Optisystem components

Kindly help me out in finding the alternate source for Phase Modulators or tell me the most suitable phase modulator for my free space QKD system. Also, guide me for the voltage source (currently using NRZ pulse generator but is has only 2 options for voltage option and I want 4 voltages for my system) for this PM and how can I change the voltages of that source so I get the output at PM of (0, 45, 90 and 135 degrees).