Numerical simulation of ultrawideband supercontinuum generation covering a 2-20 µm waveband in cascaded all-soft-glass fiber.

We designed a cascaded all-soft-glass fiber structure and simulate midinfrared 2-20 µm ultrawideband supercontinuum (SC) generation numerically. The cascaded fiber structure consists of a 1.5 m I n F 3 fiber, a 0.2 m chalcogenide photonic crystal fiber, and a 0.2 m tellurium-based chalcogenide photonic crystal fiber. Using a 2 µm pulse pumping this cascaded structure, the generated SC covering the wavelengths longer than 20 µm has been demonstrated theoretically. The 30 dB bandwidth reaches 20.87 µm from 1.44 to 22.31 µm. The effect of different pulse widths on SC generation is considered. With the increase of peak power and the decrease of pulse width, the energy of SC in the 15-20 µm waveband increases gradually. The mechanism of SC broadening process has also been analyzed. The SC generation of more than 20 µm in this cascade structure is caused by the self-phase modulation, soliton effects, four-wave mixing, and redshifted dispersive wave. This method demonstrates the possibility of generating ultrawide bandwidth SCs up to a 20 µm waveband by a commercial 2 µm pump source and all-fiber structure.

A Targeted Multi-Crystalline Manganese Oxide as a Tumor-Selective Nano-Sized MRI Contrast Agent for Early and Accurate Diagnosis of Tumors.

Introduction: Magnetic resonance imaging (MRI) is an important tool for the accurate diagnosis of malignant tumors in clinical settings. However, the lack of tumor-specific MRI contrast agents limits diagnostic accuracy. Methods: Herein, we developed αv integrin receptor-targeting multi-crystalline manganese oxide (MCMO) as a novel MRI contrast agent for accurate diagnosis of tumors by coupling iRGD cyclopeptide PEGylation polymer onto the surface of MCMO (iRGD-pMCMO). Results: The MCMO consisted of numerous small crystals and exhibited an oval structure of 200 nm in size. The iRGD-pMCMO actively recognizes tumor cells and effectively accumulates at the tumor site, consequently releasing abundant Mn2+ ions in a weakly acidic and high-GSH-expressing tumor microenvironment. Subsequently, Mn2+ ions interact with cellular GSH to form Mn-GSH chelates, enabling efficient T1-weighted MR contrast imaging. In vivo experiments indicated that iRGD-pMCMO significantly improved T1-weighted images, achieving an accurate diagnosis of subcutaneous and orthotopic tumors. The results verified that the T1 contrast effect of iRGD-pMCMO was closely associated with the expression of GSH in tumor cells. Conclusion: Altogether, the novel tumor-targeting, highly sensitive MRI contrast agent developed in this study can improve the accuracy of MRI for tumor diagnosis.

Pulse energy exchange of vector solitons in a fiber laser.

The energy exchange between orthogonal polarization components is crucial for the build-up of vector solitons (VSs). Unlike previous observations of energy exchange in the frequency domain, our experiments analyzed pulse energy flows in the time domain. We provide evidence to demonstrate the influence of the four-wave mixing (FWM) and cross-phase modulation (XPM) effect on VSs build-up in passive mode-locked fiber lasers through a perspective of pulse energy exchange. The results indicate that the energy exchange of PRVS caused by FWM and XPM is stronger than that of PLVS. The liner energy exchange caused by the birefringence of fiber and PC influences the period of energy exchange. After stabilization, the intra-cavity energy evolution period is one roundtrip for PLVS while serval roundtrips for PRVS. In the future, we can achieve PLVS by adjusting the linear energy exchange through cavity birefringence, thereby meeting the industrial demand for stable and uniform pulse trains.

Decaying dynamics of harmonic mode-locking in a SESAM-based mode-locked fiber laser.

The entire decaying dynamics of harmonic mode-locking (HML) are studied utilizing the dispersive Fourier transform (DFT) technique in a SESAM-based mode-locked fiber laser. It is unveiled that the harmonic solitons do not disappear directly, but undergo transitional processes from the higher-order HML to the lower-order HML and then to the fundamental mode-locking (FML), and finally vanish. The "big corner" can also exist in the decaying process rather than just in the buildup process of HML, and there is at least one "big corner" during the decaying process between the consecutive multi-pulsing states. The energy stabilization phase (ESP) cannot be observed during every transitional process. A breathing behavior and a vibrating soliton molecule are observed in the decaying process from the 2nd HML to the FML and in the decaying process of the FML, respectively. Our work would enrich the understanding of HML behaviors and may contribute to the laser designs.

