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A high-precision tunable single-frequency fiber laser (T-SFFL) at 1.5 μm based on self-injection locking is experimentally demonstrated. By virtue of an effective filtering and self-injection locking scheme, a stable single-longitudinal-mode operation of the fiber laser is obtained. The fine wavelength tunability is implemented by stretching a uniform fiber Bragg grating in the self-injection loop, and the laser wavelength is tuned from 1550.28 to 1560.40 nm with a tuning accuracy of less than 54 pm. In the whole tuning range of 10.12 nm, an output power of approximately 5 mW and an optical signal-to-noise ratio of 71 dB are synchronously obtained with this laser system. Additionally, the measured laser linewidth is less than 630 Hz and the relative intensity noise is lower than -149 dB/Hz at frequencies from 0.4 to 7.5 MHz. It is believed that this 1.5 μm high-precision T-SFFL can be a promising candidate for the optical communications system applications.

A pulse compressing technology of single-frequency Q-switched laser based on the cascaded four-wave mixing (CFWM) effect is demonstrated theoretically and experimentally, for the first time to the best of our knowledge. A theoretical model of the pulse compression is established through deconstructing the pulse duration evolution in the high-order Stokes and anti-Stokes lights of CFWM. A pulse compression ratio of (2|m|+1)1/2 is quantificationally obtained with m corresponding to the order number of the CFWM light. Utilizing dual-wavelength (DW) single-frequency Q-switched laser injected into a highly nonlinear fiber (HNLF), the pulse compression and the spectral broadening phenomenon are observed simultaneously. As the order number of the CFWM light increases from 0-order to 3-order, the pulse duration has reduced from 115 ns to 47 ns with a compression ratio of 2.45, which is essentially consistent with the theoretical analysis. The pulse compressing technique by CFWM is conducive to promoting the performance development of the single-frequency Q-switched laser, which can improve the system precision in the Lidar, trace gas detection, and high-precision ranging. Furthermore, this technology based on time-frequency transformation dynamics may be generally applicable to other single-frequency pulsed fiber lasers.

In this paper, a sub-kHz-linewidth wavelength-tunable single-frequency ring-cavity fiber laser operating in C- and L-band is demonstrated experimentally. In our design, a single-longitudinal mode is achieved in a wide tuning range by a narrow-band filtering device composed of a fiber Fabry-Perot interferometer and a 1.6-m-long un-pumped Er3+-doped fiber as a dynamic grating. Under the control of a fiber Fabry-Perot tunable filter, a wavelength tuning range of 76.69 nm from 1535.50 to 1612.19 nm with a tuning interval of about 0.2 nm is finally achieved. In the entire tuning range of the fiber laser, the laser linewidth is less than 310 Hz. The measured optical signal-to-noise ratio is over 40 dB and the relative intensity noise is lower than -143 dB/Hz at frequencies above 1 MHz. Our results suggest that such fiber laser with narrow-linewidth and superior wavelength tunability can serve as a promising candidate applied in optical communication system.

Based on several centimeters long heavily Tm3+-doped germanate fibers (TGFs) and in-band-pumped technique, a short-wavelength distribute Bragg reflector (DBR) single-frequency fiber laser (SFFL) emitting at $1.7~\mu \text{m}$ is investigated experimentally. A stable single-longitudinal-mode laser output with a signal-to-noise ratio of greater than 60 dB and an operation wavelength of 1727 nm is realized. The maximum output power of 12.4 mW and the slope efficiency of 4.81% for the absorbed pump power are obtained from a 1.8-cm-long TGF pumped by a 1610 nm fiber laser. The measured relative intensity-noise of the SFFL reaches to around −130 dB/Hz at frequencies of over 10 MHz and the laser linewidth is 8.6 kHz. To the best of our knowledge, this is the first demonstration of the DBR Tm3+-doped SFFL with an operation wavelength in $1.7~\mu \text{m}$ region. It is suitable for optical coherence tomography, methane gas detection and optical medical technology.

