Showing papers on "Step-index profile published in 2020"
TL;DR: In this article, a short absorption length ytterbium (Yb)-doped large-mode area (LMA) fiber is presented as a step forward to mitigate the stern problem of nonlinear scatterings in a tandem pumping scheme adopted for high-power fiber laser.
Abstract: A short absorption length ytterbium (Yb)-doped large-mode area (LMA) fiber is presented as a step forward to mitigate the stern problem of nonlinear scatterings in a tandem pumping scheme adopted for high-power fiber laser. The short absorption length was realized by incorporating high Yb concentration in the fiber core. Furthermore, by replacing the inherent silica cladding with a Ge-doped cladding, we were able to obtain low core numerical aperture (NA) and negate the detrimental effect of index-raising by high Yb concentrations. This overcomes the long-standing limitation in step-index Yb-doped fibers (YDFs) where high cladding absorption inevitably results in high NA, thus hampering single-mode operation. We report an LMA (∼575 μm2) YDF with NA of 0.04 and absorption of 27 dB/m at 976 nm—both traits promote power scaling of single-mode tandem pumped fiber lasers. To our knowledge, this is the highest cladding absorption attained in a low-NA step-index fiber to date. An all-fiber tandem-pumped amplifier was built using only ∼14 m of the YDF. The amplifier delivered a near-Gaussian beam (M2∼1.27) at 836 W output power (pump power limited) with a high slope efficiency of ∼83%. Thanks to the short length and the tandem pumping, no indication of limiting factors such as stimulated Raman scattering, photodarkening, and transverse mode instability was observed.
22 citations
TL;DR: In this article, a novel active fiber with Yb doping confined to the central 30% of the core area is fabricated and its performance is directly compared to a fiber with a conventional homogeneously doped core with almost identical parameters.
Abstract: We present a detailed investigation on higher order mode suppression due to differential gain in large mode area step index fiber amplifiers with confined Yb doping using spatially and spectrally resolved imaging (S2). A novel active fiber with Yb doping confined to the central 30% of the core area is fabricated and its performance is directly compared to a fiber with a conventional homogeneously doped core with almost identical parameters. At high pump rates, S2 and beam pointing stability measurements clearly demonstrate fundamental mode operation of the confined doping few mode fiber, even under imperfect launching conditions and environmental perturbations. In addition, we discuss the mode content as a function of gain in co-pumped fiber amplifiers with and without confined rare earth core doping using a power propagation model for fibers with similar parameters to those used in our experiments. Our simulation results as well as amplification experiments indicate the great potential of the confined doping concept for single mode high power operation.
7 citations
TL;DR: Third harmonic generation in a circular liquid core step-index fiber filled with a highly transparent inorganic solvent is demonstrated experimentally using ultrafast pump pulses of different durations in the telecom domain for the first time and intermodal phase matching to HE13 higher order mode is achieved.
Abstract: We provide a correction due to an erroneous repetition rate of one of the laser systems (90 fs pulse duration) in our previously published paper [Opt. Express28, 25037 (2020)10.1364/OE.399771].
4 citations
TL;DR: In this paper, a promising 5-cm-long supercontinuum (SC) source was designed and modeled using a step-index fiber structure employing highly nonlinear chalcogenide (ChG) materials such as As$$_2$$Se$$_3$$ glass as a core and Ge$$_{11.5} glass for its outer cladding.
Abstract: Mid-infrared region supercontinuum (SC) generation through designing broadband light sources recently attracts considerable attention in the field of nonlinear optics owing to their numerous applications in sensing and biological imaging. Broadband light sources designed based on different waveguiding structures adopted until today, the SC generation using optical step-index fiber is the prominent one due to its design and fabrication flexibility. In this study, a promising 5-cm-long SC source has been designed and modeled using a step-index fiber structure employing highly nonlinear chalcogenide (ChG) materials such as As$$_2$$Se$$_3$$ glass as a core and Ge$$_{11.5}{\hbox {As}}_{{24}}$$Se$$_{64.5}$$ glass for its outer cladding. Fiber structure is suitably modeled through its group-velocity dispersion optimization by varying core diameter. The optimized fiber structures are excited using a pump source having 170-fs pulses at 5.5 μm with a peak power of 10 kW. Initial all-normal dispersion excitation produces SC broadening up to 9.5 μm. Further study in a new optimization shows that spectral evolution can be expanded beyond 17 μm covering the wavelength from 3.2 to beyond 17 μm if the fiber structure is excited in the anomalous dispersion regime through a suitably tailored flat group-velocity dispersion curve with smaller in magnitude over a wide wavelength range. Such a promising SC source, which is designed based on typical step-index fiber principle using highly nonlinear ChG glass system, can be utilized in a variety of mid-infrared region applications.
3 citations
01 Jul 2020
TL;DR: In this article, the expression for far field pattern is presented using the method of power series for the fundamental LP 01 mode in optical fiber with step type refractive index profile and the same power series expression is used for determination of the far field in fibers with Kerr type nonlinearity by applying iteration technique.
Abstract: In this paper the expression for far field pattern is presented using the method of power series for the fundamental LP 01 mode in optical fiber with step type refractive index profile. The same power series expression is utilised for determination of the far field in fibers with Kerr type nonlinearity by applying iteration technique. We have presented the comparison of the pattern graphically for linear case and with Kerr nonlinearity. Far field pattern estimation in presence of nonlinearity is extremely important to understand and comprehend the performance of a single mode optical fiber particularly in the field of sensors. The presented method which utilizes Chebyshev technique involves prescription of the expression for estimation of the far field in an optical fiber and eliminates the requirement of solving complex mathematical expression. Further, the results obtained are in excellent agreement with the actual results. Thus our simple yet accurate method will prove to be of great assistance to the professionals in the fiber optics domain.
