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In recent years, graphene-based supercapacitors have become one of the most promising new energy devices. However, the re-stacking of graphene during the preparation process and the toxicity of reducing agents limit its further development. Therefore, in this work, we used resveratrol (RA), a novel and green reducing agent, to prepare reduced graphene oxide (rGO). The results of X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy and Raman spectroscopy proved that the reducing effect of RA is equivalent to that of hydrazine hydrate (HH). Subsequently, the composite was prepared and cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests were conducted to study the electrochemical performance. The results show that the composite reduced by RA for 24 hours exhibits the largest specific capacitance (916 F g−1 at 1 A g−1), which is higher than that of the composite reduced by HH (822 F g−1 at 1 A g−1), and has the best rate performance and stable cycle performance (retention rate is 87.24% after 10 000 cycles). A symmetric supercapacitor was assembled with the obtained composites reduced by RA exhibiting a maximum specific capacitance of 461 F g−1 at 1 A g−1, an energy density of 31.38 W h kg−1 at 0.701 kW kg−1, and ultrahigh-rate performance (retained 61.4% capacitance at 40 A g−1).

We report on the experimental observation of wavelength-switchable bound solitons in a passively mode-locked erbium-doped fiber ring laser based on a tapered graded-index multimode fiber. Due to the multimode interference filtering effect, by adjusting the polarization controller while maintaining the pump power of 158 mW at 1480 nm, the center wavelength of the fiber laser output can be switched between 1565 nm and 1595 nm. At the same time, bound soliton pairs and bound soliton triplets can be both observed in these two wavelengths. Such a simple, compact all-fiber mode-locked laser with switchable wavelength has great potential for high capacity optical communication.

A mode-locked high pulse energy fiber laser with a linear cavity by using an all-fiber structured graded index multimode fiber (GIMF) based saturable absorber (SA) is presented. The saturable absorption effect of the SA is based on the nonlinear multimode interference (NL-MMI). This is the first time the GIMF-based SA has been used in a mode-locked all-fiber laser with a linear cavity. The stable fundamental mode-locking operation can still be maintained at the maximum pump power. The output solitons have the center wavelength, spectral width, pulse duration, and repetition rate of 1571 nm, 4 nm, 675 fs, and 11.69 MHz, respectively. The maximum average output power reached is 61.4 mW, corresponding to the pulse energy up to 4.72 nJ and the pulse peak power of 7.79 kW. The proposed GIMF-based SA opens a promising way for a practical fiber-integrated mode-locker for large pulse energy fiber laser technology.

A Mach–Zehnder interferometer constructed by femtosecond-laser written in-fiber waveguides in no-core fiber (NCF) is demonstrated. Such an interferometer device consists of a section of the NCF in which a waveguide has been inscribed, fusion spliced with single-mode fiber at its two ends. One of the interferometer arms is formed by the waveguide inscribed and the other follows the diverging light path inside the NCF before arriving at the end of single-mode fiber core. Such an internal structure-based device can be used not only for strain sensing but also for external refractive index measurement.

We experimentally demonstrated a passively mode-locked all-fiber Tm laser using a no-core-graded-index multimode fiber structure as a saturable absorber based on the nonlinear multimode interference. Stable fundamentally mode-locking operation was obtained at a pump threshold of 180 mW. The output soliton pulses had a centre wavelength, spectral width, pulse duration, and repetition rate of 1895.7 nm, 3.3 nm, 1.25 ps, and 18.91 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator, with many potential applications in eye-safe ultrafast photonics.

Adsorption of five 2-arylpropionic acids on graphene indicated that there was a competition between the solute molecules remaining in water solution and depositing on the graphene surface. The pH-dependent experiments showed that the adsorption of five 2-arylpropionic acids on graphene was significantly restrained by the effects of solvent–solute interactions. To find out the relevance between the adsorption capacity and solvent effects, a distribution coefficient (Log D) was introduced and employed to reflect the variation of solvent effects with different pH. An unexpected accordance was observed between the curves of adsorption capacity and Log D values. Then, we extended our work to probe the interactions between 2-arylpropionic acids and graphene. It was found that the experimental adsorption coefficients (Kd) of five adsorbates were closely related to their aromatic features, such as the numbers and distribution of the aromatic rings in their structures, rather than their hydrophobicity, suggesting ...

