Photonic Generation of Phase Coded Microwave Pulses Using Cascaded Polarization Modulators

We demonstrate a technique of generating a binary phase coded microwave pulse based on two cascaded polarization modulators (PolMs). The first PolM (PolM1) followed by an optical band-pass filter is used to generate two phase-locked and polarization orthogonal optical frequencies. The second PolM (PolM2) aims to change their polarization states. A polarizer attached to the output of PolM2 allows only one of the two optical frequencies passing, or combines them with positive/negative phase difference. By changing the voltage level of the electrical modulation signal applied to PolM2, a series of binary phase coded microwave pulses is directly generated from a continuous wave microwave signal in the optical domain. In the proposed system, the precise amplitude control or amplification of the modulation signal are avoided. The waveform of the generated pulse is very stable. For a proof-of-concept experiment, a series of 25-GHz pulses with ~ 2.08-ns pulse duration and ~ 10.24-ns repetition time is generated. The pulses are phase coded by a 13-bit Barker code.