1283-1460 nm continuously tunable, watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to a visible laser.

We report, to the best of our knowledge, the first demonstration of an O + E-band tunable watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to tunable red laser. Benefiting from the two types of bismuth active centers associated with silicon and phosphorus introduced in one fiber, an ultrabroad gain is available in the designed low-water-peak bismuth-doped phosphosilicate fiber (Bi-PSF) pumped by a self-made 1239 nm Raman fiber laser. The high-efficiency tunable lasing is achieved with a maximum output power of 1.705 W around 1320 nm and a slope efficiency of 33.0%. The wavelength can be continuously tuned from 1283 to 1460 nm over a 177 nm spectral range, almost covering the whole O+E-bands. We further employ a polarization beam splitter in the cavity to output an O + E-band linear-polarization laser for second-harmonic generation by a designed multi-period MgO2:PPLN crystal, and a 650-690-nm tunable visible laser is correspondingly obtained. Such an O+E-wideband tunable high-power laser and the SHG red laser may have great potential in the all-band optical communications, biophotonics, and spectroscopy.

Direct generation of a 635 nm red random laser based on praseodymium (Pr)-doped ZBLAN fiber.

Visible random fiber lasers have garnered significant attention due to their unique emission properties and potential applications in various fields. We first, to the best of our knowledge, demonstrated a compact all-fiber structure, red wavelength, and random fiber laser (RFL) based on a double-clad Pr-doped ZBLAN fiber. The simple half-open cavity consists of a high-reflectivity fiber pigtail mirror and the Pr-doped ZBLAN fiber. The Pr-doped ZBLAN fiber not only served as a gain medium but also offered random backward scattering. We investigated the effects of different lengths on output power and slope efficiency of the RFL. For 21 m Pr-doped fiber, the RFL emitted a maximum output power of 208.50 mW with a slope efficiency of 11.09%. For 15 m Pr-doped fiber, the maximum power decreased to 120.18 mW with the slope efficiency of 7.27%. We are also numerically simulating the output power versus the pump power at different fiber lengths based on power steady-state light propagation equations. This novel RFL has the potential for broad applications in fields such as display technology, spectroscopy, biomedical imaging, and optical sensing due to its unique properties and simple all-fiber structure.

High-efficiency fiber-cladding power stripper based on all-dielectric optical thin films.

Although conventional fiber-cladding power strippers (CPSs) based on the techniques of high-index adhesive or corrosive liquids onto fiber inner cladding have been well developed, they are still facing challenges in special applications such as spaceborne or radiation-environment fiber lasers and amplifiers. In this paper, we propose and fabricate high-efficiency CPSs based on all-dielectric optical thin films. By numerically analyzing the propagation characteristics of cladding light at the thin film interface, we design a high-index T a 2 O 5 CPS and A l 2 O 3 CPS with single- and cascaded-layer films coated onto the fiber inner cladding, respectively. In our experiment, the CPSs are successfully fabricated onto the inner-cladding surface of 10/125 double-clad fiber based on ion-beam-assisted deposition technology. The stripping efficiency for the 976 nm residual cladding power was measured up to 99.38%, and the stripping power of the fiber CPS without active cooling can be 24 W at least. Such CPS could be advantageous for applications in spaceborne-based fiber lasers or amplifiers (e.g., gravitational wave detection, spaceborne lidar).

Soliton polarization dynamics in a fiber laser of zero dispersion.

Polarization properties of a soliton generated in a fiber laser of zero dispersion are investigated. Similar to the solitons generated in a fiber laser of all anomalous dispersion, the polarization ellipse of the soliton rotated during pulse evolution inside the cavity. The number of rotations relies on the cavity averaged birefringence with nonlinear bias. The larger the cavity averaged birefringence is, the bigger the bias is. When the period multiplying of solitons appears, the number of rotations depends on both multiplying periods and the cavity averaged birefringence. Multiple polarization states can be observed at a fixed position in the cavity depending on the multiplying period. When the cavity length is equal to n times of the averaged beat length, the polarization ellipse of the soliton rotates n∗m times at a fixed position, where m is equal to the multiplying period.

Potential application of a green fiber laser in laser display systems.

