Abstract

With the advances of dense wavelength-division-multiplexing technology in fiber-optic communications, there is a great demand for wavelength filters to multiplex and demultiplex tens of wavelength channels with a bandwidth of approximately 10 Å or less. Recently we reported an optimum design guideline for vertically coupled directional coupler filters, whose bandwidth is predicted to be less than 10 Å when implemented in InP/InGaAsP.¹ The basic design concept is to enhance the difference between the slopes of the dispersion curves of the top and bottom waveguides of the coupler, where, according to the directional-coupling theory,² the bandwidth of the power transfer is reduced when the intersecting angle of the two dispersion curves is increased. In this design, a ridged structure is employed for the top guide to achieve strong two-dimensional optical confinement and is vertically coupled to a weekly confined bottom guide.

© 1991 Optical Society of America