Control of temperature dependent viscosity for manufacturing of Bi-doped active fiber

Bi-activated photonic materials are promising for various applications in high-capacity telecommunication,tunable laser,and advanced bioimaging and sensing.Although various Bi-doped material candidates have been explored,manufacturing of Bi heavily doped fiber with excellent optical activity remains a long-standing challenge.Herein,a novel viscosity evolutional behavior mediated strategy for manufacturing of Bi-doped active fiber with high dopant solubility is proposed.The intrinsic relation among the evolution of Bi,reaction temperature and viscosity of the glass system is established.Importantly,the effective avenue to prevent the undesired deactivation of Bi during fiber drawing by tuning the temperature dependent viscosity evolution is built.By applying the strategy,for the first time we demonstrate the success in fabrication of heavily doped Bi active fiber.Furthermore,the principal fiber amplifier device is constructed and broadband optical signal amplification is realized.Our findings indicate the effectiveness of the proposed temperature dependent viscosity mediated strategy for developing novel photonic active fiber,and they also demonstrate the great potential for application in the next-generation high-capacity telecommunication system.

Simultaneously Suppressing Low-Frequency and Relaxation Oscillation Intensity Noise in a DBR Single-Frequency Phosphate Fiber Laser

Effective multiple optoelectronic feedback circuits for simultaneously suppressing low-frequency and relaxation oscillation intensity noise in a single-frequency phosphate fiber laser are demonstrated. The forward transfer function, which relates the laser output intensity to the pump modulations, is measured and analyzed. A custom two-path feedback system operating at different frequency bands is designed to adjust the pump current directly. The relative intensity noise is decreased by 20dB from 0.2 to 5kHz and over lOdB from 5 to lOkHz. The relaxation oscillation peak is suppressed by 22dB. In addition, a long term （24h） laser instability of less than 0.05% is achieved.

A Single-Frequency Linearly Polarized Fiber Laser Using a Newly Developed Heavily Tm3+-Doped Germanate Glass Fiber at 1.95 μm

A compact linearly polarized, low-noise, narrow-linewidth, single-frequency fiber laser at 1950nm is demonstrated. This compact fiber laser is based on a 21-mm-long homemade Tm3＋-doped germanate glass fiber. Over 100-mW stable continuous-wave single transverse and longitudinal mode lasing at 195Ohm are achieved. The measured relative intensity noise is less than -135dB/Hz at frequencies over 5 MHz. The signal-to-noise ratio of the laser is larger than 72dB, and the laser linewidth is less than 6kHz, while the obtained linear polarization extinction ratio is higher than 22 dB.

In situ instant generation of an ultrabroadband near-infrared emission center in bismuth-doped borosilicate glasses via a femtosecond laser

Bismuth(Bi)-doped photonic materials, which exhibit broadband near-infrared(NIR) luminescence(1000–1600 nm), are evolving into interesting gain media. However, the traditional methods have shown their limitations in enhancing Bi NIR emission, especially in the microregion. Consequently, the typical NIR emission has seldom been achieved in Bi-doped waveguides, which highly restricts the application of Bi-activated materials.Here, superbroadband Bi NIR emission is induced in situ instantly in the grating region by a femtosecond(fs)laser inside borosilicate glasses. A series of structural and spectroscopic characterizations are summoned to probe the generation mechanism. And we show how this novel NIR emission in the grating region can be enhanced significantly and erased reversibly. Furthermore, we successfully demonstrate Bi-activated optical waveguides.These results present new insights into Bi-doped materials and push the development of broadband waveguide amplification.

Fabrication of crystalline selenium microwire

A method of fabricating selenium（Se） microwire is demonstrated.A multimaterial fiber with amorphous selenium（a-Se） core and multicomponent phosphate glass cladding is drawn by using a conventional optical fiber drawing technique.Then the a-Se core of the fiber is crystallized by a post thermal process at 150 ℃.After the multicomponent phosphate glass cladding is stripped from the multimaterial fiber by marinating the fiber in HF acid solution,a crystalline selenium（c-Se）microwire with high uniformity and smooth surface is obtained.Based on microstructure measurements,the c-Se microwire is identified to consist of most hexagonal state particles and very few trigonal state whiskers.The good photoconduction property of c-Se microwire with high quality and longer continuous length makes it possible to apply to functional devices and arrays.

