Search Results (134)

A promising approach to alleviate the emerging capacity limitations in backbone optical networks is to employ the Super C+L-band, which provides an available spectrum of roughly 12 THz. Network throughput is a key metric for analyzing the performance of such networks; however, evaluating this metric is a complex task due to the interplay between physical and network layer aspects. Physical modeling, which accounts for signal impairments, is particularly complex in these scenarios due to the presence of Stimulated Raman Scattering (SRS), which transfers energy from the C to the L band. On the other hand, network layer modeling is also challenging due to the influence of numerous factors, including physical topology, routing, and traffic characteristics. For the networks considered here, we propose a machine learning approach to predict both the network throughput and the average channel capacity for the Shannon and real cases, and to investigate how these metrics depend on various physical topology parameters. The approach relies on an Artificial Neural Network (ANN) model, whose predictions are interpreted using the SHapley Additive exPlanations (SHAP) method to identify the importance of various topological parameters. Furthermore, the ANN is trained using data obtained from a previously developed simulator that takes into account both physical and network aspects. The analysis provides valuable insights for designing future ultra-high-capacity optical backbone networks. Full article

Fiber lasers operating at 1.7 μm have significant application value in fields such as gas detection and material processing due to their characteristics, including compact structure and ease of thermal management. Based on the stimulated Raman scattering (SRS) of gas molecules in hollow-core fibers (HCFs), fiber gas Raman lasers (FGRLs) are a novel and effective method for generating 1.7 μm fiber lasers. We report here, to the best of our knowledge, the first FGRL based on the anti-resonant hollow-core fiber (AR-HCF) filled with sulfur hexafluoride (SF₆) molecules. A nanosecond pulsed fiber amplifier tunable from 1540 to 1560 nm was used to pump a 17.8-m-long AR-HCF filled with SF₆ molecules. By virtue of the vibrational SRS of SF₆ molecules, laser output in the range of 1748–1774 nm was achieved. At a gas pressure of 15 bar, a maximum average power output of ~3 W was obtained, corresponding to an optical-to-optical conversion efficiency of ~22%. The output linewidth of the Raman laser was measured to be approximately 2.1 GHz using a Fabry–Pérot (F-P) scanning interferometer. The research results enriched the methods for 1.7 μm fiber laser output. Full article

We demonstrate a 1.5 μm methane-filled hollow-core fiber (HCF) amplifier that delivers 7.1 W of narrow-linewidth (<0.1 nm), near-diffraction-limited (M² < 1.2) pulsed Raman output. The system is pumped by a 1064 nm pulsed fiber laser and amplifies a 1543 nm continuous-wave seed via stimulated Raman scattering in methane. Using a 45-m HCF, we systematically investigated the influence of seed injection on key laser characteristics, covering the spectral profile, power scaling, and beam properties. This work provides an effective strategy for realizing high-performance fiber lasers in the 1.5 μm band. Full article

Fiber lasers operating at 2.8 μm have important applications in fields such as polymer material processing and medical surgery. Fiber gas lasers (FGLs) based on stimulated Raman scattering (SRS) in hollow-core fibers (HCFs) provide a superior approach to generating tunable, high-power laser at 2.8 μm. Here, we demonstrated a watt-level mid-infrared FGL with a tuning range from 2812 nm to 2862 nm by the SRS of methane molecules in a 26.7 m long HCF. By pumping with a tunable pulsed fiber amplifier at 1.5 μm, an average output power of approximately 1 W was obtained, with a low Raman threshold peak power of 1.7 kW. Additionally, we observed transverse mode instability (TMI) in the HCFs, which has rarely been reported previously, and propose that the TMI was caused by the thermal effect generated when methane molecules absorbed the pump laser. This work achieved both the wavelength flexibility and watt-level power of FGLs based on methane-filled HCFs in the 2.8 μm waveband. It also found that the TMI was a key factor limiting further improvement in output power. This work provides important experimental basis and optimization directions for the future realization of higher-power tunable fiber lasers in the 2.8 μm waveband. Full article

