<title>Integrated polymer waveguide mode size transformer with a vertical taper for improved fiber coupling</title>

Abstract

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single-m,ode fibers. The taper smoothly converts a highly elliptical waveguide mode into a bigger and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5-2 mm in length is made in the low index upper cladding to reduce its thickness from several micrometers to zero, followed by the coating of a second upper cladding with index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows bigger a light propagates, whereas the confinement by the lower cladding and lateral confinement are hardly affected. The waveguide mode grows in the vertical direction away from the lossy ground electrode and substrate; therefore no compromise between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and tapered photoresist etching mask, are develop for making this vertical taper. Mode expansion and a 1.8 dB reduction in coupling los, which is not sensitive to waveguide width and polarization, is obtained in our preliminary experiment.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.