A Y-branch Wavelength Multi/Demultiplexer by K+ and Ag+ Ion-exchange for λ=1.31 and 1.55μm-Device Fabrication and Measurement Results

An optical waveguide Y-branch, with a small branch angle and two asymmetric arms, can function as a wavelength multi/demultiplexer (see Fig.1)[1,2]. A small branch angle θ will cause the Y-branch to perform as a mode splitter. Two asymmetric arms, differing either in the geometric shape or refractive index, will yield two intersecting waveguide dispersion curves between the two wavelengths to be demultiplexed. The intersection is designed to be between λ2 = 1.31μm and λ1 = 1.55μm as shown in Fig.2. Thus, the effective index of arm 1 will be higher than that of arm 2 at λ1 = 1.55μm and lower at λ2 = 1.31μm. The waves at λ1 and λ2 from the main branch can then be separated into arm 1 and arm 2, respectively [2]. Generally, the stronger asymmetric two branch arms are, the higher will be the extinction ratios, which are defined as the ratios of the output power from the two arms.