3 citations
21 Aug 2020
TL;DR: In this paper, the decay rate of a single quantum emitter located at the center of a polystyrene/PMMA core/closest step index fiber was analyzed and shown to be within 2.2% of its initial value upon changes of the core radius.
Abstract: For years, colloidal quantum dots (cQDs) have been optimized to offer great optical properties customizable through varying size and composition, and become the mature nanomaterial they currently are. However, their optical properties are affected by their environment. Hence, optical behaviour inconsistencies across experiments emerge from using cQDs inside different matrices. Therefore, their scope of applications has hitherto been greatly limited to specific applications. Recently, a new protocol to incorporate cQDs inside step index polymer optical fibers was developed by Whittaker and co-workers. It enables a cheap and robust fabrication of light-generating optical fibers. In addition to shielding cQDs from their outer environment, optical fibers also support optical modes. Hence, according to cavity quantum electrodynamics principles, these modes must alter the local density of optical states of the system, thus modifying the decay rate for each emitter located within the optical fibers. The current work revealed through finite difference time domain simulations only minimal modifications of the decay rate of a single quantum emitter located at the center of a polystyrene/PMMA core/clad step index fiber. Purcell factors staying within 2.2% of its initial value upon changes of the core radius were obtained. Thus, the Purcell enhancement offered by step index fibers is negligible compared to that of current semiconductor microcavities. Consequently, more exotic fiber geometries that offer greater Purcell effect must be identified before fast and cheap light-generating optical fiber can be made from this fabrication process.
3 citations
10 May 2020
TL;DR: In this article, the authors reported 9.2dB Raman amplification of pulses at 1121 nm in an orbital angular momentum mode with charge 15 in 30 m of 50-μm-diameter step-index-core fiber.
Abstract: We report 9.2-dB Raman amplification of pulses at 1121 nm in an orbital angular momentum mode with charge 15 in 30 m of 50-μm-diameter step-index-core fiber. The amplified signal mode-purity is measured to 78.4%.
2 citations
TL;DR: This is the first demonstration of stable mode propagation and Raman amplification of a single Bessel-like higher-order mode in a fiber of hundreds of meters, and shows the potential for efficient power scaling of asingle signal mode with low-brightness pumping, comparable with that from continuous-wave multimode diode lasers.
Abstract: We experimentally demonstrate Raman amplification of signal pulses in a high-order Bessel mode (LP06) at a wavelength of 1121 nm in a 335-m step-index fiber with a 70-µm diameter, 0.227-NA pure-silica core. This was pumped by 5-ns multimode pulses at 1065 nm from a Yb-doped fiber master oscillation power amplifier. The mode purity of the amplified pulses is well preserved to 23 dB of average-power gain, to 774 W of peak power in 2 ns pulses at a 20 kHz repetition rate, when pumped with a peak power of 942 W. The pump depletion as averaged over the signal pulses reaches 59%. We believe, to the best of our knowledge, that this is the first demonstration of stable mode propagation and Raman amplification of a single Bessel-like higher-order mode in a fiber of hundreds of meters. This shows the potential for efficient power scaling of a single signal mode with low-brightness pumping, comparable with that from continuous-wave multimode diode lasers.
1 citations
Patent•
06 Aug 2020
TL;DR: In this paper, the authors provided an optical fiber consisting of a core region (102) and a cladding region (104), where the core region is defined along a central longitudinal axis (106) of the optical fibre (100).
Abstract: The present disclosure provides an optical fibre. The optical fibre includes a core region (102) and a cladding region (104). The core region (102) is defined along a central longitudinal axis (106) of the optical fibre (100). In addition, the core region (102) of the optical fibre (100) has a first radius r1 and a first refractive index n1. Further, the cladding (104) concentrically surrounds the core region (102) of the optical fibre (100). Furthermore, the cladding region (104) of the optical fibre (100) has a second radius r2 and a second refractive index n2. Moreover, the optical fibre (100) has a step index profile.
TL;DR: In this paper, a detailed experimental study on noise-seeded intermodal modulation instability (IM-MI) in normal dispersion region of a conventional step-index fiber is presented.
Abstract: We present detailed experimental study on noise-seeded intermodal modulation instability (IM-MI) in normal dispersion region of a conventional step-index fiber. The sharp refractive index contrast between core and cladding leads to large group velocity mismatch between the spatial modes, coaxing to efficient IM-MI and generation of multiple spectral peaks along with Raman peaks. Evolution of the spectrum with pump powers and fiber lengths are observed. Experimental findings are well supported with the theoretical framework based on bimodal-MI model considering the distinct dispersion parameters of the participating modes.
01 Oct 2020-Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems
TL;DR: In this article, the authors study the phenomenon of deliberate inter-modal interactions in a specially designed index guided microstructured optical fiber (MOF) by exploiting multipole expansion method.
Abstract: We study the phenomenon of deliberate inter-modal interactions in a specially designed index guided Microstructured Optical Fiber (MOF) by exploiting multipole expansion method (White et al. 2002). The MOF is designed in such a way that the first layer of holes is judiciously filled with a material having refractive index slightly greater than the background material or core and remaining holes are filled with air. Accordingly, we find an interesting phenomenon of mode crossing between the fundamental mode and a targeted defect mode while tuning the wavelength. Exploring this transition wavelength of the mode crossing, we propose a design of a fiber optic sensor for refractive index measurement (Silva et al. 2014) with enhanced sensitivity.