Saturable Absorber Research Articles

108 fs high-power mode locked double-clad ytterbium-doped fiber laser using FePS3 saturable absorber

108 fs high-power mode locked double-clad ytterbium-doped fiber laser using FePS3 saturable absorber

Electro-Induced Phase Transformation of a Conductive Metal-Organic Framework Film for Nonlinear Optical Switching.

Achieving metal-organic frameworks (MOFs) with nonlinear optical (NLO) switching is profoundly important. Herein, the conductive MOFs Cu-TCNQ phase I (Ph-I) and phase II (Ph-II) films were prepared using the liquid-phase-epitaxial layer-by-layer spin-coating method and steam heating method, respectively. Electronic experiments showed that the Ph-II film could be changed into the Ph-I film under an applied electric field. The third-order NLO results revealed that the Ph-I film had a third-order nonlinear reverse saturation absorption (RSA) response and the Ph-II film displayed a third-order nonlinear saturation absorption (SA) response. With increases in the heating time and applied voltage, the third-order NLO response realized the reversible transition between SA and RSA. The theoretical calculations indicated that Ph-I possessed more interlayer charge transfer, resulting in a third-order nonlinear RSA response that was stronger than that of Ph-II. This work applies phase-transformed MOFs to third-order NLO switching and provides new insights into the nonlinear photoelectric applications of MOFs.

Turning effect of nonlinear optical properties depends on their phase transition behaviors of Sb2Te2Se thin film

Tetradymites have extensive application in nonlinear optical devices due to their significant nonlinear optical absorption (NOA). In this work, the NOA properties of tetradymite Sb2Te2Se was investigated. It is found that a switch from reverse saturable absorption (RSA) to saturable absorption (SA) can be achieved with relatively low annealing treatment, and the modulation depth can be finely tuned through variation of crystallinity. In addition, Influence of microstructure and composition on the NOA effect is explored by comparing Sb2Te2Se, Sb2Te3 and Sb2Se3, revealing a competitive mechanism. The study reveals the NOA properties intrinsic to Sb2Te2Se, which offers greater understanding to the improvement of novel NOA materials and nonlinear optical devices.

Vernier effect based on cascading two Mach–Zehnder interferometers for selectable comb filter and saturable absorber applications in erbium-doped fiber laser

We present the applications of a Vernier effect based on cascading two Mach–Zehnder interferometers (MZIs) as a selectable comb filter and saturable absorber (SA) in an erbium-doped fiber laser (EDFL).Each MZI is composed of bi-tapered polarization-maintaining fibers (PMFs) constructed by fusion splicing between two single-mode fibers (SMFs), which are then connected in series to produce the Vernier effect. The first tapered MZI (called MZI-1) acted as a comb filter to providea larger free spectral range (FSR). The second MZI (MZI-2) based comb filter has a smaller FSR. The combination of these two filters forms an envelope structure on the comb-like spectrum. In this work, the first implementation of the comb filterbased onthe Vernier effectwas used as a wavelength-selectable filter. Through the adjustment of the polarization controller (PC1) and (PC2) inside the cavity, the FSR of the envelope can be varied, thereby switchable and adjustable multiwavelength was achieved. The second implementation uses a graphene nanoparticle (G-Nps)/polymer composite deposited onto the MZI-1 comb filter to act as an SA. At the 80 mW pump threshold, stable Q-switching EDFL operation was successfully activated at 1560.8 nm. The shortest pulse width of 2.89 μs at a 85.91 kHz repetition rate was achieved at 330 mA (180 mW) pump power. The proposed Vernier effect based on cascading two tapered MZIs configuration can find potential applications in the fields of advancedmultiwavelength fiber lasers and short pulse generation.

