Nonlinear Saturable Absorption Research Articles

Passively mode-locked dual-wavelength Er-doped fiber laser based on antimony tin oxide as saturable absorber

As a typical transparent conductive oxide, antimony tin oxide (ATO) is widely applied in many optical fields. However, investigations of the nonlinear absorption properties of ATO have not been reported so far. In this study, ATO was employed as a saturable absorber (SA) for producing an Er-doped pulsed fiber laser. To our knowledge, this is the first time that ATO has been used to fabricate an SA. Its appearance and nonlinear saturable absorption characteristics were investigated in our experiment. The saturation intensity and modulation depth of the ATO-SA were 7.51 MW cm−2 and 2.30%, respectively. By adjusting the polarization controllers and the pump power, dual-wavelength pulses were generated within an Er-doped fiber laser. The dual-wavelength pulses were centered at wavelengths of 1558.3 nm and 1558.7 nm with a repetition rate of 1.04 MHz. The pulse width was 4.42 ns. Our results fully prove that ATO with its excellent nonlinear absorption properties will have wide potential ultrafast photonic applications.

Ternary chalcogenide Ta2NiS5 as a saturable absorber for a 1.9 μm passively Q-switched bulk laser.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta2NiS5 with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9μm has been realized with the Ta2NiS5 SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1W, 313ns, 22.0μJ, and 71.0W, respectively. This is the first demonstration of the saturable absorption property of Ta2NiS5, to the best of our knowledge. The results indicate well the promising potential of Ta2NiS5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.

Nonlinear optics in carbon nanotube, graphene, and related 2D materials

One- and two-dimensional forms of carbon, carbon nanotube, and graphene, and related 2D materials, have attracted great attention of researchers in many fields for their interesting and useful electrical, optical, chemical, and mechanical properties. In this tutorial, we will introduce the basic physics and the linear optical properties of these 1D/2D materials. We then focus on their nonlinear optical properties, saturable absorption, electro-optic effect, and nonlinear Kerr effect. We will also review and discuss a few key applications using the ultrafast nonlinear phenomena possessed by these 1D/2D materials: (1) short-pulse fiber lasers using saturable absorption, (2) electro-optic modulators, and (3) all-optical signal processing devices.

Carboxyl graphene oxide solution saturable absorber for femtosecond mode-locked erbium-doped fiber laser**Project supported by the Central University Special Fund Basic Research and Operating Expenses, China (Grant No. GK201702005), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM6091), the National Natural Science Foundation of China (Grant No. 61705183), and the Fundamental Research Funds for the Central Universities, China (Grant

The carboxyl-functionalized graphene oxide (GO-COOH) is a kind of unique two-dimensional (2D) material and possesses excellent nonlinear saturable absorption property and high water-solubility. In this paper, we prepare saturable absorber (SA) device by depositing GO-COOH nanosheets aqueous solution on a D-shaped fiber. The modulation depth (MD) and saturable intensity of the SA are measured to be 9.6% and 19 MW/cm2, respectively. By inserting the SA into the erbium-doped fiber (EDF) laser, a passively mode-locked EDF laser has been achieved with the spectrum center wavelength of 1562.76 nm. The pulse duration, repetition rate, and the signal-to-noise ratio (SNR) are 500 fs, 14.79 MHz, and 80 dB, respectively. The maximum average output power is measured to be 3.85 mW. These results indicate that the GO-COOH nanosheets SA can be used as a promising mode locker for the generation of ultrashort pulses.

