1.68 ps. The DSR has an achievable pulse duration and energy of ~32.39 ns, 30.3 nJ. The dispersion range that allows DS operation is studied, and the dynamics of the evolution from DS to DSR are observed. The versatility, flexibility, and simplicity of the SA device, combined with the possibility of scaling the pulse energy, make it highly attractive for ultrafast optics and nonlinear dynamics.

VTe2: Broadband Saturable Absorber for Passively Q-Switched Lasers in the Near- and Mid-Infrared Regions.

In this study, we demonstrate the fabrication of a novel 2D transition metal dichalcogenide, VTe2, into a saturable absorber (SA) by using the liquid phase exfoliation method. Furthermore, the first-principles calculations were conducted to elucidate the electronic band structures and absorption spectrum. The nonlinear optical absorption properties of VTe2 at 1.0, 2.0, and 3.0 μm were measured using open-aperture Z-scan and P-scan methods, which showed saturation intensities and modulation depths of 95.57 GW/cm2 and 9.24%, 3.11 GW/cm2 and 7.26%, and 15.8 MW/cm2 and 17.1%, respectively. Furthermore, in the realm of practical implementation, the achievement of stable passively Q-switched (PQS) lasers employing SA composed of few-layered VTe2 nanosheets has manifested itself with broadband operating wavelengths from 1.0 to ∼3.0 μm. Specifically, PQS laser operations from near-infrared to mid-infrared with pulse durations of 195 and 563 ns for 1.0 and 2.0 μm solid-state lasers, respectively, and 749 ns for an Er3+-doped fluoride fiber laser at 3.0 μm were obtained. Our experimental results demonstrate that VTe2 is a potential broadband SA device for achieving PQS lasers. To the best of our knowledge, this is the first demonstration of using VTe2 as an SA in PQS lasers in the near- and mid-infrared regions, which highlights the potential of VTe2 for future research and applications in optoelectronic devices.

Q-switched pulse generation by stimulated Brillouin scattering assisted four-wave mixing effect in erbium–bismuth co-doped multi-elements silica glass based optical fiber laser

We demonstrate Q-switched pulse generation at the 1562.5 nm region by using a 70 cm long erbium–bismuth co-doped alumina–germania–hafnium–yttria silica glass-based fiber as a gain medium in a simple ring resonator configured without saturable absorber and optical isolator devices. The Q-switching was obtained based on a stimulated Brillouin scattering assisted four-wave mixing effect in the gain medium, which induced the intensity modulation mechanism. The laser produced a multi-wavelength output comb centered at 1562.6 nm with a peak-to-peak spacing of about 0.09 nm due to nonlinear effects. Stable Q-switched operation of a hafnia–bismuth–erbium co-doped fiber laser was obtained at a pump power range of 129–319 mW with the repetition rate varying from 45.9 kHz to 89.3 kHz and the pulse width ranging from 8.8 µs to 3.58 µs. A maximum pulse energy of 26.9 nJ at an average output power of 2.4 dBm was achieved. This demonstrates a new passive technique based on a highly nonlinear gain medium for realizing Q-switched all-fiber laser sources.

Soliton interaction in a MXene-based mode-locked fiber laser.

MXenes are a class of two-dimensional layered structure ternary metal carbide or/and nitride materials. Recently, the MXene V2CTx has demonstrated excellent long-term stability, strong saturable absorption, and fast optical-switching capability, used to generate Q-switched and ultrashort pulsed lasers. However, bound-state fiber lasers based on V2CTx have not been reported yet. In this study, V2CTx is combined with a D-shaped fiber to form a saturable absorber device, whose modulation depth is measured to be 1.6%. By inserting the saturable absorber into an Er-doped fiber laser, bound states with different soliton separation and munbers are successfully obtained. Additionally, bound states with a compound soliton structure, such as the (2 + 2)- and (2 + 1)-type, are also realized. Our findings show that V2CTx can be developed as an efficient ultrafast photonics candidate to further understand the complex nonlinear dynamics of bound-state pulses in fiber lasers.