Investigation of pulse burst characteristics in an LD end-pumped Er:Yb:Glass/Co:MALO microchip 1.5 μm laser

Burst mode lasers, characterized by a sequence of high-intensity pulses, are integral to applications such as the examination of turbulent flows and optical metrology. This study investigates a 1.5 μm passively Q-switched pulse burst microchip laser, end-pumped by a 940 nm laser diode. Utilizing Er:Yb:glass as the gain medium and Co:MALO for passive Q-switching, delivering a pulse width of 5.5 ms and a repetition rate of 10 Hz. When the initial transmittance of the saturable absorber was 93 % and the maximum absorbed pump energy reached 85 mJ, we successfully generated up to 12, 8, and 4 pulses within a burst at 1.5 μm. These results corresponded to cavity lengths of 12 mm, 13 mm, and 14 mm, respectively. By using a saturable absorber with an initial transmittance of 90.5 %, a higher single pulse energy and a narrower pulse width were realized. The narrowest pulse width was reduced to 6.2 ns, with a corresponding single pulse energy of 272 μJ. The peak power in the Er:Yb:glass/Co:MALO pulse burst laser reached an estimated 43.9 kW.This research provides valuable experimental and theoretical insights for the development of human eye-safe lasers with adjustable pulse sequences.

Ternary ReS2(1-x)Se2xalloys of different composition for Q-switched and mode-locked all-fiber laser.

This paper systematically studied the composition-controlled nonlinear optical properties and pulse modulation of ternary ReS2(1-x)Se2xalloys for the first time. The compositionally modulated characteristics of ReS2(1-x)Se2xon the band gap were simulated based on the first principles. We investigated the effect of the band gap on the saturable absorption properties. In addition, we demonstrated the modulation characteristics of different components ReS2(1-x)Se2xon 1.5 μm Q-switched pulse performance. The Q-switched threshold, repetition rate, and pulse duration increase as the S(sulfur)-element composition rise. And pulse energy also was affected by the S(sulfur)-element composition. The ReS0.8Se1.2SA was selected to realize a conventional soliton with high energy in the all-fiber mode-locked laser. The pulse was centered at 1562.9 nm with a pulse duration of 2.26 ps, a repetition rate of 3.88 MHz, and maximum pulse energy of 1.95 nJ. This work suggests that ReS2(1-x)Se2xhas great potential in laser technology and nonlinear optics, and widely extends the material applications in ultrafast photonics.&#xD.

L-band of ∼ 1.6 μm tunable multi-wavelength mode-locked Er-doped fiber laser with an MMF- FMF based structure

1.6 μm tunable mode-locked fiber laser are mainly used in the biomedical field, laser processing, and other aspects, have excellent application prospects. We propose a novel MMF-FMF-based device, which acts both as a saturable absorber and a wavelength selection filter. The reduction of insertion loss caused by FMF affects the laser gain competition process, leading to changes in gain allocation and bandwidth allocation. The laser generated stable mode-locked pulses with a repetition frequency of 23.23 MHz at pump powers exceeding 51 mW. By adjusting the angle of the fiber optic squeezer with the PC, successfully achieved switchable single-, dual-, and triple-wavelength lasing outputs, as well as tunable single- and dual-wavelength lasing outputs. The wavelength-tuning ranges for the single- and dual-wavelength lasing outputs were 31 nm (1570 nm-1601 nm) and 24 nm, respectively. The accurately adjustable L-band novel mode-locked fiber laser exhibits enormous potential for application.

MXene-based Q-switched fiber laser and application in laser thrombolysis

Near-infrared band fiber lasers exhibit strong water absorption capabilities, and their photothermal effects are often harnessed in the field of laser medical surgery. In this work, a 1.5-μm Q-switched fiber laser was realized by incorporating MXene, demonstrating its excellent performance as a saturable absorber. The output pulsed laser was amplified to achieve a maximum power of 500 mW, after which a self-made thrombus model was ablated to observe the experimental phenomenon. The obtained pulsed laser was compared with continuous wave laser thrombolysis under the same conditions. The results indicated that the 1.5-μm Q-switched fiber laser possesses thrombolytic capabilities, and the surface ablation depth and damage area of the thrombus were determined at various time and power levels. The pulsed laser thrombolysis has a smaller damage area and a greater penetration depth compared with continuous wave laser.