Background: The use of optical microscopic techniques has gained increasing attention in recent years for studying the bioavailability (BA) and bioequivalence (BE) of topical drugs. Stimulated Raman scattering (SRS), one type of optical imaging technique, probes chemical-specific information and has excellent spatiotemporal resolution. It uses intrinsic molecular vibrational signatures, and therefore, labeling samples or other treatments is unnecessary to track a molecule. Because of its unique advantages, studies have used SRS for BA evaluations and, more recently, for BE evaluations. In BE evaluation, low data variance within a treatment group is important to ensure sensitivity and specificity in comparing treatment groups. Methods: When measuring forward-direction SRS signals transmitted through skin, the signal intensity is susceptible to variance due to several factors, such as the microscope system’s performance, the different optical features of topical drug products, and the heterogeneity of skin in transmitting light. This work closely investigated the effects of these factors on an SRS signal and developed solutions to reduce their effects on the data variance. Specifically, we constructed a method using a dual-modality detector built in-house, which simultaneously measured both the SRS signal and total light transmission synchronized in time and co-registered in space. Results: We developed equations to normalize SRS signals using the transmission intensity, and the results demonstrated a clear improvement in the SRS signal via a reduction in the signal variance (up to a 9.46% CV value decrease) that is otherwise caused by various factors associated with the use of topical drugs and the composition of the skin. We carried out an exploratory BE study using tretinoin-containing topical products and observed improvements in BE assessment with the developed method (could achieve a reduction of 0.11 in the CI value). Conclusions: This work has led to a better understanding of the factors that affect SRS imaging and has provided an effective method to compensate for these factors in BE assessments. This is a critical initial effort for better practical implementation of SRS in cutaneous pharmacokinetics (cPKs) studies of topical drugs. Full article

In inertial confinement fusion (ICF) laser drivers, large-aperture high-intensity third-harmonic (3ω, central wavelength 351 nm) laser pulses passing through KDP crystals (potassium dihydrogen phosphate) can produce strong transverse stimulated Raman scattering (TSRS). TSRS not only depletes the energy of the 3ω laser beam but also damages the KDP crystal, thus significantly limiting the enhancement of ICF laser driver capabilities. Therefore, effectively suppressing TSRS in KDP crystals is a critical issue in the design and construction of ICF laser driver systems. This paper first proposes that SSD has the ability to suppress TSRS through theoretical analysis of the characteristics of SSD beams. Secondly, through numerical simulations, it presents the influence of variations in three key parameters—modulation amplitude, modulation frequency, and grating dispersion coefficient—on the TSRS gain. The results show that the Stokes gain decreases with increasing modulation amplitude and modulation frequency; specifically, the suppression capability of SSD for TSRS gradually strengthens as modulation bandwidth increases. In addition, previous reports have demonstrated that SSD can significantly suppress stimulated rotational Raman scattering (SRRS) in air, which highlights the potential value of applying SSD in large laser facilities such as ICF driver systems. Full article

In this work, we propose and demonstrate a novel approach to suppressing stimulated Raman scattering in an oscillating–amplifying integrated fiber laser (OAIFL) by changing the spectral bandwidth of the output-coupler fiber Bragg gratings (OC-FBGs). The reflectance bandwidth of the fiber Bragg grating (FBG) in the oscillating section was systematically investigated as a critical parameter for SRS mitigation. Three types of long-period FBGs with distinct reflectance bandwidths (1.2 nm, 1.3 nm, and 2 nm) were comparatively studied as output couplers. The experimental results demonstrated a direct correlation between FBG bandwidth and SRS suppression efficiency, with the configuration of the OC-FBG with a 2 nm bandwidth achieving optimal suppression performance. Concurrently, the output power was enhanced to 5.02 kW with improved power scalability. And excellent beam quality was obtained with M² < 1.3. Remarkably, in the architecture of this laser, increasing the bandwidth of the output couplers in the oscillating section had a relatively minor effect on the optical-to-optical (O-O) efficiency, which reached up to 78%. Additionally, this modification also reduced the 3 dB bandwidth of the laser output, thereby achieving a beam output with enhanced monochromaticity. Full article

This study investigated the changes in protein composition and DNA content in damaged somatic nerves when exposed to insulin-like growth factor-1 (IGF-1). Using electrophoretic protein separation in polyacrylamide gel (PAG) and spectrophotometry, the transection was shown to be accompanied by a significant decrease in the quantitative content of total protein, certain protein fractions and DNA, both in the proximal and distal segments of the nerve conductor. Against the background of the intramuscular administration of IGF-1, intensive DNA synthesis and the protein composition stabilization of somatic nerves at the earlier post-traumatic stages were observed. By means of Raman scattering (RS-spectroscopy) and recording action potentials (APs), the enhanced recovery of the physicochemical condition of the nerve fiber membrane and its functional activity, indicating regeneration activation in the somatic nerves after damage, was revealed. IGF-1 was most likely to stimulate cytoskeleton protein synthesis through launching the mitogen-activated protein kinase signal pathway (MAPK/ERK), resulting in the increased expression of the genes related to the remyelination and functioning recovery of damaged nerve conductors. Full article