Temporal coupled-mode theory for PT-symmetric chiral metasurfaces.

We have developed a temporal coupled-mode theory based on quasi-normal modes to investigate the chiroptical effects in parity-time (PT) symmetric metasurfaces. The PT symmetry enforces a different constraint for the direct scattering matrix and the coupling constants, which is verified by calculating the transmission spectra originating from the chiral quasi-bound states in the continuum. What's more, the scattering matrix can be analytically continued to the complex frequency plane. We find that the zero and pole singularities of the transmission coefficients and scattering matrix play an important role in the optical chirality. The pole singularities carry a quantized topological charge of -1. Our work paves the way for studying the enhanced optical chirality in non-Hermitian metasurfaces.

High-efficiency mode-locked erbium-doped ZBLAN fiber laser around 2.8 µm by directly depositing Bi2S3 particles onto a cavity mirror.

Mid-infrared (MIR) pulsed lasers near a 3 µm waveband show great potential for the high absorption of water molecules and many important gas molecules. A passively Q-switched mode-locked (QSML) E r 3+-doped fluoride fiber laser with a low laser threshold and high slope efficiency around a 2.8 µm waveband is reported. The improvement is achieved by depositing bismuth sulfide (B i 2 S 3) particles onto the cavity mirror directly as a saturable absorber and using the cleaved end of the fluoride fiber as output directly. -QSML pulses begin to appear with the pump power of 280 mW. The repetition rate of the QSML pulses reaches a maximum of 33.59 kHz with the pump power of 540 mW. When the pump power is further increased, the output of the fiber laser switches from the QSML to the continuous-wave mode-locked operation with the repetition rate of 28.64 MHz and the slope efficiency of 12.2%. The results indicate that B i 2 S 3 is a promising modulator for the pulsed lasers near a 3 µm waveband, which paves the way for further development of various applications in MIR wavebands, including material processing, MIR frequency combs, and modern healthcare.

Brillouin gain spectrum characterization in an acoustic anti-guided delivery fiber for high power narrow linewidth laser.

The Brillouin gain spectrum (BGS) provides key information for stimulated Brillouin scattering (SBS), such as the Brillouin frequency shift (BFS), Brillouin spontaneous linewidth, and Brillouin gain coefficient. In this study, we theoretically investigate the field distributions and BGS characterization of Ge-doped, Al-doped, and Al/Ge co-doped fibers. Additionally, we analyzed and compared the relationship between the BGS and acoustic refractive index. In particular, we demonstrate the crucial role played by acoustic modes in anti-waveguide structures. The simulation results show that the Brillouin gain coefficient decreases with a decreasing acoustic index in the fiber core region. Furthermore, we experimentally measure the SBS threshold and BGS of the Al/Ge co-doped fiber to examine the validity of the numerical model. The simulated and experimental results are consistent.

Transverse mode switchable fiber laser with a multimodal interference-based beam shaper.

We propose a Yb-doped fiber laser with an all-fiber beam shaper based on a single-mode-graded-index multimode-few-mode fiber (SMF-GIMF-FMF) structure. The excitation coefficients of the mode can be adjusted continuously by changing the GIMF length. Numerical simulations are performed to investigate the beam shaping dynamics in the fiber structure. Through adding the simple device geometry in the laser cavity, the switchable output between the fundamental transverse (LP01) mode and the second-order transverse (LP11) mode can be achieved. Cylindrical vector beams with high mode purity are also shown by removing the degeneracy of the LP11 mode.

Spatial mode and wavelength switchable erbium-doped fiber laser based on a fiber beam shaper.

A fiber-based beam shaper to adjust the distribution of spatial modes in a few-mode fiber (FMF) is theoretically and experimentally investigated in this work. A compact and robust device, composed with a single mode fiber-graded index multimode fiber-few mode fiber (SMF-GIMF-FMF), is fabricated by simply fusion splicing of the fibers. Switchable spatial modes and multi-wavelength comb are obtained by the combination of the beam shaper and the few-mode fiber Bragg grating (FM-FBG). This combination acts as a filter to select the wavelength and spatial mode in the laser. A spatial mode switchable fiber laser with high mode purity is extended among LP01, LP11 and cylindrical vector beam (CVB) by adjusting the pressure applied on the beam shaper. Five-discrete wavelengths and their free combination wavelength comb are emitted with a slope efficiency higher than 10%. The fiber laser can be used in the spatial- and wavelength-division multiplexing (SWDM) fiber communication networks requiring particular structure light field.

Simulation and analysis of supercontinuum generation in the waveband up to 25 µm.