Hybrid Graphene–Silicon Arrayed Waveguide Gratings for On-Chip Signal–Frequency Conversion

We present the design and simulations of a novel integrated device concept enabling a frequency conversion of a broad signal. The solution is based on a hybrid silicon–graphene photonic chip, which could be used for controlled spectrometry in low-cost devices. The device is based on a silicon-on-insulator (SOI) platform on which an arrayed waveguide grating (AWG) is designed for operation at the center wavelength of λ = 1800 nm. The AWG is spectrally separating one broad input signal to thirty-two-output channels with a channel spacing of 2.72 nm. The output signals are well separated and uniform with the extinction ratio and the standard deviation of 10.00 dB and 0.04, respectively. The 3 dB channel width is 1.34 nm, which is suitable for sensing applications with significant accuracy. After spacial and spectral separation, each output signal is then converted to one signal at 1480 nm wavelength through a graphene-based saturable absorber scheme. Therefore, the device allows the detection of each separated signal with a simple near-infrared camera on which the outputs are imaged using conventional optics, leading to a classical pixel/wavelength correspondence. Crossed-waveguide couplers are designed to combine the controlling signal at 1480 nm to each channel waveguide of the AWG. The combination of the signals saturates the graphene layer at the output waveguides, allowing the pass of the controlling wavelength. This device can be applied as a spectrometer in environmental sensing and monitoring with high efficiency and low cost.

Nickel Nanoparticles as Broadband Saturable Absorbers for Ultrafast Photonics

Nickel Nanoparticles as Broadband Saturable Absorbers for Ultrafast Photonics

Inorganic Material of Magnesium Nitrate Mg(NO3)2 Film as Q-Switcher in the C-Band Region

A novel inorganic material of Magnesium Nitrate (Mg(NO3)2) thin film is successfully investigated in the C-band region. The Q-switcher is Mg(NO3)2 thin film. The solvent casting method has been applied to prepare Mg(NO3)2 thin film before being positioned within the fiber ferrule duo to act as a Q-switcher. Thereby, the modulation depth and the saturation intensity of the Mg(NO3)2 thin film exhibit at 32.40% and 0.07 MW/cm2, respectively. It is possible to produce a steady Q-switched pulse fiber laser with a maximum pump power of 403.00 mW, a repetition rate of 72.56 kHz, and a pulse width of 3.00 µs. In addition, the tunable Q-switched pulse fiber laser is also examined using a figure-of-eight cavity design incorporating a tunable bandpass filter (TBF). Consequently, the operating wavelength is changed in the range of 1528 nm to 1552 nm, even while the pump power remains the same at 403.00 mW. During this time, the pulse width and repetition rate shifted from 2.10 µs to 4.10 µs and altered from 67.90 kHz to 35.80 kHz, respectively. Consequently, the Mg(NO3)2 thin film has the opportunity to be an effective saturable absorber for generating pulsed fiber lasers and can be applied in optical communications applications.

Metallic layered VSe2 saturable absorber based single- and dual-wavelength ultrafast fiber laser

Vanadium selenide (VSe2) is a special two-dimensional (2D) transition metal dichalcogenide (TMD) material with metallic properties similar to graphene, which has been proved to have saturable absorption properties and used in mode-locked fiber lasers. As an excellent saturable absorber (SA) material, VSe2 has advantage of ultrafast carrier recovery time and broadband optical response range. However, the potential application of VSe2 in the field of ultrafast photonics has not been fully developed so far. In this work, the as-prepared VSe2 nanosheets were deposited on tapered fiber by optical deposition to obtain VSe2 SA. By inserting VSe2 SA into an Er-doped fiber laser, the mode-locked pulses with a central wavelength of 1574.4 nm can be obtained. The pulse width of the laser is measured to be ∼680 fs which is narrowest in the reported VSe2 SA-based lasers. In addition, the unique dual-wavelength mode-locked pulse is also obtained by further adjusting intracavity dispersion and polarization. This kind of dual-wavelength pulse is valuable in high order harmonic generation enhancement, terahertz wave generation, dense wavelength division multiplexing, dual-frequency comb and other applications. Our results show that metallic VSe2 is of great potential value in ultrafast fiber laser.