A hybrid structure of no-core fiber and graded-index multimode fiber (NCF-GIMF) is demonstrated, which can be used as both the saturable absorber (SA) and the wavelength selective element. By employing such a device, an L-band wavelength tunable Er-doped mode-locked laser is realized and stable single solitons of ~1.7 ps, with continuously tunable wavelengths from 1574 to 1601.1 nm, are generated. Moreover, dual-wavelength mode-locked laser operation at 1575.4 and 1603 nm is achieved, with a pulse duration of 1.2 and 1.7 ps, respectively. The proposed device is simple and compact and represents an effective approach for tunable and dual-wavelength mode-locked fiber laser operation.

In this Letter, we implement a multimode fiber (MMF) laser system mode-locked by a nonlinear polarization rotation technique for controllable synchronous multi-wavelength soliton generation. The synchronization of the repetition rates for different wavelengths is realized by the special mode transmission in MMF. For dual-wavelength mode-locking at 1566.7 nm and 1617.2 nm, each of the synchronously mode-locked solitons consists of a train of quasi-periodic beat pulses with a pulse width of 84 fs and period of 162 fs. The total output power reaches 532 mW with optimally balanced two-color intensities. Furthermore, switchable dual- and tri-wavelength synchronized femtosecond pulses are also obtained. In contrast to previous reports, this synchronously mode-locked multi-wavelength is output directly from a laser oscillator, which provides a simpler candidate to achieve pulse synchronization.

In this work, a nanocomposite, Fe3O4/graphene was prepared and characterized. Five profens (including ibuprofen, flurbiprofen, pranoprofen, indoprofen and loxoprofen sodium) were extracted from three environmental water samples by using the synthetic Fe3O4/graphene, followed by simultaneous determination of the enantiomers on a Chiralcel OJ-RH column coupled with a triple quadrupole mass spectrometry. Factors affecting the extraction efficiency, such as amount of adsorbents, solution pH, ionic strength, type and volume of desorption solvent, as well as elution time were thoroughly investigated. Method validation showed high sensitivity with method quantification limits in the range of 8.49–26.3 ng/L. Satisfactory recovery (73.6–90.2%), good intra-day precision (RSD 3.2–9.7%) and inter-day precision (RSD 5.2–10%) were also obtained. Furthermore, possible interactions between analyte and graphene, such as electrostatic attraction, charge-π interaction, hydrophobic interaction and π-π stacking were discussed by combining the experiment results and molecular docking study, which provided a new insight into the adsorption mechanism of graphene.

A novel graphene-enabled electrically tunable optical filter (ETOF) was reported in this work with high voltage response, low power consumption, and wide working bandwidth. A fiber Bragg grating (FBG) was etched in a microfiber using a femtosecond laser, and porous graphene film was coated on the surface of a tapered fiber. Metal electrodes were fabricated using which a voltage was applied to the graphene film to heat the fiber. The wavelength shift of the ETOF has a linear relationship with the applied voltage. The devices illustrated good repeatability and the voltage sensitivity was calculated as 50.36 pm/V. A maximum voltage of 30 V was applied to the devices and a 1.62-nm wavelength shift was observed. The 3-dB bandwidth of the FBG was approximately 0.38 nm, which corresponds to a power consumption of 5.76 μ W in the device. The rising and falling times of the device were measured as 44.2 and 26.7 ms, respectively.

We present a widely tunable all-fiber mode-locked laser based on semiconductor saturable absorber mirror (SESAM) with a linear cavity design. An easy-to-use tunable bandpass filter based on thin film cavity technology is employed to tune the wavelength. By tuning the filter and adjusting the polarization controller, mode-locked operation can be achieved over the range of 1023 nm–1060 nm. With the polarization controller settled, mode-locked operation can be preserved and the wavelength can be continuously tuned from 1030 nm to 1053 nm. At 1030 nm, the laser delivers 9.6 mw average output power with 15.4 ps 10.96 MHz pulses at fundamental mode-locked operation.

