Electronics Letters, Volume 13, Issue 9, 28 April 1977, p. 265 – 267
ABSTRACT
Using a simple ray theory, we show that the steady-state microbending loss of multimode square-law fibres is equal to 8γ/Δ dB/m. We have defined Δ = Δn/n, and γ is the power-spectral density of the fibre axis curvature in any meridional plane at the natural frequency of ray oscillation, expressed in reciprocal metres. The steady-state irradiance distribution in the fibre core is also given.
A numerical technique based on ray optics is presented that provides the impulse response of multimode optical fibers having arbitrary smooth index profiles ans arbitrary material disposition. The variation of dn/d… o as a function of n when the dopant concentration varies is obtained from Fleming measurements on bulk samples. This technique is applied to germania-doped multimode fibers with power-law profiles and various vaues of ∆≥ 0.005. By successive approximations, optimum profiles that minimize the impulse response widths for quasi-mono-chromatic sources are found. For these optimum profiles, the quasi-monochromatic root-mean-square (rms) impulse response width is found to be of the order of 150 ∆2nsec/km, in agreement with a recent analytical result.
L’article montre comment appliquer les techniques développées par Hamilton au calcul de l’étalement des impulsions dans les fibres optiques multimodales. En particulier, il donne une expression simple pour le profil optimal des fibres utilisant un matériau dispersif. Le passage des coordonnées rectangulaires aux coordonnées cylindriques est fait sous la forme hamiltonienne et sous la forme lagrangienne.
Electronics Letters, Volume 12, Issue 25, 9 December 1976, p. 654 – 655
ABSTRACT
We give a simple closed-form expression for the index profile of multimode fibres with arbitrary dispersion that provides transmission capacities as large as 1.6/Δ2 Mbit/s×km, where Δ ≡ Δn/n. Our result reduces to a recent result of Marcatili for the special case of circularly symmetric fibres. A transmission capacity of 150 Mbit/s over a 10 km-long fibre appears possible with l.e.d. sources
The Bell System Technical Journal, vol 55, n°10, december 1976
ABSTRACT
A novel technique for measuring the refractive index profile of optical fibers is demonstrated, which offers substantial advantages over alternative methods. The method consists of illuminating a small area of the fiber core and measuring the total transmitted power. The transmission of leaky modes is accounted for in the manner reported previously by other authors. The index profiles of germanium-doped fibers obtained by this technique are compared to interferometric measurements. The resolution is shown to be limited by wave optics effects about… where Δ… The distortion of the index profile as the wavelength and waveoptics effects are investigated.
Electronics Letters, Volume 12, Issue 7, 1 April 1976, p. 167 – 169
ABSTRACT
The r.m.s. impulse response width of germania doped fibres having power-law profiles at the carrier wavelength is evaluated with the help of a numerical method and measured values of dn/dλ. For Δn/n≈0.02, our result exceeds by more than one order of magnitude that obtained from an analytical formula based on the assumption that ndn/dλ varies linearly with n2. The optimum profiles are found to differ very significantly from power-law profiles. Our numerical technique is based on scalar-ray optics. It is applicable to any fibre having a large V-number and a smooth profile.
Electronics Letters, Volume 12, Issue 1, 8 January 1976, pp. 6 – 8
ABSTRACT
In multimode circularly symmetric fibres whose index distribution is a stairlike approximation of an optimum profile, the modal dispersion increases as the number of steps decreases. For a fibre with Δn/n=0.02 and a core radius of 40 μm, numerical calculations based on wave optics show that the r.m.s. impulse response width at λ=1 μm increases from 0.075 ns/km for the smooth optimum profile to 0.23 ns/km for 40 steps of equal areas. Thus an important conclusion of the analysis is that one should avoid introducing steps in the refractive-index profile of fibres for optimum results.
We describe a tunable Fabry-Perot type filter which has application to radio astronomy in the frequency band 80-110 GHz. The filter causes image sideband suppression when used with a heterodyne spectral line receiver having an intermediate frequency of 4.75 GHz. The transmission loss in the signal sideband is about 0.4 dB, while the image sideband rejection is more than 15 dB ; there appears to be little if any problem with scattering or distortion of the antenna radiation pattern.
Beam and Fiber Optics discusses the concepts of wave and geometrical optics that are most relevant to a deeper understanding of beam optics. This book is organized into five chapters that provide the necessary algebraic details, particularly the laws of beam propagation through unaberrated optical systems.
The first chapter presents a broad view of the subject matter and a comparison between the laws of mechanics and the laws of optics. Chapter 2 explores the laws of propagation of Gaussian beams through freespace, unaberrated lenses, or lenslike media and resonators. The simplest configurations (two-dimensional with isotropic media) are first considered, but a few advanced problems are also treated. This chapter also discusses the use of Gaussian beams at millimeter wavelengths. In Chapter 3, various wave equations relevant to beam optics are given, and their relationship is examined. This text also emphasizes the importance of the Lorentz reciprocity theorem for problems of coupling between beams or fibers. The geometrical optics limit of wave equations is addressed in Chapter 4. This chapter also considers the propagation of optical pulses in dispersive inhomogeneous (graded-index) fibers based on the point of view of Hamiltonian optics. The final chapter is devoted to piecewise homogeneous dielectric waveguides, such as the dielectric slab and the dielectric rod. A method to evaluate the bending loss of open waveguides is described.
This book will be useful to students, professors, and research engineers in the field of electromagnetic communication.