Graphene Saturable Absorber Research Articles

Intracavity losses effect on mode-locking in a waveguide laser with graphene saturable absorber

A single-wavelength compact diode-pumped solid-state laser based on a single-mode waveguide with a diameter of 20 µm and graphene saturable absorber is presented in this work. The total reflection coefficient of the intracavity interferometer has a significant effect on the level of intracavity losses. By accurate controlling the intracavity losses a stable continuous wave passive mode-locking at wavelength of 1064 nm with a pulse repetition rate of 9.5 GHz was obtained.

Performance of Graphene Nanopowder-Polyvinyl Alcohol in Optical Pulse Generation at 1.5 Micron Region

This paper explains about the performance of graphene nanopowder (GNP) based saturable absorber (SA) at 1.5-micron region which is prepared by dissolution in polyvinyl alcohol (PVA) polymer. Two different GNP flakes thickness (AO2-8 nm and AO4-60 nm) are tested. By applying a solution casting method, three weight ratio of GNP to PVA (12.04, 8.03 and 3.11 wt.%) have been prepared and fabricated as a composite thin film. To characterize for the SA performance, 4 mm2 area of GNP-PVA thin film is embedded in a 14 meters long ring cavity with 3 meters Erbium doped fiber (EDF) as a gain medium. Our characterization results show that the GNP-PVA thin film act as a Q-switcher which produce stable laser pulses for 12.04 wt.% with maximum repetition rate of 39.22 kHz and shortest pulse width of 11.79 µs. Meanwhile, unstable Q-switched pulses of 8.03 wt.% and 3.11 wt.% have been observed with recorded signal to noise ratio (SNR) of only 21 dB and 17 dB, respectively. The threshold pumping power for Q-switched lasing to emerge is recorded as low as 30 mW. Apparently, it shows that GNP concentration and flakes thickness in fabricated SA composite plays vital role in the performance of generated Q-switch laser, particularly at 1.5 µm region. Full Text: PDF ReferencesT. Hasan, Z. Sun, F. Wang, F. Bonaccorso, P.H. Tan, A.G. Rozhin, A.C. Ferrari, "Nanotube–Polymer Composites for Ultrafast Photonics", Adv. Mater. 21, 3874 (2009). CrossRef Q. Bao, H. Zhang, Y. Wang, Z. Ni, Y. Yan, Z.X. Shen, K.P. Loh, D.Y. Tang, "Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers", Adv. Funct. Mater. 19, 3077 (2009). CrossRef Z. Luo, M. Zhou, J. Weng, G. Huang, H. Xu, C. Ye, Z. Cai, Opt. Lett. 35(21), 3709 (2010). CrossRef D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, A.C. Ferrari, "Graphene Q-switched, tunable fiber laser", Appl. Phys. Lett. 98, 3106 (2011). CrossRef Y.M. Chang, H. Kim, J.H. Lee, Y. Song, "Multilayered graphene efficiently formed by mechanical exfoliation for nonlinear saturable absorbers in fiber mode-locked lasers", Appl. Phys. Lett. 97, 211102 (2010). CrossRef M. Jiang, Z. Ren, Y. Zhang, B. Lu, R. Zhang, J. Guo, Y. Zhou, J. Bai, "Passive Q-Switching with Graphene Saturable Absorber in Nd:YAG Operating at 1064nm", Mater. Sci. Forum 694, 700 (2011). CrossRef N. Hussin, M.H. Ibrahim, F. Ahmad, H. Yahaya, S.W. Harun, "Graphene Nanoplatelets (GnP)-PVA Based Passive Saturable Absorber", Telkomnika 15(2), 814 (2017). CrossRef F.C. Mat, M. Yasin, A.A. Latiff, S.W. Harun, Photonics Letters of Poland 9, 100 (2017). CrossRef E.K. Ng, K.Y. Lau, H.K. Lee, N.M. Yusoff, A.R. Sarmani, M.F. Omar, M.A. Mahdi, "L-band femtosecond fiber laser based on a reduced graphene oxide polymer composite saturable absorber", Opt. Mater. Express 11, 59 (2021). CrossRef N.H.M. Apandi, S.N.F. Zuikafly, N. Kasim, M.A. Mohamed, S.W. Harun, F. Ahmad, "Observation of dark and bright pulses in q-switched erbium doped fiber laser using graphene nano-platelets as saturable absorber", Bull. Electr. Eng. Inform. 8, 1358 (2019). CrossRef N.U.H.H.B. Zalkepali, N.A. Awang, Y.R. Yuzaile, Z. Zakaria, A.A. Latif and F. Ahmad, "Graphene Nanoplatelets as Saturable Absorber for Mode-locked Fiber Laser Generation", J. Adv. Res. Dyn. Control Syst. 12(2), 602 (2020). CrossRef X. Zhu and S. Chen, "Autoencoder-Based Transceiver Design for OWC Systems in Log-Normal Fading Channel", IEEE Photonics J. 11, 7105109 (2019). CrossRef