We have implemented wavelength-tunable and dual-wavelength in an ytterbium-doped passively mode-locked fiber laser using a single mode-graded index multimode-single mode fiber (SMF-GIMF-SMF) device as the saturable absorber (SA) without additional components. Such an all-fiber SA device exhibits fantastic properties with a large modulation depth of 22.9%, a small saturation fluence of 8.3 μJ/cm2, and the transmission curve with a capacity of gain-flattening, which are suitable for the tunable mode-locking generation. Benefiting from the intracavity birefringence-induced filtering effect of the laser cavity, tuning and dual-wavelength operations are obtained. For the tuning operation, the central wavelength of the dissipative solitons (DSs) can be tuned from 1028.5 to 1074.4 nm, with the pulse duration of tens of picoseconds. For the dual-wavelength mode-locking operation, the central wavelengths of dual-wavelength can be switched from 1032.3/1054.1 nm to 1049.3/1072.6 nm. Our results indicate that the SMF-GIMF-SMF device provides a novel platform for wavelength-tunable and dual-wavelength mode-locking in Yb-doped fiber lasers.

In this letter, by incorporating hybrid structure of no-core fiber (NCF)-graded index multimode fiber (GIMF) as the saturable absorber (SA) and spectral filter simultaneously, not only the switchable noise-like pulses (NLPs) but also the tunable single- and dual-wavelength dissipative solitons (DSs) are obtained from a net normal dispersion Yb-doped mode-locked fiber laser. The NCF–GIMF​ device plays a crucial role in the pulse generation and the wavelength tuning. By means of being stretched, the transmission peak of the NCF–GIMF device can be tuned over 60 nm which is responsible for the wavelength tuning of the oscillator. As the SA, the NCF–GIMF device affords variable saturable absorption properties during the stretching process which are suitable for the ultrafast soliton generation. Based on this device, the center wavelengths of the NLPs are demonstrated to be switchable from 1034.6 nm to 1072.2 nm. The single wavelength DSs with the pulse width at the level of tens of picoseconds can be tuned from 1026.3 nm to 1080 nm. Additionally, the dual-wavelength asynchronized DSs with a spectral interval of 21 nm have a wavelength-tunable range of 13 nm. This all-fiber ultrafast Yb-doped laser with tunable and flexible outputs can satisfy diverse application needs.

It is well known that reduced graphene oxide/polyaniline (rGO/PANI) composites exhibit extremely excellent electrochemical performance. However, in the preparation of this composite, the toxic and harmful properties of the reducing agent and the re-stacking of rGO sheets have become an obstacle. To solve these problems, in this study, with green natural tea polyphenols (GTPs) was used as the reducing agent and stabilizer of graphene oxide (TrGO), through introduced amine groups into the surface of TrGO by Mannich reaction acted as anchors for in-situ polymerization of polyaniline (PANI), we synthesized a high-electrochemical performance TrGO/PANI composites. Fourier Transform Infrared Spectrometer (FT-IR), X-ray diffraction, Raman spectra and electron microscope were used to characterize the morphology and structure of the composite, and the electrochemical performance of the composite were tested by cyclic voltammetry, galvanostatic charge-discharge and AC impedance spectroscopy. The results exhibited that the covalently grafted TrGO/PANI composites showed excellent electrochemical performance. The areal capacitance at 0.5 mA cm−2 is 732 mF cm−2, which is better than pristine graphene oxide and polyaniline. The excellent electrochemical performance of the composites can be attributed to the effect of covalent synergy between the TrGO and PANI, indicating the great potential for supercapacitors.

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 506 fs at 1572.5 nm and 416 fs at 1591.4 nm 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.

