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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) - Numerical and Experimental Study on the IR Femtosecond Laser and Phase Mask-Based Grating Inscription in Photonic Crystal Fibers
摘要： Femtosecond pulse laser sources enable the fabrication of fiber Bragg gratings (FBGs) in non-photosensitive fibers, allow for through coating grating inscription when working at infrared (IR) wavelengths and can provide for high temperature stable gratings. Target applications for such gratings include, but are not limited to, optical communications, fiber lasers and fiber sensing. When dealing with such grating inscription method in photonic crystal fibers (PCF) however, the presence of air holes in the fiber cladding impedes the delivery of the femtosecond laser pulse energy to the fiber core, which in its turn significantly affects the index change through non-linear absorption processes in the fiber core [1]. Our research focuses on this issue in view of understanding how the grating writing laser pulses interact with the PCF’s holey structure and of enabling more efficient femtosecond laser-based inscription of FBGs in PCFs. Here we report on the inscription of FBGs in a hexagonal lattice PCF using a femtosecond pulse laser operating at 1030 nm with a phase mask and a short focal length cylindrical lens (f=10 mm) that focuses light to the fiber core [2]. We first looked into the influence of the alignment on laser beam focusing in the cross-section of the PCF by comparing the focusing characteristics to those in standard step-index single mode fiber. As a figure of merit, we used the transverse coupling efficiency (TCE), which is defined as the ratio of the integrated core field intensities simulated (using Lumerical FDTD Solutions?) in the presence and absence of holey cladding. Fig. 1b shows how the TCE changes as the fiber is translated along the X and Y axes in the cross-sectional plane. X=0 and Y=0 corresponds to focused to the center of the core, and negative Y indicates translation of the fiber away from the lens (see Fig. 1a). For a step-index fiber we observe a typically elongated region in which we find optimal coupling with TCE=1 (no air holes) for a beam waist of 2.34 μm and a depth of focus of 15.7 μm. Fig. 1c shows an alignment map for a hexagonal lattice PCF (with structure shown in the inset of Fig. 1d), when light is incident along the ΓK axis of the hexagon. We can identify three distinct regions with a TCE around 0.6. Those appear when the fiber is shifted by around 15 μm and 30 μm further from the lens. This offset indicates that optimal coupling of the grating writing beam to the PCF core requires focusing to the edge of the holey cladding or closer to the silica cladding region of the fiber, rather than to the core center. Fig. 1 a) Fiber translational axes and translation dependence of the transverse coupling efficiency (TCE) for b) step-index fiber and c) PCF. d) Spectra of the IR femtosecond pulse inscribed FBG in the PCF (SEM image in the inset). We then inscribed FBGs in the above mentioned hexagonal lattice PCF with a commercial Yb:KGW ultrafast regenerative amplifier system Pharos 6W (Light Conversion) at 1030 nm and 190 fs duration pulses at a repetition rate of 100 Hz. We used high accuracy alignment stages to find the best coupling position by monitoring the luminescence (around 420 nm) from the Ge-doped core. The reflection and transmission spectra of the inscribed FBG are shown in Fig. 1c. We achieved an almost 4 dB strong FBG in around 4 seconds using a laser power of 450 mW. To the best of our knowledge it is the first time that the difference between regular step-index fibers and PCFs in best focusing conditions for IR femtosecond laser-based FBG writing is studied and that such a FBG is realized in a PCF using a 1030 nm source and a phase mask technique with a short focal length cylindrical lens.