Preparation of ultrathin ReS2 nanosheets and their application to Q-switched Er-doped fiber lasers

We study the exfoliation of ultrathin ReS2 nanosheets from the prepared ReS2 powder and their application to Q-switched Er-doped fiber laser.XRD,Raman,and XPS spectra confirm the successful preparation of the layered ReS2.SEM images show that the obtained ReS2 sheets have lateral size below 200 nm.The thickness of the ReS2 nanosheets is smaller than 5 nm according to the AFM results.ReS2/PVA film is applied as a saturable absorber in an Er-doped Q-switched fiber laser,and a minimum pulse duration of 2.4μs and an output power of 1.25 mW are obtained,indicating the potential application to Q-switched lasers.

High-efficiency and high-power single-frequency fiber laser at 1.6μm based on cascaded energy-transfer pumping

In this paper,a technique combining the cascaded energy-transfer pumping(CEP)method and master-oscillator power-amplifier(MOPA)configuration is proposed for power scaling of 1.6-μm-band single-frequency fiber lasers(SFFLs),where the Er^(3+)ion has a limited gain.The CEP technique is fulfilled by coupling a primary signal light at 1.6μm and a C-band auxiliary laser.The numerical model of the fiber amplifier with the CEP technique reveals that the energy transfer process involves the pump competition and the in-band particle transition between the signal and auxiliary lights.Moreover,for the signal emission,the population density in the upper level is enhanced,and the effective population inversion is achieved thanks to the CEP.A single-frequency MOPA laser at 1603 nm with an output power of 52.6 W and an improved slope efficiency of 30.4%is experimentally obtained through the CEP technique.Besides,a laser linewidth of 5.2 k Hz and a signal-to-auxiliary laser ratio of 60.7 d B are obtained at the maximum output power.The proposed technique is anticipated to be promising for increasing the slope efficiency and power scaling for fiber lasers operating at L band.

Realization of one-dimensional 2^(n)-root topological states in photonic lattices

Square-root topological insulators recently discovered are intriguing topological phases.They possess topological properties inherited from the squared Hamiltonian and exhibit double-band structures.The mechanism of the square root was generalized to 2^(n)-root topological insulators,giving rise to more band gaps.In this study,we describe the experimental realization of onedimensional 2^(n)-root topological insulators in photonic waveguide arrays using the archetypical Su-Schrieffer-Heeger(SSH)model.Topological edge states with tunable numbers are clearly observed under visible light.In particular,we visualized the dynamic evolutions of the light propagation by varying the sample lengths,which further proved the localization and multiple numbers of edge states in 2^(n)-root topological systems.The experiment,which involves constructing 2^(n)-root topological photonic lattices in various geometric arrangements,provides a stable platform for studying topological states that exhibit a remarkable degree of flexibility and control.

Stable ultraviolet ultrafast laser based on all-polarizationmaintaining fiber femtosecond laser

We report a high-stability ultrafast ultraviolet(UV)laser source at 352 nm by exploring an all-fiber,all-polarizationmaintaining(all-PM),Yb-doped femtosecond fiber laser at 1060 nm.The output power,pulse width,and optical spectrum width of the fiber laser are 6 W,244 fs,and 17.5 nm,respectively.The UV ultrashort pulses at a repetition rate of 28.9 MHz are generated by leveraging single-pass second-harmonic generation in a 1.3-mm-long BiB_(3)O_(6)(BIBO)and sum frequency generation in a 5.1-mm-long BIBO.The maximum UV output power is 596 mW.The root mean square error of the output power of UV pulses is 0.54%.This laser,with promising stability,is expected to be a nice source for frontier applications in the UV wavelength window.

Tailoring microstructure and electrical transportation through tensile stress in Bi_(2)Te_(3) thermoelectric fibers

Bismuth telluride(Bi_(2)Te_(3))has attracted much attention in the field of thermoelectrics since it is one kind of commercial room-temperature thermoelectric material.Herein three kinds of Bi_(2)Te_(3) thermoelectric fibers with internal tensile stress are fabricated utilizing an optical fiber template method.The effects of internal stress on the microstructure and the electrical transportation of Bi_(2)Te_(3) thermoelectric fibers are investigated.The Bi_(2)Te_(3) cores in the fibers are highly crystalline and possess a tensile nanosheet structure with preferential orientation as evidenced by X-ray diffraction and Raman studies.Tensile stress can enhance electrical properties of the fibers.And a paper cup generator covered with 20 pieces of optimized fibers provides a μW-level output power.It is inferred that tensile stress tuning can be an effective tool for the material optimization of thermoelectric performance.