This study explores the application of optical fiber lasers in display systems by integrating a P r3+-doped green all-fiber laser into a laser projection display system. As a control group to compare the results, a 520 nm semiconductor green laser diode module was integrated, similar to the experimental group. The color gamut and speckle performances were studied and compared. The results showed that the experimental group performed slightly better in the color gamut volume. The speckle contrast decreased rapidly in the experimental group when power increased. To our knowledge, this is the first study to apply a fiber laser to a laser display system. The results shed light on developing laser display systems with fewer or no speckle reduction elements.

Transcriptomic analysis reveals mechanisms for the different drought tolerance of sweet potatoes.

Drought is a common environmental stress with great negative impacts on plant growth, development and geographical distribution as well as agriculture and food production. Sweet potato is characterized by starchy, fresh and pigmented tuber, and is regarded as the seventh most important food crop. However, there has been no comprehensive study of the drought tolerance mechanism of different sweet potato cultivars to date. Here, we studied the mechanism for drought response of seven sweet potato drought-tolerant cultivars using the drought coefficients, physiological indicators and transcriptome sequencing. The seven sweet potato cultivars were classified into four groups of drought tolerance performance. A large number of new genes and transcripts were identified, with an average of about 8000 new genes per sample. Alternative splicing events in sweet potato, which were dominated by first exon and last exon alternative splicing, were not conserved among different cultivars and not significantly affected by drought stress. Furthermore, different drought-tolerance mechanisms were revealed through differentially expressed gene analysis and functional annotation. Two drought-sensitive cultivars, Shangshu-9 and Xushu-22, mainly resisted drought stress by up-regulating plant signal transduction. The other drought-sensitive cultivar Jishu-26 responded to drought stress by down-regulating isoquinoline alkaloid biosynthesis and nitrogen/carbohydrate metabolism. In addition, the drought-tolerant cultivar Chaoshu-1 and drought-preferred cultivar Z15-1 only shared 9% of differentially expressed genes, as well as many opposite metabolic pathways in response to drought. They mainly regulated flavonoid and carbohydrate biosynthesis/metabolism in response to drought, while Z15-1 increased photosynthesis and carbon fixation capacity. The other drought-tolerant cultivar Xushu-18 responded to drought stress by regulating the isoquinoline alkaloid biosynthesis and nitrogen/carbohydrate metabolism. The extremely drought-tolerant cultivar Xuzi-8 was almost unaffected by drought stress and responded to drought environment only by regulating the cell wall. These findings provide important information for the selection of sweet potatoes for specific purposes.

All-fiber cyan laser at 491.5 nm.

We report, for the first time to our knowledge, a compact continuous-wave all-fiber cyan laser. The all-fiber cavity consists of a 443-nm fiber-pigtail laser diode as pump source, a 4.5-cm single-clad Pr3+-doped fluoride fiber, and two custom-built dielectric-coated fiber-pigtail mirrors in the visible spectral region. Downconversion cyan lasing at 491.5 nm is directly achieved, providing a maximum output power of 97.5 mW with a slope efficiency of 23.7% and a power fluctuation of less than 0.41%. Such a compact all-fiber cyan laser may be of great significance to expand the color reproduction range of laser displays, and has potential applications in fluorescence imaging, underwater communication, and detection.

Genome-Wide Identification of DUF668 Gene Family and Expression Analysis under Drought and Salt Stresses in Sweet Potato [Ipomoea batatas (L.) Lam].

The domain of unknown function 668 (DUF668) is a gene family that plays a vital role in responses to adversity coercion stresses in plant. However, the function of the DUF668 gene family is not fully understood in sweet potato. In this study, bioinformatics methods were used to analyze the number, physicochemical properties, evolution, structure, and promoter cis-acting elements of the IbDUF668 family genes, and RNA-seq and qRT-PCR were performed to detect gene expression and their regulation under hormonal and abiotic stress. A total of 14 IbDUF668 proteins were identified in sweet potato, distributed on nine chromosomes. By phylogenetic analysis, IbDUF668 proteins can be divided into two subfamilies. Transcriptome expression profiling revealed that many genes from DUF668 in sweet potato showed specificity and differential expression under cold, heat, drought, salt and hormones (ABA, GA3 and IAA). Four genes (IbDUF668-6, 7, 11 and 13) of sweet potato were significantly upregulated by qRT-PCR under ABA, drought and NaCl stress. Results suggest that the DUF668 gene family is involved in drought and salt tolerance in sweet potato, and it will further provide the basic information of DUF668 gene mechanisms in plants.