Efficient Optical Saturable Absorbers with Graphene on Polymer Waveguides for Femtosecond Laser Pulse Formation

AbstractPhotonic integrated circuits (PICs) are notable for their enhanced functionalities with material flexibilities to find applications in wearable high‐speed data management systems. Due to the miniaturized dimensions of PICs, the employment of a nanomaterial having significant optical nonlinearity is critical. Here, it is demonstrated that a polymer waveguide can be harmonized with nonlinear graphene to form ultrashort laser pulses. The graphene works as nonlinear saturable absorber on the polymer waveguide prepared with a perfluorinated acrylic resin. The evanescent field of a laser propagating through the waveguide interacts with graphene to induce intracavity intensity modulation for femtosecond‐scale pulse formation. The laser output is characterized quantitatively as the central wavelength, spectral width, repetition rate, extinction ratio, and pulse duration, which are 1553.32 nm, 10.21 nm, 4.18 MHz, 76.03 dB, and 874 fs, respectively. Stable operation is verified over 3 h.

PbS quantum dots as a saturable absorber for ultrafast laser

Low-dimensional nanomaterials, owing to their unique and versatile properties, are very attractive for enormous electronic and optoelectronic applications. PbS quantum dots (QDs), characterized by a large Bohr radius and size-tunable bandgap, are especially interesting for photonic applications in the near-infrared region. Here, oleic acid capped colloidal PbS QDs as a saturable absorber are investigated for ultrashort-pulse generation. The PbS QDs exhibit outstanding nonlinear saturable absorption properties at 1550 nm: a modulation depth up to 44.5% and a thermal damage threshold larger than 30 mJ/cm2. By incorporating PbS QDs into a fiber laser, a transform-limited soliton pulse as short as 559 fs with a bandwidth of 4.78 nm is realized at 1563 nm. Numerous applications may benefit from the nonlinear saturable absorption properties of PbS QDs, such as near-infrared pulsed lasers and modulators.

Optical materials: Studying the role of hetropolyacid to enhance the nonlinear optical responses of porphyrin in their hybrids system

Nonlinear optical responses are measured to investigate the role of hetropolyacid (HPA) in porphyrin-Lindqvist type {∼PM@HPA} hybrid systems, {where PM@HPA = [(TBA)8{(MTPPN4)(Mo6O18)4}]; M = 2H (1) and Mn (2)}. The well-known Z-scan technique with wavelength (λ) = 532 nm and pulse duration of τ = 6 ns is used. The results clearly show the significant enhancement in nonlinear self-defocusing effect and reverse saturable absorption under closed and open-aperture configuration for PM@HPA hybrids. It is also observed that the second hyperpolarizability γ values, {1 (4.639 × 10−29 esu) < 2 (5.214 × 10−29 esu)}, are directly proportional to the discrepancy of LUMO level (ΔE) values {1 (2.214 eV) < 2 (2.339 eV)} while they are inversely proportional to the HOMO−LUMO energy gap Eg values {1 (2.003 eV) > 2 (1.862 eV)} in the PM@HPA hybrid system where the porphyrin moiety acts as electron donor whilst HPA acts as electron acceptor. Therefore, the emergence of a facile electron transformation from the porphyrin moieties to the low-lying LUMO levels of HPA is mainly responsible for the enhancement in nonlinear optical responses of PM@HPA hybrids system. As a consequence the hybrid compounds can be fascinating for optical limiting applications.

Laser ablation–induced synthesis and nonlinear optical characterization of titanium and cobalt nanoparticles

The studies of third-order nonlinear optical processes (nonlinear saturable absorption, reverse saturable absorption, two-photon absorption, and nonlinear refraction) in the titanium and cobalt nanoparticles synthesized by laser ablation of bulk materials in deionized water, toluene, and ethylene glycol are reported. The nanoparticle suspensions are systematically characterized by absorption spectroscopy, scanning electron microscopy, and Z-scan technique using 800 nm and 400 nm, 60 fs pulses as well as 355 nm, 6 ns pulses. The concurrence of different nonlinear absorption processes in nanoparticle-containing suspensions is discussed. We also demonstrate the optical limiting of these nanoparticles in water using the 800 nm, 60 fs pulses.

