Abstract

Manipulation and control of individual channel’s state of polarization (SOP) of a high-capacity DWDM signal has been discussed as key functionality to avoid channel power drift in the presence of residual polarization dependent loss (PDL) or gain (PDG) of transmission link components like modulator, multiplexer, demux, etc.¹ The proposed polarization controller, if manufacturable as low-cost device, might also play an important role in WDM PMD compensation. A further application of efficient signal polarization control are ultra high-bitrate transmission system targeting at channel rate of 160 Gb/s and beyond. These systems is currently based on optical time division multiplexing (OTDM) technique with optical multiplexer gates working for a single SOP only or often exhibiting a strong residual polarization dependency. Polarization diversity schemes are commonly proposed to overcome single polarization operation. Nevertheless they mean a duplication of costly components and might suffer from additional synchronisation demands of the two gates. At this point it might be more efficient to apply a polarization controller (PC) prior to a single SOP demux gate rather than realizing a diversity set-up. However, so far the adaptation of a PC is mainly accomplished by the tuning of two or more phase shifters or polarization cross couplers, since the degrees of freedom (DOF) of a PC is two. Commonly the phase shifter setting is done by the application of “dithering” techniques (also referred to as steepest descend technique) which means consecutively dithering of the individual phase shifters around the actual operation point and by observation of a scalar output which has to be maximized (or minimized), e.g., for a PC the power in the target output polarization.

© 2002 Optical Society of America