In this article, the vector dynamics of semiconductor optical amplifiers (SOAs) are systematically analyzed and developed to explore its mechanism of intensity noise suppression. First, theoretical investigation on the gain saturation effect and carrier dynamics is performed via a vectorial model, and the calculated result unravels desynchronized intensity fluctuations of two orthogonal polarization states. Particularly, it predicts an out-of-phase case, which allows the cancellation of the fluctuations via adding up the orthogonally-polarized components, then establishes a synthetic optical field with stable amplitude and dynamic polarization, and thereby enables a remarkable relative intensity noise (RIN) reduction. Here, we term this approach of RIN suppression as out-of-phase polarization mixing (OPM). To validate the OPM mechanism, we conduct an SOA-mediated noise-suppression experiment based on a reliable single-frequency fiber laser (SFFL) with the presence of relaxation oscillation peak, and subsequently carry out a polarization resolvable measurement. By this means, out-of-phase intensity oscillations with respect to the orthogonal polarization states are clearly demonstrated, and consequently enable a maximum suppression amplitude of >75 dB. Notably, the RIN of 1550-nm SFFL, suppressed by joint action of OPM and gain saturation effect, is dramatically reduced to -160 dB/Hz in a wideband of 0.5 MHz∼10 GHz, and the performance of which is excellent by comparing with the corresponding shot noise limit of -161.9 dB/Hz. The proposal of OPM here not only facilitates us to dissect the vector dynamics of SOA but also offers a promising solution to realize wideband near-shot-noise-limited SFFL.

The upconversion of manganese (Mn2+) exhibits a green light output with a much longer lifetime than that of lanthanide ions, showing great potential in the frontier applications like information security and anti-counterfeiting. Mn2+ can be activated by energy migration upconversion. However, there exists serious quenching interactions between Mn2+ and the lanthanides at the core–shell interfacial area, which would markedly reduce the role of Tm3+ as a ladder to facilitate the up-transition and subsequently limit the upconversion of Mn2+. Here, we propose a mechanistic strategy to enhance the upconversion luminescence of Mn2+ by spatial control of energy migration among Gd sublattice through introducing an additional migratory NaGdF4 interlayer within the commonly used core–shell nanostructure. This design can not only isolate the interfacial quenching interactions between the sensitized core and luminescent shell, but also allow an efficient channel for energy transport, resulting in enhanced upconversion of Mn2+. Moreover, the relatively long lifetime of Mn2+ (around 32.861 ms) provides new possibilities to utilize the temporal characteristic for the frontier application of multi-level anti-counterfeiting through combining the time-gating technology.

Plant natural products (PNPs) are valuable resources for the development of pharmaceuticals and agrochemicals, yet the biosynthesis and metabolism of PNPs are largely unknown. Heterologous pathway reconstitution is a heavily adopted strategy in secondary metabolism characterization. Yeast systems have been broadly utilized in the heterologous production of PNPs and have been considered as a promising platform to investigate plant biosynthetic pathways. Here, we describe the reconstitution and verification of the upstream part of brassinolide biosynthesis in S. cerevisiae using this method.

As essential structural molecules for plant plasma membranes, phytosterols are key intermediates for the synthesis of many downstream specialized metabolites of pharmaceutical or agricultural significance, such as brassinosteroids and withanolides.Saccharomyces cerevisiaehas been widely used as an alternative producer for plant secondary metabolites. Establishment of heterologous sterol pathways in yeast, however, has been challenging due to either low efficiency or structural diversity, likely a result of crosstalk between the heterologous phytosterol and the endogenous ergosterol biosynthesis. For example, in this study, we engineered campesterol production in yeast using plant enzymes; although we were able to enhance the titer of campesterol to ~40mg/L by upregulating the mevalonate pathway, no conversion to downstream products was detected upon the introduction of downstream plant enzymes. Further investigations uncovered two interesting observations about sterol engineering in yeast. First, many heterologous sterols tend to be efficiently and intensively esterified in yeast, which drastically impedes the function of downstream enzymes. Second, yeast can overcome the growth deficiency caused by altered sterol metabolism through repeated culture. By employing metabolic engineering, strain evolution, fermentation engineering, and pathway reconstitution, we were able to establish a set of phytosterol-producing yeast strains with decent growth and titer of campesterol (~ 7mg/L), β-sitosterol (~2mg/L), 22-hydroxycampesterol (~1mg/L), and 22-hydroxycampest-4-en-3-one (~4mg/L). This work resolves the technical bottlenecks in phytosterol-derived pathway reconstitution in the backer’s yeast and opens up opportunities for efficient bioproduction and pathway elucidation of this group of phytochemicals.