Research on the Frequency Stabilization System of an External Cavity Diode Laser Based on Rubidium Atomic Modulation Transfer Spectroscopy Technology

To achieve high-frequency stability on the external cavity diode laser (ECDL), a 780 nm ECDL serves as the seed light source, and its frequency is precisely locked to the saturated absorption peak of rubidium (Rb) atoms using modulation transfer spectroscopy (MTS) technology. For improving the performance of frequency locking, the scheme is designed to find the optimal operating conditions. Correlations between the frequency discrimination signal (FDS) and critical parameters, such as the temperature of the Rb cell, the power ratio of the probe and pump light, and the frequency and amplitude of the modulation and demodulation signals, are observed to attain the optimal conditions for frequency locking. To evaluate the performance of the frequency-stabilized 780 nm ECDL, a dual-beam heterodyne setup was constructed. Through this arrangement, the laser linewidth, approximately 65.4 kHz, is measured. Then, the frequency stability of the laser, quantified as low as 4.886 × 10−12 @32 s, is determined by measuring the beat-frequency signal with a frequency counter and calculating the Allan variance. Furthermore, using the realized frequency locking technology, the 780 nm ECDL can achieve long-term stabilization even after 25 h. The test results show the exceptional performance of the implemented frequency stabilization system for the 780 nm ECDL.

Spatial Writing of Ultrafast All-Optical Switching.

Writing spatial information on ultrafast all-optical switching is essential for constructing ultrafast processing units in photonic applications, such as optical communication and computing networks. However, most methods ignore the fabrication and imaging of controllable switching area, limiting its spatial information and the further design in ultrafast devices. Here, we propose a method to spatially write in ultrafast all-optical switching based on MAPbI3 perovskite with nanocone structure and visualize the switching effect in arbitrary designed area. Due to the light confinement effect of nanocone fabrication using a fs laser, the light is strongly absorbed by perovskite and reach saturable absorption. It leads to ultrafast broadband transmittance change with 25 fs switching time and 10% modulation depth in nanocone perovskite area. Our preparation method offers high efficiency, performance, and flexibility for the spatial writing of ultrafast all-optical switching, which is promising for developing ultrafast all-optical networks and the next generation of communication technology.

High-performance 1.06 μm continuous-wave and passive Q-switched laser with a novel Nd: CTGAS crystal

This paper reported continuous-wave and passive Q-switched laser at 1.06 μm with a novel langasite Nd3+: Ca3TaGa2.1Al0.9Si2O14 crystal. A high-efficiency continuous-wave laser with an output power of 1.71 W was obtained at an absorbed pump power of 3.92 W; the corresponding slope efficiency was 46.5 %, and optical conversion efficiency was 43.6 %. A high-performance passive Q-switched laser was realized with Cr4+: Y3Al5O12 as a saturable absorber. The shortest pulse width was 8.2 ns, and the maximum single pulse energy and peak power were 75.5 μJ and 3.83 kW, respectively.

