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Nonlinear Fiber Optics || Highly nonlinear fibers
摘要： As seen in the preceding chapters of this book, three major nonlinear effects occurring inside optical fibers—self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)—are governed by a single nonlinear parameter γ, defined in Eq. (2.3.30). For conventional optical fibers γ has values of ～1 W?1/km. It was realized during the 1990s that this value is too small for optical fibers to be useful as a nonlinear medium for applications requiring short lengths. To solve this problem, several new kinds of fibers with γ > 10 W?1/km were developed; they are collectively referred to as highly nonlinear fibers (HNLFs). This chapter deals with the properties of such fibers. The techniques used to measure the nonlinear parameter are described first in Section 11.1. The following four sections then focus on the four kinds of HNLFs that have been developed to enhance the nonlinear effects. In each case, dispersive properties of the fibers are also described because they play an important role whenever HNLFs are used for practical applications. It will be seen in Chapters 12 and 13 that the combination of unusual dispersive properties and a high value of γ makes HNLFs useful for a variety of novel nonlinear effects. Section 11.6 shows how the design of some HNLFs modifies the effective value of the nonlinear parameter in the case of narrow-core fibers.
关键词： four-wave mixing,highly nonlinear fibers,optical fibers,nonlinear parameter,self-phase modulation,dispersion,cross-phase modulation
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 Single-Mode PM Yb-Doped Pre-Amplifier at 0.976 μm
摘要： Yb-doped fiber lasers operating near 0.98 μm attract considerable interest in recent years. In particular, the pulsed lasers at 0.98 μm are promising for frequency doubling and quadrupling. At the same time, the Yb-doped fibers optimized for 0.98 μm generation have been designed to achieve high laser efficiency at a high average output power and hardly can be used in preamplifier stages or in scheme of master oscillator lasers. Such fibers have a large core diameter (in excess of 25 μm) and high splicing losses with standard single-mode step-index fibers (maximum diameter of those does not exceed 10 μm). The pulsed lasers based on such fibers require utilization of bulk elements [1, 2] that eliminate advantageous of all-fibers schemes (compactness, reliability, low-cost). Moreover, due to a very high lasing threshold (tens of Watts) such fibers are unsuitable for signal amplification to a middle-level output power (0.1-1 W), required for pre-amplifiers and for many of master-oscillator schemes. In opposite, core-pumped schemes are power-limited by available single-mode pump diodes at 915 nm and typically do not allow output power higher than ~100 mW. In the present work, to create efficient pre-amplifier for 0.98 μm spectral range we designed and fabricated a special polarization-maintaining (PM) Yb-doped fiber with reduced mode field diameter (MFD) to make it compatible with standard single-mode fibers. The developed fiber was based on a ring-doping design (cladding was partially doped with Yb-ions), which allowed us to fabricate a relatively small core and, simultaneously, keep a reasonably high lasing efficiency. The lasing threshold was reduced by choosing of the silica cladding size as small as 80 μm. The fiber core was fabricated based on a photodarkening free P2O5-Al2O3-SiO2 glass matrix. The fiber end image is shown in Fig.1a. The MFD of the fundamental mode along the x and y axes were 12 μm and 15 μm, respectively, which ensured reasonably low splicing losses of the fabricated fiber and standard single-mode optical fibers. The cladding absorption near 915 nm was 3.4 dB/m, optimal fiber length was about 45 cm. To create an all-fiber amplifier scheme, we developed a special pump and signal combiner (2+1-to-1 configuration) based on a PM step-index fiber with core and cladding diameters of 10 μm and 80 μm, respectively. The slope pump to signal conversion efficiency was 11.5% in the scheme with co-propagated signal (100 mW) and pump (Fig. 1b). A low lasing threshold (about 4 W) allowed us to achieve output power of few hundred mW using pump power of less than 10 W, which outperforms more “efficient” amplifier designs where to achieve positive gain the pump power as high as 10-20 W is required [3, 4]. Furthermore, the fiber was found to be promising for a small signal amplification (Fig. 1c). Ratio of amplified signal power to power of amplified spontaneous emission (ASE) near 0.98 μm was about 20 dB even for input signal as small as 1 mW.
