Beam Propagation Method Analysis of the Digital Switch

Abstract

The ”digital switch” 1,2, see also ref 3, has attracted considerable attention recently due to its digital response versus applied voltage and due to its comparative insensitivity to wavelength. This switch does not rely on interference or coupling between normal modes in the two moded structure which constitutes a basic switch, but rather on adiabatic propagation of the normal modes through the structure (cf ref 4). This feature accounts for the insensitivity to wavelength. However, an important question relates to the voltage requirements of this switch and the shape of its transfer characteristics, i e the extent to which it can be employed as an ordinary switch characterized by a voltage length product, as is the case for a directional coupler, such that shorter switches with the same crosstalk performance are achieved by increasing the drive voltage proportionally. In this paper we use the beam propagation method (BPM)5,6 to analyze the switching characteristics of a digital switch, implemented in Ti : LiNbO3, with the channel crossing angle as a parameter. The analysis is carried out for Z-cut LiNbO 3 switches; comparisons are made to published experimental data as well as to directional coupler switches. Possible optimizations are discussed.