Equilibrium mode distribution

About: Equilibrium mode distribution is a research topic. Over the lifetime, 928 publications have been published within this topic receiving 14939 citations.

Field distribution in the input coupling region of planar single-mode waveguides

Abstract: Institute of Commu nications and Rad i o-Freque cy Eng neering, Vienna University f Technology, Gusshausstrasse 25/389, A-1040 Wien, Austria, Email: walterleeb@tuwienacat ABSTRACT We apply a numerical method for calculating the field distribution in the region immediately behind the input facet of a dielectric step-index single-mode slab waveguide The input waves considered are focused plane waves and Gaussian beams of various diameters, with and without misalignment The figures obtained show the formation of radiation modes and the development of the fundamental guided mode and thus give hints on how to design pieces of single-mode fibers that are to be used as modal filters, eg, in astronomical interferometers with excessive nulling requirements 1 INTRODUCTION Optical single-mode waveguides constitute a key device in instruments for astronomical interferometry aiming at the investigation of extra-solar planets To give an example: In ESA's DARWIN mission, the optical fields collected by telescopes will be propagated through a piece of single-mode fiber Only then they will exhibit the highly identical amplitude distribution and phase distribution required for destructive interference of the (unwanted) radiation originating from the star whose planet is under investigation Propagating the light through an ideal single-mode waveguide achieves just this One attempt to analytically estimate the minimum length (as required to achieve proper background suppression by modal filtering) of an otherwise ideal fiber waveguide is found in [1] This approach, however, could not take into account many of the real-world aspects occurring in fibers Here we demonstrate the usefulness of a numerical method in calculating – and visualizing – the distribu-tion of the optical field in the input coupling region of a single-mode waveguide Examining a 2-dimensional single-mode waveguide in a first step already gives an excellent insight into the power flow immediately after the input facet, shows how a steady state intensity distribution in the vicinity of the core is eventually reached, and also yields the coupling efficiency into the waveguides’ fundamental mode Eventually this method will allow taking into account a non-perfect core-cladding geometry, a finite cladding thickness, an absorbing coating, an input taper, etc After explaining the system model in Sect 2 we shortly describe the numerical method applied (Sect 3) before presenting results for cases where the input radiation is either a focused plane wave (Sect 4) or a focused Gaussian beam (Sect 5) We visualize the power flow, show how the fundamental mode develops, and obtain the coupling efficiency as a by-product Section 6 summa-rizes the findings 2 SYSTEM MODEL Fig 1 shows the system model used The step-index slab waveguide consists of a core of thickness 2d (index of refraction n

Influence of fiber bends on mode-dependent loss and mode coupling in mode division multiplexing systems

Abstract: In this paper physical effects caused by macro- and micro bends of optical fiber including additional mode-dependent loss, mode coupling and spurious mode excitation in fiber MDM-system are considered. The effects described below can dramatically decrease capacity and maximum data rate in such systems because of inevitability of fiber bends due to system exploitation thus making MDM-system commercialization much more difficult and expensive. Mathematical approach used to describe these effects and applied in the simulation model is based on well- known refractive index profile approximation [1] of bent step-index fibers and mathematical field coupling model [8].

Analysis of constant phase contours of evaporation duct mode functions for waveguide mode propagation

Abstract: : The M-Layer program tracks the constant phase lines Im(D(q)) = 0 and looks for their intersections with the lines Re(D(q)) = 0 for the locations of the zeros of the mode function D(q). These two types of constant phase lines are tracked and plotted over a search region which contains modes having a range attenuation rate of no more than 5 dB per km. Several new parameters for use in mode search are deduced from the results and some old ones are verified. Future studies is waveguide mode propagation theory pertaining to atmospheric ducts may benefit from this work. An improved mode search strategy is also proposed. Evaporation duct, Waveguide mode propagation.