关键词： polarization-maintaining,Yb-doped fiber lasers,pre-amplifier,single-mode fibers,ring-doping design
更新于2025-09-12 10:27:22
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Continuous and Controllable Liquid Transfer Guided by a Fibrous Liquid Bridge: Toward High‐Performance QLEDs
摘要： Solution processing is widely used for preparing quantum dot (QD) films for fabricating QD light-emitting diode display (QLED) devices. However, current approaches suffer from either the coffee-ring effect or a large amount of wasted solution, leading to low performance and high cost. Here, a facile approach guided by a fibrous liquid bridge is developed for the continuous and controllable transfer of QD solution into ultrasmooth films by using a taut fiber with its two ends placed into capillary tubes. Guided along the fiber, a liquid bridge is formed between the horizontal fiber and the substrate, with a large mass of liquid steadily being held within the vertically placed tubes. Directionally moving the liquid bridge generates a high-quality QD film on the substrate. Particularly, the liquid consumption is quantitative, namely, in proportion to the area of the as-prepared film. Moreover, multilayered ultra-smooth red/green/blue QD films are prepared by multiple transfers of liquid onto the same targeted area in sequence. The as-prepared white QLEDs show a rather high performance with a maximum luminance of 57 190 cd m?2 and a maximum current efficiency of 15.868 cd A?1. It is envisioned that this strategy offers new perspectives for the low-cost fabrication of high-performance QLED devices.
关键词： liquid transfer,quantum-dot light-emitting diodes,liquid bridges,fibers,quantum-dot films
更新于2025-09-12 10:27:22
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An optical fiber daylighting system with large Fresnel lens
摘要： Because of flexible installation and natural spectrum, the concentrated sunlight transmission systems via PMMA (Polymethyl methacrylate) fibers for indoor illumination are concerned widely in areas of building energy saving. Due to the long-term indoor work, the daily working population in cities lacks of natural light and is susceptible to various diseases. Therefore, from the health point of view, it is necessary to develop deep indoor daylighting. In this work, a sunlight concentration and transmission system was developed and tested, which uses a Fresnel lens with a diameter of 1m to achieve large flux collection. A reflection design of light path was adopted to resolve the problem of long focal length of the Fresnel lens. A hot mirror and a homogenizer were used to protect the optic fiber bundle from burned by high temperature. The results showed that the daylighting efficiency is about 11%-13%. The operability of the equipment was verified through experiments, proving that the equipment can be combined with buildings for daylighting. It is hoped that this research will be of some reference value to the design of optical fiber daylighting systems in buildings.
关键词： optic fibers,transmission,daylighting
更新于2025-09-12 10:27:22
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Efficient Mode Multiplexer for Few-Mode Fibers Using Integrated Silicon-on-Insulator Waveguide Grating Coupler
摘要： We propose a novel and highly efficient multimode waveguide grating coupler which can simultaneously launch four channels including two polarizations of the linear polarized (LP) modes, LP01 and LP11 of a step-index few-mode fiber (FMF). The waveguide grating coupler on the silicon-on-insulator (SOI) platform is based on a subwavelength structure which was optimized using the genetic optimization approach with 2-dimensional finite-difference time-domain (2-D FDTD) simulations combined with the second?order effective medium theory (EMT). Simulations predicted the coupling efficiencies to be ?4.3 dB for LP01 mode and ?5.0 dB for the LP11 mode. The design was fabricated in a multi-project wafer (MPW) run for silicon photonics. Coupling efficiency of ?4.9 dB and ?6.1 dB was experimentally demonstrated for LP01 mode and LP11 mode, respectively. The proposed mode multiplexer is entirely passive and suitable for future applications with FMFs in space-division-multiplexing (SDM) networks.
关键词： few-mode fibers,space-division multiplexing,diffraction gratings,Integrated optics
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) - Spatial Kerr Beam Self-Cleaning in Yb-Doped Multimode Fiber Taper
摘要： Spatial Kerr beam self-cleaning (KBSC), which transforms an output speckled beam in a quasi-single mode beam in graded index (GRIN) multimode optical fibers (MMFs), has been reported recently [1,2]. GRIN MMFs are also interesting waveguides for supercontinuum (SC) generation in the visible and near infrared regions, as successfully demonstrated by launching femtosecond or subnanosecond pulses in the anomalous (1550 nm) or normal (1064 nm) dispersion regime, respectively [1,3]. The spectral broadening features were explained through the interplay between spatiotemporal multimode soliton oscillations and dispersive wave generation in fibers with parabolic index profile. On the other hand, tapered optical fibers are well known to provide a number of useful features, including strong mode confinement capability, small scale diameter and broad SC generation [4,5]. Herein, we report visible-short infrared SC generation in combination with KBSC in long (~10 m) tapered Yb-doped MMFs, with parabolic index profile and parabolic doping concentration.
