A PMD emulator with tunable second-order PMD and constant mean first-order DGD

We present, for the first time, a second-order polarization mode dispersion (SOPMD) emulator with tunable SOPMD and constant mean first-order differential group delay (DGD). The emulator is based on a variable DGD line (variable from /spl tau//sub variable//sup min/ to /spl tau//sub variable//sup max/), a polarization controller, and a high birefringent (HiBi) fiber segment with a DGD value of /spl tau//sub fixed/. Theoretical calculations predict that after careful calibrations, by tuning the variable DGD line, the emulator can provide a variable SOPMD value from /spl Phi//sub 0/ to (1/2)/spl tau//sub fixed//sup 2/+/spl Phi//sub 0/ (/spl Phi//sub 0/ is a constant), while its mean first-order DGD is kept at a constant value of about /spl tau//sub fixed/. The implications of this SOPMD emulator on high-speed (/spl ges/10 Gb/s) optical communications are discussed.