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A randomly connected single-walled carbon nanotube (CNT) network film is suggested as an optically homogenous thin film to implement a tunable diffractive optical element with a subwavelength thickness. A Fresnel zone plate (FZP) as a thin-film lens is successfully realized by mask-free direct laser writing onto the CNT network film with a thickness of 450 nm. The fabricated FZP exhibits an intense three-dimensional focus having lateral and axial focal sizes of 0.95λ and 7.10λ, respectively, at the wavelength of 1550 nm. Furthermore, we show that the intensities at focal points of the first and second diffraction orders can be significantly modulated by 72% and 40% through ion-gel gating between +1.8 V and −1.8 V. These results may offer the potential for electro-optic tunability in multifocal diffraction flat optics and the like.

Generating high stability ultrafast pulse laser using constituents of the most powerful biomolecules in nature (Adenine, Guanine, Cytosine, and Thymine).

We conducted a study to explore a real-time monitoring variable of a coherently combined beam returned from a scattering target. The effect of a spatial filtering on the speckle pattern generated from the interference of the scattered beam was examined in a coherent beam combining (CBC) system, including three-channel laser output, the scattering target, and receiver optics in free space. We were able to recognize the arrangement of the original beams from the speckle pattern by applying a proper spatial filter with a size of 2 mm. The power-in-the-bucket value in the monitoring system was also investigated as a function of the spatial filter size. Our research implies that a complex speckle pattern can be analyzed using spatial filtering to derive a single-output real-time variable in the CBC monitoring system.

An efficient electro-optic transition control is reported in all-fiber graphene devices over a broad spectral range from visible to near-infrared. The ion liquid–based gating device fabricated onto a side-polished fiber with high numerical aperture significantly enhances the light-matter interaction with graphene, resulting in strong and nonresonant electro-optic absorption of up to 25.5 dB in the wavelength ranging from 532 to 1950 nm. A comprehensive analysis of the optical and electrical properties of the device fabricated with monolayer and bilayer graphene revealed that the number of graphene layers significantly impacts on the performance of the device, including modulation depth and driving voltage. Wavelength-dependent optical response is also measured, which clearly characterizes the electronic bandgap dispersion of graphene. The device exhibited more efficient electro-optic modulation in the longer wavelength region, where the maximum light modulation efficiency of 286.3%/V is achieved at a wavelength of 1950 nm.

Large-scale growth of mostly monolayer molybdenum disulfide (MoS2) on quartz, sapphire, SiO2/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeter-scale areas with large flakes and films of MoS2 on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS2 is monolayer with high quality and uniformity. The MoS2 field effect transistors based on the as-grown MoS2 exhibit carrier mobility of 1–2 cm2V−1s−1 and On/Off ratio of ~104 while showing large photoresponse. Our results provide a simple approach to realize MoS2 on various substrates for electronics and optoelectronics applications.

We report high-efficiency optical amplification with near-extreme-limit gain from a diode-pumped Cs vapor cell. We used wavelength-division multiplexing to couple 852 nm pump and 895 nm seed lasers to achieve nearly overlapping spatial modes in the Cs vapor cell. We investigated the amplification factor as a function of the focal length of the lens focusing on the combined pump and seed signals and determined the optimal focal length under our experimental conditions. The small-signal amplification factor from the Cs vapor cell reached >30 dB at 240 mW pump power, and the optimal optical amplification factor per pump power was 4171/W.

A theoretical model to describe in-band pumped holmium doped silica fiber lasers is presented. The model is established based upon theory and parameters obtained from published research works. Both core-pumped system and cladding-pumped system are simulated with the model. The simulation results agree well with most experimental results, and for the cases in which the simulation results show discrepancy with the experimental results the disagreement can be reasonably explained. Through numerical analysis it is found that besides common negative factors such as non-radiative decay, fiber loss, and non-optimized resonator configuration, energy transfer upconversion plays a deleterious role in the performance of in-band pumped holmium doped silica fiber lasers. In particular, inhomogeneous upconversion associated with ion clustering is found to cause significant degradation of slope efficiencies of lasers, a fact that is useful to understand the unsolved problem regarding the lower-than-expected slope efficiencies observed in previous studies of in-band pumped holmium doped fiber lasers.