Coupling scheme for graphene saturable absorber in a linear cavity mode-locked fiber laser.

A saturable absorber based on a graphene layer covered single-mode fiber with inner short waveguides is proposed and demonstrated for a linear cavity Er-doped mode-locked fiber laser. A pair of short waveguides is written in the fiber by using femtosecond micromachining technology, and the propagating light is guided by one short waveguide to the cladding-air interface and interacts with the graphene layer in the form of evanescent waves before being collected back to the core by another short waveguide, and, as a result, the saturable absorption is excited. The designed saturable absorber is used in the passively mode-locked fiber laser to generate traditional soliton mode-locked pulse output with the center wavelength of 1564.9 nm and pulse width of 758 fs at the fundamental frequency of 22.58 MHz. The fabricated saturable absorber device is stable in operation, compact in structure, safe for thermal damage, and can effectively overcome the shortcomings of poor robustness of the saturable absorbers based on a tapered fiber and D-shaped fiber. This provides a new optical coupling scheme for saturable absorbers based on 2D materials such as graphene and has great potential application in the field of ultrashort pulse lasers.

Mid-infrared nanosecond pulse generation from a graphene modulated Er3+-doped fluoride fiber laser

We demonstrate a 2792.0 nm passively Q-switched Er3+-doped fluoride fiber laser using a graphene saturable absorber mirror (GSAM). Through optimizing the cavity design and the parameters of the GSAM, stable pulses are obtained with a repetition frequency ranging from 60.2 to 221.8 kHz. The shortest pulse duration is 238.2 ns, which, to the best of our knowledge, is the shortest passively Q-switching pulse obtained in 3 μm mid-infrared wavelength region. The maximum average output power is 535 mW, and the single pulse energy is 2.53 μJ. Further improvement of the pulse energy and pulse width is possible by optimizing the bleaching energy of the GSAM.

Wavelength-switchable 9.5 GHz graphene mode-locked waveguide laser

A multi-wavelength compact ultrafast laser based on a single-mode waveguide inscribed in Nd:YAG and graphene saturable absorber is developed. By changing the pump parameters, we demonstrate single-, dual- and multi- wavelength mode-locking regimes. Accurate control of intracavity losses provides stable CW passive mode-locking at a wavelength of 1064 nm and dual-wavelength mode-locking at 1061 and 1064 nm with a pulse repetition rate of 9.5 GHz.

Wavelength-changeable thulium-doped fiber laser based on monolayer graphene

We propose and demonstrate a wavelength changeable thulium-doped fiber laser (TDFL) based on a monolayer graphene saturable absorber (SA). With different pump powers and polarization controller states, the laser can operate in different operation modes including continuous wave, single solitons, harmonic mode-locked pulses of 2nd to 4th order, and soliton molecules. Wavelength changing over a range of 7–11 nm for different operation regimes was realized by stretching the tapered fiber and adjusting the polarization controller in the cavity. To the best of our knowledge, this is the first TDFL that is changeable in wavelength under different operation modes and that is based on a monolayer graphene SA.

Generation of noise-like pulses and soliton rains in a graphene mode-locked erbium-doped fiber ring laser

We demonstrate the generation of noise-like pulses (NLPs) and soliton rains in a graphene saturable absorber mode-locked erbium-doped fiber laser. Typical NLPs are obtained at a proper pump power and in a cavity polarization state. The soliton rain operation with multiple solitons can be achieved by finely adjusting the cavity polarization state. In addition, distinctive multi-soliton interactions are observed and investigated, including the fundamental mode-locking and multiple pulses. The experimental results can help further understand nonlinear pulse dynamics in ultrafast optics.

