Branching Waveguides with Truncated Structure and Phase Matching

Abstract

We have studied mask based process for the microfabrication of polymeric (IXn) branching waveguides both theoretically and experimentaly. The simulation is based on the two-dimensional finite-difference beam propagation method (FDBPM) for the design of the waveguiding devices. The transmission efficiency of truncated structural Y-branch (TSYB) for wide angle (IX2) splitter with a full branching angle 2A greater than 20 is improved compared to that of normal Y-branch (NYB) structure. The maximum transmission at the output is obtained in phase matching between the inner and the outer paths at the point of bending of the truncated structure. An analysis for the optimum phase matching taking symmetric cladding refractive index at the branching zone, is made to improve the transmission efficiency η. For more output ports in (IXn) multiple branching waveguides it is observed that equal output power is not obtained for normal (IXn) branching waveguides. We have designed here a new truncated structural (IX3) branch [TS(IX3)B] structure for obtaining equal transmissions in higher branching angle structure using same phase matching consideration. Phase matching consideration is also followed in designing TS(IXn) B structures. We have fabricated the polymeric devices over Si-SiO2 substrate. The cladding and the waveguiding layers are the Epoxy and PMMA/DRI, respectively. The thickness and refractive index of the waveguiding layers are controlled either by spinning speed or viscosity of the solution and its mixing ratio, respectively. The standard photolithography technique is used here with positive resist coating and followed by dry plasma etching in presence of oxygen. Experiments for the transmission efficiency of the devices are made and compared with the theoretical values.