Wide-spectral saturable absorption (SA) in low-dimensional (LD) nanomaterials such as zero-, one-, and two-dimensional materials has been proven experimentally with outstanding results, including low saturation intensity, deep modulation depth, and fast carrier recovery time. LD nanomaterials can therefore be used as SAs for mode-locking or Q-switching to generate ultrafast fiber laser pulses with a high repetition rate and short duration in the visible, near-infrared, and mid-infrared wavelength regions. Here, we review the recent development of emerging LD nanomaterials as SAs for ultrafast mode-locked fiber laser applications in different dispersion regimes such as anomalous and normal dispersion regimes of the laser cavity operating in the near-infrared region, especially at ~1550 nm. The preparation methods, nonlinear optical properties of LD SAs, and various integration schemes for incorporating LD SAs into fiber laser systems are introduced. In addition to these, externally (electrically or optically) controlled pulsed fiber laser behavior and other characteristics of various LD SAs are summarized. Finally, the perspectives and challenges facing LD SA-based mode-locked ultrafast fiber lasers are highlighted.

Nonlinear optic processes have been extensively used in diverse fields, including ultrafast optical signal control, wavelength conversion, and generation of entangled light sources in quantum technology.

Twisted bilayer graphene (tBLG) has received substantial attention in various research fields due to its unconventional physical properties originating from Moiré superlattices. The electronic band structure in tBLG modified by interlayer interactions enables the emergence of low-energy van Hove singularities in the density of states, allowing the observation of intriguing features such as increased optical conductivity and photocurrent at visible or near-infrared wavelengths. Here, we show that the third-order optical nonlinearity can be considerably modified depending on the stacking angle in tBLG. The third-harmonic generation (THG) efficiency is found to significantly increase when the energy gap at the van Hove singularity matches the three-photon resonance of incident light. Further study on electrically tuneable optical nonlinearity reveals that the gate-controlled THG enhancement varies with the twist angle in tBLG, resulting in a THG enhanced up to 60 times compared to neutral monolayer graphene. Our results prove that the twist angle opens up a new way to control and increase the optical nonlinearity of tBLG, suggesting rotation-induced tuneable nonlinear optics in stacked two-dimensional material systems., Nonlinear optics: When graphene ‘does the twist’ Modifying the angle between the two layers of twisted bilayer graphene can considerably improve how photons interact with it to generate higher-energy photons. Dong-Il Yeom of Ajou University and colleagues in Korea shined laser light onto twisted bilayer graphene stacked at various angles, and measured the outcoming optical signals. Twisted bilayer graphene is made by stacking two monolayer graphenes at an angle. The interlayer interaction in this material leads to intriguing properties. The scientists found that changing the angle could enhance a nonlinear optical property, called third-harmonic generation, by 60 times compared to monolayer graphene. The team then conducted Raman measurements and modeling calculations to understand how this process occurs. They say their findings could pave the way towards novel designs for enhancing optical nonlinearity in two-dimensional stacked materials.

We report the characteristics of GHz bandwidth amplified spontaneous emission (ASE) from a hot Cs atom vapor cell, where the optical feedback was inhibited. When pumped by an 852 nm laser, both forward and backward ASE output near 894 nm showed a nonlinear increase in its power without a pump power threshold. A continual decrease in spectral width down to 4.7 GHz was experimentally observed as the ASE output power increased. Using the same vapor cell, we injected a 1mW signal to configure a single-pass optical amplifier, and we monitored the forward output both in temporal and spectral domains. We found the signal laser efficiently suppressed the ASE and obtained a large amplification factor over 700 at the pump power of 1.2 W.

Electrical characteristics of ion gels prepared by loading different amounts of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) in Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) are investigated and compared with those of ion liquid, [EMIM][TFSI] for possible application as a gate stack for flexible electronic devices. Capacitance and impedance as a function of frequency are measured, which can be well accounted for by a simple circuit model identifying the local device components. The operation of a flexible field effect transistor based on graphene and the ion gel as a top gate stack is also demonstrated.