Nickel oxide-embedded tapered fibre as a saturable absorber for ultrafast photonics

This work demonstrates a femtosecond pulse generation of erbium-doped fibre laser utilising nickel oxide (NiO) as saturable absorbing material. The prepared composite of NiO/polydimethylsiloxane (PDMS) was successfully transferred onto a plane of tapered fibre through spin-coating technique. Based on the evanescent field interaction of NiO at tapered fiber region, the fabricated NiO/PDMS-saturable absorber exhibited 4.0% modulation depth and 135.5 MW/cm2 saturation intensity. The integration of this saturable absorber device established a mode-locked operation at 50.0 mW pump power, with ultrafast pulse width of 793 fs operating at the centre wavelength of 1561.27 nm. The pulse repetition rate of 8.0 MHz, with 0.89 nJ energy was attained at 250.0 mW pump power. These research findings open an avenue for further advancement of transition metal oxides in the future of ultrafast photonics.

Silver indium selenide composite as a saturable absorber for passive Q-switched and mode-locked pulsed generation in erbium-doped fiber laser

We have successfully accomplished a Q-switched and mode-locked pulse in an Erbium-doped fiber (EDF) laser cavity by integrating a new composite material silver doped Indium Selenide (Ag/In2Se3)-based saturable absorber (SA). Ag/In2Se3 film was synthesized by using pulsed laser ablation and a common dry cast method to form a free-standing thin film SA. This SA device exhibits a nonlinear optical property of modulation depth, saturable intensity, and non-saturable loss of 2.27%, 847.20 MW/cm2, and 16.82% respectively. By implementing Ag/In2Se3 film into the EDF laser cavity, a Q-switched pulsed began to generate at a threshold pump power of 27.63 mW. Then as 100 m single-mode fiber (SMF) was implemented into the EDF laser cavity, a traditional soliton pulse began to appear with 1.873 MHz, at the threshold pump power of 76.63 mW with a narrow pulse width of 3.11 ps, and remarkable temporal stability, as demonstrated by a signal noise ratio (SNR) of 79.62 dB. The peak power of 2.61 kW was recorded. This contribution further verifies the improved optical qualities of the Ag/In2Se3 composite and offers a new possibility for developing broadband SA devices for various photonics applications.

Sol-Gel growth of zinc oxide particles on graphene sheets for mode-locking in Thulium/Holmium-doped fiber laser

This work used Graphene/Zinc Oxide (G/ZnO) nanocomposite to generate mode-locked pulses in Thulium/Holmium-doped fiber (THDF). The sol-gel method was used to synthesize the ZnO particles decorated graphene sheets. The G/ZnO nanocomposite solution was deposited onto the arc-shaped fiber that had been fabricated to act as the saturable absorber (SA) device. The nonlinear optical response of G/ZnO-based SA was investigated via the twin detection approach, in which it exhibits a modulation depth of 14.11% and a saturation intensity of 4.23 MW cm−2. After incorporating the fabricated SA into the THDF laser cavity, mode-locked pulses were produced at a threshold pump power of 274.3 mW with a center wavelength of 1895.11 nm, fundamental frequency of 11.82 MHz, and a pulse duration of 1.7 ps. The maximum average output power and single pulse energy were determined to be 1.39 mW and 117 pJ, respectively. The mode-locked pulses generated were exceptionally stable, giving a signal-to-noise ratio (SNR) of 58.2 dB. According to the findings of the current research, it is anticipated that the G/ZnO-arc-shaped fiber-based SA has the potential to produce stable mode-locked lasers in the 2.0 μm region.

Black Phosphorus Coated D-Shape Fiber as a Mode-Locker for Picosecond Soliton Pulse Generation

We demonstrate the production of a picosecond pulse from an Erbium laser cavity using black phosphorous (BP) on side-polished fiber saturable absorber (SA) as a mode-locker. The surface of the fiber was removed utilizing a polishing wheel, and then BP was mechanically deposited onto it to develop an excellent evanescent field on the polished surface area. The SA device was used in a 56 m long Erbium-doped fiber laser (EDFL) ring cavity to generate soliton mode-locked pulses with a center wavelength of 1556.2 nm and a 3 dB spectral bandwidth of 2.2 nm. Stable 3.48 MHz soliton pulses with pulse width as short as 1.17 ps were achievable by setting the pump power within 92 mW to 145 mW. The highest pulse energy and peak power obtainable were 5.4 nJ and 4.7 kW, respectively. The results show that BP deposited onto side-polished fiber can be used as an SA in an EDFL cavity. Its easy construction makes it suitable for producing a portable mode-locked laser source.