1.3/1.4 µm dual-wave band dissipative soliton resonance in a passively mode-locked Bi-doped phosphosilicate fiber laser.

We report the 1.3/1.4 µm dual-wave band dissipative soliton resonance (DSR) in a passively mode-locked bismuth-doped phosphosilicate fiber (Bi-PSF) laser. The low-water-peak Bi-PSF with two bismuth active centers associated with silicon and phosphorus supports the O+E-band gain. Using a 1239 nm home-made Raman fiber laser as pump source and nonlinear amplifying loop mirror for initiating mode-locking, stable DSR operation at 1343 and 1406 nm is achieved with the spectral bandwidth of 12 and 16 nm. The pulse duration with the pump power increases from 62 to 270 ps with a repetition frequency of 4.069 MHz. The average power is 11.05 mW corresponding to the maximum energy of 2.7 nJ. This is, to the best of our knowledge, the first demonstration of a mode-locked fiber laser in the ∼1.38 µm water absorption band and the O+E dual-wave band operation for applications in all-spectral-band communications, bio-medical imaging, and terahertz difference frequency generation.

On-chip mid-IR octave-tunable Raman soliton laser.

Photonic chip-based continuously tunable lasers are widely recognized as an indispensable component for photonic integrated circuits (PICs). Specifically, mid-infrared (mid-IR) laser sources are of paramount importance in applications such as photonic sensing and spectroscopy. In this article, we theoretically investigate the propagation dynamics of mid-IR Raman soliton in Ge28Sb12Se60 chalcogenide glass waveguide. By carefully engineer the waveguide dispersion and nonlinear interaction, we propose a suspended chalcogenide glass waveguide device that allows an octave-tuning, from 1.96 µm to 3.98 µm, Raman soliton source. The threshold pump energy is in the low pico-Joule range. Our result provides a solution to continuously tunable on-chip mid-IR ultrafast laser sources.

Ultra-Small 2D PbS Nanoplatelets: Liquid-Phase Exfoliation and Emerging Applications for Photo-Electrochemical Photodetectors.

2D PbS nanoplatelets (NPLs) form an emerging class of photoactive materials and have been proposed as robust materials for high-performance optoelectronic devices. However, the main drawback of PbS NPLs is the large lateral size, which inhibits their further investigations and practical applications. In this work, ultra-small 2D PbS NPLs with uniform lateral size (11.2 ± 1.7 nm) and thickness (3.7 ± 0.9 nm, ≈6 layers) have been successfully fabricated by a facile liquid-phase exfoliation approach. Their transient optical response and photo-response behavior are evaluated by femtosecond-resolved transient absorption and photo-electrochemical (PEC) measurements. It is shown that the NPLs-based photodetectors (PDs) exhibit excellent photo-response performance from UV to the visible range, showing extremely high photo-responsivity (27.81 mA W-1 ) and remarkable detectivity (3.96 × 1010 Jones), which are figures of merit outperforming currently reported PEC-type PDs. The outstanding properties are further analyzed based on the results of first-principle calculations, including electronic band structure and free energies for the oxygen evolution reaction process. This work highlights promising applications of ultra-small 2D PbS NPLs with the potential for breakthrough developments also in other fields of optoelectronic devices.

Towards visible-wavelength passively mode-locked lasers in all-fibre format.

Mode-locked fibre lasers (MLFLs) are fundamental building blocks of many photonic systems used in industrial, scientific and biomedical applications. To date, 1-2 µm MLFLs have been well developed; however, passively mode-locked fibre lasers in the visible region (380-760 nm) have never been reported. Here, we address this challenge by demonstrating an all-fibre visible-wavelength passively mode-locked picosecond laser at 635 nm. The 635 nm mode-locked laser with an all-fibre figure-eight cavity uses a Pr/Yb codoped ZBLAN fibre as the visible gain medium and a nonlinear amplifying loop mirror as the mode-locking element. First, we theoretically predict and analyse the formation and evolution of 635 nm mode-locked pulses in the dissipative soliton resonance (DSR) regime by solving the Ginzburg-Landau equation. Then, we experimentally demonstrate the stable generation of 635 nm DSR mode-locked pulses with a pulse duration as short as ~96 ps, a radio-frequency signal-to-noise ratio of 67 dB and a narrow spectral bandwidth of <0.1 nm. The experimental results are in excellent agreement with our numerical simulations. In addition, we also observe 635 nm noise-like pulse operation with a wide (>1 nm) and modulated optical spectrum. This work represents an important step towards miniaturized ultrafast fibre lasers in the visible spectral region.

