Graphene Saturable Absorber Research Articles

Vanadium Aluminium Carbide Saturable Absorber in Passively Q-switched Erbium-doped Fibre Laser

Following the success of graphene saturable absorber (SA) in the development of passively Q-switched fibre lasers within the past decade, research on two-dimensional (2-D) nanomaterials SAs have shown a significant rise in demands. Nonetheless, there have been several unavoidable setbacks due to the nature of certain nanomaterials, in terms of optical, electronic and physical properties up until the reveal of transition metal carbide (MXene) nanomaterials. These metal-ceramic materials exhibit excellent optical and electrical properties as well as outstanding physical characteristics. However, their synthesis processes involve hazardous and highly acidic chemicals, which drove the researchers to adopt their precursors— ternary nanolaminate carbides (MAX phases) nanomaterials with a simpler and more exquisite fabrication process. This paper presents a passively Q-switched erbium-doped fibre laser (EDFL) with the utilisation of a MAX phases nanomaterial, vanadium aluminium carbide (V4AlC3) as SA. The V4AlC3 SA was fabricated through the solution casting technique with polyvinyl alcohol as the host polymer. The V4AlC3 SA was then integrated into a passively Q-switched EDFL configuration. The performance of V4AlC3 SA as a Q-switcher was determined with the assistance of an optical spectrum analyser (OSA), mixed domain oscilloscope (MDO), and optical power meter (OPM). The maximum pulse repetition rate and minimum pulse width were 54.37 kHz and 6.43 ms, respectively. The minimum repetition interval was 18.33 ms and the duty cycle was 0.326. The highest attained output power was 2.5 mW. Through calculation, the maximum pulse energy and peak power were identified as 45.246 nJ and 6.602 mW. The extensively gigantic pulses in nanosecond duration at 1560.16 nm was accomplished by the V4AlC3 SA, thus proving its stability which also signifies good applications especially those acquiring stable high power and energy.

Modulation instability in a microresonator with graphene saturable absorber, frequency selective feedback and external potential

Modulation Instability is studied in the presence of an external periodic potential in microresonator comprising of a vertical cavity surface emitting laser with saturable absorber and frequency selective feedback. The role of intensity of input field, pump parameter, diffraction coefficient and saturable absorption on the modulation instability has been investigated. Thus, Modulation instability can be tuned by varying the system parameters. This aspect would be beneficial for the purpose of encryption. It is also observed that modulation instability is not explicitly dependent on externally applied potential whereas the effect of potential is shown implicitly by using numerical analysis. The presence of an external potential give the operating range of resonance frequency of the optical cavity instead of one value at the same system parameters. This operating range of resonance frequency is spatially dependent and varies with the system parameters.

Transform-Limited Sub-100-fs Cr:ZnS Laser with a Graphene-ZnSe Saturable Absorber

In this work, we present ultrashort pulse generation from passively mode-locked Cr:ZnS laser with a monolayer graphene-coated ZnSe substrate exhibiting high nonlinearity. The femtosecond Cr:ZnS laser produces output power up to 330 mW at a 233 MHz repetition rate. Even in the presence of an uneven negative dispersion profile, the enhanced self-phase modulation by the ZnSe substrate of the graphene saturable absorber enables the polycrystalline Cr:ZnS laser to produce slightly chirped 99 fs pulses at 2373 nm. With extracavity dispersion compensation using a mixture of 3 mm and 2 mm thick ZnSe plates, the pulse width was compressed from 99 fs to 73 fs, resulting in an improved time–bandwidth product from 0.431 to 0.318. Assuming a sech2 pulse shape (0.315), the pulses were almost transform-limited. These results indicate that utilizing a graphene saturable absorber on a substrate with high nonlinearity presents an effective method for developing sub-100 fs solid-state lasers within the mid-IR spectral range.

Passively Q-Switched Thulium-Holmium Doped Fibre Laser with Electrochemical Exfoliation Graphene in Chitin Based Passive Saturable Absorber

Recent years saw low-dimensional carbon nanostructures like graphene as excellent saturable absorber (SA) for its unique electric and optical properties. Graphene exhibits ultrafast recovery times and high damage thresholds and can be manufactured by relatively simple methods. In this work, Graphene was synthesized using the electrochemical exfoliation (ECE) method. Chitin biopolymer was used to develop graphene-based SA as a more environmentally friendly alternative to conventional synthetic polymers. The fabricated passive SA was then integrated into Thulium-Holmium-doped fibre laser (THDFL) in ring cavity for pulsed laser generation via Q-switching. The optical and physical properties of the graphene-based SA were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM) and energy-dispersive x-ray spectroscopy (EDS). Q-switched pulse was successfully demonstrated using the fabricated graphene SAs. ECE graphene-chitin SA generated a Q-switched pulse region at 2 micro-metre with the repetition rate and shortest pulse width of 67.78 kHZ and 10.03 micro-second, respectively. The signal-to-noise ratio (SNR) values obtained was 40 dB indicating high stability of the pulse laser-generated. This study demonstrated the potential of graphene embedded in chitin biopolymer as a sustainable and environmentally friendly SA for a wide range of applications, particularly for pulsed fibre lasers.

