- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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On the Characterization of Novel Step-Index Biocompatible and Biodegradable poly(D,L- lactic acid) Based Optical Fiber
摘要： We report on the first step-index biodegradable polymer optical fiber (bioPOF) fabricated using commercially available polyesters, with a core made from poly(D,L-lactic-co-glycolic acid) and a cladding made from poly(D,L-lactic acid). We prepared the preforms with a rod-in-tube technique and the fibers with a standard heat drawing process. We discuss the chemical and optical properties of the polyesters along the fabrication process from polymer granulates to optical fiber. More specifically, we address the influence of the processing steps on the molecular weight and thermal properties of the polymers. Cutback measurements return an attenuation of 0.26 dB∕cm at 950 nm for fibers with an outer diameter of 1000 ± 50 μm, a core of 570 ±30 μm and a numerical aperture of 0.163. When immersed in phosphate-buffered saline (PBS), bioPOFs degrade over a period of 3 months, concurrent with a 91% molecular weight loss. The core decomposes already after 3 weeks and features a 85% molecular weight loss. There is no any additional optical loss caused by immersion in PBS during the first 30-40 min for a bioPOFs with a diameter of about 500 μm. Our result demonstrates that bioPOF can be suitable for applications requiring light delivery deep into living tissue, such as photodynamic therapy.
关键词： optical polymers,biodegradable materials,optical fibers,optical fiber materials,plastic optical fiber
更新于2025-09-12 10:27:22
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Fourier transform infrared imaging and quantitative analysis of pre-treated wood fibers: A comparison between partial least squares and multivariate curve resolution with alternating least squares methods in a case study
摘要： Pretreated lignocellulosic fibers were used as a case study to compare two chemometric methods for the quantification of chemical components in Fourier transformed infrared (FT-IR) images. Partial least squares (PLS) and multivariate curve resolution with alternating least squares (MCR-ALS) methods were applied to the images to quantify glucans, lignin and hemicellulose content. The main problem for calibration in samples from natural origin is to obtain proper reference material for pixel to pixel quantification. Furthermore, chemical components in wood experience changes after different pretreatment conditions; therefore commercially available reference material may not have the same identity of the components present in the sample. Concentration information of bulk samples obtained by wet chemistry methods, along with the median spectrum of whole images, was used as an alternative for PLS calibration in this scenario. Results show that both methods provided similar spatial distribution for lignin and hemicellulose in the concentration maps, but image reconstruction of glucans shows differences in distribution between the two methods. PLS models used to quantify pixels in an image were previously validated through the prediction of global concentration of samples, using the median spectrum of different images (RMSEP ? 1.3% for glucans, 1.0% for lignin and 0.9% for hemicelluloses); The range of pixel concentration predicted in a single image was too narrow possibly due to the lack of a calibration set with a wider dynamic range. Concentration maps obtained with MCR-ALS were satisfactory and the range of concentration for pixels was more consistent with what would be expected. A quantification approach that does not need a calibration set was used to transform concentration profiles into real concentration units for pixels. Therefore MCR-ALS was a more suitable method for quantification in this specific case study.
关键词： PLS,Lignocellulosic fibers,Hyperspectral imaging,Quantitative analysis,MCR-ALS
更新于2025-09-12 10:27:22
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Laser refrigeration of gas filled hollow-core fibres
摘要： We evaluate prospects, performance and temperature limits of a new approach to macroscopic scale laser refrigeration. The considered refrigeration device is based on exciplex-mediated frequency up-conversion inside hollow-core fibers pressurized with a dopant - buffer gas mixture. Exciplexes are excited molecular states formed by two atoms (dopant and buffer) which do not form a molecule in the ground state but exhibit bound states for electronically excited states. The cooling cycle consists of absorption of laser photons during atomic collisions inducing light assisted exciplex formation followed by blue-shifted spontaneous emission on the atomic line of the bare dopant atoms after molecular separation. This process, closely related to reversing the gain mechanism in excimer lasers, allows for a large fraction of collision energy to be extracted in each cycle. The hollow-core fiber plays a crucial role as it allows for strong light-matter interactions over a long distance, which maximizes the cooling rate per unit volume and the cooling efficiency per injected photon while limiting re-absorption of spontaneously emitted photons channeled into unguided radiation modes. Using quantum optical rate equations and refined dynamical simulations we derive general conditions for efficient cooling of both the gas and subsequently of the surrounding solid state environment. Our analytical approach is applicable to any specific exciplex system considered and reveals the shape of the exciplex potential landscapes as well as the density of the dopant as crucial tuning knobs. The derived scaling laws allow for the identification of optimal exciplex characteristics that help to choose suitable gas mixtures that maximize the refrigeration efficiency for specific applications.
关键词： quantum optical rate equations,exciplex-mediated frequency up-conversion,laser refrigeration,hollow-core fibers,cooling efficiency
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Polarization effects
摘要： A major simplification was made in Section 2.3 while deriving the nonlinear Schr?dinger (NLS) equation. It consisted of assuming that the polarization state of the incident light is preserved during its propagating inside an optical fiber. This is not really the case in practice. In this chapter we focus on the polarization effects and consider the coupling between the two orthogonally polarized components of an optical field induced by the nonlinear phenomenon known as cross-phase modulation (XPM). The XPM is always accompanied with self-phase modulation (SPM) and can also occur between two optical fields of different wavelengths, a situation covered in Chapter 7.