Full waveform inversion (FWI) is a non-linear inverse problem that can be sensitive to noise. The tolerance of the noise-interference characteristics depends on the types of misfit functions. To date, different misfit functions, such as the least-squares norm (L2), the least-absolute-value norm (L1), and combinations of the two (e.g., the Huber and hybrid criteria), have been applied to FWI. The L2 norm is highly sensitive to non-Gaussian errors in the data and gives rise to high-amplitude artifacts in reconstructed models. For non-Gaussian noise data, the L1 norm and the Huber and hybrid criteria always reliably reconstruct models. However, the Huber and hybrid criteria require tedious error investigations to estimate their threshold criterion. Thus, the L1 norm is adopted here to improve the anti-noise ability of the FWI. The step length is closely related to the misfit function, and an optimal step-length estimation method can rapidly make the FWI algorithm reach the global minimum, with a reduced number of iterations and fewer extra forward modeling simulations during each iteration. The step length can usually be obtained using the exact or inexact line search method. Generally, the exact line search method is faster than the inexact one. Therefore, we derived an exact line search method for the L1 norm in the FWI process. Its effectiveness was tested using noise-free data from Overthrust and the SEG/EAGE salt models. The results demonstrate that this method can recover high-resolution velocity models with low computational costs. Numerical tests using the synthetic Overthrust model contaminated by strong noise were used to further validate the robustness of this exact line search method.

With the rapid development of synthetic biology and metabolic engineering technologies, yeast has been generally considered as promising hosts for the bioproduction of secondary metabolites. Sterols are essential components of cell membrane, and are the precursors for the biosynthesis of steroid hormones, signaling molecules, and defense molecules in the higher eukaryotes, which are of pharmaceutical and agricultural significance. In this mini-review, we summarize the recent engineering efforts of using yeast to synthesize various steroids, and discuss the structural diversity that the current steroid-producing yeast can achieve, the challenge and the potential of using yeast as the bioproduction platform of various steroids from higher eukaryotes.

Based mainly on the distributed Bragg reflector (DBR) short linear cavity with a 1.6-cm-long heavily T m 3 + -doped germanate glass fiber and semiconductor saturable absorber mirror (SESAM), a compact passively Q -switched single-frequency fiber laser at around 1950 nm is demonstrated experimentally. By comparing pulse characters of Q -switched operations fulfilled via SESAMs with different parameters, a stable output pulse is optimized to deliver a maximum average power of 22.2 mW, a peak power of 0.67 W, and an optical signal-to-noise ratio over 61 dB. Moreover, the repetition rate of the output pulse can be tuned from 92 to 520 kHz with a narrowest pulse width of 64 ns. To the best of our knowledge, this is the first time a 2.0 µm passively Q -switched single-frequency DBR T m 3 + -doped fiber laser has been realized, and it shows great potential application in remote sensing, biomedical science, and nonlinear optics.

Based on a fiber Fabry–Pérot tunable filter and a 3.0 m long unpumped gain fiber for forming dynamic grating, an in-band pumped tunable Tm3+-doped single-frequency fiber laser covering a wavelength tuning range from 1857.01 to 2020.17 nm and a tuning interval of −1 at frequencies over 1 MHz are obtained. To date, it is the broadest wavelength tuning range that has been reported in the 2 μm region, which is highly competitive in atmospheric detection.

