Ultrasmall waveguide bends: the corner mirrors of the future?

Abstract

Curved waveguides with strong lateral modal confinement have been fabricated on InGaAsP/InP by etching through the waveguide core. This has resulted in extremely sharp bends (radii as small as 30 Im) with negligible bend loss, enabling fabrication of very low loss 90" turns on a chip area as small as that of a corner mirror.

Micron-size bending radii in silica-based waveguides

“…Use of air trenches for sharp bending radii in silica waveguides has been discussed previously in the context of optical fiber and slab 4 and ridge waveguide bend loss. 3 For tight bends, trenches are placed immediately against the waveguide core, and provide higher lateral mode confinement at the expense of some junction loss. 3 In typical silica index contrasts, the abrupt junction (Figs.…”

“…3 For tight bends, trenches are placed immediately against the waveguide core, and provide higher lateral mode confinement at the expense of some junction loss. 3 In typical silica index contrasts, the abrupt junction (Figs. 2a) loss becomes intolerable.…”

“…2 Air trenches have been proposed for suppressing bend radiation in several ways. 3,4 When they replace the cladding to enhance lateral mode confinement, mode mismatch-induced junction loss is incurred at points of abrupt change in refractive index and limits the success of the approach in low index contrast. To our knowledge, no attempt has been made to use air trenches to design small, low-loss bends in low index contrast by properly addressing the mode mismatch issue introduced by the present air trench.…”

Relaxed Dimensional Tolerance Whispering Gallery Microbends

“…For radii of order tens of micrometers, high refractive index contrast is required in the plane of the microbend to minimize radiation losses. This is readily achieved with deeply etched waveguides [13]- [16] and has been exploited in ultracompact arrayed waveguide gratings [17], [18]. Performance does, however, become increasingly sensitive to waveguide bend modal properties, fabrication tolerance, and polarization rotation, leading even to a body of research on polarization converters [19]- [21].…”

ASOC/sup TM/-a silicon-based integrated optical manufacturing technology

“…For waveguide Sbends with a radius of 8mm an excess loss of about -0.55dB was obtained. By modifying the waveguide geometry to produce deep-etched bend regions [9] it is found that waveguide bends with radii as small as 0.1" can be obtained.…”