In this Letter, a simple and passively mode-locking Yb-doped all fiber laser using a nonlinear polarization rotation technique operating under dissipative soliton (DS) or dissipative soliton resonance (DSR) conditions is proposed. Furthermore, using a combination of a bandpass filter and a Loyt filter, tunable single-wavelength or dual-wavelength operation under two different conditions is realized, respectively. The tunable single-wavelength DS laser has a 5 nm tuning range from 1029 to 1034 nm with a pulse width of 110 ps. The tunable single-wavelength DSR operation laser has a range of 4 nm. In-depth research on the mechanism of the conversion between DS and DSR is carried out. Particularly, under dual-wavelength DSR operation, the obtained step-like pulses consist of two rectangular pulses with different energies. This work could help give a deeper insight into normal dispersion pulses.

We report on the amplification of high-average-power and high-efficiency picosecond pulses in a self-made very-large-mode-area Yb-doped photonic crystal fiber (PCF). The PCF with a core diameter of 105 μm and a core numerical aperture of 0.05 is prepared by the sol-gel method combined with the powder sintering technique. The fiber amplification system produces the highest average power of 255 W at a 10 MHz repetition rate with a 21 ps pulse duration corresponding to a peak power of 1.2 MW. This result exemplifies the high-average-power and high-peak-power potential of this specifically designed fiber.

We demonstrate a mode-locked all-fiber Tm laser using a single mode-step index multimode-graded-index multimode-single mode fiber structure as a saturable absorber based on the nonlinear multimodal interference. Stable fundamentally mode-locking operation was obtained at a pump threshold of 180mW. The output soliton pulses had a center wavelength, spectral width, pulse duration, and repetition rate of 1888 nm, 3.6 nm, 1.4 ps, and19.82 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator with many potential applications in eye-safe ultrafast photonics.

A new type of Mach–Zehnder interferometer device based on in-fiber optical waveguides, fabricated by direct femtosecond laser pulse inscription in a single-mode fiber has been demonstrated and successfully employed for temperature and strain measurement. The in-fiber waveguide can couple the light out from the fiber core and guide it along the cladding region before directing it back into the fiber core. Such an inner structured interferometer device is compact and robust, can be constructed in a flexible and precisely controlled manner, and hence is expected to have many potential applications.

A wavelength-tunable and dual-wavelength mode-locking operation is achieved in an Er-doped fiber laser using a hybrid no-core fiber graded index multimode fiber as the saturable absorber. In the tuning operation, continuously wavelength-tunable pulses with a tuning range of 46.7 nm, stable 3-dB bandwidth of around 5 nm, and pulse duration of ∼850 fs are obtained by increasing the intracavity loss of a variable optical attenuator. In the dual-wavelength operation, the two solitons at different wavelengths demonstrate the characteristics of mutual coherence. By increasing the intracavity loss, the spectral spacing can be tuned from 11 to 33.01 nm while maintaining the coherence of the solitons. Such coherent solitons have high potential for applications in dual-comb frequency and multicolor pulses in nonlinear microscopy.

We report a high-peak-power, single-polarized master oscillator power amplification system employing polarization- maintaining Yb-doped rod-type photonic crystal fiber. The MOPA system comprises of a Q-switched microchip laser generating ~630ps pulses at 8.6 kHz repetition-rate and two amplification stages employing double cladding fiber and rod-type PCF respectively. The MOPA system obtains narrow spectral bandwidth, single-polarized pulses of 9W maximum output average power, corresponding to peak power of 1.7MW.

In this paper, we demonstrate a dual-wavelength mode-locked thulium-doped fiber laser. The single-wall carbon nanotube is used as the mode-locker due to its large and ultrafast nonlinear optical responses. By tuning the pump power and adjusting the PC properly, stable dual-wavelength output can be achieved. The center wavelength of the dual-wavelength pulses are 1894 nm and 1907 nm, respectively. The repetition rate is about 17.64 MHz which exactly corresponds to the total length of the ring cavity. The signal-to-noise ratio is over 30 dB. It is a reliable method to realize dual-wavelength mode-locking operating at the range of 2 µm.

