<i>Fundamentals of Optical Fibers</i>

Buck, John A.; Jacobs, Ira

doi:10.1063/1.2807510

Cited by 97 publications

(146 citation statements)

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“…According to wave-guide theory (Buck 1995), power is transmitted through a fiber by constructive interference in an ensemble of modes. In a step-index fiber with a diameter of ∼100 mm, the type typically used in astronomy, there are several thousand modes which present a highly unstable, irregular light distribution across the fiber output.…”

Section: Introductionmentioning

confidence: 99%

Modal Noise in High‐Resolution, Fiber‐fed Spectra: A Study and Simple Cure

Baudrand

Walker²

2001

PUBL ASTRON SOC PAC

112

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ABSTRACT. The transmission modes of a fiber introduce an unstable intensity distribution in high-resolution spectra which cannot be eliminated by flat-fielding because the pattern is sensitive to any small changes in fiber position or illumination. These instabilities, rather than photon shot noise, limit the achievable signal-to-noise ratio (S/N). In controlled laboratory experiments at a resolution of ∼150,000, we found S/N limited to ≤500 for a range of fiber perturbations and illumination geometries from simple displacement to simulated seeing variations. We find an empirical relation between the number of monochromatic modes and the level of modal noise for which we offer no rigorous explanation. More important, we demonstrate that continuous, low-amplitude agitation of the fiber close to its output completely eliminates the problem.

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Section: Introductionmentioning

confidence: 99%

Modal Noise in High‐Resolution, Fiber‐fed Spectra: A Study and Simple Cure

Baudrand

Walker²

2001

PUBL ASTRON SOC PAC

112

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“…As the refractive indices of the unclad fiber and the surroundings differ considerably ͑n sapphire Ϸ3.1 for the ordinary ray 2 ͒, the ''weakly guiding'' approximations commonly employed for optical fibers 3 are not valid for our experimental situation. To calculate the dispersion of the fiber, the propagation constant was numerically evaluated from the transcendental characteristic equation applicable to the HE 11 mode of a dielectric rod with circular cross section.…”

Section: The Reference Spectrum E Ref ( ) Is the Fourier Transform Ofmentioning

confidence: 87%

“…The fields associated with the HE 11 mode can be readily calculated once the propagation constant has been determined, 3 from which the overlap coefficient C 11 is evaluated. The input beam profile E input is assumed to be a frequency independent Gaussian beam with a diameter of 200 m. In contrast to metal walled waveguides, the mode patterns E mn are frequency dependent.…”

Section: The Reference Spectrum E Ref ( ) Is the Fourier Transform Ofmentioning

confidence: 99%

Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers

Jamison¹,

McGowan²,

Grischkowsky³

2000

Applied Physics Letters

204

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Waveguide propagation of sub-ps terahertz pulses in single-crystal sapphire fibers is reported. An incident THz pulse of approximately 0.6 ps duration undergoes considerable reshaping due to the absorptive and dispersive waveguide propagation, resulting in transmitted chirped pulse durations of 10-30 ps. Good agreement between theory and experiment is obtained by analyzing the propagation in terms of the single HE 11 waveguide mode. The dominance of the single HE 11 mode, despite the fiber dimensions allowing for multimode propagation, is attributed to the free-space to waveguide coupling. © 2000 American Institute of Physics. ͓S0003-6951͑00͒02215-4͔The technical capability to optoelectronically transmit and detect single cycle pulses of freely propagating THz electromagnetic radiation has generated much interest in the guided wave propagation of such pulses. At the present time, the highest guided-wave performance has been obtained with a 240-m-diam stainless steel waveguide over the frequency range from 0.8 to 3.5 THz and with a power absorption coefficient of less than 1 cm Ϫ1 . 1 This performance far exceeds that of coplanar and microstrip transmission lines. 1 An alternative approach would be to use dielectric waveguides. Such waveguides would not have the sharp lowfrequency cutoff of metal waveguides and would thereby extend the low frequency limit of the waveguide. Given a suitable low loss dielectric, such as high-resistivity silicon with a power absorption coefficient of less than 0.05 cm Ϫ1 over our frequency range, 2 dielectric waveguides could have much less absorption than metal waveguides. In addition, due to boundary considerations it should be possible to more cleanly couple, and with a much higher coupling efficiency, linearly polarized THz radiation into the single dominant mode for dielectric waveguides than for metal circular waveguides. Such dielectric single-mode THz waveguides would have the promise of an extremely low-loss, flexible interconnect and communications channel, with advantages similar to that of single-mode optical fiber.Here, we report demonstrations of single-mode propagation of sub-ps THz pulses in dielectric waveguides ͑fibers͒. These demonstrations prove the efficient quasioptical input and output coupling to and from such fibers and show the viability of the single-mode THz fiber interconnect. The fact that the diameters ͑325, 250, and 150 m͒ of the THz fibers are similar to those of optical fibers, including the core and cladding, gives the THz fibers similar flexibility and handling properties. Because this work was performed with single-crystal unclad fibers, the waveguide propagation characteristics vary significantly over the extensive frequency spectrum of the nearly single-cycle input pulses, giving rise to considerable absorptive and dispersive reshaping.The waveguides used are unclad single-crystal sapphire fibers, with the c axis directed along the length of the fiber, supplied by Saphikon Inc. In our analysis we assume a circular fiber cross-section, although ...

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“…The second issues would result in a smooth overall increase in attenuation at all wavelengths. Loss increase caused by microbending is commonly not wavelength dependent (Buck, 2004). Chemical degradation is most probably caused by the ingression of hydrogen, released from the cable itself .…”

Section: Attenuation Measurementsmentioning

confidence: 99%

Thermal, mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well

Reinsch

Henninges

Ásmundsson³

2013

Environ Earth Sci

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Structural wellbore integrity is an important issue for a sustainable provision of geothermal energy. Raman scattering based fiber optic distributed temperature sensing (DTS) can help to monitor the status of a well and therefore help to optimize expensive work-over activities. This study reports on the installation of a fibre optic cable in the cemented annulus behind the anchor casing in the high temperature geothermal well HE-53, Hellisheiði geothermal field, SW Iceland. Although the cable has been damaged during the installation, temperature data could be acquired during the entire length of installation down to 261.3 m. Temperature measurements were performed during the installation in spring 2009, during the onset of a flow test in summer 2009 and after a 8.5 month shut-in period in summer 2010. During the flow test, maximum temperatures of 230• C were measured after two weeks fluid production. Using optical time domain reflectometry (OTDR), attenuation measurements at 850 and 1300 nm enabled to identify mechanical, thermal, and chemical degradation along the optical fibre. The observed degradation led to erroneous temperature readings and limits, due to the optical budget of the DTS system, the accessible length of the fibre. The characteristics and the influence of the different degradation mechanisms on the accuracy of the DTS measurements are discussed and recommendations for an optimized installation are given.

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Fundamentals of Optical Fibers

Cited by 97 publications

References 0 publications

Modal Noise in High‐Resolution, Fiber‐fed Spectra: A Study and Simple Cure

Modal Noise in High‐Resolution, Fiber‐fed Spectra: A Study and Simple Cure

Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers

Thermal, mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well

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