关键词： optical fibers,nonlinear Schr?dinger equation,polarization effects,self-phase modulation,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Cross-phase modulation
摘要： So far we have focused on optical pulses whose spectrum is centered at a single wavelength. When two or more pulses, launched at different wavelengths, propagate simultaneously inside a fiber, they interact with each other through the fiber’s nonlinearity. In general, such an interaction can generate new waves under appropriate conditions through a variety of nonlinear phenomena such as stimulated Raman or Brillouin scattering and four-wave mixing; these are discussed in Chapters 8 to 10. The nonlinearity can also couple two optical fields through cross-phase modulation (XPM), without inducing any energy transfer between them [1]. The XPM phenomenon is discussed in this chapter. A set of two coupled nonlinear Schr?dinger (NLS) equations is derived in Section 7.1, assuming that each wave maintains its state of polarization. These equations are used in Section 7.2 to discuss how the XPM affects the phenomenon of modulation instability. Section 7.3 focuses on the soliton pairs whose members support each other through their XPM-mediated nonlinear interaction. The effects of XPM on the shape and the spectrum of ultrashort pulses are described in Section 7.4 by solving the coupled NLS equations. Several applications of XPM are discussed in Section 7.5. A vector theory of XPM is developed in Section 7.6 to account for the polarization effects. In Section 7.7 we extend this theory to the case of birefringent fibers. The case of two counterpropagating waves is discussed in Section 7.8.
关键词： modulation instability,soliton pairs,counterpropagating waves,birefringent fibers,polarization effects,ultrashort pulses,nonlinear Schr?dinger equations,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Stimulated Raman scattering
摘要： Stimulated Raman scattering (SRS) is an important nonlinear process that can turn optical fibers into broadband Raman amplifiers and tunable Raman lasers. It can also severely limit the performance of multichannel lightwave systems by transferring energy from one channel to the neighboring channels. This chapter is devoted to a thorough study of SRS phenomenon in optical fibers. Section 8.1 presents the basic theory behind SRS with emphasis on the pump power required to reach the Raman threshold. SRS under continuous-wave (CW) and quasi-CW conditions is considered in Section 8.2, where we also discuss the performance of fiber-based Raman lasers and amplifiers. Ultrafast SRS occurring for pulses of 100-ps width or less is considered in Sections 8.3 and 8.4 for normal and anomalous group-velocity dispersion (GVD), respectively. In both cases, attention is paid to the walk-off effects together with those resulting from self-phase modulation (SPM) and cross-phase modulation (XPM). Section 8.5 focuses on the polarization effects.
关键词： Raman amplifiers,optical fibers,Stimulated Raman scattering,nonlinear processes,group-velocity dispersion,Raman lasers,polarization effects,self-phase modulation,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Stimulated Brillouin scattering
摘要： Stimulated Brillouin scattering (SBS) is a nonlinear process that can occur in optical fibers at input power levels much lower than those needed for stimulated Raman scattering (SRS). It manifests through the generation of a backward-propagating Stokes wave that carries most of the input power, once the Brillouin threshold is reached. For this reason, SBS limits the channel power in optical communication systems. At the same time, it can be useful for making fiber-based Brillouin lasers and amplifiers. This chapter is devoted to the SBS phenomenon in optical fibers. Section 9.1 presents the basic concepts behind SBS with emphasis on the spectrum of Brillouin gain. Section 9.2 focuses on the Brillouin threshold in the case of a continuous-wave (CW) pump and the techniques used to control it. Fiber-Brillouin amplifiers and their properties are discussed in Section 9.3. The dynamic aspects of SBS are the focus of Section 9.4, where we discuss SBS for a pulsed pump together with phenomena such as SBS-induced modulation instability and optical chaos. Section 9.5 is devoted to Brillouin lasers operating continuously or pulsed.