Full waveform inversion (FWI) is a nonlinear data fitting process that can derive high-resolution model parameters through iteration. In this process, step length is related to inversion accuracy and computational efficiency. It can be calculated efficiently with the inexact line search method, which does not require a misfit function to achieve the exact minimum. This method is aimed toward obtaining the appropriate descent using evaluation conditions and initial step length. Moreover, it does not depend on the form of the misfit function. In the inexact line search method, the evaluation condition and initial step length are obviously important factors. In this work, the classical Armijo, Wolfe, and Goldstein evaluation conditions in solving optimization problems in mathematics are studied and compared in detail. Numerical examples from the synthetic data of the overthrust model show that the convergence characteristics of Armijo and Goldstein are similar and that the computational efficiency is high and conducive to seismic FWI. In addition, the adaptive Barzilai-Borwein (ABB) method is adopted in FWI. The ABB method maximizes the changes in model parameters and gradients to adaptively calculate the initial step length. The threshold value of the ABB method for the initial step length estimation is also studied to explore a suitable threshold value that can ensure that large and small step lengths are frequently adopted in FWI. Numerical examples from the synthetic data of the overthrust model demonstrate the validity of the ABB method. Moreover, the inversion is superior when the threshold value is less than 0.5.

The tapping of municipal wastewater for potable reuse significantly enhances drinking water supply in drought-stricken regions worldwide. Membrane-based potable reuse treatment trains commonly employ ultraviolet-based advanced oxidation processes (UV-AOPs) to degrade trace organic contaminants in water to produce high-quality recycled water. Hydrogen peroxide (H2O2) is used as the default photo-oxidant. Meanwhile, chloramines, which are added to prevent biofouling, pass through the membranes and impact the treatment efficiency of UV-AOP. Water reuse facilities therefore face the dilemma of optimizing H2O2 (an added photo-oxidant) and chloramines (a carry-over photo-oxidant) doses. Utilizing a uniquely designed pilot-scale reactor and real-time recycled water, we evaluated treatment efficiencies of UV-AOP on six important indicator contaminants, with monochloramine (NH2Cl) and H2O2 as photo-oxidants. Hydroxyl radical (HO•) and reactive chlorine species, such as the chlorine atom (Cl•) and chlorine dimer (Cl2•-), were the major reactive species. Overall, radicals generated from photolysis of NH2Cl alone achieved removal of indicator compounds, which can be further improved by optimizing UV fluence, i.e., the UV dose. Furthermore, the addition of H2O2 enhanced HO• formation and improved contaminant removal. However, the addition of H2O2, when the background NH2Cl level was above 2 mg L-1 (as Cl2), provided limited improvement in treatment efficiency. These trade-offs between chloramine and H2O2 as oxidants, and the recommended optimization of the associated effective UV fluence, are critical for energy-efficient and cost-effective potable reuse to address the challenges of global water scarcity.

Full waveform inversion (FWI) is a powerful tool for reconstructing high-resolution subsurface parameters estimated by iteratively minimising the difference between calculated and observed ...

A passively Q-switched single-frequency fiber laser with stable multi-wavelength operation is presented in this report. The laser cavity is constructed by using a 13-mm Er 3+ /Yb 3+ co-doped phosphate fiber with a multi-channel fiber Bragg grating and a semiconductor saturable absorber mirror attached to each fiber end, respectively. Quad-wavelength pulsed lasers are obtained and all of them maintain single-frequency operation. By controlling the pump power and the temperature of laser cavity, the Q-switched pulse operation is realized with repetition rates range of 126.6-350.9 kHz, a narrowest pulse duration of 104 ns, and a maximum pulse energy of 55.4 nJ. To the best of our knowledge, this is the first study to realize a Q-switched fiber laser operating at multiple wavelengths with single longitudinal mode. Furthermore, the evolutions of the pulse energy and repetition rates for different wavelength numbers are further analysis theoretically. This type of single-frequency pulsed fiber laser has extensive application prospect in fiber sensing and lidar systems.

A theoretical analysis of the influence of laser's linewidth on phase-OTDR sensing system is proposed and corresponding experiment is demonstrated. The linewidth factor of laser source is introduced into the signal expressions of phase-OTDR system under the nonquasi monochromatic light condition. The effect of linewidth can be transformed into an exponential decay item of the signal. Even if the sensing range is always smaller than the coherent length of the laser source, the detection SNR will decrease as the linewidth increases. A Phase-OTDR strain detection experiment with linewidth controllable laser is performed to verify the derived theoretical analysis result. The result shows that when linewidth increases from 2 kHz to 1 MHz, the detection SNR of the same vibration signal will decrease 4.3 dB. In order to select the appropriate laser source for phase-OTDR system, the coherent length and influence of linewidth ought to be taken into account to ensure the detection performance of the system.

