Graphene Saturable Absorber Research Articles

Modelling of graphene Q-switched Tm lasers

We report on a model of diode-pumped Thulium lasers passively Q-switched by a graphene saturable absorber applicable also for any other “fast” saturable absorber. It reasonably predicts the dependence of the pulse duration, pulse energy and pulse repetition frequency on the absorbed power. The model is applied in the present work for a Tm: KLuW microchip laser passively Q-switched with a multi-layer graphene saturable absorber. The laser generates ~1W at 1926nm with a slope efficiency of 39%. Stable 190ns /4.1 μJ pulses are achieved at a pulse repetition frequency of 260kHz. The potential of graphene for the generation of few-ns pulses at ~2µm is discussed.

Quasi mode-locking of coherent feedback random fiber laser.

Mode-locking is a milestone in the history of lasers that allows the generation of short light pulses and stabilization of lasers. This phenomenon is known to occur only in standard ordered lasers for long time and until recently it is found that it also occurs in disordered random lasers formed by nanoscale particles. Here, we report the realization of a so-called quasi mode-locking of coherent feedback random fiber laser which consists of a partially disordered linear cavity formed between a point reflector and a random distributed fiber Bragg grating array with an inserted graphene saturable absorber. We show that multi-groups of regular light pulses/sub-pulses with different repetition frequencies are generated within the quasi mode-locking regime through the so-called collective resonances phenomenon in such a random fiber laser. This work may provide a platform to study mode locking as well as pulse dynamic regulation of random lasing emission of coherent feedback disordered structures and pave the way to the development of novel multi-frequency pulse fiber lasers with potentially wide frequency tuning range.

Observation of wavelength-switchable solitons in an all-polarization-maintaining erbium-doped fiber cavity based on graphene saturable absorber reflector**Project supported by the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. PCSIRT: 1212), the Key Grant Science and Technology Planning Project of Beijing, China (Grant Nos. PXM2013_014224_000077 and PXM2012_014224_000019), and the Science and Technology Planning Project of Beijing Municipal

We present the generation of wavelength-switchable single-polarization solitons in an all-polarization-maintaining erbium-doped fiber laser mode-locked by a graphene saturable absorber. Ultrashort pulses centered at the wavelength of 1531.6 nm with the duration of 816 fs and centered at the wavelength of 1557.8 nm with the duration of 402 fs are separately obtained from the same fiber laser cavity. The cavity loss adjusted by the gold reflector plays a crucial role in wavelength switching.

Passively synchronized Q-switched and mode-locked dual-band Tm3+:ZBLAN fiber lasers using a common graphene saturable absorber.

Dual-band fiber lasers are emerging as a promising technology to penetrate new industrial and medical applications from their dual-band properties, in addition to providing compactness and environmental robustness from the waveguide structure. Here, we demonstrate the use of a common graphene saturable absorber and a single gain medium (Tm3+:ZBLAN fiber) to implement (1) a dual-band fiber ring laser with synchronized Q-switched pulses at wavelengths of 1480 nm and 1840 nm, and (2) a dual-band fiber linear laser with synchronized mode-locked pulses at wavelengths of 1480 nm and 1845 nm. Q-switched operation at 1480 nm and 1840 nm is achieved with a synchronized repetition rate from 20 kHz to 40.5 kHz. For synchronous mode-locked operation, pulses with full-width at half maximum durations of 610 fs and 1.68 ps at wavelengths of 1480 nm and 1845 nm, respectively, are obtained at a repetition rate of 12.3 MHz. These dual-band pulsed sources with an ultra-broadband wavelength separation of ~360 nm will add new capabilities in applications including optical sensing, spectroscopy, and communications.

1.38 MW peak power dual-loss modulated sub-nanosecond green laser with EO and graphene

By simultaneously employing electro-optic (EO) modulator and Graphene saturable absorber (SA) in a dual-loss-modulated Q-switched and mode-locking (QML) Nd:Lu0.15Y0.85VO4/KTP green laser, the sub-nanosecond single mode-locking green laser is demonstrated with high peak power, low repetition rate and high stability. The monolayer and 3-layer graphene sheets grown by chemical vapor deposition (CVD) method were used as SAs in the experiment. When the pump power reached 10.72 W, the maximum peak power obtained from the doubly QML laser with EO and monolayer graphene-SA was 1.38 MW, corresponding to a pulse duration of 480 ps. The shortest pulse width of 340 ps was obtained with a 3-layer graphene-SA.