We demonstrated four different laser operational states in the same passive fiber ring laser cavity by controlling solely the polarization state in a saturable absorber. The demonstrated laser operational states were continuous wave, mode-locking, Q-switching, and Q-switched mode-locking. The saturable absorber was fabricated by spin-coating a single-walled carbon nanotubes (SWCNT)/polymer composite on a side polished fiber providing enhanced nonlinear interaction with the SWCNT. The wide tuning range of the saturable absorber allows the simple means to generate different forms of laser output from a single laser cavity.

Spatiotemporal changes in the surface temperature of an absorbing medium irradiated by using 532-nm laser pulses were measured using an infrared camera. Relevant numerical simulations of the heat transfer equation were performed. The simulations showed that the maximum temperature increase was linearly proportional to the absorption coefficient with no dependence on the thermal conductivity and that the decay time constant depended on both the absorption coefficient and the thermal conductivity. The absorption coefficient and the thermal conductivity of the medium were determined by fitting the simulated results for the maximum temperature increase and decay time constant to the measured results.

We examine the radiation-induced properties changes of evanescent-field-interacting type graphene-saturable absorbers (SAs). The graphene-SA inserted to the mode-locked laser was exposed to 60Co gamma-ray radiation up to 1.02 kGy at a 50 Gy/hr dose rate. To see how the graphene-SA affects to the laser performance, the graphene-SA-based mode-locked laser was also monitored simultaneously. The mode-locking was broken at 0.75 kGy irradiation dose, which corresponds to 15.6 years operation in low-earth orbit satellites. The optical properties of the graphene-SA was also compared before and after radiation.

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.

We implemented a single-walled carbon nanotube (SWCNT)-based saturable absorber (SA) that evanescently interacts with light on a side-polished polarization-maintaining fiber (PMF) platform. A high-quality SWCNT/polymer composite was spin-coated onto a side-polished PMF embedded in a quartz block, where the slow optical birefringence axis of the PMF was perpendicular to the polished surface. The fabricated in-line SA had an insertion loss of –1.5 dB with a modulation depth of 0.5% for the polarization direction associated with the transvers magnetic mode. An all-PMF laser was built using the fabricated in-line SA to demonstrate self-starting, turn-key operation of Er-doped, all-fiber lasers delivering stable scalar soliton pulses. The measured 3-dB spectral bandwidth and pulse duration of the laser output were 5.1 nm and 510 fs, respectively, resulting in a time-bandwidth product of 0.320. We examined the polarization state of the soliton fiber laser output and found that the laser stably generated linearly polarized ultrashort pulses with a polarization extinction ratio of –18.4 dB.

We studied the thermal and the mechanical effects induced by pulsed laser absorption in human skin by numerically solving the heat-transfer and the thermoelastic wave equations. The simulation of the heat-transfer equation yielded the spatiotemporal distribution of the temperature increase in the skin, which was then used in the driving term of the thermoelastic wave equation. We compared our simulation results for the temperature increase and the skin displacements with the measured and numerical results, respectively. For the comparison, we used a recent report by Jun et al. [Sci. Rep. 5, 11016 (2015)], who measured in vivo skin temperature and performed numerical simulation of the thermoelastic wave equation using a simple assumption about the temporal evolution of the temperature distribution, and found their results to be in good agreement with our results. In addition, we obtained solutions for the stresses in the human skin and analyzed their dynamic behaviors in detail.

A straightforward method of controlling laser-induced mechanical effects in biological tissues is to regulate the pulse energy of the irradiating laser. Because the local temperature of the irradiated region rises as the laser’s pulse energy increases, this method cannot independently control purely mechanical effects without changing the thermal effects. Here, a dual-wavelength irradiation method is proposed in which biological tissues are irradiated simultaneously by using two laser pulses with different wavelengths, and laser-induced mechanical effects are continuously controlled with no change in the maximum temperature increase by systematically varying the energy of each laser pulse. The proposed method is analyzed, and its feasibility is demonstrated through numerical simulations.