CrPS4 Nanoflakes as Stable Direct-Band-Gap 2D Materials for Ultrafast Pulse Laser Applications

Two-dimensional (2D) materials have attracted considerable attention due to their potential for generating ultrafast pulsed lasers. Unfortunately, the poor stability of most layered 2D materials under air exposure leads to increased fabrication costs; this has limited their development for practical applications. In this paper, we describe the successful preparation of a novel, air-stable, and broadband saturable absorber (SA), the metal thiophosphate CrPS4, using a simple and cost-effective liquid exfoliation method. The van der Waals crystal structure of CrPS4 consists of chains of CrS6 units interconnected by phosphorus. In this study, we calculated the electronic band structures of CrPS4, revealing a direct band gap. The nonlinear saturable absorption properties, which were investigated using the P-scan technique at 1550 nm, revealed that CrPS4-SA had a modulation depth of 12.2% and a saturation intensity of 463 MW/cm2. Integration of the CrPS4-SA into Yb-doped fiber and Er-doped fiber laser cavities led to mode-locking for the first time, resulting in the shortest pulse durations of 298 ps and 500 fs at 1 and 1.5 µm, respectively. These results indicate that CrPS4 has great potential for broadband ultrafast photonic applications and could be developed into an excellent candidate for SA devices, providing new directions in the search for stable SA materials and for their design.

All-fiber saturable absorber based on slightly tapered graded index multimode fiber for conventional and bound soliton generation.

A slightly tapered graded index multimode fiber (GIMF) is demonstrated as the saturable absorber (SA) for a conventional soliton and tightly bound soliton generation. The SA device is simply a GIMF spliced with single-mode fiber (SMF) at its two ends. The waist diameter of the slightly tapered fiber is ∼23.8µm, located at one of the splicing points of SMF and GIMF. The mode-locked output of conventional solitons and tightly bound solitons can be obtained in a ring fiber laser based on such a SA. The central wavelength of the output conventional solitons is 1563.5nm, and the pulse width is as short as 473fs at the fundamental frequency of 19.53MHz. The central wavelength of the tightly bound solitons is 1563.5nm, with a pulse width of 636fs and a separation of 1.89ps. The device is featured with a simple and robust structure and stable operation capability and can effectively overcome the difficulty in requirement of precise control of the GIMF length, which make it attractive in ultrafast lasers and optical fiber communication systems.

Membrane saturable absorber mirror (MESAM) in a red-emitting VECSEL for the generation of stable ultrashort pulses.

We present a new saturable absorber device principle which has the potential for broad spectral range applications. An active region membrane is separated from the substrate and placed on a dielectric end mirror. By combining the absorbing membrane with the dielectric mirror to one device we get a membrane saturable absorber mirror (MESAM) which is similar to the well-known semiconductor saturable absorber mirror (SESAM) without the restriction of the stop-band reflectivity of the distributed Bragg reflector (DBR). Stable mode-locking with the MESAM was achieved in a red-emitting VECSEL at a pump power of 4.25 W with a pulse duration of 3.06 ps at 812 MHz repetition rate. We compare the performance and pulses of both SESAM and MESAM in a z-shaped VECSEL cavity.

Q-switched and noise-like mode-locked fiber laser based on ternary transition-metal carbide Nb2AlC saturable absorber

The saturable absorption of layered ternary transition-metal carbide (MAX) Nb2AlC is investigated in this work. Nb2AlC-based saturable absorber (SA) device is prepared and applied in an Er-doped fiber laser (EDFL). The EDFL can generate Q-switched and noise-like mode-locked pulses based on the excellent Nb2AlC SA. The EDFL operates in a Q-switched pulses mode state when the pump power is up to a threshold value of 50 mW. For the Q-switched pulse, the maximum single pulse energy is 66 nJ. The laser pulse generation mode switches to a noise-like mode-locked state when the pump power increases to 170 mW. The coherent spike duration is 2.8 ps and the corresponding maximum single pulse energy is 1.5 nJ at a pump power of 439 mW. A preliminary review of available literature indicates no reports of layered ternary carbide Nb2AlC as SA in an EDFL to generate switchable laser pulse modes. Results of this study suggest that ternary MAX Nb2AlC can be a remarkable nonlinear optical (NLO) device to explore switchable laser pulse generation modes and can encourage further studies on the ternary transition-metal carbides.