Optically controlled in-line graphene saturable absorber for the manipulation of pulsed fiber laser operation.

We demonstrate an optically tunable graphene saturable absorber to manipulate the laser operation in pulsed fiber laser system. Owing to the strongly enhanced evanescent field interaction with monolayer graphene, we could realize an efficient control of modulation depth in the graphene saturable absorber by optical means through cross absorption modulation method. By integrating the tunable graphene saturable absorber into the fiber laser system, we could switch the laser operation from Q-switching through Q-switched mode-locking to continuous wave mode-locking by adjusting only the optical power of the control beam. In addition, we realized a hybrid Q-switching of fiber laser by periodical modulation of the absorption of the graphene saturable absorber, where we observed that the repetition rate of the Q-switched laser could be continuously tuned according to the modulation frequency of the applied external signal.

Graphene mode-locked femtosecond Cr2+:ZnS laser with ~300 nm tuning range.

Graphene has proved to be an excellent broadband saturable absorber for mode-locked operation of ultrafast lasers. However, for the mid-infrared (mid-IR) range where broadly tunable sources are in great needs, graphene-based broadly tunable ultrafast mid-IR lasers have not been demonstrated so far. Here, we report on passive mode-locking of a mid-IR Cr:ZnS laser by utilizing a transmission-type monolayer graphene saturable absorber and broad spectral tunability between 2120 nm and 2408 nm, which is the broadest tuning bandwidth ever reported for graphene mode-locked mid-IR solid-state lasers. The recovery time of the saturable absorber is measured to be ~2.4 ps by pump-probe technique at a wavelength of 2350 nm. Stably mode-locked Cr:ZnS laser delivers Fourier transform-limited 220-fs pulses with a pulse energy of up to 7.8 nJ.

Amplification of noise-like pulses generated from a graphene-based Tm-doped all-fiber laser.

We report on the generation of noise-like pulse (NLP) trains in a Tm-doped fiber laser mode-locked by multilayer graphene saturable absorber. The spectral bandwidth obtained directly from the oscillator exceeds 60 nm, centered at 1950 nm, with 23.5 MHz repetition rate. The pulses were also amplified in a fully fiberized amplifier based on a double-cladding Tm-doped fiber. The system was capable of delivering 1.21 W of average power, which corresponds to 51.5 nJ energy stored in the noise-like bundle. We believe that the presented source might serve as a pump for supercontinuum generation in highly nonlinear fibers.

Multi-gigahertz repetition rate ultrafast waveguide lasers mode-locked with graphene saturable absorbers

We report the development of an approach to build compact waveguide lasers that operate in the stable fundamental mode-locking regime with multigigahertz repetition rates. The approach is based on the use of depressed cladding multi- or single-mode waveguides fabricated directly in the active laser crystal using the femtosecond laser inscription method and a graphene saturable absorber. Using this approach we achieve the stable self-starting mode-locking operation of a diode-pumped waveguide Nd:YAG laser that delivers picosecond pulses at a repetition rate of up to 11.5 GHz with an average power of 12 mW at a central wavelength of 1064 nm. The saturable absorbers are formed through the chemical vapor deposition of single-layer graphene on the output coupler mirror or directly on the end facet of the laser crystal. The stable self-starting mode-locking operation is achieved by controlling the group delay dispersion in the laser cavity with an intracavity interferometer. The method developed for the creation of compact ultrashort pulse laser generators with gigahertz repetition rates can be extended further and applied for the development of compact high-repetition rate lasers that operate at a wide range of IR wavelengths.

Mode-locked semiconductor disk lasers

This paper will review the recent advances in the field of ultrashort pulse generation from optically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs). In this review, we will summarize the most significant results presented over the last 15 years, before highlighting recent breakthroughs related to mode-locked VECSELs by different research groups. Different mode-locking techniques for OP-VECSELs are described in detail. Previously, saturable absorbers, such as semiconductor saturable absorber mirrors—external, or internal as in mode-locked integrated external-cavity surface emitting lasers (MIXSEL)—, and recently, novel-material-based carbon-nanotube and graphene saturable absorbers have been employed. A new mode-locking method was presented and discussed in recent years. This method is referred to as self-mode-locking or saturable-absorber-free operation of mode-locked VECSELs. In this context, we particularly focus on achievements regarding self-mode-locking, which is considered a promising technique for the realization of high-power, compact, robust and cost-efficient ultrashort pulse lasers. To date, the presented mode-locking techniques have led to great enhancement in average powers, peak powers, and repetition rates that can be achieved with passively mode-locked VECSELs.