Controlling upconversion through interfacial energy transfer(IET):Fundamentals and applications

Photon upconversion has received substantial attention owing to its great promise in broad applications from bioimaging to other frontier fields like display,upconversion laser,information security and anticounterfeiting.A smart control and manipulation of the upconversion luminescence has always been a key topic,however,to date the most efficient mechanism for upconversion nanoparticles remains the energy transfer upconversion and recently reported energy migration mediated upconversion.Recently,we found that the interfacial energy transfer(IET)is also an efficient approach for enabling and tuning photon upconversion of lanthanide ions.Moreover,it can be used for the mechanistic understanding of the interionic interactions such as energy transfer and energy migration on the nanoscale.In this review,the recent advances of the research on the IET are summarized,the principles for designing IET process and typical examples are discussed together with its applications in both mechanistic research and frontier information security.The challenges and perspectives for future research are also commented.

Multi-functional bismuth-doped bioglasses: combining bioactivity and photothermal response for bone tumor treatment and tissue repair

Treatment of large bone defects derived from bone tumor surgery is typically performed in multiple separate operations,such as hyperthermia to extinguish residual malignant cells or implanting bioactive materials to initiate apatite remineralization for tissue repair;it is very challenging to combine these functions into a material.Herein,we report the first photothermal(PT)effect in bismuth(Bi)-doped glasses.On the basis of this discovery,we have developed a new type of Bi-doped bioactive glass that integrates both functions,thus reducing the number of treatment cycles.We demonstrate that Bi-doped bioglasses(BGs)provide high PT efficiency,potentially facilitating photoinduced hyperthermia and bioactivity to allow bone tissue remineralization.The PT effect of Bi-doped BGs can be effectively controlled by managing radiative and non-radiative processes of the active Bi species by quenching photoluminescence(PL)or depolymerizing glass networks.In vitro studies demonstrate that such glasses are biocompatible to tumor and normal cells and that they can promote osteogenic cell proliferation,differentiation,and mineralization.Upon illumination with near-infrared(NIR)light,the bioglass(BG)can efficiently kill bone tumor cells,as demonstrated via in vitro and in vivo experiments.This indicates excellent potential for the integration of multiple functions within the new materials,which will aid in the development and application of novel biomaterials.

Experimental demonstration of transverse mode instability enhancement by a counter-pumped scheme in a 2 kW all-fiberized laser

Transverse mode instability(TMI)has become the major limitation for power scaling of fiber lasers with nearly diffraction-limited beam quality.Compared with a co-pumped fiber laser,a counter-pumped fiber laser reveals TMI threshold enhancement through a semi-analytical model calculation.We demonstrated a 2 kW high-power counter-pumped all-fiberized laser without observation of TMI.Compared with the co-pumped scheme,the TMI threshold is enhanced at least 50%in counter-pumped scheme,moreover,stimulated Raman scattering and four-wave mixing are suppressed simultaneously.

PbS quantum dots and Ba F_(2):Tm^(3+) nanocrystals co-doped glass for ultra-broadband near-infrared emission [Invited]

With the rapid growth of optical communications traffic,the demand for broadband optical amplifiers continues to increase.It is necessary to develop a gain medium that covers more optical communication bands.We precipitated PbS quantum dots(QDs) and Ba F_(2):Tm^(3+) nanocrystals (NCs) in the same glass to form two independent emission centers.The Ba F_(2)NCs in the glass can provide a crystal field environment with low phonon energy for rare earth (RE) ions and prevent the energy transfer between RE ions and PbS QDs.By adjusting the heat treatment schedule,the emission of the two luminescence centers from PbS QDs and Tm^(3+) ions perfectly splices and covers the ultra-broadband near-infrared emission from 1200 nm to 2000 nm with bandwidth over 430 nm.Therefore,it is expected to be a promising broadband gain medium for fiber amplifiers.

Correction:Multi-functional bismuth-doped bioglasses:combining bioactivity and photothermal response for bone tumor treatment and tissue repair

In this originally published article,we have noticed several mistakes.They should be corrected as follows:1.On page 1,the second affiliation(No.5)of the author“Chuanbin Mao”should be deleted as he does not belong to that affiliation.Namely,he should be only listed with(Department of Chemistry and Biochemistry Stephenson Life Sciences Research Center,University of Oklahoma,Norman,OK 73072,USA).

