The digital directional coupler: improved design

Using a simple analytic model (weak-coupled mode theory), a new design is presented for digital directional couplers (i.e., directional couplers with tapered velocity mismatch and tapered coupling). These have relative immunity to variations in fabrication and operating conditions, and have a steplike switch response. The analysis shows that significantly improved performance can be obtained by simple modifications to the device shape given by R.R.A. Syms and R.G. Peall (1989).<
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