Dual-Channel Phase-Tunable Down Converter With LO Frequency Doubling

A dual-channel phase-tunable down converter with local oscillator (LO) frequency doubling is proposed by using a commercial dual-polarization dual-drive Mach-Zehnder modulator (DP-DMZM) and a specially designed dual-channel phase modulator (DP-PM). A radio frequency (RF) signal is injected to one of sub-DMZMs in the DP-DMZM, and a LO signal modulates another sub-DPMZM. An optical bandpass filter (OBPF) is used to filter out the unwanted sidebands, and only the +2nd-order LO and +1st-order RF sidebands are remained and output to the DP-PM. The DP-PM is composed by two parallel PMs with different modulation efficiency between orthogonal polarizations. Each bias voltage of the DP-PM can linearly vary the phase shift between the RF and LO modulated optical sidebands. After detected by a photodetector, the down converted signal with doubled LO frequency and dual-channel phase shift can be obtained. The principle of the proposed link is verified and the experiments are carried out. The experimental results show that the average spur suppression ratio of the down-converted signals is 29.15 dB. The spurious-free dynamic range (SFDR) of the down converter is 103.94 dB·Hz
^2/3
. The continuous and dependent dual-channel phase shift with the full range of 360° can be experimentally achieved. The proposed down converter integrates multiple function in a link, and has the merit of high electrical purity and convenient operation.