A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide (GO) selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation. Using the GO colloid droplet with sub-nanoliter volume, we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc. The prepared fiber facet was then included in an Er-doped fiber laser (EDFL) cavity and we obtained a few layers of GO having nonlinear optic two-dimensional (2D) characteristics selectively on the fiber core by the laser-driven self-exfoliation. The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation at λ = 1600.5 nm , the longest Q -switched laser wavelength in EDFLs. Pulse characteristics were analyzed as we varied the pump power at λ = 980 nm from 105.2 mW to 193.6 mW, to obtain the maximum repetition rate of 17.8 kHz and the maximum output power of 2.3 mW with the minimum pulse duration of 7.8 μs. The proposed method could be further applied to other novel inorganic 2D materials opening a window to explore their novel nonlinear optic laser applications.

Electro-optic modulators which modulates the intensity or phase of the light through the electric signal control, have been extensively investigated for the diverse field applications including optical communication, bio-sensing, and security-monitoring based on lightwave. With recent technological advance of the fabrication of high quality graphene over large area, graphene have been intensively studied as a basic element to build novel photonic and electro-optic devices. However, low optical absorption in ultra-thin layered graphene often limits the performance of the device. Although there have been several attempts to increase graphene-light interaction, realization of efficient and broadband graphene-based electro-optic modulators is still challenging. In this work, we demonstrate an all-fiber graphene-based electro-optic modulator with a modulation depth of > 25 dB. In order to achieve non-resonant strong interaction with graphene, we employed a side-polished fiber (SPF) with high numerical aperture (NA) as a novel platform that evanescently interacts with graphene. The high NA fiber has about six times smaller mode-field area than that of the standard single-mode fiber, and we found that this can critically enhance the graphene-light interaction without significantly sacrificing the insertion loss. We experimentally fabricate the bi-layer graphene field-effect transistor onto the high-NA SPF, and covered index matched ion-liquid for further increase of the graphene-light interaction and effective gating. As a result, we observed that the fabricated device exhibits the modulation depth of 27.6 dB with low scattering loss at the applied voltage range within 2.5 V, which well agrees with our numerical expectation.

We demonstrated a high pulse energy, passively mode-locked thulium-doped fiber (TDF) laser with a repetition rate of 427 kHz, the lowest repetition rate at 2 μm to the best of our knowledge. Two stages of TDF amplifier is applied to obtain sufficient gain over high attenuation of 485 m long oscillator. The self-starting of passively mode-locking is realized by using a nonlinear polarization rotation technique in association with an in-line graphene saturable absorber. The mode-locked TDF laser delivers stable femtosecond pulses with a pulse energy of 54 nJ.

Using two-dimensional (2D) hybrid organic-inorganic (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 perovskite thin film as an in-line saturable absorber, we experimentally demonstrate an all-fiber mode-locked laser in both C and L band. We successfully generated self-started ultrafast pulses at the anomalous dispersion regime with a spectral bandwidth of 7 nm and a pulse duration of 381 fs at the center wavelength of 1565.9 nm. Moreover, by adjusting the optical gain, we also achieve a transform-limited soliton pulses with the spectral bandwidth of 6 nm at the center wavelength of 1604 nm.

We demonstrate the passive Q-switching operation of an erbium-doped fiberlaser using a few-layer WS 2 -based saturable absorber with evanescent field interaction.WS 2 flakes have been synthesized via a liquid-phase exfoliation method, and an opticalfiber taper was selected as a light-material template that causes to achieve a long inter-action length of the evanescent wave. Subsequently, the prepared solution was opticallydeposited around the 3-mm interaction length of the fabricated optical fiber taper with a5- m waist diameter. The proposed Q-switched fiber laser based on the WS 2 -depositedfiber taper saturable absorber could generate stable output pulses at 1565 nm, with apulsewidth ranging from 1.3 to 3 s and a repetition rate of 33–108 kHz.Index Terms: Tungsten disulfide, nonlinear optical materials, saturable absorber,Q-switched fiber laser. 1. Introduction Q-switched fiber lasers have attracted great attention owning to the relatively large pulse energyat relatively low repetition rates and pulse width of the scale from microsecond to nanosecond.These short pulsed lasers have extensive applications in material processing, telecommunica-tions, medicine, and sensing [1]. Q-switched pulses can be obtained via active or passiveQ-switching techniques. Passively Q-switched lasers have several advantages such as sim-plicity, compactness, and low cost compared to that of active techniques which require anactive optical component such as electro-optic or acousto-optic modulators [2].Passive Q-switched technique of lasers based on saturable absorber (SA) is the well-knownand most effective method to achieve Q-switching operation which has been widely investigated.In the past few decades, researchers investigated various kinds of SA materials, including toxicdye materials [3], semiconductor saturable absorber mirrors (SESAMs) [4], carbon nanotubes(CNTs) [5], and graphene [6], [7]. Although the SESAMs are very mature and commercialized