A self-powered photodetector based on two-dimensional boron nanosheets.

Owing to their intriguing characteristics, the ongoing pursuit of emerging mono-elemental two-dimensional (2D) nanosheets beyond graphene is an exciting research area for next-generation applications. Herein, we demonstrate that highly crystalline 2D boron (B) nanosheets can be efficiently synthesized by employing a modified liquid phase exfoliation method. Moreover, carrier dynamics has been systematically investigated by using femtosecond time-resolved transient absorption spectroscopy, demonstrating an ultrafast recovery speed during carrier transfer. Based on these results, the optoelectronic performance of the as-synthesized 2D B nanosheets has been investigated by applying them in photoelectrochemical (PEC)-type and field effect transistor (FET)-type photodetectors. The experimental results revealed that the as-fabricated PEC device not only exhibited a favourable self-powered capability, but also a high photoresponsivity of 2.9-91.7 µA W-1 in the UV region. Besides, the FET device also exhibited a tunable photoresponsivity in the range of 174-281.3 µA W-1 under the irradiation of excited light at 405 nm. We strongly believe that the current work shall pave the path for successful utilization of 2D B nanosheets in electronic and optoelectronic devices. Moreover, the proposed method can be utilized to explore other mono-elemental 2D nanomaterials.

2166 nm all-fiber short-pulsed Raman laser based on germania-core fiber.

We report a compact 2166 nm germania-fiber short-pulsed Raman laser based on the cavity matching scheme. The all-fiber Raman cavity is formed by a pair of 2166 nm fiber Bragg gratings. High-power noise-like pulses from a 1981 nm fiber laser are used to pump a 22 m germania-core fiber for providing Raman gain at ∼2166 nm, and readily realizes the Raman-cavity synchronization with high mismatching tolerance. Stable Raman pulses at 2166 nm are therefore generated with the tunable pulse width of 0.9-4.4 ns and the large pulse energy up to 12.15 nJ. This is, to the best of our knowledge, the first demonstration of all-fiber short-pulsed Raman laser in the mid-infrared region.

Compact all-fiber 2.1-2.7 µm tunable Raman soliton source based on germania-core fiber.

Although ultrafast rare-earth-doped fiber lasers mode-locked at near-infrared and ∼3 µm wavelengths have been well developed, it is relatively difficult to achieve ultrafast fiber laser emitting in the 2.1-2.7 µm spectral gap between ∼2 µm (Tm fiber) and ∼2.8 µm (Er or Ho fluoride fiber). In this paper, we report the generation of 2.1-2.7 µm tunable femtosecond Raman solitons from a compact fusion-spliced all-fiber system using a home-made 1.96 µm ultrafast pump source and a MIR-available germania-core fiber. At first, a Tm-doped double-clad fiber amplifier is used to not only boost up the power of 1957 nm femtosecond seed laser, but also to generate the first-order soliton self-frequency shift (SSFS). The first-order Raman solitons can be tuned from 2.036 to 2.152 µm, have a pulse duration of ∼480 fs and can reach a pulse energy of 1.07 nJ. The first-order Raman solitons are further injected into a 94 mol.% germania-core fiber to excite the second-order SSFS. The second-order solitons can be tuned to longer wavelengths, i.e. from 2.157 µm up to 2.690 µm. Our work could provide an effective way to develop compact, all-fiber ultrafast MIR laser sources with the continuous wavelength tuning of 2.1-2.7 µm.

Direct generation of orthogonally polarized dual-wavelength continuous-wave and passively Q-switched vortex beam in diode-pumped Pr:YLF lasers.

We report on direct generation of an orthogonally polarized dual-wavelength vortex laser, for the first time to our knowledge, by means of a diode-pumped V-shaped Pr:YLF laser platform. A method of misaligning the folded mirror is proposed to realize the simultaneous orthogonally polarized dual-wavelength laser, while a method of orthogonally rotating the laser gain medium is proposed to generate an intracavity vortex beam (LG01 mode). With the two methods, in continuous-wave (CW) mode, we have achieved simultaneous lasing of an orthogonally polarized dual-wavelength vortex laser at 604 and 607 nm with maximum output power of 237.7 mW. Moreover, based on this operation, a simultaneous orthogonally polarized dual-wavelength passively Q-switched vortex laser is also realized by inserting a Co:ASL crystal into the laser resonator as a saturable absorber. This work provides the simplest way for direct generation of an orthogonally polarized dual-wavelength vortex laser for potential applications.