High-power single-frequency fiber lasers with exceptional properties, such as mode-hop-free and narrower linewidths, lower noise, and compact all-fiber designs, have been attractive in many applications, including high-resolution sensing, coherent telecommunications, optical frequency domain reflectometry, and as a seed laser for light detection and ranging (LIDAR). However, the development of high-power single-frequency fiber lasers is constrained greatly by the lack of high-gain optical fiber and components. In this review, we discuss the basic considerations of advanced techniques for soft glass fiber and fiber preform as well as three key issues among them. Then, the recent advances in RE-doped soft glass and fiber lasers operating at near-infrared (NIR) and mid-infrared (MIR) wavelengths are evaluated in detail. Finally, prospects, applications and challenges for the realization of high-efficiency soft optical fibers in single-frequency fiber laser applications are analyzed and discussed. The review is organized as follows: Sections 1–3 introduce the basic requirements for the rare-earth (RE) ions and host matrix material for obtaining efficient NIR-MIR laser output, a review of the background of processing fundamentals on the fabrication and characterization for newly developed soft optical glass fibers, an outline of the key issues of platinum removal and the dehydration technique, effective doping of RE, and low splicing loss together with the recent theoretical and experimental results. Section 4 summaries the design and development of RE-doped soft optical glass and fiber lasers operating at 1, 1.5, 2, and 3 μm with emphatical discussions on the related luminescence mechanism and laser foundation as well as single-frequency lasers. Section 5 reviews the recent progress of various novel glass fibers and fiber lasers with unique photoelectricity properties, such as transparent glass-ceramic fiber and fiber lasers, quantum-dot fiber and fiber lasers, Bi-doped fiber and fiber lasers, as well as other novel glass fibers and devices, and outlines their prospects, applications, and challenges. Furthermore, Section 6 presents the conclusions of this review, which include the following: (1) From the single-component silica fiber to the multicomponent soft optical glass fiber, the glass compositions become more and more complex and the corresponding preparation method is constantly developing and improving. Various new types of optical fiber materials and components greatly expand their applications in the fields of fiber amplifiers, fiber lasers, and nonlinear optics, etc. (2) High-gain optical fiber is the key to the development of high-power single-frequency fiber lasers. To achieve intense and highly-efficient luminescence and lasers at the NIR and MIR regions from soft glass and optical fiber, the following methods were adopted, including using RE sensitization, uniform doping with high-concentration RE, hydroxyl and impurity-removing, new optical fiber and laser cavity design, low fusing loss, and the high-efficiency pumping method, etc. These novel glass systems and luminescence mechanisms enrich the glass systems of the past and provide a wealth of valuable data for optoelectronic materials and devices.

Fiber lasers, especially single-frequency fiber lasers, are highly desirable due to their long coherent length and narrow spectral linewidth that are unattainable in common photonic devices. However, significant challenges in the fabrication of high quality fiber laser devices still exist. In this paper, fibers with 1.55 μm laser output have been achieved using Er3+/Yb3+-codoped glass-ceramic (GC) as a core material and a “molten core” fiber-drawing technique. The prepared GC fibers demonstrate enhanced laser output with an optical signal-to-noise ratio of 65 dB and a slope efficiency of 11.8%, which are higher than those of the as-prepared glass fiber. Furthermore, a single-longitudinal mode laser with a linewidth of 7.4 kHz and a relative intensity noise (RIN) of −148.8 dB/Hz is achieved, manifesting the potential applications of the GC fibers in optoelectronic fields. Theoretical calculations and simulations are employed to understand the relation between the optical performance of the fiber laser and the atomic structure in the phase-separated region of the oxyfluoride glass cores. The demonstrated GC fibers provide a new platform for the development of multifunctional fiber lasers and open a new avenue towards practical applications for crystallized fibers.