We investigated nonlinear optical characteristics of Tungsten disulfide (WS2) films and experimentally demonstrated their high potential for application as nonlinear saturable absorbers in passively mode-locked fiber lasers. Side polished fiber (SPF) was fabricated and WS2 film was overlaid to provide an efficient evanescent field interaction. The WS2 film was prepared using two methods: liquid phase exfoliation to form few-layer nano-sheets, and chemical vapor deposition (CVD) to grow uniform multilayer WS2 on a SiO2 substrate. Two SPF saturable absorbers were prepared by either spin coating WS2 solution or lifting off the multilayer CVD WS2 on SPF. An all-fiber ring cavity was built and the WS2 film overlaid on SPF was employed as a mode locker along with Er-doped fiber as a gain medium. Using the spin-coated WS2 SPF, stable soliton-like pulses were generated with a spectral width of 5.6 nm and 467 fs pulse duration. The fiber laser cavity containing CVD WS2 SPF generated a transform-limited soliton pulse train with a spectral width of 8.23 nm and a pulse duration of 332 fs. Our study confirmed a high potential of WS2 film as a novel 2-D nonlinear optical material for laser applications.

We demonstrate all-fiber mode-locked laser based on a tapered optical fiber saturable absorber (SA) enclosed in tungsten disulfide (WS2) nanosheets. Tapered fibers were fabricated using the standard flame brushing method to an interaction length of 3 mm with waist diameters of 10 and 15 $\mu \text{m}$ . WS2 nanosheets were prepared via a liquid phase exfoliation method to form a uniform dispersion. Subsequently, the WS2 nanosheets were optically deposited along the interaction length of the tapered fibers by evanescent field interactions. We built a ring laser including the fabricated mode-lockers. The SA with a 10- $\mu \text{m}$ taper diameter delivers the pulses with a pulse duration of 369 fs and 3-dB spectral bandwidth of 7.5 nm; on the other hand, the output pulses using the mode-locker with 15- $\mu \text{m}$ waist diameter were found to have 563-fs pulse duration and 5.2 nm of 3-dB bandwidth. It is shown that the smaller waist diameter of tapered fiber causes wider spectral bandwidth of the ultrafast pulses and narrower 3-dB bandwidth.

We demonstrate an all-fiberized mode-locked laser by employing Molybdenum Disulfide (MoS 2 ) spin-coated onto a side-polished fiber (SPF) as an in-line saturable absorber. Single crystal MoS 2 has been exfoliated via the Li intercalation method and then dispersed with large population of few-layer MoS 2 nano-sheets in ethanol. Subsequently, a saturable absorber has been prepared using a relatively simple method: spin-coating the uniform MoS 2 solution on the fabricated SPF without using any polymer or toxic procedure. Power-dependent transmission property of the prepared MoS 2 nano-sheets on the SPF was experimentally analyzed, providing the feasibility to apply it as an efficient in-line saturable absorption behavior. By deploying the MoS 2 SPF into a fiber laser cavity with finely tuned laser pump power and cavity dispersion, mode-locked pulses were obtained at anomalous and normal dispersion of the laser cavity. The self-started soliton pulses at the anomalous dispersion regime were generated with a spectral bandwidth of 9.96 nm at 1584 nm and a pulse duration of 521 fs. Moreover, by managing the dispersion to the normal regime, stable pulses at net-normal intra-cavity dispersion with 11.9 ps pulse duration were obtained with a spectral bandwidth of 18.2 nm at 1570 nm. The results prove the effectiveness of developing MoS 2 saturable absorbers and applications for pulsed laser operation.

