A normalized approach to the design of low-loss optical waveguide bends

Abstract

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Transmission of slow light through photonic crystal waveguide bends

“…It is known that the mode in curved waveguides is pulled away from the center of curvature toward the outer edge of the bend, thus seeing a lower average refractive index with respect to the mode in the straight waveguide 17 . If this mechanism can be extended to describe mode behavior in PhC waveguide bends, the PhC Bloch mode is pulled toward its outer corner where it samples more holes.…”

“…This spectral blueshift can be explained by making analogy to conventional strip and rib waveguide bends 17 . It is known that the mode in curved waveguides is pulled away from the center of curvature toward the outer edge of the bend, thus seeing a lower average refractive index with respect to the mode in the straight waveguide 17 .…”

“…Hence, the average refractive index that the mode encounter at the bend is smaller, which explains the experimentally observed blueshift of the cutoff. In integrated optics, the usual way to compensate the distortion of the mode profile at the bend is to offset the bend section with respect to the straight section or to increase the refractive index at the bend by increasing its width 17 . Recent theoretical calculations have confirmed that a similar hypothesis is applicable to PhC waveguide bends 18 .…”

The design of low-loss curved waveguides

“…These are the constant curvature bend, the constant curvature bend with offset (Smit et al 1993), the linear continuous curvature bend, the trapezoidal continuous curvature bend and the non-linear continuous curvature bend. The waveguide used in the discussion is a single mode slab waveguide operating at λ = 1.55 µm, whose width is d = 0.9 µm, core refractive index is n core = 3.35222 and cladding refractive index is n clad = 3.27156.…”

Integrated Mach-Zehnder Interferometer on SU-8 Polymer for Designing Pressure Sensors

“…Thus, the width, the respective thicknesses of the core and the lower cladding together with the effective index of the whole structure are validated. Secondly, the bent waveguides properties are worked out by way of the conformal transformation theory [7,8]. Thus, an optimal radius of curvature is confirmed so as to reduce any optical loss and improve the optical confinement and propagation of the mode.…”