Diode-Pumped Solid-State Q-Switched Laser with Rhenium Diselenide as Saturable Absorber

We report a solid-state passively Q-switched Nd:YVO4 laser adopting rhenium diselenide (ReSe2) as saturable absorber (SA) materials. ReSe2 belongs to a type of transition metal dichalcogenides (TMDs) materials and it has the weak-layered dependent feature beneficial for the preparation of few-layer materials. The few-layer ReSe2 was prepared by ultrasonic exfoliation method. Using a power-dependent transmission experiment, its modulation depth and saturation intensity were measured to be 1.89% and 6.37 MW/cm2. Pumped by diode laser and based on few-layer ReSe2 SA, the Q-switched Nd:YVO4 laser obtained the shortest Q-switched pulse width of 682 ns with the highest repetition rate of 84.16 kHz. The maximum average output power was 125 mW with the slope efficiency of 17.27%. Our experiment, to the best of our knowledge, is the first demonstration that used ReSe2 as SA materials in an all-solid-state laser. The results show that the few-layer ReSe2 owns the nonlinear saturable absorption properties and it has the capacity to act as SA in an all-solid-state laser.

TiS2-based saturable absorber for ultrafast fiber lasers

We fabricate titanium disulfide (TiS2) using a liquid exfoliation method and subsequently a TiS2-based device by optically depositing the TiS2 material onto the microfiber. This device exhibits a strong nonlinear saturable absorption property with an optical modulation depth of 8.3% at 1560 nm. With the implementation of this all-fiber TiS2-based saturable absorber, we demonstrate that both mode-locking and Q-switching operation can be obtained in a turn-key all-fiber erbium-doped laser cavity. Our findings constitute the first example, to the best of our knowledge, of a TiS2-based saturable absorber for ultrashort pulse generation and highlight the great potential of such devices in two-dimensional nanomaterials-related photonics.

Nonlinear saturable absorption properties of indium selenide and its application for demonstrating a Yb-doped mode-locked fiber laser

Recently, two-dimensional materials have shown excellent nonlinear absorption properties and have practically promoted the development of ultrafast lasers. As one of the typical III-VI semiconductors, InSe has already been widely applied in designing photo-sensors and other optical devices due to its outstanding electrical transport, quantum physics and dramatic photo-response properties. However, the nonlinear absorption characteristics of InSe have not been experimentally investigated within ultrafast lasers so far. In our work, the nonlinear absorption properties of InSe were investigated. InSe-PVA film was successfully prepared and employed for achieving a mode-locked Yb-doped fiber laser. A stable mode-locked operation with a maximum output power of 16.3 mW and a minimum pulse width of 1.37 ns at a pulse repetition rate of 1.76 MHz was obtained, and the corresponding pulse energy was as high as 9.26 nJ. Our findings suggest that InSe may have wide potential ultrafast photonic applications due to its suitable bandgap value and excellent nonlinear saturable absorption characteristics.

Low‐Dimensional Saturable Absorbers in the Visible Spectral Region

AbstractVisible light has an important and unique value in research and practical applications, because of its perceptible characteristics by the human eye. Directly pumped bulk visible pulsed lasers are booming in recent years stimulated by the advances of blue laser diodes. As critical components, novel and favorable saturable absorbers in view of distinct nonlinear saturable absorption properties are desired, which can promote the development of ultrafast photonics in the visible range. Over the years, low dimensional materials with the advantages of ultrafast carrier recovery rate and distinct nonlinear saturable absorption have originated a class of innovative applications in photonics and optoelectronics, especially as saturable absorbers in the pulsed lasers. Here, the low dimensional saturable absorbers in the visible range are reviewed, including the fabrication, linear and nonlinear optical response, and applications in the pulsed visible lasers of low dimensional semiconductors and noble metal nanoparticles. The design criteria of the low dimensional saturable absorbers for generating laser pluse by Q‐switching and mode‐locking are proposed and discussed. Finally, some possible development tendency and directions of saturable absorbers for the visible pulsed lasers are proposed in this review by focusing on some potential strengths.

