Generation of a frequency-quadrupled phase-coded signal using optical carrier phase shifting and balanced detection

A novel approach for photonic generation of a frequency-quadrupled phase-coded signal using optical carrier shifting and balanced detection is proposed and demonstrated. The key component of the scheme is an integrated dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. In the modulator, an RF signal is applied to the upper QPSK modulator to generate high-order optical sidebands, while an electrical coding signal is applied to the bottom QPSK modulator to perform optical carrier phase shifting. After that, a frequency-quadrupled phase-coded signal with an exact π-phase shift is generated through balanced detection. The proposed scheme has a simple, compact structure and good tunability. Besides, a phase-coded pulse can be directly obtained when a three-level rectangular coding signal is applied. A proof-of-concept experiment is carried out. The generation of a 2-Gbit/s phase-coded signal with a frequency tuning from 12.12 to 28 GHz is experimentally demonstrated, and the generation of a phase-coded microwave pulse is also verified.