There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Preface.Introduction.Chapter 1. Selected Topics in Electromagnetic Wave Propagation.1.1. Maxwell's Equations and the Fundamental Fields.1.2. Electromagnetic Wave Propagation in Sourceless Media.1.3. Power Transmission.1.4. Group Velocity.1.5. Reflection and Transmission of Waves at Plane Interfaces.1.6. Material Resonances and Their Effects on Wave Propagation.Problems.References.Chapter 2. Symmetric Dielectric Slab Waveguides.2.1. Ray Analysis of the Slab Waveguides.2.2. Field Analysis of the Slab Waveguides.2.3. Solutions of the Eigenvalue Equations.2.4. Power Transmission and Confinement.2.5. Leaky Waves.2.6. Radiation Modes.2.7. Wave Propagation in Curved Slab Waveguides.Problems.References.Chapter 3. Weakly-Guiding Fibers with Step Index Profiles.3.1. Rays and Fields in the Step Index Fiber.3.2. Field Analysis of the Weakly-Guiding Fiber.3.3. Eigenvalue Equation for LP Modes.3.4. LP Mode Characteristics.3.5. Single Mode Fiber Parameters.3.6. Derivation of the General Step Index Fiber Modes.Problems.References.Chapter 4. Loss Mechanisms in Silica Fiber.4.1. Basic Loss Effects in Transmission.4.2. Fabrication of Silica Fibers.4.3. Intrinsic Loss.4.4. Extrinsic Loss.4.5. Bending Loss.4.6. Source-to-Fiber Coupling.Problems.References.Chapter 5. Dispersion.5.1. Pulse Propagation in Media Possessing Quadratic Dispersion.5.2. Material Dispersion.5.3. Dispersion in Optical Fiber.5.4. Chromatic Dispersion Compensation.5.5. Polarization Dispersion.5.6. System Considerations and Dispersion Measurement.Problems.References.Chapter 6. Special Purpose Index Profiles.6.1. Multimode Graded Index Fiber.6.2. Special Index Profile Optimization.Problems.References.Chapter 7. Nonlinear Effects in Fibers I: Non-Resonant Processes.7.1. Nonlinear Optics Fundamentals.7.2. Nonlinear Phase Modulation on Pulses.7.3. The Nonlinear Schrodinger Equation.7.4. Additional Non-Resonant Processes.Problems.References.Chapter 8. Nonlinear Effects in Fibers II: Resonant Processes and Amplification.8.1. Raman Scattering.8.2. Stimulated Brillouin Scattering.8.3. Rare-Earth-Doped Fiber Amplifiers.Problems.References.Appendix A: Properties of Bessel Functions.Appendix B: Notation.Index.

Fundamentals of optical fibers

The dependence of temperature on the fluorescence lifetime and fluorescence intensity ratio using Stark sublevels and thermally coupled (close lying) levels in triply ionized rare earth ions, doped into a variety of glasses and fibers, have been reviewed. Also, it is claimed that not only for the two closely lying levels of triply ionized rare earth ion of the same kind, but also for two different triply ionized rare earth ions, having their excited levels very close to each other, may be used to monitor the temperature.

Temperature sensors and optical sensors

Photonic lanterns are made by adiabatically merging several single-mode cores into one multimode core. They provide low-loss interfaces between single-mode and multimode systems, where the precise optical mapping between cores and individual modes is unimportant.

The photonic lantern

A taper transition can couple light between a multimode fiber and several single-mode fibers. If the number of single-mode fibers matches the number of spatial modes in the multimode fiber, the transition can have low loss in both directions. This enables the high performance of single-mode fiber devices to be attained in multimode fibers. We report an experimental proof of concept by using photonic crystal fiber techniques to make the transitions, demonstrating a multimode fiber filter with the transmission spectrum of a single-mode fiber grating.

/pdf/multimode-fiber-devices-with-single-mode-performance-2njua7brsf.pdf

Multimode fiber devices with single-mode performance.

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 /spl mu/m is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 /spl mu/m in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed.

Bragg gratings in multimode and few-mode optical fibers

Temperature sensing to as low as 80 K was demonstrated with 1.55-μm fiber Bragg gratings. The gratings were bonded on substrates to increase sensitivity, and a shift of the reflection wavelength was measured. The temperature sensitivity was 0.02 nm/K at 100 K when an aluminum substrate was used and 0.04 nm/K at 100 K when a poly(methyl methacrylate) substrate was used. These values are smaller than those at room temperature because of the nonlinearity of both the thermal expansion and the thermo-optic effect. Extension to the liquid helium temperature is also discussed.

Fiber Bragg grating cryogenic temperature sensors

Low-temperature sensing was studied using a fibre Bragg grating fixed on Teflon substrate that has a large thermal expansion coefficient. The wavelengths of reflected light from 1.55 µm fibre Bragg gratings were measured in the temperature range from 77 to 300 K. By bonding the fibre Bragg grating in between two Teflon substrates, the temperature sensitivity of 39 pm K-1 was obtained at 77 K, which is 1.5 times higher than that of the sensor using a poly(methyl methacrylate) substrate. At room temperature, the sensitivity increased to 150 pm K-1. For a more compact structure using one substrate only, the temperature sensitivity decreased by 5% compared with the sensor using two Teflon substrates. Comparisons with theoretical values are also discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/12/7/329/pdf

High-sensitivity cryogenic fibre-Bragg-grating temperature sensors using Teflon substrates

Gain saturation characteristics of Raman amplification in silica and fluoride glass optical fibers

Fabrication and temperature sensitivity were studied for long-period gratings (LPGs) in a high-Ge photosensitive fibre and the standard single-mode fibre. Using a high-Ge fibre, the irradiation time with a KrF excimer laser can be decreased to one order of magnitude less than that of the single-mode fibre. LPGs in the single-mode fibre near the dispersion turning point showed a large wavelength shift to the longer wavelength during the irradiation, and even after the irradiation the wavelength continued to shift in the same direction. Diffusion of hydrogen into the core is considered to be responsible for the latter wavelength shift. Increase in the temperature sensitivity by a grating period near the dispersion turning point was discussed. The absolute value of the temperature sensitivity of an LPG in a photosensitive high-Ge fibre was about 1/3 of that of the single-mode fibre, and the dependence on fibre materials and the fabrication conditions was discussed.

http://iopscience.iop.org/article/10.1088/0957-0233/15/8/006/pdf

Toru Mizunami

Papers

Bragg gratings in multimode and few-mode optical fibers

Fiber Bragg grating cryogenic temperature sensors

High-sensitivity cryogenic fibre-Bragg-grating temperature sensors using Teflon substrates

Gain saturation characteristics of Raman amplification in silica and fluoride glass optical fibers

Fabrication and characterization of long-period-grating temperature sensors using Ge-B-co-doped photosensitive fibre and single-mode fibre