Nonlinear absorption properties of indium selenide and its application for demonstrating pulsed Er-doped fiber laser

Two-dimensional materials are now receiving continuously increasing attention due to their exceptional optical properties. Recently, it has been proved that indium selenide (InSe) is also an excellent photoelectric material, with wide applications in the field of photodetecters and so on. In our work, layered InSe was prepared through the liquid-phase exfoliation method, and the nonlinear saturable absorption properties of InSe were also experimentally investigated. In addition, InSe-polyvinyl alcohol film was successfully prepared and employed as an saturable absorber for demonstrating an Er-doped passive Q-switched mode-locked fiber laser for the first time. The largest Q-switched pulse energy was as high as 112.97 nJ and the narrowest mode-locked pulse duration was 2.96 ns at a repetition rate of 1.74 MHz. Our results fully indicate that InSe also has excellent nonlinear absorption properties in comparison with other commonly used 2D materials. Thus, the applications of InSe can be deeply investigated to promote the development of ultra-fast optics in the near future.

THz absorption spectrum employed for characterize the mixed Gallium selenide-Tin disulfide saturable absorber and its application for passively Q-switched solid state laser

Due to the ultra-short recovery time and the wider absorption range, graphene-like 2D material have been widely employed as saturable absorbers (SAs) in passively Q-switched and mode-locked lasers. Due to the low photon energy, noninvasive and high resolution, THz wave was widely used to characterize samples. In this paper, the nonlinear saturable absorption property and THz absorption spectrum of Gallium selenide/Tin disulfide (GaSe/SnS2) is reported. Passively Q-switched Nd:GdTaO4 laser with GaSe/SnS2 SA is demonstrated. The maximum output power of 551 mW under the pump power of 5 W. The minimum pulse width is 365 ns at the pulse repetition rate of 89 kHz. Our results indicate that GaSe/SnS2 nanosheets could be used in Q-switched lasers. The GaSe/SnS2 SA with good nonlinear absorption properties and easy fabricating process will promote the ultrafast photonics applications in solid state lasers.

Nonlinear optical response of a Co:ZnO epitaxial thin film for large spectral range pulse modulation

We demonstrate the large spectral range nonlinear optical response of a Co:ZnO epitaxial thin film (with single crystal structure) with the absorption range from 1.0 μm to 2.0 μm, for the first time to our knowledge. The third-order nonlinear optical properties and saturable absorption of Co0.15Zn0.85O (Co:ZnO) were studied with the modulation depth of 0.68% and saturation fluence of 1.532 μJ/cm2. Passive Q-switched lasers at the wavelengths of a 1.4 μm Nd:YGG laser and a 1.9 μm Tm:LuVO4 laser were realized with the Co:ZnO epitaxial thin film as the saturable absorber. In the case where the wavelength is 1.4 μm, we obtained the shortest pulse width, the largest pulse energy and the highest peak power, which were recorded at 89 ns, 2.3 μJ and 25.8 W, respectively. Moreover, when the laser output wavelength is 1.9 μm, we got the smallest pulse width of 274 ns. This work provides a promising saturable absorber with a large spectral range response.

Theoretical and experimental studies on a Q-switching operation in an erbium-doped fiber laser using vanadium oxide as saturable absorber

We introduce theoretical analysis for a passively Q-switching operation in an erbium-doped fiber laser (EDFL) with a saturable absorber (SA). Peak power, repetition rate, and pulse duration have been calculated as functions of pump power and cavity length. The simulation results are compared with the passively Q-switched EDFL demonstrated using vanadium oxide (V2O5) as SA. The nonlinear saturable absorption of the V2O5-SA is characterized by a modulation depth of 7% with a saturation intensity of 71 MW cm−2. This is the first demonstration of a fiber laser based on a V2O5-SA that introduces new opportunity for photonic applications. The introduced theoretical model could be highly useful for understanding and improving Q-switched EDFLs based on a SA.