Characterizing Passively Q-switched Fiber Laser in LiDAR Application

A LiDAR system consists of a Q-switched fiber laser that emits light pulses to measure the distance from the target. We have experimentally demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) by employing graphene saturable absorber (SA). The SA was prepared by dipping a polyvinyl alcohol (PVA) thin film into the graphene solution. Once the SA was fabricated, it can be placed in the cavity to perform pulses and it is operating at 1558.92 nm. The shortest pulse received is 3.9 μs and generated at the repetition rate of 115 kHz. The pulses are stable between pump powers of 59.6mW and 127.1 mW. At the maximum pump power value of127.1 mW, thelaser cavity produced pulses with a 1.4mW output power and a 1.1nJ pulse energy.

Hybrid Mode-Locked Fiber Ring Laser Using Graphene Saturable Absorbers to Generate 20 and 50-GHz Pulse Trains

Optical pulses at high repetition rates are generated using rational harmonic mode locking and saturable absorber made of graphene nanoparticles in a fiber laser. The pulse generation from the fiber laser is modeled by solving the Generalized Nonlinear Schrodinger Equation. The computation involved varying the various saturable absorption parameters, such as linear and nonlinear absorption coefficients. Experimentally stable pulse trains at 20 GHz and 50 GHz are generated with a pulse width of ∼ 2.7 ps. This result agrees with the simulation.

SiO2 Passivated Graphene Saturable Absorber Mirrors for Ultrashort Pulse Generation.

Owing to its broadband absorption, ultrafast recovery time, and excellent saturable absorption feature, graphene has been recognized as one of the best candidates as a high-performance saturable absorber (SA). However, the low absorption efficiency and reduced modulation depth severely limit the application of graphene-based SA in ultrafast fiber lasers. In this paper, a single-layer graphene saturable absorber mirror (SG-SAM) was coated by a quarter-wave SiO2 passivated layer, and a significantly enhanced modulation depth and reduced saturation intensity were obtained simultaneously compared to the SG-SAM without the SiO2 coating layer. In addition, long-term operational stability was found in the device due to the excellent isolation and protection of the graphene absorption layer from the external environment by the SiO2 layer. The high performance of the SAM was further confirmed by the construction of a ring-cavity EDF laser generating mode-locked pulses with a central wavelength of 1563.7 nm, a repetition rate of 34.17 MHz, and a pulse width of 830 fs.

Study on the mechanically exfoliated graphene saturable absorption dependence on the number of layers and its influence on passive mode-locking erbium-doped fiber laser dynamics

We experimentally investigated the saturable absorption influence of graphene layers with natural stacking order in an erbium-doped fiber laser passive mode-locking. Mechanically exfoliated graphene saturable absorber (MEGSA) samples, ranging from 1 to 6 layers, were fabricated preserving their natural ABA stacking order and precisely characterized by 2D band profile from Raman spectroscopy. By incorporating the samples as saturable absorbers (SA) in the fiber laser, mode-locking performances with pulse duration from 670–780 fs and bandwidth from 3.8–4.6 nm could be generated. Also, we identified a transition in the mode-locking activation mechanism from non-self-starting, for monolayer and bilayer graphene, to self-starting, for trilayer and few-layer graphene, which is a strong indicative of fast-to-slow saturable absorption response dependence on the number of graphene layers.

Graphene saturable absorber mirror for passive mode-locking of mid-infrared QCLs

Passive mode-locking in quantum cascade lasers (QCLs) remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around $$50~\mathrm {ps}$$ were proposed. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. In this paper, we demonstrate that a single-layer graphene used as a saturable absorber permits to generate stable pulses in such structures. The graphene is integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. The dynamic of the QCL is modeled with Maxwell-Bloch equations while Maxwell-Ampere equation is used for the graphene layer by considering a nonlinear conductivity. This system of equations is solved using the one-dimensional Finite-Difference Time-Domain ( FDTD) method. To model the single-layer graphene of a $$0.33~\mathrm {nm}$$ thickness, a specific sub-cell is implemented based on Maloney method. Simulation results of a $${\mkern 1mu} 6.2~\mu {\text{m}}$$ QCL with a diagonal radiative transition show a generation of isolated pulses with a peak electric field of $$80~\mathrm {MV.m^{-1}}$$ and a duration of $$51~\mathrm {fs}$$ . The mode-locking remains stable for QCLs with a vertical transition having a relaxation time below $$5~\mathrm {ps}$$ .

