Determination of core diameter and refractive-index difference of single-mode fibres by observation of the far-field pattern

Review of the basic methods for characterizing integrated-optic waveguides

“…The intensity at a point outside the end face is termed as the far-field intensity. It is the Fraunhoffer diffraction of the near field [30] (or the modal field) and can be calculated by substituting the modal field in the Fraunhoffer diffraction equation.…”

“…The far-field intensity has been used to characterize single-mode step-index [30] as well as graded-index [31] fibers. One can also characterize a step-index symmetric [15], a step-index asymmetric [16] planar waveguide, or a two-dimensional waveguide [ 171 from the far-field intensity measurements.…”

Characterisation of Single-Mode Asymmetric Slab Waveguide from Far Field Intensity Pattern

“…In this paper, we have proposed a method for characterising a single-mode step-index asymmetric slab waveguide from the far field intensity measurements. A symmetric waveguide is characterised by measuring the far field at two points only i.e., at -3 dB and zero intensity points [1][2][3][4]. However, in the present work we emphasize that, to characterise an asymmetric slab waveguide by the far field technique, it is necessary to measure the intensity in the far field at 1 three points because of an additional asymmetry parameter.…”

“…An accurate knowledge of the core refractive index, the normalised frequency V and the dimension of such waveguides is essential to design and optimise the performance of optical waveguide devices. The far field radiation pattern of the fundamental mode is extensively used to characterise single-mode step index as well as graded index optical fibers [1][2][3]. Boucouvalas [4] has extended this technique to characterise step-index symmetric slab waveguides.…”

Evolution of the diffraction pattern during the transition from the near-field toward the far-field region

“…In the cases the MOF structures are reduced to step-index fiber with the circular or slab geometry and the refractive index of the cladding equals to the effective refractive index of the fiber. After such reduction, the methods known for analyzing modality of traditional fibers may be applied [19][20][21]. The other approach bases on analysis of a near-field pattern [22].…”