Design and simulation of fabrication-error-tolerant triplexer based on cascaded Mach-Zehnder inteferometers

A planar lightwave circuit triplexer with good fabrication-error-tolerance is proposed and its characteristics are analyzed through simulations. To separate 1310 nm and 1480- to 1560-nm channels properly, the path length difference of two-stage Mach-Zehnder interferometers (MZIs) is set to be a multiple and half of the upstream wavelength (1310 nm) and the balance of the employed 3-dB directional couplers is optimized in 1480- to 1560-nm band. Two downstream channels (1490- and 1550-nm channels) are further separated using additional two-stage MZIs. A three-dimensional beam propagation method and transfer matrix method analysis predicts that the channel crosstalk at 1310-nm port would be less than -35 dB from 1290 to 1330 nm. The crosstalk could be less than -22 dB at two downstream channels and less than -55 dB at the upstream channel when the waveguide width error is as much as +/- 0.2 mu m.