Fiber lasers operating at around 900 nm based on Nd3+ doped fibers have attracted intense attention recently for generating high performance pure blue laser sources by frequency doubling, which could be applied in the fields of laser color displays, laser driven solid lighting and high density storage. Although several approaches have been proposed to realize laser operation at this band, for example by nitrogen cooling or utilizing fibers with a special waveguide design, the intrinsic low fluorescence branching ratio of the three-level 4F3/2 → 4I9/2 transition (900 nm) is still a serious problem that limits the development of laser devices towards compactness and high efficiency. Here, we report a crystal field strength and structural engineering strategy; accordingly, not only can the branching ratio of Nd3+ be tuned towards enhancing the 4F3/2 → 4I9/2 transition, but also the near-infrared (NIR) emission intensity could be improved by six times. Furthermore, the lifetimes of the upper 4F3/2 level were also prolonged from 124 to 246 μs, simultaneously. Systemically, optical and structural analysis implies that the fine-tuning of Stark splitting, the spectroscopic quality factor (χ) and the dispersed state of Nd3+ are the main reasons for this intriguing scenario. These results will help us design optical glass fibers by an inherent local structure based strategy to realize efficient and compact 0.9 μm fiber lasers for high performance pure blue fiber lasers.

The structural, thermal, and luminescent properties of germanate glass containing heavily Dy2O3 content are systematically investigated by means of differential scanning calorimetry, X-ray diffraction, Raman spectra, absorption and emission spectra, and dynamic lifetime decay curves. To seek a suitable composition, the optimal glass forming region is first predicted through the thermodynamic calculation method and their basic physical properties are further forecasted according to the phase diagram model. The experiment results show that the density, refractive index, characteristic temperature, and phonon energy of the glass host all exhibit a close connection with the rare earth concentration. Strikingly, when the amount of Dy2O3 is up to 10.5 mol%, the transition temperature of the glass reaches 747 °C, which is higher than any other known germanate glass and is much advantageous to achieve a higher laser damage threshold. Moreover, the high doping caused the refractive index to increase significantly, which also prompted the glass to obtain a larger emission section and quality factor, increasing the possibility of laser output. Besides, three visible luminescence peaks of Dy3+ at 480 nm (blue) and 575 nm (yellow), and 665 nm (red) are observed even at an extremely high Dy3+ concentration. All the results demonstrate that this kind of germanate glass containing significant amounts of RE could be of interest for implementation of high-gain fiber lasers.

An over-20-octaves-bandwidth ultralow-intensity-noise 1064-nm single-frequency fiber laser (SFFL) is demonstrated based on a comprehensive all-optical technique. With a joint action of booster optical amplifier (BOA) and reflective Yb-doped fiber amplifier (RYDFA), two-fold optical gain saturation effects, respectively occurring in the media of semiconductor and fiber, have been synthetically leveraged. Benefiting from the gain dynamics in complementary time scales, i.e., nanosecond-order carrier lifetime in BOA and millisecond-order upper-level lifetime in RYDFA, the relative intensity noise (RIN) is reduced to −150 dB/Hz from 0.2 kHz to 350 MHz, which exceeds 20-octaves bandwidth. Remarkably, a maximum suppressing ratio of >54 dB is obtained, and the RIN in the range of 0.09–10 GHz reaches −161 dB/Hz which is only 2.3 dB above the shot-noise limit. This broad-bandwidth ultralow-intensity-noise SFFL can serve as an important building block for squeezed light generation, space laser communication, space gravitational wave detection, etc.

Global public health is increasingly threatened by the fast emergence of antibiotic resistance, and novel types of antibiotics are urgently needed. Metazoans have evolved their own antimicrobial mechanism, such as human group IIA secreted phospholipase A (sPLA2), which can efficiently inhibit the growth of gram-positive bacteria, but with much lower efficiency toward gram-negative bacteria. Here, we verified the antibacterial activity of a plant lipase, PLIP1 from Arabidopsis thaliana, against the gram-negative bacteria Escherichia coli, which belongs to the WHO priority 1 (critical) pathogen Enterobacteriaceae family. We also explored the potential of evolving PLIP1 as a more potent antimicrobial agent towards E. coli. Our results imply the possibility of using plant lipases as a potential antimicrobial and shed light on the future exploration of plant enzymes for novel and more efficient antibacterial agents.