Optical networks today constitute the fundamental backbone infrastructure of telecom and cloud operators. A possible medium-term solution to address the enormous increase in traffic demands faced by these operators is to rely on Super C+ L transmission optical bands, which can offer a bandwidth of about 12 THz. In this paper, we propose a methodology to compute the throughput of an optical network based on this solution. The methodology involves detailed physical layer modeling, including the impact of stimulated Raman scattering, which is responsible for energy transfer between the two bands. Two approaches are implemented for throughput evaluation: one assuming idealized Gaussian-modulated signals and the other using real modulation formats. For designing such networks, it is crucial to choose the most appropriate technological solution for optical amplification. This could either be a band-dedicated scheme, which uses a separate amplifier for each of the two bands, or a single-wideband amplifier capable of amplifying both bands simultaneously. The simulation results show that the single-wideband scheme provides an average throughput improvement of about 18% compared to the dedicated scheme when using the Gaussian modulation approach. However, with the real modulation approach, the improvement increases significantly to about 32%, highlighting the benefit in developing single-wideband amplifiers for future applications in Super C+L-band networks. Full article

Photoacoustic imaging is an advanced biomedical imaging technique that has been widely developed and applied in diverse biomedical studies. By generating optical-absorption-based signals with ultrasound resolution, it enables in vivo visualization of molecular functional information in biological tissues. Extensive research has been conducted to develop the multispectral light sources required for functional photoacoustic imaging. Among the various approaches, multispectral light sources generated using stimulated Raman scattering have shown considerable promise, particularly in photoacoustic microscopy, where achieving multispectral illumination remains challenging. This review summarizes photoacoustic imaging systems that employ stimulated Raman scattering for multispectral light sources and delves into their configurations and applications in the functional analyses of biological tissues. In addition, the review discusses the future directions of multispectral light sources by comparing different technologies based on key factors such as wavelength tunability, repetition rate, and power, which critically affect the accuracy and quality of multispectral photoacoustic imaging. Full article

In future hybrid fiber and radio access networks, wavelength division multiplexing passive optical networks (WDM-PON) based fifth-generation (5G) fronthaul systems are anticipated to coexist with current protocols, potentially leading to non-linearity impairment due to stimulated Raman scattering (SRS). To meet the loss budget requirements of 5G fronthaul networks, this paper investigates the power changes induced by SRS in WDM-PON based 5G fronthaul systems. The study examines wavelength allocation schemes utilizing both the C-band and O-band, with modulation formats including non-return-to-zero (NRZ), optical double-binary (ODB), and four-level pulse amplitude modulation (PAM4). Simulation results indicate that SRS non-linearity impairment causes a power depletion of 1.3 dB in the 20 km C-band link scenario, regardless of whether the modulation formats are 25 Gb/s or 50 Gb/s NRZ, ODB, and PAM4, indicating that the SRS-induced power changes are largely independent of both modulation formats and modulation rates. This effect occurs when only the upstream and downstream wavelengths of the 5G fronthaul are broadcast. However, when the 5G fronthaul wavelengths coexist with previous protocols, the maximum power depletion increases significantly to 10.1 dB. In the O-band scenario, the SRS-induced maximum power depletion reaches 1.5 dB with NRZ, ODB, and PAM4 modulation formats at both 25 Gb/s and 50 Gb/s. Based on these analyses, the SRS non-linearity impairment shall be fully considered when planning the wavelengths for 5G fronthaul transmission. Full article

Stimulated Raman Scattering (SRS) nanoscopy imaging offers unprecedented insights into tissue molecular architecture but often requires stitching multiple high-resolution tiles to capture large fields of view. This process is time-consuming and frequently introduces vignetting artifacts—grid-like intensity fluctuations that degrade image quality and hinder downstream quantitative analyses and processing such as super-resolution deconvolution. We present VIgnetted Stitched-Tile Adjustment using Morphological Adaptive Processing (VISTAmap), a simple tool that corrects these shading artifacts directly on the final stitched image. VISTAmap automatically detects the tile grid configuration by analyzing intensity frequency variations and then applies sequential morphological operations to homogenize the image. In contrast to conventional approaches that require increased tile overlap or pre-acquisition background sampling, VISTAmap offers a pragmatic, post-processing solution without the need for separate individual tile images. This work addresses pressing concerns by delivering a robust, efficient strategy for enhancing mosaic image uniformity in modern nanoscopy, where the smallest details make tremendous impacts. Full article