Nonlinear chirped pulse amplification for a 100-W-class GHz femtosecond all-fiber laser system at 1.5μm

In this work,we present a high-power,high-repetition-rate,all-fiber femtosecond laser system operating at 1.5μm.This all-fiber laser system can deliver femtosecond pulses at a fundamental repetition rate of 10.6 GHz with an average output power of 106.4 W–the highest average power reported so far from an all-fiber femtosecond laser at 1.5μm,to the best of our knowledge.By utilizing the soliton-effect-based pulse compression effect with optimized pre-chirping dispersion,the amplified pulses are compressed to 239 fs in an all-fiber configuration.Empowered by such a high-power ultrafast fiber laser system,we further explore the nonlinear interaction among transverse modes LP01,LP11 and LP21 that are expected to potentially exist in fiber laser systems using large-mode-area fibers.The intermodal modulational instability is theoretically investigated and subsequently identified in our experiments.Such a high-power all-fiber ultrafast laser without bulky free-space optics is anticipated to be a promising laser source for applications that specifically require compact and robust operation.

Spectral manipulation in a high-power ultrafast fiber laser system generating ultrashort pulses with GHz repetition rate

In this work,we demonstrate the spectral manipulation in an ultrafast fiber laser system that generates ultrashort pulses with a repetition rate of 1.2 GHz and two switchable modes—a 1064-nm fundamental laser mode with a maximum output power of 66.6 W,and a 1125-nm Raman laser mode with a maximum output power of 17.23 W.The pulse width,beam quality,and power stability are carefully characterized.We also investigate a method to switch between the two modes by manipulating the duty cycle of the modulation signal.It is anticipated that this bi-mode ultrafast fiber laser system can be a promising ultrafast laser source for frontier applications,such as micromachining,bioimaging,and spectroscopy.

Three-level all-fiber laser at 915 nm based on polarization-maintaining Nd^3+-doped silica fiber

Nd3+-doped fiber lasers at around 900 nm based on the 4F3/2→4I9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through the frequency doubling.Here,an all-fiber laser at 915 nm was realized by polarization-maintaining Nd3+-doped silica fiber.A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber,which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber.The optical-to-optical conversion efficiency varies with the active fiber length and the reflectivity of the output fiber Bragg grating(FBG),presenting an optimal value of 5.3%at 5.1 cm fiber length and 70%reflectivity of the low reflection FBG.Additionally,the linear distributed Bragg reflector short cavity was constructed to explore its potential in realizing single-frequency 915 nm fiber laser.The measurement result of longitudinal-mode properties shows it is still multi-longitudinal mode laser operation with 40 mm laser cavity.These results indicate that the Nd3+-doped silica fiber could be used to realize all-fiber laser at 915 nm,which presents potential to be the seed source of high-power fiber laser.

Enhancing upconversion of Nd3+ through Yb^(3+)-mediated energy cycling towards temperature sensing

Photon upconversion of lanthanides has been a powerful means to convert low-energy photons into high-energy ones.However,in contrast to the mostly investigated lanthanide ions,it has remained a challenge for the efficient upconversion of Nd^(3+)due to the deleterious concentration quenching effect.Here we report an efficient strategy to enhance the upconversion of Nd^(3+)through the Yb^(3+)-mediated energy cycling in a core-shell-shell nanostructure.Both Nd^(3+)and Yb^(3+)are confined in the interlayer,and the presence of Yb^(3+)in the Nd-sublattice provides a more matched energy for the upconversion transitions occurring at the intermediate state of Nd^(3+)towards much better population at its emissive levels.Moreover,this design also minimizes the possible cross-relaxation processes at both intermediate level and the emissive levels of Nd^(3+)which are the primary factors limiting the upconversion performance for the Nd^(3+)-doped materials.Such energy cycling-enhanced upconversion shows promise in temperature sensing.

Pressureless crystallization of glass toward scintillating composite with high crystallinity for radiation detection

The construction of scintillating ceramics is of great technological importance for various fundamental applications, including medical diagnostic, security inspection, resource exploration and particle physics. The chief challenge is the facile and scalable synthesis of scintillating ceramics with the desirable combination of pore-free, reliable mechanical properties and excellent scintillating performance. Here we present a pressureless glass crystallization strategy for the construction of scintillating composite with high crystallinity. The fabricated scintillating composites are featured by small optical turbidity, excellent mechanical properties, and efficient scintillating luminescence with the scintillating light yield of 15,000 pH/MeV and about 2.46 times higher than that of the commercial BGO single crystal. Moreover, the scintillating composite derived radiation detector device is successfully elaborated. The practical application for monitoring gamma ray is demonstrated and the precision of the device is less than that of the tolerable deviation of 30%. Our results suggest an innovative approach for expanding the category of scintillating material candidates, pointing to practical application in the field of radiation detection.