We demonstrate an all-fiberized mode-locked laser by employing Molybdenum Disulfide (MoS2) spin-coated onto a side-polished fiber (SPF) as an in-line saturable absorber. Single crystal MoS2 has been exfoliated via the Li intercalation method and then dispersed with large population of few-layer MoS2 nano-sheets in ethanol. Subsequently, a saturable absorber has been prepared using a relatively simple method: spin-coating the uniform MoS2 solution on the fabricated SPF without using any polymer or toxic procedure. Power-dependent transmission property of the prepared MoS2 nano-sheets on the SPF was experimentally analyzed, providing the feasibility to apply it as an efficient in-line saturable absorption behavior. By deploying the MoS2 SPF into a fiber laser cavity with finely tuned laser pump power and cavity dispersion, mode-locked pulses were obtained at anomalous and normal dispersion of the laser cavity. The self-started soliton pulses at the anomalous dispersion regime were generated with a spectral bandwidth of 9.96 nm at 1584 nm and a pulse duration of 521 fs. Moreover, by managing the dispersion to the normal regime, stable pulses at net-normal intra-cavity dispersion with 11.9 ps pulse duration were obtained with a spectral bandwidth of 18.2 nm at 1570 nm. The results prove the effectiveness of developing MoS2 saturable absorbers and applications for pulsed laser operation.

The modification of deoxyribonucleic acid (DNA) samples by sequencing the order of bases and doping copper ions opens the possibility for the design of novel nanomaterials exhibiting large optical nonlinearity. We investigated the nonlinear characteristics of copper-ion doped double crossover DNA samples for the first time to the best of our knowledge by using Z-scan and four-wave mixing methods. To accelerate the nonlinear characteristics, we prepared two types of unique DNA nanostructures composed of 148 base pairs doped with copper ions with a facile annealing method. The outstanding third-order nonlinear optical susceptibility of the copper-ion-doped DNA solution, 1.19 × 10(-12) esu, was estimated by the conventional Z-scan measurement, whereas the four-wave mixing experiment was also investigated. In the visible spectral range, the copper-ion-doped DNA solution samples provided competent four-wave mixing signals with a remarkable conversion efficiency of -4.15 dB for the converted signal at 627 nm. The interactions between DNA and copper ions contribute to the enhancement of nonlinearity due to structural and functional changes. The present study signifies that the copper-ion-doped double crossover DNA is a potential candidate as a highly efficient novel material for further nonlinear optical applications.

Molybdenum disulfide (MoS 2 ) nano-sheets have been successfully deposited directly on the cleaved facet of a silica optical fiber using optical trapping forces. By controlling the incident laser power, various types of MoS 2 films were deposited near the fiber core. An area selective deposition was successfully realized during the optical deposition process by using an optical reflectometry method. The presence of MoS 2 deposited layer at the fiber end was confirmed by microscopic Raman spectroscopy as well as scanning electron microscope images. Nonlinear response and power dependent transmission of the prepared sample was observed at the wavelength of 1552 nm, which can be used as an all-fiber saturable absorber. Moreover, the fabricated sample was inserted in a Er-doped fiber ring laser cavity and stable Q-switched pulses with the repletion rate from 26.6 kHz to 40.9 kHz were generated, which confirmed the potential of MoS 2 as a saturable absorber.

We demonstrate an all-fiber dissipative soliton fiber laser (DSFL) with a very broad spectral bandwidth by optimizing the cavity design of the fiber laser. Two different cavity schemes of the DSFL with simple cavity structures were built by employing a hybrid component, and their properties were investigated while varying the net cavity dispersion of the laser. By optimizing the cavity dispersion of the fiber laser, we achieved a DSFL that stably deliver linear chirped pulses with a pulse duration of 912.5 fs at a repetition rate of 52.2 MHz without additional pulse compression. The measured spectral bandwidth of the laser was 68 nm, which is the largest value ever reported for Er-doped DSFL oscillators.

An all-fiberized, in-band pumped Ho-doped fiber laser is presented. The laser is pumped by an in-house built Tm-doped fiber laser operating at 1.95 μm, and its operation wavelength is stabilized by a high-reflection (HR) FBG at 2.1 μm. 18.1 W output at 2.1 μm is generated by the laser, with a slope efficiency of 74.7 %.