关键词： phase mask,photonic crystal fibers,Femtosecond pulse laser,fiber Bragg gratings,transverse coupling efficiency
更新于2025-09-12 10:27:22
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Application of Raman and Brillouin Scattering Phenomena in Distributed Optical Fiber Sensing
摘要： We present a review of the basic operating principles and measurement schemes of standalone and hybrid distributed optical fiber sensors based on Raman and Brillouin scattering phenomena. Such sensors have been attracting a great deal of attention due to the wide industrial applications they offer, ranging from energy to oil and gas, transportation and structural health monitoring. In distributed sensors, the optical fiber itself acts as a sensing element providing unique measurement capabilities in terms of sensing distance, spatial resolution and number of sensing points. The most common configuration exploits optical time domain reflectometry, in which optical pulses are sent along the sensing fiber and the backscattered light is detected and processed to extract physical parameters affecting its intensity, frequency, phase, polarization or spectral content. Raman and Brillouin scattering effects allow the distributed measurement of temperature and strain over tens of kilometers with meter-scale spatial resolution. The measurement is immune to electromagnetic interference, suitable for harsh environments and highly attractive whenever large industrial plants and infrastructures have to be continuously monitored to prevent critical events such as leakages in pipelines, fire in tunnels as well as structural problems in large infrastructures like bridges and rail tracks. We discuss the basic sensing mechanisms based on Raman and Brillouin scattering effects used in distributed measurements, followed by configurations commonly used in optical fiber sensors. Hybrid configurations which combine Raman and Brillouin-based sensing for simultaneous strain and temperature measurements over the same fiber using shared resources will also be addressed. We will also discuss advanced techniques based on pulse coding used to overcome the tradeoff between sensing distance and spatial resolution affecting both types of sensors, thereby allowing measurements over tens of kilometers with meter-scale spatial resolution, and address recent advances in measurement schemes employing the two scattering phenomena.
关键词： distributed fiber optic sensing,Raman scattering,non-linear phenomena in optical fibers,Brillouin scattering,strain and temperature measurements
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) - High-Power Short-Wavelength Infrared Supercontinuum Generation in a Multimode Fluoride Fiber
摘要： Supercontinuum light (SC) is a broadband source with unique properties generated via cascaded nonlinear processes when intense light propagates in a nonlinear material. Depending on the nonlinear material and pump source used, the spectrum of a SC source can span from the visible to the mid-infrared with up to several Watt-average power. Recently, the generation of broadband SC sources operating in the mid-infrared (MIR) has attracted significant interest due to a wide range of potential applications in spectroscopy, microscopy, molecular fingerprinting, environmental monitoring and LIDAR. Fibers made of non-silica soft glasses such as fluoride, tellurite and chalcogenide are good candidates for SC generation in the MIR due to their high intrinsic nonlinearity and wide transparency window in this wavelength range. To date, most of supercontinuum sources demonstrated in the mid-infrared have been generated in single mode soft glass fibers that cannot sustain high level of average power due to their small core size and low damage threshold. This generally imposes a limit on the maximum output power which can be a limitation for practical applications, especially in long-distance remote sensing for which high power is key. In order to overcome this problem, multimode fibers with large core size and higher damage threshold are a promising alternative. Here, we demonstrate for the first time the generation of an octave-spanning SC by injecting 1 MHz, 350 fs pulses from an optical parametric amplifier in a meter-long multimode step-index InF3 fiber with 100 μm core diameter. We performed a systematic study of the SC spectrum as a function of the pump wavelength and the largest SC spectrum spanning from 1100 nm to 2500 nm with 600 mW output power was generated when injecting the pulses at 1960 nm, in the anomalous dispersion regime of the fundamental mode. The output beam profile of the SC was characterized in different wavelengths bands, illustrating the highly multimode nature of the SC generation process. Numerical simulation results shows that higher-order soliton dynamics and dispersive wave generation in multiple higher-order modes are key contributions to reaching octave-spanning bandwidth in a fiber with large core size. Our results open up a promising route towards ultra-high power broadband sources in the MIR for applications where a single-mode spatial intensity distribution is not essential such as e.g. in remote sensing.
关键词： mid-infrared,high-power,fluoride fibers,multimode fibers,Supercontinuum generation
更新于2025-09-11 14:15:04
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Enhanced Pump Absorption Efficiency in Coiled and Twisted Double-Clad Fibers for Fiber Lasers
摘要： High-power operation of fiber lasers was mainly enabled by the invention of cladding-pumping in a double-clad fiber structure. Pump absorption is enhanced by broken circular symmetry of inner cladding cross-sections and by mode-scrambling of the pump modes resulting from unconventional fiber coiling. However, theoretical studies were limited to the assumption of a straight fiber until recently, when the rigorous model accounting for double-clad fiber bending and twisting was described. It was found that squeezing of the effective area of the pump radiation due to fiber bending plays an important role in cladding-pump absorption enhancement. We review results of numerical modeling of pump absorption in various types of double-clad fibers, e.g., with cross-section shape of hexagon, stadium, and circle; two-fiber bundle (so-called GTWave fiber structure) a panda fibers are also analyzed. The presented results can have a practical application and potential impact in the construction of fiber lasers: with pump absorption efficiency optimized by our new model (the other models did not take into account fiber twist), the double-clad fiber of shorter length can be used in the fiber lasers and amplifiers. This dramatically minimizes the deleterious effect of background losses and nonlinear effects.
