Dynamic polarization-dependent loss (DPDL) of planar-waveguide-based variable optical attenuators (VOAs)

We analyze the dynamic polarization-dependent loss (DPDL) of planar-waveguide-based variable optical attenuators (VOAs). Our studies show that thermal stress is introduced in waveguides when heat is applied to achieve optical attenuation of Mach-Zehnder interferometer (MZI) coupler-based VOAs made of silica, thus resulting in an unacceptable DPDL, for such devices. The stress and its associated DPDL can be reduced significantly if two trenches are created along the waveguides. The DPDL can be further reduced to a negligible level by adopting a new VOA design based air straight waveguides and a silica-polymer hybrid structure. (C) 2004 Wiley Periodicals, Inc.