Comparative Study of Q-Switched Erbium Doped Fibre Laser with SWCNT-PVA Saturable Absorber of Different Ratios

This paper intends to compare the performance parameters of passive Q-switched erbium-doped fibre laser (EDFL) ring cavity configuration by employing SWCNT-PVA as a saturable absorber (SA). The single-wall carbon nanotube-polyvinyl alcohol (SWCNT-PVA) SA thin film fabricated by drop-casting technique is physically characterised to understand its surface morphology and thickness. The laser diode (LD) characterisation is attained to understand the attributes of LD before inserting the SWCNT-PVA into the ring cavity. The SWCNT-PVA SA of ratios 1:1, 3:2 and 2:3 is inserted into the cavity for analysis and comparison with each other. The pulses obtained from the Q-switched laser show that SWCNT-PVA SA of ratio 2:3 is the best SA as it possesses excellent power related parameters of the highest output power of 3.45 mW and highest pulse energy of 36.12 nJ with its moderate repetition rate of 96.25 kHz and pulse width 4.76 ms. The envisaged laser is presumed to have representational implications throughout fibre optic sensing, biosensors, range finding, and other fields for better possible prospects.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs.

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Passively harmonic mode-locked erbium-doped fiber laser with a gold nanofilm saturable absorber

We demonstrate a 1.5 GHz harmonic mode-locked erbium-doped fiber laser by incorporating gold nanofilm as a saturable absorber (SA). The high-quality gold nanofilm SA fabricated by the physical vapor deposition method possesses a high modulation depth of 12.9% and a low saturation intensity of 1.69 MW/cm2 at 1.56 µm, facilitating the generation of harmonic mode-locking. The fundamental mode-locked operation was obtained at 1564.7 nm, with a pulse duration of 586 fs and a repetition rate of 34.235 MHz. At the pump power of 610 mW, 44th-order harmonic mode-locking with a repetition rate of 1.506 GHz was achieved, which is the highest yet reported in mode-locked fiber lasers using gold nanomaterials as SAs. Moreover, the gold nanofilm-based harmonic mode-locked fiber laser shows relatively high signal-to-noise ratios, high output power, and good stability. These results highlight the advantage of the gold nanofilm-based SA in realizing high repetition rate laser sources.

Passively Q-Switched 1.5- μm Erbium-Doped All-Fibre Laser with Silver Saturable Absorber

This research examines the operation of a passively Q-switched erbium-doped all-fibre laser (EDFL) using a silver (Ag) based saturable absorber (SA) by comparing the output characteristics of the Q-switched laser with those of continuous wave all-fibre lasers. A study was done on how the laser's Q-factor is modified and affects the rate at which pulses are repeated, as well as their output power, width, and energy. The results showed that high-energy Q-switched pulses were successfully generated at the essential 1.5 µm wavelength within the pump power range of 83.6 mW to 171.7 mW, with repetition rates ranging from 33.46 kHz to 77.96 kHz. The EDFL generated a pulse with a width of 4.033 µs and an energy of 2.82 nJ at a pump power of 171.7 mW. The results indicate that Ag may potentially be a good SA for pulse production in the 1.5 µm wavelength area as well as for use in a wide range of applications.

Spectrally resolved nonlinearities within a laser pulse in a single-scan and spectrometer-based nonlinear optical probing.

The intricate spectrally resolved optical nonlinearities resulting from a spectrally broad femtosecond Gaussian laser pulse have been unraveled using a single-scan and spectrometer-based nonlinear optical probing technique. The interaction of the broad femtosecond laser pulse with a strongly absorbing organic dye has unveiled a remarkably distinct nonlinear absorption behavior across the broad spectral window. The nonlinear absorption behavior unveils an unusual transition from the reverse saturation absorption (RSA) to the saturation absorption (SA) as we sweep the wavelength on both sides of the central wavelength of the excitation laser pulse. A competition between the band-filling and excited-state absorption results in such a dramatic switch-over from the RSA to the SA due to the variation of the intensity distribution across the Gaussian pulse spectrum. On the other hand, the nonlinear refraction studies dictate more over the constant Kerr-type positive nonlinear refractive indices across the entire laser pulse, with a pronounced contribution from the nonlinear absorption phase dominating at the center of the pulse. The presented technique establishes a robust and simple spectrometer-based technique that offers new, to the best of our knowledge, avenues for estimating optical nonlinearities for rapid nonlinear optical measurements.