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Journal ArticleDOI

Top-hat beam output of a single-mode microstructured optical fiber: Impact of core index depression

TL;DR: A new strategy based on the use of an OVD-made high index ring deposited on a silica rod having a refractive index slightly lower than the silica used for the microstructured cladding realized the first single-mode fiber with a quasi-perfect top-hat intensity profile around 1 µm.
Abstract: A new strategy to obtain a single-mode fiber with a flattened intensity profile distribution is presented. It is based on the use of an OVD-made high index ring deposited on a silica rod having a refractive index slightly lower than the silica used for the microstructured cladding. Using this strategy, we realized the first single-mode fiber with a quasi-perfect top-hat intensity profile around 1 µm. Numerical studies clearly demonstrate the advantage of using a core index depression to insure the single-mode operation of the fiber at the working wavelength.
Citations
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Journal ArticleDOI
TL;DR: In this paper, an overview of the capabilities and limitations of established vapor deposition fiber preform technologies, and new techniques for improved and extended doping properties in fiber preparation are discussed, such as a powder-based process (REPUSIL) and an optimized glass melting method to overcome the limits of conventional vapor deposition methods concerning the volume fabrication of rare earth (RE)-doped quartz and high silica glasses.
Abstract: Abstract The increasing fields of applications for modern optical fibers present great challenges to the material properties and the processing technology of fiber optics. This paper gives an overview of the capabilities and limitations of established vapor deposition fiber preform technologies, and discusses new techniques for improved and extended doping properties in fiber preparation. In addition, alternative fabrication technologies are discussed, such as a powder-based process (REPUSIL) and an optimized glass melting method to overcome the limits of conventional vapor deposition methods concerning the volume fabrication of rare earth (RE)-doped quartz and high silica glasses. The new preform technologies are complementary with respect to enhanced RE solubility, the adjustment of nonlinear fiber properties, and the possibility of hybrid fiber fabrication. The drawing technology is described based on the requirements of specialty fibers such as adjusted preform and fiber diameters, varying coating properties, and the microstructuring of fiber configurations as low as in the nanometer range.

78 citations

Journal ArticleDOI
TL;DR: It is demonstrated for the first time a flat-top mode from a 50 µm-core Yb-doped leakage channel fiber (LCF) with an effective mode area of ~1880 µm(2) in the straight fiber, an over 50% increase comparing to that of regular LCF with the same core diameter.
Abstract: We demonstrate for the first time a flat-top mode from a 50 µm-core Yb-doped leakage channel fiber (LCF). The flat intensity distribution leads to an effective mode area of ~1880 µm2 in the straight fiber, an over 50% increase comparing to that of regular LCF with the same core diameter. The flat-top mode was achieved by using a uniform Yb-doped silica glass in the core center with an index of ~2 × 10−4 lower than that of the silica background. The fiber was also tested in a laser configuration, demonstrating an optical-to-optical efficiency of ~77% at 1026 nm with respect to the pump at 975 nm.

28 citations

Journal ArticleDOI
20 Mar 2016
TL;DR: In this article, an optical fiber that guides an approximate Airy pattern as one of its modes was made, and the optical fiber's attenuation was 11.0 dB/km at a 1550 nm wavelength, the match between the fiber's mode and the ideal infinite Airy patterns was 93.7%, and the far field resembled a top-hat beam.
Abstract: In theory, no more than 80% of the light diffracted by a circular aperture can be directly coupled into one mode of an ordinary optical fiber. To improve coupling efficiency, and illustrate an inverse method for designing optical fibers with a desired mode shape, we have made an optical fiber that guides an approximate Airy pattern as one of its modes. The fiber’s attenuation was 11.0 dB/km at a 1550 nm wavelength, the match between the fiber’s mode and the ideal infinite Airy pattern was 93.7%, and the far field resembled a top-hat beam. The guidance mechanism has strong similarities to photonic bandgap guidance.

27 citations

Journal ArticleDOI
TL;DR: By utilizing a full vectorial finite element method with perfectly matched layers, propagation properties such as birefringence, chromatic dispersion and confinement losses are numericaly evaluated for the proposed PCF structure.
Abstract: A numerical analysis of a hexagonal PCF structure with four circular air hole rings around the core has been presented in this paper. By utilizing a full vectorial finite element method with perfectly matched layers, propagation properties such as birefringence, chromatic dispersion and confinement losses are numericaly evaluated for the proposed PCF structure. Specifically, birefringence of 2.018 × 10–2, nonlinear coefficients of 40.682 W−1 km−1, negative chromatic dispersion of − 47.72 ps/km.nm at 1.55 µm and − 21 to − 105 ps/km.nm at the telecommunication band of C-U have been reported.