关键词： Brillouin amplifiers,Brillouin threshold,Brillouin lasers,optical fibers,nonlinear process,Stimulated Brillouin scattering
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - UV-Grade Silica-Based Photonic Crystal Fibers for Broadband UV Generation over 350–395 nm
摘要： A major challenge in supercontinuum (SC) generation is to overcome the shortcomings of existing fibre-based SC sources in the ultraviolet (UV) wavelength range below 400 nm. There is particular need for broadband sources of UV light in applications such as multi-photon fluorescence microscopy for simultaneous coherent excitation of multiple fluorophores. However, UV generation in conventional silica-core fibres is extremely difficult because of factors such as material absorption, large normal dispersion, glass stability, power handling, and aging, and this has motivated much recent interest in the use of alternative approaches. Although these results show great promise, compatibility with the ubiquitous silica platform remains a problem, and there is thus intense current interest in generating UV-light using modified UV-resistant silica glasses. In this paper, we report the design and fabrication of small-core highly nonlinear UV-grade photonic crystal fiber (PCF) drawn from Heraeus F110 UV-resistant silica glass, and its application to broadband UV generation over 260-400 nm. The few mode PCF is shown in Fig. 1(a) and was designed with: core diameter ~4.24 μm, hole diameter d = 3.5 μm, pitch Λ =3.88 μm, and was designed to support five LP modes in a scalar approximation. The calculated dispersion coefficients and mode profiles are shown in Figs 1(b) and (c). Figure 1(d) and (e) show experimental results pumping with picosecond laser pulses at 355 nm. For a 1m length of the PCF, we observe intermodal four-wave mixing (FWM) peaks with Fig. 1(d) showing a series of spectra as the output power varies from 0.1 – 0.2 mW. The FWM peaks are generated over the range 350-370 nm and the peak positions are in good agreement with calculations based on the fibre modal characteristics. For a longer 3 m fibre length, intermodal FWM is not observed, but rather we see cascaded Raman scattering out to 6th-order over the range 355-395 nm. The UV-emission was observed to have stable 0.3 mW output power without any detrimental photo-darkening. In this paper, we have reported the fabrication of highly nonlinear photonic crystal fiber from UV-grade glass and experimentally demonstrate nonlinear frequency conversion over 350-395 nm by pumping at 355 nm with picosecond laser pulses. These results represent an important step towards efficient UV supercontinuum generation in an all-silica fiber platform.
关键词： nonlinear frequency conversion,broadband UV generation,supercontinuum generation,UV-grade silica-based photonic crystal fibers,UV-resistant silica glass
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - All — Fiber Evanescent Wave Sensors for the Mid-Infrared Spectroscopy of Liquids
摘要： Methods of the mid-IR spectroscopy provide reliable tools for detecting chemical composition of gases and liquids. In the mid-IR spectral range (wavelengths of 3-25 μm), various molecules and functional groups have fundamental absorption bands with large absorption coefficients. Creation of materials and technologies for the remote sensors consisting of fiber-optic broadband sources of coherent mid-IR radiation, chalcogenide fibers for transmitting light to the sensing elements and spectrally-selective photodetectors is a problem of a high scientific priority. In this work, we develop the fiber-optic analytical spectroscopy for chemical analysis of aqueous solutions of acetone, ethanol, for determination of the fractional chemical composition of hydrocarbons. As a material base for the fiber-optic sensors, chalcogenide fibers with an extremely low content of impurities have been designed and fabricated by single- and double-crucible methods (including the REE-doped glass fibers). By using these fibers, technologies of fabrication of permanent fiber bends, tapers, microstructured fibers have been developed for using these structures in fiber lasers, supercontinuum generators, sensing elements. A theoretical approach based on electromagnetic theory of optical fibers has been applied for computer-aided design of the evanescent-wave sensors. A sensing element shaped as the U-bent fiber that was applied for chemical analysis of liquid consisting of a diesel oil and a fuel additive is shown. For chemical analysis, the absorption band at the wavelength of 7.83 μm, corresponding to esters, has been chosen. Output characteristics of the sensor were studied in experiment by variation of the fiber core diameter and the bend radius. In a computer model, it was shown that attenuation coefficients of evanescent modes propagating in the fiber bend grow with increase of the bend radius and with decrease of the fiber core diameter. This allows for enhancing sensitivity and decreasing the minimum detectable amount of an analyte. In fact, with an optimised sensing element, the minimum detected amount of the fuel additive was less than 0.1 vol.%.
关键词： evanescent-wave sensors,chalcogenide fibers,chemical analysis,fiber-optic sensors,mid-IR spectroscopy
更新于2025-09-12 10:27:22
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Multiple Scattering from Electrospun Nanofibers with Embedded Silver Nanoparticles of Tunable Shape for Random Lasers and White-Light-Emitting Diodes
摘要： Random lasers (RLs) are convenient, tunable, and widely applicable. However, the influence of fluorescence lifetime on the scattering and nanofiber distribution of nanofibers with various shapes of silver nanoparticles (Ag NPs) embedded within is unclear. We prepared polyvinyl alcohol (PVA) nanofibers with Ag NPs through electrospinning (ES) and pyrromethene 597 dye doping. We determined the influences of the particles on scattering enhancement and localized surface plasmon resonance (LSPR) in RLs. The distinct scattering rates and LSPR can be used to control optical properties for sensing devices and other applications. Compared with traditional films, the threshold of the nanofibers with Ag NPs is 35% lower. In addition to improved matching between the LSPR and emission spectra, enhanced coupling of the electric field with nonradiative energy amplifies the radiative emission. Furthermore, the luminescence lifetime shortened by increasing the scattering rate. An excessive scattering rate may accelerate radiative recombination and convert some recombination into nonradiative recombination to produce a more sensitive device. Finally, we applied the prepared nanofibers to a backlight display and fabricated a white-light-emitting diode (LED) with a distinct thickness of nanofibers. The fabricated device is suitable for application in other LEDs and RL devices.
关键词： light scattering,silver nanoparticles,plasmonic,electrospun fibers,random lasers
更新于2025-09-12 10:27:22