Passively Q-switched erbium doped fiber laser based on graphene and carbon nanotube saturable absorbers

A passively Q-switched erbium-doped fiber laser (EDFL) was experimented on by employing graphene, single walled carbon nanotubes (SWCNT) and multi-walled carbon nanotube (MWCNT) saturable absorbers (SA). The SA film was obtained by embedding the graphene, SWCNT and MWCNT into polyvinyl alcohol (PVA). The graphene SA was prepared by dipping a PVA thin film into the graphene solution while carbon nanotubes SAs were prepared using the casting method and placed in the ring cavity to produce a stable pulse laser. Graphene, SWCNT and MWCNT SAs were operating at wavelengths of 1558.92 nm, 1557.98 nm and 1558.51 nm, respectively, whereas the continuous wave was 1560.72 nm at the input pump power of 56 mW. The pulse energy, output power, repetition rate and pulse width were compared in graphene, SWCNT and MWCNT SAs. The shortest pulse width retrieved in graphene, SWCNT and MWCNT were 3.90 µs, 3.62 µs 4.43 µs and produced at the repetition rate of 115.00 kHz, 130.70 kHz, and 89.13 kHz, respectively. In comparison to graphene and SWCNT SAs, MWCNT SAs exhibit the best performance in terms of output power of 2.19 mW and high pulse energy of 24.57 nJ in passively Q-switched EDFL.

Low threshold Q-switched pulses based on a WTe2-graphene saturable absorber

Low-threshold and narrow-pulse-width Q-switched optical pulses are obtained using a tapered fiber-based WTe2-graphene saturable absorber (SA) in an erbium-doped fiber laser (EDFL) for the first time. Benefiting from the low unsaturated loss of graphene, the Q-switching threshold (25.8 mW) is an order of magnitude lower than that using SA with WTe2 only. Meanwhile, owing to the high carrier mobility of WTe2, the minimum pulse width (1.2 µs) is the narrowest among the graphene-based fiber lasers. The results indicate the potential of the WTe2-graphene SA in future application and development of laser pulses.

PECVD-derived graphene saturable absorber mirror for 2.8 μm pulsed Er:ZBLAN fiber laser

Graphene has been emerging as an ideal mid-infrared saturable absorber (SA) due to its broadband absorption, ultrafast nonlinear optical response, high stability and thermal tolerance. However, the current routes (e.g. chemical vapor deposition and spin coating) for constructing graphene SAs are suffering from the limited flexibility in substrate choice and the introduction of impurities during the transfer process, resulting in poor film quality and unstable laser modulation. Here, we demonstrate a high-quality graphene SA mirror (GSAM) grown directly on calcium fluoride (CaF2) substrate by a low-temperature plasma enhanced chemical vapor deposition (PECVD) method for mid-infrared pulse modulation. The controllable growth of high-quality graphene film on the nickel-modified CaF2 substrate is realized by adjusting the growth time and hydrocarbon ratio during PECVD process. Consequently, the GSAM shows excellent nonlinear optical absorption with the modulation depth of 11.2%. By inserting the GSAM into the Er:ZBLAN fiber laser, a stable passive Q-switched (QS) operation can be achieved with an average output power of 142 mW and a pulse width of 300.2 ns. The slope efficiency of QS laser is up to 17.4% and the peak power is 7.76 W. Our strategy paves the way for developing high quality and modulation stability GSAM towards industrial applications of pulsed mid-infrared lasers.

Graphene Saturable Absorber Mirrors for Silicon Photonic Platforms

We employ graphene saturable absorption for the theoretical demonstration of saturable absorption mirrors based on planar silicon photonic Bragg gratings. Two geometries are investigated, that of a silicon wire grating and a silicon slot grating, showcasing the increased light-matter interaction of the high-confinement slot waveguide. The gratings are designed in the linear regime for single mode operation, low footprint and broadband operation in the near infrared optical communications frequency range. The saturable absorption effect is introduced through the saturation of graphene’s interband surface conductivity, and we discuss the necessary biasing conditions and applicability of our CW approach on ps-long pulses. We also rigorously include other, possibly detrimental, nonlinear effects, such as silicon’s Kerr effect and two photon absorption, and graphene’s Kerr effect. These effects are proven to have a negligible impact on the operation of the graphene saturable absorber mirror, thanks to the much lower power threshold of graphene’s saturable absorption. Finally, we calculate the nonlinear reflectance and transmittance of the graphene-enhanced Bragg gratings and demonstrate that they can provide high modulation depths at low saturation powers, both highly valued characteristics of saturable absorber mirrors for mode locking applications in view of next-generation integrated pulsed photonic light sources.