关键词： fiber lasers,thulium-doped fibers,rare-earth-doped fibers,optical pumping
更新于2025-09-11 14:15:04
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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) - Fiber Fuse Effect in Hollow Core Optical Fibers
摘要： Fiber fuse effect (FFE) is one of phenomena restricting the high power/intensity/pulse energy laser radiation transport through optical fibers. FFE (alternatively, optical discharge (OD) propagation through fiber core) was initially observed in solid state silica fibers [1], and later in fibers of various materials and constructions, including microstructured fibers. Hollow core fibers developed in recent decades can transport high power laser radiation. However, it was recently discovered that FFE is present in such fibers as well [2]. In this work OD propagation through hollow-core revolver fibers (RFs) was investigated. Reflecting cladding of RFs consists of only one layer of capillaries [3]. The cross section pictures of two RFs used in experiments are shown in Fig.1(a,b: RF1 and RF2). All our RFs had transparency bands at laser radiation wavelength 1.06 m. The Q-switched mode-locked Nd:YAG solid state laser was used in our experiments to reach a high enough radiation intensity in the fiber core. The laser radiation consisted of nanosecond trains of picosecond pulses (PPs): the train duration was 130 ns, duration of PP was 100 ps at repetition rate 76 MHz. The average output power of the laser was 3 W. The laser radiation was launched into and passed the ~50 cm RF without any significant disturbances. However, touching of the output end of the fiber with a metal plate gave rise to OD propagation with an average velocity Vav of ~1m/s. In the case of RF1 the silica structure of the fiber was completely destroyed after the OD passage, and its fragments were held together only by the polymer cladding. In the case of RF2 having a twice as thick support tube the fiber can be inspected after OD passage as a whole. It turned out that Vav depends essentially on the fact whether RF was during the experiment covered by polymer or not. In the last case Vav was ~3 times higher (~3 m/s) than for coated fiber (Fig.1, e). Each PP left in the RF2 fingerprint in the form of capillary destruction region of ~100 m length, and these regions were separated from each other by ~100 m regions of undamaged capillaries (Fig.1,c). And in the case of uncoated RF2 (Fig.1,d) the fingerprints of PP trains are separated by ~1 mm from each other contributing to the Vav increase.
关键词： Fiber fuse effect,laser radiation,revolver fibers,optical discharge,hollow core optical fibers
更新于2025-09-11 14:15:04
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Fiber Laser || Active Q-switched Fiber Lasers with Single and Dualwavelength Operation
摘要： A brief explanation on Q-switched fiber laser operating principle for active technique in terms of operation characteristics is presented. Experimental analysis of proposed pulsed fiber lasers by the active Q-switched technique is demonstrated. Experimental setups include the use of Er/Yb doped fiber as a gain medium and an acousto-optic modulator as cavity elements. Setup variations include the use of fiber Bragg gratings for wavelength selection and tuning and Sagnac interferometer for wavelength selection in single wavelength operation and for cavity loss adjustment in dual wavelength operation. The experimental analysis of principal characteristics of single-wavelength operation of the fiber laser and cavity loss adjustment method for dual-wavelength laser operation are discussed.
关键词： fiber Bragg gratings,Sagnac interferometer,Er/Yb double-clad fibers,Q-switched lasers
更新于2025-09-11 14:15:04
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Self‐Assembled Polyamidoamine Dendrimer on Poly (methyl meth‐ acrylate) for Plasmonic Fiber Optic Sensors
摘要： We report a novel one-step polyamidoamine (PAMAM) dendrimer based polymethyl methacrylate (PMMA) surface functionalization strategy for the development of polymeric optical (POF) based plasmonic sensors utilizing gold nanoparticles (AuNP). Simple contact angle measurements over PMMA sheets reveal the ability of the dendrimers to strongly bind to PMMA surface without additional acid/alkali pretreatment, unlike the conventional hexamethylene diamine (HMDA) based surface modification. Subsequently, U-bent POF probes with high evanescent wave absorbance sensitivity were exploited for relative quantification of the surface amine groups using fluorescein isothiocyanate (FITC) binding and efficient chemisorption of gold nanoparticles (AuNP) in order to identify the optimum conditions viz. dendrimer concentration, incubation time and dendrimer generation. While FITC binding showed a proportional increase in amine functional density with PAMAM concentration and time, interestingly the AuNP (40 nm) binding studies revealed the formation of loose PAMAM multilayers and their desorption. PAMAM (G4) concentration as low as 5 mM and incubation time of 24 h provide faster binding rate with densely packed AuNP and the RI sensitivity of ~ 15 (A546 nm/RIU). This simpler and inexpensive strategy could also be exploited for the development of functional PMMA substrates for various applications including nanotechnology, bio-imaging, drug delivery and analytical separations.