A hybrid no-core fiber (NCF)–graded index multimode fiber (GIMF) structure is used as a saturable absorber (SA) for mode-locked laser operation. Such an SA supports various types of soliton outputs. By changing the cavity parameters, not only the spatiotemporal mode-locking states with a stable single pulse but also tightly and loosely bound solitons are generated. Single 35.5 pJ solitons centered at 1568.5 nm have a 4 nm spectral full-width at half-maximum and an 818 fs temporal duration. Tightly bound soliton pairs with continuously tunable wavelength from 1567.48 nm to 1576.20 nm, featured with an ∼700 fs pulse train with a separation of 2.07 ps, have been observed by stretching the NCF-GIMF structured device. Meanwhile, several different pulse separations from 37.57 ps to 56.46 ps of loosely bound solitons have also been realized. The results provide help in understanding the nonlinear dynamics in fiber lasers.

A fiber in-line Mach-Zehnder interferometer based on a pair of femtosecond laser inscribed short sections of waveguide is presented. One short waveguide directs part of the propagating light from the fiber core to the cladding-air interface, and experiences multiple total internal reflections before taking back to the fiber core by the other short waveguide. The device is robust in structure, can be fabricated in a fast way and with a flexible manner, and has the capability of ambient refractive index sensing, which makes it highly desirable for many "lab-in-fiber" applications.

Core-diameter adjustment, in analogy to doping management, is proposed in this letter for balancing thermal load and nonlinear effects. In this scheme, the core-to-cladding ratio increases with increasing core diameter along the direction of signal and pump propagation. An all-fiber-integrated Yb-doped master oscillator power amplification (MOPA) is successfully demonstrated. Two segments of fiber with different core diameters but same inner-cladding diameters and doping levels are spliced together and used as gain fibers in the last stage. A maximum average output power of 200 W at an overall slope efficiency of 71% is achieved from the MOPA with a pulse energy of 2 mJ and peak power as high as 80 kW.

A linearly-polarized, high peak power, short-pulse, Q-switching Yb-doped large-mode-area photonic crystal fiber (PCF) oscillator with three-level system operation is demonstrated. By optimizing cavity parameters and adopting linear polarization component, the laser can easily obtain linearly-polarized output over 2 W at 978 nm with polarization extinction ratio (PER) up to 43 dB without any additional wavelength filter. Less than 50 ns stable output pulses are achieved within repetition range of 10 kHz-200 kHz and short pulse of 9 ns pulse duration, 130 kW peak power at 10 kHz can be reached. The characteristics and the key issues of the laser, such as interpulse ASE, spectrum ASE around 1030 nm, are with detailed discussion in the paper.

We demonstrate an effective and compact 489nm laser generation from frequency doubling by linearly-polarized Q-switched rod-type PCF laser at 978nm with short pulses at adjustable repetition rate.

A high-repetition-rate pulse laser operating at 978 nm is demonstrated. 18 ns short pulses are produced at 5 MHz repetition rate. 230 mW blue light is generated through frequency doubling at 50 kHz.

A linearly polarized Q-switching large-mode-area photonic crystal fiber laser at 978 nm is demonstrated. Short pulse of 14 ns duration is achieved with 36 dB polarization extinction ratio at 10 kHz repetition rate and 2 W output power.

We report on a 200W, 2mJ, 25ns MOPA fiber laser, the last stage of which has a hybrid gain fiber composed of large-core-diameter and small-core diameter Yb doped fibers.

A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single-and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single-and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror (SESAM). Two narrow-band fiber Bragg gratings centered at 1029.9 nm and 1032 nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9 nm and 1032 nm. The laser delivers different pulse widths of 7.5 ps for 1030 nm and 20 ps for 1032 nm. The maximum output power for both could reach ~6.5 mW at single pulse operation. The output wavelength could be tuned to about 0.9 nm intervals ranging from 1030.2 nm to 1031.1 nm and from 1032.15 nm to 1033.7 nm with the temperature change of the fiber Bragg grating, respectively.