Graphene Saturable Absorber Mirror for Mode-Locked Orange Pulse Laser

Graphene Saturable Absorber Mirror for Mode-Locked Orange Pulse Laser

A Comparison for Saturable Absorbers: Carbon Nanotube Versus Graphene

Saturable absorbers (SAs) have been regarded as a low‐cost yet robust and compact solution to pulse generation in different fiber and solid‐state ultrafast lasers. Following the development of different artificial SAs and semiconductor SA mirrors, carbon nanotube (CNT) and graphene are discovered and employed as SAs for solid‐state as well as fiber lasers. In the past decade, a growing number of SAs based on new materials like MXenes and metal halide perovskites have emerged, while CNT and graphene are still irreplaceable by new materials due to their fascinating saturable absorption properties. Instead of searching for new SAs, the investigation of transient dynamics for mode‐locked pulse generation still relies on the use of CNT and graphene SAs in the fiber laser system due to their reproducible performance and facile fabrication. In this review, a comparison between CNT and graphene will be thoroughly studied in terms of optical nonlinearity, relaxation and recovery time, saturation intensity or fluence, modulation depth, non‐saturable loss, and damage threshold dynamics. In the end, this review will address the challenges in the selection of SAs and provides recommendations for CNT and graphene SAs used in different mode‐locked fiber lasers.

The passive Q-switching Tm, Ho co-doped GAGG state laser operating near 2.1 μm

In this letter, we report on a diode pumped passive Q-switching Tm, Ho:GAGG laser at 2090.8 nm with a graphene saturable absorber mirror. In continuous wave operation, a maximum output power of 297 mW at 2114.1 nm is achieved, corresponding to a slope efficiency of 8%. In the passive Q-switching regime, stable pulses are obtained with a shortest pulse width of 576.9 ns and pulse repetition rate of 69.46 kHz. The single pulse energy is 0.3 μJ, corresponding to a pulse peak power of 0.52 W. To the best of our knowledge, this is the first report on the passive Q-switching Tm, Ho:GAGG laser.

Graphene-Molybdenum Disulphide Chitin Nanocomposite Based Passive Q-switcher

A simple fabrication of graphene-MoS2 nanocomposite, as well as individual graphene and molybdenum disulphide (MoS2) film has been done through a liquid phase exfoliation method using chitin as a binder. All of the developed films are integrated as a passive Q-switcher in an Erbium doped fiber laser. The graphene-MoS2 nanocomposite based passive Q-switcher is generated by a pulsed fiber laser with the shortest width of 1.63 µs and the highest signal to noise ratio of 51.01 dB. The graphene-MoS2 nanocomposite films show a better saturable absorption response compared to an individual graphene-chitin and MoS2-chitin based passive Q-switcher. Full Text: PDF ReferencesB. Zhang et al., "Recent Progress in 2D Material-Based Saturable Absorbers for All Solid-State Pulsed Bulk Lasers", Laser Photon. Rev. 14(2), 1900240 (2020). CrossRef M. Zhang, H. Chen, J. Yin, J. Wang, P. Yan, "Recent development of saturable absorbers for ultrafast lasers [Invited]", Chinese Opt. Letters 19(8), 081405 (2021). CrossRef S.A. Hussain, "Beta rhythm events predict corticospinal motor output", Scientific Reports 9(1), 1 (2019). CrossRef B. Fu, Y. Hua, X. Xiao, H. Zhu, Z. Sun, C. Yang, "Broadband Graphene Saturable Absorber for Pulsed Fiber Lasers at 1, 1.5, and 2 μm", IEEE J. Selected Topics in Quant. Electron. 20(5), 411 (2014). CrossRef S.N.M. Halim, S.N.F. Zuikafly, M.F.M. Taib, F. Ahmad, "First Principles Study on Electronic and Optical Properties of Graphene/MoS2 for Optoelectronic Application", IEEE International Conference on Semiconductor Electronics (ICSE), 29-32, (2020), CrossRef Z. Wang, H. Mu, J. Yuan, C. Zhao, Q. Bao, H. Zhang, "Graphene-Bi2Te3 Heterostructure as Broadband Saturable Absorber for Ultra-Short Pulse Generation in Er-Doped and Yb-Doped Fiber Lasers", Quant. Electron. 23(1), 195 (2016). CrossRef E.P. Randviir, D.A. Brownson, C.E. Banks, "A decade of graphene research: production, applications and outlook", Materials Today 17(9), 426 (2014). CrossRef S.N.F. Zuikafly, N.F. Razak, R.M. Rosnan, S.W. Harun, F. Ahmad, "Graphene slurry based passive Q-switcher in erbium doped fiber laser", Bull. Electr. Engin. Informat. 8(4), 1351 (2019). CrossRef W.M.F.W. Nawawi, K.-Y. Lee, E. Kontturi, R.J. Murphy, A. Bismarck, "Chitin Nanopaper from Mushroom Extract: Natural Composite of Nanofibers and Glucan from a Single Biobased Source", ACS Sustainable Chem. Engin. 7(7), 6492 (2019). CrossRef