1.56 µm and 1.93 µm synchronized mode-locked fiber laser with graphene saturable absorber

Ultrafast pulse with short duration ranging from picosecond to femtosecond has extensive industrial and scientific applications. The laser cavity generates this ultrafast pulse, however, was typically designed to emit the light at wavebands such as at approximately 1.5–1.6 µm or 1.9–2.0 µm. This could be limited by the bandgap of certain saturable absorber material to conduct ultra-broadband laser emission. Graphene, a 2D material with gapless band structure contributes to the optical resonant excitation to emit at any wavelength. The graphene was employed as the saturable absorber and positioned in a laser cavity consisting of both erbium and thulium-doped fiber laser. A synchronized mode-locked fiber laser was generated at a centre wavelength of 1563.5 nm and 1931.9 nm, giving a pulse duration of 700 fs and 1.77 ps at a constant pulse repetition rate of 12.905 MHz. The success of this work will provide a better insight by developing the optimum utilization of a saturable absorber in generating multiple mode-locked lasers with different yet far wavelength in near-infrared red region.

L-band femtosecond fiber laser based on a reduced graphene oxide polymer composite saturable absorber

We demonstrate an L-band passively mode-locked erbium-doped fiber laser emitting at 1599.43 nm wavelength at a pulse train of 5.68 MHz. The microfiber reduced graphene oxide composite behaves as a saturable absorber that was fabricated using in-situ wet chemical and dip-coating methods. During operation, a single-pulse soliton was observed at a mode-locking threshold of 40 mW. This is a few times lower than most of the previous assessments in the same class of wavelength band and graphene saturable absorbers. The pulse duration was 568 fs with a maximum average output power of 6.75 mW. In addition, the superiority of this simple fabrication method facilitates its potential of mass production for applications in ultrafast photonics industries.

Long-cavity mode-locked thulium-doped fiber laser for high pulse energy

We demonstrate a high pulse energy and low pulse rate 2 µm femtosecond fiber laser potentially applicable to laser surgery and vehicle laser detection and ranging. The laser is configured by a half kilometer long all-fiber ring cavity with two thulium-doped fiber gains deployed separately and is hybrid mode-locked by the coaction of a graphene saturable absorber and nonlinear polarization rotation. Numerical simulations were carried out to back up the mode-locking stability and estimate the maximally extractable pulse energy. We achieved a pulse energy of about 54.6 nJ, to the best of our knowledge the highest as a seed femtosecond pulse, and a pulse rate of 427 kHz, the lowest ever reported. The pulse duration was about 456 fs as measured by an intensity autocorrelator, and the output optical spectrum showed a wide FWHM of about 51.7 nm. We also examined the stability of the laser output over tens of hours.

Graphene Capacitor-Based Electrical Switching of Mode-Locking in All-Fiberized Femtosecond Lasers.

Effective high-capacity data management necessitates the use of ultrafast fiber lasers with mode-locking-based femtosecond pulse generation. We suggest a simple but highly efficient structure of a graphene saturable absorber in the form of a graphene/poly(methyl methacrylate) (PMMA)/graphene capacitor and demonstrate the generation of ultrashort pulses by passive mode-locking in a fiber ring laser cavity, with simultaneous electrical switching (on/off) of the mode-locking operation. The voltage applied to the capacitor shifts the Fermi level of the graphene layers, thereby controlling their nonlinear light absorption, which is directly correlated with mode-locking. The flexible PMMA layer used for graphene transfer also acts as a dielectric layer to realize a very simple but effective capacitor structure. By employing the graphene capacitor on the polished surface of a D-shaped fiber, we demonstrate the switching of the mode-locking operation reversibly from the femtosecond pulse regime to a continuous wave regime of the ring laser with an extinction ratio of 70.4 dB.

