Repetition-rate-tunable return-to-zero and carrier-suppressed return-to-zero optical pulse train generation using a polarization modulator

An approach is proposed to generating return-to-zero (RZ) and carrier-suppressed return-to-zero (CS-RZ) pulse trains with a high and tunable repetition rate by using a polarization modulator (PolM). The PolM is a special phase modulator that can support both TE and TM modes with opposite phase modulation indices. A linearly polarized cw light with its polarization state oriented with an angle of 45 degrees to one principal axis of the PolM is modulated by a sinusoidal signal at the PolM. The output light from the PolM is then sent to a polarization beam splitter (PBS), with one axis of the PBS aligned at an angle of 45 degrees to one principle axis of the PolM. At the two outputs of the PBS, two optical signals with one consisting of the even-order optical sidebands and the other consisting of the odd-order optical sidebands are obtained, leading to the generation of an RZ and a CS-RZ pulse train having a repetition rate that is twice the frequency of the drive sinusoidal signal. The proposed approach is demonstrated by a proof-of-concept experiment in which an RZ and a CS-RZ pulse train with tunable repetition rates of 7.2 and 8 GHz are generated.