关键词： gold nanoparticles (AuNP),dendrimers,plasmonic sensors,polymethyl methacrylate (PMMA),polymeric optical fibers (POF),evanescent wave absorbance
更新于2025-09-11 14:15:04
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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) - Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers with Quasi-Continuous 1064 nm Pump
摘要： Polarization modulation instability (PMI) is a form of modulation instability that can exist in weakly birefringent optical fibers. Sidebands can be generated by this effect when a polarization mode of the birefringent fiber is excited with an intense optical pump. The polarization state of the sidebands is orthogonal to the polarization of the pump signal. PMI has been observed in microstructured optical fibers (MOFs). PMI was reported in a large-air-filling fraction MOF that was pumped in the normal dispersion regime with visible light. The coherent degradation of femtosecond supercontinuum light generated in all-normal dispersion (ANDi) MOFs due to PMI was recently investigated. Here, we report the experimental observation of PMI effect in ANDi MOFs with picosecond pumping at 1064 nm.
关键词： Polarization modulation instability,microstructured optical fibers,picosecond pumping,all-normal dispersion
更新于2025-09-11 14:15:04
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Suppressing Dark Counts of Multimode-Fiber-Coupled Superconducting Nanowire Single-Photon Detector
摘要： Large active-area superconducting nanowire single-photon detectors (SNSPDs) coupled with multimode fibers (MMFs) can provide high light-gathering capacity, which is essential for free-space detection applications in photon-starved regimes. However, MMF-coupled SNSPDs often suffer from large system dark count rates (DCRsys) over kHz due to blackbody radiation of the MMF at room temperature. Such large DCRsys would significantly degrade signal-to-noise ratio (SNR) of the receiving system. This paper reports an MMF-coupled large-active-area SNSPD system with low DCRsys by using a homemade cryogenic MMF filter bench. The filter bench, which consists of lenses and optical filters, can provide a high transmittance of about 80% at the central wavelength of the passband (1550 ± 12.5 nm) and a wide blocking range from 500 nm to over 6000 nm at 40 K. With using the filter bench, the DCRsys of an MMF-coupled 9-pixel SNSPD array with an active area of 50 μm in diameter is greatly suppressed by 23 dB with 1 dB loss of system detection efficiency (SDE). The detector demonstrates an SDE of 51% at a DCRsys of 100 Hz for 1550 nm photons. Thus, SNR of the detector is enhanced by about 160 times and the noise equivalent power is improved to 3×10?19 W/Hz1/2.
关键词： cryogenic MMF filter bench,multimode fibers (MMFs),Superconducting nanowire single-photon detectors (SNSPDs),dark count rates (DCRsys),signal-to-noise ratio (SNR)
更新于2025-09-11 14:15:04
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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) - L-Band Amplifiers Based on Cladding-Pumped Er-Doped (Yb-Free) Fibers with Al <sub/>2</sub> O <sub/>3</sub> -SiO <sub/>2</sub> Core Highly Doped by Fluorine
摘要： Recently we have demonstrated perspectives of application double clad (DC) highly Er-doped (Yb-free) fibers for pulse amplification to a record-high energy and peak power [1]. Single-mode propagation regime, high pump-to-signal conversion efficiency (PCE) of 25% in L-band (near 1575 nm) and a relatively short fiber length (~ 6 m) was achieved by optimization of fiber geometry and core compound. Core-to-cladding ratio was chosen as high as possible (core and cladding diameters were 35 (cid:80)m and 125 (cid:80)m correspondingly) to increase pump absorption from the cladding. Utilization of P2O5-Al2O3-SiO2 (PAS) glass matrix [2] allowed us to achieve a low core numerical aperture (NA) and, simultaneously, high PCE even for heavily Er-doped fibers.
关键词： L-band amplifiers,Fluorine doping,Er-doped fibers,Al2O3-SiO2 core,Pump-to-signal conversion efficiency
更新于2025-09-11 14:15:04