High-damage vanadium pentoxide film saturable absorber for sub-nanosecond Nd:YAG lasers

Low-dimensional materials as saturable absorber (SA) for sub-nanosecond pulse laser have attracted extensive attention due to their excellent optoelectronic properties. However, high-quality low-dimensional materials’ nonlinear optical properties, such as larger damage threshold and higher modulation depth, are essential for generation of stable sub-nanosecond pulse laser. Herein, the large-area high-quality vanadium pentoxide (V2O5) films were prepared by magnetron sputtering deposition technology, and the usage of V2O5 films as a SA for sub-nanosecond pulse passively Q-switched Nd:YAG laser generation for the first time. It was found that V2O5-SA films exhibit excellent nonlinear optical characteristics, with a larger damage threshold of 509.8 mJ/cm2 and a higher modulation depth of 21.8 %, and the shortest pulse width of 59 ns. Our experimental results demonstrate that V2O5-SA films has the advantages of larger damage threshold and stable availability, which provides a promising solution for the development of high-quality low-dimensional SA devices in short pulse solid-state lasers.

Q-switching pulse generation in multi-wavelength Brillouin Erbium-doped Fiber laser

Stimulated Brillouin scattering (SBS) was successfully used to induce Q-switching operation in a multi-wavelength Brillouin Erbium fiber laser (BEFL) operating in a long-wavelength band (L-band) regime. The SBS based self Q-switched laser used a 4.5 long highly nonlinear Erbium-doped fiber (EDF) as the hybrid gain medium to generate a multiple wavelength Q-switched pulses, which operated at the center wavelength of around 1603 nm. By changing the input pump power in a range from 59.1 mW to 162.2 mW, the repetition rate can be varied from 14.29 to 29.69 kHz and the pulse width can be grasped from 26.52 to 14.80 μs. Under 162.2 mW pump power, the maximum pulse energy was recorded at 96.0 nJ and the signal to noise ratio of the fundamental radio frequency was measured to be as high as 52.73 dB, which indicates the excellent stability of the SBS-based Q-switched laser. To the best of our knowledge, this is the first experiment of realizing a BEFL with Q-switched multi-wavelength output without any physical saturable absorber devices.

Robust mode-locking in a hybrid ultrafast laser based on nonlinear multimodal interference

We experimentally demonstrate the realization of a half-polarization-maintaining (half-PM) fiber laser, in which mode-locking is provided by a reflective multimode-interference saturable absorber (SA). In the specially designed SA, linearly polarized light is coupled into a 15-cm-long graded-index multimode fiber (GIMF) through the PM fiber, and then reflected back to the PM structure through a mirror pigtailed with a single-mode fiber (SMF). The modulation depth and saturation peak power are measured to be 1.5 % and 0.6 W, respectively. The proposed SA device is incorporated into a novel half-PM erbium-doped fiber oscillator, which generates soliton pulses with 409 fs temporal duration at a 33.3 MHz repetition rate. The proposed fiber laser is compared to a conventional non-PM fiber laser mode-locked by the nonlinear polarization evolution (NPE) in terms of essential optical properties such as the spectral bandwidth, pulse duration, and stability performance. Short- and long-time stability tests and superior noise performance corroborate robust mode-locking in this setup.

Tunable S-band mode-locked thulium-doped fluoride fiber laser using nickel phosphorus trisulfide (NiPS3) saturable absorber

Nickel Phosphate Trisulfide (NiPS3) prepared using the LPE technique was used as a saturable absorber (SA) in a thulium-doped fluoride fiber laser for the generation of mode-locked pulses. The polishing method was used to prepare the arc-shaped fiber before the NiPS3 solution was drop-casted onto it to form the SA device. The SA exhibited nonlinear optical properties, with modulation depth and saturation intensity of 29.44 % and 0.547 kW/cm2 respectively. Insertion of the SA in the TDFF cavity produced mode-locked pulses with central wavelength and 3-dB bandwidth of 1505 nm and 0.68 nm respectively, with a pulse width of 3.56 ps. The mode-locking operation also has a repetition rate of 582 kHz and an SNR of about 58 dB at a pump power of 280 mW. The maximum average output power measured was 2.4 mW at maximum pump power, with maximum pulse energy and peak power at 4.12 nJ and 1.16 kW respectively. Due to the optical interaction between NiPS3 and the evanescent wave in this arrangement, a larger damage threshold can be achieved, enabling the laser performance to operate at higher output power. Tunability was achieved by simultaneous adjustment of extinction and wavelength knob on the tunable Mach-Zehnder Filter (TMZF). The shape of spectra remained unchanged and continued exhibiting Kelly’s sidebands throughout the tunability range of about 2 nm. These results provide the first demonstration of tunable mode-locked pulses in the S-band region.