Passively Q-switched thulium fluoride fiber laser operating in S-band region using N-doped graphene saturable absorber

A passively Q-switched S-band fiber laser is proposed and demonstrated using a thulium-doped fluoride fiber as laser gain medium. The proposed design possesses significant advantages including broader tuning wavelength range as compared to previously reported Q-switched S-band lasers. The laser cavity is configured in a simple forward-pumped ring design with a 1400 nm single upconversion pumping scheme. Q-switching is achieved using a polyvinyl alcohol/nitrogen-doped graphene nanosheet (PVA–N-Gns)-based thin-film saturable absorber. Stable Q-switched pulses are obtained at a center wavelength of 1504.7 nm over a pump power range from 101.8 to 280.6 mW. The generated pulses have a maximum pulse repetition rate of 36.85 kHz and minimum pulse width of 4.8 μs at the pump power of 280.6 mW. The maximum pulse output power of 1.30 mW indicates a laser efficiency of approximately 0.63% while a signal-to-noise ratio of 57 dB shows pulse stability. The ability of the proposed cavity design to produce broad wavelength tunability range from 1450 to 1510 nm make it highly suitable for various application in the S and S + band regions.

Narrow-linewidth passively Q-switched fibre laser based on microsphere resonator

We experimentally demonstrate a stable narrow-linewidth passively Q-switched fibre laser based on a microsphere resonator (MSR) and graphene saturable absorber (SA). The MSR made by the arc discharge method has the characteristics of easy fabrication, broad free spectral range (FSR) and flexibility. And it acts as a narrow band-pass filter to ensure narrow-linewidth operation. A stable passively Q-switched pulse with 0.016 nm narrow spectral linewidth is successfully achieved. The output pulse has the pulse width of 5.2 µs, repetition frequency of 28 kHz and high signal to noise ratio (SNR) of ∼60 dB. The results demonstrate that our works may provide an effective way to achieve narrow-linewidth pulsed fibre lasers.

Er:CaF2 single-crystal fiber Q-switched laser with diode pumping in the mid-infrared region

Er3+-doped CaF2 single-crystal fibers (SCFs) were successfully grown using a modified temperature gradient technique (TGT) method. With a fiber-coupled 976 nm laser diode (LD) pump source and 4 at.% Er:CaF2 SCF, mid-infrared region (MIR) laser operations were realized for the first time. A passively Q-switched (PQS) Er:CaF2 SCF laser at 2.8 μm was demonstrated by using graphene saturable absorber (SA). Under an absorbed pump power of 1.52 W, a maximum output power of 220 mW was obtained with a pulse duration of 632.9 ns and a repetition rate of 59.41 kHz, corresponding single pulse energy and peak power are 3.70 μJ and 5.85 W, respectively. The dependence of the operational parameters on pump power was also investigated experimentally. We also found that the SCF possesses superior laser performance when compared with Er:CaF2 bulk crystal. Those results implied SCF is a kind of promising laser gain mediums.

Deterministic single-soliton generation in a graphene-FP microresonator.

Dissipative Kerr solitons (DKS) in high-Q microresonators have attracted considerable attention for their broadband optical frequency combs and ultra-short pulse generation. Owing to thermal effects, complicated tuning strategies are required to generate and sustain the single-soliton state in microresonators. In this paper, we propose a novel microresonator scheme based on the Fabry-Pérot fiber resonator and single-layer graphene saturable absorber (SA) and demonstrate that this design allows deterministic single-soliton generation without frequency tuning and has strong robustness against pump perturbation. The soliton range and thermal instability of the proposed device are also discussed. This work facilitates a novel nonlinear platform connecting high-Q microresonators and conventional SA-assisted mode-locking operations.

Graphene Q-switched Tb:LiYF4 green laser.

We report the Q-switched operation of a Tb3+-laser for the first time, to the best of our knowledge. The passiveQ-switching was realized by a 15% Tb:LiYF4 gain medium and a single-layer graphene saturable absorber. An average output power of 744 mW at 544 nm was achieved with slope efficiency of 41%, pulse width of 2.9 µs, and repetition rate of 38.7 kHz. The corresponding pulse energy and peak power were calculated to be 19.2 µJ and 6.6 W, respectively.