High-efficiency, yellow-light Dy3+-doped fiber laser with wavelength tuning from 568.7 to 581.9 nm.

We report, to the best of our knowledge, the first demonstration of a wavelength-tunable and highly efficient Dy3+-doped fiber laser operating in the yellow spectral region. A 2-m-long Dy3+:ZBLAN fiber pumped by a 447-nm GaN laser diode provides a strong down-conversion gain around 575 nm. A fiber end-facet mirror and a visible reflective grating in the Littrow configuration construct the resonant cavity and introduce the wavelength tunability. A stable yellow laser with a <0.05-nm narrow linewidth is achieved and continuously tuned from 568.7 nm to 581.9 nm, covering more than half of the yellow spectral range. The slope efficiency is as high as 34.9%, and the maximum output power is 142 mW at 576.44 nm, which is 13 times higher than previously reported. It is, to the best of our knowledge, the highest power and conversion efficiency of a yellow-light Dy3+-doped fiber laser with wavelength tunability.

Green/red pulsed vortex-beam oscillations in all-fiber lasers with visible-resonance gold nanorods.

Optical vortex beams are of tremendous interest in diverse applications for optical tweezers, high-resolution imaging, quantum information and optical communications. So far, these vortex laser sources largely rely on extra-cavity mode conversion by bulk optical elements (e.g. spatial light modulators, phase plates, etc.), resulting in a relatively poor purity, low conversion efficiency, non-compact structure and expensive package. Vortex beams generated directly from cavity-mode lasers is naturally an ideal solution, but almost all of them are not extended into the important visible spectral region. Here, we address the challenge through demonstrating, for the first time, visible-wavelength all-fiber pulsed vortex lasers. By using the fiber offset splicing technique and all-fiber visible resonators, 543.6 nm (green) and 634.7 nm (red) vortex beams are generated directly from Er3+: ZBLAN and Pr3+/Yb3+: ZBLAN fiber lasers with topological charges of ±1 and ±2, respectively. In particular, by exploiting an excellent visible-wavelength saturable absorber, visible-resonance-controlled gold nanorods, we further realize stable short-pulse operation of the 543.6 nm/634.7 nm vortex beams in the miniaturized visible fiber lasers. The green/red vortex laser pulses are ∼500 ns in duration, have a 40-400 kHz tunable repetition rate, and a >45 dB RF signal-to-noise ratio. This work may pave a path towards compact visible-wavelength pulsed vortex lasers for specific applications in STED microscopy and visible-light communications.

Determining topological charge based on an improved Fizeau interferometer.

We propose a new method to determine topological charge by using an improved Fizeau interferometer. This interferometer is very easy to realize, as well as interference fringes are very distinct. Phases of vortex, Hermite-Gaussian, and elliptical vortex beams are experimentally verified using this method. It provides a convenient way to determine the sign and magnitude of topological charge. This method may have some potential applications in space optical communication.

Ultrathin GeSe Nanosheets: From Systematic Synthesis to Studies of Carrier Dynamics and Applications for a High-Performance UV-Vis Photodetector.

Owing to the attractive energy band properties, a black phosphorus (BP)-analogue semiconductor, germanium selenide (GeSe), shows a promising potential applied for optoelectronic devices. Herein, ultrathin GeSe nanosheets were systematically prepared via a facile liquid-phase exfoliation approach, with controllable nanoscale thickness. Different from BP, ultrathin GeSe nanosheets exhibit good stability under both liquid and ambient conditions. Besides, its ultrafast carrier dynamics was probed by transient absorption spectroscopy. We showed that the GeSe nanosheet-based photodetector exhibits excellent photoresponse behaviors ranging from ultraviolet (UV) to the visible regime, with high responsivity and low dark current. Furthermore, the detective ability of such a device can be effectively modulated by varying the applied bias potential, light intensity, and concentration of the electrolyte. Generally, our present contribution could not only supply fundamental knowledge of a GeSe nanosheet-based photoelectrochemical (PEC)-type device, but also offer guidance to extend other possible semiconductor materials in the application of the PEC-type photodetector.