Passive Q-switching of microchip lasers based on Ho:YAG ceramics.

A Ho:YAG ceramic microchip laser pumped by a Tm fiber laser at 1910 nm is passively Q-switched by single- and multi-layer graphene, single-walled carbon nanotubes (SWCNTs), and Cr2+:ZnSe saturable absorbers (SAs). Employing SWCNTs, this laser generated an average power of 810 mW at 2090 nm with a slope efficiency of 68% and continuous wave to Q-switching conversion efficiency of 70%. The shortest pulse duration was 85 ns at a repetition rate of 165 kHz, and the pulse energy reached 4.9 μJ. The laser performance and pulse stability were superior compared to graphene SAs even for a different number of graphene layers (n=1 to 4). A model for the description of the Ho:YAG laser Q-switched by carbon nanostructures is presented. This modeling allowed us to estimate the saturation intensity for multi-layered graphene and SWCNT SAs to be 1.2±0.2 and 7±1 MW/cm2, respectively. When using Cr2+:ZnSe, the Ho:YAG microchip laser generated 11 ns/25 μJ pulses at a repetition rate of 14.8 kHz.

All-fiber Tm-doped soliton laser oscillator with 6 nJ pulse energy based on evanescent field interaction with monoloayer graphene saturable absorber.

We demonstrate an all-fiber Tm-doped soliton laser with high power by using a monolayer graphene saturable absorber (SA). Large area, uniform monolayer graphene was transferred to the surface of the side-polished fiber (SPF) to realize an in-line graphene SA that operates around 2 μm wavelength. To increase the nonlinear interaction with graphene, we applied an over-cladding onto the SPF, where enhanced optical absorption at monolayer graphene was observed. All-fiber Tm-doped mode-locked laser was built including our in-line graphene SA, which stably delivered the soliton pulses with 773 fs pulse duration. The measured 3-dB spectral bandwidth was 5.14 nm at the wavelength of 1910 nm. We obtained the maximum average output power of 115 mW at a repetition rate of 19.31 MHz. Corresponding pulse energy was estimated to be 6 nJ, which is the highest value among all-fiber Tm-doped soliton oscillators using carbon-material-based SAs.

All-fiber Ho-doped mode-locked oscillator based on a graphene saturable absorber.

In this Letter, we demonstrate a graphene mode-locked, all-fiber Ho-doped fiber laser generating 1.3 nJ energy pulses directly from the oscillator. The graphene used as a saturable absorber was obtained via chemical vapor deposition on copper substrate and immersed in a poly(methyl methacrylate) support. The laser generated ultrashort soliton pulses at 2080 nm with bandwidth up to 6.1 nm. The influence of the output coupling ratio and the SA modulation depth on the mode-locking performance was also investigated.

Broadband wavelength tunable mode-locked thulium-doped fiber laser operating in the 2 μm region by using a graphene saturable absorber on microfiber

A broadband wavelength tunable mode-locked Tm3+-doped fiber laser operating in the 2 μm region based on a graphene saturable absorber is experimentally investigated. A section of graphene film is transferred on a microfiber, which allows light-graphene interaction via evanescent field. The microfiber based graphene not only acts as an excellent saturable absorber for mode-locking, but also induces a polarizing effect to form an artificial birefringent filter for wavelength selection. By tuning the polarization states in the laser cavity, the laser exhibits tunable wavelength mode-locked pulses over a wide range from 1880 to 1940 nm. Such a system provides a compact, user friendly and low cost wavelength tunable ultrashort pulse source in the 2 μm region.

A passively Q-switched Ho:YVO4 Laser at 2.05 μm with Graphene Saturable Absorber

We report a passively Q-switched Ho:YVO4 laser pumped at 1.94 µm with multilayer graphene as a saturable absorber. At the absorbed pump power of 9.3 W, the maximum average output power of 2.2 W was obtained in Ho:YVO4 laser with minimum pulse width of 265.2 ns and pulse repetition rate of 131.6 kHz at 2052.1 nm. In addition, a beam quality factor of M2~1.7 was measured at the maximum output level. This is, as far as we know, the first time that graphene has been used in a passively Q-switched Ho:YVO4 laser.