Mesoporous Carbon Nanospheres as Broadband Saturable Absorbers for Pulsed Laser Generation

AbstractBroadband pulsed laser generation is demonstrated by using mesoporous carbon nanospheres (MCNs) as saturable absorbers (SAs). The MCNs are prepared by a “silica‐assisted” method, and then mixed with sodium carboxymethylcellulose (NaCMC) to form the MCNs film. The film not only shows strong absorption from visible to mid‐infrared spectral region, but also possesses the nonlinear saturable absorption properties. As the MCNs film is inserted into the laser cavity, a mode‐locked laser at 1 µm and Q‐switched lasers at 1.56 and 2 µm are realized, respectively. In addition, by depositing the MCNs onto tapered fiber as an SA, a mode‐locked fiber laser at 2 µm is also demonstrated. The results show that MCNs are promising SA material for broadband pulsed laser generation.

Near-infrared third-order optical nonlinearity in CaCu3Ti4O12 thin films

We investigate the optical nonlinearity of CaCu3Ti4O[Formula: see text] (CCTO) thin films on MgO substrates using Z-scan technique at a near-infrared wavelength of 1064[Formula: see text]nm with 25[Formula: see text]ps duration pulses. The near-infrared nonlinear saturable absorption coefficient [Formula: see text] and the nonlinear refraction coefficient [Formula: see text] of the values [Formula: see text][Formula: see text]cm/GW and 0.66[Formula: see text]cm2/GW, respectively, were deduced from the study of the nonlinear response at different excitation intensities. The three-level model is proposed to interpret the large optical nonlinearity in CCTO films in near-infrared spectrum, by considering the intermediate energy levels due to the defects or grain boundaries. The large optical nonlinearity and fast response at picosecond time-domain indicate that CaCu3Ti4O[Formula: see text] thin films are promising candidates for applications in near-infrared nonlinear photonics devices.

WS2-Clad Microfiber Saturable Absorber for High-Energy Rectangular Pulse Fiber Laser

Tungsten disulfide (WS2), which possesses broadband nonlinear saturable absorption property, displays promising applications in passively mode-locked lasers. Recent research works have demonstrated that WS2 shows much higher thermal conductivity than other transition metal dichalcogenides, which can withstand higher optical intensity and exhibit a higher damage threshold. However, the WS2-based high-energy fiber lasers have not been extensively studied. Here, a WS2-clad microfiber (WCM) saturable absorber (SA) is exploited by an effective transferring approach, which is precisely accomplished under optical microscope. The evanescent field interaction scheme has ability to further raise the optical damage threshold, as well as take full advantage of the nonlinear effect of WS2. Based on the WCM SA, high-energy rectangular pulses are achieved in an Er-doped fiber laser whose pulse duration and energy almost increase linearly with the enhancement of pump power. The maximum energy of single pulse in the cavity can reach 810 nJ under pump power of 800 mW. The experimental results open up venues to create new high-energy laser systems with rich functionalities and novel physical effects.

Stretched graded-index multimode optical fiber as a saturable absorber for erbium-doped fiber laser mode locking.

A novel mode-locking method based on the nonlinear multimode interference in the stretched graded-index multimode optical fiber (GIMF) is proposed in this Letter. The simple device geometry, where the light is coupled in and out of the stretched GIMF via single-mode fibers, is demonstrated to exhibit the temporal intensity discrimination required for mode locking. The nonlinear saturable absorber (SA) characteristics of the device are controllable by simply adjusting the strength of the stretching applied. The modulation depth of the device, which consists of ∼23.5 cm GIMF, is tuned from 10.37% to 22.27%. Such a simple SA enables the wavelength-switchable mode-locking operation in a ring Er-doped fiber laser, and ultrafast pulses with a pulse width of 506fs at 1572.5nm and 416fs at 1591.4nm were generated. The versatility and simplicity of the SA device, together with the possibility of scaling the pulse energy, make it highly attractive in ultrafast photonics.