The ultra-wideband supercontinuum generation (SCG) in a Te-based chalcogenide (ChG) photonic crystal fiber (PCF) is simulated in the mid-infrared (MIR) waveband. The PCF core and cladding materials are Ge20As20Se15Te45 and Ge20As20Se17Te43, respectively. The supercontinuum (SC) broadening affected by the core diameter and fiber absorption is considered. The selected PCFs at different pumping wavelengths can demonstrate the generation of ultra-wideband MIR supercontinuum according to the simulated results. We consider SC broadening with and without fiber absorption. A SC range from 3 to 25 µm is demonstrated by simulation in a PCF with a core diameter of 8 µm and a pump wavelength of 6 µm considering the fiber absorption. With the increase of the peak power and the pulse width and the decrease of the core diameter, the degree of coherence gradually degraded. To the best of our knowledge, this is the first demonstration of the possibility of SCG up to the waveband of 25 µm in fiber. Our results highlight the potential of a novel Te-based chalcogenide multi-material PCF for SCG. We also provide a way to generate the SCs to longer wavebands than 20 µm in fiber, especially up to the far-infrared waveband.

2†µm sub-GHz harmonic mode-locked soliton generation based on a Bi2S3 saturable absorber.

Saturable absorber (SA) based harmonic mode-locking (HML) techniques at 2 µm waveband are much less reported than those at 1.5 µm waveband, the maximum repetition rate of the harmonic pulse generated by such techniques at 2 µm waveband is also much lower than those generated at 1.5 µm waveband. In this paper, the 39th harmonic with the repetition rate of 908.6 MHz is realized in a Bi2S3-based thulium-doped fiber laser. The fundamental mode-locked pulse has a central wavelength of 1954.2 nm and a 3-dB bandwidth of 5.1 nm. The repetition rate is 23.27 MHz and the pulse width is 902 fs. The characteristics of the material and harmonic mode-locked pulse are investigated. To the best of our knowledge, this is the highest and the closest resonance frequency to GHz among the reported SA-based harmonic mode-locked fiber lasers operating at 2 µm waveband.

Efficient Magnetic Nanocatalyst-Induced Chemo- and Ferroptosis Synergistic Cancer Therapy in Combination with T1-T2 Dual-Mode Magnetic Resonance Imaging Through Doxorubicin Delivery.

Excessive iron ions in cancer cells can catalyze H2O2 into highly toxic •OH and then promote the generation of reactive oxygen species (ROS), inducing cancer ferroptosis. However, the efficacy of the ferroptosis catalyst is still insufficient because of low Fe(II) release, which severely limited its application in clinic. Herein, we developed a novel magnetic nanocatalyst for MRI-guided chemo- and ferroptosis synergistic cancer therapies through iRGD-PEG-ss-PEG-modified gadolinium engineering magnetic iron oxide-loaded Dox (ipGdIO-Dox). The introduction of the gadolinium compound disturbed the structure of ipGdIO-Dox, making the magnetic nanocatalyst be more sensitive to weak acid. When ipGdIO-Dox entered into cancer cells, abundant Fe(II) ions were released and then catalyzed H2O2 into highly toxic OH•, which would elevate cellular oxidative stress to damage mitochondria and cell membranes and induce cancer ferroptosis. In addition, the iRGD-PEG-ss-PEG chain coated onto the nanoplatform was also broken by high expression of GSH, and then, the Dox was released. This process not only effectively inhibited DNA replication but also further activated cellular ROS, making the nanoplatform achieve stronger anticancer ability. Besides, the systemic delivery of ipGdIO-Dox significantly enhanced the T1- and T2-weighted MRI signal of the tumor, endowing accurate diagnostic capability for tumor recognition. Therefore, ipGdIO-Dox might be a promising candidate for developing an MRI-guided chemo- and ferroptosis synergistic theranostic system.

Comparison of Different Linewidth Measuring Methods for Narrow Linewidth Laser.

We experimentally demonstrate a fiber laser with different linewidths based on self-injection locking (SIL) and the stimulated Brillouin scattering effect. Based on the homemade fiber laser, the error origin, resolution, and applicable range of delayed self-heterodyne interferometry (DSHI), self-correlation envelope linewidth detection (SCELD) and Voigt fitting are investigated numerically and experimentally. The selection of the linewidth measuring method should meet the following conclusions: an approximately Lorentzian self-heterodyne spectrum without the pedestal and high-intensity sinusoidal jitter is a prerequisite for DSHI; the SCELD needs a suitable length of delay fiber for eliminating flicker noise and dark noise of the electrical spectrum analyzer; a non-Lorentzian self-heterodyne spectrum without a pedestal is an indispensable element for Voigt fitting. According to the experimental results, the laser Lorentzian linewidth of SIL changes from 1.7 kHz to 587 Hz under different injection powers. When the Brillouin erbium fiber laser is utilized, the Lorentzian linewidth is measured to be 60 ± 5 Hz.