In this Letter, a bidirectional amplifier configuration suppressing the relative intensity noise in a 1950-nm linearly polarized single-frequency fiber laser (SFFL) is proposed. The scheme to amplify the signal in a nonlinear saturated amplification regime with low gain distribution for suppressing the RIN is theoretically analyzed. By optimizing the input power level and reflectivity of the bidirectional power-amplifier, the RIN is decreased maximally by > 24 d B within the frequency range of 200 kHz. A stable output power of over 5.16 W with a polarization extinction ratio of 21.2 dB is obtained. Additionally, the amplified signal maintains a linewidth of 7.1 kHz nearly identical with that of the seed, both with a signal-to-noise ratio of more than 60 dB. This all-optical technique on noise suppression applied to the fiber amplifier paves the way to realize low-noise SFFL with power improvement.

We present a novel real-time frequency-encoded spatiotemporal (FEST) focusing technology using a programmable two-dimensional optical frequency comb. This technique enables, for the first time, simultaneous spatial and temporal focusing at microseconds through thick scattering media.

Based on core- and in-band-pumped polarization-maintaining T m 3 + -doped single-cladding fiber (PM-TSF, the core diameter is 9 µm) by a 1610 nm fiber laser and a distributed Bragg reflector seed laser, a linearly polarized single-frequency fiber laser (LP-SFFL) at 1950 nm with an output power of 55.3 W and a laser linewidth of 6.95 kHz is demonstrated. The output beam qualities of M x 2 and M y 2 are measured to be 1.01 and 1.03, respectively. The slope efficiency with respect to the launched pump power is 71.0%, in comparison with a theoretical quantum efficiency of 82.6%. A polarization-extinction ratio of 19 dB and an optical signal-to-noise ratio of 58 dB are obtained from the 1950 nm LP-SFFL. To the best of our knowledge, to date, this is the highest power of 2.0 µm SFFL output directly from a strict single-mode active fiber. Our experiment offers a promising solution to the current limitations of the high-performance fiber lasers at 2.0 µm, which is particularly essential for coherent detection.

We report a narrow linewidth and low threshold single-frequency distributed Bragg reflector (DBR) fiber laser at 1120 nm based on a short 1.5 cm long Nd-doped silica fiber which, to the best of our knowledge, is the first demonstration of a Nd-doped fiber-based single-frequency fiber laser with a wavelength greater than 1100 nm. A stable single-longitudinal-mode laser operation with a signal-to-noise ratio greater than 67 dB was verified by a scanning Fabry–Perot interferometer. The laser threshold is as low as 10 mW. The DBR fiber laser has a maximum output power of 15 mW and optical-to-optical efficiency for the launched pump power reaches more than 8%. The narrow linewidth of 71.5 kHz is obtained in such a single-frequency fiber laser (SFFL). Our result is expected to offer an exciting new opportunity to realize high-performance SFFLs above 1100 nm.

A frequency-encoded spatiotemporal focusing technology enables real-time optical wavefront shaping through thick scattering media., Optical wavefront shaping is a powerful tool for controlling photons in strongly scattering media. Its speed, however, has been the bottleneck for in vivo applications. Moreover, unlike spatial focusing, temporal focusing from a continuous-wave source has rarely been exploited yet is highly desired for nonlinear photonics. Here, we present a novel real-time frequency-encoded spatiotemporal (FEST) focusing technology. FEST focusing uses a novel programmable two-dimensional optical frequency comb with an ultrafine linewidth to perform single-shot wavefront measurements, with a fast single-pixel detector. This technique enables simultaneous spatial and temporal focusing at microsecond scales through thick dynamic scattering media. This technology also enabled us to discover the large-scale temporal shift, a new phenomenon that, with the conventional spatial memory effect, establishes a space-time duality. FEST focusing opens a new avenue for high-speed wavefront shaping in the field of photonics.