Carbon Nanomaterials Based Saturable Absorbers for Ultrafast Passive Mode-Locking of Fiber Lasers

This paper emphasizes on overviewing the developing progress of the state-of-the-art carbon nanomaterial-based saturable absorbers for passively mode-locked fiber lasers, including carbon nanotube (CNT), graphene, graphite and other carbon nanomaterials. With reviewing the performances of these proposed candidates, the characteristic parameters required for initiating and stabilizing the passive mode-locked fiber lasers are summarized for comparison and discussion. At first, the basic characteristics such as saturation intensity and self-amplitude-modulation (SAM) coefficients of the CNT material with different-wall types are discussed in detail. In comparison, the single-wall CNT possesses optical nonlinearity better than double-wall CNT, whereas the doublewall CNT exhibits wavelength tenability and the multi-wall CNT fails to initiate mode-locking. Subsequently, different graphene saturable absorbers with slightly changing their optical properties made by various fabrication technologies are introduced to take over the role of typical CNT saturable absorber. The detailed analyses on graphene saturable absorber for developing various types of passively mode-locked fiber lasers are overviewed. At last, other new-aspect graphite and carbon nanomaterials related saturable absorbers have emerged because they reveal similar optical nonlinearity with graphene but exhibit cost-effectiveness and easy-production. When changing saturable absorber from graphene to other carbon nanomaterials, the modulation depth is decreased but the saturation intensity is concurrently enlarged because of the disordered structure with increased interlayer spacing and reduced graphene content. At the current stage, selecting carbon nanomaterials with high nonlinear absorbance and low saturated intensity for large SAM coefficient is the golden rule for passively mode-locked the fiber lasers in future academic and industrial applications.

188 ns pulsed Ho:Sc2SiO5 laser operating at 2107.2 m employing a few-layer graphene saturable absorber

A passively Q-switched Ho:Sc2SiO5laser operating at 2107.2 nm with a few layered graphene saturable absorber is obtained, corresponding to a beam quality factors ofMx2=1.19 andMy2 =1.21. A maximum average output power of 1.37 W and pulse energy of 16.08 μJ was achieved at an incident pump power of 13.2 W. The shortest pulse width of 188.3 ns and maximum pulse repetition rate of 85.26 kHz were observed, with a maximum peak power of 85.4 W.

Laser-micromachined zebra-patterned graphene as a mode locker with adjustable loss.

In this Letter, we describe a novel, to the best of our knowledge, device based on micro-structured graphene, referred to as zebra-patterned graphene saturable absorber (ZeGSA), which can be used as a saturable absorber with adjustable loss to initiate femtosecond pulse generation. Femtosecond laser micro-machining was employed to ablate monolayer graphene on an infrasil substrate in the form of stripes with a different duty cycle, resulting in the formation of regions with variable insertion loss in the 0.21%-3.12% range. The mode-locking performance of the device was successfully tested using a ${{\rm Cr}^{4 {+} }}{:}\,{\rm forsterite}$Cr4+:forsterite laser, operating near 1250 nm. In comparison with mode locking using non-ablated graphene, the ZeGSA device with regions of decreasing graphene, enabled improved power performance where the mode-locked output power increased from 68 mW to 114 mW, and the corresponding pulse duration decreased from 62 to 48 fs at the same incident pump power of 6.3 W. These experiments indicate that ZeGSA shows great potential as a laser mode locker with adjustable loss and that it should find applications in the development of femtosecond lasers over a broad spectral range.

Realization of high-performance tri-layer graphene saturable absorber mirror fabricated via a one-step transfer process

Graphene, as a saturable absorber (SA), has attracted much attention for its application in ultrashort pulse fiber lasers due to its ultrafast interband carrier relaxation and ultra-broadband wavelength operation. Nevertheless, during the stacking process of monolayer graphene layer, the induced nonuniform contact at the interface of graphene layers deteriorate the device performance. Herein, we report the fabrication of graphene saturable absorber mirrors (SAMs) via a one-step transfer process and the realization of the much enlarged modulation depth and the much reduced nonsaturable loss with tri-layer graphene (TLG) than single-layer graphene (SLG) due to the improved uniform contact at the interface. Moreover, the operation of 1550 nm mode-locked Er-doped fiber laser with the TLG SAM exhibits excellent output characteristics of the maximum output power of 9.9 mW, a slope efficiency of 2.4% and a pulse width of 714 fs. Our findings are expected to pave the way toward high-performance ultrashort pulse fiber lasers based on graphene SAs.