Polarization conversion in anisotropic dielectric metasurfaces originating from bound states in the continuum.

We use the semianalytical Cartesian multipole method to investigate the light transmission and reflection spectra of anisotropic dielectric metasurfaces, and extend the multipole decompositions method to account for cross-polarization conversion effects. We observe sharp high-Q resonances arising from a distortion of symmetry-protected bound states in the continuum in asymmetric dielectric metasurfaces, i.e., quasibound states in the continuum. In addition, by further introducing in-plane symmetric breaking perturbation, the polarization conversions of linearly polarized light can be achieved through quasibound states in the continuum. With the aid of temporal coupled-mode theory, we can obtain the limit of cross-conversion under single high-Q resonance, i.e., 0.25. Our work will help to design dielectric metasurfaces to control the polarization states of light.

Surgical reconstruction of primary genital lymphedema-long term therapeutic efficacy.

BACKGROUND: Primary genital lymphedema is caused by congenital lymphatic dysplasia, which is often accompanied by lymphedema of the lower extremities. A lack of effective diagnostics and treatments are available in clinical practice. The purpose of this study is to present the experience of surgical treatment of genital lymphedema and follow-up magnetic resonance lymphangiography (MRL) examinations. METHODS: The clinical records of 40 patients diagnosed with primary genital lymphedema between 2010 and 2019 were retrospectively reviewed. The surgical management of all patients consisted of complete excision of the edematous subcutaneous tissue and plastic reconstruction of the penis or scrotum. This involved excision of the affected tissue while retaining the scrotal septum, preserving the subcutaneous lymphatic tissue flap, turnover of the perididymis, and primary closure. All patients were examined by MRL to assess the extent of lymphedema pre- and postoperatively. The cosmetic results, recovery of sexual function, patient satisfaction, and complications are discussed. RESULTS: A total of 40 patients underwent surgical treatment. Scrotal hematoma (2.5%) and poor wound healing (5%) were encountered postoperatively. During follow-up period, no recurrence of edema occurred. The appearance of the scrotum and penis, as well as the sexual function was improved. MRL confirmed tissue edema and lymphatic malformation in the enlarged penis and scrotum preoperatively. In follow-up MRL, new formation or reopen of lymphatic drainage can be detect in 25 (62.5%) patients. All patients showed decreased area of dermal backflow. CONCLUSIONS: Surgical treatment is necessary for genital lymphedema when swelling develops. The use of a retained scrotal septum and subcutaneous lymphatic tissue flaps can achieve improved morphology and function. MRL is a safe and accurate diagnostic imaging method for pre- and postoperative evaluation of lymphedema in patients undergoing lymphatic surgery.

Micro-joule level visible supercontinuum generation in seven-core photonic crystal fibers pumped by a 515 nm laser.

A visible supercontinuum (SC) with high energy is of vital importance to applications in remote sensing and hyperspectral light detection and ranging. A fiber laser with a wavelength of 1030 nm is frequency doubled through a LBO (LiB3O5) crystal, and a high-energy 515 nm laser is obtained after wavelength conversion. Two kinds of seven-core photonic crystal fibers (PCFs) are used in this Letter. One is a uniform seven-core PCF (USC-PCF), and the other is a tapered seven-core PCF (TSC-PCF). Pumped by a 515 nm laser with a pulse width in nanosecond level, an SC covering 400 to 900 nm is efficiently generated in both PCFs. A maximum energy of 4.24 µJ is obtained in a USC-PCF. To prevent fiber damage of the coupling fiber end, the TSC-PCF which contains a transition fiber and a meters-long small core fiber is fabricated. One end of the transition fiber possesses a larger core diameter, and the pump laser can be coupled into the TSC-PCF without fiber damage. The meters-long small core fiber has the same core size with a USC-PCF and is utilized as the nonlinear medium to generate an SC. The dispersive wave in the short wavelength band is excited when more energy is shed into a fiber anomalous dispersion region. Up to 15th-order Raman peaks are observed during the SC evolution process.

Numerical study on supercontinuum generation by different optical modes in AsSe2-As2S5 chalcogenide microstructured fiber.