Femtosecond mode-locked fiber lasers have been actively employed in many practical applications such as micro-machining, corneal surgery and multi-photon imaging, thanks to their compactness, alignment-free operation, and low cost. To enhance the long-term stability and self-starting operation of mode-locked lasers, saturable absorber (SA) devices, such as semiconductor saturable absorber mirrors (SESAMs), have been employed. Recently, planar waveguide-type SA device based on standard planar lightwave circuit (PLC) wafer fabrication process [1] has been developed and applied to high-repetition-rate all-fiber mode-locked lasers [2].

A new extraordinary application of deoxyribonucleic acid (DNA) thin-solid-film was experimentally explored in the field of ultrafast nonlinear photonics. Optical transmission was investigated in both linear and nonlinear regimes for two types of DNA thin-solid-films made from DNA in aqueous solution and DNA-cetyltrimethylammonium chloride (CTMA) in an organic solvent. Z-scan measurements revealed a high third-order nonlinearity with n2 exceeding 10−9 at a wavelength of 1570 nm, for a nonlinarity about five orders of magnitude larger than that of silica. We also demonstrated ultrafast saturable absorption (SA) with a modulation depth of 0.43%. DNA thin solid films were successfully deposited on a side-polished optical fiber, providing an efficient evanescent wave interaction. We built an organic-inorganic hybrid all-fiber ring laser using DNA film as an ultrafast SA and using Erbium-doped fiber as an efficient optical gain medium. Stable transform-limited femtosecond soliton pulses were generated with full width half maxima of 417 fs for DNA and 323 fs for DNA-CTMA thin-solid-film SAs. The average output power was 4.20 mW for DNA and 5.46 mW for DNA-CTMA. Detailed conditions for DNA solid film preparation, dispersion control in the laser cavity and subsequent characteristics of soliton pulses are discussed, to confirm unique nonlinear optical applications of DNA thin-solid-film.

We investigate optical and electrical behaviors of a graphene saturable absorber (SA) and mode-locking performance of a graphene-SA-based mode-locked Er fiber laser in gamma-ray radiation. When irradiated up to 4.8 kGy at ∼100 Gy/hr dose rate, the overall nonlinear transmittance in transverse electric mode was increased, while maintaining modulation depth to >10%. The corresponding polarization-dependent loss was reduced at a 1.2-dB/kGy rate. In the electrical properties, the charge carrier mobility was reduced, and the Dirac voltage shift was increased to positive under gamma-ray radiation. The radiation-induced optical and electrical changes turned out to be almost recovered after a few days. In addition, we confirmed that the graphene-SA-based laser showed stable CW mode-locking operation while the inserted graphene SA was irradiated for 2-kGy at a 45-Gy/hr dose rate, which corresponds to >40 years of operation in low Earth orbit satellites. To the best of our knowledge, this is the first evaluation of graphene SAs and graphene-SA-based mode-locked lasers in gamma-ray radiation, and the measured results confirm the high potential of graphene SAs and graphene-SA-based lasers in various outer-space environments as well as other radiation environments, including particle accelerators and radiation-based medical instruments.

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 mu m 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. (C)2016 Optical Society of America

Mode-locked integrated mid-IR waveguide chip lasers with ultra-short pulse duration and high peak power are of great interest for a large range of applications like trace-gas spectroscopy and early-cancer detection. As those lasers are automatically embedded within a small block of doped glass, they are inherently robust and immune to environmental fluctuations. In this paper we investigate the suitability of various novel nanomaterials for the realisation of saturable absorbers for passive mode locking of femtosecond laser-written mid-infrared waveguide lasers. We compare and characterise saturable absorbers based on carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides as well as black phosphorus and analyse their performance in a thulium-doped waveguide laser operating around 2 micron.

Novel saturable absorbers based on carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides and black phosphorus were fabricated and characterized. Their performance for short pulse generation in Tm:ZBLAN waveguide chip lasers was analyzed. For the first time to our knowledge, Q-switched mode-locked operation of a mid-IR ZBLAN waveguide chip laser was realized using topological insulators.

We studied third order susceptibilities of mono- and randomly stacked multilayer graphene at four different wavelengths and three laser fluence regimes with z-scan experiment, and compared the values with optical Kerr gate experimental results.