We report a compact all-fiber passively mode-locked ultrafast laser with a fundamental repetition rate of 1.6 GHz that uses a self-developed long-wavelength active fiber, i.e., a fluoro-sulfo-phosphate-based Er3+/Yb3+ co-doped fiber (only 6.2 cm in length). This active fiber can provide a net gain coefficient of 0.6 dB/cm at 1610 nm. The high-repetition-rate all-fiber mode-locked laser operates at a low pump power of only approximately 90 mW. The mode-locked pulse train has a period of 625 ps and a 3 dB bandwidth of 7.0 nm, which can support a transform-limited pulse width of 390 fs.

Based on a low time-domain-instability narrow-linewidth seed and a counter-pumped power-amplifier with a 20/400 μm core/inner-cladding-diameter active fiber, an all-fiber 2.02 kW and 4.7 GHz linewidth near-diffraction-limited master-oscillator power-amplifier (MOPA) laser at 1064 nm is demonstrated experimentally. By decreasing the time-domain-instability of the signal, the stimulated Raman scattering effect in the power-amplifier stage is suppressed effectively. As a result, a measured M2 factor of 1.20, and an optical signal-to-noise ratio of >65 dB are obtained at the maximum output power without observation of the transverse mode instability effect. The further enhancement of power scaling of this MOPA laser is restricted by the stimulated Brillouin scattering effect. To the best of our knowledge, this result exhibits the highest output power of all-fiber MOPA laser with narrow linewidth (

Identification of red wine residues in archaeological potteries can yield good insight into the development of red wine culture and the history of winemaking. In this work, the ultra- sonication extraction method was developed to extract the organic acids in simulated red wine residues, while the optimization of extraction condition was studied through orthogonal methods. Moreover, the availability of the proposed research method in archaeological research was also investigated by extracting and analyzing two real archaeological samples. The results obtained from the liquid chromatography/mass spectrometry (LC/MS) proved that the tartaric acid can be acted as the biomarker of red wine. The range analysis of orthogonal methods indicated that the temperature is the main factor on the extraction efficiency of tartaric acid, followed by the proportion of methanol in the solvent, and finally is the extraction time. More importantly, tartaric acid can be identified in the real archaeological sample using the proposed extraction and analysis method, indicating its high verifiability and reliability. This work would provide a complete set of analysis method to identify the traces of wine organic residues in archaeological samples, thus understanding the production and conservation of wine or even tracking back to the start brewing process of wine.

Wideband NIR-emitting materials are crucial components in light sources and tunable lasers for sensing, metrology, and optical amplification. While traditional rare-earth (RE) doped gain media have reached their limit in bandwidth, Bismuth-doped glasses have been evolving as an interesting alternative with unmatched spectral performance. However, serious issues remain for this type of material, in particular, in achieving the desired spectral bandwidth while providing the ability of fiber drawing on part of the matrix glass, and in terms of stabilization of the active Bismuth center in secondary processing steps at high temperature. Here, we report on chemical nitridation of Bidoped glasses as a means to enhance local network rigidity and, thus, stabilize the NIR active emission species and increase Birelated NIR emission efficiency. At the same time, we show that the existence of nitride bonds leads to the emergence of germanium-related Bi emission centers, which further enhance the spectral bandwidth of...

In this paper, a polarization-maintaining quad-wavelength (QW) single-frequency fiber laser (SFFL) at the C-band with the novel and compact structure is demonstrated. Applying the rate equations and multiple coupled nonlinear Schrödinger equations, the theoretical model of QW fiber lasers is established, and then the optical spectra, temporal evolution, and stability of the QW fiber laser are analyzed numerically. Based on the theoretical analysis, a QW-SFFL having an ultrashort linear distributed Bragg reflector cavity is proposed. Utilizing a wideband fiber Bragg grating coupled with a dual-channel polarization maintaining fiber Bragg grating as the wavelength selection and a 15-mm-long Er3+/Yb3+ co-doped phosphate fiber as the gain medium has realized a robust QW laser with the wavelength spacing of 0.4 nm. All the wavelengths maintain the single-frequency operation independently with the linewidths of 20 kHz. This type of compact SFFLs with quadruple wavelengths is widely adapted to lidar systems and fiber sensing.