关键词： supercontinuum generation,Spatial Kerr beam self-cleaning,graded index multimode optical fibers,Yb-doped multimode fiber taper
更新于2025-09-12 10:27:22
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[IEEE 2019 41st Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) - Berlin, Germany (2019.7.23-2019.7.27)] 2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) - Ultrasonically Steerable Graded-Index Optical Waveguides for Deep Tissue Light Delivery: Theory and Applications
摘要： Graded-index (GRIN) fibers have been used as implantable optical waveguides to guide light and relay images through the depth of the tissue. We have recently shown that non-invasive ultrasound can generate refractive index gradients within the tissue that form virtual GRIN lenses for imaging and photostimulation deep into the tissue. Here we present the theory behind this idea by analyzing the coupled acoustic-photonic system that models the interaction of light with the ultrasonically modulated medium. We will discuss how changing the parameters of ultrasound will change the confinement and guiding of light within the modulated medium. We will also demonstrate that using a custom-designed cylindrical ultrasonic array, the pressure interference can be controlled to sculpt complex patterns of light in the medium, such as dipole and quadrupole shapes, suitable for multisite imaging. Finally, we will discuss experimental results corroborating the theoretical predictions to generate single and multisite in situ virtual lenses that can be used for fluorescent imaging of mouse brain tissue that expresses green fluorescent protein (GFP).
关键词： refractive index gradients,fluorescent imaging,Graded-index fibers,acousto-optic system,ultrasound,virtual GRIN lenses,photostimulation
更新于2025-09-12 10:27:22
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Quartz Optical Fibers with Increased Content of Fluorine for Fluorimeter Probes
摘要： A method to fabricate quartz optical fibers for probes employed in fluorescence diagnostics of tumors is proposed. It is shown that the sensitivity of fluorimeters in the near-IR spectral range can be increased using quartz–quartz optical fiber probes with the core made of the Heraeus glass and the SiO2–F cladding with an increased content of fluorine in the glass of up 7 wt %. The numerical aperture of such optical fibers amounts to 0.32. The optical fibers are used to develop a prototype of a multifiber high-aperture probe for a laser oncofluorimeter with a relatively high sensitivity in a spectral interval of 900–1100 nm.
关键词： fluorimeter probes,fluorescence diagnostics,quartz optical fibers,fluorine,near-IR spectral range
更新于2025-09-12 10:27:22
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Rare Earth Doped Optical Fibers with Multi-section Core
摘要： The gain bandwidth of a single-mode fiber is limited by the atomic transitions of one rare earth gain element. Here we overcome this long-standing challenge by designing a new single-mode fiber with multi-section core, where each section is doped with different gain element. We theoretically propose and experimentally demonstrate that this configuration provides a gain bandwidth well beyond the capability of conventional design, whereas the inclusion of multiple sections does not compromise single-mode operation or the quality of the transverse modal profile. This new fiber will be beneficial in realizing all fiber laser systems with few-cycle pulse duration or octave tunability.
关键词： Rare Earth Doped Optical Fibers,Gain Bandwidth,Fiber Laser Systems,Single-mode Fiber,Multi-section Core
更新于2025-09-12 10:27:22
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Sun light transmission through silica optical fibers for lighting: an experimental study
摘要： The process of sunlight transmission through optical fibers has received considerable interest from the scientific community in recent times. The interdisciplinary emerging field has found many applications in the field of solar lighting, solar furnace, three dimensional solar cells etc. Most of the optical fiber based solar lighting systems have employed plastic fibers as the light transmission media and the use of silica fibers in such systems has not been given much attention. Further, the actual measured data/values of the light emanating from the output ends of fibers in such systems are rarely reported. In the present study, merits and demerits of employing silica and plastic fibers in transmitting sun light are discussed. A silica optical fiber based solar lighting system has been developed and after installing it on an indigenously fabricated sun tracker, its performance has been measured and reported. Based on experimental and simulated results, multimode silica fibers could turn out to be better light transmission media than the plastic fibers, particularly for the case when light has to be transported over longer distances. The findings reported herein stress the need for tailor made customized solar lighting design for different buildings.
关键词： Sun-light transportation,Sun tracking,Solar lighting system,Optical fibers
更新于2025-09-12 10:27:22