Photonic generation of frequency-tunable biphase and quadriphase coded pulse signals without background interference...

An approach to generating frequency-tunable biphase and quadriphase coded pulse signals without background interference based on a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) is presented and demonstrated. Two ternary baseband code sequences are separately encoded into a pair of orthogonal optical carriers by exploiting a polyphase encoder on the basis of the principle of vector modulation, which in turn can be mapped to the phase shifts of the generated phase coded waveforms after the balanced detection. The frequency tunability can also be achieved by controlling the bias voltage of the associated modulator, so that the carrier frequency can be tuned to either fundamental or doubled frequency. Additionally, by designing different phase codes, the generated pulse signals can be conveniently switched between the quadriphase and biphase coding waveforms. The major advantage of the proposed approach is that four phase shifts can be obtained by simply adjusting the polarity of the ternary code sequences, overcoming the power-dependent limitation of the previous work. A proof-of-principle experiment is conducted to assess the feasibility of the proposed approach built on the Barker code and Frank code phase coded pulse signals generation. Experimental results show the phase coded pulse signals at 12 and 24 GHz carrier frequency are well behaved in terms of peak-to-sidelobe ratio (PSR), range-Doppler coupling and Doppler tolerance.