PDM is fairly straight forward other than the transmission fiber selection for reliable or realistic simulation. Simply take two transmitters - laser + modulator + random pattern generator + nrz or rz pulse shaper - connect each to a polarization rotator, one set to 0 degrees other 90, and combine the outputs in a polarization beam combiner. you may need to use a pol. maintaining fiber for transmission simulation for easy pol. demux. for receivers, the simplest one is power splitter (1X2) and pol. filters at 0 and 90 degrees at each end.
You can use a Polarization Beam Splitter to divide the input light beam to two beams, and than connect one or two modulator, and than use a Polarzation Beam Conbinor to multiplexing the two beams into one fiber.