25 citations

Journal ArticleDOI
TL;DR: The dispersion diagram of a DCF is obtained by solving the full-vector eigenvalue equations and analyzed using the theory of anti-resonant and the inhibited coupling mechanisms to contribute to a better understanding of the anti- RESONant and inhibited coupling guidance mechanisms in other complex inversed index fibers.
Abstract: The depressed core fiber (DCF), consisting of a low-index solid core, a high-index cladding and air surrounding, is in effect a bridge between the conventional step-index fiber and the tube-type hollow-core fiber from the point of view of the index profile. In this paper the dispersion diagram of a DCF is obtained by solving the full-vector eigenvalue equations and analyzed using the theory of anti-resonant and the inhibited coupling mechanisms. While light propagation in tube-type hollow-core fibers is commonly described by the symmetric planar waveguide model, here we propose an asymmetric planar waveguide for the DCFs in an anti-resonant reflecting optical waveguide (ARROW) model. It is found that the anti-resonant core modes in the DCFs have real effective indices, compared to the anti-resonant core modes with complex effective indices in the tube-type hollow-core fibers. The anti-resonant core modes in the DCFs exhibit similar qualitative and quantitative behavior as the core modes in the conventional step-index fibers. The full-vector analytical results for the simple-structure DCFs can contribute to a better understanding of the anti-resonant and inhibited coupling guidance mechanisms in other complex inversed index fibers.

15 citations


Cites background or methods or result from "Top-hat beam output of a single-mod..."

  • ...Compared to the M-type fiber, the core mode of the DCF is guided by both total internal reflection and anti-resonance guidance, and its core mode has a real effective refractive index [27,29-32]....

    [...]

  • ...However, these studies in regard to DCFs [27, 29-32] were limited to the analysis of a few modes in the strong dispersion region....

    [...]

  • ...Due to the manageable waveguide dispersion and modal field changes in a DCF, the generation of supercontinuum [27] and top-hat beams [32] can be achieved....

    [...]

  • ...Therefore, given that DCFs can readily provide manageable waveguide dispersion and exceptional modal field changes, they are worthy further study for a wide range of applications, in addition to the few existing works such as the generation of the supercontinuum [27] and top-hat beams [32]....

    [...]

  • ...The DCFs have been studied for various applications including pulse compression in fiber lasers [29-31], generation of supercontinuum [27] and top-hat beams [32], due to their manageable waveguide dispersion and exceptional modal field changes....

    [...]

References
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Journal ArticleDOI
TL;DR: This paper reviews the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in Terms of high-power performance.
Abstract: The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

1,689 citations

Journal ArticleDOI
TL;DR: The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed.
Abstract: The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

1,488 citations

Journal ArticleDOI
TL;DR: A new measurement technique, capable of quantifying the number and type of modes propagating in large-mode-area fibers is both proposed and demonstrated, based on both spatially and spectrally resolving the image of the output of the fiber under test.
Abstract: A new measurement technique, capable of quantifying the number and type of modes propagating in large-mode-area fibers is both proposed and demonstrated. The measurement is based on both spatially and spectrally resolving the image of the output of the fiber under test. The measurement provides high quality images of the modes that can be used to identify the mode order, while at the same time returning the power levels of the higher-order modes relative to the fundamental mode. Alternatively the data can be used to provide statistics on the level of beam pointing instability and mode shape changes due to random uncontrolled fluctuations of the phases between the coherent modes propagating in the fiber. An added advantage of the measurement is that is requires no prior detailed knowledge of the fiber properties in order to identify the modes and quantify their relative power levels. Because of the coherent nature of the measurement, it is far more sensitive to changes in beam properties due to the mode content in the beam than is the more traditional M2 measurement for characterizing beam quality. We refer to the measurement as Spatially and Spectrally resolved imaging of mode content in fibers, or more simply as S2 imaging.

445 citations

Journal ArticleDOI
TL;DR: A novel ytterbium-doped fiber design that combines the advantages of rod and fiber gain media is reported that has significantly reduced nonlinearity, which allows for scalability in the performance of a high-peak-power fiber laser and amplifier system.
Abstract: We report on a novel ytterbium-doped fiber design that combines the advantages of rod and fiber gain media. The fiber design has outer dimensions of a rod laser, meaning a diameter in the range of a few millimeters and a length of just a few tens of centimeters, and includes two important waveguide structures, one for pump radiation and one for laser radiation. We obtained 120-W output power in single-mode beam quality from a 48-cm-long fiber cane that corresponds to an extracted power of 250 W/m. The fiber has significantly reduced nonlinearity, which therefore allows for scalability in the performance of a high-peak-power fiber laser and amplifier system.

294 citations

Journal ArticleDOI
TL;DR: It is found that in general HF1 is less susceptible to longitudinal non-uniformities compared to the other designs for equivalent effective areas and this general property for the particular case of a macro-bending induced loss.
Abstract: In this paper we evaluate the cut-off properties of holey fibers (HFs) with a triangular lattice of air holes and the core formed by the removal of a single (HF1) or more air holes (HF3 and HF7). With the aid of finite-element simulations we determine the single-mode and multi-mode phases and also find the air hole diameters limiting the endlessly single-mode regime. From calculations of V and W parameters we find that in general HF1 is less susceptible to longitudinal non-uniformities compared to the other designs for equivalent effective areas. As an example we illustrate this general property for the particular case of a macro-bending induced loss.

94 citations