We investigate supercontinuum generation (SCG) in AsSe2-As2S5 chalcogenide microstructured optical fibers (MOFs) pumped by different optical modes. The influence on SCG by different optical modes including the fundamental and high-order modes is analyzed numerically. The evolution of the supercontinuum (SC) is investigated by changing the pump wavelength (2120, 2580, and 3280 nm) and peak power (from 200 to 1000 W) of each optical mode (LP01,LP11,LP31) in the MOFs with different fiber lengths. SCG in MOFs with different core diameters is also simulated. The different optical modes cause the variation of the chromatic dispersion profile and the effective nonlinearity, which induces different mechanisms of the SCG and changes the spectral range. The maximum SC spectral range covers 12.931 µm from 1.389 to 14.320 µm when pumped by the LP11 mode with the peak power of 1000 W at 3280 nm. The simulated results will be instructive for the experimental SCG up to the midinfrared waveband longer than 10 µm.

Asterisk-shaped microstructured fiber for an octave coherent supercontinuum in a sub-picosecond region.

We selected two thermally matched silicate glasses with fair refractive index contrast and developed an asterisk-shaped all-solid microstructured optical fiber. The fiber presents a low, ultra-flat, and all-normal dispersion in a wide wavelength range, allowing for the generation of an octave-spanning coherent supercontinuum (SC) in a 20 dB dynamic range with 0.5 ps pump pulses at 1.55 µm. This result improves pump pulse duration that is only ∼100 fs, related to the broadband and highly coherent SC generation in fibers with all-normal dispersion. This enables broadband SC sources with all-fiber, high-power, and highly coherent properties.

Far-Infrared Radiation Thermotherapy Improves Tissue Fibrosis in Chronic Extremity Lymphedema.

BACKGROUND: Fibrosis can enhance the exacerbation of lymphedema, which becomes obvious in late stage II-III lymphedema. However, whether far-infrared radiation thermotherapy (FIRT) can cure lymphedema fibrosis is still lack of research. This research was to investigate the therapeutic effect of FIRT on tissue fibrosis in the treatment of Late stage II-III lymphedema. METHODS: Patients accepted only FIRT for a total of 20 sessions. The treatment session duration was 2 hours, and a stable machine temperature of 42°C was maintained throughout treatments. Clinical evaluation and laboratory evaluation were conducted before and after FIRT. Clinical outcome measures included circumference of affected extremity, skin elasticity, ultrasound, patients' subjective assessment, and quality of life (QOL). Laboratory outcome measures included serum and local lymphedema tissue fluid concentrations of fibrosis associated cytokines, tissue growth factor beta-1 (TGF-ß1), interleukin (IL)-1ß, IL-4, IL-18, and caspase-1. RESULTS: Between 2015 and 2016, clinical evaluation of 64 patients with late stage II-III lymphedema was conducted. From this group, 12 cases (18.75%) underwent simultaneous laboratory evaluation. Circumferences of affected extremities improved significantly following treatment (p < 0.001). Skin elasticity of the affected extremity improved significantly (p < 0.05). Ultrasound investigation showed reduced fiber and dense material in the affected tissue (increased gray level 6.322% ± 7.624%, p < 0.001). Patients reported a subjective improvement of their symptoms such as decreased tightness, heaviness, solidity, pain, discomfort, and numbness (p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, and p = 0.032, respectively) and improved QOL (p < 0.001). Laboratory results revealed a significant decrease in local tissue fluid concentrations of TGF-ß1 (p = 0.041) and IL-18 (p = 0.049) after course completion. CONCLUSION: FIRT provides an effective treatment for lymphedema tissue fibrosis; it reduces the concentration of fibrosis cytokines in local lymphedema tissues. Consequently, this treatment can reduce the density of fibrosed tissue in the affected extremity, increase skin elasticity, significantly improve clinical symptoms, and improve QOL of patients.

Theoretical investigation on mid-infrared cascaded Raman fiber laser based on tellurite fiber.

A numerical simulation of third-order cascaded Raman fiber laser based on tellurite fiber at the 2-5 µm waveband is presented. The Raman fiber laser can be optimized with the most suitable tellurite fiber length of 0.5-1.0 m and the most reasonable reflectivity of the third-order Stokes output FBG32 of 10%-20%. We demonstrate numerically that the third-order Stokes wave can reach the maximum average power of 45.2 W and the maximum optical conversion efficiency of 45.2%, corresponding to the FBG32 reflectivity of 10% and the tellurite fiber length of 0.3 m with the attenuation of 0.85 dB/m, when pumped by 2 µm light with the average power of 100 W. Our simulated results provide valuable theoretical guidance for the design and experiment of tellurite Raman fiber laser at a mid-infrared waveband.