28 μm passively Q-switched Er:CaF_2 diode-pumped laser

A mid-infrared Er doped CaF2 crystal was successfully grown by the bridgeman method. Efficiently continuous wave and Q-switched laser operations were demonstrated at 2.8 μm with a 4 at.% Er doped CaF2 crystal end-pumped by a fiber-coupled 974 nm diode laser. The continuous wave output power of 295 mW was obtained in a compact linear cavity. A stable 2.8 μm passively Q-switched Er:CaF2 laser was also demonstrated with a graphene saturable absorber. Under an absorbed pump power of 2.353 W, an average output power of 172 mW was generated with a pulse duration of 1.324 μs and a repetition rate of 62.70 kHz, corresponding to the single pulse energy of 2.74 μJ and the peak power of 2.07 W, respectively. The high-quality Er:CaF2 crystal and the monolayer graphene are an ideal combination to directly obtain a near 3 μm mid-infrared region pulse laser.

Passive Q-switching of Yb bulk lasers by a graphene saturable absorber

Compact Yb:KLu(WO4)2 and Yb:LuVO4 lasers diode-pumped at 978 nm are passively Q-switched by a single-layer graphene saturable absorber. The Yb:KLu(WO4)2 laser generated 165 ns/0.49 μJ pulses at 1030 nm with 170 mW average output power and 12 % slope efficiency. With the Yb:LuVO4 laser, 152 ns/0.83 μJ pulses were achieved. The output power reached 300 mW at 1024 nm, and the slope efficiency was 10 %. Laser operation in a plano-plano cavity is achieved with both crystals with thermal lensing playing a key role in their performance. A model describing graphene Q-switched Yb lasers is developed. Our results indicate the potential of graphene for passive Q-switching of ~1 μm bulk lasers.

Graphene mode-locked and Q-switched 2 - μ m Tm/Ho codoped fiber lasers using 1212-nm high-efficient pumping

We report graphene mode-locked or Q-switched Tm/Ho-codoped fiber laser pumped by a 1212-nm phosphorus-doped fiber Raman laser. First, comparison experiments were performed for a continuous-wave 2 μm Tm/Ho-codoped fiber laser pumped by a 1565-nm laser or a 1212-nm laser, verifying that the 1212- nm pumping is more efficient than the conventional ∼1560-nm pumping. Then, we further realized 1212-nm highly efficient pumped Tm/Ho-codoped fiber lasers mode-locked and Q-switched by a graphene saturable absorber, respectively. Using only 30-cm Tm-Ho gain fiber under the 1212-nm pumping, the passive Q-switching at a center wavelength of 1976 nm was efficiently generated with tunable repetition rate between 32.2 and 43.0 kHz and shortest pulse width of 1.41 μs. Moreover, the passive mode-locking at 1913.7 nm was stably achieved with a fundamental repetition rate of 19.978 MHz and pulse energy of ∼20 pJ. To the best of our knowl- edge, it is the first demonstration of 2-μm pulsed fiber lasers high efficiently pumped by a 1212-nm laser. © 2016

Q-switching of Yb:YGG, Yb:LuGG and Yb:CNGG lasers by a graphene saturable absorber

Yb:YGG, Yb:LuGG and Yb:CNGG compact diode-pumped lasers at 977 nm are passively Q-switched by a CVD-grown single layer graphene saturable absorber. With Yb:CNGG crystal, 190 ns/1.9 μJ pulses are generated at a repetition frequency of 235 kHz. This represents the highest pulse energy extracted from any graphene Q-switched Yb laser. The maximum average output power is 440 mW at 1045.1 nm with 24 % slope efficiency. With the Yb:YGG laser, the maximum output power reaches 462 mW at 1039.8 nm and the Q-switching conversion efficiency is as high as 55 %. Graphene is promising for generation of nanosecond pulses in Q-switched bulk Yb lasers at the frequencies approaching the MHz range.

Wavelength switchable graphene Q-switched fiber laser with cascaded fiber Bragg gratings

We have demonstrated a wavelength switchable graphene Q-switched fiber laser with two cascaded fiber Bragg gratings. Stable Q-switching operation with central wavelength 1542.9nm (1543.7nm), repetition rate 28.4kHz (22.58kHz), and pulse duration 2.16μs (2.65μs) can be obtained by adjusting the intra-cavity birefringence. Moreover, stable dual-wavelength operation with wavelength spacing 0.8nm can also be observed. The cascaded fiber gratings combined with the graphene saturable absorber provide a simple and feasible way to get versatile pulsed fiber laser.