Loss of optical power in a single-mode optical fibre due to bending has been investigated for a wavelength of 1550 nm. In this experiment, the effects of bending radius (4-15 mm, with steps of 1 mm), and wrapping turns (up to 40 turns) on loss have been studied. Twisting the optical fibre and its influence on power loss also have been investigated.Variations of bending loss with these two parameters have been measured, loss with number of turns and radius of curvature have been measured, and with the help of computer curve fitting method, semi-empirical relationships between bending loss and these two parameters have been found, which show good agreement with the obtained experimental results.

Inspections of moiré fringe characteristics, such as period and orientation, conventionally are done by two approaches; namely, parametric equation and Fourier analysis methods. In some cases these methods yield different results. This inconsistency is removed by revising the derivation of the indicial equation for moiré fringes by the parametric equation method.

In this study, a Gaussian amp function related to the Gaussian family is employed to approximate the output intensity profile of various arrangements of air holes in photonic crystal fibers (PCFs) with a fixed number of air rings (N=4). It is shown that d/Λ=0.5 can be the best minimum value of air-filling fraction for all of the studied PCFs when λ=1.35  μm, whereas, for λ=1.55 and 1.65 μm, d/Λ=0.6 is suitable for achieving the maximum output intensity with very low confinement loss.

In this study, a Gaussian amp function relating to the Gaussian family is employed to approximate the output intensity profile of various arrangements of air holes in photonic crystal fibers (PCFs) with small d/Λ values. The studied structures include six distinctive designs starting with square lattice and carried on up to the PCF with Nano configuration. It is shown that d/Λ = 0.4 is the best value of low d/Λ ratios (0.2 ≤ d/Λ ≤ 0.4) which leads to the rise of the central intensity noticeably and the reduction of the full width at half maximum at three studied wavelengths (λ = 1.35, 1.55 and 1.65μm).