C+L+S multiband (MB) optical transmission has the potential to increase the capacity of optical transport networks, and thus, it is a possible solution to cope with the traffic increase expected in the years to come. However, the introduction of MB optical technology needs to come together with the needed tools that support network planning and operation. In particular, quality of transmission (QoT) estimation is needed for provisioning optical MB connections. In this paper, we concentrate on modelling MB optical transmission for provide fast and accurate QoT estimation and propose machine learning (ML) approaches based on neural networks, which can be easily integrated into an optical layer digital twin (DT) solution. We start by considering approaches that can be used for accurate signal propagation modelling. Even though solutions such as the split-step Fourier method (SSFM) for solving the nonlinear Schrödinger equation (NLSE) have limited application for QoT estimation during provisioning because of their very high complexity and time consumption, they could be used to generate datasets for ML model creation. However, even that can be hard to carry out on a fully loaded MB system with hundreds of channels. In addition, in MB optical transmission, interchannel stimulated Raman scattering (ISRS) becomes a major effect, which adds more complexity. In view of that, the fourth-order Runge–Kutta in the interaction picture (RK4IP) method, complemented with an adaptive step size algorithm to further reduce the computation time, is evaluated as an alternative to reduce time complexity. We show that RK4IP provided an accuracy comparable to that of the SSFM with reduced computation time, which enables its application for MB optical transmission simulation. Once datasets were generated using the adaptive step size RK4IP method, two ML modelling approaches were considered to be integrated in the OCATA DT, where models predict optical signal propagation in the time domain. Being able to predict the optical signal in the time domain, as it will be received after propagation, opens opportunities for automating network operation, including connection provisioning and failure management. In this paper, we focus on comparing the proposed ML modelling approaches in terms of the models’ general and QoT estimation accuracy. Full article

The core-division-multiplexed (CDM) transmission technique utilizing uncoupled multi-core fiber (MCF) is considered a promising candidate for next-generation long-haul optical transport networks (OTNs) due to its high-capacity potential. For the field implementation of MCF, it is of great significance to explore its long-haul transmission capability using high-speed OTN transceivers over deployed MCF cable. In this paper, we investigate the real-time long-haul transmission capability of a deployed seven-core MCF cable using commercial 138-Gbaud 400 Gb/s backbone OTN transceivers with a dual-polarization quadrature phase shift keying (DP-QPSK) modulation format. Thanks to the highly noise-tolerant DP-QPSK modulation format enabled by the high baud rate, a real-time 256 Tb/s transmission over a 990.64 km (14 × 70.76 km) deployed seven-core fiber cable with more than 600 fusion splices is field demonstrated for the first time, which achieves a real-time capacity–distance product of 221.9 Pb/s∙km. Specifically, the long-haul CDM transmission is simulated by cascading the fiber cores of two segments of 70.76 km seven-core fibers. And dynamic gain equalizers (DGEs) are utilized to mitigate the impacts of stimulated Raman scattering (SRS) and the uneven gain spectra of amplifiers in broadband transmissions by equalizing the power of signals with different wavelengths. This field trial demonstrates the feasibility of applying uncoupled MCF in long-haul OTN transmission systems and will contribute to its field implementation in terrestrial fiber cable systems. Full article

This paper presents an overview of the application of Raman spectroscopy (RS) in characterizing carotenoids, which have recently gained attention due to new findings on their health-promoting effects and rising demand in the food, pharmaceutical, and cosmetic industries. The backbone structure in the form of a polyene chain makes carotenoids sensitive to Raman spectroscopy, mainly due to the stretching vibrations of their conjugated double bonds. Raman spectroscopy is increasingly used in agricultural and food sciences and technologies as it is a non-preparative, environmentally friendly, fast and efficient method for characterizing target analytes. The application of RS in the qualitative and quantitative analysis of carotenoids requires the careful selection and adjustment of various instrument parameters (e.g., laser wavelength, laser power, spectral resolution, detector type, etc.) as well as performing complex chemometric modeling to interpret the Raman spectra. Most of the studies covered in this review focus more on qualitative than quantitative analysis. The most frequently used laser wavelengths are 1064, 785, and 532 nm, while 633 nm is the least used. Considering the sensitivity and complexity of RS, the present study focuses on the specific and critical points in the analysis of carotenoids by RS. The main methodological and experimental principles in the study of food carotenoids by RS are discussed and best practices recommended, while the future prospects and expectations for a wider application of RS, especially in food quality assessment, are emphasized. New Raman techniques such as Spatially Offset Raman Spectroscopy (SORS), Coherent Anti-Stokes Raman Spectroscopy (CARS) and Stimulated Raman Scattering Spectroscopy (SRS), as well as the application of artificial intelligence, are also described in the context of carotenoids analysis. Full article