J. A. Arnaud
Bell System Technical Journal, The (Volume:53 , Issue: 4 ), pages 675 – 696, April 1974
The number of modes that can propagate without radiation loss in oversized waveguides is sharply reduced if the waveguide is coupled to a structure supporting radiation modes, the loss mechanism being analogous to Cerenkov radiation. The coupling formula derived in Part I1 is used to evaluate the loss for a specific configuration: a reactive surface (e.g., a thin dielectric slab) acting as a waveguide, coupled to a semi-infinite dielectric acting as a mode sink. The method consists in first assuming that the substrate is finite in size and lossy and adding the losses associated with each substrate mode. The substrate dimensions are subsequently made infinite and the dissipation loss is made to vanish. The expression obtained for the radiation loss coincides with an expression obtained by solving the boundary value problem. The method is then applied to the problem of mode selection for dielectric rods coupled to dielectric slabs, which is of particular importance for optical communications and integrated optics. A 2-dB/m radiation loss is calculated for the first higher order mode when the rod radius is 10 µm, λ = 1 µm, n = 1.41, and the rod-to-slab spacing is 0.15 µm.
LIEN VERS L’ARTICLE : TRANSVERSE COUPLING IN FIBER OPTICS PART II : COUPLING TO MODE SINKS