Broadband cavity soliton with graphene saturable absorber

We theoretically generate broadband cavity soliton, which is known to arise only in a narrowband infrared region. This extension has been done by replacing the conventional semiconductor saturable absorber with a graphene saturable absorber in the microcavity based on a vertical-cavity surface emitting laser coupled with a frequency-selective feedback. The replacement gives rise to cavity solitons in ultraviolet and visible zone, significantly lowers down the required feedback strength as well as the threshold pump power for cavity soliton generation. The spontaneous drift as well as “push broom” dynamics of cavity solitons are observed for all wavelength zones. Since the graphene saturable absorber layer can show broadband operation, it eliminates the necessity of using different saturable absorber layer and their corresponding substrates for different spectral zones. By virtue of graphene's high nonlinearity, single layer structure and easy integration with silicon photonic microresonators our model is a step forward towards the on-chip cavity soliton generator.

Controllable Dynamic Single‐ and Dual‐Channel Graphene Q‐Switching in a Beam‐Splitter‐Type Channel Waveguide Laser

AbstractDirect inscription of structures by femtosecond‐laser pulses facilitates the flexible fabrication of diverse optical channel waveguides in dielectric laser gain media. Among them, beam‐splitter‐type waveguide lasers have been recently studied; however, there is a lack of investigations on the effect of unique characteristics of such waveguides, such as controlled splitting ratios of output powers and selectable excitation of individual channels, for pulsed laser operation. Here, dynamic single‐ and dual‐channel graphene Q‐switching of an Yb:YAG waveguide consisting of one input and two output channels is demonstrated by controlling the power‐splitting ratio. Single‐channel Q‐switched operation, exhibiting typical Q‐switched pulses, is achieved by interaction between the graphene saturable absorber and the desired one of the two channels. When both channels exceed the Q‐switching threshold, dual‐channel Q‐switching generates a pulse train that simultaneously combines the separately Q‐switched pulses induced from each channel under excitation with a single pump source. At a fixed power‐splitting ratio, the pulsed mode can be dynamically switched between the single‐ and dual‐channel Q‐switched operations by varying the pump power. The beam‐splitter‐type waveguide laser demonstrated in this study can be further developed for multiple‐channel Q‐switching, high‐repetition‐rate mode‐locking, and on‐chip dual‐comb sources advantageous for diverse applications in optical communication, metrology, and sensing.

Performance of Q-Switched Fiber Laser Using Optically Deposited Reduced Graphene Oxide as Saturable Absorber

ABSTRACT Graphene is one of the most attractive two-dimensional nanomaterials widely used as saturable absorber for pulsing laser, owing to its unique non-linear optical responses. However, fabrication and integration of graphene saturable absorber into a laser cavity involves complex processes and procedures. Mass production of graphene-based saturable absorbers requires simplification of the fabrication process with minimum material wastage. Reduced graphene oxide, a functionalized graphene, is found to have saturable absorption property as well. Comparatively, it is easier and more cost-effective to produce. On the other hand, optical deposition is a saturable absorber deposition technique that maximizes material utilization. In this work, commercially available reduced graphene oxide in N-methyl-2-pyrrolidone was used to fabricate a saturable absorber device via optical deposition, due to its simplicity and high efficacy. Optical pulse generation via Q-switching were successfully demonstrated with the optically deposited rGO-SA incorporated into a ring erbium-doped fiber laser. Pulse repetition rate of up to ~85.0 kHz and pulse durations as short as ~2.0 μs were achieved. Its performance as a saturable absorber in a Q-switched fiber laser is then compared with previous works. Comparatively, optically deposited rGO has a much lower Q-switched threshold and holds huge potential for mass production with maximum material utilization.